Investigation of Alternative Length Scale Substitutions in Detached-Eddy Simulation

The objective of this work is the comparison of three different DES-style hybrid RANS/LES implementations based on the Wilcox k– model. The three variants are designed to investigate alternative methods of substitution of the DES length scale within the background Reynolds Averaged Navier-Stokes (RANS) model. Basis for comparison is provided by both the idealised case of the decay of isotropic turbulence (DIT) as well as the practical case of the massively separated, turbulent flow around an airfoil at high angle of attack. The results of the investigations are discussed in detail, the outcome of which is an emphasis of the importance of DIT as a method for calibration, as well as of the relative freedom with which alternative DES-inspired approaches can be implemented for flows of practical relevance.     

A fast and accurate graphical method for designing an air conditioning cooling coil

The aim of this paper is to develop a fast and simple accurate graphical method for designing the required cooling coil for an air conditioning system in which both the sensible and latent heat are transferred. The method has the following advantages:

1. Direct solution utilizing only Psychrometer charts.
2. Solution of combined heat and mass transfer problems occuring at pressures other than that of atmosphere.
3. Direct determination of boundary temperature at which dehumidification begins for that type of problem where a portion of the surface is in a dry condition.
4. Less effort required than trial and error method in determination of air condition leaving a counterflow coil of a given area.

The calculated values of the method showed a good agreement with the experimental results. The average deviation for the total heat is about + 15 % and for sensible heat is + 9 %, which are of positive nature and on the safe side for practical design purposes. The method is also useful for similar practical application.     

含损伤材料的热粘塑性本构关系及其应用

对含损伤材料的热粘塑性本构关系进行了较全面和较系统的研究。首先对半径回归方法的本构公式给出了最一般性的严格证明,并讨论了其适用性和局限性。接着以应力空间中的屈服函数和Drucker公设为基础,以材料本构关系的内变量理论为工具,推导并建立了增量型热粘塑性本构关系的普适形式和计算流程。然后结合实践中最常用的几类本构模型,导出了所建立的增量型动态本构关系的具体形式,并简要总结了其各自的特点和意义。最后通过一些典型的波传播和高速冲击问题的算例,介绍了所建立的本构关系及计算方法的具体应用情况和效果,从而展示了其理论意义和应用前景。     

Stability of theoretical model for catastrophic weather prediction

Stability related to theoretical model for catastrophic weather prediction, which includes non-hydrostatic perfect elastic model and anelastic model, is discussed and analyzed in detail. It is proved that non-hydrostatic perfect elastic equations set is stable in the class of infinitely differentiable function. However, for the anelastic equations set, its continuity equation is changed in form because of the particular hypothesis for fluid, so "the matching consisting of both viscosity coefficient and incompressible assumption" appears, thereby the most important equations set of this class in practical prediction shows the same instability in topological property as Navier-Stokes equation, which should be avoided first in practical numerical prediction. In light of this, the referenced suggestions to amend the applied model are finally presented.     

On the domain of asymptotic stability of nonlinear nonconservative systems

For some nonlinear, nonconservative systems which are asymptotically stable in the small one must consider the likelihood of loss of stability in the large. In this paper an analysis of the stability of such systems is presented, with special emphasis placed on the Zubov construction procedure for Liapunov functions. Two practical engineering interpretations of the resulting n-dimensional stability domain are introduced, the first imposing a restriction on the energy of initial disturbances, and the second placing limits on the phase variables. These stability criteria are applied to a second order and a fourth order system.The results presented in this paper were obtained at the University of Waterloo in the course of research sponsored by the National Research Council of Canada, and by NASA under Grant NsG 605.     

On the Solution of Elliptic Equation (sum from k-0 to n) akΔkφ=0 and Its Application in Mechanics

In this paper, the solution of elliptic equation (sum from k-0 to n) a_kΔ^kφ=0 is discussedin detail by the method of separation of variables in complex field. The general solution which can be used in the approximation to the boundary conditions of the practical problems is presented. Two practical examples in mechanics are given.     

A practical synchronization approach for fractional-order chaotic systems

A practical synchronization approach is proposed for a class of fractional-order chaotic systems to realize perfect \(\delta \)-synchronization, and the nonlinear functions in the fractional-order chaotic systems are all polynomials. The \(\delta \)-synchronization scheme in this paper means that the origin in synchronization error system is stable. The reliability of \(\delta \)-synchronization has been confirmed on a class of fractional-order chaotic systems with detailed theoretical proof and discussion. Furthermore, the \(\delta \)-synchronization scheme for the fractional-order Lorenz chaotic system and the fractional-order Chua circuit is presented to demonstrate the effectiveness of the proposed method.     

The equations of complete depth-averaged turbulence model in general orthogonal coordinates

ＤｉｎｇＹａｎ（丁剡）;ＺｈｏｕＸｕｅｙｉ（周雪漪）;ＹｕＣｈａｎｇｚｈａｏ（余常昭）;ＬｉａｎｇＤｏｎｇ（梁栋）（ＲｅｃｅｉｖｅｄＪｕｎｅ１４,１９９４;ＣｏｍｍｕｎｉｃａｔｅｄｂｙＢｉａｎＹｉｎｇｕｉ）ＴＨＥＥＱＵＡＴＩＯＮＳＯＦＣＯＭＰＬＥＴＥ...     

Periodic heat transfer in the fins with variable thermal parameters

ＰＥＲＩＯＤＩＣＨＥＡＴＴＲＡＮＳＦＥＲＩＮＴＨＥＦＩＮＳＷＩＴＨＶＡＲＩＡＢＬＥＴＨＥＲＭＡＬＰＡＲＡＭＥＴＥＲＳ￥ＹａｎｇＸｉａｎｇｘｉａｎｇ（杨翔翔）;ＨｅＨｏｎｇｚｈｏｕ（何宏舟）（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌＥｎｇｉｎｅｅｒ...     

Über eine neue Form der Reynoldsschen Gleichung zur Schmier-Hydrodynamik

Übersicht Mit Substitutionen für die Spalthöhe und den hydrodynamischen Druck wird eine neue Differentialgleichung abgeleitet, welche an die Stelle der Reynoldsschen Gleichung tritt. Gegenüber dieser hat sie den Vorteil, nicht nur spezielle Lösungen — die mit dem physikalischen Geschehen meist nicht übereinstimmen-zu geben, sondern für alle praktisch wichtigen Fälle geschlossene Lösungen zu ermöglichen, sofern geeignete Ansätze für die Spaltkontur gewählt werden. Solche Ansätze lassen sich entsprechend dem Aufbau der neuen Differentialgleichung unschwer in einem Konturen-Katalog zusammenfassen, der für alle Bedürfnisse der Praxis ausreicht. Zwei Beispiele, deren Lösungen bekannt sind (die unendlich breite Platte und der unendlich breite Kreiszylinder), sollen der Einführung in die neue Methode dienen und die Genauigkeit aufzeigen. Im Hauptteil wird das bisher ungelöste Problem Kugel auf Ebene behandelt und der Verlauf des hydrodynamischen Druckes im Kugelspalt angegeben.

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Summary By substitutions for the distance across the gap and for the hydrodynamic pressure a new differential equation is derived which replaces the Reynolds equation. Compared to the latter the new equation has the advantage that it has analytical solutions not only in special cases which usually do not correspond to practical problems, but also in all essential practical cases if suitable expressions are chosen for the gap profile. Corresponding to the structure of the new differential equation such profile expressions can easily be listed up in a profile-catalogue which meets all practical requirements. Two examples with known results (the infinitely wide plate and the infinitely long cylinder) are presented for the purpose of introduction into the new method and for proof of accuracy. In the main part the problem of a sphere on a plate is treated which is still unsolved, and the hydrodynamic pressure profile between the two bodies is calculated.

     

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采用Ritz近似法建立客运专线下承式系杆拱桥侧向稳定承载力实用计算公式; 假定满足拱桥侧向弯扭边界条件的位移试函数, 建立系杆拱桥的主拱肋侧倾失稳结构势能的表达式,基于最小势能原理建立了下承式系杆拱桥侧倾失稳临界载荷实用计算公式. 采用该实用计算公式计算了某客运专线下承式系杆拱桥弹性侧向稳定承载力, 并与三维有限元屈曲计算结果进行比较, 结果表明: 该方法简单实用, 可准确地预测系杆拱桥侧倾临界载荷, 便于工程应用.     

The free energy of mixing for n-variant martensitic phase transformations using quasi-convex analysis

The construction of effective models for materials that undergo martensitic phase transformations requires usable and accurate functional representations for the free energy density. The general representation of this energy is known to be highly non-convex; it even lacks the property of quasi-convexity. A quasi-convex relaxation, however, does permit one to make certain estimates and powerful conclusions regarding phase transformation. The general expression for the relaxed free energy is however not known in the n-variant case. Analytic solutions are known only for up to 3 variants, whereas cases of practical interests involve 7-13 variants. In this study we examine the n-variant case utilizing relaxation theory and produce a seemingly obvious but very powerful observation regarding a lower bound to the quasi-convex relaxation that makes practical evolutionary computations possible. We also examine in detail the 4-variant case where we explicitly show the relation between three different forms of the free energy of mixing: upper bound by lamination, the Reuß lower bound, and a lower estimate of the -measure bound. A discussion of the bounds and their utility is provided; sample computations are presented for illustrative purposes.     

斜拉桥横向振动的半主动筋腱控制

对桥梁等大型土建结构在外扰作用下的振动实施控制是目前的一个研究热点,也是提高结构安全性与耐久性的一条重要途径。本文提出采用磁流变阻尼器（Ｍａｇｎｅｔｏ－Ｒｈｅｏｌｏｇｉｃａｌ Ｄａｍｐｅｒ,ＭＲＤ）与斜拉索构成的半主动筋腱（Ｓｅｍｉ－Ａｃｔｉｖｅ Ｔｅｎｄｏｎ）实现斜拉桥横向振动的半主动控制的原理,讨论了其可行性、具体控制方案和控制算法,给出了一对一双索斜拉桥模型在随机扰动作用下的振动控制仿真结果     

Theory of perfect plasticity of composite materials,taking account of volume compressibility

The practical importance and timeliness of the study of the mechanical macroscopic behavior of composite microinhomogeneous media are determined by its ability to give criteria for estimating the limiting load of various structural elements, the flow of multiphase dispersed systems, the deformation of materials made by powder metallurgy methods, etc. The theoretical prediction of the properties of composites is generally most effectively realized when their structural representations are based on the theory of random fields. Application of the strong isotropy hypothesis [1] for the statistical averaging of certain relations of a perfectly plastic body with microstructure permits the determination of its macroscopic yield surface.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 164–167, May–June, 1981.     

The turbulent boundary layer of dissociated gas in the initial section of a tube

Many theoretical and experimental papers [1–4] have been devoted to investigating the turbulent boundary layer in the initial section of a channel. For the most part, however, the flow of an incompressible fluid with constant parameters is considered. There are many practical cases in which it is of interest to treat the development of the turbulent boundary layer of gas in the initial section of a pipe when conditions are strongly nonisothermal. A solution of a problem of this type, based on the theory of limit laws, is given in paper [1]. The present article extends this solution to the case of the flow of a high-enthalpy gas when the effect of gas dissociation on the turbulent boundary layer characteristics must be taken into account. We shall consider the flow of a mixture of i gases which is in a frozen state inside the boundary layer, and in an equilibrium state on its boundaries. Formulas are derived for the laws of friction and heat exchange, and a solution is given for the turbulent boundary layer equations in the initial section of the pipe when the wall temperature is constant and the gas flows at a subsonic velocity.Finally the authors are grateful to S. S. Kutateladze for discussing the paper.     

Calculation of the rotational transition probabilities of diatomic molecules when they collide with heavy particles

The collisional rotational transition probabilities for molecule-molecule and molecule-atom interactions in three-dimensional space are calculated. The quasiclassical approach developed in [1] is used. Expressions are obtained that are suitable for practical calculations of single-quantum and double-quantum rotational transitions in diatomic molecules. The collisional rotational transition probabilities are averaged over the Maxwell velocity distribution and their dependence on the gas temperature is obtained. To illustrate the method the results of a calculation of the probabilities for HCl-HCl, HCl-He, CO-CO interaction are presented.     

Documentation and information on rheology: Present state and development in its design and application

Summary As the number of rheological and other scientific publications increases considerably year by year, documentation services should be used more extensively. The Deutsche Rheologische Gesellschaft (German Society of Rheology), 1 Berlin 45, Unter den Eichen 87, publishes at regular intervals and for an international reader audience the Documentation Rheology which contains a fairly complete collection of relevant literature subdivided into subject groups. The papers listed cover fundamentals of rheology, rheometry, rheological behaviour of polymer melts and solutions, plastics and rubber, metals, pastes, colloids and suspensions, solids, ceramics, concrete, pharmaceutical products and cosmetics, food stuffs, chemical engineering, forming processes, flow processes, mixing processes and so on.The documentation is available at a small charge. It has been published to make better use of the possibilities that lie in a systematic collection, arrangement, exploitation and application of findings achieved and published so far. Methodical and intensified research and development, as well as further rationalization and cost-saving measures in the field of practical application depend on a better utilization of existing findings. The above-mentioned documentation service covers basic research as well as technical application. With the aid of it literature search on general or more specific problems of research and practice can be done quicker and carried out much more easily. Literature search done this way guarantees that a research project will start from the current state of knowledge and that sufficient hints to solutions of practical problems are at hand. Moreover, the preparation and publication of literature reports will initiate a systematic evaluation of the numerous existing publications.With 1 table     

软岩流变的一种新的试验研究方法

研制了用于软岩流变的蠕变-松弛耦合试验仪,探讨了利用单级加载和逐级加载两种方式确定软岩流变参数和长期强度的蠕变-松弛耦合试验原理. 有关的具体试验表明,该仪器操作简便, 稳定性好,所得结果客观、可靠,可在工程中推广应用.     

沥青混合料蠕变柔量的一种实用模型及其应用

通过分析沥青混合料加载时的"固结效应"和卸载时的"永久变形"等流变学特征,提出了一个较为实用的流变学模型,并给出了模型参数的确定方法,该模型参数数目可多可少,且能满足Blotzmann叠加原理,可应用于应力随时间变化以及其它各种复杂应力状态的情况.     

Coalescence suppression in model immiscible polymer blends by nano-sized colloidal particles

The effect of nanometer sized silica particles (R16 nm) on the flow-induced morphology of immiscible polymer blends is studied. Polydimethylsiloxane (PDMS) and polyisobutylene (PIB) are chosen as model components. A stable droplet/matrix microstructure is obtained for blends of 30% PIB in 70% PDMS or vice versa. Rheological measurements are used to show that the silica particles alter the sensitivity of the of dispersed phase/matrix microstructure to shear flow. Coalescence is suppressed or at least slowed down on a practical time scale, especially when PDMS is the matrix phase. The effect of mixing conditions, pre-shear rate and particle concentration on the blend morphology are studied. Cryo-SEM is used to observe the accumulation of the particles at the interface. Blends stabilized by solid particles could provide an interesting alternative to blends compatibilized by block-copolymers.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.