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Artefact in combining diluted species with FSI

Posted 18 oct. 2017, 08:18 UTC−4 4 Replies

Dirk Jonker
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As part of my bachelor degree i have to take part in a module organized around the COMSOL interface.

For my problem i have selected the actuation of a flexible membrane. My problem is that at some point during the simulation i see a blow up of the concentration in the area where my mesh is deformed.

Please find attached an image of the situation. I have fixed the color bar of the concentration to get a better view of the problem. If not fixed values for 10^8 and beyond are found in single locations colouring everyhting else as ~0.

My hope is that somebody can give me directions into solving this problem.

Things i tried: - Changing initial concentration from 0 to 1. The result is a blow up at an earlier timestep. - Conservation of mass in the diluted species interface: no result. - Pressure point constraints: no result. - Concentration=0 point constraint at fluid-solid interface where membrane deforms: no result

Kind regards,

Dirk

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4 Replies Last Post 24 oct. 2017, 08:54 UTC−4
Dirk Jonker
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Posted: 7 years ago 18 oct. 2017, 08:25 UTC−4

Oh yeah,

Feel free to ask for more information if necessary.

Oh yeah, Feel free to ask for more information if necessary.
Dirk Jonker
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Posted: 7 years ago 18 oct. 2017, 08:53 UTC−4

Okay,

Lowering the Reynolds number does seem to negate the problem. However, when i apply a negative pressure at the top of the membrane (creating more deflection) the problem is back.

Okay, Lowering the Reynolds number does seem to negate the problem. However, when i apply a negative pressure at the top of the membrane (creating more deflection) the problem is back.
Dirk Jonker
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Posted: 7 years ago 18 oct. 2017, 15:07 UTC−4

Okay,

So i found out that removing the FSI input from the TDS node> transport properties> velocity field removes the problem.

When i plot the velocity of the fluid at the edge of the membrane, i see the magnitude of the fluid velocity passing trough zero. When i plot the concentration with it, the blow up happens at approximately the same spot.

HELP?!?!

Okay, So i found out that removing the FSI input from the TDS node> transport properties> velocity field removes the problem. When i plot the velocity of the fluid at the edge of the membrane, i see the magnitude of the fluid velocity passing trough zero. When i plot the concentration with it, the blow up happens at approximately the same spot. HELP?!?!
Dirk Jonker
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Posted: 7 years ago 24 oct. 2017, 08:54 UTC−4

Load-ramping my entrance-flow solved the problem! Created a ramp for the average speed.

Load-ramping my entrance-flow solved the problem! Created a ramp for the average speed.

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