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Time dependent simulation of single degree of freedom system

Posted 13.01.2020, 01:20 GMT-5 Structural & Acoustics, Acoustics & Vibrations, Structural Mechanics 1 Reply

陈勇勇 陈
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I use the lumped mechanical system interface to solve a single-degree-of-freedom system transient simulation. The harmonic frequency is the system natural frequency. Why does the steady-state acceleration in the calculation result change? As shown below.

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1 Reply Last Post 13.01.2020, 14:12 GMT-5
Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago 13.01.2020, 14:12 GMT-5

Hi,

The plot looks like if the excitation is reduced to 75% of it previous value at time 0.25 s. Or, similarly, that the damping is increased by 25%.

Can you see anything jumping in the solver log or the convergence graph at that time? Do the time steps increase? Which time dependent solver is used? Do the displacements behave the same way as the accelerations?

If the time steps are very large, what you see is possibly an effect of numerical damping, rather than a physical result. Try limiting time steps and tightening tolerances.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi, The plot looks like if the excitation is reduced to 75% of it previous value at time 0.25 s. Or, similarly, that the damping is increased by 25%. Can you see anything jumping in the solver log or the convergence graph at that time? Do the time steps increase? Which time dependent solver is used? Do the displacements behave the same way as the accelerations? If the time steps are very large, what you see is possibly an effect of numerical damping, rather than a physical result. Try limiting time steps and tightening tolerances. Regards, Henrik

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