bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization and Modeling of the Dynamic Behavior of a Liquid-Vapor Phase Change Actuator
Authors: Bardaweel H. , Richards R. , Weiss L. , Richards C. , Anderson M.
Published: May 2009

In this work a study of the dynamic performance of a liquid-vapor phase change actuator is presented. The actuator consists of a cavity filled with a two phase fluid bounded by a thin membrane into which heat is added and a cover slip which is displaced by the expansion of the vapor. An experimental actuator was designed so that a parametric study of geometry and operation parameters could be conducted. A lumped parameter model of the system was developed to predict forces and displacements produced by the addition of heat. The input to the model is the heat and the output is the displacement of the actuator. FFT analysis of the actuator deflection and heat input are performed. This procedure allows the measurement of the transfer function between actuator displacement as output and heat as input over a frequency range of 10 to 500 Hz. These data are compared to the predictions of the lumped parameter model. Agreement is favorable.
Failure Analysis of a Fibrous Composite Half-Space Subjected to Uniform Surface Line Load
Authors: Gururaja S. , Ramulu M.
Published: May 2009

Uni-Directional Fiber-Reinforced Plastic (UD-FRP) laminates have been modeled previously as an equivalent quasi-homogeneous monoclinic half-space subjected to an inclined line load on the surface using Lekhnitskii’s formulation simulating the orthogonal edge trimming loads in UD-FRPs. In continuation, failure analysis of the aforementioned composite half-space has been carried out in the present investigation based on Tsai-Wu criterion. In particular, the failure behavior of the half-space laminate with respect to the fiber orientation, load inclination angle and spatial coordinates has been examined in detail. The motivation behind such a study lies in correlating the failure behavior of the half-space laminate with the damage progression observed during orthogonal edge trimming experiments. The present work strives at identifying this relationship and in the process, understanding the physics of orthogonal cutting mechanisms in UD-FRP laminates.
Defect Detection of Flip Chip Solder Bumps Through Local Temporal Coherence Analysis of Laser Ultrasound Signals
Authors: Yang Jin , Ume Charles
Published: May 2009

Microelectronics packaging technology has evolved from through-hole and bulk configuration to surface-mount and small-profile ones. In surface mount packaging, such as flip chips, chip scale packages (CSP), and ball grid arrays (BGA), chips/packages are attached to the substrates or printed wiring boards (PWB) using solder bump interconnections. Solder bumps, which are hidden between the device and the substrate/board, are no longer visible for inspection. A novel solder bump inspection system has been developed using laser ultrasound and interferometric techniques. This system has been successfully applied to detect solder bump defects including missing, misaligned, open, and cracked solder bumps in flip chips, and chip scale packages. This system uses a pulsed Nd:YAG laser to induce ultrasound in the thermoelastic regime and the transient out-of-plane displacement response on the device surface is measured using the interferometric technique. In this paper, local temporal coherence (LTC) analysis of laser ultrasound signals is presented and compared to previous signal processing methods, including Error Ratio and Correlation Coefficient. The results show that local temporal coherence analysis increases measurement sensitivity for inspecting solder bumps in packaged electronic devices. Laser ultrasound inspection results are also compared with X-ray and C-mode Scanning Acoustic Microscopy (CSAM) results. In particular, this paper discusses defect detection for a 6.35mm×6.35mm×0.6mm PB18 flip chip and a flip chip (SiMAF) with 24 lead-free solder bumps. These two flip chip specimens are both non-underfilled.
An MRI Based Study of Tarsal Development During Manipulation and Casting Therapy of Infant Clubfoot
Authors: Mahmoodian Roza , Siegler Sorin
Published: May 2009

Ponseti technique is a common non-surgical treatment based on serial manipulation and casting for idiopathic infant clubfoot. We have used three dimensional MRI throughout the treatment, to investigate the effect of the casts on the clubfoot of a one week old (at the beginning of treatment) male with unilateral right idiopathic congenital clubfoot deformity. A total of 21 MRI scans were obtained during weekly serial manipulation and corrective casting. Changes in shape, volume, ossification, and positional relationships of the hind foot anlagen were studied. We found that immediate shape changes occur following casting, particularly in the talus and the navicular, and when after one week the cast is removed the anlagen do not elastically return to their original shape and position prior to casting. Furthermore, the growth rate of some of the clubfoot anlagen, in particular the talus, was faster than normal. A faster ossification was observed in the calcaneus and cuboid. Results also showed correction in parallelism of calcaneus and talus in the anteroposterior plane, minor correction of this parallelism in the lateral view necessitating a heel cord tenotomy, and correction of the medial rotation of calcaneus. Under this treatment changes in talar neck angle yielded a decreasing trend. The navicular moved with respect to the head of the talus from a medial to a lateral position. Relative to the talar body it shifted laterally. Also the geometrical center of talus ossific nucleus was noted to move towards the center of the whole anlagen suggesting that the ossification extends in the opposite direction from the head of the talus. It was concluded that the mechanism of adaptation to the casting loads was quick deformation immediately upon cast application followed by adaptation to the new shape in the cast. These were qualitative findings. It was also concluded that most of the correction occurred during the initial treatment period, primarily during the first and second weeks (1). On the quantitative end, it was confirmed that MRI and computer techniques can be utilized to ascertain and quantify the abnormalities which were impossible to well identify otherwise. MRI based studies have powerful potential to provide helpful information on the choice of treatment as well as guidance throughout. For instance, it may therefore be possible in the present case to shorten the treatment time without adverse effects on the outcome.
Physics of Pumping Methanol/Water Solutions for Fuel Cell Applications
Authors: Buie C. R. , Litster S. , Santiago J. G.
Published: May 2009

Proton exchange membrane fuel cells are environmentally friendly energy conversion devices. A special class of PEMFCs, direct methanol fuel cells (DMFCs), oxidize liquid methanol solutions at the cell anode as opposed to hydrogen gas. The use of methanol as fuel makes DMFCs highly attractive for portable applications due to the high volumetric energy density of liquid methanol. Previous work has shown that electroosmotic (EO) pumps can be used to pump pure methanol to obtain relatively high flow rates per power in applications with minimal pressure loads. This study explores the unique aspects of pumping methanol/water solutions for fuel cell applications with non negligible pressure loads. We explore EO pump figures of merit pertinent to portable fuel cell applications including flow rate per power and the ratio of EO pump power to fuel cell power. Experimental studies reveal EO pump power to DMFC power ratios of 5% or less for borosilicate glass substrates. Further, we will discuss unique aspects of pumping low ion density methanol/water solutions that affect EO pump performance including solution conductivity and transient pH gradients. Ultimately this work provides a theoretical and experimental basis for a miniature DMFC system using an EO pump for fuel delivery.
Precise Control of Carbon Nanotube Synthesis of a Single Chirality
Authors: Huitink David R. , Banerjee Debjyoti , Sinha Saion K.
Published: May 2009

This work demonstrates precise control over the synthesis conditions and location during CNT formation, such that single chirality tubes are obtainable. This technique obviates two significant hurdles that prevent the exploitation of CNTs in micro- and nano-devices. Microelectronic applications require precise location and chirality of synthesized CNTs. Conventional CVD synthesis techniques typically yield mixtures of CNTs (semi-conducting and metallic types) that grow at random locations. Dip Pen Nanolithography (DPN) techniques were used to deposit the catalysts at precisely defined locations and to pattern the catalysts on a substrate with specific sizes as well as to control the catalyst composition. After deposition of catalysts, a low temperature Chemical Vapor Deposition (CVD) process was used to synthesize CNT. Various known catalysts were deposited. Characterization studies before and after CVD synthesis of CNT showed that the CNT were of a single chirality as well as uniform diameter (with a very narrow range of variability). The results indicate that the chirality of the synthesized CNT can be controlled by changing the synthesis conditions (e.g., size of the catalyst patterns, composition of the catalysts, temperature of CVD, gas flow rates, etc.).
Multi-Scale Modeling and Experimental Validation for Component Fatigue Life Prediction
Authors: Soni Sunilkumar , Wei Jun , Chattopadhyay Aditi , Peralta Pedro
Published: May 2009

A fatigue failure prediction procedure is discussed based on a two scale micro meso mechanical model for metallic structures. This model predicts the fatigue life and accounts for physical quantities like the mean stress effect in high cycle fatigue. Another model developed at meso-scale level with BCJ (Bammann, Chiesa and Johnson, 1996, Theoretical and Applied Mechanics, Tatsumi, Watanabe and Kambe (Editors), 359–376) internal state variables, is used to predict progressive damage in ductile materials. This meso-scale model is incorporated within the general purpose finite element software ABAQUS through a user subroutine VUMAT. A lug joint specimen is simulated using the BCJ model modified for fatigue and the location of the crack initiation sites is found. Experiments are conducted with the lug joint specimen under fatigue loading and the models are validated for the fatigue life prediction and location of the damage sites.
Visco-Elastic Properties of Aligned Multi-Walled Carbon Nanotube Blocks
Authors: Suhr Jonghwan
Published: May 2009

Structural components subjected to cyclic stress can succumb to fatigue and fail at stress levels much lower than what is expected under static loading conditions. Such fatigue behavior in nanotube structures has never been reported, albeit its importance in practical devices incorporating nanotube components. In particular, cyclic compression loaded vertically aligned nanotube structures could find various applications as electro-mechanical systems. Here, this work reports the mechanical response from repeated high compressive strains on freestanding, long, vertically aligned multiwalled carbon nanotube membranes and show that the arrays of nanotubes under compression behave very similar to soft tissue and exhibit viscoelastic behavior. Under compressive cyclic loading, the mechanical response of nanotube blocks shows initial preconditioning, hysteresis characteristic of viscoeleastic materials, nonlinear elasticity, stress relaxation, and large deformations. Furthermore, no fatigue failure is observed even at high strain amplitudes up to half million cycles. The outstanding fatigue life and extraordinary soft tissue-like mechanical behavior suggest that properly engineered carbon nanotube structures could mimic artificial muscles, and their added high electrical and thermal conductivity could make excellent candidates for uses as compliant electrical contact brushes, probe cards and electromechanical systems.
A Void Growth and a Cyclic Model in Ductile Material Using Mechanism-Based Strain Gradient Crystal Plasticity Theory
Authors: Luo Chuntao , Wei Jun , Chattopadhyay Aditi , Jiang Hanqing
Published: May 2009

This paper addresses the problem of theoretically predicting the evolution of void for a single crystal in ductile material accounting to the size and orientation effects. In this paper, a new damage model is derived based on the theory of mechanism-based strain gradient crystal plasticity (MSG-CP). By imposing the Taylor dislocation model into a widely used Gurson model (1), we extend the Gurson model to account for the void size effect. Meanwhile, we consider the crystal orientation effect by using MSG-CP to describe the behavior of matrix. Numerical simulation has been conducted under axisymmetric loading condition for cylindrical void and under spherical symmetric tension for spherical void. It reveals that the damage of a ductile porous material has strong orientation-dependence and size-dependence on microscale level. The traditional conclusion that the larger the void size is the faster it grows is also verified by the new model. Additionally, we add a kinematic hardening law to the MSG-CP theory, and have analyzed a hysteresic response of a single crystal under cyclic loading.
Effects of Creep Flow and Viscous Dissipation in the Slip Regime for Isoflux Rectangular Microchannels
Authors: van Rij Jennifer , Ameel Tim , Harman Todd
Published: May 2009

The effects of rarefaction on convective heat transfer and pressure drop characteristics are numerically evaluated for uniform wall heat flux rectangular microchannels. Results are obtained by numerically solving the momentum and energy equations with both first- and second-order slip velocity and temperature jump boundary conditions. The resulting velocity and temperature fields are then evaluated to obtain the microchannel Poiseuille and Nusselt numbers. In addition to the effects of rarefaction, the effects of aspect ratio, thermal creep flow, and viscous dissipation are investigated for locally fully developed Poiseuille and Nusselt numbers. The constant wall heat flux results obtained in this study are compared to constant wall temperature results obtained previously, using the same numerical algorithm, at various aspect ratios including the limiting case of parallel plate microchannels. In addition to supplying previously unreported data on slip flow convective heat transfer and pressure drop characteristics, these results verify the numerical algorithm for more complex future slip flow analyses.
Velocity and Temperature Distributions in Bipolar Plate of PEM Electrolysis Cell
Authors: Nie Jianhu , Cohen Steve , Chen Yitung , Carter Blake , Boehm Robert F.
Published: May 2009

Numerical simulations of three-dimensional water flow were performed for the purpose of examining velocity and temperature distributions in the bipolar plate of a simplified PEM electrolysis cell. The flow range in the present study is assumed to be hydrodynamically stable and steady with uniform inlet temperature. All solid wall surfaces are maintained as being adiabatically insulated except that the walls adjacent to the active area of the MEA are supplied with constant heat flux. A minimum of the peak values of mainstream velocity component in the channels develops in the middle of the plate. The maximum of these peak values appears in the channel near the exit tube. The maximum temperature develops in the channels in the center of the plate and near the exit header section. The maximum temperature decreases with increasing flowrate.
Fabrication and Simulation of Silicon Nitride Cantilever for Low Power Nano-Data-Storage
Authors: Jeong Suk-Yong , Ahn Sung-Hoon , Lee Dae-Sung , Jin Won-Hyeog , Jang Sung-Soo , Cho Il-Joo , Kim Young-Sik , Nam Hyo-Jin , Lee Caroline Sunyong
Published: May 2009

An AFM tip silicon nitride cantilever was fabricated to observe thermal characteristics in order to increase data writing speed and lower power consumption. By using time dependent resistance and temperature dependent resistance curves of heating tip in experimental results, the changes of temperature on the tip were compared with simulated data. It was found that the thermal time constant of silicon nitride cantilever was 48 μs at 4 V input for 20 μs and 37 μs at 5 V input for 25 μs. Throughout the design modification, the model which has 0.5 μm, 2:1, 1000 Ω/□ shows the lowest power consumption. By changing the heating time, the power consumption of 0.158 mW and thermal time constant of 75 ns were finally observed.
Effect of Mold Filling on the Formation of Air Gap Along the Vertical Mold Wall During Solidification of Al-Cu Alloy
Authors: Arunkumar S. , Sreenivas Rao K. V. , Prasanna Kumar T. S.
Published: May 2009

The accuracy of the numerical simulation of casting solidification largely depends on the selection of appropriate thermal boundary conditions. The estimation of heat flux at the metal-mold interface becomes difficult due to the formation of spatially and temporally varying air gap in gravity die-casting. However, the spatial variation in the formation of air gap is often neglected in most of the previous research work. In this paper, an experimental setup that involved mold filling was devised In order to study the spatial variation of air gap and its effect on the heat flux at the metal-mold interface. A Serial-IHCP (inverse heat conduction problem) algorithm was used to estimate the multiple heat flux transients along the metal-mold interface. The estimated heat fluxes at the metal-mold interface have considerable variation during the initial stages of solidification. Further, the analysis indicates that the non-conformal contact between metal and mold begins at the bottom. However, the formation of clearance gap at the metal-mold interface follows a reverse trend as it starts from the top of the vertical mold wall and progresses towards the bottom.
The Effects of Material Composition on the Thermal Conductivity of Zeolite MFI
Authors: Greenstein Abraham M. , Hudiono Yeny C. , Graham Samuel , Nair Sankar
Published: May 2009

The thermal conductivity of zeolite MFI is modeled for different silicon/aluminum ratios using lattice dynamics and relaxation time theory. The model uses the actual phonon dispersions, Slack’s model for phonon-phonon scattering, a slightly modified form of Klemens’s model for point defect scattering, and a boundary scattering term. Our results strongly suggest that the upper limit of thermal conductivity is defined by boundary-like scattering associated with the pore structure of the material. Below this limit, silicon substitution with aluminum allows effective suppression of the thermal conductivity by point defect scattering and phonon slowing mechanisms.
Flow Distribution on the Tube Side of a High Temperature Heat Exchanger and Chemical Decomposer
Authors: Kuchi Gayatri , Ponyavin Valery , Chen Yitung , Sherman Steven , Hechanova Anthony E.
Published: May 2009

Numerical simulations of a high temperature shell and tube heat exchanger and chemical decomposer (thereafter — heat exchanger) with straight tube configuration have been performed using Fluent 6.2.16 code to examine flow distribution on the tube side. The heat exchanger can be a part of sulfur iodine thermochemical water splitting cycle which is one of the most studied cycles for hydrogen production. Uniformity of the flow distribution in the heat exchanger is very critical because the flow maldistribution among the tube or shell sides can result in decreasing of chemical decomposition and increasing of pumping power. In the current study the flow rate uniformity in the heat exchanger tubes has been investigated. Simulations of the straight tube configuration, tube configuration with baffle plate arrangement and with pebble bed region inside the tubes were performed to examine flow distribution on the tube side. It was found the flow maldistribution along the tube direction is very serious with the simple tube configuration. An improvement of the header configuration has been done by introducing a baffle plate in to the header section. With the introduction of the baffle plate, there was a noticeable decrease in the flow maldistribution in the tubes. Uniformity of flow was also investigated with catalytic bed inside the tubes. A significant decrease in flow maldistribution was observed with this arrangement. But if the catalytic bed zone is created on the shell side, then the improved header configuration with a baffle plate is best suitable to avoid flow maldistribution.
Power Management in Hydraulically Actuated Mobile Equipment
Authors: Pedersen Henrik C. , Andersen Torben O. , Hansen Michael R.
Published: May 2009

The focus of the current paper is on the control of hydraulic systems when utilizing the advances that electronic control may bring with regard to power management, prioritized flow sharing and anti-stall, arising from being able to control both pump, valves and engine electronically. A simple model of a backhoe loader is first presented. Based on this model and the dynamic properties of the system, a generally applicable power management algorithm is developed based on an optimization procedure, which takes into account the dynamics of the system and different modes of operation and saturation. Finally the algorithm is verified through simulation results and the possibilities and limitations of the algorithm are discussed.
Heavy-Duty Truck: Inverse Dynamics and Performance Control
Authors: Vantsevich V. V. , Zakrevskij A. D. , Kharytonchyk S. V.
Published: May 2009

Inverse dynamics approach has been developed to optimize a highway, heavy-duty truck vehicle dynamics and performance. Using the developed approach, a math model of the multi-body truck system was developed to optimize power distributions to the drive wheels in probabilistic road conditions including macro- and micro-profiles of the road, distributions of the friction coefficient and rolling resistance. The optimization of wheel power distributions was treated as a multi-criterion problem to provide the truck with required energy/fuel efficiency, traction and velocity operational properties, turnability, stability of motion, and handling. Criteria of the listed truck operational properties were organized in a computer algorithm and computer simulations were implemented. Based on optimal combinations of wheel power distributions, an algorithm for integrated control of driveline power dividing units, wheel brakes and fuel feeding was developed.
Finite Element Modeling of Spot Welding for Advanced High Strength Steels (AHSS)
Authors: Subramaniam Sankaran , Koganti Ramakrishna , Joaquin Armando
Published: May 2009

Weldability is a critical enabler for application of new grades of steel, which have found widespread applications in the auto industry to meet new safety regulations and reduce weight of vehicles. There are a wide variety of these grades of steel which are being used across the industry. Even within a OEM the number of material and gauge combinations becomes quite large. This requires a considerable amount of testing to prove out welding feasibility of these steels. This paper discusses the use of a finite element method (FEM) to model spot welding of DP600 and correlates the results with experiments. Improved accuracy and confidence in these tools can provide a way to better understand the physics of the process and improve the weldability of these steels in a cost effective manner.
Resistance Spot Welding (RSW) of Advanced High Strength Steels (AHSS) for Automotive Body Construction
Authors: Koganti Ramakrishna , Angotti Sergio , Joaquin Armando , Jiang Cindy
Published: May 2009

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are getting popular with superior mechanical properties and weight advantages compared to mild steel materials. These new materials have significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application in future vehicle programs. Due to high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for DP600, and DP780 steels are discussed. DP600 steels were joined with two different weld equipments and three different electrodes and their influence on mechanical properties are discussed. Development work on the effect of weld tips on button size, and shrinkage voids due to different welding variables is discussed. DP780 EG steel (1.0 mm) is also joined to itself. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of 1.0 mm DP780 EG to 1.0 mm DP780 EG weld joint results are discussed.
Motion Planning of a Group of Agents Using the Homotopy Approach
Authors: Lal Mayank , Jayasuriya Suhada , Sethuraman Swaminathan
Published: May 2009

In this paper motion planning of a group of agents is done to move the group from an initial configuration to a final configuration through obstacles in 2-D. Also we introduce a new homotopy approach which uses potential fields to find paths in polynomial space. We use the homotopy approach for changing the group shape of the mobile agents and at the same time treat the group as a single agent by finding a bounding disc for it to plan the motion of the group through obstacles. A time varying polynomial is constructed, the roots of which represent the current positions of the mobile agents in a frame attached to the bounding disc. The real and imaginary parts of the roots of this polynomial represent the x and y coordinates of the mobile agents in this frame. This polynomial is constructed such that it avoids the discriminant variety or the set of polynomials having multiple roots. This is equivalent to saying that the mobile agents do not collide with each other at all times. The bounding disc is then used to plan the motion of the agents through obstacles such that the group avoids the obstacles at all times.
A Technique for the Direct Optimization of Dynamic Systems Described by Differential-Algebraic Equations
Authors: Fabien Brian C.
Published: May 2009

This paper presents a method for the optimization of dynamic systems described by index-1 differential-algebraic equations (DAE). The class of problems addressed include optimal control problems and parameter identification problems. Here, the controls are parameterized using piecewise constant inputs on a grid in the time interval of interest. In addition, the differential-algebraic equations are approximated using a Rosenbrock-Wanner (ROW) method. In this way the infinite dimensional optimal control problem is transformed into a finite dimensional nonlinear programming problem (NLP). The NLP is solved using a sequential quadratic programming technique. The paper shows that the ROW method discretization of the DAE leads to (i) a relatively small NLP problem, and (ii) an efficient technique for evaluation the function, constraints and gradients associated with the NLP problem. The paper also investigates a state mesh refinement technique that ensures a sufficiently accurate representation of the optimal state trajectory. Two nontrivial examples are used to illustrate the effectiveness of the proposed method.
Reducing Material Waste Using Six Sigma in Printed Circuit Board Assembly
Authors: Gebara Naji E. , Jawad Badih
Published: May 2009

Material waste in the Printed Circuit Board Assembly consist of parts and components that are purchased above and beyond what is required to complete a project. Controlling such material waste identified in this paper as Quantity Variance is in a direct relationship to minimizing the cost of variance that increases the profitability of each job in a low volume high mix production. This Quantity Variance occurs as defects at key steps of the manufacturing process. Six sigma is used to define, measure, analyze and control occurrences resulting in the need to purchase additional components for the completion of the order.
Dynamics of a Simplified van der Pol Oscillator Revisited
Authors: Luo Albert C. J. , Rajendran Arun
Published: May 2009

In this paper, the dynamic characteristics of a simplified van der Pol oscillator are investigated. From the theory of nonsmooth dynamics, the structures of periodic and chaotic motions for such an oscillator are developed via the mapping technique. The periodic motions with a certain mapping structures are predicted analytically for m-cycles with n-periods. Local stability and bifurcation analysis for such motions are carried out. The (m:n)-periodic motions are illustrated. The further investigation of the stable and unstable periodic motions in such a system should be completed. The chaotic motion based on the Levinson donuts should be further discussed.
Heat Capacity and Thermal Conductance Calculations for Non-Metallic Crystalline Nanowires Based on Elastic Dispersion Relations
Authors: Tong Tao , Prasher Ravi , Majumdar Arun
Published: May 2009

We evaluate the real dispersion relations of circular non-metallic crystalline nanowires based on elasticity equations and stress-free boundary condition. Based on the dispersion relations, the nanowire heat capacity (specific heat) and ballistic conductance are calculated as functions of temperature. Distinct dimensional dependence can be clearly seen as temperature varies. Transitional point between one-dimensional (1-D) and three-dimensional (3-D) behaviors is identified. Similar to previously reported studies on the nanotube systems, at very low temperatures and/or for very thin nanowires the specific heat capacity varies as T1/2 due to the dominance of the flexural modes.
Periodic and Chaotic Oscillations of Laminated Composite Piezoelectric Rectangular Plate With 1:3 Internal Resonance
Authors: Zhang Wei , Chen Li-Hua , Yao Zhi-Gang , Yang Xiao-Li
Published: May 2009

The chaotic dynamics of parametrically excited, simply supported laminated composite piezoelectric rectangular plates are analyzed, The plates are forced by transverse loads. It is assumed that different layers are perfectly bonded to each other with piezoelectric actuator patches embedded in them. Firstly, based on von Karman-type equations and third-order shear deformation laminate theory of Reddy, the nonlinear equations of motions of the laminated composite piezoelectric rectangular plates are derived. Here, we consider the piezoelectric parametric loads and in-plane parametric loads acting in both x-direction and y-direction. Then, the Galerkin’s approach is applied to convert partial differential equations to the ordinary differential equations. The method of multiple scales is used to obtain the averaged equations. Finally, based on the averaged equations, periodic and chaotic motions of the plates are found by using numerical simulation. The numerical results show the existence of periodic and chaotic motions in averaged equations. The chaotic responses are sensitive to initial conditions especially to forcing loads and the parametric excitation.
Numerical Computation of the Effects of Brownian Motion on the Effective Thermal Conductivity of Suspensions
Authors: Phelan P. E. , Pacheco J. R.
Published: May 2009

In this paper, a numerical scheme based on the immersed boundary method is used to study the motion of nano-sized particles subjected to Brownian motion and heat transfer. Our objective is to use this numerical technique as a tool to better understand the effect that Brownian forces have on the overall heat transfer process. The conventional approach to perform Brownian dynamic simulations is based on the use of a random force in the particle motion such that the fluctuation-dissipation theorem is satisfied. Our preliminary computational results suggest an increase in the thermal conductivity of the bulk fluid. Results are presented for several particles in a two-dimensional space.
Enhancement of Chaotic Mixing in Electroosmotic Flows by Random Period Modulation
Authors: Pacheco J. Rafael , Chen KangPing , Pacheco-Vega Arturo , Chen Baisong
Published: May 2009

In this paper we propose a random period-modulation strategy as a mean to enhance mixing in electroosmotic flows. This period-modulation is applied to an active mixer of an electroosmotic flow. It is shown that under such period-modulation the Kolmogorov-Arnold-Moser (KAM) curves break up and chaotic mixing is significantly enhanced. The enhancement effect increases with the strength of the modulation, and it is much reduced as diffusion is increased.
Discrete-Time H2-Optimal Control for Hydraulic Position Control Systems
Authors: Lin Yang , Shi Yang , Burton Richard
Published: May 2009

Hydraulic position control systems play an important role in industrial automation. This paper explores the application of discrete-time H2-optimal control for a hydraulic position control system (HPCS). By minimizing the H2-norm of the system, the discrete-time robust H2-optimal control both stabilizes the plant and minimizes the root-mean-square of the servo position error simultaneously. The intuitive nature of this advanced approach helps to manage the selection of design parameters, whereas, classical methods provide less insight into strategies for parameter selection and control design. Additionally, the powerful ability to address disturbances and uncertainty in the robust H2-optimal design offers a more direct alternative to the ad hoc and iterative nature of classical methods for the hydraulic servo position system. Computer simulations illustrate the design procedure and the effectiveness of the proposed method. Experimental studies which employ the H2-optimal control on a hydraulic positioning system are also conducted and the results show that the method is suitable for practical applications.
Effect of Edge Conditions on Natural Convective Heat Transfer From a Narrow Vertical Flat Plate With a Uniform Surface Heat Flux
Authors: Oosthuizen Patrick H. , Paul Jane T.
Published: May 2009

Two-dimensional natural convective heat transfer from vertical plates has been extensively studied. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be greater than that predicted by these two-dimensional flow results. Because situations that can be approximately modelled as narrow vertical plates occur in a number of practical situations, there exists a need to be able to predict heat transfer rates from such narrow plates. Attention has here been given to a plate with a uniform surface heat flux. The magnitude of the edge effects will, in general, depend on the boundary conditions existing near the edge of the plate. To examine this effect, two situations have been considered. In one, the heated plate is imbedded in a large plane adiabatic surface, the surfaces of the heated plane and the adiabatic surface being in the same plane while in the second there are plane adiabatic surfaces above and below the heated plate but the edge of the plate is directly exposed to the surrounding fluid. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. A wide range of the other governing parameters have been considered for both edge situations and the conditions under which three dimensional flow effects can be neglected have been deduced.
Coupling Particle to Continuum Regions of Particulate Materials
Authors: Regueiro Richard A.
Published: May 2009

Following atomistic-continuum coupling methods for lattice-structured materials [1, 2], a method for coupling particle to continuum regions of particulate materials is presented. The particle region is modeled using particle mechanics and the discrete element method, whereas the continuum region is modeled using linear micropolar elasticity and the finite element method. The formulation for coupling particle and continuum degrees of freedom as well as partitioning kinetic and potential energies in the overlapping domain is presented. Details of the numerical implementation and numerical examples will follow in a forthcoming paper. The method is developed to model particulate materials at their physical length scale (particle size) in regions of large relative particle motion in a computationally tractable manner.
Account for Engineered Systems Properly to Analyze Loss Scenarios
Authors: Bhimavarapu Kumar R.
Published: May 2009

Significant resources are spent by the process industry to minimize losses due to fires, explosions, toxic releases, and equipment breakdown. Risk-based justifications for improvements require the evaluation of the loss scenarios and the needed likelihood and severity reductions. A variety of concepts such as safety barriers, safe guards, safety functions, and protection layers; and many models have been developed and used in this connection. However, these concepts and models may not be conducive to account for all the risk-impacting elements consistently, which is necessary to establish scenario events and scenarios properly. Without proper scenarios, quantification of risk components particularly the likelihood may not be possible; thus, risk-based justifications could be subjective. This paper discusses an approach to identify and account for all the risk-impacting elements in terms of engineered systems, which are the basic building blocks of the process industry. Engineered systems are simply the systems necessary to operate process plants productively and safely; thus, all engineered equipment and facilities (i.e., related to hardware) as well as procedures, and their combinations constitute engineered systems. Losses occur generally when engineered systems fail. Proper identification of engineered systems facilitates identification of proper scenario events and scenarios. Accordingly, the use of engineered systems-based approach to improve the scenario-based analyses necessary for risk assessment in the process industry is promoted.
Effect of Additive on Hardness and Brittleness in Polycarbonate Films
Authors: Ahuja Suresh
Published: May 2009

Hardness and modulus of a polymer composite is known to depend on its structure, molecular weight, number of segments between entanglements and additives (filler). Nano-indentation is used increasingly as a powerful tool to determine hardness and visco-elastic modulus of polymer surfaces linear, cross-linked or composites. Hysitron Nanoindenter was used in our investigation of contact deformation of surfaces of filled polycarbonates supported on aluminum substrate. Bar coatings of polymer films were made from solution and dried all at 110C for half an hour. The results show that filled polycarbonate gives higher hardness than unfilled polycarbonate, which can give significantly different temperature dependence depending on molecular weight of the polycarbonate and structure of the filler. Depending on the type of filler and its concentration, the polycarbonate composite exhibits brittle-ductile transition at different strains. This behavior is analyzed in terms of chain mobility and free volume in the composite.
Correlation of an Acoustic Finite Element Model of the Automobile Passenger Compartment Using Loudspeaker Excitation
Authors: Sung Shung H. , Nefske Donald J. , Feldmaier Douglas A.
Published: May 2009

An acoustic finite-element model of the automobile passenger compartment is developed and experimentally assessed for predicting the sound pressure response in the compartment. The acoustic finite-element model represents both the passenger compartment cavity and the trunk compartment cavity, with the coupling between them through the rear seats for which the acoustic properties are determined from a modified “heavy air” approximation. Measurements of the sound pressure response in the passenger compartment are obtained using a specially developed loudspeaker excitation device for assessing the accuracy of the model. Comparisons are made of the predicted versus measured sound pressure response to 300 Hz for loudspeaker excitation in both the passenger and trunk compartments.
Prospective System Assessments Used to Enhance Patient Safety: Case Studies From a Collaboration of Engineers and Hospitals in Southwest Washington State
Authors: Coles Garill A.
Published: May 2009

It is no secret that healthcare, in general, has become an increasingly complicated mixture of technical systems, complex processes and intricate skilled human interactions. Patient care processes have followed this same trend. The healthcare industry, itself, has acknowledged that it is fraught with high-risk and error prone processes and cite medication management systems, invasive procedures and diagnostic methods. Complexity represents opportunity for unanticipated events, process failures and undesirable outcomes. Traditionally when a patient care process fails, accountability was focused on the individual clinician error. However, increasing, healthcare is following the lead of other high-risk industries (e.g. chemical, aerospace, nuclear, etc.) that give attention to the characteristics the overall system that contribute to the failure. The focus has shifted to identification of systemic weaknesses and vulnerabilities. Increasing the healthcare industry is using prospective system assessment methods to evaluate the high-risk systems and processes. This paper describes results of collaboration between engineers and community hospitals in Southwest Washington State between 2002 and 2007 in applying prospective system assessment methods to a range of the high-risk healthcare systems and processes. The methods used are Failure Mode Effects and Criticality Analysis and Probabilistic Risk Assessment. The two case studies presented are: 1) an interhospital FMEA on patient transfer and 2) a risk assessment of mental health patients who present themselves in a hospital Emergency Department.
Preliminary Study on Solid-State Foaming of PMMA/CNT Nanocomposites
Authors: Wang Xiaoxi , Li Wei , Kumar Vipin , Jana Soumen , Zhong Katie W. H.
Published: May 2009

Polymer nanocomposites with carbon nano tubes (CNTs) added in the polymer matrices have been shown to have improved material properties comparing to their neat forms. Foaming of polymer nanocomposites is even more interesting because these foams promise higher strength-to-weigh ratio and multifunctionality. However, many foaming results on polymer nanocomposites are inconclusive, for example, the effect of nano-additives on the bubble nucleation. In this study, solid-state foaming of pure PMMA and PMMA/CNT composite were performed. CNTs were dispersed in PMMA solution with ultrasonication. Microcellular foams were achieved in both cases. The resulted relative density and microstructures were investigated. It was found that nano carbon tubes aggregated on the cell walls of the microcellular foams. In terms of the cell size and relative density, there is no significant difference between pure PMMA and PMMA/CNT foams. Better dispersion of CNTs is needed in order to further study the CNT effect on the solid-state foaming process.
Experimental Observation and Numerical Modelling of a Laminar Double Coflow Methane/Air Diffusion Flame
Authors: Liu Fengshan , Kong Wenjun
Published: May 2009

The effect of the central air flow rate on the structure and sooting characteristics of a laminar double coflow methane/air diffusion flame was experimentally observed and recorded by a digital camera. The double diffusion flame was generated using a modified Gu¨lder laminar coflow diffusion flame burner by introducing an air flow in the centre of the fuel pipe. Numerical calculations of the double diffusion flame at different central air flow rates were conducted by solving the elliptic conservation equations of mass, momentum, species, and energy in axisymmetric cylindrical coordinates using a standard control volume method. Detailed multi-component thermal and transport properties and detailed combustion chemistry were employed in the modelling. Soot formation was modeled using a semi-empirical acetylene based model in which two transport equations for soot mass fraction and soot number density per unit mass were solved. Thermal radiation was calculated using the discrete-ordinates method and a 9-band non-grey model for the radiative properties of the CO-CO2-H2O-soot mixture. The numerical model reproduced qualitatively the experimental observations of the effect of central air flow rate on the structure and sooting characteristics.
Model-Based Data Analysis for Thin-Film Thermal Conductivity Measurement Using Microelectrothermal Test Structures
Authors: Stojanovic Nenad , Yun Jongsin , Berg Jordan M. , Holtz Mark , Temkin Henryk
Published: May 2009

We present a new method for measuring thermal conductivities of films with nanoscale thickness. The method combines a microelectrothermal test structure with a finite-element-based data analysis procedure. The test device consists of two serpentine nickel structures, which serve as resistive heaters and resistance temperature detectors, on top of the sample. The sample is supported by a silicon nitride membrane. Analytical solution of the heat flow is infeasible, making interpretation of the data difficult. To address this, we use a finite-element model of the test structure, and apply nonlinear least-squares estimation to extract the desired material parameter values. The approach permits simultaneous extraction of multiple parameters. We demonstrate our technique by simultaneously obtaining the thermal conductivity of a 280 μm by 80 μm by 140 nm thick aluminum sample and the 360 μm by 160 μm by 180 nm thick silicon nitride support membrane. The thermal conductivity measured for the silicon nitride thin film is 2.1 W/mK, in agreement with reported values for films of this thickness. The thermal conductivity of the Al thin film is found to be 94 W/mK—significantly lower than reported bulk values, and consistent both with reported trends for thin metallic films and with values obtained using electrical resistivity measurements and the Wiedemann-Franz law.