Impact of a tennis ball against racket strings - No rebound

Matteo17

Goodmorning everyone

I am currently setting up a simulation in Radioss involving the impact of a tennis ball against racket strings. The model details are as follows:

• Racket Strings: Modeled using truss elements with initial pretension applied.
• Tennis Ball: Modeled using shell elements. I have tested both hyperelastic material (OGDEN law) and, a more rigid material as Aluminum.
• Contact Interface: I have implemented a TYPE 7 interface where the truss nodes are defined as Slave nodes and the shell surfaces of the ball are defined as the Master surface.

• Loading Condition: An initial velocity (INIVEL) has been applied to the tennis ball.

Current Issue: I am experiencing a critical issue where the ball does not rebound off the strings. Instead, it continues its trajectory indefinitely through the strings, regardless of the simulation time.

Furthermore, when using the OGDEN hyperelastic material model, the ball exhibits non-physical, excessive deformation (resembling "chewing gum" behavior) upon contact rather than an elastic response.

Could someone help me understand the reason behind this issue? Am I missing any crucial contact settings, or are there specific parameters required to accurately model the rebound effect in this scenario?

Thank you in advance for your help

PierreChristophe_Altair

Hello Matteo,

Your material laws are may be too soft (even if with tennis ball, one can actually observe such deformations at impact, depending on the velocity)

I would first check

• Units of the different entities of your model (velocity, density, thickness, Young modulus, yield stress, etc.)
• Formulation used for the shell elements (Ishell & Ismstr, Number of integration point through thickness); best practices can be found there: Radioss Modeling Best Practices

Then, possibly internal pressure should be added in the ball (using /PLOAD or /MONVOL/GAS).

Finally, solid elements could be used instead of shells to define the ball.

Regards