Controlling the diffusionless Lorenz equations with periodic parametric perturbation

Diffusionless Lorenz equations (DLE) are a simple one-parameter version of the well-known Lorenz model, which was obtained in the limit of high Rayleigh and Prandtl numbers, physically corresponding to diffusionless convection. A simple control method is presented to control chaos by using periodic parameter perturbation in DLE. By using the generalized Melnikov method, the parameter conditions could be obtained to guide the controlled DLE to a low-periodic motion. Moreover, the existence conditions of periodic orbits and homoclinic orbits in the system are given. Some results of the numerical simulation are also explained clearly by a rigorous analysis.     

Perturbation Analysis of Multiclass Stochastic Fluid Models

We use a stochastic fluid model (SFM) to capture the operation of finite-capacity queueing systems with multiple customer classes. We derive gradient estimators for class-dependent loss and workload related performance metrics with respect to any one of several threshold parameters used for buffer control. These estimators are shown to be unbiased and directly observable from a sample path without any knowledge of underlying stochastic characteristics of the traffic processes. This renders them computable in on-line environments and easily implementable in settings such as communication networks.     

Lennard-Jones Viscosities in Wide Ranges of Temperature and Density: Fast Calculations Using a Steady–State Periodic Perturbation Method

A method for fast calculation of viscosity from molecular dynamics simulation is revisited. The method consists of using a steady-state periodic perturbation. A methodology to choose the amplitude of the external perturbation, which is one of the major practical issues in the original technique of Gosling et al. [Mol. Phys. 26: 1475 (1973)] is proposed. The amplitude of the perturbation required for fast caculations and the viscosity values for wide ranges of temperature and density of the Lennard-Jones (LJ) model fluid are reported. The viscosity results are in agreement with recent LJ viscosity calculations. Additionally, the simulations demonstrate that the proposed approach is suitable to efficiently generate viscosity data of good quality.     

具有两参数的非线性非局部扰动发展方程奇摄动问题

本文研究了一类具有非线性非局部扰动发展方程的奇摄动问题.利用奇摄动方法,对该问题解的结构在两个小参数相互关联的情形和适当的条件下展开了全面研究.首先,构造了问题的外部解;然后在区域的边界邻域构造局部坐标系,再在该邻域中引入多尺度变量,得到问题解的边界层校正项,另外,通过引入伸长变量构造了初始层校正项;最后,利用不动点定理,证明了问题的解的一致有效的渐近展开式.用上述方法得到的各次近似解,具有便于求解、精度高等特点.     

微扰理论总结

电磁兼容数值仿真需要建立电子设备的仿真模型,但是实际电子设备模型比较复杂,包括有大量的微小结构,如各种安装凸台、凹槽等.如果按照实际的模型建立仿真模型会耗费大量的人力物力.同时复杂的模型会使计算量急剧的增加,过于复杂的模型也会导致网格的畸变,导致错误的仿真结果.因此在电磁兼容仿真建模过程中,必须对电子设备的仿真模型加以简化或等效处理.本文基于国内外对微扰问题研究,给出电子设备建模过程中模型简化的基本原理,即微扰理论.并对以后的研究提出相关的思路和方法.     

Adaptive Stabilization for a Class of Dynamical Systems with Nonlinear Delayed State Perturbations

The time delays and uncertainties are always encountered in varies of engineering systems, and are the major sources of instability. It is important to investigate the stability and stabilization of those systems. A great deal of attention has been devoted in recent years to the stability analysis and design of controller for the linear uncertainty systems with time-delays[1-7] . For the systems with pseudolinear delay state perturbations, the effective controller also has been designed[8]. It…     

基于匹配度量矩阵扰动校正的多对一匹配判决

对于不同分辨率传感器观测之间的匹配问题,传统的一对一匹配判决算法已不再适用.为此,提出了一种新的匹配判决算法——基于匹配度量矩阵扰动校正的多对一匹配判决算法.建立了匹配度量矩阵的扰动模型,通过扰动校正进行匹配判决并估计匹配解的质量.考虑到实际的匹配问题中难以获得关于扰动参数的先验知识,采用一组匹配门限进行匹配判决,取其中质量最高的匹配解作为最终的匹配解.仿真实验验证了所提算法的有效性.     

3-D NONLINEAR SUPERCAVITATING FLOW IN A GRAVITY FIELD

In this paper,perturbation method and Fourier-cosine-expansion method are used to solve a 3-D nonlinear problem of a supercavitating flow in an inclined field of gravity at large Froude numbers.By expanding the velocity potential into a power series of a small parameter,the original 3-D nonlinear problem is reduced to a number of 2-D ones. The solutions of the first three orders are derived in detail and expressed in terms of the complete elliptic integrals of the first and second kinds.Then the boundary integral equation method is applied to get the numerical solutions for each order.Computational results are provided for supercavitating flows past cones under various flow conditions.     

基于声表面波传感器的液体运动粘度测量方法

设计了一种用于液体运动粘度在线测量的声表面波传感器.利用液体对水平剪切模式声表面波(SHSAW)传播性质的影响,推导得出液体的密度和动力粘度与SH-SAW的传播速度变化的数学关系式,从而实现液体运动粘度的检测,设计了相应的实验设备.通过实验数据与理论数据的比较证实了该设计的可行性.