气动声学Lighthill方程的Kirchhoff积分解分析

Lighthill的声类比(acoustic analogy)是目前气动声定量预测中应用最为广泛的一种方法。使用非齐次波动方程的Kirchhoff积分公式对Ligthhill方程进行求解。Kirchhoff公式中的延迟时间表示不同位置点声源对场点声压叠加时的相位作用,推导时强调延迟时间函数的导数运算。基于Kirchhoff积分公式对于有物体存在于流场中的情况,详细推导了Curle解,并对Curle公式中的各声源项进行了分析。文章有助于气动声学初学者正确地认识声类比理论,加深对Curle公式的理解。     

基于大涡模拟和Lighthill声类比的孔腔流动发声特性研究

孔腔流动发声是气动声学研究领域重要的课题,基于大涡模拟和Lighthill声类比方法,探讨了气体在孔腔流动的流激噪声的发声特性。模拟结果表明,孔腔边界层出口剪切涡、边棱处涡街和腔体内反馈涡的运动诱导了孔腔发声,具有明显的偶极子特性,在高频段腔体内激发了声学驻波模态。通过模拟与实验对比分析了不同流量下噪声量级以及频谱分布规律,研究结果表明:24 kHz以下的声频谱会表现出波峰小范围迁移;24 kHz以上频率对应的声压级随流量增大而增大;腔体长度和特征频率近似满足Strouher公式,即声频特征频率随腔体长度的增大而减小。上述研究结果为下一步设计在线监测安全阀泄漏的报警超声波发声器提供了理论依据。     

A Theory of Complexity, Periodicity and the Design Axioms

One of the topics that has received the attention of mathematicians, scientists and engineers is the notion of complexity. The subject is still being debated, as it lacks a common definition of complexity, concrete theories that can predict complex phenomena, and the mathematical tools that can deal with problems involving complexity. In axiomatic design, complexity is defined only when specific functional requirements or the exact nature of the query are defined. Complexity is defined as a measure of uncertainty in achieving a set of specific functions or functional requirements. Complexity is related to information, which is defined in terms of the probability of success of achieving the Functional Requirements (FRs). There are two classes of complexity: time-dependent complexity and time-independent complexity. There are two orthogonal components of time-independent complexity, i.e., real complexity and imaginary complexity. The vector sum is called absolute complexity. Real complexity of coupled design is larger than that of uncoupled or decoupled designs. Imaginary complexity can be reduced when the design matrix is known. As an example of time-independent imaginary complexity, the design of a printing machine based on xerography is discussed. There are two kinds of time-dependent real complexity: time-dependent combinatorial complexity and time-dependent periodic complexity. Using a robot-scheduling problem as an example, it is shown that a coupled design with a combinatorial complexity can be reduced to a decoupled design with periodic complexity. The introduction of periodicity simplifies the design by making it deterministic, which requires much less information. Whenever a combinatorial complexity is converted to a periodic complexity, complexity and uncertainty is reduced and design simplified.     

Liquid chromatography of macromolecules at the point of exclusion–adsorption transition

Liquid chromatography of macromolecules at the point of exclusion–adsorption transition (LC PEAT) is based on a controlled balance between entropic (exclusion) and enthalpic (adsorption) effects within LC system that results in the loss of separation according to the molar mass. Consequently, polymer species exhibiting the same adsorptivity but different sizes are eluted in one single retention volume that roughly corresponds to the total volume of liquid within column. At the same time, other kinds of polymer chains with different adsorptivities are eluted according to either exclusion or adsorption mechanism. This may allow discrimination and independent characterization of chemically different species such as functionalized macromolecules, block- and graft- copolymers and polymer blends. Differences in the physical structure of macromolecules, for example in their stereoregularity represent an alternative separation parameter. Four approaches to the exclusion–adsorption transition in liquid chromatography of macromolecules were so far proposed, viz. liquid chromatography at the critical adsorption point (LC CAP), liquid chromatography at the theta exclusion-adsorption conditions (LC TEA), liquid chromatography under limiting conditions of adsorption (LC LCA) and liquid chromatography under limiting conditions of desorption (LC LCD). The principles of LC CAP, LC TEA, LC LCA and LC LCD and their applicability are elucidated and the advantages and problems of particular methods are discussed in the present review. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Tuning Parameter Tolerance Design: Foundations, Methods, and Measures

In this paper, a novel technique is presented to solve tolerance design problems. To achieve the desired performance tolerance, the technique uses a subtle, but significant, change in the design: the addition of a tuning parameter in place of an increase in component precision. Statistical models are used to develop a framework for the tuning parameter design method. Also developed is a new, dimensionless design metric which ranks candidate tuning parameters. A step-by-step method is developed for the application of tuning parameters using this metric. The step-by-step tuning parameter design method is applied to a heavy-duty manual stapler as a clarifying example.     

‘Signposting’, A Parameter-driven Task-based Model of the Design Process

This paper addresses the need for computer support in aerospace design. A review of current design methodologies and computer support tools is presented, and the need for further support is discussed, with particular reference to the early formative stages of the design process. A parameter-based model of design is proposed, founded on the assumption that a design process can be constructed from a predefined set of tasks. This is supported by knowledge of possible tasks in which the confidence in key design parameters is used as a basis for identifying, or signposting, the next task. A prototype implementation of the signposting model, for use in the design of helicopter rotor blades, is described and results from trials of the tool are presented. Further areas of research are discussed.     

Truncated branch-and-bound,schedule-construction,and schedule-improvement procedures for resource-constrained project scheduling

We present heuristic procedures for approximately solving large project scheduling problems with general temporal and resource constraints. In particular, we propose several truncated branch-and-bound techniques, priority-rule methods, and schedule-improvement procedures of types tabu search and genetic algorithm. A detailed experimental performance analysis compares the different heuristics devised and shows that large problem instances with up to 1000 activities and several resources can efficiently be solved with sufficient accuracy.

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Received: July 26, 2000 / Accepted: May 15, 2001     

Operator separation of variables for adiabatic problems in quantum and wave mechanics

Linear problems in mathematical physics where the adiabatic approximation is used in a wide sense are studied. From the idea that all these problems can be treated as problems with an operator-valued symbol, a general regular scheme of adiabatic approximation based on operator methods is proposed. This scheme is a generalization of the Born–Oppenheimer and Maslov methods, the Peierls substitution, etc. The approach proposed in this paper allows one to obtain “effective” reduced equations for a wide class of states inside terms (i.e., inside modes, subbands of dimensional quantization, etc.) with possible degeneration taken into account. Next, by application of asymptotic methods, in particular the semiclassical approximation method, to the reduced equation, the states corresponding to a distinguished term (effective Hamiltonian) can be classified. It is shown that the adiabatic effective Hamiltonian and the semiclassical Hamiltonian can be different, which results in the appearance of “nonstandard characteristics” while passing to classical mechanics. This approach is used to construct solutions of several problems in wave and quantum mechanics, particularly problems in molecular physics, solid-state physics, nanophysics and hydrodynamics.     

Interface projection techniques for fluid–structure interaction modeling with moving-mesh methods

The stabilized space–time fluid–structure interaction (SSTFSI) technique developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM) was applied to a number of 3D examples, including arterial fluid mechanics and parachute aerodynamics. Here we focus on the interface projection techniques that were developed as supplementary methods targeting the computational challenges associated with the geometric complexities of the fluid–structure interface. Although these supplementary techniques were developed in conjunction with the SSTFSI method and in the context of air–fabric interactions, they can also be used in conjunction with other moving-mesh methods, such as the Arbitrary Lagrangian–Eulerian (ALE) method, and in the context of other classes of FSI applications. The supplementary techniques currently consist of using split nodal values for pressure at the edges of the fabric and incompatible meshes at the air–fabric interfaces, the FSI Geometric Smoothing Technique (FSI-GST), and the Homogenized Modeling of Geometric Porosity (HMGP). Using split nodal values for pressure at the edges and incompatible meshes at the interfaces stabilizes the structural response at the edges of the membrane used in modeling the fabric. With the FSI-GST, the fluid mechanics mesh is sheltered from the consequences of the geometric complexity of the structure. With the HMGP, we bypass the intractable complexities of the geometric porosity by approximating it with an “equivalent”, locally-varying fabric porosity. As test cases demonstrating how the interface projection techniques work, we compute the air–fabric interactions of windsocks, sails and ringsail parachutes.     

Internet-Based Design Catalogue for the Shaft and Bearing

The Internet and World Wide Web (WWW) are evolving as an important communication technology. This paper examines the development of an Internet-based online catalogue on the WWW. An interactive website is prepared that helps a remote designer to design shafts and bearings based on various input parameters provided. The web site also provides solid models of the shaft to perform CAD and FEM analysis. This permits the user to make further investigations, and helps to modify the design satisfactory.     

Evaluation Metrics for the Rating and Optimization of Snap-fits

Current snap-fit design guides recommend sizing snap-fit features on the basis of insertion force and allowable strain during assembly. Retention force information in such guides is often inaccurate, although this is considered to be the primary attribute of the snap-fit after assembly. The authors contend that these (insertion force, allowable strain, retention force) are not the only critical performance criteria for snap-fit features. Designers have to contend with several other constraints and design requirements. Additional performance metrics for snap-fit features are proposed by drawing upon considerable experience with plastic part design issues. Locking ratio, dimensional and volumetric retention force, consideration of the characteristic dimension of the joint and snap-fit, feature stiffness, required over-insertion and consideration of snap-fit strength relative to part strength are proposed to supplement currently used metrics for evaluating and rating snap-fit designs. The applicability of these metrics is illustrated with real-life examples, and their merits and demerits discussed. A chart of achievable locking ratios for different snap-fit topologies is presented for use as a design tool for the initial selection of snap-fit topologies. Its use as a rational basis for selection and optimization of snap-fits is suggested. Adoption of proposed metrics will allow designers to better quantify, and thereby optimize the performance of, snap-fit features. These ideas will be built upon in the future, and used as a basis for a comprehensive snap-fit selection and detailed design tool.     

Quantum Dot in the Pseudo-gap Sate with Spin–Orbit Interaction

We study the linear conductance in quantum dot with spin–orbit interaction coupled to Fermi liquid leads with a power-low density of states. The conductance at zero temperature is calculated as a function of the power exponent from the density of state ρ(ω)∼|ω−E _F | ^r at the Fermi energy E _F and the different energy rates. The phase shift of the conduction electrons is also r-dependent. The model can be used in the study of the quantum phase transition.     

Synthesis of the Bi-2222 Compounds of Bi–Sr–Ln(Zr)–Cu–O (Ln = Sm,Eu, Gd,and Dy)

Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi₂Sr₂- (Ln_1−x Ce _x )₂Cu₂O_10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln_1−x Ce _x )₂O₂ block between two CuO₅ pyramids in the crystal structure. The tetravalent ions of Ce⁴⁺ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi₂Sr₂(Ln_2−x Zr _x )Cu₂O _z (Ln = Sm, Eu, Gd, and Dy) systems, where Zr⁴⁺ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce⁴⁺. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi₂Sr₂(Gd_2−x Zr _x )Cu₂O _z system are also reported.     

Improving Systems by Combining Axiomatic Design, Quality Control Tools and Designed Experiments

This paper presents an approach for solving design problems in existing designs. A design analysis with Axiomatic Design, called Design Object Analysis, describes a product or a system in terms of Customer Needs (CNs), Functional Requirements (FRs), Design Parameters (DPs) and Process Variables (PVs), as well as their associated Design Matrices (DMs). In this paper, the design analysis is combined with a thorough investigation of possible problems within the design, utilizing the seven quality tools, noise factor analysis, and designed experiments to form an approach for quality improvements and problem solving. The Design Object Analysis helps secure valid input-factors to the designed experiments, and the designed experiments correct or improve the assumptions made in the Design Object Analysis. Thus, a combination of product modeling by Axiomatic Design and designed experiments overcomes shortcomings of the two methods. The benefits of performing a Design Object Analysis, as compared to other methods, become clear when it comes to evaluating the results from the designed experiment, and preventing the problem. Once the critical parameters are confirmed, and the design matrices are updated, suggested design improvements can then be checked against the design matrices, and the system effect of a design-change-order can be estimated. The approach described in this paper was successfully applied and verified in a case study at a large automotive company.     

Planning and scheduling in the process industry

Since there has been tremendous progress in planning and scheduling in the process industry during the last 20 years, it might be worthwhile to give an overview of the current state-of-the-art of planning and scheduling problems in the chemical process industry. This is the purpose of the current review which has the following structure: we start with some conceptional thoughts and some comments on special features of planning and scheduling problems in the process industry. In Section 2 the focus is on planning problems while in Section 3 different types of scheduling problems are discussed. Section 4 presents some solution approaches especially those applied to a benchmark problem which has received considerable interest during the last years. Section 5 allows a short view into the future of planning and scheduling. In the appendix we describe the Westenberger-Kallrath problem which has already been used extensively as a benchmark problem for planning and scheduling in the process industr y.     

Symmetric collocation BEM/FEM coupling procedure for 2-D dynamic structural–acoustic interaction problems

 This paper presents a symmetric collocation BEM (SCBEM)/FEM coupling procedure applicable to 2-D time domain structural–acoustic interaction problems. The use of symmetry for BEM not only saves memory storage but also enables the employment of efficient symmetric equation solvers, especially for BEM/FEM coupling procedure. Compared with symmetric Galerkin BEM (SGBEM) where double boundary integration should be carried out, SCBEM can reduce significantly the computing cost. Two numerical examples are included to illustrate the effectiveness and accuracy of the proposed method. Received: 2 November 2001 / Accepted: 27 May 2002     

中药多糖的提取、分离纯化及其含量测定方法概述

近几年多糖备受关注,本文详细介绍了中药多糖的提取、分离纯化及其含量测定的各种方法。     

A Solution for the Incompressibility Dilemma in Partitioned Fluid–Structure Interaction with Pure Dirichlet Fluid Domains

In a subset of fluid–structure interaction (FSI) problems of incompressible flow and highly deformable structures all popular partitioned approaches fail to work. This also holds for recently quite popular strong coupling approaches based on Dirichlet–Neumann substructuring. This subset can be described as the special case where the fluid domain is entirely enclosed by Dirichlet boundary conditions, i.e. prescribed velocities. A vivid simple example would be a balloon with prescribed inflow rate. In such cases the incompressibility of the fluid cannot be satisfied during standard alternating FSI iterations as the deformation of the coupling surface is determined by the structural displacement that usually does not know about the current constraint on the fluid field. By analyzing this deficiency of the partitioned algorithm a small augmentation is proposed which allows to overcome the dilemma of incompressibility and fixed boundary velocities by introducing the volume constraint on the structural system of equations. In contrast to the original accelerated strong coupling partitioned method, the relaxation which ensures convergence of the iteration over the different fields has now to be performed on the coupling forces rather than on the displacements. In addition, two alternative approaches are discussed for the solution of the dilemma. The capability of the proposed method to deal with largely changing volumes of enclosed fluid is demonstrated by means of numerical examples.     

Evidences of the Charge–Lattice Interaction in Undoped Cuprates

The anomalous temperature dependence of the angle resolved photoemission spectra (ARPES) in undoped cuprates is investigated by using a self-consistent approach within the t-J-Holstein model. The cooperative interplay of coupling of the hole to magnetic fluctuations and strong electron–phonon interaction turns out crucial to explain the experimental data. The model is extended to take into account the longer-range hoppings t^′ and t^′′. The effect is a large anisotropy of the electron–phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments.      

Automatic Meshing and Remeshing in the Simultaneous Engineering Context

This paper presents a method to integrate in a better way the finite element method in the CAD/CAM process for two-dimensional problems, through efficient and automatic meshing and remeshing procedures. During the design step, the lack of integration between geometric modeling and numerical analysis remains a crucial problem and it still tends to restrain the use of finite element methods to a small number of engineers. Here we tackle the problem of the automatic remeshing of an object in the context of minor changes in its geometry and topology without restarting the mesh generation from the beginning. We have developed a mesh generator that is able to adapt a previous mesh, through two complementary strategies (for 2D cases) to a new geometry without destroying the whole initial discretization. We also present the possible extension of these concepts to three-dimensional problems.