分数阶Duffing振子的亚谐共振

研究了含分数阶微分项的Duffing振子的亚谐共振,利用平均法得到了系统的一阶近似解。提出了亚谐共振时等效线性阻尼和等效线性刚度的概念,分析了分数阶微分项的系数和阶次对系统动力学特性的影响。建立了亚谐共振定常解的幅频曲线的解析表达式,并得到了亚谐共振周期响应的存在条件和稳定性判断准则。最后进行了数值解和解析解的比较,证明了解析结果的准确性,并通过数值仿真研究了分数阶微分项的参数对亚谐共振解的存在条件、稳定性条件和系统幅频曲线的影响。     

用MLP法求强非线性保守系统的次谐共振周期解

在两种改进的LP解法的基础上，将它们结合起来，用于求强非线性保守系统的次谐共振周期解。研究了Dufling方程的1／3亚谐共振周期解和2次超谐共振周期解，结果表明本方法既可求得一类强非线性保守系统的次谐共振周期解又能提高解的计算精度。     

温度场中简谐激励斜梁的1/3次亚谐共振分析

以温度场中简谐激励斜梁的非线性振动方程为研究对象,应用多尺度法,求得非线性振动系统1/3次亚谐共振的一次近似解。对该解进行数值计算,分析温度、激励、几何尺寸等参数对1/3次亚谐共振幅频响应曲线的影响。随着初始温度和激励幅值的增加,1/3次亚谐共振的振幅和共振区增大。随着温度影响系数和长高比的增加,1/3 亚谐共振的振幅和共振区减小。     

分数阶van der Pol振子的超谐与亚谐联合共振

基于平均法研究了分数阶van der Pol振子3次超谐与1/3次亚谐联合共振时的动力学特性。得到了系统的一阶近似解析解,提出了超、亚谐联合共振时等效线性阻尼和等效线性刚度的概念。建立了联合共振定常解幅频曲线的解析表达式,又结合变分方程进行线性化处理,推导出分数阶van der Pol振子在联合共振时的周期解稳定性判断准则。通过与单一谐波下超谐共振、亚谐共振的对比,发现在不同基本参数下该系统可分别表现出单谐波超谐共振、单谐波亚谐共振以及两者共存时的特征现象。研究表明,分数阶微分项参数通过等效线性阻尼和等效线性刚度的形式对系统的响应幅值、共振频率、定常解稳定性、周期解数量、共振区域、曲线拓扑结构及跳跃现象等复杂动力学特性均产生重要影响。     

温度场中输电线在谐扰力作用下的1/3次亚谐共振研究

研究输电线在温度场中谐扰力作用下的1/3次亚谐共振问题,应用动力学方法建立温度场中受谐扰力作用输电线的非线性振动方程。根据非线性振动的多尺度解法,得到系统满足1/3次亚谐共振情况的近似解,并对其进行数值计算。分析温差变化、外部激励、谐调值、系统阻尼等对系统的影响。得到系统失稳的临界温度。系统随着调谐值和温差的增加,响应曲线的幅值增加;随着阻尼的增加,幅频响应曲线向开口方向移动。     

受机械力作用金属／陶瓷功能梯度板的超谐共振研究

研究机械力作用下金属／陶瓷功能梯度薄板3次超谐共振问题．按照功能梯度薄板的非线性动力学方程，得到金属／陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。应用非线性振动的多尺度法得到系统3次超谐共振近似解并进行数值计算。分析阻尼、激励、几何尺寸等参数对系统3次超谐共振幅频响应曲线的影响．     

受机械力作用金属／陶瓷功能梯度板的亚谐共振研究

研究机械力作用下金属，陶瓷功能梯度薄板1／3次亚谐共振问题。按照功能梯度薄板的非线性动力学方程，得到金属，陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。应用非线性振动的多尺度法得到系统1／3次亚谐共振近似解并进行数值计算。分析阻尼、激励、几何尺寸等参数对系统1／3次亚谐共振幅频响应曲线的影响。     

Winkler地基上四边自由矩形薄板的3次超谐波共振与奇异性

通过Galerkin方法,将Winkler地基上四边自由受横向简谐激励矩形薄板的控制微分方程转化为非线性振动方程。应用非线性振动的多尺度法,求得了系统满足3次超谐共振情况时的一次近似解以及对应的定常运动,并对其进行数值了计算。对3次超谐共振定常运动分岔响应方程进行了奇异性分析,得到了开折参数平面的转迁集和分岔图。揭示了一些新的动力学现象。     

一类周期系数力学系统的Hopf-Flip分岔

研究了一类周期系数力学系统因周期运动失稳而产生Hopf-Flip分岔的问题.首先根据拉格朗日方程给出了该力学系统的运动微分方程,并确定其周期运动的具有周期系数的扰动运动微分方程,再根据周期系数系统的稳定性理论建立了其给定周期运动的Poincaré映射,进一步根据该系统的特征矩阵的特征值穿越单位圆情况分析判断该Poincaré映射不动点失稳后将发生Hopf-Flip分岔,并用数值计算加以验证.结果表明,非共振条件下,系统的周期运动可通过Hopf-Flip分岔,进而演变成次谐运动,而三阶强共振条件下系统周期运动失稳后形成不稳定的次谐运动.     

含双时滞振动主动控制系统超谐共振及亚谐共振分析

该文采用增量谐波平衡法求解含双时滞振动主动控制系统的超谐共振和亚谐共振响应。讨论了使系统发生亚谐共振的激励频率取值范围,分析了时滞、反馈控制增益、激励幅值、非线性项系数等系统参数对系统超谐共振和亚谐共振响应的影响规律。结果表明:各参数对系统的超谐共振和亚谐共振响应有显著影响,发生亚谐共振的外激励频率的实际取值范围,受到各系统参数的影响。     

代数多重网格法在岩体力学有限元分析中的应用

代数多重网格法具有存贮量小、收敛精度高和计算时间少等优点,将代数多重网格方法引入到岩体力学有限元计算领域,论述了基于单元聚集和能量极小意义下适于岩体力学有限元求解的代数多重网格粗化策略与插值算子,并详细描述了相应的代数多重网格算法。数值试验表明:在岩体力学与工程问题的有限元数值计算中,代数多重网格求解法是高效的、适用的,较直接法和其他常用迭代方法具有明显的优越性。     

Solutions of population balance equations by double Legendre polynomial transformation

Abstract

First‐order partial differential equations of population balance are solved by employing the Legendre polynomials. The key of the method is that the dependent variable of the population density function is assumed to be expressed by a double series of Legendre polynomials with respect to time and space variables. The approach algorithm is that a series of ordinary differential equations are obtained by making the Legendre transformation with respect to the space coordinate. The series of time‐function ordinary differential equations are further transformed into algebraic equations of expansion coefficients with respect to time. The expansion coefficients of the Legendre polynomials are obtained by solving matrix equations which represent the series of algebraic equations. Illustrative examples are given, and the computational results are compared with those of other numerical values given in the literature. Satisfactory agreements are obtained.     

Numerical expansion-iterative method for analysis of integral equation models arising in one- and two-dimensional electromagnetic scattering

Most integral equations of the first kind are ill-posed, and obtaining their numerical solution needs often to solve a linear system of algebraic equations of large condition number. So, solving this system may be difficult or impossible. Since many problems in one- and two-dimensional scattering from perfectly conducting bodies can be modeled by Fredholm integral equations of the first kind, this paper presents an effective numerical expansion-iterative method for solving them. This method is based on vector forms of block-pulse functions. By using this approach, solving the first kind integral equation reduces to solve a recurrence relation. The approximate solution is most easily produced iteratively via the recurrence relation. Therefore, computing the numerical solution does not need to directly solve any linear system of algebraic equations and to use any matrix inversion. Also, the method practically transforms solving of the first kind Fredholm integral equation which is inherently ill-posed into solving second kind Fredholm integral equation. Another advantage is low cost of setting up the equations without applying any projection method such as collocation, Galerkin, etc. To show convergence and stability of the method, some computable error bounds are obtained. Test problems are provided to illustrate its accuracy and computational efficiency, and some practical one- and two-dimensional scatterers are analyzed by it.     

Plane elasticity problems by barycentric rational interpolation collocation method and a regular domain method

Barycentric rational interpolation collocation method (BRICM) for solving plane elasticity problems with high accuracy is presented. The plane elasticity problems on a circular or rectangular domain can be solved directly by BRICM. Embedded the irregular domain into a regular (circular or rectangular) domain, the governing equations of plane elasticity on regular domain are discretized by the differentiation matrices based on barycentric rational interpolation to form a system of algebraic equations. Discrete boundary conditions are obtained using barycentric rational interpolation. The irregular boundary conditions are imposed by the additional method to form an over-constraint linear system of algebraic equations. Numerical experiments are presented to illustrate the efficiency and high computing precision of proposed method.     

Solving initial and boundary value problems using learning automata particle swarm optimization

In this article, the particle swarm optimization (PSO) algorithm is modified to use the learning automata (LA) technique for solving initial and boundary value problems. A constrained problem is converted into an unconstrained problem using a penalty method to define an appropriate fitness function, which is optimized using the LA-PSO method. This method analyses a large number of candidate solutions of the unconstrained problem with the LA-PSO algorithm to minimize an error measure, which quantifies how well a candidate solution satisfies the governing ordinary differential equations (ODEs) or partial differential equations (PDEs) and the boundary conditions. This approach is very capable of solving linear and nonlinear ODEs, systems of ordinary differential equations, and linear and nonlinear PDEs. The computational efficiency and accuracy of the PSO algorithm combined with the LA technique for solving initial and boundary value problems were improved. Numerical results demonstrate the high accuracy and efficiency of the proposed method.     

A finite boundary method for fluid flow field computations

A powerful new finite boundary concept of seeking field solution, at few selected regions in the solution domain, is introduced. Also a highly economical finite boundary method (FBM) which would greatly reduce the size of the coefficient matrix of the resulting system of simultaneous algebraic equations, requiring lesser computer memory and lesser computing time, is developed. Fluid flow fields governed by the basic elliptic partial differential equations—the Laplace's and the Poisson's equations—in two independent variables are mainly considered. The computational merits of the FBM are shown by solving, as an example, a simple representative flow problem, and the relevant computational finite boundary formulae are given in tabular form. The formulae are numerically derived based on a generalized method presented here. The added feature of the FBM is that it proves to be equally economical even when the solution is sought in the entire flow domain. The problem of steady-state viscous flows governed by the Navier-Stokes equations, the system of two simultaneous partial differential equations—the Poisson's equation and the vorticity transport equation—makes the FBM doubly economical. The possibility of developing an efficient hybrid computational algorithm, for curved problem boundaries, in conjunction with the finite element method, is discussed. The extension of FBM to transient, non-elliptic problems and to three-dimensional problem fields is also indicated. The FBM has been discussed in a more detailed manner so as to clearly bring out the advantages of the new finite boundary concept.     

考虑有限深度土体运动的Winkler地基梁1/2次谐波共振响应分析

土-结构相互作用系统动力响应的基本特征之一是有限范围内弹性地基与其支承结构共同运动,将土体运动引入系统的动力学方程可体现其对系统动力学特性的影响。基于考虑有限深度土体运动影响的Winkler地基上有限长梁的非线性运动方程,利用Galerkin法和多尺度法,求得弹性地基梁1/2次谐波共振的幅频响应方程和位移的二阶近似解。进而通过数值计算,得到了梁1/2次谐波共振的幅频响应曲线,研究了地基深度、质量、弹性模量、Winkler参数和阻尼等对弹性地基梁1/2次谐波共振响应的影响。研究结果表明:有限深度土体运动对Winkler地基梁1/2次谐波共振响应影响显著。运动方程中引入土体运动的影响后,梁1/2次谐波共振区间明显减小。随地基深度、质量和弹性模量改变,弹性地基梁1/2次谐波共振的幅频响应曲线偏转程度、共振区间和响应幅值等均发生定量改变。当弹性地基刚度增大到一定程度,Winkler地基参数变化对系统1/2次谐波共振响应的影响明显减弱。阻尼对系统动力响应起抑制作用,当参数η增大到一定值后将不会出现1/2次谐波共振响应的非平凡解。     

轴向变速黏弹性Rayleigh梁非线性参数振动稳态响应

研究非线性轴向运动黏弹性Rayleigh梁因速度周期变化产生的亚谐波共振。轴向运动速度在平均速度附近做简谐周期性脉动。通过取物质导数的Kelvin本构关系描述Rayleigh梁的黏弹性。运用多尺度近似解析方法,构建轴向运动Rayleigh梁的非线性偏微分方程的可解性条件,分析参数振动稳态响应的振幅与扰动速度频率关系。并运用微分求积方法直接离散非线性Rayleigh梁的控制方程,以验证近似解析方法分析。通过数值算例,分析了系统参数对稳态响应曲线的影响。     

Non-Gaussian stochastic response of nonlinear compliant platforms

A moment function method is presented to estimate the stochastic response of compliant offshore platforms with nonlinearity in stiffness based on non-Gaussian closure. For guyed towers with clump weight, the nonlinearity in stiffness is of the softening type. The random wave loading is expressed in terms of a rational spectrum, making the system Markovian. Using Ito's rule for stochastic differentiation, differential equations for moments up to the fourth order are developed. The system of equations is closed by considering the fifth and sixth cumulants to be zero. For stationary response, differential equations become algebraic equations. The moments are obtained by solving the system of nonlinear algebraic equations. It is observed that the Gaussian closure method is inadequate for defining the complete probabilistic characteristics of the response.     

柔性梁大挠度动力响应分析的多体系统方法

研究柔性梁大挠度动力响应问题，应用多体系统方法建立起大变形振动控制方程，结合Newmark直接积分法和Newton—Raphson迭代法给出了求解该非线性代数一微分方程组的数值方法。该方法一方面在随体坐标系中把子梁作为小变形处理使得变形的描述大为简化，另一方面通过随体坐标系的运动自然计及了子梁的刚体运动。数值算例证明了该方法的正确性和有效性。