13.2. The EDSTART Command

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The EDSTART command specifies the status (new or restart) of an explicit dynamic analysis (in the GUI, pick Main Menu> Solution> Analysis Options> Restart Option). There are four analysis types available: a new analysis (the default), a simple restart, a small restart, or a full restart.

13.2.1. A New Analysis

For a new analysis, you can use the EDSTART command to change the memory to be used (for example, you can increase the value if more memory is required by the LS-DYNA solver) or to change the scale factor for binary file sizes.

13.2.2. A Simple Restart

A simple restart is one for which the database (Jobname.DB) has not been changed. You would typically run a simple restart when the ANSYS LS-DYNA solution was prematurely interrupted by a user defined CPU limit or by issuing a sense switch control SW1 (after CTRL-C). For a problem which was prematurely interrupted, enter the solution processor and issue EDSTART,1,,,d3dumpnn followed by the SOLVE command. The analysis will then be continued and all results will be appended to the results files Jobname.RST and Jobname.HIS.

13.2.3. A Small Restart

Use a small restart when minor changes to the database are necessary. For this type of restart, you must issue the command EDSTART,2,,,d3dumpnn followed by any commands appropriate for changing the database, then issue the SOLVE command. The types of changes you can make to the database during a small restart are listed below.

  • Reset the termination time (TIME)

  • Reset the output file interval (EDRST, EDHTIME)

  • Specify additional ASCII files for output (EDOUT)

  • Set more displacement constraints (D)

  • Change initial velocities (EDVEL, EDPVEL)

  • Change loading curves (EDCURVE)

  • Change LS-DYNA numerical controls such as:

    • global mass damping (EDDAMP)

    • dynamic relaxation control (EDDRELAX)

    • contact small penetration control (EDSP)

    • time step control (EDCTS)

  • Change the termination criteria (EDTERM)

  • Delete, deactivate, or reactivate contact entities (EDDC)

  • Delete elements (EDELE)

  • Clear meshes (LCLEAR, ACLEAR, VCLEAR)

  • Change selected set of parts (PARTSEL)

  • Switch parts from rigid-to-deformable or deformable-to-rigid (EDRD, EDRC)

  • Change the restart dump file frequency (EDDUMP)

Only the commands mentioned above can be used in a small restart analysis (refer to the Commands Reference for details on their usage). Because some of these commands are applicable to a restart as well as a new analysis, it is important that you issue EDSTART,2 first so that subsequent commands are processed correctly for the restart.

In a small restart, you should generally extend the time of the calculation (TIME command). If the previous analysis (new or restart) finished at the specified end-time and no new time is input for the subsequent restart, the restart analysis will stop immediately with only one step. You may also need to modify termination criteria that were set in the previous analysis using the EDTERM command. If the previous analysis terminated due to one of these criteria, that specific criterion must be modified so that it will not cause the restart to terminate immediately.

In some cases, the usage of a command in the restart depends on initial settings in the original analysis. For example, in order to perform a rigid-deformable switch in the restart analysis, you must issue the EDRD command in the original analysis, even if no switch is being made. Furthermore, inertia properties for parts that are switched in the restart must be specified in the original analysis (EDRI command). Another example is mass scaling; in order to use mass scaling (EDCTS command) in the restart, mass scaling must be active in the original analysis. Limitations related to restarts are discussed in each restart related command description.

When you issue the SOLVE command to initiate the restart analysis, ANSYS LS-DYNA creates a text file named Jobname.R which is used as input to LS-DYNA. This file contains only the changes that were made to the model for the restart. If you want to run LS-DYNA directly, you can use the EDWRITE command to output this file, then specify it as the input file on the LS-DYNA execution command.

The results for the small restart analysis will be appended to all the results files. The restart solutions are numbered as load step 2, 3, etc. in Jobname.RST. In other results files, results are appended according to the time value. Restart dump files (d3dumpnn) are consecutively numbered beginning from the last number. (All modifications to the database during the restart will be reflected in subsequent restart dump files.)

Note

When postprocessing the restart results, take care not to select parts that were unselected in the restart analysis. If you do select such parts, there will be a mismatch in the database since the associated element definitions still exist, but no postprocessing data is written for the unselected parts.

After the first small restart analysis, you may choose to perform an additional restart, or even a series of restart analyses. Be sure to issue EDSTART,2 with a different d3dump file at the beginning of each restart. The general procedure for multiple restarts is outlined below.

  1. Create the initial model and run a new analysis.

  2. Postprocess the results.

  3. Issue EDSTART,2 with an appropriate d3dump file.

  4. Issue the commands needed to change the model.

  5. Issue the SOLVE command

  6. Postprocess the restart analysis results.

  7. Repeat step 3-6, as needed.

13.2.4. A Full Restart

A full restart is appropriate when many changes to the database are needed. For example, you may need to consider more materials, to remove portions of the model, or to apply different loading conditions.

To initiate a full restart, you must issue the command EDSTART,3 to indicate that subsequent commands apply to the full restart. For example, assume that the previous analysis was run using the input file Jobname.K, and it produced a restart dump file named d3dump01. You would issue the command EDSTART,3,,,d3dump01, then make any necessary changes to the model using commands available in the ANSYS LS-DYNA product. (A few of the ANSYS LS-DYNA commands are not supported in a new restart; these are discussed below.)

When the EDSTART,3 command is issued, the jobname is automatically changed to Jobname_01 to avoid overwriting the previous results and database. In a full restart, LS-DYNA creates entirely new results files instead of appending to the existing results (as is done in other types of restart analyses). The advantage of the full restart is that the changed database and result files match each other.

An important step in performing a full restart is specifying stress initialization via the EDIS command. You must carry forward some results (deformed nodal positions and stresses/strains) from the previous analysis. Typically, you would specify stress initialization for some or all of the parts that will be kept in the full restart. To do this, you must issue the command EDIS,ADD,PIDN,PIDO for each part that will be initialized. If part IDs have changed in the full restart due to changes in the model, you need to specify the new part ID in the PIDN field, and the old part ID from the previous analysis in the PIDO field. If you issue EDIS with no arguments, stress initialization is performed for all parts that were defined in the previous analysis (that is, parts having the same part ID); this option is only appropriate if part IDs have not changed and you want all parts to be initialized.

When you issue SOLVE to initiate the full restart solution (or when you issue EDWRITE), the complete database is written as an LS-DYNA input file, Jobname_01.K. When LS-DYNA starts execution, it uses the information contained in files Jobname_01.K and d3dump01 to initialize any portions of the model which were specified by EDIS commands. The deformed positions and velocities of the nodes on the elements of each part, and the stresses and strains in the elements (and the rigid body properties, if the material of the part is rigid) are assigned at this time.

Note

Portions of the model that are not initialized will have no initial strains and stresses. However, if initialized and non-initialized parts share common nodes, those nodes will be considered by the initialized part. This will cause a sudden strain in the non-initialized part.

During the initialization, it is assumed that each part being initialized has the same characteristics (that is, the same number of elements, in the same order, with the same topology) in the full restart analysis (Jobname_01.DB) as it did in the previous analysis (Jobname.DB). If this is not the case, the part cannot be initialized. (Note that the parts may have different identifying numbers, as stated above.) To avoid a mismatch in parts, follow these recommendations when creating or changing the model:

  • If you anticipate the need to delete certain elements from the model in a future full restart analysis, use a different element type number, material number, or real constant number for those elements in the original analysis, even if they share the same attributes with other elements in the model. This will cause a unique part number to be assigned to those elements so that they may be deleted later without altering the makeup of any other parts in the model.

  • If you need to add more elements to the model during the full restart, use a different element type number, material number, or real constant number for those elements, even if they share the same attributes with other elements in the full restart analysis. Again, this will cause a unique part number to be assigned to the new elements, and previously existing parts will not be altered.

If you do not follow the above guidelines, you may inadvertently create parts in the restart analysis that do not match parts from the previous analysis. In this case, stress initialization may fail for those parts.

For discrete elements (COMBI165), the initialization is “all or nothing.” If you initialize any discrete elements in the full restart, all discrete elements will be initialized.

Although you can change almost any aspect of the analysis in a full restart, a few features are not supported or are supported in a limited way, as described below.

  • Contact specifications: You cannot add or delete any contact specifications (EDCGEN and EDDC) in the full restart. However, you can list contact specifications (EDCLIST) that were defined in the previous analysis.

  • Initial velocities: You cannot change initial velocities (EDVEL and EDPVEL) in the full restart. For any portions of the model that are carried over from the previous analysis, the velocities at the beginning of the full restart will be the same as the velocities at the end of the previous analysis. You cannot define initial velocities for new nodes or parts added in the full restart; the initial velocity of new model entities are assumed to be zero. You can list the initial velocities defined in the previous analysis by using the commands EDVEL,LIST and EDPVEL,LIST.

  • Adaptive meshing: Adaptive meshing (EDADAPT and EDCADAPT) is not supported in a full restart. In addition, a full restart is not possible if adaptive meshing was used in the previous analysis.

  • Mass scaling: As in a small restart, mass scaling (EDCTS) is only supported in a full restart if it was active in the previous analysis.

You can perform multiple full restart analyses and you can mix full restart analyses with other restart analysis types (simple or small). Just issue EDSTART,3 with a different d3dump file at the beginning of each full restart. Each time EDSTART,3 is issued, the jobname will be changed from the current jobname to Jobname_nn (nn = 01, 02,…) automatically.