bluuebunny/crossref_metadata_2025 huggingface dataset:
Designing for Rollover Impacts With Narrow Objects
Authors: Herbst Brian R. , Meyer Steven E. , Oliver Arin A. , Bell Lauren D. , Forrest Stephen M.
Published: August 2012

While some debate has existed in the literature regarding the relationship between roof crush and occupant injury, the United States (U.S.) National Highway Traffic Safety Administration (NHTSA) has identified an increased safety benefit in improving roof strength and has mandated new higher roof crush resistance requirements. Frequently, roof impacts occur in rollover crashes when a vehicle travels off the lanes of the roadway and impacts various types of narrow objects along the roadway edge such as light poles, utility poles and/or trees. A previously reported tilt-test device and methodology is presented along with a new pendulum-test device and methodology, both of which allow for dynamic, repeatable impact evaluation of vehicle roof structures with narrow objects. The data collected includes not only residual crush, but also dynamic vehicle instrumentation and high speed video analysis. Two series of full vehicle tests are reported which represent each of the methodologies. The testing conditions for each series was determined based upon analysis of a real-world narrow object rollover impact. Each testing series allows for analysis of the damage resulting from the narrow object impact to the roof structure for a production vehicle as well as one that has been structurally reinforced. Results demonstrate that the reinforced roof structure significantly reduced the roof deformation compared to that of the production roof structure. The input energy of each test and resulting damage patterns can be used as both a reconstruction tool and structural assessment test.
Development and Modeling of Water Driven Stage
Authors: Nakao Yohichi , Sano Toshiaki , Nagashima Midori , Suzuki Kenji
Published: August 2012

The water driven stage that is developed for ultra-precision machine tools is presented. The stage is designed for the diamond turning of small precise parts, such as various small lenses or mirrors. The moving table of the water driven stage is supported by water hydrostatic bearings. The stage is driven by the water hydraulic piston-cylinder mechanism that is designed inside the table. A feature of the stage is that the driving force by the piston-cylinder mechanism acts on the center of gravity of the moving table, minimizing undesirable pitching and yawing motions. In order to investigate the characteristics of the stage, a mathematical model of the water driven stage is derived. Performances of the water driven stage are examined through experiments and calculations. The present study verifies that the feed motion needed for the diamond turning operations can be obtained by supplying few flow rate of water, several tens milliliters per minutes. Stiffness of the water hydrostatic bearing is also experimentally investigated. The result shows that stiffness is approximately 330 N/μm if the supply pressure was 0.5 MPa.
A Tri-Plate Variable Capacitor for Electrostatic Energy Harvesting
Authors: Oxaal John , Kempitiya Asantha , Hella Mona , Borca-Tasciuc Diana-Andra
Published: August 2012

Electrostatic power generators employ micro-fabricated variable gap capacitors to harvest mechanical vibration energy and have applications in wireless sensors networks [1]. This paper investigates a new tri-plate architecture for an in-plane, gap-closing, electrostatic micro-generator. Unlike double-plate designs, which rely on a half sweep movement of the movable electrode from a relative extreme displacement to a central position [1], the tri-plate design allows a full sweep of the movable electrode from opposite relative displacement extremes. This results in a significantly larger capacitance ratio that can increase power output by 40% over a comparable double plate design. Dynamic simulations in Simulink are used to determine the displacement of the movable electrode in order to verify design practicality and calculate power output.
CFD Modeling of Plate Louvered Fin Heat Exchangers
Authors: Medina Julio , Bula Antonio J. , Valencia Guillermo
Published: August 2012

The flow and thermal field for Brazed Plate Fin Heat Exchanger (BPFHE) at the air side is presented in this study. Three-dimensional simulations of computational fluid dynamics were developed on a triangular section channel for the heat exchanger considered. The simulation of the fin is done for a given geometry and compared with experimental data presented by other authors, then a plane is raised keeping the original geometry and louver walls are included. The air-side performance of the heat exchanger and the hydraulic behavior is evaluated by calculating the Colburn (j) and frictional (f) factor. The result for the fin showed a deviation close to 3% when compared to experimental data for similar geometries from Keys & London. The results show how the turbulence highly increases the heat transfer phenomena.
Comparison of the Non-Equilibrium Predictions of Quantum Thermodynamics at the Atomistic Level With Experimental Evidence
Authors: Smith Charles E. , von Spakovsky Michael R.
Published: August 2012

Experimental evidence is presented and compared with theoretical predictions from Quantum Thermodynamics, (QT) to examine whether or not the claims of QT are consistent with the existence and generation of entropy at atomistic scales. QT makes the assertion that entropy is an intrinsic property of matter in the same way that inertial mass, energy, and momentum are and must, thus, exist even for single particles. Entropy as defined by QT is a measure of the distribution of a system’s internal energy at any given instant of time amongst the available internal degrees of freedom, i.e., the energy eigenlevels of the system. In this paper, it is shown that QT predicts the internal relaxation of a 5-level rubidium system that is consistent with the experimental data and not explained by current theory, i.e. by Quantum Mechanics. In addition, it is demonstrated that the decay of so-called “cat states” for single ions that are contained in Paul traps and that interact with a heat reservoir is also consistent with the idea of the existence of entropy and entropy generation at atomistic scales. This is accomplished by comparing experimental data with the predictions made using an extension of the equation of motion of QT that allows for heat interactions.
Conversion of Glycerine to Synthesis Gas and Methane by Film Boiling
Authors: Kuo Wei-Chih , Avedisian C. Thomas , Tsang Wing
Published: August 2012

This paper presents a new approach for promoting thermal decomposition reaction of subcooled liquids. It is based on establishing film boiling of the liquid. The process is illustrated by converting aqueous glycerine to synthesis gas (a mixture of carbon monoxide and hydrogen) and methane. A horizontal tube is immersed into a pool of aqueous glycerine (water weight fractions of 3% and 10%) and film boiling is established on the tube. Because of the large temperature drop that occurs across the vapor film that surrounds the tube, the potential exists to drive pyrolytic or thermal cracking reactions at high temperature but in a comparatively cold bulk liquid. The reaction products are transported away from the tube under the action of buoyancy. The reactor volume essentially forms by itself solely as a result of heating the tube.
Optimal Design of Micro-Turbine Cogeneration Systems for the Portuguese Buildings Sector
Authors: Martins Lui´s B. , Ferreira Ana C. M. , Nunes Manuel L. , Lea˜o Celina P. , Teixeira Senhorinha F. C. F. , Marques Francisco , Teixeira Jose´ C. F.
Published: August 2012

The use of combined heat and power (CHP) systems to produce both electric and thermal energies for medium-size buildings is on the increase, due to their high overall efficiency, high energy prices and political and social awareness. In this paper, an energy-economic study is presented. The main objective is to implement an analysis that will lead to the optimal design of a small cogeneration system, given the thermal power duration curve of a multi-family residential building. A methodology was developed to obtain this curve for a reference B-class building located in the North of Portugal. The CHP unit is based on a micro gas-turbine and includes an Internal Pre-Heater (IPH), typical of these types of small-scale units, and an external Water Heater (WH). A numerical optimization method was applied to solve the thermo-economic model. The mathematical model yields an objective function defined as the maximization of the annual worth of the cogeneration system. A purchase cost equation was used for each major plant component that takes into account size and performance variables. Seven decision variables were selected for the optimization algorithm, including performance of internal gas-turbine components and electrical and thermal powers. The results show that, the revenue from selling electricity to the grid and fuel costs have the greatest impact on the annual worth of the system. The optimal solution for the small CHP is sensitive to fuel price, electricity feed-in-tariff, capital cost and to the thermal load profile of the building. High European energy prices point towards future micro gas-turbines with better electrical efficiencies, achieved via a higher pressure-ratio compressor and turbine inlet temperature.
Non-Linear Analysis of Energy Absorption Systems Under Impact Loads Through FEM
Authors: Ledesma-Orozco E. R. , Diosdado-De la Pen˜a J. A. , Pe´rez–Soto G. I. , Salazar-Garibay A. , Reveles-Arredondo J. F. , Villalobos-Llamas G. , Dura´n-Rese´ndiz P.
Published: August 2012

This paper presents the non-linear simulation of the impact on a structure with different energy absorption systems using finite element models. A comparison of the damage caused to the structure in case of impact without implementing energy absorption system, and implementing energy absorption systems based on bistable structures, polystyrene foam and aluminium foam are shown here in. The results demonstrate the advantages of using energy absorption systems on structures under impact loads.
Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 1—Design Considerations and Development of a Multiphase Model
Authors: Mazumder A. K. M. Monayem , Wang Ting , Khan Jobaidur R.
Published: August 2012

A mild gasification process has been developed to provide an innovative form of clean coal technology, which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. The objectives of this study are to (a) describe the features and design considerations of this mild gasifier and (b) develop a multiphase computational model to guide the design of the mild-gasifier by investigating the thermal-flow and gasification process inside a conceptual mild gasifier. Due to the involvement of a fluidized bed, the Eulerian-Eulerian method is employed to calculate both the primary phase (air) and the secondary phase (coal particles). Multiphase constitutive equations developed from kinetic theory are employed for calculating the effective shear viscosities, bulk viscosities, and effective thermal conductivities of granular flows to simulate the hydrodynamic and thermal interactions between the solid and gas phases. Multiphase Nativer-Stokes equations and seven global reaction equations with associated species transported equations are implementd to simulate the mild gasification process. Part 1 of this paper documents the design principle of the mild gasifier as well as the development of the computational model starting from single phase, then using multiple phases, and finally including all reactions in the multiphase flow.
Thermal Fracture of Oxidized Polydimethylsiloxane and its Implications in Soft Lithography
Authors: Tooley Wes W. , Feghhi Shirin , Han Sangyoon J. , Wang Junlan , Sniadecki Nathan J.
Published: August 2012

During the fabrication of nanopost arrays for measuring cellular forces, we have observed surface cracks in the negative molds used to replicate the arrays from a silicon master. These cracks become more numerous and severe with each replication such that repeated castings lead to arrays with missing or broken posts. This loss in pattern fidelity from the silicon master undermines the spatial resolution of the nanopost arrays in measuring cellular forces. We hypothesized that these cracks are formed because of a mismatch in the coefficient of thermal expansion (CTE) of PDMS and its oxidized surface layer. To study the fracture of PDMS due to thermal effects, we treated circular test samples of PDMS with oxidizing plasma and then heated them to cause surface cracks. These cracks were found to be more abundant at 180 °C than at lower temperatures. Finite element analysis of a bilayer material with a CTE mismatch was used to validate that thermal stresses are sufficient to overcome the fracture toughness of oxidized PDMS when heated to a curing temperature for PDMS. As a consequence, we have ascertained that elevated temperatures are a significant detriment to the reproducibility of nanoscale features in PDMS during replica molding.
Numerical Investigation of the Performance of a Roadside Safety Barrier Located Behind the Break Point of a Slope
Authors: Mongiardini M. , Reid J. D.
Published: August 2012

Numerical simulations allow engineers in roadside safety to investigate the safety of retrofit designs minimizing or, in some cases, avoiding the high costs related to the execution of full-scale experimental tests. This paper describes the numerical investigation made to assess the performance of a roadside safety barrier when relocated behind the break point of a 3H:1V slope, found on a Mechanically Stabilized Earth (MSE) system. A safe barrier relocation in the slope would allow reducing the installation width of the MSE system by an equivalent amount, thus decreasing the overall construction costs. The dynamics of a pick-up truck impacting the relocated barrier and the system deformation were simulated in detail using the explicit non-linear dynamic finite element code LS-DYNA. The model was initially calibrated and subsequently validated against results from a previous full-scale crash test with the barrier placed at the slope break point. After a sensitivity analysis regarding the role of suspension failure and tire deflation on the vehicle stability, the system performance was assessed when it was relocated into the slope. Two different configurations were considered, differing for the height of the rail respect to the road surface and the corresponding post embedment into the soil. Conclusions and recommendations were drawn based on the results obtained from the numerical analysis.
Conceptual Design of Photobioreactor for Algae Cultivation
Authors: Pupo Oscar R. , Garci´a Samira , Valencia Guillermo , Bula Antonio
Published: August 2012

Algae have created a lot of interest in recent years due to their high potential for yielding oil that might be used for biodiesel production while capturing CO2 and helping clean the environment. However, to reach high productions, more efficient photobioreactors are required. Different kinds of photobioreactors configurations have been proposed but only a few of them show high productivity levels. This article presents a comparison among various promising photobioreactors by evaluating the light regime, mass transfer and scale up to achieve an efficient operation of mass algae cultures. Finally, a promising configuration for reaching high productivity is determined.
Rheological Study on Multiple Fiber Suspensions for Fiber Reinforced Composite Materials Processing
Authors: Zhang Dongdong , Smith Douglas E. , Jack David A. , Montgomery-Smith Stephen
Published: August 2012

This paper studies the rheological properties of a semi-dilute fiber suspension for short fiber reinforced composite materials processing. For industrial applications, the volume fraction of short fibers could be large for semi-dilute and concentrated fiber suspensions. Therefore, fiber-fiber interactions consisting of hydrodynamic interactions and direct mechanical contacts could affect fiber orientations and thus the rate of fiber alignment in the manufacturing processing. In this paper, we study the semi-dilute fiber suspensions, i.e. the gap between fibers becomes closer, and hydrodynamic interactions becomes stronger, but the physical/mechanical contacts are still rare. We develop a three-dimensional finite element approach for simulating the motions of multiple fibers in low-Reynolds-number flows typical of polymer melt flow. We extend our earlier single fiber model to consider hydrodynamic interactions between fibers. This approach computes the hydrodynamic forces and torques on fibers by solving governing equations of motion in fluid. The hydrodynamic forces and torques result from two scenarios: gross fluid motion and hydrodynamic interactions from other fibers. Our approach seeks fibers’ velocities that zero the hydrodynamic torques and forces acting on the fibers by the surrounding fluid. Fiber motions are then computed using a Runge-Kutta approach to update fiber positions and orientations as a function of time. This method is quite general and allows for solving multiple fiber suspensions in complex fluids. Examples with fibers having various starting positions and orientations are considered and compared with Jeffery’s single fiber solution (1922). Meanwhile, we study the effect of the presence of a bounded wall on fiber motions, which is ignored in Jeffery’s original work. The possible reasons why fiber motions observed in experiments align slower than those predicted by Jeffery’s theory are discussed in this paper.
Simulation of Combustion in a DI Diesel Engine Operating on Biodiesel Blends
Authors: Varde Keshav S. , Veeramachineni Shubha K.
Published: August 2012

There has been considerable interest in recent years in using blends of petroleum diesel and biodiesels in diesel engines. Some of the interests arise in making use of renewable fuels, or in reducing dependency on imported fossil fuels and, in some cases, to provide economic boost to agricultural industry. It is believed that substitution of a small amount of biodiesel for petroleum diesel can reduce the import of fuel and help in trade balance. Biodiesels, whether derived from vegetable oils or animal fat, have many properties that align with those of petroleum diesel. This makes biodiesel a good candidate for blending it in small quantities with petroleum diesel. Studies have shown biodiesel blends to work well in diesel engines. However, experimental investigations of biodiesel blends have shown some discrepancies in engine thermal efficiency and emissions of NOx. A combustion simulation model for diesel engine may help to understand some of the differences in engine performance when different fuels are used. This paper deals with an existing simulation model that was applied to a diesel engine operating on biodiesel blends. The model was a modified version of GT-Power that was specifically modified to fit the test engine. The model was calibrated using a single cylinder, naturally aspirated, DI diesel engine operating on ultra-low sulfur (ULSD) diesel. It was used to predict engine performance when operating on different blends of soy biodiesel and ULSD. The simulation utilized detailed physical and chemical properties of the blends to predict cylinder pressures, fuel consumption, and emissions of oxides of nitrogen (NOx). Comparison between predicted and experimental values showed good correlations. The predicted trends in fuel consumption, emissions of NOx and smoke showed comparable trends. The model allows the user to change fuel properties to assess the impact of variations in blend composition on exhaust emissions. This paper discusses comparisons between the predicted and experimental results and how fuel composition can possibly impact NOx emissions.
A Two-Step Wet Etch Process for the Facile Fabrication of Hybrid Micro-Nanofluidic Devices
Authors: Pinti Marie , Prakash Shaurya
Published: August 2012

Hybrid microfluidic and nanofluidic devices have recently been developed for a variety of applications including water desalination, molecular gates, and other lab-on-chip uses. In this paper, we report on a 2-step wet etch process to fabricate hybrid microfluidic and nanofluidic devices with controllable features including a sloped nanochannel. The nanochannels with slit-like geometry can be fabricated with dimensions as small as 50 nm depth and a width of 30 μm for a minimum aspect ratio of 0.002. The channels are several cm long.
Finite Element Analysis of the ESTELA M1 Airplane Firewall (Representative Specimen)
Authors: Ramirez-Elias V. , Ledesma-Orozco E. , Hernandez-Moreno H.
Published: August 2012

This paper shows the finite element simulation of a representative specimen from the firewall section in the AEROMARMI ESTELA M1 aircraft. This specimen is manufactured in glass and carbon / epoxy laminates. The specimen is subjected to a load which direction and magnitude are determined by a previous dynamic loads study [10], taking into account the maximum load factor allowed by the FAA (Federal Aviation Administration) for utilitarian aircrafts [11]. A representative specimen is manufactured with the same features of the firewall. Meanwhile a fix is built in order to introduce the load directions on the representative specimen. The relationship between load and displacement is plotted for this representative specimen, whence the maximum displacement at the specific load is obtained, afterwards it is compared with the finite element model, which is modified in its laminate thicknesses in order to decrease the deviation error; subsequently this features could be applied to perform the whole firewall analysis in a future model [10].
Experimental Vehicle That Avoids Collisions Through Steer by Wire and Differential Drive Systems
Authors: Gonzalez-Villela Victor J. , Gonzalez-Zavala Eduardo U.
Published: August 2012

The implementation of Drive-by-Wire systems is increasing due to their advantages. One of these advantages is the capability to be autonomous or semiautonomous. This paper investigates the collisions avoidance in a Steer-by-Wire and Differential Drive experimental vehicle. The Steer-by-Wire system is tested using the Ackerman formulation. Ackerman equations are modified in order to vary the vehicle’s steering ratio in function of the vehicle’s speed. As a result, better high speed vehicle’s control is achieved. The collision avoidance system works using infrared sensors around the vehicle, avoiding frontal and lateral collision. The distance to the obstacles is the parameter selected to avoid collisions (leaving the time for other actions like warnings to the driver). The fusion of the Autonomous Steer-by-Wire and the collisions avoidance system develops a semi-autonomous vehicle. This vehicle avoids collisions automatically, even if the driver does not avoid the collisions by himself, greatly reducing the probability of accidents.
Near-Wall Focusing of Phase Change Micro-Particles for Local Heat Transfer Enhancement
Authors: Lenert Andrej , Nam Youngsuk , Thoms Matthew W. , Yilbas Bekir S. , Wang Evelyn N.
Published: August 2012

We report the effect of confining micron-sized phase-change particles to a layer near the heated wall of a parallel plate channel. We developed a numerical model which assumes fully-developed laminar flow and a constant heat flux applied to one wall. Melting of the confined phase-change particles is incorporated in the model using a spatially-dependent and temperature-dependent effective heat capacity. We investigated the effect of channel height, height of the phase-change particle layer, heat flux, and fluid properties on the peak local Nusselt number (Nu*) and the averaged Nusselt number over the melting length (Numelt). Compared to the base Nusselt number for this geometry (Nuo = 5.385), Numelt and Nu* enhancements were determined to be as high as 15% and 45%, respectively. For a constant mass fraction of particles in the phase-change layer, Numelt is optimized when the phase-change particles are confined to within 35% of the channel width. These studies suggest a strategy to enhance heat transfer with phase change particles for various thermal-fluidic systems.
Unmanned Aerial Vehicles (UAV): Design Trends
Authors: Shetty Devdas , Manzione Louis
Published: August 2012

This paper looks at the trends in design procedures in Unmanned Aerial Vehicles (UAVs). Rapid advances in technology are enabling more and more capability to be placed on smaller airframes which is spurring a large increase in the number of UAVs being deployed in the army. The military role of UAV is growing at unprecedented rates. The UAV is an acronym for Unmanned Aerial Vehicle, which is an aircraft with no pilot on board. UAVs can be remote controlled aircraft (e.g. flown by a pilot at a ground control station) or can fly autonomously based on pre-programmed flight plans or more complex dynamic automation systems. A variety of design configurations are in use. The primary driving parameters in all UAVs is the need for maximizing available wing area and wing effectiveness, while minimizing the required storage volume. The major factors in determining the relative merit of the different concepts are the evaluation of structural viability, mechanical complexity and overall system survivability by G forces. This paper examines some of the design methodologies and hardware-in-the loop simulation environment to support and validate the UAV hardware and software development.
Incorporating Biomechanical Research Topics Into K-12 Classroom Design Projects to Broaden Participation and Increase Engineering Interest
Authors: Briggs Brandi N. , Terry Benjamin S. , Yowell Janet , Rivale Stephanie
Published: August 2012

This paper describes a successful new biomechanical engineering curriculum created and implemented in two highly diverse local high schools by two graduate TEAMS (Tomorrow’s Engineers… creAte. iMagine. Succeed.) Fellows. In the semester-long curriculum, students create robotic surgical devices to diagnose and biopsy endometriosis, a pathology that afflicts roughly 5% of the adult female population. Curriculum focusing on anatomy, physiology, and tissue mechanics was also included to enhance the students’ understanding of the human body and its response to engineering materials. Focusing this course on cutting-edge, biomechanical research that explicitly and authentically illustrates how engineering benefits society resulted in increased enrollment in engineering by underrepresented populations. This paper also discusses personal reflections by the two graduate Fellows of the benefits gained and lessons learned during the design and implementation of this innovative high school curriculum.
Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets
Authors: Yu Youmin , Simon Terrence , Zhang Min , Yeom Taiho , North Mark , Cui Tianhong
Published: August 2012

Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.
Transient Performance and Coupled Acoustic Structural and Electrostatic Modeling of a Multistage Vacuum Micropump
Authors: Kumar Karthik , Bernal Luis P. , Yee Seow Yuen , Besharatian Ali , Najafi Khalil
Published: August 2012

This paper describes the theoretical analysis used to design of a multistage peristaltic vacuum micro pump, comprising of two parts. First, three different designs for a 16 stage micropump to achieve a vacuum of 250 torr are investigated. One design produces an equal pressure distribution across each stage at steady state. A second design has equal volume ratio across each stage. The third design is a combination of the other two. The transient behavior of these designs is analyzed using a reduced order model. In the first two designs when the pressure difference across the pump is low most pumping occurs across the first few stages, while for the third design the load is almost equally distributed across all stages. The opposite is observed when the pressure difference across the pump is high. In the second part of the paper, the reduced order model is further developed to account for the effects of electrostatic actuation and membrane dynamics. A non-linear model is proposed for the motion of the membrane and used to study the steady state performance and resonance of a multistage vacuum micro pump as a function of input voltage. It is found that near the acoustic frequency, a lower voltage is required to produce a greater flow.
Investigation of Dynamic Near-Field Radiation Between Quantum Dots and Plasmonic Nanoparticles for Effective Tailoring of Solar Spectrum
Authors: Palombo Nola , Park Keunhan
Published: August 2012

This paper presents the theoretical and experimental studies of dynamic near-field interactions between quantum dots (QDs) and plasmonic gold nanoshell (GNS) nanoparticles suspended in an aquatic solution in attempts to effectively tailor the solar spectrum. The photoemission measurement of the CdTe QD/GNS nanofluid (1×1017 mL−1 for QDs and 5×108 mL−1 for GNSs) is amplified by 2.7 times when compared with the photoemission for QD-only solution with the same QD concentration. In order to investigate the mechanism of such enhancement, the direct simulation Monte Carlo (DSMC) numerical scheme combined with the Langevin formalism was developed. The modified DSMC can stochastically trace particle movements of QDs and GNSs in the nanofluid, suggesting that QDs within near-field of GNSs are responsible for the photoemission enhancement. The obtained results will provide the feasibility of using the dynamic near-field radiation to down-convert the solar spectrum with enhancement, which could be applied towards high-efficiency photovoltaics.
Size and Temperature Dependent Phonon Spectra of Spherical CdSe Quantum Dots Prepared via a Refined Phosphonic Acid Assisted Organometallic Route
Authors: Chen Liangliang , Chen Yiwen , Ruan Xiulin
Published: August 2012

Spherical CdSe quantum dots (QDs) with a narrow size distribution were synthesized using a refined phosphonic-acid-assisted organometallic route. Visible absorption spectra show that as reaction time increases the absorption peak will shift to longer wavelength. HRTEM image confirmed the high-crystallinity of the as-prepared QDs. Raman spectroscopy was used to investigate the size and temperature dependence of the phonon spectra. As temperature increases, the LO-phonon frequency will decrease and the bandwidth will increase. As size increases, the LO-phonon frequency will increase and the bandwidth will decrease. However, when the temperature is above 400 K, the LO-phonon frequency in the smaller dots is higher than that in the larger dots due to the weaker negative temperature dependence of the LO-phonon frequency in the smaller dots.
Experimental and Numerical Simulation of a Synthetic Jet for Cooling of Electronics
Authors: Huang Longzhong , Simon Terrence , North Mark , Cui Tianhong
Published: August 2012

Compared to traditional continuous jets, synthetic jets have specific advantages, such as lower power requirement, simpler structure, and the ability to produce an unsteady turbulent flow which is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a round synthetic jet flow on the tip region of a longitudinal fin surface used in an electronics cooling system. Unique to this study are the geometry of the cooled surface and the variations in geometry of the jet nozzle or nozzles. Also unique are measurements in actual-scale systems and in a scaled-up system, and computation. In the computation, the diaphragm movement of the synthetic jet is a moving wall and the flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-stagnation-line spacing, are recorded. The computational results show a good match with the experimental results. In the experiments, an actual-scale system is tested and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up is tested. The three approaches are used to determine heat transfer coefficients on the fin on and near the stagnation line. Focus is on the large scale test results and the computation. Application to the actual-size cases is discussed. The dynamically-similar mock-up matches the dimensionless Reynolds number, Stokes number, and Prandtl number of the actual setting with a scale factor of 44. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m2K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how cooling performance changes with orifice design.
Mechanistic Model-Based Method for Bio-Inspired Design and Education
Authors: Seipel Justin
Published: August 2012

Biologically-inspired design is challenging because it requires creative transfer across biological and engineering disciplines. The biologically-inspired design process could therefore be improved with new tools, methods, and pedagogy that enables a smooth transition from a biological example or concept to a conceptual engineering design based on existing engineering components and practices. Two important problems can arise immediately when an engineer or student attempts bioinspired design: I. The practitioner or student of biological inspiration or biomimicry may not understand what the biological mechanism is that underlies a particular function of interest, and may begin engineering conceptual design with a misunderstanding of the essential mechanism required. II. Even when the correct biological mechanism is identified and a conceptual biological model is developed prior to engineering design, it may remain difficult to transition from a biological conceptual model of mechanism to an engineering conceptual design because the way these systems are composed and manufactured can be entirely different. For these reasons a formal process is developed here that links biological science with engineering design: where a biological mechanism of interest is first abstracted to a mechanistic conceptual model that focuses on the scope of the function of interest and removes other levels of biological detail. This results in a physiologically-independent conceptual model that links biological and engineering concepts. Then, subsequently, this inter-disciplinary conceptual model is re-embodied as an engineering design concept utilizing the current state of engineering art, available engineering components, and best practices. An example is presented of an existing class of biologically-inspired legged robots and their relationship to an abstract mathematical model of whole-body animal locomotion. Also, a teaching method is proposed for model-based biologically-inspired engineering design.
Investigation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln With Potential Energy Saving Considerations
Authors: Zhang Zexuan , Wang Ting
Published: August 2012

Calcined coke is a competitive material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is exhausted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. To help improve the energy efficiency and reduce natural gas consumption of the calcining process, a 3-D computational model is developed to gain insight of the thermal-flow and combustion behavior in the calciner. Comprehensive models are employed to simulate the moving petcoke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The following parametric studies are conducted: rotation angles, tertiary air injection angles, devolatilization zone length, discharge end gas extractions without injecting natural gas, variations of coke bed properties (thermal conductivity and heat capacity), and coke bed sliding speed. A total of 19 cases have been simulated. The results of studying the effect of tertiary air injection angles show that employing 15° tertiary air injection angle provides the best calcining condition than using 30° and 45° injection angles by achieving a higher coke bed temperature and less coke fines entrainment and attrition rate. In an attempt to reduce natural gas consumption, employing gas extraction at the discharge end successfully draws the hot combustion gas from the tertiary air zone towards the discharge end without burning natural gas. The coke bed temperature between 6 and 21 m from the discharge end is successfully raised from 10 to 100 K, but discharge end temperature is reduced 150 K without burning natural gas. The extracted gas at 1,000 K is too low to be returned to the kiln, but it could be used to preheat the tertiary air.
Small-Scale Power Generation and Storage Using Piezoelectric Films
Authors: Hatch Theodore , Styrvoky John , Barton Jared , Zhang Hualiang , Mehta Gayatri , Boetcher Sandra
Published: August 2012

Piezoelectric materials have many applications including sensors, actuators, and motors. However, the ability of piezoelectric films to generate electricity from wind power has only recently been advanced. Piezoelectric films harvest wind energy by means of a layer of polyvinylidene fluoride (PVDF) that upon deformation generates an internal electrical voltage across two silver-ink electrodes. These films are allowed to freely flap in an airflow to cause deformation and thus electricity generation. A single small film (4.14 cm (1.63 in) × 1.63 cm (0.64 in) × 0.15 cm (0.06 in)) is tested at various wind speeds. The output of the film may be enhanced with the addition of a bluff body (in this case, a cylinder) upstream from the film. The vortex shedding from the cylinder produces a wake that can enhance the vibrations of the piezoelectric device, which in turn optimize voltage and/or power output. Voltage and power output is recorded across varying load resistances. The method of storing useful energy from the piezoelectric films is also of particular interest. Preliminary experiments using a LTC3588-1 energy harvester to various configurations of supercapacitors and Li-ion batteries are conducted. The LTC3588-1 is comprised of an efficient rectifier with a buck converter to allow the chip to efficiently charge the super capacitor while only requiring a small input to begin charging.
Deformation Modeling of Soft Tissue Scaffolds for Wound Healing
Authors: Khoda Bashir , Koc Bahattin
Published: August 2012

Within tissue engineering (TE), one of the major research theme is on synthetic scaffold design. Most research emphasis on the material that has to be biocompatible and biodegradable over time and shows proper cell attachment properties. And traditional scaffold fabrication technique use chemical process resulting in uncontrolled porosity along the structure. Development of Solid Free Form (SFF) technique and improvement in some biomaterial properties provides the leverage of using these techniques to fabricate controlled and interconnected porous scaffold structure. These improved membrane/scaffolds are mostly regular porous structure and when applied in wound area various forces like bandage, contraction and self weight act upon that and cause deformation. As a result, the geometry and the designed porosity changes which eventually alters the desired choreographed functionality such as material concentration, design parameters, cytokines distribution over the wound device geometry. This balance often presents a tradeoff between a denser scaffold providing better mechanical function and a more porous scaffold providing better biofactor delivery, cell proliferation, pathways for nutrients and waste transportation. In this work, a novel scaffold modeling approach of “desired porosity with variational filament distance” has been proposed that will minimize the change in effective porosity with the designed porosity and thus will give a better functionality of such membrane providing both structural integrity and proper bioreactor environment. The proposed methodology has been implemented in this paper and illustrative examples are provided. Also a comparison result of measured effective porosity has been presented between proposed design model and conventional fixed filament distance scaffolds membrane.
Modeling of Microstructures Actuation by the Knudsen Thermal Force
Authors: Chigullapalli Sruti , Alexeenko Alina
Published: August 2012

Heated microscale objects immersed in a gas ambient are subject to thermal Knudsen forces generated by the non-equilibrium energy exchange between gas molecules and solid surfaces. Knudsen forces are significant when the length scale of a temperature gradient is comparable to the gas molecular mean free path. This can occur for very low gas pressures or at extremely small length scales. The overall goal of this work is to study the feasibility of using Knudsen force as an alternative actuation mechanism for N/MEMS. The kinetic solution of Boltzmann equation using the discrete ordinate/finite volume discretization in the high-dimensional phase space is circumventing difficulties associated with traditional stochastic DSMC approach in dealing with the slow bulk motion. The comparison to measurements by (Passian et al, PRL, 2003) shows that Knudsen force is well reproduced by simulations assuming full momentum accommodation for nitrogen and argon gas and an incomplete accommodation for helium. It provides a pathway for design and analysis of devices taking advantage of the benign mechanism of the Knudsen forces, in particular, the absence of high electric fields. The analysis shows that the Knudsen force results in an impact velocity of only 0.9 cm/s whereas electrostatic forces with low voltages below 0.5V result in impact velocity in the range of 6–20 cm/s. We further discuss how Knudsen force can be used for low impact velocity actuation and also to overcome the stiction problem.
Ambient-Pressure, Plasma-Assisted Deposition of Conformal Nanocrystalline Zinc Oxide Thin Films
Authors: Pedersen Joachim D. , Esposito Heather J. , Teh Kwok Siong
Published: August 2012

We report a thermal induction plasma-assisted, rapid, ambient-pressure, low-temperature one-step process for depositing conformal, non-porous nanocrystalline ZnO thin film on various substrates ranging from Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), to polyimide (Kapton™). The predominantly c plane-oriented as-synthesized polycrystalline films range in thickness from 20nm to 200nm, deposited at a growth rate ranging from 2 nm/min to 50 nm/min. The lowest deposition temperature achieved with this method is 162°C and the as-deposited film is found to be conductive (12.5 S/m). Annealing in a pure argon environment at different temperatures ranging from 700–950°C changes the textures and morphologies of the thin film—higher annealing temperatures favor the restructuring of ZnO nanocrystalline film to form nanopillars of ZnO.
Semi-Autonomous Collaborative Control of Multi-Robotic Systems for Multi-Task Multi-Target Pairing
Authors: Cheung Yushing , Chung Jae H. , Patel Ketula
Published: August 2012

In many applications, it is required that heterogeneous multi-robots are grouped to work on multi-targets simultaneously. Therefore, this paper proposes a control method for a single-master multi-slave (SMMS) teleoperator to cooperatively control a team of mobile robots for a multi-target mission. The major components of the proposed control method are the compensation for contact forces, modified potential field based leader-follower formation, and robot-task-target pairing method. The robot-task-target paring method is derived from the proven auction algorithm for a single target and is extended for multi-robot multi-target cases, which optimizes effect-based robot-task-target pairs based on heuristic and sensory data. The robot-task-target pairing method can produce a weighted attack guidance table (WAGT), which contains benefits of different robot-task-target pairs. With the robot-task-target pairing method, subteams are formed by paired robots. The subteams perform their own paired tasks on assigned targets in the modified potential field based leader-follower formation while avoiding sensed obstacles. Simulation studies illustrate system efficacy with the proposed control method.
Current Rise Index (CRI) Maps of Machine Tool Motors for Tool-Wear Prognostic
Authors: Hamade R. F. , Ammouri A. H.
Published: August 2012

Quantitative polar maps of tool-wear of cutting tools (here, chisel drills) undergoing dry machining are charted based only on transducers reporting electrical current measurements from machine (spindle and feed drives) motors. Associated with these maps are qualitative descriptions of the various modes of tool-wear afflicting the drill tools. These tool-wear maps are based a novel wear criterion developed here that relies on the % increase in motor (spindle and feed drive motors) RMS current values and is dubbed the Current Rise Index (CRI). For verification in a drilling operation application, this index is found to positively track the progressive increase in tool-wear. Utilizing this CRI and the associated polar plots, monitoring of cutting tools may be achieved simply by machine tool operator via visual monitoring of polar CRI maps generated in real-time. Naturally, such plots lend themselves to automated prognosis by common control techniques utilized in machine tool operations. Such maps may also serve as indirect means of predicting tool-wear in automated cutting operations.