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Strange results in time domain analysis

Posted 16.09.2011, 15:49 GMT-4 Structural Mechanics Version 4.1, Version 4.2 2 Replies

Ying Peng
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I would like to simulate the situation of an harmonic vibration source on the surface of a kind of specified gel material. In my simulation, one silde of crosssection was taken for simulation due to less elements. I applied ”Solid Mechanics” and “time dependent study” in COMSOL.

Problem:

Vibrating source can be discribed as: d=-0.1*exp(i*2*50*pi*t), which means the source is vibrating up and down on the surface at a 50Hz freqency. The plot from MATLAB is shown in the word document (t=0:0.001:0.5;):

In COMSOL, I applied the same vibrating source and time step. But I could not obtain the same result. Data is acquired at the vibrating boundary. The result from COMSOL is shown in word file.

Can someone help me with this problem?

Thank in advance!





2 Replies Last Post 21.09.2011, 18:42 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 19.09.2011, 05:49 GMT-4
Hi

there are two things to now:

1) when applying a steady state harmonic excitation, the "harmoic" solvers are often better to use, you enter rms input BC values and get rms output values

2) if you use the time solver on harmonic BC cases, you must ensure that you also define the time steps such that COMSOL really calculates inbetween the oscilaltions, use the "strict" or Intermediate" mode of your solver settings and not the "automatic", that is talored for diffusion type solving ("exp()" type decays)

--
Good luck
Ivar
Hi there are two things to now: 1) when applying a steady state harmonic excitation, the "harmoic" solvers are often better to use, you enter rms input BC values and get rms output values 2) if you use the time solver on harmonic BC cases, you must ensure that you also define the time steps such that COMSOL really calculates inbetween the oscilaltions, use the "strict" or Intermediate" mode of your solver settings and not the "automatic", that is talored for diffusion type solving ("exp()" type decays) -- Good luck Ivar
Ying Peng
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Posted: 1 decade ago 21.09.2011, 18:42 GMT-4
It is Okay now. Thanks.

It is Okay now. Thanks.

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