Learning Forum

[anarberk]

Hello everyone, I'm new in the forum and Ls-Dyna. I'm trying to simulate a gun system that consists of cartidge, ammunition, barrel and the hydraullic fluid. I've defined the fluid in Engineering Data. When I've tried to run the simulation so many times after tries the ways that I'd found some solutions in the internet to solve the problem, I've got always "termination due to the mass increase error". Could you help me about the problem? I've attached some screenshots(2022 R2). I've also read; https://www.dynasupport.com/howtos/material/negative-volume-in-soft-materials

1-Tried to things that I don't know clearly;

2-Fluid data;

3-Mesh;

4-Settings;

5-İnfo;

[Pedram Samadian]

Hi,

To address the issue with termination due to the mass increase, you can either deactivate or reduce the mass scaling (i.e. decrease the time step size). 

The element quality graph also shows that there is a need for mesh refinement. The element metric should not fall below 0.2. Avoid using very fine mesh sizes. Try to generate more uniform mesh size distributions.  

Replace tetrahedral elements with hexahedral elements if possible. The tetrahedral elements are normally more computationally expensive and result in stiff predictions. 

I hope these tips help.

Thanks,

Pedram

[anarberk]

Thank you so much for the reply. I've deactivated "auto mass scaling" and put "section" with hourglass coefficient 0.005. Tried to hex element but it didn't work but I've got better mesh after I had simplified the geometry. With "section", I've selected ALE and started to run. I'll let you know if it runs without error. Also, I'm trying to solve the analysis with FSI. Thank you so much again for your advice.

[Raghav]

Hi,

You might check after setting the following parameters:- 

set DTMIN (control termination) to 0.5 and TSSFAC (control timestep) to 0.67.

Which kind of hourglass control are you using?

Regards,

Raghav