水力机械非定常流动的三维涡方法计算

利用拉格朗日型涡方法计算了混流式水轮机转轮内部的非定常流动. 采用高精度的边界元法计算域内势流速度以满足固体边界不可穿透条件, 通过在固体边界上导入新生涡满足边界的无滑移条件. 利用拉格朗日法计算涡元的运动, 而离散涡元之间的诱导速度则通过毕奥-萨伐尔公式结合快速多级子算法和自适应树结构算法获得. 通过对某混流式转轮水轮机在设计工况及非设计工况下的数值模拟, 以及模拟结果与实验测量的对比, 验证了该拉格朗日涡方法在计算转轮内部高雷诺数非定常流动中的有效性.     

船舶水润滑尾轴承当量半径等效计算及其摩擦学性能研究

水润滑尾轴承摩擦磨损性能是影响船舶工作性能的主要因素之一,合理预测水润滑尾轴承工作过程中的摩擦系数对其性能评估具有重要意义.目前对于水润滑尾轴承摩擦系数的理论计算公式已经存在.但由于销盘试验下无法有效获取当量半径,公式在销盘试验条件下的实用性不佳.对此在总结了边界润滑条件下,水润滑尾轴承摩擦机理的基础上,通过在CBZ-1销盘试验机上进行大量试验来进行当量半径等效参数计算公式的总结与摩擦系数经验公式的验证.研究结果表明:(a)在使用理论摩擦系数计算公式的前提下,当量半径等效参数公式拟合合理,具备较高准确性;(b)试验材料的理论摩擦系数与实际摩擦系数误差较小,为同类型试验摩擦性能研究提供了理论与试验基础;(c)水润滑尾轴承材料在工作过程中的摩擦力来源主要分为滞后摩擦力、犁沟摩擦力以及黏着摩擦力.当其处于边界润滑状态下时,滞后摩擦力为主要的摩擦力来源.该研究为水润滑尾轴承的等效当量半径在销盘试验条件下的应用提供了试验基础.     

压电体椭圆孔边的力学分析

基于复变函数的方法,以PZT-4材料为例,分别采用精确电边界条件和非导通电边界条件进行了远场均匀载荷作用下的横观各向同性压电体椭圆孔的力学分析并与相关结果进行对比。结果表明当椭圆孔退化为圆孔时,无论在远场作用力载荷或电载荷,两种电边界条件下的结果均能完全吻合。随着椭圆孔的愈加尖锐化,非导通电边界条件逐渐不能适用。     

采用黏弹性人工边界时显式算法稳定性条件

黏弹性人工边界是处理无限域波动问题常用的数值模拟方法。采用显式时域逐步积分算法进行计算时,受黏弹性人工边界的阻尼、刚度等影响,人工边界区的稳定性比内部计算域的更严格,尚无明确、实用的稳定性判别准则,这限制了黏弹性人工边界在显式动力分析中的应用。针对二维黏弹性人工边界,利用基于局部子系统的稳定性分析方法和基于传递矩阵谱半径的稳定性判别准则,给出了可代表整体模型局部特征的不同边界子系统的稳定性条件解析解。通过对比分析不同计算区域的稳定性条件及其影响因素,证明了整体模型的稳定性由角点子系统控制。在此基础上,获得了含黏弹性人工边界的整体模型在显示动力计算中的统一稳定性判别准则和简化实用计算方法。在实际应用中,令积分时间步长满足稳定性条件,即可顺利完成整体模型的动力计算。以上研究可为将黏弹性人工边界应用于显式动力计算时积分时间步长的合理选取提供参考。     

Heat flux sensor with minimal impact on boundary conditions

A technique for determining the heat transfer on the far surface of a wall based on measuring the heat flux and temperature on the near wall is presented. Although heat transfer measurements have previously been used to augment temperature measurements in inverse heat conduction methods, the sensors used alter the heat flow through the surface, disturbing the very quantity that is desired to be measured. The ideal sensor would not alter the boundary condition that would exist were the sensor not present. The innovation of this technique in that it has minimal impact on the wall boundary condition. Since the sensor is placed on the surface of the wall, no alteration of the wall is needed. The theoretical basis for the experimental technique as well as experimental results showing the heat flux sensor performance is presented.     

复合材料周期结构数学均匀化方法的一种新型单胞边界条件

数学均匀化方法是计算周期复合材料结构的有效方法之一,单胞边界条件施加的合理性直接决定了影响函数控制方程的计算效率和精度,进而影响均匀化弹性参数和摄动位移的计算精度.本文首先将单胞影响函数作为虚拟位移处理,给出了单胞在结构中真实的边界条件,结果表明,四边固支适合作为二维结构单胞边界条件;其次,针对二维结构提出了超单胞周期边界条件,有效提高了影响函数的计算精度,并使用与虚拟位移相对应的虚拟势能泛函验证超单胞周期边界条件的有效性;最后,利用数值分析验证多尺度渐进展开方法的计算精度,强调了二阶摄动的必要性.     

A VARIATIONAL INEQUALITY APPROACH FOR NON-STEADY SEEPAGE FLOW THROUGH THREE-DIMENSIONAL FRACTURE NETWORK

为了求解裂隙岩体有自由面非稳定渗流问题,将Darcy定律延拓至整个研究区域,使得潜在溢出边界条件满足Signorini型边界条件,建立了三维裂隙网络非稳定渗流问题的抛物型变分不等式（parabolic variational inequality,PVI）提法,并证明其与偏微分方程（partial differential equation,PDE）提法的等价性,从而将自由面上的流量条件以及潜在溢出边界上的互补条件转化成自然边界条件,降低该问题求解难度。同时给出了基于PVI提法的有限元数值求解方法,通过与交叉裂隙模型理论解的对比分析,证明了该方法的正确性。最后将该方法对含复杂三维裂隙网络的边坡进行非稳定渗流分析,计算结果表明该方法对于复杂裂隙网络求解具有较强的可靠性和适应性。     

AN ARTIFICIAL BOUNDARY CONDITION FOR TWO-DIMENSIONAL INCOMPRESSIBLE VISCOUS FLOWS USING THE METHOD OF LINES

We design an artificial boundary condition for the steady incompressible Navier–Stokes equations in streamfunction–vorticity formulation in a flat channel with slip boundary conditions on the wall. The new boundary condition is derived from the Oseen equations and the method of lines. A numerical experiment for the non-linear Navier–Stokes equations is presented. The artificial boundary condition is compared with Dirichlet and Neumann boundary conditions for the flow past a rectangular cylinder in a flat channel. The numerical results show that our boundary condition is more accurate.     

Development of three-dimensional disturbances in a boundary layer

In the region of transition from a two-dimensional laminar boundary layer to a turbulent one, three-dimensional flow occurs [1–3]. It has been proposed that this flow is formed as the result of nonlinear interaction of two-dimensional and three-dimensional disturbances predicted by linear hydrodynamic stability theory. Using many simplifications, [4, 5] performed a calculation of this interaction for a free boundary layer and a boundary layer on a wall with a very coarse approximation of the velocity profile. The results showed some argreement with experiment. On the other hand, it is known that disturbances of the Tollmin—Schlichting wave type can be observed at sufficiently high amplitude. This present study will use the method of successive linearization to calculate the primary two- and three-dimensional disturbances, and also the average secondary flow occurring because of nonlinear interaction of the primary disturbances. The method of calculation used is close to that of [4, 5], the disturbance parameters being calculated on the basis of a Blazius velocity profile. A detailed comparison of results with experimental data [1] is made. It developed that at large disturbance amplitude the amplitude growth rate differs from that of linear theory, while the spatial distribution of disturbances agree s well with the distribution given by the natural functions and their nonlinear interaction. In calculating the secondary flow an experimental correction was made to the amplitude growth rate.     

弹性动力学轴对称问题的理论解

本文给出了弹性动力学轴对称问题基本方程的一种理论解。它由满足非齐次边界条件的准静态解和满足齐次边界条件的动态解的叠加构成。在求得准静态解后,代入基本方程,得到动态解所需满足的非齐次方程。由相应的齐次方程的特征值问题,定义了有限Hankel变换。通过这种变换及Laplace变换,求得动态解,从而得到了一个完整的理论解。文中通过对一个实例求解,表明该方法求解过程简便,实用,求解结果精确。     

Discontinuous boundary implementation for the shallow water equations

Quasi‐bubble finite element approximations to the shallow water equations are investigated focusing on implementations of the surface elevation boundary condition. We first demonstrate by numerical results that the conventional implementation of the boundary condition degrades the accuracy of the velocity solution. It is also shown that the degraded velocity leads to a critical instability if the advection term is present in the momentum equation. Then we propose an alternative implementation for the boundary condition. We refer to this alternative implementation as a discontinuous boundary (DB) implementation because it introduces at each boundary node two independent mass–flux values that result in a discontinuity at the boundary. Numerical results show that the proposed DB implementation is consistent, stabilizes the quasi‐bubble scheme, and leads to second‐order accuracy at the surface elevation specified boundary. Copyright © 2004 John Wiley & Sons, Ltd.     

An analytical solution of rectangular laminated plates by higher-order theory

I.IntroductionSincecompositematerialshavesuperiormechanicalproperties,theyarewidelyconcernedbytechnicians.Fromtheclassicallaminatetheorytothefirst-ordersheardeformationtheoryandfromthehigher-ordertheorytotheelasticitytheory,thetheoriesoflaminatedplatesofcompositemeterialsgetfastdevelopment.TheNaviersolutionofsimplysupportedrectangularplateswasdevelopedbyWhitneyandLeissalllforclassicallaminatetheory.TheNaviersolutionwasdevelopedbyWhitneyandPaganol'1forthefirst-ordersheardeformationtheory.Th…     

CONTROL OF BLADE FLUTTER USING CASING WITH ACOUSTIC TREATMENT

Control of blade flutter by use of a nonrigid wall may have several advantages compared with the existing method of suppressing blade flutter; but it indeed leads to numerous theoretical problems which have never been clearly elucidated by the existing theories. In the present investigation a new lifting surface model has been suggested based on the application of generalized Green's function theory and double Fourier transformation technique, which is expressed as various upwash integral equations and the corresponding kernel function. In particular, it is found that the change of wall boundary condition not only affects the eigenvalues of the system but also the eigenfunction normalizing factor in comparison with a rigid boundary condition, and it is these variations that finally affect the flow and acoustic field. In addition, the numerical results show that whether a nonrigid wall has positive or negative effect on suppressing blade flutter will mainly depend on what admittance value the wall possesses. It is clear that this conclusion has two implications. One is that there is indeed some possibility for designing a liner for suppressing blade flutter. The second is that modern jet engines using a nonrigid wall or liner to suppress the noise can introduce a detrimental effect on blade flutter stability.     

插值型维数分裂无网格法中本质边界条件施加方法研究

本文以求解三维波动方程为例,介绍了改进的插值型维数分裂无单元Galerkin方法,推导了方程的弱形式,构造了具有插值特性的逼近函数,建立了可直接施加本质边界条件的离散方程组,研究不同本质边界条件施加方法对计算结果的影响．本文列举了三种常用的处理本质边界条件的方法：直接配点法、对角元素置大数法和对角元素化一法．选取了三个数值算例,分别采用不同的本质边界条件施加方法,分析计算结果,证明了三种施加方法的有效性,讨论了每种施加方法的优缺点,并针对问题需求选出合适的施加本质边界条件的方法．与改进的无单元Galerkin方法相比,改进的插值型维数分裂无单元Galerkin方法具有更高的计算精度和更快的计算速度．     

冲击下宏观相边界的传播

研究了具有CdS型相变本构材料的宏观相边界传播规律。相边界包括纯新相和混合相两段。纯新相段可用逐步近似法,混合相段则必须用数值方法求解。给出了三种加卸载应力边界条件下的算例。在突加突卸的应力边界条件下,给出了相边界传播的解析解。在算例中,各种解法得到的结果彼此很好符合。     

同轴圆柱壳流固耦合附加质量研究

论文根据堆本体内窄间隙同轴设备支承筒的结构特征、边界条件和窄间隙环腔内流体流速,将结构简化为一端固定一端自由的同轴圆柱壳,将圆柱壳内外的流体简化为无旋、无黏、不可压缩流体.同轴圆柱壳通过流体压力场实现耦合,其径向位移模态决定了窄间隙流体域的压力场,故采用级数形式的圆柱壳径向正交位移模态构建既满足一端固定一端自由边界条件...     

新型涡轮流量计的理论模型简

基于动量力矩定理和流体边界层理论,建立了一新型涡轮流量计的理论模型. 利用该理论模型可以分析叶轮几何参数对流量计计量性能的影响. 以一DN50 涡轮流量计为例,利用本文所建立的理论模型对该流量计的仪表系数进行了计算,并在一体积管标准装置对该流量计的仪表系数进行标定. 结果表明,计算值和实验值较为吻合,误差在±;3.5% 以内,验证了模型的有效性,从而为仪表的结构优化设计提供了理论依据.     

An adjoint method for the calculation of remote sensitivities in supersonic flow

This paper presents an adjoint method for the calculation of remote sensitivities in supersonic flow. The goal is to develop a set of discrete adjoint equations and their corresponding boundary conditions in order to quantify the influence of geometry modifications on the pressure distribution at an arbitrary location within the domain of interest. First, this paper presents the complete formulation and discretization of the discrete adjoint equations. The special treatment of the adjoint boundary condition to obtain remote sensitivities or sensitivities of pressure distributions at points remotely located from the wing surface are discussed. Secondly, we present results that demonstrate the application of the theory to a three-dimensional remote inverse design problem using a low sweep biconvex wing and a highly swept blunt leading edge wing. Lastly, we present results that establish the added benefit of using an objective function that contains the sum of the remote inverse and drag minimization cost functions.