Applied Mechanics and Materials Vol. 703

Abstract: Compared with the complex structure and unsatisfactory performance of traditional flywheel drive system, the proposed strategy adopts bearingless brushless DC motor as the drive actuator of flywheel. The direct torque control which combines the space voltage vector pulse width modulation is presented to control the system. Moreover, a simulation system is built with Matlab/Simulink toolbox. From the simulation results, the proposed control strategy is verified and the rotor can be stably suspended by suspension force along the central axis.

Abstract: In order to realize the solar photovoltaic (PV) system connecting with grid friendly, a PV system with voltage-controlled inverter based on virtual synchronous generator (SG) is presented. This kind of system has features of SG, which supply the virtual moment of inertia to grid. The mathematical model of PV and virtual SG is built, and the control strategy of the maximum power point tracking (MPPT) is also studied in the paper. Simulation model of the grid-connected PV power system is built on Matlab/Simulink. Finally, correctness and feasibility of this system are verified by simulation results.

Abstract: This paper is for the fact that some computer system structures impeding the current computer performance further improvement . Present the solution method and the development direction. CISC system and RISC system are introduced, together with VLIW system, Parallel architecture and multi-threading architecture and massively parallel processor system MPP and group of machines parallel system. Analyze the structure of the computer system research challenges,Look to the future about the development direction of computer system structure.

Abstract: In this paper, a maximum torque per ampere (MTPA) control strategy based on space vector pulse width modulation (SVPWM) is adopted in a dual three-phase interior permanent magnet synchronous motors (PMSMs) system with a five-leg inverter. The simulation model is established in Matlab/Simulink based on the mathematics model of PMSM and the current control method. And the simulation results of the proposed current control strategy are compared with those of i_d=0 method in order to verify the performances and characteristics of MTPA control stategy.

Abstract: In This paper, a direct torque control (DTC) method for bearingless permanent magnet synchronous motor (BPMSM) based on three-level neutral-point clamped (NPC) inverter is described. Through the analysis of virtual space vector modulation, an independent control strategy is adopted into the suspension winding control and a flux linkage error vector SVM-DTC method supplied by three-level NPC inverter is introduced into the torque windings control. By using the proposed control strategy, the neutral-point voltage variation can be greatly limited and the voltage shifting can be eliminated. The results of simulation verify the feasibility of the control algorithm, the dv/dt of output voltage and the torque ripple are restrained effectively, satisfactory robustness and the good performance of the radial levitation can be achieved in a wide speed range by using the proposed method.

Abstract: The effect of precipitated phases on the creep in 300s type austenitic stainless steel used in auto-tailpipe was studied. Flat tensile samples with marker scratches on the surface were strained at slow rate at 400°C. It show that the sensitized material decreased creep rate and needed more stress to generate deformation of grain boundary, suggesting Cr carbides decreased the grain boundary sliding. Thus, the resistance to SCC crack propagation could be improved. Characterizations of the tensile samples were carried out using a SEM in order to understand whether second phases can affect the creep behavior and grain boundary moving.

Abstract: This study researched the aerodynamic characteristics of a two-dimensional trajectory correction fuze used for the common artillery ammunition, which increases the targeting accuracy by decreasing the circular error probability. The correction fuze has a pair of fixed canard and a pair of steering canards for roll control and guidance. In this study, computational fluid dynamic (CFD) simulation is performed to study the aerodynamic characteristics of the trajectory correction fuze. The primary purpose of this performance was to predict the aerodynamic coefficients and flow field over a spin-stabilized projectile with the correction fuze. Calculation covered from-10 degrees to 10 degrees steering canards deflection over speed range from Mach 0.6 to 3. The results showed the variation law in the rotary moment of correction module and the control forces of the steering canards with the Mach varying, providing aerodynamic reference for the research of trajectory correction projectiles in the future.

Abstract: This paper develops a three dimensional elastic fracture analysis method, PDS-FEM (Particle Discretization Scheme Finite Element Method), to its elasto-plastic version. The Newton-Raphson iteration method is adopted for solving material nonlinearity, and the conjugate gradient method is applied to solve the linear equations of FEM. In order to apply the fracture analysis method to the engineering scale analysis, CPU based parallel computing technology is applied, and the computation speed is highly advanced. In this trial test, a simple stress based failure criterion is employed for the failure analysis of a cantilever steel beam. The numerical results without fracture match well with the commercial FEM software, ANSYS’s, which verifies the accuracy of the developed platform.

Abstract: The square elbows used in oil and gas fields were often failed because of serious erosion. Some of the products even burst. In this paper, the failure mechanism of square elbow was investigated by using electron microscopy (OM), electron microscopy (SEM) methods. The research results show that the elbow products failed due to its low impact toughness after carburizing and quenching. The erosion angle is nearly ninety-degree. By increasing the tempering temperature, reducing the surface hardness and improving toughness, the serious erosion phenomenon can be effectively avoided. There are two main reasons of the elbow products burst. One reason is the high inclusion content of the material. The other is the low impact toughness. Raising the quality specification of materials can appropriate increase the low impact toughness after heat treatment. It is pointed out that the product would be more safety by improve its impact toughness.

Abstract: This paper is aimed at investigating the parameter effects on dynamic crushing behavior of staggered Kelvin cellular metal using finite element method. The geometrical characteristics of the staggered cellular structure were analyzed and the finite element model was constructed using shell elements. A full factorial Design of Experiment simulation was carried out and four individual factors including two structure characteristics of the cellular metals and two mechanical parameters of the base material were selected, namely cell edge length, cell wall thickness, yield stress and tangent modulus. Their single and interaction effects on plateau stress, densification strain and densification strain energy were mainly researched. From the results it could be seen that the structure characteristics were a little more important than the base material properties for aluminum staggered Kelvin cellular metal.