115469636-ansys

Restarting an Analysis

Module 5

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Module 5

Restarting an Analysis

A. Definition & Purpose

B. Procedure

C. Additional Options

D. About Restart Files

E. Workshop

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Displacement

Fo

rce

Change mission load history

End load step here and start new load history

Time

Lo

ad

Restart point

TimeL

oad

Create RST file from the restart

files (independent of OUTRES setting)

Restarting an Analysis A. Definition and purpose

• Restarts are carried out for several reasons:– Need to specify additional portions of load time-history– Analysis intentionally stopped by user (e.g. computer down time)– Unconverged nonlinear solution– Analyze alternative load path

Restart unstable analyses from

stable configuration

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• ANSYS has always had the capability to restart from the last converged solution.

• Additionally, the Multiframe Restart option is available.

• For example, in the load history below restarts could be carried out from any of the circled points.

• In this seminar we will cover only the Multiframe Restart.

Restarting an Analysis … Definition & Purpose

TIME

LO

AD

Jobname.r001

.r002

.r003

.r004

.r005 .r006

.r007 .r008

SUBSTEP

RESTART POINTS

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Multiframe Restart Traditional restart

• Designed to restart from several points in load history

• Works from an automatically written restart file ( .r001, .r002 etc)

• Database and load history taken care of automatically

• Designed to recover from a single abort

• Requires ESAV/OSAV, EMAT files

• Requires user to provide the correct database at the point of abort

• Also known as a “singleframe” restart.


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• Multiframe restart procedure allows you to restart the analysis from any of several user-specified load history points.

– User specifies several points for restarts with RESCONTROL (similar to OUTRES)

– A single restart file (jobname.rnnn) is written at each specified restart point.

• No need for emat, esav, osav files– Two new files (jobname.rdb and jobname.ldhi) keep track of the FE

information and load history.

• No need to save DB file at the point of restart


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• A typical multiframe restart consists of 3 steps:– Specify number and frequency of restart points in the initial analysis.– Identify the point from which analysis is to be restarted.– Define additional or revised loads and SOLVE.

Restarting an Analysis B. Procedure

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1. Specify restart points– In the initial analysis, specify the number and frequency of restart points

using Solution Control dialog box or RESCONTROL command.

RESCONTROL,action,load step, frequency,maxnum

Restarting an Analysis … Procedure

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• Example: RESCONTROL,DEFINE,ALL,3 writes restart files (jobname.rnnn) every 3rd substep for ALL load steps.

RESTART FILE DUE TO ABORT

SUBSTEP

RESTART FILE

JOB ABORTED AT THIS SUBSTEP (unconverged)

LO

AD

TIME

Jobname.r001

.r002

.r003

.r005

.r006

.r004


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• Example: RESCONTROL,DEFINE,ALL,2,2 writes restart files every 2nd substep for ALL load steps with a maximum of 2 restart files per load step.

– Provides a way to limit the number of restart files.– Note that r001 file is at a later time than r002.

INTERMEDIATE RESTART FILES (overwritten)

SUBSTEP

FINAL RESTART FILES

TIME

LO

AD

Jobname.r001

.r002

.r001

.r003

.r004

.r003

.r004

.r003


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• By default, ANSYS writes a restart file at the last substep of the last load step.

• If a job is aborted either due to non-convergence or by the user (using jobname.abt file) a restart file is written at the last converged solution prior to the abort point.


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2. Identify point from which to restart using the load step and substep numbers.– Summary of all available restart files comes up automatically.

– Command: ANTYPE,,RESTART,LOAD STEP, SUB STEP,CONTINUE

ANSYS will automatically choose the Rxxx file that corresponds to this load step/ sub step .

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What does ANTYPE,,RESTART do?– Resumes the rdb file– Reads the ldhi file and gets the correct boundary conditions, time, etc.

corresponding to the restart point– Resets solution commands and status– Since ANTYPE,,RESTART resumes a previously saved database (.rdb),

you may need to manually restore any data defined after the .rdb file was written - parameters (use PARSAV/PARRES), abbreviations, etc.

Note that the .rdb file is written at the end of the first equilibrium iteration of the first substep of the first load step.


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3. Specify revised or additional loads and solve

• If restart is due to an unconverged nonlinearity, then take any corrective actions required for convergence.

• SOLVE ( Solution > Current Load Step - solve) for the new loads and continue with additional load steps (if any).

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R002

ldhi

rdb

rst

R001

ldhi

rdb

rst

R003

ldhi

rdb

rst

R004

ldhi

rdb

rst

R005

ldhi

rdb

rst

R006

ldhi

rdb

rst

R007

ldhi

rdb

rst

Restart using r003

R004 thru R007 deleted. New Restart files

written as per RESCONTROL specification

Load history after R003 deleted.

New load history from restart

added to ldhi fileRDB file unaffected

Results after r003 deleted. New

results written to RST file during

restarted analysis


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• Option to end current load step with 1 substep– Load history will be updated to reflect load step end– Typically useful for modifying the load history in the middle of a load

step

Restarting an Analysis C. Other Restart Options

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• Option to write out complete results at any restart point(s) to the RST file

– Can get results not written with OUTRES command– SOLVE required

R002

rst

R001

rst

R003

rst

R004

rst

R005

rst

Writing results using r002 does not affect any Rnnn /

RDB / LDHI files.

Restarting an Analysis … Other Restart Options

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• Rnnn file (restart file)– Written at user specified points along the load history– Binary file containing element history records (enhanced esav file)– Written ONLY after a substep has converged– About the same size as ESAV file– Has all information necessary to recreate complete results at the

restart point

Restarting an Analysis D. About Restart Files

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• RDB file– Has all the required finite element / solid model data.– Standard ANSYS database file, saved at the end of the first iteration of

the first load step– resumed upon issue of ANTYPE,,REST,ls,ss,action– All data (e.g. tabular load parameters, components, etc) should be

defined before the first solve

Restarting an Analysis … About Restart Files

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• LDHI (load history) file– ASCII file (similar to LSWRITE file) containing boundary conditions

and loading for all load steps– DO NOT modify this file– Load / BCs are automatically added to this file at each SOLVE– Tabular loads are saved as %parameter% (rdb file is expected to have

parameter definitions)

Restarting an analysis … About restart files

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Restarting an analysis E. Workshop

• In this workshop, you will continue the transient response exercise done previously.

• See your Dynamics Workshop supplement for details.Restarting a Transient Analysis - Bouncing Block, Page W-43

Documents

115469636-ansys