Stiffness stabilization in nonlinear analyses (Simcenter Samcef)

Stiffness stabilization

In a static analysis with contact conditions, if the contact is inactive, some rigid body modes can appear, depending on the boundary conditions.

The contact simulation objects of the type Uncoupled without Friction or of the type Uncoupled with Friction can handle this situation.

This is not the case for the contacts of the type Coupled without Friction or of the type Coupled with Friction: in general the contact algorithm fails because the tangent matrix is singular in this case.

To solve this problem, you can use two options in the Stabilization of Initial Rigid Body Motion group of the Solver Parameters page of the solution step.

Option	Description
Stiffness Stabilization (.SUB STAB)	When you define a value for the Stiffness Stabilization (.SUB STAB) field, a diagonal stiffness is added to structural elements.The diagonal terms of the stiffness matrix are multiplied by a (1 + STAB) factor.The value should be small enough to avoid overly changing the stiffness, but not too small to avoid numerical problems.We suggest a value of 10-8 or 10-9.In this case, the stiffness matrix is no longer (but nearly) singular.
Max Variation of Displacement by Iteration (.SUB MADI)	When the stiffness matrix is nearly singular, the variation of displacements during the iteration can be large and create numerical problems in the contact area.To minimize this variation, you can define the Max Variation of Displacement by Iteration (.SUB MADI) displacements to limit the value. We suggest a value of one quarter or one third of the mean element size in the contact area.

Note:

We recommend you use these options only in the solution steps where this problem can occur.

In most of the cases, the problem disappears when the contact is active.

For more details, see the stiffness stabilization section of the Simcenter Samcef solver documentation.

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partSimcenter Samcef as the specified solver
Simulation Navigator	Right-click the active subcase→Edit

Look up more details

Solution Step dialog box (Simcenter Samcef Structure Nonlinear Analysis)

Stiffness stabilization in nonlinear analyses (Simcenter Samcef), Simcenter 3D 2021.1 Series

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