MSTAB command in Femap 2

[SuG89]

Hello,

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?

Regards,
Su

 

[BlasMolero]

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

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[SuG89]

Dear Blas,

Thank you very much for your detailed answer.

Best regards,
Su