s telp rdb 1044135
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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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Feb 2003 HEC-RAS Version 3. 2
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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Feb 2003 HEC-RAS Version 3. 3
"#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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Feb 2003 HEC-RAS Version 3. 10
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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Feb 2003 HEC-RAS Version 3. 11
Data Re'ire!entsFlow and 4ondary Conditions5
tead!: 7ischar)e =3 at eachcross section.
nstead!: $nflow h!dro)raphs3
which are roted +! the model.
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Feb 2003 HEC-RAS Version 3. 12
*repare h!dro)raphs
+ondar! conditions3
pstream flows
Tri+tar! local flows3
n)a)ed/nmodeled flows
7ownstream ratin) cr9eB3
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Feb 2003 HEC-RAS Version 3. 13
HEC-RAS 6ain "indow
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Feb 2003 HEC-RAS Version 3. 1$
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 $nstead of calclatin) h!dralic 9aria+les for
each cross-section drin) each iteration( thepro)ram interpolates the h!dralic 9aria+les
from the ta+les.
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Feb 2003 HEC-RAS Version 3. 1
Con%eyance Calclations
Mannin) Eation
1/2
= < H f
H < Con9e!ance
f < friction/ener)! slope
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Feb 2003 HEC-RAS Version 3. 21
Cross Section Ea!le
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Feb 2003 HEC-RAS Version 3. 22
+eo!etry /rerocessor
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Feb 2003 HEC-RAS Version 3. 23
Hydralic /roerty /lot
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Feb 2003 HEC-RAS Version 3. 2$
Cross Section /roerties *able
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Feb 2003 HEC-RAS Version 3. 2&
Con%eyance Sbdi%isions
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Feb 2003 HEC-RAS Version 3. 2(
Con%eyance Sbdi%isions
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Feb 2003 HEC-RAS Version 3. 2)
Con%eyance Sbdi%isions
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Feb 2003 HEC-RAS Version 3. 2,
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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Feb 2003 HEC-RAS Version 3. 30
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
$nitial Conditions - at the start of simlation
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Feb 2003 HEC-RAS Version 3. 31
Unsteady Flow Data Editor
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Feb 2003 HEC-RAS Version 3. 32
4ondary Conditions
Editor shows reired
eternal +ondaries
ondar! T!pe shows
a9aila+le options
pstream options: ta)e #!dro)raph
&low #!dro)raph ta)e L &low
#!dro)raph
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Feb 2003 HEC-RAS Version 3. 33
4ondary Conditions - contined
7ownstream ondar! 'ptions: ta)e #!dro)raph
&low #!dro)raph ta)e L &low #!dro)raph
,atin) Cr9e
%ormal 7epth
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Feb 2003 HEC-RAS Version 3. 3$
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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Feb 2003 HEC-RAS Version 3. 3&
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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Feb 2003 HEC-RAS Version 3. 3(
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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Feb 2003 HEC-RAS Version 3. 3)
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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Feb 2003 HEC-RAS Version 3. 3,
File and :tions 6ens
d l i l i
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Feb 2003 HEC-RAS Version 3. 3
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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Feb 2003 HEC-RAS Version 3. $1
Sta7e and Flow Hydro7ra#s
User Selected ;ocations
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Feb 2003 HEC-RAS Version 3. $2
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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Feb 2003 HEC-RAS Version 3. $3
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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Feb 2003 HEC-RAS Version 3. &1
9!erical Accracy
$f we assme that the 1-dimensionalnstead! flow eations are a trerepresentation of flow mo9in) thro)h a ri9er
s!stem( then onl! an anal!tical soltion ofthese eations will !ield an eact soltion.
&inite difference soltions are approimate.
n eact soltion of the eations is notfeasi+le for comple ri9er s!stems( so #EC-, ses a finite difference scheme.
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Feb 2003 HEC-RAS Version 3. &2
6odel Stability
n nsta+le nmerical model is one for
which certain t!pes of nmerical errors
)row to the etent at which the soltion+e)ins to oscillate( or the errors +ecome
so lar)e that the comptations can not
contine.
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Feb 2003 HEC-RAS Version 3. &3
Factors Aectin7 6odel Stability
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Feb 2003 HEC-RAS Version 3. &$
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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Feb 2003 HEC-RAS Version 3. (1
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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Feb 2003 HEC-RAS Version 3. (2
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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Feb 2003 HEC-RAS Version 3. (3
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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