Two-Level Block Decompositions for Solving Helmholtz Equation via Chebyshev Pseudo Spectral Method

In this paper, we consider solving the Helmholtz equation in the Cartesian domain , subject to homogeneous Dirichlet boundary condition, discretized with the Chebyshev pseudo-spectral method. The main purpose of this paper is to present the formulation of a two-level decomposition scheme for decoupling the linear system obtained from the discretization into independent subsystems. This scheme takes advantage of the homogeneity property of the physical problem along one direction to reduce a 2D problem to several 1D problems via a block diagonalization approach and the reflexivity property along the second direction to decompose each of the 1D problems to two independent subproblems using a reflexive decomposition, effectively doubling the number of subproblems. Based on the special structure of the coefficient matrix of the linear system derived from the discretization and a reflexivity property of the second-order Chebyshev differentiation matrix, we show that the decomposed submatrices exhibits a similar property, enabling the system to be decomposed using reflexive decompositions. Explicit forms of the decomposed submatrices are derived. The decomposition not only yields more efficient algorithm but introduces coarse-grain parallelism. Furthermore, it preserves all eigenvalues of the original matrix.

Chebyshev Pseudo-Spectral Method for Solving Fractional Advection-Dispersion Equation

Fractional differential equations have recently been applied in various areas of engineering, science, finance, applied mathematics, bio-engineering and others. However, many researchers remain unaware of this field. In this paper, an efficient numerical method for solving the fractional Advection-dispersion equation (ADE) is considered. The fractional derivative is described in the Caputo sense. The method is based on Chebyshev approximations. The properties of Chebyshev polynomials are used to reduce ADE to a system of ordinary differential equations, which are solved using the finite difference method (FDM). Moreover, the convergence analysis and an upper bound of the error for the derived formula are given. Numerical solutions of ADE are presented and the results are compared with the exact solution.

Comparison of finite difference and pseudo-spectral methods in forward modelling based on metal ore model of random media

With more applications of seismic exploration in metal ore exploration,forward modelling of seismic wave has become more important in metal ore. Finite difference method and pseudo-spectral method are two important methods of wave-field simulation. Results of previous studies show that both methods have distinct advantages and disadvantages: Finite difference method has high precision but its dispersion is serious; pseudospectral method considers both computational efficiency and precision but has less precision than finite-difference. The authors consider the complex structural characteristics of the metal ore,furthermore add random media in order to simulate the complex effects produced by metal ore for wave field. First,the study introduced the theories of random media and two forward modelling methods. Second,it compared the simulation results of two methods on fault model. Then the authors established a complex metal ore model,added random media and compared computational efficiency and precision. As a result,it is found that finite difference method is better than pseudo-spectral method in precision and boundary treatment,but the computational efficiency of pseudospectral method is slightly higher than the finite difference method.

An Accurate Numerical Solution for the Modified Equal Width Wave Equation Using the Fourier Pseudo-Spectral Method

In this study, the numerical solution for the Modified Equal Width Wave (MEW) equation is presented using Fourier spectral method that use to discretize the space variable and Leap-frog method scheme for time dependence. Test problems including the single soliton wave motion, interaction of two solitary waves and interaction of three solitary waves will use to validate the proposed method. The three invariants of the motion are evaluated to determine the conservation properties of the generated scheme. Finally, a Maxwellian initial condition pulse is then studied. The L2 and L∞ error norms are computed to study the accuracy and the simplicity of the presented method.

Solving a Nonlinear Multi-Order Fractional Differential Equation Using Legendre Pseudo-Spectral Method

In this paper, we apply the Legendre spectral-collocation method to obtain approximate solutions of nonlinear multi-order fractional differential equations (M-FDEs). The fractional derivative is described in the Caputo sense. The study is conducted through illustrative example to demonstrate the validity and applicability of the presented method. The results reveal that the proposed method is very effective and simple. Moreover, only a small number of shifted Legendre polynomials are needed to obtain a satisfactory result.

Pseudo-Spectral Method for Space Fractional Diffusion Equation

This paper presents a numerical scheme for space fractional diffusion equations (SFDEs) based on pseudo-spectral method. In this approach, using the Guass-Lobatto nodes, the unknown function is approximated by orthogonal polynomials or interpolation polynomials. Then, by using pseudo-spectral method, the SFDE is reduced to a system of ordinary differential equations for time variable t. The high order Runge-Kutta scheme can be used to solve the system. So, a high order numerical scheme is derived. Numerical examples illustrate that the results obtained by this method agree well with the analytical solutions.

Stability of weighted spectral distribution in a pseudo tree-like network model

The comparison of networks with different orders strongly depends on the stability analysis of graph features in evolving systems. In this paper, we rigorously investigate the stability of the weighted spectral distribution（i.e., a spectral graph feature） as the network order increases. First, we use deterministic scale-free networks generated by a pseudo treelike model to derive the precise formula of the spectral feature, and then analyze the stability of the spectral feature based on the precise formula. Except for the scale-free feature, the pseudo tree-like model exhibits the hierarchical and small-world structures of complex networks. The stability analysis is useful for the classification of networks with different orders and the similarity analysis of networks that may belong to the same evolving system.

VTI介质修正声学近似qP波波动方程与模拟

各向异性介质中纵横波通常耦合在一起传播,纵横波解耦是地震波传播理论研究的重要内容。经典的声学近似通过设置垂向qSV波速度V_(S0)为0来解耦qP波场,但是存在退化qSV波等问题。本研究将垂向qSV波速度V_(S0)考虑成波数k_(x)、k_(z)和各向异性参数ε、δ的函数,对声学近似进行修正,推导了VTI介质修正声学近似qP波频散关系和波动方程。VTI介质修正声学近似qP波波动方程包含椭圆项和非椭圆项两部分,因此采用混合有限差分/伪谱算法进行求解,即采用有限差分法求解椭圆项、伪谱法求解非椭圆项。频散关系分析和数值示例表明,基于修正声学近似的qP波波动方程不包含退化qSV波,是纯qP波方程,与弹性波方程模拟结果吻合较好,且具有较高精度;该方程在ε≥δ和ε<δ的VTI介质中均是稳定的,并且精度高于声学近似模拟结果。

广义概率密度演化方程的Chebyshev拟谱法

概率密度演化方法(probability density evolution equation,PDEM)为非线性随机结构的动力响应分析提供了新的途径.通过PDEM获得结构响应概率密度函数(probability density function,PDF)的关键步骤是求解广义概率密度演化方程(generalized probability density evolution equation,GDEE).对于GDEE的求解通常采用有限差分法,然而,由于GDEE是初始条件间断的变系数一阶双曲偏微分方程,通过有限差分法求解GDEE可能会面临网格敏感性问题、数值色散和数值耗散现象.文章从全局逼近的角度出发,基于Chebyshev拟谱法为GDEE构造了全局插值格式,解决了数值色散、数值耗散以及网格敏感性问题.考虑GDEE的系数在每个时间步长均为常数,推导了GDEE在每一个时间步长内时域上的序列矩阵指数解.由于序列矩阵指数解形式上是解析的,从而很好地克服了数值稳定性问题.两个数值算例表明,通过Chebyshev拟谱法结合时域的序列矩阵指数解求解GDEE得到的结果与精确解以及Monte Carlo模拟的结果非常吻合,且数值耗散和数值色散现象几乎可以忽略.此外,拟谱法具有高效的收敛性且序列矩阵指数解不受CFL (Courant-Friedrichs-Lewy)条件的限制,因此该方法具有良好的数值稳定性和计算效率.

基于切比雪夫拟谱法的移动荷载作用下简支梁动力响应计算

采用切比雪夫拟谱法求解移动荷载作用下简支梁的动力响应问题,该方法通过重新选取插值点的方式并借助转换矩阵对边界条件进行施加,对集中荷载采用高斯函数法进行正则化处理。将本文方法计算结果与解析解和有限元解进行比较,结果表明,在划分较少单元数量时,采用本文方法计算结果与解析解吻合良好,求解效率高于有限元方法。采用本文方法对Dirac函数的正则化参数σ_(n)进行敏感性分析,结果表明,当在±3σ_(n)范围内布置配点数6~10个时,计算结果能取得较好的精度。

考虑云团衰减作用的激光制导炮弹弹道规划

针对多云天气条件下,云团对激光信号产生较大衰减作用从而影响末制导性能这一问题,提出一种考虑云团对激光衰减作用的滑翔增程激光制导炮弹弹道规划方法。经过合理假设建立云团近似模型,在此基础上设计云团规避—控制能量最优复合规避目标函数(Compound Evasion Objective Function,CEOF)。根据激光导引头工作特性和制导炮弹的飞行特性建立弹道规划模型,采用Radau伪谱法将弹道规划问题转化为非线性规划问题(Non-linear Programming,NLP)。调用NLP求解器SNOPT求解。选取多组云团算例进行仿真分析,仿真结果验证所提弹道规划方法的有效性。研究结果表明,与传统弹道规划方法进行仿真对比,新的弹道规划方法以增加较少动能损耗、控制能量消耗和攻击时长为代价,大幅减少了云团对激光的衰减作用,验证了其优越性。

面向突防的滑翔制导炮弹弹道规划方法

针对滑翔制导炮弹在不可避免的威胁区域内选择突防方案的问题,从量化威胁值的角度建立了敌方防御手段的数学模型,基于模型设计了全程综合威胁值最低的规划指标,提出考虑目标防御威胁的弹道规划方法。为实现滑翔制导炮弹全程飞行过程中初始弹道倾角、偏角、火箭点火时刻、滑翔启控时刻等各参数的最佳匹配,建立了多阶段全弹道规划模型,并采用hp自适应伪谱法将最优控制问题转换为非线性规划问题求解。通过仿真验证了在该指标下滑翔制导炮弹对目标防御的规避效果,分析了影响有效性的因素。与传统弹道规划方法进行对比,证明了所提方法的优越性。

制导炮弹协同方案弹道快速规划

为求解复杂的多弹多阶段协同弹道规划问题,提出一种增广集中式-协同弹道规划算法(AC-CTPM)。首先根据制导炮弹飞行过程中各阶段特性建立5阶段弹道规划模型,之后将n_p发制导炮弹的5阶段弹道规划问题组合扩展为较为复杂的5n_p阶段最优控制问题,然后采用多阶段Radau伪谱法将无限维最优控制问题(OCP)离散为有限维非线性规划问题(NLP),最后调用成熟的NLP求解器SNOPT求解。为提高对复杂的5n_p阶段最优控制问题的求解效率,在AC-CTPM中提出一种将2D标称弹道转换为3D预测方案弹道的协同弹道规划问题初始值获取方法(IGVAM),每一发制导炮弹分别以各自发射点为原点建立新地面坐标系,在新地面坐标系内快速规划出2D方案弹道,之后通过扩展和坐标转换将新坐标系中规划的2D方案弹道转换成原地面坐标系中的3D方案弹道,这些3D方案弹道组合构成协同弹道规划问题的初始预测。采用AC-CTPM算法对单炮多发、多炮齐射同时弹着任务场景进行仿真求解,获得了满足炮弹自身约束以及协同约束的协同方案弹道,验证了AC-CTPM算法的有效性。与分布式协同弹道规划算法(D-CTPM)以及传统集中式协同弹道规划算法(TC-CTPM)进行仿真对比,结果表明:AC-CTPM算法规划的协同方案弹道的目标函数平均比TC-CTPM算法优5.07%,比D-CTPM算法优32.98%,而AC-CTPM算法的求解耗时却比TC-CTPM算法减少86.48%,比D-CTPM减少82.36%,验证了AC-CTPM算法的优越性。

奇异鞍点问题的NESS迭代法半收敛性分析

最近一些学者对于非奇异鞍点问题提出了一种新的外推移位分裂(NESS)预处理,并研究了NESS迭代方法的收敛性以及NESS预处理矩阵的谱分布。本研究进一步将NESS迭代方法用于求解奇异的鞍点问题,给出NESS迭代法在(1,1)块子矩阵是对称正定情况下的半收敛性分析。最后通过数值实验,验证了在适当参数下NESS迭代法求解奇异鞍点问题的可行性和有效性。

无人机四绳吊挂运输系统动力学与控制

针对四旋翼吊挂运输系统,本文引入了四绳吊挂运输方式,开展了四旋翼四绳吊挂运输系统的动力学建模、轨迹规划与控制研究。根据四旋翼和负载的相对位姿推导了绳索张力,建立了四旋翼四绳吊挂运输系统的动力学模型。为平衡运输时间与负载摆动抑制,引入时间和负载摆幅作为复合性能指标,利用伪谱法将原本的最优控制问题转换为非线性规划问题,求解了四旋翼四绳吊挂运输系统的最优位置轨迹,设计了轨迹跟踪算法,并通过数值仿真和实验验证了这一轨迹的合理性。

一种高超声速滑翔式导弹轨迹优化方法

以高斯伪谱法为基础,考虑多段多复杂约束,提出了一种面向突防任务需求,通过罚函数法处理非全程飞行高度与飞行攻角约束的高超声速滑翔式导弹轨迹优化方法。通过仿真结果可以看出,初始状态约束、控制约束、过程约束与终端状态约束均得到了有效控制,且罚函数法处理突防任务段约束相较于常规分段约束法在约束量收束方面更具备优势,能够为后续设计工作保留更多的余量。此外,仿真结果还验证了该方法在不同射程、不同发射点高度和目标点高度条件下的有效覆盖能力。

基于危险斥力场的车间AGV挂接路径规划算法研究

自动导航车辆(AGV)要实现物料的运输,需要通过车钩等装置挂接料车。在对车间AGV物流车的导航算法研究中,避障路径规划一直都是研究的重点。借鉴人工势场法和万有引力定律,使用危险斥力场对车间自动导航小车挂接工况中的道路和障碍物建立模型,考虑到AGV慢速行驶的特点,选择线性二自由度动力学模型对车辆建模,进一步分析AGV挂接过程中的约束条件,采用危险斥力场积分最小的“最安全”及兼顾快速的性能指标作为优化目标,建立最优控制问题数学模型,使用高斯伪谱法进行求解。求解结果和仿真分析验证算法的有效性,基于危险斥力场的车间AGV挂接路径规划算法能够规划出一条安全无碰撞的路径。

高超声速飞行器编队协同飞行轨迹规划方法

针对多高超声速飞行器编队协同飞行问题,提出基于多飞行阶段建模和自适应伪谱法的轨迹规划方法。首先,建立了高超声速飞行器运动模型。然后,面向编队协同飞行问题,建立了任务终端约束和构形约束,并基于编队形成段、稀疏编队段、紧凑编队段的多阶段划分对轨迹规划问题进行建模,在此基础上给出编队飞行综合性能指标函数。随后,提出基于hp自适应Radau伪谱法和序列二次规划的编队协同飞行轨迹规划方法。最后,通过仿真实验验证了多飞行阶段协同飞行轨迹规划方法的有效性。

Analysis on Pseudo Excitation of Random Vibration for Structure of Time Flight Counter

Traditional computing method is inefficient for getting key dynamical parameters of complicated structure.Pseudo Excitation Method（PEM）is an effective method for calculation of random vibration.Due to complicated and coupling random vibration in rocket or shuttle launching,the new staging white noise mathematical model is deduced according to the practical launch environment.This deduced model is applied for PEM to calculate the specific structure of Time of Flight Counter（ToFC）.The responses of power spectral density and the relevant dynamic characteristic parameters of ToFC are obtained in terms of the flight acceptance test level.Considering stiffness of fixture structure,the random vibration experiments are conducted in three directions to compare with the revised PEM.The experimental results show the structure can bear the random vibration caused by launch without any damage and key dynamical parameters of ToFC are obtained.The revised PEM is similar with random vibration experiment in dynamical parameters and responses are proved by comparative results.The maximum error is within 9%.The reasons of errors are analyzed to improve reliability of calculation.This research provides an effective method for solutions of computing dynamical characteristic parameters of complicated structure in the process of rocket or shuttle launching.