The expansion pass is where you start with the reduced solution and calculate the results at all degrees of freedom in the superelement. If multiple superelements are used in the use pass, a separate expansion pass will be required for each superelement.
The procedure for the expansion pass assumes that the Jobname.esav, Jobname.full, Jobname.sub, Jobname.LN22, Jobname.db, and Jobname.seld files from the generation pass and the Jobname.dsub file from the use pass are available. The file Jobname.emat, and for larger substructures, the files Jobname.LN09 and Jobname.LN20 will also be required if they were created in the generation pass. It is possible to use .sub and .seld files created in previous releases as they are forward compatible, see Program-Generated Permanent Files in the Basic Analysis Guide. The expansion pass logic automatically detects which, if any, factorized matrix files are available and chooses the appropriate expansion pass method and solver accordingly. If an offset of node numbers was used in the use pass (SETRAN or SESYMM), it will automatically be taken into account in the expansion pass.
The backsubstitution method uses the reduced solution from the use pass and substitutes it back into the available factorized matrix file to calculate the complete solution. The full resolve solution reforms the element stiffness matrices originally used to create the superelement. The global stiffness matrix for these elements is then assembled. The reduced solution is applied to the model as displacement boundary conditions, and the complete solution within the superelement is solved.
Note: The displacement boundary conditions are automatically applied internally at the master degrees of freedom during the expansion pass solution and are automatically deleted when the solution completes.
The expansion pass logic for substructuring analyses first searches for the superelement Jobname.LN22 file and, if found, chooses the sparse solver to perform a backsubstitution (the EQSLV command is ignored). Otherwise, the program will stop the expansion pass and give a message suggesting an alternate expansion method.
If the Jobname.LN22 file is not detected for the specified superelement, the full resolve method is chosen. The PCG solver is chosen by default for the full resolve method. You can select the sparse solver using the EQSLV command to override the default. Other equation solvers cannot be used with the full resolve method.
The key procedural steps and related commands are listed below.
Clear the database (/CLEAR). This has the same effect as leaving and re-entering the program.
Change the jobname (/FILNAME) to the name that you specified in the generation pass so that the program can easily identify the files required for the expansion pass.
Restore the generation pass database (RESUME).
Enter the SOLUTION processor (/SOLU).
Activate the expansion pass (EXPASS,ON).
Specify the name of the superelement matrix file created by the substructure generation pass to be expanded, the name of the reduced solution file from the use pass, and other options for the substructure expansion pass via the SEEXP command.
If the use pass was a harmonic analysis (ANTYPE,HARMIC), set
Imagkyon the SEEXP command to specify whether or not to include the imaginary component of the DOF solution. If all solutions are to be expanded (NUMEXP,ALL),Imagkyis ignored and both the real and imaginary solutions are expanded.Identify the use pass solution(s) to be expanded. You can either expand a single solution (EXPSOL) or a range of solutions (including all) (NUMEXP):
For a single solution (EXPSOL) - Use either the load step and substep numbers or the time (or frequency) to identify a solution.
Note: If the load step being expanded contains nonzero DOF constraints, the database must have matching DOF values. If it does not, the DOF constraints must be respecified (D) in the expansion pass.
For a range of solutions (NUMEXP) - Identify the number of solution and time or frequency range.
Specify load step options. The only options valid for a substructure expansion pass are output controls to specify the extrapolation of results, printed output, and output written to the database and results file as listed in the following table.
Start expansion pass calculations by issuing the SOLVE command
Note: By default, Jobname.dsub only contains the reduced solution in terms of nodal DOF displacement. Thus, in the expansion pass following a transient analysis or a harmonic analysis use pass, quantities using nodal velocities and nodal accelerations (damping force, inertial force, kinetic energy, etc.) can not be computed and postprocessed.
To have access to these results, the OUTRES command with
DSUBres= ALL must be issued in the first load step of the use pass. With this setting, the real and imaginary parts of the reduced solution are written to Jobname.dsub at each iteration for a harmonic analysis, and the reduced velocities and accelerations are written at each iteration for a transient analysis.OUTRES with
DSUBres= ALL is not supported if large-deflection effects are included (NLGEOM,ON) or if the expansion pass method RESOLVE (SEOPT,,,,,RESOLVE) was specified in the generation pass.Repeat steps 6 to 8 for additional use pass solutions to be expanded. If you need to expand the solution for a different superelement, you will need to leave and re-enter SOLUTION.
Note: If the superelement to be expanded contains contact elements and has multiple use passes, use separate expansions (repeating steps 1 through 7) or issue the NUMEXP command to expand multiple load steps together.
Leave the SOLUTION processor (FINISH).
Postprocess results in the superelement using standard techniques.
Note: An expansion pass is not valid if the use pass was a PSD analysis.