非线性弹性体的弹性动力学变分原理

本文根据文献[1],对非线性应力应变关系的弹性体,导出了弹性动力学问题的变分原理和广义变分原理,提出了混合位移协调元和混合应力协调元的瞬时广义变分原理.     

非线性弹性杆的异常动态响应

讨论了拉伸速度呈周期变化的受拉非线性弹性直杆的动力行为。采用Melnikov方法研究时发现,材料的非线性使得动力响应发生异常,对确定的直杆而言,当拉伸速度超过某个临界值时,动力系统将出现次谐分岔和混沌。     

一类弹性振动系统的控制问题

本文讨论具结构阻尼系数的细长体飞行器的弹性振动方程支配系统的最优控制问题 .本文将结构阻尼系数作为控制变量 ,以“范数最小”来衡量其最优性 .证明了弹性振动系统存在唯一的最优控制元     

Regularity Results for a Nonlinear Elliptic-Parabolic System with Oscillating Coefficients

In this paper we study the initial boundary value problem for the system $\mbox{div}(\sigma(u)\nabla\varphi)=0,$ $ u_t-\Delta u=\sigma(u)|\nabla\varphi|^2$. This problem is known as the thermistor problem which models the electrical heating of conductors. Our assumptions on $\sigma(u)$ leave open the possibility that $\liminf_{u\rightarrow\infty}\sigma(u)=0$, while $\limsup_{u\rightarrow\infty}\sigma(u)$ is large. This means that $\sigma(u)$ can oscillate wildly between $0$ and a large positive number as $u\rightarrow \infty$. Thus our degeneracy is fundamentally different from the one that is present in porous medium type of equations. We obtain a weak solution $(u, \varphi)$ with $|\nabla \varphi|, |\nabla u|\in L^\infty$ by first establishing a uniform upper bound for $e^{\varepsilon u}$ for some small $\varepsilon$. This leads to an inequality in $\nabla\varphi$, from which the regularity result follows. This approach enables us to avoid first proving the Hölder continuity of $\varphi$ in the space variables, which would have required that the elliptic coefficient $\sigma(u)$ be an $A_2$ weight. As it is known, the latter implies that $\ln\sigma(u)$ is "nearly bounded''.     

Dynamics of flow near a separation point

Dynamical behavior of a boundary layer separation is studied using the experimental approach. The dynamical nature of the phenomenon is demonstrated on a simple case of a flat–plate boundary layer in adverse pressure gradient. The Time–Resolved PIV technique was utilized for monitoring instantaneous structure of the separation region and its time development. Distinctive coherent structures and their dynamical behavior were identified using the Proper Orthogonal Decomposition method. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamics of Delay Systems with Rapidly Oscillating Coefficients

The problems of generalization of the averaging principle to delay systems are considered. New effects are revealed in the study of bifurcation problems, as are new phenomena that arise in the case of rapid oscillations of the delay. As an application of the results, the dynamics of a logistic equation with rapidly oscillating coefficients is studied.     

A Plane Shear Wave Excited in an Elastic Half-Space by Oscillating Normal Pressure Distributed Nonuniformly

Excitation of an elastic half-space by an oscillating normal load distributed nonuniformly over its surface is considered. The medium is assumed to be linear, isotropic, and homogeneous. The external load is distributed smoothly, and the extent of variation in it is large in comparison with the wavelength. A simple expression describing the shear wave with a plane front set, running away from the surface, is found. This wave disappears if the load is constant. Bibliography: 10 titles.     

一类非线性弹性杆波动方程的求解

对计入横向惯性效应后的非线性弹性杆纵向波动方程进行了分析,得到了一类非线性波动方程,并用完全近似方法求出了该方程的近似解析解．     

On an Adaptive Estimator of the Least Contrast in a Model with Nonlinear Functional Relations

We consider an implicit nonlinear functional model with errors in variables. On the basis of the concept of deconvolution, we propose a new adaptive estimator of the least contrast of the regression parameter. We formulate sufficient conditions for the consistency of this estimator. We consider several examples within the framework of the L ₁- and L ₂-approaches.     

Homogenization of a Nonlinear Convection-Diffusion Equation with Rapidly Oscillating Coefficients and Strong Convection

A Cauchy problem for a nonlinear convection-diffusion equationwith periodic rapidly oscillating coefficients is studied. Underthe assumption that the convection term is large, it is provedthat the limit (homogenized) equation is a nonlinear diffusionequation which shows dispersion effects. The convergence ofthe homogenization procedure is justified by using a new versionof a two-scale convergence technique adapted to rapidly movingcoordinates.     

Boundary Layer Flow near a Discontinuity in Wall Conditions

A numerical method for integration of the laminar boundary layerequations past a discontinuous chage in the boundary conditionsalong a flat palte is presented, together with some resultscomputed for slot-injection of fluid from the plate. The method,which is discussed in detail, is a two-region matching procedurethat follows very closely the mathematical development of thesolution near the singularity and seems capable of being adaptedto more general non-linear parabolic problems.     

On the Dynamics of Elastic Strips

Summary. {The dynamics of elastic strips, i.e., long thin rods with noncircular cross section, is analyzed by studying the solutions of the appropriate Kirchhoff equations. First, it is shown that if a naturally straight strip is deformed into a helix, the only equilibrium helical configurations are those with no internal twist and whose principal bending direction is either along the normal or the binormal. Second, the linear stability of a straight twisted strip under tension is analyzed, showing the possibility of both pitchfork and Hopf bifurcations depending on the external and geometric constraints. Third, nonlinear amplitude equations are derived describing the dynamics close to the different bifurcation regimes. Finally, special analytical solutions to these equations are used to describe the buckling of strips. In particular, finite-length solutions with a variety of boundary conditions are considered. } Received February 16, 1999; accepted October 24, 2000 Online publication February 20, 2001     

Stress Distribution in an Infinite Elastic Body with a Locally Curved Fiber in a Geometrically Nonlinear Statement

Within the framework of a piecewise homogeneous body model, with the use of three-dimensional geometrically nonlinear exact equations of elasticity theory, a method for determining the stress—strain state in unidirectional fibrous composites with locally curved fibers is developed for the case where the interaction between the fibers is neglected. All the investigations are carried out for an infinite elastic body containing a single locally curved fiber. Numerical results illustrating the effect of geometrical nonlinearity on the distribution of the self-balanced normal and shear stresses acting on the interface and arising as a result of local curving of the fiber are presented.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 433–448, July–August, 2005.     

Dynamics near extinction time of a singular diffusion equation

We will show that if u is the solution of the equation , in is an even function on and is monotone decreasing in on , , where is a monotone increasing function satisfying with being given by and , then the rescaled function , will converge uniformly on every compact subset of to as where . Received: 25 May 2000 / Revised version: 26 October 2001 / Published online: 28 February 2002     

孤波在非线性弹性杆中的传播

本文利用逆散射方法,对非线性弹性杆中的应变孤波[1],[2]进行了详细分析,闸明了孤波特性及其对固体结构的影响,并给出了某些定量的结果.     

壁面结构对三维可压缩气泡群影响的数值模拟研究

基于流体体积(VOF)法追踪自由液面,研究了壁面结构对三维可压缩气泡群流动的影响.通过在待测壁面上设置不同形状的壁面结构(长方体、椭球体和圆锥体)并改变它们各自的几何参数(位置和长度),来研究壁面结构对壁面附近的气泡群流动的影响,该影响表现为气泡群对壁面的空间平均压力.研究发现,壁面结构对气泡群的拓扑结构的影响会造成壁...     

飞行器内裂纹转子系统的非线性动力学特性研究

在Jeffcott转子的开闭裂纹及方波模型基础上,建立了飞行器内裂纹转子系统的运动模型．数值研究表明:当飞行器以不同的等速度飞行时,转子轴与水平面之间夹角的变化将造成重力分量的变化,从而使转子运动在周期解、拟周期或浑沌状态之间变化,而且出现非线性现象的转速比、刚度变化比等参数的范围、进入和退出浑沌的路径、响应中的频率成份也会发生变化．飞行器的飞行速度变化还会改变裂纹转子响应的稳定性．飞行器等速飞行后的加速过程将引起转子振幅的突升及其后的下降,而且会使裂纹转子系统响应可能在不同的非线性状态下交替改变．     

一类非线性微分代数系统的零动态

控制系统的零动态是系统一种内部动态品质,其行为与系统的许多性质相联系,如系统的稳定性,反馈镇定与输出跟踪等.针对一类非线性微分代数系统,提出了输出零子流形和零动态的概念.利用M-导数方法,探讨了此类系统的输出零子流形的性质,并给出了此类系统的输出零子流形和零动态算法,也讨论了该算法的一些性质.最后,给出一个例子说明如何利用系统的零动态来讨论系统的反馈稳定化问题.     

Dissipative Dynamics for a Class of Nonlinear Pseudo-Differential Equations

We study a class of nonlinear evolutionary equations generated by an elliptic pseudo-differential operator, and with nonlinearity of the form G(u _x ) where cη² ≤ G(η) ≤ Cη² for large |η|. For the evolution in spaces of periodic functions with zero mean we demonstrate existence of a universal absorbing set and compact attractor. Furthermore, we show that the attractor is of a finite Hausdorf dimension. The dissipation mechanism for the class of equations studied in the paper is akin to the nonlinear saturation in the Kuramoto-Sivashinsky equation. A similar generalization of the Kuramoto-Sivashinsky equation was studied by Nicolaenko et al. under the assumption of a purely quadratic nonlinearity and reflection invariance of both: the equation and solutions.