A traditional restart requires that certain files from the initial run of the job are present, and requires that you make any changes to the input before the SOLVE command.
When restarting from a static or full transient analysis, the following files must be available from the initial run:
Jobname.db - The database file saved immediately after the initial SOLVE. If you save the database at any point later in the analysis, boundary conditions and other variables may be changed from their initial values, which would prevent the restart from running properly. (For non-converged solutions, the database file is saved automatically; see the note below.)
Jobname.emat - Element matrices (if created).
Jobname.esav or .osav - Element saved data (.esav) or old element saved data (.osav). Jobname.osav is required only if the .esav file is missing, incomplete, or otherwise corrupted because of a diverging solution; because the displacement limit was exceeded; or because of a negative pivot (see Table 3.1: Restart Information for Nonlinear Analyses). It is written if
KSTOPis set to 1 (default) or 2 on the NCNV command, or if automatic time stepping is active. If the .osav file is required, you must rename it as Jobname.esav before restarting the analysis.Results file - Not required, but if available, results from the restart run will be appended to it with the proper, sequential load step and substep numbers. If the initial run terminated because the number of results sets on the results file were exceeded, you will need to rename the initial results file to a different name before restarting. To do so, issue /ASSIGN.
When restarting from a mode-superposition transient analysis, the following files must be available from the initial run:
Jobname.db -- The database file saved immediately after the initial solve operation (SOLVE). If you save the database at any point later in the analysis, boundary conditions and other variables may be changed from their initial values, which would prevent the restart from running properly.
Jobname.rdsp -- The reduced displacement file with information from the last substep of the last load step needed for restart.
Note: In a nonlinear analysis, if the program terminates due to nonconvergence, time limits, the abort file (Jobname.ABT), or other program-detected failure, the database is automatically saved, and the solution output (Jobname.OUT) will list the files and other information required for restarting. See also Table 3.1: Restart Information for Nonlinear Analyses for a list of termination causes and the element saved data file needed to restart.
If the files .RDB, .LDHI, or
.Rnnn
/.Mnnn
were accidentally created from a previous run, you must delete
them before performing a singleframe restart.
In interactive mode, an existing database file is first written to a backup file (Jobname.dbb). In batch mode, an existing database file is replaced by the current database information with no backup.
Table 3.1: Restart Information for Nonlinear Analyses
| Cause of Termination | Element Saved Data File | Required Corrective Action |
|---|---|---|
| Normal (that is, no errors) | Jobname.esav | Add more load steps at the end of your job. |
| Nonconvergence | Jobname.osav | Define a smaller time step, change the adaptive descent option, or take other action to enhance convergence. Rename Jobname.osav as Jobname.esav before restarting. |
| Nonconvergence due to insufficient equilibrium iterations | Jobname.esav | If the solution was converging, allow more equilibrium equations (NEQIT command). |
| Cumulative iteration limit exceeded (NCNV command) | Jobname.esav | Increase ITLIM on
NCNV command. |
| Time limit exceeded (NCNV) | Jobname.esav | None (simply restart the analysis). (If you were running the analysis interactively and you want to restart it from within the same Mechanical APDL session, reset the time limits before attempting the restart.) |
| Displacement limit exceeded (NCNV) | Jobname.osav | (Same as for nonconvergence.) |
| Negative pivot | Jobname.osav | (Same as for nonconvergence.) |
Jobname.ABT
| Jobname.esav, Jobname.osav | Make whatever changes are necessary to address the behavior that caused you to voluntarily terminate the analysis. |
| "Killed" job (system break), system crash, or system time-limit exceeded | Not applicable | No restart is possible. |
If you are performing a mode-superposition transient analysis, Mechanical APDL sets up the parameters for a single-frame restart by default.
The procedure for performing the restart analysis is as follows:
Enter Mechanical APDL and specify the same jobname that was used in the initial run (/FILNAME).
Enter the SOLUTION processor (/SOLU),then resume the database file (RESUME).
Indicate that this is a restart analysis (ANTYPE,,REST).
Specify revised or additional loads as needed. Modified ramped loads start from their previous values. Newly applied ramped loads are ramped from zero; newly applied body loads start from initial values. Deleted loads which are reapplied are treated as new, not modified, loads. In static and full transient analyses, surface and body loads to be deleted should be ramped to zero, or to the initial value, so that the Jobname.esav and Jobname.osav files are consistent with the database.
For a mode-superposition transient analysis, steps 5, 6, 7, and 8 below do not apply.
Take whatever corrective action is necessary if you are restarting from a convergence failure.
If you are running a linear static or linear full transient analysis (with AUTOTS,OFF and the timestep fixed) using the sparse solver, you can realize additional savings by using the
KeepFilefield on the EQSLV command. SettingKeepFile= KEEP on your initial solve will force the program to keep all necessary files from the sparse solver in the working directory. In the subsequent singleframe restart, the sparse matrix files are available for reuse with KUSE,1.By default, the program calculates a new factorized matrix for the first load step of a restart run. By issuing the KUSE,1 command, you can force the program to reuse the existing matrix at the first solve of the restart and at all subsequent solves, thereby saving a significant amount of computer time. However, you can reuse factorized matrix files with the sparse solver only under certain conditions, in particular if the specified degree-of-freedom constraints have not changed and it is a linear analysis.
By issuing KUSE,-1, you can cause the program to redo the element matrices. This can be useful for debugging analyses and for handling error cases.
Sometimes, you may have to analyze the same model for different constraint conditions, for instance a quarter-symmetry model with symmetry-symmetry (SS), symmetry-antisymmetry (SA), antisymmetry-symmetry (AS), and antisymmetry-antisymmetry (AA) conditions. In such a situation, keep the following points in mind:
All four cases (SS, SA, AS, AA) require a new factorized matrix.
You can use substructuring (with the constrained nodes as master DOF) to minimize computing time. (See Benefits of Substructuring in the Substructuring Analysis Guide.)
Initiate the restart solution by issuing the SOLVE command. (See Obtaining the Solution for details.)
Repeat steps 4 and 6 for additional load steps, if any. For static and full transient analyses, you can also use the load step file method to create and solve multiple load steps (not supported for mode-superposition transient analyses). Use the following commands:
Command(s): LSWRITEGUI:
Command(s): LSSOLVEGUI:Postprocess as desired, then exit the program.
Following is an example restart input listing:
! Restart run: /FILNAME,... ! Jobname RESUME /SOLU ANTYPE,,REST ! Specify restart of previous analysis ! ! Specify new loads, new load step options, etc. ! Take appropriate corrective action for nonlinear analyses. ! SOLVE ! Initiate restart solution SAVE ! Optional SAVE for possible subsequent singleframe restart FINISH ! ! Postprocess as desired ! /EXIT,NOSAV
Sometimes, postprocessing is performed prior to a restart. If you issue SET and SAVE commands during this postprocessing, the boundary conditions in your database might be altered and become inconsistent with those needed for a restart. By default, the program saves your file automatically when you exit. At the end of solution, the boundary conditions for the last load step are stored in the database memory. (The database contains only one set of boundary conditions.)
A SET command in POST1 (other than SET,LAST) reads the boundary conditions for the specified results into the database, and overwrites the database stored in memory. If you subsequently save your file or exit, the program overwrites the boundary conditions in the database file with the D's and F's from the current results file. However, to perform a restart which ramps boundary conditions from the last solved substep, you need the boundary conditions for the last successfully solved load substep.
To re-establish the correct boundary conditions for the restart, first run a "dummy" load step. The procedure is as follows:
Rename Jobname.osav as Jobname.esav.
Enter Mechanical APDL and specify the same jobname that was used in the initial run (/FILNAME).
Enter the SOLUTION processor (/SOLU), then resume the database file (RESUME).
Indicate that this is a restart analysis (ANTYPE,,REST).
Respecify boundary conditions from the last substep that was successfully solved. One substep is sufficient since the solution will converge immediately.
Solve (SOLVE).
Apply final loads and load step options as desired. You will need to adjust the number of substeps (or time step size) if this load step is a continuation of the previous (before the dummy) load step. Time step numbering may be altered from your initial intent. Use a small time increment in step 6 if you need to preserve the time step numbering (such as for a transient analysis).
Continue the procedure as outlined in Restarting an Analysis.