Writing your own `ALTERS'

The `ALTERS' given in Appendices E and F are for MSC/NASTRAN levels 63 and 65, for other levels the `ALTERS' may be different. This appendix describes how to revise the `ALTERS' for other levels of NASTRAN or for new solution sequences.

The first step is to obtain a listing of the `DMAP' sequence preferably with a cross-reference map. Note that all lines with the following modules; `SDR2', `SDRX', `SDRCOMP', `MDATA', `GPFDR' and `GPSTR2'. These modules perform the following tasks:

SDR2 Stress data recovery (can also recover strains)

SDRX Stress data recovery extra (intermediate point data produced for BAR and BEAM)

SDRCOMP Composite Stress data recovery

MDATA Element Pressure data recovery

GPFDR Grid point force and strain energy data recovery

GPSTR2 Grid point stress recovery (NASTRAN surface and volume stresses)

The module GPSTR2 is not available before level 63 and for some some solution sequences is loaded by a rigid format alter.

The data blocks required by the interface program consist of geometry data blocks which must always be present and result data blocks choosen by the user. The geometry data blocks consist of the following:-

CASECC - Analysis information

GPL - Grid point list

BGPDT - Grid points in basic coordinate system

ECT - Element topology

CSTM - Coordinate system transformations (not needed if no local coordinate systems)

These names remain the same except for CASECC which may alter for some solution sequences and the rest which may be suffixed by the letter S for superelement solutions.

The geometry tables must always be written in the order CASECC GPL BGPDT ECT CSTM with no other tables between them.

The results data blocks which can currently be processed are :-

OES1 Stresses

OES1C Composite Stresses

OEF1 Moments and Forces

OEF1X Moments and Forces (BAR and BEAM results extended to station points)

OEFIT Composite Failure Indices

OEP Element Pressures

OGS1 Surface and Volume stresses

OPG1 Load Vectors

OPHIG Eigenvectors

OQG1 Forces of single point constraint

OSTR1 Strains

OUGV1 Displacements (also velocities and accelerations if calculated)

The names of these data blocks do change between solutions.

The existance of a data block name can change during the course of the solution sequence especially with data base solutions as they are written and read from the data base. If a data block does not exist at a point where an alter has been placed to write to the OUTPUT2 file then an error will occur upon compilation. If a data block is mentioned as input or output form a module then this is reasonable grounds for assuming it's existance.

The geometry data blocks exist where the `SDR2' module is and so is a good place to put an alter to write them to the `OUTPUT2' file even though the user does not wish to write any of the result produced by the module. For solutions with more than 2 `SDR2' modules the user should satisfy themselves that the solution will reach that line. This can be achieved by looking at the NASTRAN monitor for a run of that sequence which shows the main modules and their line numbers that the solution has passed through.

The following is a list of the modules with their input using the data block names so that you can spot any data block name changes. One can ignore names not mentioned above.

For result data blocks OPG1, OQG1, OES1, OEF1 :

SDR2 CASECC,CSTM,MPT,DIT,EQEXIN,SIL,GPTT,EDT,BGPDT,PGG,QG, UGV,EST,XYCDB/OPG1,OQG1,OUGV1,OES1,OEF1,PUPV/ C,N,NAME/V,N,NOSORT2/V,N,NOCOMP $

For result data block OSTR1 :

SDR2 CASECC,CSTM,MPT,DIT,EQEXIN,,GPTT,EDT,BGPDT,PGG,QG, UGV,EST,/,,,OSTR1,,/ C,N,NAME/V,N,NOSORT2/V,N,NOCOMP $

For result data block OEF1X :

SDRX CASECC,OEF1,OES1,GEOM2,GEOM3,EST,CSTM,MPT,DIT/ OEF1X,OES1X/V,N,NOX $

For result data block OGPF1 :

GPFDR CASECC,UGV,KMAT,KDICT,ECT,EQEXIN,GPECT,PG,QG,BGPDT, SIL,CSTM/ONRGY1,OGPF1/C,N,NAME/V,Y,TINY/V,Y,RQPREC $

For result data block OGS1 :

GPSTR2 CASECC,EGPSF,GPL,OES1/OGS1,EGPSTR//S,N,NOEGPSTR/V,N,APP $

The result data block names given are all in SORT1 order the interface cannot process result tables in SORT2 order or if they contain complex results.