Contact controls usually apply only to surface-based contact pairs, not
to general contact.
Contact stabilization can be helpful to obtain cost-effective solutions
for models involving complicated geometries and numerous contact interfaces, as
well as for models in which rigid body motions are initially not constrained.
Contact stabilization helps control rigid body motion in static problems before
contact closure and friction restrain the motion.
Use contact stabilization in
simulations
where rigid body motion occurs before contact is fully established. Using
stabilization activates damping in the normal and tangential directions based
on the stiffness of the underlying
mesh
and the time step size.
Note:
The automatic stabilization capability is meant to be used in cases
in which it is clear that contact will be established, but the exact
positioning of multiple bodies is difficult during modeling. It is not meant to
simulate general rigid body dynamics; nor is it meant for contact chattering
situations or to resolve initially tight clearances between mating surfaces.
You should initially try to stabilize rigid body motion through modeling
techniques (modifying geometry, imposing
boundary
conditions, etc.).
Contact Control Options
- Stabilization factor
- Increase or decrease the amount of damping by specifying the
stabilization factor by which the automatically calculated damping coefficient
is multiplied.
Typically, you change the default damping by one or more orders
of magnitude. When you get a converged solution, you can do some fine-tuning of
this factor. In some cases, you need to use a larger or smaller factor; this is
not a problem as long as the dissipated energy and contact damping stresses are
sufficiently small.
- Stabilization coefficient
- Use the stabilization coefficient to specify the damping coefficient directly.
Direct
specification of the damping value is not easy and might require some
trial and error. For efficiency, you can experiment with a similar model
of reduced size. When the damping coefficient is specified directly, any
multiplication factor specified for the default damping coefficient is
ignored.
- Tangent fraction
- Enter a tangent fraction to vary the amount of damping in the
tangential direction.
By default, the damping in the tangential direction is the same
as the damping in the normal direction. You can use this parameter to increase
or decrease the tangential damping.
- Fraction of damping at end of step
- Enter the Fraction of damping at the end of step to retain a
portion of the damping when the step ends.
By default, the damping coefficient ramps down to zero at the
end of the step. You can enter a nonzero value for this factor in cases where
the rigid body modes are not fully constrained by the end of the step, and you
want to maintain a small amount of the damping in the next step. This parameter
is used as the multiplication factor for the damping coefficient at the end of
the step. You can maintain the full magnitude of the damping in the next step
by setting the ramp-down factor equal to one.