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DTCHull Ship Resistance Tutorial - Morphing vs Overset Dynamic Mesh

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Old   August 13, 2022, 13:00
Default DTCHull Ship Resistance Tutorial - Morphing vs Overset Dynamic Mesh
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Nick
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Hello everyone,

This is my first time posting a question on this forum.

Normally, ship resistance tests do not require an overset mesh for the dynamic mesh. Even for a planning hull, a morphing mesh approach is sufficient. DTCHullMoving tutorial from "multiphase/interFoam/RAS" uses that approach.

When I was running resistance simulations (2DOF, free pitch and heave) in shallow water, I found that there is not enough room for mesh morphing below the ship hull in certain cases where the trim and sinkage are significant. Some of the cells get squeezed until their volumes become essentially zero leading to the simulation divergence. Adjusting mesh morphing diffusivity method and morphing range (innerDistance and outterDistance) can help in some cases, but it does not solve the whole problem. Different adjustments might be needed for different ship speeds depending on the sinkage and trim history. This kind of problem is more likely to happen when a finer mesh is used.

To solve that, I wanted to test the overset mesh approach. I modified the DTCHullMoving tutorial for overset mesh by combining it with rigidBodyHull tutorial from the overInterDyMFoam. I was successfully able to run the simulation. The resistance convergence histories are attached. The total resistance values are similar for all DTCHull, DTCHullMoving and DTCHullMovingOverset (mine). But, the pressure and viscous components of Overset version is different from the those of DTCHull and DTCHullMoving.

My question is: Why are they different? Forces calculation/decomposition method in overset mesh is different from the normal one?

If you are interested in the case files, I will upload them.
Attached Images
File Type: jpg DTCHullFixed.jpg (142.6 KB, 36 views)
File Type: jpg DTCHullMoving.jpg (137.5 KB, 31 views)
File Type: jpg DTCHullMovingOverset.jpg (146.7 KB, 31 views)
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Old   September 1, 2022, 16:03
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Hello myozinaung, can you post your case files so we can go over them? That might help to determine the differences.
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Old   September 15, 2022, 09:38
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The problem is now resolved. The resistance values are similar for both morphing and overset cases.
If you are interested in the case files, check the link below.

https://github.com/myozinaung/DTCMoving_Overset
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Old   September 25, 2022, 22:04
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Happy to hear things are better for you! I found this document which outlines best practices for overset, maybe it would be of use to you if you do some larger motions. I found the tutorials for overset had different values for the fvSolution dictionary than what these guys are recommending. http://www.wolfdynamics.com/training...s_2021_OF8.pdf
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Old   October 6, 2022, 07:38
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Hi,
If you could throw some light on how the problem got resolved, that will really be a great insight. in the snapshots you uploaded earlier, we see, even though the total resistance is similar, the pressure and viscous components are showing significant differences.
Thanks and regards.
akram
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Old   October 6, 2022, 10:59
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Hello,

Previously I used the solver settings (fvSolution and fvSchemes) from the rigidBodyHull tutorial because that is the overset mesh tutorial with a ship and propeller. The problem is the solver settings are not suitable for the resistance calculation. So I modified the solver settings to match the original DTCHullMoving tutorial settings which are set up for the resistance calculation.
The new results are attached for your reference.

Regards,
Myo
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File Type: jpg DTCMoving_Overset_Resolved.jpg (96.7 KB, 7 views)
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Old   October 6, 2022, 11:04
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Thank you so much for the quick reply.
I shall check that. Are you working in Openfoam.com or openfoam.org?
Thanks and regards,
akram
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Old   October 6, 2022, 11:12
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I used OpenFOAM v2206 (openfoam.com).
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