1. Chapter 9
Restarting

2. Chapter Objectives
Upon completion of this chapter, students will be able to perform a Restart Using the ANSYS/LS-DYNA Program.
1. Define what a Restart means in an Explicit Dynamic Analysis
2. Describe the reasons for performing a restart
3. List and describe the different types of a restart
4. Define how to perform a restart using the EDSTART command
5. Describe how the EDSTART command is used in a new analysis
6. Given step-by-step guidance, a small restart will be performed
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3. Restarting Definition
Restarting means performing an analysis which continues from a previous analysis. A restart can begin from either the conclusion of or the middle of a prior analysis.
Possible Reasons for Performing A Restart
The previous analysis was killed by the operating system or the user (sw1)
The previous analysis exceeded the user defined CPU limit.
There was an error in the previous analysis and a restart is used to diagnose and/or correct the error.
The previous analysis was not run to a long enough termination time.
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4. Types of Restart
A simple restart is one for which the original database (Jobname.db) has not been altered in the new analysis. A simple restart is performed when the LS-DYNA solution was prematurely interrupted by the exceeding of a user defined CPU limit or by the issuing of the sense switch control sw1.
A small restart is used to run an analysis to a longer termination time than initially specified and/or to make minor modifications to the model. The following commands can be used in a small restart.
EDRC - Specifies rigid/deformable switch controls
EDRD - Switches parts from deformable to rigid & back
EDRI - Define inertia props. for new rigid body from EDRD
EDTERM - Specifies various termination criteria
EDDUMP - Specifies output frequency for D3DUMP file
EDSP - Small penetration checking for contact entities
EDDC and EDVE commands (previously discussed).
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5. Performing a Simple Restart
The EDSTART command specifies the status of a restart in an explicit analysis. The menu path for the EDSTART command is:
Solution -> Analysis Options -> Restart Option...
There are two specifications required during a Simple Restart
1. Choose Simple Restart from the Restart Option Pull-Down Box
2. Specify the file name for the dump file to be used during the restart. The dump files are created when an LS-DYNA run is terminated. The default dump files created by the LS-DYNA program are d3dumpnn, where nn=01,
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6. (continued) Performing a Simple Restart
During a simple restart, default values for the words of requested memory and binary file scale factor should be used.
After issuing a simple restart, immediately issue the SOLVE command as no changes are allowed to the database in a simple restart.
Upon issuing the SOLVE command, the analysis will be continued from the specified d3dumpnn file and all results will be appended to the results files Jobname.his and Jobname.rst.
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7. Performing a Small Restart
There are four steps required to perform a small restart:
1. Choose Small Restart from the Restart Option Pull-Down Box
2. Specify the file name for the dump file to be used during the restart. The default dump file is d3dumpnn, where nn=01,
3. Change the termination time with the TIME command.
4. Make other minor modifications to the model such as changing bodies from rigid to deformable. The following slides describe the available restart commands.
Note: As with a simple restart, default values for the requested words of memory and binary size scale factor should be used.
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8. Small Restart Commands
The EDRD command allows switching between rigid and deformable bodies.
Solution: Rigid-Deformable->Switch…
Select the desired action: Initialize, Deform to Rigid, Rigid to Deform, or List
Specify the Part Number to be switched
Specify the master rigid body number (only when switching from deformable to rigid).
The ability to switch a part from deformable to rigid and back to deformable enables longer duration analyses to be performed.
By switching the parts to rigid while in the air, the CPU time can be greatly reduced. Proximity to the ground (i.e., a coordinate location), initiation of contact, etc. can be used to trigger termination of the run. A restart can then be performed in which the rigid body is converted back into a deformable body for the rest of the transient.
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9. Small Restart Commands
The EDRC command controls parameters used in switching between rigid and deformable bodies.
Solution: Rigid-Deformable->Controls…
Select the desired action: Add, Delete, or List
Welds and nodal constraints can be Activated or Deactivated
The maximum time step size can be specified after switching.
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10. Small Restart Commands
The EDRI command allows specification of rigid body properties after switching from a deformable body.
Solution: Rigid-Deformable->Inertia Property…
Select the desired action: Add, Delete, or List
Specify the part number for the rigid body.
Specify the rigid body properties:
1) Center of Mass
2) Total mass
3) Moments of Inertia
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11. Small Restart Commands
The EDDC and EDSP commands allow specification of contact properties for a restart analysis.
Preprocessor: Ls-DYNA Options->Activate/Deactivate Entity…
Select the type of contact to activate or deactivate
Specify the contact and target components for contact type
Preprocessor: Ls-DYNA Options->Advanced Control…
Select an action Add, delete or list
Specify the contact ID range (from EDCLIST) and increment for small penetration checks to be performed.
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12. Small Restart Commands
The EDDUMP command specifies the output interval for the D3DUMP file in a restart analysis.
Solution: Output Controls->Number of Steps…
Specify the number of output steps for the restart output interval
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13. Small Restart Commands
The EDTERM command specifies termination criteria for an explicit dynamic analysis.
Solution: Analysis Options->Criteria to Stop…
Analysis can be terminated when a selected node or rigid part reaches a specified location (global coordinate) or makes contact
Termination information can also be listed
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14. Small Restart Commands
The model size in a restart can also be reduced by deleting elements (EDELE) or unselecting parts (PARTSEL).
Preprocessor: -Modeling- Delete-> Elements…
Utility Menu: Select->Parts…
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15. Performing a Small Restart - General
Loading curves may not be extended in a small restart. Therefore, it is suggested that original load definitions be extended past the original termination time in anticipation that a small restart may be needed.
Upon issuing the SOLVE command, the analysis will be continued and all results will be appended to the results files Jobname.his and Jobname.rst.
Additional results from a small restart will be shown in loadstep 2 of Jobname.rst.
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16. Using EDSTART in a New Analysis
In addition to being used for a restart, the EDSTART command can be utilized in a new analysis for:
Changing the memory size to be used.
Changing the scale factor for binary files.
For both of these options:
1. Specify New Analysis from the Restart Option pull down menu
2. Enter the memory size to be used (in words) for the new analysis
3. Enter the scale factor for binary file sizes (Default is 7).
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17. (continued) Using EDSTART in a New Analysis
For a new analysis, you do not need to use the EDSTART command unless the memory and the file scale factor options need to be changed.
In a new analysis, do not specify the dump file so that the default d3dump01 file will be created.
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18. Restarting Exercise
The exercise for this chapter begins on page E9-1 of Volume II.
A rubber block is thrown at a wall and the analysis is terminated after 2 ms. After reviewing the results, the analysis is restarted and the transient is continued for an additional 2 ms.
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