Interaction of Two-Dimensional Trailing Vortex Pair with a Shear Layer

The basic laws governing the interaction of a two-dimensional vortex pair with a shear layer of constant thickness are considered. The main idea of the study is to develop and adapt a simplified representation of a hydrodynamic flow based on a point-vortex model simulating the actual interaction of full-scale vortex patterns over the ground surface. It is shown that vortices with vorticity opposite in sign to the shear layer may stop or even ricochet from this layer, while the other vortex may penetrate through the layer. Numerical results are presented as plots and analyzed     

变参数层状地基动力柔度系数的近似计算方法

介绍一个求解参数层状地基动力柔度系数的近似求解方法，这一方法的基本思想是将变参数层状地基等效的为均匀层状地基，这样便可应用目前已经获得的各种解析解的研究成果，使问题简化。     

Interaction of a submerged turbulent jet with a solid wall

The turbulent layer of a wall jet has been analyzed in many theoretical and experimental studies [1–10]. Most theoretical investigations are based on the simultaneous solution of the equations of the turbulent jet and the boundary layer that forms at the wall. The differences lie in the methods used to correlate the velocity and temperature distributions, as well as in the friction and heat-transfer laws employed. In this article we present a method based on the further development of the idea of conservation of the laws governing wall turbulence with respect to change in boundary conditions.     

Boundary layer separation and asymptotics from 1904 to 1969

The aim of this Note is to follow the spreading of the idea of asymptotic analysis in fluid mechanics (more precisely the laminar boundary layer). We will focus on the actors who worked on the problem of boundary layer separation from 1904 to 1969. This correspond to the invention of the “boundary layer” concept by Prandtl in 1904 and the invention of the “triple deck” in three different papers in 1969. The rationalization of the methods by the GALCIT group allowed one to solve, with exactly the same tools, problems at small and large Reynolds number (or problems with a small parameter). This story starts in Göttingen and goes to California before coming to London and Moscow.     

A Rigorous Derivation of the Coupling of a Kinetic Equation and Burgers’ Equation

In this article, we investigate the kinetic/fluid coupling on a toy model, which we obtain rigorously from a hydrodynamical limit. The idea is that at the level of the full kinetic model, the coupling is obvious. We then investigate the coupling obtained when passing into the limit. We show that, especially in presence of a shock stuck on the interface, the coupling involves a kinetic layer known as the Milne problem. Due to this layer, the limit process is quite delicate and some blow-up techniques are needed to ensure its strong convergence.     

风浪充分发展下海面阻力系数的数值研究

考虑海气界面附近大气边界层内海浪充分发展情况下的海气动量交换．根据Ｄｏｎｅｌａｎ（１９８２）的观点建立海气界面模型，采用ｋ ε模式以计算湍流流场．所得流场结构包括风速、湍流动能、湍能耗散及湍流粘性系数等都较合理；计算的海面阻力系数ＣＤ在中等风速时与实测结果符合良好．     

Diffraction of solitary water waves around three-dimensional floating bodies

By using the matched asymptotic expansion method and the idea of edge layer, a mathematic model for describing the interaction between weakly nonlinear shallow-water waves and three-dimensional floating bodies is formed in the paper. As a numerical example, the diffraction of a solitary wave around a vertically floating circular cylinder has been investigated and the results are presented. The present method can further be extended to the study of wave diffraction around floating bodies of general shape. The project is supported by the National Natural Science Foundation of China.     

Calculation of nonstationary elastic waves in an isotropic layer

A plane problem of nonstationary waves in an infinite isotropic layer is considered. A normal force begins to act on the boundary of the layer at the instant t=0. The opposite side of the layer is free from stresses. Using integral transformations, the solution of the problem is obtained in terms of transforms. Expanding the transform solution in a series of exponential powers and inverting each term of the resulting series, the exact solution of the problem is analytically determined. The fields of stresses and velocities in the layer are calculated. The use of analytical relationships for the calculation, in contrast to the calculation with finite-difference methods, allows us to fairly accurately determine the wave pattern and to eliminate the specific effects inherent in the difference equations. The calculation algorithm used in this work allows us to calculate the solutions of the problem at any point of the layer. The results presented give an idea about the distribution of stresses and velocities of particles across the thickness and in the longitudinal direction. The calculation of nonstationary problems by summing over waves, as is done in the present work, side by side with the methods presented in [1, 2], allows transient wave processes in the layer to be represented in a more complete manner.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnlcheskoi Fizikl, No. 4, pp. 148–155, July–August, 1973.     

Numerical method for the system of reaction-diffusion equations with a small parameter

This paper deals with the numerical method for the system of reaction-diffusionequations with a small parameter.It is difficult to solve the problems of this kindnumerically because of the boundary layer efect.Besed on singular perturbed theory andGreens’function,we have established the difference scheme that is suited for the solution tothe problems.It e introduce an idea of feasilbe equidistant degree a here.And this provesthat if a≥2.the scheme converges in l,m norm with speed O.h \t)uniformly.     

NON-LINEAR DYNAMIC MODEL RETRIEVAL OF SUBTROPICAL HIGH BASED ON EMPIRICAL ORTHOGONAL FUNCTION AND GENETIC ALGORITHM

Aiming at the difficulty of accurately constructing the dynamic model of subtropical high, based on the potential height field time series over 500 hPa layer of T106 numerical forecast products, by using EOF(empirical orthogonal function) temporal-spatial separation technique, the disassembled EOF time coefficients series were regarded as dynamical model variables, and dynamic system retrieval idea as well as genetic algorithm were introduced to make dynamical model parameters optimization search, then, a reasonable non-linear dynamic model of EOF time-coefficients was established. By dynamic model integral and EOF temporal-spatial components assembly, a mid-/long-term forecast of subtropical high was carried out. The experimental results show that the forecast results of dynamic model are superior to that of general numerical model forecast results. A new modeling idea and forecast technique is presented for diagnosing and forecasting such complicated weathers as subtropical high.     

Circumferential temperature distribution during nucleate pool boiling outside smooth and modified horizontal tubes

In the work an approach to avoid a circumferential temperature distribution existing during nucleate pool boiling on a horizontal cylinder within low heat flux densities is presented. The idea of the approach is local heat transfer enhancement by a porous layer application on a part of the heating surface. An experiment on nucleate pool boiling heat transfer from horizontal cylinders to saturated R141b and water under atmospheric pressure is reported. Experiments have been conducted using stainless steel tubes with the outside diameter between 8 mm and 23 mm with the active length of 250 mm. The outside surface of the tubes was smooth or partially coated with a porous metallic layer. In particular, measurements of inside circumferential temperature distribution have been performed.     

Hypersonic flow of nonequilibrium air over blunt bodies

A numerical method is described for computing nonequilibrium three-dimensional supersonic flow of a gas in the shock layer over the forward surface of blunt bodies with discontinuities of shape. The basic idea is to divide the original system of differential equations into two subsystems, which are solved in succession: first for the gasdynamic variables, the velocity components and the pressure, and then for the relaxation parameters and the enthalpy. To calculate the velocity components and the pressure we use the iterative marching method [1, 2] in the form given in [3]. The relaxation equations and the enthalpy equation are integrated numerically along the stream lines. A discussion is given of the effect of nonequilibrium of physical and chemical reactions on the distribution of parameters in the inviscid shock layer and on the aerodynamic coefficients of blunt bodies in hypersonic air flow. The unsteady aerodynamic coefficients are calculated by the curved body method [4]. The computational algorithm takes the form of a program in “ALGOL-60” for the BéSM-6 computer.     

基于分层数据搜索的数据驱动算法研究

数据驱动计算力学是一种直接利用材料应力应变数据驱动力学仿真计算的新技术.该方法通过反复遍历数据库,为数据驱动模型中的每一个积分点搜索并匹配最佳应力应变数据,使得在高维度和高密度的大规模数据库时计算效率不高.在此背景下,论文提出一种分层数据搜索方案,替换原有的遍历式数据搜索方式,以提升数据驱动的计算效率.该方案的核心思想是将大规模数据库切割成多层级子数据库,并利用树形搜索原理,减小单次搜索数据的范围,降低数据搜索的时间成本,达到提升计算效率的目的.文中简要介绍了数据驱动计算力学的基本步骤,并给出了分层数据库的构造方案,最后结合算例,讨论了数据库分层数量和分层方式对数据驱动计算效率的影响.     

高超声速溢流冷却实验研究

高超声速溢流冷却是一种新型的飞行器热防护方法,基本思想为:在高热流区布置溢流孔,控制冷却液以溢流方式流出,之后通过飞行器表面摩阻作用展布为液膜,形成热缓冲层以降低飞行器表面热流. 目前,溢流冷却技术还处于探索阶段,实现工程应用前还需开展大量的实验验证和机理研究工作. 本文首次开展溢流冷却的实验研究工作,采用热流测量、液膜厚度测量及液膜流动特性观测技术,搭建了完善的溢流冷却风洞实验平台,对溢流冷却热防护性能和高超声速条件下液膜流动规律进行了初步研究. 研究表明:(1) 高超声速流场中通过溢流能够在飞行器表面形成液膜并有效隔离外部高温气流,可降低飞行器表面热流率;(2) 楔面上的液膜前缘流动是一个逐渐减速的过程,增加冷却液流量液膜厚度变化不明显,但液膜前缘运动速度增大;(3) 液膜层存在表面波,在时间和空间方向发生演化,导致液膜厚度的微弱扰动;(4) 液膜层存在横向展宽现象,即液膜层宽度大于溢流缝宽度. 原因是液膜层与流场边界层条件不匹配,存在压力梯度,迫使冷却液向低压区流动,从而展宽液膜层,并且流量越高,横向展宽现象越明显.      

湍流的相干结构:推演方法和结果

本文讨论壁面湍流发展的相干结构的观点.在简要的历史文献综述后,我们回顾一些基本观点, 并且介绍相干结构的思想.基于大量主要是由实验所得的结果,本文通过广泛运用的事件检 测技术,探讨湍流边界层内部和外部区域发生的现象.我们从边界层内部区域发生的现象、 边界层外部大尺度运动的发展和涡结构动力学的角度来描述流动的现象.在文章的 第2部分,介绍从背景流动中推演出湍流相干结构的各种方法以及在各种方法框架下所得到的结果, 讨论速度梯度张量不变量、压力的Hessian矩阵分析和本征正交分解等方法.每一个过程 都有``相干结构'的特定的定义,满足恰当的数学构架,并可以对湍流数据做相干结构动力 学分析.这一工作可能会对当前流体动力学家在湍流研究中用到的最新理论和技术的传播有 所贡献.     

浅水孤立波在三维浮体上的绕射

浅水域中非线性水波运动的控制方程通常是经过深度平均的Boussinesq方程。然而,这一方程在浮体近旁或水下障碍物附近不再适用,在这些区域,流动在水深方向的变化不容忽略,本文应用匹配渐近展开法和边缘层(edge layer)思想,建立了浅水弱非线性波与三维浮体相互作用的数学模型,作为算例,求解了浅水孤立波在垂直圆柱形浮体上的绕射.本方法可以推广到波在一般浮体上绕射的情况。     

Self-consistent parabolized stability equation (PSE) method for compressible boundary layer

The parabolized stability equation (PSE) method has been proven to be a useful and convenient tool for the investigation of the stability and transition problems of boundary layers. However, in its original formulation, for nonlinear problems, the complex wave number of each Fourier mode is determined by the so-called phase-locked rule, which results in non-self-consistency in the wave numbers. In this paper, a modification is proposed to make it self-consistent. The main idea is that, instead of allowing wave numbers to be complex, all wave numbers are kept real, and the growth or decay of each mode is simply manifested in the growth or decay of the modulus of its shape function. The validity of the new formulation is illustrated by comparing the results with those from the corresponding direct numerical simulation (DNS) as applied to a problem of compressible boundary layer with Mach number 6.     

Exact Solutions for a Thick Elastic Plate with a Thin Elastic Surface Layer

A procedure has been developed in previous papers for constructing exact solutions of the equations of linear elasticity in a plate (not necessarily thin) of inhomogeneous isotropic linearly elastic material in which the elastic moduli depend in any specified manner on a coordinate normal to the plane of the plate. The essential idea is that any solution of the classical equations for a hypothetical thin plate or laminate (which are two-dimensional theories) generates, by straightforward substitutions, a solution of the three-dimensional elasticity equations for the inhomogeneous material. In this paper we consider a thick plate of isotropic elastic material with a thin surface layer of different isotropic elastic material. It is shown that the interface tractions and in-plane stress discontinuities are determined only by the initial two-dimensional solution, without recourse to the three-dimensional elasticity theory. Two illustrative examples are described.     

Application of generalized images method to contact problems for a transversely isotropic elastic layer on a smooth half-space

The idea, first used by the author for the case of crack problems, is applied here to solve a contact problem for a transversely isotropic elastic layer resting on a smooth elastic half-space, made of a different transversely isotropic material. A rigid punch of arbitrary shape is pressed against the layer’s free surface. The governing integral equation is derived; it is mathematically equivalent to that of an electrostatic problem of an infinite row of coaxial charged disks in the shape of the domain of contact. The case of circular domain of contact is considered in detail. As a comparison, the method of integral transforms is also used to solve the problem. The main difference of our integral transform approach with the existing ones is in separating of our half-space solution from the integral transform terms. It is shown that both methods lead to the same results, thus giving a new interpretation to the integral transform as a sum of an infinite series of generalized images.