lab#2 single frame analysis - memorial university of

6002 Lab#2: more ANSYS, page 1

Engineering 6002 - Ship Structures I

Lab#2

Single Frame analysis By C. Daley

Overview

In this lab we will model a single tee-section frame. Once

again, we will use SpaceClaim to create the geometry model

of the problem, and then use ANSYS to model the structural

behavior. We will explore some more features of both

SpaceClaim and ANSYS.

The lab will focus on;

- Build skills in SpaceClaim

ANSYS Model #2 – Single tee frame model

Step 1: describe and sketch the problem:

The aim is to model a beam that represents a single tee frame in a ship. The whole section looks

like an unsymmetrical I beam as shown below. To compare with beam results we will analyze

the case of a cantilever beam, with a load 0.2MN on the first half of the beam.


Step 2: estimate expected results (analytically):

The first step is to determine the moment of inertia of the beam, and then the value of EI.

The response that we might expect is;

Step 3: open ANSYS Workbench 19.0

1) First, save the (empty) project as Beam1.wbpj 2) The left-hand window shows a set of analysis type options. Select Static Structural and

drag the icon to the right, placing it in the Project Schematic window.


Step4: open Geometry and create the CAD model

1) By Clicking Geometry in the Project window, ANSYS will open a CAD modeling

program called SpaceClaim. You will see a window like this;

2)

3) If you want to change options or units, you can go to the file tab and select SpaceClaim

Options. This will let you change Units (mm are default) and many other options.


You now see the main window where the CAD model will be displayed, just as in Lab#1.

4) In the Design tab there are many drawing and editing tools. Let’s start by changing the

sketch plane to a vertical plane, so we can draw cross sections of our beam in a vertical

plane and then extrude them (pull them) to make a horizontal beam. To do this select the

sketch plane icon at the bottom of the screen.

Then move the mouse above the existing sketch plane and click.

NOTE: anytime you wish you can hit Undo to erase mistakes and re-do your steps.

5) Draw the component rectangles.

We need to draw the cross section of the beam. There are many ways to do this,

depending on the user’s knowledge of various commands and features. Here we will use

a way that will work with a few simple steps, and without much chance of error. We will

draw half the beam and mirror it to produce the whole x-section.

Start by selecting Plan View . Now zoom in so you see the origin. Now

select the rectangle creation tool in the Sketch area of the Design tab. By default

snapping to the grid (and many other features) is on. As you move the mouse over the

grid you will see a + snapping to the grid. Move the mouse so the + is at the origin


and left-click-hold-drag the mouse. As you drag you will see something like the

following;

Both rectangle dimensions are shown. If you start typing (while dragging or after) the

dimension will become what you type. By hitting Tab you can change to the other

dimension. So while you are dragging (or after) type 150 for the horizontal dimension

and 15 for the vertical dimension. You should see;

Now create a second rectangle, starting at the upper left corner of the first rectangle, of

dimensions 4 and 160. You should see;

Now create a third rectangle, starting at the upper left corner of the second rectangle, of

dimensions 37.5 and 20. You should see;


6) Mirroring

Now click on Mirror in the Create part of the menu. You will see

in the upper left of the main window. Click on the left side of one

of the rectangles;


You will now see at the upper left.

To select everything. Move the mouse above and to the left of the sketch and click-hold-

drag to select everything. As soon as you release, everything will be mirrored.

7) Trimming

Now we need to remove all interior lines so we only have the profile. There is a

command called Trim-Away . Select it and zoom into the sketch near the top. As

you move the mouse over a line, it will highlight the line. If you click, the line (line


portion) will be deleted. The interior lines are actually duplicates (bounding two

rectangles), so you will have to click twice to remove them. Remove all interior lines and

you will see;

8) Filleting

Now we need to add the 5mm fillets to the underside of the flange. We will use the pull

tool and do all four fillets at once. Click on the Pull tool . The mode will change

to 3D , the cursor will change and the sketch will fill in;

You need to select four points at the lower edge of the upper flange. Hold the Ctrl key

down and select just the four points. After you select the first you will see;

Then after selecting all four you will see;


With all 4 points selected, click and drag. You will see something like;

with the corners all being filleted. If you tap the space bar, you will be able to edit the

fillet radius. Type 5. When complete you will see;

9) Check Dimensions

You can check your final cross section by using the dimension tool to all

various dimensions. The tool is under the Detail tab. Everything should be as expected.


10) Extrude the X-Section

The next step is to extrude the section to create a beam 1000 mm long. Use the center

mouse button to rotate the section a bit (so it not a perfect plan view);

Now select the pull tool. Click in the cross section and start dragging to create a solid

beam. You will see the pull length highlighted in blue (177.93 below) . You can just type

1000 and the beam will snap to its full length.


11) Create patches for loads

The last thing to do is to draw a line splitting the bottom of the plate into two parts, so

that we will later be able to apply a load on half the beam. While we are at it we may as

well split the flange face as well. To do this we need to create a sketch plane on the plate

face. In 3D view, rotate the model, so you can see the bottom. Then select sketch mode

and select the bottom face. A grid will form, aligned to the bottom face. Selecting plan

view will make drawing easier. Select the line toll and draw a line across the exact middle

of the plate. As you hover the mouse over the edge of the plate, you will see a small icon

indicating the middle of the edge of the plate. Draw a line splitting the plate. Hit Esc to

stop the drawing.

Repeat these steps for the top flange;

This completes all work in SpaceClaim.


Step5: open Model and create the Finite Element model

1) Return to the ANSYS window, and click on the Model feature in the Project window.

This will start the ANSYS ‘Mechanical’ program, to setup the actual finite element

model.

2) The Mechanical window shows the 1 part.

At first the model is shown with no mesh or loads yet. On the left is a list of the model

features that have to be set. By default, the material to be used will be structural steel.

Note:

A green checkmark means that everything is OK

A yellow lightning bolt means that something hasn’t been done, but its ready to be

done.

A question mark means that there is something missing, or not yet set. ANSYS can’t

solve the model if there are any question marks.

Select the Mesh icon in the Project and right-click Generate Mesh.

The mesh on the body is ;


3) Now we will set the applied load and support condition on the beam.

First we fix the near end of the beam. Right-click on static structural, select Insert

and select Fixed Support;

Now click on the end face of the beam (ensure that faces are selected )

Now click Apply in the panel on the left that lists Details of Fixed Support.

You should see the face highlighted in purple and a green check by fixed support

under Outline.


Right-click on static structural, select Insert

and select Force;

Now select the top face of the flange (the ½ near the fixed support)

Now click Apply in the panel on the left that lists Details of Force.

Edit the magnitude to be 200,000N and have its direction as down.

Now you can the system/

4) To specify output, right click on Solution in the tree, and select Insert, then Stress, then

Equivalent Stress. Do the same to select Total Deformation.


5) When you select the Equivalent Stress under Solution in the tree, the von-Mises

equivalent stresses will be plotted on the deformed shape. The max stress is 3.3188e8,

which is in Pa. This is 332 MPa, and is not close to our simple estimate of 172Pa. If you

click on Total Deformation, it shows a max value of .0013682, or 1.37 mm, compared

with our estimate of 0.825 mm. These values are not close to our simple analytical

estimates. What has gone wrong?

Note that the deformation pattern doesn’t even have a shape as expected. This pattern is

indicative of shear.

So I calculated what the shear deformation would be and added it to the bending. The

new estimate (from Desmos) is 1.34 mm, which is much closer to the ANSYS result.

Note also that the shape of deflection in Desmos is similar to ANSYS. See

https://www.desmos.com/calculator/07813vczty

https://www.desmos.com/calculator/07813vczty


Self Study Exercises: Student:________________________

For each of these exercises, modify the model that you have developed above to explore

the model behavior and answer the questions given. Show the instructor your results and

make sure that it is recorded that you have completed the exercises.

Exercise #1 – Add a cutout (draw on surface and pull through) to the beam and

determine the effects.

How much has the max stress changed?

Exercise #2 – Redo the analysis by extending the free end by 2m (to 3m), and load

the free end only with 20000N down. What situation does the new analysis represent?

lab#2 single frame analysis - memorial university of

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