Transcript Overview of Unsteady Flow Modeling With HEC-RAS Gary W. Brunner, P.E. 1

Overview of Unsteady Flow Modeling With
HEC-RAS
Gary W. Brunner, P.E.
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Introduction
Overview
 New Geometric Features for HEC-RAS
 Geometric pre-processor
 Boundary and initial conditions
 Unsteady flow simulation manager
 Post-processor
 Additional graphics/tables to view results

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Overview
Common geometry and hydraulic
computations for steady & unsteady flow
 Using the UNET equation solver (Dr.
Robert Barkau)
 Can handle simple dendritic streams to
complex networks
 Able to handle a wide variety of hydraulic
structures
 Extremely fast matrix solver

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New Geometric Features for RAS
Existing Geometric Features all work for
unsteady flow (XS, bridges, Culverts,
inline weirs/spillways)
 Lateral Weirs/Spillways
 Storage Areas
 Storage Area Connections (weirs, gated
spillways, and culverts)
 Pump Stations

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Pre-processing Geometry

For unsteady flow, geometry is preprocessed into tables and rating curves
 Cross
sections are processed into tables of
area, conveyance, and storage
 Bridges and culverts are processed into a
family of rating curves for each structure
 Weirs and gated structures are calculated
on the fly during unsteady flow calculations
 Pre-processor results can be viewed in
graphs and tables
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Cross Section Properties Plot
Property Table
RS = 138154.4
700
Legend
Conv. Channel
Elevation (ft)
690
Conv. Valley
Conv. Total
680
Storage
670
660
650
0
1000
2000
3000
4000
5000
6000
7000
Conveyance/1000 (cfs) Storage (cu ft)
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Cross Section Properties Table
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Bridge Hydraulic Properties Plot
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Boundary and Initial Conditions

Boundary conditions must be established
at all ends of the river system:
 Flow
hydrograph
 Stage hydrograph
 Flow and stage hydrograph
 Rating curve
 Normal depth
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Boundary and Initial Conditions

Interior boundary conditions can also be
defined within the river system:
 Lateral
inflow to a node
 Uniform lateral inflow across a reach
 Ground water interflow
 Time series of gate openings
 Elevation controlled gate
 Navigation Dams
 Observed internal stage and/or flow hydrograph
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Boundary and Initial Conditions

Initial conditions must be established for
the entire system:
 Specify
flows and perform a steady flow
backwater analysis
 Read in flow and stage at every node from
a previous run, “hot start” file
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Unsteady Flow Simulation
Simulation Manager
1. Define a Plan
2. Select which
programs to run
3. Enter a starting and
ending date and time
4. Set the computation
settings
5. Press the Compute
button
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HEC-RAS Computation Window
Geometric
Pre-Processor
Unsteady Flow
Simulation
Post Processor
Computational
Messages
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Simulation Options
Stage and Flow Output Locations
 Flow Distribution Locations
 Flow - Roughness Change Factors
 Seasonal Roughness Factors
 Friction Slope Method
 Output Options:

 Write
out Restart File
 Detailed Log level output
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Simulation Options- Continued
Encroachments - Method 1 Only
 Dam Breaching
 Levee Breaching
 Mixed Flow Regime
 Checking Data Before Computations
 Viewing Computation Log File

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Calculation Options and
Tolerances
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Post-processing Results
Used to compute detailed hydraulic
information for a set of user-specified
time lines and an overall maximum
water surface profile.
 Computed stages and flows are passed
to the steady flow program for the
computation of detailed hydraulic results

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Viewing Unsteady Flow Results
All of the output that was available for
steady flow computations is available for
unsteady flow (cross sections, profile, and
3D plots and tables).
 Stage and flow hydrographs
 Time series tables
 Animation of cross section, profile and 3dimensional graphic

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Stage and Flow Hydrograph
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Time Series Table
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Animation of Profile Plot
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HEC-RAS Demonstration
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