改进的串级调速系统

本文介绍一种实用的串级调速线路——内反馈串级调速，它省去了逆变变压器，占地面积少，谐波小，逆变器采用强迫关断换流环节，产生超前无功送回电源，提高了系统的功率因数，转子用可控整流电路，它可以减少死区，控制逆变故障电流，采用补脉冲，有效地防止了逆变颠覆，提高了系统的可靠性。这些措施克服了原串级调速的很多缺点，如功率因数低、谐波大、死区大、占地多等，当然亦可根据实际情况采用不同线路，使系统简化，满足使用要求。     

FORCED OSCILLATION AND APPLICATION OF FUNCTIONAL DIFFERENTIAL INEQUALITIES

In this paper we study the oscillations for a class of functional differential inequalities. By using these properties some forced oscillations to the boundary value problems of functional partial differential equations are established.     

Dynamics of oscillators with periodic dichotomous noise

The dynamics of bistable oscillators driven by periodic dichotomous noise is described. The stochastic differential equation governing the flow implies smooth trajectories between noise switching events. The dynamics of the two-branched map induced by this flow is a Markov process. Harmonic and quartic models of the bistable potential are studied in the overdamped limit. In the linear (harmonic) case the dynamics can be reduced to a stochastic one-dimensional map with two branches. The moments decay exponentially in this case, although the invariant measure may be multifractal. For strong damping, relaxation induces a cascade leading to a Cantor set and anomalous decay of the density in this case is modeled by a Markov chain. For the physically more realistic case of a quartic potential many additional features arise since the contraction factor is distance dependent. By tuning the barrier-height parameter in the quartic potential, noise-induced transition rates with the characteristics of intermittency are found.     

Statistics of strange attractors by generalized cell mapping

It is proposed in this paper to use the generalized cell mapping to locate strange attractors of dynamical systems and to determine their statistical properties. The cell-to-cell mapping method is based upon the idea of replacing the state space continuum by a large collection of state space cells and of expressing the evolution of the dynamical system in terms of a cell-to-cell mapping. This leads to a Markov chain which in turn allows us to compute all the statistical properties as well as the invariant distribution. After a general discussion, the method is applied in this paper to strange attractors of a variety of systems governed either by point mappings or by differential equations. The results indicate that it is a viable, effective and attractive method. Some comments on this method in comparison with the method of direct iteration will also be made.     

等速输送运动纱线的横向振动分析

本文讨论在非齐次边界条件下由端点运动激励的纱线强迫振动问题。首先讨论了相应的齐次方程的特征值问题,给出了两端无横动时等速移动(即等速输送运动)纱线的各阶固有频率与复振型函数。然后,利用傅立叶级数理论寻求非齐次边界条件下的齐次方程的解,从而求出了等速输送纱线在卷绕端运动激励下的稳态响应的精确解。     

两分量Bose-Einstein凝聚态系统的混沌与分支

研究了两分量Bose-Einstein凝聚态的混沌性态；用Melnikov方法严格地证明了该系统的混沌解和各阶次调和解的存在性；并用数值计算结果验证了理论的正确性．     

A dynamical (time-harmonic) axisymmetric stress field in a finitely prestretched multilayered slab on a rigid foundation

Within the framework of a piecewise homogeneous body model, with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies, the dynamical (time-harmonic) axisymmetric stress field in a finitely prestretched multilayered slab resting on a rigid foundation is studied. It is assumed that the slab consists of two-layer packets. The elasticity of layer materials is described by the Treloar potential. It is assumed that the material of the lower layer in the packets is more rigid than that of the upper one. Numerical results are presented for the cases where the number of layers (packets) in the slab is 2 (1), 4 (2), or 6 (3). These results concern the normal stresses acting on the interface between the layers of the first, upper packet and on the interface between the first and second packets. The influence of the number, prestretch level, and thickness of the layers on relation ships between the stresses and the frequency of the external force is analyzed. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 667–680, September–October, 2006.     

一类二阶强迫非线性微分方程的振动性

利用广义变分原理和Riccati变换建立了带有阻尼项的二阶强迫非线性微分方程(r(t)Ψ(y(t))︱y′(t)︱α-1 y′(t))′+p(t)Ψ(y(t))︱y′(t)︱α-1 y′(t)+q(t)f(y(t))=e(t)的振动准则,并改进和推广了已有的研究成果.     

Forced Nonstationary Vibrations of a Sandwich Cylindrical Shell with Cross-Ribbed Core

The equations of nonaxisymmetric vibrations of sandwich cylindrical shells with discrete core under nonstationary loading are presented. The components of the elastic structure are analyzed using a refined Timoshenko theory of shells and rods. The numerical method used to solve the dynamic equations is based on the integro-interpolation method of constructing finite-difference schemes for equations with discontinuous coefficients. The dynamic problem for a sandwich cylindrical shell under distributed nonstationary loading is solved with regard for the discreteness of the core__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 60–67, February 2005.     

Nonlinear Analysis of Store-Induced Limit Cycle Oscillations

Flight tests of modern high-performance fighter aircraft reveal the presence of limit cycle oscillation (LCO) responses for aircraft with certain external store configurations. Conventional linear aeroelastic analysis predicts flutter for conditions well beyond the operational envelope, yet these store-induced LCO responses occur at flight conditions within the flight envelope. Several nonlinear sources may be present, including aerodynamic effects such as flow separation and shock-boundary layer interaction and structural effects such as stiffening, damping, and system kinematics. No complete theory has been forwarded to accurately explain the mechanisms responsible. This research examines a two degree-of-freedom aeroelastic system which possesses kinematic nonlinearities and a strong nonlinearity in pitch stiffness. Nonlinear analysis techniques are used to gain insight into the characteristics of the behavior of the system. Numerical simulation is used to verify and validate the analysis. It is found that when system damping is low, the system clearly exhibits nonlinear interaction between aeroelastic modes. It is also shown that although certain applied forcing conditions may appear negligible, these same forces produce large amplitude LCOs under specific realizable circumstances.