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Frequency Response for a clamped beam with many vibration absorbers.
Posted Mar 21, 2019, 1:03 p.m. EDT Structural & Acoustics, Acoustics & Vibrations 4 Replies
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Hello all,
I have a thin plate modeled as 3D in solid mechanics module. On the top of this plate, I have places a mass-spring resonator (vibration absorber) (please see the attached figure) where I have modeled it in COMSOL using the lumped mechanical system. The helix spring is just for schematic where the actual 3D plate is shown in second figure. I coupled the two systems using the “External Source” from the lumped mechanical system and I exert the reactions from this external source to the solid 3D plate. The eigenfrequencies obtained from the eigenfrequency study matched perfectly with the in-house FE code. However, now I am trying to study frequency response to a harmonic force of an amplitude 1 while changing its frequency. Since I am applying the reaction forces from the external source of the lumped mechanical system to the 3D solid plate, how can I apply the harmonic force?
I tried to add something like this:
“-lms.E136_f2 + linper(1)”
where “-lms.E136_f2” is the reaction force from the external source and “linper(1)” is my harmonic force but still I could not succeed. I will be really appreciated if I can find an answer.
Thank you
Abdullah
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Hi,
The first question here is whether you are using an ordinary Frequency Domain study, or one that is of 'perturbation type'. The linper() operator only contributes to a perturbation type of study.
To me it seems that you should use the expression “-lms.E136_f2 + 1” and use ordinary Frequency Domain. All loads are then implicitly assumed to be periodic.
Regards,
Henrik
Henrik Sönnerlind
COMSOL
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Hi,
The first question here is whether you are using an ordinary Frequency Domain study, or one that is of 'perturbation type'. The linper() operator only contributes to a perturbation type of study.
To me it seems that you should use the expression “-lms.E136_f2 + 1” and use ordinary Frequency Domain. All loads are then implicitly assumed to be periodic.
Regards,
Henrik
Thenk you Henrik for your reply.
Yes I want to do an ordinary Frequency response where I want only one force which has a magnitude of 1 N to be periodic where the other reactions forces are staionary.
Abdullah
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Hi Abdullah,
If you want part of the forces to be stationary, and part to be harmonic, then you need to use an analysis setup which is similar to 'Frequency Domain, Prestressed'. That is: one Stationary step for the static preload and one Frequency Domain step of perturbation type with the stationary solution as linearization point.
In such a setting, your original expression contating linper(1) for the harmonic part is the correct one.
Regards,
Henrik
Henrik Sönnerlind
COMSOL
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Hi Abdullah,
If you want part of the forces to be stationary, and part to be harmonic, then you need to use an analysis setup which is similar to 'Frequency Domain, Prestressed'. That is: one Stationary step for the static preload and one Frequency Domain step of perturbation type with the stationary solution as linearization point.
In such a setting, your original expression contating linper(1) for the harmonic part is the correct one.
Regards,
Henrik
Hello Henrk,
Yes it does work. Thank you very much. I will really appreciate your help and I am sorry if I cause any trouble.
Abdullah