06 additional hec-ras modeling.ppt
TRANSCRIPT
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Additional HEC-RAS Modeling Features
First CoordinateLeft BankRight BankLast Coordinate
Invert
Downstream Section
Upstream Section
InterpolatedSection
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Objective• To allow you to become familiar with some of the
optional capabilities in HEC-RAS
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Optional Capabilities• Multiple Plan Analysis• Effective Area Option• Cross Section Interpolation• Graphical Editing Features• Mixed Flow Regime Calculations• Flow Distribution Calculations• Inline Weirs and Gated Spillways
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Multiple Plan AnalysisProject File: filename.prj
Plan 1filename.p01
Plan 2filename.p02
Plan 3filename.p013
Steady Flow Datafilename.f01
Geometry Datafilename.g01
Geometry Datafilename.g02
Geometry Datafilename.g03
Run File 1 Run File 2 Run File 3filename.r01 filename.r02 filename.r03
Output File 1 Output File 2 Output File 3filename.o01 filename.o02 filename.o03
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Notes on Plans• Modifications can be made to the geometry
and/or flow data, and then saved in separate files.
• Plans are formulated by selecting a particular geometry file and a particular flow file.
• The multiple plan option is useful when, for example, a comparison of existing conditions and future channel modifications are to be analyzed.
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Multiple Plan Option• Can be used to perform a design of a specific
geometric feature. • For example, if you are sizing a bridge
opening, a separate geometry file could be developed for a base condition (no bridge), and then separate geometry files could be developed for each possible bridge configuration.
• A plan would consist of a flow file and one of the geometry files. Computations are performed for each plan individually.
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Viewing tables and graphs• Once the computations are performed for all the plans,
the user can then view output in a graphical and tabular mode for any single plan or combination of plans.
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Ineffective flow areas
KE = V2/2g, where V =Q/A
• Velocity head is associated with flow in downstream direction
• If area in the cross section is not carrying flow it should not be included
• The “ineffective area” option of RAS is used for this
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Example:Ineffective Flow Areas at a Bridge
LeLc
typical flowtransition pattern
assumed flow transitionpattern for 1-dimensionalmodeling
3 2 14
Flow
1
ERCR1
BU BD
B b
Four cross sections are needed to describe the active flow area for flow through the bridge opening
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Designation of Ineffective Area Related to Type of Bridge Flow
Types of Bridge Flow• Low flow through bridge opening• Pressure flow through bridge opening• Weir flow • Pressure and weir flow• High flows over bridge and approaches
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Cross Sections at BridgeLocation of Cross Sections 2 and 3
• Bounding sections for bridge• Define bridge interior for upstream and downstream bridge sections• Must be defined before bridge data are input• Usually have ineffective flow area defined
LeLc
typical flowtransition pattern
assumed flow transitionpattern for 1-dimensionalmodeling
3 2 14
Flow
1
ERCR1
BU BD
B b
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Ineffective Flow Areas at Cross Section 2
Ineffective Flow Area Stations and Elevations
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Defining Ineffective Area• Permanently block out area• Block out area until water surface reaches a given
elevation• Multiple blocks• Use a levee• Use very high n-value in regions with very low velocity
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Normal Blocked Obstructions
Blocked obstructions decrease flow area and add wetted perimeter when the water comes in contact with the obstruction
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Multiple Blocked Obstructions
Up to 20 individual blocks can be defined. The left station, right station, and an elevation are entered for each of the blocks.
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Ineffective Area Option
Left Ineffective Flow Station
Right Ineffective Flow Station
The area is included in the storage calculations, but it is not included as part of the active flow area. No additional wetted perimeter is added to the active flow area.
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Levee Option
Left Levee Station
No water can go to the left of the left levee station or to the right of the right levee station until the levee elevations are exceeded.
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Levee Added
Left Levee Station and Elevation
A vertical wall is placed up to the established levee height. Additional wetted perimeter is included when water comes into contact with the levee wall.
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Cross Section InterpolationMay Be Needed When: • The change in velocity head is too large• To better model friction losses• To prevent the program from defaulting to critical
depth• To generate a smoother plot of the water surface
profile
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Cross Section Interpolation
First CoordinateLeft BankRight BankLast Coordinate
Invert
Downstream Section
Upstream Section
InterpolatedSection
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Interpolation within a Reach
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Interpolation between 2 Sections
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Adding Additional Master Cords
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Cross Section Interpolation• CAUTION: Automatic interpolation should not be used
as a replacement for required cross section data!• Interpolation can improve model calculations
(especially for unsteady flow analysis)
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Graphical Editing Features
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Modified geometry
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Mixed Flow CalculationsSteady Flow Calculations
• Subcritical Flow• Supercritical Flow• Mixed Flow
Unsteady Flow Calculations• Subcritical Flow• Supercritical Flow• Mixed Flow
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Mixed Flow
0 500 1000 1500 2000 2500 300060
62
64
66
68
70
72
74
76
Mixed Flow Plan: Mixed Flow Plan
Main Channel Distance (ft)
Elev
atio
n (ft
)
Legend
EG PF 1
WS PF 1
Crit PF 1
Ground
Mixed Reach
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Specific Force Equation
222
222
111
121 YA
AgΒQYA
AgΒQ
maFonacceleratimassForce
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Flow Distribution Option The flow distribution
option allows the user to see in different parts of the cross section:
• The amount of flow• The flow velocity
700 720 740 760 780 800
1804
1806
1808
1810
1812
1814
1816
Critical Creek - Example 1 Plan: Existing Conditions Upstream Boundary - XSec 12
Station (ft)
Ele
vatio
n (ft
)
Legend
EG 100 yr
WS 100 yr
Crit 100 yr
0 ft/s
1 ft/s
2 ft/s
3 ft/s
4 ft/s
5 ft/s
6 ft/s
7 ft/s
8 ft/s
9 ft/s
10 ft/s
11 ft/s
12 ft/s
13 ft/s
Ground
Bank Sta
.1 .04 .1
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Setting the Flow Distribution Locations
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Plotting Velocity Distribution
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Velocity Distribution Plot
700 720 740 760 780 800
1804
1806
1808
1810
1812
1814
1816
Critical Creek - Example 1 Plan: Existing Conditions Upstream Boundary - XSec 12
Station (ft)
Elev
atio
n (ft
)
Legend
EG 100 yr
WS 100 yr
Crit 100 yr
0 ft/s
1 ft/s
2 ft/s
3 ft/s
4 ft/s
5 ft/s
6 ft/s
7 ft/s
8 ft/s
9 ft/s
10 ft/s
11 ft/s
12 ft/s
13 ft/s
Ground
Bank Sta
.1 .04 .1
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Flow Distribution Output
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CAUTION
• Flow distribution varies vertically and horizontally (all flows are 3-D in nature )
• HEC-RAS is a 1-D model
• Flow distribution is based on area and wetted perimeter of each flow slice (using fewer slices is generally better)
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Inline Weirs and Gated Spillways
0 200 400 600 800 1000-20
-10
0
10
20
30
Inline Weir and Gated Spillay - Ex 12 Plan: Gated Spillway
Station (ft)
Elev
atio
n (f
t)
Legend
Ground
Ineff
Bank Sta
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Sluice and Radial Gates
Sluice Gate
Broad Crested Spillway
Radial Gate
Ogee Spillway Crest
Gate openings can handle both submerged and unsubmerged conditions
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Cross Section Layout
FLOWFLOW
1234
EXPANSIONREACH REACH
CONTRACTION
Gated Spillways
Overflow Weir
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Inline Weir Editor
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Weir/Embankment
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Gate Editor
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Setting the Gate Opening
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RecapWe covered:
• Multiple Plan Analysis• Effective Area Option• Cross Section Interpolation• Flow Regimes• Flow Distribution Calculations• Inline Weirs and Gated Spillways