

Re: Simulation
Mallikarjuna B. S. Oct 30, 2018 12:51 AM (in response to Benjamin Modic)Hi Benjamin Modic,
Thank you for the reply. If so, how one can tackle the problem to know exact natural frequencies of a given structure, especially when one worried about the contacts?
Regards,
Mallikarjuna

Re: Simulation
Bill McEachern Oct 30, 2018 7:36 AM (in response to Mallikarjuna B. S.)Typically, you bound the problem. More than this and less than that.



Re: Simulation
Scott Stuart Oct 26, 2018 1:00 PM (in response to Mallikarjuna B. S.)Dang. I thought you said "stimulation". I got excited.

Re: Simulation
Erik Kostson Oct 30, 2018 9:34 AM (in response to Mallikarjuna B. S.)Not heard of such a term as nonlinear frequency analysis. Frequency analysis assumes linearity so we can establish a dynamic solution based on a linear summation of modes (with certain amplitude). In nonlinear analysis superposition is not valid.
Other than that the dynamic equations ([K][M]*w^2=0) solved by these solvers assume small deformation, no change in BC and linear material.
If we want to include these nonlinear effects then a transient nonlinear solver can be used, but that does not use natural modes to produce a solution (as say in a harmonic response analysis where modes are typically used), it integrates the nonlinear dynamic equations. The results is a general time disp./stress history data (not modes and freq.).
Thus if you have a real contact situation (not bonded) one would need to use the nonlinear transient solver, since in solidworks only free and bonded contacts can be used in a natural frequency analysis.
Some FEA software like Strand7, Nastran, will allow one to use some form of contacts in the natural frequency solution, but how well that works really depends on the situation I think (many time they import the contact stiffness from a nonlinear analysis in to the natural frequency solver, which assume that contacts will not change during this linear analysis, thus small displacements about a contact equilibrium found in the nonlinear static analysis – so if contact status change s this is not valid anymore).

Re: Simulation
Bill McEachern Oct 30, 2018 10:09 AM (in response to Erik Kostson)FYI: I run Abaqus and what it does is that it can take an NL analysis (say bolt tightening) and then do a frequency analysis (more explicitly for the OP it does an eigenvalue extraction of the stiffness matrix). However, what it assumes is that there is no change in any contact status from the previous analysis  if a contact is closed then it remains closed (ie bonded, tied or whatever you choose to call it) when the extraction is done. The value in this is that the span of the contact patch is a better approximation for small amplitudes of vibration which what happens when vibrations start to emerge. It also allows any other preloads which may contribute to stress stiffening of softening effects to be included (SWX Sim can do some of this but not the contact status carry over)

Re: Simulation
Mallikarjuna B. S. Nov 1, 2018 1:15 AM (in response to Erik Kostson)Hello,
Thank you for the info.
As per your statement, I understand that there is NO FEA solver, has facility to deal nonlinear frequency analysis.
What is the best approximation method (whether bonding or rigid connection etc) for imposing contacts while doing a modal analysis in SolidWorks. just for e.g., we have a block of size 1mx1mx1m and is clamped onto the floor with few screws and assume that there is no gap between the block and the floor. In this situation, what kind of boundary condition you impose, whether you arrest at the screw region or the whole surface where the block and floor touches?, assuming that you only consider the block for analysis, treating that floor is infinitely rigid.

Re: Simulation
Erik Kostson Nov 1, 2018 6:54 AM (in response to Mallikarjuna B. S.)According to the SW documentation the only available contact options for modal/frequency analysis is bonded and free contact, so that is what you can choose from.

