Hou Xuyan

Research on the shape model of particles in lunar regolith fluid based on the fractal theory

Lunar dust is the most important problem need to be solved in the process of returning to the moon. The extremely complex irregular form is the most prominent feature of lunar dust. From a mechanical viewpoint, the overall mechanical behavior of granular materials is strongly affected by grain properties such as size, shape and crushability. Among these properties, grain shape has a considerable influence on the bulk mechanical properties. Therefore, the research on the microstructure characteristics of lunar dust is imperative. Fractal geometry is a powerful theoretical tool for dealing with irregular shapes in nature and engineering. In fractal theory, people usually use the fractal dimension to represent self-similar geometric shapes. In terms of micro particle shape analysis, fractal geometry is proved to be a practical and feasible measure to irregular particle shape. Therefore, a research of the shape of lunar dust based on the fractal theory is presented in this paper to give a quantitative description of irregular shape. It provides an important reference for the further understanding of the mechanical properties of lunar dust.

The study of normal force model for the flow of lunar dust particles

Lunar dust can cause mechanical clogging and seal failures in lunar events, so it is essential to study the contact state of lunar dust particles which stuck in the mechanisms. The soft ball model based on Hertz theory is commonly used in particle contact problem. However, the assumptions of soft ball model are not applicable to lunar dust particles with irregular shapes and rough surfaces. To solve the problem, the power function model and exponential function model were proposed based on discrete element theory and nonlinear models in the rock and soil mechanics. The nonlinear relationship between normal force and displacement was obtained by static load compression test and the experimental data were imported into MATLAB to finish curve fitting. The experimental results show that the nonlinear stress-strain relationship of lunar dust particles can be most accurately described by the power function model. Meanwhile, the concept of equivalent elastic coefficient was introduced to simplify the simulating process. The lunar dust particles can be modeled as smooth spherical particles and the nonlinear stress-strain relationship can be described by equivalent elastic coefficient. With the new method, the theoretical model can be simplified and the simulation efficiency can be improved without affecting the model accuracy.

Ultrasonic propagation simulations in biological tissues with application to the sonodynamic therapy based on ACTRAN

Compared with conventional therapy techniques, sonodynamic therapy of atherosclerosis can achieve non-invasive radical treatment. Currently the treatment parameters are mostly determined empirically. This paper is to describe the establishment of ultrasonic propagation simulation model of atherosclerotic biological tissues by identifying and extracting the medical image feature, together with the study of parameters of the ultrasonic properties of a single type of tissue and the study of the ultrasonic properties of boundary conditions of tissues in simulation model. Based on it, an acoustic simulation software ACTRAN is used to make the simulation analysis for the ultrasonic propagation in biological tissues with the parameters in sonodynamic therapy process. These works can provide the basis for formulating of precise treatment parameters and lay the foundation for the clinical application of sonodynamic therapy for atherosclerosis.

Path Planning of Lunar Rover Group Based on Theory of Dynamic Programming and Multi-objective Optimization

A path planning of lunar rover group composed of one six-wheeled rocker-bogie master lunar rover and three spherical slave lunar rovers was presented for efficiency, safety and energy saving. The slave lunar rovers moved back and forth among nodes of every step for path survey. The objective value of every path to objects, which were energy and time consumption of the master rover and length of path, was calculated according to the concerted motion control based on the calculation on the pitch angle of rockers, kinematics analysis based on the velocity projection theorem and quasi-static analysis of the master lunar rover. Then dynamic programming and optimization of path was carried to the master lunar rover, using method of max relative membership degree of policy. Compared with the result of multi-attribute decision of path without the slave lunar rovers moving back and forth among nodes of every step, the dynamic programming and optimization of path saves energy.