bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Noise Emissions of a Passenger Vehicle
Authors: San Roma´n Jose´ Luis , Di´az Vicente , Cobo Pedro , A´lvarez-Caldas Carolina , Calvo Jose´ Antonio , Garci´a-Pozuelo Daniel , Gauchi´a Antonio , Ibarra David , Olmeda Ester , Quesada Alejandro
Published: August 2012

One of the main sources of noise pollution in cities is vehicle traffic. In this paper a characterization of the noise emission of a passenger vehicle has been carried out. With this aim a representative driving route for noise emission has been defined in order to study the influence of the driver typology and vehicle type. Therefore, this investigation has been developed in three phases: Firstly, usual driving in an urban area like Madrid has been characterized with a specific driving route. In addition, several vehicle models with great presence in the existing fleet of cars have been selected. Several drivers have covered the driving route at different times of the day and previous parameters have been measured in each test in order to determine average values of behavior. Secondly, the type of vehicles and drivers influence in noise emissions has been deeply analyzed. To achieve this aim a sample of vehicles has been instrumented to obtain physical measurements of the variables that can influence the noise emission level. Positions, velocities, accelerations (longitudinal and lateral) and time have been analyzed using a GPS sensor. Parameters such as, engine speed, engine load, throttle position and engine temperature have been studied through the vehicle CAN BUS and a set of microphones has measured the emitted noise in several points of the vehicle. In order to study the ecological and safety impact in urban and interurban roads by means of the measurement of noise emissions the analysis of the driver behaviour is of paramount importance. To conclude, the previous data has been analyzed and noise equivalent levels have been identified with different test configurations.
Natural Frequency Improvement of a Suspended FGM Bridge
Authors: Hadipour M. , Ahmadian M. T. , Lashkari S. G. , Barari A.
Published: August 2012

In this paper application of Functionally Graded Materials (FGMs) in suspension bridge structures for the purpose of vertical vibration improvement is investigated. Functionally graded materials are inhomogeneous composites, which are usually made from a mixture of metal and ceramic. Initially the classical equation of motion is modified based on the FGM model and natural frequencies of structure are extracted by Galerkin method. The material properties of structure vary continuously in the longitude direction according to power law form. In this regard, combination of materials is structured in such a way that the desired frequencies of the bridge are achieved by designing the proper power law of the FGM. Natural frequencies are evaluated to avoid any resonant due to environmental vibration. A bridge structure based on FGM made of steel and aluminum oxide is designed and improved for proper frequency. For the simple case of homogenous structures results are compared with those reported in the literature and very good agreements are obtained.
Study of Multifractal Parametrization for Prediction of Structural State of Properties of Metal Materials
Authors: Galimov Engel , Kudrin Alexei , Kuryntsev Sergei , Gorbunov Alexei
Published: August 2012

Among the pressing problems of powder metallurgy is to establish relationships between the properties of carbon powder alloys based on iron and multifractal parameters of their microstructure. Solution to this problem will enable the indirect determination of the strength characteristics of alloys without the need for costly mechanical testing.
A Three-Axis Thermal Accelerometer
Authors: Dinh Thien X. , Ogami Yoshifumi
Published: August 2012

The paper presents the numerical design and performance of a triple-axis thermal accelerometer. In a typical thermal accelerometer, a heater is suspended at the center and sensing elements are located around the heater on the opening side of a cavity. Consequently, the sensitivity of the vertical axis measurement is very low in comparison with the horizontal axes measurements and the cross-sensitivity between these measurements is very high. In our new design, the heater is formed a wide ring and the sensing elements are located both inside and outside of the heater ring with a small elevation from the heater plane. The obtained results show that the sensitivity of the vertical axis measurement attains to the order of the horizontal axes measurements. The cross-sensitivities among three axes are less than 4%. For instance, at the supplied power of 15mW to the heating resistor, the sensitivity of the accelerometer is 0.12°C/g in the vertical axis and 0.25°C/g in the horizontal axes.
Flow About an Oscillating Plate Used to Extract Sea-Wave Energy
Authors: Mahmood Faraz , Huynh B. P.
Published: August 2012

As a sea wave comes to the shore then recedes from it, there is significant energy associated with the movement of the wave’s water. One way to extract this energy is to have the moving water push and pull on an oscillating vane. This work examines numerically the flow and forces associated with such a vane in a typical wave condition, using a commercial Computational Fluid Dynamics (CFD) software package. The vane is a rectangular plate hinged at one edge and oscillating about it. Effects of plates shape on the flow pattern and developed forces are investigated. Changing the plate shapes can results in more energy extraction from the device.
A Model for the Evaluation of Energy Indicators in End Users Audit for Hospital Sector
Authors: Lucentini Marco , Rottenberg Flavio , Di Palma Diego
Published: August 2012

Hospitals are complex building systems and they uses a large amount of energy in many different ways. Generally energy efficiency is not one of the main priorities in such structures, where the management mainly focuses on the continuity and the reliability of the energy supply. As a consequence this sector shows a high potential for energy savings. Furthermore the energy efficiency measures enforce the energy systems reliability. The first step in implementation of energy efficiency objectives and measures is the audit phase where the initial energy performance is assessed. Generally a complete audit needs the collection of many parameters and data (indicators) and that makes this procedure very long and expensive. Sometimes it is impossible to completely estimate the energy performance because of a lack of information. This paper proposes an algorithm able to operate a substantial reduction of all the indicators to be collected for the evaluation of the performance of energy end users. The model makes possible to estimate all the energy performance indicators (dependent) as a function of a small number of indicators (independent) whose estimation is simpler. It has been applied to the hospitals sector, but can be applied also to domestic energy sector and to a large number of the tertiary and commercial end users. The model operates the implementation of the mutual relationships among all the indicators involved in the energy performance evaluation. The indicator values are defined by applying mainly a statistical analysis of an adequate number of energy efficiency case studies. Furthermore design standards are applied in order to improve the indicators definitions. The model has been tested and validated in some case studies discussed.
Non-Newtonian Models for Blood Flow Through an Arterial Stenosis
Authors: Tazyukov F. Kh. , Khalaf H. A. , Hassan Jafar M.
Published: August 2012

The problems of non-Newtonian blood flow through a stenosed artery are solved numerically using Finite Volume Method where the non-Newtonian rheology of the flowing blood is characterised by the Generalised Power-law, Carreau-Yasuda and Cross models. In view of the haemodynamical mechanisms related to atherosclerosis formation and the role of the wall shear stress in initiating and further developing of the disease, the investigation is focused on the two-dimensional flow field and in particular on the distribution of the wall shear stress in the vicinity of the stenosis. A comparison is made between the effects of each rheological model on the aforementioned parameters for different Re number.
Auto Generative Capacitive Mixing for Power Conversion of Sea and River Water by the Use of Membranes
Authors: Burheim O. , Sales B. B. , Schaetzle O. , Liu F. , Hamelers H. V. M.
Published: August 2012

The chemical potential of mixing two aqueous solutions can be extracted via an Auto Generative Capacitive Mixing, AGCM, cell using anionic and cationic selective membranes together with porous carbon electrodes. Alternately feeding sea and river water through the unit allows for the system to spontaneously deliver charge and discharge the capacitive electrodes so that DC electric work is supplied. Having a stack of eight cells coupled in parallel demonstrated the viability of this technology. An average power density of 0.055 W m−2 was obtained during the peak of the different cycles, though reasonable optimisation suggests an expectation of 0.26 W m−2 at 6.2 A m−2. It was found that 86 ± 8 percent of the theoretical driving potential was obtained during the operating process. By studying the polarisation curves during charging and discharging cycles, it was found that optimising the feed fluid flow is among the routes to make AGCM with ionic selective membranes a viable salinity difference power source by mixing river and sea water. Another parallel route for increasing the exergy efficiency is lowering the internal ohmic resistances of the cell by design modifications.
Experimental Investigation of CH4 and C3H8 Combustion in a Packed Bed Burner
Authors: Gao H. B. , Qu Z. G. , Tao W. Q. , Lu T. J.
Published: August 2012

The main object of this work is to investigate combustion in a two-layer packed beds porous burner, in particular, to study the effect of methane and propane on flame stability, pressure drop and pollutant emissions. The equivalence ratio of both methane and propane varied from 0.55 to 0.70. The results indicated that flame stability limits of both methane and propane enlarged with the increasing of equivalence ratio, however, the stability limits of methane is more widely than propane. The macroscopic flame shapes of methane and propane remains approximately the same but the later has a larger flame thickness. The NOx emissions are seen to be increased and the CO decreased with the equivalence ratio, HC emissions firstly decreased and then increased with the equivalence ratio for both methane and propane.
On the Static Pull-In of Circular Microplates Under Capillary Force
Authors: Kahrobaiyan M. H. , Fallah A. , Bozorgzadeh S. , Firoozbakhsh K. , Ahmadian M. T.
Published: August 2012

In this paper, the static pull-in phenomenon is investigated in circular micro-plates subjected to capillary force. The capillary force appears in micro-scale structures due to presence of a liquid bridge. The governing equation of a circular micro-plate subjected to capillary force is presented and the static deflection of a fully-clamped circular plate is evaluated. Moreover, the effect of the normalized adhesion tension caused due to the capillary force on the static pull-in of the micro-plate is assessed.
Applicability of Continuum Fracture Mechanics in Atomistic Systems
Authors: Cheng Shao-Huan , Sun C. T.
Published: August 2012

Stress intensity factor is one of the most significant fracture parameters in linear elastic fracture mechanics (LEFM). Due to its simplicity, many researchers directly employed this concept to explain their results from molecular simulation. However, stress intensity factor defines the amplitude of the singular stress, which is the product of continuum elasticity. Under atomistic systems without the stress singularity, the concept of stress intensity factor must be examined. In addition, the difficulty of studying the stress intensity factor in atomistic systems may be traced back to the ambiguous definition of the local atomistic stress. In this study, the definition of the local virial stress is adopted. Subsequently, through the consideration of K-dominance, the approximated stress intensity factor based on the atomistic stress can be projected within a reasonable region. Moreover, the influence of cutting interatomic bonds to create traction free crack surfaces and the critical stress intensity factor is also discussed.
Flow Field Around Dimpled Pin-Fins in a Staggered Array
Authors: Nagar R. K. , Meyer J. P. , MahbubAlam Md. , Spedding G.
Published: August 2012

Pin fins are low aspect ratio rods of circular cross section that are used to enhance heat transfer inside turbine blades. Although modifying the basic circular geometry with numerous shallow depressions (dimples) has been linked with enhanced heat transfer rates, the fluid mechanical mechanisms have remained speculative. Here we investigate numerically the effects of dimples onthe mean and turbulence velocities that lead to increased heat transfer. It has been found that dimples result in an increased turbulence intensity which may possess a greater potential to extract and transport more heat from the pin-fin.
Dry Etching Process on a Conducting Interpenetrating Polymer Network Actuator for a Flapping Fly Micro Robot
Authors: Khaldi Alexandre , Plesse Ce´dric , Soyer Caroline , Cattan Eric , Vidal Fre´de´ric , Chevrot Claude , Teyssie´ Dominique
Published: August 2012

In this paper we report on conducting polymer micro-actuators which have been fully patterned using photolithography and plasma dry etching processes. The interpenetrating polymer network (IPN) architecture used in this work resolves interface and adhesion problems which have been reported for traditional conducting polymer-based actuators. Actuator films 17 μm thick can be obtained and then patterned using microfabrication technologies. IPN-actuators were etched to obtain 2*5mm2 beams operating in air. These micro-sized actuators are potential candidates in numerous low frequency applications, including micro-valves, micro-optical instrumentation and micro-robotics. Moreover, due to the rapid response of our IPN architecture, this material has been considered as the main actuator for the flapping wings of an artificial insect.
Damping of Oscillatory Rolling Contact by Piezoelectric Actuators
Authors: To¨ho¨nen Mika , Keskinen Erno , Seemann Wolfgang
Published: August 2012

A common treatment in manufacturing web-like thin materials like paper is to manipulate it between two cylinders under rolling contact. A roll press is sensitive to vibration, which is unwanted, because it marks the web by periodical stripes. The excitations can be external ones, which are transmitted by the web in terms of periodic thickness or stiffness distributions, or internal ones, which are related to the shape or elasticity distributions of the roll and cover layer. When such excitation mechanisms are working and the rolls are interacting over the contact zone, the role of the roll cover becomes very important. Because the cover material is visco-elastic, the delayed recovery response of the polymer during each roll revolution starts to initialize self-excited vibrations. This contact vibration is known as barring. A piezoelectric actuator is an excellent device for vibration control applications because of its large force generation, very short response time and easy controllability. Control of piezoelectric actuator is straightforward by direct compensation of input voltage, which in turn can be generated from vibration data measured from the system. This presentation gives an overview how to approach the vibration control problem of complex roll press systems. A vibration damping system based on piezoelectric actuators with a feedback control loop and with a passive electric circuit is introduced to eliminate/reduce resonance oscillations.
Unit Cell Approach as a Multi Scale Modeling Technique for Predicting the Behaviour of Fiber Reinforced High Strength Concrete Under Compression
Authors: Hassan Sunir , Lakshmana Rao C. , Ganesh Babu K.
Published: August 2012

Fiber reinforced concrete has been identified as a particulate composite consisting of hardened cement paste, fine aggregates, coarse aggregates, particulate fibers etc. and each constituent plays a significant role in the combined quasi brittle behaviour of the material. From the view point of a numerical modeler, a two phase model consisting of a matrix phase and a coarse aggregate phase is simple and sufficient enough to take care of the heterogeneity without affecting the capability of the model to predict the material behaviour as reported by Ghouse et al [1]. Thus the unit cell under consideration is modeled as a square with an inner circle (Fig. 1), the square representing the total volume fraction of combined properties of cement paste, fine aggregates, particulate fibers and water. The inner circle represents the total volume fraction of coarse aggregates in the material. This representative volume fraction is assigned with periodic boundary conditions to ensure uniformity in deformation and to avoid any discontinuities in the material once the unit cell has been repeatedly arranged to build up the macro sized material and has undergone deformation in elastic range. Ghouse et al [1] could identify only slight variations in the compressive strength of normal low strength concrete with varying aggregate volume fractions. A comparatively decreasing trend in compressive strength has also been observed initially when glass fiber reinforced high strength cement composite (GFRCC) was analyzed by Sunir et al [2]. Investigations proceed in the direction of predicting the material behaviour by replacing the glass fiber and its volume fraction with polypropylene fibers considered by Pavan [3] as being significant in improving the mechanical characteristics of the macro composite under consideration. An analysis of polymer fiber reinforced high strength concrete (PFRC) with similarly varying aggregate volume fractions could predict significantly decreasing trends in compressive strength for lower volume fractions. In future, the ease with which the unit cell approach predicts the behaviour of fiber reinforced plain mortar is also to be investigated in a similar manner.
Semantic Analysis of Function-Solution Duality
Authors: Christophe Franc¸ois , Ritola Tuomas , Coatane´a Eric , Bernard Alain
Published: August 2012

Methodologies of the literature tend to separate clearly the design problem definition from the solutions to this problem. Nevertheless, this paper argues that conceptual design solutions are deeply rooted in the definition of the design problem. Hence, it is shown that conceptual solutions can emerge from the semantic analysis of the functional definition of a problem. This paper addresses the recursive aspect of conceptual design and the iterative loops between each step of design methodologies which are usually presented as a sequential flow. This paper presents that, in fact, in the early design phases, the functional representation of the design problem may often emerge from ideas of potential solutions. Afterward, this functional representation can be refined into concept of solutions, which can then give emergence to another functional representation. We hence argue here that the conceptual design process involves a constant duality between the functional representation of a problem and the potential solutions to this problem. Furthermore, we argue that the concepts of solution to a design problem can already be embedded semantically in the description of the problem as well as the description of these potential solutions enables the discovery of new design problem. This article presents these developments through the study of the sub-system of a robot used for harvesting fruits in a robot competition.
Measuring Paint Droplet Size, Velocity, and Charge-to-Mass Ratio Distribution for Electrostatic Rotary Bell Spray Simulation
Authors: Fan Hua-Tzu , Kuo Harry , Simmer Joseph
Published: August 2012

High-speed electrostatic rotary bells are widely used in the automotive industry as they provide high quality paint films with better transfer efficiency compared to air-atomizing guns. However, due to its highly turbulent spray pattern, transfer efficiency is still not ideal, i.e. some portion of paint will not reach intended target surfaces and becomes overspray. Numerical simulation of the electrostatic spraying process provides a tool to model this process as well as a way to optimize transfer efficiency. Currently, the state-of-the-art simulation model can simulate the flying trajectories of paint droplets from the edge of the rotating bell cup to the target surfaces. It requires some input information to start the simulation. The input information includes paint droplet size, velocity, and charge-to-mass ratio. Due to its large number of droplets, distributions based on droplet diameters are used to represent the entire droplet population. This paper describes experimental and mathematical methods to measure and calculate paint droplet size, velocity, and charge-to-mass ratio distributions. The resulting information can then be organized and used as the input data files for Electrostatic spray painting simulation.
Preparation for the Fundamentals of Engineering Examination at Virginia Tech
Authors: Dillard David A. , Nipper Melissa D. , Case Scott W. , Kornhauser Alan A.
Published: August 2012

The first step most engineers take toward professional engineering licensure is taking the Fundamentals of Engineering examination administered by the National Council of Examiners for Engineering and Surveying. The examination is typically taken by students near completion of an undergraduate engineering degree. By following up with engineering experience and the Professional Engineering examination, engineers can be licensed in any of the 50 states of the U.S. Professional licensure is both an aid and an incentive to professionalism in engineers. Licensure provides a publicly recognized credential for engineering competence and professional ethics. The licensing process, together with state requirements for maintaining licensure, ensures that professional engineers have the depth and breadth of knowledge required for engineering practice. Knowledge of licensing requirements helps young engineers set their own standards for engineering competence. Virginia Tech has, for many years, assisted its senior engineering students in preparing for the Fundamentals of Engineering examination. The program began in the 1970’s as an unofficial series of review lectures offered by engineering faculty. Later, it became a two credit hour course administered by the Department of Engineering Science and Mechanics with modules taught by faculty from many engineering disciplines as well as mathematics and chemistry. The course was taught every spring, using a set of notes and problems prepared by the instructors and available to students at reproduction cost. Lectures were scheduled in the evening to reduce interference with other courses. In spring 2011, the course was taught for the first time as an asynchronous online course developed by the instructors working in conjunction with Virginia Tech’s Institute for Distance and Distributed Learning. Updated lecture notes and problems were available for download, and lectures, recorded for the online course, were available for viewing as audio/video slide presentations using streaming video format. Since different faculty had different prior experience with computer-aided and online teaching, the different course modules used various online teaching techniques. The course website has been organized so that student response to the online materials may be monitored. Historically, Virginia Tech has had both high levels of undergraduate participation in the Fundamentals of Engineering examination and a high pass rate. Statistics on course registration, exam participation, and pass rate over the past decade are presented and compared with statistics for the new online course. In spite of a few technical and other issues, the online course appears to be a success. It is anticipated that feedback from this initial online offering will result in even better student acceptance and utilization of the online content, as well as examination performance, in the future.
Fabrication of the Superhydrophobic Surface Using SU-8 Photoresist With Black Silicon
Authors: Lee Sang Eon , Lee Dongjin , Kim Jin-Ha , Lee Kang Won , Lee Kwang-Cheol , Hong Seong Uk , Lee Seung S.
Published: August 2012

A novel change method of surface wettability using both micro- and nano-sized geometrical shape is presented in this paper. After the black silicon is formed in reactive ion etching, SU-8 mold is fabricated on top of the black silicon that has nano-sized holes. After the microfabrication of SU-8 photoresist mold, poly-dimethysiloxane (PDMS) is poured into the mold. As a result, the molded PDMS surface has both micro- and nano-sized structures, which is similar to lotus leaf. The diameter of cylindrical pillar micro structures ranges from 50 to 100 μm. The water contact angle of 150° is obtained on the molded PDMS surface with pillars diameter of 50 μm. The superhydrophobic surface made of micro- and nanostructures is straightforwardly formed, increasing water contact angle on the engineered surface.
Influence of Injection Molding Parameters on Mechanical Properties of Low Density Polyethylene Filled With Multiwalled Carbon Nanotubes
Authors: Fetecau Catalin , Stan Felicia , Dobrea Daniel , Birsan Dan Catalin
Published: August 2012

In this paper, we investigated the effect of injection molding parameters such as melt temperature, mold temperature, injection speed and holding pressure on the mechanical properties of low density polyethylene reinforced with 2.5 wt% multi-walled carbon nanotubes. The Taguchi methodology with four factors and two levels was used for the design of the injection molding experiments. The mechanical properties were evaluated by tensile tests in the flow direction at room temperature (23 °C) at crosshead speeds of 1 and 5 mm/min. It was found that the mechanical properties can be modified by manipulating the injection molding parameters. The Young’s modulus of the LDPE-MWNTs composite decreased as the melt temperature increased, while mold temperature, injection molding speed and holding pressure have a moderate influence on the Young’s modulus.
Utilization of Instructional Technology for Development of Web-Based Mechanical Engineering Courses
Authors: Duan Shanzhong Shawn , Bassett Kurt
Published: August 2012

Though face to face class interaction is still a dominant-teaching approach in most higher education institutes, online teaching has become increasingly popular with the development of internet technology [1,3]. The authors have used instructional technology and computer software to develop web-based lectures in a mechanical engineering program for online delivery at their institution. This paper highlights how computer software Camtasia Studio and Windows Journal have been integrated with a Gateway tablet PC, a webcam and wireless speaking receiver device to produce web-based lectures for online delivery. The paper intends to share experiences, myths, and lessons that the authors have learned during production of audio and video online course materials. Integration of instructional technology with computer software has made online course preparation and production much more effective and efficient. The paper also summarizes the steps taken by the authors to accomplish this instructional project from start to finish. It includes integration of instructional technology, pedagogical concepts, development of audio and video materials, difficulties faced and how they were handled, software used, and existing issues for the future work.
Effect of Filling Ratio on an Uneven Turn Oscillating Heat Pipe
Authors: Hathaway Aaron A. , Ma Hongbin
Published: August 2012

An experimental investigation of the effect of filling ratio on the thermal performance for a flat plate oscillating heat pipe with uneven turns was conducted. The OHP was designed to have 14 long turns running from the evaporator to the condenser and 6 short turn occurring only in the evaporator. The factors varied for this experimental investigation were the input power, condensing temperature, and charging ratio. Experimental results show that for all test conditions, the OHP functioned very well and could operate with an input power of up to 1200 W and could reach a thermal resistance of 0.028 °C/W in the inverted position with a filling ratio of 70%.
Assessment of the Holland Model for Silicon Phonon-Phonon Relaxation Times Using Lattice Dynamics Calculations
Authors: Zhu Zimu , Sellan Daniel P. , Nabovati Aydin , Amon Cristina H.
Published: August 2012

We assess the ability of the Holland model to accurately predict phonon-phonon relaxation times from bulk thermal conductivity values. Lattice dynamics calculations are used to obtain phonon-phonon relaxation times and thermal conductivities for temperatures ranging from 10 to 1000 K for Stillinger-Weber silicon. The Holland model is then fit to these thermal conductivities and used to predict relaxation times, which are compared to the relaxation times obtained by lattice dynamics calculations. We find that fitting the Holland model to both total and mode-dependent thermal conductivities does not result in accurate mode-dependent phonon-phonon relaxation times.
Numerical Analysis of Erosion and Sediment Control Using Lake-Shore Extensions in Lake Charles
Authors: Zhang Ning , Li Puxuan , Gonzalez Pons Eric , Kurt Jasmin , Silva Miloban Correa
Published: August 2012

CFD simulations in Lake Charles were conducted to investigate the hydrodynamics and sediment transport in Lake Charles water system, assisting the design optimization of a lake-shore extension project. The extensions not only aim to create addition lands for recreation, but also to serve as flow/erosion control and sediment reduction structures. In the simulation model, 2D depth-averaged shallow-water equation set as well as the scalar transport equation are solved. The particle settling effect is included in the transport equation. In addition to the unsteady distribution of sediment concentration, the distribution of the mass of deposited sediments on the seabed is also calculated, and used as an indicator for the severeness of sedimentation in the area. The wind effect is included in the model, and a hurricane is simulated to study its effects on the designed structures. The present shore-line was surveyed and the depth of the lake was measured using a GPS depth finding system to ensure the accuracy of the simulation.
Simulation of Two-Phase Flow and Heat Transfer for Practical Design of Mini- and Micro-Channel Heat Exchangers
Authors: Pellicone Devin , Ortega Alfonso , del Valle Marcelo , Schon Steven
Published: August 2012

Mini- and micro-scale heat exchangers provide the means for large heat transfer coefficients with single phase flow due to the inverse proportionality of Nusselt number with respect to the hydraulic diameter. For very high heat flux situations, single phase forced convection in micro-channels may not be sufficient and hence convective flow boiling in small scale heat exchangers has gained wider scrutiny due to the much higher achievable heat transfer coefficients due to latent heat of vaporization and convective boiling. The purpose of this investigation is to explore a practical and accurate modeling approach for simulating multiphase flow and heat transfer in stacked mini- and micro-channel heat exchangers. The work is specifically aimed at providing the framework for the optimization of such devices. The model algorithm is described in detail and the effects of channel hydraulic diameter ranging from 150–300 μm and number of stacked layers on the thermal and hydrodynamic performance of the heat sinks are explored. The results from the two parameter study are used to suggest a design path for creating an optimal two-phase stacked microchannel heat exchanger.
Numerical Simulation of Impinging Cooling on the Leading Edge of a Turbine Blade
Authors: Cheng Keyong , Huai Xiulan , Cai Jun , Guo Zhixiong
Published: August 2012

In the present study, numerical simulation is carried out for impingement/effusion cooling on the leading edge of a turbine blade similar to an experimental model tested previously. The k-ε turbulence model is used, and simulation parameters are set in accordance with the experimental conditions, including temperature ratio, blowing ratio, and Reynolds number of the main stream. The accuracy and reliability of the simulation is verified by the experimental data, and the influence of various factors on fluid flow and heat transfer is analyzed in detail. The results indicate that the blowing ratio is one critical factor which affects the cooling effectiveness. The greater the blowing ratio is, the higher the cooling effectiveness is. In addition, a staggered-holes arrangement is numerically studied and compared with a line-holes arrangement. The results show that the staggered-holes arrangement has a lower temperature on the outer surface of the leading edge and has improved the cooling effectiveness.
A New Phase Function Normalization Approach for Radiative Transfer Analysis in Highly Anisotropic Scattering Media
Authors: Hunter Brian , Guo Zhixiong
Published: August 2012

A new phase function normalization approach is applied to both the DOM and FVM for predicting radiative heat transfer in an extreme condition — highly anisotropic scattering media. Previous attempts to normalize the DOM result in a distortion of the overall phase function asymmetry factor. The splitting of each solid angle into numerous sub-angles in the FVM is shown to also produce a lack of conservation of asymmetry factor, even though scattered energy is conserved. The current normalization technique is crafted such that scattered energy and asymmetry factor are accurately conserved after both DOM and FVM discretization. The change in scattering effect when asymmetry factor is not conserved is examined for both methods. Wall flux profiles generated by DOM with old and new normalization techniques as well as FVM with and without phase function normalization are compared to isotropic scaling law profiles to gauge the accuracy of the techniques. The effects of changes in both optical thickness and scattering albedo are investigated. It is found that the current normalization approach vastly improves accuracy of flux profiles. The current procedure also greatly decreases FVM convergence time by eliminating the need for large amounts of solid angle splitting.
Influence of Superhydrophobic Walls on the Thermal Transport to Liquid Droplets
Authors: Maynes D. , Tullett N. , Nielson R. , Vanderhoff J. , Webb B. W.
Published: August 2012

This paper presents an experimental investigation of the thermal transport to liquid droplets resting on heated horizontal superhydrophobic surfaces. The superhydrophobic surfaces considered here exhibit alternating micro-ribs and cavities. Specifically, we consider the transient thermal response to water droplets as they are placed on heated superhydrophobic surfaces. For comparative purpose we also consider the same scenario with smooth hydrophobic and smooth hydrophilic surfaces. Experiments were conducted over a range of surface temperatures varying from 60 to 165 °C. The results show radically different behavior in the transient thermal transport for the three surface types considered. At all temperatures the total droplet evaporation time on the superhydrophobic surfaces was nearly an order of magnitude greater than on the smooth hydrophilic surface. At temperatures elevated above the saturation temperature, where vigorous boiling was evident on the hydrophilic surface, the droplets on the superhydrophobic surfaces remained at bulk temperatures significantly lower than the saturation temperature. Further, the droplets on the superhydrophobic surfaces exhibited Leidenfrost-like behavior at surface temperatures far below the typical Leidenfrost point. Analysis of the data reveals overall heat transfer coefficients that are much lower on the superhydrophobic surfaces than on the other surfaces, over the entire range of temperatures explored.
Use of a Quasi-Steady Ablation Model for Design Sensitivity With Uncertainty Propagation
Authors: Anzalone R. , Barr B. W. , Upadhyay R. R. , Ezekoye O. A.
Published: August 2012

Sensitivity analysis and design calculations are often best performed using low-order models. This work details work done on adding complementary pieces to a low-order, quasi-steady-state ablation model to facilitate uncertainty propagation. The quasi-steady-state ablation model is a one-dimensional, quasi-steady-state, algebraic ablation model that uses finite-rate surface chemistry and equilibrium pyrolysis-gas-production submodels to predict surface recession rate. The material response model is coupled to a film-transfer boundary layer model to enable the computation of heat and mass transfer from an ablating surface. For comparison to arc jet data, a simple shock heated gas model is coupled. A coupled model consisting of submodels for the shock heated gases, film heat and mass transfer, and material response is exercised against recession rate data for surface and in-depth ablators. Comparisons are made between the quasi-state-state ablation model and the unsteady ablation code, Chaleur, as well as to other computations for a graphite ablator in arcjet facilities. The simple models are found to compare reasonably well to both the experimental results and the other calculations. Uncertainty propagation using a moment based method is presented. The results of this study are discussed, and conclusions about the utility of the method as well as the properties of the ablation code are drawn.
Parametric Study of Nanostructure Variations on the Macroscopic Thermal and Electrical Behavior of Neat CNT Thin Film Networks
Authors: Ashtekar Nikhil A. , Jack David A.
Published: August 2012

Carbon nanotube thin films are considered by many researchers as a material for the future in many electrical and thermal applications, but a lack of systematic physics-based modeling approaches to quantify the bulk thermal and electrical response due to nanostructure variations makes employing these thin films difficult for commercial applications. In this work we employ the previously presented 3D physics-based computational model for characterizing the bulk thermal and electrical response of a neat carbon nanotube thin film network involving stochastic distributions of length, diameter, chirality, orientation and values of intercontact resistivity obtained from the literature. The model is employed to test the sensitivity of bulk thermal and electrical conductivity on stochastic variations in the nanostructure parameters. We examine the sensitivity of the thin film networks to the experimentally obtained Weibull probability distribution for length and diameter. Additionally, we present a study to quantify the macroscopic conductivity dependence on the nanotube chirality ratio. Through these studies we present an approach that is very generic and can be used for the sensitivity analysis due to variations within the nanostructure.
Reactive Heat Source for Standalone Thermoelectric Power Generator: Thermal Analysis of Pyrophoric Iron Mixture
Authors: Huang Dale H.-Y. , Tran Thanh N. , Yang Bao
Published: August 2012

The idea of a small size, light weight, robust, scalable and standalone power generators has always been of great interest in personal and commercial transportation systems as well as military weapon systems. One potential source of portable power is electricity produced from heat sources through the use of thermoelectric materials. The heat can come from the combustion of fossil fuels, from sunlight, or as a byproduct of various processes (e.g. combustion, chemical reactions and nuclear decay) and in our case, a pyrophoric iron mixture that spontaneously generates heat as soon as it reacts with air. In this study, to apply the pyrophoric powder as a portable heat source for the thermoelectric power generators (TPGs), the final mixture composition is determined to be iron powder, activated carbon, and salt. With the characterization of thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), this exothermic reaction generates 9000+ J/g of heat with peak temperature ranges from 400 to 500 degrees Celsius.
Thermal Imaging of Laser Powder Deposition for Process Diagnostics
Authors: Hammell Joshua J. , Ludvigson Christopher J. , Langerman Michael A. , Sears James W.
Published: August 2012

Thermal imaging is an important tool for future developments in Laser Powder Deposition (LPD). Thermal imaging of the LPD process is typically used for the verification of mathematical models describing the process and/or dynamic melt pool control. The research discussed here shows how thermal imaging can be used to improve our understanding of the connection between deposition parameters, thermal gradients, and final part quality. Data gathered from melt pool and bulk-part thermal images were used to correlate deposition parameters to final part quality. The results presented here are for applications in internal barrel cladding and laser brazing.
Uncertainty Analysis of Structural Dynamics by Using Two-Level Gaussian Processes
Authors: Xia Z. , Tang J.
Published: August 2012

Uncertainty analysis is an important part of structural dynamic analysis in various applications. When a large complex structure is under consideration, component mode synthesis (CMS) is frequently used for reduced-order numerical analysis. But even so, in some situations the computational costs are still high for repeated running of a computer code which is required in uncertainty analysis. Gaussian processes offer an emulation approach to realization of fast sampling over a given parameter configuration space. However, both the low-fidelity data obtained by CMS and the corresponding sample obtained by Gaussian process emulation need to be assessed by comparing with high-fidelity data which can be obtained but are usually very expensive. When obvious bias exist in the low-fidelity data, two-level Gaussian processes are introduced for processing both the low- and high-fidelity data simultaneously to make more accurate predictions of quantities of interest. CMS can serve not only to provide low-fidelity data but also to locate problematic areas on complex structures. Comparisons of the results obtained by Monte Carlo sampling, which is performed using both a full finite element model and a CMS model, indicate that two-level Gaussian processes can be an efficient tool to emulate high-fidelity sampling with guaranteed accuracy.
A Finite Element Analysis of a Subject Specific Single-Leg Drop Landing at Varied Heights
Authors: Tse Chi-Yin , Nayeb-Hashemi Hamid , Vaziri Ashkan , Canavan Paul K.
Published: August 2012

The pathomechanics of knee anterior cruciate ligament (ACL) injury related to the female athlete is of high interest due to the high incidence of injury compared to males participating in the same sport. The mechanisms of ACL injury are still not completely understood, but it is known that single-leg landings, stopping and cutting at high velocity are some of the non-contact mechanisms that are causing these injuries. This study analyzed a subject specific analysis of a single-leg drop landing that was performed by a female subject at 60%, 80% and 100% of her maximum vertical jump. The femur, tibia, articular cartilage, and menisci were modeled as 3-D structures and the data collected from the motion analysis was used to obtain the knee joint contact stresses in finite element analysis (FEA). The four major ligaments of the knee were modeled as non-linear springs. Material properties of previously published studies were used to define the soft tissue structures. The articular cartilage was defined as isotropic elastic and the menisci were defined as transverse isotropic elastic. Two different styles of single-leg landings were compared to one another, resembling landing from a basketball rebound. The first landing style, single-leg arms up (SLAU), produced larger knee flexion angles at peak ground reaction forces, while single-leg arms across (SLAX) landings produced higher peak vertical ground reaction forces along with lower knee flexion angles. The mean peak vertical ground reaction force was 2.9–3.5 bodyweight for SLAU landings, while they were 3.0–3.8 for SLAX landings. The time to peak vertical ground reaction force with SLAU landings were 69 ms (60%), 60 ms (80%), and 55 ms (100%); SLAX landings were 61 ms (60%), 61 ms (80%), and 51 ms (100%).
Development of a Dual-Axis Phase-Locked Resonant Excitation Test Method for Fatigue Testing of Wind Turbine Blades
Authors: White Darris , Desmond Michael , Gowharji Waleed , Beckwith Jenna A. , Meierjurgen Kenneth J.
Published: August 2012

Collaborative efforts between Embry-Riddle Aeronautical University (ERAU) and the National Renewable Energy Laboratories (NREL) have resulted in an innovative dual-axis phase-locked resonant excitation (PhLEX) test method for fatigue testing of wind turbine blades. The Dual-axis phase-locked test method has shown to provide more realistic load application as compared to wind loading experienced through field operation conditions. The current concepts involved exciting the blade at its fundamental edgewise natural frequency while applying a force in the flap direction at that same frequency. This advanced test method incorporates existing commercially available test hardware, known as the Universal Resonant Excitation (UREX), combined with an additional hydraulically actuated member to dynamically force the blade using adaptive algorithms and advanced control strategies in order to provide cycle-to-cycle phase control and decreased testing time. In short, this paper will outline the development of a finite element model for predicting performance and evaluation of the results.
Our First Online Offering of Introduction to Thermal-Fluid Engineering
Authors: Hall Simin , Dancey Clint , Amelink Catherine T. , Conn Samuel
Published: August 2012

In this paper the researchers reflect on the use of various communication technologies from the first online offering of our introductory thermodynamics course. The asynchronous (i.e., forums) and synchronous communication technologies such as Centra™ were employed for instruction and explication of useful feedback and self-explanation to promote students’ collaboration. The instructors outline the types of questions used in these guided activities that challenged students to search for multiple ways to demonstrate their conceptual understanding of very fundamental physical notions. The discussion in this paper outlines ways to improve forum questions, instructor’ feedback, and the frequency of the feedback to improve students’ metacognitive strategies in learning and the application of the course material. The observational data are also examined to note if there were any differences in forum contributions online versus students’ contributions in a face-to-face class. This paper provides a platform for research about learning and evaluation of instruction in abstract engineering courses in an online environment. The study is significant and of interest to faculty and administrators who have taught courses in traditional classrooms and who are now considering online teaching to increase access to engineering education.