bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Modeling of Top Roller Position for Multiple Pass (3-Roller) Cylindrical Forming of Plates
Authors: Gandhi A. H. , Raval H. K.
Published: April 2008

As forming of the double or multiple curvature surfaces, includes roller forming at least once in the sequential process; its efficient performance is of great importance for controlling the final product dimensions. Most efficient and economical way to produce the cylinder is to roll the plate through the roller in single pass. Literature review revels that, most of the reported analytical models for the prediction of springback were developed with the assumption of zero initial strain. However, in practice multiple pass bending is recommended to work within the power limitation of the machine and to improve the accuracy of the final product. An attempt is made to develop the analytical model for estimation of top roller position as a function of desired radius of curvature, for multiple pass 3-roller forming of cylinders, considering real material behavior. Due to the change of Young's modulus of elasticity (E) under deformation, the springback is larger than the springback calculated with constant E. Developed analytical model was modified to include the effect of change of Young's modulus during the deformation. Developed multiple pass analytical models were compared with the single pass analytical model and experiments (on pyramid type 3-roller bending machine).
Flow Bifurcations and Transition Scenarios in Confined Flows: Channel Geometry and Operational Parameter Dependency
Authors: Guzma´n Amador M. , Aracena Tania A. , Urzua Felipe A. , Escobar Rodrigo A.
Published: April 2008

We have performed numerical simulations of confined flows in both symmetric and asymmetric wavy channels to investigate the flow bifurcations and transition scenarios dependency on geometrical and operational parameters. Laminar and time-dependent transitional flow regimes are obtained by direct numerical simulations of the mass and momentum equations using a computational program based on the spectral element method. Computational meshes for periodic computational domains are used to determine the transitional flow behavior for increasing Reynolds numbers and changing geometrical parameters. For the asymmetric wavy channel, the transition scenarios are highly dependent on the aspect ratio of the channel geometrical parameters. Depending on a specific geometric aspect ratio—one of the control parameters, the following scenarios develop: a) a first transition scenario with one flow bifurcation to a relatively low Reynolds numbers, Rec; b) a second scenario, with also one flow bifurcation, to a relatively high Reynolds numbers, Rec*; and, c) a third flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively, similar to the Ruelle-Takens-Newhouse scenario. In this third scenario, fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from laminar to transitional flow regimes. For the symmetric wavy channel and a high aspect ratio of r=0.375, a transition scenario with one flow bifurcation develops to a critical Reynolds numbers Rec** leading to a periodic flow. Further increases in the Reynolds number leads to successive periodic flows where the fundamental frequency ω1, increases continuously, in a scenario of frequency-doubling.
Morphology Development of Polymer Blend With Different Viscosity Ratios Along an Extruder
Authors: Huang Han-Xiong , Li Xiao-Jing , Huang You-Fa
Published: April 2008

The properties of polymer blends are largely determined by their morphology. So it is significant to investigate the morphology development of polymer blends during processing. In this work the morphology development of polymer blend was studied during flow along a single screw extruder. The polymer blend used incorporated polypropylene (PP) as its matrix phase and a high-viscosity or low-viscosity polyamide-6 (PA6) as the disperse phase. The samples of blends were taken from different positions using specially designed sampling device along the extruder online during the processing and were then examined using scanning electron microscopy (SEM). The morphology of the dispersed phase was quantitatively analyzed using image analysis software. The morphology evolution of blends along the melt conveying zone of screw was simulated. Theoretically predicted morphology evolution is in reasonable agreement with the experimental results. The aim of this work is to provide a better insight in the morphology development of blend during processing.
Unsteady Viscous Flows and Stokes's First Problem
Authors: Muzychka Y. S. , Yovanovich M. M.
Published: April 2008

Unsteady viscous flows and Stokes's first problem are examined. Three problems are considered: unsteady Couette flow, unsteady Poiseuille flow, and unsteady boundary layer flow. The relationship between these three fundamental unsteady flows and Stokes' first problem is illustrated. Scaling principles are used to deduce the short time and long time characteristics of these three problems. Asymptotic analysis is used to obtain exact short and long time characteristics and to show the relationship of each problem to Stokes's first problem for short times. Finally, compact robust models are developed for all values of time using the Churchill-Usagi asymptotic correlation method to combine the short and long time characteristics.
A Pseudospectral Analysis of Laminar Natural Convection Flow and Heat Transfer Between Two Inclined Parallel Plates
Authors: Kasapoglu Serkan , Tari Ilker
Published: April 2008

Three dimensional laminar natural convection flow of and heat transfer in incompressible air between two inclined parallel plates are analyzed with the Boussinesq approximation by using spectral methods. The plates are assumed to be infinitely long in streamwise (x) and spanwise (z) directions. For these directions, periodic boundary conditions are used and for the normal direction (y), constant wall temperature and no slip boundary conditions are used. Unsteady Navier-Stokes and energy equations are solved using a pseudospectral approach in order to obtain velocity and temperature fields inside the channel. Fourier series are used to expand the variables in × and z directions, while Chebyshev polynomials are used to expand the variables in y direction. By using the temperature distribution between the plates, local and average Nusselt numbers (Nu) are calculated. Nu values are correlated with φ, which is the inclination angle, and with Ra·cosφ to compare the results with the literature.
A Multivariable Approach to EGR-VGT Actuator Control Problem
Authors: Gayaka Shreekant , Yao Bin , Meckl Peter H.
Published: April 2008

The combined use of Variable Geometry Turbine (VGT) and Exhaust Gas Recirculation (EGR) gives us an opportunity to reduce emissions, without compromising the need to generate more power. In the present work, a multivariable approach is used to tackle the EGR-VGT actuator control problem. A linear multivariable controller is designed using Lyapunov's Indirect Method, based on the Jacobian matrix of the system. Then, some stronger conditions are sought to be satisfied by the Jacobian matrix, which would ensure the Global Asymptotic Stability of the system. These conditions are derived using Nonlinear Contraction Analysis. Finally, simulations are performed on a simplified model with three states to evaluate the performance of the controllers.
The Influence of Magneto-Rheological Fluid Time Response on the Performance of Semi-Active Automotive Suspensions
Authors: Conway A. , Stanway R.
Published: April 2008

In recent years the automotive industry has been working towards intelligent suspension systems that adapt to various road conditions to provide a superior ride and improved road handling. So called semi-active devices, in particular smart fluid dampers, are a viable method of implementing such a system. Despite the fact that magnetorheological (MR) dampers have been used in a number of commercially produced vehicles to date, there is little published information on the control of such devices. Building upon a successful modelling approach developed initially for electrorheological (ER) dampers at the University of Sheffield, a computational model was developed and implemented to simulate the behavior of an MR damper. A proportional force feedback control methodology was adopted and applied to the model with the intention of linearizing the output response. The smart fluid damper is therefore forced to behave in a manner equivalent to a linear damper, with the advantage of having a controllable viscous damping coefficient. Whereas previous research has almost exclusively concentrated upon the controller gain and its influence on the range of linearization which is possible to achieve, this investigation focuses on the time response of the MR fluid and its profound impact on the ability of the control method to linearize the output. Results will be presented which show that the fluid time response introduces a high frequency oscillation into the force/velocity output responses. Simultaneously, at higher excitation frequencies non-linear output responses will be demonstrated. As the fluid time response increases, the oscillations seen at low frequencies reduce but conversely the non-linear output of even moderate excitation frequencies becomes apparent. This result shows the need for a compromise between a larger range of controllability with the introduction of noise at low frequencies, or a smaller, yet noise-free range of controllability. This result may have significance when considered in the wider context of smart fluid applications. The instability and long-term degradation of smart fluids alongside other smart fluid phenomena such as 'in-use fluid thickening' indicate that the fluid time response is apt to change as the fluid is used. With a control system which has been demonstrated to be sensitive to fluid time response this change would of course be detrimental. The authors hope to highlight fluid time response as an important consideration in the design of smart fluid control systems.
GANESH: A GUI Approach to SI Engine Simulation
Authors: Vijayashree P. , Kumar V. Jyothish , Ganesan V.
Published: April 2008

This paper is mainly concerned with the simulation of a four-stroke SI engine processes. To this effect a numerical approach has been followed and this has resulted in the development of a software by the name GANESH. It is an acronym that stands for Graphical And Numerical Engine Software Hub. The results are obtained by solving appropriate process governing equations and presented in the form of animated graphs and data. The software is developed using Visual C++ and OpenGL. The proposed approach for analysis involves step-by-step procedure in developing various models. For a four-stroke spark ignition engine, ideal Otto cycle provides the foundation. Assuming fuel-air mixture as working fluid modifies the analysis bringing fuel into account. This allows fuel vaporisation effect as well as instantaneous adiabatic combustion. Intake and exhaust stroke is modeled in a simplified manner. As a next step the progressive combustion analysis has been carried out. To determine burning rate three empirical models are considered in the analysis. The intake and exhaust stroke analysis are modelled by taking into consideration gas exchange process. Detailed gas exchange analysis tries to determine exact mass of the working fluid at the start of the compression stroke. The heat transfer between the working fluid and cylinder surface is by forced convection which is taken care of by empirical correlations. Empirical relations available in the literature are used to determine the loss due to friction. Thus all processes involved in a four-stroke SI engine are simulated and the user friendly software can be used with ease and it will be particularly useful for getting results which will reduce the development time.
Web-Based and Interactive E-Learning Framework for Supporting Mechanical Education Systems
Authors: Mohamed Khaled A.
Published: April 2008

This paper presented a framework for an e-based mechanical engineering course learning. It utilizes the Internet technology and standards to communicate between the educator and students in an interactive matter. It discusses a novel way of delivering course content for students over the Internet. Using the developed framework, the instructor can set up his/her online course materials and resources, manage class student groups, and administrate student evaluation. It may be used on-site by full time students to establish an efficient interaction between the student, course content and instructor. It also offers online courses that make education accessible to distance learning students. The new system utilizes Internet technology to demonstrate class material using text, images, sound, video, 3D images and visualization, and even simulates the 3D and physical models according to the class requirements. This research also introduces a model for randomly generating exam to help the user practice taking the exam. The practice exam is graded instantly and reported to the user through web. It also provides a model for collaborative learning environments and synchronizing. Using the developed framework improves the way engineering students can understand mechanical engineering principals. It also relaxes the geographical boundaries between the students and the instructor without significantly changing the quality of learning experience. We introduce a case study and developed system implementation for CAD/CAM learning principals and Integration.
Study on Heat Transfer and Flow Mechanism in Loop-Type Micro Heat Pipe
Authors: Sakurai Hisashi , Koizumi Yasuo , Ohtake Hiroyasu
Published: April 2008

A simple design micro-heat pipe was proposed. It was composed of 20.0 × 20.0 mm square flow circuit which had two adjacent narrow-sides (1.0×1.0 mm or 0.5×1.0 mm) and two adjacent wide-sides (5.0×1.0 mm, 5.0×0.5 mm, 3.0×1.0 mm or 2.5 × 1.0 mm). A heating spot was at the narrow side and a cooling spot was at the wide side. Working fluid was ethanol. The flow circuit was placed horizontally. It was confirmed experimentally that the circulation flow was formed in the micro flow circuit without any pump and the gravity effect. It was also analytically proved by solving a simple flow equation that the net circulation flow could be formed when the flow circuit; the flow resistance, was asymmetric. The boiling phenomena of the narrow space of the present scale (~ 1 mm) could be expressed with the existing correlation. Further examination is necessary for the narrow space condensation phenomena. It was proved that the micro heat pipe proposed is advantageous in the high heat road condition and in the light weight condition.
Identification and Defect Detection of Continuous Dynamic Systems
Authors: Siami A. , Farid M.
Published: April 2008

This paper presents a systematic and efficient algorithm using a coupled finite element - finite difference - least square method for identification and defect detection of continuous system using dynamic response of such systems. First the governing partial differential equations of motion of continuous systems such as beams are reduced to a set of ordinary differential equations in time domain using finite elements. Then finite difference method is used to convert these equations into a set of algebraic equations. This set of equations is considered as a set of equality constraints of an optimization problem in which the objective function is the summation of the squares of differences between measured data at specific points and the predicted data obtained by the solution of the governing system of differential of equations. This method has been successfully applied to find mechanical properties of aforementioned systems in an iterative procedure.
A Model for Implementing Practical Design in the Education of Mechanical Engineers
Authors: Hansen Michael R. , Mouritsen Ole O̸. , Andersen Torben O.
Published: April 2008

In this paper the PBL model used at Aalborg University in the mechanical engineering is shortly presented. A specific semester with a both theoretical and practical content that allow the students to is presented in detail. It is then used as a reference project for a subsequent discussion on three potential concerns with respect to the continued succes of problem and project based learning in mechanical and mechatronics engineering namely: individual assessment, bologna (student exchange) model and research based teaching.
Design Considerations for the Effects of Liquid Compressibility in Microchannel Flow Boiling
Authors: Fogg David W. , Goodson Ken E.
Published: April 2008

Forced convective flow boiling in microchannels is characterized by the nucleation and rapid growth of vapor bubbles in confined geometries. Confined boiling flows are highly transient yielding periods of rapid vapor formation followed by a refilling of the channel with liquid. This behavior in a single microchannel with constant flow rates can only be correlated with the growth of single bubbles in the channel. Using a one-dimensional Lagrangrian-Eulerian model, Fogg and Goodson [1] showed that reflections of these pressure waves create local pressure depressions that may trigger nucleation at temperatures not predicted by incompressible analysis. This study extends the work of Fogg and Goodson [1] by examining the influence of channel and chip geometry on the propagation of pressure perturbations within microchannels. A set of equations are proposed to estimate the amplitude of the initial pulse and its evolution through various geometries such as converging/diverging channels and sudden expansions/contractions. Simulations of two single channel experimental structures show that the flow delivery condition plays a minimal role in the reflection and propagation of pressure perturbations and that channel design may impact the nucleation characteristics of microchannels.
Numerical Simulation on Nucleation and Cell Growth in Microcellular Injection Molding Without Mold
Authors: Wang Jian-Kang , Huang Han-Xiong
Published: April 2008

A mathematical model to predict the nucleation and cell growth during the microcellular injection molding without mold, was developed. The nucleation equation, energy equation, equation of cell growth, and equation of gas content were solved numerically. The predicted nuclei density and cell diameter were compared with the experimental results. The experimental equipment including a conventional injection molding machine, specially designed nozzle, and supercritical fluid conveying system, is used to validate the predicted results. The polymer-gas solution ejected from the injection molding machine was foamed in nozzle and cooled in the air, rather than in the mold.
Film Cooling Predictions for Cratered Cylindrical Inclined Holes
Authors: Lu Yiping , Ekkad Srinath V.
Published: April 2008

Film cooling is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes occur when blades are coated with thermal barrier coating layers by masking the hole area during TBC spraying. The film performance and behavior will be different for the cratered holes compared to standard cylindrical holes. FLUENT is used to simulate film cooling for the different crater geoemtries and compared to baseline uncratered cylindrical holes. Film effectiveness is reduced by the cratering compared to earlier studies which had two-dimensional trenches instead of craters. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at one different coolant-to-mainstream blowing ratio of 1.0.
Development of an Experimental Facility to Test Polymer Extrusion
Authors: Lobarinhas P. A. M. , Teixeira S. F. C. F. , Teixeira J. C. F.
Published: April 2008

A wide variety of plastic profiles are produced in extrusion lines, which are basically comprised by an extruder, a die and a calibrator. Because the initial cooling stages will determine the final quality of the extrudate, the study of the thermal modeling of the calibrator is of great interest. In this context the use of computational tools is becoming increasingly useful for the calibrator design and optimization. Therefore, reliable experimental data is of paramount relevance to validate thermal models. For that purpose, an experimental apparatus was set-up at the laboratory, which includes: a calibrator, a heat chamber, a data acquisition system, a traction system and various polymer test samples. The experimental facility is designed to obtain data inside the polymer. Based upon computer simulations a calibrator was built in a aluminum alloy with 600×150×80 mm. The cross section aperture for the polymer profile is of 30×16 mm. Low inertia thermocouples were located at various positions and at depths varying between 1.0 to 5.0 mm from the calibrator/polymer interface. This is the region where greater thermal gradients are expected. Other sensors (at the surface) can be used to determine the interface thermal resistance. Data were collected by a high-speed data acquisition board (data a rate up to 500 kHz), with electronics for signal conditioning in order to compensate the low level signal of thermocouples. The data are stored for subsequent processing. All the process is controlled using an interface developed in LabView. Preliminary testes were carried out in PVC samples due to its high melting point and availability. The results proved the usefulness of the test facility to obtain relevant data concerning the thermal behavior of calibrators.
A Robust Nonlinear Tracking Control Approach for Multi-Body Flexible Dynamic Systems
Authors: Xue X. , Tang J.
Published: April 2008

In this research, a multi-input multi-output (MIMO) integral continuous sliding mode design approach is proposed to achieve multi-objective robust tracking control for nonlinear dynamic systems. Instead of employing the equivalent control and switching control concepts in conventional variable structure methodology, here we develop a new design procedure using continuous control law with a tunable order of state feedback. As a result, the chattering phenomenon can be completely eliminated and the control sensitivity can be adjusted using the proposed sensitivity parameter. This design procedure can be applied to a general class of mechanical systems. The performance of the controller is verified using a series of simulation studies on flexible rotating beam and robotic manipulator.
Investigation Into the Effects of Geometric Tolerances on Freight Car Dynamics
Authors: Tunna John , Shu Xinggao , Dasher Jeremy
Published: April 2008

When a 3-piece truck is assembled there are clearances between components that are intended to allow relative movement, and to limit excessive movement. The magnitudes of the clearances are affected by manufacturing tolerances and wear in service. They have important effects on freight car dynamics including hunting stability and curving performance. A study has been made of the effect of varying clearances on the dynamic performance of a typical freight vehicle. The clearances that have been considered are in the areas of the: • sideframe window, • pedestal and bearing adapter • gibs • wheel diameters Combinations of maximum and minimum allowable tolerances and maximum allowable wear have been modeled with TTCI's NUCARS™ simulation software. Most of the test cases in the Association of American Railroads Manual of Standards and Recommend Practices, Chapter XI (1) have been studied. Results were produced from a NUCARS™ model of a 100 ton coal hopper. Empty and loaded simulations were performed. The trucks were modeled with variable load friction wedges. Conclusions have been drawn on the appropriateness of the currently allowable tolerances and wear limits. A new tolerance is suggested for the center of the sideframe window relative to the centerline of the pedestals. The conclusions only apply to the specific vehicle, suspension type and truck type analyzed. This work was sponsored by the Association of American Railroads, Strategic Research Initiative program.
Optimization of a 180 Degree Bend for Internal Turbine Blade Cooling by Using the Ice-Formation Method: First Results
Authors: Zehner Sebastian , Steinbru¨ck Helga , Weigand Bernhard , Neumann Sven Olaf
Published: April 2008

This paper presents the first results of an approach for the optimization of a 180° bend used in internal cooling configuration of turbo-machinery components by applying the iceformation method. The iceformation method is based on a coupling between momentum and heat transfer and their interaction with a surface which consists of a solidified phase (ice layer). The investigated surface is cooled to temperatures below the freezing temperature of water and is therefore covered with an ice layer. Different cooling levels of the "parent surface" and different fluid flow velocities result in different contours of the ice layer which are determined from a local heat balance. The final shape of the ice layer at steady state conditions is determined by 2D optical measurement methods. The iceformation method provides a natural evolutionary approach to obtain contours that are optimized in terms of energy dissipation as have been shown in several studies by LaFleur [1–3]. The present study focuses on ice layer contours in a bend determined by experiments and classified with regards to thermal, flow, and geometrical constraints. In a further step, "good candidates" of the obtained surface contours can be parameterized and then used as starting geometries for numerical optimization by applying genetic algorithms in order to reduce pressure loss and to improve heat transfer performance. This procedure, using the iceformation method as a generator of new ideas, leads to larger solution ranges but also to "unusual results" and promising geometries compared to traditional optimization approaches. First results presented in this paper show those unusual and unexpected results in terms of ice layers shaping a separating web of a 180 degree bend by natural fluid flow. These ice layer contours even give a reduced pressure drop of 7% in this bend.
Modeling and Control of a 2-D Membrane Mirror With a PZT Bimorph
Authors: Ruggiero Eric J. , Inman Daniel J.
Published: April 2008

The future of space satellite technology lies in ultra-large mirrors and radar apertures for significant improvements in imaging and communication bandwidths. The availability of optical-quality membranes drives a parallel effort for structural models that can capture the dominant dynamics of large, ultra-flexible satellite payloads. Unfortunately, the inherent flexibility of membrane mirrors wrecks havoc with the payload's on-orbit stability and maneuverability. One possible means of controlling these undesirable dynamics is by embedding active piezoelectric ceramics near the boundary of the membrane mirror. In doing so, active feedback control can be used to eliminate detrimental vibration, perform static shape control, and evaluate the health of the structure. In the present work, a piezoceramic wafer was attached in a bimorph configuration near the boundary of a tensioned rectangular membrane sample. A finite element model of the system was developed to capture the relevant system dynamics from 0 – 500 Hz. The finite element model was compared to experimental results with fair agreement. Using the validated finite element models, structural control using Linear Quadratic Regulator (LQR) control techniques were then used to demonstrate effective vibration control. Typical results show that less than 12 V of actuation voltage is required to eliminate detrimental vibration of the membrane samples in less than 15 ms. The functional gains of the active system are also derived and presented. These spatially descriptive control terms dictate favorable regions within the membrane domain to place sensors.
Characterization of Polyvinylidene Fluoride (PVDF)-Double-Walled Carbon Nanotubes (DWNT)
Authors: Ounaies Zoubeida , Almasri Atheer , Kim Yeon Seok , Grunlan Jaime
Published: April 2008

In this work, we propose a new generation of sensors and actuators based on a piezoelectric polymer (PVDF) with embedded carbon nanotubes. Polyvinylidene fluoride (PVDF) double walled carbon-nanotubes (DWNT) composite films are prepared with the goal to develop new polymeric materials with enhanced electrical and electromechanical properties. Electrical conductivity and dielectric properties of polyvinylidene fluoride- double-walled carbon nanotubes composites are investigated as a function of frequency (10 Hz -1 MHz), and as a function of weight fraction (0.01-2 wt%). DWNT and PVDF are mixed under mechanical stirring and sonication. The dispersion is assessed by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM), indicating a good dispersion. Differential Scanning Calorimetery (DSC) is used to study the effect of DWNTs inclusions on the glass transition temperature, Tg, and the crystallinity of the resulting PVDF composite. The percolation threshold is computed by using the bulk conductivity data and it is found that percolation occurs at about 0.19wt%.
Optimum Connection Positions for the Redundant Limb in Cable-Based Parallel Manipulators
Authors: Hassan Mahir , Khajepour Amir
Published: April 2008

Cable-based Parallel Manipulators (CPM) are light-weight manipulators that can reach high accelerations. The difference between the design of CPM and that of rigid-link parallel manipulators is due to the fact that cables can only perform while under tension. Keeping the cables under tension can be achieved by applying a force to the mobile platform by a redundant limb (e.g., cable, spring, or a cylinder) to generate tensile forces in the cables. In this study, an optimization procedure is developed to determine the optimum direction and connection position for the redundant limb. The optimum solution is that at which the difference between the largest and smallest tensions generated in the cables is minimized. The optimization procedure is based on a bounded-search algorithm that minimizes an objective function that represents the difference in the cable tensions generated due to the redundantlimb force. The bounds established in this study on the search increases the speed and efficiency of the search algorithm. The optimization procedure is successfully applied to a spatial 6degree-of-freedom cable parallel manipulator for demonstration.
The Dual State Variable Formulation as an Alternative to Perturbation Methods for the Analysis of Non-Linear Oscillators
Authors: Post Alvin , Stuiver Willem
Published: April 2008

The "dual" state variable (DSV) formulation is a new way to represent ordinary differential equations. It is based on a framework that is consistent with the analysis of linear systems, and it allows the state space representation of a system to exhibit considerable symmetry. Its use in modeling requires a clear understanding of its unique four-dimensional state space, but it can be computationally simple. The DSV formulation has been successfully applied to model the nonlinear pendulum, the Duffing oscillator, and the van der Pol oscillator, with results that are superior to those of perturbation methods. An introduction to the DSV formulation and a framework for its systematic application as a modeling tool for nonlinear oscillators are presented.
Thermal Conduction Switch for Thermal Management of Chip Scale Atomic Clocks
Authors: Laws A. D. , Chang Y. J. , Bright V. M. , Lee Y. C.
Published: April 2008

We report the first use of a bimetallic buckling disk as a thermal conduction switch. The disk is used to passively alter the thermal resistance of the package of a chip scale atomic clock. A vertical-cavity surface-emitting laser (VCSEL) and a cesium vapor cell, contained in the clock, must be maintained at 70±0.1°C even under an ambient temperature variation of -40°C to 50°C. A thermal test vehicle has been developed to characterize a sample package with a thermal conduction switch and has been modeled using Finite Element Analysis (FEA). Three cases are presented for the temperature control of the test vehicle under different load placements and environmental conditions: 1) the center resistor in a vacuum package; 2) the center resistor packaged in air; and 3) the side resistor in a vacuum package. At 38°C, the switch snaps upward to reduce the thermal resistance. As a result, the heating power needed to maintain the same temperature is increased from 118 to 200 mW for Case 1. Such a significant change of the thermal resistance demonstrates the effectiveness of the novel thermal switch. However, the switch becomes less effective with air filling the gap, as in Case 2. More interestingly, the switch is not effective at all if the side resistor's temperature is to be controlled as in Case 3.
Numerical Analysis of Marangoni Convection in Liquid Bridge With Liquid Encapsulation: Effect of Temperature Coefficient of Tension
Authors: Peng Lan , Li Yourong , Liu Juanfang , Jen Tien-Chien , Chen Qinghua
Published: April 2008

The physical and mathematical models of the Marangoni convection in liquid bridge with liquid encapsulation (two immiscible coaxial liquid columns) were established. With these models a series of numerical simulations of the Marangoni convection in liquid bridge with liquid encapsulation have been performed by the vorticity-stream function method and the Alternative Direction Implicit scheme in finite difference. The distributions of temperature and flow in liquid columns were then obtained. In this paper, it is mainly considered that the ratio of the temperature coefficient of interface tension to surface tension affects on the Marangoni convection in liquid bridge with liquid encapsulation.
Investigation of Break-Up, Splash, and Fingerlike Instabilities for a Large Water Slug Impact
Authors: Jepsen Richard A. , Yoon Sam S. , James Scott C.
Published: April 2008

The fluid physics of splashing, spreading, and dispersion of a large-scale water droplet is investigated both experimentally and with model simulation. Several new phenomena of the droplet impact beyond conventional Rayleigh-Taylor instability theory are reported. First, our experimental data show that the number of fingers or instabilities along the spreading rim cannot be predicted by Allen's (1975) Rayleigh-Taylor equation. Second, we report that the surrounding medium (air) along with impact angle and droplet shape upon impact affect ejection velocity and splashing. Finally, the fundamental instability of the finger formation along the spreading rim may be due to interactions initiated by the compressed and displaced air, rather than the spreading of the liquid decelerating through the air. Several important correlations between the droplet impact velocities, the amount of spray ejected, the spray ejection speed, and the number of fingers or instabilities are presented.
Multibody Modeling of Gear Dynamics With 3-D Contacts: Advances and Challenges
Authors: Zeid Ashraf
Published: April 2008

This paper describes the application of modeling of multibody systems to high-precision mechanical gears. Although the context of the paper is applied in nature, the objective is to present recent advances in computer-aided modeling of multibody systems with three-dimensional (3-D) contacts and to explore the limits of the technology, theory, and methods. Gear systems are traditionally modeled as single dimensional object with a simple transformation ratio. However, when we are interested in high precision gear systems, all joints and flexibility of gear shafts bearings are accounted for in the model. In this paper we discuss challenges in using recent advances in computer-aided multibody modeling (CAMM) with 3-D contacts applied to the design of a steering gear system. These advances in CAMM have made it possible to produce detailed dynamic simulation of constrained multibody motion in a much shorter time than the traditional Finite Element approach. Extracting position and velocity information from simulation of multibody models using CAMM is routine work today save for the most complex systems. However, extracting information about contact force between rigid bodies during impact subsequent rolling and sliding motions is a more challenging problem. This paper discusses these challenges and presents possible numerical and modeling solutions. Gears move in three-dimensional space, their surfaces undergoing continuous contact and separation; we distinguish between large dominant motion and microscopic motion along constraints axis. In an effort to understand motion of steering gear at the microscopic level, we modeled gears as multibody systems with their surfaces in a dynamic state of contact and separation. These models capture the dynamics of gears traveling distances of around 50 microns in less than 10 milliseconds. We applied newly developed analytic, numeric, and computer-aided tools to gain insight into gear forces, specifically, those forces responsible for the inception of mechanical knock in steering gear. The results provided a 3-D view of the sequence of events of gears with their surfaces in motion, in sudden contact, sliding, and the resulting force generation. The models include effect of friction on impact mechanics of the gears. First we briefly present a discussion of the state-of-knowledge in CAMM with three-dimensional surface contacts. Computer aided engineering requirements necessary to solve the problem are discussed together with computer hardware, software, and analysis methods that are necessary for successful modeling of multibody gear systems with 3-d contacts. We finally present a model of a generic gear system that demonstrates both the potential and the limitations of the current technology.
An Efficient Scaling Methodology for Dynamic Models Using Dimensional and Activity Analyses
Authors: Kittirungsi Burit , Fathy Hosam K. , Stein Jeffrey L.
Published: April 2008

Previous work in the literature developed similitude-based design scaling techniques that make it possible to take a proven system design and scale it to meet new desired dynamic characteristics. However, such similitude-based scaling is often too restrictive because it may not be feasible to satisfy all of the resulting scaling laws exactly. This paper uses a novel combination of activity-based model reduction and dimensional analysis to scale only the important components of a given dynamic system, thereby providing more freedom than pure similitude-based scaling. The viability of this proposed method is highlighted by two examples. The first example demonstrates the proposed efficient scaling methodology on a simple two-degree-of-freedom mass-spring-damper system. The second example uses the developed methodology to scale a fuel cell stack's air supply system design for a new set of fuel cell system power requirements. The examples highlight the flexibility that activity analysis adds to similitude-based scaling methods.
Experimental Evaluation of a Hydraulically Actuated Tilt System for a Narrow Track Three-Wheeled Vehicle
Authors: Drew Benjamin , Barker Matt , Edge Kevin , Darling Jos , Owen Geraint
Published: April 2008

The objective of the EU-funded CLEVER Project (Compact Low Emission VEhicle for uRban transport) is the design and development of a novel two-seat vehicle for individual urban transport providing car-like levels of comfort, safety and convenience with the lower emissions, noise levels and road footprints of motorcycles. A narrow three-wheeled tilting vehicle has been identified as the best method of achieving these goals. One problem with vehicles with a narrow track is the unstable roll moment created when cornering. To solve this issue, the vehicle's centre of gravity is moved towards the centre of the corner by tilting the vehicle in a similar manner to that of a motorcycle. An active tilting system using hydraulic actuation has been employed, allowing for car-like controls. A prototype vehicle has been built to test this active tilting system. Initial testing revealed that while basic steady state handling was good, transient response required improvement. The evidence indicating this poor response is examined, and the necessary methods employed within the control system to solve the issue are discussed. Improved results are presented following an increase in the system gain. The effects of different filter cutoff frequencies on the objective and subjective vehicle handling characteristics is also investigated and presented here. It is shown that when designing a three-wheeled tilting vehicle with the arrangement used in CLEVER, safe handling can only be achieved at the expense of fast tilt response. This is a result of fundamental limitations of the vehicle design.
Functionally Graded Nanocomposites: Manufacturing and Characterization
Authors: Rud Jared A. , Shkel Yuri M. , Matthys Donald R. , Davidson Jeffrey P.
Published: April 2008

Multi-walled carbon nanofiber (MWCN) composites having tailored internal structure are created using Field Aided Micro Tailoring (FAiMTa) technology. FAiMTa is a technique that relies on the application of an electric field to a suspension while it cures. The particles in the suspension align in the direction of the electric field while the matrix material hardens, locking the aligned particles in place. The outcome is an orthotropic micro-tailored composite. Three 1% by volume MWCN/epoxy composite systems are manufactured and characterized: (a) random orientation, (b) fibers aligned through the thickness of the sample, and (c) half-aligned through the thickness and half random orientation. Electronic Speckle Pattern Interferometry (ESPI) and Dynamic Mechanical Analysis (DMA) are used to evaluate mechanical material properties as a function of particle alignment. The half aligned sample demonstrates the ability of FAiMTa to locally tailor a material.
Electric Field Driven Control and Manipulation of Particles in Multiple Designs of Microfluidic Devices Including the Electrothermal Effects
Authors: Mulukutla Vishwanath , Khusid Boris , Song Hongjun , Bennett Dawn J. , James Conrad
Published: April 2008

Micro-total-analytical systems for analyzing chemical/biological substances are now used across a wide variety of applications ranging from biological warfare agent detection to the healthcare industry. The first step in the operation of such systems consists of concentrating and separating the analytes of interest from the background matrix and positioning these analytes into selected locations for subsequent analysis. Electro-kinetic and electro-hydrodynamic techniques for manipulating particles in suspension are highly used in microsystems eliminating the need for movable parts. In addition, because of the high surface to volume ratio there is efficient dissipation of Joule heating. Here, we analyze the electric field distribution and particle motion in microfluidic devices with a variety of electrode configurations. First, we consider the particle motion and electric field gradient in our recently developed technique of dielectric gating. We consider the particle motion and numerical simulation results using the Computational Fluid Dynamics Research Corporation (CFDRC) code in 2D designs. In addition, the electrothermal effects within the channel are examined. Next, we consider triangular and trapezoidal electrode configurations as well as single stream particle delivery. We study the particle motion, electric field gradients, and electrothermal effects in these designs. Computer simulations and experimental results are compared.
3-D Modeling of Particle Laden Density Current
Authors: Hormozi S. , Firoozabadi B. , Ghasvari-Jahromi H. , Hekmati S. M. H. Moosavi
Published: April 2008

The gravity currents on the inclined boundaries are formed when the inflow fluid has a density difference with the ambient fluid and a tangential component of gravity becomes the driving force. If the density difference arises from the suspension of particles, the currents are known as particle-driven density currents, in which the local density of the gravity current depends on the concentration of particles. A low Reynolds k-ε turbulence model is used to simulate three dimensional turbidity currents. Also a laboratory apparatus was built to study the 3D flow resulting from the release of particle laden density currents on a sloping surface in a channel of freshwater via a sluice gate and Kaolin was used as the suspended material. The height, width, velocity and concentration profiles are calculated and compared with the laboratory experiments which show good agreement. Averaged parameters were obtained and Entrainment coefficients against Richardson number were acquired without any approximation and simplification which show the same trend as previous 2D experimental data.
A Preliminary Study on the Mechanical Performance of Tiled Polymer Composites
Authors: Qidwai M. A. , Baucom J. N. , Leung A. C. , Thomas J. P.
Published: April 2008

We are developing and exploring the concept of in-plane tiling of composite laminates, called MOSAIC, to mitigate or control delamination at free edges due to interlaminar stresses. Initial mechanical testing has shown that MOSAIC composites with uniaxial graphite-fiber reinforced tiles retain the stiffness levels of traditional uniaxially reinforced composites but with reduced strength. The reduction in strength is attributed to the formation of resin-rich pockets between adjacent tiles. In this study, we have performed detailed finite element analyses to identify the critical design parameters that affect the mechanical performance of uniaxially reinforced MOSAIC composites. We have found that using continuous laminae on the outer surfaces significantly increases the overall loadcarrying capacity. Increasing aspect ratio of the pocket and decreasing material property differences between resin and tiles also cause better load transfer between tiles but may not necessarily improve overall strength due to increasing stress concentration. The tiling scheme and density of pocket placement influence the interaction of local stress concentrations. Consequently, a novel composite joint is proposed and found to have superior performance.