## General Mechanical

#### Rock impact onto grid

• maetha
Subscriber

Hey there

I'm trying to model a rock impact onto a grid with a Transient Dynamic Analysis in Ansys 18.1. Unfortunately the model is not converging, the modal analysis shows some modi with a frequeny of 0hz.

If someone could give me some advice how to handle that I would really appreciate it.

• Sandeep Medikonda
Ansys Employee

Hi Maetha,

If there are 0 Hz modes, plot the mode shapes to identify if any parts are free floating. Check if you are constraining the model well? Also, it will help if you can post the question in terms of snapshots of the model, setup etc along with the errors.

Regards,

Sandeep

• peteroznewman
Subscriber

Hi Maetha,

From the previous post where I uploaded a model that could solve Static Structural, I just moved the rock down 100 mm to touch the top and added frictional contact between the rock and the tops of the U channels and let it run for 15 hours on 4 cores.  It is working, but all the materials are linear and I only used a 1 m/s impact velocity.

I forgot to drag and drop the two hinges from Static Structural to Transient Dynamics, so there is no hinges in this model!

Attached is an ANSYS 18.1 archive that I copied the Hinges down and increased the Impact Velocity to 20 m/s.

Regards,

Peter

• maetha
Subscriber

Thank you! So that is what I did. I then had just too less patience.

• peteroznewman
Subscriber

Maetha,

A small modification to the Transient Dynamics model is to apply the proper preload to the springs.  In the Static Structural version of this model, suppress the pressure force you had and add a gravity load, then solve. The force in each spring will be calculated. That force should be added as a preload to the springs for the Transient Dynamics model, which has a gravity load (you can drag and drop it from Transient to Static).

Without this preload, the response to the rock impact will be slightly in error.

Regards,

Peter

• peteroznewman
Subscriber

Here is the model with working hinges and a 20 m/s impact velocity of the rock. It looks like the support springs, which are linear, should have some nonlinear properties.  All the material properties are linear elastic. This represents 100 ms of time that took 30 hours of computation on a 4-core computer.

Right click on the video and select Loop to keep the video looping.