全封闭活塞式压缩机CFD模拟

提出了全封闭活塞式压缩机热力性能和流体流动的CFD模拟方法。模拟采用了一维稳态的模型,建立了通用的控制方程形式（能量、动量和连续方程）,充分考虑了各部分的换热和整个区域的热平衡,并对R12和R600a进行了模拟计算和对比。     

Free vibration analysis of joined conical-cylindrical shells by matched Fourier-Chebyshev collocation method

A free vibration analysis of joined conical-cylindrical shells based on the first order shear deformation theory is developed. Deflections and rotations are represented by the expansions of Chebyshev polynomials and Fourier series. Equations of motion are collocated to yield the system of algebraic equations. Boundary conditions and compatibility conditions are considered as side constraints, and the set of algebraic equations is condensed so that the number of degrees of freedom matches the number of expansion coefficients. Numerical examples are provided for a joined conical-cylindrical shell, a complete conical shell attached to a cylindrical shell and a hermetic can.     

导电板上方涡流检测探头阻抗的快速计算与仿真

采用一种基于Maxwell方程组、矢量磁位和空间解域截取的级数展开快速计算方法,导出级数形式的导电板上方通电线圈阻抗变化表达式;通过设定适当的解域截取半径和级数求和项数,可以在保证计算精度的同时提高计算速度。在多种线圈激励频率下,分别采用级数展开法与有限元仿真法,对线圈的阻抗变化进行了计算,两种方法的计算结果非常吻合,相互验证了两种涡流检测计算模型的正确性。     

A trigonometric series expansion based method for the research of static and dynamic characteristics of eccentric seals

Static and dynamic characteristics of labyrinth seals are important in the prediction of the stability of turbomachinery. The paper presents an effective numerical method to predict the static and dynamic performance characteristics of seals at off-center conditions with different rotor whirling frequency. Modifications are introduced for the traditional turbulent bulk flow model to consider the circumferentially varying flow. A trigonometric series expansion method is used to approximate parameters such as pressure and velocity in seals cavity. Numerical simulations show that 8–10 series terms with 5–10 iterations are enough for the solution of this set of nonlinear equations. The resulting nonlinear algebraic equations can be solved rapidly. The analytical results are verified by comparison with the simulated CFD results. Parametric investigations showing the influence of eccentricity and whirling frequency on seals dynamics are also presented. The results show that the trigonometric series expansion based method gives an effective prediction of the static and dynamic characteristics of the eccentric seals.     

The finite volume flic method and its stability analysis

In this study, a general finite volume Fluid-in-cell method (FVFLIC) for solving the Navier—Stokes equations is introduced. The stability of the numerical method is then analysed by directly using two-dimensional Euler equations instead of a linear model equation. This direct approach to the analysis of non-linear stability is based on the Taylor expansion of the discretized Euler equations and some basic principals that have been used for analysing linear model equations. The exact forms of numerical viscosity or truncation errors are derived and discussed. The influences of the numerical viscosity as well as the artificial viscosity on numerical solutions are investigated. Results from this analysis can be used to construct appropriate artificial viscosity terms. Based on the above methodology, a stability criterion is proposed for the calculation of time steps for general three-dimensional computation using non-orthogonal grids.     

The application of the pseudospectral method to the analysis of helical springs of arbitrary shape

The pseudospectral method is applied to the static analysis of helical springs of arbitrary shape. The displacements and the rotations are approximated by series expansions of Chebyshev polynomials. The entire domain is considered as a single element and the governing equations are collocated to yield the system of algebraic equations. The boundary conditions are considered as the constraints, and the set of equations is condensed so that the number of degrees of freedom of the problem matches the total number of the expansion coefficients. Displacements and rotations are computed for noncylindrical helical springs as well as cylindrical helical springs, and parameters that affect the convergence of the solution are discussed. This paper was recommended for publication in revised form by Associate Editor Jeong Sam Han Jinhee Lee received B. S. and M. S. degrees from Seoul National Uni-versity and KAIST in 1982 and 1984, respectively. He received his Ph.D. degree from University of Michigan in 1992 and joined Dept. of Mechano-Informatics of Hongik University in Choongnam, Korea. His research interests include inverse problems, pseudospectral method, vibration and dynamic systems.     

Differential quadrature solution for the free vibration analysis of laminated conical shells with variable stiffness

The free vibration analysis of laminated conical shells with variable stiffness is presented using the method of differential quadrature (DQ). The stiffness coefficients are assumed to be functions of the circumferential coordinate that may be more close to the realistic applications. The first-order shear deformation shell theory is used to account for the effects of transverse shear deformations. In the DQ method, the governing equations and the corresponding boundary conditions are replaced by a system of simultaneously algebraic equations in terms of the function values of all the sampling points in the whole domain. These equations constitute a well-posed eigenvalue problem where the total number of equations is identical to that of unknowns and they can be solved readily. By vanishing the semivertex angle (α) of the conical shell, we can reduce the formulation of laminated conical shells to that of laminated cylindrical shells of which stiffness coefficients are the constants. Besides, the present formulation is also applicable to the analysis of annular plates by letting α=π/2. Illustrative examples are given to demonstrate the performance of the present DQ method for the analysis of various structures (annular plates, cylindrical shells and conical shells). The discrepancies between the analyses of laminated conical shells considering the constant stiffness and the variable stiffness are mainly concerned.     

Mass Transfer in a Rigid Tube With Pulsatile Flow and Constant Wall Concentration

An approximate-analytical solution method is presented for the problem of mass transfer in a rigid tube with pulsatile flow. For the case of constant wall concentration, it is shown that the generalized integral transform (GIT) method can be used to obtain a solution in terms of a perturbation expansion, where the coefficients of each term are given by a system of coupled ordinary differential equations. Truncating the system at some large value of the parameter N, an approximate solution for the system is obtained for the first term in the perturbation expansion, and the GIT-based solution is verified by comparison to a numerical solution. The GIT approximate-analytical solution indicates that for small to moderate nondimensional frequencies for any distance from the inlet of the tube, there is a positive peak in the bulk concentration C(1b) due to pulsation, thereby, producing a higher mass transfer mixing efficiency in the tube. As we further increase the frequency, the positive peak is followed by a negative peak in the time-averaged bulk concentration and then the bulk concentration C(1b) oscillates and dampens to zero. Initially, for small frequencies the relative Sherwood number is negative indicating that the effect of pulsation tends to reduce mass transfer. There is a band of frequencies, where the relative Sherwood number is positive indicating that the effect of pulsation tends to increase mass transfer. The positive peak in bulk concentration corresponds to a matching of the phase of the pulsatile velocity and the concentration, respectively, where the unique maximum of both occur for certain time in the cycle. The oscillatory component of concentration is also determined radially in the tube where the concentration develops first near the wall of the tube, and the lobes of the concentration curves increase with increasing distance downstream until the concentration becomes fully developed. The GIT method proves to be a working approach to solve the first two perturbation terms in the governing equations involved.     

Generation automatique et simplification des equations litterales des systemes mecaniques articulesAutomatic generation and simplification of literal equations modeling articulated mechanisms

This paper presents a method of automatic generation and simplification of literal equations for modeling articulated mechanisms. This method is based both upon a formal representation leading to easy implementation on a micro-computer and a very careful design of the symbolic calculus modules constituting the software. Throughout the computation of the terms of the equations they are systematically simplified and condensed so that the final literal equations are as short as possible and so that their numerical solution requires the lowest possible number of equations. The efficiency of the method increases with the complexity of the modeled mechanism.     

Computational method for dynamic analysis of constrained mechanical systems using partial velocity matrix transformation

A computational method for the dynamic analysis of a constrained mechanical system is presented in this paper. The partial velocity matrix, which is the null space of the Jacobian of the constraint equations, is used as the key ingredient for the derivation of reduced equations of motion. The acceleration constraint equations are solved simultaneously with the equations of motion. Thus, the total number of equations to be integrated is equivalent to that of the pseudo generalized coordinates, which denote all the variables employed to describe the configuration of the system of concern. Two well-known conventional methods are briefly introduced and compared with the present method. Three numerical examples are solved to demonstrate the solution accuracy, the computational efficiency, and the numerical stability of the present method.     

Vibration and buckling of cross-ply laminated composite circular cylindrical shells according to a global higher-order theory

Natural frequencies and buckling stresses of cross-ply laminated composite circular cylindrical shells are analyzed by taking into account the effects of higher-order deformations such as transverse shear and normal deformations, and rotatory inertia. By using the method of power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional higher-order theory for laminated composite circular cylindrical shells made of elastic and orthotropic materials is derived through Hamilton's principle. Several sets of truncated approximate higher-order theories are applied to solve the vibration and buckling problems of laminated composite circular cylindrical shells subjected to axial stresses. The total number of unknowns does not depend on the number of layers in any multilayered shells. In order to assure the accuracy of the present theory, convergence properties of the first natural frequency and corresponding buckling stress for the fundamental mode r=s=1 are examined in detail. The internal and external works are calculated and compared to prove the numerical accuracy of solutions. Modal transverse shear and normal stresses can be calculated by integrating the three-dimensional equations of equilibrium in the thickness direction, and satisfying the continuity conditions at the interface between layers and stress boundary conditions at the external surfaces. It is noticed that the present global higher-order approximate theories can predict accurately the natural frequencies and buckling stresses of simply supported laminated composite circular cylindrical shells within small number of unknowns.     

Distinct element simulation of grain alignment in mushy-state forging of magnets

A method for simulating the motion of grains in mushy-state forming of magnets is proposed on the basis of the distinct element method. The grains of the magnet are modelled to be a lot of elliptical elements, and the effect of the liquid phase on the motion of the grains is treated as viscous resistance to the movement. The motion of individual grains is obtained by solving the equations of motion for a time increment under the action of the elastic repulsive, frictional and viscous forces. Macroscopic plastic deformation of a metallic capsule containing the magnet is calculated by the viscoplastic finite element method, and the obtained motion of the interface between the capsule and magnet is used as a boundary condition in the distinct element simulation. The motion of grains in mushy-state plane-strain upsetting of a rare earth magnet contained in a steel capsule is chosen as an example of the simulation. The degree of grain alignment due to the upsetting increases as the reduction in height increases. The calculated degree of grain alignment agrees well with that for a model experiment using acrylic resin grains and a plasticine capsule.     

旋转压缩机内润滑油分布的模拟

压缩机内润滑油分布对压缩机性能有一定影响,但由于滚动转子式压缩机的全封闭性,对观察其内的润滑油的流动状况就造成了一定的困难,因此本文利用CFD商业软件STAR-CD,采用拉格朗日法模拟滚动转子式压缩机内润滑油的分布情况。同时还计算出了高转速下旋转式变频压缩机的油循环率(OCR)的大小,压缩机的电机各个部分的油滴数量、逃逸油滴数量及质量百分比等随曲轴角度的变化情况。计算结果表明冷媒及润滑油通过定子通孔和转子气隙流到电机上部,上升不是直线上升,而是随转子转动呈螺旋式上升。在高转速下,压缩机油循环率(OCR)较高且处于波动状态。     

An efficient method to predict steady-state vibration of three-dimensional piping system conveying a pulsating fluid

The dynamic equations of motion for a three-dimensional piping system conveying a harmonically pulsating fluid contain time-varying terms attributable to the fluid pulsating in the pipe. In this study, finite element formulation for this three-dimensional piping system was performed. The stiffness and damping matrices in the finite element modeling vary according to time because of the effects of the harmonically pulsating fluid. The frequency-domain method based on eigenvalue analysis cannot be used in this kind of problem. Conventional numerical time-domain methods require substantial computational efforts. An efficient numerical method to predict the steady-state time response of the piping system was presented. In this method, simultaneous equations were constructed by comparing the coefficients of a Taylor series expansion instead of directly solving the problem in the time domain. The accuracy and efficiency of this method were validated by comparison with a conventional numerical integration method.     

求解非定常不可压湍流的SMAC隐式方法

基于简化标记和单元(Simplified marker and cell,SMAC)方法,发展一种在任意曲线坐标系中求解三维非定常不可压湍流Reynolds时均方程的隐式数值方法。控制方程包括以逆变速度为变量的动量方程、压力Poisson方程和k–e 湍流模型方程,控制方程的离散在三维标记和单元(Marker and cell,MAC)交错网格系统中进行。为提高方程数值计算的稳定性,动量方程、k方程和e 方程对流项离散均采用Chakravarthy-Osher总变差衰减(Total variation diminishing,TVD)格式。动量方程、k方程和e 方程离散后的代数方程组采用循环三对角阵算法(Cyclic tridiagonal matrix algorithm,CTDMA)方法进行求解,Poisson方程离散后的代数方程组采用Tschebyscheff超线性松弛(Successive linear over relaxation,SLOR)方法交替方向迭代求解。用该方法自编程序对简化后的射流放水阀内非定常流场进行数值模拟,计算结果和试验结果吻合。     

Coupled modification of natural frequencies and buckling loads of composite cylindrical panels

This paper proposes a new method for performing predefined simultaneous modification of natural frequencies and buckling loads of composite cylindrical panels. The method is based on the fact that both natural frequencies and buckling loads are eigenvalues of an algebraic system of simultaneous equations. First- and second-order derivatives of these eigenvalues are calculated and the first two terms in Taylor expansion are used for developing a modification procedure that is defined as an inverse eigenvalue problem. A four-layered composite cylindrical panel with an arbitrary angle-ply stacking sequence is considered as a case study and several simultaneous modifications for natural frequencies and buckling loads are carried out. It is shown that the proposed method can perform the predefined modification with an acceptable accuracy even for large perturbations in objective functions.     

Stress singularities at angular corners in first-order shear deformation plate theory

The first-known Williams-type singularities caused by homogeneous boundary conditions in the first-order shear deformation plate theory (FSDPT) are thoroughly examined. An eigenfunction expansion method is used to solve the three equilibrium equations in terms of displacement components. Asymptotic solutions for both moment singularity and shear-force singularity are developed. The characteristic equations for moment singularity and shear-force singularity and the corresponding corner functions due to ten different combinations of boundary conditions are explicated in this study. The validity of the present solution is confirmed by comparing with the singularities in the exact solution for free vibrations of Mindlin sector plates with simply supported radial edges, and with the singularities in the three-dimensional elasticity solution for a completely free wedge. The singularity orders of moments and shear forces caused by various boundary conditions are also thoroughly discussed. The singularity orders of moments and shear forces are compared according to FSDPT and classic plate theory.     

Prediction of turbulent heat transfer downstream of an abrupt pipe expansion

Turbulent flow and heat transfer characteristics downstream of a sudden circular pipe expansion are predicted by using the full Reynolds stress model. The uniform wall temperature condition is imposed to the downstream wall. The governing differential equations are discretized by finite volume method with power-law scheme. The results show that the precise inlet conditions taken from the experimental data improve the results, but that the overall magnitude of Nusselt number is still under-predicted due to the use of conventional wall functions.     

求解复杂轴扭振动力特性的一种近似分析方法

应用模态摄动法求解非均质变截面复杂轴的扭转振动的模态特性。在这一方法中,选择与复杂轴约束条件相同、等截面均匀轴的扭转振动解析模态函数作为近似分析的基函数,采用Ritz展开和摄动分析相结合的方法,把复杂轴扭振的变系数微分方程的求解,转化为一组代数方程组的求解。虽然这一方法应用了结构振动分析中常用的Ritz展开原理,但避免了关于模态广义坐标的特征值问题的求解,通过代数方程组的求解,可逐一求得复杂轴的扭转振动的模态特性,简化了求解的难度。通过2个算例的分析表明,该方法简单实用,且具有较高的精度。     

机械密封静环密封性试验工装设计

机械密封的制造质量是终缩聚釜能否正常运行生产出合格产品的关键.设备的密封由动静环的接触面与0形圈来保证.密封试验原理即设备实际使用过程中的密封原理.从动、静环的制造工艺及结构来看,如果动、静环本身密封性不合格的话,那么问题应该出在镶装处.密封试验时,气体只能从镶四氟块处泄露,这就达到了静环四氟在不受压力情况下测试其密封...