# Multiphysics problem with non-linear material

Hello,

This is the first time I am posting a query. I am working on a project that involves a non-linear material (Nitrile rubber) O-ring. I am first applying temperature which is giving good results. Then I am importing the solution in static structural to apply pressure (giving result) after this I am again importing the solution in transient structural analysis to give a sinusoidal displacement but I am getting the following errors:

> Element 101371 located in Body "20 MM OD O-RING" (and maybe other elements) has become highly distorted. You may select the offending object and/or geometry via RMB on this warning in the Messages window. Excessive distortion of elements is usually a symptom indicating the need for corrective action elsewhere. Try incrementing the load more slowly (increase the number of substeps or decrease the time step size). You may need to improve your mesh to obtain elements with better aspect ratios. Also consider the behavior of materials, contact pairs, and/or constraint equations. If this message appears in the first iteration of first substep, be sure to perform element shape checking. Named Selections for the offending element can be created via the Identify Element Violations property on the Solution Information Object.

Also I am not clear how to what do the options in step controls mean. Eg: Steps, minimum steps, time steps etc. Please help me to understand these.

Thanking you in advance.

## Comments

What is the period (or frequency) of the sinusoidal displacement? There should be 20 displacement values per cycle in the load.

Is the displacement at time 0 equal to 0? It should be.

What is the end time (how many cycles are you computing)?

The initial time step can be 1% of the period of the sinusoidal displacement. The solver will automatically increase the time step as it can.

Thank you for the reply Peter. I have applied a sinusoidal displacement with 30hz frequency in Z direction according to the relation: Z = D*Sin(2*pi*f*t) from time 0 to 1 sec with an increment of 0.01 selecting the tabular data option. Can you please tell me how to set the step parameters to not get an excess elongation error and also what do they mean ?

If f = 30 cycles/sec, then 20 samples/cycle means 600 samples/sec or 0.00167 seconds/sample. That is the appropriate time increment for the displacement data.

I suggested a 1% period of the 30 Hz frequency for the initial time step. That means an initial time step of .01/30 = 3.33E-4 seconds. Have a maximum time step of 0.002 seconds and a minimum time step of 3E-5 seconds.

This is a good setup, but there may be other changes in the model that need to be made to allow the solver to converge such as smaller elements.