Research On Contact Mechanical Properties Of Lunar Dust Particles Based On Discrete Element Method

Lunar dust is a powdery substance attached to the surface of the moon. Because of the adhesion and electrostatic properties, lunar dust stands a good chance of being deposited on the lunar probe. Also, some of the lunar dust may get into the clearances of mechanisms and cause problems such as jamming of devices and clogging of mechanisms. In the commonly used contact mechanics model, the particles are simplified as smooth homogeneous spherical particles. Therefore, the contact characteristics of irregular lunar dust particles cannot be depicted reasonably using the model. In this thesis, the existing contact model is improved based on the properties of lunar dust particles and a new shape-based contact mechanical model is proposed to research on the influence of lunar dust particles on joint kinematics.The limitations of contact mechanics model is analyzed after considering the irregular shape of lunar dust particles, based on which the shape modeling of fractal theory and Fourier theory is conducted and a new shape-based mathematical model is established using Fourier series. In addition, the image acquisition is conducted to acquire the 2D projection profile image of lunar simulant, and the probability model of shape distribution is obtained by picture processing and statistical method.After establishing a new shape description model, the contact mechanics model of irregular lunar dust particles based on shape descriptors is also proposed. Meanwhile, the compression test of lunar dust particles is carried out to validate the improved model. Besides, the precise equivalent algorithm based on polynomial fitting and the approximately equivalent algorithm based on piecewise function fitting are proposed in order to simplify the modeling process of irregular particles. Also, a plug-in model is written by discrete element software EDEM to verify the reliability of the algorithm.To simulate the influence of lunar dust particles on joint kinematics, a large number of particles are generated in accordance with the shape probability distribution of lunar simulant. Also, the wheel burying test is carried out to verify the accuracy of simulation results. Moreover, an integrated simulation is conducted to predict whether factors such as eccentricity, speed and mating surface roughness have impact on joint kinematics so that reasonable proposal can be proposed to optimize the design of lunar probe in the future.