bluuebunny/crossref_metadata_2025 huggingface dataset:
Micromechanics-Based Elastoplastic and Damage Modeling of Particle Reinforced Composites
Authors: Liu H. T. , Sun Lizhi , Ju J. W.
Published: April 2008

A micromechanical damage model is proposed to predict the effective elastoplastic behavior of ductile composites containing randomly dispersed particles. The interfacial debonding between particles and the matrix is considered as the primary micromechanical damage mechanism. The debonded isotropic elastic reinforcements are replaced by equivalent anisotropic elastic inclusions. The interfacial debonding process is simulated by three-dimensional debonding angles. After the local stress field in the matrix is calculated, the homogenization averaging procedure is employed to estimate the effective elastic stiffness and yield function of the composites. The associative plastic flow rule and the isotropic hardening law are postulated based on the continuum plasticity theory. As applications, the overall elastoplastic and damage constitutive behavior of the composites under various loading conditions is numerically simulated and compared with available experimental results.
A Novel Approach for Distribution of Reacting Gases With Enhanced Mass Transfer in Fuel Cells
Authors: Li P. W. , Chen S. P. , Chyu M. K.
Published: April 2008

In order to improve the power output of a fuel cell, a novel approach for gas delivery and mass transfer enhancement in a gas distributor is proposed. A model analyzing the power output against the dimensions of a novel gas delivery channel and current collector is also presented. Experimental study for some proton-exchange-membrane fuel cells and numerical analysis for a planar type solid oxide fuel cell are carried out. Significant improvement of power output was obtained for the newly designed fuel cells compared to conventional ones. Both the experimental results and modeling analysis are of great significance to the design of fuel cells.
Multi-Operational Machining Processes Modeling for Sequential Root Cause Identification and Measurement Reduction
Authors: Wang Hui , Huang Qiang , Katz Reuven
Published: April 2008

Variation propagation modeling has been proved to be an effective way for variation reduction and design synthesis in multi-operational manufacturing processes (MMP). However, previously developed approaches for machining processes did not directly model the process physics regarding how fixture, and datum, and machine tool errors generate the same pattern on part features. Consequently, it is difficult to distinguish error sources at each operation. This paper formulates the variation propagation model using the proposed equivalent fixture error (EFE) concept. With this concept, datum error and machine tool error are transformed to equivalent fixture locator errors at each operation. As a result, error sources can be grouped and root cause identification can be conducted in a sequential manner. The case studies demonstrate the model validity through a real cutting experiment and model advantage in measurement reduction for root cause identification.
Real-Time Implementation of Intelligent Control and Internet Based Remote Activation of Simple Mechatronic Devices in the UMESMAL
Authors: Nagchaudhuri Abhijit
Published: April 2008

In this paper digital control solutions for speed control of direct current motor and level control of dual water tank system are described using conventional control algorithms such as (PID (Proportional + Integral + Derivative) and PI (Proportional + Integral)) as well as intelligent control algorithms based on fuzzy logic. Appropriate software tools are used to allow remote activation of the systems. Observation of the system behavior from remote terminals is made possible using novel tele-reality capability. This capability allows realistic CAD (Computer Aided Design) drawings that accurately represent the physical systems on the remote terminals to exhibit appropriate motion corresponding to the actual movement of the physical system in the University of Maryland Eastern Shore Mechatronics and Automation Laboratory (UMESMAL).
Kinematic Model of Dynamic Drilling Process
Authors: Roukema Jochem C. , Altintas Yusuf
Published: April 2008

A mathematical model of the torsional-axial chatter vibrations in drilling is presented. The model considers the exact kinematics of both rigid body, and coupled torsional and axial vibrations of the drill. The drill is modeled as a pretwisted beam that exhibits axial deflections due to torque and thrust loading. A mechanistic cutting force model is used to model the cutting torque and thrust as a function of feedrate, speed, radial depth of cut, and drill geometry. The drill rotates and feeds axially into the workpiece while the structural vibrations are excited by the cutting torque and thrust force. The exact location of the drill edge is predicted using the model, and the generated surface is digitized at discrete time intervals. The distribution of chip thickness, which is affected by both rigid body motion and structural vibrations, is evaluated by subtracting the presently generated surface from the previous one. The model considers nonlinearities in cutting coefficients, tool jumping out of cut and overlapping of multiple regeneration waves. The dynamic chip thickness obtained from the true kinematics model allows simultaneous prediction of force, torque, power and dimensional form errors left on the surface. The time domain simulation model allows prediction of stability lobes. The paper provides details of the mathematical model, supported by experimental results of both stable and unstable cuts.
A Novel Economical Method to Improve the Toughness of Carbon/Epoxy Long Fiber Components by the Integration of Tow Loops Cores
Authors: Sancaktar E. , Asiri A. Y. , Kumar G. S.
Published: April 2008

In this research, solid and sandwich carbon/epoxy composite plates were developed, fabricated, and tested at two different crosshead speeds of 10 and 500 mm/min, under monotonic penetration tests, which perpendicularly applied a concentrated load to the simply supported plates. The cores of sandwich plates were made of carbon prepreg (with epoxy resin), as well as glass tow loops (without resin). The plates’ lay-up configuration sequence was {[0/90]n}s, where n was 1, 2 or 4. The objectives of this study were to determine the general sandwich plate behavior, as well as to analyze the effects of the test rate, the number of internal loops and the number of plate facesheet plies on the failure mode, ultimate plate deflection, ultimate load, plate’s flexural rigidity, plate’s absorbed energy, and the extent of damage. The use of carbon fiber prepreg tow loops impregnated with epoxy resin, as well as dry glass tow loops without any resin provided information on the effect of resin presence in these core layers. For these purposes, the load versus plate deflection data were recorded and analyzed. The load-deflection curves were used to interpret the plate behavior in terms of flexural rigidity and absorbed energy. The plate’s absorbed energy values at both speeds were used to assist in the dynamic response analysis. The results of our experiments revealed that, at higher loading rates, the internal loops of carbon prepreg material with epoxy resin enhanced the energy absorption capability of the plates more significantly than those containing dry glass tow loops without resin impregnation.
A Study of Magnetic Impact Type Micro-Stepping Actuator to Drive Large Payload Reflector for 4S Reactor
Authors: Kobayashi Yuko , Takahashi Hiroshi , Takakura Shinji , Yokono Yasuyuki , Matsumiya Hisato , Kinoshita Izumi , Higuchi Toshiro
Published: April 2008

A small and fast reactor employing sodium-cooling system is expected and 4S (Super Safe, Small and Simple) Fast Reactor generating 50 or 10 Megawatts electric has been designed. This reactor pursues simple operation system, less maintenance, higher safety and improved economic features. The electric power is controlled by a neutron reflector, which is required to be elevated at a very low speed. In the present study, a reflector drive system by a magnetic impact type micro-stepping actuator has been proposed for the 4S reactor. The actuator is composed of electromagnets, air-core coils and internal inertia guided by linear slider. This internal inertia carries air-core coils, which are opposed to air-core coils arranged inside the actuator. The actuator adheres to a metal base wall and supports a payload by electromagnet adsorption force. The actuator moves by a magnetic repulsion force of internal inertia by adding momentary large electric current to opposed pair of air-core coils. A miniature model of “internal inertia” magnetic impact type actuator was made. Two different ways to support the internal inertia were proposed to restore the internal inertia to the original state. In this paper, experiment was performed to evaluate the basic characteristics of the two types of actuator. As a result, the actuator elevated about 4 micrometers per step in the case of the “electromagnet support type” and about 25 micrometers per step in the case of the “spring support type” with 10-kilogram payload. Also, it was found that the payload carries out minute quantity separation instantaneously with the actuator by the shock of a repulsion force. This separation decreases the magnetic force by which the payload pulls down the actuator and makes the actuator upward movement easy. Moreover, it became clear that the driving distance could be sorted by “effective magnetic impact impulse,” which can be calculated from current waveform. Therefore, driving distance can be controlled by condenser capacity and charged voltage that generates current waveform of the air-core coils. In light of these results, improvements will be made for design of an enlarged engineering model of the actuator. Experiments with larger payload are planned.
Elastic-Plastic Partial Slip Rolling Wheel-Rail Contact With an Oblique Rail Crack
Authors: Chen Yung-Chuan , Kuang Jao-Hwa
Published: April 2008

The effect of rail surface crack on the wheel-rail contact pressure distribution under partial slip rolling was studied in this work. The elastic-plastic finite element model was employed for stress analyses. The numerical simulations were used to explore the effects of the contact distances and tractive force on the normal and tangential contact pressure distributions, tip plastic energy and critical wheel applied load. Contact elements were used to simulate the interaction between wheel and rail and crack surfaces. Numerical results indicate that the contact pressure distributions are significantly affected by the rail crack. Traditional contact theories are not available to describe the contact pressure distribution on the contact crack surfaces. Results also indicate that a higher friction force on the contact crack surfaces is observed for wheel subjected a larger tractive force. A larger crack surfaces friction force can reduce the sliding between crack surfaces and leads to a smaller tip plastic energy.
A Reduced Order Model for Robust Control of Optical Fiber Drawing
Authors: Wei Zhiyong , Lee Kok-Meng , Zhou Zhi
Published: April 2008

We present here a method of deriving a reduced-order-model (ROM) from physical principles in the design of a mixed H∞/LQG controller for general applications. The ROM has been derived using the Karhunen-Loeve decomposition and Galerkin’s procedure from the high-fidelity computational fluid dynamics (CFD) model. As an illustration, the mixed H∞/LQG controller has been designed for an optical fiber draw process, where traditional designs relying on empirical lumped-parameter models for regulating the fiber diameter are less than optimal due to difficulties in making practical measurements in the furnace domain of the drawing process. Simulations show that the transient dynamics of the ROM closely matches those of the CFD model. The effects of the modeling errors on the robust control system have been studied numerically, which show that the robust controller effectively reduces the fiber-diameter fluctuations, and that the close-loop system is rather insensitive to different kinds of modeling errors.
Molecular Dynamics Study of Metal Fatigue Process
Authors: Kwon Y. W.
Published: April 2008

Molecular dynamics study was conducted to understand fatigue process in metals and to predict fatigue failure. As the first step, a pure metal like copper was considered for the study with defects at the atomic level such as vacancies or dislocations. The study was focused on identifying parameters which can provide indications of progressive damage accumulation in the material under cyclic loading. The results obtained by simulations were compared to macroscopic observations in the experimental studies
Stability of Corpectomy With Anterior Cervical Plating Depends on the Angular Placement of the Screws: An FE Model Study
Authors: Hussain M. , Natarajan R. N. , Deol G. S. , Andersson G. B. J. , An H. A.
Published: April 2008

The stability of the plate-screw constructs as well as the stresses and strains in the implant and bone graft depend on many factors including the angular positioning of the screws with respect to the end plate attached to the vertebra. It is hypothesized that the placement of the screw parallel to the endplates provide greater stability and reduced stresses in the implant and bone graft as compared to constructs in which the screws are placed oblique with respect to the end plates.
Exploration of Nanoscale Features of Thin Liquid Films on Solid Surfaces Using Molecular Dynamics Simulations
Authors: Wemhoff Aaron P. , Carey Van P.
Published: April 2008

Thin liquid films on solid surfaces are seen in a variety of systems including bubble growth during nucleate boiling and microgroove heat pipe evaporators and condensers. The small thickness of such films leads to difficult experimental observation of phenomena within various regions of the film: the wall-affected region, the bulk liquid, and the liquid-vapor interfacial region. A novel hybrid simulation methodology is used that combines a deterministic molecular dynamics simulation of the liquid regions with a stochastic treatment of the far-field vapor region boundary. In this simulation scheme, the imposed far-field pressure is iterated as the simulation is advanced in time until the mass in the system stabilizes at the specified temperature. This establishes the equilibrium saturation vapor pressure for the specified temperature as dictated by the intermolecular force interaction models for the fluid and molecules near the solid surface. Simulation results are presented for an argon liquid film on a metallic surface. The simulated surface tension values compare favorably with those from ASHRAE tables, although the simulated saturation density and pressure values behave as though the system is at a slightly higher temperature. The method presented here is a viable tool for simulating thin films on solid surfaces for systems operating far from the critical point.
Passive Vibration Damping of Aluminum by 1-3 Piezocomposites
Authors: Saigal A. , Greif R. , Nakhwa S.
Published: April 2008

The effective properties of 1-3 piezocomposites are used to examine their passive vibration damping characteristics. An aluminum cantilever beam bonded with 1-3 piezocomposite dampers is modeled by means of “ANSYS” and “SIMULINK” softwares to investigate the dynamic behavior of the system. A method of determining the damping ratio introduced by the piezocomposite damper in conjunction with a simple resistive electrical circuit is established. The effect of volume fraction of the 1-3 piezocomposite on the damping of the system is analyzed. Damping ratio is observed to increase with rising volume fraction. At low volume fractions, the participation of piezoelectric fibers in the load-bearing pattern is to a lesser extent and hence the damping ratio is low. On the contrary as the volume fraction rises, the involvement of piezoelectric fibers increases resulting in higher damping ratios. Given that the inherent material damping in the aluminum beam is 0.0002, the additional damping provided by the bonded piezoelectric strips goes up to a maximum of 0.0042. Finally, the methodology developed in this paper can be used to model any type of vibratory structural system to determine the damping introduced by the piezocomposites.
A Model for Orthogonal Machining of Metal Matrix Composite Using Finite Element Method
Authors: Zhu Yao Peng , Kannan S. , Kishawy H. A.
Published: April 2008

In this paper, a thermo-elasto plastic finite element model for machining of aluminium based particulate composite is presented. The presented model accounted for the thermoelasto-plastic properties of the material under consideration and explicit finite element solution was used. The aluminium oxide particles were modeled as perfectly elastic and the shapes considered were irregular. The interface between the aluminium oxide particulate and aluminium matrix was incorporated in this model. The effective and the shear stress profiles on the aluminium oxide particles were analyzed. The simulation values of cutting and feed forces were compared with the experimental data and were found to be well within the limits of divergence, thus, validating the proposed finite element model.
Conjugate Natural Convection in a Square Cavity Heated From Below
Authors: Sa´nchez F. , Solorio F. , A´vila Ruben
Published: April 2008

This paper presents numerical results for two-dimensional steady-state natural convection in a square cavity. The upper and lower walls are kept at different constant temperatures, whereas the lateral walls have certain thickness and thermal conductivity and are externally insulated. Under these conditions we deal with a conjugate natural convection problem in which the heat conduction in the lateral walls is coupled with the internal convection. The continuity, momentum and energy equations were solved by using the finite volume method. The results here presented include: (i) the temperature distribution in the lateral walls and in the fluid, (ii) the velocity field, and (iii) the average Nusselt number at the upper and lower walls. It was found that the steady state fluid flow is strongly dependent on the initial temperature condition, when the fluid is initially at rest. The PIV technique allowed us to get some experimental data by measuring the velocity field in a two-dimensional square cavity. A good agreement between numerical and experimental results was found.
Human Step Rehabilitation Using a Robot Attached to the Pelvis
Authors: Aoyagi D. , Inchinose W. E. , Reinkensmeyer D. J. , Bobrow J. E.
Published: April 2008

This paper describes a new robot capable of manipulating pelvic motion during human step training on a treadmill. The robot, PAM (Pelvic Assist Manipulator), uses two pneumatically actuated subsystems arranged in a tripod configuration to measure and control the pelvis of a person during body weight supported stepping on a treadmill. The device can be used in a back-drivable mode to record pelvic trajectories, either specified manually by a therapist or pre-recorded from unimpaired subjects, then replay these trajectories using a PD position feedback control law in the task space and a non-linear force control algorithm for each piston chamber. The control laws are presented, along with data that demonstrate the ability of the device to record and replay the pelvic motions that occur during normal walking.
Heat Transfer of Two-Phase Impinging Jet: Heat Transfer Enhancement
Authors: Osakabe Masahiro , Horiki Sachiyo
Published: April 2008

To study the enhancement and degradation mechanism of impinging two-phase heat transfer, air/water two-phase jet was applied on the cooling of copper surface of 30 mm in diameter. The two-phase jet impinged vertically on the horizontal heat transfer surface from capillary nozzle holes of 2, 4 and 6 mm in inner diameter. The non-dimensional heat transfer coefficient (HTC) was defined as the experimental HTC divided with the predictive HTC where the superficial two-phase velocity jG+jL and the physical properties of water were used in the empirical HTC correlation for single-phase flow. The larger non-dimensional HTC and stagnation pressure fluctuation were obtained with the nozzle of larger diameter. The larger nozzle could provide the more significant enhancement of heat transfer and pressure fluctuation with an addition of air. It was considered that the enhancement of heat transfer was due to the stimulation of thermal boundary layer with an addition of air.
Finite Element Stress Analysis and Strength Evaluation of Adhesive Butt Joints of Circular Pipes Combining Coupling Collar With Adhesive Subjected to Internal Pressure, Temperature Change and External Bending Moments
Authors: Katsuo Masahide , Sawa Toshiyuki
Published: April 2008

The interface stress distributions between the coupling collar, the adhesive and the pipes of the joint subjected to an internal pressure, a temperature change and bending moments are analyzed by using the elastic finite element method (FEM). The experiment of the rupture test of the joints manufactured by pipes made of structural steel (S45C, JIS) and epoxide adhesive was carried out by applying the above loads to the joints. From the numerical calculations, the following results were obtained: (1) the stress distributes uniformly at the interface except near the edges, (2) the stress becomes singular at the edges of the interfaces and (3) the stress distribution at a half part of the interface increase as the external bending moments increase and also Young’s modulus of the adhesive increases. From the experiments, the following results were obtained: (1) the joint strength (evaluated as a 95% non-rupture probability) under both the internal pressure and the temperature change increases as the coupling length increases and (2) the joint strength under both the internal pressure and the temperature change decreases when the external bending moment is applied to the joint. Furthermore, the numerical results are in fairly good agreement with the experimental results.
Finite Element Stress Analysis and Estimation of the Sealing Performance in Pipe Fittings With PTFE Tape for Threaded Connections Under Internal Pressure
Authors: Ishimura Mitsutoshi , Katsuo Masahide , Sawa Toshiyuki
Published: April 2008

The interface stress distributions between the unsintered PTFE (Polytetrafluoroethlene) tape and threads of the fittings under an internal pressure are analyzed by using the finite element method (FEM). From the numerical calculations, the following results were obtained: (1) the stress distributes uniformly at the interface except near the edges, (2) the stress becomes singular at the edges of the interfaces and (3) the stress increases as the Young’s modulus of the PTFE tape thickness increases. The experiment of the leakage test of the connections consist of the socket and the plug manufactured of cast iron or stainless steel, which was also carried out by applying an internal oil pressure to the threaded connections. From the experiments, the following results are obtained: (1) the sealing performance in pipe fittings with PTFE tape increased as the number of turns in the PTFE tape increased, and it was not proportional to the numbers of turns, and (2) also as the number of turns in the screw plug increased, and it became a quadratic form, (3) the flow rate of leakage oil from the fittings under the internal pressure decreased as the number of turns in the screw plug increased, and (4) it could be estimated by using the Darcy-Weisbach and the Hagen-Poiseuille equations in the laminar-flow.
PML: An Object-Oriented Language for Modelling Automation
Authors: Ramos Juan Jose´ , Piera Miquel A`ngel
Published: April 2008

To cope with the growing demands for simulation models of ever increasing complex industrial systems, the research community effort has been mainly focused in creating different software tools which simplify the modeling process. This work describes how the Object-Oriented Modeling language PML (Physical Modeling Language) automates the modeling process by using physical knowledge in order to set the mathematical model of the system. PML introduces new modular structures to represent the physical knowledge required to model a system, making a clear separation between the physical behaviour representation (declarative knowledge) and the computational aspects of model simulation (procedural knowledge).
Permeability and Effective Pore Radius Measurements for Heat Pipe and Fuel Cell Applications
Authors: Holley Brian M. , Faghri Amir
Published: April 2008

Permeability and effective pore radius of sintered metal powder and carbon paper samples, with specific application to fuel cells and heat pipes, were measured using the rate-of-rise test. The performance of wicks in heat pipes is characterized by effective pore radius and permeability, while the permeability measurement by itself is useful for modeling in-plane phenomena of gas diffusion layers in fuel cells. The rate-of-rise measurement technique is characterized by its simplicity and non-intrusiveness, but previous results have been considered inaccurate. In this study the amount of liquid in the samples was measured by sight for some samples but also by weight change for other samples, which is a new adaptation of the rate-of-rise test. Data is analyzed using an equation resulting from a simple model of the rising meniscus. Knowing the behavior of the equation is important when reducing data in order to obtain more accurate results. The methods used in experimentation and data reduction demonstrate the wider use and increased accuracy of the rate-of-rise test.
Analytic Modeling and Experimental Verification of Thin-Film Piezoelectric Vibration-Induced Micro Power Generator
Authors: Chen Shi-Lun , Wang Gou-Jen , Yu Wen-Chin
Published: April 2008

In this article, a novel electromechanical energy conversion model of a piezoelectric cantilever bimorphs micro transducer is proposed. In this new piezoelectric-base power generator modeling, the coupling relationship between the mechanical strain and the piezoelectric polarization, rather than the curvature basis approach, is adopted to deduce the vibration-induced voltage and electrical power. In addition to the working equation for piezoelectric sensors, the damping effect is included to enable the resonance frequency, the maximum induced voltage at the resonance, the conversion power, and the dimensions of the piezoelectric micro power generator to be analytic estimated. The analytic model shows that the vibration-induced voltage is proportional to the excitation frequency and the width of the device but is inverse proportional to the length of cantilever beam and the damping factor. To verify the theoretical analysis, two clusters of micro transducers are fabricated. Experimental results demonstrate that the maximum output voltages and the power conversion are only little derivations from the analytic model.
Active Foot Pressure Control for Diabetic Patients
Authors: Nandikolla Vidya K. , Schoen Marco P. , Mahajan Ajay
Published: April 2008

Foot Ulcer in diabetic patients is a serious medical problem. A major contributor for the development of diabetic foot ulcers is a high, localized plantar foot pressure. It is believed that in diabetes the nerves in the extreme parts of the human body are damaged and cause deregulated blood flow, which may cause an insufficient blood supply. This can lead to a loss of feeling, change in shape of the feet, necrosis and ulcerations, and ultimately to partial or total amputation of the body part. The loss of feeling in the feet results in a loss of feedback to control the foot pressure distribution. It is proposed that high foot pressure concentration can be avoided by using an active, intelligent shoe insert, which is based on the mechanics of smart materials. This paper investigates the controls schemes necessary to accomplish an external foot pressure distribution scheme for preventing ulcerations or the progression of existing ulcers. A simple mathematical model of the shoe insert is developed. Foot pressure distributions for healthy subjects are used as a basis to control elevated foot pressures by changing the shape of the shoe insert. The optimal shape of the shoe insert with regard to the existing pressure distribution is computed. The optimal shape is implemented using different control schemes. The performance and the efficiency of the proposed control schemes are compared and analyzed. The main advantage of the proposed active shoe insert is its capability to sense the pressure peaks, change the pressure distribution, and provide stimuli for increased blood flow in the diabetic feet. [1,2,3]
A New Multicomponent Diffusion Formulation for the Finite-Volume Method
Authors: Pope Daniel N. , Gogos George
Published: April 2008

A new multicomponent formulation, which is appropriate for use with the finite-volume method, has been developed to accurately describe the diffusion velocity. The new formulation is presented and applied to the numerical simulation of n-heptane fuel droplet combustion in a zero-gravity, forced convection environment at 1 atm. Combustion is modeled using finite-rate chemical kinetics and a one-step overall reaction. Results obtained using the complete formulation are compared to the results obtained while assuming (1) thermal diffusion (Soret effect) is negligible and (2) thermal diffusion is negligible and all binary diffusion coefficients are the same. The effect these assumptions have on the results at a fixed Reynolds number (Re∞=10) is investigated for a low (300 K) and a high (1200 K) ambient temperature. The use of a single binary diffusion coefficient produces results that are significantly different from the results obtained using the complete formulation. These differences include a much lower maximum temperature (700 K lower), a “longer” flame and lower (8–20%) values for the evaporation constant and drag coefficient. Thermal diffusion caused only minor changes (~1%) in the numerical predictions for the maximum temperature, evaporation constant and drag coefficient.
A Comparative Study of AC and MFDC Resistance Spot Welding
Authors: Li Wei , Cerjanec Daniel
Published: April 2008

This paper presents a comparative study of the AC and MFDC resistance spot welding process. Two identical welders were used; one with a single phase AC and the other with a median frequency DC weld control. Both welders were instrumented such that the primary and secondary voltage and current could be collected. A nugget growth experiment was conducted to compare the weld size and energy consumption in the AC and MFDC welding processes. It is found that the MFDC process generally produces larger welds with the same welding current. However, this difference is more prominent when the welding current is low. Overall the AC welding process consumes more energy to make a same size weld. The larger the welding current is used, the less efficient the AC process becomes.
An Unstructured Discontinuous Finite Element Method for Three-Dimensional Radiative Transfer in Participating Media
Authors: Cui X. , Li B. Q.
Published: April 2008

This paper presents a discontinuous finite element (or discontinuous Galerkin) computational methodology for the numerical solution of internal thermal radiation problems in three-dimensional geometries using unstructured meshes. Mathematical formulation and numerical details using the discontinuous Galerkin method for internal radiation heat transfer calculations are given. Computational procedures are presented. Numerical examples are given for radiative transfer in 3-D geometries filled with a non-scattering or scattering medium. The computed results are given and are compared well with analytical solutions whenever available or the data reported in references.
Stick-Slip Behaviour of Seals With Respect to Time Dependent Friction Forces
Authors: Lindner Markus , Kro¨ger Matthias , Popp Karl , Gime´nez Manuel
Published: April 2008

In the present paper dynamic friction processes in seals are investigated. The undesired stick-slip effect of these components under real technical conditions is analyzed. Starting with the basics of stick-slip vibrations the development of an advanced seal design with improved properties is presented that prevents stick-slip. Finally, an optimization based on the extensive but simple stability analysis is shown by an expanded theory of stick-slip simulations.
Simulation Study of Adaptive Magneto-Rheological Seat Suspension
Authors: Song Xubin , Ahmadian Mehdi , Southward Steve , Miller Lane
Published: April 2008

This paper describes the details of the simulation analysis of a nonlinear model-based adaptive suspension control system[1, 2]. The numerical aspect of the simulation study of a seat suspension with application of magneto-rheological dampers will be presented. Magneto-rheological (MR) dampers have strong nonlinearities such as bi-linearity, hysteresis, and saturation related to magnetism, which can be represented by appropriate mathematic functions, respectively. Thus the model-based adaptive algorithm becomes complicated because of involvement of MR damper models. One objective of this study is to investigate the effect of MR damper model simplifications on the adaptive suspension performance. Furthermore, simulation is also applied to do parametric study of adaptive algorithm parameters such as filtering and step size. The simulation results compare the proposed adaptive controller with passive dampers to validate not only its effectiveness but also obtain some guidance information for its experimental implementation.
Modeling Compressible Fluid Struts for Active Suspension Development
Authors: Song Xubin
Published: April 2008

In this paper, a non-parametric model is presented for representing compressible fluid struts (CFS) that are based on silicon fluid. The strut can be properly designed to replace the traditional spring and shock absorber for vehicle suspension application. For this study, the strut does not include damping function so that the analysis focuses on modeling the fluid compressibility of the spring function. The approach is to derive a series of mathematics equations in correspondence to the extracted data sets from the strut testing data. The pressure data can be characterized as dependent on precharge pressure, vibration applied on the strut, and friction existing between sealing and the strut rod surface. Every characteristic is represented by a (group of) simple equation, which is optimized based on characterized data sets, respectively. Finally the model is programmed in SIMULINK and validated by the collected testing data.
Numerical Prediction of Film Cooling and Heat Transfer on the Leading Edge of a Rotating Blade in a 1-1/2 Turbine Stage
Authors: Yang Huitao , Chen Hamn-Ching , Han Je-Chin , Moon Hee-Koo
Published: April 2008

In modern gas turbines, the blade leading edge region is one area that experiences high heat transfer due to the stagnation flow. Many cooling techniques have been applied to blades, so they can withstand these high heat loads; one of the common methods in cooling turbine blades is to apply film cooling. In the present study, numerical simulations were performed to predict the film cooling effectiveness and heat transfer coefficient on the leading edge of a rotating blade in a 1-1/2 turbine stage using a Reynolds stress turbulence model together with a non-equilibrium wall function. In addition, the unsteady characteristics of the film cooling and heat transfer at different time phases during a passing period were also investigated.
Web-Based Collaborative Concurrent Engineering for Product Design and Manufacturing
Authors: Mohamed Khaled A.
Published: April 2008

We present a developed Web-based product design and manufacturing system that supports collaborative Concurrent Engineering. It models distributed systems and databases using Web technologies, so that these distributed system and databases can be accessed anywhere in the world. In such system, product developers can exchange and share product data, communicate with other team members, modify geometry data on particular aspects of the design and maintain operations consistency in all the distributed cooperative sites on a wide variety of platforms. The new system is a Client/Server architecture. The server manages the sharing of the common model, as well as the coordination among multiple users, in which different users can modify different parts of the shared model. In addition, the server supports many client through the Internet, and it also allows peer to peer negotiation, sharing different databases located in different machines, establishing relations between them at run time. A group of users can work together in a common single write mode, which continuously synchronized with the master copy on the central server. The proposal model is producing a new manner and has many algorithms for viewing, editing, synchronizing, and collaboration coordination. It utilizes Java 3D to view 3D CAD files in interactive manner. It introduces an intelligent user interface for editing and modification. STEP, which is international standard introduced by the International Standards Organization (ISO), is used to exchange engineering information. Java Server Page (JSP) is used for Collaboration coordination and semantic-based coordination.
Ultrasonic-Based Fabrication of Bulk Aluminum Matrix Nanocomposite
Authors: Yang Yong , Lan Jie , Li Xiaochun
Published: April 2008

Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal for casting. This paper presents a fabrication method for casting of bulk aluminum MMNCs by use of ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming. Nano-sized SiC particles have been dispersed in molten aluminum alloy A356 for casting. Microstructural study was carried out and it validates a good distribution and dispersion of nano-sized SiC in aluminum alloy matrix. Hardness of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-sized SiC. The ultrasonic fabrication methodology is promising to produce a wide range of other MMNCs.
Development and 3D Finite Element Implementation of a Multiaxial Constitutive Relation for Abdominal Aortic Aneurysms
Authors: Vande Geest Jonathan , Bohra Ajay , Sun Wei , Di Martino Elena , Sacks Michael S. , Vorp David A.
Published: April 2008

Abdominal aortic aneurysm (AAA), a localized dilation of the infrarenal aorta, represents a significant disease in the western population. There are approximately 200,000 patients in the US and 500,000 patients worldwide diagnosed with AAAs every year (Bosch, et al. 2001), and rupture of AAAs currently ranks as the 13th leading cause of death in the US. (Silverberg and Lubera 1987) In the past 30 years, the diagnosis of AAA has tripled in the Western world, and this will likely increase in the coming years as the average age of the population is increasing. (Bosch, et al. 2001)
Unsteady Flow of a Non-Linear Viscoelastic Fluid in Pipes
Authors: Letelier Mario F. , Madariaga Nicola´s , Siginer Dennis A.
Published: April 2008

Flow of a viscoelastic fluid in round pipes is analyzed for the case where the pressure gradient is oscillatory with varying amplitude. The fluid is modelled according to Phan-Thien-Tanner’s constitutive equation. The analysis is carried out by using the perturbation method in which a material parameter is considered small. Velocity field and other kinematic and dynamic variables are evaluated for a range of relevant parameters. The results are compared with the base Newtonian and linear Maxwell flows. The effect of the PTT model in these type of flows is highlighted.
Models of Airflow Transport in the Human Lung
Authors: Asgharian Bahman , Price Owen T.
Published: April 2008

Accurate assessment of airflow travel in the human lung is crucial in determining the fate of inhaled particles. Three models of air transport are presented in this study. In model 1, lung airways are fixed, and air travels through the airways by convective transport and in the absence of airway resistance. Airways expand uniformly during inhalation in model 2. Model 3 considers the air transport to be the result of lung compliance and resistance; as a result, different regions of the lung expand at nonuniform rates. The airflow rates and volume of air inhaled in each lobe of the human lung are calculated and compared for each model. Models 1 and 3 predict larger expansion of upper lobes, while the same expansion rate is observed for uniform airway expansion (model 2). The fraction of airflow rates going to each lobe is similar between models 2 and 3 and drastically different from that predicted by model 1.
Theoretical Effects of Hydroforming on Crashworthiness of Straight Sections
Authors: Mayer Robert R.
Published: April 2008

This paper considers the effect of hydroforming on the downstream crashworthiness for tubes. Three types of aluminum tubes were chosen as examples. Hydroforming will affect both strains and thickness of a tube, which will have opposite effects on the tubes mean crush load for crashworthiness. For hydroforming, the theoretical assumptions of no friction versus sticking friction will result in very different values for thickness, strains, stresses and mean loads when the corner radius is less than half the original tube radius. The theoretical effect on mean crush load can be as much as 25% different than without considering forming effects.
Viscoelastic Behavior of Heart Valve Tissues Under Biaxial Stretch
Authors: Sacks Michael S. , Grashow Jonathan , Yoganathan Ajit P.
Published: April 2008

Recent in-vitro studies have demonstrated the peak strain rates of the anterior leaflet of the mitral valve (MV) to be between 500–1000%/s. Quantification of the MV biaxial mechanical behavior is a critical step in the development of a comprehensive constitutive model to predict in-vivo stresses from in-vitro or in-vivo strain data. However, previously reported biaxial testing methods have been limited to quasistatic strain rates on the order of 10%/s or less, which is insufficient to quantify the MV visco-elastic behavior. In order to address these issues, a novel high-speed biaxial stretching device was developed. This new device was used to fully characterize the biaxial mechanical properties of the anterior leaflet of the MV at physiological strain rates.
Determining Model Accuracy as a Function of Inputs and System Parameters
Authors: Sohns Bryon J. , Stein Jeffrey L. , Louca Loucas S.
Published: April 2008

Vital to the effectiveness of simulation-based design is having a system model of known quality. Previous research introduced an algorithm called AVASIM for assessing model validity systematically and quantitatively. AVASIM assess the accuracy and validity of a model based on a specific input and set of system parameters. The purpose of this paper is to present a AVASIM-based methodology that defines a range of validity of a model with respect to input and system parameter variations Two illustrative examples are presented to explore the feasibility of the proposed procedure. The first example analyzes a linearized version of a nonlinear transient vehiclehandling model. This model’s accuracy and validity are evaluated with respect to variation of two system parameters, resulting in a two-dimensional range of validity. Then a complex nonlinear hydrogen fuel cell model is linearized in order to investigate its accuracy and validity with respect to two input parameters. This again results in a two-dimensional range of validity, but with respect to input rather than system parameters. The results agree well with what is expected for the various models based on knowledge of the effects of linearization on model accuracy. The proposed algorithm for assessing model range of validity is a promising tool for determining model quality and thus potentially useful for simulation-based design.
Application of Stochastic Network Models for the Study of Molecular Transport Processes in Bone
Authors: Steck Roland , Knothe Tate Melissa L.
Published: April 2008

Osteocytes are the most abundant cells in bone. They are entombed in lacunae within the bone matrix, but are interconnected via their processes that run within the canaliculi with other osteocytes, as well as with the osteoblasts and bone lining cells on the bone surfaces, and thus from a cellular syncytium. However, the osteocytes are not immediately connected with the vasculature of bone, which means that the transport of nutrients and hormones to the cells and the removal of waste products from the cells, as well as transport of signaling molecules between the cells, has to occur either via the pericellular fluid spaces in the lacunocanalicular network, via the matrix micropores between the collagen fibers and the apatite crystals, or via intracellular transport mechanisms. Only recently our laboratory and other research groups have started to examine the transport pathways of different molecular size substances within bone systematically, using experimental tracer methods (e.g. [1, 7]). These experiments have unveiled the molecular sieving characteristics of bone: While small tracers with molecular weights of 300 Daltons (Da, e.g. glucose and small amino acids) are found in abundance throughout the bone matrix and the lacunocanalicular network, larger molecules (e.g. cytokines and serum derived proteins) are only transported through the pericellular spaces of the lacunocanalicular network. Furthermore, the transport of these substances through the lacunocanalicular network can be enhanced by mechanical loading of bone [1]. These findings highlight the importance of the lacunocanalicular network for the survival of the osteocytes and thereby tissue health. However, the state of the osteocyte syncytium is affected by age and bone diseases. It has been shown that the number of osteocytes in cortical bone decreases with age [6]. Furthermore, a histological study of cortical bone tissue samples from donors undergoing hip replacement surgery has shown that the morphology of the lacunocanalicular network is altered in diseased bone [2].
Dynamic Behaviour of Flexible Mechanical Couplings Under General Misalignment Conditions
Authors: Catania Giuseppe , Maggiore Alberto
Published: April 2008

A complete dynamic model of flexible couplings is presented, and a study of the dynamic actions transmitted between two generally oriented shafts is shown. Numerical results concerning transmitted force spectra show that second and higher harmonics can generally be present, depending on the particular misalignment conditions. Moreover, every component of the resulting force and moment vector seems to be differently influenced by these conditions. Experimental testing was also done, to better understand the problem involved. Correlation between experimental measured velocities and numerically-computed transmitted forces was also proposed. A filtering transfer function model was defined and experimentally evaluated, and some results are given.