manual de grid builder gridbldr

GRID BUILDERA pre-processor for 2-D, triangular element,

finite-element programs

R.G. McLaren, University of Waterloo

c©R.G. McLarenGroundwater Simulations Group

September 18, 2008

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Problems?

Authorized users encountering problems with the codes, or requiring specific imple-mentations not supported in this version, are encouraged to contact the author atthe following location for possible assistance.

Waterloo Centre for Groundwater ResearchUniversity of WaterlooWaterloo, Ontario, CanadaN2L 3G1

Telephone: (519) 888-4567Extension: 32257 (Rob McLaren)FAX : (519) 746-7484E-MAIL : [email protected]

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About this manual

The following conventions are used throughout the manual.

Typed commands, filenames and GRID BUILDER prompts are presented in atypewriter-style font (e.g. run77 gb, INSTALL.BAT, etc.). This includes promptsand field labels in I/O boxes.

GRID BUILDER menu items and I/O box button labels are presented in a sansserif font. When listed in sequence, menu and submenu options are separated bythe backslash character ’/’. For example, the instruction choose menu option Gen-erate/Irregular/Import indicates that you should choose the menu option Generate,which leads to a submenu where you should choose Irregular which leads to anothersubmenu where you should choose Import.

The following keyboard key indicators are used throughout:

Key Symbol Key to be pressed

Enter Return or enter

Esc Escape

← Cursor left

→ Cursor right

↑ Cursor up

↓ Cursor down

Spc Spacebar

End End

F1 F1

F2 F2

F7 F7

Contents

1 Introduction 3

1.1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 Quitting GRID BUILDER . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 In the event of trouble... . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Grid generation 7

2.1 Rectangular grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Wedge grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3 Layered Grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4 Irregular grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.4.1 Defining grid boundaries . . . . . . . . . . . . . . . . . . . . . 12

2.4.1.1 Using the mouse to define grid boundaries . . . . . 12

2.4.1.2 Retrieving previously saved grid boundaries . . . . . 13

2.4.1.3 Importing grid boundary data . . . . . . . . . . . . 13

2.4.1.4 Importing reference information . . . . . . . . . . . 13

2.4.2 Modifying grid boundaries and grid generation parameters . 14

2.5 Regenerating the grid . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3 Grid Checks 19

3.1 Closest nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2 Zero area elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.3 4 node connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.4 Relax grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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vi CONTENTS

4 File Input/Output 21

4.1 Saving grid data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2 Retrieving grid data . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.3 Exporting grid data to other applications . . . . . . . . . . . . . . . 23

4.4 Importing foreign grid data . . . . . . . . . . . . . . . . . . . . . . . 23

4.5 Grid-related data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.6 Grid-independent data . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5 Special tools 27

5.1 Modifying the screen image . . . . . . . . . . . . . . . . . . . . . . . 27

5.2 Examining grid subregions in detail . . . . . . . . . . . . . . . . . . . 29

5.3 Changing mouse precision . . . . . . . . . . . . . . . . . . . . . . . . 30

5.4 Generating plotted output . . . . . . . . . . . . . . . . . . . . . . . . 30

5.5 Refreshing the screen . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.6 Getting general information . . . . . . . . . . . . . . . . . . . . . . . 31

5.7 Changing the current drive . . . . . . . . . . . . . . . . . . . . . . . 31

5.8 Shifting menu position . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.9 Distance estimator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.10 Changing the pick mode . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.11 Exporting area boundaries . . . . . . . . . . . . . . . . . . . . . . . . 32

6 Editing grid data 33

6.1 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.2 Nodes and related data . . . . . . . . . . . . . . . . . . . . . . . . . 34

6.2.1 Modifying nodal property values . . . . . . . . . . . . . . . . 35

6.2.2 Other considerations . . . . . . . . . . . . . . . . . . . . . . . 37

6.3 Elements and related data . . . . . . . . . . . . . . . . . . . . . . . . 39


6.4 Segments and related data . . . . . . . . . . . . . . . . . . . . . . . . 41

6.5 Boundary condition data . . . . . . . . . . . . . . . . . . . . . . . . . 41

CONTENTS 1


6.6 Field data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

6.7 Overlay data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

6.8 Raster data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

6.9 Hydrographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6.10 Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7 GRID BUILDER Demonstration 53

7.1 Starting GRID BUILDER . . . . . . . . . . . . . . . . . . . . . . . . 53

7.2 Importing grid boundary data . . . . . . . . . . . . . . . . . . . . . . 54

7.3 Changing the mouse precision . . . . . . . . . . . . . . . . . . . . . . 56

7.4 Modifying grid boundary data . . . . . . . . . . . . . . . . . . . . . . 57

7.5 Changing the current directory and prefix . . . . . . . . . . . . . . . 59

7.6 Grid checks and conditioning . . . . . . . . . . . . . . . . . . . . . . 61

7.7 Grid refinement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

7.8 Modifying the default plot . . . . . . . . . . . . . . . . . . . . . . . . 62

7.9 Quitting GRID BUILDER . . . . . . . . . . . . . . . . . . . . . . . . 65

7.10 Restarting GRID BUILDER with existing grid data . . . . . . . . . 65

7.11 Assigning element property values . . . . . . . . . . . . . . . . . . . 66

7.12 Examining property values using fills . . . . . . . . . . . . . . . . . . 66

7.13 Generating hardcopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

7.14 Defining field data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

7.15 Generating node property values using kriging . . . . . . . . . . . . . 69

7.16 Examining property values using contouring . . . . . . . . . . . . . . 70

7.17 Assigning boundary conditions . . . . . . . . . . . . . . . . . . . . . 72

7.18 Importing results from a finite-element program . . . . . . . . . . . . 76

7.19 Importing old grid data . . . . . . . . . . . . . . . . . . . . . . . . . 79

8 References 83

A Importing DXF formatted boundary data 85

2 CONTENTS

Chapter 1

Introduction

GRID BUILDER allows you to generate a variety of two-dimensional, finite-elementgrids. It was designed primarily to produce triangular element meshes but there aresome facilities for producing rectangular meshes.

One of the most time consuming tasks involved when doing finite-element mod-elling is the preparation, debugging and subsequent refinement of the finite-elementgrid. For small problems with a few thousand nodes and elements, this stage inmodel development would take days or weeks to finish by hand. Unfortunately, largegrids are often required to satisfy the accuracy requirements of the finite-elementapproach, and so access to an automated grid generation procedure becomes critical.With GRID BUILDER you can reduce the time needed in this step, usually to fewhours at most, even for irregular grids with several thousand nodes.

How does GRID BUILDER do this? Briefly, it presents you with an interactive,graphical interface for grid creation and manipulation. First, the outer boundaryand any internal grid boundaries can be defined with the mouse or read from afile. Once the boundaries are defined to your satisfaction, the grid is automaticallyfilled with triangular elements. You can then, for example, use the mouse to chooseareas of the grid to be refined. There are several other options available throughcontext-sensitive menus. Because the program is menu-driven, you can move aroundquickly, and perform any desired task. During these steps, you do not have toconcern yourself with element or node numbers, because the program handles thisinternally and just presents you with a picture of the current state of the grid.

The purpose of this manual is to introduce the general structure of GRIDBUILDER and illustrate its use with a few examples. For help in more specificareas I will refer you to the on-line documentation, which supplies detailed, context-sensitive help screens while you are running the program. For information aboutfinite-element methods, I will refer you to any of the basic texts on the subject, forexample Huyakorn et al. [1983] or Pinder and Gray [1977].

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4 CHAPTER 1. INTRODUCTION

1.1 Getting started

The recommended method for running GRID BUILDER is to open a Commandprompt, make the directory in which you want to store your finite-element mesh thecurrent directory, and then to type the command:

gb

Assuming everything is installed and the program has been started, you will cur-rently have the title screen on your monitor. Press any key or click the mouse onthe OK button and the title screen will be replaced by the Main menu, shown below:

This menu appears at the top left-hand corner of the screen. You should alsosee a mouse cursor (white arrow) near the centre of the screen. Usually, each menuitem begins with a unique letter, and one of the items will be highlighted. To picka menu item you can either point and click with left or right mouse buttons, typeit’s first letter or move the highlight with the keys ↑ , ↓ or Spc and then pressEnter to select the highlighted menu item.

The first time you run GRID BUILDER I would urge you to choose the Helpoption. This gives an on-line help screen which explains how you interact with GRIDBUILDER using such things as menus, I/O boxes or the mouse. This general helpscreen is the only one which can be accessed from a menu. Many other help screensare available and can be accessed by pressing the F1 function key. If you pressF1 you will see the Help screen which is specific to the menu, I/O box or mouseprocedure that is currently active.

The first four items in the Main menu (File, Generate, Edit and Check) lead tosubmenus which can be accessed to perform specific tasks. The entire set of menusand submenus which are accessible from the Main menu are referred to as regularmenus. There is another set of menus, which will be referred to as the Tool menus,which are accessible from any regular menu by pressing F7 or by clicking the left orright mouse button outside a regular menu. The Tool menu contains options whichneed to be easily accessible at any time. For example, the Zoom option allows youto zoom in on a subregion of the domain and examine it in detail. The Tool menupops up near the current location of the mouse cursor and does not have a title so it

1.2. QUITTING GRID BUILDER 5

can be easily distinguished from the regular menu. The Tool menu procedures arediscussed in detail in Chapter 5.

When you start GRID BUILDER and first enter the Main menu, there will beno grid information stored in memory. Only those menu options which produce griddata (Generate or File) or don’t require grid data (Help or Quit) are enabled. Theoptions Edit and Check will be enabled when you have a grid in memory.

1.2 Quitting GRID BUILDER

Quit allows you to exit GRID BUILDER. It is included to avoid accidentally exitingthe program and losing data. Should you choose this option, the following promptwill appear:

Are you sure you want to quit? Yes/No

If you answer yes, and if there is grid data in memory which has not been savedto disk the following prompt will appear:

Save changes to grid? Yes/No

If you answer yes you can save the information in the normal manner. If yousay no, you will exit to DOS and any current changes to the grid will be lost.

1.3 In the event of trouble...

In some cases (e.g. GRID BUILDER is unresponsive or taking too long to performa task) you may wish to halt execution and start over.

In Windows 2000 or XP press Ctrl-Alt-Delete, choose Task Manager/Applicationsand then choose GRID BUILDER and End Task.

6 CHAPTER 1. INTRODUCTION

Chapter 2

Grid generation

The menu option Generate leads to a submenu with four options, which representthe basic types of grids which can be generated with GRID BUILDER. The proce-dures for generating the different grid types are discussed below. We will start ourdiscussion with the simple grid generation options Rectangular, Wedge and Layeredand then move on to the more complex procedures associated with the Irregular gridgeneration option.

You may find it helpful to run the appropriate sections of GRID BUILDER asyou read about them in the following chapters. Many of the procedures are discussedin detail in the on-line help screens so you should examine these if you have anyproblems. They can be accessed by pressing the F1 key while in a menu or I/Obox or when the mouse is active.

2.1 Rectangular grids

Many simple, conceptual problems can be simulated using a rectangular grid. Theoption Generate/Rectangular/Uniform spacing presents an I/O box in which you spec-ify the title, range (minimum and maximum in X and Y) of the rectangular domain,number of nodes in each direction and numbering scheme (e.g. along Y first). AnI/O box is a window which appears on-screen, and contains a number of fields inwhich you can enter the required text or numeric data. See on-line help for furtherdetails. Once these input parameters are supplied, a simple, rectangular grid isgenerated. An example is shown in Figure 2.1. Nodes are numbered starting at thebottom left-hand corner and moving up the left-most column parallel to the y-axis.

The option Generate/Rectangular/Variable spacing reads x and y grid line coordi-nates from a file and then automatically generates the grid. When you choose thisoption you are presented with a menu made up of files in the current directory withthe extension .GLINES. Here is an example of a file which defines 5 grid lines in xand y.

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8 CHAPTER 2. GRID GENERATION

Figure 2.1: Example grid generated by Generate/Rectangular/regular

2.2. WEDGE GRIDS 9

NX 5910722.00 910739.50 910789.50910839.50 910889.50

NY 56891334.56891372.56891422.56891472.56891522.5

The first line defines the number of grid lines in x, and then the x coordinatesare listed in order from smallest to largest. The file is read in free format mode soone or more coordinates can be given per line.

NOTE: Frac3dvs/HydroGeoSphere users should know that the format of thexy glines .dat file is the same as that generated by Frac3dvs/HydroGeoSpherewhen they write grid line information to the .eco file when the instruction ’Generateblocks interactive’ is used. So you can use these programs in conjunction with GRIDBUILDER to generate rectangular meshes with regions of graded mesh refinement.

2.2 Wedge grids

Wedge grids are useful for simulating systems which are radially symmetric (e.g.flow to a pumping well).

The option Generate/Wedge presents an I/O box in which you specify the title,inner and outer radius, number of degrees of arc, and the number of nodes alongthe edge and arc. Once these input parameters are supplied, a wedge-shaped gridis generated. An example is shown in Figure 2.2.

This grid is really just a deformed, rectangular grid (i.e. node numbering pat-terns are similar to a regular rectangular grid). In most situations, wedge grids canbe limited to 2 or 3 nodes around the arc, since the problem is radially symmetric.For flow to a well, the inner radius is usually taken to be the well radius, while theouter radius could be extended so that a Theis-type aquifer (infinite areal extent) isrepresented. As long as pumping effects do not reach the outer boundary this holdstrue.

2.3 Layered Grids

This grid type was originally developed to facilitate the generation of finite-elementmeshes for cross-sections which were constructed from borehole data. This type ofproblem could also be handled in a more general way using the Generate/Irregular-/Cross-section option.


Figure 2.2: Example grid generated by Generate/Wedge

2.4. IRREGULAR GRIDS 11

Figure 2.3: Example grid generated by Generate/Layered

NOTE: This option was restored from an old version of GRID BUILDER andso the I/O boxes have not been updated and will behave and appear a bit strange.

The option Generate/Layered uses a series of I/O boxes to supply the inputparameters. The domain is defined by a number of control points and layers. Acontrol point is like a borehole in a cross-section, for which layer elevations areknown. For each control point, the base elevation, layer top elevations and elementlength to the next control point are required. Finally, the number of nodes acrosseach layer is required. Once these input parameters are supplied, a layered grid isgenerated. An example with 2 layers and 3 control points is shown in Figure 2.3.

For comparison, we generated the rectangular, wedge and layered grid exampleswith approximately the same dimensions and number of nodes in the X and Ydirections.

2.4 Irregular grids

One of the most useful features of GRID BUILDER is its ability to generate ir-regular finite-element grids. These types of grids are necessary in a host of 2-Dfinite-element problems where complex geometry (e.g. a real watershed boundary)is encountered. As opposed to finite-difference techniques in which irregular bound-


aries are incorporated by making elements lying ‘outside’ the region of interest inac-tive, the finite-element technique only defines the mesh inside the boundaries of theregion of interest. This can result in a significant reduction in the size of the arraysrequired to solve a given problem. Another advantage of the finite-element methodis that grid refinement can be a local feature without affecting distant portions ofthe mesh.

2.4.1 Defining grid boundaries

The first step in generating an irregular grid is to define the geometry of the outer(and inner if required) grid boundaries. The option Generate/Irregular leads to asubmenu with three choices, two of which (Plan-view and Cross-section) allow youto interactively define the boundaries using the mouse. The third, Import, leads toa submenu which allows you to read previously defined or digitized boundaries orread an overlay which can be used as a reference during grid generation.

2.4.1.1 Using the mouse to define grid boundaries

The first two options; Generate/Irregular/Plan-view and Generate/Irregular/Cross-section, present an I/O box in which you specify the title, range (minimum andmaximum in X and Y) of the domain and the desired element length (which affectsthe size of the elements generated). Once the values are supplied, the screen willbe scaled automatically and you will enter the procedure which allows you to definethe outer boundary interactively using the mouse. Isotropic scaling in X and Y isalways maintained in the Plan-view option, while in the Cross-section option, verticalexaggeration is allowed.

Generally, when the mouse is active, a window will appear in the upper left-handcorner of the screen which contains the coordinates of the current position of themouse cursor. The precision of the coordinates can be altered with the Tool menuoption Mouse. For example, for a particularly large problem, you might want mousecoordinates to be rounded to the nearest 10 metres. Note that while the mouse isactive, the Tool menu cannot be accessed. You will have to exit the mouse procedureand then activate the Tool menu.

The disadvantage of defining node coordinates with the mouse is that the re-turned values change in discrete jumps, which are a function of the screen resolution,therefore the exact coordinate at which you wish to define a node may not be avail-able. If this is a problem, you can either correct the locations later using the Moveoption (which allows keyboard input), or try importing the boundary informationin a .DIG file, which is described in section 2.4.1.3. In the file you can define thenode locations exactly.


2.4.1.2 Retrieving previously saved grid boundaries

The option Generate/Irregular/Import/Boundary .GEN is used to retrieve previouslydefined grid boundary data, which was stored in a .GEN file using the Save .GENmenu option in the Gen Edit menu, which is described in Section 2.4.2. When youchoose this option you are presented with a menu made up of files in the currentdirectory with the extension .GEN. See Section 4.2 for detailed information aboutretrieving files. Once they are retrieved, the boundary data can be altered as desired,and a new grid can be generated.

2.4.1.3 Importing grid boundary data

The option Generate/Irregular/Import/Digitized .DIG is used to import a file of dig-itized (or manually generated) boundary node information. When you choose thisoption you are presented with a menu made up of files on the current directory withthe extension .DIG. See online help for a description of the file structure. An exam-ple of such a file can be found in gridbldr\demo\bnds.dig, which can be examinedwith a text editor.

Once you choose a file the outer boundary will be drawn on-screen, followed byany internal boundaries. This boundary data is treated in a way similar to thatgenerated using the mouse, so the rules which apply there also apply here (see on-line help for details). For example, the outer boundary should be defined first, andany internal boundaries should start and end by crossing an existing boundary.

2.4.1.4 Importing reference information

The option Generate/Irregular/Import/Overlay .OVR is used to import a file of dig-itized (or manually generated) graphical reference information (e.g. a watershedboundary). The file structure is identical to a .DIG file. An example can be foundin gridbldr\demo\waterloo moraine.ovr, which can be examined with a text ed-itor. When you choose this option you are presented with a menu made up of fileson the current directory with the extension .OVR.

Once you choose a file the reference information will be be drawn on-screen.Since this data is not used to define grid boundaries, none of the normal rules applyand you are free to enter it in any way you see fit, as long as you adhere to the properfile format. The screen will be scaled to accomodate the reference data. Whetherthe system is treated as plan-view or cross-sectional is determined by the value ofthe true/false switch on the second line of the .OVR file. You will then be asked ifyou want to read a previously saved .GEN file or define the outer boundary usingthe mouse.


2.4.2 Modifying grid boundaries and grid generation parameters

Once the grid boundaries have been defined, control passes to the Gen Edit menuwhich allows you to manipulate and save the grid boundaries and grid generationparameters. The menu options are described below:

Cut Subdivide the current grid areas by defining a new internal boundary. Newnodes are created by a mouse click or by the intersection of the new boundaryand an existing boundary. The situation sometimes arises where a new node isextremely close to an existing node. This can be remedied with the Fix option,described below. Some useful tips are outlined below:

• If you want to insert a new node on a boundary segment, you can do soby cutting a single line segment across the boundary (i.e. by defining 2nodes). This will insert one node at the intersection point.

• If a cut ending inside an area has more than 1 node inside that area, itwill be extended to the area boundary automatically.

• If you want to define an interior node at a specific location (e.g. for apumping well in a two-dimensional flow simulation) you should define itas part of a cut.

Move node Pick a node with the mouse and move it to a new location. You canenter exact coordinates from the keyboard should you so desire.

Parameters This option is used to modify the three grid generation parameters:target element length, stretch factor and node drop rate as explained below.It leads to the following submenu:

Info This option allows you to click the mouse inside an area to find out thecurrent values for target element length, stretch factor and node droprate.

Single area Click the mouse inside an area to open a dialogue box which allowsyou to modify the target element length, stretch factor and node droprate. The target element length specifies the target size of the elements tobe generated. This is a guide only, final element sizes may vary somewhat.Stretch factor controls the aspect ratio of elements in zones of transitionfrom fine boundary elements to larger target elements while node droprate controls the frequency at which nodes are removed as we go fromfine to coarse elements.

Multiple areas This option allows you to choose one or more areas and modifythe target element length, stretch factor and node drop rate. Area num-bers are shown on-screen at the area centroid. White numbers indicatethat the area is not chosen, while yellow numbers indicate a chosen area.The following submenu allows you to change which areas are chosen:

Flip Reverses the current state of each area.


Off Turns all areas off (i.e. they are not chosen).Area Click the mouse in an area to reverse its current state.

Hole Assign an area as a hole and do not generate elements in that area. Thearea should not touch the outer boundary or be adjacent to another areawhich is made into a hole.

Fix interactive This leads to a submenu which allows you to interactively eliminateboundary nodes which are too close together. This often occurs when makinga cut or when importing digitized boundary data. When entered, the twonodes at the ends of the shortest boundary segment are shown, one blue andone yellow. You can cycle through all the boundary segments or press Esc

at any time to return to the Gen Edit menu.

The Fix submenu options are as follows:

Info For the blue and yellow nodes, show the node number, X- and Y-coordinateand the distance separating them. Press any key to remove the window.

Blue Keep the blue node and delete the yellow node.Yellow Keep the yellow node and delete the blue node.Average Create a new node halfway between the blue and yellow nodes and

delete the blue and yellow nodes.Skip Leave the blue and yellow nodes as they are.Zoom Zoom in on the region around the blue and yellow nodes.Undo Restore the boundaries as they were prior to the last fix

Fix batch This option allows you to automatically eliminate boundary nodes whichare closer together than a defined tolerance. A dialogue box allows you toenter the minimum segment length (i.e. tolerance)

Refine boundary This option allows you to choose a subset of nodes using the pro-cedure described in Section 6.2.1. Once you exit the procedure, a dialoguebox allows you to enter the element length to apply to any boundary sectionswhich lie bewteen the chosen nodes. If you want different section to havedifferent element lengths, they must be defined one at a time.

Fill boundary This option generates nodes along the outer and inner boundariesusing the current set of grid generation parameters.

Disconnect boundary nodes This option allows you to disconnect nodes along a por-tion of a subarea boundary. This could be used, for example, to preventsurface water from flowing across the boundary where the nodes have beendisconnected.

You must choose a subset of at least 3 nodes which are contiguous and locatedon a single subarea boundary. The nodes located between the two end nodesare duplicated, and element lists are modified so that elements on one side ofthe disconnected boundary contain the original nodes, while elements on theopposite side contain the duplicate nodes.


Undo This option restores the grid boundary state to what it was before the lastaction. It only works for options located above Undo in the Gen Edit. Forexample, if you executed the Fix Batch option and the results were not sat-isfactory, you could restore the grid boundaries as they existed prior to theoperation and try again.

Do Generate the triangular finite-element grid. If the boundary information has notbeen saved you will be prompted to do so before grid generation begins. Youshould see GRID BUILDER fill each area with triangular elements. One ofthe most common problems at this stage is that GRID BUILDER slowly fillsthe grid with tiny elements. This is most likely because you specified a smallelement target length. You can either let the program proceed or try halting itby pressing the Ctrl-Pause/Break. This should exit the program and put youin the debugger window, which can be exited by pressing Shift-F1. Hopefully,you saved the boundary data in a .GEN file. If you did, you can retrieve itwith Generate/Irregular/Import Boundary .GEN and increase the element targetlength before you generate it again.

No Grading This menu item indicates the current element size grading scheme ineffect. The default No grading indicates that uniformly sized elements will begenerated.

Choosing this option will change the menu item to Grading, and activate theelement size grading feature. It leads to a submenu which allows you to enterelement grading factors, which are similar to field data points (see section 6.6).Grading factors are used in conjunction with the target element size to generateelements of a certain size. For example, if the target size is 10, a grading factorof 0.1 would generate elements of size 1 in that region, while a grading factor of2.0 would generate elements of size 20. If you subsequently choose the Gradingoption, you will be presented with the prompt

Edit grading factors or disable grading? Edit/Disable

Choose disable to resume generating uniformly sized elements. The menuoption will return to No grading.

Save .GEN Save the current grid boundary data and generation parameters in a.GEN file. See Section 4.1 for detailed information about saving files. Whenthe grid boundaries are defined to your satisfaction, I would advise you to savethe data before you proceed to generate the grid. This will allow you to returnto this point in the grid generation process at a later time.

Node info Obtain information about a specific node, such as the X and Y coordinate.You will be prompted as to whether you want to choose nodes with the mouseor by entering a node number. The mouse is most commonly used to picknodes but if you have a node number and do not know its exact location youcan use the latter method to find it quickly. When you pick a node, a windowappears which contains information specific to that node.

2.5. REGENERATING THE GRID 17

Area info Obtain information about a specific area, such as area number and gridgeneration parameters target length, stretch factor and node drop rate. Youwill be prompted as to whether you want to choose areas with the mouse orkeyboard. The mouse is most commonly used to pick areas but if you have anarea number and do not know its exact location you can use the latter methodto find it quickly. When you pick an area, a window appears which containsinformation specific to that area.

2.5 Regenerating the grid

Once a grid has been generated using one of the three Generate options, you will bepresented with the prompt

Regenerate? Yes/No

If you say yes you can alter the grid generation parameters and regenerate the grid.In the case of the Rectangular, Wedge and Layered options you are returned to theI/O box where you can alter the appropriate parameters. In the case of the Irregularoption you are returned to the Gen Edit menu where you can make the appropriatechanges. Once you get the grid the way you want, you should answer no to theRegenerate... prompt. You will be returned to the Main menu where you can saveor edit the grid and its associated files.

Chapter 3

Grid Checks

Some general grid checking options can be performed from the Check menu.

3.1 Closest nodes

The option Closest nodes leads to a submenu which allows you to investigate nodeswhich are potentially too close together. When entered, the two nodes which havethe shortest separation distance are shown, one blue and one yellow. You can cyclethrough all the node pairs using Skip or press Esc at any time to return to theEdit/Check menu.

The Closest nodes submenu options are as follows:

Info For the blue and yellow nodes, show the node number, X- and Y-coordinateand the distance separating them. Press any key to remove the window.

Skip Move on to the pair of nodes with the next shortest separation distance.

Zoom Zoom in on the region around the blue and yellow nodes.

Relax nodes Each of the two closest nodes are moved to the centroid of the nodesto which they are connected. Nodes lying on a boundary (outer or inner) arenot moved.

3.2 Zero area elements

The option Zero area elements looks for elements with area less than or equal tozero. If there are any such elements, a message window will indicate this and a listof the element numbers will be written to the file prefix.chk.

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20 CHAPTER 3. GRID CHECKS

3.3 4 node connections

If so desired, nodes which are only connected to 4 neighbours can be deleted if theydo not define a break in a boundary. The 4 elements connected to the node will bereduced to 2 elements.

Such nodes are flagged with filled blue circles as the procedure is carried out,and the final result can be plotted using the option Tool/Refresh.

3.4 Relax grid

Evenly distribute all nodes in the grid by moving each node to the centroid ofthe nodes to which it is connected. Nodes lying on a boundary (outer or inner)are never moved. In some cases, particularly around sharp corners on an interiorboundary, this operation may result in a corrupt grid (elements may overlap). Also,smoothing of a rectangular or wedge grid may give undesirable results. Therefore,you are strongly advised to save any grid information prior to smoothing.

Chapter 4

File Input/Output

As you build a finite element model of a physical system, GRID BUILDER createsmany files to store various types of data. These files are linked together with a com-mon prefix, and are differentiated using unique extensions and descriptors. GeneralI/O operations can be performed from the File menu but it should be noted thatthere are other types of files which can be saved and retrieved from other submenus.These other files are discussed briefly in section 4.5.

4.1 Saving grid data

The option File/Save .GRD allows you to save grid data in a format which canbe retrieved later by GRID BUILDER. When performing this and other file saveoperations (e.g. the Save .GEN option in the Gen Edit menu) you will be presentedwith an I/O box which allows you to enter a prefix, with the current prefix usedas the default. Once you enter a valid prefix, it will become the prefix for all filenaming operations.

If you supply a prefix of a set of files which exist in the current directory, you willbe asked whether you want to overwrite them or not. If not, you will be promptedto enter a new prefix.

The directory you are in when you start GRID BUILDER automatically becomesthe current directory, which is where GRID BUILDER reads and writes all files. Thecurrent directory is shown below the prefix in the I/O box, and can be changed ifdesired using the Change directory button. Should you wish to change the defaultdrive, you will need to do so using the instructions outlined in Section 5.7.

Besides creating a .GRD file, there are other associated files created by this op-eration for which GRID BUILDER assigns certain file extensions. The extensionsand contents of these files are:

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22 CHAPTER 4. FILE INPUT/OUTPUT

EXTENSION CONTENTS FORMAT.grd General grid data ascii.xyc Nodal x-, y-coordinates binary.in3 Triangular element node list binary.seg Line segment node list binary.gbc Node, element, segment and binary

boundary condition data.ean Element area numbers binary.bni Area information and boundary node lists binary

Most of these files are saved using binary format (also referred to as unformat-ted). Internally, GRID BUILDER uses binary files to store most of the data. Theseare smaller and more efficient than ascii files. However, if you wish to view the files(using a text editor), transfer the files to another platform (e.g. Unix workstation)or import them to another program, they can be converted to ascii format using theinstruction File/Export/All to ASCII format described in Section 4.3.

4.2 Retrieving grid data

File/Get .GRD allows you to retrieve GRID BUILDER grid data which was storedpreviously using the option File/Save .GRD. It reads all associated files as discussedin section 4.1.

Any time you execute this or other file read operations which show a defaultfile extension (e.g. Generate/Irregular/Import/Boundary .GEN) you will be presentedwith a context-sensitive menu of files to choose from. In this case they will have theextension .GRD. The entries in the menu are the files in the current directory whichmatch the extension type, and any subdirectories in the current directory. If thereare no files with the appropriate extension found in the current directory, you canchange directories by clicking the mouse on any given subdirectory or {..} (i.e. theparent directory to the current directory). In this menu you are limited to changingdirectories on the current drive only. To change drives, you must do so as describedin section 5.7.

You can pick a file with the mouse or by highlighting the appropriate one withthe keys ↑ , ↓ or Spc and then pressing Enter . Alternatively, you can typethe first letter of a file name, and GRID BUILDER will immediately read that file,providing the first letter is unique. If the first letter is not unique, you will jump tothe first file in the menu which begins with that letter, and that file will be read.

If you pick a file, the file descriptor becomes the current prefix, and will bepresented as the default (with the appropriate extension) in any subsequent fileread/write operation, such as File/Save .GRD.

4.3. EXPORTING GRID DATA TO OTHER APPLICATIONS 23

4.3 Exporting grid data to other applications

By using the File/Export/All to ASCII format option, files generated by GRID BUILDERcan be read directly by a finite-element program which has appropriately formattedread statements, even if they are running on other platforms (e.g. UNIX). You canalso create your own intermediate programs which read these files and write themout in a format which is compatible with a third-party program.

In this version of GRID BUILDER, File/Export leads to a submenu with theseoptions:

GMS Mesh .2DM This option can be used to write the current 2D mesh to a filewhich is compatible with the Department of Defense Groundwater ModellingSystem (GMS) software. The file name used to store this information is gen-erated from the current prefix and the extension .2DM.

Element node lists are written as triangles unless the option Edit/Mesh/Treatas rectangles (see Section ??) has been chosen, in which case they are writtenas rectangles.

Tecplot This option can be used to write the current 2D mesh to a file which iscompatible with Tecplot software. The file name used to store this informationis generated from the current prefix, current nodal property name and theextension .tec.dat.

Element node lists are written as triangles unless the option Edit/Mesh/Treatas rectangles (see Section ??) has been chosen, in which case they are writtenas rectangles.

OB as .dig file This option writes out the x and y coordinates of the outer boundaryin .DIG file format. The file name used to store this information is generatedfrom the current prefix and the extension _ob.dig.

OB ordered node list This option writes out the list of node numbers in counterclock-wise order around the outer boundary. The file name used to store this infor-mation is generated from the current prefix and the extension ’_ob.ordered_node_list.

All to ASCII format This option writes a copy of each file with the current grid prefixto an ascii file whose name is made of the original name with the string ascii_preceding the file extension. For example, mygrid.xyc is written in asciiformat to mygrid.ascii_xyc and mygrid.nprop.nodal property is writtenin ascii format to mygrid.ascii_nprop.nodal property.

4.4 Importing foreign grid data

The menu option File/Import allows you to import triangular finite-element grid datafrom other programs GRID BUILDER. It leads to a submenu with these options:


Lists .IMP This option reads 2-D grid data created by the user. The file name usedto store this information must have the extension .IMP.

If you have used finite-element programs in the past and have problems forwhich detailed grids have already been defined, you can import these gridsinto GRID BUILDER and use them without further modification. The on-line help provides a detailed discussion of how to set up the .imp file. Thereis also an example which you can examine in gridbldr\demo\agrid.imp.

GMS .2DM This option reads 2-D grid data created by the Department of DefenseGroundwater Modelling System (GMS) software. The file name used to storethis information must have the extension .2DM.

4.5 Grid-related data

There are certain types of data in GRID BUILDER which are associated withthe grid that is currently in memory. For example, while you are running GRIDBUILDER, room is set aside in the computer memory for one set of node propertyvalues. This conserves computer memory but means that in order to work withmultiple sets of property values, we have to be able to save and retrieve them fromdisk. In order to keep track of these files, GRID BUILDER uses a special namewhich is composed of the current prefix, the extension .nprop. and a descriptor.The extension indicates what type of data the file contains, and the conventionsused are:

EXTENSION CONTENTS.nprop. Node property data..nchos. Chosen node data..eprop. Element property data..echos. Chosen element data..evec. Element velocity vector data..bc. Boundary condition data.

Once you define a grid, GRID BUILDER will scan the contents of the currentdirectory to find the files which are associated with the current prefix and have theappropriate extension (i.e. if reading a nodal property files with extension .nprop.are found). The user is then presented with a menu composed of the file-specificdescriptors. These descriptors are usually defined by the user during the file saveoperation.

Because GRID BUILDER scans the current directory each time a read opera-tion on a file is performed, the user can manipulate the file names (e.g. in WindowsExplorer) and any changes will be immediately reflected in the list of found descrip-tors. For example, to remove a file from the list of nodal property files associatedwith a specific grid, just rename it so that the prefix or extension do not matchthe required values. For example, a file called mygrid.nprop.topography could be

4.6. GRID-INDEPENDENT DATA 25

renamed either agrid.nprop.topography or mygrid.nprop_old.topography andits descriptor would no longer be picked up by the read operation.

There are many other output files in which the extensions and descriptors aregenerated automatically by GRID BUILDER (or by a separate application) whenthe file is written. For example, the option Edit/Boundary/Export creates a file nameusing the current prefix, the extension .bc_exported. and the current boundarycondition descriptor (e.g. mygrid.bc_exported.boundary data).

4.6 Grid-independent data

Some data are more general in nature and are not associated with a specific grid. Forexample, ground surface elevation may be collected at a set of arbitrary locationsdefined by x and y coordinates. Such data can be used by GRID BUILDER togenerate a set of node elevations for a finite-element mesh, but the data itself is notassociated with a specific grid. In this case we store the data in a file whose namedoes not contain the current prefix.

There are currently three types of files which contain such data whose namesare made up of a descriptor and an extension. The extension indicates what typeof data the file contains, and the conventions used are:

EXTENSION CONTENTS.fld Field data values..ovr Overlay data..asc Raster data (e.g. DEM Digital Elevation Model data)..wel Well data.

So for example, our ground surface data could be stored in a file called topo.fld.

When asked to load a specific type of data, GRID BUILDER will scan thecontents of the current directory to find all files which have the appropriate extension(i.e. if reading a field data files with extension .fld are found). The user is thenpresented with a menu composed of the file-specific descriptors.

Chapter 5

Special tools

The Tool menu contains options which you can access from any regular menu bypressing F7 or by clicking the left or right mouse buttons outside a regular menu.The options available in the Tool menu are discussed below. While in the Toolmenus, pressing the left or right mouse buttons outside the menu is equivalent topressing the Esc key, and causes you to exit the current menu.

5.1 Modifying the screen image

The Tool menu option Plot leads to a submenu which allows you to modify thegraphic information which is shown on the screen. The screen image is composedof a number of objects which can be manipulated in various ways. The submenuoptions are described below:

Size Change the size of the screen image. It presents a rubber box which is controlledby moving the mouse and is initially sized to reflect the extreme extents ofthe current mesh. Because of this using the option while you are zoomed inon a subregion of the mesh is not recommended. In plan-view grids, isotropicscaling between X and Y is maintained so that no distortion occurs. For cross-sectional grids horizontal movement controls X scaling and vertical movementcontrols Y scaling.

All objects are affected by the change, but text aspect ratios are maintainedin spite of changes in the X/Y scaling factor ratios.

Although changes in size are automatically reflected in plotted output, youshould be aware that there are other options which can be used to scale theplotted output when it is generated (see section 5.4).

Move mesh Change the position of the screen image. Click the mouse inside anelement and drag it to make a rubber band line and element appear. Positionthe mesh as desired and release the mouse button.

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28 CHAPTER 5. SPECIAL TOOLS

All objects are affected by this option.

Although changes in position are automatically reflected in plotted output, youshould be aware that there are other options which can be used to positionthe plotted output when it is generated (see section 5.4).

Flags Presents a submenu where each menu item represents a plot object which canbe toggled on or off (i.e. drawn or not drawn). An item whose toggle is on willbe highlighted with an asterisk to the left of the object name. You can togglethe option on or off by clicking on it with the mouse. Alternatively, you canmove up and down with the cursor keys and turn a flag on or off by pressingF2 . The screen will be re-plotted with the new set of items when you exitthe Plot Flags submenu.

Areas Spawns a submenu which controls the plotting of individual grid area bound-aries. The option Plot Areas All can be used to toggle on (ie. plot) all areaboundaries. Plot Areas Pick is used to pick individual area boundaries to toggleon or off. This can be useful, for example, if you want to show an isolated area(e.g. a lake) without showing the surrounding area boundaries. Note that toget a segment of area boundary to disappear, it is necessary to toggle off thearea boundaries on each side of the segment.

X-axis, Y-axis Change the parameters which control the position and appearanceof the axes. They each produce an I/O box which allows you to modify thedesired parameters.

Each axis is plotted from a start value to an end value and tick marks andlabels are controlled by an increment value.

Titles, Our name, Date These three options each produce I/O boxes which allow youto edit, position, size and toggle (ie. on or off) the appropriate object.

Changing the company name (ie. with Our name) from this menu affectsthis set of grid data only. In order to change the default company namefor all subsequent grids you should alter the name as it appears in the file\GRID\GRIDBLDR.CNF. You can do so using an appropriate text editor.

A changed date will only remain in effect for the current session of GRIDBUILDER. The current date (as set with the DOS DATE command) will beused as the default the next time you start GRID BUILDER.

Colours Changes the colour of individual plot objects. On the screen you will seea menu which contains the list of objects whose colours can be changed anda matrix of available colours to choose from. When you choose an object, itsname will be plotted over the colour matrix, and its current colour will beoutlined. Simply click the mouse on the new desired colour. The screen willbe re-plotted with the new colours when you exit the Plot/Colours submenu.

Palette Change the colour palette used when colour contouring or colour fillingnode or element property values. On the screen you will see a submenu, a

5.2. EXAMINING GRID SUBREGIONS IN DETAIL 29

matrix of available colours and colour numbers, and a colour bar showing thecurrent palette. The size of the matrix shown is dependent on the capabilitiesof your graphics card and the current Interacter settings. It will contain 16colours for Windows 95/NT colour palettes of 256 colours or less (see ‘display,colors, changing the number of’ in Windows 95 Help Index) and 256 coloursfor Windows 95 ‘High color’ or ‘True color’ settings

The submenu, which allows you to modify the current palette, has the followingoptions:

Manual Specify the palette start and end colour numbers manually.

Reverse Reverses the start and end numbers of the current palette.

Greyscale Set the palette start and end numbers to 208 and 255 respectively,which corresponds to the greyscale portion of the default palette. If youload a custom palette these numbers may no longer be meaningful.

Tecplot .MAP Reads colour palette information which is in Tecplot’s colourmapformat. These files can be produced by Tecplot. There are a few samplespalettes in the CMAPS directory.

The screen will be re-plotted with the new colours when you exit the Plot/Palettesubmenu.

General allows you to change character size factor for all plotted text, the size ofplotted nodes and the general numeric format for numbers presented in I/Oboxes.

White BG Change the background screen colour to white and change this option toBlack BG. Many plot objects which are by default white are changed to black.If the default colours of these plot objects has been changed they will be lostif the user reverts back to a black background.

5.2 Examining grid subregions in detail

The Tool menu options Zoom +/- and Restore allow you to examine subregions ofthe mesh in greater detail and then restore the view to its default state. This isuseful if you want to see a region where the elements are very small or when you wantto check node or element numbers which, at the normal scale, are often obscuredbecause of overlap.

When you choose Zoom +/- you are in effect activating the mouse buttons sothat the view is zoomed in (left button) or out (middle mouse button or scroll wheelif present) by a factor of 2 if pressed. Also, a zoom rectangle can be activated bydragging the mouse while holding down the left button.

The zoomed view remains in effect until you execute the Restore option, even ifyou return to the regular menus. This aids in refining finely discretized grid regions.


Note that if you do grid refinement while zoomed in, chosen elements may lie off-screen. Therefore it is advisable to first execute the option Edit/Element/Pick/Off.When you zoom, the plot will be clipped to leave an empty border and the axes willbe redrawn so that they lie on the screen. The axis start, end and increment values,as well as the placement values are temporarily altered. Once the grid is restoredto full-screen, the original axes are re-drawn. Therefore, any modifications made tothe axes while you are zoomed in will be lost.

The option Plot/Move mesh can be used to pan the zoomed subregion up, down,left or right.

5.3 Changing mouse precision

The Tool menu option Mouse can be used to alter the precision of the X- andY-coordinates returned by the mouse. A cycling menu is presented with optionsranging from 0.00001 to 10000.0 units. You can cycle through the choices using the↑ or ↓ keys and press Enter to make your choice.

5.4 Generating plotted output

The Tool menu option Hardcopy can be used to modify the graphical output gener-ated by GRID BUILDER. It produces a submenu with the following options:

Adjust Produces an I/O box which can be used to change the output driver andthe size and position of the plotted output with respect to the screen. Thereare currently five output drivers available; normal Postscript, encapsulatedPostscript, HP-GL, raster image and DXF. You can alter three parameterswhich allow you to scale and shift (up/down and left/right) the plotted outputin relation to the screen output. Although shifting the plot on the screen usingPlot/Move is reflected in the plotted output, it is preferable to leave the screencontents centered, and align the plotted output with Plot/Hardcopy/Adjust.Default plotter adjust data is stored in the file \GRID\GRIDBLDR.CNF. This datais used every time you run GRID BUILDER and generate a grid. Dependingon the peculiarities of your plotter (such as where you place paper etc.) youmay want to adjust these parameters (by editing the file with a text editor)and then use them on all subsequent plotted output. However, there may beindividual cases in which you will want to change these values. You can doso (in the input box), and the new values will automatically be saved in the.GRD file and used whenever plotted output for that specific grid is generated.

File Sends the output to a file in the current directory. The name of the file dependson how many plots have been sent to file in the current session and whichoutput driver is currently being used. The prefix PICnn is initially set to PIC1

5.5. REFRESHING THE SCREEN 31

and is incremented each time a file is produced. If you restart GRID BUILDERthe counter will be reset to 1, and earlier files with the same extension willbe overwritten. The extensions depend on the current hardcopy output driverand are as follows:

EXTENSION CONTENTS.HP HP-GL.PS Normal Postscript.EPS Encapsulated Postscript.PCX Raster Image.DXF Autocad DXF format

Plotter Outputs the plot commands directly to the plot-device which is connectedto the port which is set with a plotter statement in the INTERACT.INI file.See Appendix ?? for details. Be careful to send output to a device with theappropriate driver.

5.5 Refreshing the screen

The Tool menu option Refresh cause the screen to be re-drawn.

5.6 Getting general information

The Tool menu option Info outputs general information to the screen. There aretwo columns on the right-hand side of the screen called CURRENT and MAXI-MUM. Under these headings are the current and maximum (dimensioned) value ofthe property if appropriate (e.g. number of segments). This information includesthe number of nodes and node property files, bandwidth, number of elements andelement property files, node connections, grid areas, colour fills, boundary nodes,field data files, field data points, menu files and the current directory and prefix.

5.7 Changing the current drive

The option Change drive presents a menu made of the drive letters available on yourcomputer, excluding drives A: and B:, which are normally reserved for floppy drives.

When you choose a drive letter the root directory on that drive will become thecurrent directory. You can then use any file save or retrieve option to navigate tothe desired directory.


5.8 Shifting menu position

The Tool menu option Shift Menus allows you to move the regular menus to somelocation other than the default (top left hand corner). Just click the mouse in thedesired position and the menu will be re-drawn.

5.9 Distance estimator

The Tool menu option Distance can be used to output the distance between twopoints. When active, a window will show the current mouse XY coordinates. Movethe mouse to the starting point a click once to anchor one end of a rubber line.Move the mouse to the end point and click again to output the distance betweenthe endpoints of the rubber line.

5.10 Changing the pick mode

The Tool menu option Pick mode can be used to change the way that grid compo-nents (e.g. nodes) are chosen. It produces a submenu with the following options:

Toggle When choosing grid components (e.g. Edit/Node/Pick) the current state ofthe component (i.e. chosen vs not chosen) is toggled (i.e. switched to theother state).

Off When choosing grid components the current state of the component is set to benot chosen.

On When choosing grid components the current state of the component is set to bechosen.

5.11 Exporting area boundaries

The Tool menu option Area bn as .DIG prompts the user for an area number. Notethat you can get area numbers using the Edit/element/info/mouse option.

Given an area number, GRID BUILDER writes the boundary node x and ycoordinate list for the area in the file area.dig, which can be imported into GRIDBUILDER using the Generate/Irregular/Import/Digitzed .DIG option.

The Tool menu option All area bn as .DIG causes GRID BUILDER to write theboundary node x and y coordinate lists for all areas to a series of files area_001.dig,area_002.dig ... etc, which can be imported into GRID BUILDER using theGenerate/Irregular/Import/Digitzed .DIG option.

Chapter 6

Editing grid data

6.1 Mesh

Trim Allows you to remove elements from the current mesh, either by choosing asubset of element or nodes. In the case of nodes, if any node in an element ischosen, then that element will be removed.

Elements are removed as triangles unless option Edit/mesh/Treat as rectangles(see below) has been activated, in which case they are removed as rectangles.

Fit in .OVR Fits the current rectangular mesh into an irregular boundary as definedin the .OVR file. The file must contain four sections (representing the foursides of the domain) entered in counter-clockwise order.

Area numbers from .GEN Reads a .GEN file and resets the element area number ofeach element in the current mesh. If the element centroid falls within an areadefined by the .GEN file, then it is assigned that area number.

If an element does not lie in any area, it is assigned an element area numberof -999 (i.e. a missing value).

Elements are treated as triangles unless the option Edit/mesh/Treat as rectan-gles (see below) has been activated, in which case they are treated as rectangles.

No vertical exaggeration Forces the mesh to be drawn to scale (i.e. with no verticalexaggeration). If the mesh is already being drawn to scale, then this optionappears as Allow vertical exaggeration. If you choose to allow vertical exagger-ation, then the mesh can be rescaled and redrawn using the option Reset griddefaults described below.

Treat as rectangles Certain meshes are constructed of pairs of triangles which formrectangles, and are produced by the grid generation options Generate/Rectangular,Generate/Wedge, Generate/Layered and File/Import/GMS Mesh .2DM, if theGMS mesh is composed of rectangualr elements.

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34 CHAPTER 6. EDITING GRID DATA

This option causes the mesh to be re-drawn, with each pair of triangularelements being treated and shown as a single rectangular element. It alsochanges the behaviour of the following instructions:

File/Export/GMS mesh .2DM Mesh written to file as rectangular elements.

File/Export/Tecplot Mesh written to file as rectangular elements.

Edit/Mesh/Trim/Element(chosen) Both triangular elements must be chosen toeliminate rectangular elements.

Edit/Mesh/Trim/Node(chosen) Any rectangular element with a single nodechosen is eliminated.

Edit/Mesh/Area numbers from .GEN Centroids are computed for rectangularelements.

Edit/Element/Info Element numbers and node lists are shown for rectangles.

Edit/Element/Pick/Within .OVR Centroids are computed for rectangular ele-ments.

Edit/Element/Pick/Within .GEN Centroids are computed for rectangular ele-ments.

Edit/Node/Xras/Pond NPROP Node connection data are computed for rec-tangles.

Plot/Flags/Element numbers This Tool menu option shows the rectangular el-ement number.

If the mesh is being treated as rectangles, then the option is displayed as Treatas triangles, and can then be used to switch back to treating the mesh as beingcomposed of triangular elements, in which case the options listed above willbehave in the normal manner.

Reset grid defaults Causes the default plotting parameters to be recalculated andthe mesh to be redrawn. This is useful if you have modified the way themesh is being shown in an unintended fashion of if you decide to allow verticalexaggeration and want to regenerate the default plotting parameters.

6.2 Nodes and related data

The Edit/Node menu can be used to perform a variety of operations on nodes andnode-related data such as location or property value. The menu options are de-scribed below:

Info After choosing a node with the mouse or by entering a node number, a windowappears which contains information specific to that node, such as the X andY coordinate and current property value.

6.2. NODES AND RELATED DATA 35

If you use the keyboard and enter a node number which is greater than thenumber of nodes in the 2D mesh, GRID BUILDER assumes that the numberrepresents a 3D node number, and that the 3D mesh was constructed of anumber of 2D meshes stacked vertically. In this case, we can use the modulooperation (i.e. the remainder of division of one number by another) to deter-mine an equivalent 2D node number from the 3D number. This is useful fordebugging mesh-related problems if the 3D node number is given.

Move node Move individual nodes by pointing and clicking with the mouse.

Optimize Reduce the grid bandwidth by renumbering the grid in the optimal way.The bandwidth is determined by the largest difference between any two nodeson any given element in the grid. During grid generation and refinement,no attempt is made to keep the bandwidth to a minimum. Therefore, thisprocedure should be invoked on a newly generated or refined grid, prior tosaving it to disk. Whether you need to do this depends on the type of matrixsolver used by the finite-element model which will use the grid data. Mostconventional direct solvers construct an array whose size is equal to the numberof unknowns times the bandwidth. Therefore the memory required to solve agiven problem is a direct function of the bandwidth. Because the node numbersare shuffled during this procedure, it should be executed before you generatenodal property values or determine node numbers which are significant to yourfinite-element program (i.e. boundary nodes, pumping nodes etc.).

Relax Evenly distribute all nodes in the grid by moving each node to the centroidof the nodes to which it is connected. Nodes lying on a boundary (outer orinner) are never moved. In some cases, particularly around sharp corners on aninterior boundary, this operation may result in a corrupt grid (elements mayoverlap). Also, smoothing of a rectangular or wedge grid may give undesirableresults. Therefore, you are strongly advised to save any grid information priorto smoothing, unless you are sure that the results will be satisfactory.

6.2.1 Modifying nodal property values

For each node in the mesh, there is an associated numeric value, which we willrefer to as a nodal property value. These values could represent variables such ashydraulic head, aquifer thickness or hydraulic conductivity. The options which areused to manipulate the property values are delineated by the two lines in the menu,and are described below:

Pick Presents a submenu which allows you to modify the chosen subset of nodes.There are a variety of options for defining, modifying, saving and retrievingthe subset. When you enter the submenu, the system will be re-plotted, withthe chosen subset of nodes coloured yellow, and the unchosen nodes colouredgrey. By default, all of the nodes in the grid will be chosen initially. Once the


subset is defined correctly, you can return to the Edit Node menu and modifythe nodal property values for the chosen nodes. Some of the options whichfollow work only with the selected subset.

Assign Assign a new property value to the chosen subset of nodes. You will beprompted to enter the value in an I/O box.

Krige Presents a submenu which allows you to use the method of universal Krigeingto interpolate nodal property values from the current set of field data for thechosen subset of nodes. The options in the submenu are described below:

Field data Presents a submenu which allows you to modify the current setof field data and the semivariogram which will be used in the Krigeingprocedure. By default, a linear semivariogram with unit slope is usedunless a different one is defined by the user. Detailed information aboutfield data and semivariograms is given in Section 6.6. The two menus areidentical and this one is duplicated for convenience.

Go Presents an I/O box which allows you to define some Krigeing parametersand then start the procedure.

Result Presents an I/O box which allows you to change the contouring pa-rameters which are being used to display the results of the Krigeingprocedure. Note that these are the same values which are used in theEdit/Node/Contour option (i.e. the nodal property values.

Error Presents an I/O box which allows you to change the contouring parame-ters which are being used to display the standard error of the estimatesfrom the Krigeing procedure.

Drift Presents an I/O box which allows you to change the contouring para-meters which are being used to display the first-, second- or third-orderdrift (if calculated) from the Krigeing procedure.

Keep error/drift By default, error and drift calculations are not saved to diskand there no options in this menu to do so. This option allows you tooverwrite the current nodal property data with either the error or driftvalues. You can then exit this menu and save them to a file in thenormal fashion. NOTE: The results will no longer be available unlessyou regenerate them by krigeing.

Transform Presents a submenu which allows you to transform the nodal propertyvalues of the chosen subset of nodes in various ways. If necessary, you will beprompted to enter a constant or pick a file to perform the transformation.

Get nprop Get a new set of nodal property values from a file. Produces a menu ofavailable nodal property names to choose from.

Save nprop Save the current nodal property values in a file. The property name,current contour and colour fill information is stored along with the nodalproperty values.

6.2. NODES AND RELATED DATA 37

Contour Produces an I/O box which allows you to contour (simple or colour filled)the current nodal property values.

Fill Produces an I/O box which allows you to colour fill groups of nodes which havethe same property value. For example, hydraulic conductivity is often definedby layer in a cross-sectional model. Thus we have a few discrete values, onefor each layer. The region associated with each node is determined as the areabounded by the node, the element centroid and the midpoints of the elementsides which meet at the node.

Name Produces an I/O box which allows you to edit, position, size, orient and toggle(ie. on or off) the Nodal property name.

6.2.2 Other considerations

The option Edit/Node/Xtras leads to a submenu which contains some procedureswhich were added for our own specific reasons but may be of more general use.They are described below:

Draw flownet from 2 NPROP files Produces I/O boxes which allow you to choose twonodal property files and define two independent sets of contouring parameters.The results are displayed simultaneously, with the first file contoured with solidlines, and the second file contoured with dotted lines. If you choose appropriatehead and stream function data files, the resulting plot will be a ground waterflow net.

Save node connection info to CONNECT.LST Writes a list of nodal connection datato a file called CONNECT.LST. The file contains a single line for each node, whichconsists of the node number and a list of all nodes to which it is connected.Nodes are connected if they occur in the same element.

NPROP to GMS scalar .SCL Writes a GMS compatible ascii scalar data file contain-ing the current set of nodal property values. The file name is made up of thecurrent prefix, the string .nprop_to_gms_scalar., the current nodal propertyname and the extension .SCL.

Pressure head from NPROP - Y coordinate Converts the current nodal property val-ues to pressure head by subtracting the y-coordinate value at each node. Thisis only meaningful if the grid is a cross-section and the current nodal propertyvalue is hydraulic head.

List NPROP if node chosen Writes an ascii file containing a list of node number andproperty value for the set of currently chosen nodes to the file prefix.nch-nprop list.npname where prefix is the current grid prefix and npname is thecurrent nodal property descriptor. This could be used for example, to choosethe nodes along a section of the outer boundary corresponding to the water


table, and write the list of node numbers and hydraulic head values to a file,which could then be read in as a boundary condition for another model. Thefile name is made up of the current prefix and the extension .OUT.

Import GMS scalar as NPROP Reads GMS formatted scalar data from a file whosename is made up of the current prefix and the extension .SCL and overwritesthe current nodal property data.

Import raw ascii NPROP Reads data from a file whose name is raw_ascii_nprop.datand overwrites the current nodal property data.

Relax chosen nodes only This is like the Edit/Node/Relax option but only applied tothe current set of chosen nodes.

Overlay to TECPLOT from NPROP Prompts for the name of an overlay file and theninterpolates a z coordinate for each xy-coordinate pair from the current nodalproperty function. The output is written in TECPLOT format to the fileoname.tec geometry.dat where the first part of the file name is the descrip-tive portion of the overlay file.

Boundaries to TECPLOT from NPROP Interpolates a z coordinate for each xy-coordinatepair of all current mesh outer and area boundaries from the nodal propertyfunction. The output is written in TECPLOT format to the file prefix.bnd-.tec geometry.dat where the first part of the file name is the current gridprefix.

Nprop vs npoints at a node This option is useful for determining the optimum num-ber of data points to be used in the krigeing procedure. Before executing it,you should read in a set of field data, krige the nodal property values and plotthe standard error of estimates. When you then choose this option, you will bepresented with the Krigeing parameters I/O box. You can set the minimumand maximum numbers of data points to be used in the krigeing procedure tospan a range of values to be tested. For example, if you had several hundreddata points, you might specify a minimum of 5 and a maximum of 100 pointsto test. When you exit the I/O box, you can click the mouse in a few regionswith large error. For each mouse click, GRID BUILDER will search for thenearest node and then interpolate a value using first 5 nearest data points,then 10, then 15 etc. up to 100. Each interpolated value is written to a filekrig.npoints.dat in Tecplot format, along with the number of data pointsused to generate it and the standard error of estimate. You may find that20 points for example, is the optimum number of data points to use in thekrigeing procedure, and that increasing it does not significantly change theinterpolated value or reduce the standard error of estimate.

Nprop to TECPLOT file .tec.dat This is the same option as File/Export/Tecplot.

Set origin at xmin,ymin BEWARE!!! This option translates the grid in the xy planeso that the minimum x and y coordinates become zero.

6.3. ELEMENTS AND RELATED DATA 39

List XYZ if node chosen Writes an ascii file containing a list of node number andxyz-coordinates for the set of currently chosen nodes to the file prefix.nch-xyz list where the first part of the file name is the current grid prefix.

Relax NPROP surface This option can be used to smooth the current nodal propertyfunction. For each node, it calculates the average nodal property value of allconnected nodes and then sets the current nodal property to that value.

Pond NPROP This option is used to generate a guess of initial head values for asurface water flow problem. Before using this option you must read a set ofnodal properties (i.e. surface elevations), and choose the nodes which are toprovide outlets for surface water flow (e.g. the outer boundary). It determinesa drain elevation for each sub-basin in the watershed. If the nodal propertyof a node in a sub-basin is less than the sub-basin drain elevation, then thenodal property is set equal to the drain elevation.

Element node connections are computed for triangles unless the option Edit/Mesh/Treatas rectangles (see Section ??) has been chosen, in which case they are computedfor rectangles.

6.3 Elements and related data

Much of the Edit/Element menu options are very similar to those described abovefor nodes, and only some notable exceptions will be mentioned here.

• There is no Edit/Element/Move option.

• Edit/Element/Info After choosing an element with the mouse or by enteringan element number, a window appears which contains information specific tothat element, such as the incidence and X, Y coordinates of the corner nodes,the current property value and the area number that the element falls in.

Element information is written for triangles unless the option Edit/Mesh/Treatas rectangles (see Section ??) has been chosen, in which case they are writtenfor rectangles.

If you use the keyboard and enter an element number which is greater than thenumber of elements in the 2D mesh, GRID BUILDER assumes that the num-ber represents a 3D element number, and that the 3D mesh was constructedof a number of 2D meshes stacked vertically. In this case, we can use themodulo operation (i.e. the remainder of division of one number by another)to determine an equivalent 2D element number from the 3D number. This isuseful for debugging mesh-related problems if the 3D element number is given.

• The Edit/Element/Pick option is used to choose a subset of elements. This sub-set affects the Refine option, described below, as well as the element propertyvalues.


• When interpolating elemental property values using Krigeing, the elementcentroid is used as the point at which the value is interpolated.

• When contouring element data, because the contouring routine works withnodal data only, such a set is generated by averaging the element propertyvalues of all elements of which the node is part.

• In the Edit/Element/Fill option, the entire element is filled with the appropriatecolour.

The following items are unique to the Edit/Element menu:

Refine Subdivide the chosen subset of elements. The refinement process will beplotted on the screen as it executes. Each chosen element will be subdividedinto four elements, and the elements touching the boundary of the chosenregion will be subdivided into two elements.

Make sure you have enough array space available before you do the refinement.For each chosen element, there will be four elements after the refinement pro-cedure is completed. You can check the current number of elements using theTool menu option Info.

Avoid doing successive refinements of the same area, as this results in rapidlyincreasing numbers of nodal connections for the nodes around the boundary ofthe chosen area. The maximum number of nodal connections for a given nodeis currently 15. If you want to do successive refinements of a given region, youshould either decrease or increase the size of the area to be refined at eachstep.

Vectors Presents a menu which allows you to manipulate element vector information.Each vector is composed of an X and Y components which can then be plottedwith arrows that indicate direction and magnitude. The menu options aredescribed below:

Info

Edit Produces an I/O box which allows you to modify the appearance of theplotted vectors.

Legend Produces an I/O box which allows you to modify the appearance ofthe reference vector.

Get vectors Get a new set of element vector values from a file. Produces amenu of available element vector names to choose from.

Save vectors Save the current element vector values in a file. The vector name,and current plotting information is stored along with the nodal propertyvalues.

6.4. SEGMENTS AND RELATED DATA 41


The option Edit/Element/Xtras leads to a submenu which contains some procedureswhich were added for our own specific reasons but may be of more general use. Theyare described below:

NPROP → EPROP Creates a set of element property values by averaging the cur-rent nodal property values for each node in the element.

Calculate gradient from nprop Creates a set of element property values by comput-ing the gradient of the current nodal property. The element side with themaximum gradient is used.

Write chosen elements as quads Assuming the mesh is constructed such that trian-gles 1,2 form a rectangle then 3,4 etc., this option writes the current set ofchosen elements to a file in Grid Builder format (i.e. .echos.). The file nameis generated from the current prefix, the extension .np_ech_as_quads.’ andthe current chosen element descriptor.

Element area number → EPROP Creates a set of element property values from thecurrent element area number set.

EPROP → Element area number Creates a set of element area numbers from thecurrent element property values. Element property value should be integers(i.e. no fractional component).

Import raw ascii EPROP Reads data from a file whose name is raw_ascii_eprop.datand overwrites the current elemental property data.

Max angle → EPROP For each triangular element, the interior angle at each corneris computed and the maximum angle is saved as the element property value.

6.4 Segments and related data

The Edit/Segment menu was developed specifically for use with the HTS1 finite-element program (Ph.D thesis of VanDerKwaak, 1998) and has not been used ortested extensively. If you require further information about this option please con-tact the author.

6.5 Boundary condition data

GRID BUILDER allows you to assign boundary conditions to any nodes in thecurrent mesh. A finite-element model can use such information, but it is up to youto ensure that it does so in a meaningful way.


There are three types of conditions which can be assigned which are referred toas 1st- , 2nd- and 3rd-type. When you enter the Edit Boundary submenu, a specialplot will be presented which shows the current set of boundary data. Nodes arecolour-coded according to the following convention:

COLOUR TYPEBlue First-type, value can be shownGrey Second-type, zero-valued, value not shownRed Second-type, non-zero valued, value can be shownGreen Third type, value can be shown

The options in the Edit Boundary menu are described below:

1st-type Choose a subset of nodes and assign a 1st-type value to them. The valuecould, for example, represent a constant head node in a finite-element model.

2nd-type Choose a subset of nodes and assign a 2nd-type value to them. Thesevalues can be assigned directly to each chosen node or they can be multipliedby the contributing length (for boundary nodes) or area (for internal nodes)of the adjoining elements. Furthermore, when computing the contributinglength, you can consider only the X components (i.e. this could representrecharge due to rainfall, which is measured with respect to a horizontal planeonly) and ignore the contributions from elements beyond the start or end ofthe boundary node segment, which is often preferred at corners.

3rd-type Choose a subset of nodes and assign a 3rd-type value to them. The valuecould, for example, represent the combined fluid flux and concentration ofcontaminant in the fluid entering the system at a node. GRID BUILDERdoes not attribute any particular significance to the values you enter here.That depends on how they are treated by the finite-element model in whichthey are being used.

Clear Choose a subset of nodes and return them to the default state (2nd-type, zerovalued).

Info Get information about the current boundary condition at a node picked withthe mouse. Particularly useful if the node is time-varying as this shows thevalues which will be generated.

Get conditions Get a new set of boundary condition values from a file. Produces amenu of available boundary condition names to choose from.

Save conditions Save the current boundary condition data in a file.

Plot parameters Produces an I/O box which allows you to control node plot size,boundary node value size and format and whether to plot boundary values.

Export conditions This file can be used by a finite-element model to assign thesenodes the appropriate boundary type and value. This file consists of a title

6.5. BOUNDARY CONDITION DATA 43

line, a line containing the number of first-type nodes and a list of first-typenode numbers and values (one per line). Two additional sections providesimilar data for the second- and third-type boundary nodes.


The option Edit Boundary/Xtras leads to a submenu which contains some procedureswhich were added for our own specific reasons but may be of more general use. Theyare described below:

Head=elev For all chosen nodes in the mesh this option makes them 1st-type nodesand assigns the elevation (Y-coordinate) as the boundary condition value.

The most obvious use for this is to choose boundary nodes along the topsurface of the grid, which has been configured to represent the water table,and then set their hydraulic head to be equal to the elevation. It was designedto be used with the FLOW2D 2D groundwater flow model, but could be usefulfor other similar models.

Head=func For all chosen nodes in the mesh this option makes them 1st-type nodesand assigns the current nodal property value as the boundary condition value.

Sfunc .SFC The option Edit Boundary/Sfunc can be used to generate a set of second-type stream function values along segments of the boundary which are cur-rently specified as first-type head values.

You may recall that the second-type stream function along such a boundaryis defined in terms of the specified head as:

Fψi =

φi−1 − φi+1

2

where Fψi is the stream function second-type boundary value at node i, φ is

the potential (head) function and i− 1 and i + 1 are the nodes on either sideof i.

For every first-type node which has two first-type neighbours, this value iscalculated, and the node number and the values are written to the file withthe extension .SFC. This file can be incorporated into a finite-element data setat a later time.

Ltg3 Loops around the outer boundary of a grid and searches for elements whichhave both boundary nodes assigned a 3rd-type boundary condition. For eachsuch element, a record is written to an ascii file called ’LTG3.DAT’ containingthe element number, incidences of the two nodes forming the boundary seg-ment, the magnitude and sign of the velocity vector component normal to theboundary and it’s 3rd-type boundary condition value.


The current set of element velocity vectors are used when calculating thenormal component, and it is recommended (although not necessary) that youread the set of velocity vectors produced by a related flow solution before youchoose this option.

It was designed to be produce input for the LTGPLAN quasi-3D groundwatertransport model using flow velocities from the 2D groundwater flow modelFLOW2D, but could be useful for other similar models.

Flux leaving This routine requires that a set of velocity vectors from a flow solutionare loaded. When executed it computes the flux leaving the domain at allelement edges that have 3rd-type nodes at each corner and writes the resultsto the file prefix.flux leaving.bcname.vecname

6.6 Field data

A set of field data consists of a list of X-, Y-coordinate pairs, each with an associatedvalue. These coordinates need not coincide with node locations and can even falloutside the mesh. They are primarily used as input for the Edit/Node/Krige andEdit/Element/Krige routines which are used to generate node and element propertyvalues for the mesh. The Edit/Field data submenu allows you to manipulate differentsets of field data. This menu is also accessible from within the Edit/Node/Krige andEdit/Element/Krige submenus. The menu options are described below:

Add Allows you to add a field data point at a location chosen with the mouse.

Remove Allows you to remove a field data point using the mouse.

Edit Allows you to edit a field data point value using the mouse.

Clear Clears the existing field data values and sets the number of points back tozero.

Get field data Get a new set of field data values from a file. Produces a menu ofavailable field data names to choose from. You will be asked whether you wantto clear the existing data first (if there is any) If you don’t, the two data setswill be merged.

Save field data Save the current field data values in a file. The field data name andsemivariogram information is stored along with the field data values. You willbe asked if you want to create a new file, the alternative being to overwritean existing file. If the current number of saved field data sets is equal toMAXPROP, you must overwrite an existing file.

Name An I/O box allows you to change the field data name and the appearance ofthe field data values.

6.6. FIELD DATA 45

Variogram Leads to a submenu which allows you to modify the semivariogram forthis set of field data, which is used when krigeing values for nodes or elementcentroids. When you enter this menu, the screen is re-drawn and a plot of thevariogram of the current field data and the current best-fit semivariogram isshown. It is not my objective to give a rigorous description of semivariogramanalysis. For this the reader is referred to Davis, [1986], David () or Olea ().The Variogram menu options are described below:

Type Produces a menu which allows you to change the type of function whichis used to generate the best-fit semivariogram. The menu options corre-spond to the available function types and are described below:

Linear Defines a linear semivariogram which can be described by theequation:

γh = αh for h < aγh = σ2 for h ≥ a

where α is the slope, h is the lag distance, a is the range and σ2 isthe variance.

Spherical Defines a spherical semivariogram which can be described bythe equation:

γh = σ2(3h2a − h3

2a )

where h is the lag distance, a is the range and σ2 is the variance.Exponential Defines an exponential semivariogram which can be described

by the equation:γh = σ2(1− exp−h/a)

where h is the lag distance, a is the range and σ2 is the variance.Gaussian Defines a gaussian semivariogram which can be described by

the equation:γh = σ2(1− exp(−h/a)2)

where h is the lag distance, a is the range and σ2 is the variance.X-corr Defines a cross-correlated exponential exponential semivariogram,

which can be described by the equation:

γ(~s) = σ2

1− exp

−

(s21

λ21

+s22

λ22

)1/2

where λ1, s1 and λ2, s2 are the X and Y correlation lengths and lagdistances respectively and σ2 is the variance.

Bins Produces an I/O box which lets you change the number of bins thefield data is divided into when constructing the semivariance plot. Toomany bins may cause the semivariogram to be noisy, since some binsmay contain too few data. Too few bins may result in a loss of significantdetail in the semivariance plot.


Residual Plot the semivariances of the residual of the field data. The residualis a measure of how well the best-fit semivariogram matches the semi-variance of the original data. The menu option label will be changedfrom Residual to Original, and the residuals will be used to construct thesemivariance plot until the Original menu option is chosen, at which timethe original data will be used to construct the semivariance plot.

6.7 Overlay data

Overlay data consists of lists of x-, y-coordinate pairs, and are stored in files whosenames are formed from a descriptor and the extension .ovr. The coordinates neednot coincide with node locations and can even fall outside the mesh. The formatof a .ovr file is the same as the .dig file discussed in section 2.4.1.3. The maindifference between these files is that the order of the coordinate lists is not importantin the overlay file.

Overlays can be used for reference when defining grid boundaries, choosing nodesand elements etc. All overlay files present in the current directory will be loadedautomatically by GRID BUILDER. The appearance of the overlays can be adjustedusing the menu option Edit/Overlays which leads to a submenu with the followingoptions:

Flag Individual overlays can be flagged so that they are plotted on the screen.

Colour This option allows you to set the colour of each overlay.

Enable Enable(disable) the plotting of overlay data on the screen.

Overlay from contours Writes the current line contours as overlay data to the filewhose name is generated from the current nodal property name and the ex-tension .ovr

Show all All overlays are flagged so that they are plotted on the screen.

Info Click the mouse on an active overlay and it will be highlighted and a windowwill show the overlay number and file name. For the chosen overlay, each listof x-, y-coordinate pairs will be labelled with a tag number corresponding toit’s position in the overlay file, starting with zero for the first list, 1 for thesecond list etc. The Tool menu option Refresh can be used to remove the tagnumbers from the display.

Tag ovr file Click the mouse on an active overlay and it will be highlighted and awindow will show the overlay number and file name. A file with the samename as the overlay file, but with the prefix tagged will be created. It isidentical to the original file, except a third column is written which containsthe tag numbers described above in the Info option.

6.8. RASTER DATA 47

These last two options are useful if you are working with large overlay filescontaining many separate list of node coordinates. You can display the list numberswith Info, then create the tagged file and find individual lists using the tag numbers.

6.8 Raster data

Raster data consists of a set of values that are laid out of a rectangular grid withuniform spacing in x and y which are stored in files whose names are formed froma descriptor and the extension .asc. The coordinates need not coincide with nodelocations and can even fall outside the mesh.

The .asc file must consist of header information containing a set of keywords,followed by cell values in row-major order. The file format is based on the ArcGISascii file conventions and must consist of the following:

NCOLS xxxNROWS xxxXLLCORNER xxxYLLCORNER xxxCELLSIZE xxxNODATA_VALUE xxxrow 1row 2...row n

where NCOLS and NROWS are the number of rows and columns in the raster respec-tively, XLLCORNER and YLLCORNER are the x and y coordinates of the lower left cornerof the raster, CELLSIZE is the size of each raster cell, NODATA_VALUE is the value inthe ASCII file representing cells whose true value is unknown and xxx is a number.Row 1 of the data is at the top of the grid, row 2 is just under row 1, and so on.

For example:

ncols 480nrows 450xllcorner 378923yllcorner 4072345cellsize 30nodata_value -3276843 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 635 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...


Cell values should be delimited by spaces. No carriage returns are necessary atthe end of each row in the grid. The number of columns in the header is used todetermine when a new row begins. The number of cell values must be equal to thenumber of rows times the number of columns.

Raster files can be used for assigning node or element property values to thecurrent 2D mesh. For example, you could generate a set nodal property valuesrepresenting the ground surface elevation by using DEM (Digital Elevation Model)data to define the raster. This procedure involves a search to find which raster cella node falls in followed by a bilinear interpolation to compute the value at the nodefrom the four DEM values for the cell. This procedure is much faster than krigeingfrom scattered field data. In cases where successive 2D meshes are generated itcan be advantageous to first krige the field data to a rectangular grid and storethe results in a raster file, and then interpolate from that to the most recent 2Dfinite-element mesh as required.

All raster files present in the current directory will be detected automaticallyby GRID BUILDER. The Edit/raster option leads to a submenu with the followingoptions:

Read raster .ASC Loads the chosen raster data into memory.

Read raster .E00 This option supports the older Arcview interchange format andloads the chosen raster data into memory. Only files with the extension E00are considered.

Create raster by Krigeing field data Before executing this option the current direc-tory should contain a field data file which will be used in the krigeing proce-dure and also a raster or raster header file which will be used as a templatefor constructing the new raster file. You will first be prompted to load theraster and field data files if necessary and then modify the krigeing parame-ters as desired. A value will be interpolated for each grid point in the raster,which can take a long time depending on the size and spacing parameters ofthe raster. The file name used to store this information is generated from thecurrent field data name and the extension .asc (e.g. Aquifer 1 top.asc).This file can be loaded using Edit/Read raster .asc and used, for example, tointerpolate a nodal property values for a 2D mesh.

Relax raster Each value in the raster is adjusted by assigning it the value of theaverage of its 9 neighbours (inclusive). Figure 6.1 shows the effect of applyingraster relaxation 10 times to a raster of surface elevation.

Trim raster to grid The minimum and maximum grid extents are used to trim theraster. A new file is created using the original raster file name with the prefixtrimmed_. Consider doing this if the raster covers an area much larger thanthe grid and it takes a significant amount of time to read or consumes a lot ofmemory and disk space.

6.8. RASTER DATA 49

Figure 6.1: Effect of Relax raster option: (a) original (b) 10 times relaxation


Save raster Saves the raster data in a file.

Kill raster Removes the current raster data from memory.

NPROP from raster

Chosen NPROP from raster

EPROP from raster

Chosen EPROP from raster These 4 menu items interpolate a property value for eachnode (or element) by searching for the raster cell containing the node (orelement centroid) and then either:

1. doing a bilinear interpolation based on the four raster cell values.2. assigning the raster value which is closest to the node. This can be useful

if the raster contains discrete valued data such as soil type.The instructions starting with Chosen... only interpolate values for thechosen subset of nodes or elements.

Overlay to TECPLOT from raster Interpolates a z value for each coordinate pair inan overlay by searching for the raster cell containing the point and doing abilinear interpolation based on the four raster cell values. The file name used tostore this information is generated from the current prefix, the string .overlayas tecplot geometry, the current overlay name and then the extension .dat(e.g. mygrid.overlay as tecplot geometry.rivers.dat). This file can beimported into TECPLOT to show, for example, rivers on a relief map of thetopographic surface.

Field data to TECPLOT from raster Interpolates a new z value for each coordinatepair in a field data file by searching for the raster cell containing the pointand doing a bilinear interpolation based on the four raster cell values. Thefile name used to store this information is generated from the current pre-fix, the string .field data as tecplot geometry, the current field dataname and then the extension .dat (e.g. mygrid.field data as tecplotgeometry.borehole locations.dat). This file can be imported into TEC-PLOT to show, for example, borehole locations on a relief map of the topo-graphic surface.

Show raster Plots the raster grid on the screen. The Tool menu option Refresh canbe used to remove the raster from the display.

6.9 Hydrographs

The Edit/Hydrograph menu options were developed specifically for use with the InHmfinite-element program (Ph.D thesis of VanDerKwaak, 1998) and have not been usedor tested extensively. If you require further information about this option pleasecontact the author.

6.10. WELLS 51

6.10 Wells

A well data file consists of a target element size on the first line, followed by lists ofx-, y-coordinate pairs, which represent well locations. These data are stored in fileswhose names are formed from a descriptor and the extension .wel. The coordinatesneed not coincide with node locations.

Well data can be used to position nodes in the finite-element mesh and refinethe mesh around the well. All well files present in the current directory will bedetected automatically by GRID BUILDER. The Edit/Wells option which leads toa submenu with the following options:

Show potential well locations Nodes which might become wells are shown with afilled blue circle and a yellow line to the potential node location. If two linesare shown this means that two wells are competing for the same node. Youmay want to refine the mesh near the competing wells to the point that theyeach choose a unique node before using the Make wells option.

Make wells For the x and y coordinates of each well in the chosen file, the nearestnode in the 2D mesh is found. This node is then moved to the location of thewell and flagged as a well node and the mesh is relaxed. The grid around thenode is then refined successively until the elements around the well are smallerthan the target element size given in the first line of the well file.

Note that nodes flagged as wells are not moved during grid relaxation andmesh deformation may result if the grid is relaxed after the wells have beenadded.

Chapter 7

GRID BUILDERDemonstration

The demonstration consists of a list of step-by-step instructions which guide youthrough the creation and manipulation of a set of finite-element grid data. It coversmany of the most common procedures you will need to know to use GRID BUILDER.As you read through the demo, you should run GRID BUILDER and execute thebulleted instructions.

For the purpose of this discussion, we will assume that GRID BUILDER hasbeen installed in the default directory called C:\Program Files\gridbldr, and thatyou will run GRID BUILDER from the Command Prompt. If you are not in thedirectory C:\Program Files\gridbldr\demo then issue the DOS command:

cd c:\program_files\gridbldr\demo

During the demo, portions of the GRID BUILDER window may become blank ifyou use another windows program and then return to GRID BUILDER. To refreshthe screen just do the following:

• Press F7 or click the mouse outside the regular menu to activate the Toolmenu.

• Execute Refresh to replot the screen contents.

7.1 Starting GRID BUILDER

• To start GRID BUILDER, issue the command:

gb

53

54 CHAPTER 7. GRID BUILDER DEMONSTRATION

You should see the title screen.

• Press any key (e.g. Enter ). You should see the Main menu.

7.2 Importing grid boundary data

When you start working on a new finite-element problem, the first step is to definethe grid boundary information. The example below reads the information from afile which was created with a digitizer.

• Execute Generate/Irregular/Import/Digitized .DIG. Since, in this case, the menuitems all start with unique letters, you can either type the sequence GIID orgiid or point and click on each menu item with the mouse to do so. Youshould see a menu with a single file entry, bnds.dig, at the top and directoryinformation at the bottom.

• Press Enter , point and click with the mouse, or type b (i.e. the first letterof the file name, which does not have to be upper case) to read this file. AsGRID BUILDER reads the file it draws the outer boundary and some internalboundaries. The screen should now resemble Figure 7.1, with the exceptionthat the Gen edit menu will be visible.

• Execute Fix interactive to check for potential problems with boundary segmentswhich are very short. You should now see the Fix submenu appear, and thenodes on the ends of the shortest line segment will be coloured yellow and blue.In this case, you can only see the yellow node, which is located (approximately)at the X-, Y-coordinates 11000, 3400.

• Execute Zoom to see the region around the segment at a larger scale.

• Execute Info to see some information about the segment, including the distanceseparating the two nodes, in this case 8.45 metres.

• Press any key to remove the dialogue window.

• If the separation distance is insignificant compared to the overall size of thedomain, we can take the average without losing any significant geometric in-formation. Execute Average to create a node halfway between the blue nodeand the yellow node, at the same time removing the blue and yellow nodes.You will be returned to the normal scale, the boundaries will be adjusted andre-drawn, and the next shortest line segment will be highlighted.

• Execute Zoom to see the region around the next segment at a larger scale. Itlooks as if the blue node was created when the cutting segment was draggedacross the existing boundary, so the yellow node was probably created at alegitimate break in the first cutting segment.

7.2. IMPORTING GRID BOUNDARY DATA 55

Figure 7.1: Initial grid boundaries

• Execute Yellow to keep the yellow node and remove the blue node.

• Execute Zoom to see the region around the next segment at a larger scale.

• Execute Blue to keep the blue node and remove the yellow node.

• Execute Info to check the separation distance between the highlighted nodes,in this case 127.67 metres. This is a legitimate boundary segment (ie. it definesa break in the boundary).

• Press any key to remove the dialogue window.

• Press Esc to exit the Fix interactive submenu without making any morechanges and return to the Gen edit submenu. Remember that you can alsoexit regular menus by clicking the mouse outside the menu.

• Execute Do to generate the grid. You should see the following prompt:

Save changes to grid generation file? Yes/No

• Since we modified the original boundaries, it’s a good idea to save them beforecontinuing. Type Y or Enter to pick a yes response. You will see the I/Obox which allows you to change the current prefix.


Figure 7.2: Initial generated grid

• Press Enter to accept the current prefix bnds and exit the I/O box. You willsee the following prompt:

File exists...overwrite? Yes/No

• Type Y or press Enter to pick a yes response to exit the I/O box and savethe boundary information to the file bnds.gen.

You should now see the domain being filled with triangles, and the screenshould eventually resemble Figure 7.2. You should see the following prompt:

Regenerate? Yes/No

• Type Y or press Enter to pick a yes response. You will be returned to theGen Edit menu, and the elements will disappear.

7.3 Changing the mouse precision

You can alter the precision of the coordinates returned by the mouse. In this partof the demonstration, a mouse precision of 100 units is sufficiently accurate.

7.4. MODIFYING GRID BOUNDARY DATA 57


• Execute Mouse. You should see the Precision x menu. This is a cycling menu inwhich only one of several options is displayed at a time, in this case 0.00001.

• Press ↓ , ↑ , ← , → or Spc until the Precision x value is 100.0.

• Press Enter to accept the values and exit the menu. You should now see thePrecision y menu.

• Make the Precision y value 100.0.

• Press Enter to accept the values and exit the menu. You should now see theTool menu.

• Press Esc or click the mouse outside the menu to return to the Gen Editmenu.

7.4 Modifying grid boundary data

Once the boundary data is defined, you can alter it in the Gen Edit menu. In thissection of the demonstration, we make a few simple changes and then regeneratethe mesh to see the effects.

• Execute Parameters/Hole, and a window will appear at the top left-hand cor-ner of the screen which contains the X-, Y-coordinates of the current mouseposition.

• Press F1 and a help screen will appear which explains what the mouse but-tons do in the current situation.

• Press Esc to exit the help screen.

• Move the mouse to the X-, Y-coordinate 2400, 4500 and click the left mousebutton. The boundary of the area in which you clicked the mouse should nowbe hatched. This represents an area which will not be filled with triangles (i.e.a hole).

• Click the right mouse button to exit the Hole option.

By default, all areas of the grid have uniform grid generation parameter values.You can see the defaults using the Info option, and change them for a single area ormultiple areas.


• Execute Info and click the mouse inside an area and a dialogue box shows thegrid generation parameters for that area. Currently, the target element lengthis 271.48 m.

• Press a key to exit the dialogue box and click the right mouse button to retrnthe the Parameters menu.

• Execute Multiple areas and a new menu will appear which allows you to modifythe current set of chosen areas.

• Execute Off and Flip to activate all areas. If an area is active, the area numberis plotted in yellow.

• Press Esc to exit the menu and an I/O box will appear which allows you tochange the grid generation parameters for the chosen areas.

• Press F3 to delete text from the cursor to the beginning of the line. Thisapplies to any I/O box field.

• Make the Target element length 500.

• Press Enter or click the mouse on the OK button to exit the I/O box.

• Press Esc to return to the Gen edit menu.

You can position nodes precisely if desired.

• Execute Move node, and move the mouse to 6000, 5400.

• Click the left mouse button. A yellow rubber-band line now connects themouse position and the node closest to 6000, 5400.

• Move the mouse to 6700, 5400 and click the left mouse button. The yellowline becomes fixed, showing the new position of the node.

• Move the mouse to 6600, 3800 and click the left mouse button.

• Click the right mouse button and an I/O box appears which allows you toenter the new coordinates from the keyboard.

• Click the mouse anywhere in the X-coordinate input field to position the cur-sor. Although you can move through the fields in the I/O box using the ↑ ,↓ , Tab and SHIFT- Tab keys and move within a field using ← and →keys, it is often quicker to use the mouse.

• Make the X-coordinate 6811.

• Make the Y coordinate 3794.

• Press Enter to exit the I/O box. The yellow line shows the new position ofthe node.

7.5. CHANGING THE CURRENT DIRECTORY AND PREFIX 59

Figure 7.3: Modified grid boundaries

• Click the right mouse button to exit the Move node option. The screen shouldnow resemble Figure 7.3.

7.5 Changing the current directory and prefix

You can easily save the current mesh data to any existing directory on the currentdrive. To change drives, you must first do so as described in section 5.7.

• Execute Save .GEN. You will see the I/O box which allows you to change thecurrent prefix.

• Click the mouse on the Change directory button and you will see a menu whichallows you to navigate through the directories on the current drive.

• Click the mouse on the Mydata option and the current directory will bechanged.

• Click the mouse on the . option to exit the menu and return to the dialoguebox.

• Change the current prefix from bnds to mygrid.


Figure 7.4: Modified generated grid

• Press Enter to exit the I/O box and save the boundary information.

• Execute Do and the grid will again be filled with elements. When the grid iscomplete, you should see the following prompt:

Regenerate? Yes/No

• Type N or press → Enter to pick a no response.

• You should see the following prompt:



You will be returned to the Main menu. The screen should look like Figure 7.4.

7.6. GRID CHECKS AND CONDITIONING 61

7.6 Grid checks and conditioning

Before proceeding it is a good idea to perform grid relaxation and also to carry outa few checks of grid topology. These operations can be found in the Check menu. Itcan be seen from figure 7.4 that there are a few skinny elements in the mesh. Gridrelaxation can reduce this to a large extent.

• Execute Relax grid and you will see a marked improvement in the mesh (i.e.skinny elements are now more equilateral).

• Execute Closest nodes and the two closest nodes will be highlighted with blueand yellow circles, and a menu appears which allows you to zoom in on thesegment, find out how far apart the nodes are, skip to the next closest pairor relax the node pair. In this case the two closest nodes are an acceptabledistance apart. Press Esc to exit the procedure.

• Execute Zero-area elements. A dialogue box informs you whether or not anybad elements were found. Press Enter to exit the dialogue box.

• Press Esc to return to the Edit menu.

7.7 Grid refinement

Often you will want to refine a portion of the grid. To do so, you must first choosea subset of elements.

• Execute Edit/Element/Pick and the screen will be redrawn with the chosenelements flagged with a yellow circle.

• Execute Off to clear the chosen elements.

• Execute Circle and move the mouse to 2400,4500.

• Click the left mouse button to anchor the circle centre

• Move the mouse to 4500, 4500. A rubber circle should follow the mouse.

• Click the left mouse button to anchor the circle and elements within the circlewill be chosen.

• Click the right mouse button to exit the Circle procedure.

• Press Esc to return to the Element menu.

• Execute Refine to refine (subdivide) the currently chosen set of elements. Awarning is issued about backing up grid data before refining. Press any keyto continue.


• You will see the following prompt:

Refine anyway? Yes/No

• Type Y or press ← Enter to pick a yes response, and the results of the asthe refinement process will be plotted on-screen as it progresses.

• A warning is issued that data files associated with the grid are no longercompatible. Press any key to continue.

• Press Esc to return to the Element menu. The screen is not automaticallyredrawn.


• Execute Refresh to replot the screen contents.

7.8 Modifying the default plot

This section illustrates some modifications that could be made using the Tool menuoption Plot, to customize the position and characteristics of the default plot as itappears on the screen and plotted output.

• Execute Plot/Move mesh.

• Move the mouse into any element, then drag the element to a new position bydepressing the left mouse button while moving the mouse. A ghosted imageof the element follows the mouse and a rubber line connects the centroid ofthe ghosted element to its original location. Position the element as desiredand release the mouse button to fix the grid in the new position. The screenwill be redrawn.

• Click the right mouse button to return to Plot edit menu.

• Execute Our name. An I/O box appears which allows you to modify theattributes which control the position and appearance of the company name.

• Press F4 to delete text from the cursor to the end of the field. This appliesto any I/O box field. Since the cursor was positioned at the start of the field,this clears the old name Groundwater Simulations Group.

• Make the company name My Company.

• Point and click the left mouse button on the digit 6 in the Company name sizefield to position the cursor.

7.8. MODIFYING THE DEFAULT PLOT 63

• Make text size 0.9.

• Click the left mouse button on the Move Company name button. A rubberline drawn from the start of the name to the current mouse position shows thepotential new location of the name.

• Click the left mouse button repeatedly to anchor and re-anchor the Companyname in a new location.

• Click the right mouse button to return to the I/O box.

• Press Enter to exit the I/O box.

• Execute X-axis and make the Starting value 0.

• Make the Ending value 12000.

• Make the Tic label increment 2000.

• Change the label from X-axis label to Distance(m).

• Click the left mouse button on the Move All button. A rubber line drawn fromthe midpoint of the axis to the current mouse position shows the potentialnew location of the axis. Note that movement of the X-axis is restricted tothe vertical direction.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the axis in a new location.



• Execute Y-axis and make the Starting value 0.

• Make the Ending value 9000.

• Make the Tic label increment 1000.

• Change the label from Y-axis label to Distance(m).

• Click the left mouse button on the Move All button. A rubber line drawn fromthe midpoint of the axis to the current mouse position shows the potentialnew location of the axis. Note that movement of the Y-axis is restricted tothe horizontal direction.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the axis in a new location.



Figure 7.5: Modified default plot

• Click the left mouse button on the Move Label button. A rubber line drawnfrom the midpoint of the label to the current mouse position shows the poten-tial new location of the label. Note that movement of the label is restrictedto the horizontal direction.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the label in a new location.



• Execute Flags. A menu will appear which shows which entities are currentlybeing plotted.

• Click the left mouse button on the Elements option to toggle the plot flag (i.e.don’t plot the elements). Note that you can also position the highlight withthe cursor keys and toggle the plot flag by pressing the F2 key.

• Press Enter to exit the Flags menu. The screen will be re-drawn and shouldresemble Figure 7.5.

7.9. QUITTING GRID BUILDER 65

7.9 Quitting GRID BUILDER

You can exit GRID BUILDER at any time. Before you do so you will be promptedto save any changes to the grid data set.

• Press Esc until you are back to the Main menu.

• Execute Quit to exit the program. You should see the following prompt:


• Type Y or use ← Enter to pick a yes response. You should see the followingprompt:


• Type Y or press Enter to pick a yes response. You will see the I/O boxwhich allows you to enter the file prefix, in this case mygrid.

• Press Enter to use the current prefix. You will see the following prompt:


• Type Y to pick a yes response. The grid data will be saved to disk.

You should now be back in DOS, in the directory C:\Program Files\gridbldr-\demo.

7.10 Restarting GRID BUILDER with existing grid data

If the grid data for your particular problem was saved correctly, it is a simple matterto retrieve it and continue working with it.

• From the Command Prompt, issue the following command:

cd mydata

• Start GRID BUILDER. You should see the title screen.


• Execute File/Get .GRD. You should see a list of files, in this case it will containonly one item, mygrid.grd.

• Press Enter to read this data. The screen should now resemble Figure 7.5.


7.11 Assigning element property values

You can assign element property values for a subset of elements manually or byusing Kriging. Here, we will assign values to two portions of the mesh. These couldrepresent for example, aquifer hydraulic conductivity.

• Execute Edit/Element/Pick and the screen will be redrawn with the chosenelements indicated as filled, yellow triangles.

• Execute Off to clear the chosen elements.

• Execute Area and move the mouse into the upper righthand area at about8800, 4800.

• Click the left mouse button to choose the elements in this area.

• Move the mouse to the lower righthand area at about 8800, 1800.

• Click the left mouse button to choose the elements in this area. Note thatthe effect of toggling elements is cumulative. This applies to most of the Pickmenu options.

• Click the right mouse button to exit the Area procedure.


• Execute Assign and enter the value 1.e-4 in the I/O box.


• Execute Pick/Flip to toggle all the elements.


• Execute Assign and enter the value 1.e-5 in the I/O box.


7.12 Examining property values using fills

When element or node properties are assigned as we did in the last section, the mostuseful way to examine them is by using colour fills.

• Execute Fill. You will get an I/O box which reports the number of discretevalues found, in this case 2, as well as some parameters which affect the colourfill plot.

7.12. EXAMINING PROPERTY VALUES USING FILLS 67

• Press Enter to accept the current defaults and a menu will appear whichcontains a list of discrete values sorted in descending order of frequency ofoccurence. Values which will be colour filled are marked with asterisks.

• Press Enter to accept the current configuration. The screen will be re-drawn.The 2 colours used to fill the elements denote which property value they wereassigned. The legend to the right of the grid shows which value is associatedwith each colour. Currently they are both labelled 0.

• Execute Fill to activate the I/O box again.

• Click the left mouse button in the Fill bar label format field, which is apop-up menu consisting of available format options.

• Press F2 or click the mouse on the dropdown arrow at the right end of thefield to pop-up the menu of choices.

• Click the left mouse button on (1PE20.1). Note that you could also cycle themenu using the cursor keys.

• Press Enter twice to first exit the I/O box and then the fill value menu andre-draw the plot. You should now see meaningful fill legend labels, but thelegend itself is too large and the name is poorly placed.

• Execute Fill to activate the I/O box again.

• Click the left mouse button in the Size fill bar field. A rubber box drawnaround the fill bar legend shows the potential new size of the legend.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the legend at its new size.


• Click the left mouse button in the Move fill bar field. A rubber line drawnfrom the centre of the fill bar legend to the current mouse position shows thepotential new location of the legend.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the legend in a new location.


• Press Enter twice to first exit the I/O box and then the fill value menu andre-draw the plot.

• Execute Name and change Element property to Hydraulic conductivity.

• Make the Property name angle value 0.0.


Figure 7.6: Element property values shown using Fill

• Click the left mouse button on the Move property name button. A rubber linedrawn from the centre of the name to the current mouse position shows thepotential new location of the name.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the name in a new location, above the fill bar legend.


• Press Enter to exit the I/O box. The screen will be re-drawn and shouldresemble Figure 7.6.

• Execute Save eprop. You should see the I/O box which allows you to enterthe property name, which is written in the file with the property values andis also used to create a meaningful file name.

• Press Enter to accept the default Hydraulic conductivity and exit the I/Obox. The current element property values will be saved to the file mygrid-.eprops.hydraulic conductivity.

7.13. GENERATING HARDCOPY 69

7.13 Generating hardcopy


• Execute Hardcopy/Adjust and you will see the I/O box which allows you tomodify the hardcopy driver option.

• Press F2 to pop-up the menu of available drivers.

• Choose Normal Postscript.


• Execute File and the output will be written to a file called pic1.ps and plottedon the screen simultaneously.

7.14 Defining field data

Field data consists of a set of points for which we have a location (X, Y coordinate)and a value. These may be, but are not necessarily coincident with node locations.They can be used to generate a set of node or element property values.

• Press Esc three times to return to the Edit menu.

• Execute Field data/Get field data. You should see a menu consisting of allfilenames in the current directory which have the extension .fld. In this casethere is one item, elevation.

• Press Enter to read this data. The screen will be redrawn with the the fielddata points shown with small crosses and elevations.


7.15 Generating node property values using kriging

Given a set of field data, we can use them as input to a kriging routine to generatethe node or element property values. In this demonstration, we will generate a setof nodal property values.

• Execute Node/Pick and the screen will be redrawn with the chosen nodescoloured yellow. In this case all nodes are currently chosen.

• Press Esc to return to the Node menu.


• Execute Krige/Go to start the Krigeing procedure. You will see an I/O boxwhich allows you to modify the Krigeing parameters.

• Press Enter to accept the default data (including a linear semivariogram withunit slope) and exit the I/O box. As each node property value is generated,a countdown is shown in a message window along bottom of the screen, withthe final output being the time it took to complete the kriging procedure.

• Press any key to close the message window.

• Execute Result to contour the results. You will see an I/O box which allowsyou to modify the contouring parameters.

• Click the left mouse button on the Default contours button to generate moremeaningful contouring values.

• Press Enter to exit the I/O box and contour the kriged nodal function.

• Execute Error to contour the standard error of estimates. You will see an I/Obox which allows you to modify the contouring parameters.

• Press Enter to accept the default contouring parameters, exit the I/O boxand contour the standard error of estimates.

7.16 Examining property values using contouring

Kriging normally produces a node or element property value function which is con-tinuously variable. In this case contouring is more appropriate for examining thevalues than the simple colour fill used earlier.

• Press Esc to return to the Node menu.

• Execute Contour. You will get an I/O box which reports the range of thegenerated values and allows you to modify the contouring parameters.

• Make the Contouring minimum value 0.

• Make the Contouring maximum value 110.

• Make the Contouring increment value 10.

• Make the Plot colour fills?’ toggle Yes.

• Make the number of contour labels 11.

• Press Enter to return to the Node menu. The plot will be redrawn with thenode values represented by colour filled contours. A legend also appears whichshows the range associated with each colour.

7.16. EXAMINING PROPERTY VALUES USING CONTOURING 71

• Execute Contour to re-activate the I/O box.

• Click the left or right mouse button on the Colour bar size button. A rubberbox drawn around the fill bar legend shows the potential new size of the legend.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the legend at its new size. Make the legend shorter and narrower.


• Click the left or right mouse button on the Move colour bar button. A rubberline drawn from the centre of the colour bar legend to the current mouseposition shows the potential new location of the legend.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the legend in a new location. Move the legend down and to theright.


• Click the mouse on the Colour Bar Tic label format field and make it(F20.0).

• Click on the Move tic labels button. A rubber line drawn from the centreof the colour bar labels to the current mouse position shows the potential newlocation of the labels.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the labels in a new location. Move them to the left, closer to thecolour bar.



• Execute Name and change Node property to Elevation.

• Click on the Move property name button. A rubber line drawn from thecentre of the name to the current mouse position shows the potential newlocation of the name.

• Move the mouse and click the left mouse button repeatedly to anchor andre-anchor the name in a new location. Move it to the left of the colour bar.




• Execute Plot/Flags.


Figure 7.7: Node property values shown using colour contours

• Click the left mouse button on the Field data markers and Field data valuesoptions to toggle the plot flags (i.e. don’t plot the field data values).

• Press Enter to exit the Flags menu.

• Execute Palette/Greyscale to switch to a monochrome palette.

• Press Esc three times to return to the Node menu. The screen should nowresemble Figure 7.7.

• Execute Save nprop. You should see the I/O box which allows you to enterthe property name, which is written in the file with the property values andused to identify the contents at a later time.

• Press Enter to accept the default Elevation, exit the I/O box and write thenodal property data to the file mygrid.nprop.elevation.

7.17 Assigning boundary conditions

This section shows how to define a simple set of hydraulic head boundary conditiondata for our problem. It is assumed that the right side is a river whose elevation

7.17. ASSIGNING BOUNDARY CONDITIONS 73

varies from 90 m at the bottom to 95 m at the top. The hole inside the grid isassumed to be a pond with an elevation of 130 m.


• Execute Boundary and the screen will be redrawn showing the current bound-ary conditions. By default they are all 2nd-type with value zero and shown asfilled grey circles.

• Execute 1st-type/Segment and move the mouse to the lower right hand nodeat about 12200, 1000.

• Click the left mouse button to define the start of the boundary segment.

• Move the mouse to the upper right hand node at about 12300, 7100 and clickthe left mouse button to define the end of the segment. One possible set ofchosen nodes will be highlighted and you should see the prompt:

Correct nodes? Yes/No

• Type Y or press Enter to pick a yes response.

• You should see the prompt:

Spatially distribute how? Uniform/Variable

• Choose Variable as the distribution option. An I/O box will appear whichallows you to define the start value.

• Make the Current value (i.e. start value) 90.

• Press Enter to exit the I/O box. An I/O box will appear which allows youto define the end value.

• Make the Current value (ie. end value) 95.

• Press Enter to exit the I/O box. The values will be interpolated and plot-ted along the chosen boundary segment. The nodes will be coloured blue toindicate a first-type boundary condition.

• Execute Plot parameters to activate the boundary condition plot parametersI/O box.

• Make the Plot boundary values? toggle Yes.

• Press Enter to exit the I/O box. The plot will be redrawn with head valuesplotted beside the 1st-type nodes.



• Execute Zoom +/- and move the mouse to the middle of the lake, at about2300, 4500.

• Click the left mouse button and release it. The mesh is redrawn at about twiceits original size and with the lake in the centre of the screen. Click the mouseonce more in the middle of the lake to zoom in a bit more.

• Click the right mouse to exit the Zoom +/- procedure and then press Esc toreturn to the Boundary menu.

• Execute 1st-type/Segment and move the mouse to 2200, 5100.

• Click the left mouse button to define the start of the boundary segment, andwatch closely which node is selected. Although you were pointing at the nodeat the top of the hole, the node to the left was chosen. This is because themouse precision is still set to 100, and the node closest to 2200, 5100 is theone that was picked.

• Press the right mouse button to abort the Segment procedure.


• Execute Mouse.

• Make the mouse precision 10.0 in X and Y.

• Press Esc to return to the Boundary menu.

• Execute 1st-type/Segment and move the mouse to 2250, 5180.

• Click the left mouse button to define the start of the boundary segment.

• Move the mouse to 2130, 5150 and click the left mouse button to define theend of the segment. One possible set of chosen nodes will be highlighted andyou should see the prompt:


• Type N or press → Enter to pick a no response. A second possible set ofchosen nodes will be highlighted and you should again see the prompt:


• Type Y or press Enter to pick a yes response.

7.17. ASSIGNING BOUNDARY CONDITIONS 75

• You should see the prompt:

Spatially distribute how? Uniform/Variable

• Choose Uniform as the distribution option. An I/O box will appear whichallows you to define the value.

• Make the Current value 130.

• Press Enter to exit the I/O box. The values will be assigned and plotted alongthe chosen boundary segment. The nodes will be coloured blue to indicate afirst-type boundary condition.


• Execute Restore and the plot will be redrawn at full scale.

• Press Esc to return to the Boundary menu.

• Execute Save conditions and you will see the I/O box which allows you to enterthe current prefix.

• Change the name from Boundary conditions to Flow.

• Press Enter to exit the I/O box and save the boundary data to the filemygrid.bc.flow.

• You may want to produce an ascii file containing the current node numbers andboundary condition values. Such a file could be used by a third-party finiteelement program to define boundary conditions. Execute Export conditionsand you will see the I/O box which allows you to enter the exported boundarycondition name.

• Press Enter to accept the current name, exit the I/O box and save the bound-ary data to the file called mygrid.bc exported.flow.

• Press Esc twice to return to the Main menu.



• Type Y or use ← Enter to pick a yes response.


7.18 Importing results from a finite-element program

Before you can import data written by a finite-element program, the files should benamed according to the conventions used by GRID BUILDER. In this case, we havesupplied the files mygrid.nprop.flow2d head solution and mygrid.evec.flow2dvelocity vectors in the mydata directory. The first file contains a set of nodalhead data calculated by a 2-D aquifer simulation program using, as input, the gridand flow boundary conditions produced earlier on in the demonstration. The secondfile contains a set of element velocity vector data calculated by the same program.

Before you start this section you should make sure the current directory in thecommand prompt window is:

c:\program_files\gridbldr\demos\mydata



• Execute File/Get. You should see a list of files, in this case it will contain onlyone item, mygrid.grd.

• Press Enter to read this data.

• Execute Edit/Node/Get nprop. You should see the following menu of nodalproperty names:

Elevationflow2d head solution

• Press ↓ or ↑ to highlight the option flow2d head solution.

• Press Enter to read this set of data. A dialogue box informs you that defaultcontouring information has been generated for the data. Press Enter to con-tinue. The screen will be redrawn and the heads will be displayed with simplecontours.

• Execute Contour.

• Make the Contouring minimum value 90.

• Make the Contouring maximum value 200.

• Make the Contouring increment value 5.

• Change the Plot colour fills? toggle to Yes.

• Make the Number of contour lables value 11.

7.18. IMPORTING RESULTS FROM A FINITE-ELEMENT PROGRAM 77

• Make the Colour bar tic label format value (F20.0).

• Press Enter to return to the Node menu.

• Changes to the way the data are displayed, including krigeing parameters, canbe appended to the data file so that it appears the same way the next timeit is loaded. To do so execute Save nprop and you will see the I/O box whichallows you to define the property name. Press Enter to accept the nameflow2d head solution. You will see the following prompt:


• Type Y or press Enter to pick a yes response. The nodal property filemygrid.nprop.flow2d head solution will be overwritten.


• Execute Element/Vectors/Get vectors. You should see a menu with one item,flow2d velocity vectors.

• Press Enter to read this data. A dialogue box informs you that default vec-tor plot parameter values have been generated for the data. Press Enter tocontinue.

• An I/O box appears which allows you to modify the velocity vector plot para-meters. Press Enter to accept the default plot parameters. The screen will bere-drawn with the velocity vectors, some of which have very large arrowheads.

• Execute Edit to re-activate the I/O box.

• Make the Arrowhead size factor value 0.2.


• Execute Legend. You should see an I/O box which allows you to modify thereference vector.

• Make the Reference vector value value 1.0.

• Make the Reference vector format (F20.0).


• press Esc and you should see the prompt:

Save changes to element vector file? Yes/No


Figure 7.8: Imported heads and velocity vectors

• Type Y or press Enter to pick a yes response. You will see the I/O box whichallows you to define the vector name. Press Enter to accept the name flow2dvelocity vectors and exit the I/O box and then Type Y to overwrite thefile mygrid.evec.flow2d velocity vectors.


• Execute Node.

• Press F7 or click the mouse outside a regular menu to activate the Tool menu.

• Execute Refresh to update the screen image. The screen should now resembleFigure 7.8.

• Press Esc 3 times to return to the Main menu.




7.19. IMPORTING OLD GRID DATA 79

7.19 Importing old grid data

We have supplied the file c:\program files\gridbldr\demos\agrid.imp. Thisfile contains an old set of grid data.

• To return to the directory c:\program files\gridbldr\demos issue the DOScommand:

cd ..



• Execute File/Lists .IMP. You should see a list of files, in this case it will containonly one item, agrid.imp.

• Press Enter to read this data. You should see a window in which the resultsof the import procedure are reported, and the prompt:

Does list include node numbers? Yes/No

• Type Y or use ← Enter to pick a yes response. You should see the prompt:

Does list include element numbers? Yes/No

• Type Y or use ← Enter to pick a yes response. You should see the prompt:

Read element area numbers? Yes/No

• Type N or use → Enter to pick a no response. You should see the prompt:

Plan view? Yes/No


• A message window reports the results of the import procedure. Press Enter

to close the message window. After the outer boundary is constructed, thescreen should resemble Figure 7.9.

• Press Esc to return to the Main menu.

• Execute Edit/Node/Relax. The screen will be redrawn once the procedure isdone and should now resemble Figure 7.10.

• Press Esc twice to return to the Main menu.



Figure 7.9: Original grid data

7.19. IMPORTING OLD GRID DATA 81

Figure 7.10: Relaxed grid data



• Type Y or use ← Enter to pick a yes response. You should see the followingprompt:



This ends the GRID BUILDER demonstration.

Chapter 8

References

Davis, J.C., Statistics and data analysis in geology, 2nd edition, John Wiley andsons, New York, 1986.

Pinder, G.F., and W.G. Gray, Finite element simulation in surface and subsurfacehydrology, Academic Press, New York, 1977

Huyakorn, P.S., and G.F. Pinder, Computational methods in subsurface flow, Aca-demic Press, New York, 1983.

83

84 CHAPTER 8. REFERENCES

Appendix A

Importing DXF formattedboundary data

A utility program called DXF2GB can be used to extract boundary geometry froma file which has been saved in DXF format. To date, this utility has been usedsuccessfully with DXF files created by ArcGIS and CorelDraw. The steps involvedusing Coreldraw are:

1. scan a scaled image of the domain and import it into CorelDraw. It is impor-tant that the image be scaled accurately in the x and y directions. Verticalexaggeration is allowed.

2. Define grid outer and inner boundaries using the freehand tool. Vertices de-fined in CorelDraw will become nodes in GRID BUILDER.

3. Arrange boundaries in Object Manager so that they are in the reverse orderto that required by the .DIG file. E.g. outer boundary first, inner boundarywhich connects to outer boundary, inner boundary which connects to outerboundary and first inner boundary etc. See Figure A.1.

4. Select all the grid boundaries

5. File Export as DXF format, selected only and name e.g. cs.dxf

6. Run DXF2GB on the file cs.dxf to create cs.ovr. The coordinates in this filewill be in inches so they must be scaled properly into user coordinates (e.g.metres).

7. If the domain is a cross-section, edit the file cs.ovr and change the second linefrom .true. to .false.

8. Run GRID BUILDER and choose Generate/Irregular/Import/Overlay .OVR.

9. Define a roughly rectangular outer boundary which contains the overlay asdscribed in Section 2.4.1.4.

85

86 APPENDIX A. IMPORTING DXF FORMATTED BOUNDARY DATA

10. Choose Do to generate the mesh, No to Save grid generation data? prompt,No to the Regenerate? prompt.accept it.

11. Choose Edit/Overlays/Enable and Edit/Overlays/Colour to show the overlaysfor reference in the next steps.

12. Press F7 or click the left mouse button outside the regular menu to activatethe Tool menu. Choose Mouse and set the mouse precision to the finest possiblee.g. 0.00001 for both x and y.

13. Determine the coordinates in inches, of two points on the overlay, at the ex-treme ends (lower left and upper right) of the cross-section for which truecoordinates are known.

14. Create a file called cs.scl (in this case) which contains the following data:

-4.24947 -1.30418 0.0 ! lower left x, y, z in inches0.0 125.2 0.0 ! lower left x, y, z in true coordinates10.57883 3.44682 0.0 ! upper right x, y, z in inches752.78 186.3 0.0 ! upper right x, y, z in true coordinates.false. .false. false. ! log scaling in x, y, z

15. Run DXF2GB again. If present, the file cs.scl causes DXF2GB to scale thecoordinates accordingly. Copy the scaled cs.ovr to cs.dig.

16. Run GRID BUILDER and choose Generate/Import/Irregular/Auto-fix Digitized.DIG and load cs.dig.

17. Choose Fix and remove short segments as necessary and save as a .GEN file.

87

Figure A.1: Defining boundaries in CorelDraw

manual de grid builder gridbldr

Documents

gridrelated data

exporting grid data

retrieving grid data

editing grid data

foreign grid data

grid subregions

starting grid builder

grid builder prompts