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eigenfrequency after calculation of the equilibrium state
Posted 03.11.2011, 10:34 GMT-4 Fluid & Heat, Interfacing, Structural Mechanics Version 4.2 1 Reply
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Hello,
I try to model a water bubble between two stones with smooth texture. I describe the problem theoreticaly with the Navier-Stokes equation and create a 2D-model in Comsol with the use of PDE's to calculate in the first step the equilibrium state. My starting geometry is a square and I can calculate the equilibrium state with the use of time dependent studies.
My problem is the calculation of the eigenfrequencies of this new structure.
When I just add a secound step to evaluate the eigenfrequency the results are trivial and make no sense.
I tried to get the mass- and stiffnessmatrix of the FE-mesh with the matlab link to calculate the eigenvalues with Matlab but all values in the massmatrix are zero.
Does anyone find a mistake in my approach or has another idea to calculate the eigenvalues or frequencies?
Maybe some more words to my model:
the only loads are the surrounding pressure and the surface tension.
Thank you very much!
Greetings,
Christopher
I try to model a water bubble between two stones with smooth texture. I describe the problem theoreticaly with the Navier-Stokes equation and create a 2D-model in Comsol with the use of PDE's to calculate in the first step the equilibrium state. My starting geometry is a square and I can calculate the equilibrium state with the use of time dependent studies.
My problem is the calculation of the eigenfrequencies of this new structure.
When I just add a secound step to evaluate the eigenfrequency the results are trivial and make no sense.
I tried to get the mass- and stiffnessmatrix of the FE-mesh with the matlab link to calculate the eigenvalues with Matlab but all values in the massmatrix are zero.
Does anyone find a mistake in my approach or has another idea to calculate the eigenvalues or frequencies?
Maybe some more words to my model:
the only loads are the surrounding pressure and the surface tension.
Thank you very much!
Greetings,
Christopher
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1 Reply Last Post 07.11.2011, 05:27 GMT-5
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Posted:
1 decade ago
Maybe I should add that I only have a student license. Thats why I cannot create a laminar flow model.
The navier stokes equation describes the velocity of the flow. The massmatrix is connected with the secound derivative of the displacements of the FE nodes. Maybe I described the problem with the wrong terms and comsol cant connect the velocity with the displacement.
Does anyone ever calculated the eigenvalues of a static fluid problem which is described with the navier stokes equation?
The navier stokes equation describes the velocity of the flow. The massmatrix is connected with the secound derivative of the displacements of the FE nodes. Maybe I described the problem with the wrong terms and comsol cant connect the velocity with the displacement.
Does anyone ever calculated the eigenvalues of a static fluid problem which is described with the navier stokes equation?