STUDY ABUT NONLINEAR FACTOR INFLUENCE ON THE VIBRATION ISOLATION EFFECT OF DAMPER

本文在同时考虑刚度和阻尼非线性的基础上, 研究了非线性因素对隔振器隔振效果的影响;获得了同时考虑立方刚度非线性和椭圆阻尼非线性的非线性系统运动响应和传递率计算公式;讨论了非线性因素对系统运动响应和传递率的影响.     

A modified time domain subspace method for nonlinear identification based on nonlinear separation strategy

Nonlinear factors existing in engineering structures have drawn considerable attention, and nonlinear identification is a competent technique to understand the dynamic characteristics of nonlinear structures. Therefore, in this paper, a novel nonlinear separation subspace identification (NSSI) algorithm based on subspace algorithm and nonlinear separation strategy is proposed to conduct nonlinear parameter identification of nonlinear structures. For the proposed NSSI algorithm, the low-level excitation test is firstly conducted to obtain the transfer matrix in the linear response formula. Then, the obtained transfer matrix is used in the high-level excitation test to calculate the nonlinear response part by the proposed nonlinear separation strategy, and the subspace algorithm is utilized to identify the nonlinear parameter on the modified state-space model including only the nonlinear part. The proposed NSSI algorithm can reduce the coupling error caused by simultaneously processing both the large number part (corresponding to the linear part) and small number part (corresponding to the nonlinear part) in the traditional nonlinear subspace identification (NSI) algorithm. At last, two numerical experiments are given to validate the effectiveness of the developed novel nonlinear identification method. Furthermore, some influence factors are discussed to show the stability of the identification algorithm, and some comparisons between the proposed NSSI method and traditional NSI method are also conducted to demonstrate the advantages of the novel method.     

Hopf bifurcation control for stochastic dynamical system with nonlinear random feedback method

Hopf bifurcation control in nonlinear stochastic dynamical system with nonlinear random feedback method is studied in this paper. Firstly, orthogonal polynomial approximation is applied to reduce the controlled stochastic nonlinear dynamical system with nonlinear random controller to the deterministic equivalent system, solvable by suitable numerical methods. Then, Hopf bifurcation control with nonlinear random feedback controller is discussed in detail. Numerical simulations show that the method provided in this paper is not only available to control the stochastic Hopf bifurcation in nonlinear stochastic dynamical system, but is also superior to the deterministic nonlinear feedback controller.     

横向磁场中细长压杆的分岔特性

在磁弹性非线性运动方程、物理方程、电动力学方程及洛仑兹力表达式的基础上,应用Lagrange描述法建立了横向磁场中两端铰支受压细长杆的非线性磁弹性动力学模型.通过对该模型的简化,分别讨论了静力学模型、线性动力学模型和含三次非线性项的动力学模型的分岔特性.最后通过数值计算,给出了横向磁场中受压细长杆的失稳临界载荷与相关参量之间的关系曲线,并对计算结果及其变化规律进行了分析讨论.     

Effect of damping and wave parameters on offshore structure under random excitation

This paper describes the linearized and nonlinear dynamic response of a tension leg platform (TLP) to random waves and current forces. The forcing term of the equation of motion is inherently nonlinear due to the nonlinear drag force. Two analysis procedures are used: nonlinear time domain analysis and linear frequency domain analysis. For the nonlinear analysis, the random wave particle velocities and accelerations are simulated for a given wave spectrum. The nonlinear equation of motion is then integrated directly to obtain the system response statistics. For the linear frequency domain analysis, the nonlinear drag force is linearized through an introduction of linearization coefficients. The main objective of this paper is to investigate the effect of the structural damping and wave parameters on both nonlinear and linear dynamic response of the TLP by parametric studies. The results of stochastic nonlinear and linear dynamic response of the TLP, with and without the presence of current, are presented and compared.     

从非线性动力学的视角认识细长压杆的稳定性

工程上大部分机构和结构都处于动载的作用下，受压细长杆的失稳是复杂的动力破坏事件．应用Lagrange描述法建立了两端角铰支受压细长杆的非线性动力学模型，通过对这种模型简化分别得到非线性静力学模型、线性动力学模型和含三次非线性项的动力学模型．利用谱截断方法，讨论了线性动力学模型的局部分岔．通过讨论平衡态存在性和稳定性，得到了含三次非线性项的动力学模型分岔条件．研究表明，受压细长杆的非线性动力学模型中存在叉形分岔．     

Normal Vibrations in Near-Conservative Self-Excited and Viscoelastic Nonlinear Systems

A perturbation methodology and power series are utilizedto the analysis of nonlinear normal vibration modes in broadclasses of finite-dimensional self-excited nonlinear systems closeto conservative systems taking into account similar nonlinear normal modes.The analytical construction is presented for some concretesystems. Namely, two linearly connected Van der Pol oscillatorswith nonlinear elastic characteristics and a simplesttwo-degrees-of-freedom nonlinear model of plate vibrations in agas flow are considered.Periodical quasinormal solutions of integro-differentialequations corresponding to viscoelastic mechanical systems areconstructed using a convergent iteration process. One assumesthat conservative systems appropriate for the dominant elasticinteractions admit similar nonlinear normal modes.     

多自由度柔性结构非线性随机振动响应分析方法

随机等效线性化方法是多自由度结构非线性随机振动分析的有效方法,然而柔性结构隐式的系统方程限制了该方法的应用.本文首先提出了把多自由度柔性结构隐式系统方程显式化的等效非线性系统建立方法,该方法结合模态分析,将系统几何非线性作用等效为模态坐标的高次多项式组合,把多自由度物理系统转化为容易求解的模态系统;在此基础上运用随机等效线性化技术建立柔性结构非线性随机振动响应分析方法.该方法通过引入虚拟激励原理,大幅提高了计算效率,使对多自由柔性结构的非线性随机振动响应分析成为可能.通过算例分析,本文分析结果和精确解与数值模拟解的比较结果表明,本文方法具有较好的计算精度和较高的计算效率,能够应用于实际柔性工程结构的随机振动响应分析.     

Nonlinear convection in a non-Darcy porous medium

In this paper, the natural convection in a non-Darcy porous medium is studied using a temperature-concentration-dependent density relation. The effect of the two parameters responsible for the nonlinear convection is analyzed for different values of the inertial parameter, dispersion parameters, Rayleigh number, Lewis number, Soret number, and Dufour number. In the aiding buoyancy, the tangential velocity increases steeply with an increase in the nonlinear temperature parameter and the nonlinear concentration parameter when the inertial effect is zero. However, when the inertial effect is non-zero, the effect of the nonlinear temperature parameter and the nonlinear concentration parameter on the tangential velocity is marginal. The concentration distribution varies appreciably and spreads in different ranges for different values of the double dispersion parameters, the inertial effect parameter, and also for the parameters which control the nonlinear temperature and the nonlinear concentration. Heat and mass transfer varies extensively with an increase in the nonlinear temperature parameter and the nonlinear concentration parameter depending on Dacry and non-Darcy porous media. The variation in heat and mass transfer when all the effects, i.e., the inertial effect, double dispersion ef- fects, and Soret and Dufour effects, are simultaneously zero and non-zero. The combined effects of the nonlinear temperature parameter, the nonlinear concentration parameter and buoyancy are analyzed. The effect of the nonlinear temperature parameter and the nonlinear concentration parameter and also the cross diffusion effects on heat and mass transfer are observed to be more in Darcy porous media compared with those in non- Darcy porous media. In the opposing buoyancy, the effect of the temperature parameter is to increase the heat and mass transfer rate, whereas that of the concentration parameter is to decrease.     

Nonlinear free vibration of nanotube with small scale effects embedded in viscous matrix

In this paper, the nonlinear free vibration of the nanotube with damping effects is studied. Based on the nonlocal elastic theory and Hamilton principle, the governing equation of the nonlinear free vibration for the nanotube is obtained. The Galerkin method is employed to reduce the nonlinear equation with the integral and partial differential characteristics into a nonlinear ordinary differential equation. Then the relation is solved by the multiple scale method and the approximate analytical solution is derived. The nonlinear vibration behaviors are discussed with the effects of damping, elastic matrix stiffness, small scales and initial displacements. From the results, it can be observed that the nonlinear vibration can be reduced by the matrix damping. The elastic matrix stiffness has significant influences on the nonlinear vibration properties. The nonlinear behaviors can be changed by the small scale effects, especially for the structure with large initial displacement.     

Nonlinear evolution analysis of T-S disturbance wave at finite amplitude in nonparallel boundary layers

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圆柱壳的非线性有限元分析及其并行求解

采取16节点曲线边等参元对圆柱壳的几何非线性进行有限元分析. 分析考 虑了完全非线性运动关系以便预测在非线性区域的稳定平衡路径. 建立了基于广义非线性位 移的有限元公式. 提出了基于全Lagrangian格式的非线性有限元分析的并行计算策略. 在集 群环境下, 对圆柱壳的几何非线性分析进行了并行计算. 计算结果表明: 在集群环境下, 所提并行算法具有良好的加速比和效率.     

非线性振动一种稳定的模糊控制方法研究

由于非线性振动系统的非线性本质,在于传统控制理论的线性控制器用于非线性振动控制效果不佳。本文针对非线性振动系统提出了一种模糊自适应滑模控制方案。     

具有组合非线性阻尼的非线性能量阱振动抑制响应分析

非线性能量阱是一种振动能量吸收装置,其在结构振动抑制中具有十分重要的作用.文章对具有组合非线性阻尼非线性能量阱的系统进行振动抑制相关的分析.首先对具有组合非线性阻尼非线性能量阱的系统进行理论模型的描述,对系统模型的运动方程利用复变量平均法进行推导,得到系统的慢变方程.其次对系统的慢变方程运用多尺度法进行强调制响应的分析,通过对系统进行慢不变流形和相轨迹的研究,描述系统强调制响应发生的条件基础.此外,还利用一维映射对系统进行分析,揭示外激励幅值对强调制响应存在时频率失谐系数取值区间的影响规律.最后利用能量谱、时间响应和庞加莱映射对耦合组合非线性阻尼非线性能量阱系统进行了振动抑制的相关研究,揭示组合非线性阻尼的非线性能量阱不同阻尼比、阻尼和刚度对其振动抑制效果的影响规律,得出组合非线性阻尼非线性能量阱和主结构响应存在一致性的现象,并验证所提出的组合非线性阻尼非线性能量阱模型具有较好的振动抑制能力.     

Nonlinear aeroelastic stability analysis of wind turbine blade with bending–bending–twist coupling

In this study, the nonlinear aeroelastic stability of wind turbine blade with bending–bending–twist coupling has been investigated for composite thin-walled structure with pretwist angle. The aerodynamic model used here is the differential dynamic stall nonlinear ONERA model. The nonlinear aeroelastic equations are reduced to ordinary equations by Galerkin method, with the aerodynamic force decomposition by strip theory. The nonlinear resulting equations are solved by a time-marching approach, and are linearized by small perturbation about the equilibrium point. The nonlinear aeroelastic stability characteristics are investigated through eigenvalue analysis, nonlinear time domain response, and linearized time domain response.     

A linear approach to generalized minimum variance controller design for MIMO nonlinear systems

Designing minimum variance controllers (MVC) for nonlinear systems is confronted with many difficulties. The methods which are able to identify MIMO nonlinear systems are scarce, and linear models are not accurate in modeling nonlinear systems. In this paper, Vector ARX (VARX) models are proposed for designing MVC and generalized minimum variance controller (GMVC) for linear and nonlinear systems, and the accuracy of these models in approximating the nonlinear MIMO system is studied. However, the VARX is a linear model. It is shown that this model can identify some kinds of nonlinear systems with any desired accuracy. Therefore, the controller designed by the VARX is accurate, even for these nonlinear systems. The proposed controller is tested on a both linear system and a nonlinear four-tank benchmark process. In spite of the simplicity of designing GMVCs for the VARX models, the results show that the proposed method is accurate and implementable.     

具有非线性homologous变形约束的桁架结构形态分析

研究了具有非线性homologous变形约束条件的桁架结构形态分析问题。在已有的线性homologous变形约束桁架形态分析的基础上,将结构的节点分成三类:homologous变形约束节点,形状可变节点和边界点。运用Moore-Penrose广义逆矩阵性质,将基础方程组解的存在条件表示为包含形状可变节点未知坐标的非线性方程组,为采用Newton-Raphson方法求解非线性方程组,对AA (A为任意矩阵,A 为A的Moore-Penrose广义逆矩阵)求偏导数,找到了满足保型要求的形态,给出的桁架算例说明了本文方法的有效性。     

The response analysis of several,nonlinear isolation systems subjected to random excitation

The nonlinear isolation system is popular in modern isolation mounting. By using Fokker-Planck equation and the statistical linearization method and under the condition of random excitation are discussed in this article the best damping selection of the dashpots of the stiffening nonlinear stiffness, the response characteristics of the single-degree-offreedom isolation system of non-antisymmetrical and nonlinear stiffness, and the response analysis of two-degree-of-freedom nonlinear isolation systems. The selection of some parameters of the nonlinear isolation system is also dealt with by virtue of calculation examples.     

单层平面索网幕墙结构的几何非线性问题研究

单层平面索网支承式玻璃幕墙结构是近年来在国内外应用较为广泛的一种新型幕墙结构形式,由于单层平面索网不具有负高斯曲面形式,结构在平面外方向的刚度偏柔,表现出较明显的几何非线性特征.本文采用连续化方法建立了单层平面索网结构考虑几何非线性影响的静力平衡方程和振动方程,得到了结构刚度的解析表达式,并采用谐波平衡法求得非线性频率的简化解析表达式,以此为基础研究了单层平面索网结构的静力非线性和动力非线性问题.研究结果表明:结构的非线性和结构的初始位置密切相关;结构的非线性频率主要取决于索的初始应变、结构振动幅值与跨度的比值,几何非线性对于结构动力性能的影响要小于对结构静力性能的影响;本文得到的结构在地震荷载和平均风荷载作用下的非线性振动方程和非线性频率为结构在地震荷载和脉动风荷载作用下动力响应的求解奠定了基础.