Advanced Materials Research Vols. 308-310

Abstract: By using the theory and method of topology structure design of parallel robotic mechanisms, the degrees of freedom (DOF) is analyzed based on 4-DOF(3T1R) asymmetric parallel robots in this paper. Then, the inverse and forward kinematics of the manipulator are calculated through establishment of constrained equations with analytical approach.

Abstract: The main structure of DVG850 high-speed vertical machining center is instructed in the paper, the solid 3D model of the machine is established by SolidWorks, and then improted into ANSYS Workbench to do static and dynamic analysis. Firstly, the static analysis of high-speed vertical machining center is studied to get the deformation figures. From the analysis of the deformation figures, we can find the locations of weak static stiffness. Next, the modal analysis is studied and the order of natural frequencies we need are obtained. Through the analysis of the vibration modes of this machine tools, its relative weaker parts are pointed. Finally, The structure of the machine tools is improved according to the analysis results. The static and dynamic characteristics of the improved structure are apparently better than that of the original design. It makes a base for optimized design and remanufacturing. .

Abstract: A new method based on finite element analysis and wavelet analysis for the fault diagnosis of wind turbine main bearings is presented in the paper. Firstly, take example for low speed bearing, the three-dimension models of the good and fault bearings are set up, which was discussed with using finite element method. The stress, strain and contact stress distribution were computed by this method. Then the wavelet transform of data signals collected in experiment was carried out with db6 wavelet and 4 scales on the basis of the stress wave analysis. The frequency D3 and D4 signals were reconstructed and characteristic frequencies of stress waves with the simulative faults were extracted. It has been shown that the method applying finite element analysis and wavelet analysis is an efficient method for the fault diagnosis of wind turbine main bearings.

Abstract: The reactive power is out of control near the fundamental voltage vector in traditional direct power control system, which leads to the current distortion at AC side and the voltage fluctuation at DC side. The mechanisms of the instantaneous active power and the reactive power are analyzed based on the instantaneous power mathematical model of the PWM rectifier. A new direct power control strategy is researched based on novel sector division and novel switching table. This method not only has the advantage of rapid regulation for active power, but also can restrain reactive power fluctuation and reduce switching frequency. Simulative and experimental results verify its feasibility and effectiveness.

Abstract: In view of the demands in multidisciplinary design optimization (MDO) of valve products, the MDO model for valves is established, which takes account of mechanical analysis, fluid mechanics analysis, thermal-mechanical coupled analysis and seismic analysis. On this basis, the MDO integrated system is constructed combined with some new techniques to solve the common and critical problems of optimal design of valves. The system takes interplay and coupling of each discipline into account, applies effective optimization strategy, information transmitting and concurrent design to get the synergistic effect produced by interaction of each discipline, and finally obtains the total optimum solution of valves, which, moreover, could provide technical reference for the practicality and commercialization of the integrated system in valves design optimization.

Abstract: The random formula on fatigue crack growth is deduced by the fatigue crack data and the improved Taguchi method, and the sample estimates of random variables are received by the least square method in the random formula. Fatigue fracture life and reliability of structure are analyzed by the random model. The result show the model is correct and practical, and get the same result with Monte Carlo simulation, moreover its calculation is very simple.

Abstract: This paper adopts contacting finite element method to perform exact stress and strain analysis on bolt joint structure, and the curve of pre-tension stress-life σp-N was drawn. According to the curve, production practice can be well guided and the optimum pre-tension stress may be obtained .By the means of curve between load and deformation, the curve shape of σp-N was analyzed in detail, the results showed that the analysis by finite element was coincident with mechanics analysis.

Abstract: The multi-spiral layout pattern has been widely adopted in practice during the layout design of the cutters. Considering the engineering technical requirements and the corresponding structure design requirements of the cutter head, this study formulates a nonlinear multi-objective mathematical model with multiple constraints for the cutters plane layout design based on a multi-spiral layout pattern. And then a genetic algorithm is employed to solve a cutters’ multi-spiral layout problem. An instance of the cutters’ plane layout design was solved by the proposed methods using a multi-spiral layout pattern. Experimental results showed the effectiveness of the method of combining the mathematical model with the algorithms, and the pros and cons of the multi-spiral layout pattern.

Abstract: Five-axis CNC machine tool is the top product of numerically controlled machine tool. Kinmatic accuracy is an important index to evaluate the quality of mechanism. Kinematic accuracy analysis of the Five-axis machine tool in previous study ignores the randomness of each input error component, so the conclusions are imprecise. Using the homogeneous transformation, inverse kinematics of VMC650 Five-axis machine tool is calculated. Based on Multi-body System Theory, error model of the machine tool is presented. Considering the randomness of every input error components, applying the Monte Carlo method, math model of kinematic reliability of the mechanism is deduced. The calculation method of kinematics reliability are put forward applying point evaluation and track evaluation. Kinematic reliability analysis provides some theoretical reference for improving the machining accuracy and operation life of machine tool.

Abstract: The post-buckling behavior of a stiffened panel is investigated in this paper. Firstly, the buckling mode of the stiffened panel is obtained using the linear buckling eigenvalue method. Then, the collapsing strength of the stiffened panel is calculated using the ultimate strength method based on large deflection orthotropic plate theory. In addition, nonlinear finite element analysis is performed to predict the post-buckling behavior of the stiffened panel. By comparing the model prediction and the analytical results of ultimate strength, it is shown that good accuracy can be achieved, especially for the method referring to membrane stress in mid-thickness of equivalent orthotropic plate. It suggests that the proposed method can predict the ultimate strength of whole stiffened panel accurately and effectively.