Piezoelectric harmonic analysis

[usker]

I have an assembly of piezoelectric discs stack with the hole in the center, sitting on a stainless steel bar and fastened from both sides. I have done harmonic analysis applying potential difference of 150 Volt at the each interface of the piezoelectric disk and at the interface of piezoelectric disk and stainless steel. I did not apply any force. In the Time History Variables Viewer when I select "Add" -> Nodal Solution -> Y-Component of displacement, in order to get a graph Amplitude over Frequency, it does not show any value (Minimum, Maximum)for the amplitude. I guess I need to add a spring into my model so that I can immitate the vibration of the model assembly. So, now I have meshed model assembly of piezoelectric discs and stainless steel bar, how I can introduce spring element into my model? As I know COMBIN 14 element does not have mass. Do I have to create additional area and mesh it to immitate the spring and specify material properties like density, EX etc., or there is some other way to introduce spring element into my model.

Appreciate you help

 

[Drej]

First of all, you're carrying out a harmonic response analysis applying voltage as the "load"? Typically you would expect to return current (or the like) during post-processing - I wouldn't expect displacement (which is why you're not seeing anything available in /post26). I expect you're using electro-type elements, and so if you check the DOF from these you wouldn't expect to see displacement as a freedom. If this is true then your combin will give you nada and I don't follow what your thinking is on this. If you explain the details of your model the team might be able to shed some more light on your problem.


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[cloche]

Piezoelectric materials have the property that they "shrink" when they are subjected to a potential difference, so it makes sense that a displacement response may be expected from a sine voltage.
BUT, as Drej says, you must ensure that:
1) the elements you use have the correct DOFs (not "pure electrical" elements)
2) the relation "voltage / displacement" is set up in some way (electro-structural is far from my fields, so I can't help you on this. I seem to remember that there are some elems especially designed to simulate piezos). If there is no other way, you have to set it up by yourself (constrain equations)
3) the correct - and complete !!! - material properties are set up.

I don't see too what you would like to achieve with the COMBIN14. If it's to "stabilize" a completely unconstrained model, "soft spring" option could be more efficient I think.

As general rule, COMBIN14 has no mass but you can simply add a MASS element on the node you want.