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Ball Moving Causing Stokes Flow in Viscous Fluid

Posted Oct 28, 2021, 5:18 p.m. EDT Structural & Acoustics, Fluid & Heat Version 5.6 3 Replies

Chloe Boucher
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I am trying to use the Fluid Structire Interface (FSI) Module to have a ball moving in an otherwise stationary fluid without using the phase field or level set activation.

My doimain is big, 1000 high and a 500km radius and the ball has a radius of 50km and is located 300km below the surface which is an open boundary. The fluid that the ball is in is very visous (1E19[Pa*s]). The velocity of the ball is only in the z direction and is on the order of magnitude of E-8 [m/s].

Where I am running into problems is with initial conditions convergence (which seems to be a comon problem) but I am not sure how to solve it. I have tried using a ramp function but do not know how to couple it to the time. I am hesitant to lower convergence tolerance.

So my question: How to get initail conditions for a system where structure causing a fluid to move from rest?

3 Replies Last Post Nov 4, 2021, 9:19 a.m. EDT
Dave Greve Certified Consultant
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Posted: 3 years ago Oct 28, 2021, 8:19 p.m. EDT

I'm not able to access the creeping flow physics but a couple thoughts.

  • Fluid flow problems often don't converge without a pressure point constraint.
  • Try a fully coupled solver
  • There don't seem to be any forces or imposed velocity, or am I missing something?
I'm not able to access the creeping flow physics but a couple thoughts. - Fluid flow problems often don't converge without a pressure point constraint. - Try a fully coupled solver - There don't seem to be any forces or imposed velocity, or am I missing something?
Chloe Boucher
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Posted: 3 years ago Nov 1, 2021, 1:49 p.m. EDT

Hey Dave,

Thanks for the reply.

  1. I have attemped a pressure point constraint by setting the initial pressure to 1atm at the top surface
  2. I haven't tried a fully coupled solver. This is a great idea, thank you!
  3. the sphere has an imposed (and constant) velocity which I would like to be translated to the fluid.
Hey Dave, Thanks for the reply. 1. I have attemped a pressure point constraint by setting the initial pressure to 1atm at the top surface 2. I haven't tried a fully coupled solver. This is a great idea, thank you! 3. the sphere has an imposed (and constant) velocity which I would like to be translated to the fluid.
Diotima University of Manchester/Material Science
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Posted: 3 years ago Nov 4, 2021, 9:19 a.m. EDT

I only know two possiable way to solve it and I don't know whether it will help you. 1. Do a stationary study before your calculation, use its solution as your initial condation. 2. a step function, and set your initial condition as the form below: 1[m/s]*step1(t[1/s]).

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I'm the loser student who really want a PHD placement.
I only know two possiable way to solve it and I don't know whether it will help you. 1. Do a stationary study before your calculation, use its solution as your initial condation. 2. a step function, and set your initial condition as the form below: 1[m/s]*step1(t[1/s]).

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