How to create a properly nested grid

csei20059 · October 28, 2023, 23:02

I modeled a two-phase flow model by flow3d. I used to make a stretched mesh at the mesh is stretched from the free surface to the boundaries. but after I added the two-phase flow model the calculation stopped halfway because the pressure did not converge.

The length of the numerical wave tank is 20m and the width is 1m with the height of 1.5m. The wave period is 1.5s and the wave height is 0.02m. It is a linear wave.

Due to this question, I created a nested mesh block near the 3D model, and the grid size was one-half the size of the mesh of the numerical wave tank , but the calculation still stopped halfway because the pressure did not converge.

Also, I want to make a nested mesh block around the free surface to get the right wavelength and wave height. Is this possible?

I would like to ask how to create a good nested mesh. It would be greatly appreciated if you could explain the details.

GranuleFlow · November 20, 2023, 19:42

Double-check that your meshes have aligned mesh planes, especially if they are nested, partially overlapping, or conforming to geometry. Importing the mesh planes from the nested mesh to the containing mesh will make sure that the meshes are "snapped" together and rounding errors do not result in misaligned cells. I had some geometry issues and found that rewatching the tutorial videos on meshing on the Getting Started page reminded me of some concepts I had forgotten.

Do you have the number of fluids set to two, or is it set to one fluid? Recall that setting the number of fluids to two results in the software computing values (e.g., pressure) for cells that are filled with the second fluid (I am assuming air is your second phase). This could result in the software needing more iterations for the pressure to converge, especially if your boundary conditions are not set properly. If fluid values in the second phase are not important, the one fluid setting still enables the modeling of a two-phase free surface, but it does not try to calculate any values for the second phase and simply uses it to define a boundary condition for the main fluid. This is described in much greater detail in the software documentation.

Hope this helps your troubleshooting!

October 28, 2023, 23:02	How to create a properly nested grid	#1
csei20059 New Member chang Join Date: Oct 2023 Posts: 1 Rep Power: 0	I modeled a two-phase flow model by flow3d. I used to make a stretched mesh at the mesh is stretched from the free surface to the boundaries. but after I added the two-phase flow model the calculation stopped halfway because the pressure did not converge. The length of the numerical wave tank is 20m and the width is 1m with the height of 1.5m. The wave period is 1.5s and the wave height is 0.02m. It is a linear wave. Due to this question, I created a nested mesh block near the 3D model, and the grid size was one-half the size of the mesh of the numerical wave tank , but the calculation still stopped halfway because the pressure did not converge. Also, I want to make a nested mesh block around the free surface to get the right wavelength and wave height. Is this possible? I would like to ask how to create a good nested mesh. It would be greatly appreciated if you could explain the details.

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November 20, 2023, 19:42		#2
GranuleFlow New Member Derek Join Date: Nov 2023 Posts: 1 Rep Power: 0	Double-check that your meshes have aligned mesh planes, especially if they are nested, partially overlapping, or conforming to geometry. Importing the mesh planes from the nested mesh to the containing mesh will make sure that the meshes are "snapped" together and rounding errors do not result in misaligned cells. I had some geometry issues and found that rewatching the tutorial videos on meshing on the Getting Started page reminded me of some concepts I had forgotten. Do you have the number of fluids set to two, or is it set to one fluid? Recall that setting the number of fluids to two results in the software computing values (e.g., pressure) for cells that are filled with the second fluid (I am assuming air is your second phase). This could result in the software needing more iterations for the pressure to converge, especially if your boundary conditions are not set properly. If fluid values in the second phase are not important, the one fluid setting still enables the modeling of a two-phase free surface, but it does not try to calculate any values for the second phase and simply uses it to define a boundary condition for the main fluid. This is described in much greater detail in the software documentation. Hope this helps your troubleshooting!