基于分数阶模型的传输线瞬态分析与研究

研究传输线上波的传播特性,采用解析方法对整数阶传输线模型和分数阶模型进行研究,同时建立实验环境分析2种传输线模型瞬态,实验证明整数阶模型和分数阶模型是对传输线的不同程度描述,整数阶模型比分数阶模型相对简单,但是时间分数阶有损传输线模型能够更好地表征传输线上电压电流波的反常扩散,分数阶模型开辟了传输线瞬态分析的新方向,同时应用Adomain分解公式,可以求得分数阶模型的终端电压或电流的时域瞬时响应近似解析解.     

液压型风力发电机组低电压穿越过程主传动系统瞬态特性研究

针对液压型风力发电机组低电压穿越过程存在的问题,对该过程机组主传动系统瞬态特性展开了研究。建立了液压主传动系统瞬态模型,并通过AMESim与Matlab/Simulink仿真技术搭建了联合仿真平台。仿真分析了不同工况和管道长度对主传动系统瞬态特性的影响规律。研究结果表明,提升泵转速有利于系统快速响应,缩短管道长度有利于发电功率快速调整。研究工作为开展低电压穿越控制、主传动系统液压管路优化等提供理论依据和先进的技术手段。     

A ghost fluid method for sharp interface simulations of compressible multiphase flows

A ghost fluid based computational tool is developed to study a wide range of compressible multiphase flows involving strong shocks and contact discontinuities while accounting for surface tension, viscous stresses and gravitational forces. The solver utilizes constrained reinitialization method to predict the interface configuration at each time step. Surface tension effect is handled via an exact interface Riemann problem solver. Interfacial viscous stresses are approximated by considering continuous velocity and viscous stress across the interface. To assess the performance of the solver several benchmark problems are considered: One-dimensional gas-water shock tube problem, shock-bubble interaction, air cavity collapse in water, underwater explosion, Rayleigh-Taylor Instability, and ellipsoidal drop oscillations. Results obtained from the numerical simulations indicate that the numerical methodology performs reasonably well in predicting flow features and exhibit a very good agreement with prior experimental and numerical observations. To further examine the accuracy of the developed ghost fluid solver, the obtained results are compared to those by a conventional diffuse interface solver. The comparison shows the capability of our ghost fluid method in reproducing the experimentally observed flow characteristics while revealing more details regarding topological changes of the interface.     

A semi-implicit method for the analysis of two-dimensional fluid flow with moving free surfaces

Flow with moving free surfaces is analyzed with an the Eulerian coordinate system. This study proposes a semi-implicit filling algorithm using VOF in which the PLIC (Piecewise Linear Interface Calculation)-type interface reconstruction method and the donor-acceptor-type front advancing scheme are adopted. Also, a new scheme using extrapolation of the stream function is proposed to find the velocity of the node that newly enters the computational domain. The effect of wall boundary conditions on the flow field and temperature field is examined by numerically solving a two-dimensional casting process.     

Interaction of high-speed compressible viscous flow and structure by adaptive finite element method

Interaction behaviors of high-speed compressible viscous flow and thermal-structural response of structure are presented. The compressible viscous laminar flow behavior based on the Navier-Stokes equations is predicted by using an adaptive cell-centered finite-element method. The energy equation and the quasi-static structural equations for aerodynamically heated structures are solved by applying the Galerkin finite-element method. The finite-element formulation and computational procedure are described. The performance of the combined method is evaluated by solving Mach 4 flow past a flat plate and comparing with the solution from the finite different method. To demonstrate their interaction, the highspeed flow, structural heat transfer, and deformation phenomena are studied by applying the present method to Mach 10 flow past a flat plate.     

Transient analysis of hybrid rocket combustion by the zeldovich-novozhilov method

Hybrid rocket combustion has a manifestation of stable response to the perturbations compared to solid propellant combustion. Recently, it has revealed that the low frequency combustion instability about 10 Hz was occurred mainly due to thermal inertia of solid fuel. In this paper. the combustion response function was theoretically derived by use of ZN (Zeldovich-Novozhilov) method. The result with HTPB/LOX combination showed a quite good agreement in response function with previous works and could predict the low frequency oscillations with a peak around 10 Hz which was observed experimentally. Also, it was found that the amplification region in the frequency domain is independent of the regression rate exponentn but showed the dependence of activation energy. Moreover, the response function has shown that the hybrid combustion system was stable due to negative heat release of solid fuel for vaporization, even though the addition of energetic ingredients such as AP and Al could lead to increase heat release at the fuel surface.     

A neural network developed in a Foundation Fieldbus environment to calculate flow rates for compressible fluid

This paper proposes the development of an artificial neural network multilayer perceptron, implemented in a Foundation Fieldbus environment, to calculate the flow rate of natural gas by using an orifice plate in a closed pipe. The principal benefit of using neural networks lies in their low computational cost and simplicity of implementation, which allows just standard blocks to be used, making the technology independent of the Foundation Fieldbus system manufacturer. To perform the calculation, the proposed methodology relies on static pressure, temperature and differential pressure measurements, which are typically available in industrial plants. The developed methodology generates highly accurate results, and this approach can be implemented at a relatively low cost for Foundation Fieldbus system users.     

Magnetic field effect on fluid flow characteristics in a pipe for laminar flow

The influence of a magnetic field on the skin friction factor of steady fully-developed laminar flow through a pipe was studied experimentally. A mathematical model was introduced and a finite difference scheme used to solve the governing equations in terms of vorticity-stream function. The model predictions agree favourably with experimental results. It is observed that the pressure drop varies in proportion to the square of the product of the magnetic field and the sine of the magnetic field angle. Also, the pressure drop is proportional to the flow rate. This situation is similar to what applies in the absence of a magnetic field. It is found that a transverse magnetic field changes the axial velocity profile from the parabolic to a relatively flat shape. At first, the radial velocity rises more rapidly and then gradually decreases along the pipe until falling to zero. A numerical correlation can be written for the considerable distance required for the new axial velocity profile to establish. Owing to the changes taking place in the axial velocity profile, it exhibits a higher skin friction factor. The new axial velocity profile asymptotically approaches its limit as the Hartmann number becomes large.     

Wet clutch transmission fluid for AWD differentials: base fluid influence on friction characteristics

During the past few years several electronically controllable automotive transmission systems, where wet clutches are used as intelligent differentials, have emerged in the market. In this type of application the anti‐shudder properties of the lubricants are of vital importance. This paper investigates the influence of base fluids on the anti‐shudder properties of transmission fluids for wet clutches in all‐wheel‐drive systems. The investigated all‐wheel‐drive system featuring a wet multi‐plate clutch with a sintered brass‐based friction material is described. The test equipment used to determine the frictional characteristics of the transmission fluid is described. The parameters studied include base fluid type and base fluid viscosity. It is shown that the choice of base fluid has no impact on torque capacity, but that the base fluid influences the temperature dependence of the dynamic friction and the anti‐shudder properties. It is also shown that the major effect on the friction characteristics is caused by additive effects rather than base fluid effects. Copyright © 2006 John Wiley & Sons, Ltd.     

微波传输线上的波导力学分析

微波传输线是聚变工程机械的重要组成部分,它常采用矩形波导作为传输介质。对复合材料的矩形波导采用了两种不同方法进行力学分析,并对结果做了比较,这对其在聚变工程中的实际应用具有重要意义。     

The Taylor-Proudman column in a rapidly-rotating compressible fluid II. asymptotic analysis

A matched asymptotic analysis is conducted for compressible rotating flow in a cylindrical container when a mechanical and/or a thermal disturbance is imposed on the wall. The system Ekman number is assumed to be very small. The conditions for the Taylor-Proudman column in the interior, which were also given in the companion paper (Ref. [1]) for energy transports by means of the energy balancing analysis, have been re-derived. The concept of the grouping of variables, the energy flux content e ≡ T + 2α²rv, is reformulated, and its effectiveness in characterizing the energy transport mechanism is delineated. It is seen that, under the condition of the Taylor-Proudman column, there exist numerous admissible theoretical solutions for interior flow pertinent to the imposed wall boundary condition. Some canonical examples are illustrated. The differential heating problem on the top and bottom endwall disks is revisited by using the concept of the energy flux content. The results are shown to be in line with the previous findings.     

FDM analysis for MHD flow of a non-Newtonian fluid for blood flow in stenosed arteries

A computational model is developed to analyze the effects of magnetic field in a pulsatile flow of blood through narrow arteries with mild stenosis, treating blood as Casson fluid model. Finite difference method is employed to solve the simplified nonlinear partial differential equation and an explicit finite difference scheme is obtained for velocity and subsequently the finite difference formula for the flow rate, skin friction and longitudinal impedance are also derived. The effects of various parameters associated with this flow problem such as stenosis height, yield stress, magnetic field and amplitude of the pressure gradient on the physiologically important flow quantities namely velocity distribution, flow rate, skin friction and longitudinal impedance to flow are analyzed by plotting the graphs for the variation of these flow quantities for different values of the aforesaid parameters. It is found that the velocity and flow rate decrease with the increase of the Hartmann number and the reverse behavior is noticed for the wall shear stress and longitudinal impedance of the flow. It is noted that flow rate increases and skin friction decreases with the increase of the pressure gradient. It is also observed that the skin friction and longitudinal impedance increase with the increase of the amplitude parameter of the artery radius. It is also found that the skin friction and longitudinal impedance increases with the increase of the stenosis depth. It is recorded that the estimates of the increase in the skin friction and longitudinal impedance to flow increase considerably with the increase of the Hartmann number.     

相贯线简化画法的误差分析

针对两圆柱体轴线垂直相交时相贯线的简化画法 ,从理论上进行了误差分析 ,得出了随着小圆柱半径的增大其误差也随之增大的结论 ,为工程技术方面研究和应用两曲面立体相交求交线提供了理论依据     

Tables for boundary-layer thicknesses of similar compressible laminar flow

Similarity solution of the compressible, laminar boundary-layer equation depends on pressure gradient parameter β and wall to inviscid stagnation temperature ratiog _w . However, the derived quantities, such as various thicknesses, also depend on speed parameter S, thereby requiring three dimensional tables for the tabulated results. A new formulation is provided that enables all quantities of interest to be determined by the two-dimensional tables in which β andg _w are the input parameters. With such a set, accurate values can be found for the skin-friction coefficient, Stanton number, and the five most common viscous and thermal boundary-layer thicknesses for arbitrary values of the speed parameter. A comprehensive set of tables is provided in which β ranges from its separation value to 100 andg _w ranges 0 to 5. Quasi-linearization method is applied to the governing equations and generalized Newton-Raphson method is used to obtain successive initial condition. As a result computation time is reduced significantly.     

基于阻抗法和行波法组合的输电线距离保护

为了在某些特殊情况下,使用组合继电器提高保护的可靠性和速度,提出了一种基于阻抗法和行波法组合的距离保护方案.对于死区故障,采用了不受故障初始角及反射波等影响的阻抗法定位;对于一般性故障,采用了不受过渡电阻影响的行波法进行定位;将两种测量方法的优缺点互补组合,并进行了相应仿真试验.仿真试验结果表明:该保护方案能使继电器可靠、灵敏、高速地动作.     

Transient dynamic large deflection analysis of elastic viscoplastic plates by the finite element method

The transient response of plates subjected to impulsive loads is analyzed by the finite element method taking into account the influences of geometry changes and material nonlinearities due to plasticity and strain rate sensitivity. The equations of motion are derived using the principle of virtual work in total lagrangian formulation. For plates the large deflection theory by von Kármán and the theory including the effect of transverse shear strain by Mindlin are employed. Time integration of the nonlinear system of finite element equations is effected using central difference and Newmark schemes. Numerical examples include beams and circular and rectangular plates. Comparisons are made to available experimental, analytical, and numerical results.     

Comparison of unsteady flow calculations in a pipe by the method of characteristics and the two-step differential Lax-Wendroff method

This paper introduces a comparison of two of the methods which are most frequently used, at present, for the solution of an unsteady flow in the pipe system of internal combustion engines. These are (i) the method of characteristics and (ii) the two-step differential Lax-Wendroff method. In the case of homentropic flow a comparison is made between the lattice-point and mesh method of characteristics, and the two-step differential method is shown. In the case of non-homentropic flow the mesh method and two-step differential methods are also compared. The results show that for non-homentropic flow the two-step Lax-Wendroff method is faster and for engineering applications it is easier to implement on the computer.     

基于相位场模型的稀疏液固两相流场特性分析方法

针对在模具结构化表面精密加工过程中稀疏液固两相流场特性参数难以求解的问题,提出了一种基于相位场模型的稀疏液固两相流场特性分析方法。相位场模型中速度场和压力通过Navier-Stokes方程控制,两相流的分界面动力学方程由Cahn-Hilliard方程控制,从而建立了面向软性磨粒两相流流型分析的动力学模型;采用传统的二阶中心差分格式逼近粘性项和表面张力项,同时采用五阶WENO格式近似的对不可压缩两相流进行了空间离散化重构,并采用TVD Runge-Kutta方法提高了求解过程中时间的离散精度;以加工常用的长方形直流道为具体仿真实验对象,研究了稀疏液固两相流流经不同尺寸流道过程中的速度场与压力场变化。研究结果表明,两相流数值仿真结果与理论分析相符,且与国外仿真结果相吻合,从而验证了该方法的有效性,为软性磨粒流精密加工方面的研究提供了可靠的理论依据。     

输电线电磁式防振锤的工作原理及建模分析

文中首先提出电磁式防振锤的新型设计思路,分析其工作原理;然后根据动力学理论建立机械部分的振动模型,吸收风振的能量;根据电磁感应原理及电桥理论,将输电线微风振动的机械能转换成了电能,并以热能的形式消耗在电桥的电阻上,由基尔霍夫定律建立一组非线性数学模型。与FKH-5Z机械防振锤比较,电磁防振锤频带响应宽,防振效果好。     

Wet clutch transmission fluid for AWD differentials: influence of lubricant additives on friction characteristics

In recent years, several electronically controllable automotive transmission systems using wet clutches as intelligent differentials have emerged on the market. These applications place great demands on the anti‐shudder properties of the transmission fluids used. The aims of this study were (i) to investigate the influence of different additives on the friction characteristics of a transmission fluid for all‐wheel drive systems featuring wet multi‐plate clutch with a sintered brass‐based friction material and, based on this knowledge, (ii) to formulate a new transmission fluid with the desired frictional properties. In addition to excellent anti‐shudder properties, the new fluid was required to lubricate hypoid gears under high load. To meet this requirement, it is necessary to add significant amounts of extreme pressure additives to the base oil, which are known to have an unfavourable influence on anti‐shudder properties, necessitating the adoption of novel additive technologies. The additives studied include anti‐wear additives, friction modifiers, corrosion inhibitors, detergents, antioxidants and extreme pressure additives. This paper shows how different additives affect friction in different ways, and that the interactions between the different additives are important to consider. It was concluded that it is feasible to combine good anti‐shudder properties for wet clutches with good lubrication of hypoid gears. Copyright © 2006 John Wiley and Sons, Ltd.