4 restart upd
TRANSCRIPT
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RESTART SIMULATIONS WITH OLGA
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What is RESTART ?
a way of simulating a sequence of events as separate cases
e.g.
Steady state
Shut-in Cool-down
Blow-down
Start-up
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Basic formalism
First case
case1-input
case1.rsw
1st Restart case
case2-input
case2.rsw
2nd Restart case
case3-input
case3.rsw
the file case1.rsw contains the values of all model parameters of case1 at a given time point e.g. at the end of the simulation.
case-2 reads these values from the file case1.rswand use them as a starting point for its simulation, etc.
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How to make a restart case Make and run the first case Case1
Save the case as Case2 Include the keyword RESTART and specify which file to start
from e.g. Case1.rsw Introduce your modifications *)
*) Most keywords - apart from GEOMETRIES, WALLs and a few others can be modifed or added in a RESTART case.
In OLGA 5, all keywords that can be modified or added in a RESTART case are moved behind the RESTART statement in the .geninp file. This is done by the OLGA 5 GUI. This is new to OLGA 5 and may cause trouble if you try to run a case created by the OLGA 5 GUI with an OLGA 2000 version of the simulator. They may not tolerate that certain keywords are moved after the RESTART statement.
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!INTEGRATION ENDTIME=1 h, STARTTIME=0 s,...!! HEATTRANSFER Definition!****************************************************** HEATTRANSFER BRANCH=FLOWLINE, HAMBIENT=1000!!****************************************************** ! OUTPUT Definition!****************************************************** OUTPUT DTOUT=1 d, VARIABLE=( PT, TM, HOL, ID )!****************************************************** ! ENDCASE
e.g. case1 (incomplete)
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! HEATTRANSFER BRANCH=FLOWLINE, HAMBIENT=1000,... !**************************************************OUTPUT DTOUT=1 d, VARIABLE=( PT, TM, HOL, ID)!**************************************************RESTART FILE = "Case1.rsw"!**************************************************! INTEGRATION is modified:!**************************************************INTEGRATION ENDTIME=2 h!! a valve is added:!VALVE LABEL= V-1,TIME=(60, 61) m,OPENING=( 1, 0 )...!ENDCASE
e.g. Restart1 (incomplete)
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How to make a restart case cont.
You can change fluid file in a restart
BUT You cannot change pipeline data (GEOMETRY)
and pipe wall structures in a restart !
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How OLGA handles STARTTIME
if STARTTIME = void in the restart case: then restart case continues from the last time point
in Case1.rsw ENDTIME must be > ENDTIME in Case1
this is the safe (best) way to do it
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How OLGA handles STARTTIME cont.
if STARTTIME = 0 in the restart case: then restart case start time will be set to 0
regardless of end point of time in Case1.rsw
if STARTIME = e.g. 1 h in the restart case: restart case start time will be set to 1 hour
regardless of end point of time in Case1.rsw
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Input time tables
VALVE LABEL = V1,\TIME = (0, 1) m, OPENING = (1,0),......
SOURCE LABEL = S1,\TIME = (0,60), MASSFLOW = (10,0),..
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Input time tables cont.
ASSUME:
Case1:INTEGRATION STARTTIME = 0, ENDTIME = 1 hVALVE ...., TIME = (0, 60, 61) min, OPENING =(1,1,0)
Restart1:INTEGRATION ENDTIME = 2 h
Valve opening at end of Restart1 = ?
but what if
Restart1:INTEGRATION STARTTIME = 0, ENDTIME = 1 h
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Input time tables cont.
In a sequence of restarts: All input time series (previous and current) refer
to the simulation timeline in the current case e.g. Restart1
Therefore: Check all time series in the complete input
sequence
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How OLGA handles time-stepping
if DTSTART = void then the restart case starts with last time step from
previous case e.g. from Case1.rsw this is the best solution due to stability
if the restart imposes an immediate transient use a low value of DTSTART
prepares OLGA for e.g. the closing of a valve
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!**************************************************! RESTART Definition!************************************************ RESTART FILE = "Case1.rsw"!INTEGRATION ENDTIME=2 h, DTSTART = 0.001 s!VALVE LABEL=V-1,TIME=(3600, 3601) s,OPENING=( 1, 0 )...!ENDCASE
e.g. Restart1
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What is RESTART ?Basic formalismHow to make a restart caseHow to make a restart case cont.How OLGA handles STARTTIMEHow OLGA handles STARTTIME cont.Input time tablesInput time tables cont.Input time tables cont.How OLGA handles time-stepping