Workflow for Virtual Wind Tunnel
Altair EmployeeHello,
there were a few questions coming up, concerning the workflow for virtual wind tunnel analysis. You can have a look at the tutorials in the help of VWT (File --> Help --> Tutorials) to get a first idea of how to set up a model from the beginning. Additionally, you will find a video on
http://training.altairuniversity.com/analysis/cfd/virtual-wind-tunnel/
To answer the questions in detail:
1) What CAD formats can be read into VWT
The VWT does not read CAD data directly. You have to provide an Finite Element Surface Mesh in Nastran (Fluent) format instead. This mesh can be done in HyperMesh (Engineering Solutions --> CFD user profile). HyperMesh can read solidworks, Catia, ProE, Siemens NX, STEP, Iges and other CAD formats. Go to File --> import --> geometry and choose the filter type in this menu
2) How should you save the Mesh File in HyperMesh?
After meshing, you need to check if your surface mesh is enclosed and of good quality. Go to the Checks Toolbar --> Edges and see for free edges and T-Connections. The status bar should say 'no edges / T-Connections were found, selected elements enclose a volume'. Next go to the element check (F10) and look for elements with poor quality (tria angle < 5°, Skew > 80), duplicates and connectivity. Clean up the failed elements. After the element check is complete, export under file --> export --> solver deck and choose Nastran (Fluent) format as solver type
3) Meshing Tutorials:
The tutorials on meshing can be found in the Altair HyperMesh Help, e.g. CFD-1400: Wind Tunnel Mesh
Note, that for VWT, only the 2D surface mesh is needed.
Best Regards
Jan
Answers
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Troubleshooting tips for VWT.
In case VWT run does not start or appears to be doing nothing, make the following checks:
Check for a directory with Name_ of_Run _time_stamp under the run path (VWT > File > Options > AcuSolve > Run Path > Directory name for VWT run)
1. In case mesh_intersections.dat and/or mesh_intersections.nas exist in this folder, it means there were some issues with .Nas file exported from HyperMesh.
Go back to HyperMesh and make the following checks before exporting .Nas (Fluent) file.
- Connectivity
- Duplicates
- Free Edges
- Intersections and Penetrations
Check for scaling before exporting. VWT imports in Meters.
2. If intersection issue is not there then, check if CAD.DIR and MESHSIM.DIR were created in the run folder (Name_ of_Run _time_stamp).
This indicates that the meshing process was started. Open the file vwtAnalysis.MeshSim.txt in a text editor. This is meshing log file that indicates how far the meshing process went. In case volume mesh was successfully created, the last few lines of this file would be similar to:
acuMeshSim: --------------------------------------------------------------
acuMeshSim: Number of Nodes =
acuMeshSim: Number of Elements =
...
acuMeshSim: Total Memory Size =e+002 MbytesIf such a section is missing from this file, it probably means that RAM on the computer was not enough for meshing. Either use a computer with higher RAM or reduce the element size.
...TBC
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Troubleshooting tip:
In case a run does not proceed beyond 2%, check the VWT Run Path folder for the directory with current run (hint: this would be time stamped with the time of starting the run).
Open the vwtAnalysis.MeshSim.txt file in a text editor.
acuMeshSim: <SIMM_INFO_MSG>:Number of BL regions created = ########
acuMeshSim: <SIMM_PRG>:Creating volume mesh
acuMeshSim: <SIMM_INFO_MSG>: MeshCubeRefine
acuMeshSim: <SIMM_INFO_MSG>: MeshCubeRefine
acuMeshSim: <SIMM_WRN_MSG>:Circumsphere with <= 0 height
....acuMeshSim: <SIMM_WRN_MSG>:Zero volume: verts 25486988 25486989 25487020
......acuMeshSim: Encountered an error in meshsim
acuMeshSim: <SIMM_ERR_MSG>:Code: 60 String: General error
acuMeshSim: <SIMM_PRG>:Volume Meshing
acuMeshSim: Error generating volume mesh
acuMeshSim: Extract volume meshing errors
acuMeshSim: Error Msg : <General error>
acuMeshSim: Error Code: <60>In case something similar appears in this file, it means that that the car/body/wheel were not positioned correctly. Move the body to have slight penetration with ground.
It is recommended to have the wheel penetrating the ground, in order to avoid highly skewed elements. See help for details
.
<?xml version="1.0" encoding="UTF-8"?>
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Troubleshooting Tip:
In case VWT is not able to mesh, check vwtAnalysis.MeshSim.txt in the run folder.
acuMeshSim: *** ASSERTION in Function <amsCheckMissingTags> File <amsSim.cpp> Line <1002>
acuMeshSim: *** model has unassigned face tagsIf it contains error messages like above, import the .Nas file in HyperMesh and check for any special characters in the component names (ä.ö,ü, etc).
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