Shell elements for the computation of magnetic forces

The local application of the principle of virtual work for the computation of magnetic forces requires a layer of elements around the object. It fails to work when the object is touching other objects or when the boundary element method is applied on its boundary. To overcome this difficulty, a shell element is introduced on the boundary of the object. Derivation of magnetic co-energy (or energy) is performed on the shell element with the help of edge element basis and the local Jacobian derivative technique. The force expression derived from this method shows a close similarity to the Maxwell stress tensor. Efficiency of the method is shown through the computation of magnetic force on the moving core of an electromagnet when it touches the fixed yoke.