MULTI-STEPPING AND RESTARTING SECTION 5 MULTI-STEPPING AND RESTARTING

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………………………………………………………………………………………………... 5-11 The “Last Converged Increment” Parameter……………………………………………………………………. 5-14 Files Generated By MSC.Patran Marc Preference……………………………………………………………... 5-15 Files Generated By MSC.Marc…………………………………………………………………………………… 5-17

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

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?

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?

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:

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.

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

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?)

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?

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.

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.

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.)

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.

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)

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.

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.