Learning Forum

[JxBx]

Hi everyone,
I’m having trouble implementing a contact algorithm in my numerical wave tank that uses the ICFD method. My setup has a floating body that is supposed to collide with a fixes structure, but as they get closer, there’s always an artificial gap between them that’s filled with the fluid mesh. This leads to a volume mesh error in my simulation.
Does anyone know how to avoid this problem? Or is it even possible to simulate contact between two bodies with the ICFD solver?
Any advice or ideas would be really appreciated!
Thanks!

[Raman Babu]

You can try with *ICFD_CONTROL_GAP card in ICFD simulation which will allow a flow blockage between two 
surfaces in close proximity based on a user defined contact distance.

For structural simulation, you can use higher contact thickness to avoid direct contact between two structural bodies.

 

[JxBx]

Hi Raman,

Thank you for the suggestion regarding the *ICFD_CONTROL_GAP card. I already included it in my simulation, but unfortunately, I’m still encountering the issue. I have a numerical wave tank designed using the ICFD method with two freely floating plates, one of which is assigned an initial velocity (no waves at this stage).

Despite using the ICFD_CONTROL_GAP card to manage flow blockage, I keep getting the following error:

ICFD ERROR: Invalid surface mesh. Two faces intersect.

Error 120003 (ICFD+3): Volume mesh error.

Here’s what I suspect might be causing the problem or what I’ve tried so far:

1. Mesh Quality: I suspect the surface mesh might have intersecting or overlapping elements, which could be causing the issue. I’ve tried refining the mesh near the plates but haven’t resolved it yet.

2. Contact Distance Settings: I double-checked the user-defined contact distance for the *ICFD_CONTROL_GAP card, but I might need to tweak it further.

3. Gap Tolerance: I’ve considered increasing the contact thickness for the structural simulation, though this hasn’t seemed to alleviate the error so far.

Do you have any additional recommendations for resolving surface mesh intersections in ICFD simulations? For example, would further increasing the fluid domain mesh refinement or modifying boundary conditions be a helpful approach? I appreciate any insights you might have.

[Raman Babu]

This error, "ICFD ERROR: Invalid surface mesh. Two faces intersect," occurs when the ICFD volume mesh fails to generate. To troubleshoot:

1. Inspect the Mesh Before Failure: Write out more d3plots to examine the ICFD mesh just before the issue occurs.

2. Check Surface Mesh Quality: Poor surface mesh quality may impact volume mesh generation. Refining the volume mesh periodically using the *MESH_SIZE,  *MESH_SIZE_SHAPE and 

   *ICFD_CONTROL_ADAPT_SIZE card can help. Refer to this ICFD refinement example for guidance.

3. Maintain Gaps Between Structural Bodies:

   • Ensure the gap between structural bodies does not close.
   • Use the contact offset definition to maintain a sufficient gap during closing conditions of the structural region.
   • Confirm you are using ICFD surface part IDs when defining *ICFD_CONTROL_GAP cards.

[Michael]

Hi. I am having the same kind of issues with ICFD. My problem is fluid flow past three solid valve leaflets that are able to close. When the leaflets close, the ICFD surface mesh of two separate leaflets collide and then the simulation fails. The error is "ICFD ERROR: Invalid surface mesh. Two faces intersect."

As suggested, I have tried using ICFD_CONTROL_GAP with an appropriate gap thickness set, but this did not work. When I visualise the results, this keyword does seem to successfully stop the SOLID_GROUP leaflet meshes from colliding, but when I check the icfd_tmp_sm.k file, the leaflet surfaces in the fluid mesh are still contacting and causing the simulation to fail.

Could there be something missing in my simulation set up that ensures the ICFD fluid surface mesh on the leaflets does not deviate from the surface of the solid leaflet volume mesh? 

Also, for this suggestion: 

• Confirm you are using ICFD surface part IDs when defining *ICFD_CONTROL_GAP cards

I found that this keyword only allows the solid problem PART IDs to be specified rather than ICFD PART IDs. Is there some mistake in my set up or is it not possible to set CONTROL_GAP for the ICFD parts? 

Any help would be appreciated. Thanks. 

[Raman Babu]

ICFD_CONTROL_GAP will work only with ICFD surface parts that are expected to come into close proximity.

Could you please confirm which LS-DYNA version you are using?

I recommend trying LS-DYNA V15.0, as it allows you to view the GAP status in LS-PrePost.

Please try this and let me know how it goes.

Regards,

Raman Babu

[Michael]

Thank you for your quick response!

Is there a way to define which ICFD surface parts will come into close proximity? The solid parts that I apply the ICFD_CONTROL_GAP keyword to begin the simulation in the same location as the corresponding fluid surface mesh parts. 

I am running the simulations with LS-Dyna 15.0.2 (on HPC), but I am viewing the results locally using version 4.11.3.