3.7.           Localizing Errors

Residual forces in TAMKIT can be calculated for the full mass and stiffness matrices using dynamically expanded mode shapes with the expand_modes alter, or using the reduced mass and stiffness matrix with the ortho alter. In either case, residual forces and the MRPT stiffness matrix perturbation calculations are activated using the RESFOR parameter.  Both methods store the residual forces as forces of single point restraint.  These can be viewed in any post-processor by including an SPCF=ALL request.  The MRPT stiffness matrix calculation writes three matrices to the .pch file in DMIG format.  The first matrix (DKGG) is the perturbation to the stiffness matrix (DK).  The second matrix (RKGG) normalizes the perturbation matrix on a term by term basis by the nominal reduced stiffness matrix, and the third matrix (RKGGD) lists the diagonal terms of RKGG.  The DKGG matrix can be added back into the original model (using a K2GG=DKGG case control card) to match the test data, while the third matrix can be examined to see which regions of the model require the largest relative change to the stiffness matrix.

The execution of the ortho and expand modes alters are described in Sections 3.3 and 3.6.