1_HydraulicStructures

7/30/2019 1_HydraulicStructures

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MIKE 11Structures


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MIKE 11Structures

Structure Types:

Weirs, spillways

Culverts

Pumps

Reservoir operations

Advanced controllable structures

Dambreak

Bridge module


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MIKE 11

General Structure Features

Structures are located at Q-points

Flow equations substituted by energy equation

QH

QQ H


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MIKE 11

General Structure Features

Upstream and downstream cross sections mustexist in database

at a distance < dx-max from the structure, preferably about half a

channel width upstream and downstream of structure

Valve regulation to allow flow in one direction only - e.g. for flap

gate operation

Group structures in parallel to describe complex geometries (eg

combined overflow and throughflow). These can be placed at same

Branch, Chainage and differentiated by the ID.


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MIKE 11InternalConditions

Structures impose internal boundary conditions:

a) due to a control somewhere in the structure Qstr= f(Hu/s)

b) due to energy losses through the structure, Qstr=f(Hu/s, Hd/s )

MIKE 11 looks at both cases and decide which is the governingmechanism.

Replace momentum equation with control equation (a) or local

energy balance (b).


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MIKE 11UpstreamControl

Control somewhere in the structure, Qstr= f(Hu/s)

Egs:

- Weir; Free flow over the weir

- Culvert; Inlet critical

Outlet critical

Orifice flow at inlet


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MIKE 11Upstream Control

Zero flow,Upstream or inlet controlled


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MIKE 11Downstream Control

Energy losses through the structure, Qstr= f(Hu/s, Hd/s )

Egs:

- Weir; Drowned flow over the weir- Culvert; Drowned flow through the culvert


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Downstream or outletcontrolled


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Qstr= f (Hu/s, Hd/s) comes from energy equation which gives

the headloss as a function of flow.

lostD/S-U/S HHH

Hlost

is a function of Q and is due to:

Eddy losses / vortices / turbulence

Contraction / expansion of streamlines


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MIKE 11Head Loss in Structures

g

v

g

vh

g

vh s

222

22

22

2

11

h1

h2

HU/S

HD/S

lostD/S-U/S HHH


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MIKE 11

A1 A

sA2

J-1 J J+1

h Q h

Loss Coefficient,

Contributions from inflow and outflow:

2

21

21

11

A

A

A

A sout

sin

Note!

As < A1 and A2


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MIKE 11Total Headloss

Contributions from:

inflow (note As1, str.area at inlet)

friction (for culverts, note Asa, average str. area)

bend (for culverts, note Asa, average str. area)

outflow (note As2 , str. area at outlet)

subject to min specified in the HD11 file, default

values page.


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MIKE 11Specifying Loss Coefficients

Defaults:

in

= 0.5

out

= 1.0

Determine from:

Flume tests

Field measurements

Model calibration

Function of :

Degree of smoothness of

entry, exit


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MIKE 11Free Overflow

Q = ac Qc

For culverts and weirs

Qc is tabulated, ac is applied during simulation

Irregular sections: H not horizontal, v not uniform.

To be used when known, otherwise ac = 1

ac > 1, for non-parallel flow (curved streamlines) over

weir as in the case of a sharp-crestred weir

ac < 1, for side effects.


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MIKE 11Weirs


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MIKE 11Culverts


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MIKE 11Culverts

Rectangular

Circular

Irregular H-B

Irregular h-B

Cross-section DB


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MIKE 11Weir cf. Culverts

Weirs and culverts are very similar, except:

Culverts have a length, therefore a friction loss

Culverts have a length, therefore an outlet critical plus

friction loss control mechanism

Culverts have a soffit therefore a possible orifice control

mechanism

Culverts have a bend loss option


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MIKE 11Tabulated Structures

Defined as:

Qstr= f(Hu/s, Hd/s)

Hu/s = f(Qstr, Hd/s)

Hd/s = f(Qstr, Hu/s)

Some pumps can be modelled as a tabulated structure with Qpump

= f(Hu/s, Hd/s)


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MIKE 11Local Energy Losses

Abrupt change in river alignment

Gradual change in river alignment,

User defined energy loss

Flow contraction loss

Flow expansion loss where, = 0.1 to 0.2


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MIKE 11(In)Stability at Structures

Ensure there is sufficient headloss through the structure. A very small

headloss leads to an ill-conditioned solution Increase energy loss or

remove structure

Ensure a monotonically increasing Q/h-relation

Edit the Q/h-relation by hand or change structure geometry

Ensure gradual variation in structure area

Alter structure area slightly

Also play with Delta, Delhs, Zetamin and Inter1Max in the HD11 file, default

values page

MIKE 11 B id S


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MIKE 11MIKE-11 Bridge Structures

B id M d l


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MIKE 11Bridge Module

Simplifies approach to bridges

Specific menu for including bridges

Uses recognised approaches for estimating

head loss at bridge structures

B id M d l A h


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MIKE 11Bridge Module - Approach

User specified physical bridge parameters

and user selected approach.

Bridge module pre-calculates a rating table.

Uses rating table in fully dynamic model

mode to calculate bridge flow impacts

Ei ht B id T


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MIKE 11

FHWA WSPRO

USBPR Bridge Method

Fully Submerged Bridge

Arch Bridge (Biery and Delleur)

Arch Bridge (Hydraulic Research)

Bridge Piers (DAubuisson Formula) Bridge Piers (Nagler)

Bridge Piers (Yarnell)

Eight Bridges Types

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