A Comparative Analysis of Computational Stability for Linear and Non-Linear Evolution Equations

For several difference schemes of linear and non-linear evolution equations, taking the one-dimensional linear and non-linear advection equations as examples, a comparative analysis for computational stability is carried out and the relationship between non-linear computational stability, the construction of difference schemes, and the form of initial values is discussed. It is proved through comparative analysis and numerical experiment that the computational stability of the difference schemes of the non-linear evolution equation are absolutely different from that of the linear evolution equation.

An Engineering Computational Method of Calculating Wave Forces on the Mat and Platform's Sit-on-Bottom Stability

- In this paper, an engineering method is employed to calculate the horizontal and vertical wave forces on the mat of the submersible platform under Froude-Krylov hypothesis. According to some model tests, appropriate diffraction coefficients are selected. And the results of the formulae given in the paper agree satisfactorily with those experimental data now available. The proposed computational method is effective and convenient to use in evaluating the horizontal and vertical wave forces on the mat. An exmaple is also given in this paper. Finally, the effects of the vertical wave force on the platorm's sit-on-bottom stability are analyzed.

Computational Stability of the Explicit Difference Schemes of the Forced Dissipative Nonlinear Evolution Equations

The computational stability of the explicit difference schemes of the forced dissipative nonlinear evolution equations is analyzed and the computational quasi-stability criterion of explicit difference schemes of the forced dissipative nonlinear atmospheric equations is obtained on account of the concept of computational quasi-stability, Therefore, it provides the new train of thought and theoretical basis for designing computational stable difference scheme of the forced dissipative nonlinear atmospheric equations. Key words Computational quasi-stability - Computational stability - Forced dissipative nonlinear evolution equation - Explicit difference scheme This work was supported by the National Outstanding Youth Scientist Foundation of China (Grant No. 49825109), the Key Innovation Project of Chinese Academy of Sciences (KZCX1-10-07), the National Natural Science Foundation of China (Grant Nos, 49905007 and 49975020) and the Outstanding State Key Laboratory Project (Grant No. 40023001).

The Impacts of Initial Perturbations on the Computational Stability of Nonlinear Evolution Equations

The impacts of initial perturbations on the computational stability of nonlinear evolution equations for non-conservative difference schemes and non-periodic boundary conditions are studied through theoretical analysis and numerical experiments for the case of onedimensional equations.The sensitivity of the difference scheme to initial values is further analyzed.The results show that the computational stability primarily depends on the form of the initial values if the difference scheme and boundary conditions are determined.Thus,the computational stability is sensitive to the initial perturbations.

Problems of Nonlinear Computational Instability in Evolution Equations

Some problems of nonlinear computational instability are discussed in this article, which are shown as follows: 1) Three types of representative evolution equations are analyzed, and the close relationship between the nonlinear computational stability or instability in their corresponding difference equations and the properties of their solution is revealed. 2) The problem of nonlinear computational instability in conservative differencing equations with the periodic boundary condition is further discussed, and some effective ways to avoid nonlinear computational instability are proposed. 3) The problem of nonlinear computational instability in non-conservative difference equations with the aperiodic boundary condition is focused on by using nonlinear advection equations as examples, and u synthetic analysis method' is given to judge their computational stability.

A Computational Study on Lateral Flight Stability of the Cranefly in Hover

The dynamic flight stability of hovering insects includes the longitudinal and lateral motion.Research results have shown that for the majority of hovering insects the same longitudinal natural modes are identified and the hovering flight in longitudinal is unstable.However,in lateral,the modal structure for hovering insects could be different and the stability property of lateral disturbance motion is not as robust as that of longitudinal motion.The cranefly possesses larger aspect ratio and lower Reynolds number,and such differences in morphology and kinematics may make the lateral dynamic stability different.In this paper,the lateral flight stability of the cranefly in hover is investigated by numerical simulation.Firstly,the stability derivatives are acquired by solving the incompressible Navier–Stokes equations.Subsequently,the dynamic stability characteristics are checked by analyzing the eigenvalues and eigenvectors of the linearized system.Computational results indicate that the lateral dynamic modal structure of cranefly is different from most other insects,consisting of three natural modes,and the weakly oscillatory mode illustrates the hovering lateral flight is nearly neutral.This neutral stability is mainly caused by the negative derivative of roll-moment vs.sideslip-velocity,which can be attributed to the weaker‘changingLEV-axial-velocity’effect.These results suggest that insects in nature may exhibit different dynamic stabilities with different morphological and kinematic parameters,which should be considered in the designs of flapping wing air vehicles.

Numerical Analysis of Bacterial Meningitis Stochastic Delayed Epidemic Model through Computational Methods

Based on theWorld Health Organization(WHO),Meningitis is a severe infection of the meninges,the membranes covering the brain and spinal cord.It is a devastating disease and remains a significant public health challenge.This study investigates a bacterial meningitis model through deterministic and stochastic versions.Four-compartment population dynamics explain the concept,particularly the susceptible population,carrier,infected,and recovered.The model predicts the nonnegative equilibrium points and reproduction number,i.e.,the Meningitis-Free Equilibrium(MFE),and Meningitis-Existing Equilibrium(MEE).For the stochastic version of the existing deterministicmodel,the twomethodologies studied are transition probabilities and non-parametric perturbations.Also,positivity,boundedness,extinction,and disease persistence are studiedrigorouslywiththe helpofwell-known theorems.Standard and nonstandard techniques such as EulerMaruyama,stochastic Euler,stochastic Runge Kutta,and stochastic nonstandard finite difference in the sense of delay have been presented for computational analysis of the stochastic model.Unfortunately,standard methods fail to restore the biological properties of the model,so the stochastic nonstandard finite difference approximation is offered as an efficient,low-cost,and independent of time step size.In addition,the convergence,local,and global stability around the equilibria of the nonstandard computational method is studied by assuming the perturbation effect is zero.The simulations and comparison of the methods are presented to support the theoretical results and for the best visualization of results.

不同Cs、O电流比激活对GaAs光阴极灵敏度和稳定性的影响

鉴于不同的铯氧电流激活GaAs光阴极时会对激活过程和结果产生不同的影响,从而影响GaAs光阴极的灵敏度和稳定性。以固定铯源电流,改变氧源电流的方式获取不同铯、氧电流比,激活同类GaAs光阴极,得到了3组实验数据。对数据进行分析,结果表明:同类光阴极在相同条件下激活时,光电流出现的时间几乎一致,并且首个光电流峰值也非常接近;激活时ICs/IO=1.07是目前获得高灵敏度、高稳定性GaAs光阴极的最佳电流比,而ICs/IO=1.10时光阴极灵敏度低但稳定性好,ICs/IO=1.03时光阴极灵敏度高但稳定性差。双偶极层模型认为Cs、O激活后GaAs表面形成了稳定均匀的GaAs-O-Cs:Cs-O-Cs双偶极层,并达到了负电子亲和势,这一点与实验数据的分析结果相一致。该方法可用于提高GaAs光阴极灵敏度和稳定性。

基于无源控制方法的TCSC控制器及其仿真研究

简要介绍了一类基于无源系统理论的最优控制方法—— PBC方法 ,基于该方法设计了晶闸管控制的串联补偿器 ( TCSC)无源控制器。由于该控制器中的变量均可实现本地测量 ,故使其能有效地应用于实际电力系统中。针对川渝电力系统的仿真结果 ,证明了基于 PBC控制器的

TCSC系统暂态稳定控制的动态模拟实验研究

基于暂态能量函数 (TEF)方法 ,讨论了可控串联补偿 (TCSC)装置对电力系统暂态稳定的作用 ,设计了相应的稳定控制策略。针对不同的故障类型 ,应用数值仿真和动态模拟实验进行了验证 ,结果均证明了该控制策略的有效性。

基于多目标进化算法的TCSC非线性控制器设计

提出了一种利用多目标进化算法设计可控串联补偿 (TCSC)非线性稳定控制器的方案 ,设计目标是选取合适的控制器参数 ,达到提高电力系统暂态稳定性的效果。将非线性控制器反馈增益的选择归结为参数优化问题 ,并且在优化过程中同时考虑电力系统响应的多项性能指标。采用该方法优化的非线性控制器参数可以较有效地阻尼电力系统振荡。

基于算法组件动态组合的固体火箭发动机计算机辅助设计/计算机仿真(SRMCAD/CS)

提出了一种新的软件模型根据发动机设计人员的设计/仿真任务动态地组合算法组件得到所需的设计/仿真算法,模型可以灵活地胜任发动机设计领域变化多样的设计/仿真计算任务,并且可以使整个软件系统具有很好的扩展性.该研究意图在于创建一个规范、开放的算法组件接口体系,在此基础上建立一个可重用、可扩展的算法组件库和一个算法组件动态组合机制,从而将设计人员编制设计/仿真算法的任务转变成利用已有算法组件动态地组合出所需的设计/仿真算法.该模型让设计人员在设计/仿真工作中重用算法组件库中已有的算法成果,同时又保持了设计人员的自主性,使设计人员的工作变得更加容易和高效.

含Cs、Sr、U模拟核素的地质水泥固化体热稳定性研究

分别针对包含Cs、Sr、U模拟核素的地质水泥固化体,以热处理温度为变量,通过考察固化体热处理前后质量、体积、抗压强度以及物相等参量的变化规律,以此评价地质水泥的热稳定性。实验结果表明,当T≤300°C时,三类水泥固化体的外观无明显变化,体积收缩率控制在3%以下,抗压强度损失率低于25%,仅部分水化产物脱水引起较大失重,体现为显微结构中针状、网状特征组织减少,孔隙增加;当T>700°C时,水泥外表面出现明显裂纹,水化产物已完全相变,但结构仍未见崩塌,显微组织变得更加致密并具有陶瓷结构特征,导致抗压强度随温度升高反向增大,展现出良好的高温热稳定性。新生成的硅灰石相Ca3Si3O9发生同素异构转变是导致固化体表面开裂的主要原因。

浅议计算机图形图像处理技术——Photoshop CS平面设计操作

本文简要介绍了计算机图形图像处理技术,展示电脑美术创作中平面设计方面的应用方法与技巧。对于从事广告创意、平面设计与多媒体制作方面有较高的利用价值,能够较熟练地在广告装饰公司等企、事业单位从事图形图像处理及相关平面设计工作,提高就业能力。

变化信道稀疏度的CSI反馈方法

在大规模多输入多输出(multiple input multiple output,MIMO)系统中,压缩感知(compressed sensing,CS)技术常用于具有稀疏特性的信道状态信息(channel state information,CSI)反馈。针对CS重构时信道稀疏度通常未知的问题,基于深度展开技术提出了一种变化信道稀疏度的CSI反馈方法(a CSI-feedback method for varying channel sparsity,AVCS)。AVCS将信道稀疏度作为训练参数,学习得到通用的网络架构。随着天线数量增大导致信道(矩阵)维度激增,学习网络所得的相互抑制矩阵会呈现二次增长问题,AVCS利用相互抑制矩阵托普利兹(Toeplitz)特性设计了降维卷积网络,解决CSI反馈时的计算复杂度问题。仿真结果表明,所提方法提高了在大规模MIMO系统下CSI重构的适用性,减少了反馈开销且对信道稀疏度具有鲁棒性。

一类双调和方程边值问题的四阶和六阶Richardson外推法

首先,对双调和方程建立了具有二阶精度的差分格式,证明了该差分格式的解存在唯一性,并利用极值原理证明了其收敛性和稳定性;利用双重Richardson外推法对该差分格式做了一次外推和二次外推,在内结点处使得计算结果分别具有四阶精度和六阶精度。研究结果表明,外推算法在一定条件下对于提高差分格式解的精度有显著的作用。

InGaAs光电阴极的Cs/NF_(3)激活

为了提高InGaAs光电阴极的光电发射性能,探究新型激活工艺,采用Cs/NF_(3)和Cs/O两种激活方式对InGaAs样品进行激活实验。对同一结构的InGaAs阴极样品,分别进行了激活实验、衰减实验、光谱响应测试和表面成分分析,分别从白光光电流、衰减稳定性、光谱响应和表面成分等角度测试并分析了不同激活工艺下阴极的性能参数。通过对比Cs/NF_(3)和Cs/O两种激活方式的实验结果可知:Cs/NF_(3)激活后的InGaAs光电阴极在白光光电流、截止波长和光谱响应方面明显优于Cs/O激活后的样品,光谱响应的增强效果在近红外波段尤为明显,在1064 nm处Cs/NF_(3)激活后阴极光谱响应是Cs/O激活后的4.7倍;然而,与GaAs光电阴极Cs/NF_(3)激活能够获得更高的阴极稳定性这一现象不同,Cs/O激活的InGaAs光电阴极的稳定性明显优于Cs/NF_(3)激活,Cs/NF_(3)激活在截止波长和光谱响应方面的优势在连续光照衰减后消失。

改进“yo-yo”Cs/O交替激活方法对GaAs光阴极稳定性影响

为提高激活后GaAs光阴极的稳定性,延长微光夜视器件的工作寿命,围绕Cs/O激活方法和衰减特性进行实验研究。通过对比传统“yo-yo”激活法和改进“yo-yo”激活法在Cs/O激活光电流、光谱响应以及光照衰减方面的差异,发现采用改进“yo-yo”激活法的GaAs光阴极光谱灵敏度更高且稳定性更好。利用四极质谱仪监测真空腔内残气成分和分压强变化,基于衰减模型拟合光电流实验曲线,求得不同残气成分对GaAs光阴极性能衰减影响的权重因子。结果表明水蒸气和二氧化碳的影响最大,甲烷和一氧化碳次之,氢气几乎不产生影响,而其它碳氢有机分子也会产生负面影响。总体看来,改进的“yo-yo”激活法对GaAs光阴极表面吸附含氧气体分子造成的性能衰减具有明显的改善效果,这将有助于提高微光夜视器件中GaAs光阴极的稳定性。

Rock-soil slope stability analysis by two-phase random media and finite elements

To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simulate the two-phase random media, such that the soil(or rock) volume fraction and the inclination of the soil layer can be examined. The finite element method with random media incorporated as the material properties is used to determine the factor of safety of the rock-soil slope. Monte-Carlo simulations are used to estimate the statistical characteristics of the factor of safety. The failure mode of the rock-soil slope is examined by observing the maximum principal plastic strain at incipient slope failure. It is found that the critical surface of a rock-soil slope is fairly irregular, and it significantly differs from that of a pure soil slope. The factor of safety is sensitive to the soil volume faction, but it is predictable. The average factor of safety could be well predicted by the weighted harmonic average between the strength of soil and rock; the prediction model is practical and simple. Parametric studies on the inclination of the soil layer demonstrate that the most instable scenario occurs when the slope angle is consistent with the inclination of the soil layer.

Interval finite element method and its application on anti-slide stability analysis

The problem of interval correlation results in interval extension is discussed by the relationship of interval-valued functions and real-valued functions. The methods of reducing interval extension are given. Based on the ideas of the paper, the formulas of sub-interval perturbed finite element method based on the elements are given. The sub-interval amount is discussed and the approximate computation formula is given. At the same time, the computational precision is discussed and some measures of improving computational efficiency are given. Finally, based on sub-interval perturbed finite element method and anti-slide stability analysis method, the formula for computing the bounds of stability factor is given. It provides a basis for estimating and evaluating reasonably anti-slide stability of structures.