bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Tree Shading on the Thermal Load of a House in a Warm Climate Zone in Mexico
Authors: Chagolla M. A. , Alvarez G. , Simá E. , Tovar R. , Huelsz G.
Published: October 2013

This paper presents the effect of the shade of a tree on the indoor temperature and thermal loads of a house (test house) located in the State of Morelos, Mexico, 18° 50′ 43″ north latitude and 99° 10′ 44″ west longitude. Energy Plus was used to simulate different geometries of the shadow of a tree and the simulation results were compared with experimental measurements of the house without air-conditioning, for one warm and one cold week of the year 2011. The results showed that the maximum temperature difference between the measured and simulated temperatures with both geometry models of tree-shading was 1.7°C. When the effect of tree shading is not considered, it was found that there is a maximum temperature increase of 4°C in the warm week compared with the measured results. In the cold week, the temperature increase was 1.3°C compared with the measured results. Simulation results for an air-conditioned tree-shaded test house show that total annual energy consumption for cooling and heating to achieve thermal comfort represents a substantial energy savings of 76.6% when compared with an unshaded house.
Dynamic Response of a Floating Cylinder Subjected to Coupled Wave and Wind Loading
Authors: Yu H. , Srivastava N.
Published: October 2013

The broad objective of the research presented herein is to analyze dynamical interactions in offshore structures under combined wind and wave loads for enhanced power delivery and reliability of hybrid wind-wave generation systems. As an offshore structure representative, a model for an inclined floating cylinder at finite depth is developed employing linear wave theory coupled with wind-induced effects. Although detailed wave models have often been incorporated while studying the dynamics of such cylinders, wind-induced effects have been mostly modeled as an axial drag term that affects the drift of the structure along the wind direction. In this article, the effects of not only wind-induced drag, but also lift and oscillations on the structure (i.e. the floating inclined cylinder) are studied. Further, the effects of vortex shedding are considered. Cross-flow principle is used to calculate the wind loads on the cylinder. Assuming small wave steepness and a large radius of cylinder (in comparison to the wavelength), linear wave diffraction and radiation theory coupled with wind-induced effects is employed to analyze the dynamic response of the inclined floating cylinder. Numerical results on the dynamic response of an inclined floating cylinder subjected to coupled wind-wave loading system are presented and discussed while highlighting the increasing relevance of such modeling strategies for hybrid wind-wave power generation systems and their control.
Conductivity Measurement of Genetically Annealed Zirconia From Molecular Dynamics Simulations
Authors: Miller Steven P. , Fleischer Amy S.
Published: October 2013

Characteristics of the annealed state of yttria and scandia stabilized zirconia have been investigated using molecular dynamics simulations. A genetic algorithm was used to find the minimal energy configuration of dopant ions to simulate the effects of annealing for compositions of 8 mol% Y2O3 in ZrO2, and compositions with 9, 10 and 11 mol% Sc2O3 with, respectively, 2, 1 and 0 mol% Y2O3 in ZrO2. Conductivity and diffusion coefficients were calculated in each case, and it was discovered that the conductivity increased when the dopant ions were located distant to each other, and the number of first neighbor dopant-dopant pairs were reduced. Furthermore, the Haven ratio was calculated to be on the order of 0.9 for the 11 mol% doped specimens, but substantially lower for the 8 mol% yttria in zirconia specimens.
Prompt Transient Heat Transfer Effects in Low-Fluence Laser Induced Incandescence
Authors: Memarian F. , Daun K. J.
Published: October 2013

Recent time-resolved laser-induced incandescence (TiRe-LII) experimental studies have revealed anomalies in particle cooling rates that cannot be explained using steady-state conduction models. This is the first study to use Direct Simulation Monte Carlo (DSMC) to investigate possible transient effects in heat conduction between the laser-energized particle and surrounding gas. While the DSMC results reveal an increased cooling rate shortly after the laser pulse, this effect is small relative to experimentally-observed anomalous cooling.
The Role of Strength in Determining Composite Material Toughness Using the Interface Indentation Fracture Test
Authors: Grimm Brian A. , Parmigiani John P.
Published: October 2013

Understanding fracture behavior at the interfaces of brittle composite materials requires appropriate measurement techniques for fracture toughness. Due to their simplicity and convenience, indentation techniques are attractive solutions. One such technique is the interface indentation fracture (IIF) test, which measures the relative toughness of interfaces between brittle materials by introducing a series of indents at various angles of incidence (0–90°) to the interface, from which crack growth will either be by penetration through the interface or by deflection (debonding) along it. Larger angles of incidence promote penetration and smaller angles promote deflection, so by noting the critical angle at which propagation changes from penetration to deflection, the IFF test can make inferences about relative fracture toughness of different interfaces tested under similar conditions. However, as previous work by Parmigiani and Thouless has shown, the penetration vs. deflection behavior of a crack incident to an interface is a function not only of interface fracture toughness but also of interface strength. Interface cohesive zone elements in a finite element model incorporating both fracture toughness and strength criteria were used to study the propagation behavior of cracks normally incident to brittle composite interfaces. In the follow up work presented here, the cohesive zone method (CZM) has been extended to study cracks that occur at varying angles of incidence to these interfaces. Results show that IIF testing does not always result in unique values for relative fracture toughness; when interface strength is varied, it is possible for identical IIF-test critical angles to correspond to differing interface toughness values and, conversely, for differing critical angles to correspond to identical fracture toughness values. To properly employ the IFF test method, this phenomenon must be taken into account.
Virtual Thermal Sensing and Control of Heat Distribution Using State Estimation
Authors: Fathian Kaveh , Hassanipour Fatemeh , Gans Nicholas R.
Published: October 2013

Many industrial applications require or can be improved by strict control of the temperature distribution on a surface. This initial investigation presents modeling and control of heat flow on an aluminum plate. Temperature distribution is modeled using a dense equivalent electrical circuit. An observer is designed based on the model to estimate the temperature distribution on the plate. The estimation is used in a controller to regulate the temperature of a desired point on the plate, given discrete heat input elements but no cooling elements. Experiments are conducted to compare the realism of the heat flow model and efficacy of the control method with experimental data. Results show that the steady state error between the actual and estimated temperatures at different points on the surface is always less than 0.5°C, which indicates accurate estimation of the temperature. The RMS error between desired and actual temperatures through all experiments is less than 2°C which indicates fast regulation and low steady state error.
Using a Semi-Active Tuned Mass Damper to Limit the Motion of a Nonlinear Absorber and Attenuate Structural Vibrations
Authors: Eason R. Parker , Sun Chao , Dick Andrew J. , Nagarajaiah Satish
Published: October 2013

When optimally tuned, a tuned mass damper (TMD) can be very effective for reducing the response amplitude of a structure or mechanical system when it is excited near resonance. If the stiffness of the TMD were to develop nonlinear properties, either due to operation outside of its linear range or component degradation, its ability to function can be significantly compromised. Previous work has demonstrated that semi-active tuned mass dampers (STMDs) are able to provide better vibration attenuation than passive devices with significantly lower power requirements than active devices. In this paper, the authors numerically explore the use of an STMD to address the undesirable conditions resulting from a TMD developing nonlinear (cubic) hardening properties. It is found that by adding the STMD in series to the structure/nonlinear TMD (NTMD) system, the response of the NTMD can be reduced, limiting its motion to the linear range where it is able to better attenuate the response of the primary structure.
Impact of Spindle Speed on Micro-Milling Stability
Authors: Halfmann Eric B. , Suh C. Steve
Published: October 2013

Milling efficiency is hampered by excessive tool vibrations that negatively impact the work-piece quality. This is more of a concern in micro-milling where sudden tool breakage occurs before the operator can adjust cutting parameters. Due to different chip formation mechanisms in micro-milling, an increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly non-linear process which can produce multiple and broadband frequencies which increase the probability of tool failure. Micro-milling is studied through the development and analysis of a 3-D nonlinear micro-milling dynamic model. A lumped mass, spring, damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantages of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the work-piece is presented. The effective rake angle and helical angle is accounted for resulting in a 3-D micro-milling model. The model is shown to resolve the high frequency force components that are seen in experimental data available in literature. Also, exciting the system at various spindle speeds results in dynamic states of motion that negatively impact the process through increased vibration amplitude and a broad frequency bandwidth.
Extremely Large Deflection Actuators for Translation or Rotation
Authors: Chigullapalli Aarti , Clark Jason V.
Published: October 2013

In this paper we propose a new type of piezoelectric microactuator to produce extremely large translational (> 100 microns) or rotational deflections (> 10 degrees). Many micro electro mechanical systems (MEMS) are capable of deflecting 1 to 10s microns using the electrostatic or thermoelectric phenomenon. The problem with electrostatic actuators is that they are usually constrained to operate in clean environments, which limits their utility to physically interact with the environment. The problem with thermal actuators is that they usually require a relatively large amount of power since they rely on heat. Achieving large deflection actuators without such constraints may find applications in biomedical engineering, optics, micro/nano-assembly, scanning probe microscopy, etc. What is novel about our piezo actuator is we exploit lateral deflection to create an actuator that forms an ‘S’ shape upon actuation. We then explore the use of this S-drive for large translational and rotational actuators. For feasibility analysis, we consider nonlinear deflection, voltage limit due to dielectric breakdown, strain limit, and gravitational effects.
Multi-Scale Modeling of Tubular Cross-Flow Microfiltration of Metalworking Fluids
Authors: Sullivan Nathan P. , Wentz John E. , Abraham John P.
Published: October 2013

Metalworking fluids are a vital part of modern machining processes but have significant negative economic, health, and environmental impacts. In-process purification of these fluids by microfiltration has been shown to reduce these impacts. This research uses a two-stage computational modeling methodology to investigate how particles within the membrane are transported from the turbulent flow within the center of the tubular membrane to the laminar sub-layer near the membrane wall and finally into the membrane pores. A macro-model of the complete flow within the tubular membrane is used to determine the steady-state flow profile within 25 microns of the membrane surface. This flow profile is then used to develop a micro-model of the flow at the membrane wall using a flat-plate assumption. The micro-model includes individual pores randomly located and sized based on statistical analysis of alumina membrane surfaces. A 23 full factorial design of experiments was used with variables of cross-flow velocity, transmembrane pressure, and membrane resistance. The responses of effective filtration region and total mass flowing through the pores were analyzed. Based on the simulation results, recommendations are made for future membrane design to provide the most efficient transport of particles from the bulk into the pores.
High Fidelity Methods for Modeling Nonlinear Wave Propagation in One-Dimensional Waveguides
Authors: Liu Yu , Ghaderi Pooya , Dick Andrew J.
Published: October 2013

In this paper, two new methods are proposed to study wave propagation in materials with constitutive law that have nonlinear terms. In the first method, the gauge transformation is used to derive the dynamic shape function. A perturbation method is then applied in order to derive an equation for the wavenumber. The influence of the nonlinearity takes the form of a dependence of the wavenumber on the magnitude of the corresponding frequency component. Under the small amplitude and weak nonlinearity assumptions of the perturbation method, the wavenumber is incorporated into the spectral finite element method (SFEM). The second approach is a numerical method based on alternating frequency-time (AFT) iterations. The nonlinear term represented as a residual nonlinear force term is reduced through the alternating iterations between the time-domain and the frequency-domain. Finally, response behaviors under impact loading predicted with these methods are studied and compared to equivalent linear response behavior.
Elasto-Plastic Analysis of Prismatic Folded Plates by the Finite Element Method
Authors: Sitaram Pattabhi , Pai Bipin , Mok Rachel
Published: October 2013

Folded plate structures are used for roofing large column-free areas for auditoriums, supermarkets, gymnasiums, hangars for aircraft, and other similar applications. The loads on these structures could cause stresses to go beyond the elastic range. Therefore, a thorough understanding of their elasto-plastic behavior is of utmost importance in designing these structures. An attempt is made to study the elasto-plastic behavior of prismatic metal folded plates by the finite element method using the commercial software, ANSYS. The method is first validated by analyzing typical plates and shells, and comparing them with available solutions in the literature. The elasto-plastic behavior of some prismatic folded plates is then studied, and their force-deflection responses and evolution of plastic zones are evaluated.
The Dynamic Properties of a Non-Pneumatic Tire With Flexible Auxetic Honeycomb Spokes
Authors: Lee Chihun , Ju Jaehyung , Kim Doo-Man
Published: October 2013

Motivated by our previous study on the flexibility and low local stress of auxetic hexagonal honeycombs in uni-axial loading, we explore the dynamic characteristics of a flexible auxetic hexagonal lattice structure when it is used as the flexible spokes of a non-pneumatic tire. In this study, a modal analysis and the steady state vibration characteristics of NPTs with cellular spokes are investigated with a series of vertical loads and rolling speeds using a commercial finite element code, ABAQUS/Explicit. The angular velocity and the displacement at the hub center and the reaction force on the ground were investigated in the time and frequency domains for the steady state rolling condition for vehicle speeds of 60km/h and 80km/h. The orthotropic properties of the honeycomb spokes create different modal behaviors compared with those of pneumatic tires; e.g., the in-plane shear at the initial mode. The discrete spoke geometry induces a non-homogeneous mass (non-uniformity) distribution, which also causes local vibration effects.
Materials Testing of a Lithium Ion Battery Separator for Use in Finite Element Analysis
Authors: Avdeev Ilya V. , Martinsen Michael J. , Francis Alex B.
Published: October 2013

The use of lithium-ion batteries in the automotive industry has become increasingly popular. As more hybrid and electric vehicles take to the road an understanding of how these batteries will behave structurally will be of greater concern. Impact testing can give a valuable overview of the strengths and weaknesses of a batteries design, however, these tests can be time consuming, expensive, and dangerous. Finite element analysis can deliver a reliable low cost approximation of physical testing results. The accuracy of FE results depends greatly on the mathematical representation of the material properties of Li-ion battery components. In this study, the material properties of polymer thin film used as a separator between an anode and a cathode are tested experimentally under various temperatures and strain rates. Experimental results were used to develop a constitutive model for semi-crystalline polymers that is well suited for the finite element analysis.
Three-Dimensional Micromechanical Modeling of Continuous Fiber Reinforced Ceramic Composites With Interfaces
Authors: Bheemreddy V. , Dharani L. , Chandrashekhara K. , Hilmas G. , Fahrenholtz W.
Published: October 2013

Continuous fiber reinforced ceramic composites (CFCCs) are widely used in high performance and high temperature applications. The behavior of CFCCs under various conditions is not easily predicted. Micromechanical modeling of CFCCs using a representative volume element (RVE) approach provides useful prediction of the composite behavior. Conventionally, the effect of fiber-matrix interface on effective property prediction of the CFCCs is not considered in the micromechanical modeling approach. In the current work, a comprehensive three-dimensional micromechanical modeling procedure is proposed for effective elastic behavior estimation of CFCCs. Application of the micromechanical model for various interfaces has been considered to evaluate the effect of different interfaces and highlight the applicability of current model. Cohesive damage modeling approach is used to model the crack growth along with fiber bridging. The finite element model is validated by comparing with available data in the literature.
Thermal Annealing: A Technique to Improve the Performance of Cadmium Zinc Telluride (CZT) Material for Semiconductor Radiation Detector Applications
Authors: Adams Aaron L. , Kassu Aschalew , Chan Wing , Drabo Mebougna , Pinder Rodney , Egarievwe Stephen , Radja Asja , Yang Ge , James Ralph B.
Published: October 2013

Extensive research was undertaken over the past 20 years to investigate the suitability of cadmium zinc telluride (CZT) crystals as a material for room-temperature nuclear-radiation detectors. Large-volume CZT crystals, with thicknesses up to 2 cm and large effective areas of roughly 5–10 cm2, are needed to fabricate efficient detectors that meet the working requirements of federal agencies, such as the DOE/NNSA (Department Energy National Nuclear Security Administration), Department of Homeland Security (DHS), and the Department of Defense (DOD). However, because of the imperfect methods for growing crystals, the resulting large-volume crystals most often are not perfect single ones, and contain structural defects such as voids, pipes, impurities from source materials, tellurium inclusions and precipitates, vacancies, and vacancy-impurity complexes generated during the process of their production. Other extended defects that may be present include grain boundaries, micro twins, and walls of dislocations (sub-grain boundaries). Identifying these defects, controlling their occurrence and eliminating them from the bulk CZT material currently are important tasks that will improve the yield of detector-grade crystals from ingots, and ultimately better their performance. In this study, we used a post-growth thermal annealing technique to remove the performance-limiting defects caused by tellurium inclusions and associated impurities in the CZT crystals. We realized a 66% ± 16% reduction in the size of the inclusions, with an overall elimination of 17% ± 2% of them. We believe that our experimental results offer a better understanding of the optimal annealing parameters, and of the dynamic properties of post-growth annealing processes.
Thermo-Mechanical Study of the Role of Gd2Zr2O7 (GZ) in Improving Life of YSZ and GZ Double Layered Thermal Barrier Coatings
Authors: Mensah Patrick F. , Diwan Ravinder , Nandikolla Swamy , Coker Omotola , Sahoo Purush
Published: October 2013

Thermo-mechanical properties and thermal cycling behavior of gadolinium zirconate Gd2Zr2O7 (GZ) based thermal barrier coatings (TBCs) was investigated in this study in comparison to conventional yttria-stabilized zirconia (YSZ) coatings. This paper presents results focusing on coefficient of thermal expansion (CTE) measurements, thermal cycling tests, measured elastic properties and porosity of the multilayered GZ/YSZ TBCs deposited by atmospheric plasma spraying (APS) on an Inconel 738 (IN738) superalloy substrate. SEM microstructural images of failed TBC specimens are also presented. Samples of different double layer combinations with one layer being either 100% YSZ or 100% GZ and the second containing varying amounts of the two compounds were prepared to determine optimum combination that maintains good insulating properties while reducing the CTE mismatch between the TBC layers. The temperature range of the tests was 25°C to 1300°C. The samples are processed by APS on (Ø −12.7 mm, thickness 3 mm) IN738. Using a dilatometer, CTEs of the as sprayed top coat (TC) combinations are measured and compared. The elastic properties are measured using a Hysitron nanoindenter. Results showed that the 10%GZ/ 90%YSZ+ 100YSZ double layered structure was the best among the tested GZ based TBCs and the delamination of GZ/YSZ coating first initiated in the GZ layer close to the interface of GZ and YSZ layers, which was mainly caused by the sintering effect of the GZ layer.
Non-Invasive Sorting of Lipid Producing Microalgae With Dielectrophoresis Using Microelectrodes
Authors: Schor Alisha R. , Buie Cullen R.
Published: October 2013

In order to advance the algae biofuel industry, we are constructing a dielectrophoretic, single-cell sorter that selects algae based on lipid content. This tool can lower production costs by aiding in strain selection, online culture monitoring, or directed evolution studies. Dielectrophoresis (DEP) is the polarization of particles or cells in a non-uniform electric field, which leads to a Coulomb force on the cell. Lipids and cell cytoplasm have vastly different dielectric properties. Therefore, as a cell accumulates lipid, we predict a change in the overall DEP response. Our models show that in algae culture medium, we should be able to distinguish between high and low lipid content cells at frequencies above 100 MHz. This was confirmed by experiments, in which high and low lipid cultures of Neochloris oleoabundans have DEP crossover frequencies of 190 MHz and 125 MHz, respectively. We have also fabricated a proof-of-concept device validating that cells can be manipulated under DEP. However, in order to achieve sorting, we will require higher frequencies as well as a modified design to eliminate non-uniformities in the electric field through the channel height.
A Numerical Model of In-Channel Pebble Bed Thermal Storage for a Solar Chimney
Authors: Schulte Brandon , Plumb O. A.
Published: October 2013

In this study, solar chimney performance is numerically modeled. Previously published models have considered water bags and natural earth as means to store daytime thermal energy for nighttime operation of the system. The present model considers in-channel pebble bed thermal storage. A one-dimensional, implicit time stepping numerical model is developed to predict solar chimney performance throughout a 24 hour period. The model is partially verified with available experimental data. The daily energy, daily efficiency and heat transfer characteristics of the solar chimney with pebble bed thermal storage are summarized. The numerical simulation showed that by introducing a pebble bed, nightly exit velocities reach 40% of the peak daytime velocity. However, the daily kinetic energy delivered by a solar chimney with pebble bed thermal storage is much less than a traditional solar chimney, suggesting pebble bed thermal storage is more practicable in building heating applications as opposed to power generation.
Oscillating Bubbles on a Hot Surface
Authors: Pillutla Srikrishna , Choi Wonjae
Published: October 2013

This presentation describes a nonlinear dynamics of bubbles forming on a hot surface. In particular, we compare the behavior of bubbles in three regimes — evaporative, nucleate boiling, and film boiling regimes. A bubble appears on a hot surface when the heat flux from the surface is high enough to overcome the Laplace pressure across the surface of the bubble. Once a bubble nucleates on a surface, one might expect that the subsequent evaporation of the liquid phase would make the bubble expand monotonically until it leaves the surface. In real, nucleating bubbles expand monotonically only in evaporative regime. In the other two regimes, the size of the bubbles oscillates with varying frequency and amplitude depending on the heat flux and the convection patterns in the bulk liquid. We suspect that such a behavior suggests that the bubbling dynamics in these three regimes are fundamentally different: while the growth of a bubble in evaporative regime is determined essentially by the evaporation rate on the hot surface, the much more dynamic behavior of a bubble in nucleate and film boiling regime is the result of the interplay between two driving forces — evaporation near the solid surface and condensation near the top of a bubble. Such a competition becomes unsteady when the heat flux is high; therefore, boiling pattern switches from a quasi-static evaporative one to periodic nucleate boiling, and eventually to chaotic film boiling.
Buckling of Stiffened Curved Panels and Cylindrical Shells: A Study of Comparison Among Various Theories
Authors: Harutyunyan S. , Hasanyan D. J. , Davis R. B.
Published: October 2013

Formulation is derived for buckling of the circular cylindrical shell with multiple orthotropic layers and eccentric stiffeners acting under axial compression, lateral pressure, and/or combinations thereof, based on Sanders-Koiter theory. Buckling loads of circular cylindrical laminated composite shells are obtained using Sanders-Koiter, Love, and Donnell shell theories. These theories are compared for the variations in the stiffened cylindrical shells. To further demonstrate the shell theories for buckling load, the following particular case has been discussed: Cross-Ply with N odd (symmetric) laminated orthotropic layers. For certain cases the analytical buckling loads formula is derived for the stiffened isotropic cylindrical shell, when the ratio of the principal lamina stiffness is F = E2/E1 = 1. Due to the variations in geometrical and physical parameters in theory, meaningful general results are complicated to present. Accordingly, specific numerical examples are given to illustrate application of the proposed theory and derived analytical formulas for the buckling loads. The results derived herein are then compared to similar published work.
Polyurea With Hybrid Polymer Grafted Nanoparticles: A Parametric Study
Authors: Holzworth Kristin , Williams Gregory , Arman Bedri , Guan Zhibin , Arya Gaurav , Nemat-Nasser Sia
Published: October 2013

The basis of this research is to mitigate shock through material design. In this work, we seek to develop an understanding of parametric variations in polyurea-based nano-composite materials through experimental characterization and computational modeling. Blast-mitigating applications often utilize polyurea due to its excellent thermo-mechanical properties. Polyurea is a microphase-separated segmented block copolymer formed by the rapid reaction of an isocyanate component and an amine component. Block copolymers exhibit unique properties as a result of their phase-separated morphology, which restricts dissimilar block components to microscopic length scales. The soft segments form a continuous matrix reinforced by the hard segments that are randomly dispersed as microdomains. The physical properties of the separate phases influence the overall properties of the polyurea. While polyurea offers a useful starting point, control over crystallite size and morphology is limited. For compositing, the blending approach allows superb control of particle size, shape, and density; however, the hard/soft interface is typically weak for simple blends. Here, we overcome this issue by developing hybrid polymer grafted nanoparticles, which have adjustable exposed functionality to control both their spatial distribution and interface. These nano-particles have tethered polymer chains that can interact with their surrounding environment and provide a method to control well defined and enhanced nano-composites. This approach allows us to adjust a number of variables related to the hybrid polymer grafted nanoparticles including: core size and shape, core material, polymer chain length, polymer chain density, and monomer type. In this work, we embark on a parametric study focusing on the effect of silica nanoparticle size, polymer chain length, and polymer chain density. Preliminary results from experimental characterization and computational modeling indicate that the dynamic mechanical properties of the material can be significantly altered through such parametric modifications. These efforts are part of an ongoing initiative to develop elastomeric composites with optimally designed compositions and characteristics to manage blast-induced stress-wave energy.
Performance Improvement of a Wind Turbine Blade Designed for Low Wind Speeds With a Passive Trailing Edge Flap
Authors: Ahmed Mohammed Rafiuddin , Nabolaniwaqa Epeli
Published: October 2013

The flow characteristics and the lift and drag behavior of a newly designed thick trailing-edged airfoil that was provided with fixed trailing edge flaps (Gurney flaps) of 1% to 5% height right at the back of the airfoil were studied at different low Reynolds numbers (Re) and angles of attack for possible applications in wind turbines suitable for the wind speeds of 4–6 m/s that are common in the Pacific Island Countries. A thick trailing-edged blade section, AF300, that was designed and tested in a recent work for small horizontal axis wind turbines to improve the turbine’s startup and performance at low wind speeds was chosen for this study. Experiments were performed on the AF300 airfoil in a wind tunnel at different Re, flap heights and angles of attack. Pressure distributions were obtained across the surface of the airfoil and the lift and drag forces were measured for different cases. It was found that the flap considerably improves the suction on the upper surface of the airfoil resulting in a high lift coefficient. For some of the angles, in the case of 3 mm and 4 mm flaps, the peak Cp values on the suction surface were significantly higher compared to those without the flap. However, at angles of attack of 12° and above, this unusually high Cp on the upper surface close to the leading edge caused flow separation for some cases as the flow could not withstand the strong adverse pressure gradient. The CFX results matched most of the experimental results without flaps, except that the suction peak was lower numerically. The difference was higher for the case with flaps. It is clear from the results that trailing-edge flaps can be used to improve the performance of small wind turbines designed for low wind speeds.
Design of an Approximate Control Law Using Input-State Linearization for the Ball on a Plate System
Authors: Hoover Randy C. , St. Amand Joe
Published: October 2013

This paper demonstrates an approximate full state feedback linearizing control law for the nonlinear ball on a plate system. It is shown that true full state feedback is not possible due both to the centrifugal acceleration terms and the nonlinear coupling between both coordinate axis. In an effort to make the system feedback linearizable, the dynamics corresponding to the centrifugal acceleration and the nonlinear coupling are simply treated as nonlinear disturbances to the original dynamics. The derived approximate full state feedback linearizing control law is evaluated via simulation of the original dynamics illustrating that the nonlinear disturbances are indeed small, and that the system controlled by the approximate control law is capable of more effective position and trajectory tracking than the standard Jacobian linearization.
Hole Surface Quality and Damage When Drilling Unidirectional CFRP Composites
Authors: Eneyew Eshetu D. , Ramulu M.
Published: October 2013

In this study, an experimental investigation on the drilling of unidirectional carbon fiber reinforced plastic (UD-CFRP) composite was conducted using polycrystalline diamond (PCD) tipped eight facet drill. The quality of the drilled hole surface was examined through surface roughness measurements and surface damage by scanning electron microscopy (SEM). It was found that, fiber pullout occurred in two specific sectors relative to the angle between the cutting direction and the fiber orientation. The thrust force was highly influenced by the feed rate than the cutting speed and it shows a significant variation throughout the rotation of the drill.
Convective Heat Transfer Enhancement With Micro Pin-Fin Surfaces Cooled by a Piezoelectrically-Driven Translational Agitator
Authors: Yeom Taiho , Simon Terrence W. , Zhang Tao , North Mark T. , Cui Tianhong
Published: October 2013

Air cooling of electronic equipment continues to hold many advantages over liquid cooling in terms of simplicity, reliability, cost, etc. Many active and passive air cooling techniques have been developed to meet the thermal challenges of modern, high-power electronics. Active cooling includes such features as piezoelectric flapping fans and synthetic jets that could directly break down and thin the thermal boundary layers on heated surfaces. A microchannel bank of fins, micro pin-fin surfaces, etc. are passive methods for increasing heat transfer area. In the current study, both active and passive methods, piezoelectric translational agitators and micro pin fin arrays, are employed to dramatically enhance convective heat transfer rates. A piezoelectric stack actuator coupled with an oval loop shell displacement amplifier was utilized to generate high-frequency and large-displacement translational agitation over the micro pin fin surface. Two different micro pin-fin surfaces were fabricated using copper and the LIGA process. Heat transfer experiments were performed in a single channel that houses a one-sided, heated surface with attached micro pin fins. The piezoelectric translational agitator oscillates at a high frequency of 596 Hz with a large displacement of up to 1.8 mm. The heat transfer coefficients on the micro pin-fin surface cooled by the agitator and various channel through-flows were compared with those of plain surfaces under the same channel flow rates. A maximum improvement of 222% in the heat transfer rate was achieved when the agitator was operated, the micro pin-fin surface was in place and the channel flow velocity was 11.6 m/sec, compared to that of a non-agitated plain surface case with the same flow rate.
Numerical Modeling of Coal Gasification in an Entrained-Flow Gasifier
Authors: Zhang Cheng
Published: October 2013

The gasification technology has been applied in Integrated Gasification Combined Cycle (IGCC) plants for the production of power, and polygeneration plants for the production of industrial chemicals, fuels, hydrogen, and power. The major advantages of the gasification technology are its potential for feed-stock flexibility, product flexibility, and relative simple removal of harmful emissions of nitrogen oxides (NOx), sulfur oxides (SOx), and CO2. Entrained-flow gasifiers are the preferred gasifier design for future deployment due to their high carbon conversion, high efficiency and high syngas purity. Current entrained-flow gasifier designs still have serious problems such as injector failure, refractory failure, slag blockages, downstream fouling and poisoning, poor space efficiency, and lack of dynamic feedstock flexibility. To better understand the entrained-flow gasification process, we performed steady Reynolds-averaged Navier-Stokes (RANS) modeling of the laboratory-scale gasifier developed at Brigham Young University (BYU) using ANSYS Fluent. An Eulerian approach is used to describe the gas phase, and a Lagrangian approach is used to describe the particle phase. The interactions between the gas phase and particle phase is modeled using the particle-source-in-cell approach. Turbulence is modeled using the shear-stress transport (SST) k–ω model. Turbulent particle dispersion is taken into account by using the discrete random walk model. Devolatilization is modeled using a version of the chemical percolation devolatilization (CPD) model, and char consumption is described with a shrinking core model. Turbulent combustion in the gas phase is modeled using a finite-rate/eddy-dissipation model. Radiation is considered by solving the radiative transport equation with the discrete ordinates model. Second-order upwind scheme is used to solve all gas phase equations. First, to validate the flow solver, we performed numerical modeling of a non-reacting particle-laden bluff-body flow. For the non-reacting flow, the predicted mean velocities of the gas phase and the particle phase are in good agreement with the experimental data. Next, we performed numerical modeling of the gasification process in the BYU gasifier. The predicted profiles of the mole fractions of the major species (i.e. CO, CO2, H2, and H2O) along the centerline are in reasonable agreement with the experimental data. The predicted carbon conversion at the gasifier exit agrees with the experimental data. The predicted temperature at the gasifier exit agrees with the estimated value based on water-gas shift equilibrium considerations. The numerical model was further applied to study the effects of the equivalence ratio, particle size, and swirl on the gasification process.
Finite Element-Based Brownian Dynamics Simulation of Nano-Fiber Suspensions in Nano-Composites Processing Using Monte-Carlo Method
Authors: Zhang Dongdong , Smith Douglas E.
Published: October 2013

This paper presents a computational approach for simulating the motion of nano-fibers during polymer nano-composites processing. A finite element-based Brownian dynamics simulation is proposed to solve the motion of nano-fibers suspended within a viscous fluid. In this paper, a Langevin approach is used to account for both hydrodynamic and Brownian effects. We develop a stand-alone Finite Element Method (FEM) for modeling the hydrodynamic effect exerted from the surrounding fluid. The Brownian effects are regarded as the random thermal disturbing forces/torques, which are modeled as a Gaussian process. Our approach seeks solutions using an iterative Newton-Raphson method for the fiber’s linear and angular velocities such that the net forces and torques, i.e. the combination of hydrodynamic and Brownian effects, acting on the fiber are zero. In the Newton-Raphson method, the analytical Jacobian matrix is derived from our finite element model. Fiber motion is then computed with a Runge-Kutta method to update the fiber positions and orientations as a function of time. Instead of re-meshing the fluid domain as fiber moves, we applied the transformed essential boundary conditions on the boundary of fluid domain, so the tedious process of updating stiffness matrix of finite element model is avoided. Since Brownian disturbance from the fluid molecules is a stochastic process, Monte-Carlo simulation is used to evaluate the motion of a great many fibers associated with different random Brownian forces and torques. The final fiber motion is obtained by averaging a numerous fiber motion paths. Examples of fiber motions with various Péclet numbers are presented in this paper. The proposed computational methodology will be used to gain insight on how to control fiber orientations in micro- and nano-polymer composite suspensions in order to obtain the best engineered products.
Model-Free Controller for a Pick-Up Semi-Active Suspension System
Authors: Tudón-Martínez Juan C. , Lozoya-Santos Jorge de Jesús , Vivas Carlos A. , Morales-Menendez Ruben , Ramirez-Mendoza Ricardo A.
Published: October 2013

A model-free controller for the full semi-active suspension system of a pick-up truck is proposed. The controller is focused in the passengers comfort and stability of the vehicle. A Combinatory quasi-Optimum Damping (COD) controller defines the best combination of damping force by analyzing the frequency response of the vehicle for all possible combinations among the semi-active dampers. The solution is defined in bandwidths by using a frequency estimation module of the road profile based on a Kalman filter. A model in CarSim™ was used as Software-in-the-Loop (SiL). The semi-active suspension system is composed by four experimental Magneto-rheological (MR) damper models. Simulation results show the controller benefits in comfort in the Bounce Sine Sweep (BSS) test, specially at frequencies close to the resonance frequency of the sprung mass (reduction of 50%). In the Double-Lane Change (DLC) test, the COD controller improves the roll control by reducing 28% the roll rate and 21% the roll angle. For the FishHook (FH) test, the improvement is high-lighted in the vehicle slip angle (reduction of 26%); however, the transient response of the yaw angle, yaw rate and lateral acceleration is better when the COD controller is used because the oscillations have lower amplitude with shorter settling time.
Computational Study of the Effects of Particle Size, Particle Injection Configuration, and Operating Pressure Gradient on Turbulent Dispersion of Spherical Micron-Sized Particles in a Generic Mockup Aircraft Cabin
Authors: Ebrahimi Khosrow , Zheng Zhongquan C. , Hosni Mohammad H.
Published: October 2013

Computational study of dispersion of particles is one way to evaluate the spread of contaminants and viruses amongst occupants of an enclosure, such as an aircraft cabin. In this investigation, the turbulent dispersion of particles in a ventilated generic cabin is studied. The generic cabin resembles one-half of a Boeing 767-300 aircraft cabin. In the first phase, the turbulent dispersion of particles injected through stainless steel straight vertical tube is simulated. A Lagrangian approach is used to predict the particle concentration in specified monitoring location inside the cabin. The steady RANS solutions for the airflow velocity data are used to initialize the particle-tracking calculations through the Discrete Phase Model (DPM). To calculate the effects of turbulence on the dispersion behavior of particles, a Discrete Random Walk (DRW) model is employed. The particle concentration field under steady-state, zero-gauge-pressure conditions for 3 μm and 10 μm spherical liquid particles are calculated. Through the comparisons between the measured and the calculated particle concentration data for the two examined sizes of mono-disperse particles, the effect of particle size on distribution behavior of micron-sized particles is investigated and discussed. In the second phase, in order to reduce the effect of initial injection velocity for 10 μm particles on their distribution, the straight injection tube is replaced by a cone diffuser while maintaining the upstream primary flow conditions. Using the same RANS model and under the new particle injection configuration, the characteristics of turbulent airflow in the cabin are found to be very similar to those of turbulent airflow without particle injection. A grid independency study is performed for the airflow velocity data prior to validation of the particle distribution results. The steady-state DPM simulations are performed initially for the zero-gauge-pressure condition and then the effect of pressurizing the cabin on particle distribution is investigated by increasing the gauge-pressure up to 0.025 inches of water. Through a detailed study, carried out to obtain an optimum number for the number of tries in the DRW, it is realized that the optimum number of tries is 175 for both cases of pressurized and non-pressurized cabin.
Micro-Fluidic Assisted Passive Direct Methanol Fuel Cells
Authors: Garza Gladys , Li Peiwen , Loy Douglas
Published: October 2013

A novel design of micro-fluidic structure has been proposed to facilitate passive methanol supply and ventilation of carbon dioxide in direct methanol fuel cells (DMFC). Experimental study was conducted for three in-house fabricated cells which have different membrane-electrode-assemblies (MEA) and cathode-side air-breathing current collectors. Low rate of passive methanol supply and control was accomplished through capillary-force-driven mass transfer in the in-plane of carbon paper wicks. The low methanol supply rate using this passive method only meets the need of fuel of the electrochemical reaction, and there is almost no surplus methanol that could cross over the membrane. The micro-fluidic structure on the anode plate also makes passive removal of the CO2 gas from the electrochemical reaction. The influence of the concentration of methanol and cell operation temperature was examined and compared in the study. The results reveal very promising performance in the passive DMFCs when a methanol concentration is above 8M.
Modeling Approaches to Accurately Predict Minimum Fluidization Characteristics of Gas-Solid Fluidized Beds
Authors: Kanholy Santhip Krishnan , Battaglia Francine
Published: October 2013

The hydrodynamics of fluidized beds involving gas and particle interactions are very complex and must be carefully considered when using computational fluid dynamics (CFD). Modeling particle interactions are even more challenging for binary mixtures composed of varying particle characteristics such as diameter or density. One issue is the presence of dead-zones, regions of particles that do not fluidize and accumulate at the bottom, affecting uniform fluidization. In Eulerian-Eulerian modeling, the solid phase is assumed to behave like a fluid and the presence of dead zones are not typically captured in a simulation. Instead, the entire bed mass present in an experiment is modeled, which assumes full fluidization. The paper will present modeling approaches that account for only the fluidizing mass by adjusting the initial mass present in the bed using pressure drop and minimum fluidization velocity from experiments. In order to demonstrate the fidelity of the new modeling approach, different bed materials are examined. Binary mixture models are also validated for two types of mixtures consisting of glass-ceramic and ceramic-ceramic compositions. It will be shown that adjusting the mass in the modeling of fluidized beds best represents the measured quantities of an experiment for both single-phase and binary mixtures.