Download - Steel Structure Lecture - Torsion
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CEE 599: MODELING SEDIMENT TRANSPORT USING HEC-RASSTABLE CHANNEL DESIGN
Roxanne J CariniSpring 2016
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Choices for computing
n
• Manning• Kuelegan• Strickler• Limneros• Brownlie• Soil Conservation Service
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Manning
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KueleganRecall Chezy C, related to n:
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Strickler
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Upper Regime v.
Lower Regime
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LimnerosUpper Regime (Gravels & Cobbles) only!!
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Brownlie
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Soil Conservatio
n ServiceManning n versus VRH for 5 grass classes
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Stable Channel
Design Methods
• Copeland– based in Brownlie’s work (~7,000 lab and field records)
• Regime theory– from study of irrigation canals in Pakistan and India
• Tractive Force method– analytical shear stress balance
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Copeland • Predicts channel parameters and whether bed is aggrading or degrading (eroding) based on the following variables:
– Grain-related Froude number– Critical grain –related Froude number– Slope– Bed hydraulic radius– Median grain size (D50)– Sediment gradation coefficient (standard
deviation of gradation) – Kinematic viscosity– Manning “n” for side slopes
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Regime Theory
(Blench)
Mostly works for the uniform steady flow sand bed trapezoidal channels for which it was developed.
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Tractive Force
Method
• Calculates uniform shear on a “slice” of the channel.
• Compares this with a critical tractive force – Either from Shield’s analysis:
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Tractive Force
Balance from Lane
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Tractive Force from
Lane
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HEC-RAS Tutorial
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Stable Channel
Design Functions
1. Allow users to easily compute the hydraulic parameters of a given cross section.
2. Use that information to design a stable channel with regard to its size and armoring.
3. Determine the sediment transport capacity of that cross section.
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Uniform Flow Computations• Open Hydraulic Design Functions
window• Select Type Uniform Flow• HEC-RAS will automatically select a
cross section (XS) from the geometry file to display. User can choose any XS from the dropdown menu.
• S/Q/y/n tab: calculate normal slope, discharge, depth, and roughness for the current XS
• Width tab: calculate bottom width for uniform flow in a user-defined compound channel
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Solve for S/Q/y/n
• Enter 2 out of 3 fields (Slope, Discharge, W/S Elev) and solve for the third.
• Roughness, n: Automatically taken from geometry file, but can be changed. Function to define roughness can be chosen (6 options).
• Do not need to define n everywhere, only where it changes.
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Solve for S/Q/y/n
• Roughness options: Manning, Keulegan, Strickler, Limerinos, Brownlie, Grass-lined channels
• Limerinos & Brownlie require gradation distribution (only applied to main channel) d85, d50, d16
• Brownlie requires sediment specific gravity =2.65• Kuelegan requires temperature • COMPUTE button will not become active until all
necessary parameters have been entered!• To solve for roughness, click on and delete only one
roughness value in the table. HEC-RAS will then compute a Manning’s n value to satisfy the uniform flow equation for the portion of XS that is desired. Then the roughness value is back-calculated to match the selected roughness function.
• Computed value will appear in bold.
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Solve for Bottom
Width• Only occurs when user defines
compound channel.• Only trapezoidal compound channel
supported, with up to three levels: low flow channel, main channel, overbank channel.
• Bottom width, B, of main channel or overbank channel may be solved for.
• Subtraction or addition of width may be applied to right of centerline, left of centerline, or equally to both sides.
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Solve for Bottom
Width• SSL/ SSR: Side slope of left/ right of channel• WL/ WR: Bottom width of left/ right side of channel from
centerline to the toe of side slope• Height: Distance from to top of side slope of a respective
channel (low flow channel, main channel, overbank channel)• Invert: invert of a respective channel• Click Apply Geometry to plot the data.• Default Manning’s n applied in Station-Elevation table below.
User may change these as before, but do so in the Width tab.• Click Apply Geometry after making any changes.
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Solve for Bottom Width
• Enter energy slope, discharge, and water surface elevation in appropriate fields.
• Select Compute Widths and choose how: – Solve for main channel or overbank channel – Apply computed width left of CL only, right of CL only,
or centered equally (Total)• When all required data entered, COMPUTE
button will become active. Click it!• Unrealistic Geometries: Bottom width of upper
channel cannot become less than top width of the channel below it.
• Acceptable Geometries: Top width of lower channel can become greater than bottom width of channel above it. HEC-RAS automatically increases the upper channel’s bottom width to compensate.
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Solve for Bottom Width
• Click Copy XS to Geometric Data.• Enter the river station you want this XS to be
applied to. If the river station already contains a XS, will be asked if you want to replace it. If not, XS will be added and distances between the XSs will be adjusted.
• Must check bed elevations to ensure all are referenced to the same datum.
– Go to Geometry window, click Cross Sections button.
– Select Options Adjust Elevations… • File SAVE!!! in the Hydraulic Design
Uniform Flow window.
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Stable Channel
Design
• Open Hydraulic Design Functions window• Select Type Stable Channel Design
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Copeland Method
• Choose Copeland tab.• Set Design Discharge.• Fill in other Required Input, including
Gradation.• Choose Manning or Strickler to compute
roughness n or k.• Optional Input includes choosing Default,
Upper, or Lower Regime. HEC-RAS will report if Transitional Regime found in calculations, although it will still use whichever method you chose (upper or lower).
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Copeland Method
• Once all Design section inputs complete, click Inflow Sediment button to add information about the upstream sediment concentrations that will enter your Design section.
• Option 1: Set Inflow Sediment Concentration.• Option 2: Ask HEC-RAS to calculate Inflow
Sediment Concentration. – Enter necessary inputs for the Supply Reach.– Click OK.• When all required data entered, COMPUTE
button will become active. Click it!• Will receive 20 different options for Stable
Channel Design!
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Copeland Output
• Select one to view plot.
• Click OK.
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Copeland Output
• Once computation run, these buttons will activate.
• Click to see Table again.
• Click to see Stability Curves.
• Click to Copy results into Geometry File.
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Regime Theory
• Choose Regime tab and fill in Required Input.– Side Factor based on Blench work: 0.1 for friable
banks, 0.2 for silty, clayey, or loamy banks, or 0.3 for tough clay banks. Default value is 0.2.
• When all required data entered, COMPUTE button will become active. Click it!
• The Stable Channel Regime values for depth, width, and slope will be solved for and will appear in their appropriate fields.
• Plot window will display resulting XS.• Click Copy XS to Geometric Data to add XS as before.
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Tractive Force Method• Choose Tractive Force tab and fill in Required Input.– Angle of Repose: see RM Figure 12-9 for suggested
values.• Choose method with which to solve or critical shear:
Lane or Shields.• Remaining values are dependent variables. Only two
can be solved for at a time. Must provide other two. (Note: all three fields for particle diameter are considered just one variable.)
• When all required data entered, COMPUTE button will become active. Click it!
• Plot window will display resulting XS.• Click Copy XS to Geometric Data to add XS as
before.
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Next Time...
1. Allow users to easily compute the hydraulic parameters of a given cross section.
2. Use that information to design a stable channel with regard to its size and armoring.
3. Determine the sediment transport capacity of that cross section.
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Sediment Transport Capacity
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Example Setup
• Open BEAVCREK.prj project file in HEC-RAS.• Run Steady Flow Analysis with: – Geometry File: Bvr. Cr. + Bridge – P/W: New Le, Lc– Steady Flow File: Beaver Cr. – 3 Flows• Run subcritical steady flow analysis.• Save Plan File.• View water surface profile plot with all 3
flows.
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Hydraulic Design
• Click HD button.• Choose Type Sediment Transport
Capacity.• Sediment Reach: Series of cross-sections for
which sediment transport capacity is computed.
– Can have multiple Sediment Reaches within one River Reach, but they cannot overlap.
– Cannot have a Sediment Reach span more than one River Reach.
• File New Sediment Reach: Name the reach and define its spatial extent (river, reach, US RS, DS RS)
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Save and Define
Sediment Reach• File Save Hydraulic Design
Data As... And name the file.• River = Beaver Creek• Reach = Kentwood• US RS = 5.99 (US most XS)• DS RS = 5.49 (just US of bridge)• Profiles = select all 3 flows• Temperature = 55 F• Specific Gravity = 2.65• Concentration Fines (optional)
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Define Sediment
Reach• Bed Stations: XS stations that
separate LOB from main channel and ROB from main channel for sediment transport computations.
– Default = main bank stations– Values can be changed for every XS
in sediment reach– Appear as yellow nodes and
bracketed by “Mobile Bed” (MB) arrows at top of plot
• Bed Station Left = 866• Bed Station Right = 948
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Define Sediment
Reach
• Functions = Check boxes for whichever functions you’d like HEC-RAS to use to compute sediment transport.
• When you select a function, the dialog box below lists its specifications and assumptions. Really helpful for deciding which is most appropriate for your river!!!
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Define Sediment Reach
• Gradation = User can enter up to 50 particle size/ percent finer relationships. Right-click to expand the chart. Typically 5-10 gradation points is sufficient. If a 0% and 100% diameter are not specified, HEC-RAS will use first and last specified diameters for those percentages, respectively.
• Enter Gradation from HW 3 and 4 into the LOB, Main Channel, and ROB charts.
• Plot Gradation = graphical representation of % Finer versus grain size curve
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Compute Sediment Transport
• Choose Compute for this Sediment Reach, or Compute for all Sediment Reaches, if you’ve created more than one and they all have the same conditions.
• Options Menu: – Fall Velocity: Default chooses method used in the
research of the selected function(s).• Options = Toffaleti, Van Rijn, Rubey– Depth/Width: Default chooses depth/width
combination used in the research of the selected function(s).
• Options = Effective Depth/ Effective Width, Hydraulic Depth/ Top Width, Hydraulic Radius/ Top Width
– Compute for Small Grains Outside Applicable Range: Default for HEC-RAS to perform calculations for grain sizes which are smaller than the applicable range for a given transport function. Select “No” to override and only make computations within the applicable range for each transport function (Table 12.7 in RM).
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Compute Sediment Transport
• Click Apply anytime to save current changes to the file.
• Click Compute once all specifications are made.
• Click Close once computations finished.• Use Sediment Rating Curve Plot button
to view plot of sediment transport capacity rates for a selected cross section within a sediment reach.
• Use Sediment Transport Profile Plot button to view sediment transport capacity rates along a selected sediment reach.
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Sediment Rating
Curve
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Sediment
Transport Profile
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Report • Click Report button within each plot window to get table of results with description.
• Report will show only those results selected and plotted on the graph.
• River Station: choose amongst those within the sediment reach (5.99 to 5.49 here)
• Sediment Reach: choose sediment reach (only 1 here)
• Profiles: choose all or only select certain flows (3 flows here)
• Functions: choose from those computed
• Subsections: Total, LOB, Main, ROB
• Grain Size: All, or only selected ranges
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In Class Exercise
1. Create 2 Sediment Reaches: one from US-most RS to just US of bridge, the other from just DS of bridge to DS-most RS.
2. Choose 3 Sediment transport functions to run and compare.
3. Answer these questions:• Which station has the highest sediment
transport capacity? Which has the lowest?• Is this what you would expect based on the
results for velocities, shear stress, stream power etc.?
• If you had to actually assess a value for sediment transport capacity, which of the methods would you choose? Why?