# Generating an inelastic collision between two objects using damping

Question asked by Jessie Brambell on Dec 31, 2014
Latest reply on Jan 3, 2015 by Jared Conway

Hello everybody,

I'm currently trying to perform a simulation in which a caged aluminum frame rolls over and strikes a flat aluminum surface. However, I've run into a problem. It seems the collision that occurs between the frame and the aluminum surface is completely elastic in the simulation, meaning when the frame strikes the surface, it rebounds upwards with the same velocity which it hit (momentum/energy is conserved). From what I have read online and around these forums, to combat this issue I need what is called damping, which is a mechanism to dissipate energy within a system to more closely simulate reality. So, with that in mind, I've recently been trying to find ways to calculate appropriate alpha and beta values for the damping matrix, [C]. From what I've read in the SolidWorks help files, the appropriate way to do this is using the two equations: The damping ratio I found from another table listed in the SolidWorks help files, namely:

For my purposes, I used 0.05 as the damping ratio.

To calculate the two frequencies (w1, and w2), I understand I have to do a frequency test, which is readily available in SolidWorks simulation. Here is where my problem starts. I'm not entirely sure how I should perform this simulation. What should I fix on my model? Should I add gravity? What frequencies am I looking for to get accurate alpha and beta coefficients? And most importantly, am I even approaching this problem correctly? I ended up attempting a frequency simulation with no fixtures on the model just to see if beginners luck would give me the right results. I picked two frequencies close to each other in value, and then calculated alpha and beta to be 4.74x10^-4 and 5.2655, respectively. Needless to say, these did not give accurate results in the collision simulation.

To sort of bring my question to a conclusion, I'm trying to generate an inelastic collision between two aluminum bodies, from research, it seems damping is the way to do this, however, I am having troubles calculating the alpha and beta coefficients in a correct manner.

Thank you for your time, any help would be greatly appreciated.