宽带压缩真空下运动梯型三能级原子的辐射压力

主要研究了宽带压缩真空下,双色驱动激光场对运动梯型三能级原子的辐射压力及其稳态表达式。从宽带压缩真空下,双色激光场对运动梯型三能级原子的驱动的主方程出发,得到了原子密度矩阵元!ij的布洛赫方程;利用合适的标度化变量,得到了关于原子布居的布洛赫方程,再由原子动量的海森堡运动方程,利用绝热近似重要条件,得出平圴辐射压力的表达式;考虑到稳态下,原子布居数不随时间变化以及"11 "22 "33=1的条件,得出原子的辐射压力的稳态表达式。     

杆支撑换热器壳侧单元流道的三维模拟

1 Introduction The traditional segmental baffle heat exchangers(SHE) can be si mply manufactured and run reliably,but they are mainly suitable for the situation of lowerflow velocity. When fluid velocity becomes higher inthe shell side ,the pressure dropi…     

有界区域内具有非线性阻尼项可压缩欧拉方程组

运用能量估计研究了带非线性阻尼项等熵欧拉方程组在有界区域中的全局经典解的整体存在性问题。当初始数据在某一常状态附件的小扰动时,证明了经典解整体存在,并得到了该解在大时间以指数衰减的方式趋于常状态的平衡解。     

基于CFD的电动截止阀内流道数值模拟及改进设计

电动截止阀是流体输送的重要元件.阀的传统设计方法很少从流体角度对其流道进行设计,其流阻系数比较大,容易造成局部压力损失.流体介质通过阀口时,流动方向发生变化,可能产生诸如局部涡流、空化、水锤和死水区等水流现象及湍流脉动噪声,对阀体有很强的破坏性,降低阀的使用寿命.基于RAN-S方程组和RNG k-ε湍流模型,利用CFD技术对全开启状态下的电动截止阀的内流道进行三维的湍流数值模拟,获得其总压图、速度矢量图、湍动能强度图.通过数值模拟,可以直观地显示阀的内流道中流体的流动过程.改变进出口段流道的长度、曲率以及阀杆在流道中的布局等,进出口的压力差相对于未改进前减少30%左右,速度突变区域明显缩小,局部涡流现象消失,湍动能强度也降低了15%左右.     

A meshless method based on moving least squares for the simulation of free surface flows

In this paper, a meshless method based on moving least squares (MLS) is presented to simulate free surface flows. It is a Lagrangian particle scheme wherein the fluid domain is discretized by a finite number of particles or pointset; therefore, this meshless technique is also called the finite pointset method (FPM). FPM is a numerical approach to solving the incompressible Navier-Stokes equations by applying the projection method. The spatial derivatives appearing in the governing equations of fluid flow are obtained using MLS approximants. The pressure Poisson equation with Neumann boundary condition is handled by an iterative scheme known as the stabilized bi-conjugate gradient method. Three types of benchmark numerical tests, namely, dam-breaking flows, solitary wave propagation, and liquid sloshing of tanks, are adopted to test the accuracy and performance of the proposed meshless approach. The results show that the FPM based on MLS is able to simulate complex free surface flows more efficiently and accurately.     

A new method for studying the 3D transient flow of misaligned journal bearings in flexible rotor-bearing systems

The effects of journal misalignment on the transient flow of a finite grooved journal bearing are presented in this study. A new 3D computational fluid dynamics (CFD) analysis method is applied. Also, the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearing and rotor dynamics is considered in the analysis. Based on the structured mesh, a new approach for mesh movement is proposed to update the mesh volume when the journal moves during the fluid dynamics simulation of an oil film. Existing dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The movement of the journal is obtained by solving the moving equations of the rotor-bearing system with the calculated film pressure as the boundary condition of the load. The data exchange between fluid dynamics and rotor dynamics is realized by data files. Results obtained from the CFD model were consistent with previous experimental results on misaligned journal bearings. Film pressure, oil film force, friction torque, misalignment moment and attitude angle were calculated and compared for misaligned and aligned journal bearings. The results indicate that bearing performances are greatly affected by misalignment which is caused by unbalanced excitation, and the CFD method based on the fluid-structure interaction (FSI) technique can effectively predict the transient flow field of a misaligned journal bearing in a rotor-bearing system.     

非理想约束系统的Boltzmann-Hamel型方程及其正则式

本文在文献[1]、[2]的基础上,提出带有非理想约束的分析力学的普遍中心方程,建立非理想非线性非完整非保守系统准坐标形式的广义BoltZmann—Hamel方程,并建立与其对应的正则方程,最后讨论线性系、保守系、完转系和理想系情形。     

低温下气体的焦汤系数研究

对低温气体作了简要分析,并以低温气体为工质,以低温下气体高精度三参数方程为基础,结合低温气体的特性以及热力学理论,导得低温气体焦汤系数的解析表达式,并计算了焦汤系数．     

关于常系数线性齐次微分方程解的级数表示式

常系数线性齐次微分方程是一类基本而又重要的微分方程,它在数学理论和应用方面都有重要的意义.给出了常系数线性齐次微分方程解的仅与系数和初始值有关的级数表示式.     

大脑协同学、Lorenz模型和认知科学

从认知科学及其脑科学的前沿，探讨了大脑神经网络巨系统的功能特点。知觉及思维的产生正是大脑复杂的神经网络巨系统中各子系统的协同综合作用的结果。基于这一机制和特点，初步提出了大脑协同学的一些基本原理和方法。由协同学的基本方程，我们定量导出Lorenz方程和Lorenz模型。其中的两翼对应于大脑的两个半球，两翼之间的跳来跳去形象地描述思维。由此说明生命在于混沌中的协同。大脑协同学具有三个层次：大脑的结构、活动和思维，及进一步的心身协同学。在此，我们尝试以一种新的理论模型对认知科学及脑科学进行某些探讨。     

应用基矢量的物质导数公式简化流体运动微分方程式的推导

推导柱坐标系及球坐标系下流体运动微分方程组通常采用的方法是根据矢量形式的运动微分方程式,利用物质导数的基本公式和正交曲线坐标系各基矢量的偏导数公式来进行,推导过程相当繁琐,尤其在教学过程中,在课堂内完成上述具体推导过程几乎是不可能的。为了寻找一种简捷的推导方法,本文依据基矢量物质导数的基本公式,计算得出了柱坐标系及球坐标系下的基矢量物质导数公式,并将它们分别应用于柱坐标系及球坐标系下的流体运动微分方程组的推导过程中。结果表明:如果将柱坐标系及球坐标系下基矢量的物质导数公式作为基本公式使用,则可以使上述坐标系下流体运动微分方程组的推导过程得到很大程度的简化。     

3D numerical simulation and structural optimization of the rod baffle heat exchanger

Because of the complexities of fluid dynamics equations and the structure of heat exchangers, few theoretical
solutions have been acquired to specify the shell side characteristics of the rod baffle heat exchanger (RBHE)．Based on the
platform of PHEONICS version 3.5.1, a three-dimensional numerical method for predicting the turbulent fluid flow behavior
in the shell side of the rod baffle heat exchangers is developed in this paper. With this method, modeling of the tube bundle
is carried out based on the porous media concept using volumetric porosities and applicable flow resistance correlations.
Turbulence effects are modeled using a standard κ-ε model. It is shown that the simulation results and experimental results
are in good agreement in the shell side. The maximum absolute deviation value of pressure drops is less than 5%, and that
of the heat transfer coefficients is less than 8%. Furthermore, the numerical model is used to optimize the structure of the
RBHE and improves its performance.     

论激励电流的广义函数性质

根据电磁场理论，由电子注在波导中的辐射过程，推导出由电流所激励的电磁波的辐射功率等于电流对场所作的功，证明了电子流辐射过程中的能量守恒关系，直接由麦克斯韦方程组推导出微波电子器件理论的解析解。     

抛物型积分-微分方程有限元解的高精度分析

研究抛物型积分─微分方程的初边值问题，利用插值的积分展开式及后处理技巧，得到双二次有限元解的高精度算法．     

Unsteady simulation for a high-speed train entering a tunnel

In order to study the unsteady aerodynamics effects in railway tunnels, the 3D Reynolds average Navier-Stokes equations of a viscous compressible fluid are solved, and the two-equation k-? model is used in the simulation of turbulence, while the dynamic grid technique is employed for moving bodies. We focus on obtaining the changing tendencies of the aerodynamic force of the train and the aerodynamic pressures on the tunnel wall and train surface, and discovering the relationship between the velocity of the train and the intensity of the micro pressure wave at the tunnel exit. It is shown that the amplitudes of the pressure changes in the tunnel and on the train surface are both approximately proportional to the square of the train speed, so are the microwave and the drag of the train.     

具有非凸条件的单个守恒律初边值问题的粘性逼近解的L^1模误差估计

研究具有非凸条件的单个守恒律初边值问题的粘性逼近解的L^1模误差估计．在流函数有一个拐点的条件下,就初始值为两段常数和边界值为常数的情形,根据弱熵解的几何结构,使用匹配行波解方法导出其粘性逼近解和无粘性解间的L^1模误差界为0（ε^1/2＋ε ｜lnε｜）．     

求解瞬态Naiver-Stokes问题的一种稳定化方法

在压力投影及多尺度变分法的基础上,本文针对瞬态Naiver-Stokes问题提出一种新的稳定化方法,此方法采用非协调且不满足inf-sup条件的速度及压力有限元空间。文中的稳定化方法具备一些优势:能避免高阶微分的计算,数据结构与单元边界无关;只在好的尺度上增加离散的速度项,对高雷诺数的流体很有效;不增加计算成本。     

Research on a Rigid Rotor—Sliding Bearing System with a Squeeze Film Damper

In this paper,a dynamic model on a rigid rotor-sliding bearing system with a SFD is established.The stability and bifurcation behaviors of the system are studied,on The basis of the differential equations of fluid momentum and mass continuity,the distribution pressure function is derived by taking oil film inertia force into consideration.Damping force, clearance excitation force,interference force of different frequencies and static load are also considered in the model,Finally,the governing equations of the stability and bifurcation behaviors of the system are solved by Floquet theory,Simulation of dynamic model shows that the rigid rotor-sliding bearing system can maintain stability and exhibit a Hopt bifurcation phenomenon in a certain range.     

给定曲率和挠率为常数的空间曲线方程

通过解向量微分方程组的特解的方法，给出了曲率函数和挠率函数为常数的空间曲线的方程，并通过分析说明具有该特征的曲线就是圆柱螺线，在此基础上进一步探讨了曲率和挠率为非常数但它们的比值为常数的空间曲线的方程．     

具有分段常数超前变元微分方程的振动性

本文讨论了一类具有分段常数超前变元微分方程解的表示及其振动性。