Analytical design of the integrated motor used in a hubless rim-driven propulsor

The rim-driven integrated motor propulsor (IMP) has received much attention in recent years, owing to its superiority in flexibility, reliability, and space occupation. For this propulsion system, radially thin motors with high torque and large air gaps are essential. Two-segment Halbach array permanent magnets with unequal segment-arc are adopted to enable a thin rotor and a large air gap. The general analytical solution of the magnetic field is presented. Based on the analytical calculation of the Halbach motor performance, the necessity of the rotor core was discussed, and the Halbach array was optimised with an analytical method to maximise the electromagnetic torque. This study also tried and compared three designs of the integrated motor stator to further reduce the radial thickness, and the slotted stator proved more reasonable. The fabrication of an IMP prototype was completed, and the experimental data of the integrated motor are presented and compared with the calculated results. This study also conducted the water tunnel experiment of the IMP prototype to test the integrated motor performance in the overall IMP system. The measured rotational speed and output thrust are less than expected, so the friction loss in the IMP gap flow field is calculated and analysed.