Friction in 3D Rigid Contact in MotionSolve

Davide_21943

Hello, 

I'm modelling the contact between two rigid rollers with an applied motion at one of them.

I'm using Poisson Model to compute the normal force and Dynamic only option for the friction force.

In the MotionSolve guide (check this link: https://2021.help.altair.com/2021/hwsolvers/ms/topics/solvers/ms/xml-format_57.htm) there is no formula for friction force, it just says that Coulomb friction model is applied. 

I have found a formula at this link: https://2021.help.altair.com/2021/hwsolvers/ms/topics/solvers/ms/modeling_contacts.htm

The law is mu*F_N*velocity and not just mu*F_N. Is the first one correct?

Furthermore, there is a function to evaluate the coefficient of friction in DYNAMIC ONLY option, but I don't understand how it interpolates if the value is always mu_d. Refer to the attached image.

dynamic only.png

Ganesh Shanmugam

Hi Davide,

MotionSolve computes the instantaneous friction coefficient based on slip velocity at every simulation step and use it for calculating the friction force. So Mu is a function of slip velocity friction force is Mu for slip velocity * Normal force.
In case of dynamic only the friction is transitioned from zero to max friction at friction transition velocity.

below image illustrates the functional relation between coefficient of friction and slip velocity

The blue curve depicts the full friction model covering all three regimes: static, transition to sliding friction, and sliding friction. This is the friction model applied when you select cff_type = "COULOMB_ON".

• The static regime shown in light blue.
• The transition from static to dynamic friction show in white.
• The dynamic friction regime shown in light orange.

The red curve depicts the friction model covering only the sliding friction regime. This is the friction model applied when you select cff_type = "DYNAMICS_ONLY".

Coefficient of friction as a function of slip velocity

Refer point 7 in Force: Contact document (https://2021.help.altair.com/2021/hwdesktop/mv/topics/solvers/ms/xml-format_57.htm#comments)

Regards,
S. Ganesh