Contact Models in Altair MotionView

Hello @VKR

Impact Model (Penalty-Based Contact) :

This model is based on Hertzian contact theory, where the contact force is defined using a combination of stiffness and damping.

Poisson Model (Restitution-Based Contact):

This model is based on coefficient of restitution (e), which determines the energy lost during a collision.
You can go through the following Motionsolve documentation for more details regarding each models:

Best Practices for Running 3D Contact Models in MotionSolve

Hope this helps!

Hello @Vishvam,

thank you very much for your reply. This is very helpful!

Do you perhaps have any recommendations for simulating aluminum-aluminum impact of flat surfaces?

Thank you very much :)

Hi @VKR,

In general, the IMPACT method is used to capture most contact interactions. It is simple to understand and can easily have the stiffness increased if there is too much penetration. If contact is not the focus of the study, but is simply featured in the model, this is normally as intricate as you need to get with the contact definition.

However, if there are specific materials that are being used for contact and experimental data available, then the POISSON method could be explored for a more representative contact. The coefficient of restitution can often be found in literature and the stiffness can be tuned to match experimental data or observable trends.

Regardless of the method your choose, please follow the great link that @Vishvam posted for best practices. There are several tips about how to initially set values, adjust them, and when to activate advanced features.

Hope this helps!

Adam Reid

Hello @VKR,

@GTT Adam and @Vishvam already covered your question so I will just attach some more documentation that you might find useful while setting up contacts.

In Force: Contact you can find detailed documentation on how contact models work. More specifically in comment 5 you can find some recommendations for coefficient of restitution based on the materials in contact. In comment 6, it's explained how to maybe use the hertzian contact of two spheres to calculate the contact stiffness as a starting point. At the end of comment 6 thought it is highlighted that

"This should be considered a starting point for the penalty or stiffness value. You may need to tune this parameter, as high values of stiffness can degrade the performance of the solver. However, you may find that you are able to allow a smaller penalty, and thus more penetration, and still capture the overall system behavior."

I am attaching also this gearbox example model as a reference where contact stiffness was calculated by using the hertzian model of two cylinders in contact.

Hope this helps!

Best regards,
Orestes

Hello

@Vishvam, @GTT Adam, @Orestis_YB,

I would like to thank you very much for your contribution and the help and advice you have provided.

I would like to continue with a new question that came up -

How (in)accurate are the default settings in the MotionView for contact mechancis? At this stage I do not need a very very accurate resault but a result that might be close to reality. The bodies I am modelling in collisions are considered solid and rigid - as if they were made out of solid blocks.

The problem I am dealing with is low speed collisions in space during payload separation. In the environment there is no gravity or airrestitance and the coefficient of restitution is quite hard to tune. There are some literature sources for it tho. Do you have any recommendations and/or experience dealing with such situations/problems?

Thank you, you are awesome!

Hi @VKR,

The default contact settings are an appropriate starting point for the stiffness and damping required to have minimal penetration on small to medium sized objects. How 'accurate' they are is entirely up to you.

The formulations for contact can be thought of as a spring-damper system. When the bodies are close enough, imagine that a tiny spring-damper is activated between the contact elements that have stiffness and damping properties. The springs will compress and then extend until they either settle or the contact body moves away from the target body. To not have the springs compress too much, they need to be appropriately stiff. To reduce the oscillation of contact, there needs higher damping.

By the sounds of it, you are dealing with objects that are much larger, with higher mass and inertia properties. Therefore, you will essentially need stiffer springs than what is defined by default.

If you do not have all information for the other contact methods, such as the coefficient of restitution, the recommended practice is still to use the Impact method and to increase the stiffness coefficient as needed to minimize penetration into the target body.

Hope this helps!

Adam Reid