which is the correct boundary conditions for frame modal analysis?
some do modal analysis with no restrain(free-free) and some do it with apply restrain, for example restrain frame rear at x,y,z and front in y,z (x is roll axis)
or some do it with weight of driver and engine and...

It all depends on what YOU want, and what the data is going to be used for.

I want natural frequency of frame

quote:

Originally posted by ffarshadd:
I want natural frequency of frame

BOOOYYY-yoy-yoy-yoy-yoy-yoy-yoy-yooooiiiiinggggggg!!!



Natural frequency around what axis or axes?

EDIT: It took me a minute of thinking this over, but I think you are looking for the stiffness of the frame, you could do the stiffness analysis in terms of frequency, but usually you want to know the actual stiffness (spring rate) of the frame in some mode, torsionally for example. Stating what the frequency of the frame is will get you funny looks from the judges...

Can I ask why? (You're on the right track, you will have to pick representative points to hold the frame still, points to load it from, and points that you don't want to move [to resist rotation] but don't want held perfectly ridgid to accidentally induce any bending into your frame, you may have to restrain points translationally in some axes and not others to achieve that.)

Best,
Drew