bluuebunny/crossref_metadata_2025 huggingface dataset:
Stable Response of Nonclassically Damped Mechanical Systems
Authors: Nicholson D. W.
Published: June 2009

Selected recent literature is surveyed on several topics pertaining to the time response of a discrete, time-invariant, linear, multiple degree-of-freedom mechanical system. These topics have been the subjects of extensive recent investigation, and are believed to be useful in design, modeling and computational simulation. Attention is restricted to systems with nonclassical damping, by which is meant that the systems do not observe classical normal modes. Several specific results are described in some detail. Topics covered include conditions for asymptotic stability, conditions for underdamping and overdamping, localization of system eigenvalues, and response bounds under various types of excitations. The final topic presented is the relation between system stability and the numerical stability of time integration methods used to calculate the system time response.
On Some Developments in Direct Methods of the Calculus of Variations
Authors: Leipholz H. H. E.
Published: June 2009

One of the significant events in mathematical physics, in this century, is the introduction and further development of the so-called direct methods which were first applied by Rayleigh and Ritz to possibly extremum but at least stationary variational problems; they have been extended by Galerkin to problems which are not even stationary but involve only variations in the sense of the principle of virtual work. It is shown in this paper how, in the course of a further development of direct methods, the question of a proper choice of coordinate functions and of a proof of convergence of the method in the case of nonextremum and nonstationary variational functionals have been solved. Since an application of direct methods depends largely on the availability of basic functionals preferably with at least the property of stationarity, it is shown how such functionals can be obtained by switching from the conventional energy space to more abstract spaces involving adjoint problems or variations of operators rather than functions. Also, the question of an application of direct methods to initial value problems has been considered, as well as a modification of Galerkin’s equations which allows one to avoid cumbersome boundary conditions. To sum up, one can say: the paper shows how recent research has made direct methods much more general and more broadly applicable than was the case at the time of their introduction to mathematical physics at the beginning of this century.
Composite Laminate Components for Robotic and Machine Systems: Research Issues in Design
Authors: Thompson B. S.
Published: June 2009

Composite materials, which have already revolutionized the aerospace industry and are being increasingly utilized in the automotive industry to fabricate lightweight, high-stiffness components are an essential ingredient for the next generation of robotic and machine systems. This trend in the increasing utilization of composite materials has been precipitated by the insatiable demands in the international marketplace for machinery which has superior performance characteristics than the current products. As more stringent performance characteristics are imposed upon the design specifications for the next generation of machine systems, it is becoming increasingly apparent that the conventional metals are already being employed near the limits of their inherent physical properties and the designer must now utilize the superior properties of modern polymeric composite materials. This paper examines the proposition of fabricating machine systems with these advanced materials by reviewing the advantages to be gained from this approach prior to identifying the frontier problems and discussing potential solution strategies.
Plate Vibration Research in Japan
Authors: Yamada G. , Irie T.
Published: June 2009

A variety of plates has been extensively used as important structural elements in many industrial fields. Therefore, there have been many papers available on the vibration of plates in Japan as well as in other countries. Unfortunately, most of them have been written in Japanese, and they are unknown in other countries. The aims of this article are to review approximately 200 papers published in 1951 through 1985 in this country, and present important engineering information on plate vibrations.
Mechanics of “Bumps” in Coal Mines: A Discussion of Violent Deformations in the Sides of Roadways in Coal Seams
Authors: Lippmann Horst
Published: June 2009

Since long ago rock bursting has belonged to the most hazardous of events causing damage to material and loss of human life in underground cavities. Nevertheless, attempts to understand the physical principles of rock bursting from the point of view of the mechanical and material sciences seem to be of fairly recent origin. The following article deals especially with rock bursting in coal mines. After a general introduction, approaches based on a specific property of the excavated material called “proneness-to-bursting” are reviewed. This is followed by a survey of structural approaches to the problem. Finally, an elementary structural model is presented, leading to simple approximate conditions for the risk of initiating rock bursts, or for its efficiency.
Advance in Ice Mechanics in Finland
Authors: Ma¨a¨tta¨nen Mauri
Published: June 2009

In Finland, 110 years of winter navigation has been a natural initiator of ice mechanics research. It has brought with it sea ice monitoring and statistics, ice forecasting, the testing of mechanical properties, ship and icebreaker model testing and full-scale trials, ice resistant aids-to-navigation, and theoretical modelling and numerical simulations. Lately, a lot of ice mechanics research has been devoted to arctic offshore applications. A summary of the major developments is given in this paper.
Advances in Ice Mechanics in West Germany
Authors: Schwarz Joachim
Published: June 2009

Ice research in West Germany (Federal Republic of Germany) started after World War II with the first small ice tank built at HSVA in Hamburg in 1958. The discovery of hydrocarbons in the Arctic and the membership in the Scientific Committee for Antarctic Research led to the need for model tests and the advancing ice modelling techniques. In 1984 a new, large ice model basin was built at HSVA. Substantial progress has been made in the experimental research of basic ice mechanics and ice forces for the past 20 years. Computational methods and quantum statistical approach have recently been introduced for the study of ice properties. Predicting methods of ice forces with model and full scale experiments have been investigated. This paper highlights West German contributions for the last 20 years.
Studies in Chaotic Vibrations of Buckled Beams
Authors: Hanagud S. , Abhyankar N. S. , Chander R.
Published: June 2009

We have studied chaotic vibrations of buckled beams with base excitations. Nonlinearities due to the stretching of the neutral axis, transverse stops and their combination have been studied. The resulting ordinary and partial differential equations have been integrated numerically. Results have been presented in the form of phase plane plots and bifurcation diagrams.
Some Engineering Applications of the Probabilistic Strength of Materials
Authors: Kittl P. , Di´az G.
Published: June 2009

Three types of aleatory variables can be considered here as determinants of the probabilistic strength of a structure, namely, material properties, boundary conditions, and external agents. The probability of fracture or yielding of some material subjected to external forces verifies F˜(V1 + V2, σ) = F˜(V1, σ) F˜(V2, σ), where F = 1 – F˜ is the cumulative probability of fracture or yielding and σ is a constant stress on the material. In this manner there can be treated general frameworks or truss structures, soil problems, pressure vessels in general, tunnels in the rock, fatigue, and finally seisms caused by sudden earth-crust fractures.
Nonconservative Components of Follower Forces in the Classical Shell Theory
Authors: Altman Wolf , Bevilacqua Luiz
Published: June 2009

An analysis of follower forces acting on shell structures is presented. Attention is focussed on the expressions of such forces as functions of the generalized displacements. Specific expressions for the follower forces are obtained, according to the order of magnitude of the strains and angles of rotation. For small strains the follower forces allow a decomposition into conservative and non-conservative components. This leads to the equations of dynamic stability of shell problems subjected to follower loads. The dynamic counterparts of Donnell-Mushtari-Vlasov stability equations are presented, by either retaining or omitting the prebuckling rotations.
A Case and Elastomer Annulus Under Lateral Impulse
Authors: Lindberg Herbert E. , Murray Yvonne D.
Published: June 2009

Fourier series and finite element solutions are given for stresses in a cylindrical case filled with an annulus of elastomeric material. The Fourier series solutions are for membrane stresses, which dominate at early time, and are given for three case-elastomer models: (1) a slide boundary model in which the case wall moves as a unit with the elastomer in radial motion but, with a weak bond between the case and elastomer, is free to slide relative to the elastomer in tangential motion, (2) a unit motion model for a well-bonded elastomer in which the case wall and elastomer are assumed to move together as a unit in both radial and tangential motion, and (3) a radiation boundary model in which tangential motion of the case wall radiates energy into a well-bonded elastomer. For typical case, elastomer and bond mechanical properties, the radiation boundary model gives the most appropriate solution, which differs substantially from the other solutions even for very soft elastomers. Finite element solutions agree closely with and support the validity of all three analytical models, which were used to guide the finite element “experiments” and interpret and generalize their results.
New Mixed Finite Element Formulations for Transient and Steady State Creep Problems
Authors: Loula Abimael F. D. , Guerreiro Joa˜o Nisan C.
Published: June 2009

We apply the mixed Petrov–Galerkin formulation to construct finite element approximations for transient and steady-state creep problems. With the new approach we recover stability, convergence, and accuracy of some Galerkin unstable approximations. We also present the main results on the numerical analysis and error estimates of the proposed finite element approximation for the steady problem, and discuss the asymptotic behavior of the continuum and discrete transient problems.
Subcritical Large-Amplitude Vibrations of Imperfect Rotating Shafts
Authors: Mazzilli C. E. N.
Published: June 2009

The effect of a geometrical imperfection, such as the axis flexural deformation, on the large-amplitude vibrations of a horizontal rotating shaft is analyzed with the aid of the Multiple Scales Method. Internal viscous damping and linear elasticity are assumed in the model. It is then seen that no matter how small the imperfection is, a “critical” speed of the order of half the classical critical speed arises, with relevant practical implications. A number of reported large-amplitude cases may eventually be explained this way. It is possible that events such as this will not appear in systems with high dry friction.
State Equations for a Spacecraft With Maneuvering Flexible Appendages in Terms of Quasi-Coordinates
Authors: Meirovitch L. , Kwak M. K.
Published: June 2009

This paper is concerned with the derivation of the state equations of motion for a spacecraft consisting of a main rigid platform and a given number of flexible appendages changing the orientation relative to the main body. The equations are derived by means of Lagrange’s equations in terms of quasi-coordinates. Assuming that the appendages represent distributed-parameter members, the state equations of motion are hybrid. Moreover, they are nonlinear. Following spatial discretization and truncation, the hybrid equations reduce to a system of nonlinear discretized state equations, which are more practical for numerical calculations and control design. To illustrate the effect of nonlinearity on the dynamic response during reorientation, a numerical example involving spacecraft with a membrane-like antenna is presented.
Dynamic Model for an Automotive Overhead Valve-Gear System
Authors: Me´ndez-Adriani J. A.
Published: June 2009

This research presents a lumped-parameter model, distinct from the ones developed until the present time, easily adaptable for its analog/hybrid simulation, and that combines favorably its simplicity and precision to represent appropriately an automotive valve gear system by means of the inclusion of the hydraulic lifter and of the viscous forces produced by its guide. The checking of this new mathematical model has been accomplished by means of a qualitative comparison with other models previously devised. This model will be useful in the design stage to predict the speed at which the valve jump occurs.
Damage in a Random Microstructure: Size Effects, Fractals, and Entropy Maximization
Authors: Ostoja-Starzewski Martin
Published: June 2009

In this paper a micromechanical approach to damage growth in graph-representable microstructures is presented. Damage is defined as an elastic-inelastic transition in the grain boundaries and is represented in terms of a binary or ternary random field Z on the graph. A method based on the percolation theory brings out the size effects in scatter of strength, and the fractal character of damage geometry, and thus provides a basis for a multifractal model of a range of damage phenomena. The Markov property of field Z leads to a description of Z in terms of Gibbs probability measures and establishes a link between the entropy of disorder of Z and the physical entropy of damage in the ensemble of material specimens. Derivation of stochastic constitutive laws is outlined using the formalism of free energy and the dissipation function extended to random media.
Towards the Unification of Acoustics and Fluid Mechanics
Authors: Branda˜o Mauri´cio P.
Published: June 2009

A comprehensive study of a modern acoustic technique is presented. The conservation laws of mass, momentum, and surface boundary conditions are cast in the form of an inhomogeneous wave equation, known today as Ffowcs Williams and Hawkings’ equation. The result is general, capable of addressing three-dimensional, nonlinear, and unsteady flow problems of compressible and viscous fluids. The Green’s function solution is used to transform the differential equation into integral form. The formulation is then linearized and viscosity is neglected. The pressure distribution on the surface of the NACA 0012 airfoil in subsonic non-lifting motion is determined. Comparison with experimental results shows good agreement, provided flow perturbations remain small. It is considered that the technique may evolve into an alternative aerodynamic method to current computational approaches.
Kinematic Approach in the Impact Problem of Rigid Bodies
Authors: Sinopoli A.
Published: June 2009

The aim of this work is to analyze, by means of a kinematic approach, the problem of the impact between rigid bodies, when the surfaces involved in the impulsive phenomenon are of finite extent. The formulation here adopted permits to use the Gauss variational principle of “least compulsion” and to formulate the dynamic evolution of the system, after an impact, as a minimization problem. In this case, among all the possible subsequent motions, the real one is that which minimizes the kinetic energy connected to the sudden velocities variations. Interesting results are obtained in the case of the impact between a rigid column (either monolithic or made of several blocks) and a rigid ground. In particular, it can be shown that if the previous motion of a rigid block is a rotation around its base corner edge, the motion after the impact is either a rototranslation or merely a translation, depending on the dimensional ratio. In any case, the subsequent motion is characterized by a component of sliding, so that the impact plays the role of filter between the possible degrees of freedom of the system and, at the same time, determines a possible coupling between rotation and translation. This conclusion is a novelty with respect to the results obtained in other papers [4–6], where a classical approach for the impact has been adopted.
The Influence of Hardening of the Supports on the Response of Structural Elements Liable to Buckling
Authors: Souza M. A.
Published: June 2009

Support conditions which change during the loading process are simulated by a simplified model. Equilibrium paths and characteristic curves are used to illustrate how the hardening of the supports can affect the response of structural elements under compressive loading. Damping is not included in the analysis.
Influence of Mass Distribution, Shear Deformation, and Rotatory Inertia on Flutter Loads
Authors: Suanno R. L. M. , Rosas e Silva R.
Published: June 2009

Classical problems of columns under tangential (follower) loads are analyzed for stability. A generalized Ritz technique is used in conjunction with a computer-oriented algorithm suitable for the flutter analysis of complex structural systems. A brief description of this technique is presented. The numerical approach allows for easy consideration of additional effects in classical problems such as the Beck and Leipholz columns. The influence of shear deformation, rotatory inertia, and concentrated mass at the tip of the column is shown in graphs and discussed.
Thermally Induced Interfacial Stresses in Elongated Bimaterial Plates
Authors: Suhir E.
Published: June 2009

The interfacial thermally induced shearing and peeling stresses in elongated bimaterial plates are determined on the basis of an elementary beam (long-and-narrow plate) theory. The utilized approach enables one to satisfy the stress-free boundary conditions at the short edges within the framework of an elementary analytical model. The obtained formulas are simple, easy-to-use, and clearly indicate how material and geometric characteristics affect the magnitude and the distribution of stresses. The suggested approach is applicable, generally speaking, to any elongated bimaterial or adhesively bonded structure, subjected to thermal or external loading. As an example of an external loading, we examine bending of a bimaterial plate on a circular mandrel. Such a test vehicle is being currently regarded by many reliability engineers in the microelectronics industry as an attractive means to evaluate attachment materials in adhesively bonded and soldered assemblies.
Exact Solutions of the Unsteady Navier-Stokes Equations
Authors: Wang C. Y.
Published: June 2009

The unsteady Navier-Stokes equations are a set of nonlinear partial differential equations with very few exact solutions. This paper attempts to classify and review the existing unsteady exact solutions. There are three main categories: parallel, concentric and related solutions, Beltrami and related solutions, and similarity solutions. Physically significant examples are emphasized.
A Natural Convection Problem Arising From the Study of Flame-Bubbles
Authors: Weeratunga S. , Buckmaster J. , Johnson R. E.
Published: June 2009

We describe numerical solutions of the flow-field generated by heat sources distributed continuously over a spherical surface that is rising at a fixed speed in a viscous fluid. This is a model for small, highly curved flames of the type that can be supported by very lean hydrogen/air mixtures (flame-bubbles). Heat swept into the wake behind the sphere generates finite disturbances at downstream infinity, and the boundary conditions there should be chosen accordingly. We compare results obtained in this way with results generated by imposing uniform conditions (Dirichlet or Neumann) at the downstream boundary.
Stable and Unstable Axisymmetric Solutions for Membranes of Revolution
Authors: Weinitschke Hubertus J.
Published: June 2009

Axisymmetric boundary value problems in nonlinear elastic membrane theory are studied, with prescribed tensile stresses or radial displacements at the edge(s). The membrane of revolution is subjected to a load parallel to the axis or normal to the deformed surface. Analytical and numerical methods are presented to determine the range of boundary data for which the solutions are tensile and stable in the sense that the principal stresses are nonnegative everywhere in the membrane.
A Gradient-Dependent Flow Theory of Plasticity: Application to Metal and Soil Instabilities
Authors: Zbib H. M. , Aifantis E. C.
Published: June 2009

We propose a gradient-dependent flow theory of plasticity for metals and granular soils and apply it to the problems of shear banding and liquefaction. We incorporate higher order strain gradients either into the constitutive equation for the flow stress or into the dilantancy condition. We examine the effect of these gradients on the onset of instabilities in the form of shear banding in metals or shear banding and liquefaction in soils under both quasi-static and dynamic conditions. It is shown that the higher order gradients affect the critical conditions and allow for a wavelength selection analysis leading to estimates for the width or spacing of shear bands and liquefying strips. Finally, a nonlinear analysis is given for the evolution of shear bands in soils deformed in the post-localization regime.
Axisymmetric Thin Shell Analyses With Reduced Degrees-of-Freedom
Authors: Almeida C. A. , de Souza F. M. N.
Published: June 2009

The formulation of a simple but effective unidimensional isoparametric displacement-based thin axisymmetric element is presented. The geometry is approximated by using cubic interpolation functions along the shell midsurface generatrix line and the element displacement field is represented by two spatial translation degrees-of-freedom only. The element kinematics incorporates membrane and bending strain components with the assumption of zero transverse shear deformations in the longitudinal and circumferential directions of the shell. This condition allows formulation of the element without using rotation as an independent degree-of-freedom, but continuity conditions between elements should be properly accounted for. The interaction effects between two adjoining elements or between an element and a rigid flange are modeled by using a penalty procedure to enforce continuity on the derivatives in the element midsurface radial displacements. The element formulation has been implemented and the results of various sample analyses are given to illustrate its effectiveness.
Use of an Advanced Shear-Lag Model to Obtain the Optimum Internal Damping in Short-Fiber Composites
Authors: Hajela P. , Shih C.-J.
Published: June 2009

The present paper examines a modified shear-lag model for predicting the stress distribution in short fiber reinforced composite materials. The model assumes perfect bonding between the fiber and the matrix materials, and allows for the matrix material to partially sustain axial loads. The stress distribution obtained on the basis of this model is used to predict the internal damping characteristics of the composite material. These characteristics are a function of both the material properties and the geometrical layout of the composite, and are optimized by combining the analytical model with a nonlinear programming optimization algorithm. Representative numerical results are obtained for glass–epoxy and graphite–epoxy composites
Recent Developments Concerning Saint-Venant’s Principle: An Update
Authors: Horgan Cornelius O.
Published: June 2009

The simplifications arising in elasticity theory from consideration of resultant boundary conditions instead of mathematically exact pointwise conditions have been the key to widespread application of the subject. Thus, for example, theories for strength of materials, plates, and shells rely on such relaxed boundary conditions for their development. The justification of this approximation is usually based on some form of the celebrated Saint-Venant’s principle. A comprehensive survey of contemporary research concerning Saint-Venant’s principle (covering primarily the period 1965–1981) was given by Horgan and Knowles (1983). Since that time, several developments have taken place demonstrating continued interest in understanding the ramifications of Saint-Venant’s principle from both a physical and mathematical point of view. In this article we review these developments, thus providing an update on contributions to this fundamental engineering principle.
Causal Theories of Evolution and Wave Propagation in Mathematical Physics
Authors: Kranysˇ M.
Published: June 2009

There are still many phenomena, especially in continuum physics, that are described by means of parabolic partial differential equations whose solution are not compatible with the causality principle. Compatibility with this principle is required also by the theory of relativity. A general form of hyperbolic operators for the most frequently occurring linear governing equations in mathematical physics is written down. It is then easy to convert any given parabolic equation to the hyperbolic form without necessarily entering into the cause of the inadequacy of the governing equation. The method is verified on the well-known example of Timoshenko’s correction of the Bernoulli–Euler–Rayleigh beam equation for flexural motion. The “Love–Rayleigh” fourth-order differential equations for the longitudinal and torsional wave propagation in the rod is generalized with this method. The hyperbolic version (not to mention others) of the linear Korteweg–de Vries equation and of the “telegraph” equation governing electromagnetic wave propagation through relaxing material are given. Lagrangians of all the equations studied are listed. For all the reasons given we believe the hyperbolic governing equations to be physically and mathematically more realistic and adequate.
Numerical Methods for Viscous Flows With Moving Boundaries
Authors: Floryan J. M. , Rasmussen H.
Published: June 2009

A review of numerical algorithms for the analysis of viscous flows with moving interfaces is presented. The review is supplemented with a discussion of methods that have been introduced in the context of other classes of free boundary problems, but which can be generalized to viscous flows with moving interfaces. The available algorithms can be classified as Eulerian, Lagrangian, and mixed, ie, Eulerian-Lagrangian. Eulerian algorithms consist of fixed grid methods, adaptive grid methods, mapping methods, and special methods. Lagrangian algorithms consist of strictly Lagrangian methods, Lagrangian methods with rezoning, free Lagrangian methods and particle methods. Mixed methods rely on both Lagrangian and Eulerian concepts. The review consists of a description of the present state-of-the-art of each group of algorithms and their applications to a variety of problems. The existing methods are effective in dealing with small to medium interface deformations. For problems with medium to large deformations the methods produce results that are reasonable from a physical viewpoint; however, their accuracy is difficult to ascertain.
Chaotic Dynamics and the Newtonian Legacy
Authors: Thompson J. M. T.
Published: June 2009

The legacy of Sir Isaac Newton’s Principia is evident today throughout the mathematical sciences. Applications of his mechanics range from protein dynamics through macroscopic engineering and space flight, to pattern formation in galactic superclusters, and beyond mechanics the Newtonian paradigm of differential evolution has blossomed into biology, ecology, and economics. Computers have naturally had a profound impact, making long, precise time integrations a routine facility. They have, moreover, played a seminal role in the revolutionary new theory of chaotic motions. These unexpected, noisy motions arise in well-posed, deterministic systems of differential equations, a recent illustration from conservative Hamiltonian dynamics being the chaotic tumbling of the Saturnian satellite, Hyperion. They are typical responses of nonlinear dissipative models once the phase dimension exceeds two: Lorenz’s historic study of turbulent atmospheric convection, and fractal escape boundaries of a potential well, are here used to illustrate salient features. Of particular philosophical significance is the exponential divergence from adjacent starts, whose finite precision implies a definite time-horizon, beyond which prediction is impossible. Coupled with the repetitive mixing of the chaotic flows, this divergence dictates that macroscopic features (such as the occurrence of clockwise as opposed to anticlockwise convective rolling in the Lorenz model) can occur in any sequence, and in this respect the motions are as random as a coin toss.
Assessment of Shear Deformation Theories for Multilayered Composite Plates
Authors: Noor Ahmed K. , Burton W. Scott
Published: June 2009

A review is made of the different approaches used for modeling multilayered composite plates. Discussion focuses on different approaches for developing two-dimensional shear deformation theories; classification of two-dimensional theories based on introducing plausible displacement, strain and/or stress assumptions in the thickness direction; and first-order shear deformation theories based on linear displacement assumptions in the thickness coordinate. Extensive numerical results are presented showing the effects of variation in the lamination and geometric parameters of simply supported composite plates on the accuracy of the static and vibrational responses predicted by six different modeling approaches (based on two-dimensional shear deformation theories). The standard of comparison is taken to be the exact three-dimensional elasticity solutions. Some of the future directions for research on the modeling of multilayered composite plates are outlined.
Optimal Structural Design in the USSR
Authors: Reitman Mark I.
Published: June 2009

Studies in structural optimization in Russia began more than a century ago and initially satisfied the needs of railroad engineering. Later Soviet academic researchers and engineers considered the optimum design of compressed and twisted bars, beams, arches, rigid frames, plates, shells, and various 3D structures under single and multiple statical, dynamical, and moving loads. Some new formulations of the optimization problems have been introduced and solved using classical and new mathematical methods. Several hundred contributions are briefly covered with references to 50 bibliographical sources.
Methods of Random Vibration for Inelastic Structures
Authors: Wen Y. K.
Published: June 2009

Structures often become nonlinear and inelastic under severe lateral force produced by natural hazards such as earthquakes, severe winds and waves. The restoring force of the structures under such load may become hysteretic and deteriorate in strength or stiffness, or both. This paper gives an overview of the major developments in the modeling and response analysis of inelastic structures under random excitation. It includes: (1) modeling of the hereditary behavior of inelastic system; (2) methods of solution based on semi-empirical approaches, Fokker–Planck equation, and equivalent linearization; and (3) applications to performance and safety evaluation of real structural systems. Limitations of current methods are mentioned and suggestions of areas for further research are given.
A Concept Review of Low-Heat-Rejection Engines
Authors: Smith James E. , Churchill Randy
Published: June 2009

Insulated engines have become popular ideas with the development of new materials and material processing techniques. Several research groups have been involved and are producing needed, quality information about low-heat-rejection engines. To date, a comprehensive review has not been presented, like the work included here, that identifies and discusses the various programs and results, or even the breadth of the different topics being undertaken. This paper presents a comprehensive literature review of low-heat-rejection engine concepts and brief discussions of some modeling techniques, both heat transfer models and engine models, being used to further the knowledge base in this field. The general, established concepts and history of low-heat-rejection engines are briefly covered before each individual area of interest is presented. These are temperatures of low-heat-rejection engines, new material requirements, new construction techniques to facilitate the new materials, tribology, emissions, noise concerns, new fuel capabilities, and exhaust heat utilization. The importance of a “whole system” approach is stressed. Inconsistencies in the literature are also discussed.
Recent Studies on the Dynamic Plastic Behavior of Structures
Authors: Jones Norman
Published: June 2009

This article contains a review of the literature, which has been published recently, on the dynamic plastic behavior of simple structures. The dynamic loads cause large plastic strains which dominate material elastic effects. Thus, the accuracy of various refinements of simple rigid-plastic methods are discussed, together with the phenomena of pseudoshakedown under repeated loads, dynamic plastic buckling, and dynamic progressive buckling. Recent studies are also reported on similitude under large impact loads, and on the ductile-brittle fracture transition due to the changes in the physical dimensions of a structure.
Mechanics and Finite Elements of Shells
Authors: Wempner Gerald
Published: June 2009

This article begins with a brief review of the foundations: The classical theory of Love is described with attention to the underlying hypothesis and consequent limitations. A more general theory is described which removes the constraints of Love; the inclusion of transverse strains admits simpler finite elements, accommodates the thick shell via layers and even a transition to the three-dimensional approximation. The concept of the finite element is reviewed in the context of the discrete approximation of shells. Specific attention is given to those problems which are peculiar to shells: The predominant roles of flexural and extensional deformations, the lesser role of transverse shear, can lead to excessive stiffness (“locking”). Origins and procedures are described to circumvent these problems. The review is intended to bridge some chasms between the mechanics of the continua and the discrete models of finite elements. As such, the emphasis is upon those mechanical attributes of shells and elements which play key roles in forming practical models. Since the limitations of space, time and the author’s knowledge, preclude a full expose, the review includes only commentaries on some topics, such as inelasticity, nonlinearity and instability. Citations include original sources and some recent works which provide entree to contemporary developments.
Micromechanical Analysis of Composites by the Method of Cells
Authors: Aboudi Jacob
Published: June 2009

A micromechanics theory based on the analysis of a repeating cell in a fiber-reinforced material is reviewed. The analysis leads to the prediction of the overall behavior of various types of composites from the known material properties of fiber and matrix. The capability of the theory in providing the response of elastic, thermoelastic, viscoelastic, and viscoplastic composites, as well as their initial yield surfaces, strength envelopes, and fatigue failure curves, is demonstrated.
Optimal Topologies of Structures
Authors: Kirsch Uri
Published: June 2009

Topological design, where the member connectivity is sought in addition to member sizing, is perhaps the most challenging and economically the most rewarding of the structural optimization tasks. Due to the basic difficulties involved in the solution process, various simplifications and approximations are often considered. The present review introduces first the typical characteristics and properties of the problem. Two main solution approaches are surveyed: (a) analytical methods for optimization of gridlike continua; (b) numerical methods for optimization of discrete structures. The various difficulties involved in the solution process are presented and the common approximations and simplifications assumed in the problem formulation are discussed. Some fundamental problems that have not yet been solved are emphasized. The significant progress that has been made recently in optimization of gridlike continua by analytical methods provides insight into the design problem and it is often possible to find the theoretical lower bound. However, these methods have limitations in practical design. Numerical methods for topological optimization of discrete structures are still in the stage of early development. Progress is much needed in this area and the development of a general solution approach for practical design of structures remains a challenge. Although both analytical and numerical methods are intended for similar structural applications, a wide gap between researchers of the two groups does exist. It is believed that the present review will contribute to bridge this gap.
Radiative Transfer in Dispersed Media
Authors: Viskanta R. , Mengu¨c¸ M. P.
Published: June 2009

In this paper the continuum and noncontinuum (discrete) theories for radiative properties and radiative transfer models in dispersed particulate, porous and cellular media capable of absorbing, emitting, and scattering thermal radiation are reviewed. The governing equations for the radiative transfer are presented. Different models for the radiative properties of dispersed media are discussed. The methods for solving the inverse radiation problems to determine the spectral and total properties of homogeneous and nonhomogeneous radiatively participating dispersed media and other relevant parameters are also reviewed.
Electroacoustic analysis of an electret loudspeaker using combined finite-element and lumped-parameter models
Authors: Bai Mingsian R. , Chen Rong-Liang , Wang Chun-Jen
Published: June 2009

An unconventional type of electrostatic loudspeaker is presented in this paper. The loudspeaker made of thin, light, and flexible electret material lends itself well to the space-concerned applications. Electrical impedance measurement reveals that the coupling between the electrical system and the mechanical system is weak, which renders conventional parameter identification based on electrical impedance measurement impractical. A different approach is thus employed to model the electret loudspeaker. To predict the loudspeaker’s dynamic response, finite-element analysis (FEA) is conducted on the basis of a simple model and a full model. In the simple model, FEA is applied to model the electret membrane, leaving the rest of system as rigid parts. In the full model, FEA is applied to model the entire membrane-spacer-back plate assembly. Velocity response of the membrane subject to a uniformly distributed force is calculated using FEA harmonic analysis. Mechanical impedance is then calculated with the velocity response. The acoustical impedance due to the back cavity, pores, and the radiation loading at the front side is calculated by theoretical formulas. The volume velocity of the membrane and the resulting on-axis sound pressure level are predicted with electrical-mechanical-acoustical analogous circuits. The response data predicted by the simulation compare very well with experimental measurements.
Subharmonic analysis using singular-value decomposition of ultrasound contrast agents
Authors: Mamou Jonathan , Ketterling Jeffrey A.
Published: June 2009

Ultrasound contrast agents (UCAs) are designed to be used below 10MHz, but interest is growing in studying the response of agents to high-frequency ultrasound. In this study, the subharmonic response of polymer-shelled UCAs with a mean diameter of 1.1μm excited with 40-MHz tone-bursts of 1–20cycles was analyzed. UCAs were diluted in water and streamed through a flow phantom that permitted single-bubble backscatter events to be acquired at peak-negative pressures from 0.75to5.0MPa. At each exposure condition, 1000 single-bubble-backscatter events were digitized. Subharmonic content at 20MHz was screened using a conventional and a singular-value-decomposition (SVD) method. The conventional method evaluated each event spectrum individually while the SVD method treated the 1000-event data set at one time. A subharmonic score (SHS) indicative of how much subharmonic content a 1000-event data set contained was computed for both methods. Empirical-simulation results indicated that SHSs obtained from the two methods were linearly related. Also, experimental data with both methods indicated that subharmonic likelihood increased with pulse duration and peaked near 2MPa. The SVD method also yielded quantitative information about subharmonic events not available with the conventional method.
The vertical structure of shadow-zone arrivals at long range in the ocean
Authors: Van Uffelen Lora J. , Worcester Peter F. , Dzieciuch Matthew A. , Rudnick Daniel L.
Published: June 2009

Multimegameter-range acoustic data obtained by bottom-mounted receivers show significant acoustic energy penetrating several hundred meters into geometric shadow zones below cusps (caustics) of timefronts computed using climatological databases [B. D. Dushaw et al., IEEE J. Ocean. Eng. 24, 202–214 (1999)]. This penetration is much larger than predicted by diffraction theory. Because these receivers are horizontal arrays, they do not provide information on the vertical structure of the shadow-zone arrivals. Acoustic data from two vertical line array receivers deployed in close proximity in the North Pacific Ocean, together virtually spanning the water column, show the vertical structure of the shadow-zone arrivals for transmissions from broadband 250-Hz sources moored at the sound-channel axis (750m) and slightly above the surface conjugate depth (3000m) at ranges of 500 and 1000km. Comparisons to parabolic equation simulations for sound-speed fields that do not include significant internal-wave variability show that early branches of the measured timefronts consistently penetrate as much as 500–800m deeper into the water column than predicted. Subsequent parabolic equation simulations incorporating sound-speed fluctuations consistent with the Garrett–Munk internal-wave spectrum at full strength accurately predict the observed energy level to within 3–4-dB rms over the depth range of the shadow-zone arrivals.
Greater sensitivity to prosodic goodness in non-native than in native listeners
Authors: Cutler Anne
Published: June 2009

English listeners largely disregard suprasegmental cues to stress in recognizing words. Evidence for this includes the demonstration of Fear et al. [J. Acoust. Soc. Am. 97, 1893–1904 (1995)] that cross-splicings are tolerated between stressed and unstressed full vowels (e.g., au- of autumn, automata). Dutch listeners, however, do exploit suprasegmental stress cues in recognizing native-language words. In this study, Dutch listeners were presented with English materials from the study of Fear et al. Acceptability ratings by these listeners revealed sensitivity to suprasegmental mismatch, in particular, in replacements of unstressed full vowels by higher-stressed vowels, thus evincing greater sensitivity to prosodic goodness than had been shown by the original native listener group.
A Fabry–Pérot fiber-optic ultrasonic hydrophone for the simultaneous measurement of temperature and acoustic pressure
Authors: Morris Paul , Hurrell Andrew , Shaw Adam , Zhang Edward , Beard Paul
Published: June 2009

A dual sensing fiber-optic hydrophone that can make simultaneous measurements of acoustic pressure and temperature at the same location has been developed for characterizing ultrasound fields and ultrasound-induced heating. The transduction mechanism is based on the detection of acoustically- and thermally-induced thickness changes in a polymer film Fabry–Pérot interferometer deposited at the tip of a single mode optical fiber. The sensor provides a peak noise-equivalent pressure of 15 kPa (at 5 MHz, over a 20 MHz measurement bandwidth), an acoustic bandwidth of 50 MHz, and an optically defined element size of 10 μm. As well as measuring acoustic pressure, temperature changes up to 70 °C can be measured, with a resolution of 0.34 °C. To evaluate the thermal measurement capability of the sensor, measurements were made at the focus of a high-intensity focused ultrasound (HIFU) field in a tissue mimicking phantom. These showed that the sensor is not susceptible to viscous heating, is able to withstand high intensity fields, and can simultaneously acquire acoustic waveforms while monitoring induced temperature rises. These attributes, along with flexibility, small physical size (OD∼150 μm), immunity to Electro-Magnetic Interference (EMI), and low sensor cost, suggest that this type of hydrophone may provide a practical alternative to piezoelectric based hydrophones.
Underwater noise from three types of offshore wind turbines: Estimation of impact zones for harbor porpoises and harbor seals
Authors: Tougaard Jakob , Henriksen Oluf Damsgaard , Miller Lee A.
Published: June 2009

Underwater noise was recorded from three different types of wind turbines in Denmark and Sweden (Middelgrunden, Vindeby, and Bockstigen-Valar) during normal operation. Wind turbine noise was only measurable above ambient noise at frequencies below 500 Hz. Total sound pressure level was in the range 109–127 dB re 1 μPa rms, measured at distances between 14 and 20 m from the foundations. The 1/3-octave noise levels were compared with audiograms of harbor seals and harbor porpoises. Maximum 1/3-octave levels were in the range 106–126 dB re 1 μPa rms. Maximum range of audibility was estimated under two extreme assumptions on transmission loss (3 and 9 dB per doubling of distance, respectively). Audibility was low for harbor porpoises extending 20–70 m from the foundation, whereas audibility for harbor seals ranged from less than 100 m to several kilometers. Behavioral reactions of porpoises to the noise appear unlikely except if they are very close to the foundations. However, behavioral reactions from seals cannot be excluded up to distances of a few hundred meters. It is unlikely that the noise reaches dangerous levels at any distance from the turbines and the noise is considered incapable of masking acoustic communication by seals and porpoises.
Influence of a gradient of material properties on ultrasonic wave propagation in cortical bone: Application to axial transmission
Authors: Haïat Guillaume , Naili Salah , Grimal Quentin , Talmant Maryline , Desceliers Christophe , Soize Christian
Published: June 2009

The aim of this work is to evaluate the effect of a spatial gradient of material properties (mass density and stiffness coefficients) of cortical bone on its ultrasonic response obtained with an axial transmission device. Therefore, a two-dimensional finite element time-domain method is derived to model transient wave propagation in a three-layer medium composed of an inhomogeneous transverse isotropic solid layer sandwiched between two acoustic fluid layers and excited by an acoustic linear source located in one fluid layer, delivering broadband ultrasonic pulses. The model couples the acoustic propagation in both fluid media with the elastodynamic response of the solid layer. A constant spatial gradient of material properties is considered for two values of bone thicknesses corresponding to relatively thick and thin bone widths. For a thin bone (0.6mm) compared to wavelength (around 4mm at 1MHz), the results are in good agreement with a S0 Lamb wave assuming a homogeneous material with spatially averaged material properties. For a thick bone (4mm), the results are in agreement with the propagation of a lateral wave and allow the derivation of an equivalent contributing depth in the case of a transverse isotropic inhomogeneous solid layer.