Transition Matrix Method for Determining Stress Distribution of an Inhomogeneity in Elastostatic Medium

The transition matrix method has been extensively utilized to solve scattering in elastodynamic media. It is based on the reciprocity theorem, continuity of the interface boundary conditions, and applicable to arbitrary shape of inhomogeneity in systematic matrix multiplication. However, the transition matrix method has never been applied to determine stress distribution in elastostatic media. One important reason is the problem of the shortage of the basis functions of the elastostatic media that must be used to develop the transition matrix. This study investigates the required basis functions, and finds a set thereof that include Love??s special solutions of three dimensional elastostatics and three vector functions that are applicable to elastic waves. The proposed basis functions also can be adopted to derive the three significant orthogonality conditions for reciprocity at the surface of the inhomogeneity, which are useful in developing the transition matrix. The novel basis functions make the process of derivation of the T-matrix in elastostatics similar to that in elastodynamics. This process is illustrated for a spherical inhomogeneity that embedded in an elastic medium and stress patterns are compared with Goodier??s solutions, demonstrating high accuracy.     

The Multi-point Optimization of Shock Control Bump with Constant-Lift Constraint Enhanced with Suction and Blowing for a Supercritical Airfoil

Both shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of SCB and suction and blowing. These flow control methods are used separately or together on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow equations are solved using Roe’s averages scheme and a gradient-based adjoint algorithm is used to find the optimum location and shape of all devices. It is shown that the simultaneous application of blowing and SCB (hybrid blowing/SCB) improves the average aerodynamic efficiency at off-design conditions by 18.2 % in comparison with the clean airfoil, while this increase is only 16.9 % for the hybrid suction/SCB. We have also studied the SWBLI and how the optimization algorithm makes the flow wave structure and interactions of the shock wave with the boundary layer favorable.     

用于吸力式基础离心机模拟的动力加载设备

吸力式桶形基础广泛地应用于海洋油气开发的海洋平台。在冬季，渤海冰排会对平台产生强烈的冲击，引起振动。本文介绍了一套用于土工离心机实验的动力加载设备，并介绍了该套设备在模拟吸力式桶形基础在受到等效动冰载作用下的响应的实验研究情况及实验结果。结杲表明，当载荷幅值超过一个临界值时，地基上部会发生软化甚至液化。超孔隙水压从土体上部到下部，从桶形基础壁面到远处逐渐减小。在动载荷作用下，桶形基础和临近土体会发生大的沉降。桶形基础尺寸越小，动载荷响应越大。     

Similarity Laws for the Velocity Distribution and the Reynolds Tensor Components in the Wall Region of a Turbulent Boundary Layer with Injection and Suction

Similarity laws of the distributions of the average velocity, tangential stress, and mean-square transverse velocity fluctuation are established in an intermediate zone of a turbulent boundary layer with injection and suction. This zone is located in the neighborhood of the wall outside the viscous sublayer. The similarity relationship for the velocity profile is a generalization of the well-known logarithmic law to include the case of the presence of a mass flow at the wall.     

Optimum nozzle configurations for two-phase flows

The structure of the optimum supersonic contour of an axisymmetric Laval nozzle is investigated within the framework of the nonequilibrium polydisperse two-phase flow model. In formulating the variational problem attention is focused on taking into account a restriction that makes it possible to construct an optimum contour with no or limited particle fall out. Tomsk. Translated from Izvesriya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 36–45, March-April, 1994.     

离心压缩机径向吸气室的流动损失分析和改进设计

为提高在径向吸气务件下的离心压缩机性能,在吸气室内采用分流叶片方法控制径向吸气导致的畸变流动.结果表明,分流叶片虽然增加了吸气室内的流动损失,但是能够降低叶轮进口进气畸变,改善叶轮叶片受力分布及提高压缩机级的性能.在此基础上,进一步通过改进分流叶片叶型而减小流动分离损失,提高了压缩机的级性能.     

直接控制网格节点分布的曲线网格生成技术研究

指出了Thompson与Thomas曲线网格生成方法中控制网格分布的调节函数的问题所在,克服了Thomas曲线网格生成法中边界处局部线性化近似假定的缺陷,经过严格推导得出一组新的调节函数P、Q的表达式,并给出了曲线网格生成实例.实例检验表明,该调节函数能够对复杂边界的单连通域或多连通域生成理想的曲线网格,即边界处网格正交,内部网格分布能够适应物理量场变化的情形.在实际水利工程流场数值模拟中,该方法能够准确地使用边界条件,提高求解的精确度.     

Optimum plastic design for multiple sets of loads

Summary We study optimum plastic design of structures made up, or conceived as assemblies of finite elements, each having an elemental piece-wise linear rigid-plastic behaviour. Since cost function linearly dependent on design variables are considered, optimization problems in linear programming are encountered. Allowance is made for design dependent mass forces, and for some technological constraints. The design growing process is studied in the case of various sets of alternative applied loads, and the optimality conditions are written in a proper geometrical form which leads to a generalization of the concept of Foulkes mechanism.

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Sommario Si studia il progetto plastico ottimale di strutture formate di elementi finiti, ciascuno avente un comportamento globale rigido-plastico linearizzato a tratti. Si considerano funzioni costo dipendenti linearmente dalle variabili di progetto, e pertanto si va incontro a problemi di ottimizzazione nell'ambito della programmazione lineare. Tenendo conto delle forze di massa e di eventuali vincoli tecnologici, viene analizzato il processo di crescita del progetto nel caso in cui la struttura è sottoposta a diversi sistemi alternativi di carichi, e si scrivono le condizioni di ottimalità in una appropriata forma geometrica, la quale conduce a una generalizzazione del concetto di meccanismo di Foulkes.

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Capital bold-face letters are matrices, small bold-face letters are vectors. 0 is a vector having only zero entries. The tilde posed upon a vector or a matrix means “traspose of”. Other meanings are:     

Optimum shape of lifting bodies for hypersonic velocities

An attempt is made at solving the variational problem as to the shape of the body possessing a maximum aerodynamic quality, without using some of the simplifying assumptions proposed earlier [1–4]; an attempt is also made to discover the effect of blunted leading edges on the parameters of the optimum bodies.Kazan'. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 82–86, January–February, 1972.     

Optimum material design for functionally gradient material plate

Summary Steady thermal stresses in a plate made of a functionally gradient material (FGM) are analyzed theoretically and calculated numerically. An FGM plate composed of PSZ and Ti-6Al-4V is examined, and the temperature dependence of the material properties is considered. A local safety factor is used for evaluation of the FGM's strength. It is assumed that top and bottom surfaces of the plate are heated and kept at constant thermal boundary conditions. The pairs of the surface temperatures, for which the minimum local safety factor can be of more than one, are obtained as available temperature regions. The temperature dependence of the material properties diminishes, available temperature region as compared with that for an FGM plate without it. The available temperature region of the FGM plate is wider than that of the two-layered plate, especially for the surface temperatures which are high at the ceramic surface and low at the metal side. The influence of different mechanical boundary conditions is examined, and available temperature regions are found to be different, depending on the mechanical boundary conditions. The influence of the intermediate composition on the thermal stress reduction is also investigated in detail for the surface temperatures which are kept at 1300 K at the ceramic surface and 300K at the metal side. Appropriate intermediate composition of the FGM plate can yield the local safety factor of one or more for the four mechanical boundary conditions at once. For the two-layered plate there does not exist, however, any appropriate pair of metal and ceramic thicknesses which would yield the local safety factor of one or more for the four mechanical boundary conditions at once. The influence of the intermediate composition on the maximization of the minimum stress ratio depends on the mechanical boundary conditions. Finally, the optimal FGM plates are determined.     

简支梁大变形的优化算法

提出一种求解几何非线性问题的优化算法,并研究了简支梁的几何非线性大变形问题。首先取简支梁大变形后的平衡状态为研究对象,分别创建它的变分模型和微分模型;然后基于微分模型,通过动坐标的迭代关系式求得微段端点坐标,构建微段端点未知坐标的目标函数;最后确定简支梁几何非线性大变形的最优化问题,并编制相应优化程序进行求解。通过分析典型算例,并同有限元方法的计算结果相比较,表明提出的优化算法在求解强几何非线性大变形问题中的正确性,为处理几何非线性大变形问题提供了一种新方法。     

Transition Modelling for General Purpose CFD Codes

The paper addresses modelling concepts based on the RANS equations for laminar-turbulent transition prediction in general-purpose CFD codes. Available models are reviewed, with emphasis on their compatibility with modern CFD methods. Requirements for engineering transition models suitable for industrial CFD codes are specified. A new concept for transition modeling is introduced. It is based on the combination of experimental correlations with locally formulated transport equations. The concept is termed LCTM – Local Correlation-based Transition Model. An LCTM model, which satisfies most of the specified requirements is described, including results for a variety of different complex applications. An incremental approach was used to validate the model, first on 2D flat plates and airfoils and then on to progressively more complicated test cases such as a three-element flap, a 3D transonic wing and a full helicopter configuration. In all cases good agreement with the available experimental data was observed. The authors believe that the current formulation is a significant step forward in engineering transition modeling, as it allows the combination of transition correlations with general purpose CFD codes. There is a strong potential that the model will allow the 1st order effects of transition to be included in everyday industrial CFD simulations.     

圆管过渡流态的间歇因子

用激光测速方法研究圆管流动的湍流间歇现象．实验表明,间歇湍流首先在管壁发生,逐渐向下游扩张．随着雷诺数的增加,间歇因子γ＝０．５的转捩界面逐渐向入口推移,一直到Ｒｅ＝９８８７,整个管流才变成间歇湍流和充分湍流     

评定磨合表面的最佳形貌参数

磨合是新机器设备投入使用之前的必经过程，而且对摩件的表面形貌都要发生明显的变化，因此，如何评定磨合表面形貌值得深入研究，实际上，磨合是对摩件的表面形貌由初始状态逐渐趋于相互吻合的过程，因而磨合之后配对表面的形貌具有相关性，在此基础上上，研究提出了利用互相关结构函数评定磨合，这种评定方法具有能够同时反映两个表面形貌和对表面形貌变化反映敏感，以及能够将表面轮廓的峰和谷分开考虑等优点，理论分析和应用实例     

基于功能的基础隔震结构一体化优化设计

“投资-效益”准则作为基于功能的抗震设计的一个基本原则，反映了现代结构抗震设计思想的一个重要转变，即从以往只注重结构安全，向全面注重结构的功能、安全及经济等诸多方面发展。本文根据“投资-效益”准则，建立了基于功能的基础隔震结构一体化优化设计模型，其中目标函数考虑了结构生命周期内的总造价，包括结构初始造价和不同发生概率的大震、中震、小震作用下的结构损失期望，约束条件包括隔震层水平位移、上部结构层间变形等，优化过程中同时对上部结构截面尺寸和隔震器参数进行优化。算例表明，本文建立的基于功能的隔震结构优化模型是合理可行的，可为实际隔震结构的优化设计提供参考。     

Optimum design of hierarchical stiffened shells for low imperfection sensitivity

A concept of hierarchical stiffened shell is proposed in this study, aiming at reducing the imperfection sen- sitivity without adding additional weight. Hierarchical stiffened shell is composed of major stiffeners and minor stiff- eners, and the minor stiffeners are generally distributed between adjacent major stiffeners. For various types of geo- metric imperfections, e.g., eigenmode-shape imperfections, hierarchical stiffened shell shows significantly low imper- fection sensitivity compared to traditional stiffened shell. Furthermore, a surrogate-based optimization framework is proposed to search for the hierarchical optimum design. Then, two optimum designs based on two different opti- mization objectives （including the critical buckling load and the weighted sum of collapse loads of geometrically imperfect shells with small- and large-amplitude imperfections） are compared and discussed in detail. The illustrative example demonstrates the inherent superiority of hierarchical stiffened shells in resisting imperfections and the effectiveness of the proposed framework. Moreover, the decrease of imperfection sensitivity can finally be converted into a decrease of structural weight, which is particularly important in the development of large-diameter launch vehicles.     

网壳结构健康监测中的传感器优化布置

针对网壳结构健康监测提出了一种以损伤可识别性与模态可观测性相协调为目标的传感器优化布置的方法.由于模态数目的选取对基于损伤灵敏度分析的传感器优化布置有很大的影响,因此本文建立了一种同时包含模态独立性信息和损伤灵敏度信息的Fisher信息矩阵,并选取合适的模态数目,然后发展了一种以信息矩阵最大和条件数最小为准则的多目标优化算法.空间网壳数值算例表明,本文提出的传感器优化方法能简单、有效地为空间结构传感器优化布置提供可行方案.     

Optimum Geometric Design of the Edge Curves for Cutting Blades

Abstract

This paper reports on an investigation of the effect of the curvature of the profile of rotary blades, scissors, and similar cutting instruments on the cutting process, and attempts to identify the optimal blade profile for particular mechanical requirements. Neglecting friction, the mechanics of cutting with rotary blades are reflected by a governing differential equation, which is derived from the geometry of the blade profile by following a method suggested by Freudenstein (1990 Freudenstein , F. ( 1990 ). On the mechanics and the design optimization of scissors . ASME Design Engin. Div. DE Cams, Gears, Robot and Mechanism Design 21st Biennial Mechanism Conf. 26 : 177 – 180 . [Google Scholar]). The optimal edge curves of the cutting blades are obtained through the solution of this equation. It is demonstrated that desirable relationships between input force and output force can be achieved by adjusting the curvature of the blades. As examples, the solutions of optimal profiles of scissors and teeth of rotary blades requiring constant ratio between input and output force are presented.     

Suction Induced Effects on the Fabric of a Structured Soil

This paper presents the mathematical modelling of the modification of the pore space geometry of a structured soil subjected to suction increase. Structured soil concepts are first introduced considering different fabric units, such as aggregates and fissures. The numerical modelling of the structural evolution is based on experimental test results in which the evolution of the structure of the samples subjected to different suctions is determined using the mercury intrusion porosimetry technique. From this information, the macro and micropore volume evolutions are determined. The results show that drying produces a reduction in the soil total porosity which mainly corresponds to a reduction of the macropore volume. Associated with this phenomenon, an increase in micropore volume is also observed. The proposed model divides pore size distribution into three pore classes (micropores, macropores and non-affected areas). Using the concept of a suction-influenced domain, the proposed model is able to reproduce the main observed fabric evolution between the saturated and dry states.