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Old   May 22, 2001, 04:16
Default oscillations
  #1
murugesh
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hi all Iam doing a transient analysis involving free surface. My solution is oscillating. What are the parameter that I should change to control oscillation. I tried reducing the time step and increasing the number of sweeps but it is still oscillating. please help me.

thanks in advance.
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Old   May 22, 2001, 06:35
Default Re: oscillations
  #2
Sebastien Perron
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1) Are you sure that it is a laminar permanent flow?

2) Did you use any kind of upwinding? (if no, than you have instabilities....)

3) Is your program bug free (tough question...)?
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Old   May 22, 2001, 13:25
Default Re: oscillations
  #3
murugesh
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1) Are you sure that it is a laminar permanent flow? Iam pretty sure that it laminar.

2)Did you use any kind of upwinding? I am using the upwind differencing scheme

3)Is your program bug free (tough question...)? Iam using the STAR CD package and my model is similar to one of the tutorial(15) in it with some modification. The tutorial is a free surface model. I have added to the model a droplet to fall on the free surface and studying the deformation characteristics.

Thanks

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Old   May 22, 2001, 18:40
Default Re: oscillations
  #4
Barney
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IF the model is a VOF or levelset... ------------------------------------- What are the density and viscosity ratios???

Is it a water droplet falling through air??

If it is, try lowering these ratios and check the results...

also check to see if the surface tension (CSF) is damaging your results... lower the surface tension coefficient and check again..

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