Modeling Drop Structuresmti.ntu.edu.iq/wp-content/uploads/2019/02/drops.pdf · March 2003 HEC-RAS...
Transcript of Modeling Drop Structuresmti.ntu.edu.iq/wp-content/uploads/2019/02/drops.pdf · March 2003 HEC-RAS...
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Modeling Drop
Structures in
HEC-RAS
Version 3.1
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March 2003 HEC-RAS Version 3.1 Slide 2 of 27
Modeling Drop Structures
Overview
Modeling a Drop Structure as an
Inline Structure (Weir).
Modeling a drop structure with cross-
sections through the drop.
Example using Lab Data.
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March 2003 HEC-RAS Version 3.1 Slide 3 of 27
Overview
What is a Drop Structure?
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March 2003 HEC-RAS Version 3.1 Slide 4 of 27
Overview
Why do we use Drop Structures ?
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March 2003 HEC-RAS Version 3.1 Slide 5 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 6 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 7 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 8 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 9 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 10 of 27
Overview
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March 2003 HEC-RAS Version 3.1 Slide 11 of 27
Components of Drop Structure
yc yb
3 or 4
yb
yb = 0.715 ycRectangular
channel
stilling basin:used
to dissipate energy
subcritical
subcritical
•Control Section
•Energy Dissipation Section
•Adjacent Protection
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March 2003 HEC-RAS Version 3.1 Slide 12 of 27
Overview
How can we Model a Drop Structure
with HEC-RAS ?
Inline Weir Option
Using Cross Sections
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March 2003 HEC-RAS Version 3.1 Slide 13 of 27
Overview
Which is more appropriate?
Using Cross Sections - better if interested
in profile through the structure.
Inline Weir Option - probably better if
just interested in elevations upstream
and downstream of structure.
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March 2003 HEC-RAS Version 3.1 Slide 14 of 27
Cross-Section Locations
When placing cross-sections near and
through a drop structure, they need to
be placed where the water surface
and velocity are changing rapidly (this
applies when using an inline weir also).
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March 2003 HEC-RAS Version 3.1 Slide 15 of 27
Modeling a Drop Structure
as an Inline Weir
The standard weir equation is used:
where: C = 2.6 - 4.0 (dependent on shape)
L = Length of weir
H = Upstream Energy Head
Q = CLH3/2
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March 2003 HEC-RAS Version 3.1 Slide 16 of 27
Inline Weir - Submergence
Submergence
is defined as
H2/H1
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March 2003 HEC-RAS Version 3.1 Slide 17 of 27
Inline Weir - Submergence
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March 2003 HEC-RAS Version 3.1 Slide 18 of 27
Inline Weir - Cross Section
Layout
1
2
345
6 Inline Weir Structure
Cross Sections
Model the floor
blocks as
blocked
obstructions.
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March 2003 HEC-RAS Version 3.1 Slide 19 of 27
Modeling a Drop Structure
as an Inline Structure
Under the
“Geometric
Data”click on
“Inline Structure”
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March 2003 HEC-RAS Version 3.1 Slide 20 of 27
Modeling a Drop Structure
as an Inline Structure
A series of windows allow for entry of weir characteristics
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March 2003 HEC-RAS Version 3.1 Slide 21 of 27
Modeling a Drop Structure
with Cross Sections
Cross Sections
Model the floor
blocks as
blocked
obstructions.
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March 2003 HEC-RAS Version 3.1 Slide 22 of 27
Cross Section Layout for Ogee
Shapes Drop Structure
Cross Sections
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March 2003 HEC-RAS Version 3.1 Slide 23 of 27
Modeling Baffles in the Stilling
Basin
Increase ‘n’
values at
baffle blocks to
account for
increased
roughness
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March 2003 HEC-RAS Version 3.1 Slide 24 of 27
Example Using Lab Data
WES Physical Model Study (WES, 1994)
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March 2003 HEC-RAS Version 3.1 Slide 25 of 27
Example - Modeled as a
Weir
Cross Sections
Inline Weir
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March 2003 HEC-RAS Version 3.1 Slide 26 of 27
Example - Modeled with Cross
Sections Only
Cross Sections
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March 2003 HEC-RAS Version 3.1 Slide 27 of 27
Example - Comparison of
Two Methods
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March 2003 HEC-RAS Version 3.1 Slide 28 of 27
Example - Comparison
Zoomed In
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The End