Papers by Keyword: Nonlinear

Abstract: to study the nonlinear oscillation principle of new robofish’s two joints tail, the relationship between tilt angle of tail fin that produces thrust and cycle offer quency produced by two joints fin tail propulsion system can be calculated applying reciprocating motion principle in theory; by means of contrastive analysising the results of calculation model, and making use of MATLAB simulation environment to experimental simulate motion model, the fin tail NLSST can be further proved.

Abstract: In the past few years, owing to the vital role in maritime safety monitoring and marine hazard warning, stratospheric airship has become a research hotspot around the world. The structure of stratospheric airship is a typical aerated flexible membrane one. It is geometrical nonlinear in essence and it bears a distinct mechanical nature of large deformation. Therefore it makes optimizing the structure more difficult. The current studies of air-supported flexible membrane structural optimization ignore the uncertainty influence which is resulted from the loading environments, material properties and structural parameters. According to the Lagrangian Coordinate method, the deformed configuration is used as a reference in order to build accurate strain/displacement geometry. The Equilibrium equation is created by using the principle of virtual work. Meanwhile, the accuracy and stability of the solution is ensured by using the Updated Lagrangian Formulation. The uncertain parameters which are introduced during the analysis and optimization of the aerated flexible membrane structure are portrayed by interval mathematical theory. With respect to engineering application, the factors of uncertainty are considered. Maximizing the structural fundamental frequency (or first-order natural frequency) is taken as the objective, while structural integrity is taken as the constraint. Then the dynamic optimization is carried out under interval uncertainty. In this way the reliability of the membrane structure in complex conditions is improved and the probability of failure is reduced.

Abstract: The principle of Z-scan and its application on nonlinear refractive index and absorption coefficient measurement are introduced. Besides, two methods of improving sensitivity of Z-scan are described.

Abstract: There is very rich fault information in vibration signals of rotating machineries. The real vibration signals are nonlinear, non-stationary and time-varying signals mixed with many other factors. It is very useful for fault diagnosis to extract fault features by using time-frequency analysis techniques. Recent researches of time-frequency analysis methods including Short Time Fourier Transform, Wavelet Transform, Wigner-Ville Distribution, Hilbert-Huang Transform, Local Mean Decomposition, and Local Characteristic-scale Decomposition are introduced. The theories, properties, physical significance and applications, advantages and disadvantages of these methods are analyzed and compared. It is pointed that algorithms improvement and combined applications of time-frequency analysis methods should be researched in the future.

Abstract: The effects of large-span truss geometry of the double-plane stable orthogonal design. The use of finite element analysis software Midas double space truss were linear buckling analysis and nonlinear buckling analysis, research process and through its buckling load - examine issues outside of the structure of the plane stable displacement curve. For double truss draw some outside reference plane stability study conclusions.

Abstract: An improved cooperative method to control a nonlinear uncertain system is raised in this paper. First, the optimal control law is introduced to attain the desired dynamics of the linear part of original system. Then, a nonlinear PI controller is used to remove the influence of uncertain unit. It is proved by simulation that this method is effective to control this special system and is easy to be carried in applications.

Abstract: Bolt load in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. When the separating force is applied off the bolt center, although the materials for the bolted joint remain in the linear elastic range, the interface contact area between the clamped plates is sensitive to both the magnitude and the location of the separating force. This often causes nonlinear variation of the bolt load, the deformation etc. An analytical model is proposed to obtain the expression for the nonlinear bolt load under a separating service load. Finite element modeling is used for evaluating the accuracy of the proposed model.

Abstract: Classical linear PID controllers have such disadvantages as the derivative signal unable to be used owing to the noise amplification effect, and the contradiction between the more swiftness and less overshoot. We develop a practical nonlinear PID controller based on a tracking differentiator (TD) in the high precision servo system of the three-axis flight simulator, which could eliminate above disadvantages. The nonlinear PID controller adopts the tracking differentiator to arrange the response process and produce the ideal derivative signal of the reference signal. We use a nonlinear combination function of the error proportional, integral and derivative item in the PID controller. The simulation results in Matlab Simulink demonstrate that the nonlinear PID controller makes the flight simulator servo system with the friction disturbance realize the higher position tracking precision and velocity tracking precision. The nonlinear PID controller with the TD is superior to the classical PID one in control performance.

Abstract: A class of general nonlinear neutral differential equations for its special cases are discussed. sufficient conditionsfor all solutionsof the equations to be oscillatory are obtained. It can be treated in the extreme limite theorem.

Abstract: Based on a brief review of the developing history of vehicle handling inverse dynamics. Using radial basis function neural networks, completely considered the cornering force of tyres, the nonlinear mapping relation between lateral angular velocity and steering angle input is found. The identification results of step steering angle input show the feasibility of the approach and its advantage in accuracy, convergence and stability.