Optimal design of inverted rotary MR brake with waveform boundary using a novel combined magnetostatic approach

In the present work, an inverted rotary drum magneto rheological (MR) brake with waveform arc boundary suitable for prosthetic knee application is optimally designed. Often, the magnetostatic analysis is performed assuming linear magnetic systems and solving a lumped parametric equivalent magnetic model (EMM). Although, this reduces the computational time but compromises the accuracy of the solution. On the other hand, finite element magnetostatic (FEMS) analysis combined with a search-based optimization technique requires more time and effort. In this work, an approach combining the EMM and FEMS methods is proposed to optimally design the MR brake. This method requires the optimization algorithm to maintain an external repository so that individuals which are non-dominated at each generation get stored in the repository and only those individuals are allowed to use FEMS method. This approach reduces the number of function calls made to FEMS method and thus reduces the computational time substantially. A recently proposed multi-objective particle swarm optimization (MOPSO) which evaluates the global best using minimum distance of point of line (MDPL) method is implemented with the proposed combined magnetostatic method. While FEMS method alone resulted in an average computational time of 7.25 h, the proposed method evaluated a similar Pareto front solution in 38 min. Finally, the optimal design is compared to other prosthetic knee MR brakes from the literature.