How to determine the K coefficient in the Impact and Bistop functions?

hoangthuy324

I have read through this article and I'm wondering how the coefficients of the Impact and Bistop functions are determined.

Link: "https://community.altair.com/discussion/64607/modeling-motion-limits-and-single-impact-forces-using-impact-and-bistop-functions"

The impact function is:

With the example: Disk on Disk Impact, the impact function is founded as follow:
`IMPACT(DZ({m_free_disk.idstring}, {m_lower.idstring}), VZ({m_free_disk.idstring}, {m_lower.idstring}), 0,1000.0,2.1,1,0.1 )`

How can we define the value of k = 1000. e = 2.1, cmax = 1 . and d = 0.1 for the function. Are there any criteria to define these coefficients?

Thanks in advance!!!!!!

Christopher_Fadanelli

Hi @hoangthuy324 ,

In the additional resources I have linked, there are two good references. Yes they are for contacts, but the impact function uses the same properties from the impact contact.

• Contact Between Bodies in Multibody Simulations
• Best Practices for Contacts

Initially set "low" values for stiffness (penalty) for the normal force. This will enable fast simulations. Review the contact overview table for the maximum penetration seen in the simulation result. If these are higher than expected, increase the stiffness. While using large values for stiffness (penalty) if the contact force is noisy, reduce the simulation step size.

I would also look over this post in validating the parameters and solver tuning.

https://community.altair.com/discussion/64630/model-validation-and-solver-tuning-for-contact-simulations

Hope this helps!

Christopher Fadanelli