bluuebunny/crossref_metadata_2025 huggingface dataset:
A Continuum Theory of a Lubrication Problem With Solid Particles
Authors: Dai Fuling , Khonsari M. M.
Published: April 2008

The governing equations for a two-dimensional lubrication problem involving the mixture of a Newtonian fluid with solid particles at an arbitrary volume fraction are developed using the theory of interacting continuua (mixture theory). The equations take the interaction between the fluid and the particles into consideration. Provision is made for the possibility of particle slippage at the boundaries. The equations are simplified assuming that the solid volume fraction varies in the sliding direction alone. Equations are solved for the velocity of the fluid phase and that of the solid phase of the mixture flow in the clearance space of an arbitrary shaped bearing. It is shown that the classical pure fluid case can be recovered as a special case of the solutions presented. Extensive numerical solutions are presented to quantify the effect of particulate solid for a number of pertinent performance parameters for both slider and journal bearings. Included in the results are discussions on the influence of particle slippage on the boundaries as well as the role of the interacting body force between the fluid and solid particles.
Gravity-Driven Flows of Smooth, Inelastic Disks Between Parallel Bumpy Boundaries
Authors: Babic´ M.
Published: April 2008

The problem of a steady gravity-driven granular flow of identical, smooth, slightly inelastic, circular disks between parallel bumpy boundaries is analyzed. The balance laws, constitutive equations and boundary conditions obtained by the kinetic theory (Richman and Chou, 1988) are utilized. Both collisional and transport contributions to the fluxes of momentum and fluctuation energy are considered. The problem is reduced to a system of coupled differential equations governing the transverse variations of granular temperature, shear stress, and solid fraction with the appropriate boundary conditions. The numerical procedure is developed using a variation of shooting method in order to simultaneously satisfy all of the boundary conditions. The particle flux (discharge) calculated using the present theory compares favorably with the data from numerical simulations and air table experiments reported by Sanders et al. (1988).
An Inviscid Analysis in Polar Coordinates of Flow Between Two Flat Plates
Authors: Contractor D. N.
Published: April 2008

An inviscid analysis is conducted of two-dimensional flow between a flat plate pivoting about an external point and falling onto another plate at rest. The motion of the fluid between the two plates is analyzed by the simultaneous solution of the unsteady Bernoulli equation, the equation of continuity, and the equation of motion for the plate. Numerical solution of the equations resulted in velocities and pressures along the plate as a function of time. The pressures were integrated to yield forces and moments on the falling plate. The results are compared with the motion of a horizontal flat plate falling vertically onto a rigid stationary flat plate. The two results are similar to one another.
Predicting Wear for Metal Surfaces in Sliding Contact Using a Low-Cycle Fatigue Wear Model
Authors: Hockenhull B. S. , Kopalinsky E. M. , Oxley P. L. B.
Published: April 2008

The frictional force when a hard surface slides over a relatively soft one is explained as the force needed to push waves of plastically deformed material along the soft surface ahead of asperities on the hard one. Using plastic strain increments determined from the wave model and assuming that wear occurs as a result of low-cycle fatigue, predictions are made of wear which take account of the surface roughness and lubrication conditions and a comparison is made with experimental results. Metallographic results are given which support the assumption that low cycle fatigue is important in causing surface damage and hence wear. These results also show that ironing of the surface by the passage of waves leads to surface damage and wear. It is concluded that in future work account will have to be taken of both low-cycle fatigue and ironing in making wear predictions.
Effective Mechanical Properties of Composites at Finite Deformations
Authors: Fares N.
Published: April 2008

A new representation theorem for the deformation gradient rate in the presence of cracks and kinematic constraints is presented. This representation theorem uses an extension of the concept of transformation strains to finite deformations. Based on the representation theorem the overall concentration factor was decomposed into contributions from the opening and sliding of cracks and from material nonhomogeneities. Also, inelastic deformations at the microscale were related to those at the macroscale through elastic concentration factors, where it was found that some of the elastic deformation at the microscale may contribute to the macroscale inelastic deformations.
Photoelastic Determination of Stress Intensity Factor of an Interfacial Crack in a Bi-material
Authors: Lu Hua , Chiang F. P.
Published: April 2008

The stress intensity factor of an interfacial crack in a bi-material can be represented by a complex vector whose phase changes as a function of r, the radial distance from a crack tip. Two photoelasticity approaches are proposed for the determination of both the magnitude and the phase angle of this complex vector. It is shown that within the K-dominated zone the complex stress intensity factor can be determined at any r and then converted to any other r. The case of an interfacial crack under remote tension is used as an example for the illustration of the proposed techniques.
Antisymmetric Bifurcations in a Compressible Pressure-Sensitive Circular Cylinder Under Axisymmetric Tension and Compression
Authors: Chau K. T.
Published: April 2008

This paper examines antisymmetric bifurcations of geometric diffuse modes, including buckling and surface rumpling modes, for a compressible pressure-sensitive circular cylinder of finite length under axisymmetric loadings. The analysis includes the effects of nonnormality, transverse isotropy, and confining stress on the appearance of antisymmetric geometric diffuse modes and their relationship to the onset of localization. The long wavelength limit of the eigenvalue equation is found corresponding to the Euler’s buckling load; the short wavelength limit corresponds to the eigenstress for the surface rumpling mode if the cylinder is incompressible and satisfies plastic normality. If the lateral stress is nonzero, a finite solution exists for the antisymmetric long wavelength limit; for the cases that the in-plane bulk modulus becomes unbounded, this finite eigenstress equals to the plane-strain results obtained by Chau and Rudnicki (1990). The lowest possible bifurcation stresses are plotted for various constitutive parameters by combining the results of the bifurcation analyses for both the axisymmetric (Chau, 1992) and the antisymmetric modes. This eigenvalue surface also provides a condition that determines whether buckling (antisymmetric) or bulging (axisymmetric) appears first for a fixed specimen geometry under compression. For typical specimen size (length/radius ratio from 4 to 6), the numerical results suggest that the first possible bifurcation is always the antisymmetric buckling mode under compression; however, for specimen sizes with length/radius ratio approximately less than π/2, bulging mode becomes the first possible bifurcation. The hypothesis that the prepeak and antisymmetric bifurcation triggers the subsequent localization of deformation is further discussed.
A Study on Plastic Shakedown of Structures: Part II—Theorems
Authors: Polizzotto Castrenze
Published: April 2008

For a continuous elastic-perfectly plastic solid body subjected to a combination of cyclic (mechanical and/or kinematical) load and of a steady (mechanical) load, two theorems of plastic shakedown are presented, one stating a necessary condition, another stating a sufficient condition. The problem of the direct determination of the plastic shakedown boundary is also briefly addressed.
Dynamics of Bipedal Gait: Part II—Stability Analysis of a Planar Five-Link Biped
Authors: Hurmuzlu Y.
Published: April 2008

A general approach based on discrete mapping techniques is presented to study stability of bipedal locomotion. The approach overcomes difficulties encountered by others on the treatment of discontinuities and nonlinearities associated with bipedal gait. A five-element bipedal locomotion model with proper parametric formulation is considered to demonstrate the utility of the proposed approach. Changes in the stability of the biped as a result of bifurcations in the four-dimensional parameter space are investigated. The structural stability analysis uncovered stable gait patterns that conform to the prescribed motion. Stable nonsymmetric locomotion with multiple periodicity was also observed, a phenomenon that has never been considered before. Graphical representation of the bifurcations are presented for direct correlation of the parameter space with the resulting walking patterns. The bipedal model includes some idealizations such as neglecting the dynamics of the feet and assuming rigid bodies. Some additional simplifications were performed in the development of the controller that regulates the motion of the biped.
Power Spectral Density of Nonlinear System Response: The Recursion Method
Authors: Roy R. Vale´ry , Spanos P. D.
Published: April 2008

Spectral densities of the response of nonlinear systems to white noise excitation are considered. By using a formal solution of the associated Fokker-Planck-Kolmogorov equation, response spectral densities are represented by formal power series expansion for large frequencies. The coefficients of the series, known as the spectral moments, are determined in terms of first-order response statistics. Alternatively, a J-fraction representation of spectral densities can be achieved by using a generalization of the Lanczos algorithm for matrix tridiagonalization, known as the “recursion method.” Sequences of rational approximations of increasing order are obtained. They are used for numerical calculations regarding the single-well and double-well Duffing oscillators, and Van der Pol type oscillators. Digital simulations demonstrate that the proposed approach can be quite reliable over large variations of the system parameters. Further, it is quite versatile as it can be used for the determination of the spectrum of the response of a broad class of randomly excited nonlinear oscillators, with the sole prerequisite being the availability, in exact or approximate form, of the stationary probability density of the response.
A Time Integration Algorithm for Structural Dynamics With Improved Numerical Dissipation: The Generalized-α Method
Authors: Chung J. , Hulbert G. M.
Published: April 2008

A new family of time integration algorithms is presented for solving structural dynamics problems. The new method, denoted as the generalized-α method, possesses numerical dissipation that can be controlled by the user. In particular, it is shown that the generalized-α method achieves high-frequency dissipation while minimizing unwanted low-frequency dissipation. Comparisons are given of the generalized-α method with other numerically dissipative time integration methods; these results highlight the improved performance of the new algorithm. The new algorithm can be easily implemented into programs that already include the Newmark and Hilber-Hughes-Taylor-α time integration methods.
Separation of Strain Components in Composite Materials From Thermoelastic Temperature Measurements
Authors: Dunn S. A.
Published: April 2008

In this paper experimental data is used to demonstrate how point-to-point strain components can be determined from thermoelastic temperature data. This is done by making use of the very obvious effects of thermal conduction on the cyclic surface temperature changes which can occur as a composite material undergoes an oscillating stress. By observing the cyclic surface temperature changes for different loading frequencies, the adiabatic heat generated in the different plies may be determined. With this knowledge, the strain components experienced by a composite laminate may be found.
On the Thermal Expansion Coefficient and Specific Heat at Constant Strain for Finite Plastic Deformation
Authors: Bert C. W. , Huang S.
Published: April 2008

General expressions for thermal expansion coefficient and specific heat at constant strain in the case of finite plastic deformation are derived from a general analysis of thermodynamics and finite plasticity theory. The present results show that these two thermal parameters are dependent, in a very complicated way, on the mechanical behavior of the material, such as the plastic yielding and flow, work-hardening and stress-strain relation. They are not constants but vary with the stress state, deformation state, and deformation history. It is shown that previously published experimental observations on thermal expansion coefficient can be described by the theory presented in this paper.
On Uncoupling and Solving the Equations of Motion of Vibrating Linear Discrete Systems
Authors: Felszeghy S. F.
Published: April 2008

The equations of motion governing the vibrations of a linear, viscously damped, discrete system are generally mutually coupled. This article examines the problem, when the viscous damping is nonclassical, of how best to uncouple and solve by approximation the governing second-order differential equations of motion. It is shown that when the equations of motion are expressed in normal coordinates, the equations can then be transformed by an orthogonal coordinate transformation to a new generalized coordinate system in which a bound on the relative error introduced in the response by discarding all the coupling terms is a minimum. This approach extends the applicability of undamped modal analysis to certain types of nonclassically damped systems. The analytical results and the effectiveness of the proposed method are illustrated with four examples taken from other previously published approaches to the stated problem.
Thickness Expansions for Higher-Order Effects in Vibrating Cylindrical Shells
Authors: McDaniel J. G. , Ginsberg J. H.
Published: April 2008

In the spirit of Mindlin and others who have used series expansions to express transverse dependences in thin bodies, the present work uses Ritz expansions in a variational formulation for cylindrical shell vibrations. By expanding displacements in spatial coordinates, integral expressions for strain and kinetic energy are converted to quadratic sums involving time-dependent generalized coordinates. Hamilton’s principle provides ordinary differential equations for these coordinates. This view-point yields physical insight into the mechanisms of energy storage and avoids the geometrically thin assumption inherent to many formulations. A set of Legendre polynomials multiplied by a radial factor represent the radial dependences of displacement components, while circumferential variations are represented by sinusoidal functions. Excellent agreement in natural frequencies is found between this approach and analytical solutions over the entire range of shell thicknesses, including the limiting case of a solid cylinder. Comparisons to several thin shell theories are given, leading to conclusions about the range of validity of these theories.
On the Dynamic Response of Continuous Systems Including Model Uncertainty
Authors: Iwan W. D. , Jensen H.
Published: April 2008

This paper presents a technique for obtaining the response of linear continuous systems with parameter uncertainties subjected to deterministic excitation. The parameter uncertainties are modeled as random fields and are assumed to be time independent. The general formulation of the method is developed for a particular class of partial differential equations with random coefficients. Random shape functions are introduced to approximate the solution in the spatial domain and in the random space. A system of linear ordinary differential equations for the unknowns of the problem is derived using the weighted residual method. The system of equations is integrated in time and the response variability is computed. Application of the new method is made to a continuum described by the one-dimensional wave equation in which the stiffness properties exhibit a spatial random variation. Validation calculations show that the results from the method agree well with those obtained by direct numerical integration.
Elastic Wrinkling of a Tensioned Circular Plate Using von Ka´rma´n Plate Theory
Authors: Adams G. G.
Published: April 2008

A circular elastic plate, with a uniform tension field applied at its outer edge, is acted upon by a centrally applied transverse force. As the force is increased, the tension state as determined from von Ka´rma´n plate theory, changes. In particular for sufficiently large values of the transverse force or displacement, the plate can develop a compressive circumferential membrane stress. When this compressive stress becomes sufficiently large, wrinkling can result. The corresponding value of the transverse displacement is determined by investigating an eigenvalue problem in which wrinkling is indicated by the vanishing of the lowest eigenvalue. The results are the values of the central transverse deflection which induces wrinkling for a range of in-plane tensions and are sensitive to the in-plane boundary support conditions at the outer edge.
Post-buckling of Geometrically Imperfect Shear-Deformable Flat Panels Under Combined Thermal and Compressive Edge Loadings
Authors: Librescu L. , Souza M. A.
Published: April 2008

The static post-buckling of simply-supported flat panels exposed to a stationary nonuniform temperature field and subjected ’to a system of subcritical in-plane compressive edge loads is investigated. The study is performed within a refined theory of composite laminated plates incorporating the effect of transverse shear and the geometric nonlinearities. The influence played by a number of effects, among them transverse shear deformation, initial geometric imperfections, the character of the in-plane boundary conditions and thickness ratio are studied and a series of conclusions are outlined. The influence played by the complete temperature field (i.e., the uniform through thickness and thickness-wise gradient) as compared to the one induced by only the uniform one, is discussed and the peculiarities of the resulting post-buckling behaviors are enlightened.
Analytic Study of Linear and Nonlinear Mode Localization
Authors: Vakakis A. F.
Published: April 2008

The localization of the normal modes of weakly coupled vibrating systems is examined with a new exact, analytical method. Both linear and nonlinear systems are considered and the mode localization is examined by means of “balancing diagrams.” This study complements previous studies of the author and co-workers on investigating mode localization in systems with nonlinear stiffness elements.
Arbitrarily Oriented Crack Inside an Elliptical Inclusion
Authors: Anlas G. , Santare M. H.
Published: April 2008

The plane problem of an elastic elliptic inclusion containing a crack is solved. Complex potentials presented by Qaissaunee (1992) for an edge dislocation inside an elastic elliptical inclusion are used to obtain the Green’s function for this problem. The problem is formulated in terms of systems of singular integral equations which are solved numerically. Some detailed results are given for various crack inclusion geometries and material combinations.
An Inverse Problem in Elasticity With Partially Overprescribed Boundary Conditions, Part I: Theoretical Approach
Authors: Yeih Weichung , Koya Tatsuhito , Mura Toshio
Published: April 2008

A Cauchy problem in linear elasticity is considered. This problem is governed by a Fredholm integral equation of the first kind and cannot be solved directly. The regularization method, which has been originally employed by Gao and Mura (1989), is formulated from a different perspective in order to address some of the difficulties experienced in their formulation. The theoretical details are discussed in this paper. Numerical examples are treated to Part II.
Singular Stress Field Near the Corner of Jointed Dissimilar Materials
Authors: Chen Dai-heng , Nisitani Hironobu
Published: April 2008

In this paper, the characteristics of the stress field near a corner of jointed dissimilar materials are studied as a plane problem. It is found that the order of singularity is dependent not only on the elastic constants of materials and the local geometry of corner, but also on the deformation mode. The dependence of the order of singularity was established for the case of mode I and the case of mode II. An explicit closed-form expression is given for the singular stress field at the close vicinity of the corner, in which the stress field is expressed as a sum of the symmetric state with a stress singularity of 1/r1-λ1 and the skew symmetric state with a stress singularity of 1/r1-λ2. When both λ1 and λ2 are real the singular stress field around the point singularity is defined in terms of two constants K1, λ1, K11, λ2, as in the case of crack problems.
On the Anisotropic Elastic Inclusions in Plane Elastostatics
Authors: Hwu Chyanbin , Yen Wen J.
Published: April 2008

By combining the method of Stroh’s formalism, the concept of perturbation, the technique of conformal mapping and the method of analytical continuation, a general analytical solution for the elliptical anisotropic elastic inclusions embedded in an infinite anisotropic matrix subjected to an arbitrary loading has been obtained in this paper. The inclusion as well as the matrix are of general anisotropic elastic materials which do not imply any material symmetry. The special cases when the inclusion is rigid or a hole are also studied. The arbitrary loadings include in-plane and antiplane loadings. The shapes of ellipses cover the lines or circles when the minor axis is taken to be zero or equal to the major axis. The solutions of the stresses and deformations in the entire domain are expressed in complex matrix notation. Simplified results are provided for the interfacial stresses along the inclusion boundary. Some interesting examples are solved explicitly, such as point forces or dislocations in the matrix and uniform loadings at infinity. Since the general solutions have not been found in the literature, comparison is made with some special cases of which the analytical solutions exist, which shows that our results are exact and universal.
Frictionless Contact of Layered Half-Planes, Part II: Numerical Results
Authors: Pindera M.-J. , Lane M. S.
Published: April 2008

In Part I of this paper, analytical development of a method was presented for the solution of frictionless contact problems of multilayered half-planes consisting of an arbitrary number of isotropic, orthotropic, or monoclinic layers arranged in any sequence. The local/global stiffness matrix approach similar to the one proposed by Bufler (1971) was employed in formulating the surface mixed boundary condition for the unknown stress in the contact region. This approach naturally facilitates decomposition of the integral equation for the contact stress distribution on the top surface of an arbitrarily laminated half-plane into singular and regular parts that, in turn, can be solved using a numerical collocation technique. In Part II of this paper, a number of numerical examples is presented addressing the effect of off-axis plies on contact stress distribution and load versus contact length in layered half-planes laminated with unidirectionally reinforced composite plies. The results indicate that for the considered unidirectional composite, the load versus contact length response is significantly influenced by the orientation of the surface layer and the underlying half-plane, while the corresponding contact stress profiles are considerably less affected.
Jumps to Resonance: Long Chaotic Transients, Unpredictable Outcome, and the Probability of Restabilization
Authors: Soliman M. S.
Published: April 2008

For nonlinear oscillators with the ability to escape from a potential well, jumps to resonance from a fold can result in qualitatively different types of response. They may be safe where the system always restabilizes onto a oscillation within the well; unsafe where the system always escapes out of the well; or indeterminate where the outcome is unpredictable. In the indeterminate case, long chaotic transients may persist before the system decides to which long-term behavior it will settle upon. We determine at which control parameters indeterminate jumps occur. We also examine how the transients scale as well as the probability of restabilization after the bifurcation.
Convex Models of Uncertainty in Radial Pulse Buckling of Shells
Authors: Ben-Haim Y.
Published: April 2008

The buckling of shells subject to radial impulse loading has been studied by many investigators, and it is well known that the severity of the buckling response is greatly amplified by initial geometrical imperfections in the shell shape. Traditionally, these imperfections have been modeled stochastically. In this study convex models provide a convenient alternative to probabilistic representation of uncertainty. Convex models are well suited to the limitations of the available information on the nature of the geometrical uncertainties. A n ellipsoidal convex model is employed and the maximum pulse response is evaluated. The ellipsoidal convex model is based on three types of information concerning the initial geometrical uncertainty of the shell: (1) which mode shapes contribute to the imperfections, (2) bounds on the relative amplitudes of these modes, and (3) the magnitude of the maximum initial deviation of the shell from its nominal shape. The convex model analysis yields reasonable results in comparison with a probabilistic analysis due to Lindberg (1992a,b). We also consider localized imperfections of the shell. Results with a localized envelope-bound convex model indicate that very small regions of localized geometrical imperfections result in buckling damage which is a substantial fraction of the damage resulting from full circumferential initial imperfection.
Maxwell Critical Loads for Axially Loaded Cylindrical Shells
Authors: Hunt G. W. , Neto E. L.
Published: April 2008

It is proposed that the classical Maxwell criterion for instability of gradient systems has significance as a lower bound on the appearance of localized as opposed to repeated periodic buckling. The hypothesis is tested against experiments, for the classic nonlinear problem of diamond-pattern buckling in the long thin axially loaded cylindrical shell. Excellent correlation is achieved.
Free-Edge Stress Intensity Factor for a Bonded Ductile Layer Subjected to Shear
Authors: Reedy E. D.
Published: April 2008

The stress state found in a thin, power-law hardening ductile layer bonded between a pair of rigid adherends and subjected to a shear loading is investigated. Within the context of a work-hardening plasticity theory, a stress singularity of type Krδ (δ < 0) exists at the point where the interface between one of the rigid adherends and the ductile layer intersects the stress-free edge. The intensity of this singularity (i.e., K) has been calculated for a plane strain condition using a technique that combines results of an asymptotic analysis of the stress singularity with those of a detailed finite element analysis. A dead-soft aluminum layer is considered first with emphasis placed on an assessment of the region dominated by the plastic stress singularity. Results for a fully plastic layer with negligible elastic strains are presented next. The relation defining the fully plastic, free-edge stress intensity factor for a shear loading depends only on a characteristic shear stress, layer thickness, and the layer’s hardening exponent.
Momentum and Energy Approximations for Elementary Squeeze-Film Damper Flows
Authors: Crandall S. H. , EI-Shafei A.
Published: April 2008

To provide understanding of the effects of inertia on squeeze-film damper performance, two elementary flow patterns are studied. These elementary flows each depend on a single generalized motion coordinate whereas general planar motions of a damper are described by two independent generalized coordinates. Momentum and energy approximations for the elementary flows are compared with exact solutions. It is shown that the energy approximation, not previously applied to squeeze films, is superior to the momentum approximation in that at low Reynolds number the energy approximations agree with the exact solutions to first order in the Reynolds number whereas there are 20 percent errors in the first-order terms of the momentum approximations.
A Computational Model for Fe Ductile Plastic Damage Analysis of Plate Bending
Authors: Shi Guangyu , Voyiadjis G. Z.
Published: April 2008

This paper presents a computational model for the finite element plastic damage analysis of ductile flexural plates. The phenomenological damage model proposed by Lemaitre is adopted here. The damage effect parameters of a cross-section are defined and employed to account for the damage effect across the thickness of a bending plate. Similar to the effective stresses used in many damage models, the effective stress couples are introduced in this work and used in the yield function. The damage criterion is defined in terms of damage strain energy release rates. Based on the damage node model proposed here, the elastoplastic-damage stiffness matrix of element is derived. When the corresponding elastic stiffness matrix is given explicitly, the resulting elastoplastic-damage stiffness matrix can be evaluated without use of numerical integration. The feature of the expicit form of element stiffness matrix makes the computational model proposed here very efficient. Several numerical examples of ductile plastic damage analysis of plates are also given in this work to demonstrate the validity of the computational model.
On the Convergence of Karhunen-Loeve Series Expansion for a Brownian Particle
Authors: Paff W. G. , Ahmadi G.
Published: April 2008

A linear Langevin equation for the velocity of a Brownian particle is considered. The equation of motion is solved and the Karhunen-Loeve expansion for the particle velocity is derived. The mean-square velocity as obtained by the truncated Karhunen-Loeve expansion is compared with the exact solution. It is shown, as the number of terms in the series increases, the result approaches that of the exact solution asymptotically.
Effect of DC Bias on Microwave Plasma Enhanced Chemical Vapor Deposition Synthesis of Single-Walled Carbon Nanotubes
Authors: Maschmann Matthew R. , Amama Placidus B. , Fisher Timothy S.
Published: April 2008

The physical properties of carbon nanotubes (CNTs) make them outstanding candidates for introduction into technologies ranging from high resolution flat panel displays to nanoscale transistors. Integration of carbon nanotubes into devices, however, requires precise control over the manufacturing processes used during their synthesis. To meet the specific requirements of a given application, alignment, diameter, length and chirality of carbon nanotubes must be strictly addressed. This work demonstrates the controlled synthesis of single-walled carbon nanotubes (SWCNTs) with low amount of undesired carbonaceous species using plasma enhanced chemical vapor deposition (PECVD). This report elucidates the role of DC bias applied to the growth substrate during synthesis, including the field-enhanced alignment of SWCNTs, selectivity in the diameter distribution and selectivity of semiconducting versus metallic nanotubes. Carbon nanotubes are characterized using Raman spectroscopy and electron microscopy.
An Improved Streamline Curvature Approach for Off-Design Analysis of Transonic Compressors
Authors: Khaleghi H. , Tousi A. M. , Boromand M.
Published: April 2008

Streamline curvature is still a powerful method in predicting the performance of turbomachines whose results will be more realistic if a good combination of losses and deviation is incorporated in the calculations. A streamline curvature through flow numerical approach is modified to better approximate the flow field and performance of a single stage transonic compressor by incorporating shock and profile losses using previous correlations. Deviation is estimated on the basis of several correlations and results are then compared with the present experimental data. Looking at the effect of above mentioned methods on design and off-design performance of compression system, it is possible to recommend that a suitable combination of these methods be incorporated in the solution procedure.
Study on Dimension Effect of Punch on Nanoimprint Process for Cu-Ni Alloy
Authors: Hsu Quang-Cherng , Wu Cheng-Da , Fang Te-Hua
Published: April 2008

The effects of punch size and molding mechanism on the nanoimprint process of Cu(85%)-Ni(15%) alloy were investigated by molecular dynamics method. The distribution for Cu and Ni atoms was random. In order to examine the punch size effect on nanoimprint process, three punch sizes were studied, namely: 3nm × 3nm, 6nm × 6nm and 9nm × 9nm. The results showed that it was difficult for the material to fully fill into die corner, i.e. at non-smooth geometry in the die, during final period of loading. The forming energy and force increased rapidly, because inter-atomic repulsive energy increased as formed pattern became small. It was not successfully imprinted after unloading in the case of 3nm × 3nm, due to larger spring back. Comparing to nano imprint of pure copper, the current study of nano imprint of Cu-Ni alloy presented a cyclically vibrated relationship of force and displacement showing a more complicated interaction between different kinds of atoms.
Inverse Dynamics Based Fuzzy Logic Controller for a Single-Link Flexible Manipulator
Authors: Renno Jamil M.
Published: April 2008

This paper presents a novel method for an inverse dynamics based fuzzy logic controller (FLC) of a single-link flexible manipulator. The control action is distributed between two FLCs: a joint angle controller and a tip controller. A method for varying the ranges of the variables of the two controllers as a function of the motion parameters and the inverse dynamics of the system is presented. Simulation results show that the joint trajectory tracking is accomplished and the residual vibration of the flexible link is suppressed.
Performance Enhancement of Single Flash Geothermal Power Plants
Authors: Barsin S. , Aung K.
Published: April 2008

The present work investigates thermodynamic optimum conditions with respect to resource utilization by varying the operating pressure of flash drum for an existing geothermal power plant. The main focus of the study is to maximize the power output by minimizing the waste of liquid geothermal fluid re-injected to the well. For this purpose a double-flash system has been incorporated and the effect of operating at optimum flash pressures for both primary and secondary flash units is studied. An economic model is developed that calculates the total capital investment based on the cost of major equipments including pumps, flash drums, turbine generators, and condensers. From the results obtained it can be concluded that the plant at Svartsengi currently is working close to the optimum flashing pressure for the single-flash geothermal power plant. Providing an additional flash unit to convert the high temperature liquid coming from primary flash for Svartsengi and Nevada power plants increases the net power output by 12.7% and 28.9% respectively.
Pallet Leveling Sensor System
Authors: Derby Stephen J. , Bringmann Bernhard
Published: April 2008

A computer controlled pallet leveling system allows for a partially filled mixed case pallet to be placed underneath a second upper pallet during transport. An inclinometer is used to trigger the amount of compressed air used in pneumatic chambers to achieve a properly leveled stack. A single computer system on the forklift is used during the loading process for multiple pallet leveling systems. A prototype was built and its performance was evaluated.
Computing the Entropy Generation Rate for Turbomachinery Design Applications: Can a Diagnostic Tool Become a Predictive One?
Authors: Sciubba Enrico
Published: April 2008

The calculation of the entropy generation rate ds/dt in turbomachinery passages is a straightforward task once the velocity and temperature fields are known. The global entropy generation rate in the passage, dS/dt = ∫V(x,y,z)(ds/dt)dxdydz, is of course directly related to the cascade efficiency, but its functional dependence on the local characteristics of the flowfield is not immediately detectable: the left-hand side is a single-valued quantity that cannot, as such, be used as the objective function of an inverse design procedure (because a local modification of a single detail of the blade geometry invariably produces non-negligible effects on the entire flow domain). On the contrary, knowledge of the local entropy generation rate in each point of a channel provides immediate useful insight into the relative importance of the different sources of irreversibility in the process. There are numerous examples of the application of entropy generation maps as a diagnostic design tool, i.e., to locate problematic areas that demand for design “improvements”: these are, though, basically heuristic and intrinsically non-systematic approaches. On the other hand, the adoption of a functional based on the local entropy generation rates is difficult both from a theoretical and from a practical point of view, and there is no example yet of a blade profile optimization in which the objective function is ∫V(x,y,z)(ds/dt)dxdydz, to be minimized over the design domain V. This paper presents a rational derivation of the relationships between the local and global entropy generation and the local features of the flow, and illustrates them by means of two examples derived from applications developed in the last years by the Turbomachinery Group led by the author at the University of Roma 1. The merits and limits of the use of such a “local” approach are critically discussed, and in the Conclusions a procedure is proposed for the development of an inverse design approach based on a properly constrained objective function based on ds/dt: though quite intensive from a computational point of view, there are indications that such an approach may become feasible on realistic geometries in the near future.
On the Internalization of Monetary and Environmental Externalities in the Exergetic Analysis of Energy Conversion Systems
Authors: Sciubba Enrico
Published: April 2008

The article describes and discusses to some detail a method for computing the cost of a commodity in terms of its resource-base equivalent value (as opposed to its monetary cost). The method is called the extended exergy accounting technique (EEA), and its proper application enables the analyst to perform more complete and meaningful assessments of a complex production system, including of course energy conversion processes. The novelty as well as the decisive advantage of EEA consists in its being entirely and uniformly resource-based: the so-called externalities (labor, capital and environmental remediation costs) are included in the system balance by means of their equivalent exergetic fluxes, which represent the gross amount of primary exergy required to locally generate the specified amount of capital, the specified number of work-hours, or to reduce the emissions below a certain specified level. EEA owes some of its structural formalism to Sraffa’s “network” representation of the economic production of commodities by means of other commodities, which it extends by accounting for the unavoidable energy dissipation in every productive chain. The method has also borrowed several definitions, concepts and procedures from Georgescu-Roegen’s classical work on the economic implications of irreversibility on production chains, from Daly’s pioneering work in resource-oriented economics and from Szargut’s “cumulative exergy content” method. The representation of a general energy conversion process by means of its extended exergy flow diagram is discussed in this article, and it is argued that some of the issues that are difficult to address with a purely monetary approach can be properly resolved by EEA. It is also shown how EEA, being intrinsically “localized” both in time and in space, can account for the non-uniformity of societal conditions without the need of patching the theory with artificial features external to its paradigm. In the conclusions, some indications are given as to the possibility of using the extended exergy accounting technique to supplement and substantially improve Thermo-Economics on one side and Life-Cycle Assessment or Environmental Footprint Analysis on the other side.
Design of Simulation Tools for Training Programs in Lean Manufacturing
Authors: Verma Alok K. , Hirkannawar Harsh , Devulapalli Jyotsna
Published: April 2008

Lean Manufacturing is a powerful philosophy, which advocates minimization of waste throughout the value stream both within the organization and enterprise which includes the supply chain. A concept, which was first used by automobile manufacturers to enhance their operational efficiencies, Lean focuses on driving out non-value added activities from a company’s operation, while streamlining its value added activities. A number of companies in the United States have adopted the Lean Manufacturing philosophy to reduce cost and increase efficiency. To augment the existing training programs five new simulation tools in Ship Design Processes, Supply Chain Integration, Ship Repair Processes, Value Stream Mapping and Scheduling were developed under a grant from National Shipbuilding Research Program (NSRP) by Old Dominion University, Northrop Grumman Newport News and South Tidewater Association of Ship Repairers. The paper will discuss the design, development and implementation of two of these new simulation tools.
Strain Model for Ni-Mn-Ga With Collinear Field and Stress
Authors: Faidley LeAnn E. , Dapino Marcelo J. , Washington Gregory N.
Published: April 2008

Ferromagnetic shape memory alloys in the Ni-Mn-Ga system exhibit large reversible deformations of up to 9.5% in response to magnetic fields. Prior experimental measurements by the authors demonstrated large reversible strains of −0.41% along the [001] crystal direction of a cylindrical Ni50Mn28.7Ga21.3 rod driven with a magnetic field along the same direction and no external restoring force. This represents an unusual configuration which can lead to solenoid transducers with enhanced energy density and bandwidth relative to standard electromagnet devices. The paper builds on a previous thermodynamic framework which accurately quantifies several reversible and irreversible effects in the polarization of ferroic materials. The switching between two variant orientations in the presence of Zeeman energy and pinning energy is formulated through a Gibbs energy functional for the crystal lattice. The presence of nonhomogeneous local interaction fields, nonhomogeneous pinning distributions, and complex crystallographic features in real Ni-Mn-Ga alloys is addressed through stochastic homogenization techniques. Attributes of the model are illustrated through comparison of model results with experimental data.
Harmonic Wave Propagation and Testing of a Piezoelectric Curvilinear Arc Driver
Authors: Smithmaitrie P. , Tzou H. S.
Published: April 2008

A piezoelectric curvilinear driver designed for an ultrasonic curvilinear motor is presented in this study. The design of piezoelectric curvilinear arc driver is proposed. The system governing equations, vibration behavior and wave propagation are investigated. Then, a conceptual model of piezoelectric circular arc driver is built and tested to demonstrate that the design of the curvilinear arc motor is feasible. Fabrication of the piezoelectric circular arc driver and implementation are respectively discussed, followed by results of the finite element model, and testing of the conceptual model. The demonstrations show that the curvilinear arc motor performs as expected. The experimental data is compared with the finite element results showing that the operating frequency of the conceptual motor compares well with the finite element result.
Differences of Induction Motor Field Efficiency Measuring Techniques
Authors: Eromon David I.
Published: April 2008

Contrary to testing of motor efficiency in a laboratory, certain methods given in IEEE Standard 112 cannot be used for motor efficiency evaluations in the field. For example, it is difficult to load a motor in the field with a dynamometer when the motor is already coupled to driven equipment. The motor efficiency field evaluation faces a different environment from that for which IEEE Standard 112 is chiefly written. A field evaluation method consists of one or several basic methods. This paper separates and compares the basic methods according to their physical natures. Their accuracies are also discussed. This paper is useful for field engineers to select or to establish a proper efficiency evaluation method by understanding the theories and error sources of the methods.
Chatter Stability Mapping for Simultaneous Machining
Authors: Olgac Nejat , Sipahi Rifat
Published: April 2008

A novel analytical tool is presented to assess the stability of simultaneous machining (SM) dynamics, also known as parallel machining (PM). In SM, multiple cutting tools, which are driven by multiple spindles at different speeds, operate on the same work-piece. Its superior machining efficiency is the main reason for using SM compared with the traditional single tool machining (STM). When SM is optimized in the sense of maximizing the rate of metal removal constrained with the machined surface quality, typical “chatter instability” phenomenon appears. Chatter instability for single tool machining (STM) is broadly studied in the literature. When formulated for SM, however, the problem becomes notoriously more complex. There is practically no literature on the SM chatter, except a few ad-hoc and inconclusive reports. This study presents a unique treatment, which declares the complete stability picture of SM chatter within the mathematical framework of multiple time-delay systems (MTDS). We utilize our recent methodology, called the Cluster Treatment of Characteristic Roots (CTCR), which is developed for this general class of dynamics. As an end result CTCR offers the regions of stability completely in the domain of the spindle speeds. This new methodology opens the research to some interesting directions. They, in essence, aim towards duplicating the “stability lobes” concept of STM for SM, which is clearly a nontrivial task.
Reliability Evaluation of Smart Structural Systems
Authors: Hassan Maguid H. M.
Published: April 2008

Smart Structural Systems are defined as systems that are capable of modifying their characteristics, intentionally, to reduce the effects of external actions. Such capability is attained through the integration of several basic components. Sensors, processors and actuators are examples of such components. The reliability of such integrated systems pose a major concern hindering their practical application Recent research activities are directed toward the evaluation of such reliability-based measures to evaluate such systems. Performance measures are currently identified and employed in the comparison of potential smart systems. In this paper, a reliability assessment model for smart structural systems is proposed. The proposed reliability assessment technique comprises reliability assessment algorithms for every individual underlying system component. Failure modes are identified for each individual component. Such failure modes are further expressed in a limit state format. An overall reliability measure is then evaluated, knowing the individual reliability assessments of all underlying components. By developing suitable reliability measures for such systems, it is possible to select the most reliable and effective smart system, based on their overall reliability and performance measures.