bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-Accurate Predictions for a Fully Cooled High-Pressure Turbine Stage—Part I: Comparison of Predictions With Data
Authors: Southworth S. A. , Dunn M. G. , Haldeman C. W. , Chen J.-P. , Heitland G. , Liu J.
Published: April 2009

The aerodynamics of a fully cooled axial single stage high-pressure turbine operating at design corrected conditions of corrected speed, flow function, and stage pressure ratio has been investigated. This paper focuses on flow field predictions obtained from the viewpoint of a turbine designer using the computational fluid dynamics (CFD) codes Numeca’s FINE/TURBO and the code TURBO. The predictions were all performed with only knowledge of the stage operating conditions, but without knowledge of the surface pressure measurements. Predictions were obtained with and without distributed cooling flow simulation. The FINE/TURBO model was run in 3-D viscous steady and time-accurate modes; the TURBO model was used to provide only 3-D viscous time-accurate results. Both FINE/TURBO and TURBO utilized phase-lagged boundary conditions to simplify the time-accurate model and to significantly reduce the computing time and resources. The time-accurate surface pressure loadings and steady state predictions are compared to measurements for the blade, vane, and shroud as time-averaged, time series, and power spectrum data. The measurements were obtained using The Ohio State University Gas Turbine Laboratory Turbine Test Facility. The time-average and steady comparisons of measurements and predictions are presented for 50% span on the vane and blade. Comparisons are also presented for several locations along the blade to illustrate local differences in the CFD behavior. The comparisons for the shroud are made across the blade passage at axial blade chord locations corresponding to the pressure transducer locations. The power spectrum decompositions of individual transducers (based on the fast Fourier transform (FFT)) are also included to lend insight into the unsteady nature of the flow. The comparisons show that both computational tools are capable of providing reasonable aerodynamic predictions for the vane, blade, and stationary shroud. The CFD model predictions show the encouraging trend of improved matching to the experimental data with increasing model fidelity from mass averaged to distributed cooling flow inclusion and as the codes change from steady to time-accurate modes.
Validation of MISES Two-Dimensional Boundary Layer Code for High-Pressure Turbine Aerodynamic Design
Authors: Andrew Philip L. , Kahveci Harika S.
Published: April 2009

Avoiding aerodynamic separation and excessive shock losses in gas turbine turbomachinery components can reduce fuel usage and thus reduce operating cost. In order to achieve this, blading designs should be made robust to a wide range of operating conditions. Consequently, a design tool is needed—one that can be executed quickly for each of many operating conditions and on each of several design sections, which will accurately capture loss, turning, and loading. This paper presents the validation of a boundary layer code, MISES, versus experimental data from a 2D linear cascade approximating the performance of a moderately loaded mid-pitch section from a modern aircraft high-pressure turbine. The validation versus measured loading, turning, and total pressure loss is presented for a range of exit Mach numbers from ≈0.5 to 1.2 and across a range of incidence from −10 deg to +14.5 deg relative to design incidence.
Numerical Investigation on Unsteady Effects of Hot Streak on Flow and Heat Transfer in a Turbine Stage
Authors: An Bai-Tao , Liu Jian-Jun , Jiang Hong-De
Published: April 2009

This paper presents a detailed flow and heat transfer characteristic analysis on gas turbine first-stage turbine under hot streak inlet conditions. Two kinds of inlet total temperature conditions are specified at the turbine stage inlet. The first is uniform inlet total temperature, and the second is hot streak 2D total temperature contour. The two kinds of inlet conditions have the same mass-averaged total temperature and the same uniform inlet total pressure. The hot streak total temperature contours are obtained according to the exit shape of an annular-can combustor. The ratio of the highest total temperature in the hot streak to the mass-averaged total temperature is about 1.23, and one hot streak corresponds to two vane passages and four blade passages. Six hot streak circumferential positions relative to the Vane 1 leading edge varied from −2% to 81% pitch are computed and analyzed. The results show that hot streak obviously increases the nonuniform degree of vane heat load in comparison with the uniform total temperature inlet condition. The change in hot streak circumferential position leads to the circumferential parameter variation at stator exit and also leads to different transient periodic fluctuating characteristics of heat load and pressure on the rotor blade surface. The hot streak of relative pitch at 65% obtains a similar heat load for the two vanes corresponding to one hot streak and small fluctuation in the averaged heat load on the rotor blade.
Extended Models for Transitional Rough Wall Boundary Layers With Heat Transfer—Part I: Model Formulations
Authors: Stripf M. , Schulz A. , Bauer H.-J. , Wittig S.
Published: April 2009

Two extended models for the calculation of rough wall transitional boundary layers with heat transfer are presented. Both models comprise a new transition onset correlation, which accounts for the effects of roughness height and density, turbulence intensity, and wall curvature. In the transition region, an intermittency equation suitable for rough wall boundary layers is used to blend between the laminar and fully turbulent states. Finally, two different submodels for the fully turbulent boundary layer complete the two models. In the first model, termed KS-TLK-T in this paper, a sand roughness approach from Durbin et al. (2001, “Rough Wall Modification of Two Layer k-ε ,” ASME J. Fluids Eng., 123, pp. 16–21), which builds upon a two-layer k-ε-turbulence model, is used for this purpose. The second model, the so-called DEM-TLV-T model, makes use of the discrete-element roughness approach, which was recently combined with a two-layer k-ε-turbulence model by the present authors. The discrete-element model will be formulated in a new way, suitable for randomly rough topographies. Part I of the paper will provide detailed model formulations as well as a description of the database used for developing the new transition onset correlation. Part II contains a comprehensive validation of the two models, using a variety of test cases with transitional and fully turbulent boundary layers. The validation focuses on heat transfer calculations on both the suction and the pressure side of modern turbine airfoils. Test cases include extensive experimental investigations on a high-pressure turbine vane with varying surface roughness and turbulence intensity, recently published by the current authors as well as new experimental data from a low-pressure turbine vane. In the majority of cases, the predictions from both models are in good agreement with the experimental data.
On the Role of the Deterministic and Circumferential Stresses in Throughflow Calculations
Authors: Simon J.-F. , Thomas J. P. , Léonard O.
Published: April 2009

This paper presents a throughflow analysis tool developed in the context of the average-passage flow model elaborated by Adamczyk. The Adamczyk’s flow model describes the 3D time-averaged flow field within a blade row passage. The set of equations that governs this flow field is obtained by performing a Reynolds averaging, a time averaging, and a passage-to-passage averaging on the Navier–Stokes equations. The throughflow level of approximation is obtained by performing an additional circumferential averaging on the 3D average-passage flow. The resulting set of equations is similar to the 2D axisymmetric Navier–Stokes equations, but additional terms resulting from the averages show up: blade forces, blade blockage factor, Reynolds stresses, deterministic stresses, passage-to-passage stresses, and circumferential stresses. This set of equations represents the ultimate throughflow model provided that all stresses and blade forces can be modeled. The relative importance of these additional terms is studied in the present contribution. The stresses and the blade forces are determined from 3D steady and unsteady databases (a low-speed compressor stage and a transonic turbine stage) and incorporated in a throughflow model based on the axisymmetric Navier–Stokes equations. A good agreement between the throughflow solution and the averaged 3D results is obtained. These results are also compared to those obtained with a more “classical” throughflow approach based on a Navier–Stokes formulation for the endwall losses, correlations for profile losses, and a simple radial mixing model assuming turbulent diffusion.
Some Aerodynamic Problems of Aircraft Engines: Fifty Years After -The 2007 IGTI Scholar Lecture-
Authors: Greitzer Edward M.
Published: April 2009

Problems of high technological interest, for example the development of gas turbine engines, span disciplinary, and often organizational, boundaries. Although collaboration is critical in advancing the technology, it has been less a factor in gas turbine research. In this paper it is proposed that step changes in gas turbine performance can emerge from collaborative research endeavors that involve the development of integrated teams with the needed range of skills. Such teams are an important aspect in product development, but they are less familiar and less subscribed to in the research community. The case histories of two projects are given to illustrate the point: the development of the concept of “smart jet engines” and the Silent Aircraft Initiative. In addition to providing a capability to attack multidisciplinary problems, the way in which collaboration can enhance the research process within a single discipline is also discussed.
Developments in the Mechanics of Reinforced Soil: Empirical Background and Analytical Approaches
Authors: Sawicki Andrzej
Published: April 2009

Reinforced soil (RS) is a composite material built of a soil matrix reinforced with other materials such as metal strips, geosynthetics etc. RS has been increasingly used in civil engineering, either as a cheaper alternative to classical geotechnical structures, or as an independent technical solution. The aim of this article is to present a state-of-the-art review concerning the mechanics of RS and mechanics of RS structures. Research on both subjects was initiated by pioneering works of H Vidal in the 1960s. First, a brief introduction is presented followed by a review of mechanical models of RS, including rigid-plastic, elasto-plastic, and rheological. Then, the methods of analysis of RS structures are discussed. These methods include the limit states approach, determination of stresses, creep etc. Some research needs are also outlined. The article is presented in the form of a tutorial review which also includes a state-of-the-art review and a basic bibliographical survey. There are 200 references.
Applied Mechanics in Science and Engineering
Authors: Pao Yih-Hsing
Published: April 2009

This article traces the development of applied mechanics and its relation to science and engineering by reviewing first the history of mechanics from 1600 to 1900, the physics of the 19th century, and the engineering education in the same period. The review is followed by a discussion on modern physics and modern engineering, and the formation of applied mechanics as a discipline in science and one in engineering, which is classified into 94 subjects in 10 categories by Applied Mechanics Reviews. The article concludes with a chart to summarize the relation between science and engineering, and the interactions of applied mechanics with other disciplines. There are 15 references included in this article.
Main Ukrainian Historical and Modern Sources on Mechanics: Focus on the SP Timoshenko Institute of Mechanics
Authors: Guz’ A. N. , Rushchitsky J. J.
Published: April 2009

The aim of this article is to present a list of main books and monographs on mechanics by Ukrainian scientists in a rather broad sense. The focus includes main works in different scientific directions originated by scientists from the SP Timoshenko Institute of Mechanics. This Institute is the oldest and largest among institutes of mechanics of the former USSR. It is located in the capital city of the Ukraine, Kiev. Cited books represent the majority of Ukrainian sources on mechanics in the years 1918-1996. A total of 286 books are listed.
Three Versions of the Finite Element Method Based on Concepts of Either Stochasticity, Fuzziness, or Anti-Optimization
Authors: Elishakoff Isaac
Published: April 2009

In this review article, we describe in some detail three versions of the FEM pertinent to the uncertainty triangle, introduced by the present writer; in particular, to describe various types of uncertainties in the structure, namely a) non-perturbational finite element method for stochastic structures, b) finite element method associated with determination of least favorable responses through the method of anti-optimization in interval setting of parameters, and c) finite element method based on the fuzzy sets. The comparison between the probabilistic and convex modeling of uncertainty is conducted. The combined optimization and anti-optimization due to presence uncertainty is advocated. The author trusts that hybrid approaches, rather than a) genuine probabilistic treatment, b) anti-optimization, or c) fuzzy-sets-based modeling are called for to rigorously treat the realistic structures. In the end, the issue of relative robustness of these approaches is discussed. This review should be viewed as a continuation of our previous essays about non-probabilistic modeling of uncertainty, random vibrations, and introduction of initial imperfection-sensitivity concept into design, respectively (Comput Struct, 1995; Appl Mech Rev, 1995; NASA SP, 1998; Comput Meth in Appl Mech Eng, with Ren YJ, 1998), devoted to various aspects of uncertainty modeling in engineering. As its predecessors, it contains personal perspectives on the subject. It is envisioned, that at a later stage, these reviews, combined, will be published as a book, Thoughts on Uncertainty. This review article contains 126 references.
A Historical Review on Dry Friction and Stick-Slip Phenomena
Authors: Feeny Brian , Guran Arde´shir , Hinrichs Nikolaus , Popp Karl
Published: April 2009

This article gives a historical overview of structural and mechanical systems with friction. Friction forces between sliding surfaces arise due to complex mechanisms and lead to mathematical models which are highly nonlinear, discontinuous and nonsmooth. Humankind has a long history of magnificent usage of friction in machines, buildings and transportation. Regardless, our state of knowledge of the friction-influenced dynamics occurring in such systems as well as in our daily lives was, until recently, rather primitive. To represent our understanding of friction in nonlinear dynamics, we first trace examples from the earliest prehistoric technologies and the formulation of dissipation laws in mechanics. The work culminates with examples of friction oscillators and stick-slip. This review article contains 304 references.
Damage Analysis in Fiber Composite Sheets and Uncoated Woven Fabrics
Authors: Rossettos J. N. , Godfrey T. A.
Published: April 2009

The mechanics of damage of fiber composite sheets has been reviewed, including cases where the analytical models have been compared to experiments. The emphasis has been on the micromechanics approach, where equilibrium of the constituents of the composite lead to appropriate equations for determining stress distributions. The damage mechanisms that have been treated include fiber breaks, matrix cracking (splitting), and debonding at the fiber/matrix interface. Effects of matrix yielding, hybrid composites, the hybrid effect, and thermal response have also been discussed. The usefulness of the shear lag model (SLM) in both stress and fracture considerations is clearly exhibited by the results in the literature. Work on damage growth in uncoated woven fabrics has also been reviewed, together with its importance in Army applications. In the study of the localized mechanics of woven fabrics near damage sites (eg, yarn breaks), the important deformation mechanisms include crimp interchange between yarns, yarn slipping, and yarn rotation. Growth of slit-like damage as a progression of yarn breaks is reviewed. The structure of the equations in the analytical models is similar to the SLM, and a parameter appears which can be used to compare fabrics as to their damage tolerance. This review article includes 117 references.
Nonholonomic Systems Revisited Within the Framework of Analytical Mechanics
Authors: Ostrovskaya S. , Angeles J.
Published: April 2009

Nonholonomic mechanical systems are revisited. This review article focuses on Lagrangian formulations leading to a system of governing equations free of constraint forces. While eliminating the constraint forces, the number of scalar Lagrange equations is reduced to a number of independent equations lower than the original system with constraint forces. In the process of constraint-force elimination and dimension-reduction, a matrix that appears to play a relevant role in the formulation of the mathematical models of mechanical systems arises naturally. We call this matrix here the holonomy matrix. It is shown that necessary and sufficient conditions for the integrability of the constraints in Pfaffian form are readily derived using the holonomy matrix. In the same vein, a class of nonholonomic systems is identified, of current engineering relevance, that is termed quasiholonomic. Examples are included to illustrate these concepts. This review article contains 40 references.
Optimization and Experiments: A Survey
Authors: Haftka Raphael T. , Scott Elaine P. , Cruz Juan R.
Published: April 2009

This article is a review of optimization in relationship to experiments in four aspects. The first is the use of optimization for designing experiments to provide the maximum amount of insight and information on the phenomena being investigated. Second, the use of experiments to perform optimization is reviewed. Third, the use of techniques developed for experimental optimization in numerical optimization is discussed. These first three aspects of optimization in relationship to experiments are discussed with an emphasis on reducing the number of required experiments or analyses. Finally, the importance of experimental validation of optimization is presented. Applications from a variety of fields are provided for each of these aspects. This review article contains 119 references.
Intelligent Material Systems: Application of Functional Materials
Authors: Tani Junji , Takagi Toshiyuki , Qiu Jinhao
Published: April 2009

This article presents a review of recent important developments in the field of intelligent material systems. Intelligent material systems, sometimes referred to as smart materials, can adjust their behavior to changes of external or internal parameters analogously to biological systems. In these systems, sensors, actuators and controllers are seamlessly integrated with structural materials at the macroscopic or mesoscopic level. In general, sensors and actuators are made of functional materials and fluids such as piezoelectric materials, magnetostrictive materials, shape memory alloys, polymer hydrogels, electro- and magneto-rheological fluids and so on. This article is specifically focused on the application of piezoelectric materials, magnetostrictive materials and shape memory alloys to intelligent material systems used to control the deformation, vibration and fracture of composite materials and structures. This review article contains 188 references.
Asymptotic Theory of Global Separation
Authors: Chernyshenko S. I.
Published: April 2009

This article aims to review the recent achievements and the state of the art in the high Reynolds number asymptotic theory of steady separated flow past bluff bodies for a general reader specializing in fluid dynamics who is not necessarily familiar with modern asymptotic techniques. A short historical overview is given. The ideas of the mathematical methods used are briefly outlined. Then the general structure of the solution for a plane flow past a bluff body is described. The physical mechanisms of such a flow are discussed, and quantitative results are given and compared with numerical calculations. Existing extensions of the theory and the latest results for axisymmetric flows are described. In conclusion, the relationship between asymptotic theory and real turbulent flows is discussed. This review article contains 76 references.
A Finite Element Bibliography for Biomechanics (1987-1997)
Authors: Mackerle Jaroslav
Published: April 2009

This article gives a bibliographical review of the finite element method (FEM) applied to biomechanics. The bibliography at the end of the article contains references to published papers, conference proceedings, and theses/dissertations on the subject that were published from 1987 through 1997. The following topics are included: orthopaedic mechanics, dental mechanics, cardiovascular mechanics, tissue and organ mechanics, impact injury, biological flow, and other topics. This bibliography contains 2188 citations.
Adaptive Finite Element Methods: A Review
Authors: Li Long-yuan , Bettess Peter
Published: April 2009

The adaptive finite element method (FEM) was developed in the early 1980s. The basic concept of adaptivity developed in the FEM is that, when a physical problem is analyzed using finite elements, there exist some discretization errors caused owing to the use of the finite element model. These errors are calculated in order to assess the accuracy of the solution obtained. If the errors are large, then the finite element model is refined through reducing the size of elements or increasing the order of interpolation functions. The new model is re-analyzed and the errors in the new model are recalculated. This procedure is continued until the calculated errors fall below the specified permissible values. The key features in the adaptive FEM are the estimation of discretization errors and the refinement of finite element models. This paper presents a brief review of the methods for error estimates and adaptive refinement processes applied to finite element calculations. The basic theories and principles of estimating finite element discretization errors and refining finite element models are presented. This review article contains 131 references.
Review of Mechanics of Shape Memory Alloy Structures
Authors: Birman Victor
Published: April 2009

This article presents a review of constitutive theories, mechanics, and structural applications of shape memory alloys. Although these materials possess a number of unique features, this review is concerned with the shape memory effect and superelasticity, since they are most often discussed in the context of possible applications. The article begins with a discussion of these effects and a reference to a number of studies elucidating the properties of shape memory alloys. In the next section, a number of constitutive theories are listed and some recent theories are discussed in detail. The work related to numerous technological problems that arise in the process of manufacturing shape memory alloy structures is considered. Structural problems of shape memory structures, such as buckling, vibration, acoustic control, etc are discussed. The work related to development and design of shape memory sensors and actuators is also reviewed. Finally, some applications of shape memory alloy actuators, particularly those in the aerospace and medical fields, are considered. This review article contains 195 references.
Applications of Fractional Calculus to Dynamic Problems of Linear and Nonlinear Hereditary Mechanics of Solids
Authors: Rossikhin Yuriy A. , Shitikova Marina V.
Published: April 2009

The aim of this review article is to collect together separated results of research in the application of fractional derivatives and other fractional operators to problems connected with vibrations and waves in solids having hereditarily elastic properties, to make critical evaluations, and thereby to help mechanical engineers who use fractional derivative models of solids in their work. Since the fractional derivatives used in the simplest viscoelastic models (Kelvin-Voigt, Maxwell, and standard linear solid) are equivalent to the weakly singular kernels of the hereditary theory of elasticity, then the papers wherein the hereditary operators with weakly singular kernels are harnessed in dynamic problems are also included in the review. Merits and demerits of the simplest fractional calculus viscoelastic models, which manifest themselves during application of such models in the problems of forced and damped vibrations of linear and nonlinear hereditarily elastic bodies, propagation of stationary and transient waves in such bodies, as well as in other dynamic problems, are demonstrated with numerous examples. As this takes place, a comparison between the results obtained and the results found for the similar problems using viscoelastic models with integer derivatives is carried out. The methods of Laplace, Fourier and other integral transforms, the approximate methods based on the perturbation technique, as well as numerical methods are used as the methods of solution of the enumerated problems. This review article includes 174 references.
Mechanical Models of Helical Strands
Authors: Cardou A. , Jolicoeur C.
Published: April 2009

Cables, ropes, and overhead electrical conductors are complex helical wire assemblies. Several analytical models are currently available for predicting their mechanical behavior or, at least, some technically interesting aspects of it. In these models, the underlying theory is generally based on a common elementary system, which can be termed a helical wire strand, generally consisting of a core surrounded by one or several wire layers. Depending on strand geometry, loading type (axial or bending), and also, on the required specifications (stiffness, strength, damping), a wide variety of hypotheses can be made. To address this problem, the following tentative classification is presented: fiber models, taking into account only axial wire forces; curved rod models, which include wire bending stiffness and in the most general case, twisting stiffness; and semi-continuous models, in which each wire layer is replaced with an equivalent elastic orthotropic medium. The different models are compared, together with the corresponding experimental data when available. The review is restricted to the elastic behavior under small deformations, which may include contact conditions, with or without friction, and possible stick-slip behavior. Studies related to more complex situations (multi-strand cables, contact with mechanical elements such as pulleys or clamps, viscoelasticity, fatigue, etc) are not included. This review article contains 107 references.
Mechanical Separation Process and Flow Patterns of Cyclone Dust Collectors
Authors: Ogawa Akira
Published: April 2009

A cyclone dust collector (called herein a cyclone) is applied in many industrial fields, for example, powder technology, combustion chambers, various chemical plants, etc. Until now, there are many types of cyclones for the purpose of separation of solid particles; however generally-speaking, the following types of the cyclone are typical: returned flow or reversed flow type, axial flow type, and rotary flow cyclone with tangential injection of the second gas flow to the cyclone body. In order to understand the performance of the cyclone and the problems of turbulent rotational flow and the separation mechanism for solid particles, this review article describes the flow pattern and distribution of the tangential velocity for pure gas flow and for dust laden gas flow, which are most important factors for estimating the pressure drop and the separation characteristics of the solid particles, and also the mechanical separation process in the centrifugal flow field. This review article includes 162 references.
Designing Against Capsize in Beam Seas: Recent Advances and New Insights
Authors: Thompson J. M. T.
Published: April 2009

The mechanics of ship capsize under steady and transient conditions is reviewed, focusing on recent applications of global geometrical techniques of nonlinear dynamics. These yield significant new ideas about capsize in waves and its generalization, the escape of a driven oscillator from a potential well. These ideas are robust against gross changes in the forms of the stiffness and damping functions. Fractal basin boundaries in phase and control space yield useful design criteria against transient capsize, which have been applied to real ships. Invariant manifolds are used to explain and predict the sudden loss of safe basin in the space of the starting conditions, and indeterminate resonant jumps to capsize. Further work is concerned with capsize suppression by heave-roll coupling; effects of parametric excitation; and capsize under a propagating wave front. After this historical review, the practical relevance of the results is assessed, and suggestions are made for a standardized transient testing procedure for hulls. A systematic formulation for rolling in beam waves, employing the effective gravitational field perpendicular to the wave surface and the Froude-Krilov assumption, allows the use of the calm-water GZ curve. With general stiffness and damping functions, dimensional analysis offers insights that are often overlooked: for example, the sustainable wave slope is always proportional to the angle of vanishing stability. A degree of quantification is provided by a design formula derived from the displacement magnification of linear resonance. This is validated by Melnikov theory and simulation. It predicts that under worst-case excitation we have: sustainable wave slope = 2 ζθv, where θv is the angle of vanishing stability and ζ is a damping ratio appropriate for heavy roll. So in ocean waves of slope 0.5 (≈30°), a vessel with a θv of one radian needs a damping ratio of about 1/4. Implications for the design of hulls reveal counter-intuitive results: it is the distance of the potential barrier, not its height, that prevents escape or capsize. The formula helps to define a universal capsize diagram. New results on symmetry breaking are finally presented. These show that capsize studies of a symmetric unbiased vessel can give seriously unsafe results. The sustainable wave slope is so sensitive to a symmetry-breaking bias (due to wind or cargo imbalance) that a static heel of 2.5° can halve the sustainable slope over a wide range of sea states. This review article has 112 references.
Wear of Power Plant Components Due to Impact and Sliding
Authors: Ko P. L.
Published: April 2009

In nuclear power plants, major tribological problems can occur among the interacting components, such as those in the control assembly, the reactors and the steam generators, due to a combination of impact and sliding motion. Many experimental wear tests have been performed in either room temperature or simulated high pressure, high temperature water environments to study the effects of materials and various operating parameters on wear. Although several successful numerical models are now available for the prediction of dynamic responses during component interaction, only empirical models having limited practical applications are available for wear damage prediction. In recent years, with the advances in tribology and the availability of sophisticated instruments for metallurgical analysis, there have been attempts to develop predictive wear models based on the more fundamental aspects of wear particle formation and detachment. This review article gives a comprehensive account of the past and present work on wear of power plant components. It also includes a brief review of the general wear processes and wear mechanisms. There are 162 references.
Scaling Laws for Fully Developed Turbulent Flow in Pipes
Authors: Barenblatt G. I. , Chorin A. J. , Prostokishin V. M.
Published: April 2009

Mathematical and experimental evidence is presented to the effect that the velocity profile in the intermediate region of turbulent shear flow in a pipe obeys a Reynolds-number dependent scaling (power) law rather than the widely believed von Ka´rma´n-Prandtl universal logarithmic law. In particular, it is shown that similarity theory and the Izakson-Millikan-von Mises overlap argument support the scaling law at least as much as they support the logarithmic law, while the experimental evidence overwhelmingly supports the scaling law. This review article includes 39 references.
Aerospace Thermal-Structural Testing Technology
Authors: Thornton Earl A.
Published: April 2009

This review article describes aerospace thermal-structural testing technology. It begins with discussions of aerodynamic heating and space radiation heating. The review continues with a general discussion of thermal-structural test technology including heating and cooling, instrumentation, and thermal-structural boundary conditions. Then illustrative thermal structural tests are presented for high speed flight in the atmosphere and flight in space. Experiments conducted in the laboratory as well as flight tests are described. Several experiments are reviewed to demonstrate the diversity of thermal-structural phenomena. This article includes 120 references.
Using Nonlinearities for Improved Stress Analysis by Thermoelastic Techniques
Authors: Dunn S. A.
Published: April 2009

Stress analysis by thermoelastic techniques has become a growing field since the application of sensitive infra-red measuring devices in the late 1960s. It is commonly asserted that by observing the variation in temperature on the surface of a body as the body undergoes a change in stress, the surface stress changes may be determined via a simple linear relation between temperature and stress. In making this assertion, two fundamental approximations are made: i) the stress changes in such a manner that adiabatic conditions are attained; and, ii) the material properties which relate the change in temperature to the change in stress remain constant throughout the loading process and are not significantly affected by either the stress or temperature change. The aim of this review article is to show the potential applications that can arise when the above two assumptions are not made. It will be shown that in many situations, these effects can significantly bias the experimental data. At first glance, such a bias can pose difficulties in the quantitative assessment of the data; if, however, the nature of these effects are understood sufficiently to be modeled mathematically, then important information can be gained which leads to a more powerful tool for stress analysis. If the assumption of adiabaticity is not applied, then the thermoelastic heat generation and conduction process which occurs when a composite laminate is stressed can be modeled. It will be shown how by observing the manner in which the surface generated temperature is biased by heat conducted from subsurface plies, that the strain components may be determined, even though such stress analysis techniques are typically assumed to measure only bulk stresses. Also, if the material properties are not assumed to remain constant with stress, it can be shown how an understanding of the variation in coefficient of thermal expansion with stress can lead to the potential for measuring residual stresses and plastic zones by thermoelastic techniques. This article contains 53 references.
Tensile Instability of Liposomes in the Presence of Surfactants
Authors: Pamplona D. , Santana M. H.
Published: April 2009

Light scattering and electron microscopy have been utilized in some research in order to study the transition induced by adding surfactant to the aqueous solution of small liposome vesicles. Using the theory of elastic membranes to describe the mixed bilayer of the liposome, an extensive deformation analysis of the enlarged vesicle is reported in the present work. An investigation of pressure versus radius reveals the existence of stable and unstable configurations of equilibrium. From obeservation of the Total Potential Energy function, the instability is recognized and discussed in detail. Besides its value in explaining some very interesting phenomena observed in the experimental study of liposomes in the presence of surfactant, the analysis presented in this paper can be useful in pointing out a way to predict the surfactant critical concentration when the liposome breaks into micelles. This rupture is an undesired phenomenon since the liposomes can be used to transport drugs.
Optimization of Circular Arches Under Multimodal Creep Buckling Constraints With Two Independent Design Functions
Authors: Rysz Marek , Wroblewski Adam
Published: April 2009

The paper deals with the optimal design of circular arches against creep buckling in Rabotnoov-Shesterikov sense. Fundamental buckling modes corresponding to two lowest critical loads both for out-of-plane and in-plane buckling of the arch are studied. Both depth and width of a rectangular cross-section are treated as independent control functions. The design variables are determined so as to minimize the total volume of an arch under given external load (radial pressure) and the critical time. The effect of the behavior of loading in the course of buckling on optimal shapes is analyzed. The problem is solved by the use of Pontriagin’s maximum principle.
Adjoint Shape Sensitivity Analysis for Steady Creep Torsion Problems
Authors: Buscaglia Gustavo C. , Feijo´o Rau´l A. , Taroco Edgardo
Published: April 2009

Taking the total complementary dissipation energy as the cost function and the compatibility as the state equation, the first and second order shape sensitivity analysis for steady-state creep torsion problems are presented in this paper. Using the variational formulation, the fixed domain technique and the adjoint approach, integral expressions over the domain are obtained. Moreover, a particular case with known analytical solution is analyzed in order to show the equivalence between exact differentiation and the shape sensitivity approach. Finally, this example is also used to stress that the extension of the velocity field to the interior of the domain is irrelevant.
Finite Element Analysis of Beams With Constrained Damping Treatment Modeled Via Fractional Derivatives
Authors: Sua´rez Luis E. , Shokooh Arsalan , Arroyo Jose´
Published: April 2009

This paper presents a finite element formulation for the modeling of beams and frames with artificial damping provided by means of a constrained single layer of damping material. The behavior of the damping material is described using the fractional derivative model of viscoelasticity. In this model, the first order derivatives of the strains in the constitutive equations of the viscoelastic materials are replaced by derivatives of order α < 1. The finite element model developed is a one-dimensional beam element with three degrees of freedom per node. The dynamic response is calculated with a procedure involving a transformation of the original equations of motion to the state space and its decoupling with the eigenvectors of a special eigenvalue problem. The accuracy of the modal properties obtained with the beam model is compared with those calculated from a more elaborate plane stress finite element model. It was found that the proposed beam element provides very accurate results and with much lower computational costs than the 2-D model.
Dual Extremum Principles in Finite Deformation Theory With Applications to Post-Buckling Analysis of Extended Nonlinear Beam Model
Authors: Gao David Yang
Published: April 2009

The critical points of the generalized complementary energy variation principles are clarified. An open problem left by Hellinger and Reissner is solved completely. A pure complementary energy (involving the Kirchhoff type stress only) is constructed, and a complete duality theory in geometric nonlinear system is established. We prove that the well-known generalized Hellenger-Reissner’s energy L(u,s) is a saddle point functional if and only if the Gao-Strang gap function is positive. In this case, the system is stable and the minimum potential energy principle is equivalent to a unique maximum dual variational principle. However, if this gap function is negative, then L(u,s) is a so-called ∂+-critical point functional. In this case, the system has two extremum complementary principles. An interesting trinity theorem for nonconvex variational problem is discovered, which can be used to study nonlinear bifurcation problems, phase transitions, variational inequality, and other things. In order to study the shear effects in frictional post-buckling problems, a new second order 2-D nonlinear beam model is developed. Its total potential is a double-well energy. A stability criterion for post-buckling analysis is proposed, which shows that the minimax complementary principle controls a stable buckling state. The unilaterial buckling state is controled by a minimum complementary principle. However, the maximum complementary principle controls the phase transitions.
Rotorcraft Subfloor Design for Enhanced Crashworthiness Characteristics
Authors: Hajela P. , Lee E.
Published: April 2009

The present paper describes an approach for the optimal sizing of rotorcraft subfloor structures to minimize structural damage and the incidence of severe injury to the occupants under crash loads. The crash analysis in the present work was modeled through the use of a discrete analysis code (KRASH), which uses lumped masses, linear and nonlinear beam elements, and nonlinear spring elements to model the primary and secondary structures. The optimal load-deflection characteristics of the subfloor components, and the placement of these components in the subfloor region were then obtained through the use of a genetic algorithm-based search procedure. Finally, an inverse design approach was used to recover the dimensions of typical energy absorbing structural components that would yield the load deflection behavior derived in the previous step. A neural network-based response surface was constructed to alleviate the stiff computational requirements of this numerical procedure.
Simple Shear in Granular Media
Authors: Haythornthwaite Robert M.
Published: April 2009

The ring shear box is analyzed using an isotropic strain hardening/softening model for granular media, permitting an estimate to be made of the stresses developed under conditions of simple shear, at the critical void ratio. Observation of the radial stress on the inner or outer walls of the test chamber would provide a measure of the relative value of the otherwise unknown intermediate principal stress. In a series of five tests on a quartz sand, average pressures exerted by the sand on the outer wall of the test chamber reached well defined, repeatable levels. As interpreted by the theory, the tests showed that the intermediate principal stress was equal to the direct stress on the Coulomb friction planes during simple shear: (1−sinφcv)σ1=σ2=(1+sinφcv)σ3 where σ1 > σ2 > σ3 (compression positive), and φcv is the angle of internal friction at the critical void ratio, ie, during continuing displacement at constant volume. Similar observations are impossible for plane strain in general because displacement cannot be controlled so completely, but it is reasonable to conjecture that the same relationship holds for all such deformations, including those associated with the active and passive Rankine states.
Localization, Scaling, and Diffuse Transport of Wave Energy in Disordered Media
Authors: Weaver Richard
Published: April 2009

The Anderson localization literature in structural acoustics has to date been concerned largely with applications to the vibrations of one dimensional structures, whether mono-coupled or multi-coupled, and to steady state responses in such systems. This paper presents a brief tutorial on the theory of wave localization in one and higher dimensions with an emphasis on the scaling theory of localization. It then reviews the acoustic and optical literature on wave localization with an emphasis on diffuse time domain responses to transient loads. Numerical and laboratory experiments demonstrating localization in higher dimensions and investigating the time-domain behavior of such systems are discussed. Scaling theory is shown to provide predictions for localization lengths in weakly disordered multi-coupled systems, and for localization lengths in weakly disordered two-dimensional systems as well. Theoretical arguments for rates of diffuse transport are contrasted with the experimental evidence. The paper concludes with a discussion of wave energy confinement in non-localizing disordered systems.
Nonlinear Mode Localization in Systems Governed by Partial Differential Equations
Authors: Vakakis Alexander F.
Published: April 2009

The concept of nonlinear normal mode (NNM) is used to study localized oscillations in certain classes of oscillators governed by nonlinear partial differential equations. NNMs are synchronous free oscillations during which all positional coordinates of the system reach their extreme values or pass through the equilibrium position at the same instant of time. Although such motions can be regarded as nonlinear analogs of the linear normal modes of classical vibration theory, not all NNMs are analytic continuations of linear ones. Continuous systems of finite and infinite spatial extent are considered. For periodic assemblies consisting of a finite number of nonlinear structural members, the NNMs are computed asymptotically by solving nonlinear sets of equations possessing regular singular points. Some of the computed NNMs are spatially localized to only a limited number of components of the assembly. The bifurcations giving rise to nonlinear mode localization are examined using the perturbation method of multiple-scales. The implications of nonlinear mode localization on the vibration and shock isolation of periodic flexible structures are discussed. In particular, localized NNMs lead to passive motion confinement of disturbances generated by impulsive loads. Finally, the concept of NNMs is extended to analytically study standing waves with spatially localized envelopes in a class of nonlinear partial differential equations defined over infinite domains. It is shown that NNM-based methodologies can be an effective tool for analyzing such motions.