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Can anyone tell me how to increase the mesh elements for the mesh independency , need |
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April 26, 2020, 15:18 |
Can anyone tell me how to increase the mesh elements for the mesh independency , need
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#1 |
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Can anyone tell me how to increase the mesh elements for the mesh independency , need I to increase all the direction mesh size or just study one direction that is important?
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April 26, 2020, 16:07 |
Grid Sensitivity
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#2 |
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There is no fixed method for this. The only objective of grid sensitivity analysis is to ensure that the effect of the mesh is not significant on the solution. And its a misconception that the mesh size should only be increased to do a grid sensitivity analysis. You can try by reducing from its current state as well. And you can do that in a particular direction or in two or three directions. It doesn't really matter.
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April 27, 2020, 21:46 |
But I find the variable that I monitor does not reach a steady state after the mesh
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#3 | |
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April 28, 2020, 07:57 |
Probably other problems
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#4 | |
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mCiFlDk
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If the problem you're facing is the lack of convergence, probably the problem is very different than the mesh size. It means that it may have problems (e.g. free faces), a lack of quality or, if you're using inflation, a bad usage of it. Check the mesh out first. |
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April 29, 2020, 12:12 |
Yes, it may be, I can find some bad mesh element in my mesh model, but I do not know
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#5 | |
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not know how to improve it in Mesh software, do you know how to improve it ? |
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April 29, 2020, 15:40 |
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#6 | |
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duri
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Mesh resolution is critical near the flow gradients. Mesh independence can be achieved by targeting the gradients. In case of direction it is better to maintain the mesh metrics like aspect ratio which would again influence the gradient estimation. So, if your are refining 4 times in x direction it is better to refine at least twice in other directions. Overall mesh count can be optimized by coarsening mesh in non-gradient region. This can be done based on the observed flow feature from initial runs. |
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April 29, 2020, 15:50 |
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#7 | |
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duri
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There are two possibilities, 1. Mesh near the monitor point is bad and error doesn't settling down. In case of flux balance or force monitors few bad cells doesn't prevent reaching steady state solution. In this case check the max residuals it should be always on the bad cells for all iterations. 2. If the monitor oscillation is periodic or bounded then probably mesh is picking up some unsteady flow feature which has been dampened by coarse mesh. Switching to unsteady solver could give more insight. |
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April 29, 2020, 17:07 |
1.How to check the max residuals it should be always on the bad cells for all itera
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#8 | |
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2.I just used the unsteady solver, what is the max aspect ratio for the mesh? Should it be less than 5? You mean we should change all the direction when we refinement the mesh? |
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April 29, 2020, 22:04 |
Can't I use the inflation and face meshing in the same time? Why does it show can not
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#9 | |
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April 29, 2020, 22:22 |
What’s wrong with the '-' beside the face meshing 2?
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#10 | |
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What’s wrong with the '-' beside the face meshing 2? |
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April 30, 2020, 06:46 |
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#11 | |
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Regards. http://oss.jishulink.com/upload/2016...9%E7%A8%8B.pdf |
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April 30, 2020, 07:51 |
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#12 | ||
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duri
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Some solvers would give the location of max residual. I don't know how to get in fluent for each iterations. But you can stop randomly and check the post processing option. Quote:
Max aspect ratio within 5 is very difficult to achieve. Near wall mesh would be in order of 1000s. But let say your mesh is 2D and it has 1e-5 as first cell height and along surface the node distance is 1e-2. This gives AR of 1000. When you make the first cell height to 1e-6 AR jumps to 10000. Now it is difficult to understand the mesh dependency of the solution. If possible it is better to maintain the same mesh metrics but this will lead to 8 times increase in mesh size which is again lead to computational cost in terms of memory and time step size. Also fine mesh has more high frequency error components which can reduced the numerical stability and take more time to die down. So it is up to the user to decide what need to be compromised. |
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April 30, 2020, 09:28 |
What is fluent meshing? Where can I open it ? I use the Ansys mesh software, are they
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#13 | |
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What is fluent meshing? Where can I open it ? I use the Ansys mesh software, are they the same? |
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April 30, 2020, 09:33 |
But if the AR is too high, I think the calculation may easily divergence, how to so
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#14 | |
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But if the AR is too high, I think the calculation may easily divergence, how to solve it ? |
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April 30, 2020, 12:23 |
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#15 | |
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You can access both of them from the workbench interface, and there are (not many) tutorials, but everything is practice! PD: How have you attached thumbnails from your PC? I haven't found anything in FAQs section |
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April 30, 2020, 23:52 |
Do you have some material to learn the fluent meshing? Does it easy to learn? You
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#16 | |
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You can see the image I send for you, just click the smiling face, you can send the image. |
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May 1, 2020, 04:22 |
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#17 | |
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The only material I can let you was the PDF I sent you in the other quote and two attached docs here. There's a lack of info about it, but you can manage it quite well in a couple of projects. Video URL: https://www.youtube.com/watch?v=_4C7vhIUpPo&t=1184s PDF: http://dl.mr-cfd.com/tutorials/ansys..._Workflows.pdf PD: cheers for the thumbnail, it works |
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May 1, 2020, 11:33 |
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#18 |
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duri
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May 1, 2020, 21:29 |
Thanks. Do you know how to use the Mesh software, I have some problems. For example
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#19 | |
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May 2, 2020, 11:42 |
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#20 | |
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mCiFlDk
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It seems that you're trying to run before starting to walk, and that's a very bad idea using Fluent and leads to frustration. Go step by step. My advice is to write a specific post about it, but meanwhile start looking for information. Many times it works much better than simply asking. Best of luck hitzhwan. |
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