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overset simulation with abnomal force and motion at beginning

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Old   September 19, 2024, 22:25
Default two phase flow overset simulation with abnomal force and motion at beginning
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Shen Tsao Hung
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Hi all,

I tested a still water case with a floating cylinder and ran the simulation. However, abnormal forces and motions occurred in the z-direction at the beginning. Upon restarting, I suspected this might be due to an unbalanced initial water level. To address this, I tried adjusting the height of the water surface to reduce the initial imbalance, but it didn't seem to solve the problem.

Additionally, I ran another simple test case and noticed that the interpolation between the water surface (alpha=0.5) of the overset and background grids is discontinuous at the overset patch, as shown in the attached figure. I'm not sure how to fix this. Could this discontinuity be the main cause of the issue?

I'm using OpenFOAM version 2312. Could anyone help me figure this out?

Best regards,
Santhou
Attached Images
File Type: jpg 0.4993z.jpg (29.1 KB, 12 views)
File Type: jpg 0.4993fz.jpg (28.0 KB, 11 views)
File Type: jpg overset.jpg (72.5 KB, 15 views)
File Type: jpg water_surface3.jpg (56.9 KB, 9 views)
Attached Files
File Type: zip overset.zip (48.5 KB, 3 views)

Last edited by santhou; September 26, 2024 at 04:50.
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Old   January 2, 2025, 03:25
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Shen Tsao Hung
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Hello everyone:

I have found oscillation issues, but as a beginner, I am unable to resolve them. The oscillations stem from the overset mesh's interpolation. While other physical quantities seem to interpolate without major issues, the problem arises with alpha.water. Using the default interpolation methods causes discontinuities in the water surface. This is because the water surface is a discontinuous physical quantity (in terms of analytical solutions, it's either 0 or 1). The interpolation uses nearby points with a weighted least squares approach, which leads to unrealistic interpolation results.

Attachmnet shows the beginning time for alpha.water interpolation and the velocity.

Best regards,
Santhou
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File Type: jpg 1.jpg (62.3 KB, 6 views)
File Type: jpg 2.jpg (81.5 KB, 7 views)
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