I modelled a bimorph in ANSYS Mechanical(2015). It is a simple cantiliver structure. When I use Modal, the natural frequency of the first mode matches well with the theoretical value(188 Hz). But when I use "Harmonic", I assign a downward force and obtain the frequency response , the displacement peaks not at 188 Hz but at a slightly large value(200 Hz). Why could this happening?
When you use "Modal", you get the eigenvalues, which correspond to the natural frequencies of the beam. However, when you use "Harmonic", you obtain the frequency response function at a certain node. I would expect that you should get closer estimate if both the harmonic excitation and the frequency response are associated with the same node.
Harmonic analysis results are from many modes (check how many modes you have selected) at a particular point as Prof. Khulief pointed out. If you provide a single mode for the total response , you will get the fundamental peak exactly matching with the eigen value.
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