bluuebunny/crossref_metadata_2025 huggingface dataset:
Visualization and Analysis of Flow in an Offset Channel
Authors: Walter J. A. , Chen C.-J.
Published: May 2008

This paper investigates flow characteristics for a benchmark experiment that is important for thermal hydraulic phenomena in nuclear power plant design. The flow visualization experiment is carried out for flow in a rectangular offset channel covering both the laminar and turbulent flow regimes. The Reynolds number, based on the inlet velocity and the height of the inlet channel, ranges from 25 to 4600. The offset channel is an idealized thermal hydraulic geometry. Duct flow expands in a rectangular chamber and exits to a duct that is offset from the entrance duct. The offset geometry creates zones of recirculation for thermal-hydraulic mixing. Flow patterns are visualized by a laser light sheet in the symmetry plane of the primary flow direction and in three cross-sectional planes. A charge-coupled device (CCD) images the flow field, simplifying the experimental process and subsequent image analyses. The flow pattern and size of the recirculation zones change dramatically with Reynolds number until the flow is fully turbulent. While the velocity field itself is predominantly two dimensional, it is shown that the walls of the chamber produce a fully three-dimensional flow that could not be predicted properly by a two-dimensional calculation. Quantitative measurements of particle pathlines from several images are superimposed to give a composite view of the velocity field at one of the Reynolds numbers examined.
Holographic Interferometry Temperature Measurements in Liquids for Pool Fires Supported on Water
Authors: Ito A. , Saito K. , Inamura T.
Published: May 2008

This study provides detailed temperature and physical structure measurements for liquid pool fires supported on water within both the liquid fuel layer and the supporting water sublayer from ignition to the onset of the boiling water sublayer, WSB. Understanding the mechanism of WSB is important to predict the so-called “boilover phenomenon,” which is associated with an intense spattering of water and fuel droplets. The in-depth physical structure and temperature profiles were obtained using a holographic interferometer for n-decane supported on water in rectangular Pyrex containers with large aspect ratios to provide two-dimensional conditions. The experiments demonstrated that: maximum temperature was achieved 0.1–0.15 cm below the fuel surface due to the combined effect of evaporation heat loss at the fuel surface and in-depth radiation absorption. As a result, Rayleigh convection was generated in the fuel near the fuel surface, and the total heat transfer rate to the fuel-water interface increased by approximately 30 percent. Hence, the water at the fuel-water interface was superheated, so that sporadic spattering of water and fuel droplets (boilover) resulted. To check the applicability of those results to a larger pool fire system and to different fuels, a rectangular container (10 cm long × 5 cm wide × 9 cm high) was designed and eight different liquid hydrocarbon fuels were tested; for all fuels the occurrence of Rayleigh convection was confirmed using fine thermocouples and a streak shadowgraph technique.
Unifying the Controlling Mechanisms for the Critical Heat Flux and Quenching: The Ability of Liquid to Contact the Hot Surface
Authors: Unal C. , Daw V. , Nelson R. A.
Published: May 2008

We investigated the hypothesis that the critical heat flux (CHF) occurs when some point on a heated surface reaches a temperature high enough that liquid can no longer maintain contact at that point, resulting in a gradual but continuous increase in the overall surface temperature for most power-controlled systems. This hypothesis unifies the occurrence of the CHF with the quenching of hot surfaces by relating them to the same concept: the ability of a liquid to contact a hot surface, generally defined as some fraction of the liquid’s homogeneous nucleation temperature, depending on the contact angle. The proposed hypothesis about the occurrence of the CHF is investigated through a study of the boiling mechanism of the second transition region of nucleate pool boiling of water on copper. An idealized two-dimensional transient conduction heat transfer model was developed to investigate the heat transfer mechanism. The initial macrolayer thickness on the dry portion of the heater, in the second transition region, was found to be bounded between 0 and 11 μm. The radius of the dry patch varied from 15 to 23 mm (60 and 92 percent of the heater radius, respectively) for initial macrolayer thicknesses of 0 and 11 μm, respectively. The results indicated that the critical liquid-solid contact temperature at the onset of CHF (the surface temperature at the center of the dry patch) must be lower than the homogeneous nucleation temperature of the liquid for the pool boiling of water on a clean horizontal surface. The liquid-solid contact temperature was dependent on the initial dry patch liquid macrolayer thickness, varying from 180°C to 157°C for initial macrolayer thicknesses of 0 and 11 μm, respectively. Independent assessment of these values shows good agreement with extrapolated contact temperature data at the onset of film boiling. This indicates that the mechanism for the occurrence of the CHF could be similar to the mechanism generally accepted for the quenching of the hot surfaces. Further study of this mechanism to understand better the observed trends in other experimental results show qualitative agreement with those results. These include a significant decrease in the radius of the dry patch to 4 mm (16 percent of the heater radius) when the thermal conductivity of the heater was decreased to that corresponding to nickel. When the thickness of a copper heater was decreased from 10 mm (representing an infinitely thick medium) to 0.1 mm, a dry patch radius of 2.25 mm (9 percent of the heater radius) was found to be sufficient for the temperature at the center of the dry patch to reach the critical contact temperature. These comparisons are felt to provide some understanding as to why the second transition region has been observed only in limited cases.
Mass Air Flow Sensor Diagnostics for Adaptive Fueling Control of Internal Combustion Engines
Authors: Buehler Patrick J. , Franchek Matthew A. , Makki Imad
Published: May 2008

Presented in this paper is an information synthesis (IS) approach for the mass air flow (MAF) sensor diagnosis on internal combustion engines. An information synthesis solution is attractive for diagnostics since the algorithm automatically calibrates itself, reduces the number of false detections and compresses a large amount of engine health information into the model coefficients. There are three primary parts to information synthesis diagnostics. First, an IS model is used to predict the MAF sensor output based on the engine operating condition. The inputs to this IS model include the throttle position sensor (TPS) and the engine speed sensor information. The second part concerns an online adaptation process that is used to reduce the errors between the IS model output and the actual MAF sensor output. Finally the adapted model coefficients are used to diagnose the sensor as well as identify the source for changes in the sensor characteristics. This proposed solution is experimentally tested and validated on a Ford 4.6 L V-8 fuel injected engine. The specific MAF sensor faults to be identified include sensor bias and a leak in the intake manifold.
System Identification and Multivariate Controller Design for a Satellite Ultraquiet Isolation Technology Experiment (SUITE)
Authors: Joshi Alok A. , Kim Won-jong
Published: May 2008

A mathematical model of a six-degree-of-freedom hexapod system for vibration isolation was derived in the discrete-time domain on the basis of the experimental data obtained from a satellite. Using Box-Jenkins model structure, the transfer functions between six piezoelectric actuator input voltages and six geophone sensor output voltages are identified empirically. The 6×6 transfer function matrix is symmetric, and its off-diagonal terms indicate the coupling among different input/output channels. Though the coupling was observed among various input/output channels up to 10 Hz, the single-input single-output (SISO) controllers were designed neglecting the effect of coupling. The SISO controllers demonstrated limited performance in vibration attenuation. Using multi-input multi-output (MIMO) control techniques such as Linear Quadratic Gaussian (LQG) and H∞, high-order controllers were developed. The simulation results using these controllers obtain 33 dB, and 12 dB attenuation at 5, and 25 Hz corner frequencies, respectively.
Time-Frequency Based Sensor Fusion in the Assessment and Monitoring of Machine Performance Degradation
Authors: Djurdjanovic Dragan , Ni Jun , Lee Jay
Published: May 2008

Machines degrade as a result of aging and wear, which decreases their performance reliability and increases the potential for faults and failures. In contemporary manufacturing it becomes increasingly important to predict and prevent machine failures, rather than allowing the machine to fail and then fixing the failure. In this paper, methods of time-frequency signal analysis will be used to capture information from multiple machine sensors. This information could be used to assess machine performance degradation and subsequently take appropriate action. Signals emanating from three different sensors were collected when a sharp and a worn tool have been mounted on a CNC lathe machine. Several combinations of sensors and signal features have been tried in order to demonstrate the ability to use the information from multiple sensors and increase sensitivity to tool wear.
Temperature Control of an Ill-Conditioned Thermal Process Using Regularization
Authors: Gwak Kwan-Woong , Masada Glenn Y.
Published: May 2008

New regularization embedded nonlinear control designs are proposed for the temperature control of an ill-conditioned thermal process. A classic nonlinear controller applied to such a process is shown to provide good temperature tracking but generates physically unreasonable actuator solutions. Tikhonov and truncated singular value decomposition (TSVD) methods, embedded in the design of feedback linearizing controllers (FBL) and sliding mode controllers (SMC), also provide good temperature tracking and generate physically reasonable and actuator-constraint-satisfying solutions for the ill-conditioned system, in spite of the modeling errors inherent in applying regularization. These nonlinear controllers are also robust to changes in process parameters of the ill-conditioned process.
A Thermal-Based Spindle Bearing Load Controller: Preliminary Experimental Evaluation
Authors: Harder John E. , Stein Jeffrey L.
Published: May 2008

Thermally induced bearing loads are a serious problem for high-speed machining spindles used in metal cutting. Ideally, the bearing loads can be set to provide the necessary spindle stiffness to achieve the desired dynamic performance, while at the same time achieving long bearing life. Unfortunately, this is difficult to do because many process conditions affect these loads, sometimes in difficult to predict ways with significant degradation of spindle performance and life. The purpose of this paper is to describe a preliminary experimental evaluation of controlling bearing loads by controlling the heat generated by a thermal actuator placed around the spindle housing. A box spindle modified with an electric heating tape placed around its front ball bearings is used for this evaluation. The results show that significant control over the bearing load can be achieved for the conditions tested. However, it is discovered that asymmetrical placement of the heater with respect to the pair of back-to-back angular-contact bearings makes it difficult to regulate the loads on each bearing to the set point. Solutions to this problem are discussed and further research outlined. Nevertheless, the feasibility of the control of thermally induced bearing spindle loads with an externally mounted heater appears promising.
Limitations of an Indentation Model for Grinding Gamma Titanium Aluminide
Authors: Razavi H. Ali , Danyluk Steven , Kurfess Thomas R.
Published: May 2008

This paper explores the limitations of a previously reported indentation model that correlated the depth of plastic deformation and the normal component of the grinding force. The indentation model for grinding is studied using force control grinding of gamma titanium aluminide (TiAl-γ). Reciprocating surface grinding is carried out for a range of normal force 15–90 N, a cutting depth of 20–40 μm and removal rate of 1–9 mm3/sec using diamond, cubic boron nitride (CBN) and aluminum oxide (Al2O3) abrasives. The experimental data show that the indentation model for grinding is a valid approximation when the normal component of grinding force exceeds some value that is abrasive dependent.
The Management of Technology: An Opportunity for Research Universities
Authors: Phillips Winfred M.
Published: May 2008

Technology transfer and industry creation are increasingly identified with university research. Increasing this activity may stimulate initiatives to enhance progress in economic opportunity. A high standard of living is dependent upon a leading position in high technology, engineering and technology-relaled research and development, resulting in high tech jobs. Universities will carry a part of these new responsibilities. Emphasis on higher education will be a focus of opportunity over the next decade. Curricula content will include social, international, economic and environmental issues. The education community will review the pros and cons of the opportunity technology affords. However, in parallel, university research will become increasingly the source of, and universities the partners of continued technological development. It is timely to explain this opportunity and explore the challenges of this new partnership.
Bioengineering: A History With a Future
Authors: Phillips Winfred M.
Published: May 2008

Bioengineering is a technological miracle of health care and future health hope. From the entrepreneurial contributions of William Kolff with the original handmade dialysis machine to the application of the x-ray to medical diagnostics and treatment, biomedical pioneers brought technology to medical care, often at great personal risk. Few can conceive the magnitude of the impact of technology on our ability to return the sick and disabled to function. The “simple” steel and plastic hip implant is a technological wonder. The human is the most demanding of systems to be repaired by technology. The stress levels, cycle loading, chemical degradation and even biological rejection are without precedent in engineering application. Reliability is expected to be near 100%. Psychological and cosmetic compatibility are severe constraints. The current quality of life of many (if not most) of us is dependent upon technology, and forefront technology at that. The dentist no longer hurts and our teeth last longer. Numerous “replacements” are cosmetically acceptable. Medical diagnosties are everywhere, but have a long way to go. Emergency medicine is high-tech. The wonders of bioengineering are in our present and in our future. It is informative to review our bioengineering heritage from early orthopedics (splints, peg legs and crutches), through mobility facilitation (wheelchairs) and internal repair (aortic patches and arterial replacement) to modern diagnostics (MRI) and organ replacement (artificial hearts, kidneys, etc.). A recent renewed interest in biomedical devices paralleling the decoding of the genome and the proposed genetic future portends what Dr. Francis Fukuyama of Johns Hopkins called “Our Post Human Future.” We will explore our historical pathway to what we will call “our better human future through bioengineering.”
Finite Element Analysis of Radio-Frequency Ablation in a Reconstructed Realistic Hepatic Geometry
Authors: Pandey Ajit K. , Chang Isaac , Myers Matthew R. , Banerjee Rupak K.
Published: May 2008

Radio-frequency (RF) ablation is a minimally invasive procedure that has the potential for widespread use in hepatic cancer therapy. In the procedure, RF current is applied to the tissue, resulting in the conversion of electrical to heat energy and thus, a rise in temperature, with the goal of eventual tumor necrosis. Potential complications from the procedure include insufficient heating of large tumors, resulting in tumor recursion, as well as excessive thermal damage to healthy tissue. Mathematical models are valuable in predicting the temperature rise within the organ during RF ablation, thereby enhancing the success rate of the procedure. Eventually, models can be used to guide ablation procedures, by predicting the optimal set of operational parameters e.g., catheter probe geometry and placement, given patient-specific information. The present study focuses on the analysis of temperature rise within a reconstructed model of a realistic three-dimensional (3D) section of a porcine liver during RF ablation. This study calculates the effect of blood flow through arteries as well as perfusion through the liver on the time-dependent temperature distribution near the RF ablation probe (Figure 1). For a time duration of 30 min of an ablation procedure, a temperature of about 80°C could be achieved over a diameter of about 4 cm with the present RF probe. As an initial step, the present study includes isotropic hepatic tissue and blood properties.
Potential for Thermal Injury During Surgical Osteotomies
Authors: Allen James W. , Hitt Darren L. , Sarnow Marc R.
Published: May 2008

Medical literature indicates that permanent tissue damage can occur when exposed to temperature elevations of as little as 5°C for times as short as a few seconds. Clinically, it has also been observed that during surgical osteotomies (bone cutting procedures) significant amounts of heat are typically generated. We present experimental data that suggests critical conditions for thermal injury are regularly exceeded during simulated surgical procedures using cadeveric metatarsal bones.
Investigation of the Thermal and Injury Behavior During Microwave Thermal Therapy of Porcine Kidney
Authors: He Xiaoming , Mcgee Shawn , Coad James E. , Iaizzo Paul A. , Swanlund David J. , Kluge Stan , Rudie Eric , Bischof John C.
Published: May 2008

In this paper, we report on the characterization of microwave therapy of normal porcine kidneys both in vitro and in vivo. This technology is being developed for eventual use in the treatment of small renal cell carcinoma (RCC) by minimally invasive procedures. During experiments, microwave energy was applied through an interstitial microwave probe (Urologix, Plymouth, MN) to the kidney cortex with occasional involvement of the kidney medulla. The thermal histories at several locations were recorded. After treatment, the kidneys were bisected and small tissue slices were cut out at approximately the same depth as the thermal probes. The tissue slices were further processed for histological study. Both cellular injury and the area of microvascular stasis were quantitatively evaluated by histology. Absolute rate kinetic models of cellular injury and vascular stasis were developed and fit to this data. A 3-D finite element thermal model based on the Pennes Bioheat equation was developed and solved using a commercial software package (ANSYS, V5.7). The Specific Absorption Rate (SAR) of the microwave probe was measured experimentally in tissue equivalent gel-like solution. The thermal model was first validated by the measured in vitro thermal histories. It was then used to determine the blood perfusion term in vivo.
Heat Transfer Study of Direct Contact Condensation in the Presence of Noncondensable Gas
Authors: Xu Yiban , Revankar Shripad T. , Ishii Mamoru
Published: May 2008

Direct Contact Condensation tests have been conducted by injecting a mixture of steam and nitrogen into a subcooled water pool in a stainless steel tank through a vertical nozzle. The condensation rate, related to the heat transfer rate in the liquid side, was obtained by the difference of the gas inlet flow rates and the mass accumulation due to the bubble growth. By the measurements of steam and nitrogen flow rates and visualization of the bubble size variation, the heat transfer parameters in the liquid domain during the bubble formation, are obtained. The Nusselt number has been correlated with the dimensionless combination of fluid flow, system state and thermal properties of fluids. A least square approach has been applied to determine the exponent coefficients of dimensionless numbers in the correlations. It was found that the Nusselt number can be correlated by a function of the Jakob number, gas Peclet number, noncondensable concentration, liquid and gas density ratio and Eotvos number based on the current database.
Direct Contact Condensation in Falkner-Skan Flows
Authors: Davis J. , Yadigaroglu G.
Published: May 2008

In this paper we present a method for solving direct contact condensation problems involving Falkner-Skan flows. Using this method we then perform a parametric study for the problem of coupled two-fluid (saturated vapor on subcooled liquid) stagnation flows with direct contact condensation. Selected results and the resulting correlations are discussed.
Numerical Investigations on the Explosion Effects of Fuel Air Mixtures
Authors: Zhou Tian , Guo Yonghui , Zhang Haibo
Published: May 2008

To investigate the explosion parameters of Fuel Air Mixtures, the two-phase gas-droplet conservation equations are used. The model includes the following aspects: the deformation and fragmentation of the fuel droplet, the formation of fuel gas through evaporation and stripping of the boundary layer of the fuel droplet, the chemical delay and chemical reaction velocity between fuel gas and oxygen in the air. The high-resolution implicit TVD schemes are applied to gas phase equations and MacCormack schemes to liquid phase equations. The formation and propagation process of gas-droplet detonation wave inside the fuel air cloud and the attenuation process of the shock wave outside the cloud are simulated numerically. The simulation results keep good agreement with others’ study. The explosion effects of the height of the second ignition inside the cloud and the ratio of the cloud height to the cloud diameter are investigated numerically, too.
Design of Controller and Data Acquisition System for a Gear Dynamometer
Authors: Moellenberndt Anne Marie , Rowlands Tasia , Masha Toha , Kim Dean H. , Morris Martin J.
Published: May 2008

This paper describes the development of a controller and data acquisition system for a gear dynamometer that will monitor and control the motor speed and dynamometer torque. This project work is motivated by the lack of adequate design information describing the low-cycle, mechanical performance of plastic gears, despite the increasing usage of plastic gears. This is in contrast to the abundant amount of information available for metal gears. The control system for the test apparatus has numerous additional features which facilitate the gathering of information about the performance of plastic gears. This work has been performed by an undergraduate team for the two-semester capstone design course for the Mechanical Engineering Department at Bradley University. This project incorporates many aspects of a mechanical engineer’s education such as system design, sensor selection, and software mastery. This project also connects the specialty areas of material science, instrumentation, measurement, data acquisition, and design of experiments.
Nonlinear Adaptive Robust Observer for Velocity Estimation of Hydraulic Cylinders Using Pressure Measurement Only
Authors: Garimella Phanindra , Yao Bin
Published: May 2008

This paper considers the design of an observer to estimate the velocity of an electro-hydraulic system using pressure measurements only. The difficulties involved in the design of an observer for such a system include the highly nonlinear system dynamics, severe parametric uncertainties like large variation of inertial load and unmatched model uncertainties. In order to tackle these problems a nonlinear model based Adaptive Robust Observer (ARO) is designed which provides not only a robust estimate of the velocity of the system but also the robust identification of the system parameters. Online monitoring of certain persistence of excitation conditions allow us to improve the quality of the parameter and velocity estimates. Simulation and experimental results on the swing motion control of a three-degree-of freedom hydraulic robot arm demonstrate the effectiveness of the proposed observer.
Design and Implementation of a Hybrid Control Strategy for an Active Vibration Isolation System
Authors: Zhang Yisheng , Alleyne Andrew G. , Zheng Danian
Published: May 2008

Controller design methodologies based on a single controller are often unable to provide both high performance (i.e., tracking bandwidth) and desired robustness (i.e. retaining stability) in the presence of uncertainty or plant variation. This paper presents a hybrid control strategy to circumvent the basic trade-off between performance and robustness from an individual controller. This hybrid control strategy utilizes a robust controller for guaranteed robustness when the plant model is not well known, and makes an adaptive controller active for high performance after sufficient plant information has been collected on-line. To avoid a degraded transient after controller switching, a bumpless transfer scheme is designed and incorporated into this hybrid control strategy. This bumpless transfer design is a novel extension from a conventional latent tracking bumpless transfer design for a SISO plant with 1 DOF controllers to either a SISO plant with multiple DOF controllers or a MIMO plant. Experimental results implemented on an active vibration isolation testbed demonstrate the effectiveness of the hybrid control strategy including the bumpless transfer design.
Compact Carbon-Carbon Composite Heat Exchanger
Authors: Alam M. Khairul , Watts Roland J. , Price John
Published: May 2008

Composite heat exchangers can provide significant reduction in the weight of a compact heat exchanger in comparison to metal heat transfer units. A Carbon-Carbon (C-C) composite heat exchanger core has been fabricated to study the heat transfer and friction characteristics of single layer plate-fin geometry. The plate and fins are both C-C composites, in which the carbon matrix is reinforced by high conductivity graphitic carbon fibers to improve the fin effectiveness of the heat exchanger. A heat flux is applied to the top and bottom of the heat exchanger core to heat an air stream passing through the channels. The heat transfer coefficient and the friction coefficient are determined and the experimental results are compared with data for a standard plate fin heat exchanger of similar geometry. It was determined that the C-C heat exchanger had lower Colburn heat transfer factor than a similar metal plate-fin heat exchanger; but had high surface temperature effectiveness. The friction factor of the C-C heat exchanger was slightly lower than the metal plate-fin heat exchanger.
CFD Analysis of Liquid-Cooled Exhaust Manifolds in a Real Time Engine Cycle
Authors: Kresovic Uros , Hussein Wallid , Zhou Chenn Q. , Majdak Jim , Cantwell Robert
Published: May 2008

Liquid-cooled exhaust manifolds are used in turbocharged diesel and gas engines in the marine and various industrial applications in order to minimize heat rejection to surrounding areas, maximize energy to the turbocharger, and maintain a maximum allowable skin temperature. A commercial CFD software FLUENT® was used to analyze liquid-cooled exhaust manifolds in a real time engine cycle. Detailed information of flow property distributions and heat transfer were obtained in order to provide a fundamental understanding of the manifold operation. Experimental data was compared with the CFD results to validate the numerical simulation. Computations were performed to investigate the parametric effects of operating conditions on the performance of the manifold. Two different geometries were compared. One of them was found to have better performance, resulting in an approximately 2 to 3% fuel consumption improvement.
Control Design of an Automotive Urea SCR Catalyst
Authors: Upadhyay Devesh , Van Nieuwstadt Michiel
Published: May 2008

The leading aftertreatment technologies for NOx removal from the exhaust gas of lean burn engines, Diesels in particular, are urea based Selective Catalytic Reduction (SCR), Lean NOx Traps (LNT) and Active Lean NOx Catalysts (ALNC). It is generally believed that the SCR technique has the potential of providing the best NOx conversion efficiency relative to the other techniques. Nonetheless, it is crucial that the high conversion efficiencies be achieved with a minimum slippage of unreacted ammonia as tail pipe emissions. This necessitates a precise control over the urea injection process. The complex behavior of the catalyst substrate with respect to adsorption and desorption of ammonia in conjunction with a lack of “stored ammonia” sensing capabilities makes the control problem challenging. In this paper we present a model-based control design approach using a lumped parameter model of an SCR system that includes the essential dynamics of the plant. The model includes the adsorption, desorption and surface coverage dynamics, along with the NOx reduction and ammonia oxidation dynamics based on the relevant chemical reaction rates.
Modeling of a Urea SCR Catalyst With Automotive Applications
Authors: Upadhyay Devesh , Van Nieuwstadt Michiel
Published: May 2008

A zero order lumped parameter control oriented model of a Selective Catalytic Reduction (SCR) catalyst is presented. The lumped parameter model is developed using two approaches. in the first approach it was assumed that the catalyst behaves as an Isothermal Continuously Stirred Tank Reactor (ICSTR). The second approach involved deriving the lumped parameter model from a 1D model using the method of weighted residuals. Both approaches led to a three state model, with the gas phase concentrations of NOx and NH3 and the surface coverage fraction as the states. The model depends on chemical properties specific to the SCR catalyst; consequently model validation requires knowledge of these parameters, either via laboratory-based experiments or as supplied by the catalyst supplier. We present an alternate approach that allows estimation of the essential parameters through a minimization of the l2 errors between measured and simulated results.
Rheological Study of Micro Particle Laden Polymeric Thermal Interface Materials: Part 1 — Experimental
Authors: Prasher Ravi S. , Shipley Jim , Prstic Suzana , Koning Paul , Wang Jin-Lin
Published: May 2008

Particle laden polymers are one of the most prominent thermal interface materials (TIM) used in electronics cooling. Most of the research groups have primarily dealt with the understanding of the thermal conductivity of these types of TIMs. Thermal resistance is not only dependent on the thermal conductivity but also on the bond line thickness (BLT) of these TIMs. It is not clear that which material property(s) of these particle laden TIMs affects the BLT. This paper discusses the experimental measurement of rheological parameters such as non-Newtonian strain rate dependent viscosity and yield stress for 3 different particle volume fraction and 3 different base polymer viscosity materials. These rheological and BLT measurements vs. pressure will be used to model the BLT of particle-laden systems for factors such as volume fraction.
Nano-to-Macroscale Transport Modeling Through Approximations
Authors: Chen Gang , Yang Ronggui
Published: May 2008

Heat transfer and energy conversion in electronic and thermoelectric devices often involve multiple length scales ranging from nanometer to millimeters. For example, heat is typically generated in a nanometer-scale region at the drain of a MOSFET and is subsequently conducted through the millimeter thick substrate to the surroundings. As another example, cooling in a thermoelectric device occurs at one interface while the heat is rejected at the other end millimeter away. Modeling the energy transport and conversion processes in such multiple length scale devices is very challenging. Boltzmann equation-based approaches for phonons and electrons transport, although appropriate, are time consuming and not practical in near term. In this paper, we will summarize two approximations we have recently introduced to model transport processes, particularly for phonons, from nano to macroscales. One is the diffusion-transmission interface condition that attributes size effects to the interfacial region only. The other are the ballistic-diffusive equations that group the energy carriers into a ballistic and a diffusive component and that are much easier to solve than the Boltzmann equation. Examples on phonon heat conduction will be given to demonstrate the effectiveness of these two approaches. The approximations can also be extended to electron transport.
Monte Carlo Modeling of Heat Generation in Electronic Nanostructures
Authors: Pop Eric , Sinha Sanjiv , Goodson Kenneth E.
Published: May 2008

This work develops a Monte Carlo (MC) simulation method for calculating the heat generation rate in electronic nanostructures. Electrons accelerated by the electric field scatter strongly with optical phonons, yet heat transport in silicon occurs via the faster acoustic modes. The MC method incorporates the appropriate energy transfer rates from electrons to each phonon branch. This accounts for the non-equilibrium energy exchange between the electrons and phonon branches. Using the MC method with an electron energy-dependent scattering rate intrinsically accounts for the non-locality of the heat transfer near a strongly peaked electric field. This approach provides more information about electronically generated heat at nanoscale dimensions compared to traditional macroscopic field-dependent methods. The method has applications in any region of high spatial or temporal non-equilibrium between electrons and phonons, and particularly facilitates careful microscopic analysis of heating in a nanoscale transistor.
Workpiece Deflection Compensation Using Two Dimensional Toolpost
Authors: Yan W. Y. , Al-Jumaily A. M.
Published: May 2008

Considering the workpiece elastic deflection in a turning process, a simulation model that accounts for the radial and tangential vibrations and their abatement using active control is developed. The model is simulated using Simulink in a Matlab environment to assess the possibility of using an active actuator to reduce vibrations in two directions. The results demonstrate the significance of the workpiece elastic deformation and its compensation using active actuators. Actuators that can compensate for the piece deflection and the vibrations due to the surface roughness are speculated on.
On the Causes of Rolling Instability and Chatter
Authors: Lin Yun-Jeng , Suh C. Steve , Noah Sherif T.
Published: May 2008

Dynamic rolling instability known as fifth-octave chatter is studied using a nonlinear model developed to describe the responses of work rolls subjected to the exertion of sheet forces of various spectral characteristics. The model enables the dynamic instability of sheet rolling to be correlated with work roll stiffiness, rolling speed, inter-stand tension, roll-bite entry and exit thickness, and the sheet force resulted from the interactive action of the work roll with the plastic deformation of the rolled strip. It is found that roll-bit elastic-plastic deformation sheet force is nonlinearly coupled with the rollstack stiffness and also plays a dominant role in affecting rolling instability. In addition, whenever the frequency spectrum of the normal sheet forces containing spectral components that match the fundamental modes of the roll stand, resonance-like beating would occur. This highly linear physical phenomenon, which is accompanied by large vibration amplitudes in the active work rolls, is recognized as chatter. Although many different dynamic modes of instability including mode excitation and beating are induced in response to sheet forces of nonlinear and non-stationary in nature, however, the rolling system never responds chaotically.
Investigation of a Friction-Induced Source of Excitation in Disc Brake Systems
Authors: Pilipchuk V. N. , Tan C. A.
Published: May 2008

Friction-induced vibration of a two-degrees-of-freedom mass-spring system interacting with a decelerating rigid strip is considered. The friction law is approximated by an analytic function to facilitate the numerical integration, whereas the truncated Taylor expansion of this function gives good qualitative results. It was shown that after a quasi-harmonic transient period, accompanied by viscous energy dissipation, a relatively short period of intensive stick-slip vibration occurs, with its out-of-phase component generating a series of micro-impacts on the strip. It was further shown that, because of the impulsive character of such kind of loading, its Fourier spectrum is sufficiently rich. Based on the simplified ‘normal form’ equations, it was shown that the out-of-phase vibration mode of the block system absorbs more energy from the decelerating strip if the corresponding natural frequencies satisfy the resonance condition. The out-of-phase stick-slip vibration of the blocks creates an impulsive bending moment applied to the strip, and therefore can be considered as a possible source of flexural vibration. In particular, the results are applied to explanation of squeal generation in automotive disc brakes, although the technique can be extended on other ‘squealing systems’ including geophysical fault (earthquake) models.
A New Regularization of Coulomb Friction
Authors: Quinn D. Dane
Published: May 2008

We present a new regularization for Coulomb’s law of friction for single point contacts. This modification permits a straightforward application of friction within existing numerical simulations. Similar to existing regularizations, the proposed modification to Coulomb frictions leads to continuous representation of friction and does not require the separate identification of transitions between slip and stick. However, unlike more common regularizations, the current reformulation maintains an equilibrium structure identical to the classical, discontinuous form of Coulomb friction. The implementation and performance of this regularization is illustrated by a simple one degree-of-freedom system in which stick-slip motion induced by sliding friction is of primary importance. The simulations illustrate the existence of non-trivial equilibrium states and the ability of the current regularization toprovide a computationally efficient scheme for simulating the dissipation arising from sliding friction.
Feedback Linearization of the Lorenz System: Stabilization and Tracking Control
Authors: Crespo L. G. , Sun J. Q.
Published: May 2008

This paper presents a control study of the Lorenz system by using feedback linearization. The effects of the state transformation on the dynamics of the Lorenz system are studied first. Then, composite controllers are developed for both stabilization and tracking of the system. The controls are designed to overcome the barrier in controllability imposed by the state transformation. The transition through the manifold defined by such a singularity is achieved by inducing the chaotic response within a boundary layer that contains the singularity. Outside this region, a conventional feedback nonlinear control is applied. In this fashion, the authority of the control is enlarged to the whole state space and the need for high control efforts is substantially mitigated. Tracking problems that involve single and cooperative objectives are studied by using the differential flatness property of the system. A good understanding of the system dynamics proves to be invaluable in the design of better controls. In all numerical examples, the proposed approach led to excellent control performances.
Convective Heat Transfer in a Triple-Cavity Structure Near Turbine Blade Trailing Edge
Authors: Chyu Minking K. , Uysal Unal , Lee Pei-Wen
Published: May 2008

The present study explores the internal heat transfer in a triple-cavity cooling structure with a ribbed lip for a turbine blade trailing edge. The design consists of two impingement cavities, two sets of crossover holes, a third cavity and an exit slot with eleven ribs attached to it. Local heat transfer in each subregion is determined. Results indicate that the highest heat transfer occurs in the second impingement cavity. The exit slot area between the ribs is identified as a region of low heat transfer in the overall design. A comparison with enhancement induced by arrays of pin fins and fins of other geometries reveals that the triple-cavity design represents a lesser quality cooling scheme in the range of Reynolds numbers tested. Further improvement of the convective heat transfer at the exit slot with either film cooling, or different rib geometries appears to be essential to make the triple-cavity strategy superior to those of the traditional approaches for cooling of blade trailing edge.
Control of Flexible Payloads Grasped by Actuated Grippers Undergoing Large Rigid-Body Motions: Part II — Controllability and Observability
Authors: Park Edward J. , Mills James K.
Published: May 2008

Part I of this work models the dynamics of a flexible payload grasped by an actuated gripper undergoing large rigid body motion by a robotic manipulator. In Part II, the controllability and observability conditions of the system are discussed. In Part I, the dynamic model of the actuated flexible payload is derived using the component mode synthesis (CMS) method with addition of actuator constraint, fixed-interface vibration and quasi-static modes. Here, the two-time scale modeling (TSM) technique is employed taking advantage of the two-time scale behavior between the quasi-static modes and vibration modes in the dynamic model. Due to the complexity of the resulting system, the controllability and observability conditions are not trivial. Hence, the controllability and observability study addressed herein becomes essential in showing the advantages of using the CMS and TSM techniques in control system design for the problem. A simulation example demonstrates that simultaneous vibration and quasi-static deformation control is achievable by proper selection of each type of modes.
The Construction of Nonlinear Normal Modes for Systems With Internal Resonance: Application to Rotating Beams
Authors: Jiang Dongying , Pierre Christophe , Shaw Steven W.
Published: May 2008

A numerical method for constructing nonlinear normal modes for systems with internal resonances is presented based on the invariant manifold approach. In order to parameterize the nonlinear normal modes, multiple pairs of system state variables involved in the internal resonance are kept as ‘seeds’ for the construction of the multi-mode invariant manifold. All the remaining degrees of freedom are constrained to these ‘seed’ variables, resulting in a system of nonlinear partial differential equations governing the constraint relationships, which must be solved numerically. The solution procedure uses a combination of finite difference schemes and Galerkin-based expansion approaches. It is illustrated using two examples, both of which focus on the construction of two-mode models. The first example is based on the analysis of a simple three-degree-of-freedom example system, and is used to demonstrate the approach. An invariant manifold that captures two nonlinear normal modes is constructed, resulting in a reduced-order model that accurately captures the system dynamics. The methodology is then applied to a more large system, namely an 18-degree-of-freedom rotating beam model that features a three-to-one internal resonance between the first two flapping modes. The accuracy of the nonlinear two-mode reduced-order model is verified by time-domain simulations.
Resonant Bands of a Mathieu-Duffing Oscillator With a Twin-Well Potential
Authors: Luo Albert C. J.
Published: May 2008

The (M:1)-resonant bands in the left and right potential wells are skew-symmetric, and the (2M:1)-resonant bands of the large orbit motion are symmetric. The analytical conditions for the onset and destruction of a resonant band are developed through the incremental energy approach. The numerical predictions of such the onset and destruction are also completed by the energy increment spectrum method. The sub-resonance interaction occurs for strong excitations, which needs to be further investigated. These results are applicable to the small orbit and large orbit motions of post-buckled structure under a parametric excitation.
Nonlinear Free Vibration of a Cable Against a Straight Obstacle
Authors: Han Seon , Grosenbaugh Mark
Published: May 2008

The purpose of this study is to investigate the nonlinear effect of gravity on the free vibration of a cable against a straight obstacle. The cable model is expressed in terms of nonlinearly coupled transverse and axial displacements. The penalty method is used to simulate the obstacle, which is equivalent to inserting a stiff elastic foundation. The first symmetric frequencies are obtained when the depth of the obstacle is 1/2 and 1/3 of the initial transverse displacement. The effects of varying amplitude and equilibrium curvature are investigated.
On the Rigid-Body Motion of Traveling, Sagged, Elastic Cables
Authors: Luo Albert C. J. , Wang Yuefang
Published: May 2008

This paper presents a methodology for modeling very flexible structures. A theory for the dynamics of traveling, arbitrarily sagged, elastic cables is developed for demonstration of this methodology. In this theory, the cable motion is modeled through the rigid-body motion and elastic deformation, and the rigid-body motion of cable configuration is modeled as an inextensible cable model. The dynamic, rigid-body configuration of a cable is a referenced base to describe its elastic deformation motion for any instantaneous moment. In this paper, the analytical solution for the rigid-body motion of the cable under a certain loading is developed as Part I of this investigation. From the dynamical configuration of the rigid-body motion of cable, an elastic motion of nonlinear cables is further investigated in sequel as the part II. This theory can be applied any cable structures and the methodology is useful for the perfectly flexible structures such as membranes.
Obtaining Temperature-Dependent Thermal Properties of Investment Casting Mold
Authors: Pohanka Michal , Woodbury Keith A. , Woolley Jonathan
Published: May 2008

An experiment is conducted to determine the temperature dependent thermal properties (k, ρcp) of a fused silica shell commonly used as a mold material for investment castings. The mold is constructed by building up alternating layers of binder and silica. Different binder and silica are used for the inner layer, resulting in a thin region with different thermal properties than the rest of the shell. A search algorithm based on the simplex method is used to determine the thermal properties of both kinds of layers by finding the minimum of the error between measured and computed temperatures. Two approaches are used to find the thermal conductivity: steady state and dynamic.
Convection at the Entrance of Micropipes With Sudden Wall Temperature Change
Authors: Tunc Gokturk , Bayazitoglu Yildiz
Published: May 2008

Transient heat convection in a circular microchannel for hydrodynamically fully developed and thermally developing flow conditions is analytically solved by the integral transform and the Laplace transform techniques. A prescribed wall temperature boundary condition is assumed. The effects of velocity slip, temperature jump, and viscous heating are investigated. The results confirm that the viscous heating effects increase the Nusselt number for the specified conditions.