bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Response of an Elastic Homogeneous Half-Space to Suddenly Applied Rectangular Loading
Authors: Guan F. , Novak M.
Published: April 2008

A closed-form solution of transient response to suddenly applied loading distributed over a rectangular area on the surface of an elastic homogeneous half-space is developed for special purposes such as analysis of dynamic soil-structure interaction or contact problems. The solution is obtained using Laplace transform with respect to time and Fourier transform with respect to space. Inverse Laplace transform is implemented analytically. As extreme cases of rectangular loading, the solutions for a point force or finite line load can also be obtained. The advantages of this solution over most other solutions by numerical analyses are that the multiple integrations are reduced by one order, the singularity is removed from the integral kernel, and no additional discretization in the vicinity of the region of interest is required.
A Strip Element Method for Stress Analysis of Anisotropic Linearly Elastic Solids
Authors: Liu G. R. , Achenbach J. D.
Published: April 2008

A new numerical method, the strip element method, is presented for the stress analysis of anisotropic linearly elastic solids. For two-dimensional problems the domain is discretized in one direction into strip elements. By using the principle of virtual work, approximate governing differential equations are derived for the field dependence in the second direction. These differential equations can be solved analytically. For infinite bodies, some special features such as infinite elements and nonreflecting boundary conditions are introduced and a viscoelastic nonreflecting boundary is also presented. Numerical results for static and dynamic problems are presented and compared with exact solutions. Very good agreement is observed. The strip element method maintains the advantages of the finite element method, but it requires much less data storage. The technique can easily be extended to solids that are inhomogeneous in one direction.
A Hypoelastic Model for Computing the Stresses in Center-Wound Rolls of Magnetic Tape
Authors: Zabaras N. , Liu S. , Koppuzha J. , Donaldson E.
Published: April 2008

A hypoelastic finite element model for the calculation of continuous internal stress and deformation distributions in wound rolls used in center winding is presented. The stress problem is formulated as an initial boundary value problem and its solution satisfies continuity of deformation as one rewinds more layers on the growing roll. Hypoelasticity is shown to be a natural way to account for the growing body nature of a magnetic tape during winding. Several cases are examined with constant and radial stress dependent radial elastic modulus. The agreement with Hakiel’s model and experimental data obtained through the sandwiched pull strip method is very good. The results for the static linear and nonlinear cases examined found to be weakly dependent on the winding speed. The present analysis is more versatile than previous models in simulating the growing nature of the tape pack and it can naturally be extended to include nonlinear time and history-dependent phenomena.
Large Amplitude Vibrations of Strings
Authors: Leissa A. W. , Saad A. M.
Published: April 2008

The study of nonlinear, free, undamped transverse vibrations of a stretched string may be traced back to an equation of motion developed by Kirchhoff more than a century ago. Subsequent studies have typically assumed small slopes and done little to incorporate longitudinal coupling effects. In the present work a new set of coupled equations is derived. These highly nonlinear equations are solved by means of a newly developed Galerkin procedure which determines variations of the transverse and longitudinal displacements in both space and time. Time variation is determined by incremental use of polynomials. Validity of solutions is verified by independent finite difference solutions. Numerical results are presented for three example problems wherein the string is displaced transversely into a half-sine wave, and released from rest. The problems include: (1) moderate strain (ε0 = 0.005) in the straight line equilibrium position and moderate transverse displacement (δ = 0.1L), (2) moderate strain and large displacement (δ = 0.4L), and (3) small strain (ε0 = 10 −5) and moderate displacement. Plots of transverse and longitudinal displacement with time are shown for all three examples. From these plots it is seen that higher modes are generated when only a single mode is initiated, and that the motion is definitely nonperiodic.
Vibration of Circular Rings With Local Deviation
Authors: Hong Jin Sun , Lee Jang Moo
Published: April 2008

An analytical method is presented for predicting the effects of local deviations such as a point mass, a sharp decrease in stiffness and variation of thickness on the free in-plane bending vibration characteristics of nearly axisymmetric rings. The approach is based on the Laplace transformation method and the expression of local deviation as the variation of heaviside unit step function. The effects of local deviation on the natural frequencies and mode shapes of the rings are predicted for the proposed nondimensional mass and stiffness parameters. The validity of the approach was examined through modal testings and/or finite element computation.
Excitation of Guided Waves in Generally Anisotropic Layers Using Finite Sources
Authors: Ditri J. J. , Rose J. L.
Published: April 2008

The excitation of guided wave modes in generally anisotropic layers by finite sized strip sources placed on the surfaces of the layer is examined. The general problem of arbitrarily applied harmonic surface tractions is first solved using the normal mode expansion technique in conjunction with the complex reciprocity relation of elastodynamics. This general solution is then specialized to loading situations modelling those commonly used to excite guided waves in layers for use in nondestructive evaluation. The amplitudes of the generated modes are written as the product of an “excitation function” which depends only on the distribution of the applied tractions and an “excitability function” which depends only on the properties of the specific mode(s) being excited and which determines how receptive the modes are to the applied tractions. Expressions are obtained for the −9 dB wave number and phase velocity bandwidths (σβ and σν respectively) which determine the widths of the wavenumber or phase velocity excitation spectra at the −9 dB generation point. Finally, the problem of transient loading is addressed by superimposing time harmonic solutions via an integration over the dispersion curves of the layer.
Effective Elastic Moduli of Two-Dimensional Brittle Solids With Interacting Microcracks, Part I: Basic Formulations
Authors: Ju J. W. , Chen Tsung-Muh
Published: April 2008

Statistical micromechanical formulations are presented to investigate effective elastic moduli of two-dimensional brittle solids with interacting slit microcracks. The macroscopic stress-strain relations of elastic solids with interacting microcracks are micromechanically derived by taking the ensemble average over all possible realizations which feature the same material microstructural geometry, characteristics, and loading conditions. Approximate analytical solutions of a two-microcrack interaction problem are introduced to account for microcrack interaction among many randomly oriented and located microcracks. The overall elastic-damage compliances of microcrack-weakened brittle solids under uniaxial and biaxial loads are also derived. Therefore, stationary statistical micromechanical formulation is completed. Moreover, some special cases are investigated by using the proposed framework. At variance with existing phenomenological continuum damage models, the proposed framework does not employ any fitted “material parameters. ” “Cleavage 1” microcrack growth and “evolutionary damage models” within the proposed context will be presented in Part II of this series. It is emphasized that microstructural statistical informations are already embedded in the proposed ensemble-averaged equations and, therefore, no Monte Carlo simulations are needed.
Effective Elastic Moduli of Two-Dimensional Brittle Solids With Interacting Microcracks, Part II: Evolutionary Damage Models
Authors: Ju J. W. , Chen Tsung-Muh
Published: April 2008

In Part I of this series, basic formulations of stationary micromechanical theory and overall responses are presented for two-dimensional brittle solids with randomly dispersed microcracks. The basic formulations hinge on an ensemble average approach which includes pairwise microcrack interactions. In this paper, statistical micromechanical evolutionary models are proposed to account for “cleavage 1” growth of randomly oriented and located microcracks under microcrack interaction effects. Biaxial tension/compression loadings are also considered to take into account mixed microcrack opening and closure effects. Efficient numerical integration algorithms for the proposed ensemble averaged constitutive equations are subsequently given. Further, uniaxial and biaxial tests are presented to illustrate the proposed models and procedures. Finally, a higher-order microcrack interaction model within the proposed micromechanical framework is discussed.
Asymptotic Stress Field of a Mode III Crack Growing Along an Elastic/Elastic Power-Law Creeping Bimaterial Interface
Authors: Hui C.-Y. , Saif M. T. A.
Published: April 2008

The asymptotic stress field near the tip of a crack subjected to antiplane shear loading is analysed. The crack is growing quasi-statically along an elastic/elastic power-law creeping bimaterial interface. We find there is a separable solution with the following characteristics: for n < 3, where n is the power-law creeping exponent, the asymptotic stress field is dominated by the elastic strain rates and has an inverse square root singularity, r−1/2, where r is the distance from the current crack tip. For n ≥ 3, the near-tip stress and strain fields has a singularity of the form r−1/(n−1). The strength of this field is completely specified by the current crack growth rate, besides material properties, and is otherwise independent of the applied load and of the prior crack growth history.
Electron Beam Moire´ Study of Fracture of a Glass Fiber Reinforced Plastic Composite
Authors: Read D. T. , Dally J. W.
Published: April 2008

Using the method of electron beam moire´, a small region at an interface of a [O2/ 90]s glass fiber reinforced plastic composite has been examined during tensile testing. The tensile test was conducted inside a scanning electron microscope, with a high spatial frequency line grating (10,000 lines/mm) at the interface between a longitudinal ply and a transverse ply. During the test, this region was observed at a magnification of 1900 × . Local strain measurements were made by interpreting the moire´ fringe patterns over gage lengths that varied from 10 to 30 μm. The magnitude and distribution of the local strains depended on the damage that occurred with monotonically increasing load. Load shedding by the transverse ply was evident from the fringe patterns. Extremely high local strains were observed: longitudinal fiber strains up to three percent, normal strains up to three percent, and shear strains up to 40 percent in the epoxy matrix.
Biaxial Ratcheting Under Strain or Stress-Controlled Axial Cycling With Constant Hoop Stress
Authors: Xia Z. , Ellyin F.
Published: April 2008

Strain or stress-controlled tension-compression cyclic tests were conducted on pressurized thin-walled tubular specimens of 304 stainless steel. In strain-controlled mode ratcheting strains in hoop direction, and under stress-controlled mode ratcheting in both hoop and axial directions, were observed. To predict the observed ratcheting behavior, an additional evolution rule for the stress memory surface has been introduced in the constitutive model developed recently by the authors. Qualitative and quantitative comparisons with the test results indicate a fairly good agreement in predicting ratcheting deformations.
Imposition of Constraints
Authors: Djerassi S.
Published: April 2008

This paper deals with problems in dynamics in which a moving system is subjected to imposition (or relaxation) of constraints. Three phases of motion are associated with these types of problems: an unconstrained motion, imposition of constraints, and constrained motion. The equations governing each of the phases are derived and an algorithm for combining these into one coherent computer code is built and used in connection with an illustrative example.
On the Boltzmann-Hamel Equations of Motion: A Vectorial Treatment
Authors: Papastavridis J. G.
Published: April 2008

This paper presents a direct vectorial derivation of the famous Boltzmann-Hamel equations of motion of discrete mechanical systems, in general nonlinear nonholonomic coordinates and under general nonlinear (velocity) nonholonomic constraints. The connection between particle and system vectors is stressed throughout, in all relevant kinematic and kinetic quantities/principles/theorems. The specialization of these results to the common case of linear nonholonomic coordinates and linear nonholonomic (i.e., Pfaffian) constraints is carried out in the paper’s Appendix.
Both Bounds to Buckling Loads and Fundamental Frequencies
Authors: Schmidt R.
Published: April 2008

A simple procedure for improving the Krylov-Bogolyubov-Weinstein-Isaacson-Keller (KBWIK) lower bound and the Rayleigh upper bound to the first eigenvalue is described and illustrated by examples. The procedure makes use of the method of successive approximations, the Rayleigh-Schwarz quotients, the Krylov-Bogolyubov enclosure theorem, and the Temple inequality.
The Buckling Behavior of Rectangular-Bar Helical Compression Springs
Authors: Becker L. E. , Cleghorn W. L.
Published: April 2008

Buckling design charts are presented for rectangular-bar helical compression springs with clamped ends, demonstrating the 1 effect of the number of turns of the spring.
Longitudinal Impact of a Shaped Projectile on a Hopkinson Bar
Authors: Bacon C.
Published: April 2008

A computational method is developed to calculate numerically the normal force generated by the impact of a nonuniform linearly elastic projectile on a Hopkinson bar. One-dimensional relations are used. In order to assess the validity of the method, it is compared with an analytical solution in the case of the impact of a truncated cone on a rigid half-space. Then some practical applications are performed to predict the force generated by the impact of different truncated cones on a Hopkinson bar. We show that a perfect ramp load is only generated by the impact of a truncated cone on a rigid half-space.
Constrained Elastic-Plastic Materials
Authors: Lin H. C. , Naghdi P. M.
Published: April 2008

The main purpose of this paper is to present a general (purely mechanical) constrained theory of finitely deforming elastic-plastic materials. Our development is based on a strain-space formulation of plasticity and requires a detailed examination of the effect of constraint on various constitutive ingredients in the unconstrained theory, including the yield functions (in both the stress and strain spaces), the loading criteria, and various response functions. Also examined is the effect of constraint on the restrictions arising from the work inequality of Naghdi and Trapp (1975b).
Some Remarks on the Wedge Paradox and Saint-Venant’s Principle
Authors: Markenscoff X.
Published: April 2008

The solutions for the wedge loaded by a concentrated couple at its vertex, known as the Carothers-Sternberg-Koiter problem, are examined critically. The cause of the divergence are terms which are fundamental self-equilibrated solutions with unbounded energy arising from the eigenvalues of the wedge and with exponent depending on the angle. The “paradox” occurs at the angle at which the term of the (angle-independent exponent) r−2 stress singularity is superseded by the next eigenvalue. These terms are conjectured to be the weight functions of the wedge. The breaking down of St. Venant’s principle for the wedge in connection with these terms is also demonstrated. As for the definition of a concentrated couple, it can only exist if the limiting solutions are independent of the path of loading (stable node); for wedge angles bigger than a half-space, they depend on the path of loading, and the loadings that give path independence are characterized.
An Energy Criterion for the Onset of Shear Localization in Thermal Viscoplastic Materials, Part II: Applications and Implications
Authors: Shawki T. G.
Published: April 2008

Necessary and/or sufficient conditions for the onset of shear flow localization in thermal viscoplastic materials were derived by Shawki (1994) through the analysis of a one-dimensional model of dynamic simple shear with velocity-controlled boundaries. In the former work, an energy-based viewpoint of localization allows for the association of the positive rate of change of the total kinetic energy of the absolute perturbations with the onset of shear strain localization. Here, we derive explicit conditions for the onset of shear localization without the need to obtain exact linear solutions. Explicit localization conditions are then applied to a number of empirical constitutive descriptions of material response. The effects of inertia, heat conduction, thermal softening, strain hardening, and strain rate sensitivity as regards the onset of shear localization are thoroughly discussed. Furthermore, the validity of conclusions based on a constant homogeneous solution is quantified together with the validity of conclusions based on a quasi-static approximation. Moreover, we examine the inadequacy of the notion of asymptotic stability for shear localization in the presence of heat conduction effects. A critical wavelength threshold is derived, for a general description of material response, below which perturbations will not grow. This threshold may also serve as a lower bound for shear band thickness.
Analysis of the Second Mixed Boundary Value Problem for a Thin Plate
Authors: Hasebe Norio , Nakamura Takuji , Ito Yoshihiro
Published: April 2008

The second mixed boundary value problem is solved by the classical theory of thin plate bending. The mixed boundary consists of a boundary (M) on which one respective component of external force and deflective angle are given, and on the remaining boundary the external forces are given. The boundary (M) is straight and the remaining boundary is arbitrary configuration. A closed solution is obtained. Complex stress functions and a rational mapping function are used. A half-plane with a crack is analyzed under a concentrated torsional moment. Stress distributions before and after the crack initiation, and stress intensity factors are obtained for from short to long cracks and for some Poisson’s ratio.
Crack Propagation at and Near Bimaterial Interfaces: Linear Analysis
Authors: Geubelle P. H. , Knauss W. G.
Published: April 2008

The problem of the growth of a crack located at the interface between two linearly elastic solids is considered when conditions promoting propagation along and/or away from the interface prevail. Both a stress and a maximum energy release rate criterion are examined. It is found that in contrast to the corresponding problem for crack growth in homogeneous solids, no unique propagation direction results when continuum considerations prevail alone. Uniqueness is established only upon invoking a presumably material dictated minimum crack extension size. The result for this linearized analysis are compared with experimental observations on kink fracture involving two elastomers of small strain capabilities.
Load Diffusion and Absorption Problems From a Finite Fiber to Elastic Infinite Matrix
Authors: Lee Ven-Gen , Mura Toshio
Published: April 2008

The load transfer behavior of a finite fiber perfectly bonded to an infinite matrix of distinct elastic moduli is investigated in this paper. The fiber is subjected to the uniformly distributed loading applied at infinity or on one cross-section of the fiber. The stress disturbance due to the existing fiber is simulated by the equivalent inclusion method, which formulates the inhomogeneity problem to a system of integral equations. By dividing the fiber into finite numbers of ring elements with uniform distributed eigenstrains, the integral equations can be further reduced to a system of algebraic equations with coefficients expressed in terms of the integrals of Lipschitz-Hankel type. Numerical results are presented for resultant axial force for various fiber length and material properties. The limiting cases of the infinite and semi-infinite fibers are also compared with the exact and approximate solutions.
An Inverse Mode Problem for the Continuous Model of an Axially Vibrating Rod
Authors: Ram Y. M.
Published: April 2008

An inverse mode problem for the continuous model of an axially vibrating rod is formulated and solved. It is shown that the density and axial rigidity functions are determined by two eigenvalues, their corresponding eigenfunctions, and the total mass of the rod. The necessary and sufficient conditions for the construction of a physically realizable rod with positive parameters are given. It is shown that when these conditions are satisfied, the solution is unique. Since the data required for the construction may be available from measurements, the presented approach is well-suited for modal analysis applications.
Finite Element Analysis of Quasi-static Contact Problems Using Minimum Dissipation of the Energy Principle
Authors: Kishore N. N. , Ghosh A. , Rathore S. K. , Kishore P. V.
Published: April 2008

There are many practical situations where two bodies are directly in contact and are subjected to dynamic or varying loads. The contact area and the contact conditions are functions of load and load history and are not known a priori at any load thus making the problems nonlinear. The conditions of contact are determined by the kinematic constraints and the Coulomb’s law of friction. Direct solutions do not give unique results if the load steps are large and the finite element mesh is coarse. In the present work a method using the principle of minimum dissipation of energy is proposed and is applied to finite element analysis of a two-dimensional elastic contact problem under quasi-static loading. A combined incremental and iterative procedure is adopted to solve this problem. The results obtained are in good agreement with physical reasoning. The proposed method obtains new results apart from greatly reducing computational time and efforts.
Transient Response of Multiple Rigid Foundations on an Elastic, Homogeneous Half-Space
Authors: Guan F. , Novak M.
Published: April 2008

Three-dimensional transient response of both massless and massive multiple, rigid foundations, bonded to an elastic, homogeneous half-space, is investigated to study the effect of dynamic interaction through-soil. The numerical procedure is formulated in terms of the boundary element approach by means of the transient fundamental solutions developed by the authors (1994). This procedure works efficiently for the problem addressed here since the separated foundations are analyzed without discretizing the surface of the half-space outside the contact areas between the half-space and the foundations. It also provides the possibility to study nonlinear problems involved with semi-infinite soils.
Reconsideration of the Stress-Focusing Effect in a Uniformly Heated Solid Cylinder
Authors: Hata T.
Published: April 2008

The stress-focusing effect is the phenomenon that, under an instantaneous heating, stress waves reflected from the free surface of the cylinder result in very high stresses at the center. Ho solved the problem by using Laplace transform on time and presented the solution as infinite series summations, which converge very slowly for certain combinations of time and the radius of a cylinder. However, adopting a concept of the ray theory, the solution of stress waves in the cylinder is sorted out into rays according to the ray path of multiply reflected waves. The results expressed in an infinite series reveal that stresses peak out periodically at a constant period and the order of singularity of the stresses in a cylinder is O(ρ−2).
Marangoni Convection With a Deformable Surface
Authors: McCaughan F. , Bedir H.
Published: April 2008

Double diffusive convection is considered in a semi-infinite domain, bounded below by a solid surface and above by a gas interface. Temperature and concentration gradients are imposed normal to the free surface and the linear stability of the fluid is examined. Traditional analyses are extended to include the effects of a deformable free surface. The governing equations are nondimensionalized and the parameter groupings are identified. We particularly focus on the effects of the capillary number, the Nusselt number and the Marangoni temperature and concentration numbers.
Three-Dimensional Frictional Contact Analysis Using the Homotopy Method
Authors: Park J. K. , Kwak B. M.
Published: April 2008

A three-dimensional contact problem with the orthotropic Coulomb friction is formulated in the form of a system of nonlinear equations. The nonlinear complementarity formulation derived naturally from the three-dimensional frictional contact phenomenon is used in the numerical analysis without such linearization as previously introduced. The probability-one homotopy method known as a globally convergent zero-finding algorithm is implemented as an exact method and applied to each incremental step. The method is illustrated by two three-dimensional problems and the results are compared with those of commercial package and other approximations.
Materials With Negative Poisson’s Ratio: A Qualitative Microstructural Model
Authors: Phan-Thien N. , Karihaloo B. L.
Published: April 2008

Materials with negative Poisson ’s ratio are peculiar in that they expand laterally when stretched. Examples of such type of behavior have been discovered with foams by Lakes (1987); however, it is only recently that isotropic materials with negative Poisson’s ratio have been shown by Milton (1992) to exist within the framework of classical theory of elasticity. In this Note, we demonstrate qualitatively that a composite material with a reentrant microstructure can also have a negative Poisson’s ratio, even though the composite may be isotropic owing to a completely random distribution of the microstructure.
The Folding of Triangulated Cylinders, Part I: Geometric Considerations
Authors: Guest S. D. , Pellegrino S.
Published: April 2008

This study was inspired by a model of a triangulated cylindrical shell made by C. R. Calladine during an investigation of the mechanics of biological structures. The model consisted of identical triangular panels on a helical strip and had a small-displacement internal inextensional mechanism. It is shown that many triangulated cylinders broadly similar to Calladine’s model can be folded down to a compact stack of plates: only small strains, whose magnitude can be made arbitrarily small by the choice of suitable design parameters, are imposed during folding. A general geometric formulation of the problem is presented and then, assuming that the folding process is uniform, the folding properties of any triangulated cylinder of this generic type are discussed.
The Interface Anticrack and Green’s Functions for Interacting Anticracks and Cracks/Anticracks
Authors: Markenscoff X. , Ni Luqun , Dundurs J.
Published: April 2008

Solution is obtained for an anticrack-a bonded rigid lamella inclusion-at the interface between two isotropic elastic solids. The problem is formulated in terms of distributed line-loads at the anticrack which constitute the Green’s functions and the system of the governing coupled integral equations is solved analytically in closed form for the cases of uniform biaxial tension and of anticracks loaded by concentrated forces or moment. Solutions are also obtained by the interaction of an interface anticrack with a first-order singularity (concentrated force and dislocation) and second-order singularity (doublet of forces) at the interface. In the latter case the limit as the second-order singularity approaches the tip of the anticrack does not exist, but neither can a finite limit be obtained by reseating as in the homogeneous material. The solution of the interface anticrack exhibits the oscillatory singularities that appear at interface cracks which indicates that the overlapping of the displacement on the crack faces is not’the reason for this anomalous behavior. Moreover, it should be pointed out that the material condition that the stress does not exhibit oscillatory behavior is not the same as for interface cracks: for anticracks it is κ1 (1−β) = κ2 (1 + β) while for cracks it is β = 0.
The Stress Field and Intensity Factor due to Crazes Formed at the Poles of a Spherical Inhomogeneity
Authors: Xiao Z. M. , Pae K. D.
Published: April 2008

The problem of two penny-shaped crazes formed at the top and the bottom poles of a spherical inhomogeneity has been investigated. The inhomogeneity is embedded in an infinitely extended elastic body which is under uniaxial tension. Both the inhomogeneity and the matrix are isotropic but have different elastic moduli. The analysis is based on the superposition principle of the elasticity theory and Eshelby’s equivalent inclusion method. The stress field inside the inhomogeneity and the stress intensity factor on the boundary of the craze are evaluated in the form of a series which involves the ratio of the radius of the penny-shaped craze to the radius of the spherical inhomogeneity. Numerical examples show the interaction between the craze and the inhomogeneity is strongly affected by the elastic properties of the inhomogeneity and the matrix. The conclusion deduced from the numerical results is in good agreement with experimental results given in the literature.
Free Vibrations of Laminated Composite Noncircular Thin Cylindrical Shells
Authors: Suzuki K. , Shikanai G. , Leissa A. W.
Published: April 2008

An exact solution procedure is presented for solving free vibration problems for laminated composite noncircular cylindrical shells. Based on the classical lamination theory, strain energy and kinetic energy functional are first derived for shells having arbitrary layer stacking sequences. These functional are useful for a general analysis based upon energy principles. However, in the present work equations of motion and boundary conditions are obtained from the minimum conditions of the Lagrangian (Hamilton’s principle). The equations of motion are solved exactly by using a power series expansion for symmetrically laminated, cross-ply shells having both ends freely supported. Frequencies are presented for a set of elliptical cylindrical shells, and the effects of various parameters upon them are discussed.
A Perturbation Method for Inverse Frequency Modification of Discrete, Undamped Systems
Authors: Smith M. J. , Hutton S. G.
Published: April 2008

A method is described for determining the stiffness and mass modifications required in order to modify the natural frequencies of undamped discrete nongyroscopic vibrating systems in a prescribed manner. The method is based upon a new perturbation formulation. Structural changes are represented by perturbed stiffness and mass matrices defined in terms of linear design parameters of the discrete model. The equations are subject to frequency constraints defined by the analyst, and the modified mode shapes are assumed confined to a subspace of the baseline modes. The proposed method provides a complete solution of the perturbation equations without deleting or approximating coupling terms in the unknowns and is therefore suitable for large and small changes alike. Numerical results demonstrate that the new method is superior to the predictor-corrector method for determining large structural changes and that solutions of a high accuracy can be obtained provided a sufficiently rich subspace of baseline modes is used.
Doubly Asymptotic Approximations for Submerged Structures With Internal Fluid Volumes: Formulation
Authors: Geers T. L. , Zhang Peizhen
Published: April 2008

Doubly asymptotic approximations (DAAs) are approximate temporal impedance relations for a medium in contact with a flexible body. In this paper, the method of operator matching previously used for external acoustic domains is used to develop first- and second-order boundary integral DAAs for internal acoustic domains. Corresponding boundary element forms permit the numerical solution of transient structural acoustics problems with complex geometry. The accuracy of the DAAs is assessed in the following companion paper by comparing DAA and exact solutions for a canonical problem with spherical geometry.
Doubly Asymptotic Approximations for Submerged Structures With Internal Fluid Volumes: Evaluation
Authors: Geers T. G. , Zhang Peizhen
Published: April 2008

The accuracy of the doubly asymptotic approximations formulated in the previous companion paper is examined through the comparison of DAA and exact transient response histories for a fluid-filled, submerged spherical shell excited by an incident plane step-wave. The numerical results indicate that second-order DAAs are satisfactory for problems of this type.
Power Density of the Floating Cup Axial Piston Principle
Authors: Achten Peter A. J.
Published: April 2008

The floating cup principle is a new concept for hydrostatic pumps, motors and transformers. It features a large number of pistons, which enables a strong reduction of the pressure pulsations and fluid borne noise. The pistons are arranged in a double ring, back-to-back configuration, and are locked onto the rotor. Each piston has a separate, cuplike cylinder, which is floating on a rotating barrel plate. This article will discuss the consequences of the floating cup design on the power density of pumps and motors. For current axial piston units the trend is towards larger tilt angles of the barrel. In slipper type machines, the tilt angles can be as large as 21°, whereas in bent axis machines the tilt angle can even be increased to 45°. For a 24 piston floating cup machine, the tilt angle of each barrel is however limited to about 12°. The object of the article is to prove that the reduced tilt angle does not need to have a detrimental effect on the power density of the hydrostatic machine. After giving a brief description of the floating cup principle, the article will focus on the design aspects that limit the barrel tilt angle. After this, the main parameters that govern the power density are discussed. A comparison with a slipper type pump is made.
Theoretical and Experimental Study on Suspended Circular Disk Motion in Centrifugal Casting Device
Authors: Torii Shuichi , Tanaka Satoyuki , Yano Toshiaki , Watanabe Yoshimi
Published: April 2008

Functionally Graded Materials are high performance composite materials, in which physical and/or chemical properties of these material structures are graded in the several directions. Centrifugal solid-particle method is one of the effective fabrication methods by use of centrifugal casting devices. The casting mold that includes reinforcement particle and molten metal are centrifuged and particles move in the mixture due to density differences of these materials. However, there is no information on the particle motions. The aim of the present study is to disclose on suspension particle motion in the axially rotating drum. The particle velocity of the circular disk is measured by PTV (Particle Tracking Velocimetry) method and is theoretically predicted by BBO (Basset-Boussinesq-Ossen) equation. It is found that (1) each particle motion is affected by the rotating speed, (2) the measured velocity is compared with theoretical result, and (3) when the particle moves in the Stokes’ regime, its velocity is linearly increased with the distance from the center of the drum and this trend is intensified with an increase in the rotating speed.
Experimental Investigation of Heat Transfer From a Discretely Heated Protruding Pedestal to a Single Round Impinging Air Jet
Authors: Fleischer Amy S. , Nejad Sharareh R.
Published: April 2008

An experimental investigation to understand the influence of the impingement surface geometry on the heat transfer from a discretely heated surface to a single round impinging jet is conducted. In this study, heat transfer at the stagnation region of a discretely heated pedestal protruding into an air stream is compared to the heat transfer on a discretely heated flat plate to determine the influence of impingement surface geometry on heat transfer for various Reynolds numbers, jet diameters and jet exit-surface spacings. The round jet issues from a tube of diameter 3.5 mm, 9.5 mm or 21 mm at jet exit-to-surface distances of 2–5 diameters with Re = 10,000–30,000. Under all operating conditions, the presence of a protruding pedestal is found to increase heat transfer.
The Effect of Aging on the Respiratory Movement of Human Rib Cage: Some Preliminaries
Authors: Vaziri A. , Akhavan-Tafti B. , Nayeb-Hashemi H.
Published: April 2008

It is clear that costal cartilage and rib articulation calcification, as well as, weakness of the respiratory muscles reduce the rib cage volume displacement. Usually, calcification begins from costochondral junction and extends toward the sternocostal junction. Teale et al [1] reviewed seven hundred chest radiographs to determine the site and extent of the calcification over an age range of 20 to 90 years. They concluded that the prevalence of the costal cartilage calcification increases from 6% in the 3rd decade to 45% in the 9th and is more common in men. In addition, it is generally assumed that muscle strength decreases 30–40%, between 30 and 80 years of age. The effect of these age-related changes on the respiratory volume change can be realized by studying the transverse and anteroposterior expansion of the ribs during respiration. Here, we try to estimate the respiratory volume change through the changes in the “bucket-handle” movement of the 5th rib utilizing finite element model. The effect of costal cartilages calcification in both transverse and anteroposterior movement of the rib cage can be attained by modeling the total rib cage.
Directional Control of a Dual-Path Hydrostatic Transmission for a Track-Type Vehicle
Authors: Peterson Jeremy T. , Manring Noah D. , Kluever Craig A.
Published: April 2008

Dual-path hydrostatic transmissions are commonly used in the off-highway construction industry for propulsion and steering of track-type vehicles. While these transmissions provide simplicity of design, they often suffer from a lack of straight-line controllability due to the varying terrain conditions beneath each independent track. In this paper, the dynamics of the track-type vehicle are modeled using kinetic energy relationships. In this process, an equation describing the effective inertia of each track is derived, which is shown to be dependent upon vehicle mass, track geometry, and the amount of slip that occurs during track operation. The development of this equation is considered to be a significant and unique contribution to the literature. Using a directional compass as a solitary feedback signal, a PID controller is then designed to ensure straight-line tracking for the vehicle. In this research, a typical track-type vehicle is simulated, and it is shown that the PID controller provides robust straight-line controllability as the vehicle is subjected to conditions of extreme terrain-slippage.
Modeling Spool-Valve Flow Forces
Authors: Manring Noah D.
Published: April 2008

This paper has been written to reconsider the important topic of transient flow forces that act on spool-type hydraulic control valves. Though this subject has been addressed and somewhat laid to rest many years ago, the high-speed applications of our present day require a fresh look at this topic for gaining deeper insight into the significant contributions that determine the stability and frequency response of the hydraulic control valve. Over thirty years ago, it became an accepted practice to neglect the pressure transient flow-forces acting on the spool valve as they were deemed to be minor compared to the velocity effects of the spool itself. In this paper, flow force models with and without the pressure transient term are compared and it is shown that the historic practice of neglecting pressure transients may no longer be valid. As a result, this paper provides justification for considering the pressure transients in the analysis and may provide an explanation for some of the discrepancies that have existed between theoretical expectations and laboratory results.
Pre-Delivery Testing of Centrifugal Compressors Within the Petroleum Industry: A User’s View
Authors: Taherimoghaddam Mahdi , Binaie Halat
Published: April 2008

In oil and gas applications where centrifugal compressors play a central role, their availability is essential for continued production; typically the loss of a day’s revenue can far exceed the capital value of the machine. Performing more rigorous inspection and testing prior to accepting delivery of centrifugal compressors can reveal a fairly large percentage of mechanical and performance failures. This paper is devoted to illustrate the crucial importance of centrifugal compressors testing within the petroleum industry with a special attention to the performance test and complete-unit test.
Inferring Viscoelastomer Dynamic Material Properties From Finite Element and Experimental Studies of Constrained Layer Damping Systems
Authors: Hambric Stephen A. , Jarrett Andrew W. , Lee Gilbert F. , Fedderly Jeffry J.
Published: April 2008

Viscoelastic materials are often used to add damping to metal structures, usually via the constrained layer damping method. The added damping is strongly dependent on material temperature and frequency, as are the underlying material properties of the viscoelastomer. Several standardized test methods are available to characterize the dynamic material properties of viscoelastomers. However, they rely on limited test data which is extrapolated using the time-temperature superposition technique. The authors have found that the different testing methods typically produce significantly different material properties. A new approach to inferring viscoelastomer material properties is suggested here. Several metal bars are treated using constrained layer damping. Experimental modal analyses are conducted on the bars at different temperatures to produce sets of system resonance frequencies and loss factors. Corresponding finite element (FE) models of the treated bars are analyzed using assumed viscoelastomer material properties. The properties are adjusted by trial and error until the FE-simulated system loss factors match those of the measurements.
Geometric Dimension and Tolerance Modeling and Validation System Based on Object Oriented Paradigm for 3D Solid Model
Authors: Koura Monir M. , Elewa Ibrahiem M. , Gadh Rajit , Prabhu Shiv , Mohamed Khaled A.
Published: April 2008

This paper introduces an approach for modeling and representation of geometric tolerances on any 3D solid model using the Objected Oriented Programming (OOP) paradigm. The modeling scheme is supported by a comprehensive validation engine, which certifies the tolerance type against the 3D geometry context both syntactically and semantically. The major objective of this work is to develop a methodology for interfacing tolerance modeling with boundary representation (B-Rep) based 3D solid model geometry. We will demonstrate that the OOP paradigm is very efficient and flexible for tolerance model representation, which is required within the interactive design process. Six categories of tolerance classes have been developed for size, form, orientation, position, runout and profile, which extend a general tolerance class through inheritance. An instance of the general tolerance class will be initialized when picking a feature or a group of features to tolerance, depending upon feature(s’) characteristics and attributes. To apply a tolerance object the system obtains the 3D geometric data from the solid model using the feature extraction paradigm. When the required tolerance type is selected for modeling, an instance from the specified tolerance type class will be initialized through inheritance from the general feature tolerance class and gathers the necessary information / tolerance data. An intelligent validation engine that supports the modeler is introduced. The engine validates any selected tolerancing activity in two stages. First, it ensures that the selected feature or group of features is suitable for the selected tolerance type. Second, it ensures that the data specified does not lead to over/under-dimensioning. The paper also discusses a prototype system implemented to test the modeler and the validation engine. The results have been very encouraging while testing the system on a number of engineering models.
An Experimental Comparison of a Sliding Mode Estimator to an Extended Kalman Filter Applied to a Cold Flow Circulating Fluidized Bed
Authors: Park Juchirl , Boyle Edward J. , Turton Richard , Famouri Parviz
Published: April 2008

Circulating fluidized beds (CFB) have been applied to a wide variety of chemical industry processes to reduce pollution and increase efficiency. Identifying the void fractions and the bed-height in the standpipe of the CFB is required for designing a controller to improve the overall system operation. An extended Kalman filter (EKF) algorithm has been applied in order to successfully estimate the states and the bed-height of the standpipe in the cold flow circulating fluidized bed (CFCFB) at the Department of Energy, National Energy Technology Laboratory. However, for some oscillating input cases, this method does not perform well. In addition, covariance matrices Q and R need to be assumed initially and depending upon initial conditions, for some cases, the EKF behaves unstably. In this research, a sliding mode estimator (SME) is applied in order to estimate the state, and the bed-height of the standpipe in the CFCFB. The sliding mode estimator requires the proper gain for tuning in order to have proper estimations. Test results show improvement in state estimation performance of SME over EKF.
A Simple Vibration Analysis for Running Boards and Other Attached Components
Authors: Richmond Shaun
Published: April 2008

Vibration of attached components such as running boards, hand grabs, brake components, etc. has become a serious problem. This paper sets out a simple analysis method for ensuring the survival of these components. A simple mass spring model is used to develop a transfer function into the car body. The frequency components of a wheel flat and 39/33 foot jointed track are then established and the excitation amplitudes for components attached to the car body calculated. The response of these components at their natural frequency is then used to calculate their resulting stress levels. Simple methods for performing this analysis are described