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SOS: About VOF-Dynamic mesh unsteady problem

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Old   April 24, 2006, 03:38
Default SOS: About VOF-Dynamic mesh unsteady problem
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whpsoft
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My model is about a VOF-Dynamic mesh unsteady problem. As with the simulation, the fluent require to decrease the time step, even decreased to 1e-8. how to improve the stability of simulation of VOF-Dynamic mesh unsteady problem?

In addition, Can somebody send me a paper " VOF-Dynamic Mesh Simulations of Unsteady Ship Hydrodynamics" in MARINE CFD 2005? Maybe it can give me some tips. Thanks!
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Old   April 24, 2006, 10:45
Default Re: SOS: About VOF-Dynamic mesh unsteady problem
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whpsoft
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help me
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Old   April 25, 2006, 00:06
Default Re: SOS: About VOF-Dynamic mesh unsteady problem
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CFDtoy
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Hello Whp... I have done some VOF, dynamic mesh unsteady problems..tell me wht u r facing ..i can try to resolve a few things..if i can..

CFDtoy
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Old   April 25, 2006, 02:53
Default Re: SOS: About VOF-Dynamic mesh unsteady problem
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whpsoft
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Hi, CFDtoy

Thanks for your information!

My model is just like a bottle filled with high pressure gas, sinking underwater, with a cylindical cover in its open mouth. one moment, the high pressure gas will push the cover and leak out of the bottle mouth. I want to simulate the process of gas-water interaction. It's a VOF-Dynamic mesh unsteady flow simulation.

Initially, Fluent converge very well when time step is set to 1e-5. But as with the simulation, fluent tell me that: "Error: Too many (4258) VOF sub-timesteps. The velocity field is probably diverging. Please check the solution, and reduce the time-step if necessary. Error Object: ()" Even when I set the time step to 1e-8, fluent also warns me this information. I know that fluent requires timestep smaller as with the simulation, but how to set a reasonable timestep to conform suitable computation time.

please tell me how to set URF and any other parameters to fit my need, Thanks!

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Old   May 9, 2006, 19:26
Default Re: SOS: About VOF-Dynamic mesh unsteady problem
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CFDtoy
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Depends on your meshing procedure.If you remesh quite often with smaller length scales, VOF cannot adjust at the same length scales and hence the simulation diverges. Few things you can do: (1) change dynamic meshing procedure with increased length scales (2) pressure velo coupling: use presto and PISO procedure. (3) do a coupled simulation: (a) simulate bottle sinking until sometime (b) stop, now open up the bottle and allow transient simulation with lid open. This is little discrete ..but works !

Let me know wht u think.

CFDtoy
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