Learning Forum

[Jiazhi Zhang]

之前的例子可以跑起来，但是总是提示负体积。粒子失效，在ls-run的时间显示数百天，甚至出现负体积，怎么解决这个问题

[Ashish Khemka]

Translated text:

The previous example can be run, but the prompt is always negative.

 

The volume. Particles are lost, the time displayed by ls-run is hundreds of days, even the negative volume appears, how to solve this problem

[Chris Quan]

Does your model contain a soft material? Were the elements with negative volume coming from a soft material? If yes, it is true that for low modulus materials such as rubbers, you may encounter error message about "negative volume". You may also observe high hourglass energy as well in these elements. Thus check the hourglass energy in GLSTAT and MATSUM to see if the soft material has large hourglass energy comparing with its internal energy. If yes, you need to refine the mesh of the soft material.

 

More explanations and instructions on negative volume can be found from LSDYNA Negative volume in soft materials (ansys.com)

 

If your model doesn't contain a soft material, you can try the following method to prevent negative volume error:

1. Set ERODE = 1 in *Control_TimeStep to erode elements by small time step. The small time step limit can be specified in *Control_Termination.
2. Reduce time step safety factor. The default is 0.9. You can try smaller time step safety factor such as 0.45, 0.33, etc.
3. Use different hourglass controls such as IHQ = 6 to 9.
4. Use different contact keyword such as *Contact_Interior.

More instructions and discussions about negative volume error can be found in LSDYNA Negative volumes in brick elements (ansys.com)

 

 

[Ram Gopisetti]

Hi Jiazhi, 

Try with the following pointers by giving importance to the first point as in the follows 

The way to avoid the negative volume error in SPG is to try the following changes in the SPG section card.

1. Turn off erode and mass scale in the control timestep ( most recommended).
2. Increase the dilation  DX, DY, and DZ parameters to say 1.8
3. Set the SMSTEP = 5 and increase pdamp to -0.01.  ( 8th parameter in the row 3 of section SPG card)

Cheers, Ram 

[Jiazhi Zhang]

sorry，sir，I've been working on something else for a while now, and recently I tried to follow your advice, but it still doesn't work.Is there any other way

[Jiazhi Zhang]