分数阶微分方程耦合系统边值问题解的存在性

应用Green函数将微分方程边值问题可转化为等价的积分方程.近来此方法被应用于讨论分数阶微分方程边值问题正解的存在性.本文讨论非线性分数阶微分方程耦合系统的两点边值问题,应用Green函数,将其转化为等价的积分方程耦合系统,并设非线性项在无穷远处有增长条件,应用Schauder不动点定理证明解而非限于正解的存在性.     

奇异分数阶微分方程边值问题正解的唯一性(英文)

应用Green函数将分数阶微分方程边值问题可转化为等价的积分方程.近来此方法被应用于讨论非线性分数阶微分方程边值问题解的存在性.本文讨论奇异非线性分数阶微分方程边值问题正解的唯一性.应用Green函数将其转化为等价的积分方程,利用偏序集上的不动点定理证明正解的唯一性.     

一类三阶两点边值问题单调迭代正解的存在性

本文利用锥上的不动点理论和单调迭代的方法研究了一类三阶两点边值问题单调迭代正解的存在性,得到了正解存在的充分条件,同时也给出了解的相应迭代序列来逼近解,并且给出了应用实例.值得一提的是,本文所讨论的边值问题中,非线性项显含未知函数的一阶和二阶导数.     

非线性分数阶耦合泛函微分方程组边值问题的可解性

由于运动速度是有限的，因此在信号传输等过程中时滞现象往往是不可避免的。分数阶泛函微分方程是研究时滞系统运动规律的重要模型，当系统中具有两个或多个状态变量且这些状态变量相互作用时，常常运用耦合微分方程组来刻画。对一类具有 Riemann-Liouville 分数阶导数的非线性时滞耦合泛函微分方程组边值问题正解的存在唯一性进行了研究。首先，根据方程与边界条件的特点，建立了比较定理，构造了上解与下解的单调序列，并确定了上下解的关系。运用上下解的方法建立并证明了边值问题正解的存在性定理，同时得到了正解的取值范围。然后，利用迭代技术建立并证明了边值问题正解的存在唯一性定理。最后，给出了具体例子用于说明所得主要结论的适应性与广泛性。     

分数阶微分方程边值问题解的存在性

应用Green函数将分数阶微分方程边值问题可转化为等价的积分方程.近来此方法被应用于讨论非线性分数阶微分方程边值问题解的存在性.本文讨论非线性分数阶微分方程边值问题,应用Green函数,将其转化为等价的积分方程,并设非线性项满足Carathéodory条件,利用非紧性测度的性质和M(o)nch,s不动点定理证明解的存在...     

分数阶时滞微分方程边值问题解的存在性与唯一性

时滞因素对分数阶微分系统的解有重要影响,系统解的变化不仅取决于现在状态,而且受到过去状态的约束,因此在分数阶微分系统中考虑时滞效应具有重要的意义.本文主要研究一类分数阶时滞微分方程边值问题解的存在性与唯一性问题.首先通过构建Green函数并利用分数阶微积分的相关性质给出该类分数阶时滞微分方程的等价方程.然后将此等价方程的求解问题转换为Banach空间中的不动点问题.再利用Banach压缩映像原理和Schauder不动点定理分别给出了保证分数阶时滞微分方程边值问题解的唯一性与存在性的充分性条件.最后,通过两个例子验证了定理结论的有效性.在考虑该类边值问题解的存在唯一性时,本文利用Banach空间中一个特殊的范数,得到系统解的存在唯一性充分性条件较以往的研究结果更为简单.这种方法是新颖的,在后续的研究过程中将尝试利用这种方法讨论带有时滞的分数阶Langevin方程边值问题的正解存在唯一性问题。     

联合噪声激励下分数阶三稳van der Pol振子的随机P分岔

研究了联合高斯白噪声激励下含分数阶导数项的三稳态van der Pol系统的随机P分岔问题。利用均方误差最小原则,将分数阶导数项等效为阻尼力与回复力的线性组合,从而将原系统转化为等价的整数阶系统。运用随机平均法得到了系统幅值的稳态概率密度函数(PDF),利用奇异性理论,得到了系统发生随机P分岔的临界参数条件。在转迁集曲线围成的各区域内分别选取相应参数定性分析了系统幅值稳态概率密度曲线的类型,并通过Monte Carlo模拟的方法将所得数值结果与解析结果进行了比较,从数值仿真与解析结果的符合程度来看,该研究的推导过程及系统转迁集的计算是准确的。该方法对于设计用于调整系统响应的分数阶控制器有直接的指导作用。     

分数阶脉冲微分方程初值问题解的存在性

利用Green函数可以将分数阶微分方程初值问题转化为等价的积分方程.近来此方法被应用于讨论非线性分数阶微分方程初值问题解的存在性.本文讨论菲线性分数阶脉冲微分方程初值问题,应用Green函数,将其转化为等价的积分方程,并设非线性项满足Carathéodory条件,利用非紧性测度的性质和M(o)nch,8不动点定理证明解的存在性.     

分数阶退化时滞微分系统的稳定性问题

本文主要研究了含有退化和时滞因素的分数阶微分系统的稳定性．首先,利用分数阶Laplace变换讨论了在Caputo分数阶导数意义下的具有不同分数阶导数的多时滞退化微分系统的稳定性条件,并且对于不同的情况给出了相应的判别方法．其次,利用特征方程的根的分析结果研究了分数阶退化时滞微分系统的全时滞稳定性问题,给出了判定该系统全时滞稳定的充分性条件,获得的结果推广了相关文献的结论．最后给出了具体例子说明了定理条件的有效性．     

时间分数阶Fokker-Planck方程的Jacobi谱配置方法

分数阶微分方程在工程、生物、金融等领域有广泛的应用．本文利用分数阶积分和微分公式的关系,针对一类带Dirichlet边值条件的时间分数阶Fokker-Planck方程,将其转化为与之等价的带有奇异核的积分微分方程,然后用高斯积分公式数值求解积分项,在时间和空间上都采用Jacobi谱配置法来离散求解积分微分方程．数值算例的结果表明,该方法是非常有效的,数值解具有谱精度,并且该方法容易推广到高维和非线性的情形．     

黏弹性土中衬砌隧道振动响应的解析解

该文采用解析方法在频率域内对黏弹土层和衬砌结构简谐振动特性进行了研究。首先, 将土骨架视为具有分数阶导数本构关系的黏弹性体, 根据黏弹性理论, 推导得到了简谐荷载作用下分数导数型黏弹性土层的位移和应力等解析表达式。其次, 建立了两种类型的衬砌运动方程:第一, 将衬砌结构视为均匀弹性介质, 研究了分数导数黏弹性土中弹性衬砌结构的动力特性;第二, 将衬砌等效为薄壁壳体结构, 利用Flügge薄壳理论, 得到了衬砌结构的运动方程, 并对分数导数黏弹性土和壳体衬砌的动力相互作用进行了分析。根据连续性边界条件, 得到了相关待定系数的表达式。再次, 与以往的解析解进行了对比。最后, 通过算例分析了土体和衬砌各参数对系统动力特性的影响, 结果表明:薄壁壳体衬砌结构条件下系统的动力响应大于均匀弹性衬砌结构条件下系统的动力响应;随着土体和衬砌模量比的增加, 响应幅值逐渐减小。分数导数本构参数对系统的动力特性有较大影响。     

A new approach to solving stochastic programming problems with recourse

A new numerical approach to the solution of two-stage stochastic linear programming problems is described and evaluated. The approach avoids the solution of the first-stage problem and uses the underlying deterministic problem to generate a sequence of values of the first-stage variables which lead to successive improvements of the objective function towards the optimal policy. The model is evaluated using an example in which randomness is described by two correlated factors. The dynamics of these factors are described by stochastic processes simulated using lattice techniques. In this way, discrete distributions of the random parameters are assembled. The solutions obtained with the new iterative procedure are compared with solutions obtained with a deterministic equivalent linear programming problem. It is concluded that they are almost identical. However, the computational effort required for the new approach is negligible compared with that needed for the deterministic equivalent problem.     

An iterative rounding search-based algorithm for the disjunctively constrained knapsack problem

This article proposes an iterative rounding search-based algorithm for approximately solving the disjunctively constrained knapsack problem. The problem can be viewed as a variant of the well-known knapsack problem with some sets of incompatible items. The algorithm considers two key features: a rounding strategy applied to the fractional variables of a linear relaxation and a neighbouring strategy used for improving the quality of the solutions at hand. Both strategies are iterated into a process based on adding a series of (i) valid cardinality constraints and (ii) lower bounds used for bounding the objective function. The proposed algorithm is analysed computationally on a set of benchmark instances of the literature. The proposed algorithm outperforms the Cplex solver and the results obtained improve on most existing solutions.     

分数阶单自由度间隙振子的受迫振动

研究了含有分数阶微分项的单自由度间隙振子的受迫振动,利用KBM渐近法获得了系统的近似解析解。分析了分段线性系统的主共振,得到了分数阶阶次在0～2时分数阶项的统一表达式;发现分数阶微分项在分段系统中以等效线性阻尼和等效线性刚度的形式影响着系统的动力学特性,而间隙以等效非线性刚度的形式影响着系统的动力学特性。获得了主共振幅频响应的表达式,并得到了系统的稳定性条件;比较了系统主共振幅频响应的近似解析解和数值解,发现两者符合程度较高,验证了近似解析解的正确性;详细分析了分数阶项和间隙对系统主共振幅频响应的影响。研究表明KBM渐近法是分析分数阶分段光滑系统动力学的有效方法。     

A Wiener path integral technique for determining the stochastic response of nonlinear oscillators with fractional derivative elements: A constrained variational formulation with free boundaries

A technique based on the concept of Wiener path integral (WPI) is developed for determining approximately the joint response probability density function (PDF) of nonlinear oscillators endowed with fractional derivative elements. Specifically, first, the dependence of the state of the system on its history due to the fractional derivative terms is accounted for, alternatively, by augmenting the response vector and by considering additional auxiliary state variables and equations. In this regard, the original single-degree-of-freedom (SDOF) nonlinear system with fractional derivative terms is cast, equivalently, into a multi-degree-of-freedom (MDOF) nonlinear system involving integer-order derivatives only. From a mathematics perspective, the equations of motion referring to the latter can be interpreted as constrained. Second, to circumvent the challenge of increased dimensionality of the problem due to the augmentation of the response vector, a WPI formulation with mixed fixed/free boundary conditions is developed for determining directly any lower-dimensional joint PDF corresponding to a subset only of the response vector components. This can be construed as an approximation-free dimension reduction approach that renders the associated computational cost independent of the total number of stochastic dimensions of the problem. Thus, the original SDOF oscillator joint PDF corresponding to the response displacement and velocity is determined efficiently, while circumventing the computationally challenging task of treating directly equations of motion involving fractional derivatives. Two illustrative numerical examples are considered for demonstrating the reliability of the developed technique. These pertain to a nonlinear Duffing and a nonlinear vibro-impact oscillators with fractional derivative elements subjected to combined stochastic and deterministic periodic loading. Note that alternative standard approximate techniques, such as statistical linearization, need to be significantly modified and extended to account for such cases of combined loading. Remarkably, it is shown herein that the WPI technique exhibits the additional advantage of treating such types of excitation in a straightforward manner without the need for any ad hoc modifications. Comparisons with pertinent Monte Carlo simulation data are included as well.     

分数导数黏弹性准饱和土中球空腔振动特性

在频率域内用解析方法研究分析了简谐轴对称荷载和流体压力作用下分数导数黏弹性准饱和中球空腔的稳态响应问题。将土骨架等效为具有分数阶导数本构关系的黏弹性体,基于Biot两相饱和介质模型,通过势函数推导求得了边界部分透水时分数导数粘弹性准饱和土中球空腔的位移、应力和孔压等的解析解。根据界面连续性条件,确定了待定系数的表达式。在此基础上,考察了准饱和土各参数对动力响应的影响,结果表明：轴对称荷载和流体压力两种情况时,相对渗透系数对动力响应的影响有较大的差异。分数导数本构模型更合理地描述了准饱和土中球空腔的振动特性。     

Stochastic stability of Duffing oscillator with fractional derivative damping under combined harmonic and white noise parametric excitations

The stochastic stability of a Duffing oscillator with fractional derivative damping of order α (0 < α < 1) under parametric excitation of both harmonic and white noise is studied. First, the averaged Itô equations are derived by using the stochastic averaging method for an SDOF strongly nonlinear stochastic system with fractional derivative damping under combined harmonic and white noise excitations. Then, the expression for the largest Lyapunov exponent of the linearized averaged Itô equations is obtained and the asymptotic Lyapunov stability with probability one of the original system is determined approximately by using the largest Lyapunov exponent. Finally, the analytical results are confirmed by using those from a Monte Carlo simulation of the original system.     

Asymptotic analysis of axisymmetric plane strain problem involving fractional order heat conduction

This work is concerned with the asymptotic solutions of the axisymmetric plane strain problem involving the fractional order heat conduction. The governing equations for the axisymmetric plane strain problem are derived by means of fractional calculus. The Laplace transform technique is used to obtain the general solutions for any set of boundary conditions in the physical domain. The asymptotic solutions for a specific problem of an infinite cylinder with the boundary subjected to a thermal shock is derived by means of the limit theorem of Laplace transform. Utilizing these solutions, the thermoelastic behavior induced by transient thermal shock can be clearly illustrated, and the jumps locating at the position of each wavefront can also be accurately captured. Some comparisons for the predictions of thermoelastic response are conducted to estimate the effect of the fractional order parameter on the thermoelastic behavior.     

Identification of dynamical systems with fractional derivative damping models using inverse sensitivity analysis

The problem of identifying parameters of time invariant linear dynamical systems with fractional derivative damping models, based on a spatially incomplete set of measured frequency response functions and experimentally determined eigensolutions, is considered. Methods based on inverse sensitivity analysis of damped eigensolutions and frequency response functions are developed. It is shown that the eigensensitivity method requires the development of derivatives of solutions of an asymmetric generalized eigenvalue problem. Both the first and second order inverse sensitivity analyses are considered. The study demonstrates the successful performance of the identification algorithms developed based on synthetic data on one, two and a 33 degrees of freedom vibrating systems with fractional dampers. Limited studies have also been conducted by combining finite element modeling with experimental data on accelerances measured in laboratory conditions on a system consisting of two steel beams rigidly joined together by a rubber hose. The method based on sensitivity of frequency response functions is shown to be more efficient than the eigensensitivity based method in identifying system parameters, especially for large scale systems.