Learning Forum

[Mateusz Łukaszewicz]

Hello,

I am trying to perform transient analysis of energy harvesting system consisting of cantilever beam with a magnet at the end to determine how magnetic forces influence it's resonant frequency. Mentioned magnet is repelled by 3 other magnets situated outside the cantilever. Here's the screenshot of the system:

I want to model nodal forces which are an approximation of magnetic forces exerted on magnet. I know that it's possible to create those forces as a function of time but i'd like to base them on distance between magnet on cantilever and external magnets to create 3 dynamic vectors. Is it even possible to do in ansys mechanical or should i choose different approach?

[Bill Bulat]

If you already have a good idea what the force-deflection relationship due to the permanent magnets is, you might try defining a nonlinear spring (or combination of nonlinear springs if needed) to mimic the magnetic forces. The spring in the image below connects a pair of remote points (one of which is "free standing"):

You can then apply remote displacement(s) to the remote point(s) to "preload" the spring(s) if you want to define non-zero forces acting at zero beam deflection.

If, on the other hand, you want to use FEA to calculate the magnetic field and associated forces, you could use coupled field elements. The coupled field element options that include magnetic DOFs are not natively exposed in Mechanical, but they can be defined with command objects. If motion is large enough to excessively distort the "air" mesh in the gap between the beam tip and the fixed PMs, you might replace the elements types created by Mechanical with legacy SOLID5/98, which use the magnetic scalar potential for magnetostatic field calculations (induced eddy curents are not accounted for). In a "large motion" application, these have a companion contact element (CONTA174 with keyopt(1)=7) that you might use in a "sliding interface" in the "air" to relieve mesh distortion.

Yet another option for calculating magnetic forces might be to use system coupling between Maxwell and Mechanical.

Best,

Bill