bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization Based Design of Thermoelectric Heat Pump Unit of Active Building Envelope Systems
Authors: Khire Ritesh A. , Messac Achille , Van Dessel Steven
Published: April 2008

Active Building Envelope (ABE) systems represent a new thermal control technology that actively uses solar energy to compensate for passive heat losses or gains in building envelopes or other enclosures. This paper introduces the first steps in exposing the community to this new technology, and explores an optimization based design strategy for its feasible application. The overall system is discussed, while this paper also gives particular focus to the design of a key constituent component. Namely, the collection of thermoelectric heat pumps; or, the TE unit. The latter becomes an integral part of the generic enclosure, and is a collection of thermoelectric coolers, or heaters. As a critical component of the optimization based design strategy, select computationally inexpensive approximate analytical models of generic TE coolers/heaters (TE Cooler) are developed. The optimization technique is implemented to evaluate different design configurations of the TE unit. The preliminary results indicate that the total input power required to operate the TE unit decreases as the distribution density of the TE coolers increases. In addition, the thermal resistance of the heat sink (attached to the TE cooler) plays a key role in determining the number of TE coolers required. These preliminary findings may have practical implications regarding the implementation of the ABE system.
Non Isothermal Hybrid Approach Using the Perfect Gas Law and Explicit Dynamic Finite Element Method for Modeling of Thermoforming and Blow Molding Processes
Authors: Erchiqui F.
Published: April 2008

Thermoforming of cut sheets is extensively used in the industry for various commercial applications. In this process, the sheet is heated to a softened state and subsequently deformed into the mould due to an applied pressure, a vacuum, a moving plug or a combination of these media. The thermoforming-process market is expanding to complex geometries and to a list of potential materials. In this work, I use a no isothermal hybrid approach which combines the dynamic finite element method and the thermodynamic law of perfect gases to study the effect of the temperature of the air flow on the blowing of a thin, isotropic and incompressible thermoplastic membrane. The viscoelastic behaviour of the K-BKZ model is considered. The Lagrangian formulation together with the assumption of the membrane shell theory is used. The numerical validation is performed by comparing the obtained results with the theoretical results for the HDPE grade. Moreover, the effect of the temperature on the thickness and stresses distribution is presented.
Towards a Unified In-Process Geometrical Model for Multiple Machining and Layered Manufacturing
Authors: Liu Peiling , Zhu Cheng-Feng , Song Bin , Lu Wen Feng , Lu YiQiang , Ding Xiaoming
Published: April 2008

There are many fabrication processes in modern manufacturing, but current modeling and simulation tools only simulate a few unit processes based on different geometry models. To overcome the data exchange problem between different models, this paper studies various in-process geometry models together with their working systems / prototypes for traditional manufacturing processes. Novel hybrid multiple-machining and layered manufacturing processes are presented to identify critical issues. Working towards a vision of pervasive modeling and simulation, a unified Voxel-based in-process geometry model for multiple-machining and layered manufacturing simulations is proposed and discussed.
Boiling Performance of Flourinert PF 5060 on Confined and Unconfined Wire Meshes Soldered to the Substrate
Authors: Gerlach David W. , Joshi Yogendra K.
Published: April 2008

The boiling performance of the dielectric fluorocarbon liquid PF 5060 was measured on submerged 0.9 cm square tin-plated copper and bronze wire meshes soldered to a copper block. Three mesh sizes were tested: 8 wires/cm (20 wires/inch) with 406 micron diameter, 20 wires/cm (50 wires/inch) with 229 micron diameter, and 59 wires/cm (150 × 150 wires/inch) with 66 micron diameter. The curves were measured with top of the mesh open in a pool boiling arrangement and with the mesh covered with a plate so that bubbles must exit sideways.
Dynamics Analysis of Self-Steering Railway Trucks for Assessing Curving Performance
Authors: Ahmadian Mehdi
Published: April 2008

The primary purpose of this study is to provide a qualitative analysis of the dynamics of the self-steering trucks that are commonly used for freight locomotives on improving curving performance and increasing adhesion in curves. Although there are a number of anecdotal statements on the ability of steerable trucks to reduce curving forces and increase adhesion in curves, to the best of our knowledge, there exists no study that provides a qualitative or quantitative analysis of these features of steerable trucks. Two aspects of locomotive trucks are essential for their ability to deliver small curving forces and high adhesion in curves. First, the ability to allow the axles to yaw sufficiently relative to the truck frames, such that they can hold a small angle of attack with the rail. Second, to provide sufficiently large longitudinal stiffness between the end axles and the axles and truck frame, in order to accommodate high adhesions. An equivalent stiffness analysis is used to show that the two steerable trucks that are considered for this study are far superior to conventional, three-axle, straight trucks in providing both a smaller angle of attack and a higher longitudinal stiffness for better curving and adhesion characteristics. The qualitative analysis of this study agrees with the experience the railroads have had with their self-steering trucks. The findings of this study indicate that self-steering trucks can result in lower lateral forces, accommodate tighter curves, and deliver higher adhesion in curves; without lowering the critical hunting speed of the locomotive. The results further show that the steering mechanism stiffness can have a large effect on the lateral, longitudinal, and yaw stiffness between the end axles; therefore, significantly lowering curving forces, and increasing adhesion and critical hunting speed of the truck.
Transient Analysis of an Experimental Mercury Flow Loop for SNS Validation
Authors: DeLauder Nathan P. , Ruggles Arthur E. , Riemer Bernard W. , Burgess Thomas W.
Published: April 2008

A transient fluid acoustic model is compared with experimental data obtained from induced pump trips in a mercury loop. The facility consists of a stainless steel loop filled with 19,000 kg (21 tons) of mercury that is motivated by a 41 KW (55 hp) centrifugal pump through 37 m of piping in a full transit. At nominal operation, the volumetric flow rate from the pump discharge is 1400 LPM and velocities throughout the loop range from 0.3 to 3 m/s. A computer model of the mercury loop was made using the fluid transient code from Applied Flow Technology Impulse™. Loss of power to the mercury centrifugal pump may lead to fluidhammer, in which a cavity formed in low pressure regions created downstream of the pump outlet after the pump power is lost, collapses and gives rise to a pressure pulse. Fluidhammer has been created experimentally through a series of induced trips of the mercury centrifugal pump. Pump speed, volumetric flow rates, and dynamic pressures were gathered during the transient events. This data has provided information about the initialization, magnitude, and propagation of the pressure pulses associated with fluidhammer. The data gathered from these tests is presented and compared to simulation results gained from the computer model. Pressure magnitudes found in trip simulations at normal operating conditions nearly match those found in experiments, and other trends of the time traces show reasonable agreement.
Parallel Genetic Algorithm for Design of Morphing Cellular Truss Structures
Authors: Ramrakhyani Deepak S. , Lesieutre George A. , Frecker Mary , Bharti Smita
Published: April 2008

A parallel genetic algorithm is developed for the design of morphing aircraft structures using tendon actuated compliant truss. The wing structure in this concept is made of solid members and cables. The solid members are connected through compliant joints so that they can be deformed relatively easily without storing much strain energy in the structure. The structure is actuated using cables to deform into a required shape. Once the structure is deformed, the cables are locked and hence carry loads. Previously an octahedral unit cell made of cables and truss members was developed to achieve the required shape change of a morphing wing developed at NASA. It was observed that a continuously deformable truss structure with required morphing capability can be achieved by a cellular geometry tailored to local strain deformation. A wing structure made of these unit cells was sized for a representative aircraft and was found to be suitable. This paper describes the development of new unit cell designs that fit the morphing requirements using topology optimization. A ground structure approach is used to set up the problem. A predetermined set of points is selected and the members are connected in between the neighboring nodes. Each member in this ground structure has four possibilities, 1) a truss member, 2) a cable that morphs the structure into a required shape, 3) a cable that is antagonistic and brings it back to the original shape 4) a void, i.e., the member doesn’t exist in the structure. This choice is represented with a discrete variable. A parallel genetic algorithm is used as an optimization approach to optimize the variables in the ground structure to get the best structural layout. The parallelization is done using a master slave process. A fitness function is used to calculate how well a structural layout fits the design requirements. In general, a unit cell that has lesser deflection under external loads and higher deflection under actuation has a higher fitness value. Other requirements such as having fewer cables and achieving a required morphing shape are also included in the fitness function. The finite element calculations in the fitness function can be done using either linear or nonlinear analysis. The paper discusses the different ways of formulating the fitness function and the results thereof.
Non-Equilibrium Dissolution Kinetics of Micro-Size Metal Particles in Lead-Free Solders
Authors: Faizan M. , Wang G.-X.
Published: April 2008

Soldering is the default joining process in the electronic packaging industry. Solder joints are obtained by interaction of the substrate with the molten solder. Soldering reaction and the resulting dissolution of substrate material is a complicated process. Reliability and strength of solder joints during service have always been the critical issues in electronic packaging industry. Mechanical strength of solder joints can significantly be increased by employing composite solders. These composite solders are sometimes obtained by incorporation of micro- and nano-size metal particles in the solder paste before the soldering process. Better understanding of substrate-solder interaction is important for the proper selection of the reinforcing particle size and composition. In the present research the relative importance of interface reaction and diffusion has been studied. Dissolution kinetics of a planar substrate and spherical particles has been investigated. Our results show that the dissolution is governed both by interface kinetics and long-range diffusion. Non-equilibrium behavior has been observed in the early stage of the process. It has been observed that at the early stage the dissolution process is governed by interface kinetics, while diffusion became the rate controlling mechanism at the later phase. A mathematically rigorous model has been proposed for simulating the dissolution of the substrate in the liquid lead-free solders. The study is extended to investigate the dissolution of spherical particles in molten solders. The results show that the initial particle dimension plays a critical role in the end particle size after the reflow process.
Product Information Exchange Using Open Assembly Model: Issues Related to Representation of Geometric Information
Authors: Baysal Mehmet Murat , Roy Utpal , Sudarsan Rachuri , Sriram Ram D. , Lyons Kevin W.
Published: April 2008

The objective of this paper is to discuss the main issues for product information exchange through the Open Assembly Model (OAM). The OAM model provides a base level product model that is open, simple, generic, expandable, independent of any vendor software and product development process, and capable of engineering context that is shared throughout the product lifecycle. Two of the main issues in the OAM model are the representation of geometric information of the artifacts (and assembly features) and maintenance of the consistency of the product information among relevant classes based on geometry information. This paper considers the geometry information at three levels: 1) basic geometric information of artifact with position and orientation information, 2) assembly features and their interrelations, and 3) detailed geometric information of all features in the artifact. In addition to geometric information, other relations/associations between the classes in the Unified Modeling Language (UML) based OAM model are maintained by constraints written in Object Constraint Language (OCL). This information structure in the UML and OCL is then mapped into the Extensible Markup Language (XML) for easy information exchange. XML is commonly used and supported by many softwares. Therefore, integration of XML with UML will provide an excellent tool for internet based collaboration.
Numerical Modeling of the Tissue Freezing-Thaw Cycle During Cutaneous Cryosurgery Using Liquid Nitrogen Spray
Authors: Sun Feng , Wang G.-X. , Kelly K. M. , Aguilar G.
Published: April 2008

It is common in some cryosurgical procedures to rely on freeze-thaw cycle(s) to destroy undesirable tissues. Most research in cryosurgery focuses on the freezing process and much less attention has been paid to thawing or re-warming. However, as ice melts during thawing, the extracellular solution can become locally hypotonic, driving water into cells, resulting in cell expansion and ultimately, membrane rupture. Therefore, the thermal history of the target tissue during both the freezing and thawing processes is critical for cell viability. To better understand and predict the thermal history during cryosurgery, we developed a two-dimensional numerical model to describe the complete freeze-thaw cycle during liquid nitrogen cutaneous cryosurgery. A stratified anatomical structure of human skin is considered in the model. The numerical simulation applies temperature-dependent thermal and physical properties for human skin tissue and considers the typical thermal boundary conditions for clinical practice. Parametric studies are performed to explore the influence of spray cooling, spray duration and surface heating. Results are discussed concentrating on iceball front propagation, lethal temperature isotherm evolution, tissue temperature variation and cooling rates. These results are expected to provide both quantitative and graphical support to cutaneous cryosurgery and suggest approaches to optimize current cryosurgical protocols.
Control of Liquid Impingement With Electrical Field
Authors: Feng Xin , Bryan James E.
Published: April 2008

An initial experimental study was performed to better understand the effect of various operating and geometrical parameters on mode transition in EHD spray impingement. Detailed experimental data is provided for the different modes observed with ethanol. Previous research has focused on the effects of applied voltage and volume flow rate with limited experimental data. Using high-speed digital video imaging, details of eight different spray modes are presented.
Control of Liquid-Bubble Interface to Create a Two-Phase, Dielectrophoretic Mesopump
Authors: Helberg Christopher M. , Jackson Jenny E. , Bryan James E.
Published: April 2008

A system was developed to study electrostatic force control in mesoscale and microscale fluidic phenomena. Utilizing the polarization (dielectrophoretic) force in a simple planar electrode configuration, control of a liquid-bubble interface is achieved. By applying a +dc voltage a 1Hz switching frequency to an array of four electrode pairs, pumping was produced with four fluids covering a wide range of electrical properties; the range of dielectric constant and electric conductivity was over 1 order of magnitude and 5 orders of magnitude, respectively. Simple analysis and initial experimentation provide evidence that the normal polarization stress at the liquid-bubble interface and surface tension are the primary driving force and retarding force, respectively that affect bubble motion.
Magnetorheological Measurements in Suspensions of Magnetic Nanoparticles
Authors: Chaves A. , Gutman F. , Rinaldi C.
Published: April 2008

We report measurements of the torque required to restrain a polycarbonate spindle surrounded by ferrofluid in a cylindrical container and subjected to the rotating field generated by a two-pole magnetic induction motor stator, as a function of applied field amplitude and frequency, and for various values of the geometric aspect ratios of the problem. Simultaneously, an ultrasonic method was used to measure the azimuthal velocity profiles in the ferrofluid contained in the annular gap of our apparatus. These measurements are compared to a rigorous regular perturbation solution in the small parameter Ωτ (Ω = frequency and τ = ferrofluid magnetic relaxation time) of the ferrohydrodynamic flow problem in the zero spin viscosity and linear magnetization limits.
Corrosion Prevention Compound on the Fatigue Life of 2024-T3 Aluminum Alloy
Authors: Wahab M. A. , Park J. H. , Pang S. S.
Published: April 2008

Corrosion-Prevention-Compounds (CPC) are commonly used to prevent corrosion in the aircraft industry. The presence of corrosive environment on aircraft structures has detrimental effects on the aircraft components which reduces the fatigue life and may also accelerate the crack growth rate in the structures. This is an experimental study on 2024-T3 aluminum alloy to investigate the effect of fatigue crack growth (life from threshold crack growth to final failure) using CPC on fatigue life. The corrosion fatigue with the presence of water-vapor reduces the total fatigue life. The fatigue life with the CPC treatment is shown to increase the fatigue life due to the protection from the corrosive environment containing water-vapor. Test results are obtained for various stress ratios and frequencies with and without the CPC treatment under constant amplitude fatigue loading in water vapor. The second aspect of this work is to investigate the effect of periodic overloads and the limitation in their spacing cycles on the fatigue life under constant amplitude fatigue loading. The results confirm the earlier work that the fatigue life increases due to the periodic overloads in 2024-T3 aluminum alloy. The interactions between overloads that are controlled by the spacing cycles between overloads are also examined. From scanning electron microscopic work the transition from the ductile to brittle mode is observed clearly in this experimental work.
Modeling of Displacement Micropump With Passive Check Valves
Authors: Jayatissa Ahalapitiya H. , Chintakunta Sandeep
Published: April 2008

Finite element analysis (FEA) of piezoelectrically actuated micropump was carried. The actuator was designed using a PZT (Lead zirconate titanate) layer coated on a flexural PVDF (Polyvinylede fluoride) membrane. The flow of liquid was controlled by the cantilever valves at both the inlet and outlet. The flow rate of the pump was estimated using the stroke volume due to the deflection of diaphragm. The optimum flow characteristics were estimated using the stroke volume as a function of frequency of power supply. The performance of the pump with and without the effect of valve on flow rate was also studied. The operation of the PZT actuator at higher frequencies would lead to self-heating of the material. This limitation on temperature was studied and the ways to reduce the self-heating were verified.
The Surface Plasmon Scattering Patterns of Gold Nanoparticles and Agglomerates
Authors: Venkata Pradeep Garudadri , Aslan Mustafa M. , Mengu¨c M. Pinar , Videen Gorden
Published: April 2008

Metallic nanoparticles display considerably different optical properties than those of their bulk counterparts. They have long been of interest in several novel applications, from colored glass production of medieval times to molecular-level sensors of today. Recently, there has been significant interest in characterization of such small particles via surface plasmons, for example for monitoring of the actual self-assembly purposes. For such characterization, we need scattering patterns by different type of particles and agglomerates on or near the surface. Here we present a methodology to predict the required scattering patterns of single particles and agglomerates on or near a surface subjected to surface plasmon waves. We investigate the effect of size, shape and orientation of gold nano particles on their scattering patterns both in the visible spectrum and at resonance wavelengths. The results show that the normalized scattering matrix elements (Mij) at certain observation angles and incident wavelengths provide significant information to monitor self-assembly process of gold nanoparticles on a gold substrate.
Performance Comparison of Flat Plate Collectors Fitted With Non Circular Risers With Integral Fins
Authors: Bhore V. R. , Thombre S. B.
Published: April 2008

The present study deals with comparison of experimentally determined performance characteristics of solar flat plate collectors fitted with novel designs of absorber plate involving non-circular risers with integral fins and operating under natural circulation mode. The main flow passages considered were square, triangular and semicircular in cross section. One standard solar flat plate collector with circular risers was also tested simultaneously for direct comparison. The test results indicate that the absorber fitted with the triangular sectioned risers yields the best performance in terms of the efficiency (63%), and the buoyancy induced flow per unit area (76 kg/hr-m2) from amongst the collectors investigated. It is followed by the absorbers fitted with the semicircular and square sectioned risers respectively. The standard solar flat plate collector is found to yield the lowest values i.e. 46 % and 40 kg/hr-m2 respectively.
Multiple Hypothesis Sequential Probability Test for Correlated Process With Application to System Health Monitoring
Authors: Ng Hok K. , Speyer Jason L.
Published: April 2008

Conventional Shiryayev Multiple Hypothesis Sequential Probability Test (MHSPT) can be applied only to an independent measurement sequence. We extend Shiryayev MHSPT to applications where the measurements are a correlated sequence generated by known dynamics, and is called here the MHSPTC. This test, which serves as a decision rule, is derived from a dynamic programming approach, and can be applied to announce system failure with probability from residuals generated from analytical redundancy methods. The decision policy is determined by considering cost of measurement, false alarm, and miss detection. This test announces failure disruption in minimum time when false alarm and miss detection rates are specified. The MHSPTC is implemented and verified in the health monitoring system of an automated vehicle.
Thermodynamic Analysis of a Magnetic Liquefier for Hydrogen
Authors: Rosario Luis , Rahman Muhammad M.
Published: April 2008

The aim of this paper is to present a thermodynamic analysis of a magnetic liquefier for hydrogen. A hydrogen liquefaction cycle is examined. A magnetic refrigerator, a liquid-nitrogen pre-cooling system, an expansion valve and a liquid-hydrogen separator integrate the system. The magnetic refrigerator consists of two heat exchangers and two stages of beds of magnetic materials. The analysis considered that the system operates with gaseous hydrogen entering at high pressure and ambient temperature. A fraction of this incoming flow is liquefied by the system. One magnetic material GdNi2 is used in the upper stage and another magnetic material GdPd is used in the lower stage. The heat transfer fluid for the magnetic refrigerator is helium. The beds in both stages are periodically magnetized and demagnetized and the fluid flows are arranged to meet the cycle liquefaction requirements. Sensitivity analysis has been performed to study the thermodynamic behavior of the magnetic liquefier cycle. Liquefaction efficiency, the nitrogen boil-off rate per unit mass of hydrogen, the fraction of the hydrogen gas that is liquefied and the magnetic refrigerator performance trends are evaluated. Simulations indicate that the higher the performance of the magnetic refrigerator is the higher the liquefaction efficiency of the system is with the same intermediate temperature. It was also observed that the liquefaction efficiency increases with the decrease in the nitrogen boil-off rate per unit mass of hydrogen. Magnetic liquefier exhibits a great potential by showing a very high efficiency when compared to small and large scale commercial liquefiers for hydrogen.
Element Free Structural Acoustics for Efficient Shape Optimization
Authors: Zellers Brian , Koopmann Gary , Hwang Yongsin , Naghshineh Koorosh
Published: April 2008

Optimal shape design to acoustically tailor arbitrary radiating structures is one approach to optimal structural acoustic design that has not been extensively employed due to the added complexities inherent in the grid remeshing requirements. In the research described in this paper, the acoustic superposition method is used to determine the sound power radiation objective function and relies on prescribed virtual acoustic sources to match the structural surface volume velocity. The acoustic surface pressure over each element of the discretized model is then determined via straightforward matrix multiplication. Finally, the sound power radiated can be written in terms of a set of constant independent structural basis vectors each being modified by a dependent modal participation factor. However, using structural geometry as a design variable requires that the structural volume velocity be expanded using a new set of basis vectors upon each iteration. As such, the Raleigh-Ritz Method of determining modal participation factors which modify predetermined structural basis vectors cannot be used as this original set of basis vectors has changed with the geometry iteration. Therefore, the acoustic superposition elements must be numerically revaluated for each design iteration converging to meet the objective function. This results in a computationally intensive method that degrades design efficiency. Furthermore, the possibility of element distortion must be efficiently monitored and corrected if necessary during shape movements which further complicate the optimization. As such, a new meshless acoustic method is being developed that removes the need for the costly element by element integration of traditional boundary element analysis and relies only on matrix operations to evaluate the objective function. This results in rendering shape optimization more efficient in optimal structural acoustic design. To demonstrate, using a model of a simple radiation problem, it will be shown that numerical instabilities such as singularities and nonuniqueness problems can be avoided using meshless acoustics.
Automated Assembly and Hermetic Packaging of MOEMS for Applications Requiring Extended Shelf-Lives
Authors: Popa Dan O. , Deeds Michael , Fasoro Abiodun , Beardsley Heather , Sin Jeongsik , Lee Woo Ho , Fernandez Raul
Published: April 2008

In this paper we describe two modular automated microassembly systems, along with a several packaging processes that have been integrated to produce reliable and cost-effective MOEMS devices. The automated and packaging systems consists of robotics such as pick and place, insertion and fastening, machine vision and controls, and processes such as die attach, solder reflow by laser, wire bonding and seam sealing. The target MOEMS devices are intended for applications requiring a minimum twenty year shelf-life.
Operating Parameters of Catalysts With Catalytic Converter for Compression Ignition Engine
Authors: Walke P. V. , Deshpande N. V. , Daddamwar L. P.
Published: April 2008

Testing of catalytic converter with exhaust gas re-circulation system for diesel engine to reduce pollute gases is chosen for present work. The emphasis is given on hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen. The catalytic converter was developed with variations of catalyst plates. Perforated plates of copper and combination of copper oxide and cerium oxide (CeO2 +CuO) were used as the catalyst. Copper spacer was used in between plates to vary the distance. Secondary air was injected into the converter to aid oxidization of HC and CO. Experimental study was carried out on computerized kirloskar single cylinder four stroke (10 B.H.P, 7.4 KW) diesel engine test rig with an eddy current dynamometer. The converter was tested with various combination with exhaust gas re-circulation (EGR) system. There are some improvements in the reduction and conversion efficiency of HC & CO. Exhaust gas re-circulation has proved to be effective in reducing NOx.
A New Hierarchical Technique for the Multiscale Modeling of Carbon Nanostructures
Authors: Mahdavi Arash , Mockensturm Eric
Published: April 2008

We present a new hierarchical modeling technique called the Consistent Atomic-scale Finite Element (CAFE´) method [1]. Unlike traditional approaches for linking the atomic structure to its equivalent continuum [2-7], this method directly connects the atomic degrees of freedom to a reduced set of finite element degrees of freedom without passing through an intermediate homogenized continuum. As a result, there is no need to introduce stress and strain measures at the atomic level. This technique partitions atoms to masters and salves and reduces the total number of degrees of freedom by establishing kinematic constraints between them [5-6]. The Tersoff-Brenner interatomic potential [8] is used to calculate the consistent tangent stiffness matrix of the structure. In this finite element formulation, all local and non-local interactions between carbon atoms are taken into account using overlapping finite elements (Figure 1b). In addition, a consistent hierarchical finite element modeling technique is developed for adaptively coarsening and refining the mesh over different parts of the model (Figure 2a, 2b). The stiffness of higher-rank elements is approximated using the stiffness of lower-rank elements and kinematic constraints. This process is consistent with the underlying atomic structure and, by refining the mesh, molecular dynamic results will be recovered. This method is valid across the scales and can be used to concurrently model atomistic and continuum phenomena so, in contrast with most other multiscale methods [4-7], there is no need to introduce artificial boundaries for coupling atomistic and continuum regions. Effect of the length scale of the nanostructure is also included in the model by building the hierarchy of elements from bottom up using a finite size atom cluster as the building block (Figures 2a, 2b). In this method by introducing two independent field variables, the so-called inner displacement is taken into account (Fig. 3b). Applicability of the method is shown with several examples of deformation of carbon nanostructures such as graphene sheet, nanotube, and nanocone, subjected to different loads and boundary conditions.
Monte Carlo Schemes for Radiative Transfer in Media Represented by Particle Fields
Authors: Wang Anquan , Modest Michael F.
Published: April 2008

Monte Carlo ray-tracing schemes are developed for the evaluation of radiative heat transfer for problems, in which the participating medium is represented by discrete point-masses, such as the flow field and scalar fields in PDF Monte Carlo methods frequently used in combustion modeling. Photon ray tracing in such cases requires that an optical thickness is assigned to each of the point-masses. Two approaches are discussed, the Point Particle Model (PPM), in which the shape of particle is not specified, and the Spherical Particle Model (SPM) in which particles are assumed to be spheres with constant radiation properties. Another issue for ray tracing in particle fields is the influence region of a ray. Two ways of modeling a ray are proposed. In the first, each ray is treated as a standard volume-less line. In the other approach, the ray is assigned a small solid angle, and is thus treated as a cone with a decaying influence function away from its center line. Based on these models, three different interaction schemes between rays and particles are proposed, i.e., Line-SPM, Cone-PPM and Cone-SPM methods, and are compared employing several test problems.
Assessing the Sustainability of Technological Developments: An Alternative Approach of Selecting Indicators in the Case of Offshore Operations
Authors: Khan Ibrahim , Islam M. R.
Published: April 2008

In general, ‘sustainability’ implies accountability for effects on the natural environment and to future generations. This accountability should be extended at least to the whole Earth (in space) and several generations (in time). If this criterion is implied, most of the widely accepted technological developments are not sustainable. Moreover, conventional evaluation methods of sustainability using inappropriate indicators usually misrepresent unsustainable technologies as ‘sustainable’. In this study we developed a framework for analyzing indicators of sustainable technological developments. Problems and misconceptions about conventional indicators/indices selection were identified and discussion was carried out about how they mislead in measuring the real progress in environmental and socio-economic developments. Following the proposed framework, a set of indicators were analyzed and selected in the case of offshore hydrocarbon operations. To select these indicators, the ‘multi-criteria analysis’ method was used and was found advantageous when applied in a complex and stochastic system, such as the marine environment. The selected set of indicators were evaluated in terms of their degree of importance by simply ranking each indicator, following a modified semantic and finally appropriate indicators were sorted out based on the cognitive mapping analyses. This indicator selection process helps us discard misleading indicators and selecting appropriate sustainability indicators. Correct indicators will be useful to evaluate status of sustainability and will lead to achieve the overall objective of sustainable developments.
Innovative Configurations of Large Scale Heat Pipes
Authors: Sheehan Jessica , Jordan Donald , Queheillalt Douglas T. , Norris Pamela M.
Published: April 2008

A large-scale heat pipe is one of many possible solutions to the modern day problem of quickly dissipating high amounts of concentrated heat. While heat pipes are a proven technology, little research has been directed at large-scale heat pipe systems. Two configurations of large-scale heat pipes are investigated in this study. The two configurations examined were a 2’ × 2’ heat spreader plate (a type of heat pipe) and an innovative heat pipe system that combines traditional heat pipes and heat spreader plates. The heat spreader plate, when tested, quickly becomes isothermal and works as a traditional heat pipe. This demonstrates the ability of this large-scale heat pipe configuration to work effectively to spread out high amounts of deposited heat. The experimentation on the innovative heat pipe system gave similar results, showing that the configuration works as a traditional heat pipe.
Simulation of Anthrax Spore Transport and Inactivation in a Room: Scaling Analysis
Authors: Soni Sankalp , Farouk Bakhtier , Haas Charles N.
Published: April 2008

Decontamination of large indoor spaces and buildings following release of biological agents is challenging, as the response to the fall 2001 anthrax-release events indicate. The ability to efficiently and rapidly decontaminate rooms/buildings is limited by the lack of quantitative understanding of the behavior of agent transport, and decontaminants. In response to any new releases it would be necessary to rapidly determine the optimal way to decontaminate the enclosed spaces. In the present study, we numerically simulate a biological agent (anthrax spores) transport and its inactivation by a decontaminant (chlorine dioxide). Such simulations can help us in deciding on decontamination strategies and also in better designs of the buildings and the associated air circulation system to minimize the risks in case of potential agent release. Furthermore, the study also determines the impact of scaling on predicted behavior of the agent distribution and disinfection process. From numerical simulations, a relationship for the inactivation time is obtained as a function of room geometry, ventilation rate, initial number of anthrax spore release, disinfectant injection rate and reaction kinetics. Such a relationship would help in determining decontamination strategies and in optimization of the decontamination processes.
The Characterization of Underfill-Passivation Interface Under Monotonic and Fatigue Loading and Its Application to Flip Chip Reliability Prediction
Authors: Mahalingam Saketh , Tonapi Sandeep , Sitaraman Suresh K.
Published: April 2008

Flip chip packaging technology is an attractive technique to achieve mechanical and electrical interconnection between the silicon chip and the substrate. Solder joint reliability in flip chip on organic board (FCOB) is enhanced by underfill application. The failure of solder joints in a flip chip package is usually associated with underfill delamination, esp. from the chip passivation. In this work, the fracture toughness of this interface is characterized for a novel no-flow underfill material using an innovative residual stress induced decohesion (RSID) test. Numerical modeling of the chip passivation-underfill interface indicates that the delamination will not progress under monotonic loading. However, the progress of delamination occurs under repeated thermal cycling. An empirical Paris law for underfill delamination has been developed and has been applied to predict delamination in actual flip chip packages. A reasonable agreement between the two is shown.
Single Pixel Evaluation of Microchannel Flows
Authors: Wereley Steve , Meinhart Carl , Gui Lichuan , Tretheway Derek , Sud Arjun
Published: April 2008

Recently a new μPIV interrogation algorithm has been proposed in which the interrogation window size is reduced to a single pixel. Such small interrogation window sizes are possible using correlation averaging to increase the effective particle concentration to levels required for correlation analysis to succeed. The random error exhibits the expected behavior of decreasing roughly in proportion to N−1/2 while the bias error exhibits unexpected peak-locking behavior with zero bias error at integer and half integer pixel displacements and maximal errors at one-quarter and three-quarter pixel displacements. Accompanying experiments show the potential of this technique but have not yet been sufficiently refined to confirm this unexpected bias error behavior.
Direct Cyclic Method for Solder Joint Reliability Analysis
Authors: Du Zhen-Zhong , Wang Jianfeng , Fan Xuejun
Published: April 2008

Low-cycle fatigue is a common failure mechanism in solder joints of a BGA in electronics packaging industry. Cyclic thermal loading leads to stress reversals and the accumulation of inelastic strain in the joints. In this paper the direct cyclic technique implemented in ABAQUS [1] has been used to predict the stabilized response of a BGA model subjected to cyclic thermal loading and cyclic bending loading respectively. The results are compared with the classical incremental simulation. Significant performance gains with very good accuracy of the direct cyclic approach are clearly demonstrated.
Strength and Fracture of a Multifunctional Polystyrene Nanocomposite
Authors: Ayewah Daniel O. , Davis Daniel C. , Lagoudas Dimitris C. , Krishnamoorti Ramanan
Published: April 2008

A polystyrene polymer has been reinforced with single wall carbon nanotubes (SWNTs) to effect multifunctional capabilities. The SWNTs are produced by the HipCo process and are subsequently dispersed in the polystyrene resin matrix. The dispersion of the SWNTs in the polystyrene is enhanced by the use of a surfactant and composite samples at 0.0%, 0.1%, 0.2% 0.3% and 1.0% SWNT by weight are made. A multifunctional material is defined as a material with at least one additional property other than mechanical properties, and the desire is that the mechanical properties are not deteriorated due to the added nano-constituents. In this study SWNT reinforced polystyrene nano-composites are evaluated for their electrical conductivity as a function of SWNT weight percentage. The reinforced polystyrene nanocomposites are then evaluated for static strength, ductility and fracture properties to determine the effect of the nano-constituents on these mechanical properties.
Material Orientations and Geometric Effects in Piezoelectric Actuators
Authors: Wimmer Stephanie A. , DeGiorgi Virginia G.
Published: April 2008

Piezoelectric materials are active materials that deform in response to both electrical and mechanical loadings. Traditional piezoelectric actuators are designed to exploit this deformation by aligning the material poling axes with the loading axes. However for complex loading or complex geometry this alignment may not maximize the desired actuation due to the anisotropic piezoelectric and elastic properties. A computational study of material and loading axes misalignment was completed to examine the performance of piezoelectric components. The study used finite element analysis to model difference geometries; a simple cylinder, an ASTM E8 tensile specimen, and a customized ASTM E8 tensile specimen. This study looked at electrical only and mechanical only loading. The material axes for each component is rotated from being aligned with the loading axes to various angles. The effect of rotating the material axes is discussed. Variations in stress, electric fields and deformations are noted.
The Relations Between Entropy and Energy of Black-Body Radiation
Authors: Gaggioli Richard A.
Published: April 2008

The entropy content of electromagnetic ("black-body") radiation at equilibrium in an enclosure is represented, on a per unit volume basis, by s = [4/3]aT3 and the internal energy content by u = aT4, so s = [4/3]u/T. The entropy transfer rate Sτ associated with emission from the radiation is related to the internal energy trans-fer rate Q by Sτ = Q/T. In both cases, content and flux, the entropy is proportional to energy divided by temperature. But, in one case the proportionality factor is [4/3] and in the other it is unity. The question has been raised, "Why, this difference?" The following develop-ment explains the source of the difference.
Thermal Radiative Transport in Dense Absorbing and Scattering Nano and Micro Particulate Media
Authors: Prasher Ravi
Published: April 2008

Dispersion relation (relation between frequency and wave vector) for electromagnetic wave is obtained in dense (high volume fraction of particulates) nano/micro particulate media using effective field approximation (EFA) and quasi crystalline approximation (QCA) with Percus-Yevick distribution function. This work is the extension of the previous work by the author where absorption was assumed to be negligible (Prasher, R.S., 2005, J. Heat Transfer, Vol. 127, pp. 903-910). The particulates are both scattering and absorbing. Nano/micro particles are considered due to their promise for future applications such as nanofluids and also for current technologies such as fluidized and packed beds combustors. Only Rayleigh regime is investigated which is a good approximation for nano and micro particles assuming that the photon wavelength is much larger than the size of nano and micro particles. Comparison of photon velocity and effective attenuation based on EFA and QCA are made. Results show that heat flux and temperature predictions made by models in the literature for multiple and dependent scattering and absorption are not very accurate as these models do not take the modification of equilibrium emissive power due to the modification of photon velocity into account.
Fabrication and Characterization of MEMS Deformable Mirrors for Adaptive Optics
Authors: Park Hyunkyu , Horsley David
Published: April 2008

A bimorph deformable mirror (DM) for use in ophthalmologic adaptive optics is presented. The fabrication process and the results of characterization of the DM are described. Interferometric measurements of the DM surface shape and voltage-to-displacement characteristics are shown. The response of the DM to a step voltage input is measured using a commercial laser Doppler vibrometer (LDV). Experimental measurements of the DM are compared with both finite-element and analytical models. Analysis of the experimental measurements compared to the theoretical model will be used to design and fabricate an optimized DM for vision science.
Dynamic Stability of a Base-Excited Thin Beam With Top Mass
Authors: Mallon Niels J. , Fey Rob H.-B. , Nijmeijer Henk
Published: April 2008

This paper deals with a base-excited clamped-clamped vertical thin beam carrying a top mass. The thin beam is considered to be inextensible and initially not perfectly straight. Based on Taylor series expansions of the inextensibility constraint and the exact curvature, and by using one or more basis functions, a semi-analytical model is derived. This model is numerically validated through a comparison with quasi-static and modal analysis results obtained using finite element modelling. The steady-state nonlinear dynamics of the base-excited beam are investigated using numerical continuation of periodic solutions and bifurcations. Using these numerical tools, the dynamic stability of the beam is investigated for various parameter settings, including the effect of nonlinear damping. The continuation of bifurcations appears to be very suitable to determine whether or not parametric resonance occurs for certain parameter settings.