广义Birkhoff系统与一类组合梯度系统

提出一类组合梯度系统, 即将梯度系统与斜梯度系统相加而组成的一个系统, 并研究组合梯度系统的重要性质. 将广义Birkhoff系统在一定条件下化成组合梯度系统, 并利用组合梯度系统的性质来研究广义Birkhoff系统的积分和稳定性.     

双级热管转轮除湿空调系统性能研究

转轮除湿空调系统是将转轮除湿机与常用冷却方式相结合实现空调制冷的新型空调系统。为降低转轮除湿空调系统的再生能耗以及提高系统的冷却能力,本文提出双级热管转轮除湿空调系统,系统利用重力热管的冷凝段实现转轮除湿机的再生,蒸发段实现处理空气的冷却。建立了双级热管除湿转轮空调系统传热传湿模型,模拟分析了系统在不同工况下系统的降温除湿特性。研究表明,处理空气进口温度越高,系统的冷却能力越强但系统的除湿能力降低;处理空气湿度越高,系统的除湿能力越强,但系统的冷却能力降低;再生温度越高,系统除湿能力越强,系统热力性能系数越低,但冷却能力降低。综合降温除湿能力及节能要求,双级热管转轮除湿空调系统的再生温度不宜过高,推荐≤80℃。     

非线性振动系统的预测同步方法研究

对于非线性振动系统,如果通过线性耦合可以实现派生系统与原系统的同步,则可以建立相应的预测派生系统,使得预测派生系统的响应与经τ时间以后的原系统响应同步,实现对原振动系统的非线性响应,特别是混沌响应的预测.也可以建立多级的预测派生系统,预测较长一段时间以后的振动系统未来的非线性响应.对于Duffing系统建立了6级的预测派生系统,可以比较精确地预测3s左右的原系统混沌响应. 关键词： 预测同步 派生系统 响应     

计算全息法检测离轴凸非球面照明镜组初始结构设计

设计一种特殊的应用于计算全息法(CGH)高精度检测离轴凸非球面系统的照明系统。该照明系统一方面用作参考系统,另一方面将检测光近似垂直投射到待检测镜面上,使得检测系统为近似共光路系统,降低照明系统的制造精度。分析了照明系统的几何光路模型,将复杂的两用途系统简化,得到照明系统工作距离、照明系统焦距以及参考面曲率半径三个特征参量之间的关系。设计时,通过控制这几个特征参量,得到满足检测要求的系统初始结构。设计结果表明,该方法可以满足系统使用要求。     

中低轨可见光遥感器光学系统方案的优化

可见光遥感器光学系统可以采用折射系统、折反系统和反射系统来实现。长焦距,宽光谱,体积小是中低轨可见光遥感器光学系统设计的难点,针对f=400mm,F=2.0,2W=3°的可见光遥感器系统的要求,分别设计了折射系统,R-C改进型折反系统和离轴三反系统的遥感器光学系统,这三个系统均能满足遥感系统的技术要求,并分析了每个系统的特点。     

一个unified系统与Rssler系统的组合研究

将Unified系统和Rssler系统凸组合构造了新的混沌系统,包括含两个参数的Unified-Rssler系统,以及含一个参数的Lorenz-Rssler系统和Chen-Rssler系统,通过计算最大Lyapunov指数谱、维数谱和计算机仿真,确定Chen-Rssler系统的混沌区域.     

一类自治混沌系统的动力学分析与电路实现

分析讨论一类新的三维二次自治混沌系统.通过理论分析、数值仿真,计算系统的Lyapunov指数谱和Lyapunov维数,以及系统的分岔图等,对系统的基本动力学特性进行分析.设计实现该系统的混沌电路,建立系统参数和电路参数的对应关系,运用Pspice软件对电路进行仿真实验,证实分析的正确性.所讨论的系统不同于Lorenz系统、Rössler系统、Chen系统和Lü系统等,且电路实现很简单实用.     

飞行模拟器用投射系统设计

研究了一种瞄准镜用飞行模拟器投射镜头的设计,并给出了模拟器投射镜头的设计实例。模拟器由显示系统、屏幕、投射系统、反射镜组成,模拟图像信号送入模拟器的显示系统,显示系统将视景仿真模拟图像信号投射到屏幕上,屏幕位于投射系统的焦平面上,瞄准镜对由模拟器进入的光线成像实现成像模拟。投射系统由周边系统、中心系统共9路光学镜头组成,投射系统周边系统、中心系统对应于瞄准镜的中心系统与周边系统,中心系统与周边系统的物面位置重合即共物面;中心系统采用摄远物镜镜形式缩短了镜头长度结构更加紧凑。周边系统焦距为f=263．02mm,视场角为2ω=17°,全视场畸边〈0．4％,在屏幕的Nyquist频率处全视场的MTF〉0．9,系统长度330mm;中心系统焦距为f=295．00mm,视场角为2ω=17°,全视场畸变〈0．37％,在屏幕的Nyquist频率处全视场的MTF〉0．9,系统长度283．2mm。投射系统采用全口径出光,同时系统通光口径略大于敏感器的通光口径,降低了系统装配的精度。     

振动对电视成像系统传递函数的影响研究

为了研究系统平台振动对电视成像系统传递函数的影响,通过将不同振动条件下系统的传递函数进行对比分析,利用能量积分法,建立系统平台在不同振动条件下系统传递函数仿真模型。利用快速反射镜系统和I SITE测量平台组合,对振动条件下系统传递函数进行测量和验证。仿真和实验数据结果表明:对于在研电视成像系统,当振动频率低于曝光频率时,随着系统平台振动频率的增加,系统传递函数的下降速度由静止时的0.167逐渐增加到0.237;当振动频率高于曝光频率时,随着系统平台振动频率的增加,系统的传递函数的下降速度波动性增加,并逐渐趋于在静止时的1.42倍附近。     

转动相对论Birkhoff约束系统积分不变量的构造

研究转动相对论Birkhoff约束系统积分不变量的构造首先,建立转动相对论系统的约束Birkhoff方程;其次,利用等时变分与非等时变分之间的关系建立系统的非等时变分方程;然后,研究转动相对论Birkhoff约束系统的第一积分与积分不变量之间的关系,证明由系统的一个第一积分可以构造一个积分不变量,并给出自由Birkhoff系统的相应结果;最后,讨论转动相对论Hamilton系统、相对论Birkhoff系统和Hamilton系统、经典转动系统和等时变分情形下的积分不变量的构造,结果表明相关的结论均为该定理的特款给出一个例子说明结果的应用 关键词： 转动相对论 Birkhoff系统 约束 第一积分 积分不变量     

虚边界元法与强流电子枪的电子轨迹模拟

以位势问题为分析对象,从格林公式出发严格导出了虚边界元法的基本积分方程.并以虚边界元法基本积分方程为出发点,从理论上导出了虚边界元法对虚边界形状位置的基本要求.理论结果表明,虚边界元法本身是一种严格的方法,但在一定条件下,它是一种近似方法.基于虚边界元方法开发了一套适用于强流电子枪的电子轨迹模拟程序,并对强流电子枪进行了计算.对强流电子枪的计算表明,在同等条件下,取定最佳的虚实边界距离与边界单元数,虚边界元法较边界元法的精度要高.     

Temperature dependence of the structure and shear response of a Σ11 asymmetric tilt grain boundary in copper from molecular-dynamics

We investigate the effect of temperature on the structure and shear response of a Σ11 asymmetric tilt grain boundary in a classical embedded-atom model of elemental copper using molecular dynamics simulations. As the temperature is increased the structure of the boundary disorders considerably, but with a boundary width that remains finite at the melting point. The disordering of the boundary structure becomes significant for homologous temperatures above 0.83 (1100?K). As temperature increases above this point the boundary width and roughness increases monotonically. Near the temperature where the boundary starts to disorder we observe a change in the temperature dependence of the ideal shear strength of the boundary, as well as the value of the coupling parameter β, defined as the ratio of the velocity of relative translation of the grains parallel to the boundary plane to that corresponding to the motion of the boundary normal to its plane.     

NLIE of Dirichlet sine-Gordon model for boundary bound states

We investigate boundary bound states of sine-Gordon model on the finite-size strip with Dirichlet boundary conditions. For the purpose we derive the nonlinear integral equation (NLIE) for the boundary excited states from the Bethe ansatz equation of the inhomogeneous XXZ spin 1/2 chain with boundary imaginary roots discovered by Saleur and Skorik. Taking a large volume (IR) limit we calculate boundary energies, boundary reflection factors and boundary Lüscher corrections and compare with the excited boundary states of the Dirichlet sine-Gordon model first considered by Dorey and Mattsson. We also consider the short distance limit and relate the IR scattering data with that of the UV conformal field theory.     

Atomistic Simulation of Curvature Driven Grain Boundary Migration

We present two dimensional molecular dynamics simulations of grain boundary migration using the half-loop bicrystal geometry in the experiments of Shvindlerman et al. We examine the dependence of steady-state grain boundary migration rate on grain boundary curvature by varying the half-loop width at constant temperature. The results confirm the classical result derived by absolute reaction rate theory that grain boundary velocity is proportional to the curvature. We then measure the grain boundary migration rate for fixed half-loop width at varying temperatures. Analysis of this data establishes an Arrhenius relation between the grain boundary mobility and temperature, allowing us to extract the activation energy for grain boundary migration. Since grain boundaries have an excess volume, curvature driven grain boundary migration increases the density of the system during the simulations. In simulations performed at constant pressure, this leads to vacancy generation during the boundary migration, making the whole migration process jerky.     

不同边界条件下的渗吸驱动因素

建立不同边界条件下的渗吸数学模型, 分别研究在单一边界(OEO边界条件)和混合边界条件(TEO-OW边界条件)下重力和毛管压力对渗吸作用的驱动。结果表明: OEO边界条件下, 只存在逆向渗吸, 并且当开启端面在下端时, 重力抑制渗吸进行; 当开启端面在上端时, 重力促进渗吸进行; TEO-OW边界条件下, 同时存在逆向渗吸和同向渗吸, 对于逆向渗吸, 重力是阻力, 对于同向渗吸, 重力是动力, 当Bond数倒数较小时, 重力在渗吸作用中占主导地位, 当Bond数倒数较大时, 毛管力占主导地位。对比OEO开启端面在上端时和TEO-OW边界条件下重力和毛管力对渗吸作用的大小。结果显示, 在相同Bond数倒数下, OEO边界条件下重力作用的渗吸排油比例要高于TEO-OW边界条件下重力作用的渗吸排油比例。对比不同Bond数倒数下OEO和TEO-OW渗吸速度发现, 当Bond数倒数较小时, 重力起主导作用, OEO边界渗吸速度更快; 当Bond数倒数较大时, 毛管力起主导作用, TEO-OW边界条件渗吸速度更快。     

波动方程的人工边界条件

讨论了求解无限区域内波动方程的人工边界条件问题。利用简单而方便的直接差分方法构造了两个新的人工边界条件。严格地证明了它们的稳定性及其与解析边界条件的相容性。数值结果表明,这些新的人工边界条件在计算中颇为有效。     

Stimulation and Suppression of Grain Boundary Sliding by Intragranular Slip in Zinc Bicrystals

The influence of intragranular slip on grain boundary sliding is studied in originally compatible zinc bicrystals with symmetric tilt boundary. The experiment is designed to separate different effects of intragranular slip on the boundary sliding and establish their mechanisms. Grain boundary sliding with and without development of intragranular slip is observed. The rate of sliding accompanied by slip is more than five times of that without slip. A good correlation between the boundary sliding and intragranular slip prior to slide hardening is established. Slide hardening followed by the negative sliding near one end of the boundary and strain hardening in the boundary vicinity, are observed at the last stages of deformation. For the case of formation of slip induced glissile grain boundary dislocations of opposite signs the possibility of their contribution to total grain boundary sliding, is analyzed. The effect of the increase in the rate of sliding is explained in terms of the accommodation of sliding by slip and appearance of additional glissile grain boundary dislocations of one sign due to strain incompatibility. Contribution of these different dislocation mechanisms to the increase in the sliding rate is determined for the stage of deformation preceding slide hardening. It is supposed that the effect of slide hardening and negative sliding as well as boundary curving is created by non-smooth boundary and small degree of incompatibility caused by straining.     

Heat Kernel Asymptotics of Zaremba Boundary Value Problem

The Zaremba boundary-value problem is a boundary value problem for Laplace-type second-order partial differential operators acting on smooth sections of a vector bundle over a smooth compact Riemannian manifold with smooth boundary but with discontinuous boundary conditions, which include Dirichlet boundary conditions on one part of the boundary and Neumann boundary conditions on another part of the boundary. We study the heat kernel asymptotics of Zaremba boundary value problem. The construction of the asymptotic solution of the heat equation is described in detail and the heat kernel is computed explicitly in the leading approximation. Some of the first nontrivial coefficients of the heat kernel asymptotic expansion are computed explicitly. This revised version was published online in July 2006 with corrections to the Cover Date.     

SPH方法进出口数值边界条件研究

基于虚粒子概念,提出进出口数值边界条件处理方法.在进口边界外设置进口区域,并赋予进口虚粒子相应的物理量;出口边界外设置出口和缓冲区域,出口虚粒子的物理量由计算获得,缓冲区的虚粒子初始物理量是指定的;根据每个时间步的流动情况,改变粒子的区域属性,添加/删除相应的粒子.利用拉格朗日形式的SPH方法,通过管内流动问题验证数值进出口边界方法的适用性,研究进出口边界条件在激波管、绕流问题中的应用.提出的进出口边界处理方法,避免了边界附近流体粒子积分截断问题,保证流体粒子能够流出边界,激波能够透射边界.     

Exact boundary condition for time-dependent wave equation based on boundary integral

An exact non-reflecting boundary conditions based on a boundary integral equation or a modified Kirchhoff-type formula is derived for exterior three-dimensional wave equations. The Kirchhoff-type non-reflecting boundary condition is originally proposed by L. Ting and M.J. Miksis [J. Acoust. Soc. Am. 80 (1986) 1825] and numerically tested by D. Givoli and D. Cohen [J. Comput. Phys. 117 (1995) 102] for a spherically symmetric problem. The computational advantage of Ting–Miksis boundary condition is that its temporal non-locality is limited to a fixed amount of past information. However, a long-time instability is exhibited in testing numerical solutions by using a standard non-dissipative finite-difference scheme. The main purpose of this work is to present a new exact boundary condition and to eliminate the long-time instability. The proposed exact boundary condition can be considered as a limit case of Ting–Miksis boundary condition when the two artificial boundaries used in their method approach each other. Our boundary condition is actually a boundary integral equation on a single artificial boundary for wave equations, which is to be solved in conjunction with the interior wave equation. The new boundary condition needs only one artificial boundary, which can be of any shape, i.e., sphere, cubic surface, etc. It keeps all merits of the original Kirchhoff boundary condition such as restricting the temporal non-locality, free of numerical evaluation of any special functions and so on. Numerical approximation to the artificial boundary condition on cubic surface is derived and three-dimensional numerical tests are carried out on the cubic computational domain.