Learning Forum

[Vahidebrahimistudent]

Hi Everyone,

I wanted find the stress and strain responses inside a rubber support undergoing vibration excitation from a vibrating motor (see photo attached). Provided that I have all the input data what should I insert on the surface of the rubber support to represent the vibration? I have used a series of relations to calculate the frequencies (Hz), the force of eccentric rotating mass (N) , and the overall displacement (X) considering both vibrating motor and the rubber band stiffness (K). 

Can you please help me with the inputs I should give to the surface of the rubber model to best represent the excitation by the vibrating motor?

Should I introduce the force (F=mrw^2) from the rotating mass and insert the frequecy (w) to represent F=F0Sin(wt) ? (please see the photo for equations.) Ansys input : Force on rubber surface + Frequency ?

OR, instead of force, should I calculate the amplitude considering the rubber stiffness (K)? (please see the photo for equations.) Ansys input : Displacement of rubber Surface + Frequency 

I really appreciate any suggestion,

Thank you, Vahid

[peteroznewman]

You have idealized and linearized a complex 3D nonlinear structure where a 6 DOF system has been reduced to a 1 DOF linear elastic oscillator. Since you have already solved for the displacement, X0, you can calculate the strain, and since you know the modulus of the material, you can compute the stress. It seems there is nothing left to do in ANSYS. Perhaps some other members or ANSYS staff with a deeper knowledge of vibration and rubber material response may comment.
A different approach is to build a model of the complex 3D structure and represent the connection to ground with more fidelity. Perhaps in reality there are three or more pads and the response on one is greater than the others due to the 3D shape of the base and the location of the unbalanced mass.