bluuebunny/crossref_metadata_2025 huggingface dataset:
Pool Boiling in Saturated and Subcooled FC-72 Dielectric Fluid From a Porous Graphite Surface
Authors: El-Genk Mohamed S. , Parker Jack L.
Published: April 2008

Experiments are conducted that investigated pool boiling of FC-72 liquid at saturation and 10, 20, and 30 K subcooling on porous graphite and smooth copper surfaces measuring 10 × 10 mm. The nucleate boiling heat flux, Critical Heat Flux (CHF), and surface superheats at boiling incipience are compared. Theses heat fluxes are also compared with those of other investigators for smooth copper and silicon, etched SiO2, surfaces and micro-porous coating. No temperature excursion at boiling incipience on the porous graphite that occurred at a surface superheats of < 1.0 K. Conversely, the temperature excursions of 24.0 K and 12.4–17.8 K are measured at incipient boiling in saturation and subcooled boiling on copper. Nucleate boiling heat fluxes on porous graphite are significantly higher and corresponding surface superheats are much smaller than on copper. CHF on porous graphite (27.3, 39.6, 49.0, and 57.1 W/cm2 in saturation and 10 K, 20 K, and 30 K subcooled boiling, respectively) are 61.5%–207% higher than those on copper (16.9, 19.5, 23.6, and 28.0 W/cm2, respectively). The surface superheats at CHF on the porous graphite of 11.5 K in saturation and 17–20 K in subcooled boiling are significantly lower that those on copper (25 K and 26–28 K, respectively). In addition, the rate of increase of CHF on porous graphite with increased subcooling is ~ 125% higher than that on copper.
Micro-Scaled Surface Profile Measurement on Packages by Digital Projection Moire´
Authors: Chang Chia-Shou , Shao Ching-An , Wu Enboa
Published: April 2008

With the rapid trend for miniaturization of electronic products, new optical techniques are increasingly needed for measuring the surface profile or deflection/warpage in the micro-scale for electronic packages mounted on printed circuit boards. In this paper, we reduced the grating spacing of the digital projection moire´ (DPM) by directing the grating pattern into a stereo zoom microscope and performed surface profile measurement under this microscope. In this method, the reference grating is generated digitally having sinusoidal intensity. Another digitally generated grating is projected by the means of a digital light processing (DLP) projector and a set of carefully arranged optical lens into the microscope to form the object grating. The pitch of micro-scaled object gratings can be adjusted by the reduction ratio of the microscope. As a result, this micro-scaled digital projection moire´ method produces micro object gratings on the order of 10-um pitch and is suitable for surface profile measurement in a square dimension on the order of 100-um. The method of linear mismatch is utilized to obtain more fringes in each measurement and the guideline to achieve the optimal degree of linear mismatch between the reference and the object gratings is proposed. In addition, the phase shifting technique is employed to extract the data between the recorded fringes. Verification of the method is demonstrated by measuring an inclined plane of a micro prism. The deviation between the measured data and the given values was found to be less than 5%, which demonstrates the validity of the developed method.
Dynamic Magnetic Resonance Imaging as a Means of Validating Finite Element Modeling Assumptions for Abdominal Aortic Aneurysms
Authors: Marra Steven P. , Whittaker David R. , Chen David T. , Fillinger Mark F. , Teutelink Arno , Dwyer Jeffrey M. , Tsapakos Michael J. , Kennedy Francis E.
Published: April 2008

The assessment of patient-specific abdominal aortic aneurysm (AAA) rupture risk using finite element (FE) modeling has been shown to be an improvement over current diameter-based prediction techniques (Fillinger, 2002, 2003). However, certain modeling assumptions are made which may have significant effects on the computed AAA wall stresses. For example, the FE meshes are based on composite computed tomography (CT) images obtained during multiple cardiac cycles. This results in meshes that are averaged representations of pressurized AAAs, yet are assumed to represent AAAs at the zero-stress state. Also, the proximal and distal ends of the AAA FE models are assumed to be fixed in place, which may be satisfactory boundary conditions, but have yet to be validated. Recent developments in dynamic magnetic resonance (dMR) imaging allow AAA cross-sectional images to be obtained at multiple locations and time points throughout a cardiac cycle. These images are used to determine the geometries and positions of AAAs at various times throughout the cardiac cycle.
Analysis of Steady State Conjugate Heat Transfer in a Circular Microtube Inside a Substrate
Authors: Rao P. Sharath C. , Rahman Muhammad M.
Published: April 2008

The steady state heat transfer for laminar flow inside a circular microtube within a rectangular substrate has been investigated. Silicon, Silicon Carbide, and Stainless Steel were the substrates used and Water and FC-72 were the coolants employed. Equations governing the conservation of mass, momentum, and energy were solved in the fluid region. Within the solid wafer, the heat conduction was solved. A thorough investigation for velocity and temperature distributions for different substrates and coolants was performed by varying geometrical dimensions and Reynolds number. At a constant diameter and Reynolds number, for combinations comprising same coolant but different substrates, one with the lowest solid to fluid thermal conductivity ratio (ks/kf) attains the highest local peripheral average interface temperature. It was found that the Nusselt number is more for a system with Silicon as the substrate and FC-72 as the working fluid and the least for a system with Stainless Steel as the substrate and Water as the working fluid. The lower ks/kf ratio of Stainless Steel-Water combination is the main reason for the lower Nusselt number. With the increase in hydraulic diameter and Reynolds number, the average Nusselt number increased. It was also observed that the maximum temperature of the substrate and hence the outlet temperature of the fluid increased as the Reynolds number decreased.
Development of a Non-Linear Model of a Double Wishbone Suspension for the Characterization of Force Transmission to the Steering Column and Chassis
Authors: Cherian Vinod , Jalili Nader , Haque Imtiaz
Published: April 2008

A non-linear model of a double wishbone suspension is developed to investigate the effects of variation of suspension parameters on the transmission and distribution of tire forces acting on the wheel spindle to the steering system and the vehicle chassis. The suspension is idealized as a four degree-of-freedom model, with suspension members considered as rigid links and the bushings idealized as linear spring-damper elements. Degrees-of-freedom representing the longitudinal compliance of the suspension mounting bushings, steering and the rotation of the control arms are considered. The equations of motion are derived using the Lagrange multiplier method, and solved numerically using MATLAB. A system of relative co-ordinates is used to reduce the number of equations due to the large number of geometric and kinematic constraints for an efficient numerical simulation. The equations retain all the non-linearity’s associated with large changes in the geometric configuration of the suspension system. The analytical model can be used to develop a quantitative measure of the importance of the parameters such as mass, inertia of the control arms, suspension bushing stiffness and damping and spatial geometry of installation to the force distribution and force transmissibility to the vehicle chassis and the steering system. The results of numerical simulation are compared with simulation data obtained from ADAMS.
Comparison of Molten Carbonate and Solid Oxide Fuel Cells for Integration in a Hybrid System for Cogeneration or Tri-Generation
Authors: Karvountzi Georgia C. , Price Clifford M. , Duby Paul F.
Published: April 2008

High temperature fuel cells, such as molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC) can be integrated in a hybrid cycle with a gas turbine and a steam turbine and achieve overall lower heating value (LHV) efficiencies of about 70%. A hybrid cycle designed for cogeneration or tri-generation applications could lead to even higher overall LHV efficiencies. Tri-generation is the combined generation of power, heat and cooling from the same fuel source. The purpose of the present paper is to compare the performance of a 20MW MCFC system and a 20MW tubular SOFC system and assess their potential to cogeneration and tri-generation applications. The system includes a fuel cell, a gas turbine, a multiple pressure heat recovery steam generator (HRSG), a steam turbine and an absorption chiller (for cooling). The systems were designed and sized using GatecycleTM heat balance software by GE Enter Software, LLC. In order to optimize each system we developed curves showing LHV “electric” and “cogeneration” efficiency versus power for different ratios of “MCFC and SOFC fuel cell-to-gas turbines size.” At atmospheric pressure and at 675°C (1247°F) the 20MW MCFC system achieves “electric” efficiency of 69.5%. The SOFC at the same pressure and at 980°C achieves 67.3% “electric” efficiency. The MCFC alone is more efficient (58%) than the SOFC alone (56%). However the SOFC produces more heat than the MCFC leading to slightly higher cogeneration and tri-generation efficiencies. Pressurized operation at 9atm boosts the performance of the SOFC system to higher efficiencies (70.5%). Pressurized operation is problematic for the MCFC due to increased cathode corrosion leading to cathode dissolution as well as sealant and interconnection problems. However we can pressurize the MCFC system independently of the fuel cell with the integration of a gas turbine with a compressor pressure ratio of 10 to 16. Thus we achieve efficiencies close to 69%. In conclusion SOFC is more efficiently integrated in a hybrid configuration with gas turbine and a steam turbine for trigeneration applications when pressurized. MCFC is more efficiently integrated at atmospheric and pressures below 6 atm.
RBC Distribution in Stenosed Arterial Geometries Using Hematocrit Dependent Viscosity Model (HDVM)
Authors: Hyun Sinjae , Kleinstreuer Clement
Published: April 2008

Human blood is a concentrated suspension of mainly red blood cells (RBCs) in plasma and exhibits some non-Newtonian behavior at low shear rates. Traditionally, computational simulations have employed non-Newtonian viscosity models, such as the power-law, Casson, or Quemada model, which are a function of the local shear rate and depend on two to four constant parameters, including the hematocrit. In this study the non-Newtonian behavior of the blood viscosity is expressed as a function of the hematocrit. Specifically, a convection-diffusion equation for the RBCs has been solved, integrated into an apparent viscosity model, and applied to blood flow in a stenosed arterial segment. The computational results provide detailed information of non-Newtonian flow characteristics including distributions of the local hematocrit as well as near-wall hematocrit, shear rate, and viscosity. The new model can be used for more realistic hemodynamics simulations, including calculations of comprehensive physico-biological indicators of sites susceptible to the onset and progression of arterial diseases.
Design of Nozzle-Less Radial Inflow Gas Turbine for Small Capacity (20 kW) Gas Turbine Engine
Authors: Mistry Chetan S. , Channiwala S. A.
Published: April 2008

In recent years, looking to the advantages of radial inflow gas turbine much research is focused in this area. The various applications like auxiliary drives in aircraft engine and automobile application where very high speed, compact size and greater specific power are the prime requirements, radial inflow is there by choice. The present work for the design of nozzle-less radial inflow turbine begins with power requirement of 20 kW, the parameters like temperature; pressure and mass flow rate required for the design are obtained from the detailed gas turbine cycle analysis. Based on the available data from cycle analysis initially preliminary design of rotor was developed, from the available loss models the efficiency of the turbine was found. The preliminary design provides the leading dimensions of the rotor with inlet and exit conditions. The objective of most designs will be to maximize the efficiency and/or to develop the compact size. After completion of the preliminary design of turbine, it was felt necessary to optimized the result for best efficiency accordingly an analytical study was undertaken to study the influence of different parameters like inlet absolute Mach number, relative exit Mach number, solidity, relative velocity ratio and hub to shroud radius ratio on efficiency. VISUAL BASIC program is developed to study the effect of different parameters on efficiency. From the detailed loss analysis the selection of these parameters can be made to achieve optimum performance. It is believed that present work will provide necessary guidelines for the optimal design of radial inflow gas turbine.
The Theoretical and Experimental Evaluation of Gas-Particle Flow in Laser Cladding Repairing of Three Dimensions
Authors: Li Hui-Shan , Yang Xi-Chen , Wang Chun-Xian
Published: April 2008

In this paper, the powders transportation in laser cladding repairing during the coaxial powder-feeding was evaluated. The theoretical evaluation is based on a two-fluid approach in which both the gas and particulate phase is treated each phase separately, and the only link between the phases is through the drag force in the momentum equations. The particles velocities are calculated with changes of the gas flow and mass flow rate. This is important for the coaxial nozzle and the carrier-gas powder transportation equipment characteristics determined. An experimentally of the influence of carrying gas on the powder stream was set up. The gas-particles flowing from the nozzle was illuminated by a 2D sheet of light. A typical image from the CCD camera is captured. The axial velocity and cross section were described. According to the results, it was found that: (1) Different mass flow rate Mp=0.5g/s, 0.67g/s, 0.83g/s, 1g/s, the powder stream luminance intensity and distribution will change. (2) The distribution of powder concentration at longitudinal axis from the nozzle exit is shown. The faster particulates stream has the less density per unit volume for a given mass flow rate. (3) The gas velocity for transportation is the most important parameter.
Dynamics and Control of Supercavitating Bodies
Authors: Lin G. , Balachandran B. , Abed E.
Published: April 2008

Analytical and numerical investigations conducted into the control of dive-plane dynamics of supercavitating bodies are presented. Particular attention is paid to tail-slap behavior. A fundamental understanding of the solution structure in terms of equilibrium and other solutions developed through the effort is discussed, and control schemes used to realize stable inner loop dynamics are presented. Dominant nonlinearities associated with planning forces are taken into account in the model and controllability of the system with the fin input and/or the cavitator input has been examined. The describing function method is brought to bear upon this problem and the presence of limit cycles in the controlled and uncontrolled cases are explored. The nonlinear planing force associated with tail-slap behavior is approximated as a piecewise linear function and the results obtained from switching feedback control analysis are provided.
Model for Pulsating Heat Pipe With Capillary Wick and Varying Channel Diameter
Authors: Holley Brian M. , Faghri Amir
Published: April 2008

Variation in channel diameter is investigated as a means of enhancing heat transfer in a pulsating heat pipe with capillary wick using the model presented here. The model is one-dimensional with slug flow where the momentum equation is solved for each liquid slug. The number and mass of liquid slugs are allowed to vary throughout a simulation. The energy equation is solved both in the wall and wick and in the working fluid. The effects of diameter profile, gravity, fill ratio, and heating and cooling schemes can be studied with the model. Results yield similar trends to what has been experimentally observed. Results also indicate that heat transfer can be enhanced when the diameter of the channel is varied along the channel length, thereby providing increased range of heat load capability, less sensitivity to gravity, and in some cases smaller temperature differentials.
Design Compensation for Fabrication Imperfections of Microgyroscopes
Authors: Poreddy Surender , Pai P. Frank , Feng Z. C.
Published: April 2008

MEMS microgyroscopes consist of proof masses which are driven in vibration. The sensing of angular motion requires certain symmetry in the driven motion. This symmetry is destroyed by imperfections introduced during the device fabrication. We propose strategies at the design stage that can compensate for the effect of fabrication imperfections. Our analyses are conducted through a discrete coupled oscillator model. The results are further verified through a finite element model of a tuning-fork microgyroscope design.
The Influence of Underfill Properties on the Fatigue Life of Ball Grid Array Packages
Authors: Verges Melody Arthur , Chilakamarthi Geetha
Published: April 2008

The influence of underfill material properties on the fatigue life of a Ball Grid Array (BGA) package in the presence of thermal cycling is investigated in this study. The underfill material properties that are varied include Young’s modulus, Poisson’s ratio, and the coefficient of thermal expansion. The range in values are in accordance with typical underfills used in packages today. A finite element model is created using general purpose Ansys code by assuming that there exists an infinite array of solder interconnects, cylindrical in shape, surrounded by underfill material. The finite element geometry generated consists of a unit cell of concentric cylinders, with the inner being solder material and the outer being underfill material. The interconnect material is modeled as eutectic solder that behaves elastically-perfectly plastic. The Mode I cyclic stresses in the solder are determined as a temperature loading is applied. These stresses are then compared to the residual compressive stresses that are induced as a result of underfill shrinkage upon curing. Results suggest that Mode I stresses induced in the interconnects upon thermal cycling are not negligible in comparison to the beneficial compression that they provide upon curing. Even in the presence of this residual compression, for several material combinations a substantial amount of tension is induced in the connections while being cycled.
Effect of Dynamic Contact Angle on Single Bubbles During Nucleate Pool Boiling
Authors: Mukherjee Abhijit , Kandlikar Satish G.
Published: April 2008

Nucleate pool boiling at low heat flux is typically characterized by cyclic growth and departure of single vapor bubbles from the heated wall. It has been experimentally observed that the contact angle at the bubble base varies during the ebullition cycle. In the present numerical study, dynamic advancing and receding contact angles obtained from experimental observations are specified at the base of a vapor bubble growing on a wall. The complete Navier-Stokes equations are solved and the liquid-vapor interface is captured using the level-set technique. The effect of dynamic contact angle on the bubble dynamics and vapor removal rate are compared to results obtained with static contact angle. The results show that bubble base exhibits a slip/stick behavior with dynamic contact angle though the overall effect on the vapor removal rate is small. Higher advancing contact angle is found to increase the vapor removal rate.
Feasibility Study of Parametric Excitations of a Tuning Fork Microgyroscope
Authors: Lee Yongsik , Feng Z. C.
Published: April 2008

In this paper, we use parametrically excited pendulums as a model of a tuning fork microgyroscope to explore the feasibility of exciting the symmetric mode of two coupled oscillators. For the tuning fork microgyroscope to work, the two proof masses must be driven into oscillations which are opposite in directions. We study the nonlinear dynamics of the coupled pendulums under parametric excitations. The results show that there is a range of parameters for which pendulum responses are opposite in directions. Moreover, this phase relationship persists even in the presence of structural asymmetry, which is often unavoidable in device fabrication. Our study indicates the feasibility of using the parametric excitation to replace electrostatic comb-drives in current microgyroscope designs. The advantage of the parametric excitation is that it can be externalized. The fabrication is thus simplified.
Fallacies of a Hydrogen Economy
Authors: Kreith Frank , West Ronald E.
Published: April 2008

This article presents a critical analysis of all the major pathways to produce hydrogen and to utilize it as an energy carrier to generate heat or electricity. The approach taken is to make a cradle to grave analysis, including the production of hydrogen, the conversion of hydrogen to heat or electricity, and, finally, the utilization of that heat or electricity for a useful purpose. This methodology shows that no currently available hydrogen pathway, irrespective of whether it uses fossil fuels, nuclear fuels, or renewable technology as the primary energy source to generate electricity or heat is as efficient as using the electric power or heat from any of these sources directly. Furthermore, electric vehicles using batteries to store electricity are shown to be more efficient and less polluting than fuel cell powered vehicles using energy stored in hydrogen produced by electrolysis of water.
Effect of Estrogen on the Mechanical Properties of Prepubertal Rabbit ACL
Authors: Cowden Courtney , Chandrashekar Naveen , Hashemi Javad , Lee Vaughan H. , Hardy Daniel M. , Slauterbeck James R.
Published: April 2008

Recent research suggests that estradiol affects the material properties of the Anterior Cruciate Ligament (ACL). Here we experimentally determine the cross-sectional area and tensile properties of ACLs from the groups of prepubertal rabbits: untreated control (C), estrogen treated (E) and estrogen and epidermal growth factor treated (E+EGF). Estradiol decreased the ultimate tensile strength and toughness of the ACL. Addition of EGF decreased the modulus of elasticity.
Modeling of Pneumatic Actuator System for High Performance Nonlinear Controller Design
Authors: Tai Meihua , Xu Ke
Published: April 2008

Modern applications in robotics such as teleoperations and haptics require high performance force actuators. Pneumatic actuators have significant advantages over electrical motors in terms of force-to-mass ratio. However, position and force control of these actuators in applications that require high bandwidth is not trivial because of the compressibility of air and highly non-linear flow through pneumatic system components. In this paper, we develop a detailed model of a pneumatic actuator system comprised of a double acting cylinder and a proportional servo valve to be used in position, force or hybrid position and force control.
A Direct Machining System for Commercial CAD/CAM Packages
Authors: Cheng Zhenyu , Li Wei , Cheatham Robert , Wang Jianguo , Jensen C. Greg , Red W. Ed
Published: April 2008

Although modern machine tools and controllers have evolved along with the personal computer over the years, the standard input (M&G code files) for CNC machines has not changed. A new method of control called Direct Machining And Control (DMAC) is being developed at Brigham Young University. DMAC is a revolutionary new paradigm for rapid prototyping and CNC control by directly connecting a CAD system with software based DMAC controller. DMAC technology completely eliminates all intermediate files (APT, M&G code, STEP-NC, etc) between the CAD model and the CNC controller by directly processing the geometric tool path entities that are sent from the CAD/CAM system to the motion buffer of the controller. Direct machining maintains the efficiency and accuracy improvements seen in NURBS tool path representation, and also retains associativity between the CAD model and the tool paths driving the CNC machine tool. This paper presents a Direct Machining system designed to directly connect a commercial CAD/CAM systems (Unigraphics, CATIA, CM2 and Alias) with a software-based DMAC controller. In this paper, Direct Machining, with its requirements and implications, is explored. The overall DMAC architecture is presented. Parts from the Ford GT car were machined on a Tarus five-axis mill by the DMAC system, and were compared with traditional method which used M&G codes.
A Comparative Study of Supervisory Control Strategies for Hybrid Electric Vehicles
Authors: Pisu Pierluigi , Rizzoni Giorgio , Musardo Cristian , Staccia Benedetto
Published: April 2008

Hybrid Electric Vehicles (HEVs) improvements in fuel economy and emissions strongly depend on the energy management strategy. Big obstacles to the control design are the model complexity and the necessity of “a priori” knowledge of torque and velocity profiles for optimal torque split. This paper presents and compares four different energy management approaches for the control of a parallel hybrid electric sport-utility-vehicle.
Engineering Monolayers With Strain Field
Authors: Kim Dongchoul , Lu Wei
Published: April 2008

A binary monolayer on an elastic substrate may self-organize into ordered nanoscale patterns. Here we report a work of using a substrate strain field to guide the self-assembly process. The study shows that straining a substrate uniformly does not influence the pattern. However, a non-uniform strain field significantly influences the size, shape and distribution of self-assembled features. The study suggests a method of strain field design to make various monolayer patterns.
Determination of the Directional Dependent In-Plane Thermal Conductivity of K63B12 Pitch-Fiber/Epoxy Composite
Authors: McClay Jessica N. , Joyce Peter , Smith Andrew N.
Published: April 2008

Measurements of the in-plane thermal conductivity and the directional dependence of Mitsubishi K63B12 pitch-fiber/Epoxy composite from Newport Composites are reported. This composite is being explored for use in the Avanced Seal Delivery System for effective thermal management. The thermal conductivity was measured using a steady state technique. The experimental results were then compared to a model of the thermal conductivity based on the direction of the fibers. These estimates are based on the properties of the constituent materials and volume of fibers in the sample. Therefore the density and the fiber volume fraction were experimentally measured. The thermal conductivity is clearly greatest in the direction of the fibers and decreases as the fibers are rotated off axis. In the case of pitch fiber composite materials, the contribution of the fibers to the thermal conductivity dominates. The experimental data clearly followed the correct trends; however, the measured values were 25% to 35% lower than predicted.
Pressure Distribution Along the Casing of a Centrifugal Pump and Its Effect on Support Bearing Temperature Distribution
Authors: Gandhi Bhupendra K. , Bharani Sanjeev
Published: April 2008

In a centrifugal pump, impeller transfer energy to liquids and a part of the transferred kinetic energy converts into the pressure energy in the surrounding casing. Any asymmetric pressure distribution around the impeller gives rise to radial force, which increases temperature at support bearings of the pump. An effort has been made in the present work to relate rise in the bearing temperature with the pressure distribution around the impeller with and without minor change in its position (by 0.5–1.0 mm) relative to the casing. The maximum bearing temperature is found at full open delivery valve (low delivery pressure). It has been observed that the reduction in asymmetric pressure distribution reduces the bearing temperature rise to the order of 10°C. It is seen that a small eccentricity of 1.0 mm in the position of impeller with respect to the volute casing gives less asymmetric pressure distribution at the low delivery pressure where as at high delivery pressures, it results in higher asymmetric pressure distribution compare to the concentric mounting of the impeller.
Backstepping Control of an SMA-Actuated Manipulator
Authors: Elahinia Mohammad H. , Koo Jeong-Hoi , Woolsey Craig , Ahmadian Mehdi
Published: April 2008

In this paper a nonlinear model-based controller is designed to globally asymptotically stabilize a single-degree-of-freedom shape memory alloy (SMA) actuated manipulator. A three part model was constructed based on the dynamics/kinematics of the arm, the thermomechanical behavior of SMA’s, and an assumed heat transfer model consisting of electrical heating and natural convection. The backstepping control is used to calculate the applied voltage to the SMA wire. Initially, the SMA’s wire stress is assumed to be the control input of the system. The stress is then chosen to asymptotically stabilize the desired position. The applied voltage to the SMA wire is the actual control input. This voltage is calculated based on the desired stress and the SMA’s thermomechanical and heat transfer models. It is shown that the calculated voltage can globally asymptotically stabilize the system. Numerical simulations are performed to investigate stabilizing performance as well as other issues such as robustness. The results demonstrate that the backstepping controller designs is highly accurate in stabilization.
Finite Element Modeling of Ankle Joint Replacement Incorporating Subject-Specific Soft Tissue Constraints for Prediction of Intercomponent Motion and Loading
Authors: McIff Terence E. , Horton Greg A.
Published: April 2008

This paper describes the use of finite element modeling methods to predict intercomponent sliding, rotation, constraint, and contact mechanics in a total ankle replacement device. Ligaments are modeled to constrain motion occurring during physiologic loading and articulation over a full gait cycle.
Sensor Fault Isolation Using Qualitative Quantized Modeling With Application to a 3-DOF Nonlinear Vehicle
Authors: D’Silva S. , Pisu P. , Serrani A. , Rizzoni G.
Published: April 2008

Fault detection and isolation has become one of the most important aspects in vehicle control system design. In this paper, we present a technique for single sensor fault detection and isolation in automotive on-board applications. It combines model-based diagnostics and a qualitative modeling approach. The proposed method is appealing as it shifts the computational effort from on-line to off-line, making the algorithm suitable for low-cost real-time applications. The methodology can be cast in the framework of discrete-event fault diagnosis. A depth one transition relation algorithm for qualitative identification which guarantees completeness is developed and applied to a 3-degree-of-freedom (DOF) nonlinear vehicle model. The paper concludes with preliminary simulation results showing the effectiveness of the proposed scheme.
Nonlinear Positioning Compensation of Thin-Disc Ultrasonic Motor Using Fuzzy Sliding-Mode Control
Authors: Wen Fuh-Liang , Yen Chi-Yung
Published: April 2008

The study intends to focus on the design of a thin-disc piezoceramic-driving ultrasonic actuator dedicated to discrete stepping motors. By the improved design and construction, the innovative ultrasonic actuator was developed and used as a stator. The electromechanical coupling characteristics based on the composite structure would produce the flexural wave on the stator, which consisted of a piezoceramic membrane bonded on a metal sheet. Due to the converse piezoelectric effect, the driving ability of the actuator came from the vibration of extension-shrinkage of a metal sheet corresponding to the frequency of a single-phase AC power. Under constraints at the specific geometry positions on the metal sheet, the varying behaviors of flexural waves were formed. The simple structure of an actuator demonstrated that the mechanical design of the actuator and the rotor could be separated, depending on what we need in pragmatic applications. And, its positioning accuracy could be reached through a closed loop servo control, i.e. Fuzzy Sliding Mode Control (FSMC). FSMC was used to automatically compensate nonlinearly mechanical behaviors such as dead-zone and hysteresis phenomena. Furthermore, FSMC scheme has successfully overcome the high frequency chattering phenomena with lower control effort while the motor is applied to position tracking, and also has been proven in the excellent robust ability for noise rejection.
Procedures for the Verification and Validation of Working Models for Structural Shells
Authors: Szabo´ Barna A. , Muntges Daniel E.
Published: April 2008

Verification of computed data and validation of mathematical models for structural shells with reference to particular applications and goals of computation are discussed and illustrated through the example of a cylinder-to-cylinder intersection problem investigated experimentally and analytically at Oak Ridge National Laboratory.
Increased Stiffness of Bioresorbable Plates Following Heating and Three-Dimensional Contouring
Authors: McIff Terence E. , Lark Richard , Hilty Andrea , Cooper Andrew , Toby E. Bruce
Published: April 2008

A wide copolymer bioresorable plate offers increased structural stiffness following heated contouring of the plate to various diameters which increases its resisting moment of inertia. The increase in bending and torsional stiffness of this design is measured as a function of cross-sectional radius of curvature achieved. Its structural stiffness is compared to three other standard fixation methods used for metacarpal fracture. Substantial increases in stiffness are found after contouring of the wide bioresorbable plate to fit diameters similar to those found in metacarpal bones.
An Acoustic Emission In-Situ Measuring System for the Investigation of White Layer Effect on Rolling Contact Fatigue
Authors: Schwach Dale , Guo Y. B.
Published: April 2008

Hard turning has begun to compete with grinding in manufacturing various mechanical components because of the significant potential technical and economical benefits for improving fatigue life. However under certain cutting conditions, a phase-transformed white layer (WL) may form on the machined surface that could drastically affect a component’s service life. The presence of WL causes great concerns in machining industry just because the WL effects on component performance such as fatigue life are yet to be understood. Therefore the significant benefits of hard turning would not be realized fully unless this issue is solved. A novel real-time acoustic emission (AE) based rolling contact fatigue (RCF) testing system was presented to study the WL effects on component life. AISI 52100 bearing steels were machined to generate two distinct surfaces: free of white layer (NOWL) and with WL. The real life loading of contact pressures and rolling speeds was applied to the test specimens. The applied load throughout the experiment was in-process monitored using a load cell which enabling the record of a Hertzian pressure history during rolling contact. It was found that the RCF testing system is simple and inexpensive, but very sensitive to fatigue crack initiation and propagation. Compared with AE count rate, AE parameters such as energy, RMS, and amplitude are more sensitive to fatigue crack initiation and propagation in rolling contact. The NOWL samples are more resistive to fatigue crack initiation/propagation and therefore have a longer life when compared to the WL samples with equivalent surface finish. The WL samples have shorter life or at most comparable with the NOWL samples with relative rough surface finish.
Using Internal State Variable Plasticity to Determine Dynamic Loading History Effects in Manufacturing Processes
Authors: Guo Y. B. , Wen Q. , Horstemeyer M. F.
Published: April 2008

Worked materials in large deformation processes such as forming and machining experience a broad range of strain, strain rate, and temperatures, which in turn affect the flow stress. However, the flow stress also highly depends on many other factors such as strain path, strain rate and temperature history. Only a model that includes all of these pertinent factors is capable of predicting complex stress state in material deformation. In this paper, the commonly used phenomenological plasticity models (Johnson-Cook, Usui, etc.) to characterize material behavior in forming and machining were critically reviewed. Although these models are easy to apply and can describe the general response of material deformation, these models lack the mechanisms to reflect static and dynamic recovery and the effects of load path and strain rate history in large deformation processes. These effects are essential to understand process mechanisms, especially surface integrity of the manufactured products. As such a dislocation-based internal state variable (ISV) plasticity model was used, in which the evolution equations enable the prediction of strain rate history and temperature history effects. These effects can be quite large and cannot be modeled by the equation-of-state models that assume that stress is a unique function of the total strain, strain rate, and temperature, independent of the loading path. The temperature dependence of the hardening and recovery functions results in the prediction of thermal softening during adiabatic temperatures rises, which are common in metal forming and machining. The dynamic mechanical behaviors of three different benchmark work materials, titanium Ti-6Al-4V, AISI 52100 steel (62 HRc), and aluminum 6061-T6, were modeled using the ISV approach. The material constants were obtained by using a nonlinear regression fitting algorithm in which the stress-strain curves from the model were correlated to the experiments at different (extreme) temperatures. Then the capabilities of the determined material constants were examined by comparing the predicted material flow stress with the test data at different temperatures, strains, and strain rate history. The comparison demonstrates that the internal state plasticity model can successfully recover dynamic material behavior at various deformation states including the loading path effect. In addition, thermal softening due to adiabatic deformation was also captured by this approach.
Powertrain Optimization for an Earthmoving Vehicle
Authors: Gupta Pinaki , Alleyne Andrew
Published: April 2008

The advent of integrated powertrain technologies offers great potential for improvements in efficiency and transient performance of powertrains. This work examines the integration of various powertrain subsystems onboard an earthmoving vehicle. The nature of the variable displacement pumping subsystem is similar in concept to other forms of continuously variable transmissions. Separate controllers are designed using gain scheduled H∞ synthesis to address the problems of efficiency and performance. Both controllers are combined through switching logic to enable explicit tradeoffs between the objectives and thus improve the powertrain productivity. The devised control strategies are implemented on a hardware-in-the-loop representation of an earthmoving vehicle powertrain. The baseline efficiency controller is further improved by a hybrid design that effectively deactivates part of the powertrain system when not in use.
Modeling the Geometry, Hemodynamics and Tissue Mechanics of Cerebral Aneurysms
Authors: Ma Baoshun , Harbaugh Robert , Lu Jia , Raghavan Madhavan
Published: April 2008

The relationship between cerebral aneurysm geometry and biomechanics was investigated. Human cerebral aneurysm geometry was reconstructed from computed tomography angiography (CTA) and refined. Various indices of global geometric (size and shape) features were computed based on differential and computational geometry techniques. Computational fluid dynamics (CFD) simulations were performed to model both steady and pulsatile blood flow in the aneurysm and surrounding vasculature. Hemodynamic indices such as wall shear stress, pressure and particle residence time were obtained. Nonlinear finite element method (FEM) and a reported finite strain constitutive model were employed to estimate the distribution of mechanical stress in the aneurysm wall under static pressure. Shear stress, sac pressure and mechanical stress correlated better with lesion shape while particle residence time correlated better with lesion size.
UDP Network Communications for Wireless Control With Loop Coordination
Authors: Kawka Paul A. , Ploplys Nicholas J. , Alleyne Andrew G.
Published: April 2008

With the advent of Bluetooth and wireless 802.11 Ethernet protocols having transmission speeds up to 54 Mbps, wireless communication for closed-loop control is becoming more and more achievable. Some researchers have utilized Bluetooth networks for wireless control, resulting in successful stabilization of an unstable plant with a network controller. Previously, the authors of this paper developed a novel event-based control with time-based sensing and actuation communication method using 11 Mbps wireless Ethernet with the user datagram protocol (UDP). Near real-time control of an unstable Furuta pendulum with up to 250 Hz closed loop bandwidth was obtained using off the shelf hardware, Matlab, and Windows 2000 operating systems. The present work extends that communication scheme to two independent wireless loops that share a mutual goal, making additional communication between the two controllers advantageous. The communication framework for the coupled control in this ad hoc peer-to-peer network is presented along with some practical limitations. Data from a physical system implementing this framework demonstrates its effectiveness in application. The test plant couples a simple light tracking plant with a Furuta pendulum and a shared goal of maintaining line of sight (LOS) under normal conditions as well as reestablishing LOS in the case of lost contact due to sudden obstacles.
A Time-Space Multi-Level Boundary Element Approach for Time-Dependent Heat Diffusion
Authors: Grigoriev M. M. , Dargush G. F.
Published: April 2008

A new space-time multi-level boundary element method (MLBEM) is developed for transient heat diffusion problems in two-dimensions. This approach extends the MLBEM approach for steady heat diffusion [1] to accommodate fast time convolution algorithm [2]. The space-time MLBEM algorithm developed in this presentation provides fast, accurate and memory efficient numerical solutions for time-dependent heat diffusion problems. Conventional BEM approaches using M boundary elements result in operation counts of order O(M2N2) for the discrete time convolution over N time steps. Here we focus on the formulation for linear problems of transient heat diffusion and demonstrate reduced computational complexity to order O(M log MN3/2) for a two-dimensional model problem using the multi-level boundary element algorithm. Memory requirements are also significantly reduced, while maintaining the same level of accuracy as the conventional time domain BEM approach.
A Simulation Study on Welding Induced Distortion Control for Large Box Beam Structures
Authors: Xu Jun , Li Wei
Published: April 2008

Welding induced distortion in large structures is a major quality concern in industry. Many methods have been proposed in recent years to minimize the welding induced distortion. Among the available methods, transient thermal tensioning has been shown effective for minimizing the welding induced buckling distortion for T-joints. Due to the complexity of the welding process, different structures may require different strategies for distortion control. This paper presents a finite element simulation study on the distortion control for large box beam structures. The transient thermal tensioning method is applied through differential preheat on the two side plates of the beam. The effects of the preheating parameters including the average preheating temperature, temperature differential, and the preheating location are analyzed. It has been found that differential preheating control is effective in adjust the welding induced twist distortions. However, excessive differential preheating could generate bowing distortions. To determine an optimal preheating strategy, the distortions in all the three dimensions of a beam need to be considered simultaneously.
FCBGA Footprints and Solder Joint Reliability
Authors: Liang Frank Z. , Williams Rick L.
Published: April 2008

As electronic package input/output density increases and cost constraints drive the package size smaller, the one area where a designer can not compromise is solder joint reliability. Maintaining flip chip ball grid array (FCBGA) solder joint reliability (SJR) has been at the top of the designer’s critical list with decreasing package size. The FCBGA footprint will need to be modified for a variety of reasons to meet routing optimization, power delivery, electrical performance to name a few. The designer must deal with several competing proposals (electrical performance, cost and use conditions) trying to optimize the FCBGA footprint while being aware that some modifications can negatively affect SJR. This paper investigates solder ball layouts and their effect on SJR through both finite element (FE) models and empirical tests. In addition, consideration of next generation layout is presented to optimize routability while preserving SJR. When feasible, empirical tests were run to validate predictive models.
Stress and Strength of Butt Circular Shaft With Metal Columns Subjected to Torques
Authors: Liu Jiemin , Liu Jintang , Sawa Toshiyuki
Published: April 2008

Stress analysis of the butt circular shaft with three uniformly distributed metal columns subjected to external torques are carried out by using three-dimensional finite element method. The loading capability of the butt circular shaft is measured. It was found that torque acting on the cross-section of adhesive layer is simultaneously withstood by the adhesive layer and the metal columns; The ratio of the torque withstood by metal columns to that withstood by adhesive layer increases with increase of the ratio of Young’s modulus of metal columns to that of the circular shaft; The metal columns enhance and improve the reliability of the joints; The strength of the butt adhesive circular shafts increases with increase of the ratio of the yield stress of the metal columns to that of circular shafts.
Canceling Induced Master Motion in Force-Reflecting Teleoperation
Authors: Kuchenbecker Katherine J. , Niemeyer Gu¨nter
Published: April 2008

Providing the user with high-fidelity force feedback has persistently challenged the field of telerobotics. This paper presents a new approach for achieving stable, high-gain force reflection via cancellation of the master mechanism’s induced motion. In a classic position-force controller, high force-feedback levels drive the system’s internal master-slave loop unstable during contact with the remote environment. Lowering the force-feedback gain ensures stability but diminishes the haptic cues available to the user, masking contacts and preventing hard objects from feeling appropriately stiff. The proposed cancellation approach permits high levels of force feedback by attenuating only the controller’s internal loop. Using a model of the master mechanism’s response to applied force feedback, an estimate of induced high-frequency movement is substracted from the master’s measured position to approximate the user’s intended path for the slave. The cancellation technique is described, modeled, and validated herein, including testing on a one-degree-of-freedom telerobotic system. It is shown to improve the feel of the system, tripling the testbed’s achievable force-feedback gain without compromising stability.