bluuebunny/crossref_metadata_2025 huggingface dataset:
Renewable Hydrogen Production Using Sailing Ships
Authors: Platzer Max F. , Sarigul-Klijn Nesrin , Young J. , Ashraf M. A. , Lai J. C. S.
Published: August 2012

Vast ocean areas of planet Earth are exposed year-round to strong wind currents. We suggest that this untapped ocean wind power be exploited by the use of sailing ships. The availability of constantly updated meteorological information makes it possible to operate the ships in ocean areas with optimum wind power so that the propulsive ship power can be converted into electric power by means of ship-mounted hydro-power generators. Their electric power output then is fed into ship-mounted electrolyzers to convert sea water into hydrogen and oxygen. In this paper we estimate the ship size, sail area and generator size to produce a 1.5 MW electrical power output. We describe a new oscillating-wing hydro-power generator and present results of model tests obtained in a towing tank. Navier-Stokes computations are presented to provide an estimate of the power extraction efficiency and drag coefficient of such a generator which depends on a range of parameters such as foil maximum pitch angles, plunge amplitude, phase between pitch and plunge and load. Also, we present a discussion of the feasibility of sea water electrolysis and of the re-conversion of hydrogen and oxygen into electricity by means of shore-based hydrogen-oxygen power plants.
Mass Balance and Exergy Analysis of a Fast Pyrolysis System
Authors: Osgood-Jacobs Logan , Boateng Akwasi A. , Carlson Peregrine , Mullen Charles A. , Macken Nelson
Published: August 2012

Mass balance closure and exergetic efficiency is evaluated for a bench scale fast pyrolysis system. The USDA Agricultural Research Service (ARS) has developed this system for processing energy crops and agricultural residues for bio-oil (pyrolysis oil or pyrolysis liquids) production. Mass balance closure cannot be achieved due to the system size and complexity of inputs and outputs. A linear programming optimization model is developed to use the experimental data to achieve improved closure of elemental balances without losing the overall representation of the pyrolysis products. Having improved the mass balance, it is then possible to evaluate the exergy of the system. Exergy flows are computed using statistical relationships and other standard techniques. Computational details and results are discussed for switchgrass, a typical candidate biomass. Solutions for the minimum and maximum bio-oil outputs were generated. These particular results indicated that bio-oil accounted for approximately 10% of the loss mass. Considering all products as useful, the exergy destruction is approximately 20%. If the bio-oil alone is considered useful, the exergy destruction is about 40%. Further exercise of the model can be useful in evaluating mass losses and exergy for other feedstock and experimental runs.
Passive Multi-Scale Alignment
Authors: Kazmer David O. , Johnston Stephen P. , Moriarty Mary E. , Santeufemio Christopher
Published: August 2012

Methods are presented for self-alignment and assembly of objects with micron and nanometer-level features. The approach is a combination of kinematic coupling and elastic averaging in which mating alignment features spanning multiple length scales are successively brought into contact. When the objects are pressed together, the larger alignment features cause necessary deformation to ensure adequate alignment at the smaller length scales. Analytical and numerical modeling indicate that the largest alignment features can be designed to generally resolve global systematic errors while the smaller alignment features can correct local errors to achieve sub-micron alignment. Physical realization with ion beam etching, deposition, and thermal imprint lithography are also discussed.
Hydrogen Induced Fracture Near the Surface
Authors: Germanovich L. N. , Balueva A. V.
Published: August 2012

We consider fracture growth controlled by fluid diffusion into the fracture. If the fluid is accumulated inside the fracture, after some incubation period, it starts growing under the pressure of the accumulated fluid. An important example is given by hydrogen induced cracking. Hydrogen absorbed by a metal is typically dissolved in the lattice in the proton form. Some of the protons reach the surface of a pre-existing or freshly created crack where they recombine with electrons and form molecular hydrogen in the crack cavity. Because the molecular form of hydrogen usually is thermodynamically more stable, this process leads to accumulation of gas hydrogen inside the crack. Then the fracture can propagate even in the absence of any external loading, that is, only under the excessive hydrogen pressure. Another example is given by the heating of water saturated rock. If due to the heat, the water evaporates or boils inside the crack, the pressure exerted by the vapor can cause the cracks to propagate, increasing the crack size by orders of magnitude. This mechanism underlies the process of phreatic eruptions, which involves the transfer of magmatic heat to groundwater and subsequent eruption of steam and rock fragments, often without any eruption of magma. In this work we consider several important cases of diffusion-controlled fracture growth. We consider an axisymmetric crack (1) in the infinite space, (2) in the half-space, and (3) in the layer/plate. By implementing asymptotic analysis, we obtain in the closed form simple and robust expressions for the corresponding dependencies of the fracture size upon time. The results reveal some intriguing features worth checking experimentally. For example, although the driving pressures for identical axisymmetric fractures located far and close to the half-space boundary are very different, the expressions for their radii and velocities are exactly the same (i.e., within the accuracy of the higher-order terms with respect to the distance between the fracture and the free-surface). In a fluid-saturated layer (plate) an axisymmetric fracture located in the middle plane first depletes the region around itself but then starts growing towards the saturated regions. The process manifests itself as if the fracture were “sucked” into the saturated zone. This example shows, for example, that hydrogen-induced cracking may occur at very low hydrogen concentrations even if the crack (e.g., mechanical part) is no longer in the hydrogen-rich environment and only residual hydrogen is present. The developed model gives the time to failure and its dependence upon the concentration of diffusing fluid.
The Comparision of Hybrid and Quadrilateral Discretization Models for the Topology Optimization of Compliant Mechanisms
Authors: Zhou Hong , Dhembare Nitin M.
Published: August 2012

The design domain of a synthesized compliant mechanism is discretized into quadrilateral design cells in both hybrid and quadrilateral discretization models. However, quadrilateral discretization model allows for point connection between two diagonal design cells. Hybrid discretization model completely eliminates point connection by subdividing each quadrilateral design cell into triangular analysis cells and connecting any two contiguous quadrilateral design cells using four triangular analysis cells. When point connection is detected and suppressed in quadrilateral discretization, the local topology search space is dramatically reduced and slant structural members are serrated. In hybrid discretization, all potential local connection directions are utilized for topology optimization and any structural members can be smooth whether they are in the horizontal, vertical or diagonal direction. To compare the performance of hybrid and quadrilateral discretizations, the same design and analysis cells, genetic algorithm parameters, constraint violation penalties are employed for both discretization models. The advantages of hybrid discretization over quadrilateral discretization are obvious from the results of two classical synthesis examples of compliant mechanisms.
Exploring a Manufacturing Route to Produce WC-Based Micro-Cutting Tool With Nanostructured Material
Authors: Mekid Samir , Laoui Tahar , Patel Faheemuddin
Published: August 2012

Micro cutting tools used for micro machining by material removal (e.g. milling, turning) exhibit a high breakage rate due to various physical problems. This is partly due to the material characteristics. The present feasibility study intends to develop and manufacture a micro-tool by taking advantage of nano-structured powder material, prepared by mechanical milling process, with an ultimate objective to enhance the properties of the developed micro-tool. Cemented carbide, WC-Co, was used to produce the micro-tool. Hence, a processing route was defined to obtain nano-structured powders ultimately leading to the production of high performance cutting tools by appropriate consolidation. A couple of dies were designed and tested to understand limitations and issues related to the production of such micro tools. The introduction and compaction of the nano-structured WC-Co powder inside the die micro cavity features proved to be a challenge. Following compaction, the micro-tool shaped compacts were sintered at 1400°C for two hours under inert atmosphere. Samples with a large aspect ratio are shown and a couple of challenges are discussed.
Near-Field Radiative Transfer Between Heavily Doped SiGe at Elevated Temperatures
Authors: Zhang Z. M. , Enikov E. T. , Makansi T.
Published: August 2012

SiGe alloys represent an important type of high-temperature semiconductor material for solid-state energy conversion. In the present study, the near-field radiative heat transfer between heavily doped SiGe plates is investigated. A dielectric function model is formulated based on the previously reported room-temperature mobility and temperature-dependent electric resistivity of several silicon-rich alloys with different doping type and concentration. The fluctuational electrodynamics is used to evaluate the near-field noncontact heat transfer coefficient. The variation of the heat transfer coefficient with doping concentration and temperature is explained according to the change in the optical constants and in the spectral distribution of the near-field heat flux.
Numerical Simulation of Thin-Film Photovoltaic Solar Cells
Authors: Sayed Khairy , Abdel-Salam Mazen , Ahmed Mahmoud , Ahmed Adel A.
Published: August 2012

The objective of this work is to develop a detailed numerical simulation of solar photovoltaic cells in one, two, and three-dimensions. Such kind of numerical simulation can be used as a flexible research tool for the design and analysis of solar cells. The developed in-house simulation code has the advantage of conducting modifications of the suggested configurations to include effects not covered by the commercial simulation models. In addition, this tool is to serve as a test-bed simulator for the development of solar cells modeling and to design new material models. The photovoltaic solar cells governing equations are Poisson’s equation, the hole and electron continuity equations. Poisson equation is generally used to get the voltages across the device. However, in the present work, it is used to obtain the value of the electrical charge. The governing equations along with the appropriate boundary conditions are solved numerically using a finite difference based method. The resulting system of coupled nonlinear equations is then solved using Newton method for nonlinear systems. The predicted results include illuminated current-voltage characteristic, and dark current-voltage characteristics of photovoltaic module. Comparisons between predicted results and corresponding measured values by manufacturer are conducted in order to validate the numerical simulation. A good agreement between predicted and measured results was prevailed.
Dynamic Response of Underwater Structures Subject to Impact Loads
Authors: Sun Lingyu , Chen Weiwei , Wang Xiaojie , Kang Ning , Xu Bin , Hu Dayong
Published: August 2012

The present paper studied the dynamic response of an underwater system with its navigation plate rotated relative to the main body until it was blocked by an energy absorber. In this process, the relation between fluid-driving moment and speed of main body, as well as the relation between rotation angle of the plate and design parameters of absorber, was investigated through combined finite element method and finite volume method. Before the plate contacted with the energy absorber, it was modeled by linear elastic material, the movement process was solved by finite volume method with dynamic boundary. When the plate started to contact and crash with the absorber, it was modeled by elastic-plastic material, and the interaction of fluid-structure coupling was simulated by explicit finite element method in LSDYNA and finite volume method in FLUENT. The two-way data exchange on the interface between fluid and structure was carried out through equivalent force and moment on each patch of the interface. In addition, the simulation accuracy on large plastic deformation of absorber was verified through a group of drop hammer experiments. After the energy absorber was crushed to ultimate shape, the open angle of plate reached the maximum value and the plate kept relative static to the rigid body. The maximum structural stress and deformation, the opening time and angle of the plate were evaluated by numerical method. It is demonstrated that the proposed method can effectively predict the dynamic response of underwater system under impact loads, and both the absorption capability of the block and the speed of moving body affect the dynamic response history and structural safety.
Identifying Indicators of Driving in a Hurry
Authors: Rendon-Velez Elizabeth , Horva´th Imre , van der Vegte Wilhelm Wilfred F.
Published: August 2012

Due to an increase in the use of cars and the growing complexity of driving situations, the number of people injured in traffic accidents has increased to 50 million. One of the most crucial factors contributing to accidents is driver’s behavior. A driver state which is known to provoke risky driver behavior is haste. Haste is defined as the state where the driver has feelings of urgency or pressure due to a lack of temporal resources. If it would be possible to automatically detect when a driver starts hurrying for being late for an appointment, this could be used to develop novel accident-prevention systems. The research reported on in this paper aims at exploring knowledge for the development and implementation of a car subsystem that can reliably detect driving in haste. Identification of indicators of haste has not received much attention in research so far. In this paper we present how we gathered the necessary knowledge and qualified indicators by contrasting the findings of a literature study with that of five focus group sessions, involving drivers and experts. These explorative studies have confirmed our assumption that haste not only manifests in changed human behavior, but it also influences human-car interaction, the state of the car and the car-environment interaction. Accordingly, we have sorted the proposed indicators into groups, and validated them from several aspects. This knowledge provides a good basis for the follow-up research cycles, in which we will test the strongest indicators, investigate the opportunities of detecting them within cars, and propose a technical solution for detecting driving in haste.
Dynamic Modeling of Tape Head Actuator Lateral Motion With Elastica Suspension
Authors: Chang Jen-Yuan James
Published: August 2012

A combined elastica and magnetic modeling is presented in this paper with focus given to understanding effect of flexible printed circuit cable and voice coil motor’s dynamic effect on tape head actuator’s lateral motion in advanced, high capacity tape drives. The flexible printed circuit cable which connects the actuator to printed circuit board is first examined through establishment of analytical model to predict its profile with considerations of boundary conditions and mechanical design parameters. Secondly, equivalent stiffness produced by the flexible printed circuit cable when the linear tape head actuator is positioned along its lateral positions is examined. Finally, effect of tape head actuator’s voice coil motor is studied and modeled as a magnetic suspension, contributing to stability and controllability of the actuator lateral motion dynamics. Validated by calibrated laboratory experiments, the work presented in this paper can add to the literature regarding dynamics and control of LTM in modern LTO drives.
Investigation of Polygonal Airflow Structure in Hard Disk Drives With and Without Spoiler by Using Fluid Simulations and Measurements
Authors: Ikegawa Masato , Mukai Hiroshi , Sugii Taisuke , Watanabe Masatoshi
Published: August 2012

The polygonal airflow patterns between disks in hard disk drives (HDDs) were investigated by using fluid simulations and pressure measurements. These patterns were found from the radial velocity distributions of airflows on the mid-plane between disks. Several peaks of pressure increases caused by rotating polygonal-airflow patterns with several modes were measured with a pressure sensor placed on the tip of the carriage arm and spoiler. Several modes of polygonal patterns were observed at the outer diameter (OD) and the middle diameter (MD) arm positions, but not at the inner diameter (ID) arm position. These peaks on the arm were weakened by the spoiler.
Tensile and Bending Properties of Jute Fiber Mat Reinforced Unsaturated Polyester Matrix Composites
Authors: Elbadry E. A. , Aly-Hassan M. S. , Hamada H.
Published: August 2012

Jute fiber mat reinforced unsaturated polyester matrix composites having different fiber weight contents (11, 22, 32 wt%) were fabricated by modifying the hand lay-up technique with resin pre-impregnation into the jute mats in the vacuum. Tension and three-point bending tests were carried out to evaluate the effect of fiber contents on these mechanical properties of above-mentioned composites. The results showed that as the fiber weight content increases, tensile strength and modulus increase and the improvement had occurred at 22 wt% of fiber weight content with respect to that of neat resin. As the fiber weight content increases, flexural strength and modulus increase and the improvement had occurred at 11 and 32 wt% fiber contents for the flexural modulus and strength respectively compared to those of neat resin. Fiber pull out mechanism is the failure mode revealed at the fracture surfaces under tensile loading as well as at tension side of composites under bending loading.
The Optimization of Vibration Induced by a V6 Engine Cooling Module
Authors: Yang Ji , Hao Zhiyong , Ge Ruwei , Wang Liansheng , Zheng Kang
Published: August 2012

The engine cooling module consists of condenser, radiator and fan (CRFM), which has long been recognized as a main source of sound and vibration in the automotive industry. As the engine becomes increasingly compact and powerful, customers gradually have higher expectations for automobile NVH performance than ever before. Thus the reduction of noise and vibration induced by CRFM becomes critical, which can greatly influence overall NVH performance. Combined with experimental and numerical methods, this paper focuses on the identification and optimization of steering wheel (SW) vibration induced by CRFM for a vehicle with V6 engine while engine idling. The numerical model established in this paper, based on Matlab and taking chassis vibration into account, can predict and optimize the vibration of CRFM under specific working condition with the help of energy decoupling and Newmark-Beta methodology. The optimization design of CRFM mainly involves the stiffness, position and angle of isolators. The numerical simulation results are validated experimentally, which can help further design of CRFM.
Modeling Constrained Layer Frictional Interfaces With Discontinuous Basis Functions
Authors: Brake M. R. , Starr M. J. , Segalman D. J.
Published: August 2012

Constrained layer frictional interfaces, such as joints, are prevalent in engineering applications. Because these interfaces are often used in built-up structures, reduced order modeling techniques are utilized for developing simulations of them. One limitation of the existing reduced order modeling techniques, though, is the loss of the local kinematics due to regularization of the frictional interfaces. This paper aims to avoid the use of regularization in the modeling of constrained layer frictional interfaces by utilizing a new technique, the discontinuous basis function method. This method supplements the linear mode shapes of the system with a series of discontinuous basis functions that are used to account for nonlinear forces acting on the system. A symmetric, constrained layer frictional interface is modeled as a continuous system connected to two rigid planes by a series of Iwan elements. This symmetric model is used to test the hypothesis that symmetric problems are not subjected to the range of variability seen in physical structures, which have non-uniform pressure and friction distributions. Insights from solving the symmetric problem are used to consider the case where a non-uniform distribution of friction and pressure exists.
Residual Stress and Wave Reflectivity When Laser Peening Thin Curved Sections
Authors: Malik Arif , Lai Xiaopeng , Langer Kristina
Published: August 2012

Laser Peening is an emerging technology that shows promise for extending the fatigue life of special-purpose metal components in the aerospace, automotive, medical, manufacturing, and other industries. While laser peening has been shown to extend the fatigue life of metal components such as turbine blades and other high value-added components, the technology is not yet understood well enough to deploy it cost-effectively, without extensive experimental testing, for widespread application in diverse industries. Because laser peening can adversely affect fatigue life if the process parameters are not selected appropriately, identification of tamping layers, pulse energy densities, shot patterns, and other parameters is critical to the component geometry, material, and loading. When laser peening thin sections, preliminary finite element studies indicate that reflectivity of shock waves can induces regions of residual stress or damage on opposing surfaces. Through a series of finite element simulations, this work explores the effects of stress wave reflectivity on component life for thin, curved, 6061-T6 aluminum alloy sections. The simulations are based on an 800 mJ, 5 ns pulsed, near-infrared laser, serves to define the pressure pulse boundary condition, and allow more reliable deployment of laser peening technology.
Enhancing Student Performance by Promoting Self-Regulated Learning
Authors: Shih Hui-Ru , Zheng Wei , Leggette Evelyn J. , Skelton Gordon
Published: August 2012

Self-regulated Learning (SRL) focuses on the use of self-evaluation and self-motivation to aid the student in developing the correct habits, techniques, and tools necessary for success in a learning environment. With self-regulated learning, students can evaluate their study and learning strategies. Training programs that promote self-regulated learning have been found to be beneficial for students’ learning. SRL is currently viewed as a vital prerequisite for the successful acquisition of knowledge in school and beyond. However, SRL is not well known and utilized by the Engineering and Technology education community for facilitating student learning. Self-regulated learning is an important but difficult concept to present to students. The application of self-regulation to learning is a complicated process involving not only the awareness and application of learning strategies but also extensive reflection and self-awareness. This paper describes the design and development of the SRL instructional strategies, their implementation, and the evaluation of their effectiveness. The outcomes are provided and recommendations are discussed.
Waypoint-Based Robot Navigation Using NURBs-Based Metamodels
Authors: Steuben John , Turner Cameron J.
Published: August 2012

Effective path planning techniques for mobile robots have potential uses and ramifications in a wide range of fields. As a result, the study of these techniques is highly diverse, and historically rich. In this vein we present a path planning methodology for a particular type of robot — one which flies above a terrain but must periodically land at waypoints. The approach demonstrated here is notable for drawing its inspiration and working basis from several different engineering fields. NURBs-based metamodels, a concept developed in the field of engineering design, are used to represent terrain to be navigated. Goal programming, largely used in operations research, is used to determine optimal landing waypoints. Graph theory concepts (derived from the field of computer science) are used to generate robot paths, and more broadly as data structures for information management. We demonstrate the new method on a variety of terrain maps, and present our conclusions on the effectiveness of the algorithm. We close with remarks regarding potential future developments and improvements that may be made to increase the utility of this approach.
Scale Analysis of Thermocapillary Weld Pool Shape With High Prandtl Number
Authors: Wei P. S. , Lin C. L. , Liu H. J.
Published: August 2012

The molten pool shape and thermocapillary convection during melting or welding of metals or alloys are self-consistently predicted from parametric scale analysis for the first time. Determination of the molten pool shape is crucial due to its close relationship with the strength and properties of the fusion zone. In this work, surface tension coefficient is considered to be negative values, indicating an outward surface flow, whereas high Prandtl number represents the thermal boundary layer thickness to be less than that of momentum. Since Marangoni number is usually very high, the scaling of transport processes is divided into the hot, intermediate and cold corner regions on the flat free surface, boundary layers on the solid-liquid interface and ahead of the melting front. Coupling among distinct regions and thermal and momentum boundary layers, the results find that the width and depth of the pool can be determined as functions of Marangoni, Prandtl, Peclet, Stefan, and beam power numbers. The predictions agree with numerical computations and available experimental data.
Hardware Demonstration of Classical Undergraduate Control Design Methods Using MATLAB Real-Time Windows Target Environment
Authors: Enikov Eniko T. , Polyzoev Vasco , Gill Joshua
Published: August 2012

Engineering education has the objective of not only presenting the scientific principles, i.e., engineering science, but also of teaching students how to apply these to real problems. Therefore, hands-on laboratories have been an integral part of the engineering curriculum since its inception [1–3]. This presentation will demonstrate the use of a novel low-cost experimental apparatus for use in a typical undergraduate course in control systems taught to mechanical engineering students, i.e. students with limited exposure to electrical engineering. A simple to use, low cost system has been designed that provides a platform for experimentation in areas from basic open loop control, to frequency domain and digital control systems. This paper presents the design of the system, and demonstrates the ability of MATLAB tools such as Simulink Real Time Windows Target to illustrate implementation of various aspects of control design. The system setup consists of a DC micro-motor attached to a carbon fiber rod. The angular displacement is measured with an analog potentiometer, which acts as the pivot point for the carbon fiber rod. The DC micro-motor is powered by a low cost, custom circuit board, whos H-bridge allows the motor rotate in either forward or reverse directions. Attached to the micro-motor is a small propeller, providing thrust force to rotate the pendulum about its potentiometer. The circuit board communicates to the host computer using the USB protocol, utilizing usbser.sys to create a virtual COM port. MATLAB uses the serial port object to read and write from the control board. The control board is powered through two USB ports, requiring no external power adaptor or extra cabling. This paper shows the use of feedback linearization to arrive at a system where classical linear control design methods can be used. The project was tested in a classical control systems design class offered to senior-level mechanical engineering students. Student feedback and survey data on the effectiveness of the module is also presented.
Modeling and Simulation of a Bio-Mimetic, Antagonistically Actuated, Limb Joint
Authors: Noble Frazer K. , Potgieter Johan , Xu W. L. Peter , Chang Jen-Yuan James
Published: August 2012

Wearable assistive devices’ (WADs) development is impeded by traditional actuators’ and control paradigms’ lack of compliance and adaptability; as such, the central nervous system’s (CNS) actuation and control principles have been investigated in order to overcome these limitations in a novel way. A bio-mimetic model of a limb joint, which is antagonistically actuated by two Hill-type muscles, is presented. Limb joint stability and transient response, as functions of co-activation, have been investigated. Three simulations have been carried out: equal (Af(f,f)), unequal (Af(3,f)), and differential (Af(3,Ramp(g))) co-activation. For normalized stimulus frequency range: 1 ≤ f ≤ 3, equal and unequal co-activation leads to increased limb joint damping and reduced transient oscillation. For the equally/unequally co-activated case, the linearized model’s dominant complex-conjugate poles become increasingly negative and tend towards the real axis, which indicate that increased co-activation leads to increased joint stability. With respect to differential co-activation, increasing the limb joint’s antagonistic muscle’s normalized stimulus frequency’s (f) rate of change (g) leads to increased angular velocity (ω); however, at a cost of increased overshoot. Differential activation of the antagonistic muscle results in positive angular rotation (Θ).
Bearing Strength Analysis of Pin-Loaded Elliptical Holes in Laminated Composite Joints
Authors: Aluko O. , Whitworth H. A.
Published: August 2012

An analysis was performed to predict bearing strength and mode of failure of pin loaded orthotropic plates with elliptic holes of varying sizes using two dimensional stress analyses and a characteristic curve model. The stresses required to analyze joint failure were obtained by utilizing complex stress functions that were determined from assumed displacement expressions that satisfy the boundary conditions around the hole. Three different joint geometries with major-to-minor diameter ratios ranging from 1 to 5 were evaluated and the analysis revealed that the joint strength was found to vary with increasing major-to-minor diameter ratios. The material properties of graphite/epoxy laminates were used in this investigation.
Hydrodynamic Added Mass and Damping of the Kaplan Turbine
Authors: Keto-Tokoi Jyrki M. , Matusiak Jerzy E. , Keskinen Erno K.
Published: August 2012

Kaplan turbine runner rotates in water flow inside an enclosed discharge ring. The vibratory runner motion in the fluid flow induces pressure forces onto the wet runner surfaces with inertia effects conveniently described by the so-called hydrodynamic added mass and damping. These inertia effects influence the wet natural frequencies and the amplitudes. The role of the hydrodynamic added mass and damping in the Kaplan turbine shaft rotor dynamics has not been sufficiently well understood. This paper focuses on comprehensive understanding of these phenomena across the Kaplan design range. The results are based on a method derived from Theodorsen’s unsteady thin airfoil theory and on the Finite Element Method (FEM). The former method includes the water flow, the runner rotation and the circulatory effects, which makes it possible to calculate the added damping and evaluate the accuracy of FEM. The most critical vibration modes and shaft line configurations have been identified with inherent weaknesses in typical shaft line models. The added damping has been quantified. The numerical results have been compared to the experimental results.
Determination of Minimum Fluidization Velocity for Gas-Solid Beds by Experimental Data and Numerical Simulations
Authors: de Souza Braun Meire Pereira , Palma Geraldo Luiz , Navarro Helio Aparecido , Varoto Paulo Sergio
Published: August 2012

The purpose of this work is to predict the minimum fluidization velocity Umf in a gas-solid fluidized bed. The study was carried out with an experimental apparatus for sand particles with diameters between 310μm and 590μm, and density of 2,590kg/m3. The experimental results were compared with numerical simulations developed in MFIX (Multiphase Flow with Interphase eXchange) open source code [1], for three different sizes of particles: 310mum, 450μm and 590μm. A homogeneous mixture with the three kinds of particles was also studied. The influence of the particle diameter was presented and discussed. The Ergun equation was also used to describe the minimum fluidization velocity. The experimental data presented a good agreement with Ergun equation and numerical simulations.
Numerical Study of Cavitation Characteristics of Profiles for Use in Marine Current Turbines
Authors: Ladino Alexander
Published: August 2012

Kinetic energy in the oceans offers an important and promising source of renewable energy which can be exploited by marine current turbines (MCT). One of the key issues related with design of MCT’s is the cavitation inception along turbine blades. Cavitation occurrence in MCT’s blades generates erosion and poor power performance with similar effect in the hydraulic turbine case. In this work, a numerical investigation using the vorticity–stream function code XFOIL in order to study cavitation characteristics in NACA 4 series profiles was performed. The study was developed systematically starting from NACA 4415 profiles and varying independently camber percentage, camber position and thickness. Other study carried out was the effect of trailing edge deflection in the cavitation bucket. Results show a symmetrical increment in cavitation free zone for profiles with increasing thickness. Also for camber increment, the cavitation free zone is incremented, especially at high angles of attack. For variation of camber percentage, increasing camber produces the cavitation bucket moves to high lift zone which suggest that the profile could cavitate at low and negative Cl in wide range of cavitation numbers. Finally the effect of trailing edge deflection produces a slight increment in cavitation free zone which is similar to the effect of camber increment. Also, the trailing edge deflection shows that a same Cl can be achieved with lower angle of attack and lower pressure coefficient compared with the standard profile, constituting a desired behavior from the cavitation point of view. Finally, local dimensionless correlations were developed which can be used for parametric studies of cavitation performance of MCT’s in the design stage.
Development of a Practical Broadband Active Vibration Control System
Authors: Schiller Noah H. , Perey Daniel F. , Cabell Randolph H.
Published: August 2012

The goal of this work is to develop robust, lightweight, and low-power control units that can be used to suppress structural vibration in flexible aerospace structures. In particular, this paper focuses on active damping, which is implemented using compact decentralized control units distributed over the structure. Each control unit consists of a diamond-shaped piezoelectric patch actuator, three miniature accelerometers, and analog electronics. The responses from the accelerometers are added together and then integrated to give a signal proportional to velocity. The signal is then inverted, amplified, and applied to the actuator, which generates a control force that is out of phase with the measured velocity. This paper describes the development of the control system, including a detailed description of the control and power electronics. The paper also presents experimental results acquired on a Plexiglas window blank. Five identical control units installed around the perimeter of the window achieved 10 dB peak reductions and a 2.4 dB integrated reduction of the spatially averaged velocity of the window between 500 and 3000 Hz.
Combined Experimental and Numerical Study of a New Configuration of Multiple Microchannel Heat Sink for Heat Removal
Authors: Zhang Jingru , Jaluria Yogesh
Published: August 2012

In this paper, single phase incompressible liquid flow in a new microchannel heat sink design, which includes flow bifurcation, is studied experimentally and numerically. The experimental setup and device fabrication are briefly explained. The experimental results are presented with uncertainty in the measurements. The numerical model is based on a commercial code and is validated by experimental results with the same initial and boundary conditions. Numerical results with both constant fluid properties and variable properties are compared with the experimental data. The thermal-hydraulic performance of the new design is investigated. The effects of the resulting fluid flow and the geometry on the thermal resistance of the system are discussed.
Flow Distribution Measurements From an Air Cooled Condenser in a ~400MW Power Plant
Authors: Walsh E. J. , Grimes R. , Griffin G.
Published: August 2012

The use of air cooled condensers in power generation is increasing in many arid regions of the world. The classical A-frame condenser design is implemented in most new installations despite significant empirical evidence that such designs suffer from poor efficiencies and weather effects, and therefore provide significant scope for improvements. An inefficient condenser results in higher back pressure on the turbine, over-sized condensers and increased fan power. This paper addresses the flow distribution from an air cooled condenser for a ∼400MW gas and steam power plant. The results indicate that the flow patterns from the large scale fans results in a severe inhomogeneous distribution of cooling on the condenser fins. These region of high and low velocity are closely related to the outlet flow pattern from the fans, where in the hub region the air mass flow rate is reduced, while in the tip region it is increased. These measurements provide an excellent basis for both understanding the existing deficiencies of the A-frame designs and moreover provide direction for improved designs in the future.
Electro-Thermal Modeling of Solar Photovoltaic Arrays
Authors: Sayed Khairy , Abdel-Salam Mazen , Ahmed Mahmoud , Ahmed Adel A.
Published: August 2012

The objective of the present work is to develop a dynamic electro-thermal model for photovoltaic cells to optimize both electrical and thermal performance of such systems. The thermal model is developed by generating the equivalent RC network (resistance-capacitance) parameters. Then, the thermal model is combined with electrical model and implemented by PSIM simulation program to evaluate performance parameters for any predefined operating condition. The electro-thermal model predicts instantaneous temperature of photovoltaic device at the actual circuit working conditions. Consequently, the temperature rise during the system startup and during load transient is investigated. The thermal model predicts the junction temperature based on transient heat dissipation calculated from the electrical model. The calculated junction temperature is used as an input to the electrical model. The factors that control the junction temperature are module reaching irradiance, optical properties of the photovoltaic cell, photovoltaic conversion efficiency, heat transfer and electrical characteristic of the load. If the junction temperature exceeds a certain limit, it causes hotspot on the photovoltaic module surface. Consequently, the formed hotspots result in reducing the system efficiency and life time. The predicted dynamic behavior of photovoltaic cell is compared with theoretical predictions and other reported data in order to validate the developed model. The obtained results show a good concurrence with the predictions of other works. Detailed comparisons between predicted and measured results are reported and discussed.
Impact of CHP System Component Efficiencies on the Economic Benefit of CHP Systems Using Spark Spread Analysis
Authors: Smith Amanda D. , Mago Pedro J. , Fumo Nelson
Published: August 2012

A combined heating and power system (CHP) can take the place of a conventional system with separate heating and power (SHP) where electricity is purchased from the grid. The CHP system provides electrical energy through a prime mover located near the building it serves, and waste heat from this generation is captured and delivered to the building to provide thermal energy. For a CHP system to show an economic advantage over a conventional system, its operating costs must be lower when providing the same amount of thermal energy and electricity that would have come from the SHP system. The spark spread (SS), or price difference between purchased electricity and fuel, is used as a simple indicator as to whether the CHP system is economically viable. Rather than using a single value of SS as a cutoff for viability of the CHP system, a more detailed spark spread expressed in terms of the efficiencies of the CHP system and SHP system components can be used to determine if a CHP system is economically viable. In an initial feasibility study, the calculation of the SS is based on estimates of a number of variables. It is important to assess the likely impact of changes in certain of some of these variables, as such changes can affect the SS calculations. This paper presents a sensitivity analysis to determine the effects of different parameters on the cost ratio which is used to calculate SS, including: reference heating system efficiency, power generation unit (PGU) efficiency and CHP overall system efficiency. Because CHP system efficiency itself is a function of the PGU efficiency as well as the thermal efficiency, these two parts of the total system efficiency are also investigated separately. Since the cost of purchased electricity and fuel varies by geographic region, the required spark spread for a given system may indicate favorable economics for a CHP system in one location while the CHP system shows no potential for savings in another location. Therefore, the sensitivity analysis is considered for three different U.S. locations.
Effect of Prelube, Surface Coating and Substrate Materials on Initial Strength of Adhesive Joints Between Al Alloy and Steels
Authors: Zhang Fan , Wang Hui-Ping , Hicks Christina , Carlson Blair E. , Yang Xin , Zhou Qing
Published: August 2012

Growing usage of lightweight materials such as Al and Mg alloys in automotive body manufacture has come to a point that bonding of dissimilar materials is a realistic problem to address. A significant issue related to the bonding of dissimilar materials is that the differences in substrate surface conditions and substrate strengths often lead the bond to fail at strength far less than the bond strength established by adhesive manufacturer for a balanced joint. This research experimentally studied several factors potentially influencing initial strengths and debonding modes of adhesively-bonded Al-steel joints using single lap-shear coupons with comparison to like-substrate joints. Three commonly-used SLS coupon fabricating processes were investigated to determine which provided consistent bond strength and was efficient in making large quantities of coupons for the subsequent study. Next, the effect of prelube on the initial bond strength and debonding mode was investigated since the amount of prelube varies from sheet to sheet in automotive production. It was observed that even a very small change in the amount of prelube being applied on Al affected the initial bond strength. The more the prelube the weaker the bond became and the more adhesive failure occurred on the bonded Al surface. On the other hand, varying amount of the mill oil on the steel surface did not make much change to the bonding strength. Finally, various combinations of Al and steel substrates were studied to observe the effect of substrate materials on the initial bond strength and failure behavior. It revealed that the strength of joints between a relatively strong substrate and a relatively weak substrate fell below the strength of identical material joint made of the relatively strong substrate, and was closer to the strength of identical material joint made of the relatively weak substrate. For bonds having a high joint efficiency, adhesive failures were observed mostly on the surfaces of relatively weak substrates in the dissimilar material bonds due to large deformation in the weak substrate resulting in higher loading on that interface.
Heat Transfer Enhancement in Rectangular Channels Using a Corona Jet Caused by Longitudinal Flat Electrodes
Authors: Lakeh Reza Baghaei , Molki Majid
Published: August 2012

Heat transfer in rectangular channels can be significantly enhanced by formation of secondary flows. Secondary flow fields appear within the channels and influence the boundary layer growth and improve the convective heat transfer. When a high potential is applied to two electrodes, the consequent high electric field in the gap between the electrodes may exceed the partial break-down limit of the gas molecules. The neutral gas molecules are ionized close to the emitting electrode and accelerate in the direction of the electric field. The accelerating ions impose an electric body-force to the gas and induce a bulk flow. Depending on the location and geometry of the electrodes, the electrically-induced flow field might have different specifications. If the electrodes are laid on the opposite walls of channel and extended in the longitudinal direction, the electric body-force would cause a secondary flow on the cross section of the channel. The electrically-induced flow field disturbs the boundary layer and enhances the convective heat transfer coefficient. However, the enhancement level is more remarkable in natural convection. In this study, the influence of a corona jet on heat transfer in rectangular channels with flat and longitudinal electrodes will be studied. The emitting and collecting electrodes are metallic strips attached to opposite walls of the channel and are extended along the axis of the channel. The electric field governing equations are solved numerically using finite-volume method and the third-order QUICK scheme is utilized for discretization of the charge fluxes. The distribution of electric field and charge density on the cross section of the channel is obtained to find the electric body-force at each point. In the presence of electric and buoyancy forces, the momentum and energy equations are solved to determine the level of enhancement of convective heat transfer using corona discharge.
A Variant Algorithm for Solving Eigenvalue Equation in Linear Stability Problems
Authors: Qiao Zongchun , Kaloni P. N.
Published: August 2012

We present a new approach, based upon the chebyshev tau-QZ algorithm, quesi-Newton technique, and the minimum optimization routine, to study the numerical solutions of the non-linear eigenvalue problem, arising in the linear stability analysis of non-Newtomian fluid. One principal advantage of our approach is that the resolution of the non-linear eigenvalue problem is changed into a search algorithm, and the calculation leading to the determination by both natural stability and overstability can be unified in a single code. Numerical results show that our results, obtained by this approach, are in excellent agreement with the worthy previous authors.