Dear Mark, I have simulated transient magnetic problem with DC + AC coil placed on the same axis and fed with the same current. Please see the picture attached. In this simulation we ignore the coil inductance, so the flux density change occurs the same instant the electric current changes. The transient process could be decomposed in a set of static problems: AC DC Force +I +I zero (symmetrical flux density) .... +I/2 +I **** .... 0 +I Just like a single coil .... -I/2 +I **** .... I +I zero (zero flux density) For some combinations of currents we have already calculated the force. I believe the force for the intermediate current values should be somewhere in between. 1 hour spent.