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Forced vibration

Here is how I have carried out the forced vibration
simulation. After an “intial step”, I chose “Linear Perturbation” to first
extract the natural frequency. My next step was “Modal Dynamics”. I then
applied the load in the form of a sine wave under the same step. I have an
isotropic material. When I try to submit the job, I received following warning:

A steady state subspace projection based, or mode based
dynamic analysis is required for a model with non-diagonal mass matrix.
Abaqus/standard subspace projection based or modal based dynamic analysis for a
model with non-diagonal mass matrix (e.g. using substructure) might give
incorrect reaction forces. However other output quantities will be correct.

I am unaware of how severe this warning is. Can anyone
please guide me regarding this? Have I selected correct approach for the forced
vibrational analysis?

Thanks a lot!





I am still clueless at the procedure. I already have the results for the job. However, the animation of the simulation looks really weird. I earnestly request to please take out your valuable time and let me know method to be adopted for carrying out the forced vibration simulation.

Thanks a lot!


Bhisham Sharma's picture


Unless you are interested in the reaction forces, the warning should not be of concern. 

As far as your results looking "weird", why do you think they are weird? If you post a bit about what you are trying to solve and what you expect, they people could help you better. Are you aware that Abaqus gives out only the relative positions (U,V,A) when you use the modal dynamics step for a base excitation problem? Perhaps that's why your results look strange. Or perhaps you did not ask it to use all the modes, of the number of modes used in the analysis is insufficient.


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