bluuebunny/crossref_metadata_2025 huggingface dataset:
The Post-Graduation Attrition of Engineering Students: An Exploratory Study on Influential Career Choice Factors
Authors: Margolis James , Kotys-Schwartz Daria
Published: July 2010

Attrition issues with undergraduate engineering students, while concerning, are well documented. However, little research has explored post-graduation attrition. U.S. Department of Labor statistics suggest that as many as 45 percent of workers with engineering degrees are not employed in engineering jobs. As China and India increasingly compete with the U.S. in the production of engineers and enrollment in U.S. engineering programs continues to lag behind other four-year degrees, training a consistent number of quality engineers is a critical issue for the American workforce. Anecdotal evidence of problematic post-graduation attrition—that is, attrition related to controllable factors in students’ educational experiences that push them away from engineering careers, as opposed to attrition of students who wish to creatively apply their skills in other occupations—coupled with the need for engineers in the workforce motivated this research. This study investigated the post-graduation plans of senior level mechanical engineering students at the University of Colorado at Boulder. Over the course of one year, two surveys were administered to 169 students, a mix of graduating seniors and students in a Senior Capstone Project course. Students were classified into four groups based on their post-graduation plans: 1. Pursuers (35% of total sample): students pursuing an engineering career immediately after graduation without reservations or plans to leave the field in the future. 2. Returners (22% of total sample): students not pursuing an engineering career immediately after graduation but with plans for an engineering career in the future. 3. Pursuers with Reservations (34% of total sample): students pursuing an engineering career immediately after graduation who currently had reservations about their career choice and/or planned to leave the field in the future. 4. Leavers (9% of total sample): students not pursuing an engineering career immediately after graduation with no plans for an engineering career in the future. The results indicated that 65% of the sample had, at least, some reservations about pursuing an engineering career. Results also suggested five factors that may influence post-graduation attrition: 1. Feeling prepared to pursue an engineering career, 2. Internship experiences, 3. Senior Capstone Project course experiences, 4. Satisfaction with the quality of instruction in the engineering program, and 5. Career values related to financial rewards and enjoying co-workers.
Transparency Enhancement of Haptic Systems Based on Compensation of Device Dynamics
Authors: Tajaddodianfar F. , Ahmadian M. T. , Vossoughi G. R. , Motamedi M.
Published: July 2010

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices. Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this paper instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand dynamics. Two design methods are implemented and their performance and stability are evaluated. The first strategy is based on H-infinity controller synthesis technique applied to a generalized control plant which involves the target impedance as a performance weighting function. Human hand dynamics is not present in the controller synthesis stage, because it does not affect the robot impedance and consequently has no effect on performance. The obtained results depend on the weighting function parameters. In the second approach a controller is designed based on the inverse model of the device. The advantage of the latter method is that it can reduce the device impedance in a wide frequency range and results in non-passive robot impedance which is much more transparent than the impedances obtained by passivity based methods. Simulation results confirm the effectiveness of the proposed methods.
Air-Conditioning Employing Indirect Evaporative Cooling Can Be Shown to Derive Its Energy From the Solar Source
Authors: Dartnall W. John , Revel Alex , Giotis Vasilios
Published: July 2010

This paper explains how Indirect Evaporative Cooling (IEC) uses water as a refrigerant. This water refrigerant may be seen as part of the rain cycle, whereby the environment (not a heat pump) returns water as the refrigerant to the system after re-condensing it. Since the rain cycle is largely driven by the solar source, so then is IEC. Indirect Evaporative Cooling (IEC) may be efficiently produced by wetting the room exhaust stream plates of an air-to-air heat exchanger so that water evaporation caused by the cool, relatively dry exhaust air effectively cools the incoming ventilation air stream as it passes through the other (supply) side of the heat exchanger. In practice, very high Coefficients of Performance (COP’s) have been recorded with IEC’s operating in hot, dry climates. These systems perform with low energy consumption requiring energy only to power fans and small water pumps. Surprisingly, a humid climate also yields a very high COP.
Should Engineering Thermodynamics Include a Simplified Treatment of Its Underlying Molecular Basis?
Authors: Dartnall W. John , Reizes John , Anstis Geoff
Published: July 2010

Engineering Thermodynamics is commonly treated at undergraduate level as “classical thermodynamics and its applications”. Recent publications, using one dimensional simulations employing hard spheres have proposed ways to obtain the laws of thermodynamics. These models help to explain the state laws, the limitation of the Carnot cycle relationship as well as difficult concepts like entropy. The models, although deterministic, are able to demonstrate the probabilistic behaviour, normally explained by the mathematically sophisticated derivations of Statistical Mechanics. Is it time to include a simplified, mechanistic explanation of Engineering Thermodynamics by deriving it from its molecular basis?
A Numerical Study of Transient Swirling Multiphase Flow of Molten Steel From a Ladle on a Teeming Process
Authors: Hashiebaf A. , Najafi Amir F.
Published: July 2010

In the teeming process of molten steel from a ladle, a bathtub-type vortex may be formed in the ladle. The formation of such vortex will drag the slag from the top of the molten steel into the tundish which affects the cleanness of steel. In previous works water was considered to model the molten steel but we found that water is not a suitable fluid for simulation, so a dimensional analysis was applied to model the proper fluids for molten steel and slag with a composition in a real ladle. We deduced that freon or mercury can be relevant fluid models for simulating molten steel. In addition, the effects of Re, Fr and Bo number were studied and Fr and Re numbers were found to be dominant pi-numbers and the effect of interfacial tension and surface tension were ignored because of large Bo number. The selection of fluid models for slag were based on viscosity and due to fact that adding some materials like Cao-Ca F2 for modifying slag decreases the viscosity of slag from 6.5 pa-s lower than 2 pa-s. The scale models was filled with freon and slag fluids were engine oil, fuel oil, water, DRAFSH46, DRAFSH100 and glycerol at the top of the freon. Furthermore, the cases were rotated at three different axis rotations. Results show that kinematic viscosity is responsible for slag entrainment into the drain rather than DENSITY for special Bo numbers. A Computational Fluid Dynamics (CFD) modeling was also conducted to investigate the vortex formation under imposed conditions.
A Simple Experiment to Expose Misconceptions About the Bernoulli Equation
Authors: Recktenwald Gerald W. , Edwards Robert C. , Howe Douglas , Faulkner Jenna
Published: July 2010

A series of laboratory exercises has been developed to aid in the teaching of thermal and fluid sciences to undergraduate engineers. The exercises use simple hardware and a guided-inquiry approach to expose student misconceptions and to develop deeper understanding of basic concepts. This paper focuses on one of the laboratory exercises, which uses a simple duct with a sudden expansion to demonstrate the error caused by misapplication of the Bernoulli equation. The apparatus and the laboratory exercise are described. Learning gain measurements and results of attitude surveys are presented. The exercise is successful in causing students to confront their misconceptions and lack of understanding. Student attitudes about the usefulness of the exercise correlate with their grade in the course. The A students have a less favorable opinion than the B and C students.
Brownian Dynamics Simulations of Colloidal Dispersion Composed of Ferromagnetic Spherocylinder Particles in a Simple Shear Flow (For the Case of an Applied Magnetic Field Normal to the Shear Plane)
Authors: Hayasaka Ryo , Sakuda Yasuhiro , Satoh Akira
Published: July 2010

We have investigated aggregate structures and rheological properties of a colloidal dispersion composed of ferromagnetic spherocylinder particles with a magnetic moment along the particle axis direction, by means of Brownian dynamics simulations. In concrete, we have attempted to clarify the influences of the flow field, magnetic field strength, magnetic interactions between particles and volumetric fraction of particles. In order to discuss quantitatively the internal structures of clusters, we have concentrated our attention on the radial distribution and orientational distribution functions. The present results are compared with those of the theoretical analysis for dilute dispersions and also non-dilute dispersions; the results for the latter were obtained by means of the mean-field approximation, which magnetic particle-particle interactions can be taken into account. Some important results are summarized as follows. For the case of the magnetic field strength and magnetic interactions between particles are more dominant than the viscous forces due to a simple shear flow, chain-like like clusters are formed along the magnetic field direction, although they are slightly tilted to the flow direction. When magnetic particle-particle interactions become over a certain value, such cluster formation leads to a significant increase in the viscosity of the dispersion.
Exergoeconomic Analysis of an Advanced Zero Emission Plant
Authors: Petrakopoulou F. , Tsatsaronis G. , Morosuk T.
Published: July 2010

Exergy-based methods are reliable means for the comparison and the evaluation of the operation of energy conversion systems. In this paper, the Advanced Zero Emission Plant, a plant that performs combustion in a nitrogen-free environment (oxy-fuel combustion) is presented, compared to a reference plant (without CO2 capture) and evaluated based on an exergoeconomic analysis. A variation of the oxy-fuel plant with a lower CO2 capture percentage (85%) is also presented in order to (1) evaluate the influence of CO2 capture on a plant’s overall performance and cost, and (2) enable the comparison with other conventional methods, such as post-combustion with chemical absorption that also performs CO2 capture with lower effectiveness. When compared to the reference case, the oxy-fuel plants achieve a minimal decrease in exergetic efficiency, essentially due to their more efficient combustion processes. Cost calculations reveal that the membrane used for the oxygen production in the oxy-fuel plants is their main expenditure. Nonetheless, the cost of electricity and the cost of CO2 avoided for these plants are calculated to be competitive with chemical absorption.
Dependency of Air Curtain Performance on Discharge Air Velocity (Grille and Back Panel) in Open Refrigerated Display Cabinets
Authors: Gaspar Pedro Dinis , Gonc¸alves L. C. Carrilho , Vo¨geli Andreas
Published: July 2010

This study performs a Computational Fluid Dynamics (CFD) modeling of air flow and heat transfer of an open refrigerated display cabinet in order to evaluate the influence of the discharge air velocity on the performance of its recirculated air curtain. The physical-mathematical model considers the flow through the internal ducts, across the fans and the evaporator, and also the thermal response of food products. The fan boundary condition is modeled in order to vary the air velocity at the discharge grille. The back panel perforation is modeled as a porous medium. The density and dimension of the back panel perforation variation is modeled by the Darcy’s law with the Forchheimer extension, varying the viscous and inertial resistance coefficients of the porous medium, based on its porosity, permeability, air velocity and pressure loss coefficient. Experimental tests were conducted to characterize the phenomena near the physical borders and to prescribe boundary conditions as well as to validate the numerical predictions on the temperature, relative humidity and velocity distributions. The numerical results show that the lowest average temperature in the conservation area of the display cabinet is achieved at a discharge air grille velocity of 1.15 ms−1. This value is lower than the experimental one, 1.51 ms−1, measured on the real equipment. The absence of a velocity component in the third dimension, which can destabilize the air curtain, is assumed to be the reason for this discrepancy. The profiles of the numerical predictions of the air curtain indicate that in the optimum case the air curtain is not so stable to bear big disturbances from outside. In order to increase the thermal performance and to reduce the energy consumption of these equipments, it’s not recommended to run the re-circulated air curtain velocity below 1.15 ms−1. For each CFD model, the values and directions of the air mass flow rate and heat transfer across the re-circulated air curtain by unit length are predicted and compared with the experimental ones in order to evaluate its thermal energy gains and losses.
A Fundamental Study on the Reversal Behavior of an Automobile Wiper Blade
Authors: Mizokami Masato , Akuto Tsuneo , Fukuda Takayuki , Yanagisawa Dai , Yoshizawa Masatsugu
Published: July 2010

Automobile wiper systems provide a clear sight for drivers by creating a very thin layer of water about few dozen nano meters on a windshield. Several studies have been carried out to investigate the dynamic behavior of the wiper systems. However, there are few studies focused on reversal behavior of the wiper blade. Observation was conducted and analytical model is developed from the observation of the real wiper system. A water layer is considered in the analytical model between the wiper blade and the glass surface. The bottom of the model is assumed to always contact the water layer so that the fluid force is always applied. The dimensionless equations, which govern the wiping motion including the reversal behavior, were derived. The equations are discussed neglecting the nonlinear terms to understand the approximate movement and effect of the parameters. Moreover, the equation is solved numerically to obtain the time histories of the wiper blade. As a result, the effect of the fluid force, which acts on the wiper blade on the reversal behavior of the wiper blade, became clear.
Thermal Modeling of a Geothermal Well Field for Ground Source Water Heat Pump Systems
Authors: Woods Kevin D. , Ortega Alfonso , Koenig Albert
Published: July 2010

Heat pumps are mechanical systems that provide heating to a space in the winter, and cooling in the summer. They are increasingly popular because the same system provides both cooling modes, depending on the direction of the cycle upon which they operate. For proper operation, the heat pump must be connected to a constant temperature thermal reservoir which in traditional systems is the ambient air. In ground source heat pumps however, subterranean ground water is used as the thermal reservoir. To access the subterranean groundwater, “geothermal” wells are drilled into the formation. Water from the building heating or cooling system is circulated through the wells thereby promoting heat exchange between the coolant water and the subterranean formation. The potential for higher efficiency heating and cooling has increased the utilization of ground source HVAC systems. In addition, their compatibility with a naturally occurring and very stable thermal reservoir has increased their use in the design of sustainable or green buildings and man-made environments. This paper is concerned with the development of a mathematical model describing the thermal processes that occur in a circulating geothermal well as the water thermally interacts with the surrounding formation. First principles are utilized to develop a general single well model that is able to predict the heating or cooling of a well with time. The single well model is then utilized to build a simulation for an infinite line of adjacent wells that thermally interact with each other over time. The behavior of a single isolated well and a line of evenly spaced wells is discussed and compared with recent experimental data for circulation in an isolated well.
Test Methodologies for Power Cycling Experiment
Authors: Sinha K. , Al-Bassyiouni M. , Hansen P. , Dasgupta A. , McCluskey P. , Beaupre R. , Jacobsen J.
Published: July 2010

When compared to temperature distributions in an actual application, thermal cycling is not a complete representation of the thermal gradients found in functional electronics under power-on condition. This discrepancy is particularly severe in power electronics and it distorts the thermo-mechanical stresses experienced at the joints and interfaces of power devices. Accelerated stress tests for power electronics are therefore better conducted with accelerated power cycling experiments rather than with accelerated thermal cycling, because the power cycles simulate more closely accelerated versions of an application cycle where the junction temperature of the die rises and falls as the power is turned off and on. However, developing a power cycling test setup can be comparatively more challenging than temperature cycling test setup, because of the complex triggering circuitry and logic needed for rapid power cycling, power circuitry needed to supply the large wattage safely to the devices under test, thermal cooling system to remove the high amount of heat generated, and software/hardware to control the test setup to maintain the right operational parameters. In this study, a test setup has been developed to power cycle IGBT and bipolar semiconductor devices for accelerated durability tests. The test setup is described and the role of each hardware and software component in the test setup is elaborated. Sample test results are presented, to illustrate the capabilities of the test setup. This work adds to the state of the art of power cycling experiments and improves our understanding of ways to develop stable power cycling test setups for various kinds of applications.
Angular Position Control of Fluid-Driven Spindle
Authors: Nakao Yohichi , Asaoka Naoya
Published: July 2010

A precise spindle is essential to achieve precision machining, such as diamond turning. A fluid driven spindle supported by hydrostatic bearings was thus designed and tested. A feature of the spindle is that several flow channels are designed in its rotor so that driving torque can be generated by supplying pressurized flow into the channels. Rotational speed of the spindle can be controlled by the flow rate. In addition, the rotational direction of the spindle can be controlled by switching supply ports. Thus angular position control of the spindle is achieved by designing appropriate feedback controller. In the present paper, mathematical model of the spindle was thus derived in order for designing an angular position control system. Then spindle characteristics calculated by the mathematical model were compared with experimental results. Furthermore, the angular position control system that has a disturbance observer in its feedback loop was designed based on the mathematical model. The performance of the designed control system was experimentally investigated through the step response. Experimental results verified that the designed controller minimizes the steady state error of angular position of the spindle. Consequently, the steady state error was comparable with the resolution of the rotary encoder, 0.018 degree. In particular, the experimental results indicated that the disturbance observer effectively reduced the influence of various load torque on the angular position of the spindle.
Analysis of the Surface of Parabolic Collector
Authors: Fado´n Salazar Fernando , Cero´n Hoyos Jose´ Enrique , Vallejo Lobete Esther , Diego Pereda Jesu´s I. , Fuente Moreno Jesu´s
Published: July 2010

To obtain solar energy, parabolic mirrors are used which have the property, to concentrate on a spot zone. In this case it is transformed by a Stirling engine into electrical energy. This will examine, first, the kind of plate that is best suited to obtain better results, and other influences such as the geometric accuracy of the same thermal efficiency, with respect to the theoretical. This is intended for “scales” or elements of simple geometry, which optimize the prices of manufacturing, maintenance and guidance. This paper is a preliminary analysis to be able to develop a prototype to experiment with obtaining this type of energy.
Semi-Active Suspension Systems for Heavy-Duty Vehicles: Multibody Model Development, Identification and Control Algorithm Evaluation
Authors: Grott Matteo , Biral Francesco , Oboe Roberto , Cis Alberto , Vincenti Eugenio
Published: July 2010

The design of suspension systems for heavy-duty vehicles covers a specific field of automotive industry. During the past few years there has been an increasing demand in power capabilities, loads and driving speeds of heavy duty vehicles. Therefore, off-highway vehicle manufacturers have shown their interest in employing new technologies. This work focuses on the investigation of hydro-pneumatic suspension systems for heavy duty vehicles, in particular on the benefits of a semi-active solution compared to a passive one. The main targets of this activity is the study of the dynamical behaviour of agricultural tractors and the design of a cost-effective controllable suspension, capable to adapt the tractor dynamical behaviour, under different road and load conditions. The work started with the development of a multibody model of the suspension test bench to be used for control solution comparisons. The multibody model was experimentally validated by characterizing the cylinder friction, tire parameters and Frequency Response (F.R.) of the suspension bench test equipped with a passive solution. As a last step the evaluation of different control algorithms for hydraulic semi-active suspension was carried out via Adams/Matlab co-simulation technique.
Multi-Pulse Heteroclinic Orbits and Chaotic Dynamics of Laminated Composite Piezoelectric Rectangular Plate
Authors: Yao Ming-Hui , Zhang Wei , Cao Dong-Xing
Published: July 2010

The multi-pulse orbits and chaotic dynamics of the simply supported laminated composite piezoelectric rectangular plates under combined parametric excitation and transverse loads are studied in detail. It is assumed that different layers are perfectly bonded to each other with piezoelectric actuator patches embedded. The nonlinear equations of motions for the laminated composite piezoelectric rectangular plates are derived from von Karman-type equation and third-order shear deformation laminate theory of Reddy. The four-dimensional averaged equation under the case of primary parametric resonance and 1:2 internal resonances is obtained by directly using the method of multiple scales and Galerkin approach to the partial differential governing equation of motion for the laminated composite piezoelectric rectangular plates. The system is transformed to the averaged equation. From the averaged equation, the theory of normal form is used to find the explicit formulas of normal form. Based on normal form obtained, the extended Melnikov method is utilized to analyze the multi-pulse global bifurcations and chaotic dynamics for the laminated composite piezoelectric rectangular plates. The analysis of global dynamics indicates that there exist the multi-pulse jumping orbits in the perturbed phase space of the averaged equation. From the averaged equations obtained, the chaotic motions and the Shilnikov type multi-pulse orbits of the laminated composite piezoelectric rectangular plates are found by using numerical simulation. The results obtained above mean the existence of the chaos for the Smale horseshoe sense for the simply supported laminated composite piezoelectric rectangular plates.
CFD Analysis of a Constructal Flow Distributor as a Bipolar Plate for PEMFC’s
Authors: Ramos-Alvarado Bladimir , Hernandez-Guerrero Abel , Juarez-Robles Daniel , Rubio-Arana Cuauhtemoc , Vital-Flores Francisco
Published: July 2010

A plate-type constructal flow distributor is implemented as a gas distributor for a proton exchange membrane fuel cell. A 3D complete model is simulated using CFD techniques. The fuel cell model includes the gas flow channels, the gas diffusion layers and the membrane electrode assembly (MEA). The governing equations for the mass and momentum transfer are solved including the pertinent source terms due to the electrochemical reactions in the different zones of the fuel cell. Similar configurations have been already presented in previous studies but using the flow distributor as a heat remover; however, the similarity between heat transfer and mass transfer phenomena has lead to investigate the performance of such distributors in fuel cells. In terms of flow analysis, it was found that the constructal flow distributor presents a low pressure drop for a wide range of Reynolds number conditions at the inlet, as well as an excellent uniformity of flow distribution. Some of the advantages of the constructal model, over traditional flow patterns, are the uniformity of current density distribution, the adequate consumption of species and the possibility to increase the bifurcation levels to cover a larger reaction area.
Extended Near Wall Hindered Diffusion Theory for Nanoparticles Under Short and Long Range Interactions
Authors: Mukherji Suchi Subhra , Banerjee Arindam
Published: July 2010

An extension of the near wall hindered diffusion theory of Brenner [1] is considered for spherical nano-particles undergoing Brownian motion under the influence of hydrodynamic drag and electrostatic interactions. Brenner’s theory is based on hydrodynamic interactions between a levitating particle and the wall and does not consider short range interactions (like electrostatic force and van der Waals force). Recent experiments by Banerjee & Kihm [2] (henceforth referred to as BK05), with nano-particles of radii ≤ 500 nm show substantial discrepancy between the experimental and theoretical values of normal reduction coefficient (ratio of near wall normal diffusivity to bulk diffusivity). However, the experimentally measured lateral reduction coefficient (ratio of tangential diffusivity of the wall to bulk diffusivity) show good agreement with theory. It is conjectured that the absence of short range interactions become critical for particle radii ≤ 500 nm in the (sub-micron) near wall region. The current work extends Brenner’s analytical theory (henceforth referred to as B61) considering various short and long range interactions. An analytical expression is derived for hindered diffusivity of a particle normal to the wall under the influence of hydrodynamic drag and electrostatic interaction with a constant surface charge density. The theory is validated with experiments of BK05 and shows a better agreement with measured values of diffusion coefficients for particles of radii 50 and 100 nm. The dependence of electrolyte concentrations on electrostatic potential energy for spheres has also been studied. Increase in ionic strength of electrolyte concentration confirms the reduction of electrostatic potential energy for different sphere sizes. Electrostatic interaction has a significant contribution in overall potential energy of the sphere in sub-micron near wall region when wall and sphere surface charge potentials are increased.
Numerical Simulation of In-Tube Condensation Heat Transfer in the Presence of High Partial Pressure Non-Condensable Gases
Authors: Zhang Jun Xia , Wang Li , Wu Ping , Li Hong Ying , Tong Li Ge
Published: July 2010

To enhance the practicality of the separate type heat tube in large-scale industrial application, the authors have adopted a non-vacuum separate type heat tube in which quantitatively predicting condensation heat transfer of vapor in the presence of stagnant high partial pressure non-condensable (NC) gases is vital to the task of design. So the condensation heat transfer in a V-shape tube with high partial pressure non-condensable gases was simulated based on a 3D steady state VOF model coupled with the MS (Maxwell-Stefan) equation for considering the effect of stagnant high partial pressure non-condensable gases on condensation heat transfer. The results show that the high partial pressure non-condensable gases have a limited influence on the condensation heat transfer, and they are constrained in a narrow space at the rear of the tube due to the forced convective vapor, therefore, a small part of the pipe wall has lower local heat flux and condensation heat transfer coefficient, while most part of pipe wall has higher performance of condensation heat transfer. The calculated results are in agreement with the experimental data.
Condensation Heat Transfer With High Partial Pressure Non Condensable Gas Inside Tube
Authors: Zhang Jun Xia , Wang Li , Li Hong Ying , Wu Ping
Published: July 2010

An experimental study on the condensation heat transfer in a non-vacuum separate type heat tube is carried out to comprehend the effect of high partial pressure NC condensable gas on the condensation heat transfer of vapor. The outer wall temperature along the tube length and the condensation heat transfer rate at different operation parameters, including inlet pressure and temperature of vapor, inlet temperature of cooling water and flow rate of cooling water, were measured. The factors influencing the condensation heat transfer coefficient (HTC) and condensation heat transfer rate were analyzed. The results show that the non-vacuum separate type heat pipe can run steadily; the region of the stagnant high partial pressure NC gas in the condenser tube is caused by the pressing of both vapor from the inlet and the condensation liquid at the rear of the tube; vapor flow rate and vapor inlet pressure have prominent influence on the condensation heat transfer rate and condensation HTC, and inlet temperature of cooling water affects the condensation HTC slightly.
On the Origins of Elastic Stability Studies Before the XVIII Century
Authors: Godoy Luis A.
Published: July 2010

The identification of the origins of what we now call the theory of elastic stability is not an easy task. Most authors trace the origins to the pioneering work of Leonhard Euler in 1744, and some (including this author) shift this origin to the experimental works of Petrus van Musschenbroek in 1729. However, other contemporary authors interested in the history of the discipline postulate that the works of Medieval and Renaissance scholars should be considered as the true sources of the buckling studies performed in the XVIII Century. This paper reports our historical research using original manuscripts of Al-Khazini, Jordanus de Nemore, Leonardo da Vinci, and Marini Merssene, in order to discuss what kind of knowledge they had about the topics of stability and lateral deflections of columns under axial loads. Our investigation shows that there were observations of the phenomenon considered, but those observations were not translated into a deeper understanding of the phenomenon, so that the causes of this effect or the role of strength on the response were not considered. Leonardo was closer to understanding the nature of the problem and produced some tentative rules of behavior; however, those were only documented in private writings and did not make an impact in his contemporaries. We postulate that studies prior to the XVIII Century were very limited in their scope and cannot be considered as the basis of the developments of Musschenbroek and Euler.
An Optimization-Based Algorithm for Determination of Inclusive and Constant Orientation Workspace of Parallel Mechanisms
Authors: Vossoughi Gholamreza , Hassanpour Soroosh , Fazeli Amir , Paak Mehdi
Published: July 2010

Workspace of a mechanism is generally defined as the region of space which end-effector of that mechanism can reach. Determination of workspace is an important task in the design of a mechanism. However, for parallel mechanisms, due to the complexity of solving the forward kinematic equations, determination of workspace is much more complicated than for serial mechanisms. In the literature, time-consuming numerical methods, such as point-by-point searching, are usually employed for this purpose. In this paper, an optimization-based algorithm is introduced for the boundary determination of inclusive and constant orientation workspaces of parallel mechanisms. In the proposed algorithm, thanks to applying the optimization approach along with point-by-point searching, the dimension of the point-by-point searched space (and hence, the consumed time) are significantly reduced. While different optimization methods can be used in the proposed algorithm, Particle Swarm Optimization is utilized as the optimization technique in this paper. The proposed algorithm is illustrated through its application to a planar and a spatial parallel mechanism.
Parametric Study of a Symmetric Flow Distributor
Authors: Ramos-Alvarado Bladimir , Hernandez-Guerrero Abel , Juarez-Robles Daniel , Li Peiwen , Rubio-Arana J. C.
Published: July 2010

A parametric study was conducted in order to reduce the pressure drop and to improve the uniformity of flow distribution in a symmetric flow distributor. A CFD model was employed to simulate the flow behavior by solving the Navier-Stokes equations in a complete 3D model. The present work is a complete parametric study of a base model, reported in previous studies, but keeping the same flow pattern. To improve the performance of the base design, three known successive parametric ratios, as functions of the hydraulic diameters of the channels, were tested in order to study the advantages and disadvantages of each one in terms of two dimensionless parameters that measure the uniformity of flow distribution. A remarkable improvement in the performance of the base model was achieved by modifying the width ratio of the channels. The present work is a contribution to the study of flow distributors to be used as heat exchangers, PEMFC flow channels and other flow devices.
Professional Tools Instruction Within an Overall ME Design Curriculum
Authors: Schmaltz Kevin , Moore Christopher , Lenoir Joel
Published: July 2010

The Mechanical Engineering faculty at Western Kentucky University have developed and implemented a Professional Plan to assure that graduates of the program have experienced key areas of the engineering profession and demonstrated their abilities to perform in a professional manner. The Professional Components within the plan include Engineering Design, Professional Communications, Professional Tools and Engineering Ethics; students receive instruction in at least one course per academic year and are expected to develop within each component. This paper will detail the Professional Tools component, which provides students with computational design tools and prototype realization skills supporting the Engineering Design demands placed on them. Computational tools include software for traditional communication and data processing, solid modeling and analysis, engineering computation and project management. Prototype realization skills encompass the typical metal machining operations necessary to create a functioning reciprocating air-powered engine and activities required for electro-mechanical device construction and testing. Higher level prototyping skills, such as rapid prototyping and CNC machining, are presented to students who can choose to become proficient with these activities or can engage other trained students to assist with their design project needs. The foundation of the four-year Professional Plan is centered on engineering design and problem solving. By exposing freshmen to hands-on projects, sophomores to design-analyze-and-build internal projects, and juniors to team-based prototype realization and external projects, a meaningful senior capstone design sequence involving external customers can validate and refine professional competencies of graduates, rather than introducing students to project activities. Professional tools instruction is interwoven with the other Professional Component instruction. While prototyping training is structured to provide a safe and efficient environment for the students at all times, computational tools are sometimes introduced as required for a project, and at other times well before needed for projects. Refinement to the Professional Plan has been guided by ongoing assessment, which is performed at course level at the end of a semester, and through program outcome assessment reviewed on an annual basis. The paper will detail the Western Kentucky University Professional Tools component of the overall Professional Plan, which provides a framework developing necessary student competencies, building upon previous coursework, assessing student progress, and adjusting course coverage based on prior assessments to assure that departing graduates will be capable of immediately contribute in their professional careers.
Closed Form Buckling Solutions of Euler-Bernoulli Columns With Multiple Singularities
Authors: Caddemi Salvatore , Calio` Ivo
Published: July 2010

In this paper the Euler-Bernoulli column in presence of multiple concentrated open cracks and for general boundary conditions is studied. The request of an integration procedure able to lead to exact closed form buckling solutions for any number, position and intensity of the cracks is satisfied. A model of concentrated crack based on the adoption of the distributions (generalized functions) is presented. In particular, the exact buckling mode solution and the corresponding exact buckling load equation is obtained. A parametric study for different boundary conditions is presented.
Design of a High-Speed On-Off Valve
Authors: Katz Allan A. , Van de Ven James D.
Published: July 2010

On-off control of hydraulic circuits enables significant improvements in efficiency compared with throttling valve control. A key enabling technology to on-off control is an efficient high-speed on-off valve. This paper documents the design of an on-off hydraulic valve that minimizes input power requirements and increases operating frequency over existing technology by utilizing a continuously rotating valve design. This is accomplished through use of spinning port discs, which divides the flow into pulses, with the relative phase between these discs determining the pulse duration. A mathematical model for determining system efficiency is developed with a focus on the throttling, leakage, compressibility, and viscous friction power losses of the valve. Parameters affecting these losses were optimized to produce the most efficient design under the chosen disc-style architecture. Using these optimum parameter values, a first generation prototype valve was developed and experimental data collected. The experimental valve matched predicted output pressure and flows well, but suffered from larger than expected torque requirements and leakage. In addition, due to motor limitations, the valve was only able to achieve a 64Hz switching frequency versus the designed 100Hz frequency. Future research will focus on improving the prototype valve and improving the analytical model based on the experimental results.
A Cryogenic Stabilization Scheme for Radio Astronomy Applications
Authors: Smith Michael J. , Blundell Raymond
Published: July 2010

We report on a scheme to stabilize short term cryogenic temperature variations in equipment used for high frequency radio telescope receivers. A 45.9 cm3 copper helium pot is affixed to a Sumitomo/Daikin 308, GM/JT cold head. 5.7×103 cm3of helium gas is introduced at the end of the cooling cycle and condensation until zero kPaa is reached. Short term temperature stabilization is achieved through the specific heat of the liquefied helium diminishing thermal deviations up to 46%.
Performance Control of a Tape Transport Mechanism Using Entire Eigenstructure Assignment
Authors: Moradi Hamed , Hajikolaei Kambiz Haji , Motamedi Mohammad , Alasty Aria
Published: July 2010

To achieve high rate of data transfer, tape mechanisms must be able to transport the tape with a constant velocity for scanning. During this process, it is desired to make the rise time minimized without timing and data transfer errors. In this paper, three servo systems including the take-up and supply reel servos for tape tension control and capstan servo for speed control are considered. So, tape transport mechanisms can be described with a nonlinear multi-input multi-output system (MIMO). After state-space representation of the problem, feedback control is designed for tracking objective. It should be mentioned that an increase in the speed of time response of system corresponds to an increase in the control signal and leads to additional cost. So, the eigenvalues and eigenvectors are chosen optimally until an appropriate response is achieved while the gains of feedback matrix remain small simultaneously.
Natural Convection From Isothermal Horizontal Cylinders
Authors: Gorman Ian M. O. , Murray Darina B. , Byrne Gerard , Persoons Tim
Published: July 2010

The research described here is concerned with natural convection from isothermal cylinders, with a particular focus on the interaction between a pair of vertically aligned cylinders. Prime attention was focused on how the local heat transfer characteristics of the upper cylinder are affected due to buoyancy induced fluid flow from the lower cylinder. Tests were performed using internally heated copper cylinders with an outside diameter 30mm and a vertical separation distance between the cylinders ranging from two to three cylinder diameters. Plume interaction between the heated cylinders was investigated within a Rayleigh number range of 2×106 to 6×106. Spectral analysis of the associated heat transfer interaction is presented showing that interaction between the cylinders causes oscillation of the thermal plume. The effect of this oscillation is considered as a possible enhancement mechanism of the heat transfer performance of the upper cylinder.
Modeling of a Hydraulic Elevator Driven by an Open-Loop Control
Authors: Strada Roberto , Oldani Alberto
Published: July 2010

Electro-hydraulic elevators are widely used systems, especially in low level buildings, due to their very good ratio between power generation and dynamic response. Generally, the goal of an elevator system is just to reach the floor with a precision enough to be comfortable for the passengers, without the need to follow a specific law of motion; hence an open-loop control system could be enough. Otherwise such a kind of solution reduces the number of components, bringing down the costs of production. On the other hand a complete knowledge of the mechanical system’s behaviour is required. In this work we deal with the analysis of the behaviour of a commercial hydraulic elevator driven by an open loop control that monitors the downstream pressure of the proportional valve supplying the cylinder. At the end of the paper, a closed loop solution based on the pressure measurement and on the motion time is proposed.
Nonlinear Response of Shallow Shells Subjected to Simulated Non-Gaussian Pressure Fluctuations in a Thermal Environment
Authors: Dhainaut Jean-Michel M.
Published: July 2010

The nonlinear response of shallow shells subjected to combined acoustic and thermal loads is analyzed using an efficient finite element modal formulation. The acoustic loads have non-white probabilistic characteristics and are simulated by an algorithm capable of reliably converging to a target power spectral density function and marginal probability density function. Factors contributing to the softening, hardening effect and modal contribution are also investigated along with their impact on the root-mean-square responses. Illustrative examples are given for cylindrical and spherical shells subjected to different combinations of acoustic and thermal loads.
Natural Convection With Micro-Encapsulated Phase Change Material
Authors: Sabbah Rami , Yagoobi Jamal , Al Hallaj Said
Published: July 2010

This study numerically explores the effect of presence of Micro-Encapsulated Phase Change Material (MEPCM) on the heat transfer characteristics of a liquid in a rectangular cavity driven by natural convection. The Natural convection is generated by the temperature difference between two vertical walls at constant temperatures. The Phase Change Material (PCM) inside the MEPCM particles melts in the vicinity of the hot wall and solidifies near the cold wall. Unlike pure liquids, the heat transfer characteristics of MEPCM slurry cannot be simply presented in terms of corresponding dimensionless controlling parameters such as Rayleigh number. In the presence of phase change particles, the controlling parameters’ values change significantly due to the local phase change. The numerical results show significant increase in the heat transfer coefficient (up to 80%). This increase is a result of the MEPCM latent heat and the increased volumetric thermal expansion coefficient due to MEPCM volume change during melting.
Application of the Meshless Element-Free Galerkin Method to Freckle Formation in Directional Solidification
Authors: Sajja Udaya K. , Felicelli Sergio D.
Published: July 2010

Freckles or channel segregates are the most severe form of the macrosegregation that can occur in unidirectionally solidified superalloy castings used in the manufacturing of gas turbine blades. These defects are formed due to thermosolutal convection during solidification. Mathematical modeling of the solidification process involves the simultaneous solution of the conservation equations of momentum, energy and solute concentration in all regions (liquid, mush and solid). Most numerical simulations of dendritic solidification processes have been performed using finite element or the finite volume techniques. The dependence of these methods on the mesh is not always advantageous for problems in which discontinuities or regions of sharp gradients do not coincide with the original mesh lines. In the present work, the meshless element free Galerkin (EFG) method has been investigated to simulate directional solidification processes in which sharp gradients in the field variables can occur as a result of the formation of channels. Simulations of a multicomponent Ni-Al-Ta-W alloy have been performed in a two dimensional domain. The calculations are started with the alloy in all-liquid state and the growth of the mushy zone is followed in time. A projection method is used to solve the momentum equation which makes the computation more efficient than the previously used penalty method. The accuracy of the EFG results is compared with that of the finite element calculations and the potential advantages of the meshless methods for this type of problems are discussed.