RESTART SIMULATIONS WITH OLGA

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

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.

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.

!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)

! 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)

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 !

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

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

Input time tables

VALVE LABEL = V1,\TIME = (0, 1) m, OPENING = (1,0),......

SOURCE LABEL = S1,\TIME = (0,60), MASSFLOW = (10,0),..

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

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

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

!**************************************************! 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

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