bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Performance Analysis of Fan-Heat Sinks for CPU Cooling
Authors: Kim Seo Young , Webb Ralph L.
Published: May 2008

The thermal performance of plate fin, round pin-fin and offset strip-fin heat sinks with a duct-flow type fan arrangement was analytically evaluated. Heat sinks of 65mm × 60mm plan area × 50 mm height with a 4300-RPM DC fan (60mm × 15mm) were chosen for the performance comparison. A constant temperature, 6 mm thick heat sink base plate is assumed so that thermal spreading resistance is not involved. The operating point on the fan curve is based on the flow pressure drop impedance curve through a heat sink using the friction factor correlation for the chosen heat sink. The loss coefficients at both the entrance and the exit of heat sink are included in the flow impedance curve. The operating point is defined by the balance point of the flow impedance curve and the fan performance curve. After determining the operating air velocity, the convective thermal resistance of heat sinks is evaluated from the Nusselt number correlation for the chosen heat sink. Results obtained show that optimized round pin-fin heat sinks provide 32.8%-to-46.4% higher convective thermal resistance compared to an optimized plate-fin heat sink. The optimized offset strip-fin heat sink shows a slightly lower convective thermal resistance than the plate-fin heat sink. As the offset strip length decreases, however, thermal performance seriously deteriorates.
The Challenges of Electronic Cooling: Past, Current and Future
Authors: Chu Richard C.
Published: May 2008

This paper represents my personal recapitualation of my 4 decades of continuous involvement in all phases of electronic cooling, from conceptual design, through engineering development to product implementation. The cooling designs that we applied successfully in the past are reviewed chronologically. The challenges we are currently facing are also discussed and an attempt is made to forecast the challenges that will confront the electronics cooling community in the near and distant future. The paper includes a summary of IBM sponsored research spanning a period of 25 years at 12 universities on a wide range of topics related to electronic cooling technology.
Nonlinear Oscillations of an Antisymmetric Cross-Ply Laminated Composite Thin Rectangular Plate Under Parametric Excitation
Authors: Ye Min , Sun Yanhong , Ding Qian , Zhang Wei
Published: May 2008

In this paper, nonlinear dynamics of a simply supported antisymmetric cross-ply laminated composite thin rectangular plate under parametric excitation is investigated. The governing equations of motion for the antisymmetric cross-ply laminated composite plate are derived by using von Karman type plate equation. The geometric nonlinearity and nonlinear damping are included in the governing equations of motion. A two-degree-of-freedom parametrically excited nonlinear system including the quadratic and cubic nonlinear terms is obtained by using the Galerkin method. Based on the Fourier expansion and the temporal rescaling, an asymptotic perturbation method is utilized to obtained four-dimensional nonlinear averaged equations on the amplitude and the phase of nonlinear oscillations of the antisymmetric cross-ply laminated composite plate for the first time. Based on the averaged equations, the steady state nonlinear responses and their stabilities are determined by using numerical approach. The relations between the steady state nonlinear responses and the amplitude and frequency of parametric excitation are obtained. Under the certain conditions, the antisymmetric cross-ply laminated composite plate may have two steady state nonzero solutions in which the jumping phenomenon occurs.
Thermal Design of an Airborne, Military Computer Chassis With Air-Cooled, Cast Pin Fin Coldwalls
Authors: Price Donald C. , Short B. Elliott
Published: May 2008

This paper documents the thermal design process required to provide effective thermal management for an airborne, military computer, consisting of 24 modules (two P/S modules and 22 PWB modules), which are edge-cooled to two cast, pin fin coldwalls. The computer chassis is mounted in an electronics pod mounted underneath the centerline of a fighter aircraft. The pod consists of several electronics bays and a self-contained, air-cycle, environmental control system (ECS). The computer chassis is mounted in the forward bay, and the ECS is mounted in the rear bay of the electronics pod. The ECS is an air-cycle refrigeration system, which operates on captured ram air directed by an inlet/diffuser to an expansion turbine. This turbine produces low-pressure, chilled-air, which is then directed through an air-to-liquid, load heat exchanger to produce chilled-liquid. The chilled liquid is piped through small liquid lines to the forward bay of the pod, where the air-cooled, computer chassis is located. The chilled liquid is converted back to chilled-air in an air-to-liquid heat exchanger. The chilled-air is supplied to the forward bay volume and is drawn through the computer chassis coldwalls by a fan integral to the computer chassis. The temperature of the chilled-air, produced in this manner, becomes a strong function of the altitude and Mach number of the fighter aircraft, because of the effect of these two parameters on the ram air mass flow rate and temperature at the inlet to the expansion turbine. The mass flow of the air used to cool the chassis is also a variable, because the density of the air is a function of the flight altitude and the fan has altitude-dependent, operating characteristics. This fan provides the flow of air through the chassis. Emphasis is placed in the design process on the effect of the operating characteristics of the fan at altitude and the determination of the system performance curve associated with the pin fin coldwalls. This performance curve is controlled by the pressure drop characteristics of the pin fin coldwalls, which are a function of the Fanning f-factor and Colburn j-factor characteristics of the cast pin fin design. Design examples are used to demonstrate the design process.
Fast Running Pool Fire Computer Code for Risk Assessment Calculations
Authors: Greiner Miles , Suo-Anttila Ahti
Published: May 2008

The Isis-3D computational fluid dynamics/radiation heat transfer computer code was developed to simulate heat transfer from large fires to engulfed packages for transportation risk studies. These studies require accurate estimates of the total heat transfer to an object and the general characteris tics of the object temperature distribution for a variety of fire environments. Since risk studies require multiple simulations, analysis tools must be rapid as well as accurate. In order to meet these needs Isis-3d employs reaction rate and radiation heat transfer models that allow it to accurately model large-fire heat transfer even when relatively coarse computational grids are employed. In the current work, parameters for the reaction rate model were selected based on comparison with soot volume fraction and temperature measurements acquired in a recent 6 m square pool fire under light wind conditions. The soot volume fraction Isis-3D uses to define the edge of the optically thick fire was determined using temperature measurements of a pipe engulfed 20-m-diameter pool fire with a steady 9.5 m/s crosswind. Accelerated simulations, in which the specific heat of the engulfed pipe was reduced by a factor of twelve below the measured values, reproduce the temperature data in the 11-minute crosswind fire using only 3.5 hours on a standard desktop workstation.
The State of Green Engineering at Virginia Tech
Authors: Gregg Michael H.
Published: May 2008

This paper reviews the success and failures of the Green Engineering Program at Virginia Tech over the past ten years. The history of the program is examined, including the steps to offering a ‘concentration’ in the area. Both of the core courses of the eighteen credit concentration are described and their evolution tracked: Introduction to Green Engineering (ENGR3124) and Environmental Life Cycle Assessment (ENGR3134). Steps currently being considered to add graduate level courses and efforts to obtain research funding are discussed.
Thermal Radiation Heat Transfer and Biomass Combustion in a Large-Scale Fixed Bed Boiler
Authors: Nilsson T. K. , Klason T. , Bai X. S. , Sunde´n B.
Published: May 2008

The main focus of this work is to investigate the performance of some simple radiation models used in the thermal radiative heat transfer calculations in a 55 MWe fixed bed boiler with wet wood-chips as the fuel. An optically thin approach, Rosseland approximation, and the P1-approximation were utilised in the investigation. A new optimised version, as it comes to computational speed, of the exponential wide band model (EWBM) is used. The initial calculations showed that the optically thick approach failed. The optically thin approach actually gave the best prediction of the temperature, if the mean beam length (Lm) was chosen carefully. The P1-approximation gave less good predictions than the best optical thin case, but it could be the best engineering model to use if little was known about the mean beam length. The conclusion is that the optically thin model is sensitive to the chosen mean beam length (Lm) used in the EWBM. The P1-approximation is almost insensitive to the choice of Lm, due to the consideration of radiation self-absorption, where the different predicted values of the incident radiation compensate for different values of Lm. For the same reason, the use of other solution techniques, such as DOM or DTM, may lead to the same conclusion, i.e., the insensitivity of the choice of Lm.
The Impact of Area Contact Between Sensor Bulb and Evaporator Return Line in a Modular Refrigeration Unit: Part I — Computational Study
Authors: Lakhkar Nikhil , Karajgikar Saket , Agonafer Dereje , Schmidt Roger
Published: May 2008

The combination of increased power dissipation and increased packaging density has led to substantial increase in junction temperature, at both the chip and module level in computers and especially at the high-end. In the past, virtually all-commercial computers were designed to operate at temperatures above the ambient and were primarily air-cooled. However, researchers have always known the advantages of operating electronics at low temperatures. This facilitates faster switching time of semiconductor devices, increased circuit speeds due to lower electrical resistance of interconnecting materials and reduction in thermally induced failures of devices and components. Depending on the doping characteristics of the chip, performance improvement ranges from 1 to 3% for every 10°C lower transistor temperature can be realized. The paper addresses improving the cooling of IBM’s high-end server unit, which uses a conventional refrigeration system to maintain the chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperature. The IBM S/390 high-end server system is the first IBM design that employed refrigeration cooling. Advantage of using refrigeration unit is improvement in reliability, and performance improvements related to the lower operating temperature. In previous work, the focus was to study the effect of variation of evaporator outlet superheat on the flow through the thermostatic expansion valve at varying evaporator temperature. Also the effect of change in bulb location and effect of bulb time constant on the hunting at the evaporator has been reported. Currently, the evaporator return line and the sensor bulb are simply attached with a clip, with no thermal consideration. In the present study, the performance that results from varying the area of contact between the evaporator return line and sensor bulb is discussed. Subsequently, the effect of various interface materials on the performance is examined.
Non-Contact Device for Measuring Frequency Response Functions of CNC Machine Tools
Authors: Esterling Donald , Caulfield F. Donald , Kiefer Aaron , Buckner Gregory , Jaju Pavan
Published: May 2008

The frequency response function (FRF) of a CNC machine tool is composed of tool/toolholder/spindle dynamics, and plays an important role in determining the stability of high speed machining processes. This paper details the design, development and operational verification of a non-contacting, controllable, electromechanical actuator (EMA) for measuring the FRFs of tools mounted in CNC milling machines. Although standard modal testing methods are available and provide similarly accurate results, these test procedures are difficult to perform in machine shop environments and can require expensive equipment. The EMA developed as part of this research extends the capabilities of the NIST “best speeds device” to provide controllable, non-contacting excitation for modal tests on machine tools. This EMA device offers the advantages of being accurate, easy to use, and applicable to a wide variety of tools and operating conditions.
Chaotic Motion of a Two-Frequency Forced Oscillator With Dry Friction
Authors: Cheng Gong , Zu Jean W.
Published: May 2008

In this paper, the dynamic behavior of a dry friction oscillator subjected to simultaneous self- and external excitations is studied. The dry friction in the system follows the classical Coulomb’s law, and the external excitation consists of two harmonic forces with different frequencies. The focus of the paper is laid on bifurcation analysis to gain insight into the influence of the two-frequency excitation upon the qualitative features of system dynamics. Numerical simulations are performed and the simulation results are visualized by means of bifurcation diagrams, Poincare´ sections and Lyapunov exponents. New and interesting conclusions are reached from the study. It is shown that small excitation frequencies and amplitudes tend to cause chaos in the system, whereas large excitation amplitudes can induce only periodic motions. Furthermore, it is found that the probability of the occurrence of periodic motions increases, as the ratio between the two excitation frequencies increases.
Dynamic Compensation of Intelligent Sensors
Authors: Schoen Marco P.
Published: May 2008

Commercial sensors have generally, due to their own characteristics, some undesirable influences on the measured quantity and its precision. In particular, the dynamic characteristics can be reflected on to the measured quantity and lead to false or delayed interpretation of the underlying physical process. The quality and therefore the cost of the sensor is often tied with the dynamic performance of these instruments. Intelligent sensors are able to adapt to changing environments, calibrate themselves, and predict the pattern of the future signal. This paper presents algorithms to improve the dynamic performance of sensors, identify the dynamic characteristics of the sensor, and to predict the future pattern of the measured quantity. In particular, two inverse filters are proposed for the improvement of the sensors dynamic performance. One filter incorporates an optimal constant feedback gain that reduces the computational cost and increases the accuracy. A system identification method is used to identify the sensor’s dynamic properties and allows for adaptation of the inverse filter’s parameters. This identification algorithm computes the optimum input to the system i.e. the sensor. The optimization is based on the inverse correlation matrix of the information matrix. A genetic algorithm is used to perform both optimizations, for the computation of the optimal input, and for the optimal constant feedback gain. In addition, a predictive filter formulation is given that is based on the identified system. Simulation results indicate that both inverse filters are capable of recovering the original or true signal. The second filter shows superiority in terms of convergence, lower computational cost, and lower error due to its optimized parameters. The predictive filter indicates good working accuracy for the signal prediction.
Effect of Sub-Continuum Energy Transport on Effective Thermal Conductivity in Nanoporous Silica (Aerogel)
Authors: Smith Brian R. , Amon Cristina H.
Published: May 2008

This paper analyzes the effect of Fourier vs. subcontinuum heat transport through thin layers of nanoporous silica (aerogel) in the framework of an infrared focal plane array (IRFPA) sensor system. Aerogel is introduced as a compatible material for emerging microsystems applications and the comparison between aerogel and conventional insulation systems is analyzed. Correlations between aerogel’s macro-scale thermal properties and its nano-scale structure are discussed to address the effect of the material’s amorphous structure and sub-continuum phonon transport phenomena on macro-scale thermal conductivity. Simulations using the Lattice Boltzmann Method (LBM) quantify the effect of phonon scattering on silica conductivity. Techniques for extending the analysis to a three-dimensional silica matrix are discussed in light of recent advances in the simulation of aerogel morphology.
FEM Stress Analysis and Sealing Performance in Bolted Flange Connections With Cover of Pressure Vessel Subjected to Internal Pressure
Authors: Sawa Toshiyuki , Higuchi Rie
Published: May 2008

The stresses of a bolted flange connection with a cover of pressure vessel (CPV) in which a spiral wound gasket is inserted, under internal pressure are analyzed taking account a hysteresis of the gasket by using the finite element method (FEM). The leakage tests were also conducted using an actual bolted flange connection with a CPV with a spiral wound gasket. Using the contact stress distribution of the bolted flange connection with a CPV under internal pressure and the tightness parameter, the values of the new gasket constants were obtained by taking into account the changes in the contact stress. A difference in the new gasket constants between the estimated values obtained from the actual bolted flange connection with a CPV and the values obtained by the PVRC procedure was small. In addition, a method to determine the bolt preload for a given tightness parameter was demonstrated. The obtained results of the bolt preload for the bolted flange connection with a CPV were in a fairly good agreement with those obtained by the PVRC procedure under a lower pressure application. However, a difference in the bolt preload was about 7% when the internal pressure was increased.
Determination of Surface Damage in the Grinding of Silicon Wafers
Authors: Yang Fuqian , Fei Peixing
Published: May 2008

Grinding as one of the important processes for silicon manufacturing industry is the first step to reduce the cutting-caused surface-damage, which is one of key parameters determining the surface quality of silicon wafers. To understand the evolution of surface damage in grinding process, the ball-dimple technique developed for the measurement of the subsurface damage of ground glasses was applied to characterize the surface damage of silicon wafers created in the grinding process. The surface damage increases with abrasive size, which associates with the formation and propagation of surface cracks. Fracture mechanics due to the indentation of sharp indenters was used to exploit the connection between the surface damage and the process parameters. Microindentation was used to evaluate the near-surface elastic behavior of the ground silicon wafers.
Sensor Placement for Effective Diagnosis of Multiple Faults in Fixturing of Compliant Parts
Authors: Camelio Jaime A. , Hu S. Jack , Yim Hyunjune
Published: May 2008

This paper presents a new sensor placement methodology for effective fault diagnosis in an N-2-1 locating scheme used in compliant sheet metal assembly processes. The proposed approach is based on the effective independence (EfI) sensor placement method. The EfI method is a computational algorithm that starts with all feasible sensor locations and reaches the desired number of locations, by progressively eliminating those having the least contributions to the linearly independent manifestation of the fixture faults. The least squares method was adopted to identify fixture faults from the measurement data. An automotive panel part was considered to illustrate the suggested methodology. The sensors placed by the EfI method enable the effective identification of multiple fixture faults even in the presence of moderate measurement noise.
Total Power Requirements for Near-Future Refrigerated Systems
Authors: Copeland David , Chan Albert
Published: May 2008

As feature dimensions of processors shrink to 100 nanometers and smaller, leakage current becomes a significant part of total power dissipation. The magnitude of power dissipated as leakage current can approach half that of the active current at higher junction temperatures. Leakage current exhibits a strong exponential relationship with temperature. Reduction of junction temperatures from a traditional value of 85 C to a near-ambient value of 25 C can reduce leakage current to a fraction of its usual value, and total power by nearly one-third. To date, refrigeration has been used to increase operating frequency and improve reliability, at the cost of considerable power consumption. At finer feature dimensions, the energy saved by reduction of junction temperature is comparable to that used by the refrigeration system. Realistic values of refrigeration performance, representative of current equipment and refrigerants, are used to perform a case study of a typical near-future processor. Leakage, active and refrigeration power requirements over a junction temperature range from 85 to 25 C are quantified.
Intelligent Detection of Boring Tool Conditions
Authors: Liu Tien-I. , Kumagai Akihiko , Song Shin-Da , Fu Zhenwen , Wang Yann-Chiu , Lee Jay
Published: May 2008

Adaptive neuro-fuzzy inference systems (ANFIS) were used for on-line classification and measurement of tool wear for the boring of titanium parts. The input vectors consist of extracted features from cutting force data. A total of fourteen features were extracted by processing cutting force signals using virtual instrumentation. Feature selection was carried out using a Sequential Forward Search (SFS) algorithm to select the best combination of features. For the on-line classification, the outputs are boring tool conditions, which are either usable or worn out. For the on-line measurement, the outputs are estimated values of the tool wear. Using ANFIS, three features were selected for the on-line classification of boring tools. They are the average longitudinal force, average of the ratio between the tangential and radial forces, and kurtosis of the longitudinal force. Only one feature, kurtosis of the longitudinal force, was needed for the on-line measurement of tool wear using ANFIS. A 3×5 ANFIS can achieve a 100% success rate for the on-line classification of boring tool conditions. Using a 1×5 ANFIS, the average flank wear estimation error is below 5% for on-line measurement of tool wear.
Diffusion of Sustainable Systems Engineering Through Interdisciplinary Graduate and Undergraduate Education at the University of Michigan
Authors: Skerlos Steven J. , Hayes Kim F. , Zimmerman Julie B. , Morrow W. Ross
Published: May 2008

This paper provides specific examples of sustainability education programs within the engineering curriculum at The University of Michigan at Ann Arbor (UM). These programs exist at the undergraduate, Masters, and Ph.D. levels of education. At the undergraduate level, a basic literacy program has been initiated to give each graduating mechanical engineer from UM the understanding required to make design decisions less impacting on the environment. The program is designed as an educational thread consisting of three (3) course modules corresponding to each of three required courses in the Design and Manufacturing sequence in the mechanical engineering department. To compliment the thread, a new joint course between mechanical and environmental engineering in Environmentally Sustainable Engineering is under development to serve as the cornerstone undergraduate course in environmental education for the UM College of Engineering (CoE). At the Masters level, the ConsEnSus (Concentrations in Environmental Sustainability) Program is described. This program has been introduced to enhance general environmental literacy and to prepare students to integrate environmental principles into professional practice. Similarly, a joint Ph.D. program has also been developed between CoE and the School of Natural Resources and the Environment to prepare students for a career in research and education related to sustainable engineering. Both ConsEnSus and the Ph.D. program are supported by a course entitled Principles of Eco-Design and Manufacturing. This course, and the graduate and undergraduate programs it supports, is part of a college-wide effort to make Sustainable Systems Engineering a reality in practice by disseminating operational definitions of sustainability targeted to specific engineering disciplines.
Experimental Studies on the Gas-Stack Heat Transfer in a Thermoacoustic Refrigeration System
Authors: Gurijala Phani R. , Nsofor Emmanuel C.
Published: May 2008

Thermoacoustic refrigeration employs inert gases as the working fluid and uses high intensity sound waves to pump heat energy. The major components of the system are the resonator, the acoustic driver, the heat exchangers and the stack. The useful thermoacoustic process for cooling in the system takes place between the gas particles and the stack. The system was designed and constructed. Experimental studies on the gas-stack heat transport and the Streaming Reynolds Number, which play crucial roles in the heat transport behavior, were studied. Input signals for the experiments, for the data acquisition system was from thermocouples and pressure transducers. Results from the study were used to make recommendations for the system. It was observed that for a given frequency, the heat transfer increases with drive ratio. Results from the comparison of the heat losses for a stainless steel stack and a stack built of thermoplastic material show that the plate heat losses can be significantly reduced if the stack with thermoplastic material is used for the system.
In Situ Temperature Distribution Measurement in an Operating Polymer Electrolyte Fuel Cell
Authors: Mench Matthew M. , Burford Daniel J. , Davis Tyler W.
Published: May 2008

The temperature distribution in a polymer electrolyte fuel cell (PEFC) is of critical importance to the water balance, as well as to other kinetic and transport phenomena that are known to be functionally dependent on temperature. However, direct measurement of localized temperature is difficult, due to the two-phase nature of flow in the gas channels and the small through-plane dimensions of a typical electrolyte. To circumvent these difficulties, an array of microthermocouples was embedded directly between two 25 μm thick Nation™ electrolyte sheets of a membrane electrode assembly. The embedded array was used to measure electrolyte temperature as a function of current and fuel cell flow channel location. For the fuel cell tested with natural convective cooling, a temperature increase in the electrolyte of as much as 15°C is observed for current densities of 1 A/cm2.
Variation Simulations for Digital Panel Assembly
Authors: Cai Wayne , Long Yufeng , Hsieh Ching
Published: May 2008

This paper presents methodologies and results of variation simulations for digital panel assembly, using GM proprietary software called EAVS. EAVS provides two alternative algorithms for variation simulation of digital panel assembly, i.e., Taylor Series Expansion (TSE) based and Monte Carlo Simulation (MCS) based. In this paper, algorithms of the two methods are reviewed, and pros and cons are studied. Several case studies are presented to illustrate the capabilities of the two methods. Based on the case studies, the EAVS variation simulation guidelines will be established ensuring analysis accuracy at reasonable computational time.
Harmonic Wave Propagation of Ultrasonic Arc Stators
Authors: Smithmaitrie P. , DeHaven J. G. , Higuchi K. , Tzou H. S.
Published: May 2008

A piezoelectric curvilinear arc stator designed for an ultrasonic curvilinear motor is studied in this research. Design of piezoelectric curvilinear arc stator is proposed and its governing equations and vibration behavior are investigated. Then, analysis of forced vibration response or driving characteristics to harmonic excitations in the modal domain is conducted. Finite element modeling and analysis of the arc stator are also discussed. Analytical results of free vibration characteristics are compared favorably with the finite element results. Harmonic analyses of the three finite element models reveal changes of dynamic behaviors of three models and also imply operating frequencies with significant traveling wave component. Study of mathematical and finite element simulation results suggests that stable traveling waves can be generated to drive a motor on the proposed curvilinear arc stator system.
Control of Static Shape, Dynamic Oscillation, and Thermally Induced Vibration of Nozzles
Authors: Wang D. W. , Tzou H. S. , Arnold S. M.
Published: May 2008

Static shape actuation and dynamic control of nozzles can optimize their performance, accuracy, reliability, etc. A new curved laminated piezothermoelastic hexahedral finite element is formulated based on the layerwise constant shear angle theory and it is used for modeling and analysis of piezothermoelastic conical shell structures subjected to control voltages for static shape actuation, dynamic and thermally-induced vibration controls. Free vibration characteristics of an elastic truncated conical shell nozzle with fixed-free boundary conditions are studied using the new finite element. Both frequencies and mode shapes are accurately computed and compared favorably with the experimental and other numerical data. This study is then extended to evaluate control effectiveness of the conical shell with laminated piezoelectric layers. Static shape control is achieved by an applied electric potential. Vibration sensing and control are carried out using the negative velocity control scheme. Control of thermal excitation is also investigated. Analysis data suggests that the dynamic behavior and control characteristics of conical shells are quite complicated due to the coupled membrane and bending effects participating in the responses. To improve control effectiveness, segmentation and/or shaping of sensor and actuator layers need to be further investigated.
The Energy Budget in Tubular and Planar Type Solid Oxide Fuel Cells Studied Through Numerical Simulation
Authors: Li Pei-Wen , Schaefer Laura , Chyu Minking K.
Published: May 2008

The energy budget in a tubular and a planar type solid oxide fuel cell (SOFC) is studied based on numerical simulation. By solving the discretized governing equations for flow, temperature, and mass fraction of gas species in the fuel cells, the detailed local parameters determining the local electromotive forces are obtained. The energy flows of electrical power, Joule heating, thermal energy from the entropy change of the electrochemical reaction, as well as the chemical reaction heat by reforming and shift reactions are delineated and compared for the two different types of SOFCs.
Internet-Based Collaboration and Learning Environment for Efficient Simulation and Control Design
Authors: Mann Herˇman , Sˇevcˇenko Michal
Published: May 2008

A software system DYNAST for efficient modeling and simulation distributed across the Internet is freely accessible at http://virtual.cvut.cz/dyn/. DYNAST supports collaboration of remote engineering teams as well as hands-on training of Web-based-course learners. The DYNAST Server solves nonlinear algebro-differential equations, and automatically formulates them for multipole models characterizing configuration of real dynamic systems. DYNAST Server is also able to linearize the models and to provide their semisymbolic analysis in time- and frequency-domains. Clients can submit their problems and interpret the simulation results across the Internet using different user environments. The results can be animated in 3D by means of VRML. The DYNAST Server supports also publishing standardized reports on simulation experiments. The accompanying Web-based course with a knowledge-sharing system and interactively resolvable examples exploits innovative didactic approaches. In control design, the modeling efficiency of DYNAST can be combined to a great advantage with the control-design power of the MATLAB toolsets.
Prediction of Dryout in Flat Heat Pipes at High Heat Fluxes From Multiple Discrete Sources
Authors: Vadakkan Unnikrishnan , Garimella Suresh V. , Murthy Jayathi Y.
Published: May 2008

A three-dimensional model has been developed to analyze the transient and steady-state performance of flat heat pipes with discrete heat sources. Three-dimensional flow and energy equations are solved in the vapor and liquid regions, along with conduction in the wall. Saturated flow models are used for heat transfer and fluid flow through the wick. In the wick region, the analysis uses an equilibrium model for heat transfer and a Brinkman-Forchheimer extended Darcy model for fluid flow. Averaged properties weighted with the porosity are used for the wick analysis. The state equation is used in the vapor core to relate density change to the operating pressure. The density change due to pressurization of the vapor core is accounted for in the continuity equation. Vapor flow, temperature and hydrodynamic pressure fields are computed at each time step from coupled continuity/momentum and energy equations in the wick and vapor regions. The mass flow rate at the interface is obtained from the application of kinetic theory. Predictions are made for the magnitude of heat flux at which dryout would occur in a flat heat pipe. The input heat flux and the spacing between the discrete heat sources are studied as parameters. The location in the heat pipe at which dryout is initiated is found to be different from that of the maximum temperature. The location where the maximum capillary pressure head is realized also changes during the transient. Axial conduction through the wall and wick are seen to play a significant role in determining the axial temperature variation.
Net Mass Flow Components in a Three-Dimensional Unsteady Rotor Inflow Model
Authors: Yu Ke , Peters David A.
Published: May 2008

Potential flow equations are converted to ordinary differential equations by the Galerkin approach in which velocity and pressure potential functions are expanded in terms of closed-form solutions to Laplace’s Equation. The reduced number of generalized coordinates in a Galerkin approach gives advantages in real-time simulations, preliminary design, and dynamic eigenvalue analysis for aeroelasticity. Net mass injection from rotor sources is expected to occur in some situations, but cannot be treated by previous models. It is included in the present formulation. In this paper, frequency response due to pressure distributions corresponding to net mass flow in both axial and skew-angle flight are given. These results are compared with exact solutions obtained by the approach of a convolution integral. A brief analysis is also included with respect to numerical simulations of the Associated Legendre Functions, in which it demonstrates that net mass flow components are extremely sensitive to the recursive process of seeking Associated Legendre Functions.
Free Vibration of a Thin-Film Inflated Torus
Authors: Moxey L. , Hamidzadeh H.
Published: May 2008

In this paper an overview of the mathematical model for an inflated thin-film toroidal structure is provided. In particular, attention has been confined to determine the free vibrations of inflated circular toroidal members. The provided solution is based on an improved set of equations of motion for uniform membrane. From which the dependence of natural frequencies on material properties, dimension, mode of vibration, and the inner pressure can be investigated. The validity of the developed models was verified by comparing some of the computed results with those available for special cases. Numerical results for natural frequencies and mode shapes are provided for a specific thin-film inflated torus.
Physics-Based Modeling of Bearing Based on Finite Element Modeling Technique
Authors: Shirkhodaie Amir , Dubeck John
Published: May 2008

The physical condition of rolling element ball bearings can be estimated using analytical and empirical methods or predicted grossly using artificial intelligence techniques such as expert systems, fuzzy logic, and neural network, etc. When the operational condition of a bearing is dynamic and there is a need to determine the actual stresses and tolerances of the bearing concisely, then it is wiser to develop a physics-based model of the bearing using finite element modeling (FEM) techniques. Applying such FEM techniques, one can virtually examine any of the possible mechanical characteristics of different types and sizes of ball bearings operating under different speeds and environmental conditions. Understanding such mechanical characteristics is crucial to accurate fault diagnosis of the bearings in practice. For example, such mechanical characteristics can be digitized or mathematically modeled in order to reduce the computational extent of the analysis as well as serve as a reference look-up table for better and faster fault diagnosis purposes than current practices. It can also be applied to determine the remaining useful life of the ball bearing more precisely. In this paper, we present our technical approach toward the development of a physics-based finite element model of rolling element bearings and provide some examples based on results of this research effort.
Highly Flexible Final Production Stages: A New Approach for Assembly in the Variant-Rich Series Production
Authors: Wiendahl Hans-Peter , Grosse-Heitmeyer Volker
Published: May 2008

The rapid manufacture of a great range of variant products is gaining importance in global competition. Customers are increasingly demanding products which are matched to their specific requirements. The production of these customized variants gives a competitive advantage, but also leads to higher production costs. Almost every step in the process of making a product is capable of generating variants. A key element in variant management is to make the variants as late as possible in order to exploit economies of scale in the earliest stages of production and to minimize the complexity of production [9], [6]. The technique of the highly flexible final production stage consists in achieving a late emergence of variants by integrating the variant-specific manufacturing processes into the assembly stage. This means abandoning the conventional distinction between manufacture and assembly in favour of a division into a preliminary, variant-neutral production stage and a final production stage where the variants take shape. The final production stage includes all the processes that yield variants. The complete manufacture of variant-neutral parts and subassemblies takes place in the preliminary production stage, as does the prefabrication of those parts and sub-assemblies which are to undergo final manufacture as variants in the final production stage. The result is a procedure capable of producing a broad spectrum of variants economically and with minimal throughput times. This paper describes the philosophy of this new approach and concludes with a practical case study.
The Effects of the Adhesively Bonded Repair Patch on the Dynamic Response of the Composite Beam Under a Harmonic Peeling Load
Authors: Vaziri A. , Nayeb-Hashemi H. , Olia M.
Published: May 2008

The dynamic response of an adhesively patched repaired composite beam under a harmonic peeling load was obtained theoretically and experimentally. In the theoretical part, dynamic responses of the repaired composite beams were obtained by modeling the parent beam as the Euler-Bernouli beam and the repaired patch as the Euler-Bernouli beam supported on a viscoelastic foundation, which resist both peeling and shear stresses. Both axial and transverse displacements were considered in deriving the coupled equations of motion. The effects of the adhesive loss factor, as well as its elastic modulus on the vibrational behavior of the repaired composite beams were investigated theoretically. In addition, finite element modal analyses were performed to justify the results of the proposed theoretical model. In the experimental part, unidirectional fiberglass reinforced epoxy composite specimens with various repaired patch length, thickness and material properties were manufactured. The patch section was either the fiberglass epoxy or E-glass fiber reinforced composites with various ply sequences. Patches were bonded to the composite beam using an epoxy. The system response was measured by the hammer test technique using a non-contact laser vibrometer. The resonant frequencies and damping ratio of the specimens were evaluated from the dynamic response of the composite beam and the results were compared to that of the theoretical and finite element analyses. The results showed that the dynamic response of the repaired composite depended on the adhesive elastic modulus. For the composite repaired with a high adhesive elastic modulus, the beam may act as a classical Euler-Bernouli composite beam. For the composite patched with a low elastic modulus adhesive, the first resonant frequency of the system may decrease up to 22%. In contrast, the natural frequencies may not significantly change having used adhesive with a high elastic modulus.
Exergy Analysis of Data Center Thermal Management Systems
Authors: Shah Amip J. , Carey Van P. , Bash Cullen E. , Patel Chandrakant D.
Published: May 2008

Data centers today contain more computing and networking equipment than ever before. As a result, a higher amount of cooling is required to maintain facilities within operable temperature ranges. Increasing amounts of resources are spent to achieve thermal control, and tremendous potential benefit lies in the optimization of the cooling process. This paper describes a study performed on data center thermal management systems using the thermodynamic concept of exergy. Specifically, an exergy analysis has been performed on sample data centers in an attempt to identify local and overall inefficiencies within thermal management systems. The development of a model using finite volume analysis has been described, and potential applications to real-world systems have been illustrated. Preliminary results suggest that such an exergy-based analysis can be a useful tool in the design and enhancement of thermal management systems.
Experimental Modal Analysis of Rectangular and Circular Beams
Authors: Emory B. H. , Zhu W. D.
Published: May 2008

Analytical and experimental methods are used to determine the natural frequencies and mode shapes of Aluminum 6061-T651 beams with rectangular and circular cross sections. A unique test stand is developed to provide the rectangular beam with different boundary conditions including clamped-free, clamped-clamped, clamped-pinned, and pinned-pinned. The first 10 bending frequencies and mode shapes for each set of boundary conditions are measured. The effects of the bolt torque on the measured frequencies of the rectangular beam are examined. The material properties of the circular beam, including the elastic modulus, shear modulus, and Poisson’s ratio, are determined by measuring its first 20 natural frequencies. A new technique is used to mount an accelerometer to measure the torsional modes of the circular beam. A roving hammer test is conducted to measure the first 10 mode shapes. The measured mode shapes of the circular and rectangular beams are compared with their thoretical predictions using the modal assurance criterion. The Timoshenko beam theory is shown to provide better predictions of the natural frequencies for the higher modes of the circular beam than the Bernoulli-Euler beam theory. The use of the rectangular and circular beam test stands as a teaching tool for undergraduate and graduate students is discussed.
Developing Variational Vibration Models of Damaged Beams: Toward Intelligent Failure Detection
Authors: McAdams Daniel A. , Comella David , Tumer Irem Y.
Published: May 2008

Inaccuracies in the modeling assumptions about the distributional characteristics of the monitored signatures have been shown to cause frequent false positives in vehicle monitoring systems for high-risk aerospace applications. To enable the development of robust fault detection methods, this work explores the deterministic as well as variational characteristics of failure signatures. Specifically, we explore the combined impact of crack damage and manufacturing variation on the vibrational characteristics of beams. The transverse vibration and associated eigenfrequencies of the beams are considered. Two different approaches are used to model beam vibrations with and without crack damage. The first aproach uses separation of variables. This method enables the direct integration of the resulting ordinary differential equation and determination of different eigenfrequencies and eigenmodes. This approach uses a spring to model localized reduction in stiffness as a result of the cracked beam. The second approach uses a finite difference approach to enable the inclusion of both cracks and manufacturing variation to be considered. The crack model used with the finite difference approach is based on a localized decrease in the Young’s modulus. Using both beam and crack models, Monte Carlo simulations are used to explore the impacts of manufacturing variation on damaged and undamaged beams. Derivations are presented for both models. Conclusions are presented on the choice of modeling techniques to define crack damage, and its impact on the monitored signal, followed by conclusions about the distributional characteristics of the monitored signatures when exposed to random manufacturing variations.
Thermal Insulation Using Phase Change Material
Authors: Alawadhi Esam M.
Published: May 2008

This research studies the effectiveness of Phase Change Material (PCM) as a thermal insulation for a pipe. The objective of using PCM is to utilize its latent heat to minimize heat loss by absorbing heat loss from the pipe, which minimizes net heat loss from the pipe to the ambient. Finite element method is employed to solve the problem, and both conduction and natural convection of liquid PCM are considered as modes of heat transfer. The effectiveness of the PCM insulation is evaluated by comparing its thermal performance with insulation without phase change. The results indicate that the PCM is effective in reducing the heat loss from the pipe for low Rayleigh numbers condition. High resolution capturing of solid/liquid moving boundary, and the details of flow structure are presented.
What Kind of Propulsion Redundancy Is Needed for Tanker?
Authors: Kozˇuh Mitja , Petelin Stojan
Published: May 2008

In the last decade a lot of emphasis was given to the propulsion redundancy of tankers. Since there are several levels of redundancy, it not always clear to what extent these redundancies can help in difficult situations and at last what is the objective of these redundancies. When we look at the costs optimization can be made minimizing the operating costs or it can be done in such a way that probability of spill and the size of its consequences are minimal. With this approach we are minimizing environmental risk. With environmental risk in mind only the higher level of redundancy is acceptable and lower levels are not enough to first prevent and second to mitigate the consequences of possible spills.