bluuebunny/crossref_metadata_2025 huggingface dataset:
A Micro-Damage Model for High Velocity Impact Using Combined Viscosity and Gradient Localization Limiters
Authors: Abu Al-Rub Rashid K. , Voyiadjis George Z. , Palazotto Anthony N.
Published: April 2008

During dynamic loading processes, large inelastic deformation associated with high strain rates leads, for a broad class of ductile metals, to degradation and failure by strain localization. However, as soon as material failure dominates a deformation process, the material increasingly displays strain softening and the finite element computations are considerably affected by the mesh size and alignment. This gives rise to a non-physical description of the localized regions. This paper presents theoretical and computational frameworks to solve this problem with the aid of nonlocal gradient-enhanced theory coupled to visco-inelasticity. Constitutive equations for anisotropic thermo-viscodamage (rate-dependent damage) mechanism coupled with thermo-hypoelasto-viscoplastic deformation are developed in this work within the framework of thermodynamic laws, nonlinear continuum mechanics, and nonlocal continua. Explicit and implicit micro-structural length scale measures, which preserve the well-posedness of the differential equations, are introduced through the use of the viscosity and gradient localization limiters.
Holism, Biomimicry and Sustainable Engineering
Authors: Reap John , Baumeister Dayna , Bras Bert
Published: April 2008

Socially beneficial, profitable products that restore or at least leave the environment undamaged (i.e. sustainable products) remain an elusive goal. Emulation of the inherently sustainable living world through biomimetic design potentially offers one approach to creating sustainable or, at least, less unsustainable products. In this article, one learns, however, that current approaches to biomimicry do not necessarily lead to such ends. Examination of research and practice reveals a reductive mindset that limits biomimicry’s applicability within the context of sustainable engineering. To remove this limitation, this article proposes a holistic view of biomimicry that goes beyond imitation of a few features of a particular organism. A holistic view of biomimicry involves incorporation of life’s general characteristics in design and application of these characteristics across multiple spatial, temporal and organizational scales of engineering influence. The article initiates the development of holistic biomimicry as a guiding framework for designers interested in utilizing biomimicry’s potential as a sustainable design tool.
On-Line Adaptive Control of a Farm Tractor by Compensation of Parameter Variations
Authors: Gartley Evan R. , Bevly David M.
Published: April 2008

An adaptive control technique for the control of a farm tractor during low levels of excitation and at low velocities is presented. An analysis of the data is conducted to determine when it is safe to adapt. A cascaded Kalman Filter is presented to estimate the slope of the DC gain of the steer angle to yaw rate transfer function with respect to velocity and to provide faster updates of position. Given this parameter, the controller gains will be scheduled based on a lookup table of predetermined values that were calculated from system identification tests.
Towards Sustainable “Product and Material Flow” Cycles: Identifying Barriers to Achieving Product Multi-Use and Zero Waste
Authors: Kumar Vishesh , Bee Danny J. , Shirodkar Prasad S. , Tumkor Serdar , Bettig Bernhard P. , Sutherland John W.
Published: April 2008

Material and energy resource consumption is on the rise in both the industrialized and developing world (e.g., countries like India and China). In order to sustain this growth and provide resources for future generations, there is a need to design products that are easy to recover and recondition, thus enabling multiple use cycles. Processes are needed that can achieve this multi-use while producing zero (or very near zero) waste. There exist a number of barriers and challenges to achieving this vision of multi-use with zero waste; one such challenge is the development of a product recovery infrastructure that will minimize short-term impacts due to existing products and will be robust enough to recover products of the future. This paper identifies the barriers to developing such a recovery and reuse infrastructure. The aim is to achieve product multi-use and zero waste.
Fiber Scanner Modeling as the Basis for New Scanning Fiber Endoscopes
Authors: Kundrat Matthew J. , Reinhall Per F. , Brown Christopher M. , Seibel Eric J.
Published: April 2008

In order to develop a one-millimeter outside diameter endoscope we have moved away from using a bundle of optical fibers that are an integral part of current endoscopes. To achieve the field of view and the resolution requirements in spite of the small diameter we are using a single optical fiber that acts as a scanning source. Photo detectors positioned along the side of the scanning fiber detect the backscattered light and software then reconstructs the image on a monitor. The single optical fiber moves in a spiral scan pattern that is produced using a four quadrant piezoelectric tube as the actuator. The optical fiber is fed through the center of the piezoelectric tube and glued into place.
Characterization and Modeling of Thermal Buckling in Eccentrically Loaded Microfabricated Nickel Beams for Adaptive Cooling
Authors: McCarthy Matthew , Tiliakos Nicholas , Modi Vijay , Freche´tte Luc
Published: April 2008

The design, fabrication and testing of micromachined nickel beams buckling under thermal loading will be presented in this paper. The focus will be on characterizing key design parameters important to the implementation of electroplated nickel beams as the actuation mechanism in a thermally adaptive microvalve. An analytical model of the thermal buckling phenomena has been developed and validated with test results from electroplated nickel beams with slight eccentricities. Highly nonlinear deflection versus temperature curves were predicted by the closed form model and match well with experimental measurements. Buckling deflections of more than 50μm were achieved at actuation temperatures under 100°C. The nickel beam fabrication process will be presented, as well as various fabrication related issues impacting the actuation capabilities of the beams.
Treatment Protocols for Managing Transurethral Thermal Therapy for Benign Prostatic Hyperplasia
Authors: Paolini Lara , Thamire Chandrasekhar
Published: April 2008

Application of thermal therapy using microwave or ultrasound applicators is becoming increasingly popular as a minimally invasive treatment for benign prostatic hyperplasia (BPH). Successful management of the therapy using such methods requires an accurate estimation of the thermal dosage. The purpose of this study is to theoretically evaluate the thermal damage caused by different heating sources for different values of thermal doses and operating parameters. Using a 3-D finite differences method, the Pennes bio-heat transfer equation is solved for selected operating parameters. Necrosis zones are then determined from published necrosis data for prostatic tumor cells. Sample results are presented in terms of the temperature contours and necrosis zones. Results indicate that heating time and power level are the most important parameters in creating the desired necrosis zones, while coolant parameters strongly affect the temperatures of the sensitive urethra and serve as constraints for protocol parameters.
Effective Range of Micro and Synthetic Jets for Flow Control
Authors: Koklu Mehti , Erbas Nurhak , Baysal Oktay
Published: April 2008

Effectiveness of two-dimensional synthetic jet is studied using numerical simulations. A Navier-Stokes (NS) solver for moving and deforming meshes has been modified to investigate numerically the diaphragm-driven flow in and out of two synthetic jet cavity geometries. Compressible flow simulations are required for rarefied gas flows to accurately predict the micro flow field. The solver is modified to accommodate slip wall boundary condition proposed in literature for micro scale flow problems. The piezoelectric-driven diaphragm of the cavity is modeled in a realistic manner as a moving boundary to accurately compute the flow inside the jet cavity. The primary focus of the proposed paper will be on the analysis of the design space determined by the geometric and flow-type design variables that identify the effectiveness of the synthetic jet by means of the orifice jet velocity and local jet momentum rate. The design variables are the membrane oscillation frequency (f), membrane oscillation amplitude (A), orifice width (d), and membrane width (W). The present computations for jet discharging into quiescent medium reveal that these variables have determining effects on the flow control parameters, which are the jet exit velocity, local momentum rate, as well as vortex shedding from the orifice.
A Computationally Efficient Dynamic Model for the Simulation of the Stewart Platform
Authors: Oghbaei Mojtaba , Anderson Kurt S. , Perry Edward J.
Published: April 2008

This paper presents an implementation of a novel dynamic formulation on multibody systems involving closed loops. The formulation allows the treatment of time, appearing within the equations of motion, as a variable in much the same manner as having been done by the finite element community on the spatial coordinates. As a consequence, the resulting equations appear together in a single all-encompassing set of algebraic equations which may be solved simultaneously, yielding the system state for all times within the time interval considered. The approach conceivably allows the problem to be parallelized over both space and time, resulting in a far greater level of coarse grain parallelization. As the Stewart Platform is a heavily constrained system with its spatial domain being much smaller than the temporal domain of simulation, it will serve as a perfect example to test the implication of this method. Simulation results obtained from traditional dynamic techniques will be used for verification purposes.
Multi-Layered Mobile Sensor Network With Robot Team
Authors: Lee Jae-Yong , Jayasuriya Suhada
Published: April 2008

This paper presents a concept and its application of the dynamic multi-layered sensor network for gathering environment information. The architecture of the system is composed of sensor layer, physical layer, and communication layer. Sensor layer is the combination and the network of the sensor components in each sensor node. A sensor node has multiple numbers of sensors, and a number of robots for the mobile sensor network. Each mobile robot plays a role of mobile base for a sensor node, and consists of physical layer. We discuss the formation of the multi-layered sensor network, which is active, adaptive, and task oriented in the surrounding environment. As each sensor node consists of multiple numbers of heterogeneous sensors, sensor combination is not restricted to one particular objective or task. This fact allows the network to be multi-functional. Same kind of sensors can establish ad-hoc sensor network, while different kind of sensors fuse the data for improved interpretation of the environment. Experiments with mobile sensors nodes are conducted and illustrated to show the concept of the multi-layered mobile sensor network.
Development and Tribochemical Evaluation of Biobased Antiwear Additive
Authors: Erhan Sevim Z. , Sharma Brajendra K.
Published: April 2008

Seed oils are renewable resources, environmentally friendly non toxic fluids, pose no work place health hazards and are readily biodegradable. The amphiphilic character of these oils makes them an excellent candidate as lubricants and as specialty chemicals. Industrial application of seed oils is limited due to poor thermo-oxidative stability, poor low temperature fluidity, and other tribochemical degrading processes that occur under severe conditions of temperature, pressure, shear stress, metal surface and environment. This work describes the development and tribochemical evaluation of seed oil based antiwear additive through chemical modification. The current process retains the seed oil structure, eliminates poly-unsaturation in the molecule, and adds polar functional groups that significantly improve adsorption on metal surfaces. These compounds also contribute to the formation of protective films through chemical reaction during the tribochemical process. Comparative tests with commercial products demonstrate its effectiveness.
A Comparison of Approximate vs. Exact Geometrical Representations of Roughness for CFD Calculations of CF and ST
Authors: Bons J. P. , McClain S. T. , Wang Z. J. , Chi X. , Shih T. I.
Published: April 2008

Skin friction (cf) and heat transfer (St) predictions were made for a turbulent boundary layer over randomly rough surfaces at Reynolds number of 1 × 106. The rough surfaces are scaled models of actual gas turbine blade surfaces that have experienced degradation after service. Two different approximations are used to characterize the roughness in the computational model: the discrete element model and full 3-D discretization of the surface. The discrete element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection on the flat part of the surface and the convection from each of the roughness elements. Correlations are used to model the roughness element drag and heat transfer thus avoiding the complexity of gridding the irregular rough surface. The discrete element roughness representation was incorporated into a two-dimensional, finite difference boundary layer code with a mixing length turbulence model. The second prediction method employs a viscous adaptive Cartesian grid approach to fully resolve the three-dimensional roughness geometry. This significantly reduces the grid requirement compared to a structured grid. The flow prediction is made using a finite-volume Navier-Stokes solver capable of handling arbitrary grids with the Spalart-Allmaras (S-A) turbulence model. Comparisons are made to experimentally measured values of cf and St for two unique roughness characterizations. The two methods predict cf to within ±8% and St within ±17%, the RANS code yielding slightly better agreement. In both cases, agreement with the experimental data is less favorable for the surface with larger roughness features. The RANS simulation requires a two to three order of magnitude increase in computational time compared to the DEM method and is not as readily adapted to a wide variety of roughness characterizations. The RANS simulation is capable of analyzing surfaces composed primarily of roughness valleys (rather than peaks), a feature that DEM does not have in its present formulation. Several basic assumptions employed by the discrete element model are evaluated using the 3D RANS flow predictions, namely: establishment of the mid-height for application of the smooth wall boundary condition, cD and Nu relations employed for roughness elements, and flow three-dimensionality over and around roughness elements.
Investigation of Deformation Characteristics of Micropins Fabricated Using Microextrusion
Authors: Krishnan Neil , Cao Jian , Kinsey Brad , Parasiz Sunal A. , Li Ming
Published: April 2008

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions of the order of less than 1 mm. At this length scale the deformation of the workpiece is dominated by the so-called ‘size effects’, e.g. material properties and frictional behavior vary at small length scales. In recent extrusion experiments performed to produce sub-millimeter sized pins having a base diameter of 0.76 mm and an extruded diameter of 0.57 mm, certain interesting deformation characteristics were observed. When a workpiece with a relatively large grain size of 211 μm was used, the billet tended to deform inhomogenously, and the extruded pins showed a tendency to curve. This phenomenon was not seen when workpieces with a smaller grain size of 32 μm were used. It is believed that the relative size and orientation of the large grains in the 211 μm grain size sample are responsible for this behavior and the aim of this paper is to investigate this phenomenon. Microindentation tests were performed on micropins extruded from workpieces of both grain sizes to obtain a measure of the distribution of induced strain. The results obtained from this analysis show that the deformation characteristics of the extruded pins are dominated by the size and location of specific grains leading to a non-uniform distribution of plastic strain and measured hardness.
A Screw-Theoretic Analysis Framework for Payload Manipulation by Mobile Manipulator Collectives
Authors: Bhatt Rajankumar , Tang Chin Pei , Abou-Samah Michel , Krovi Venkat
Published: April 2008

In recent times, there has been considerable interest in creating and deploying modular cooperating collectives of robots. Interest in such cooperative systems typically arises when certain tasks are either too complex to be performed by a single agent or when there are distinct benefits that accrue by cooperation of many simple robotic modules. However, the nature of the both the individual modules as well as their interactions can affect the overall system performance. In this paper, we examine this aspect in the context of cooperative payload transport by robot collectives wherein the physical nature of the interactions between the various modules creates a tight coupling within the system. We leverage the rich theoretical background of analysis of constrained mechanical systems to provide a systematic framework for formulation and evaluation of system-level performance on the basis of the individual-module characteristics. The composite multi-d.o.f wheeled vehicle, formed by supporting a common payload on the end-effectors of multiple individual mobile manipulator modules, is treated as an in-parallel system with articulated serial-chain arms. The system-level model, constructed from the twist- and wrench-based models of the attached serial chains, can then be systematically analyzed for performance (in terms of mobility and disturbance rejection.) A 2-module composite system example is used through the paper to highlight various aspects of the systematic system model formulation, effects of selection of the actuation at the articulations (active, passive or locked) on system performance and experimental validation on a hardware prototype test bed.
An Applied Method of Instruction for Feedback Control Systems and Mechatronics to Undergraduate Engineering Students at the University of Central Florida
Authors: Sherman Matthew , Leonessa Alexander
Published: April 2008

By using a hands-on method of instruction, as opposed to one solely based on theory, students are able to grasp information contained within a subject in an easier manner and retain it at a greater rate. Through the application of this premise it is possible to bridge the gap between educational theory and industrial application. The purpose of this research is to develop an applied method of instruction of both Feedback Control Systems and Mechatronics to undergraduate Aerospace and Mechanical Engineering students at the University of Central Florida (UCF). This will in-turn yield an enhanced union between the classroom and real world application.
A New Approach for Modeling of Fatigue Crack Growth in Welded Cruciform and Curve T Joint Structures
Authors: Alam Mohammad S. , Wahab Muhammad A.
Published: April 2008

A new approach for the simulation of fatigue crack growth in welded joint has been developed and the concept has been applied to welded cruciform and curve T-joints. The phenomena of crack propagation and interface debonding can be regarded as the formation of new surface. Thus, it is possible to model these problems by introducing the mechanism of surface formation. In the proposed method, the formation of new surface is represented by interface element based on the interface potential energy. The properties of this interface element represent the bonding strength of the material. As the cyclic load continues, the bonding strength decreases between the interacting surfaces and the crack propagates slowly. Based on this concept, an ANSYS code has been written for the simulation of crack propagation. Using this code, fatigue crack growth rate and fatigue crack propagation life of 2-D FEM models of welded cruciform and curve T-joints for different stress/load ratios have been analyzed and presented in this paper. The method is relatively simple compared to other conventional FEM method and save computer time significantly. The predicted results are compared with experimental results and good agreement has been achieved.
System Integration and Design Optimization of Passenger Airbag Shapes
Authors: Fu Yan , Xiao Baohua , Chen Weigang , Li Guosong , Yang Ren-Jye
Published: April 2008

Passenger airbag is an important vehicle passive safety device to protect occupant safety. The shape of a passenger airbag plays an important role in determining how well the device is capable of protecting occupants. Traditionally, the airbag shape is designed manually, using a trial and error method. The lines of a passenger airbag shape are first drawn. After meshing the airbag, it is inserted into multiple occupant restraint system models. Then, run the multiple occupant models for different crash scenario and evaluate the occupant injury numbers. The process is iterated until a design meets all occupant injury criteria. The manual process is not only time-consuming, but also has little chance to find the optimal solutions if any. This paper first automates the whole design process using an advanced integration tool. Advanced optimization method is then used to find the optimal airbag shape systematically. A real-world frontal impact application with different dummies, belted and/or unbelted, at different impact speeds is used to demonstrate the methodology.
Preparation of Porous Nitinol Material by Hot-Isostatic Pressing
Authors: Xu Zhigang , Waters Cindy K. , Rajaram Gukan , Sankar Jag
Published: April 2008

In this preliminary study, porous nitinol is fabricated using elemental Ni and Ti powders. The elemental powders were mixed at the ratio of 50:50 at.% by ball milling in preparation for pressing and sintering. The compacts were obtained by uniaxial pressing with a steel die of 12.5mm diameter. They were then subjected to hot isostatic pressing (HIPing) in an argon environment. The sintering pressure, temperature and time were varied in order to acquire porous nitinol. Porosity as high as 47.3% was achieved, which was benefited by partial liquid phase sintering. X-ray diffraction and energy dispersive spectroscopy (EDS) demonstrated that diffusion in the samples sintered at the temperature higher than the eutectic point was nearly complete, while the diffusion will take much longer time to complete at temperature lower that the eutectic point.
Reduction of the 2-D Heat Equation for Straight Fins of Uniform Profile Into a Quasi 1-D Equation
Authors: Campo Antonio
Published: April 2008

Owing to the combined action of transverse convection and longitudinal conduction, the temperature in fins varies longitudinally since the transversal temperature change is practically insignificant. Textbooks on heat transfer widely employ the quasi one-dimensional approximation for the analysis of straight fins of uniform profile [1-6]. Unfortunately, justification of this simplistic approach has been based on the prevalent criterion of fins owing large slenderness ratios, i.e., large length and small thickness. This route is a mere geometric consideration that obviates the heat path implications that are inherent to fins. Beginning with the formulation with the 2-D heat conduction equation, the primary aim of this paper is to develop a systematic mathematical procedure for the validity of the quasi 1-D approximation in terms of two parameters: (1) the transverse Biot number and (2) the slenderness ratio.
Modeling of Gas-Liquid Flow in Pressure Swirl Atomizers
Authors: Ibrahim Ashraf A. , Jog Milind A.
Published: April 2008

Pressure swirl or simplex atomizers are commonly used in a number of industrial applications for liquid atomization, including fuel injection systems for gas turbine engines, spray drying, and paint sprays. Computational modeling of the two-phase flow in the atomizer coupled with a non-linear analysis of instability of liquid sheet exiting from the atomizer has been carried out. The Volume-of-Fluid method is employed to determine the two-phase gas-liquid flow inside the atomizer. Results are validated using available experimental data for film thickness at exit, spray angle, and discharge coefficient. The predictions of breakup length using the non-linear model are compared with available experimental measurements which show excellent agreement. The effect of flow conditions and nozzle geometry on the flow field and sheet breakup are investigated. The coupled internal flow simulation and sheet instability analysis provides a comprehensive approach to modeling atomization from a pressure-swirl atomizer.
Noise Studies in Implanted Piezoresistors
Authors: Davenport Andrew A. , Lim Paul , Pruitt Beth
Published: April 2008

Noise in piezoresistors can be divided into two types: Johnson or white noise and 1/f noise. Johnson noise is uniform across all frequencies and depends on the resistance and temperature. 1/f noise is a conductance fluctuation that has been shown to be related to piezoresistor fabrication parameters such as anneal temperature and surface effects. This study presents a collection of controlled piezoresistor fabrication runs with associated noise data and design rules and operation conditions for noise reduction in piezoresistors.
Theory and Application of Localized Vibration Control Strategy in Cable-Suspended Membrane Space Structures
Authors: Sakamoto Hiraku , Park K. C.
Published: April 2008

The present study explores both structural and controller design to attenuate vibration in large membrane structures especially due to low-frequency harmonic excitations. It is very difficult for membrane structures to suppress the low-frequency vibration induced by flexible support structures, because a lightly pre-stressed membrane has extremely low mode frequencies and little damping effect. The present study proposes the use of web-like perimeter cables around a membrane, and the application of simple and lightweight active controllers only along the web cables. This strategy successfully suppresses the membrane vibration when the web-cable configuration is appropriately tailored. Both linear and nonlinear finite-element analyses exhibit a clear tradeoff between structural mass and control efficiency.
Effect of Vent Aspect Ratio on Unsteady Laminar Buoyant Flow Through Rectangular Vents in Large Enclosures
Authors: Sleiti A. K. , Kumar Ranganathan
Published: April 2008

The effects of vent aspect ratio on oscillatory flow regime through a horizontal opening were studied numerically. The physical model consisted of a vertical rectangular enclosure divided into two chambers by a horizontal partition. The partitions contained a slot that connected the two chambers. The upper chamber contains cold air and the lower chamber contains hot air. A density differential due to the different temperatures drives the interaction between the two chambers. The opposing forces at the interface between the two chambers create a gravitationally unstable system, and an oscillating exchange of fluid develops. Results were obtained for cases with L/D=1, 0.5, and 2.0, where L represents the thickness of the partition and D represents the slot width of the opening in the partition. Results indicate that the flow exchange increases with partition thickness L/D=0.5 and decreases for L/D=2. The frequency of the oscillatory flow pattern is also examined for the different cases. Sudden bursts of upflow with a corresponding downflow have been documented and compared with experimental observations in the literature. The time traces of velocity and temperature fields for this flow regime reveal interesting mechanisms, which have been explained.
Significance Level of Factors for Different Airflow Management Configurations of Data Centers
Authors: Shrivastava Saurabh , Sammakia Bahgat , Iyengar Madhusudan , Schmidt Roger
Published: April 2008

Data centers are among the highest energy consuming facilities and are projected to continue to increase in their power consumption for the foreseeable future. Due to the increase of computing power and the decrease in available floor space, maintaining the reliability of the electronic equipment in data centers is a big thermal challenge and, cannot be achieved solely by increasing the cooling capacity of the room. The overall thermal performance of data centers is highly dependent upon the thermal architecture of the facility. This paper presents numerical results of a parametric study, carried out for seven, fairly common, candidate configurations available for the air ducting design for data centers. Among the many factors associated with the data center thermal performance, three main factors at different levels have been selected to characterize their effect. The factors studied are ceiling height, tile flow rate and the location of the return vents. The numerical modeling is performed using a commercially available computational fluid dynamics (CFD) code based on the finite volume approach. This study also includes a summary of the statistical analysis carried out on the data obtained from the numerical parametric analysis, to determine the significance level of each of the individual factors and their interactions, on the thermal performance of the data center. The approach used here is to take an Analysis of Variance (ANOVA) approach, as a tool for determining the significance level of the different variables that affect the overall data center thermal performance. The tile flow rate is found to have significant effect on the thermal performance of all data center configurations studied.
Shock-Induced Chemical Reactions in Multi-Functional Structural Energetic Intermetallic Nanocomposite Mixtures
Authors: Narayanan V. , Lu X. , Hanagud S.
Published: April 2008

Shock induced chemical reactions of intermetallics or mixtures of metal and metal-oxides are also used to synthesize new materials with unique phases and microstructures. These materials are also of significant interest to the energetics community because of the significant amount of heat energy released during chemical reactions when subjected to shock and/or thermal loading. Binary energetic materials are classified into two categories— metal/metal oxides and intermetallics. When these materials are synthesized at a nano level with binders and other structural reinforcements, the strength of the resulting mixture increases. Thus, these materials can be used as dual-functional binary energetic structural materials. In this paper, we study the shock-induced chemical reactions of intermetallic mixtures of nickel and aluminum of varying volume fractions of the constituents. The chemical reaction between nickel and aluminum produces different products based on the volume fraction of the starting nickel and aluminum. These chemical reactions along with the transition state are modeled at the continuum level. In this paper, the intermetallic mixture is impact loaded and the subsequent shock process and associated irreversible processes such as void collapse and chemical reactions are modeled in the framework of non-equilibrium thermodynamics. Extended irreversible thermodynamics (EIT) is used to describe the fluxes in this system and account for the associated irreversible processes. Numerical simulations of the intermetallic mixture are carried out using finite difference schemes.
Integration of Sub-Wavelength Nanofluidics With Photonic Crystals
Authors: Erickson David , Emery Teresa , Rockwood Troy , Scherer Axel , Psaltis Demetri
Published: April 2008

“Optofluidics” represents the marriage of optics, optoelectronics and nanophotonics with fluidics. Such integration represents a new approach for dynamic manipulation of optical properties at length scales both greater than and smaller than the wavelength of light with applications ranging from reconfigurable photonic circuits to fluidically adaptable optics to high sensitivity bio-detection currently under development. The capabilities in terms of fluidic control, mixing, miniaturization and optical property tuning afforded by micro-, nano-fluidics combined with soft lithography based fabrication provides an ideal platform upon which to build such devices. Here we present our technique for integrating soft lithography based nanofluidics with e-beam lithography defined silicon-on-insulator photonic crystals. We demonstrate nanofluidic addressability of single, sub-wavelength, defects within the planar photonic crystal and the dynamic tuning of the guided mode. In this paper we focus on the fabrication, integration and experimental details of this work.
Characterization of an Anechoic Wind Tunnel Facility
Authors: Mathew Jose , Bahr Chris , Sheplak Mark , Carroll Bruce , Cattafesta Louis N.
Published: April 2008

Acoustic characterization of an anechoic wind tunnel facility at the University of Florida is presented. A previously existing and ISO 3745 validated 100 Hz anechoic chamber is upgraded to incorporate an open-jet anechoic wind tunnel facility suitable for airframe noise studies. The design and preliminary characterization results at 17 m/s was initially presented in reference 1. This paper presents new acoustic characterization data with an empty test section for test section speeds up to UTS = 31.2 m/s. These new measurements show the overall SPL from 100 Hz–20 kHz ranges from 51 dB (re 20 μPa) at 13.4 m/s to 73 dB at 31.2 m/s.
Avoidance of Multiple Obstacles for a Mobile Robot With Nonholonomic Constraints
Authors: Liang Yi , Lee Ho-Hoon
Published: April 2008

In this study, a decoupled controller, consisting of a force controller and a torque controller, is designed to achieve a smooth translational and rotational motion control of a group of nonholonomic mobile robots. The proposed controller also solves the problem of obstacle avoidance, where obstacles with arbitrary boundary shapes are taken into account. Since the tangential direction of obstacle boundary is adopted as the guiding direction of a robot, the proposed controller allows a mobile robot to escape from a concave obstacle, while the robot could be trapped with most of the conventional obstacle avoidance algorithms.
Predictive Surface Generation and Characterization for Cylindrical Turning Processes
Authors: Kovvur Yashpal , Ramaswami Hemant , Anand Sam
Published: April 2008

This paper presents a generalized simulation based approach for generation and characterization of turned surfaces based on process parameters and manufacturing errors. The presented model shows that with proper analytical modeling along with appropriate process monitoring system (force signals, vibration signals, spindle motion error signals etc.,) a comprehensive surface generation model can be developed. First, the tool nose geometry and cutting-force induced vibrations are superimposed to obtain the cutting tool path. Next, the information obtained from spindle motion errors is used to analytically formulate the position of each point on the machined surface. Regression models are fit to establish the relationship between form error / surface roughness and input parameters. The simulation-based approach presented here provides a quantitative bridge between process parameters/manufacturing errors and surface characterization metrics. Such a scheme would allow manufacturing engineers to pre-select processes, parameters, and capable machines to achieve design specification. This model will allow engineers to proactively control the influence of machining parameters on product quality through computer simulation, and, thus, “do things right the first time.”
Contact Thermal Lithography
Authors: Schmidt A. , Chen X. , Chen G.
Published: April 2008

Contact thermal lithography is a method for fabricating patterns based on thermal effects. In contrast to photolithography, where resolution is limited by the wavelength of light used in the exposure process, thermal lithography is limited by thermal diffusion. A traditional metal-glass photomask is brought into contact with a wafer coated with a thermally sensitive polymer. The mask-wafer combination is flashed briefly with high intensity light, causing the metal features to heat up and conduct heat locally to the polymer. The polymer cross-links due to the temperature rise and forms an image of the mask. Simple models are presented to analyze the heating process and select appropriate geometries and heating times. In addition, an experimental version of a contact thermal lithography system has been constructed. Early results from this system are presented, along with suggestions for future development.
Microelectromechanical Wavelength-Selective Switching for Integrated Optics
Authors: Waller Laura , Takahashi Satoshi , Nielson Gregory N. , Seneviratne Dilan , Tuller Harry , Barbastathis George
Published: April 2008

In this paper, we present design, fabrication, and test results of a novel wavelength-selective MEMS switch for integrated optics. The device is based on switching of a ring resonator add-drop filter by use of an electrostatically-actuated MEMS bridge. We have demonstrated the wavelength-dependant switching capabilities of a prototype device; however, the residual stress in the bridge caused sagging of the bridge and high insertion loss to the optical output. Therefore, we are investigating the use of titanium nitride (TiN) for the MEMS bridge material. TiN has ideal characteristics both mechanically and electrically. It can also be annealed to lower the residual stress to almost zero. We have fabricated the MEMS bridge with TiN and done some preliminary experiments on the structure. The results show promise for the use of this material in our device, and more generally as a structural material. We have also designed closed-loop feedback control for precision positioning of the bridge. This enables this device to tune the selected wavelength over one full channel (30nm) for use as a tunable optical filter. The feedback scheme is based on using the bridge as one electrode of a capacitive sensor, and simulations indicate that the bridge position can be controlled to 2.5pm accuracy. Modifications of the device could also be used as a variable optical attenuator.
Reliability Study of Package Stacking Under Thermomechanical Conditions
Authors: Zhu Jiansen , Ishibahsi Kazuo , Reinikainen Tommi
Published: April 2008

With the increased requirements for smaller size and more functions, hand held devices will use more and more small components to reduce the PWB areas. One of the solutions is stacked package. There are two kinds of stacked packages: one is die stacking and the other is package stacking. The package stacking is a more flexible solution for device manufacturers because the packages to be stacked could come from different vendors. All the packages can be tested separately before stacking so that there is no need for device manufacturers to acquire good dies or intellectual properties for die testing. In this study, the focus will be on the package stacking. The package stacking can be ASIC and memory stacking or memory and memory stacking. Three different stacked packages are selected for this study. Here the focus is on FEA modeling and simulation method for package stacking. Finally, the simulation results are compared with the results of thermal cycling test. A reasonable correlation is achieved based on current simulation method.
Hybrid Simulation Method for PWB Level Drop Tests
Authors: Zhu Jiansen , Hussa Esa , Okura Juscelino , Shetty Santosh
Published: April 2008

PWB level drop tests are widely used as a standard test method to evaluate the reliability of PWB and packages under drop conditions (JEDEC Standard JESD22-B104-A). The drop height and test setup need be adjusted in order to achieve the requirements of a peak shock of 1500g and an impulse duration of 0.5 ms. Generally, the ground need be covered with a thin layer of rubber pad to absorb some of the impact energy. However, this rubber pad will bring challenges for modelling due to large deformation, nonlinear hyperelasticity, and contact. And sometimes, it may also cause the convergence problem. Therefore, a hybrid drop simulation method was developed. This hybrid method can not only circumvent the difficulties mentioned, but also increase the efficiency and reduce the CPU time of PWB drop simulation. When simulating a PWB board level drop test, generally, not only the PWB and the components assembled on it need be modelled, but also the drop vehicle, rubber pad, and ground should be included in the model. For the hybrid drop simulation, however, only part of drop vehicle need be modeled and there is no need to model the ground and the contact between the ground and the drop vehicle. Then an acceleration time curve measured from drop test is applied to the hybrid model so that the responses of the model will mimic the real drop situation. In this way, not only the simulation time is reduced due to smaller model sizes, but also can some difficulties related to large deformation, contact, and nonlinear material properties be avoided. Finally, a comparison of a bare PWB and a populated PWB drop cases was used to validate this hybrid drop simulation method. A reasonable correlation was achieved.
Pressure Sensitive Paint for Acoustic Pressure Fluctuations
Authors: Virgin Chris A. , Carroll Bruce F. , Cattafesta Louis N. , Schanze Kirk S. , Kose Mohammet E.
Published: April 2008

Full-field luminescent pressure sensors are commonly referred to as Pressure Sensitive Paint (PSP). In this paper, the suitability of PSP for the detection of acoustic pressure fluctuations is evaluated. Single point measurements utilizing a photomultiplier tube are performed in an acoustic plane wave tube capable of generating pressure levels up to 164 dB SPL for frequencies from 500 to 2100 Hz. The PSP coating employed is platinum meso-tetra(pentafluorophenyl) porphrine [PtTFPP] in poly(tBS-co-TFEM). Comparisons between a 1/4″ Bru¨el & Kjær type 4138 condenser microphone and the PSP detection system are used to evaluate the PSP system in both the time and frequency domains. The frequency response and linearity of the optical system is established and the high frequency attenuation is characterized. Experimental characterization indicates a dc sensitivity of 5.68 μV/Pa, a noise floor of 127 dB SPL and a frequency response of −2.5 dB/octave and a 45° phase delay. PSP shows the ability to avoid saturation and nonlinearities at higher sound pressure levels.
Optimization of the Adsorber in an Adsorption Solar-Powered Cooling System
Authors: Ranes Anne , Phelan Patrick , Pacheco Rafael , Frantzis Anastasios , Metchop Lionel
Published: April 2008

The adsorption solar-powered cooling system is one of several types of solar-powered cooling systems currently under development. Increasing the efficiency and decreasing the cost of this system will make it a commercially viable alternative to traditional refrigeration systems. The objective of this project was to optimize the adsorber in the adsorption system. A mathematical model of the refrigerant distribution within a cylindrical adsorber was developed using equations from Chua et al. [1]. The simulation revealed effects of varying design parameters on the theoretical refrigerant mass flow rate, which is directly proportional to the system refrigeration capacity. These results indicated parameter values to be used in designing the adsorber. It was found that decreased particle radius, decreased bed porosity, increased pipe radius, increased adsorber radius, and increased fin thickness all positively affect the performance of the adsorption system. Further simulation and experimental trials are recommended to verify these results.
3D Membrane Electrode Assemblies (MEAs) for Direct Methanol Fuel Cells (DMFCs)
Authors: Tse Laam Angela , Rosen David W.
Published: April 2008

Passive Micro-Direct Methanol fuel cells (micro-DMFCs) can be the power supply solution for the next generation of handheld devices if high volumetric power densities can be achieved. One approach to improve the volumetric power density of passive DMFC designs is to increase the reactive area without a corresponding increase in overall volume by patterning MEAs with corrugated 3-D geometries. In this paper, geometric analysis is presented that demonstrates significant active area gain in fuel cell MEAs patterned with high aspect ratio corrugations. A thermoforming process was used to pattern MEAs with 3-D corrugated geometries using aluminum molds. In order to perform functional tests on 3D corrugated MEAs, the fuel and oxidant reservoirs have been redesigned to accommodate the special packaging requirements of the 3D MEAs. Electrodes were modified to serve as the current collectors and also provided backing layers for catalyst. The simplified design avoids the large clamping force and high strength requirements of the endplate material in order to minimize the electrical contact resistance between the electrodes and the current collectors. Finally, the potential power density gain from the 3D MEAs is illustrated.
Transient Analysis on Hygroscopic Swelling Characterization Using Sequentially Coupled Moisture Diffusion and Hygroscopic Stress Modeling Approach
Authors: Zhou Jiang , Tee Tong Yan , Zhang Xueren
Published: April 2008

One of the challenges for the hygroscopic swelling characterization is to investigate the impact of non-uniform moisture distribution across the specimen using currently available metrologies. Our recent studies have shown that the current averaged approach might overestimate the coefficient of hygroscopic swelling as much as 250%. In our previous analysis, however, the hygroscopic stress induced deformation has not been taken into consideration. As a matter of fact, due to non-uniform moisture distribution during the test, the total measured deformation includes two parts—one is from the hygroscopic swelling itself, and the other is from the hygroscopic stress induced deformation. This paper provides a comprehensive study on the impacts of non-uniform moisture distribution and the effect of hygroscopic stress by using a sequentially coupled moisture diffusion and hygroscopic stress modeling approach. The results show that the hygroscopic stress induced displacement is relatively small, although the elastic strain caused by the hygroscopic stress accounts for about one third of the total strain. The results in our previous study are proved to be acceptably accurate, even through the hygroscopic stress induced deformation is neglected in the previous analysis.
The Tonatiuh Software Development Project: An Open Source Approach to the Simulation of Solar Concentrating Systems
Authors: Blanco Manuel J. , Amieva Juana M. , Mancillas Azael
Published: April 2008

The Tonatiuh project is underway at the University of Texas at Brownsville under the DOE-NREL Minority University Research Associate (MURA) Program Subcontract. It intends to improve the cost-effectiveness of solar energy technologies by advancing the state-of-the-art of the simulation tools available for the design and analysis of solar concentrating systems. The project includes the design, development, implementation, verification and validation of Tonatiuh: an open-source advanced object-oriented program, that using distributed computing, Monte-Carlo Ray tracing, and the best 3-D user interface technologies available today, will provide a sophisticated and efficient software environment for the design and analysis of solar concentrating systems. This paper presents an overview of the Tonatiuh Software Development Project, emphasizing the software design aspects of the project, and the scientific relevance of the program.