Learning Forum

[jutas5933]

Hi everyone,

I'm working on a tillage simulation using ANSYS Rocky DEM, where I am simulating the behavior of soil particles within a soilbin. I’ve generated the soil particles, allowed them to settle for a second, and then saved the project for a restart. After adding geometries (chisel, coulters and etc.) and other material and material interactions and etc., I run the simulation, leave computer over night and next morning I check simulation. Simulation works fine for a few steps. However, after a little time time, the particles begin to drop through the bottom of the soilbin geometry and completely disappear.

Here’s a summary of what I’ve done:

1. Generated soil particles and let them settle for a brief period.
2. Saved the project and proceeded to add the geometries (e.g., soilbin) and other components required for the tillage simulation.
3. When starting the simulation, everything works well for a few steps.
4. After some time, particles start dropping through the soilbin bottom and disappear from the simulation.

I decided to test the same project on a different computer, and the simulation runs fine without any particles dropping through the bottom of the soilbox geometry.

What I've tried so far:

• Reinstalled ANSYS and Rocky DEM software.
• Upgraded video drivers to the latest version.
• Tried running the simulation on another computer, and it worked fine.
• Verified the geometry and boundary conditions, but the issue persists.

Does anyone have any ideas about what might be causing this issue? It seems to be specific to the computer I'm using. Is it possibly a hardware-related issue, such as with graphics or memory settings? Or might there be some specific configuration or setting in ANSYS or Rocky DEM that could cause this?

Any help or suggestions would be greatly appreciated!

Thanks in advance!

[jutas5933]

I found out that particles fall through bottom of soilbin (disappear) when it uses more GPU VRAM than it has (uses shared, not only VRAM). In log files:
Total allocated memory: 16413377290 = 15653.02MB (127.45 %)
Free memory: 0.00MB
Allocated: 127.45% out of 12281.38MB in use

I tried making same simulation, but with less particles (everything same, just smaller soilbox), also I tried making another simulation with less modules enabled (everything same, just modules disabled).
Both times it worked, and both times in log files it shows:
Total allocated memory: 4860716184 = 4635.54MB (37.74 %)
Free memory: 6238.00MB
Allocated: 76.70% out of 6043.38MB in use

What I mean, is that when it uses only GPU VRAM - simulation works, when it tries to use more than GPU VRAM has, uses SHARED (not only VRAM, but also RAM or virtual pagefile) it fails badly.

GPU is RTX 4070TI.
So question is: How to FORCE GPU to use only GPU VRAM???

[Lucas Bertollo Baggio]

Hello, 

Starting from driver version 536.40, the Sysmem Fallback Policy automatically swaps GPU memory with RAM when needed. This behavior appears to be affecting your Rocky simulation.

To force your GPU to use only GPU VRAM, you can access the NVIDIA Control Panel and on the CUDA - Sysmem Fallback Policy option, select Prefer No Sysmem Fallback.

 

regards,

Lucas