Structure Design For Magnetohydrodynamic Momentum Wheel

Magnetohydrodynamic(MHD)momentum wheel is a kind of actuator for spacecraft attitude control system,which has the characteristics of broad band,small size,light weight,long lifetime,high precision and impact resistance.It is suitable for working under the spatial condition,and can satisfy the precision requirements of small satellites for actuators.The research of MHD momentum wheel is of vital importance to the active control technology for micro vibration of spacecraft or other payload.In this paper,the operational characteristics of MHD momentum wheel are analyzed based on its theoretical model.In addition,the mechanical structure design,processing,assembling,simulation and performance test are accomplished for MHD momentum wheel with axial magnetic field.This study mainly includes the following aspects:1.According to the transfer function model,the operational characteristics of MHD momentum wheel are analyzed through the step response and ramp response.Two control modes of MHD momentum wheel are summarized and its performance indicators are defined.Then the design requirements are put forward.2.The mechanical structure of MHD momentum wheel is designed,and the spatial layout of the current and magnetic field is completed.The key parameters are selected according to the design requirements.Based on these parameters,the design of magnetic circuit structure,electrode,filling hole,sealing method and auxiliary parts is accomplished.Based on the designed structure of MHD momentum wheel,the important indicators are calculated.3.According to the designed structure of MHD momentum wheel,the finite element analysis software is used to simulate and verify the magnetic field performance and the motion characteristics of the conductive fluid.By using Ansoft Maxwell,the intensity and uniformity of the magnetic field in working area,as well as the magnetic flux leakage of MHD momentum wheel are analyzed quantitatively.In order to improve the magnetic field uniformity of the axial magnetic circuit with single permanent magnet,a composite axial magnetic circuit is proposed and its effectiveness is verified by simulation.MHD module of the flow simulation software Fluent is used to simulate the motion characteristics of the conductive fluid under DC and slope voltage,respectively.Then the performance indicators of MHD momentum wheel are obtained.The simulation results are compared with the design requirements to verify the rationality of the structure design.4.The processing and assembling of MHD momentum wheel prototype are completed,and its performance is further tested.An indirect measurement method of the fluid speed is studied.The corresponding experimental equipment,excitation signal and data processing methods are designed.Based on the calibrated total rotational inertia and friction torque coefficient of the air bearing table,the actual amplitude-frequency response curve,nonlinear error and power characteristic of MHD momentum wheel are tested.According to the test results of amplitude-frequency response,other performance indicators of MHD momentum wheel are further estimated.The test results are compared with the design requirements,and the rationality of structure design is verified.