bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Bolt Threads on the Stiffness of Bolted Joints
Authors: Lehnhoff Terry F. , Bunyard Bradley A.
Published: July 2002

Axisymmetric finite element analysis (FEA) was performed on bolted joints to determine the effects of the threads on the bolt and member stiffnesses. For steel members, the member stiffness decreased 37.1, 37.7, 38.2, 41.0, and 49.4 percent for the 24, 20, 16, 12, and 8-mm-dia bolts, as the magnitude of the external load was increased. The external load was increased from zero to the value that caused the bolt force to equal its proof strength. The member stiffness for aluminum members decreased by 22.7 and 29.9 percent for the 24 and 20-mm bolts. The cast iron members had decreases of 26.9 and 32.3 percent for the 24 and 20-mm bolts. Likewise, the aluminum/cast iron members decreased in stiffness by 25.5 and 30.0 percent for the 24 and 20-mm bolts. The member stiffness with no external load applied decreased by approximately 65 percent when changing from steel to aluminum members, 53 percent from steel to cast iron, and 60 percent from steel to aluminum/cast iron. Bolt stiffness varied less than 1.4 percent over the total range of the externally applied load for each of the bolted joint models. The decrease in bolt stiffness for the 24 and 20-mm-dia bolts was approximately 4 percent when changing from steel to aluminum members, 7 percent when changing from steel to cast iron members, and 8 percent when changing from steel to aluminum/cast iron members. Comparison is made to research results which did not include the influence of the threads.
Steady Modes in Relay Control Systems With Time Delay and Periodic Disturbances
Authors: Fridman E. , Fridman L. , Shustin E.
Published: July 2002

We study stability of slow oscillatory motions in first order one- and two-dimensional systems with delayed relay control element and periodic disturbances, which serve as models of stabilization of the fingers of an underwater manipulator and of control of fuel injectors in automobile engines. Various types of stability observed are used to design a direct adaptive control of relay type with time delay that extinguishes parasite auto-oscillations in these models. [S0022-0434(00)04004-1]
Multiple Sliding Surface Control: Theory and Application
Authors: Hedrick J. K. , Yip P. P.
Published: July 2002

This paper discusses the development of a nonlinear controller design methodology and its application to an automotive control problem. The method is called the “Multiple Sliding Surface” method and is closely related to sliding mode control, input/output linearization and integrator backstepping. The method was developed for a class of systems, typical of automotive control systems, where the uncertainties are “mismatched” and where many of the equations contain sparse, experimentally obtained maps. The error bounds on these maps are often unknown and their sparseness makes them difficult to differentiate. The developed method does not require any derivatives and has guaranteed semi-global stability. This paper summarizes the development of the method and applies it to the design of a highly nonlinear system. The example is a combined brake/throttle controller for precision vehicle following. This controller was implemented on the California PATH vehicles in DEMO’97, an automated highway technology demonstration that occurred in San Diego, California in August of 1997. [S0022-0434(00)03004-5]
Solution of the Moving Mass Problem Using Complex Eigenfunction Expansions
Authors: Lee K.-Y. , Renshaw A. A.
Published: July 2002

A new solution technique is developed for solving the moving mass problem for nonconservative, linear, distributed parameter systems using complex eigenfunction expansions. Traditional Galerkin analysis of this problem using complex eigenfunctions fails in the limit of large numbers of trial functions because complex eigenfunctions are not linearly independent. This linear dependence problem is circumvented by applying a modal constraint on the velocity of the distributed parameter system (Renshaw, A. A., 1997, J. Appl. Mech., 64, pp. 238–240). This constraint is valid for all complete sets of eigenfunctions but must be applied with care for finite dimensional approximations of concentrated loads such as found in the moving mass problem. Numerical results indicate that the proposed method is competitive with Galerkin’s method with real trial functions in terms of accuracy and rate of convergence. [S0021-8936(00)00604-8]
Localization-Induced Band and Cohesive Model1
Authors: Hao S. , Liu W. K. , Qian D.
Published: July 2002

A localization-induced cohesive model has been proposed for shear band evolution, crack growth, and fracture. Strain gradient theory has been applied to establish the criterion of the onset of localization and the governing equation in the post-bifurcation stage. Analytical solutions in one-dimensional case are used to establish the “traction-separation” law, in which strain gradient and material intrinsic length scale present strong effects. In addition, the solution predicts a finite width for the localization-induced band. It is observed that a larger length scale contributes to the growth of a larger width of localization region and separation for softening materials. The proposed model provides a procedure to establish the fracture toughness analytically since the material length scale is taken into account. From the traction-separation analysis, it is found that damage decreases separation, whereas an increase in material length scale increases the opening displacement; however, the traction-normalized opening displacement curves (with respect to the material length scale) are identical. Based on the methodology of multiple scale analysis in meshfree method, a computational approach has been proposed to enrich the one-dimensional traction-separation law to define fracture. [S0021-8936(00)01104-1]
Improved Dynamic Friction Models for Simulation of One-Dimensional and Two-Dimensional Stick-Slip Motion
Authors: Tariku Fitsum A. , Rogers Robert J.
Published: July 2002

In many mechanical systems, the tendency of sliding components to intermittently stick and slip leads to undesirable performance, vibration, and control behaviors. Computer simulations of mechanical systems with friction are difficult because of the strongly nonlinear behavior of the friction force near zero sliding velocity. In this paper, two improved friction models are proposed. One model is based on the force-balance method and the other model uses a spring-damper during sticking. The models are tested on hundreds of lumped mass-spring-damper systems with time-varying excitation and normal contact forces for both one-dimensional and two-dimensional stick-slip motions on a planar surface. Piece-wise continuous analytical solutions are compared with solutions using other published force-balance and spring-damper friction models. A method has been developed to set the size of the velocity window for Karnopp’s friction model. The extensive test results show that the new force-balance algorithm gives much lower sticking velocity errors compared to the original method and that the new spring-damper algorithm exhibits no spikes at the beginning of sticking. Weibull distributions of the sticking velocity errors enable maximum errors to be estimated a priori.
A Mechanism of Combustion Instability in Lean Premixed Gas Turbine Combustors
Authors: Lieuwen T. , Torres H. , Johnson C. , Zinn B. T.
Published: July 2002

There has been increased demand in recent years for gas turbines that operate in a lean, premixed (LP) mode of combustion in an effort to meet stringent emissions goals. Unfortunately, detrimental combustion instabilities are often excited within the combustor when it operates under lean conditions, degrading performance and reducing combustor life. To eliminate the onset of these instabilities and develop effective approaches for their control, the mechanisms responsible for their occurrence must be understood. This paper describes the results of an investigation of the mechanisms responsible for these instabilities. These studies found that combustors operating in a LP mode of combustion are highly sensitive to variations in the equivalence ratio (ϕ) of the mixture that enters the combustor. Furthermore, it was found that such ϕ variations can be induced by interactions of the pressure and flow oscillations with the reactant supply rates. The ϕ perturbations formed in the inlet duct (near the fuel injector) are convected by the mean flow to the combustor where they produce large amplitude heat release oscillations that drive combustor pressure oscillations. It is shown that the dominant characteristic time associated with this mechanism is the convective time from the point of formation of the reactive mixture at the fuel injector to the point where it is consumed at the flame. Instabilities occur when the ratio of this convective time and the period of the oscillations equals a specific constant, whose magnitude depends upon the combustor design. Significantly, these predictions are in good agreement with available experimental data, strongly suggesting that the proposed mechanism properly accounts for the essential physics of the problem. The predictions of this study also indicate, however, that simple design changes (i.e., passive control approaches) may not, in general, provide a viable means for controlling these instabilities, due to the multiple number of modes that may be excited by the combustion process.
Massively Parallel Binary Manipulators
Authors: Mukherjee S. , Murlidhar S.
Published: July 2002

A Stewart platform in its most general form is a parallel manipulator with six linear actuators connected to the base and the end-effector with spherical joints. We introduce the concept of massively parallel binary system (MPBS), realised by increasing the number of legs beyond six to a very large number and constraining the actuators to be in one of two states, retracted or extended. Dynamic equations for such systems have been established. Based on simulation, behavior and design issues of such systems have been discussed. Some bounds for load limits and frequency response for such systems have been determined.
Life Prediction and Monitoring of Nuclear Power Plant Components for Service-Related Degradation
Authors: Simonen Fredric A. , Gosselin Stephen R.
Published: July 2002

This paper describes industry programs to manage structural degradation and to justify continued operation of nuclear components when unexpected degradation has been encountered due to design materials and/or operational problems. Other issues have been related to operation of components beyond their original design life in cases where there is no evidence of fatigue crack initiation or other forms of structural degradation. Data from plant operating experience have been applied in combination with inservice inspections and degradation management programs to ensure that the degradation mechanisms do not adversely impact plant safety. Probabilistic fracture mechanics calculations are presented to demonstrate how component failure probabilities can be managed through augmented inservice inspection programs.
Local Heat/Mass Transfer Measurement on the Effusion Plate in Impingement/Effusion Cooling Systems
Authors: Cho Hyung Hee , Rhee Dong Ho
Published: July 2002

The present study is conducted to investigate the local heat/mass transfer characteristics for flow through perforated plates. A naphthalene sublimation method is employed to determine the local heat/mass transfer coefficients on the effusion plate. Two parallel perforated plates are arranged in two different configurations: staggered and shifted in one direction. The experiments are conducted for hole pitch-to-diameter ratios of 6.0, for gap distance between the perforated plates of 0.33 to 10 hole diameters, and for Reynolds numbers of 5000 to 12,000. The result shows that the high transfer region is formed at stagnation region and at the midline of the adjacent impinging jets due to secondary vortices and flow acceleration to the effusion hole. For flows through the perforated plates, the mass transfer rates on the surface of the effusion plate are about six to ten times higher than for effusion cooling alone (single perforated plate). In general, higher heat/mass transfer is obtained with smaller gap distance between two perforated plates.
Dynamic Analysis of a One-Dimensional Poroviscoelastic Column
Authors: Schanz M. , Cheng A. H.-D.
Published: July 2002

The response due to a dynamic loading of a poroviscoelastic one-dimensional column is treated analytically. Biot’s theory of poroelasticity is generalized to poroviscoelasticity using the elastic-viscoelastic correspondence principle in the Laplace domain. Damping effects of the solid skeletal structure and the solid material itself are taken into account. The fluid is modeled as in the original Biot’s theory without any viscoelastic effects. The solution of the governing set of two coupled differential equations known from the purely poroelastic case is converted to the poroviscoelastic solution using the developed elastic-viscoelastic correspondence in Laplace domain. The time-dependent response of the column is achieved by the “Convolution Quadrature Method” proposed by Lubich. Some interesting effects of viscoelasticity on the response of the column caused by a stress, pressure, and displacement loading are studied.
Effective Permeability of a Layered Porous Cavity
Authors: Leong J. C. , Lai F. C.
Published: July 2002

The feasibility of using a lumped system approach in the heat transfer analysis of a layered porous cavity is numerically investigated in this paper. Two layered cavities are considered; in one case the sublayers are perpendicular to the imposed temperature gradient while in the other case they are parallel to the imposed temperature gradient. Numerical calculations have covered a wide range of parameters (i.e., 10⩽Ra1⩽1000,0.01⩽K1/K2⩽100, and L1/LH1/H=0.25, 0.5 and 0.75). The results are presented in term of the effective Rayleigh number which is defined based on the effective permeability. Two averaging techniques are used for the evaluation of the effective permeability; one is arithmetic average and the other is harmonic average. The results show that the lumped system approach can provide a fairly accurate prediction in heat transfer if the permeability is correctly characterized. Also found is that the effective permeability of a layered porous cavity is strongly dependent on the orientation of sublayers and the primary heat flow direction.
Maximizing Thermal Power Output of an Ammonia Synthesis Reactor for a Solar Thermochemical Energy Storage System
Authors: Kreetz H. , Lovegrove K. , Luzzi A.
Published: July 2002

Solar energy storage using a closed loop thermochemical system based on the reversible dissociation of ammonia, has been investigated at the Australian National University for over two decades. Theoretical and system studies have indicated that large scale systems offer reasonable thermodynamic and economic performance. Experimental investigation has confirmed the technical viability of the concept. This investigation has looked at the effect of operating parameters on the thermal output achievable from the heat recovery process. Pressure, massflow and inlet gas composition were all found to have significant effects on the output achievable. Maximizing the thermal output via adjustment of reactor wall temperature profiles indicates that the average temperature of the reactor walls is more significant than the shape of the profile. This investigation has indicated the potential and provided the foundations for future exergo-economic optimizations of the system.
An Experimental Study of Surface Temperature Distribution on Effusion-Cooled Plates
Authors: Gustafsson K. M. Bernhard , Johansson T. Gunnar
Published: July 2002

A parametric study of temperature distribution on effusion-cooled plates under conditions typical for combustion chambers was performed using infrared thermography. In this investigation, the effects of different temperature ratios, velocity ratios of the two air streams, the injection hole spacing, inclination angle of the injection holes, and the thermal heat conductivity of the plates were studied. For a given amount of cooling air, the cooling efficiency was found to increase markedly with a reduction in hole spacing, i.e., when the number of holes was increased. Reducing the injection angle results in more attached jets, especially for small amounts of cooling air, and marginally lowers the wall temperature. A high thermal conductivity of the plate was found to decrease its surface temperature in front of the first row of holes but not the mean temperature in downstream positions. The most important operational parameters were the temperature ratio and the velocity ratio of the hot and cold air streams. An almost linear relation was found between the temperature ratio and the surface temperature when the jet velocity was large compared to the crossflow velocity. For plates with sparse hole spacing, a change in the velocity ratio had a small effect on the surface temperature, whereas the effect was large for dense hole spacings and the same amount of cooling air.
Heat Transfer Enhancement to the Drag-Reducing Flow of Surfactant Solution in Two-Dimensional Channel With Mesh-Screen Inserts at the Inlet
Authors: Li Peiwen , Kawaguchi Yasuo , Daisaka Hisashi , Yabe Akira , Hishida Koichi , Maeda Masanobu
Published: July 2002

The heat transfer enhancement of drag-reducing flow of high Reynolds number in a two-dimensional channel by utilizing the characteristic of fluid was studied. As the networks of rod-like micelles in surfactant solution are responsible for suppressing the turbulence in drag-reducing flow, destruction of the structure of networks was considered to eliminate the drag reduction and prevent heat transfer deterioration. By inserting wire mesh in the channel against the flow, the drag-reducing function of the micellar structure in surfactant aqueous solution was successfully switched off. With the Reynolds number close to the first critical Reynolds number, the heat transfer coefficient in the region downstream of the mesh can be improved significantly, reaching the same level as that of water. The region with turbulent heat transfer downstream of the mesh becomes smaller as the concentration of surfactant in the solution increases. Three types of mesh of different wire diameter and opening space were evaluated for their effect in promoting heat transfer and the corresponding pressure loss due to blockage of the mesh. The turbulent intensities were measured downstream from the mesh by using a Laser Doppler Velocimetry (LDV) system. The results indicated that the success of heat transfer enhancement is due to the strong turbulence promoted by the mesh which destroys the network of rod-like micelles by applying high shear stress and thus relaxing the shear induced state (SIS).
Experimental Study of Water Sprays for the Attenuation of Fire Thermal Radiation
Authors: Dembele S. , Wen J. X. , Sacadura J.-F.
Published: July 2002

A laboratory experimental work is carried out to investigate the attenuation ability of water sprays subjected to thermal radiation. The objective is to analyze the key parameters involved in the mitigation properties of this fire protection technique. The spectral transmittances of two types of sprayers, TG03 and TG05, are measured with a Fourier infrared spectrometer under various conditions. The wavelength range varies from 1.5 to 12 μm. The influence on the transmittance of both the flow rate and the pressure ranging from 1 to 7 bars, as well as the effect of the number of spray nozzles are considered. The results clearly show the advantage of small drops with high concentration. An investigation on the multi-ramp curtain configuration also provides valuable information on the mitigation behavior of the whole spray. Key guidelines are provided for fire protection engineering.
Assessment of Sandwich Beam in Three-Point Bending for Measuring Adhesive Shear Modulus
Authors: He Jianmei , Chiang Martin Y. M. , Hunston Donald L.
Published: July 2002

A finite element analysis (FEA) was conducted to examine the feasibility of determining the shear modulus of an adhesive in a bonded geometry using a three-point bending test on a sandwich beam specimen. The FEA results were compared with the predictions from two analytical solutions for the geometry used to determine the impact of the assumptions that were made in these analyses. The analytical results showed significantly different to the values obtained from other experiments on bulk samples of the adhesive in the glassy region. Although there were some agreements in rubbery region, the negligible sensitivity of the beam stiffness to the presence of adhesive layer makes the agreements very questionable. To examine the possible explanations for these differences in glassy adhesives, sensitivity analysis was conducted to explore the effects of experimental variables. Some possible reasons for the differences are discussed, but none of these reasons taken alone satisfactorily account for the discrepancies. Until an explanation is found, the three-point bending test using a sandwich beam specimen to determine the adhesive shear modulus might not be a desirable test method, at least for the range of geometry examined in this study.
The Effect of Dissolving Gases or Solids in Water Droplets Boiling on a Hot Surface
Authors: Cui Qiang , Chandra Sanjeev , McCahan Susan
Published: July 2002

We conducted experiments on the effect of dissolving either a gas (carbon dioxide) or a solid salt (sodium carbonate or sodium bicarbonate) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 100°C to 300°C. We recorded the boiling of droplets with a video system, and photographed droplet impact using short-duration flash photography. At surface temperatures that were too low to initiate nucleate boiling, dissolved salts were found to reduce the evaporation rate since they lower the vapor pressure of water. Dissolved gas had the opposite effect: it came out of solution and formed bubbles in the liquid, enhancing evaporation. In the nucleate boiling regime dissolved carbon dioxide enhanced heat transfer by a small amount. However, sodium carbonate prevented coalescence of vapor bubbles and produced foaming in the droplet, greatly enhancing heat transfer and reducing the droplet lifetime to approximately half that of a pure water drop. Sodium bicarbonate, which decomposes to give carbon dioxide and sodium carbonate when heated, produced an even larger enhancement of heat transfer. When the surface temperature was raised above the Leidenfrost temperature of water, droplets went into film boiling and bounced off the surface following impact. Dissolved carbon dioxide was found to suppress heterogeneous bubble formation in the droplet during impact. However, dissolved salts promoted bubble formation and led to droplet break-up during impact.
Wavelet Analysis and Envelope Detection For Rolling Element Bearing Fault Diagnosis—Their Effectiveness and Flexibilities
Authors: Tse Peter W. , Peng Y. H. , Yam Richard
Published: July 2002

The components which often fail in a rolling element bearing are the outer-race, the inner-race, the rollers, and the cage. Such failures generate a series of impact vibrations in short time intervals, which occur at Bearing Characteristic Frequencies (BCF). Since BCF contain very little energy, and are usually overwhelmed by noise and higher levels of macro-structural vibrations, they are difficult to find in their frequency spectra when using the common technique of Fast Fourier Transforms (FFT). Therefore, Envelope Detection (ED) is always used with FFT to identify faults occurring at the BCF. However, the computation of ED is complicated, and requires expensive equipment and experienced operators to process. This, coupled with the incapacity of FFT to detect nonstationary signals, makes wavelet analysis a popular alternative for machine fault diagnosis. Wavelet analysis provides multi-resolution in time-frequency distribution for easier detection of abnormal vibration signals. From the results of extensive experiments performed in a series of motor-pump driven systems, the methods of wavelet analysis and FFT with ED are proven to be efficient in detecting some types of bearing faults. Since wavelet analysis can detect both periodic and nonperiodic signals, it allows the machine operator to more easily detect the remaining types of bearing faults which are impossible by the method of FFT with ED. Hence, wavelet analysis is a better fault diagnostic tool for the practice in maintenance.
Measurement of Transfer Matrices and Source Terms of Premixed Flames
Authors: Paschereit C. O. , Schuermans B. , Polifke W. , Mattson O.
Published: July 2002

An experimental method to determine the thermoacoustic properties of a gas turbine combustor using a lean-premixed low emission swirl stabilized burner is presented. To model thermoacoustic oscillations, a combustion system can be described as a network of acoustic elements, representing for example fuel and air supply, burner and flame, combustor, cooling channels, suitable terminations, etc. For most of these elements, simple analytical models provide an adequate description of their thermoacoustic properties. However, the complex response of burner and flame (involving a three-dimensional flow field, recirculation zones, flow instabilities, and heat release) to acoustic perturbations has—at least in a first step—to be determined by experiment. In our approach, we describe the burner as an active acoustical two-port, where the state variables pressure and velocity at the inlet and the outlet of the two port are coupled via a four element transfer matrix. This approach is similar to the “black box” theory in communication engineering. To determine all four transfer matrix coefficients, two test states, which are independent in the state vectors, have to be created. This is achieved by using acoustic excitation by loudspeakers upstream and downstream of the burner, respectively. In addition, the burner might act as an acoustic source, emitting acoustic waves due to an unsteady combustion process. The source characteristics were determined by using a third test state, which again must be independent from the two other state vectors. In application to a full size gas turbine burner, the method’s accuracy was tested in a first step without combustion and the results were compared to an analytical model for the burner’s acoustic properties. Then the method was used to determine the burner transfer matrix with combustion. An experimental swirl stabilized premixed gas turbine burner was used for this purpose. The treatment of burners as acoustic two-ports with feedback including a source term and the experimental determination of the burner transfer matrix is novel.
Genetic Spatial Optimization of Active Elements on an Aeroelastic Delta Wing
Authors: Richard Robert E. , Rule John A. , Clark Robert L.
Published: July 2002

This work outlines a cohesive approach for the design and implementation of a genetically optimized, active aeroelastic delta wing. Emphasis was placed on computational efficiency of model development and efficient means for optimizing sensor and actuator geometries. Reduced-order models of potential-flow aerodynamics were developed for facilitation of analysis and design of the aeroelastic system in the early design phase. Using these methods, models capturing “95% of the physics with 8% of the modeling effort” can be realized to evaluate various active and passive design considerations. The aeroelastic delta wing model was employed in determining the most effective locations and sizes for transducers required to provide flutter control. The basic design presented is based upon an analytical model of the structure. A comparison of optimization strategies led to the use of a genetic algorithm to determine the optimal transducer locations, sizes, and orientations required to provide effective flutter control based upon an open-loop performance metric. The genetic algorithm and performance metric essentially provided loop shaping through the adaptive structure design. An experimental model was then developed based upon the optimal transducer designs. Wind tunnel tests were performed to demonstrate closed-loop performance for flutter control. Results from this study indicate that a single sensor/actuator pair can be designed to extend the flutter boundary and selectively couple to only those modes required to control the response.
Modified Anisotropic Gurson Yield Criterion for Porous Ductile Sheet Metals
Authors: Chien W. Y. , Pan J. , Tang S. C.
Published: July 2002

The influence of plastic anisotropy on the plastic behavior of porous ductile materials is investigated by a three-dimensional finite element analysis. A unit cell of cube containing a spherical void is modeled. The Hill quadratic anisotropic yield criterion is used to describe the matrix normal anisotropy and planar isotropy. The matrix material is first assumed to be elastic perfectly plastic. Macroscopically uniform displacements are applied to the faces of the cube. The finite element computational results are compared with those based on the closed-form anisotropic Gurson yield criterion suggested in Liao et al. 1997, “Approximate Yield Criteria for Anisotropic Porous Ductile Sheet Metals,” Mech. Mater., pp. 213–226. Three fitting parameters are suggested for the closed-form yield criterion to fit the results based on the modified yield criterion to those of finite element computations. When the strain hardening of the matrix is considered, the computational results of the macroscopic stress-strain behavior are in agreement with those based on the modified anisotropic Gurson’s yield criterion under uniaxial and equal biaxial tensile loading conditions.
Dynamic Analysis of Rotating Beams with Nonuniform Cross Sections Using the Dynamic Stiffness Method
Authors: Huang K. J. , Liu T. S.
Published: July 2002

This study develops dynamic analysis based on the dynamic stiffness method for a rotating beam of nonuniform cross-section. To deal with nonuniform beams, coefficients related to material and geometric properties in the equation of motion are expressed in a polynomial form. A dynamic stiffness matrix is accordingly formulated in terms of power series. The dynamic response of the rotating beam is calculated by performing modal analysis. It is demonstrated that the present method provides an alternative to the finite element method in dealing with nonuniform rotating beams.
Higher-Order Zig-Zag Theory for Laminated Composites With Multiple Delaminations
Authors: Cho M. , Kim J.-S.
Published: July 2002

A higher-order zig-zag theory has been developed for laminated composite plates with multiple delaminations. By imposing top and bottom surface transverse shear stress-free conditions and interface continuity conditions of transverse shear stresses including delaminated interfaces, the displacement field with minimal degree-of-freedoms are obtained. This displacement field can systematically handle the number, shape, size, and locations of delaminations. Through the dynamic version of variational approach, the dynamic equilibrium equations and variationally consistent boundary conditions are obtained. The delaminated beam finite element is implemented to evaluate the performance of the newly developed theory. Linear buckling and natural frequency analysis demonstrate the accuracy and efficiency of the present theory. The present higher-order zig-zag theory should work as an efficient tool to analyze the static and dynamic behavior of the composite plates with multiple delaminations.
Constitutive and Cyclic Damage Model of 63Sn-37Pb Solder
Authors: Stolkarts V. , Keer L. M. , Fine M. E.
Published: July 2002

The proposed model describes constitutive behavior of 63Sn-37Pb solder including effects of size, thermomechanical loading, and cyclic damage. Its application to the uniaxial fatigue data shows a good agreement with the experiments.
Elastic-Inelastic Self-Consistent Model for Polycrystals
Authors: Abdul-Latif A. , Dingli J. P. , Saanouni K.
Published: July 2002

Based on a well-established nonincremental interaction law for fully anisotropic and compressible elastic-inelastic behavior of polycrystals, tangent formulation-based and simplified interaction laws, of softened nature, are derived to describe the nonlinear elastic-inelastic behavior of fcc polycrystals under different loading paths. Within the framework of small strain hypothesis, the elastic behavior, which is defined at granular level, is assumed to be isotropic, uniform, and compressible neglecting the grain rotation. The heterogeneous inelastic deformation is microscopically determined using the slip theory. In addition, the granular elastic behavior and its heterogeneous distribution from grain to grain within a polycrystal are taken into account. Comparisons between these two approaches show that the simplified one is more suitable to describe the overall responses of polycrystals notably under multiaxial loading paths. Nonlinear stress-strain behavior of polycrystals under complex loading, especially a cyclic one, is of particular interest in proposed modeling. The simplified model describes fairly well the yield surface evolution after a certain inelastic prestraining and the principle cyclic features such as Bauschinger effect, additional hardening, etc.
On Assessing the Quality of Particle Tracking Through Computational Fluid Dynamic Models
Authors: Tambasco Mauro , Steinman David A.
Published: July 2002

Quantification of particle deposition patterns, transit times, and shear exposure is important for computational fluid dynamic (CFD) studies involving respiratory and arterial models. To numerically compute such path-dependent quantities, it is necessary to employ a Lagrangian approach where particles are tracked through a pre-computed velocity field. However, it is difficult to determine in advance whether a particular velocity field is sufficiently resolved for the purposes of tracking particles accurately. Towards this end, we propose the use of volumetric residence time (VRT)—previously defined for 2-D studies of platelet activation and here extended to more physiologically relevant 3-D models—as a means of quantifying whether a volume of Lagrangian fluid elements (LFE’s) seeded uniformly and contiguously at the model inlet remains uniform throughout the flow domain. Such “Lagrangian mass conservation” is shown to be satisfied when VRT=1 throughout the model domain. To demonstrate this novel concept, we computed maps of VRT and particle deposition in 3-D steady flow models of a stenosed carotid bifurcation constructed with one adaptively refined and three nominally uniform finite element meshes of increasing element density. A key finding was that uniform VRT could not be achieved for even the most resolved meshes and densest LFE seeding, suggesting that care should be taken when extracting quantitative information about path-dependent quantities. The VRT maps were found to be useful for identifying regions of a mesh that were under-resolved for such Lagrangian studies, and for guiding the construction of more adequately resolved meshes.
Coupled Torsion-Lateral Stability of a Shaft-Disk System Driven Through a Universal Joint
Authors: DeSmidt H. A. , Wang K. W. , Smith E. C.
Published: July 2002

Understanding the instability phenomena of rotor-shaft and driveline systems incorporating universal joints is becoming increasingly important because of the trend towards light-weight, high-speed supercritical designs. In this paper, a nondimensional, periodic, linear time-varying model with torsional and lateral degrees-of-freedom is developed for a rotor shaft-disk assembly supported on a flexible bearing and driven through a U-joint. The stability of this system is investigated utilizing Floquet theory. It is shown that the interaction between torsional and lateral dynamics results in new regions of parametric instability that have not been addressed in previous investigations. The presence of load inertia and misalignment causes dynamic coupling of the torsion and lateral modes, which can result in torsion-lateral instability for shaft speeds near the sum-type combinations of the torsion and lateral natural frequencies. The effect of angular misalignment, static load-torque, load-inertia, lateral frequency split, and auxiliary damping on the stability of the system is studied over a range of shaft operating speeds. Other than avoiding the unstable operating frequencies, the effectiveness of using auxiliary lateral viscous damping as a means of stabilizing the system is investigated. Finally, a closed-form technique based on perturbation expansions is derived to determine the auxiliary damping necessary to stabilize the system for the least stable case (worst case).
Robust Control of Pulsed Gas Metal Arc Welding
Authors: Zhang Y. M. , E Liguo , Walcott B. L.
Published: July 2002

A system is developed to control the pulsed gas metal arc welding process. To achieve controlled detachment of the droplet, the welding current is switched from a peak level to a background level to induce droplet oscillation. When the droplet moves downwards, the current is switched back to peak level. The combination of downward momentum of the oscillating droplet and increased electromagnetic force guarantees detachment of the droplet. Instead of adjusting duration of the background current, the waveform of the current is adjusted to control the melting rate of the electrode wire without having to change the transfer frequency. It is found that the dynamic model of the process depends on welding operational parameters, which vary with applications, and therefore it is unrealistic for operators to provide welding machines these parameters as inputs. Hence, welding operational parameters are considered as unfixed and their ranges are used to quantify the resultant uncertainty in the dynamic model. As a result, the process is controlled using a single algorithm at different operational parameters. Experiments verified the effectiveness of the system in overcoming two common variations in welding operational parameters, wire speed and contact tube-to-work distance.
Continuum Damage Mechanics and Creep Life Analysis
Authors: Rodin G. J.
Published: July 2002

It is shown that the original continuum damage mechanics model of Kachanov is better suited for creep life analysis of creep-brittle solids and structures than continuum damage mechanics models that take into account damage-induced softening. [S0021-8936(00)03001-4]
Turbulence Characteristics Downstream of Bileaflet Aortic Valve Prostheses
Authors: Liu J. S. , Lu P. C. , Chu S. H.
Published: July 2002

This study was focused on a series of in vitro tests on the turbulent flow characteristics of three bileaflet aortic valves: St. Jude Medical (SJM), CarboMedics (CM), and Edwards Tekna (modified Duromedics, DM). The flow fields of the valves were measured in a pulsatile flow model with a laser-Doppler anemometer (LDA) at the aortic sinus area downstream of the valves. The heart rate was set at 70 beats per minute, the cardiac output was maintained at 5 liters per minute, and the aortic pressure wave forms were kept within the physiological range. Cycle-resolved analysis was applied to obtain turbulence data, including mean velocity, Reynolds stresses, autocorrelation coefficients, energy spectral density functions, and turbulence scales. The Reynolds shear stresses of all three valves induced only minor damage to red blood cells, but directly damaged the platelets, increasing the possibility of thrombosis. The smallest turbulence length scale, which offers a more reliable estimate of the effects of turbulence on blood cell damage, was three times the size of red blood cells and five times the size of platelets. This suggests that there is more direct interaction with the blood cells, thus causing more damage. [S0148-0731(00)00302-2]
Dynamic Model for a Dome-Loaded Pressure Regulator
Authors: Nabi A. , Wacholder E. , Dayan J.
Published: July 2002

A generalized physical model describing dynamic behavior of a fast-acting, dome-loaded, gas pressure regulator was developed. The regulator is designed to respond quickly to command changes, and to operate over a wide range of flow rates and pressures. The analytical lumped-parameter model developed consists of a set of nonlinear, first-order, ordinary differential equations with respect to time, accounting for mass and energy conservation at regulator outlet, command dome and internal feedback compartments. It also accounts for the equation-of-motion for the poppet and the control piston-assembly. The numerical solution, based on a Runge–Kutta method, is amenable to an extensive parametric study of regulator performance, and serves as a useful analytical tool for designing new pressure regulators. Several tests were performed on a fast-acting regulator to verify the physical model. Good agreement between predictions and measurements was obtained. The effect of several parameters, geometrical and operational, on regulator performance was studied. [S0022-0434(00)00402-0]
Slug Dynamics in Gas-Liquid Pipe Flow
Authors: Zhang Hong-Quan , Jayawardena Subash S. , Redus Clifford L. , Brill James P.
Published: July 2002

The continuity and momentum equations for fully developed and spatially developing slug flows are established by considering the entire film zone as the control volume. They are used for the calculations of pressure gradient, slug frequency, liquid holdup in the film, flow pattern transition, slug dissipation, and slug tracking. Comparison with available experimental results shows that these equations correctly describe the slug dynamics in gas-liquid pipe flow. [S0195-0738(00)00701-9]
Stick-Slip and Bit-Bounce of Deep-Hole Drillstrings
Authors: Baumgart A.
Published: July 2002

A mathematical model for the drilling process is derived and solved numerically as an initial value problem. The equations of motion are nonlinear differential equations for longitudinal, lateral, and rotational motion of the pipe as well as for the rate of flow and pressure of the mud. The model comprises a mud (Moineau) motor which rotates the bit relative to the lower end of the pipe. The model accounts for buckling of the pipe due to excessive torque and longitudinal forces, as well as for the effect of hydraulic pressure on the deformed pipe. Weight on bit and torque on bit are computed from characteristic curves which are functions of the penetration of the bit into the rock and the angular velocity of the bit. Numerical simulations show self-excited oscillations of the drillstring, including bit take-off from the bottom hole and large amplitudes in the bit’s angular velocity. [S0195-0738(00)00602-6]
Condensation of Refrigerants in Horizontal, Spirally Grooved Microfin
Tubes: Numerical Analysis of Heat Transfer in the Annular Flow Regime
Authors: Nozu S. , Honda H.
Published: July 2002

A method is presented for estimating the condensation heat transfer coefficient in a horizontal, spirally grooved microfin tube. Based on the flow observation study performed by the authors, a laminar film condensation model in the annular flow regime is proposed. The model assumes that all the condensate flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. The present and previous local heat transfer data including four fluids (CFC11, HCFC22, HCFC123, and HFC134a) and three microfin tubes are found to agree with the present predictions to a mean absolute deviation of 15.1 percent. [S0022-1481(00)01501-2]
Melting and Surface Deformation in Pulsed Laser Surface
Micromodification of Ni-P Disks
Authors: Chen S. C. , Cahill D. G. , Grigoropoulos C. P.
Published: July 2002

The nanosecond pulsed laser-induced transient melting and miniature surface deformation of Ni-P hard disk substrates has been investigated experimentally. A photothermal displacement method has been developed to detect the transient melting and surface deformation process with nanosecond time resolution. The deflection signals show the variation of the feature shape in response to different pulse energies of the near-infrared pulsed nanosecond heating laser beam. A laser flash photography system is also developed to visualize the growth dynamics of the entire feature with nanosecond time resolution and submicron spatial resolution. The feature formation is explained as a result of surface tension driven flow. The surface tension depends not only on the surface temperature, but also on the surfactant concentration. Competition between the thermocapillarity and a surfactant concentration effect is revealed in the course of the bump formation process. Smaller features with diameters of 5 μm are obtained by using visible pulsed laser radiation. On-line monitoring of the transient growth process of such small features is achieved by a new laser flash deflection microscope. [S0022-1481(00)00301-7]
An Analytical Model for Decaying Swirl Flow and Heat Transfer Inside
a Tube
Authors: Wu Hui-Ying , Cheng Hui-Er , Shuai Ren-Jun , Zhou Qiang-Tai
Published: July 2002

Decaying swirl flow can enhance the heat transfer inside a tube. For the decaying swirl flow of which maximum tangential velocity is located in the immediate vicinity of the wall, an analytical model based on the fluid theorem about the moment of momentum is proposed for the local maximum tangential velocity, local friction factor, and local Nusselt number in this paper. The analytical solutions compare favorably with the experimental data. Influences of the Reynolds number, wall roughness and initial tangential-to-axial velocity ratio on the decaying characteristics of the friction factor and Nusselt number have been analyzed. The analytical results show that the swirl flow decays more rapidly at the initial segment; for same conditions, the friction factor decays more severely than the Nusselt number; relative to the values of the nonswirl flow, the friction factor increases more intensely than the Nusselt number. [S0022-1481(00)70401-4]
Nonequilibrium Natural Convection in a Differentially Heated Cavity Filled With a Saturated Porous Matrix
Authors: Mohamad A. A.
Published: July 2002

Steady state, natural convection in an enclosure filled with a saturated porous medium is investigated numerically. Brinkman-Forchheimer’s extension of Darcy flow with a nonequilibrium model is used in the analysis. The paper intends to address the validity of the equilibrium model for natural convection. The predicted results indicated that the equilibrium model is difficult to justify for non-Darcy regime and when the solid thermal conductivity is higher than the fluid thermal conductivity. The maximum differences in the temperatures between the two phases take place at the bottom-left corner and due to skew-symmetry of the problem at the upper-right corner. [S0022-1481(00)00402-3]