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transient analysis with harmonic point load
Posted Apr 14, 2010, 10:33 p.m. EDT 1 Reply
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Hi,
I am trying to model a ractangular plate driven by sinusoidal load with very high frequency (approximately
15000 Hz). What I want to get is the time dependent displacement of a certain point on my plate.
After defining a point load (F_z = sin(15000*2*pi*t)) I pick my solver parameters as follows:
Solver Parameters 0:0.0000001:0.001
(The reason why I pick such a small delta_t (0.0000001) is because the period of the applied load is 1/15000 seconds)
I leave the absolute and relative tolerance values as they are, i.e., 0.01 and 0.010 respectively.
After doing the meshing/solving I postprocess to get my time vs z_velocity plot at a certain point. The problem
is both the displacement and velocity plots are choppy and no matter how small I pick the delta_t (time
iteration) I get the same plots. How can that happen? I am expecting to get higher resolution in time as I
decrease the delta_t but that does not happen.
What am I missing? Can it be because of the tolerance values? Or maybe e-7 is too small for an accurate
transient analysis?
Any help is greatly appreciated.
Thanks
I am trying to model a ractangular plate driven by sinusoidal load with very high frequency (approximately
15000 Hz). What I want to get is the time dependent displacement of a certain point on my plate.
After defining a point load (F_z = sin(15000*2*pi*t)) I pick my solver parameters as follows:
Solver Parameters 0:0.0000001:0.001
(The reason why I pick such a small delta_t (0.0000001) is because the period of the applied load is 1/15000 seconds)
I leave the absolute and relative tolerance values as they are, i.e., 0.01 and 0.010 respectively.
After doing the meshing/solving I postprocess to get my time vs z_velocity plot at a certain point. The problem
is both the displacement and velocity plots are choppy and no matter how small I pick the delta_t (time
iteration) I get the same plots. How can that happen? I am expecting to get higher resolution in time as I
decrease the delta_t but that does not happen.
What am I missing? Can it be because of the tolerance values? Or maybe e-7 is too small for an accurate
transient analysis?
Any help is greatly appreciated.
Thanks
1 Reply Last Post Apr 15, 2010, 1:27 a.m. EDT
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Posted:
1 decade ago
Hi
Take a look at the "Solve - Solver parametres - Time stepping tab", and check the corresponding doc, I suppose you need to tewak the "Time steps taken by the solver".
On the other side expect long calculations as you are demanding very many points N=max time/resolution*M where M is the number of sub-steps COMSOL needs to follow your time step and to converge (situation dependent) and also "point" constrints are not very clean, they represent a simplification that does not make the analysis of any derivative veryx easy, hence not that good convergence.
Have fun Comsoling
Ivar
Take a look at the "Solve - Solver parametres - Time stepping tab", and check the corresponding doc, I suppose you need to tewak the "Time steps taken by the solver".
On the other side expect long calculations as you are demanding very many points N=max time/resolution*M where M is the number of sub-steps COMSOL needs to follow your time step and to converge (situation dependent) and also "point" constrints are not very clean, they represent a simplification that does not make the analysis of any derivative veryx easy, hence not that good convergence.
Have fun Comsoling
Ivar