Vol. 4, No. 3 (2015): Regular Issue

Crises in chaotic pendulum in the presence of fuzzy uncertainty are observed by means of the fuzzy generalized cell mapping method. A fuzzy chaotic attractor is characterized by its topology and membership distribution function. A fuzzy crisis implies a simultaneous sudden change both in the topology of a fuzzy chaotic attractor and in its membership distribution. It happens when a fuzzy chaotic attractor collides with a regular or a chaotic saddle. Two types of fuzzy crises are specified, namely, boundary and interior crises. In the case of a fuzzy boundary crisis, a fuzzy chaotic attractor disappears after a collision with a regular saddle on the basin boundary. In the case of a fuzzy interior crisis, a fuzzy chaotic attractor suddenly changes in its size after a collision with a chaotic saddle in the basin interior.

By means of the degenerate semigroups theory methods the local existence of a unique solution is proved for initial-boundary value problems to a class of partial differential equations systems of generalized hydrodynamics type. General results are illustrated by examples of a system with the nonlinear viscosity and a weighted system.

Self-synchronization, compound synchronization and intelligent control synchronization widely exist in the mechanical system engineering, while lag self-synchronization movement is a special form of cooperation movement. Based on coupling Duffing system, this paper studies lag self-synchronization problem, analyses general change law of the system co-rotating synchronization frequency, antisynchronization frequency and lag phase angle by analytic analysis and numerical quantitative analysis, studies coupling parameter influences on systematic lag self-synchronization, and analyses the cause of lag self-synchronization. The results show that the root cause of lag self-synchronization is systematic stiffness namely systematic natural characteristic; that co-rotating synchronization vibration frequency and phase difference depend on coupling stiffness parameter; and that frequency and phase difference of anti-synchronization vibration are independent of coupling stiffness parameter; and when coupling stiffness parameter is larger, phase difference of two oscillators in the two kinds of synchronization is nonzero constant value.

Friction torque is the most important factor that influences stability and precision of multi-axis linkage system during low-speed running. It is primarily related to shafting structure, external load, motion state and other factors, and presents highly nonlinear characteristics. In this paper, satellite-bone multi-axis linkage system in microgravity environment is taken as the research object to focus on the coupling tribo-dynamics issues of influencing system’s precision. The shafting structural features of two degrees of freedom (2-DOF) vertical-axis turntable, source of friction torque and coating antifriction technology are studied. The corresponding tribo-dynamics model is established. The model shows motion process of multi-axis linkage system is a coupling process of tribology and dynamics. In order to eliminate the effect of friction torque fluctuations, friction compensation based on LuGre friction model is introduced. Then tracking precision of the visual axis is about 40'' (large movement range). For the imperfect situations with friction compensation, local actuator is introduced to combine with wide-range basic multi-axis system to realize the accurate movement within small range. Then the tracking precision of visual axis is expected to reach about 2'' to 4'' (small movement rang).

Stability and bifurcation of a nonlinear supersonic panel under aerothermal loads are analyzed numerically in the present study. In the structural model, von Karman’s large deformation theory is taken into account for the geometric nonlinearity of the panel. In light of Hamilton’s principle, the governing equation of motion of a twodimensional aero-thermo-elastic panel is established. Coupling with the panel vibration, aerodynamic pressure is evaluated by first order supersonic piston theory and aerothermal load is approximated by quasi-steady theory of thermal stress. By transforming the partial differential equation to a series of ordinary differential equations via Galerkin method, fixed points and their stabilities of the system are studied using nonlinear dynamic theory. The complex dynamic responses regions are discussed with temperature loads as a bifurcation parameter. The results show that the thermal stress has a significant influence in the stability of the panel. The panel system undergoes Hopf bifurcation, period doubling, quasi-period and chaos with the increase of the temperature.

Three-dimensional strongly coupled complex (dusty) plasma (SCCDP) is modeled using homogenous nonequilibrium molecular dynamics (HNEMD) simulations. The thermal conductivity (λ0) and the effects of external force field (F*) strength on the λ0 of SCCDP are calculated at higher screening strengths (κ) from generalized Evan’s algorithm. It has been shown that the presented investigations exhibit a non-Newtonian effect that the λ0(Γ) increases with increasing force field strength that represents interaction contributions in Yukawa conductivity. It is also verified that the results obtained with different external force filed strengths are in satisfactory agreement with earlier numerical results and with reference set of data showed deviations within less than ± 10% for most of the present data point. Our very recently computed thermal conductivity at lower κ is validated by comparing the results of λ0(Γ) at higher κ that also extended the range of force field strength (0.001≤F*≤ 0.1) which explains the nature of nonlinearity of SCCDP.

In this paper, the adaptive synchronization of a stochastic fractionalorder complex Lorenz system is analyzed. Firstly, the Laguerre polynomial approximation method is applied to investigate the fractionalorder system with a random parameter which obeys an exponential distribution. Based on this method, the stochastic system is reduced into the equivalent deterministic one. Besides, based on the stability theory of fractional-order systems, the adaptive synchronization for the deterministic system with unknown parameters is realized by designing appropriate synchronization controllers and estimation laws for uncertain parameters. Numerical simulations are used to demonstrate the effectiveness and feasibility of the proposed scheme.

Foreign Object Debris (FOD) is debris or article alien, which may A compared with the translational-torsional dynamic model of planetary gear transmission system (PGTS) used in wind turbine is established in order to analyze the dynamic characteristics of the PGTS more accurately. The influences of the meshing stiffness, input and output torques, meshing error, nonlinear characteristics of the support bearing and gravity are considered in the model. Based on previous model, the vibration differential equations of the drive-train are obtained through the Lagrange’s equation. The dynamic response characteristics are investigated using the Runge–Kutta numerical method, and the factors of the above proposed excitation are analyzed. The results show clearly that the vibration responses have different characteristics due to the different speeds of each component in the PGTS. The nonlinear behaviour of support bearing causes the dynamic response more complicated In addition, under the internal and external excitations, more frequency multiplication and frequency combination components appear. The vibration frequency components of the system are mainly concentrated in the frequency range below 200Hz. The results of the study in this paper can provide necessary theoretical basis for natural characteristics study, dynamic response and optimization design method of the MW wind turbine PGTS.

Foreign Object Debris (FOD) is debris or article alien, which may One of the major problems of gas turbine combustors is the combustion oscillation. The combustion oscillation of gas turbines has many complex causes such as pressure fluctuations, combustion instabilities, and mechanical designs of the combustion chamber. Although the significant research efforts have been dedicated to this topic, the combustion oscillation problems have not yet been solved because of its complexity and nonlinearity. In this study, the theoretical and experimental research has been conducted in order to develop the noncontact and fast response 2D CH4 distribution measurement method to elucidate nonlinear combustion oscillation problems. The method is based on a computed tomography (CT) method using tunable diode laser absorption spectroscopy (TDLAS). The CT-TDLAS method was applied to oscillating flames and the time resolved 2D CH4 concentration distributions were successfully measured using 16 path CT-TDLAS measurement cell. CT-TDLAS has the kHz response time and the method enables the real-time 2D species concentration measurement to be applicable to the nonlinear phenomena of combustion oscillation problems in gas turbines.

Foreign Object Debris (FOD) is debris or article alien, which may A fluid structure interaction method for an airfoil with a local flexible structure is presented for flow control of Micro Air Vehicles. An improved ALE-CBS scheme is developed for unsteady viscous flow coupling in combination with the theory of shallow arch with large deformation. After the verification of the presented algorithm, the method is used to study the interaction between flow and airfoil with a local flexible structure with different elastic stiffness. The momentum and energy exchange are investigated to reveal the unsteady coupling effects on aerodynamic performance. The results show that the coupling between fluid and structure enhances the momentum and energy exchange from main flow into the boundary layer. It induces the separation bubble moving downstream, and decreases the negative pressure in the separation zone on the upper surface, which leads to lift enhancement. The utilization of local flexible structure can be considered as an effective flow control technique for enhancement of the aerodynamic performance of Micro Air Vehicles.

Foreign Object Debris (FOD) is debris or article alien, which may This paper presents analytical results of natural frequencies and loss factors of node-diameter and node-circumferential modes of a thin shell treated with constrained layer damping (CLD) based on Rayleigh-Ritz method. General differential equations of motion of the thin CLD shell are derived firstly by following the Donnell-Mushtari shell theory. By taking the beam characteristic functions as the admissible functions, the Rayleigh-Ritz method is employed to deduce the higher degree equations of natural frequencies of the thin CLD shell under different boundary conditions. It is confirmed that the present method is accurate and convenient so that it is applicable to the thin CLD shell compared with classic analytic method or transfer matrix method. Several examples are achieved and compared to illustrate the effects of the viscoelastic material (VEM) and constrain layer’s thickness ratios on the natural frequencies and modal loss factors, besides the effect of boundary conditions. The results show that the thickness ratio of VEM affects sensitively the modal frequencies and the total damping capacity of the thin CLD shell.

Foreign Object Debris (FOD) is debris or article alien, which may In order to solve the high order fatigue test problem of thin plate composite structure with hard coating, a new test method and its technological process is proposed based on the summarizing the experience of massive experiments. Besides, by considering technical difficulties of the high order fatigue test of the hard coating composite structure, several key techniques are described in details, such as how to measure dynamic strain without damaging the hard coating, how to predict excitation amplitude required by the high order fatigue test, and how to avoid the interference resulted from the strain softening of hard coating and to measure high order nature frequencies accurately. Finally, an experimental test is done to verify the practicability and reliability of this method.