Research On Propulsion Motor Design And Vibration Noise Of Underwater Vehicle

In this paper,a permanent magnetic synchronous propulsion motor is designed for deep sea autonomous underwater vehicle sailing at 3000 m in deep sea.The motor is installed outside the vehicle to save space inside.Because the motor is directly immersed in the sea water while working,the specialty of working environment must be taken into consideration,i.e.high-pressure,anti-corrosion,sealing,insulation and etc.To solve the problem of high pressure in the sea water,the motor is filled with insulation oil in the cavity and capsule is used at the end of the motor to balance the pressure.The shell of motor is made of titanium alloy to prevent corrosion.Rubber ring is used for static seal of the motor and the axle is sealed with oil seal with secondary lip.To lower the vibration noise,the effects of electromagnetic parameters on the vibration should be considered when the parameters are determined.An integer slot structure of 8 poles and 40 slots is adopted.With this kind of structure,the lowest order of radial electromagnetic force can reach 8.Bottom of stator slots are designed to be parallel to the outer diameter of stator and the slot bottom is connected to slot body by arc,to increase the strength of stator yoke.To further reduce the noise,two strategies are proposed in this paper.One is by starting with optimizing radial air gap magnetic field density,reducing harmonic components of radial electromagnetic force and adopting nonuniform air gap,while the other one starts from considering the good cooling condition in the motor’s special working environment,increasing heating load,increasing the size of stator yoke and thus lowering the noise.Because the noise is related to both radial electromagnetic force and inherent frequency of the motor,the inherent frequency of the motor is also calculated.The propagation medium of noise is sea water instead of air in this case,so the effects of two different media are compared and analyzed.Sound propagates faster in sea water,meaning that it can travel further.Furthermore,the density of sea water and dynamic viscosity are different from those of air,which affect the propagation of noise.