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FSI Problems

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I am new to COMSOL and currently have a time dependent FSI model with numerous problems. The model is that of a fluid flow over an elastic material that should (hopefully) deform similar to the example 361 with different geometry. I used this example model for the basis of my model and am now having problem changing some of the values.

I am not able to reduce the youngs modulus of my model from 1e5 to 2e4 or even 9e4. When
doing this I recieve complaints that the non linear solver did not converge.

I also can not put in a simple equation for the velocity of u=a*t where u is the velocity
of the flow, a is an acceloration. When entering this into my model I get an error that
COMSOL could not find consistent initial values. I can get the model to run, however, if
I change the velocity equation to that given in example 361 on the website for u_in.

I have also tried automatic remeshing as I am using COMSOL 4.2, however, I coould not get
this to work either as there is NO dynamic help on this. I have also tried remeshing by
hand when the model experiences a poor mesh quality but then obtained errors about
inconsistancies in the stiffness matrix.

I will be greatful for the help

Kelly

4 Replies Last Post Jun 20, 2016, 3:13 a.m. EDT
Nagi Elabbasi Facebook Reality Labs

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Posted: 1 decade ago Mar 7, 2012, 12:19 a.m. EST
Try using the Fully Coupled Solver instead of the Segregated Solver. It sometimes works better when the structure is soft. Also, for the inlet velocity consider a ramp function instead of v=a*t. If the function has zero initial velocities and accelerations the solver should be able to find consistent initial values.

Nagi Elabbasi
Veryst Engineering
Try using the Fully Coupled Solver instead of the Segregated Solver. It sometimes works better when the structure is soft. Also, for the inlet velocity consider a ramp function instead of v=a*t. If the function has zero initial velocities and accelerations the solver should be able to find consistent initial values. Nagi Elabbasi Veryst Engineering

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Posted: 1 decade ago Mar 7, 2012, 10:30 a.m. EST
I tried using a fully coupled solver but it still wont let me put in a youngs modulus less than 1e5 it also produces a lot of inverted mesh elements

Kelly
I tried using a fully coupled solver but it still wont let me put in a youngs modulus less than 1e5 it also produces a lot of inverted mesh elements Kelly

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Posted: 1 decade ago Mar 7, 2012, 7:08 p.m. EST
Sometimes, the time-dependent problems converge better when you use the solution of the stationary problem as the initial condition to the time-dependent problem.This may help with the inverted mesh elements also.

If the stationary problem does not converge, try solving the stationary problem using a parametric solver. It usually works. Then you can use that as the initial condition for the time-dependent problem.

Sirisha
Sometimes, the time-dependent problems converge better when you use the solution of the stationary problem as the initial condition to the time-dependent problem.This may help with the inverted mesh elements also. If the stationary problem does not converge, try solving the stationary problem using a parametric solver. It usually works. Then you can use that as the initial condition for the time-dependent problem. Sirisha

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Posted: 8 years ago Jun 20, 2016, 3:13 a.m. EDT
Hello

I am simulating a solid body moving in fluid(air) giving the solid domain Prescribed velocity as a funtion of time. I have defined the inlet velocity as 10m/s and outlet pressure as 0 Pa.I am using automatic remeshing feature too. I wish to study the henceforth effects in fluid and the pressure variations over the solid body.

But i get the error: Condition for remeshing fulfilled for initial time.

Please help me through.
Thank You
Ankush
Hello I am simulating a solid body moving in fluid(air) giving the solid domain Prescribed velocity as a funtion of time. I have defined the inlet velocity as 10m/s and outlet pressure as 0 Pa.I am using automatic remeshing feature too. I wish to study the henceforth effects in fluid and the pressure variations over the solid body. But i get the error: Condition for remeshing fulfilled for initial time. Please help me through. Thank You Ankush

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