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[salvorusso946]

Hi everyone,

 

I'm running an explicit thermomechanical analysis in LS-DYNA and I'm trying to speed up the simulation using time scaling, by applying an appropriate TSF (Thermal Speedup Factor).

 

To evaluate the impact, I ran two simulations:

 

1. One with time scaling, using a TSF to modify thermal properties accordingly.

 

 

2. One without time scaling, i.e., standard time and no TSF applied.

 

 

 

Surprisingly, the simulation with TSF results in higher temperatures compared to the one without time scaling. I was expecting both simulations to show the same thermal behavior (just occurring over different time scales), but it seems that the temperature evolution is affected in a nontrivial way.

 

Has anyone encountered this issue before? I'm trying to understand:

 

Is this temperature increase a known side effect of using TSF?

 

Are there specific best practices or precautions when using TSF (e.g., adjusting boundary conditions, time step, or coupling settings)?

 

Could the discrepancy be related to how I’m scaling the thermal material properties or defining the thermomechanical coupling?

 

 

Any guidance or shared experience would be greatly appreciated. Thanks in advance!

[Nanda]

Hello user,

What's the TSSFAC value you used? Too much added mass tends to affect the results. I will let someone else comment on the temperature part. I'm sharing the general guidelines of using mass scaling:

LSDYNA Mass scaling

Is it bad practice to reduce safety factor instead of Mass Scaling?

Regards,

Nanda.

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[salvorusso946]

Thank you very much for the helpful response!

 

In my case, I used TSSFAC = 0.4. Based on your suggestion, I’ll try reducing the mass scaling and see how it affects the results. I’ll run some tests and compare again with the reference (non-scaled) simulation.

 

In the meantime, I’m still hoping to hear from others as well — especially regarding possible thermal effects or side-effects introduced by using TSF. Any further clarification on that side would be greatly appreciated.

 

Thanks again!

 

[Dennis Chen]

can you help me understand a little bit about why you are doing a thermal-mechanical coupled analysis explicitly?    Is it something specific to your problem that this is required?   In most cases, I would prefer to do this implicitly given the time scale of the problem (for a structure to reach steady state thermal condition, it takes a while)

in the docs, the use application they described is for stamping which just suggests the same thermal scaling as your mass scaling.    

This slide is really good and it described when to scale thermal velocity when mechanical velocity is scaled - https://ftp.lstc.com/anonymous/outgoing/support/FAQ_docs/heat_transfer_class.pdf