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Mesh misalignment #11374
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The case you attached only has four meshes and not five. In smokeview, when you are displaying the grid typing x,y,or z will goggle the corresponding planes. See Appendix C of the Smokeview User's Guide. Your TRNZ lines generate extremely large aspect ratios. This is not recommended (see FDS User's Guide 6.3.5). |
Thank you @drjfloyd for your answer. My apologies for the wrong input FDS file. I attach the correct file here Thank you for the keyboard shortcut for looking at multiple meshes. I found that the keys 'M/m' helps to toggle between multiple meshes if present. However I tried typing m or M, and seem to have no change in the display of the meshes I understand the problem with my mesh stretching. I will try to maintain my aspect ratio less than 3. Could you please help me with the Mesh misalignment ? |
It is helpful to get handy with Smokeview to fix these issues. In this case, the first step is to add
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@gforney run the case thrid post and load the smv file into smokeview. If turn on mesh outlines and type m, I cycle through the meshes. If I turn on the grids by typing g, then m no longer works. Is this intentional? |
Your coarse mesh is half the resolution of your fine meshes; however, you have an odd number of cells for the x and y direction of your fine meshes. This means that the midpoint cell of your coarse mesh sees cells from two meshes and this is not allowed. |
Looking at the user's guide, this requirement isn't very clear in Figure 6.2. |
FDS User Guide: Issue #11374 Clarify coarse-fine with multiple mesh.
should be fixed in smokeview's posted below (using 'm' hilight meshes while in 'grid view' mode ) |
Hello everyone, I am reopening this issue. I followed the recommendations, and I constructed the grid. I still get the mesh misalignment. However, with Smokeview, I don't see any sort of misalignment. I have attached the image here This is my fds file Any help or input would be kindly appreciated |
In the image the meshes have different Z ranges. When I look at the file you attached, all the Z ranges are the same. Did you attach the correct file? |
I think the way I had taken the screenshot (in the previous comment) might give the impression that it is the Z grid. However, the image shows the XY- grid. And the image only shows one half of the grid, because I wanted to show the two refinements in a single image. Full XY- grid is The central grid is The Z ranges are the same for the entire domain. I have attached the correct FDS file corresponding to the image |
You have the same problem. Coarse cells can only see fine cells in one mesh. It says mesh 4 + 8 and 5 +9 are not aligned. The boundary of mesh 4 is from x=5400 to x=5580 with a 9 m resolution. What are the cell edges of mesh 8 at lower x for mesh 4? The cell edges of mesh 8 are at 5382 and 5409. So the mesh 8 cell is seeing cells from two meshes. |
Thank you @drjfloyd for your answer. Could you please explain what you mean by cell edges of a mesh ? How did you get the numbers 5382 and 5409 ? I am not able to understand how mesh 8 cell is seeing cell from two meshes. If by seeing cell from two meshes, you mean that size of mesh 8 is long enough that it meets different meshes, then the y value of mesh 6 goes from y=4680 to y=6300, and therefore it meets mesh 2, mesh 8 and mesh 9. I don't see any error from this direction. Could you please tell me where I am going wrong ? |
In the input file you attached an hour ago your mesh lines for meshes 2, 4 ,and 8 are:
This means the grid cell edges for mesh 8 are 5220, 5247, ... 5382, 5409, ... 5760. So the mesh 8 cell that goes from 5382 to 5409 sees two cells from mesh 2 (5382 to 5391 and 5391 to 5400) one cell from mesh 4 (5400 to 5409). This is not allowed. The mesh 8 cell from 5382 to 5409 can only be adjacent to cells from a single mesh. |
Thank you @drjfloyd for your patience and for making it completely clear. I certainly understand where I went wrong |
I understand the importance of aligning the mesh when it comes to between different resolutions, as mentioned in the FDS User guide 6.3.4.
I have the following mesh
Mesh 5 has a two times coarser grid compared to Meshes 1, 2, 3 and 4, and the former (Mesh5) is on top of the latter (Meshes 1, 2, 3 and 4). I believe I am satisfying 'integral number of fine cells abutting a coarse cell' rule here. However I get the error stating the misalignment between 'Mesh 5' and 'Mesh 2'.
When I tried removing 'Mesh 2' and ran the code, I got the error that 'Mesh 5' is misaligned with 'Mesh 4'. So I am assuming that the 'Mesh 5' isn't aligned with any of the Meshes 1, 2, 3, 4.
Also I went through similar problem from someone else discussing how to solve the problem by visualising the grid in smoke view. In my situation, I can only see one of the grids on smoke view for xz plane. It would be helpful if you could explain how to check for my errors visually.
I have attached my input FDS file.
test_fds.txt
Any help or inputs are kindly appreciated
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