Sliding mode control with fuzzy adaptive perturbation compensator for 6-DOF parallel manipulator

This paper proposes a sliding mode controller with fuzzy adaptive perturbation compensator (FAPC) to get a good control performance and reduce the chatter. The proposed algorithm can reduce the chattering because the proposed fuzzy adaptive perturbation compensator compensates the perturbation terms. The compensator computes the control input for compensating unmodeled dynamic terms and disturbance by using the observer-based fuzzy adaptive network (FAN). The weighting parameters of the compensator are updated by on-line adaptive scheme in order to minimize the estimation error and the estimation velocity error of each actuator. Therefore, the combination of sliding mode control and fuzzy adaptive network gives the robust and intelligent routine to get a good control performance. To evaluate the control performance of the proposed approach, tracking control is experimentally carried out for the hydraulic motion platform which consists of a 6-DOF parallel manipulator.     

Nonlinear bending response of functionally graded plates subjected to transverse loads and in thermal environments

Nonlinear bending analysis is presented for a simply supported, functionally graded rectangular plate subjected to a transverse uniform or sinusoidal load and in thermal environments. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The governing equations of a functionally graded plate are based on Reddy's higher-order shear deformation plate theory that includes thermal effects. Two cases of the in-plane boundary conditions are considered. A mixed Galerkin-perturbation technique is employed to determine the load-deflection and load-bending moment curves. The numerical illustrations concern nonlinear bending response of functional graded rectangular plates with two constituent materials. The influences played by temperature rise, the character of in-plane boundary conditions, transverse shear deformation, plate aspect ratio and volume fraction distributions are studied.     

HHT-based nonlinear signal processing method for parametric and non-parametric identification of dynamical systems

This paper presents a time–frequency signal processing method based on Hilbert–Huang transform (HHT) and a sliding-window fitting (SWF) technique for parametric and non-parametric identification of nonlinear dynamical systems. The SWF method is developed to reveal the limitations of conventional signal processing methods and to perform further decomposition of signals. Similar to the short-time Fourier transform and wavelet transform, the SWF uses windowed regular harmonics and function orthogonality to extract time-localized regular and/or distorted harmonics. On the other hand, HHT uses the apparent time scales revealed by the signal's local maxima and minima to sequentially sift components of different time scales, starting from high- to low-frequency ones. Because HHT does not use pre-determined basis functions and function orthogonality for component extraction, it provides more accurate time-varying amplitudes and frequencies of extracted components for accurate estimation of system characteristics and nonlinearities. Methods are developed to reduce the end effect caused by Gibbs’ phenomenon and other mathematical and numerical problems of HHT analysis. For parametric identification of a nonlinear one-degree-of-freedom system, the method processes one free damped transient response and one steady-state response and uses amplitude-dependent dynamic characteristics derived from perturbation analysis to determine the type and order of nonlinearity and system parameters. For non-parametric identification, the method uses the maximum displacement states to determine the displacement–stiffness curve and the maximum velocity states to determine the velocity-damping curve. Moreover, the SWF method and a synchronous detection method are used for further decomposition of components extracted by HHT to improve the accuracy of parametric and non-parametric estimations. Numerical simulations of several nonlinear systems show that the proposed method can provide accurate parametric and non-parametric identifications of different nonlinear dynamical systems.     

A novel application of the FPM to the buckling differential equation of non-uniform beams

In this study the buckling load (P) of non-uniform, deterministic and stochastically heterogeneous beams, is found by applying the Functional Perturbation Method (FPM) directly to the Buckling (eigenvalue) Differential Equation (BDE). The FPM is based on considering the unknown P and the transverse deflection (W) as functionals of heterogeneity, i.e., the elastic bending stiffness “K” (or the compliance S=1/K). The BDE is expanded functionally, yielding a set of successive differential equations for each order of the (Frèchet) functional derivatives of P and W. The obtained differential equations differ only in their RHS, and therefore a single modified Green function is needed for solving all orders. Consequently, an approximated value for the buckling load is obtained for any given morphology. Four examples of simply supported columns are solved and discussed. In the first three, deterministic realizations of K are considered, whereas in the fourth, K is assumed to be the stochastic field. The results are compared with solutions found in the literature for validation.     

利用ANSYS实现零件的可靠性优化设计

基于ANSYS参数化设计语言(APDL)的数学运算功能,运用可靠性理论的摄动分析法,利用APDL编程实现零件的可靠度计算,避免了有限元建模、分析和结果的参数化提取等步骤.利用ANSYS的设计优化模块,以摄动分析法计算的零件可靠度为约束条件,以零件的最小体积为优化目标寻求设计参数的优化设计.开辟了一个利用ANSYS进行可靠性优化设计的途径,扩展了ANSYS的分析范围.     

EFFECT OF INVOLUTE CONTACT RATIO ON THE DYNAMIC PERFORMANCE OF SPUR GEAR WITH NOTOOTH PROFILE MODIFICATION

The effect of involute contact ratio on the torsional vibration behavior of spur gear-pair isstudied analytically through a mass-spring model. The tooth stiffness in model not only has a relationwith time, as many prior studies presented, but, more important, with involute contact ratio (ICR) aswell. The ICR embodies its impact on the spur gear's dynamic performance through changing theproportion of tooth stiffness when there are n+1 teeth in contact to tooth stiffness when there are n     

基于摄动方法的受损薄板模态分析

将结构的损伤用δ函数进行表达，建立损伤条件下薄板的自由振动方程。利用一阶摄动方法给出摄动项的一般表达式，并结合δ函数的性质，求出受损薄板模态参数的解析表达式。以一个四边简支的受损薄板为数值算例，计算损伤条件下其模态参数的变化。最后分析损伤情况对模态参数的影响，为利用动力学特性对板的损伤监控和检测提供理论依据。     

汽车动力学参数的相对灵敏度分析

基于灵敏度的函数求导思想,变换出单因素扰动法。用该方法首次对基于卡尔曼滤波理论进行状态估计后的汽车状态参数的相对敏感度进行分析。在线性二自由度汽车模型和卡尔曼滤波理论基础上,分析估计所得的状态量(横摆角速度、质心侧偏角)对动力学模型中的汽车的质量、转动惯量以及质心到前轴距离的灵敏度。研究汽车状态参数对汽车结构参数的相对灵敏度,通过仿真试验和实车试验数据对相对灵敏度进行分析,最终的结论将对汽车状态估计算法的研究具有指导意义。     

Singular perturbation analysis of systems with sustained high frequency oscillations

Using singular perturbation techniques, a system with high frequency oscillations is decomposed into two lower order subsystems, one containing only the slowly varying part and the other containing only the fast oscillatory part. Eigenvalue and state approximations achieved by the subsystems are given. A mass-spring-damper example shows that a stiff spring can be regarded as a perturbation of a rigid rod and an interconnected power system example illustrates the occurrence of coherency and inter-machine oscillations.     

Multiparameter singular perturbations of linear systems with multiple time scales

A joint multitime scale-multiparameter singular perturbation is formulated and resolved in the context of linear time-varying systems. An interesting feature of the solution procedure is a hierarchial scheme of aggregating and arranging of the groups of small parameters according to their order. The scheme provides a suitable framework for establishing qualitative properties of multitime scale systems.