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Feb 2003 HEC-RAS Version 3. 1

HEC-RAS Version 3.1 HEC-RAS Version 3.1Unsteady FlowUnsteady Flow

Presented by:Presented by:

slides adapted from HECslides adapted from HEC

Unsteady Flow CourseUnsteady Flow Course

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Unsteady Flow Doc!entation

Technical/theoretical - Chapters 2 and 5 from

EM 1110-2-1416

http://www.hnd.sace.arm!.mil - clic" onTEC#$%&'( then En)ineerin) *+lications(

then En)ineerin) Manals( scroll for manal

#EC-, sers Manal - Chapter data

inpt and window operations3

#EC-, pplication ide - Chapter 1

eample application3

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"#en to se Unsteady Flow

Tidal/estar! flctation

'ff-channel stora)e

7am +reach rotin) Channels with flat slopes

8e9ee o9ertoppin)

#!dralic strctres affected +! chan)in)

+ac"water

8ar)e amonts of stora)e +ehind roads or cl9erts

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Feb 2003 HEC-RAS Version 3. $

Steady %s. Unsteady

7ifference in handlin) +ondar! friction and

other losses

7ifference in nmerical soltion al)orithm 7ifference in handlin) non-flow areas

7ifference in flow and +ondar! condition data

reirements 7ifference in cali+ration strate)!

7ifference in application strate)!

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Feb 2003 HEC-RAS Version 3. &

2

o f

( /A)Q Q h gA( ) 0S S t x x

α∂∂ ∂+ + − + =∂ ∂ ∂

Momentm Eation:

Continit! Eation:

Q A + = 0 x t

∂ ∂∂ ∂

Unsteady Flow E'ations

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Feb 2003 HEC-RAS Version 3. (

2

o f

( /A)Q h + gA( - S + S ) = 0 x x

α∂ ∂∂ ∂

Ener)! momentm3 Eation:

Continit! Eation:

Q = VA

Steady Flow E'ations

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Feb 2003 HEC-RAS Version 3. )

Distance %s *i!e Soltion +rid

; < distance( feet

t < time( seconds

t

1(1 2(1

1(2 2(2

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Feb 2003 HEC-RAS Version 3. ,

Finite Dierence *er!

= = 2(23 - =1(23 =2(13 - =1(13

----- < ----------------------- > 1 - 3 ---------------------; ; ;

< theta wei)htin) factor 0.5 ? ? 1.0

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Feb 2003 HEC-RAS Version 3.

tead! @ Compte eact h!dralic

properties at a section for each trial

water srface ele9ation from the

ele9ation/station points( n-9ales.

nstead! @ #!dralic propertiesare pre-compted for all possi+le

water srface ele9ations at each

cross section h!dralic ta+le3

/re-Co!tation o Hydralic

/roerties

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EansionContraction Coes.

A %ot sed in the momentm

formlation ,-nstead!3

A hold +e in the data( howe9er( for

se with stead! flow anal!sis

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Data Re'ire!entsFlow and 4ondary Conditions5

tead!: 7ischar)e =3 at eachcross section.

nstead!: $nflow h!dro)raphs3

which are roted +! the model.

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*repare h!dro)raphs

+ondar! conditions3

pstream flows

Tri+tar! local flows3

n)a)ed/nmodeled flows

7ownstream ratin) cr9eB3

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HEC-RAS 6ain "indow

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Feb 2003 HEC-RAS Version 3. 1$

Enterin7 +eo!etric /ara!eters

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Feb 2003 HEC-RAS Version 3. 1&

Cross Section *able /roerties

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Feb 2003 HEC-RAS Version 3. 1(

/re-rocessin7 +eo!etry

&or nstead! flow( )eometr! is pre-processed into ta+les and ratin) cr9esCross sections are processed into ta+les of

area( con9e!ance( and stora)e

rid)es and cl9erts are processed into afamil! of ratin) cr9es for each strctre

Deirs and )ated strctres are calclatedon the fl! drin) nstead! flow calclations

*re-processor reslts can +e 9iewed in)raphs and ta+les

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Feb 2003 HEC-RAS Version 3. 1)

Cross Section /roerties /lot

0 1000 2000 000 4000 5000 6000 000650

660

60

60

6F0

00

*ropert! Ta+le

, < 1154.4

Con9e!ance/1000 cfs3 tora)e c ft3

E l e 9 a t i o n

2 f t 3

Legend

Con9. Channel

Con9. Galle!

Con9. Total

tora)e

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Feb 2003 HEC-RAS Version 3. 1,

+eo!etry /rerocessor

Dhat does it doB *rocesses )eometric data into a series of

h!dralic ta+les and ratin) cr9es. Dh! do we se it for nstead! flowB $nstead of calclatin) h!dralic 9aria+les for

each cross-section drin) each iteration( thepro)ram interpolates the h!dralic 9aria+les

from the ta+les.

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Con%eyance Calclations

Mannin) Eation

1/2

= < H f

H < Con9e!ance

f < friction/ener)! slope

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Cross Section Ea!le

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+eo!etry /rerocessor

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Hydralic /roerty /lot

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Cross Section /roerties *able

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Con%eyance Sbdi%isions

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4ondary and8nitial Conditions

'+Iecti9es:

Hnow +ondar! condition options

Hnow initial condition reirements

orces of data for +oth

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Unsteady Flow Data

Eternal ondaries reired

pstream and 7ownstream ends of the ri9er

T!picall! flow or sta)e h!dro)raph pstream T!picall! ratin) or Jnormal depthK downstream

$nternal ondaries can +e added

dd flow within the ri9er s!stem7efine )ate operation

$nitial Conditions - at the start of simlation

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Unsteady Flow Data Editor

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4ondary Conditions

Editor shows reired

eternal +ondaries

ondar! T!pe shows

a9aila+le options

pstream options: ta)e #!dro)raph

&low #!dro)raph ta)e L &low

#!dro)raph

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4ondary Conditions - contined

7ownstream ondar! 'ptions: ta)e #!dro)raph

&low #!dro)raph ta)e L &low #!dro)raph

,atin) Cr9e

%ormal 7epth

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Flow Hydro7ra#

,ead from 7 elect 7 file

elect *athname

Enter in Ta+le elect time inter9al

elect start date/time Enter flow data - or

ct L paste

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Sorces o *i!e-Series Data

#istoric ,ecords 3

ta)e #!dro)raphs

&low #!dro)raphs

Compted !nthetic &loods

,ainfall-rnoff modelin)

*ea" 7ischar)e with assmed timedistri+tion

'thersB

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9or!al Det#

Enter &riction ener)!3

lope

*ro)ram sesMannin)s eation to

compte sta)e

*ro9ides semi-d!namic

downstream +ondar!

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8nitial Conditions

,eires an initial flow

for all reaches

,estart file can +e

read from 7 Enter stead!-flow at

pstream +ondar!

Can add a flow-chan)e location

*ool ele9ation for

stora)e areas

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File and :tions 6ens

d l i l i

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Unsteady Flow Si!lation

Si!lation 6ana7er

1. Deine a /lan

2. Select w#ic#

ro7ra!s to rn

3. Enter a startin7 and

endin7 date and ti!e

$. Set t#e co!tation

settin7s

&. /ress t#e Co!te

btton

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Feb 2003 HEC-RAS Version 3. $0

:tt Selection

nstead! &low 'tpt

ta)e and &low

#!dro)raphs 8o) &ile 'tpt

*ost *rocessor

7etailed otpt @ Ma ta)e

@ elected Time $nter9als

Sta7e and Flow Hydro7ra#s

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Sta7e and Flow Hydro7ra#s

User Selected ;ocations

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Viewin7 Unsteady Flow Reslts

ll of the otpt that was a9aila+le forstead! flow comptations is a9aila+le for

nstead! flow cross sections( profile( and7 plots and ta+les3.

ta)e and flow h!dro)raphs

Time series ta+les nimation of cross section( profile and -

dimensional )raphic

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Sta7e and Flow /lot

Sta7e

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Feb 2003 HEC-RAS Version 3. $&

;o7 File :tt

can +e )enerated drin) comptations

information a+ot pro)ression of

simlation can ma"e a lar)e( lar)e file

are !o sre !o want to open itB

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Feb 2003 HEC-RAS Version 3. $(

/ost /rocessor

Can +e rn after the nstead!

simlation is completed

*ro9ides profiles for the maimm sta)eand at re)lar inter9als

ll re)lar )raphics and ta+les can +e

sed to 9iew the post process reslts raphics can JanimateK the simlation

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Feb 2003 HEC-RAS Version 3. $)

/roile Ani!ation

AccracyStabilitySensiti%ity

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Feb 2003 HEC-RAS Version 3. $,

AccracyStabilitySensiti%ity

:b

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Feb 2003 HEC-RAS Version 3. $

:%er%iew

Model ccrac!

Model ta+ilit!

&actors ffectin) ccrac! and ta+ilit! Cross section spacin)

Comptational time step selection

*ractical delta t( h!dro)raph rise time / 20

Common ta+ilit! *ro+lems 7etectin) ta+ilit! *ro+lems

Model ensiti9it!

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Feb 2003 HEC-RAS Version 3. &0

6odel Accracy

ccrac! can +e defined as the de)ree of closeness

of the nmerical soltion to the tre soltion.

ccrac! depends pon the followin): ssmptions and limitations of the model i.e. one

dimensional model( s+critical flow onl! for nstead! flow3

ccrac! of the )eometric 7ata cross sections( Mannin)sn 9ales( +rid)es( cl9erts( etc3

ccrac! of the flow data and +ondar! conditions

%merical ccrac! of the soltion scheme

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9!erical Accracy

$f we assme that the 1-dimensionalnstead! flow eations are a trerepresentation of flow mo9in) thro)h a ri9er

s!stem( then onl! an anal!tical soltion ofthese eations will !ield an eact soltion.

&inite difference soltions are approimate.

n eact soltion of the eations is notfeasi+le for comple ri9er s!stems( so #EC-, ses a finite difference scheme.

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6odel Stability

n nsta+le nmerical model is one for

which certain t!pes of nmerical errors

)row to the etent at which the soltion+e)ins to oscillate( or the errors +ecome

so lar)e that the comptations can not

contine.

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Factors Aectin7 6odel Stability

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Feb 2003 HEC-RAS Version 3. &$

Factors Aectin7 6odel Stability

and 9!erical Accracy

Cross ection pacin)

Comptation time step

Theta wei)htin) factor oltion iterations

oltion tolerances

Calclation :tions and

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Feb 2003 HEC-RAS Version 3. &&

Calclation :tions and

*olerances

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Feb 2003 HEC-RAS Version 3. &(

Cross Section Sacin7

Cross sections shold +e placed at

representati9e locations to descri+e the

chan)es in )eometr!.

dditional cross sections shold +e

added at locations where chan)es occr

in dischar)e( slope( 9elocit!( and

ro)hness. Cross sections mst also +e added at

le9ees( +rid)es( cl9erts( and other

strctres.

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Feb 2003 HEC-RAS Version 3. &)

Cross Section Sacin7 - Sloe

ed slope pla!s an important role in

cross section spacin).

teeper slopes reire more cross sectionstreams flowin) at hi)h 9elocities ma!

reire cross sections on the order of 100

feet or less.

8ar)er niform ri9ers with flat slopes ma!

onl! reire cross sections on the order of

1000 ft or more.

Cross Section Sacin7 - How do yo

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Feb 2003 HEC-RAS Version 3. &,

Cross Section Sacin7 How do yo

=now i yo #a%e eno7# >S?

se the #EC-, cross section

interpolation.

Ma"e a new plan and rn the model.

Compare the +efore and after.

$f no si)nificant difference( then 'HN

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Feb 2003 HEC-RAS Version 3. &

*#eta "ei7#tin7 Factor

Theta is a wei)htin) applied to the finite difference

approimations when sol9in) the nstead! flow

eations.

Theoreticall! Theta can 9ar! from 0.5 to 1.0.#owe9er a practical limit is from 0.6 to 1.0

Theta of 1.0 pro9ides the most sta+ilit!. Theta of

0.6 pro9ides the most accrac!. The defalt in #EC-, is 1.0. 'nce !o ha9e

!or model de9eloped( redce theta towards 0.6(

as lon) as the model sta!s sta+le.

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Feb 2003 HEC-RAS Version 3. (0

Co!!on Stability /roble!s

Too lar)e of a time step.

%ot eno)h cross sections

Model )oes to critical depth @ , is limited

to s+critcal flow for nstead! flowsimlations

ad downstream +ondar! condition i.e.

ratin) cr9e or slope for normal depth3 ad cross section properties( commonl!

cased +!: le9ee options( ineffecti9e flowareas( Mannin)s n 9ales( etc..

Co!!on Stability /roble!s -

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Co!!on Stability /roble!s

Contined

Cross section properties that do not )o hi)h

eno)h( or are wa! to hi)h cr9es are

spread to far apart3. ad +rid)e/cl9ert famil! of ratin) cr9es.

Dide and flat lateral weirs/spillwa!s @ send

to mch flow o9er a )i9en time step. ated spillwa!s that are opened or closed to

fast.

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Detectin7 Stability /roble!s

#ow do !o "now !o ha9e a sta+ilit!

pro+lemB

*ro)ram completel! +lows p drin) rn*ro)ram )oes to maimm nm+er of

iterations for se9eral time steps in a row.

*ro)ram has oscillations in the comptedsta)e and flow h!dro)raphs

Detectin7 Stability /roble!s -

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Detectin7 Stability /roble!s

Contined

Dhat do !o do when this happensB %ote the simlation time when the pro)ram either +lew

p or first started to oscillate.

Trn on the J7etailed 'tpt for 7e+))in)K option andre-rn the pro)ram.

Giew the tet file that contains the detailed lo) otpt of

the comptations. 8ocate the simlation otpt at the

simlation time when the soltion first started to )o +ad. &ind the ri9er station locations that did not meet the

soltion tolerances. Then chec" the data in this )eneral

area.

*rnin7 on Detailed :tt or

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Feb 2003 HEC-RAS Version 3. ($

*rnin7 on Detailed :tt or

Deb77in7

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Feb 2003 HEC-RAS Version 3. (&

Viewin7 Detailed ;o7 :tt

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Feb 2003 HEC-RAS Version 3. ()

6odel Sensiti%ity - Contined

*h!sical *arameter ensiti9it!: Mannin)s n Gales @ Dhat if the tre n 9ales were 10O

hi)her or 8owerB

Cross ection pacin) @ Test +! interpolatin)

Cross ection tora)e @ Dhat if there is reall! more orless stora)e in the cross sections $.e. ineffecti9e flowareas( etc3

Deir/pillwa! coefficients @ &or lateral weirs/spillwa!s the

coefficient selected can ha9e a )reat impact on thereslts.

rid)e/Cl9ert *arameters @ normall! onl! effect thelocall! compted sta)es( nless it is a flat area in whichthe +rid)e cases )reat +ac"water.

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*#e End

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s Telp Rdb 1044135