Learning Forum

[dxiang]

Hello,

I am trying to model isolators with joint and two questions here:

1, how to deifne siffness if compression and tension are different. (such as wire rope isolator);

2. Can I define damping ratio in joint? Or Is there any way to tranfer damping ratio to vicous damping.

Thank you

Daniel

[dlooman]

Instead of a joint consider using a nonlinear spring (COMBIN39.)  The nonlinear spring has a material property DMPR, which is short for damping ratio.  

[dxiang]

Hi Dave,

Thank you for quick response. Further quesitons:

1, I have to use 3 springs  for each isolator, right?

2. Can I make dynamics analysis such as modal, random vibration and transient if nonlinear spring is used?

Thanks

Daniel

[dlooman]

Yes, you need 3 springs if you want to specify the lateral stiffnesses of the isolator.  If the spring stiffness is not the same in tension and compression then linear analyses like modal and random vibration are not possible.  A full transient (not mode-sup) is possible with non-linearities.

[dxiang]

Hi Dave,

Some isolators only have load vs hz curve (as the picture shows). Is there any way to model it in ANSYS? Thanks

[dlooman]

In a harmonic analysis you could specify a stiffness equal to  LOAD/20 mil) for the frequency you are solving for, but in general, no, you can't specify isolator properties as a function of frequency.  The LOAD is probably a combination of damping and stiffness forces so that makes it even more ambiguous how to use these curves.

[dxiang]

Get it. About joints, can I probe them in postprocess? I defined the isolators as general joint with X,Y,Z free plus proper stiffness. After SRS simulaiton, I want to to check axial and radical inforamtion such as deflection, force etc. But I can not see joint in probe drop menu. Or there is any other way?

[dlooman]

If it's possible you will be able to drag and drop the joints onto Solution (highlighted in your image.)  If you're not allowed to drop them on Solution then no.

[dxiang]

It works in static analysis, but not for spectrum response. I am working on a product design, which is under shock load. Not sure if you have APDL script which can get joint (isolator) information after SRS simulation.