bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive Model Predictive Control for Vehicle Braking Assist System Design
Authors: Vahidi Ardalan , Stefanopoulou Anna , Peng Huei
Published: April 2008

In this paper, an adaptive model predictive control scheme is designed for speed control of heavy vehicles. The controller coordinates use of compression brakes and friction brakes on downhill slopes. Moreover the model predictive controller takes the actuator constraints into account. It is shown that accurate estimate of mass is necessary for safe and comfortable operation in closed-loop. Also knowledge of the road grade improves the results further by contributing in feedforward control. Therefore a recursive least square scheme with forgetting is used in parallel with the controller to update the estimates of mass and road grade. The mass and grade estimates converged to their actual values when rich excitations were provided. As a result the adaptation improved the closed-loop performance.
Developing Procedure for Nuclear Regulatory Vulnerability Assessment of Nuclear Power Plants
Authors: Kostadinov Venceslav , Petelin Stojan , Stritar Andrej
Published: April 2008

First attempts of developing the procedure and adopting the methodology for nuclear regulatory vulnerability assessment of nuclear power plants are presented. The development of the philosophy and computer tools could be new and important insight for management of nuclear operators and nuclear regulatory bodies who face difficult questions about how to assess the vulnerability of nuclear power plants and other nuclear facilities on external and internal threats. In the situation where different and hidden threat sources throughout the world are dispersed, the assessments of security and safe operation of nuclear power plants are very important. Most risk assessments of nuclear power plants emphasize probability more than consequences. In addition, the probabilities omit terrorists. As of 09/11/2001, the emphasis has changed and this paper tries to show how to do this. Probabilities are enhanced by showing they are dynamic, interactive, and include countermeasures. Consequences are also enhanced by their dynamic nature dividing them on short, intermediate and long term effects. Risk is enhanced by creatively distinguishing between perceived and estimated.
Using Electric Speckle Pattern Interferometry (ESPI) for the Measurement of Concentration Profiles Within a Binary Mixture
Authors: McGuire David C. , Dalton Tara M. , Davies Mark R.
Published: April 2008

This paper describes the development of a Electronic Speckle Pattern Interferometer (ESPI) for measurement of full field two-dimensional concentration gradients as one fluid diffuses into another. The construction and performance of the system is discussed with specific emphasis on developing the interferometer for investigating the mass transfer from a surface into a moving fluid. The system uses a Mach-Zehnder interferometer with a commercially available CCD camera for image acquisition. A phase-shifting algorithm is employed to give full field measurements. Theory pertaining to the optical process involved in these methods is presented with emphasis on optimising the optics by comparison to experimental data. The calculation of the Gladstone-Dale constant for each constituent within a binary mixture is necessary for qualitative measurements and is discussed.
Low-Frequency Phenomena in a Frictionally Excited Beam
Authors: Quinby J. L. , Feeny B. F.
Published: April 2008

A cantilevered beam was excited by a periodically reciprocating friction contact surface. Frequency sweeps revealed frequency regions of dynamic responses in the flexural direction of the beam. Chaotic and quasiperiodic responses were observed when the input frequency was fixed. The quasiperiodic responses sometimes were accompanied by beam oscillations normal to the friction surface. Extremely low frequencies were observed (up to over 100 times lower than the driver). Two-frequency quasiperiodicity was observed, and underlying circle maps were extracted. Winding numbers were matched to frequencies quantified in FFTs. Impending torus folding and intermittency were revealed. Three-frequency quasiperiodicity was also evident. A torus doubling bifurcation was documented.
Economical Solution of Optimal Control Problems in Biomechanics: Preliminary Performance
Authors: Erdemir Ahmet
Published: April 2008

Optimal control of the skeletal system can identify the underlying mechanisms of normal locomotion, and also has the potential for a-priori evaluation of surgical and rehabilitative procedures to correct movement disorders. Nevertheless, clinical applications are limited, particularly due to time-consuming simulations and the requirements of high-level engineering expertise. This study offers a novel strategy that reduces the computational requirements considerably. A preliminary investigation to assess performance is also illustrated using an elbow joint model.
H-Infinity Based Identification of Stiffness in the Presence of Uncertainty
Authors: Kiriakidis Kiriakos , O’Brien Richard T.
Published: April 2008

The authors propose the identification of stiffness using the H∞ performance criterion and a nominal state-space model of the flexible system. The parameter estimator takes the form of an Extended H∞ Filter, which is robust to uncertainties such as modeling error.
Ultra-Short Pulsed Laser Transport in a Multilayered Turbid Media
Authors: Katika Kamal M. , Pilon Laurent
Published: April 2008

This paper presents the modified method of characteristics for simulating the transient transport of light in an absorbing and scattering medium exposed to collimated light. This method is based on the method of characteristics that follows photons along their pathlines. After showing the validity of the method it is used to solve for the transient transport of light in human skin. Skin has been modelled as a seven layer medium with different scattering and absorbing coefficients and scattering asymmetry factors. The angular distribution of reflected light from skin is presented. This technique could be used as a tool for designing various biomedical applications.
Implementing the Learning Factory Model in a Laboratory Setting
Authors: Ssemakula Mukasa E. , Liao Gene Y.
Published: April 2008

The Learning Factory concept was first developed as part of the TRP/NSF funded Manufacturing Engineering Education Partnership (MEEP). The objective of the Learning Factory (LF) is to integrate a practice-based engineering curriculum that balances analytical and theoretical knowledge with physical facilities for product realization in an industrial-like setting. The LF model emphasizes practical experience and consequently, Engineering Technology (ET) and other programs that emphasize hands-on experiences for students are well suited to implementing the LF model. This paper describes a project whose goal is to adapt the LF model for implementation in regular academic programs oriented to practical applications without having to build an actual factory. This work is being accomplished by modifying five carefully selected courses in our programs, leading to the use of coordinated projects across those courses. The projects focus on the making of functional model engines. In the various courses, students will generate CAD drawings of all the engine components, produce process plans for and make those components, and assemble and test the engines. This will afford students a good understanding and experience of the full range of issues involved in product design, manufacturing planning, fabrication, assembly and testing of functional products. Because the project is based on modifying existing courses rather than developing new ones, we expect the results of the project to be easily adaptable to a wide range of programs.
A Sufficient Condition for Passive Virtual Walls With Quantization Effects
Authors: Abbott Jake J. , Okamura Allison M.
Published: April 2008

The “virtual wall” is the most common building block used in constructing haptic virtual environments. A virtual wall is typically based on a simple spring model, with unilateral constraints that allow the user to make and break contact with a surface. There are a number of factors (sample-and-hold, device dynamics, sensor quantization, etc.) that cause virtual walls to demonstrate energetic behavior, destroying the illusion of reality. Passive objects are incapable of generating energy, so in this paper, we find an explicit upper bound on virtual wall stiffness that is a sufficient condition for virtual wall passivity. We consider a haptic display that can be modeled as a mass with Coulomb and viscous friction, being acted upon by two external forces — an actuator and a human user. The system is equipped with only one sensor — an optical encoder measuring the position of the mass. We explicitly consider the effects of position resolution, which has not been done in previous work. We make no assumptions about the human user, and we consider arbitrary constant sampling rates. The main result of our analysis is a sufficient condition for passivity that relies on the Coulomb friction in the haptic device.
Application of Laminar Flamelet Model to a Diffusion Flame Combustor
Authors: Jiang L. Y. , Campbell I. , Su K.
Published: April 2008

The flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied. Results obtained from a laminar flamelet combustion model (228 reactions and 31 species), together with the re-normalization group (RNG) k-ε turbulence model, the discrete ordinates radiation model, and the NOx model, are presented and discussed. These results are compared with a comprehensive database obtained from a series of experimental measurements. The flow patterns and recirculation zone length in the combustion chamber are accurately predicted, and the mean axial velocities are in fairly good agreement with the experimental data, particularly at downstream sections. The mean temperature profiles are also captured fairly well by the laminar flamelet combustion model. Based the velocity and temperature field solutions, NOx simulation was performed in a post-processing mode. The numerical results indicate that the semi-empirical, post-processing NOx model can provide valuable NOx simulations as long as the velocity and temperature fields are adequately predicted.
Modeling of a Gallium Nitride Epitaxy Growth System
Authors: Cai D. , Wu B. , Zheng L. L. , Zhang H. , Mecouch W. J. , Sitar Z.
Published: April 2008

An iodine vapor phase epitaxy (IVPE) system has been designed and built at North Carolina State University to grow high quality thick gallium nitride layer at the growth rate up to 80 μm/h with the deposition temperature of 1010 °C and the pressure of 200 Torr. In order to optimize the growth process, a numerical model, which is capable of describing multi-component fluid flow, gas/surface chemistry, conjugate heat transfer, radiation heat transfer and multi-species transport, has been developed to help in design and optimization of the IVPE reactor. The gallium source weight reduce rate is converted into flow rate of gallium vapor and has been simulated as an inlet boundary condition of the tubular reactor. By matching predicted and experimental deposition rates, the heterogeneous reaction boundary condition is determined and applied to the substrate. Comprehensive two-dimensional computational simulations have been performed to study the temperature distribution, species mixing process and GaN deposition rate distribution on the substrate under different geometrical configurations and operating conditions; and the operating parameters have been optimized.
Limited Movement Machinery Roller Devices
Authors: Barnett Ralph L. , Brickman Dennis B.
Published: April 2008

Ancient Egyptians allegedly moved large stone blocks by placing cylindrical rollers beneath them and manually urging them along. This rolling procedure required that the rollers emerging from the rear of the stone be manually lifted and replaced in front. This roller replacement protocol has been automated in commercially available roller units that allow continuous movement of heavy machinery under the action of pry bars, come-a-longs, winches, or manual push efforts. Unfortunately, when slopes or asperities are encountered these heavy loads may accelerate uncontrollably or steer themselves in unsafe directions when the roller units become reoriented. This paper describes two inventions that cause the locomotion of the machinery to proceed in inchmeal fashion by intermittently braking the system while the roller units are manually reset.
A Comparative Study of the Empirical Mode Decomposition and Wavelet Analysis on Their Application for Structural Health Monitoring
Authors: Hera Adriana , Shinde Abhijeet , Hou Zhikun
Published: April 2008

The paper presents a comparative study of the effectiveness of three novel damage detection techniques namely Continuous Wavelet Transform (CWT), Empirical Mode Decomposition (EMD) and Wavelet Packet Sifting (WPS). The health condition of a mechanical or civil engineering structure can be assessed by monitoring a change in natural frequencies and mode shapes. CWT method can be used to identify the instantaneous values of these modal parameters by the wavelet ridges. Using the EMD method, intrinsic mode functions (IMF) can be sifted from a vibration signal, whereas a newly-developed WPS technique can decompose a signal into its dominant mono-frequency components. Instantaneous modal information can be extracted by incorporating the EMD and WPS with the Hilbert Transform. These techniques are illustrated for simulated vibration data from a three-degree-of-freedom system subjected to (i) sudden damage and (ii) progressive damage. The aspects related to the implementation algorithms, sensitivity to damage type and the robustness issues in case of noisy data are discussed. In case of progressive damage, all methods performed well. WPS technique performed better in case of sudden damage whereas CWT demonstrated robustness in case of noisy data.
An Experimental Study of Magnetic Damping Effect on Temperature Gradient Induced Natural Convection in Liquid Gallium
Authors: Xu B. , Li B. Q. , Stock D. E.
Published: April 2008

The results of an experimental investigation of natural convection driven flow of liquid gallium are presented. The gallium contained by a rectangular box with two opposite ends held at different temperatures and is subject to a uniform horizontal magnetic field. The objective of this study was to examine the damping effect of a magnetic field on the natural convection in a liquid metal. A hot film anemometry was used to measure the velocity profile and a thermocouple was used to measure the temperature field. The hot-film probe was calibrated over a narrow range of temperatures in a rotating container fill with liquid gallium. The velocity and temperature profiles are compared with previous numerical simulations and reasonably good agreement was found. The damping effect of the external magnetic field was observed in both the temperature and the velocity profiles and found to increase as the strength of the magnetic field increases.
Model Following Robust Neuro-Adaptive Control Design for Non-Square, Non-Affine Systems
Authors: Padhi Radhakant , Unnikrishnan Nishant , Balakrishnan S. N.
Published: April 2008

Using neural networks, this paper proposes a new model-following adaptive control design technique for nonlinear systems. The nonlinear system for which the method is applicable is assumed to be of known order. Furthermore, it is assumed that using a nominal model an appropriate nominal controller has been designed for the system. However, it is well-known that because of unmodeled dynamics and/or parameter uncertainties, a nominal controller seldom works the way it is intended to; and sometimes it even leads to instability. Hence there is a need to modify this nominal controller online, in a stable manner, to suppress these unwanted behaviors. An online control adaptation procedure proposed in this paper to achieve this objective. The control design is carried out in two steps: (i) synthesis of a set of neural networks which collectively capture the algebraic function that arises either because of the unmodeled dynamics or uncertainties in parameters and (ii) computation of a controller that drives the state of the actual plant to that of a desired nominal model. The neural network weight update rule is derived using Lyapunov theory, which guarantees both stability of the error dynamics as well as boundedness of the weights of the neural networks. Unlike existing methods, a distinct characteristic of the adaptation procedure presented in this paper is that it is independent of the technique used to design the nominal controller; and hence can be used in conjunction with any known control design technique. Moreover, this technique is applicable to non-square and non-affine systems as well. Numerical results for a fairly-challenging problem are presented in this paper, which demonstrate these features and clearly bring out the potential of the proposed approach.
Effects of Coupled Biaxial Tension and Shear Stresses on Decrimping Behavior in Pressurized Woven Fabric
Authors: Cavallaro Paul V. , Quigley Claudia J. , Johnson Arthur R. , Sadegh Ali M.
Published: April 2008

Tension structures continue to be of increasing importance to military applications requiring both minimum weight, small packing volumes and enhanced deployment operations. However, in the case of inflated fabric structures, present design methods are not well established. Analytical tools required to efficiently design these structures lag behind those for conventional structures and materials. This is partly due to nonlinearities resulting from changes in fabric architecture upon loading. In particular, constitutive relationships need to be developed to establish the pressure-dependence and coupling effects of biaxial tension and shear loads. Through analysis and experiment, the present research addresses the changes in fabric architecture and, more specifically, the combined effects of biaxial tension, shear and crimp interchange on the global behavior of woven fabrics. Engineering test standards need to be prepared that capture the fabric’s mechanical behavior under a variety of coupled loading environments. A novel fixture is introduced for use in experimental testing of fabrics subjected to combined biaxial tension and shear loads.
Dynamic Tibiofemoral Contact Mechanics in a Total Knee Replacement
Authors: Gustafson Lisa M. , Benson Lisa C. , DesJardins John D. , LaBerge Martine
Published: April 2008

Wear of the ultra-high molecular weight polyethylene (UHMWPE) tibial component of total knee replacements (TKR) depends upon the contact with the femoral component during motion. This study aimed to determine the dynamic contact mechanics within the tibiofemoral joint of a TKR while in a force-controlled knee simulator and to track the kinematics of the TKR system while in the wear simulator. These results were compared with those found in literature by the currently used simulator methods. Using a high-speed camera system, grey scale images of the contact between a transparent TKR tibial insert and the metal femoral component were captured with an industrial grade fiberscope mounted below the tibial insert within the simulator. The analysis of the images yielded quantification of contact area and its location on the tibial insert. The results compare well with those found in literature. Therefore, it has been shown that the novel instrumentation designed for this project is an accurate and feasible method to determine contact area and location on a TKR tibial insert under dynamic loading.
Film Cooling Effectiveness on the Leading Edge of a Rotating Turbine Blade
Authors: Ahn Jaeyong , Schobeiri M. T. , Han Je-Chin , Moon Hee-Koo
Published: April 2008

Detailed film cooling effectiveness distributions were measured on the leading edge region of a rotating blade using a Pressure Sensitive Paint technique. The film cooling effectiveness information was obtained from the oxygen concentration difference between air and nitrogen or air and CO2 injection cases by applying the mass transfer analogy. The blowing ratio was controlled to be 0.5, 1.0, and 2.0 while the density ratios of 1.0 and 1.5 were obtained using nitrogen and CO2 as coolant gases, respectively. Tests were conducted on the first stage rotor of a 3-stage axial turbine with off-design condition at 2400 rpm. The Reynolds number based on the axial chord length and the exit velocity was 200,000 and the total to exit pressure ratio was 1.12 for the first rotor. The film cooling effectiveness distributions were presented along with the discussion on the influence of blowing ratio, density ratio, and vortices around the leading edge region.
Thermal Modeling of Very Small Scale Devices
Authors: Bulusu A. , Walker D. G.
Published: April 2008

As electronic device dimensions shrink down to the nanoscale regime, quantum effects such as electron tunneling and quantum confinement become significant. Along with quantum effects, various scattering processes such as carrier-carrier and carrier-defect scattering will influence device performance. Many transport models are not mature enough to couple the thermal effects with electronic solutions at such small scales. Incorporation of strong scattering influences on the electron transport in most cases is extremely difficult and computationally intensive. In this paper, we study a simple model that allows for integration of electron-phonon scattering effects in a nanotransistor. An acoustic deformation potential based electron-phonon scattering model is used to incorporate scattering in the device. A 7.5% drop in channel current was observed for a scattering rate of 1013/sec while current flow dropped by 50% for higher scattering rates. The effective channel resistance due to scattering was found to increase by a factor of 1.3. The results are compared to the I-V characteristics obtained using the non-equilibrium Green’s function (NEGF) formalism and were found to match well. The effect of phase-breaking scattering was also studied using NEGF where a 25% decrease in channel current was obtained thus demonstrating the importance of including scattering effects with quantum transport.
Numerical Investigation of Heat Conduction With Unsteady Thermal Boundary Conditions for Internal Combustion Engine Application
Authors: Urip E. , Liew K. H. , Yang S. L. , Arici O.
Published: April 2008

Heat transfer is one major important aspect of energy transformation in spark ignition (SI) engines. Locating hot spots in a solid wall can be used as an impetus to design a better cooling system. Fast transient heat flux between the combustion chamber and the solid wall must be investigated to understand the effects of the non-steady thermal environment. This study investigates numerical simulation of 3D transient heat diffusion phenomena in solid, exposed to steady and unsteady thermal boundary conditions. A 3D transient finite volume method to calculate heat transfer across a solid medium will be presented first. It is then validated with steady state thermal boundary conditions. The validation extends to the effects of multiple solid materials for which large thermal property difference is investigated. Finally the effects of non-steady thermal boundary environment are discussed. Numerical results are validated with available analytical solutions and are compared with FLUENT result.
Near-Wall Modeling for Vertical Wall Fires Using One-Dimensional Turbulence
Authors: Shihn Harmanjeet , DesJardin Paul E.
Published: April 2008

This paper presents the simulation of an idealized vertical wall fire using one-dimensional turbulence (ODT) modeling. Near wall gas-phase molecular processes of conduction, gas-phase and shoot reactions, and radiative heat transfer are treated exactly while the effects of turbulent mixing processes are modeled using ODT triplet mapping stirring events that allow the effects of turbulence-chemistry-radiation interactions to be examined. Transport equations for species and temperature are solved using an operator splitting algorithm method that employs a Crank-Nicholson scheme for diffusion/conduction, and the LSODE library to integrate the numerically stiff chemical source terms. Radiative heat transfer is accounted by using a two-flux model. Results are presented for the evolution of turbulent wall fires, with and without the effects of turbulent mixing. The use of the ODT model is shown to capture a laminar to turbulent flow transition resulting in enhanced heat transfer to the wall.
The Influence of Sliding Velocity on Wear of Total Knee Arthroplasties
Authors: Borgstede Laura L. , Schwenke Thorsten , Andriacchi Thomas P. , Wimmer Markus A.
Published: April 2008

Polyethylene wear remains a major cause of aseptic loosening and subsequent revision of total knee arthroplasties (TKA). During implant development and evaluation, simulator wear tests provide valuable information on material and design performance of TKA but have not yet replicated the wear patterns seen in vivo. Recent studies indicate that the combination of contact forces, sliding velocity, and distance, impacts the wear outcome [1, 2]. However, the detailed role of sliding velocity between condyle and tibial plateau, in combination with axial loading, remained unresolved. We hypothesize that implant wear can be strongly correlated with the so-called FV-factor, the product of applied axial force and sliding velocity of the condyle on its tibial counterpart. The aim of this study was to look at wear pattern formation and overall volumetric material loss versus varying FV-factors.
A Comparative Study of Single Loop and Multiple Loop Design for Uncertain Single Input Single Output Systems
Authors: Lal Mayank , Jayasuriya Suhada
Published: April 2008

In this paper, studied are the actual advantages offered by SISO cascade loop structures. In Quantitative Feedback Theory it is emphasized that the use of cascaded loops is primarily for the reduction of bandwidth of the controllers. This in turn helps in considerable reduction of the adverse effects of high frequency noise. The question that arises then is whether or not there are any substantial benefits to be gained by cascade loop design in the low frequencies. This issue is the focus of this paper. It is shown using Quantitative Feedback Theory methodology that there aren’t any advantages gained in the low frequencies with the use of cascaded design for meeting performance specifications. In effect it is concluded that if the design is properly executed a single loop controller closed from the output to the input will be sufficient to meet the typical performance specifications. This is shown using an example where the mold level of a continuous casting process is to be controlled. The plant being used has considerable uncertainty so that features of robust control can be highlighted.
Using FlowLab, A Computational Fluid Dynamics Tool, to Facilitate the Teaching of Fluid Mechanics
Authors: Cimbala John , Moeykens Shane , Kulkarni Ashish , Parihar Ajay
Published: April 2008

Traditional fluid mechanics textbooks are generally written with problem sets comprised of closed, analytical solutions. However, it is recognized that complex flow fields are not easily represented in terms of a closed solution. A tool that allows the student to visualize complex flow phenomena in a virtual environment can significantly enhance the learning experience. Such a visualization tool allows the student to perform open-ended analyses and explore cause-effect relationships. Computational fluid dynamics (CFD) brings these benefits into the learning environment for fluid mechanics. With these benefits in mind, FlowLab was introduced by Fluent Inc. in 2002. FlowLab may be described as a virtual fluids laboratory - a computer-based analysis and visualization package. Using this software, students solve predefined CFD exercises, either as homework or in a supervised laboratory or practicum setting. Predefined exercises facilitate the teaching of fluid mechanics and provide students with hands-on CFD experience, while avoiding many of the difficulties associated with learning a generalized CFD package. A new fluid mechanics textbook is scheduled for release in early 2005. This book includes FlowLab as a textbook companion, where student-friendly CFD exercises are employed to convey important concepts to the student. Because of the unique design of end-of-chapter homework problems in this book and the intimate coupling between these problems and the CFD software, students are introduced to engineering problems and concepts, as well as to CFD, via a structured learning process. The CFD exercises are not meant to stand alone; rather, they are designed to support and emphasize the theory and concepts taught in the textbook, which is the primary learning vehicle. Each homework problem has a specific fluid mechanics learning objective. Through use of the software, a second learning objective is also achieved, namely a CFD objective. The scope, content, and presentation of these CFD exercises are discussed in this paper. Additionally, one of the exercises is explained in detail to show the value of using CFD to teach introductory fluid mechanics to undergraduate engineers.
Studies on the Application of an Ambulatory Suspension System for Gait Rehabilitation
Authors: Shetty Devdas , Campana Claudio , Bravo Julio , Fast Avital
Published: April 2008

The ambulatory suspension system outlined in this paper is presented as a method and apparatus that would assist patients during gait rehabilitation and used as a safety support for patients during exercise. The apparatus is designed to be adjustable, support the weight of the user, does not impede walking and prevents sudden fall. The paper outlines the development and implementation of a 3-axis motorized support system that provides support in a full range of motion; allowing ambulatory impaired patients to safely rehabilitate themselves under the supervision of a physical therapist. The patient requiring gait rehabilitation would be free to traverse a flat plane and climb a number of stairs. This newly designed apparatus can lift a patient from a sitting position in a wheel chair to a standing position and gives the therapist freedom to manually assist the patient in placing their feet and controlling the weight shift. As the patient begins to gain a feel for proper coordinated movement, the amount of weight borne by the patient is gradually increased to better simulate natural walking conditions. This paper details the concept, methodology, prototype, test results and performance optimization of a 3-axis automated motorized suspension system for gait rehabilitation.
CFD Study on Laminar Flow Pressure Drop and Heat Transfer Characteristics in Toroidal and Spiral Coil System
Authors: Bowman Anthony J. , Park Hyunjae
Published: April 2008

Most pressure drop and heat transfer correlations obtained from the toroidal geometric system have been applied to the analysis of helical and spiral tube systems. While toroidal (and helical) coils have a constant radius of curvature about the coil center point (and center-line), spiral coils have a continuously varying radius of curvature, in which the varying centrifugal forces contribute to further enhance the heat transfer (at the cost of additional pressure drop) over toroidal and helical tube heat exchangers of the same length. Due to lack of published analytical, numerical and experimental data on spiral coil systems, in this paper, the laminar flow pressure drop and heat transfer characteristics of spiral coil systems are investigated with a commercially available CFD package (Fluent 6). First, an isothermal flow CFD analysis for a toroidal coil system is performed to optimally predict the local flow field and compared with the available experimental, numerical and analytical results, in which various model assumptions and operating conditions are involved. As a consequence, the heat transfer analysis with constant wall temperature boundary condition has been performed on a toroidal coil. With the verified CFD modeling schemes such as curved geometry creation, mesh/gird density control and solution model selection, the work is extended to the spiral coil system. The effects of Reynolds number and tube diameter to coil curvature ratio on the average friction factor and heat transfer characteristics are investigated for specified coil geometries utilizing water as the heat transfer medium. The general correlations for laminar flow pressure drop and heat transfer applied in a toroidal coil system are compared with the CFD results obtained from the spiral coil systems. It was found that up to 10% of the additional pressure drop and 40% of the enhanced heat transfer characteristics are obtained from the spiral coil system over the toroidal. The heat exchanger effectiveness ratio for spirals and toroids are compared for a range of Dean number. It was found that the spiral heat exchanger effectiveness ratio was between 20 to 30 percent greater than for general toroidal heat exchanger systems.
Performance Evaluation of Notched Biaxial Braided Composites
Authors: Tate Jitendra S. , Kelkar Ajit D. , Bolick Ronnie
Published: April 2008

Braided composites have good properties in mutually orthogonal directions, more balanced properties than traditional tape laminates, and have potentially better fatigue and impact resistance due to the interlacing. Another benefit is reduced manufacturing cost by reducing part count. Because of these potential benefits braided composites are being considered for various applications ranging from primary/secondary structures for aerospace structures [1]. These material systems are gaining popularity, in particular for the small business jets, where FAA requires take off weights of 12,500 lb. or less. The new process, Vacuum Assisted Resin Transfer Molding (VARTM), is low cost, affordable and suitable for high volume manufacturing environment. Recently the aircraft industry has been successful in manufacturing wing flaps, using carbon fiber braids and epoxy resin and the VARTM process. To utilize these VARTM manufactured braided materials to the fullest advantage (and hence to avoid underutilization), it is necessary to understand their behavior under different loading and environmental conditions. This will reduce uncertainty and hence reduce the factor of safety in the design. It is well known fact that the strength of the composite structure reduces because of discontinuities and abrupt change in the cross-section. Accurate knowledge of strength and failure mechanism of notched and unnotched composites is very important for design of composite structures. This research addresses the behavior of notched braided composites under static tensile loading.
Distributed Monitoring of Steady-State System Performance Using Wireless Sensor Networks
Authors: Sundararajan V. , Redfern Andrew , Watts William , Wright Paul
Published: April 2008

Wireless sensor networks provide a cost-effective alternative to monitoring system performance in real-time. In addition to the ability to communicate data without wires, the sensor nodes possess computing and memory capabilities that can be harnessed to execute signal processing and state-tracking algorithms. This paper describes the architecture and application layer protocols for the distributed monitoring of the steady-state performance of systems that have a finite number of states. Protocols are defined for two phases — the learning phase and the monitoring phase. In the learning phase, an expert user trains the wireless network to define the acceptable states of the system. The nodes are programmed with a set of algorithms for processing their readings. The nodes use these algorithms to compute invariant metrics on the sensor readings, which are then used to define the internal state of the node. In the monitoring phase, the nodes track their individual states by computing their state based on the sensor readings and then comparing them with the pre-determined values. If the system properties change, the nodes communicate with each other to determine the new state. If the new state is not one of the acceptable states determined in the learning phase, an alert is raised. This approach de-centralizes the monitoring and detection process by distributing both the state information and the computing throughout the network. The paper presents algorithms for the various processes of the system and also the results of testing the sensor network architecture on real-time models. The sensor network can be used in automotive engine test rigs to carry out long term performance analysis.
An Evaluation of Production Vehicle Roof Strength
Authors: Bish Jack , Nash Carl E. , Paskin Allan , Honikman Terence , Friedman Donald
Published: April 2008

Automobile roof strength is regulated by Federal Motor Vehicle Safety Standard, FMVSS, 216, promulgated in 1971 as a temporary alternative to the dolly rollover test of FMVSS 208. The originally proposed test focused the load on the A-Pillar/Roof Rail/Header intersection and required both sides of the roof to be tested sequentially mimicking the contact sequence in a multiple rollover. The current standard is a less stringent part of the original proposal, which tests the vehicle at a shallower pitch angle with a larger platen and only stresses the first or leading side impact of the vehicle roof. A new fixture has been built that closely duplicates the originally proposed test (NHSB 1971), but with more realistic load application angles that are different on the near and far side of a vehicle during a roll. Tests performed to date illustrate the weakness of current production vehicle roofs.
Rollover Roof Test Results for a Production Vehicle
Authors: Friedman Donald , Jordan Acen , Bish Jack , Nash Carl E. , Honikman Terence
Published: April 2008

We have described the Jordan Rollover System (JRS), a dynamic rollover test fixture, in previous reports (Friedman and Nash 2002 and Friedman et al., 2003). The JRS addresses the shortcomings — lack of repeatability and control over test conditions — of previous rollover tests and test devices including various static, drop, and dynamic roll tests. The JRS is designed to emulate specific roof impacts in actual multiple rollovers in a highly repeatable, controlled test. The JRS holds a passenger compartment at the desired pitch and yaw between two drop towers. The vehicle is rotated about its roll axis and, at the appropriate time, the front end is dropped to contact a moving roadway at a prescribed road speed; roll rate; drop height; and roll, pitch and yaw angles. Vehicle parameters can be changed and anthropomorphic crash test dummies added depending upon the variables being tested. We have conducted tests with production vehicles illustrating the performance of production roofs under controlled test situations and at varying strength-to-weight ratios. One such test is described here.
Preliminary Modeling and Design of an Autothermal Reformer
Authors: Dorr J. Lars , Erickson Paul A.
Published: April 2008

As fuel cells approach commercialization, hydrogen production becomes a critical step in the overall energy conversion pathway. Reforming is a process that produces a hydrogen-rich gas from hydrocarbon fuels (i.e., methanol, gasoline, natural gas). Hydrogen production via autothermal reforming (ATR) is particularly attractive for applications that demand a quick start-up and response time in a compact size. However, further research is required to optimize the performance of autothermal reformers and accurate models of reactor performance must be developed and validated. This paper discusses the preliminary modeling and design of an experimental autothermal reformer that will be used in several research projects at the University of California at Davis. The design includes the requirement of accommodating a wide range of experimental set ups. Factors considered in the design of the reformer are capability to use multiple fuels, ability to vary stoichiometry, precise temperature and pressure control, implementation of enhancement methods, capability to implement variable catalyst positions and catalyst arrangement, ability to monitor and change reactant mixing, and proper implementation of data acquisition. A model of the system was first developed in order to calculate flowrates, heating, space velocity, and other important parameters needed to select the hardware that comprises the reformer. Predicted performance will be compared to actual data once the reformer construction is completed. This comparison will quantify the accuracy of the model and should point to areas where further model development is required. The end result will be a research tool that allows engineers to optimize hydrogen production via autothermal reformation.
Wave Motion of a Nonlinear Elastic Bar Subjected to Axial Excitation
Authors: Dai Liming , Han Qiang
Published: April 2008

This research intends to investigate the wave motion in a nonlinear elastic bar with large deflection subjected to an axial external exertion. A nonlinear elastic constitutive relation governs the material of the bar. General form of the nonlinear wave equations governing the wave motion in the bar is derived. With a modified complete approximate method, the asymptotic solution of solitary wave is developed for theoretical and numerical analyses of the wave motion. Various initial conditions and system parameters are considered for investigating the shape and propagation of the nonlinear elastic wave. With the governing equation of the wave motion of the bar and the solution developed, the characteristics of the nonlinear elastic wave of the bar are analyzed theoretically and numerically. Properties of the wave propagation and the effects of the system parameters of the bar and the influences of the initial conditions to the characteristics of the wave motion are investigated in details. Based on the theoretical analysis as well as the numerical simulations, it is found that the nonlinearity of the elastic bar may cause solitary wave in the bar. The velocity of the solitary wave propagating in the bar is related to the initial condition of the wave motion. This exhibits an obvious different characteristic between the nonlinear wave and that of the linear wave of an elastic bar. It is also found in the research that the solitary wave is a pulse wave with stable propagation. If the stability of the wave propagation is destroyed, the solitary wave will no longer exist. The results of the present research may provide guidelines for the wave motion analysis of nonlinear elastic solid elements.
Real-Time Subspace Identification and Optimal Control for Active Noise Cancellation
Authors: Pongpairoj Harin , Chaparala Vineet , Pourboghrat Farzad
Published: April 2008

In this paper, a combination of a novel recursive subspace identification and receding horizon optimal control is developed for real-time implementation, via a digital signal processor (DSP), using only input-output measurements. The proposed recursive strategy can be parameterized in terms of recursive approximation of subspace intersections and adaptive estimation of state sequences. The proposed integrated modeling-control strategy can be implemented, in real time, with minimum knowledge of the controlled system. Actual hardware experiments on feedback active noise control problem in a duct have been carried out in order to verify the performance of the proposed methodology.
Numerical Simulation of Radio Frequency Induction Plasma Spray Processing
Authors: Xiong H.-B. , Zheng L. L. , Margolies J. , Sampath S.
Published: April 2008

A two-dimensional numerical model has been developed to investigate the induction electromagnetic (EM) field and the thermo-fluid field in a radio frequency inductively coupled plasma (RF-ICP). Various physical and chemical phenomena have been considered such as the induction heating, plasma generation, and the in-flight particle interaction with the plasma jet. This model has been applied to the induction plasma spray process operated in a vacuum chamber. The partially stabilized zirconia powder (PSZ) has been used as an example for the feedstock. The effects of power input, standoff distance and powder injection position on the plasma and particle behaviors have also been investigated and discussed.
Effects of Flow Rate on the Environment in a Microbioreactor for Bone Cells
Authors: Kizito John P. , Barlow Karen L. , Adamson Jose´e R. , Griffin DeVon W.
Published: April 2008

The goal of the present paper is to report on the biophysicochemical transport processes involved in microbioreactors designed for bone cell studies. The purpose of this effort is to guide our biological testing for cell viability, growth, and morphology markers. We present a microbioreactor design that has been optimized to ensure that the flow is uniform in the direction of flow. Transport characterization results are obtained using numerical and experimental methods.
Thermoelastic Damping in the Longitudinal Vibration: Analysis and Simulation
Authors: Zhang Weibin , Turner Kimberly L.
Published: April 2008

The thermoelastic damping (TED), one of the main energy lost sources in MEMS and NMEMS, is analyzed for the longitudinal vibration mode. Two approximations based on the insulated thermal boundary condition (B.C.) and the modified fixed temperature B.C. are developed and compared. Until now, the highest reported experimental Q factors for the longitudinal vibrating MEMS device are still more than one order less than the predicted TED Q factors. Therefore, a numerical simulation approach is proposed and used for validation. The aim of this paper is to provide a prediction of TED for the fast developing bulk mode micro and sub-micro oscillators operating in a longitudinal vibrating mode.
Analysis of Penetrating Head Impact
Authors: Zhang Jiangyue , Yoganandan Narayan , Muszynski Cheryl A. , Pintar Frank A. , Gennarelli Thomas A.
Published: April 2008

Impact-induced injuries can be classified into blunt and penetrating types. Penetrating injuries are often the byproduct of gunshot wounds and these injuries to the head result in significant mortality and morbidity. The objective of the study is to determine the probability of fatality as a function of admission Glasgow Coma Scale (GCS) and injury volumes (hematoma and edema) in gunshot wounds using computed tomography (CT) scans. Head CT images from 19 patients were analyzed. Hematoma and edema volumes were computed using grayscale equivalents and special computer software. Hematoma and edema volumes were found to be better predictors than GCS. In addition to admission GCS, hematoma and edema volumes may allow more accurate prediction of outcome, and these data should provide informed counseling of relatives and improved guidelines for more efficient resource allocation during the acute care phase.