Showing papers in "Applied Mechanics Reviews in 1996"

Differential Quadrature Method in Computational Mechanics: A Review

Abstract: The differential quadrature method is a numerical solution technique for initial and/or boundary problems. It was developed by the late Richard Bellman and his associates in the early 70s and, since then, the technique has been successfully employed in a variety of problems in engineering and physical sciences. The method has been projected by its proponents as a potential alternative to the conventional numerical solution techniques such as the finite difference and finite element methods. This paper presents a state-of-the-art review of the differential quadrature method, which should be of general interest to the computational mechanics community.

Computational Models for Sandwich Panels and Shells

Abstract: The focus of this review is on the hierarchy of computational models for sandwich plates and shells, predictor-corrector procedures, and the sensitivity of the sandwich response to variations in the different geometric and material parameters. The literature reviewed is devoted to the following application areas: heat transfer problems; thermal and mechanical stresses (including boundary layer and edge stresses); free vibrations and damping; transient dynamic response; bifurcation buckling, local buckling, face-sheet wrinkling and core crimping; large deflection and postbuckling problems; effects of discontinuities (eg, cutouts and stiffeners), and geometric changes (eg, tapered thickness); damage and failure of sandwich structures; experimental studies; optimization and design studies. Over 800 relevant references are cited in this review, and another 559 references are included in a supplemental bibliography for completeness. Extensive numerical results are presented for thermally stressed sandwich panels with composite face sheets showing the effects of variation in their geometric and material parameters on the accuracy of the free vibration response, and the sensitivity coefficients predicted by eight different modeling approaches (based on two-dimensional theories). The standard of comparison is taken to be the analytic three-dimensional thermoelasticity solutions. Some future directions for research on the modeling of sandwich plates and shells are outlined.

Simulation of Multi-Dimensional Gaussian Stochastic Fields by Spectral Representation

Abstract: The subject of this paper is the simulation of multi-dimensional, homogeneous, Gaussian stochastic fields using the spectral representation method. Following this methodology, sample functions of the stochastic field can be generated using a cosine series formula. These sample functions accurately reflect the prescribed probabilistic characteristics of the stochastic field when the number of terms in the cosine series is large. The ensemble-averaged power spectral density or autocorrelation function approaches the corresponding target function as the sample size increases. In addition, the generated sample functions possess ergodic characteristics in the sense that the spatially-averaged mean value, autocorrelation function and power spectral density function are identical with the corresponding targets, when the averaging takes place over the multi-dimensional domain associated with the fundamental period of the cosine series. Another property of the simulated stochastic field is that it is asymptotically Gaussian as the number of terms in the cosine series approaches infinity. The most important feature of the method is that the cosine series formula can be numerically computed very efficiently using the Fast Fourier Transform technique. The main area of application of this method is the Monte Carlo solution of stochastic problems in structural engineering, engineering mechanics and physics. Specifically, the method has been applied to problems involving random loading (random vibration theory) and random material and geometric properties (response variability due to system stochasticity).

Modern developments in flow control

Abstract: This brief article reviews the important advances in the field of flow control that took place during the past few years. This broad area of research remains of great interest for its numerous potential benefits for both the military and civilian sectors. Spurred by the recent developments in chaos control, microfabrication and neural networks, reactive control of turbulent flows is now in the realm of the possible for future practical devices. Other less complex control schemes, passive as well as active, are more market ready and are also witnessing resurgence of interest. 115 refs., 4 figs.

Transformation-Induced Plasticity (TRIP)

Abstract: This review article attempts to explain TRIP generally and its appearance in different materials. Continuum mechanics formulations are mainly used to explain this phase change phenomenon. An overview is given of the published literature which is often not very easily accessible. Technological aspects are presented, such as constitutive equations of materials showing TRIP. Aspects of material selection and future material design are also treated. This article contains 315 references.

Buckling of Thin Shells: Recent Advances and Trends

Abstract: This paper provides a review of recent research advances and trends in the area of thin shell buckling. Only the more important and interesting aspects of recent research, judged from a personal view point, are discussed. In particular, the following topics are given emphasis: (a) imperfections in real structures and their influence; (b) buckling of shells under local/non-uniform loads and localized compressive stresses; and (c) the use of computer buckling analysis in the stability design of complex thin shell structures. I INTRODUCTION Thin-shell structures find wide applications in many branches of engineering. Examples include aircraft, spacecraft, cooling towers, nuclear reactors, steel silos and tanks for bulk solid and liquid storage, pressure vessels, pipelines and offshore platforms. Because of the thinness of these structures, buckling is often the controlling failure mode. It is therefore essential that their buckling behavior be properly understood so that suitable design methods can be established. This paper provides a review of recent research advances and trends in the area of thin shell buckling. The paper is not intended to be an exhaustive review of the field, nor is it possible to do so in a single paper of limited length. Instead, only the more important and interesting aspects of recent research, judged from a personal viewpoint, will be discussed. In particular, the following topics are given emphasis: (a) imperfections in real structures and their influence; (b) buckling of shells under local/non-uniform loads and localized compressive stresses; and (c) the use of computer buckling analysis in the stability design of complex thin shell structures. The author wishes to apologize in advance for any inadvertent omission of relevant publications.

Contact Mechanics of Rough Surfaces in Tribology: Single Asperity Contact

Abstract: Contact modeling of two rough surfaces under normal approach and with relative motion is carried out to predict the real area of contact which affects friction and wear of an interface. The contact of two macroscopically flat bodies with microroughness is reduced to the contact at multiple asperities of arbitrary shapes. Most of deformation at the asperity contact can be either elastic or elastic-plastic. In this paper, a comprehensive review of modeling of a single asperity contact or an indentation problem is presented. Contact analyses for a spherical asperity/indenter on homogeneous and layered, elastic and elastic-plastic solids with and without tangential loading are presented. The analyses reviewed in this paper fall into two groups: (a) analytical solutions, primarily for elastic solids and (b) finite element solutions, primarily for elastic-plastic problems and layered solids. Implications of these analyses in friction and wear are discussed.

Turbulence in the Ocean, Atmosphere, Galaxy, and Universe

Abstract: Flows in natural bodies of fluid often become turbulent, with eddy-like motions dominated by inertial-vort ex forces. Buoyancy, Coriolis, viscous, self-gravitational, electromagnetic, and other force constraints produce a complex phase space of wave-like hydrodynamic states that interact with turbulence eddies, masquerade as turbulence, and preserve information about previous hydrodynamic states as fossil turbulence. Evidence from the ocean, atmosphere, galaxy and universe are compared with universal similarity hypotheses of Kolmogorov (1941, 1962) for turbulence velocity u, and extensions to scalar fields θ like temperature mixed by turbulence. Universal u and θ spectra of natural flows can be inferred from laboratory and computer simulations with satisfactory accuracy, but higher order spectra and the intermittency constant μ of the third Kolmogorov hypothesis (1962) require measurements at the much larger Reynolds numbers found only in nature. Information about previous hydrodynamic states is preserved by Schwarz viscous and turbulence lengths and masses of self-gravitat ing condensates (rarely by the classical Jeans length and mass), as it is by Ozmidov, Hopfinger and Fernando scales in hydrophysical fields of the ocean and atmosphere. Viscous-gravitational formation occurred 10 4 -10 5 y after the Big Bang for supercluster, cluster, and then galaxy masses of the plasma, producing the first turbulence. Condensation after plasma neutralization of the H- 4 He gas was to a primordial fog of sub-solar particles that persists today in galactic halos as "dark matter". These gradually formed all stars, star clusters, etc. (humans!) within.

Compliant Coatings: A Decade of Progress

Abstract: This brief article reviews the important developments in the field of compliant coatings that took place in the past ten years. During this period progress in theoretical and computational methods somewhat outpaced that in experimental efforts. There is no doubt that compliant coatings can be designed to delay transition and to suppress noise on marine vehicles as well as other practical hydrodynamic devices. Transition Reynolds numbers that exceed by an order of magnitude those on rigid-surface boundary layers can be achieved. There is renewed evidence of favorable interactions of compliant coatings even for air flows and even for turbulent boundary layers, but more research is needed to confirm these latest results.

Finite Elements in Aeroelasticity of Plates and Shells

Abstract: A review of the finite element method applied to the problem of supersonic aeroelastic stability of nonlinear flat plates, linear, and nonlinear curved plates is presented. Some new contributions in the field are given and future trends are discussed.

Review of Knee Models: 1996 Update

Abstract: This paper is an update on our previous review of knee models (Hefzy and Grood [30]). We find that progress was made in the area of dynamic modeling. Since 1988, a technique was developed to solve the system of differential algebraic equations describing the three-dimensional dynamic behavior of the knee joint. This technique allows to solve complex problems. However, not a single dynamic comprehensive anatomically based mathematical three-dimensional model of the knee joint that includes both tibio-femoral and patello-femoral joints has yet been developed. In the area of meniscal modeling, we find that only one three-dimensional model of the knee joint that includes the menisci is available in the literature. This quasi-static model includes menisci, tibial, femoral and patellar cartilage layers, and ligamentous structures. This model is limited since it solves only for one position of the knee joint: full extension. From this updated survey, we conclude that the development of a comprehensive three-dimensional anatomically based mathematical model of the knee joint (that solves the three-body contact problem at the tibio-femoral joint between the menisci, tibia and femur, and includes the patello-femoral joint) continues to present major challenge.

Acoustic Scattering Resonances: Relation to External and Internal Surface Waves

Abstract: The resonance scattering theory (RST) and the singularity expansion method (SEM) are both based on the complex-frequency poles of the scattering amplitude in the scattering of acoustic, elastic, or electromagnetic waves from elastic or impenetrable objects, or from cavities. These poles, situated off the real frequency axis at locations with negative imaginary parts, are found to yield, at the real frequencies of the experiments, prominent resonances for acoustic and elastic-wave scattering from elastic objects as discussed in our earlier review (Uberall et al, Appl Mech Rev43 (10), 1990, 235). However, as the authors demonstrated before (Uberall et al, J Acoust Soc Am61, 1977, 711), the origin of these resonances lies in the phase matching of circumferential or surface waves generated on the target objects during the scattering; hence a study of the resonances will lead to an understanding of, and information on these surface waves. This has been the topic of a large number of studies in recent years, and the results are summarized in the present review for immersed elastic target objects of plane, spherical, and cylindrical geometry, including both elastic-type and fluid-borne surface waves. For multilayered elastic structures, we also describe possible layer-resonance identifications based on acoustic and elastic-wave scattering experiments.

Stable Response of Non-Classically Damped Mechanical Systems - II

Abstract: This review, like its 1987 predecessor, addresses response of a discrete, time-invariant, linear, multiple degree-of-freedom system which exhibits nonclassical damping, including active damping Unlike a classically damped system, the modes are coupled (or complex) In the intervening decade, stability issues involving nonclassical damping have received attention in applications such as high speed mechanisms, active structural control, vehicle dynamics, and seismic isolation of ground structures Much of the recent literature has concerned approximate modal decoupling There have also been contributions to the accurate calculation of the coupled modes, to general stability issues such as gyroscopic stabilization, and to eigenvalue/response bounds The present article is intended both as a survey of recent literature and as a brief exposition of selected contributions of a general nature