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[Ben_Ben]

Hi,

I am running an explicit simulation with complex contact mechanics. I am running a quasi-static simulation. I have found that my simulation is stable with a time step of 1E-7.

Does it make a difference if I reach that with:

TSSFAC = 0.1 and dt2ms = 1E-6

or

TSSFAC = 0.9 and dt2ms = 1.1E-7

Originally I had just been reducing TSSFAC until the simulation became stable.

Cheers,
B

[Nanda]

Hello Ben,

In your explicit simulation with complex contact mechanics, using different combinations of TSSFAC and DT2MS can indeed affect the added mass and stability of your simulation, even if the resulting time step is the same.

When you use TSSFAC = 0.1 and DT2MS = 1E-6, the added mass will be different compared to using TSSFAC = 0.9 and DT2MS = 1.1E-7. The idea is that a larger DT2MS (and a smaller TSSFAC while keeping TSSFAC*DT2MS constant) results in greater added mass. This can potentially improve stability as TSSFAC is reduced, similar to non-mass-scaled solutions. If stability is an issue with the default TSSFAC of 0.9, you might try reducing it to 0.8 or 0.7. By reducing TSSFAC, you can increase DT2MS proportionally to maintain the same product and hence the same time step.

I summarised the above using this article: LSDYNA Mass scaling

Let us know if this helps

Regards,

Nanda.

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[Ben_Ben]

Thanks Nanda, 

Thats a good article. Is there a rule of thumb or way of checking whether you are reducing TSSFAC to a too small value? Or a value you shouldn't go below?

Cheers, 
Ben

[Nanda]

There is no strict lower limit for TSSFAC. It is crucial to monitor the stability and energy balance of your simulation to ensure that reducing TSSFAC does not adversely affect the results. I never used below 0.6. But it's just my take, make sure that you are not altering the inertia properties of the model.

Monitor added mass via GLSTAT and MATSUM files; the general rule is to keep added mass below 5% of the total mass.

Hope this helps!

Regards,

Nanda

 

[Ben_Ben]

Thanks Nanda. 

Will focus on added mass being below 5% of total mass. 

Cheers, 

B