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CONM2: correct mass matrix with offsets and products of inertia; accept CID = -1 - #314
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RCONM2 holds I21, I31, I32 as on the CONM2 entry: products of inertia, whose negatives are the inertia tensor terms, as the mass assembly uses them. Three places treated them as tensor terms instead: - CONM2_PROC_2 moved them from the c.g. to the grid with -m*dx*dy (the tensor rule). An offset with two nonzero components then gave a mass matrix with the wrong sign on that product. It is indefinite: offset (-3, 0, -2) on mass 10 gives eigenvalue -29.2. - CONM2_PROC_1 (CID to basic) and CONM2_PROC_2 (basic to the grid's CD) rotated the matrix of products. Only the tensor rotates that way: it is now converted before and after each rotation (POI_TO_TENSOR). - The grid point weight generator added the products with the tensor sign. Tests (MYSTRAN_Validation): conm2_offset_eigen.bdf and conm2_cid_products_eigen.bdf hold the CONM2 on six springs; their six eigenvalues are checked against the exact ones from the rigid-mass matrix. Before the fix both stop with ERROR 989 (MLL not positive definite).
CONM2_PROC_1 looked CID = -1 up as a coordinate system and stopped with ERROR 1822. With CID = -1, X1-X3 are the c.g. location in basic and the inertias are in basic, so the offset is the c.g. minus the grid position and the inertias are used as given. Test (MYSTRAN_Validation): conm2_cidm1_eigen.bdf, the mass of conm2_cid_products_eigen.bdf entered with CID = -1; its eigenvalues must be the same. Before the fix it stops with ERROR 1822.
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Fixes #ISSUE (fill in the issue number after you open the issue).
Two commits, one per problem. Only
Source/LK1/L1C/CONM2_PROCESSING.f03andSource/LK1/L1C/GRID_POINT_WEIGHT.f03change.Tests: MYSTRAN_Validation MystranSolver/MYSTRAN_Validation#33, three decks in
cases_new.txt:conm2_offset_eigen.bdf: offset (-3, 0, -2), inertias 1, 1, 1.conm2_cid_products_eigen.bdf: offset and products of inertia in a rotated CID, on a grid with rotated CP and CD.conm2_cidm1_eigen.bdf: the same mass entered with CID = -1.How the tests check it:
dev, the first two stop with ERROR 989 (MLL not positive definite), and the third with ERROR 1822.Validation suite, with both PRs: 1 failure of 3,273 checks, the same one current
devhas without them ("mitc4 thermal strain free rectangle cylinder": stresses near zero in a strain-free thermal case, about 5e-3 against a 1e-2 tolerance on 4 of 18,336 values). The 18 new checks pass.