I am doing a nonlinear static analysis with substructures in version 8.1. The models that solved in v8.1 without any problem now abort in v11 (ANSYS has requested more scratch space than currently available) on 32-bit hardware with 2 GB of memory (Windows 2000 and XP). Can the v81 behavior be reproduced in v11?

The error is occurring because of the superelements in the model. There are four copies of the superelement matrices in memory during the assembly process. For normal elements, this is only a few extra megabytes of memory, but for a superelement with 10,000 master degrees of freedom (DOF), for example, the memory required for a single dense superelement matrix would be 10,000*10,000*8 bytes or 800 MB. Four copies of this would easily exhaust all of the memory that can be addressed on a Windows 32-bit machine.

Changes have been made at 12.0 to correct this issue.

Superelements are represented by large and dense matrices. Typically, sparse matrices are encountered in finite-element analysis, so the solver methods are not well-suited for this special case. At v11.0, the memory requirements quadruple every time the number of master DOF increases by a factor of 2.

To resolve the issue, you could try the following:

(1) Try using a smaller database size (-db) value. This will reserve more system-memory address space for the ANSYS scratch/workspace memory (i.e., the "-m" memory).

(2) Try using BCSOPT,,,,1 in order to force the Sparse solver to write its workspace to disk and release its memory after finishing each equation solution.

(3) Try using the undocumented command to switch back to the old frontal assembly (ASSOPT,,FRONTAL).

(4) Upgrade to a 64-bit system with more memory.

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