Numerical Model for the Drag Force Method to Evaluate Hysteresis Loss

To determine the hysteresis loss in a sample, usually the enclosed area of the loop is evaluated. In the drag force method, based on a proper energy balance, the hysteresis loss is obtained by analyzing the drag force profile when slowly moving the sample forward and backward through the strong field of permanent magnets. The aim of the method is not to be an alternative to conventional measurements, but rather to use it for nondestructive evaluation. A numerical time-stepping model is presented that calculates the drag force profile. At every time step, the sample is slightly moved relative to the magnet. The model is based on 2-D-FE computations including magnetic hysteretic material behavior using the Preisach model. The drag force is obtained by using the Maxwell stress tensor. The numerical model is validated by measurements and by comparing the ldquodrag forcerdquo hysteresis losses with the hysteresis losses computed conventionally by the integral of . Several simulations were carried out to investigate the influence of parameters such as the number of permanent magnets, the distance between the magnets and the sample, and the presence of defects in the sample.