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analisi modale in workbench ansys

Dromoaor

Guest
good day to all users of cad3d.it!:biggrin:
I wanted to ask a question about modal analysis in workbench ansys. We start from the fact that I have an assembly of many components, then I thought of doing a modal analysis since I subsequently intend to go to charge it with forceful employees from time in the transient suite.
I initially did n modal analysis for all n elements taken individually (soever not bound with the classic 6 motions of rigid body to f=0 hz and then the other ways I wanted to get) to see which was the first minimum natural frequency.
I then load all assembly in modal analysis and bind the system with joint & contacts.
now my problem is both theoretical and practical.
I would like to understand from the theoretical point of view where the constraints and contacts intervene in a modal analysis, since the problem is reduced to ([K]- omega^2 [M]) {d}={0} I would like to understand where the constraints and contacts between the various bodies affect when the solver goes to solve this equation system.
from the practical point of view the modal analysis "of assembly" gives me for example a value of the first frequency not anything about 150 hz regarding the first frequency not nothing given between all the modal analyses of the various single components that is 25 khz.
 
very simplely the stiffness, mass and damping of the individual pieces assembled changes and therefore you get a different frequency, which as you can see is lower than the individual pieces.
 

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