bluuebunny/crossref_metadata_2025 huggingface dataset:
45 deg Round-Corner Rib Heat Transfer Coefficient Measurements in a Square Channel
Authors: Taslim M. E. , Lengkong A.
Published: April 2009

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of 45 deg, round-corner ribs. Three staggered rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel wall. Comparisons were made between the surface-averaged heat transfer coefficients and channel friction factors for sharp-and round-corner ribs and 45 versus 90 deg ribs, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the ribroughened region were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. (b) The general effect of rounding the rib corners was a decrease in both rib heat transfer coefficient and channel pressure drop. (c) For the highest blockage ratio ribs (e/Dh = 0.25), 90 deg ribs performed superior to 45 deg ribs. However, this trend reversed for smaller rib blockage ratios. (d) Heat transfer coefficients for the two smaller rib geometries (e/Dh = 0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. (e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. (f) Rib thermal performance decreased with the rib blockage ratio. The smallest rib geometry (e/Dh = 0.133) at a pitch-to-height ratio of 10 and the largest rib geometry (e/Dh = 0.25) at a pitch-to-height ratio of 5, both in midstream position, produced the highest and the lowest thermal performances, respectively.
An Experimental Study on the Relationship Between Velocity Fluctuations and Heat Transfer in a Turbulent Air Flow
Authors: Denninger M. J. , Anderson A. M.
Published: April 2009

The work presented here is the first reported study to test the general correlation for turbulent heat transfer proposed by Maciejewski and Anderson (1996). A turbulent pipe flow apparatus was built for heat transfer and fluid studies. Tests were performed for a range of Reynolds numbers from 27,000 to 90,000. The heated wall temperature, adiabatic temperature, the wall heat flux, and the maximum velocity fluctuations were measured at each Reynolds number. The nondimensional groups recommended by Maciejewski and Anderson were formed and compared to the correlation. The results verify the correlation with agreement to within ±7 percent (as per Fig. 11). This study has important implications for the study of heat transfer in a wide range of fields, including the gas turbine industry. The development of a geometry independent correlation will lead to faster turn-around times and improved engine design.
Development of a Centrifugal Compressor With a Variable Geometry Split-Ring Pipe Diffuser
Authors: Salvage J. W.
Published: April 2009

Higher noise levels resulted when a compressor was scaled to larger capacity. The machine’s sound pressure level was relieved by increasing the distance between the impeller blade tip and diffuser leading edge. However, the part-load surge line deteriorated severely as a consequence. A variable geometry pipe diffuser solved this problem, permitting operation at stringent off-design conditions. The addition of a variable diffuser permits compressor selection very near its most efficient full-load operating point, without regard for limitations normally imposed by part-load requirements. The principal lessons learned during aerodynamic design refinement include (a) how performance and surge depend upon positioning the variable inlet guide vanes and variable diffuser, and (b) how to define simultaneous variation of inlet guide vanes and diffuser for specific operational objectives. Generally, each operating point requires a unique setting of the variable components to achieve maximum efficiency. However, linked movement is shown to yield both a satisfactory surge line and improved performance for most applications when compared to a compressor without the variable geometry pipe diffuser.
Multistage Centrifugal Compressor Surge Analysis: Part I—Experimental Investigation
Authors: Arnulfi G. L. , Giannattasio P. , Giusto C. , Massardo A. F. , Micheli D. , Pinamonti P.
Published: April 2009

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage, are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference data on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle. The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multistage centrifugal compressors and to validate a theoretical model of the system instability to be used for the design of dynamic control systems.
Turbomachinery Blade Design Using a Navier–Stokes Solver and Artificial Neural Network
Authors: Pierret S. , Van den Braembussche R. A.
Published: April 2009

This paper describes a knowledge-based method for the automatic design of more efficient turbine blades. An Artificial Neural Network (ANN) is used to construct an approximate model (response surface) using a database containing Navier–Stokes solutions for all previous designs. This approximate model is used for the optimization, by means of Simulated Annealing (SA), of the blade geometry, which is then analyzed by a Navier–Stokes solver. This procedure results in a considerable speed-up of the design process by reducing both the interventions of the operator and the computational effort. It is also shown how such a method allows the design of more efficient blades while satisfying both the aerodynamic and mechanical constraints. The method has been applied to different types of two-dimensional turbine blades, of which three examples are presented in this paper.
A Nonlinear Numerical Simulator for Three-Dimensional Flows Through Vibrating Blade Rows
Authors: Chuang H. A. , Verdon J. M.
Published: April 2009

The three-dimensional, multistage, unsteady, turbomachinery analysis, TURBO, has been extended to predict the aeroelastic response of a blade row operating within a cylindrical annular duct. In particular, a blade vibration capability has been incorporated, so that the TURBO analysis can be applied over a solution domain that deforms with a vibratory blade motion. Also, unsteady far-field conditions have been implemented to render the computational inlet and exit boundaries transparent to outgoing unsteady disturbances and to allow for the prescription of incoming aerodynamic excitations. The modified TURBO analysis has been applied to predict unsteady subsonic and transonic flows. The intent is to validate this nonlinear analysis partially for blade flutter applications via numerical results for benchmark unsteady flows, and to demonstrate this analysis for a realistic fan rotor. For these purposes, we have considered unsteady subsonic flows through a three-dimensional version of the 10th Standard Cascade and unsteady transonic flows through the first-stage rotor of the NASA Lewis Rotor 67 fan. Some general correlations between aeromechanical stabilities and fan operating characteristics will be presented.
Prediction and Measurement of Rotating Stall Cells in an Axial Compressor
Authors: Saxer-Felici H. M. , Saxer A. P. , Inderbitzin A. , Gyarmathy G.
Published: April 2009

This paper presents a parallel numerical and experimental study of rotating stall cells in an axial compressor. Based on previous theoretical and experimental studies stressing the importance of fluid inertia and momentum exchange mechanisms in rotating stall, a numerical simulation using the Euler equations is conducted. Unsteady two-dimensional solutions of rotating stall behavior are obtained in a one-stage low subsonic axial compressor. The structure and speed of propagation of one fully developed rotating stall cell together with its associated unsteady static pressure and throughflow field distributions are presented. The numerical capture of a stalled flow region starting from a stable high-flow operating point with an axisymmetric flow distribution and evolving at a reduced mass flow operating point into a rotating stall pattern is also discussed. The experimental data (flow visualization, time-averaged and unsteady row-by-row static pressure measurements) acquired in a four-stage water model of a subsonic axial compressor cover a complete characteristic line ranging from high mass flow in the stable regime to zero throughflow. Stall inception is presented together with clearly marked different operating zones within the unstable regime. For one operating point in the unstable regime, the speed of propagation of the cell as well as the static pressure spikes at the front and rear boundaries of the rotating stall cell are compared between computations, measurements, and an idealized theory based on momentum exchange between blade rows entering and leaving the stalled cell. In addition, the time evolution of the pressure trace at the rotor/stator interface is presented. This study seems to support the assumption that the cell structure and general mechanism of full-span rotating stall propagation are essentially governed by inertial effects and momentum exchange between the sound and stalled flow at the cell edges.
State Surfaces of Partially Saturated Soils: An Effective Pressure Approach
Authors: Bolzon Gabriella , Schrefler Bernhard A.
Published: April 2009

State surfaces may be given by interpolation of experimental data or may represent the integration of linear or nonlinear elastic constitutive equations. Anelastic behavior may also be considered if only loading is taken into account to ensure the uniqueness of the surface. State surfaces are usually defined in the (p, q, s) space, where p, q, and s represent, respectively, the excess of mean stress over air pressure, the deviatoric stresses, and suction. An alternative approach assumes similar constitutive equations but defined in the space (p′, q), where p′ represents the effective pressure. This latter approach is extended to the space (p′, q, s) and improved to carefully deal with the role of suction, in conjunction with the confining pressure, in controling soil expansion (swelling).
Phenomenological Approach to Flow and Volume Change in Soils and Other Media
Authors: Philip J. R.
Published: April 2009

We review the phenomenological approach, on the macroscopic or Darcy scale, to flow and volume change in clays and other swelling media. The formulation represents the generalization to media subject to volume change of the well-established phenomenological approach to flow in non-swelling media primarily established in the context of soil physics. The one-dimensional generalization to swelling media is straightforward, and may be usefully applied to practical one-dimensional systems, including three-component systems with solid particles, water, and air. On the other hand, the further generalizations to two- and three-dimensional systems have not yet been developed fully convincingly. Difficult questions include the mode of stress transmission and the tensorial stress-strain relations in multidimensional and multi-component systems. One means of gaining insight into these questions for media of high colloid content (such as clays) is through relevant solutions of the Poisson-Boltzmann equation governing electrical double-layer interactions in dense arrays of colloidal particles. These solutions give pertinent information on both the macroscopic and the microscopic scales. We present a progress report on work along these lines.
Experimental Investigation of Water Soaked Wood at Uniaxial and Biaxial States of Stress
Authors: Kowal M. , Kowalski S. J.
Published: April 2009

It is possible to observe a significant difference in swelling strains of unstressed and stressed water soaked wood. This paper points out that the swelling strains depend not only on the magnitude of stress in wood but also on the kind of stress state. Our main aim is to investigate the relation between various states of stress and the swelling strains in water soaked wood. Three different states of stress are studied: tension in the radial direction, compression in the tangential direction with respect to the growth rings, and both these stresses acting together (biaxial stress). Some weighty conclusions follow from the investigations. The main one is that, although the mechanical strains alone are negligibly small compared to the free swelling strains, the coupled mechanical-swelling strains, being a function of the stress state and the moisture content, have a great significance in total strains of water soaked wood.
Effect of Swelling on the Failure Mode of Foamy Materials
Authors: Theocaris Pericles S.
Published: April 2009

A study was undertaken for the mode of failure of open- or closed-cell cellular materials depending on the variation of the relative density of the material because of swelling or variation of its porosity. The cellular materials or foams were considered as transversely isotropic, an assumption which corresponds well with their mechanical behavior. Using a tensor failure polynomial criterion, and as such the elliptic paraboloid failure criterion was considered, for the study of the mode of failure of closed-cell foams of different relative densities, it was established that the failure behavior of the swelled material changes drastically its failure mode by becoming a tension strong material from a compression-strong one. Furthermore, there is a critical value of the relative density for each material where the substance passes through a quasi-isotropic state and the foam behaves like an isotropic material, where triaxiality phenomena are significant.
Some Remarks About Mechanics of Porous Elastically Deformable Media
Authors: Naili S. , Le Galo O. , Geiger D.
Published: April 2009

The traditional tools of continuum mechanics are used to describe the behavior of a solid elastic matrix saturated with a viscous fluid. Conservation equations for mass and momentum, (with particular attention to viscous incompressible fluids) are established and the total energy is introduced, Conditions concerning the coefficients characterizing the medium are obtained by considering the thermodynamically-allowed behavior.
Transport of Water in a Biconstituent Elastic Medium
Authors: Mrani I. , Be´net J. C. , Fras G.
Published: April 2009

A phenomenological equation is established for water transport in a biconstituent, isotropic, isothermal elastic medium. The equation includes a term related to the water content gradient and a term related to the deformation gradient. It is shown that in the case of an infinite plate, the transport law can be similar to Fick’s law in which water flux is proportional to the water content gradient alone. The apparent transport coefficient then depends on the hygroscopic and rheological coefficients of the medium. Experimental analysis of the evolution of water content profiles of agar gel plates validates this transport law and makes it possible to deduce the variation in apparent transport coefficient according to water content. Transport coefficients associated with water content and deformation gradients and applicable to any geometrical features are deduced.
Measurement of Suction in Materials Which Swell
Authors: Ridley A. M. , Burland J. B.
Published: April 2009

Swelling is the process of volume expansion, usually brought about by the intake of water. One mechanism by which water can be drawn into a material is if the material has less water than it would like to have, a dry sponge is a typical example. The stress which a moisture deficient material can exert on an adjacent body of water is known as the suction. As water is absorbed into the material the affinity which the material has for the water decreases as does the suction in the material. Suction is very important in the characterization of materials (particularly soils) with a moisture deficiency, but its measurement is not easy to perform. In agriculture, the ability of crops to extract water from the soil is governed by the suction of the soil. In particular the plant has to overcome the affinity of the soil for water in order to feed. The suction at which the plant can no longer do this is known as the wilting point for obvious reasons. In engineering, the strength and volume of an unsaturated soil (one in which the spaces between adjacent soil particles are filled with a mixture of water and a gas) is characterized by a combination of the external stresses applied to the soil and the suction within the soil. It is principally these two fields which have been concerned with the measurement of the suction. However only a relatively few techniques have evolved which successfully measure the quantity and only one exists which is capable of making a direct measurement under atmospheric conditions. As a consequence of the lack of direct techniques it has been necessary to use indirect methods. Indirect measurements are classified as those which actually measure another quantity such as humidity, absorbtion or conductivity, which can then be converted to a measure of suction. Ridley (1993) has reviewed the available methods of suction measurement.
Some Remarks on the Identification of Damping Parameters at the Boundary of Vibrating Systems
Authors: Hagedorn Peter , Pabst Ulrich
Published: April 2009

In many cases, vibrating mechanical systems permit a reliable mathematical modeling with parameter values which are reasonably well known beforehand, except for the joints between different subsystems and at the boundaries. The boundary stiffness, which is often assumed as infinite, and the damping at the boundary, which is frequently ignored, are typically not well known. In this note, we discuss the identification of the boundary stiffness and damping parameters from modal data. As an example, we treat an elastic steel beam, for which an experimental modal analysis had been carried out in our laboratory.
Response of Systems With Damping Materials Modeled Using Fractional Calculus
Authors: Suarez L. , Shokooh A.
Published: April 2009

The mathematical modeling of damping materials based on fractional calculus has been shown to be very effective in representing the frequency dependence of the properties of these materials. In this model, the integer order derivatives in the constitutive equations of the Kelvin model are replaced by derivatives of fractional order. In this paper, we examine the response of a single degree-of-freedom system in which the damping force is proportional to a derivative of order α < 1 of the displacements. Three methods are proposed to obtain the response: the Laplace and Fourier transform methods, and an operator method that results in a series solution. Some interesting features exhibited by the oscillator’s response due to the fractional representation of the damping are unveiled.
Planar Cosserat Elasticity of Materials With Holes and Intrusions
Authors: Jasiuk I. , Ostoja-Starzewski M.
Published: April 2009

Recently, Cherkaev, Lurie, and Milton (1992) established an invariance of stress field in planar linear anisotropic elasticity under a specific shift in bulk and shear moduli; this is now known as the CLM theorem. Motivated by the importance of micropolar models in mechanics of media with micropolar structures, Ostaja-Starzewski and Jasiuk (1995) generalized the CLM theorem to planar micropolar elastic materials and considered inhomogeneous simply-connected materials. The present study addresses inhomogeneous, multiply-connected materials (with holes), which require global compatibility conditions involving Cesa`ro integrals, as well as multi-phase simply-connected materials, where the interface conditions need to be considered. Just as in the previous paper, both of these cases display a reduction in the parameter space.
Classification of Swing-By Trajectories Using the Moon
Authors: Prado Antonio Fernando Bertachini de Almeida , Broucke Roger
Published: April 2009

In the present paper we study and classify the swing-by maneuvers that use the Moon as the body for the close approach. The goal is to simulate a large variety of initial conditions for those orbits and classify them according to the effects caused by the close approach in the orbit of the spacecraft. Special attention is given to identify the regions where the captures and escapes occur. The classical three parameters (Jacobian constant, pericenter distance and angle of approach) used to identify a Swing-By maneuver are varied in large intervals to cover a large range of possibilities for the maneuver. Letter-plots figures are made to show the results obtained in a compact form. The theoretical prediction that for 0° ≤ ψ ≤ 180° the spacecraft losses energy and for 180° ≤ ψ ≤ 360° the spacecraft gains energy is confirmed. Regions containing trajectories that are candidates to generate Belbruno-Miller trajectories are identified. The well-known planar restricted circular three-body problem is used as the mathematical model. The equations are regularized (using Lamaiˆtre’s regularization), so it is possible to avoid the numerical problems that come from the close approach with the Moon.
Structural Attenuation Due to Seismic Inputs With Adaptive Hybrid Control Systems
Authors: Burdisso R. A.
Published: April 2009

A numerical simulation of adaptive feedforward control of building structures under seismic inputs is presented. The control actuator is an active tuned mass damper (ATMD) located on the last floor of an eight-story shear type building. The properties of the tuned mass damper (TMD) are selected for optimum performance as a passive device, i.e. the natural frequency of the device is nearly the same as the fundamental frequency of the building. The feedforward compensator is implemented with a finite impulse response (FIR) filter. The ground acceleration is sensed and fed forward into the compensator to generate the control input. The adaptive algorithm updates in “real time” the compensator’s weights such that a critical response, referred as the error signal, is minimized. The relative displacement of the first floor, which is monitored with an error transducer, is the error signal to be minimized. The ground motion used for the computer simulation includes various real accelerograms. The passive TMD is able to attenuate the peak and root mean square (rms) responses by an average of 14.6 and 16.6%, respectively. The attenuation achieved for the hybrid passive/active control approach was 44.4 and 51.2%, respectively, which clearly demonstrates that the adaptive controller improves the effectiveness of the passive TMD to attenuate both the maximum and root-mean-square responses. The numerical simulation also shows that the algorithm adapts in “real time” for uncertainties and modeling errors in the system.
Damping Prediction for Stalled Rotor Flap-Lag Stability With Experimental Correlation
Authors: Tang D. M. , Dowell E. H.
Published: April 2009

A direct numerical time marching integration is used to compute the transient response (free oscillation) of the flap-lag motion of a stalled rotor. A time-domain quasilinear model identification technique is applied to identify the damping and frequency for the regressing mode, except for the chaotic lag response when stall occurs. A numerical example and correlation with the experimental results (Ref [4]) are provided. It is found that the present theoretical method has improved the flap-lag stability analysis with respect to agreement with experiment compared to earlier theoretical results.
Numerical Analysis of Compressible Fluids and Elastic Structures Interaction
Authors: Santos Maria Angela Vaz dos , Awruch Armando Miguel
Published: April 2009

A finite element algorithm to simulate two dimensional flows of viscous and inviscid compressible fluids for a wide range of Mach numbers is presented in this work. This model is coupled to immersed deformable structures through equilibrium and compatibility conditions in order to analyze its dynamic behavior. For the fluid, time integration is performed by a two-step Taylor-Galerkin explicit scheme and Newmark’s method is used to obtain the dynamic response of the structure. An arbitrary mixed Euler-Lagrange description is used to re-define a new finite element mesh in the presence of the immersed structure displacements. Finally, several examples are included showing the model behavior and possibilities for future expansions.
CVBEM Formulation for Multiple Profiles and Cascades
Authors: Storti Mario , D’Eli´a Jorge , Idelsohn Sergio
Published: April 2009

A numerical algorithm based on the CVBEM (from Complex Variable Boundary Element Method) for plane incompressible potential flow around aerofoils and cascades is described. The method is based on the representation of the complex disturbance velocity by means of a Cauchy-type integral around the foil. The Cauchy density function is approximated piecewise linearly and a linear system on the nodal values is obtained by collocation at the nodes. The Kutta condition is imposed via a Lagrange multiplier, in contrast with the least-squares formulation used in a previous work. For cascades, the problem is conformally mapped by a simple hyperbolic function (exponential or hyperbolic tangent) to a related problem with only one profile and one or two poles. Thus, the cascade problem is accurately solved with minor modifications to the single profile code and at the same cost of a single profile computation. Finally, several numerical examples are shown: single Joukowski and NACA profiles, interference coefficients for the flat plate cascade and a plane cascade at the external cylindrical section of an industrial fan.
Effect of Polymeric Additives on Turbulent Flow in Opposed Jets
Authors: Mu¨ller A. J. , Saez A. E. , Tatham J. P. , Odell J. A.
Published: April 2009

In this work we study the effect of polymeric additives on the transition to turbulence in opposed-jets flow. In this type of flow, the transition to turbulence for Newtonian fluids is characterized by a decrease in the rate of change of pressure drop with flow rate. We have used various polymers whose equilibrium molecular conformation in aqueous solution is different: poly (ethylene oxide), which exists in a conformation close to a random coil, hydroxypropyl guar, which adopts an expanded coil conformation, and hydrolyzed polyacrylamide, whose conformation is close to a random coil in the presence of an electrolyte (sodium chloride) but it changes to an expanded coil in distilled water. The results show that small amounts of either flexible or semi-rigid polymers induce a delay in the critical Reynolds number at which turbulence sets in. This delay seems to be a result of the suppression of flow instabilities in a region close to the stagnation point, which is linked to macromolecular orientation. Since, for Newtonian fluids, this flow has an increase of drag with flow rate that is slower in the turbulent flow regime than in the laminar regime, the addition of polymer causes a substantially higher pressure drop in turbulent flow with respect to that of the pure solvent. Therefore, polymer addition causes, in this particular case, a drag increase in turbulent flow, as opposed to the commonly observed drag reduction in turbulent flow through pipes.
Construction of Dynamic Fundamental Solutions for Piezoelectric Solids
Authors: Khutoryansky Naum , Sosa Horacio
Published: April 2009

Fundamental solutions are derived within the framework of transient dynamic, three-dimensional piezoelectricity. The purpose of the article is to show alternate integral representations for such solutions. Thus, a representation over the unit sphere in accordance to a methodology based on the plane wave decomposition is provided. It is shown, however, that more efficient representations from a computational point of view can be achieved through appropriate coordinate transformations. Hence, representations of the fundamental solutions over surfaces of slowness are provided as novel alternatives to more classical approaches. The computational benefits of these new representations are displayed through a numerical example involving a transversely isotropic piezoelectric solid.
Two-Dimensional Shell Element for Nonlinear Analysis
Authors: Flores Fernando G.
Published: April 2009

A 2D beam/shell element for nonlinear geometrical and material analysis is presented. The element is based on Simo’s one director tridimensional shell theory. The theory is formulated in stress resultants, so through-the-thickness integration is avoided. Elasto-plastic material behavior with both linear isotropic and kinematic hardening is considered. Yield function is described in terms of 2nd Piola-Kirchhoff stress resultants and is equivalent to von Mises. Three benchmarks are studied in order to assess the nonlinear behavior. First an elastic beam with large rotation and large displacements is presented. Then two thin sheet metal forming problems with moderate large strains are considered. The results obtained are very good and show excellent convergence properties.
Buckling Mode Interaction in Composite Plate Assemblies
Authors: Raftoyiannis Ioannis G. , Godoy Luis A. , Barbero Ever J.
Published: April 2009

The analysis of buckling mode interaction of fiber-reinforced composite columns, modeled as plate assemblies, is presented. The main assumptions are linear elasticity; a linear fundamental equilibrium path; the existence of critical states that are coincident or near coincident; and a coupled path rising from a quadratic combination of modal displacements due to interaction. The formulation adopted is known as the W-formulation, in which the energy is written in terms of a sliding set of incremental coordinates, measured with respect to the fundamental path. The energy is then expressed with respect to a reduced modal coordinate basis, and the coupled solution arising from interaction is computed. An example of a pultruded composite I-column subjected to axial compression illustrates the procedure.
Contradictory Formulas of Local Probability of Fracture
Authors: Diaz G. , Martinez V. , Kittl P.
Published: April 2009

The present work studies two deductions used to determine the local probability of fracture and whose final expressions coincide only in the case of a Weibull specific risk of fracture function of two parameters. As a result thereof, the inconsistency of one of the two deductions is shown and it is explained how to differentiate the two approaches experimentally. Three-point bending of a rectangular and a round beam is studied by resorting to the integral equations method in order to find the Weibull specific risk function.
Analysis of Free Vibrations of Conical Shells Using Donnell’s Approximations
Authors: de Souza V. C. M. , Saraiva J. M. F.
Published: April 2009

The free vibrations of conical shells, having two open rigidly clamped edges, are investigated by using a variational development of the equations of motion based upon the Classical Shell Theory, and results are compared with those obtained by using Donnell’s approximation in the development of these equations. Through suitable examples, the validity of Donnell’s approximation to compute natural frequencies and mode-shapes of conical shells is shown.
Alternative Approach for the Exact Solution of the Forced Vibrations of Beams
Authors: Filipich Carlos P. , Rosales Marta B.
Published: April 2009

The present work is an extension of a tool vastly used by the authors to solve static boundary problems in one, two, and even three dimensions. It consists in a so-called generalized solution with special trigonometric Fourier functions to solve the equations of motion of beams. An important theorem that guarantees that the classic answer is attained through an alternative way is demonstrated. In other words, it is a variational methodology to solve differential equations in engineering. An example solved numerically completes the present proposal.
Synchronization and Chaotization in Interacting Dynamical Systems
Authors: Blekhman I. I. , Landa P. S. , Rosenblum M. G.
Published: April 2009

Synchronization of systems executing periodic and chaotic motions, both oscillatory and rotatory, is considered from the general standpoint in this review article. It is shown that the synchronization phenomenon goes hand in hand with the phenomenon of chaotization. The analogy of synchronization and phase transitions is shown. Several mechanical and physical examples are discussed.
Cosserat Plasticity and Plastic Spin
Authors: Lippmann H.
Published: April 2009

A review of the present approaches to Cosserat plasticity and to its applications is presented, in comparison with the direct Theory of the Plastic Spin. In both theories, the classical rigid-plastic continuum with stress and strain rate as principal field quantities is generalized to also incorporate the relative “Plastic Spin”, ie, the average irreversible rotation of the microstructural elements (“grains” ) in a mesovolume, relative to the rotation induced by the field of point velocities or point displacements. Moreover, the Cosserat plasticity represents a complete, generalized continuum mechanical theory, where also the additional kinematic quantities, ie, the plastic spin and the internal twist are complemented by associate static quantities as, asymmetric stress or couple stress. While the direct Theory of the Plastic Spin is confined to non-isotropic materials, where the average rotation of the grains corresponds also to the rotation of the macrostructure, (texture) the Cosserat approach is also concerned with, and contemporarily even devoted to isotropic media. After presenting a general survey of the literature, experiments carried out with a generalized Couette flow, (for granular or rock-like materials) or in the torsion test, (for metals) are discussed showing that the Plastic Spin is an observable quantity generally different from zero even in an isotropic material. It can be predicted to the same extent, using the Cosserat plasticity as using any one of the much more complicated theories of crystal plasticity.
R-Functions in Boundary Value Problems in Mechanics
Authors: Rvachev V. L. , Sheiko T. I.
Published: April 2009

Described are the concepts and applications of the R-functions theory in continuum mechanics boundary value problems which model fields of different physical natures. With R-functions there appears the possibility of creating a constructive mathematical tool which incorporates the capabilities of classical continuous analysis and logic algebra. This allows one to overcome the main obstacle which hinders the use of variational methods when solving boundary value problems in domains of complex shape with complex boundary conditions, this obstacle being connected with the construction of so-called coordinate sequences. In contrast to widely used methods of the network type (finite difference, finite and boundary elements), in the R-functions method all the geometric information present in the boundary value problem statement is reduced to analytical form, which allows one to search for a solution in the form of formulae called solution structures containing some indefinite functional components. A method of constructing solution structures satisfying the required conditions of completeness has been developed. The structural formulae include the left-hand sides of the normalized equations of the boundaries of the domains or their regions being considered, thus allowing one to change the solution structure expeditiously when changing the geometric shape. Given in the work is a definition of the basic class of R-functions, solution with their help of the inverse problem of analytical geometry (construction of equations of specified configurations); generalization of the Taylor-Hermite formulae for functional spaces in which points are represented by lines and surfaces; and construction of solution structures of some types of boundary value problems. Shown are the solutions of a number of concrete problems in these application fields with the use of the RL language and POLYE system.
Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows
Authors: Brereton G. J. , Mankbadi R. R.
Published: April 2009

Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.
Dynamic Processes in Structural Thermo-Viscoplasticity
Authors: Irschik Hans , Ziegler Franz
Published: April 2009

A multiple field theory dates back to developments in linear thermo-elasticity where the thermal strain is considered to be imposed on the linear elastic background structure in an isothermal state. Load strain and thermal strain fields are coupled by the boundary conditions or exhibit volume coupling. Taking into account a proper auxiliary problem, eg, the structure loaded by a unit force under isothermal conditions, results in Maysel’s formula and thus represents the solution in an optimal manner. That approach was generalized to dynamic problems and its efficiency was enhanced by splitting the solution in the quasi-static part and in the dynamic part thus considering the inertia of mass in the latter portion. This paper reviews recent extensions of such a multiple field theory to nonlinear problems of structural thermo-viscoplasticity. Their basis is given in formulations of micromechanics. In an incremental setting, the inelastic strains enter the background material as a second imposed strain field. Considering the rate form of the generalized Hooke’s law such a three-field representation is identified by inspection. Geometric nonlinearity is not fully taken into account, only approximations based on a second order theory, and, for beams and plates with immovable boundaries, in Berger’s approximation, render a third “strain field” to be imposed on the linearized background structure. A novel derivation of the dynamic generalization of Maysel’s formula is given in the paper. An elastic-viscoplastic semi-infinite impacted rod serves as the illustrative example of the fully dynamic analysis in the multiple field approach. Ductile damage is taken into account and the dissipated energy is deposited under adiabatic conditions. Material parameters are considered temperature dependent. An extension to a finite element discretization of the background structure seems to be possible, when preserving the solely linear elastic solution technique. Quite naturally, the domain integral boundary element method of solution results from such a multiple field approach.
Transient Heat Transfer in Extended Surfaces
Authors: Aziz A. , Kraus Allan D.
Published: April 2009

This paper attempts to provide a comprehensive, coherent, and methodical review of the existing literature on the transient performance of extended surfaces (fins). With the exception of very few experimental studies, the work described is theoretical involving either analytical approaches or numerical computations. For both longitudinal and radial convecting fins, the shapes analyzed include fins of rectangular, trapezoidal, concave parabolic, and convex parabolic profiles. The boundary conditions considered are those of time-dependent base temperature or time-dependent base heat flow, or time-dependent temperature of the fluid on the unfinned side of the primary surface. Other studies discussed consider the transient responses of radiating and convecting-radiating fins, fins with stochastic base temperature and fins in which conduction, natural convection, and radiation are coupled. The paper also provides an in-depth consideration of two-dimensional analyses of a cylindrical spine (pin fin) and a composite longitudinal fin. All of the important results pertaining to the transient effect in extended surfaces are presented and these effects are illustrated with several examples. The paper concludes with an attempt to identify future investigative efforts.
Bibliography on Skin Friction Reduction With Polymers and Other Boundary-Layer Additives
Authors: Nadolink Richard H. , Haigh Wayne W.
Published: April 2009

This bibliography on skin friction reduction with boundary-layer additives including polymers, surfactants, disoaps, micelles, and particulates, covers over a seventy-year period from 1922 through 1994. Although the emphasis in this bibliography is on the fluid mechanics associated with alterations in boundary-layer momentum transfer, complementary studies on boundary-layer heat and mass transfer are also inlcuded. The emphasis in this bibliography is on turbulent flows for a wide variety of configurations and conditions, however, some publications on transitional and laminar flows have also been included for completeness. Over 4,900 publications are included in this sizable bibliography.
Cavitation in Nonlinearly Elastic Solids: A Review
Authors: Horgan C. O. , Polignone D. A.
Published: April 2009

Cavitation phenomena in nonlinearly elastic solids have been the subject of extensive investigation in recent years. The impetus for much of these theoretical developments has been supplied by pioneering work of Ball in 1982. Ball investigated a class of bifurcation problems for the equations of nonlinear elasticity which model the appearance of a cavity in the interior of an apparently solid homogensous isotropic elastic sphere or cylinder once a critical external tensile load is attained. This model may also be interpreted in terms of the sudden rapid growth of a pre-existing microvoid. In this paper, we briefly summarize some of the main results obtained to date on radially symmetric cavitation, using the bifurcation model. The paper is a review and a comprehensive list of references is given to original work where details of the analyses may be found.
Biomechanics of Growth, Remodeling, and Morphogenesis
Authors: Taber Larry A.
Published: April 2009

This review deals with biomechanical aspects of growth (mass change), remodeling (property change), and morphogenesis (shape change) in living systems. The emphasis is on theoretical models, but relevant experimental results also are discussed. As an aid to the reader, the fundamental biological terms and concepts are defined for the general problem and for each specific topic. At the outset, the processes involved in growth, remodeling, and morphogenesis are described and placed within the context of the evolution of species. Next, some of the analytical methods used in biomechanical models for these processes are presented. Then, applications of these and other techniques to specific systems are discussed, beginning at the cellular level and proceeding upward to the tissue and organ levels. At the cellular level, modeling and experimental studies are reviewed for cell division, cell movement, and pattern formation, and then morphogenetic mechanisms for epithelia (cell sheets) are discussed. At the tissue and organ levels, the musculoskeletal and cardiovascular systems are considered. Several models are described for growth, remodeling, and morphogenesis of bone, and mainly experimental results are examined in the cases of skeletal muscle, the heart, and arteries. Specific topics for the cardiovascular system include hypertrophy, residual stress, atherosclerosis, and embryonic development. Finally, some future research directions are suggested.
Effect of Grain Sorting on the Formation of Bedforms
Authors: Seminara Giovanni
Published: April 2009

Grain sorting is a process observed in fluvial, coastal, and estuarian environments whereby the selective transport of different fractions of a sediment mixture gives rise to a non-uniform spatial distribution of the grain size probability density function. The formation of some fluvial bedforms (bedloadsheets and sand ridges) is shown to be generated or dominantly controlled by grain sorting. However, most bedforms (river dunes, free and forced fluvial bars, coastal ripples) are moderately affected by the sorting mechanism which is invariably found to lead to a damping effect on bedform growth. Recent investigations of the above phenomena are reviewed and new methodologic aspects arising in treating the instability of flow and bed topography in the presence of mixtures are pointed out.