1. MULTI-STEPPING AND RESTARTING
SECTION 5
MULTI-STEPPING AND RESTARTING

2. TABLE OF CONTENTS Section Page 5.0 Multi-Stepping and Restarting
Multi-step Analysis…………………………………………………………………………………………………. 5-3
Setting Up Multi-step Jobs………………………………………………………………………………………… 5-6 Restarting Up A Job……………………………………………………………………………………………… The “Last Converged Increment” Parameter……………………………………………………………………. 5-14
Files Generated By MSC.Patran Marc Preference……………………………………………………………
Files Generated By MSC.Marc…………………………………………………………………………………… 5-17

3. MULTI-STEP ANALYSIS
punch
blank
die
blankholder
Many MSC.MARC analysis require several steps. Usually there will be several general analysis steps. Occasionally, these may be punctuated by perturbation steps.
In a series of general analysis steps, the starting condition for each step is the ending condition from the previous step.
In a general step, loads are applied as total values
Example: Modified Olson Cup Test
Step 1: close and pressurize blankholder
Step 2: move punch up
Step 3: release punch
Step 4: release blankholder
Step 5: release die
The Modified Olson Cup Test is often used to determine the materials properties of a metal for the purpose of stretch forming.
True Stress
Log Strain

4. MULTI-STEP ANALYSIS (CONT.)
Linear analysis steps are perturbations about a base state.
Example: Preloaded Cantilever Beam
Step 1: Preload P1 (Nonlinear Static)
Step 2: Natural Frequency Extraction
Step 3: Response Spectrum Analysis (Earthquake)
Step 4: Preload P2 > P1 (Nonlinear Static)
Step 5: Natural Frequency Extraction
Step 6: Response Spectrum Analysis (Earthquake)
The base state is the ending condition of the last nonlinear step prior to the linear perturbation.
In a linear analysis step, the loads are defined as the magnitudes of the load perturbations only.
If a general analysis step follows a linear perturbation step, any perturbation response is ignored.
Does the earthquake analysis in Step 6 affect the results of Step 1 and Step 4 procedures?

5. MULTI-STEP ANALYSIS (CONT.)
One may combine nonlinear (general) steps with linear (perturbation) steps in the same job.
Example:
Step 1 (pretension): general analysis step (Nonlinear Static)
Step 2 (frequency extraction): linear analysis step performed about the ending condition of step 1 (base state).
Step 3 (pull back): general analysis (Nonlinear Static) continuing from the ending condition of step 1 (last nonlinear step).
Step 4 (another frequency extraction): linear analysis step performed about the ending condition of step 3 (new base state).
Step 5 (dynamic release): general analysis (Nonlinear Transient) continuing from the ending condition of step 3
How does eliminating Steps 2 and 4 change the results of Step 5?

6. SETTING UP MULTI-STEP JOBS
Why would we run a multi-step analysis?
Step 1: Insertion (Load factor = 1)
Step 2: Insertion (Load factor = 0)
Might want to change options:

7. SETTING UP MULTI-STEP JOBS (CONT.)
How do we setup a multi-step analysis?
Key
Insert
Insert
Extract
This load case fully extracts the pin out of the clip.
If each Job Step will use different loads/BCs, start by creating adequate Load Cases
Create loads and boundary conditions for all steps. Some loads/BC’s may belong to more than one load case.
Define separate load cases for each step. Some load cases may be used by more than one step, though.

8. SETTING UP MULTI-STEP JOBS (CONT.)50 5 10
0.02
1.5
1e-4 88
Use the Analysis’ Step Create form to setup analyses
pin_job1
Full Run q
Entire Model q
Default Static Step
Insertion 1
Default Extract Insert
Insert
Create a step for each of the nonlinear steps, one by one as discussed, each one having a name

9. SETTING UP MULTI-STEP JOBS (CONT.)
Add Steps in the proper order from the “Existing Steps” panel to the “Selected Job Steps” panel, and remove unwanted steps.
Steps will be run in the selected order (“Insertion” will be run first in the example).
Use the Analysis’ Load Step Selection form to control the analysis sequence
pin_job1
Full Run q
Entire Model q
Default Static Step
Extraction Insertion
Close door
Default Static Step Insertion
Extraction
Insertion Extraction
What happens if you forget to deselect the default static step? Would the results from the other steps be any different?)

10. SETTING UP MULTI-STEP JOBS (CONT.)
Create and manage additional jobs as needed.
It is best to click on Step Selection only after you have created all cases you need for a job. The job gets created when you hit Apply in the Analysis form; if you do not want to run the analysis immediately you will select Method: Analysis Deck.
You may later create more steps and modify the list of selected steps at will.
The step selection is valid for the current Job Name only. Other jobs will have their own step selection list.
Different jobs may share some steps. Modifying a step means modifying all jobs that have that step selected.
Use job descriptions or descriptive names
How do you most easily create a job as a slight variation from an existing one without modifying the original one?

11. RESTARTING UP A JOB Why would we restart a job?
How do we restart a job?
Long job (days!) –computer might crash, power failure, Murphy’s Law…
Job goes well then fails to converge – nice to reuse converged increments…
Do not know when instability might hit and will have to switch to arclength method…
Use “Write” if this is the first job for which you are creating a restart file.

12. RESTARTING UP A JOB (CONT.)
Restart;Write Creates a Restart file named jobname.t08
Reauto immediately terminates the restarted step giving a chance to change the step parameters (in a new step)
Use Restart to continue an analysis stopped at intermediate points
Very useful for large jobs due to the excessive disk storage requirements
Useful for examining the results prior to continuing the analysis
Use “Read” if you want to continue the analysis from a previous job, in which case:
The Restart Job name has to be given. This is the name of the previous job (the restart file you will read!).
The increment number at which the analysis should be restarted. If omitted, the analysis will be restarted at the last available step in the restart file.

13. RESTARTING UP A JOB (CONT.)
Use Restart to modify loading, procedure, or output controls of a step.
Useful to continue the analysis from some intermediate point, either to run an analysis alternative or to correct the analysis
Useful to compute additional eigenvalues in a Natural Frequency analysis
Use “Read and Write” if you both want to continue the analysis from a previous job and you also want to create a restart file for the current job
Combination of “Write” and “Read” types
Reauto: Used to complete a step which may have terminated prematurely due to:
operating system (exceeded disk space or run-time limit, etc.)
premature solver termination (out of increments, failed to converge, etc.)

14. THE “LAST CONVERGED INCREMENT” PARAMETER
The job_id.t08 file contains a vast amount of data, usually becoming very large indeed
If this parameter is set to “ON”, and “Increments between Writing Data” is 0 or a very large number, the Last Increment results will be written out, saving the most disk space and still allowing a subsequent restart. This will happen even if at some point the analysis is interrupted because of a failure to converge.
If this parameter is set to “OFF”, you may enter a value for the “Increments between Writing Data” panel. Often, just changing this number justifies creating a separate step.

15. FILES GENERATED BY MSC.PATRAN MARC PREFERENCE
MSC.Marc input deck file
Text File named jobname.dat
Contains Modeling and History (Load Stepping) data
Uses MSC.Marc Parameters and Options (Volume C)

16. FILES GENERATED BY MSC.PATRAN MARC PREFERENCE (CONT.)
MSC.Patran Message File
Text File jobname.msg.01
Contains information about the creation of the MSC.Marc input deck
Very useful to detect errors in the model.

17. FILES GENERATED BY MSC.MARC
MSC.Marc Post file
Binary (optionally text) File named jobname.t16
Contains results from analysis and also contain all model information.
It can be attached to either MSC.Patran Marc Preference or MSC.Marc Mentat for job monitoring and for post-processing.
If it contains results from a Thermal analysis it can be used as a temperature-data file for a subsequent structural analysis to generate thermal loads.
MSC.Marc Restart File
Binary File named jobname.t08
Contains the entire MSC.Marc process at the end of the last or (optionally) selected (every so many) converged increment(s).
It can be used to continue the analysis on a subsequent job as originally defined or to continue it with a new set of parameters and load steps. Scratch or Temporary Files
MSC.Marc Scratch Files
These are binary files (such as jobname.t23) transferring information between internal libraries in the software. Normally deleted at job’s end. Should be deleted by user if job crashes.