bluuebunny/crossref_metadata_2025 huggingface dataset:
Identifying Faults in the Variable Geometry System of a Gas Turbine Compressor
Authors: Tsalavoutas A. , Mathioudakis K. , Stamatis A. , Smith M.
Published: July 2002

The influence of faults in the variable geometry (variable stator vanes) system of a multistage axial compressor on the performance of an industrial gas turbine is investigated. An experimental investigation has been conducted, by implanting such faults into an operating gas turbine. The faults examined are individual stator vane mistunings of different magnitudes and located at different stages. Fault identification is based on the aerothermodynamic measurement data and is achieved by employing two different techniques, namely adaptive performance modeling and monitoring the circumferential distribution of the turbine exit temperature. It is observed that the deviations of the health indices produced by an adaptive performance model form patterns that can be used to identify the faults. The patterns characterize both the kind and the magnitude of the fault. On the other hand, the turbine exit temperature profile is also influenced and its change can be used as additional information, to increase the confidence level of the diagnosis (contrary to customary practice, which expects temperatures profiles to reflect only burner or turbine malfunctions).
Experimental and Computational Investigations of Phase Change Thermal Energy Storage Canisters
Authors: Ibrahim Mounir , Sokolov Pavel , Kerslake Thomas , Tolbert Carol
Published: July 2002

Two sets of experimental data for cylindrical canisters with thermal energy storage applications were examined in this paper: 1) Ground Experiments and 2) Space Experiments. A 2-D computational model was developed for unsteady heat transfer (conduction and radiation) with phase-change. The radiation heat transfer employed a finite volume method. The following was found in this study: 1) Ground Experiments, the convection heat transfer is equally important to that of the radiation heat transfer; Radiation heat transfer in the liquid is found to be more significant than that in the void; Including the radiation heat transfer in the liquid resulted in lower temperatures (about 15 K) and increased the melting time (about 10 min.); Generally, most of the heat flow takes place in the radial direction. 2) Space Experiments, Radiation heat transfer in the void is found to be more significant than that in the liquid (exactly the opposite to the Ground Experiments); Accordingly, the location and size of the void affects the performance considerably; Including the radiation heat transfer in the void resulted in lower temperatures (about 40 K). [S0199-6231(00)00304-X]
Application of Lubrication Theory to Fluid Flow in Grinding: Part I—Flow Between Smooth Surfaces
Authors: Hryniewicz P. , Szeri A. Z. , Jahanmir S.
Published: July 2002

The present paper, which consists of two parts, proposes models of fluid flow in grinding with nonporous wheels. In this first part, a smooth wheel is employed instead of a rough grinding wheel to simplify the analysis. Fluid flow is investigated for laminar and turbulent regimes using the classical Reynolds equation of lubrication and a modified Reynolds equation for turbulent flows, respectively. The applicability of the proposed models is discussed and verified experimentally in terms of the developed hydrodynamic pressure. It is found that the classical Reynolds equation reliably predicts the hydrodynamic pressure if the Reynolds number Re (based on the minimum gap size) is lower than about 300. Experimental results for 300<Re<1500 agree with the proposed turbulent flow model. This suggests that the flow in this range of Re is turbulent, and that the fluid inertia is negligible. The influence of wheel roughness is investigated in Part II.
Fluid Dynamics of a Textured Blood-Contacting Surface
Authors: Fujisawa Naoki , Bertram Christopher D. , Woodard John C. , Poole-Warren Laura A. , Schindhelm Klaus
Published: July 2002

This study examined the fluid dynamics of a textured blood-contacting surface using a computational fluid-dynamic modeling technique. The texture consisted of a regular array of microfibers of length 50 or 100 μm, spaced 100 μm apart, projecting perpendicularly to the surface. The results showed that the surface texture served as a flow-retarding solid boundary for a laminar viscous flow, resulting in a lowered wall shear stress on the base-plane surface. However, the maximum wall shear stress on the fibers was much higher than the shear stress on the nontextured base plane. At all fractions of fiber height down past 10 μm, the permeability of the textured region greatly exceeded the analytically predictable permeability of an equivalent array of infinite-height fibers. The lowered surface shear stress appears to explain in part the enhanced deposition of formed blood elements on the textured surface.
Impact Strength of High Density Solid-State Microcellular Polycarbonate Foams
Authors: Barlow Chris , Kumar Vipin , Flinn Brian , Bordia Rajendra K. , Weller John
Published: July 2002

The effect of density (relative densities 0.33 to 0.90) on the impact behavior of microcellular polycarbonate (PC) was investigated. Cell size and foaming gas content were also considered. Flexed-beam Izod impact tests were conducted and the impact strength of these foams appears to be a strong function of both density and cell size. The impact strength was observed to improve over the unprocessed polycarbonate’s impact strength for foams with relative densities of 60 percent and above. In terms of cell size, the impact strength increased with increasing cell size at a given density.
The Role of Knowledge in Next-generation Product Development Systems
Authors: Szykman Simon , Sriram Ram D. , Regli William C.
Published: July 2002

Information technology has played an increasingly important role in engineering product development. Its influence over the past decade has been accelerating and its impact in the coming decade will undoubtedly be immense. This paper surveys several research areas relating to knowledge representation, capture and retrieval, which will have a growing influence on product development. Each of these areas could, on its own, provide sufficient material for an entire survey paper. Unlike traditional survey papers, this paper does not attempt to provide a comprehensive review of a field of research from its inception to the present. Rather, this paper aims to touch on a representative selection of recent developments in these influential technical areas. The paper provides perspectives into the kinds of technologies that are emerging from rapidly expanding fields of research, and discusses challenges that must be overcome to enable transition of these technologies into industry practice to support the next generation of product development software tools.
Performance of Chiller in a Solar Absorption Air Conditioning System With Partitioned Hot Water Storage Tank
Authors: Li Z. F. , Sumathy K.
Published: July 2002

This paper reports the performance of a lithium bromide absorption chiller in a solar powered air conditioning system, when being operated conventionally. The chiller performance based on a modified solar powered absorption air conditioning system which is integrated with a partitioned storage tank has been presented and discussed. It is shown that, by partitioning the storage tank, the chiller performance is not significantly affected, and the solar powered cooling effect can be realized much earlier, achieving a higher total solar cooling COPsystem, compared to the conventional system designs.
An Aid to Operating Decisions Based on Nonlinear Response of a Crane Barge in Waves
Authors: Schellin T. E. , Schiff C. , O¨stergaard C.
Published: July 2002

A nine-degree-of-freedom time domain mathematical model was used to numerically simulate crane ship dynamics. This model considers the elasticity and damping of the hoisting rope assembly and includes arbitrary, biangular swing of the suspended hook load coupled with surge, sway, heave, roll, pitch, and yaw motions of the hull. The linear frequency-dependent hydrodynamic response to the hull’s own motions accounted for memory effects that were approximated in the time domain by a finite state space model. The nonlinear hydrodynamic drag force acting on the oscillating hull was quadratically approximated using an empirical drag coefficient. The incident wave force on the hull consisted of the first-order force oscillating at wave frequency and the second-order slowly varying wave drift force. The nonlinear horizontal mooring system restoring force was approximated by a third-order polynomial. To specify operating limits for a shear-leg crane barge in a heavy lift offshore operation, a stochastic analysis was performed based on the system’s simulated dynamic response in an ensemble of natural seaways.
One-to-One Internal Resonance of Symmetric Crossply Laminated Shallow Shells
Authors: Abe A. , Kobayashi Y. , Yamada G.
Published: July 2002

This paper presents the response of symmetric crossply laminated shallow shells with an internal resonance ω2≈ω3, where ω2 and ω3 are the linear natural frequencies of the asymmetric vibration modes (2,1) and (1,2), respectively. Galerkin’s procedure is applied to the nonlinear governing equations for the shells based on the von Ka´rma´n-type geometric nonlinear theory and the first-order shear deformation theory, and the shooting method is used to obtain the steady-state response when a driving frequency Ω is near ω2. In order to take into account the influence of quadratic nonlinearities, the displacement functions of the shells are approximated by the eigenfunctions for the linear vibration mode (1,1) in addition to the ones for the modes (2,1) and (1,2). This approximation overcomes the shortcomings in Galerkin’s procedure. In the numerical examples, the effect of the (1,1) mode on the primary resonance of the (2,1) mode is examined in detail, which allows us to conclude that the consideration of the (1,1) mode is indispensable for analyzing nonlinear vibrations of asymmetric vibration modes of shells.
Computationally Efficient Micromechanical Models for Woven Fabric Composite Elastic Moduli
Authors: Tanov R. , Tabiei A.
Published: July 2002

This paper presents two newly developed micromechanical models for the analysis of plain weave fabric composites. Both models utilize the representative volume cell approach. The representative unit volume of the woven lamina is divided into subcells of homogeneous material. Starting with the average strains in the representative volume cell and based on continuity requirements at the subcell interfaces, the strains and stresses in the composite fiber yarns and matrix are determined as well as the average stresses in the lamina. Equivalent homogenized material properties are also determined. In their formulation the developed micromechanical models take into consideration all components of the three-dimensional strain and stress tensors. The performance of both models is assessed through comparison with available results from other numerical, analytical, and experimental approaches for composite laminae homogenization. The very good accuracy together with the simplicity of formulation makes these models attractive for the finite element analysis of composite laminates.
Reduced Mechanisms for Prediction of NO2 Formation and Ignition Delay in Methane-Air Combustion
Authors: Homma R. , Chen J.-Y.
Published: July 2002

Two new 14-step and 16-step reduced mechanisms for methane-air combustion were systematically developed by assuming the quasisteady state for 26–28 species in the starting mechanism. A series of comparison between the reduced mechanisms and the starting mechanism was carried out with the emphasis on their capabilities in predicting NO2 formation and ignition delay. The two reduced mechanisms successfully capture the complex behaviors of NO2 formation, which depends on the characteristic mixing time, pressure, and the contamination of hydrocarbon in air. The flame structure and NOx formation in diffusion flame were well predicted by the 16-step mechanism, while the 14-step showed less satisfactory performance on predicting prompt NO formation. The 16-step mechanism was shown accurate in predicting ignition delay over a wide range of equivalence ratio, temperature and pressure. The necessity of including CH2O,C2H6,C2H4, and HO2 in the reduced mechanisms was discussed.
On Bridgman’s Stress Solution for a Tensile Neck Applied to Axisymmetrical Blunt Notched Tension Bars
Authors: Valiente A.
Published: July 2002

The displacement field at the minimum cross section of an axisymmetrical notched tensile bar is analytically related to the notch root radius for large geometry changes of the notch profile. This relationship is used to complete Bridgman’s formula for the tensile load of a tensile necking in order to predict the entire load-minimum diameter curve of an axisymmetrical blunt notched bar under tension. A particular case is solved by a finite element modeling to check the theoretical results derived at different stages of the analysis.
Effects of a Magnetic Modulation on the Stability of a Magnetic Liquid Layer Heated From Above
Authors: Aniss Saı¨d , Belhaq Mohamed , Souhar Mohamed
Published: July 2002

The effect of a time-sinusoidal magnetic field on the onset of convection in a horizontal magnetic fluid layer heated from above and bounded by isothermal non magnetic boundaries is investigated. The analysis is restricted to static and linear laws of magnetization. A first order Galerkin method is performed to reduce the governing linear system to the Mathieu equation with damping term. Therefore, the Floquet theory is used to determine the convective threshold for the free-free and rigid-rigid cases. With an appropriate choice of the ratio of the magnetic and gravitational forces, we show the possibility to produce a competition between the harmonic and subharmonic modes at the onset of convection.
Precision Laser Deburring
Authors: Lee Seoung Hwan , Dornfeld David A.
Published: July 2002

The purpose of this study is to develop an effective way of automated deburring of precision components. A high power laser is proposed as a deburring tool for complex part edges and burrs. Experimental results for carbon steel and stainless steel are presented. Also, the prediction of the HAZ and cutting profile of laser-deburred parts using finite element method is presented and compared with the experimental results. This study shows that FEM analysis can effectively predict the thermal affected zone of the material and that the technique can be applied to precision components.
Coupled Macroscopic and Microscopic Scale Modeling of Fibrillar Tissues and Tissue Equivalents
Authors: Agoram Balaji , Barocas Victor H.
Published: July 2002

Collagen mechanics are crucial to the function and dysfunction of many tissues, including blood vessels and articular cartilage, and bioartificial tissues. Previous attempts to develop computer simulations of collagenous tissue based on macroscopic property descriptions have often been limited in application by the simplicity of the model; simulations based on microscopic descriptions, in contrast, have numerical limitations imposed by the size of the mathematical problem. We present a method that combines the tractability of the macroscopic approach with the flexibility of the microstructural approach. The macroscopic domain is divided into finite elements (as in standard FEM). Each element contains a microscopic scale network. Instead of a stress constitutive equation; the macroscopic problem is distributed over the microscopic scale network and solved in each element to satisfy the weak formulation of Cauchy’s stress continuity equation over the macroscopic domain. The combined method scales by order 1.1 as the overall number of degrees of freedom is increased, allowing it to handle larger problems than a direct microstructural approach. Model predictions agree qualitatively with tensile tests on isotropic and aligned reconstituted type I collagen gels.
Bridgman Crystal Growth of an Alloy With Thermosolutal Convection Under Microgravity Conditions
Authors: Simpson James E. , Garimella Suresh V. , de Groh Henry C. , Abbaschian Reza
Published: July 2002

The solidification of a dilute alloy (bismuth-tin) under Bridgman crystal growth conditions is investigated. Computations are performed in two dimensions with a uniform grid. The simulation includes the species concentration, temperature and flow fields, as well as conduction in the ampoule. Fully transient simulations have been performed, with no simplifying steady state approximations. Results are obtained under microgravity conditions for pure bismuth, and for Bi-0.1 at.% Sn and Bi-1.0 at.% Sn alloys, and compared with experimental results obtained from crystals grown in the microgravity environment of space. For the Bi-1.0 at.% Sn case the results indicate that a secondary convective cell, driven by solutal gradients, forms near the interface. The magnitude of the velocities in this cell increases with time, causing increasing solute segregation at the solid/liquid interface. Finally, a comparison between model predictions and results obtained from a space experiment is reported. The concentration-dependence of the alloy melting temperature is incorporated in the model for this case. Satisfactory correspondence is obtained between the predicted and experimental results in terms of solute concentrations in the solidified crystal.
Stress and Strain Histories of Multiple Bending-Unbending Springback Process
Authors: Huang H.-M. , Liu S.-D. , Jiang S.
Published: July 2002

A drawbead model with sheet metal passing through multiple bending-unbending processes was employed in this study to understand the springback phenomenon and to develop a numerical simulation technique for more accurate prediction of the springback process. The deformation process is simulated using an implicit finite element modeling code. The predicted results were compared with the physically measured ones, including clamping and restraining forces, thickness strains, and the curvatures of the deformed sheets. Consideration of the Bauschinger effect and employment of a combined isotropic and kinematic hardening models greatly improve the prediction accuracy. Stress and strain histories under various conditions during the drawing process are studied in detail in an attempt to provide a better basis for comparison for dynamic explicit solutions.
Feasibility of Plasma Spraying in Developing MMC Coatings: Modeling the Heating of Coated Powder Particles
Authors: Demetriou Marios D. , Lavine Adrienne S. , Ghoniem Nasr M.
Published: July 2002

Coated powder particles composed of a ceramic core and a metallic coating are being considered for plasma spray applications. The goal of using these powders is to produce particulate-reinforced metal-matrix composite coatings. In this work, the feasibility of plasma spray processing in producing these composite coatings is evaluated. A numerical model is presented to analyze the in-flight thermal behavior and physical state of moderate-size particles (10–30 μm radius) in arc-jet DC plasma under low loading conditions. The pairs of materials for the base and coating that are considered in this work are WC-Co, SiC-Ni, and SiC-Al. The plasma was taken to be atmospheric argon plasma. The study suggests that plasma processing is capable of melting the coating without excessive evaporation while retaining the base in the solid state over a range of particle sizes and base/coating proportions. Hence plasma processing appears suitable to develop particulate-reinforced metal-matrix composite coatings.
Steady Flow and Wall Compression in Stenotic Arteries: A Three-Dimensional Thick-Wall Model With Fluid–Wall Interactions
Authors: Tang Dalin , Yang Chun , Kobayashi Shunichi , Ku David N.
Published: July 2002

Severe stenosis may cause critical flow and wall mechanical conditions related to artery fatigue, artery compression, and plaque rupture, which leads directly to heart attack and stroke. The exact mechanism involved is not well understood. In this paper, a nonlinear three-dimensional thick-wall model with fluid–wall interactions is introduced to simulate blood flow in carotid arteries with stenosis and to quantify physiological conditions under which wall compression or even collapse may occur. The mechanical properties of the tube wall were selected to match a thick-wall stenosis model made of PVA hydrogel. The experimentally measured nonlinear stress–strain relationship is implemented in the computational model using an incremental linear elasticity approach. The Navier–Stokes equations are used for the fluid model. An incremental boundary iteration method is used to handle the fluid–wall interactions. Our results indicate that severe stenosis causes considerable compressive stress in the tube wall and critical flow conditions such as negative pressure, high shear stress, and flow separation which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The stress distribution has a very localized pattern and both maximum tensile stress (five times higher than normal average stress) and maximum compressive stress occur inside the stenotic section. Wall deformation, flow rates, and true severities of the stenosis under different pressure conditions are calculated and compared with experimental measurements and reasonable agreement is found.
A Dexterous Part-Holding Model for Handling Compliant Sheet Metal Parts
Authors: Li H. F. , Ceglarek D. , Shi Jianjun
Published: July 2002

Material handling of compliant sheet metal parts significantly impacts both part dimensional quality and production rate in the stamping industry. This paper advances previously developed material handling end effector layout optimization methodology for rigid point end effectors [1] by developing a dexterous part-holding end effector model. This model overcomes the shortcomings of the rigid point part-holding end effector model by predicting part deformation more accurately for various modes of deformation and for a set of part-holding end effector locations. This is especially important for handling systems which utilize vacuum cup end effectors widely used for handling of large sheet metal parts. The dexterous end effector model design method and an algorithm for estimation of model parameters are developed. The algorithm combines data from design of computer simulations and from the set of experiments by integrating finite element analysis and a statistical data processing technique. Experimental studies are conducted to verify the developed model and the model parameter estimation algorithm. The developed methodology provides an analytical tool for product and process designers to accurately predict part deformation during handling, which further leads to minimization of part deformation, improvement of part dimensional quality and increase of production rate.
Active Load Control for Airfoils using Microtabs
Authors: Nakafuji D. T. Yen , van Dam C. P. , Smith R. L. , Collins S. D.
Published: July 2002

Micro-electro-mechanical (MEM) translational tabs are introduced for active load control on aerodynamic surfaces such as wind turbine rotor blades. Microtabs are mounted near the trailing edge of rotor blades, deploy approximately normal to the surface, and have a maximum deployment height on the order of the boundary-layer thickness. Deployment of the tab effectively changes the sectional chamber of the rotor blade, thereby changing its aerodynamic characteristics. A tab with tab height to blade section chord ratio, h/c, of 0.01 causes an increase in the section lift coefficient, C1, of approximately 0.3, with minimal drag penalty. This paper presents a proof of concept microtab design and the multi-disciplinary techniques used to fabricate and test the tabs. Computational and experimental wind tunnel results for a representative airfoil using fixed as well as remotely actuated tabs are compared. Although the specifics of load control limitations, including actuation and response times will require further research, the results presented demonstrate the significant potential for using microtabs for active load control.
A Comparison of Methods for Optimizing Air-Conditioning Systems According to the Exergonomic Approach
Authors: Marletta Luigi
Published: July 2002

This paper discusses the comparison of three different methods for the optimization of an air-conditioning system from an exergonomic point of view. The reference design is an all air system in typical summer operation. To optimize the system on the basis of the exergonomic approach, it was necessary to the set up the physical model (based on mass, energy, and exergy balance equations) and the economic model in order to define the decision variables and the objective function. The latter is the total cost of the whole assembly, obtained by summing up the capital costs to the running costs. The Szargut-Tsatsaronis (S-T), the Montecarlo, and the Lagrange multipliers methods are then applied with the aim of minimizing the objective function. The results may be summarized as follows: the S-T method is an iterative procedure which allows the designer to control and guide the optimization process; however, the outcome may depend on the designer’s judgment and skill. The Monte Carlo method is an almost totally automated approach; it is based on stochastic techniques and may require relatively long run time. The Lagrange multipliers method, in addition to the optimum value for the decision variables, makes it possible to deduce the sensitivity coefficients, thus providing further information about system performance. For the case under consideration, the three methods provide comparable results in terms of decision variables and minimum global costs.
Fixturing Analysis For Stability Consideration in an Automated Fixture Design System
Authors: Roy Utpal , Liao Jianmin
Published: July 2002

Stability analysis plays a critical role in determining the applicability of a fixture design. This paper reports the development of a computational methodology for quantitatively analyzing the workpiece’s stability in the automated fixture design (AFD) environment. In stability analysis, the virtual disturbance which is expressed as a wrench in the screw coordinates and has the same tendency as those fixturing and machining forces to destabilize the workpiece is adopted in the study, and the stability of the workpiece is characterized based on its capability to overcome the virtual disturbance. The stability characteristics for each fixturing configuration (i.e., positions for fixturing components of supporters, locators and clamps) itself are obtained from the stability analysis and used in the re-design process to determine the better design of fixturing configuration.
Directionally Controllable Squeeze Film Damper Using Electro-Rheological Fluid
Authors: Ahn Young Kong , Yang Bo-Suk , Morishita Shin
Published: July 2002

Electro-Rheological (ER) fluid is a class of functional fluid whose yield stress can be changed by an electric field applied to the fluid, which is observed as a variation of apparent viscosity. This functional fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexible rotor system. In applying ER fluid to a conventional passive SFD, a pair of rings in the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can provide external damping in each direction independently. A prototype of the directionally controllable SFD was constructed and its performance was experimentally and numerically investigated in the present work.
Detailed Boundary Layer Measurements on a Turbine Stator Vane at Elevated Freestream Turbulence Levels
Authors: Radomsky R. W. , Thole K. A.
Published: July 2002

High freestream turbulence levels have been shown to greatly augment the heat transfer on a gas turbine airfoil. To better understand these effects, this study has examined the effects elevated freestream turbulence levels have on the boundary layer development along a stator vane airfoil. Low freestream turbulence measurements (0.6 percent) were performed as a baseline for comparison to measurements at combustor simulated turbulence levels (19.5 percent). A two-component LDV system was used for detailed boundary layer measurements of both the mean and fluctuating velocities on the pressure and suction surfaces. Although the mean velocity profiles appeared to be more consistent with laminar profiles, large velocity fluctuations were measured in the boundary layer along the pressure side at the high freestream turbulence conditions. Along the suction side, transition occurred further upstream due to freestream turbulence.
On the Accuracy of Benchmark Tables and Graphical Results in the Applied Mechanics Literature1
Authors: Helsing J. , Jonsson A.
Published: July 2002

Converged normalized stress intensity factors for a matrix crack interacting with an elastic cylinder are presented. The new results differ from previously published results in several examples. The need for better error analysis in computational fracture mechanics is emphasized.
Gear Hobbing Cutting Process Simulation and Tool Wear Prediction Models
Authors: Bouzakis K.-D. , Kombogiannis S. , Antoniadis A. , Vidakis N.
Published: July 2002

Gear hobbing is an efficient method to manufacture high quality and performance toothed wheels, although it is associated with complicated process kinematics, chip formation and tool wear mechanisms. The variant cutting contribution of each hob tooth to the gear gaps formation might lead to an uneven wear distribution on the successive cutting teeth and to an overall poor tool utilization. To study quantitatively the tool wear progress in gear hobbing, experimental-analytical methods have been established. Gear hobbing experiments and sophisticated numerical models are used to simulate the cutting process and to correlate the undeformed chip geometry and other process parameters to the expected tool wear. Herewith the wear development on the individual hob teeth can be predicted and the cutting process optimized, among others, through appropriate tool tangential shifts, in order to obtain a uniform wear distribution on the hob teeth. To determine the constants of the equations used in the tool wear calculations, fly hobbing experiments were conducted. Hereby, it was necessary to modify the fly hobbing kinematics, applying instead of a continuous tangential feed, a continuous axial one. The experimental data with uncoated and coated high speed steel (HSS) tools were evaluated, and correlated to analytical ones, elaborated with the aid of the numerical simulation of gear hobbing. By means of the procedures described in this paper, tool wear prediction as well as the optimization of various magnitudes, as the hob tangential shift parameters can be carried out.
Experimental Based Analysis of the Pressure Control Characteristics of an Oil Hydraulic Three-Way On/Off Solenoid Valve Controlled by PWM Signal
Authors: Jeong Heon-Sul , Kim Hyoung-Eui
Published: July 2002

Pressure control characteristics of a three-way high-speed on/off oil hydraulic solenoid valve driven by a PWM signal with a fixed pulse period were theoretically and experimentally analyzed and evaluated. By virtue of its relatively low cost, small size, robustness to contamination, and simplicity of the driving circuit, the three-way on/off solenoid valve is increasingly and widely used for hydraulic pressure or position control applications. In this paper, two formulas are newly derived for the mean and the ripple amplitude of the system pressure that oscillates with the same frequency as that of the PWM driving signal. The formulas indicate that the mean pressure and the pressure ripple amplitude depend on three major system variables that are the on- and the off-times of the valve and a parameter, the system configuration coefficient a, that characterizes the overall feature of the system. The mean pressure and the ripple are then shown to depend on both the duty ratio and the carrier frequency of the PWM driving signal, which disproves Tanaka’s claim that a single variable is enough to describe two quantities. Several aspects of the formulas are discussed. The accuracy of the new formulas is verified by comparing the calculation results to corresponding experimental test results. A method is proposed to obtain the system parameters of the opening and closing-case delay times, the time constants of the valve and a. The selection criteria are established for the major design parameters of the driving signal, i.e., the duty ratio and the carrier pulse frequency, and a basic strategy is proposed on how to suppress the undesirable ripple for a hydraulic servo control system using three-way on/off solenoid valve.
Direct Measurement of the Poisson’s Ratio of Human Patella Cartilage in Tension
Authors: Elliott Dawn M. , Narmoneva Daria A. , Setton Lori A.
Published: July 2002

Articular cartilage has been shown to exhibit large transverse contractions when loaded in tension, suggesting the existence of large values for the Poisson’s ratio. Previous studies have suggested that this effect is dependent on amplitude of applied strain, so that a single Poisson’s ratio may not be sufficient to describe cartilage behavior. In this study, the Poisson’s ratio (ν), toe region modulus Eo, and linear region modulus E of human patellar articular cartilage were calculated in simple tension tests from optical analysis of the two-dimensional strain fields at equilibrium. The Poisson’s ratio was found to be independent of strain due to the absence of viscoelastic effects during testing. The Poisson’s ratio was found to be significantly higher in the surface zone (1.87±1.11, p<0.01) than in the middle zone (0.62±0.23), with no significant correlation of ν with age of the cartilage. In general, values for Poisson’s ratio were greater than 0.5, suggesting cartilage behavior in tension deviates from isotropy. Reported values for the Poisson’s ratio of cartilage in compression have been much lower than values measured here in tension, reflecting a mechanical contribution of the collagen fibers to anisotropy in tension but not compression. The toe-region modulus Eo was significantly higher in the surface zone (4.51±2.78 MPa, n=8) compared to the middle zone (2.51±1.93 MPa, n=10). In addition, the linear-region modulus E in the surface zone, but not middle zone (3.42±2.17 MPa, n=10), was found to correlate with age R=0.97,p<0.02 with values of surface zone E equal to 23.92±12.29 MPa n=5 for subjects under 70 yr of age, and 4.27±2.89 MPa n=3 for subjects over 70 yr. Moduli values and trends with depth were consistent with previous studies of human and animal cartilage. From direct measures of two independent material properties, ν and E, we calculated a shear modulus, G, which had not been previously reported for cartilage from tensile testing. Calculated values for surface zone G were 3.64±1.80 MPa for subjects under 70 yr old and 0.96±0.69 MPa for subjects over 70 yr old, and were significantly higher in the surface zone than in the middle zone (1.10±0.78 MPa). This study provides an intrinsic measure for the Poisson’s ratio of articular cartilage and its dependence on depth which will be important in understanding the nonlinear tension-compression and anisotropic behaviors of articular cartilage.
Fundamental Design Issues of Brush Seals for Industrial Applications
Authors: Dinc Saim , Demiroglu Mehmet , Turnquist Norman , Mortzheim Jason , Goetze Gayle , Maupin John , Hopkins James , Wolfe Christopher , Florin Mark
Published: July 2002

Advanced seals have been applied to numerous turbine machines over the last decade to improve the performance and output. Industrial experiences have shown that significant benefits can be attained if the seals are designed and applied properly. On the other hand, penalties can be expected if brush seals are not designed correctly. In recent years, attempts have been made to apply brush seals to more challenging locations with high speed (>400 m/s), high temperature (>650 °C), and discontinuous contact surfaces, such as blade tips in a turbine. Various failure modes of a brush seal can be activated under these conditions. It becomes crucial to understand the physical behavior of a brush seal under the operating conditions, and to be capable of quantifying seal life and performance as functions of both operating parameters and seal design parameters. Design criteria are required for different failure modes such as stress, fatigue, creep, wear, oxidation etc. This paper illustrates some of the most important brush seal design criteria and the trade-off of different design approaches.
Experimental and Biphasic FEM Determinations of the Material Properties and Hydraulic Permeability of the Meniscus in Tension1
Authors: LeRoux Michelle A. , Setton Lori A.
Published: July 2002

Tensile tests and biphasic finite element modeling were used to determine a set of transversely isotropic properties for the meniscus, including the hydraulic permeability coefficients and solid matrix properties. Stress-relaxation tests were conducted on planar samples of canine meniscus samples of different orientations, and the solid matrix properties were determined from equilibrium data. A 3-D linear biphasic and tranversely isotropic finite element model was developed to model the stress-relaxation behavior of the samples in tension, and optimization was used to determine the permeability coefficients, k1 and k2, governing fluid flow parallel and perpendicular to the collagen fibers, respectively. The collagen fibrillar orientation was observed to have an effect on the Young’s moduli (E1=67.8MPa,E2=11.1MPa) and Poisson’s ratios (ν12=2.13,ν21=1.50,ν23=1.02). However, a significant effect of anisotropy on permeability was not detected (k1=0.09×10−16m4/Ns,k2=0.10×10−16m4/Ns). The low permeability values determined in this study provide insight into the extent of fluid pressurization in the meniscus and will impact modeling predictions of load support in the meniscus.
Heat Transfer From a Moving Surface Due to Impinging Slot Jets
Authors: Chattopadhyay H. , Biswas G. , Mitra N. K.
Published: July 2002

Turbulent flow field and heat transfer in an array of slot jets impinging on a moving surface have been numerically investigated by Large-eddy Simulation (LES) technique in the range of Reynolds numbers between 500 and 3000. The surface velocity, directed perpendicular to the jet, is varied up to two times the jet velocity at the nozzle exit. The Nusselt number distributions for various surface velocities are presented. It has been observed that on one hand increasing velocity of the impingement plate reduces heat transfer, while on the other hand distribution of Nusselt number over the impingement surface becomes more uniform with the increased surface velocity.
Influence of Material Anisotropy and Friction on Ring Deformation
Authors: Han Han
Published: July 2002

The influence of material anisotropy and friction on ring deformation has been examined in relation to the distribution of normal pressure and frictional shear stress, deformed ring shapes, and estimated errors in the coefficient of friction. Based on the flow rule associated with von Mises’ and Hill’s yield criteria, the analyses have been carried out with the finite element method (FEM) for three cases, namely, (1) an anisotropic ring oriented 90 deg to the axis of rotational symmetrical anisotropy under uniform coefficient of friction; (2) an isotropic ring under frictional anisotropy condition; and (3) an anisotropic ring oriented 0 deg to the axis of rotational symmetrical anisotropy under uniform coefficient of friction. In the first two cases, the results show that the influence of anisotropy on ring deformation is quite similar to that obtained by changing the frictional condition. Therefore, in the third case, if the anisotropic behavior is mistakenly attributed to friction, the possible estimated error for the coefficient of friction can be as high as 80 percent for a pronounced anisotropic material. Deformed ring shapes have been verified in experiments using the extruded annealed aluminum alloy AA6082 (Al-Si1Mg0.9Mn0.1).
Mold Surface Wavelength Effect on Gap Nucleation in Solidification
Authors: Hector, L. G. , Howarth J. A. , Richmond O. , Kim W.-S.
Published: July 2002

A theoretical model that predicts the time and position of gap nucleation along the metal-shell interface during solidification of a pure metal on a sinusoidal mold surface is presented. The ratio of the mold surface amplitude to its wavelength is assumed to be much less than one and hence it is used as a perturbation parameter in the analysis. The molten metal perfectly wets the mold surface prior to the beginning of solidification, and this leads to a corresponding undulation of the metal shell thickness. A nonuniform distortion develops in the shell due to the lateral temperature gradient induced by the modest spatial variation of the mold surface. This causes a variation in the contact pressure so that the growing shell pushes harder on the mold in some places, but in other places it starts to pull away from the mold. Gap nucleation is assumed to occur when the contact pressure falls to zero. The conditions for gap nucleation in the surface troughs are examined since a corresponding increase in pressure at the crests signals the possibility of a growth instability in the shell at later stages of the process. A series expansion for the contact pressure is presented which is appropriate for early solidification times. This reveals how the contact pressure varies with the mold surface wavelength. This solution is compared with a numerical solution for the contact pressure that is not limited to early solidification times. Gap nucleation times are calculated for pure aluminum and iron shells for selected mold surface wavelengths. The associated mean shell thicknesses are calculated as a function of wavelength at selected mean molten metal pressures. [S0021-8936(00)02901-9]
Prevention of Mechanical Stretch-Induced Endothelial and Smooth Muscle Cell Injury in Experimental Vein Grafts
Authors: Liu S. Q. , Moore M. M. , Yap C.
Published: July 2002

Vein grafts are subject to increased tensile stress due to exposure to arterial blood pressure, which has been hypothesized to induce endothelial cell (EC) and smooth muscle cell (SMC) injury. This study was designed to verify this hypothesis and to develop a tissue engineering approach that can be used to prevent these pathological events. Two experimental models were created in rats to achieve these goals: (1) a nonengineered vein graft with increased tensile stress, which was created by grafting a jugular vein into the abdominal aorta using a conventional end-to-end anastomotic technique; and (2) an engineered vein graft with reduced tensile stress, which was created by restricting a vein graft into a cylindrical sheath constructed using a polytetrafluoroethylene membrane. The integrity of ECs in these models was examined by using a silver nitrate staining method, and the integrity of SMCs was assessed by using a fluorescein phalloidin-labeling technique. It was found that nonengineered vein grafts were associated with early EC denudation with a change in EC coverage from 100 percent in normal jugular veins to 36±10, 28±12, 18±9, 44±15, 80±13, and 97±6 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively. Similarly, rapid SMC actin filament degradation was found during the early period with a change in SMC coverage from ∼94 percent in normal jugular veins to 80±10, 41±17, 25±9, 51±15, 79±15, 98±2 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively, in nonengineered vein grafts. In engineered vein grafts with reduced tensile stress, EC denudation and SMC actin filament degradation were prevented significantly. These results suggested that mechanical stretch due to increased tensile stress contributed to EC and SMC injury in experimental vein grafts, and these pathological events could be partially prevented when tensile stress was reduced by using a biomechanical engineering approach. [S0148-0731(00)00701-9]
Complex Dynamics in a Harmonically Excited Lennard-Jones Oscillator: Microcantilever-Sample Interaction in Scanning Probe Microscopes1
Authors: Basso M. , Giarre´ L. , Dahleh M. , Mezic´ I.
Published: July 2002

In this paper we model the microcantilever-sample interaction in an atomic force microscope (AFM) via a Lennard-Jones potential and consider the dynamical behavior of a harmonically forced system. Using nonlinear analysis techniques on attracting limit sets, we numerically verify the presence of chaotic invariant sets. The chaotic behavior appears to be generated via a cascade of period doubling, whose occurrence has been studied as a function of the system parameters. As expected, the chaotic attractors are obtained for values of parameters predicted by Melnikov theory. Moreover, the numerical analysis can be fruitfully employed to analyze the region of the parameter space where no theoretical information on the presence of a chaotic invariant set is available. In addition to explaining the experimentally observed chaotic behavior, this analysis can be useful in finding a controller that stabilizes the system on a nonchaotic trajectory. The analysis can also be used to change the AFM operating conditions to a region of the parameter space where regular motion is ensured. [S0022-0434(00)01401-5]
Sonar-Based Wall-Following Control of Mobile Robots
Authors: Bemporad Alberto , Di Marco Mauro , Tesi Alberto
Published: July 2002

In this paper, the wall-following problem for low-velocity mobile robots, equipped with incremental encoders and one sonar sensor, is considered. A robust observer-based controller, which takes into account explicit constraints on the orientation of the sonar sensor with respect to the wall and the velocity of the wheels, is designed. The feedback controller provides convergence and fulfillment of the constraints, once an estimate of the position of the mobile robot, is available. Such an estimate is given by an Extended Kalman Filter (EKF), which is designed via a sensor fusion approach merging the velocity signals from the encoders and the distance measurements from the sonar. Some experimental tests are reported to discuss the robustness of the control scheme. [S0022-0434(00)01101-1]
Consistent and Minimal Springback Using a Stepped Binder Force Trajectory and Neural Network Control
Authors: Cao Jian , Kinsey Brad , Solla Sara A.
Published: July 2002

One of the greatest challenges of manufacturing sheet metal parts is to obtain consistent part dimensions. Springback, the elastic material recovery when the tooling is removed, is the major cause of variations and inconsistencies in the final part geometry. Obtaining a consistent and desirable amount of springback is extremely difficult due to the nonlinear effects and interactions between process and material parameters. In this paper, the exceptional ability of a neural network along with a stepped binder force trajectory to control springback angle and maximum principal strain in a simulated channel forming process is demonstrated. When faced with even large variations in material properties, sheet thickness, and friction condition, our control system produces a robust final part shape. [S0094-4289(00)01801-6]