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MSTAB command in Femap

MSTAB command in Femap

MSTAB command in Femap


I just know that assigning a very small value to the MSTAB parameter (for example: 1e-12) helps in convergence of non-linear problems.

Does this parameter help the solver in effectively handling the zero-energy modes or is it doing something else?


RE: MSTAB command in Femap

Dear Su,
MSTAB is matrix stabilization parameter for the Multi-Step Structural NonLinear (SOL401) solver of Simcenter Nastran to allow a solution to proceed when an unconstrained condition exists.
For example, if you are relying on contact conditions to prevent a mechanism, but they may not be well established at the start of a solution. This matrix stabilization option is available by setting the parameter MSTAB to 1 on the NLCNTL bulk entry.
The MSFAC parameter, also on the NLCNTL bulk entry, is available to define a scale factor for matrix stabilization. Specifically, when you define MSTAB=1, the software scales the diagonal terms by the factor (1+MSFAC).

Some causes for singularities can include:
  • Contact conditions are not established at the start of a solution.
  • Degrees of freedom without stiffness because of missing elements.
  • A 2-dimensional plate problem with the normal rotation unconstrained.
  • A solid model with rotational DOFs at the corners unconstrained.
  • Incorrect modeling of offset beams.
  • Incorrect multipoint constraints.
  • Mechanisms and free bodies, such as sloped plates, beam to plate connections, beam to solid connections, and plate-to-solid connections.
  • Low stiffness in rotation.
  • A stiff element adjacent to a very flexible element.

Best regards,

Blas Molero Hidalgo
Ingeniero Industrial

WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

RE: MSTAB command in Femap

Dear Blas,

Thank you very much for your detailed answer.

Best regards,

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