bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer in Water-Cooled Silicon Carbide Milli-Channel Heat Sinks for High Power Electronic Applications
Authors: Bower C. , Orgega A. , Skandakumaran P. , Vaidyanathan R. , Phillips T.
Published: May 2008

Heat transfer and fluid flow in a novel class of water-cooled milli-channel heat sinks are investigated. The heat sinks are manufactured using an extrusion freeform fabrication (EFF) rapid prototyping technology and a water-soluble polymer material. EFF permits the fabrication of geometrically complex, three-dimensional structures in non-traditional materials. Silicon carbide, SiC, is TEC-matched to silicon and is an ideal material for heat exchangers that will be mounted directly to heat dissipating electronic packages. This paper presents experimental results on the heat transfer and flow in small SiC heat exchangers with multiple rows of parallel channels oriented in the flow direction. Rectangular heat exchangers with 3.2 cm × 2.2 cm planform area and varying thickness, porosity, number of channels, and channel diameter were fabricated and tested. Overall heat transfer and pressure drop coefficients in single-phase flow regimes are presented and analyzed. The per channel Reynolds number places the friction coefficients in the developing to developed hydrodynamic regime, and showed excellent agreement with laminar theory. The overall heat transfer coefficients for a single row SiC heat exchanger compared favorably with a validation heat exchanger fabricated from copper, however the heat transfer coefficient in multiple row heat sinks did not agree well with the laminar theory.
Experimental Investigation of High-Speed Rotating Heat Pipes
Authors: Song F. , Home D. , Robinson T. , Ewing D. , Ching C. Y.
Published: May 2008

The steady state heat transfer characteristics of high-speed rotating heat pipes were measured using a newly commissioned high-speed rotating heat pipe test facility. The performance of two cylindrical and two tapered rotating heat pipes with different fluid loadings were tested for rotational speeds of 2,000 to 4,000 RPM and heat transfer rates up to 0.6 kW. The measurements were used to characterize the effects of rotational speed, working fluid loading, and heat pipe geometry on the performance of rotating heat pipes. The results were compared to previous theoretical models. There is a general agreement between test results and predictions from a model that accounts for natural convection within the liquid film at the evaporator at high accelerations. However, some results indicate that the model is not yet accounting for all the physics in a high-speed rotating heat pipe.
A Multi-Functional Stiffness/Energy Sensor for Health Monitoring of Structures
Authors: Wakha Celestine K. , Pines Darryll J.
Published: May 2008

A mechanical multi-functional dual-stiffness sensor for in-situ real-time stiffness and energy density measurements was developed at the University of Maryland [1]. The sensor has the ability to predict the elastic field of a given host structure based on the strain state of two strain sensors of different stiffnesses integrated into the structure. This study has demonstrated the posibility of using the sensor to predict the local instantaneous host stiffness and the strain energy density. The complete analytical derivation is given in a paper by Majeed and Dasgupta [2]. The present study evaluates the use of a dual stiffness/energy sensor to diagnose damage and to determine the remaining life of structures. The detection of the onset of any damage, the subsequent monitoring of its growth and the help in predicting the remaining life of the structure constitute the important goals of the sensor. An evaluation of the use of the dual stiffness sensor with active piezoelectric sub-sensors for dynamic analysis is also presented. A numerical verification using finite element analysis (FEA) is presented and the results indicate that the sensor can be used to monitor structures. A distributed array of sensors is used to determine the onset and location of damage. Experimental results are presented for uniaxial experimental tests under monotonic quasistatic loading conditions and indicate that the concept can easily be implemented.
Development of an Electro-Rheological Fluidic Actuator and Haptic Systems for Vehicular Instrument Control
Authors: Fisch Avi , Nikitczuk Jason , Weinberg Brian , Melli-Huber Juan , Mavroidis Constantinos , Wampler Charles
Published: May 2008

Force-feedback methanisms have been designed to simplify and enahance the human-vehicle interface. The increase in secondary controls within vehicle cockpits has created a desire for a simpler, more efficient human-vehicle interface. Haptic system, or systems that interact with the operator’s sense of touch, can be used to consolidate various controls into fever, haptic feedback control devices, so that information can be transmitted to the operator and the operator can change control settings without requiring the driver’s visual attention. In this paper an Electro-Rheological Fluid (ERF) based actuator and mechanisms are presented that provide haptic feedback. ERSs are fluids that change their viscosity in response to an electric field. Using the electrically controlled rheological properties of ERFs, haptic devices have been developed that can resist human operator forces in a controlled and tunable fashion. The design of an ERF-based actuator and its application to a haptic knob and haptic joystick is presented. The analytical model is given, analyses are performed, and experimental systems and data are presented for the actuator. Conceptual methods for the application to the haptic devices are presented.
Rheological Study of Time/Temperature Dependent Viscosity Curves of Mayonnaise
Authors: Gopalakrishnan Senthil L. , Hirschi Stanley , Rakesh Leela
Published: May 2008

The shelf-life of mayonnaise is a major concern for manufacturers and restaurateurs especially in regions where adequate refrigeration is scrace. Temperature, climate and food additives affect the properties of mayonnaise. When subjected to torsional flow at constant temperature and stress, mayonnaise reveals a quasi-exponential time-dependent viscosity curve, with a shere thinning and temperature dependent phenomena. These behaviors cannot be characterized by a single well-known mathematical equation and thus must be fitted with additional piecewise functions.
Theoretical Study of the Three-Dimensional Flow Field in the Calender Bank
Authors: Luther S. , Mewes D. , Schuster R. H.
Published: May 2008

The three-dimensional flow field in the calender gap is calculated with consideration of the free surface of the bank. Calender units with rotating rolls are used to produce foils or sheets from polymer material with viscous or elastometric flow properties. The flow field and the adjusting form of the bank determine the properties of the product. The results of the calculations include the determiniation of vortex patterns inside the bank for fluids with viscous non-Newtonian and Newtonian flow behaviour as well as the determination of the influence of gap height and speed ratio on the coordinates of the free surface and the flow field. Additionally the influence of the flow field on the product quality is presented. Due to the requirement of a good product quality the influencing parameters are subject to boundaries. Such boundaries of the parameters are discussed and a schematic processing window for a specific product geometry is given. Analysed product properties are thickness, surface appearance, air inclusions, mixing and temperature. The numerical calculation is based on a decoupled calculation method for the free surface. The transport equation for mass and impulse are solved with the fluid dynamics analysis package Polyflow. The coordinates of the free surface are shifted until the free surface becomes a stream line. To analyse the flow behaviour polymeric fluids the power-law model of Ostwald-de-Waele is used.
Investigation of Performance of Active Microcapsule Actuation
Authors: Tan Honghui , Leo Donald J. , Park Taigyoo , Long Timothy E.
Published: May 2008

Microcapsules are micron-sized hollow particles that can be synthesized with fluid encapsulated in the interior. The microcapsules can be used as a potential actuation technique by incorporating stimulus-responsive materials, such as permeselective, light-sensitive and electrically sensitive materials. The microcapsules range from 10 to 80 microns in diameter and wall thickness normalized to radius might range from 0.05 to 0.5. The actuation concept is to control the size of the microcapsules by varying the interior fluid pressure using an external stimulus. This paper presents efforts to model the performance and capabilities of microcapsules as micro actuators. We assume the pressure of the fluid inside of the microcapsules can be controlled by certain technique, such as thermal, electro or optical stimulus to the fluid. This paper will focus at modeling the performance of microcapsules under known pressure variation of fluid inside. First the paper compares a thin-wall model to a thick-wall model and identifies that thin-wall theory is not accurate enough for microcapsules. Simulation results show that energy density inthe order of 3J/cm3 is theoreticaly achievable for thick microspheres. Two type of materials are studied as the materials encapsulated in microcapsules. Their constitutive equations are then incorporated into the thick-wall model. Simulations show hydrocarbon solvents are much more efficient than ideal gas in terms of actuation performance.
Electroactive Polymers Based on Novel Ionomers
Authors: Akle Barbar J. , Hickner Mike , Leo Donald J. , McGrath James E.
Published: May 2008

A majority of research on ionic polymer transducers has used Nafion™ as the base material. Varying the physical and chemical properties of Nafion is difficult, which limits the understanding and development of ionic transducers. In this study we investigate a novel class of polymers called BPSH (sulfonated poly(arylene ether sulfone)s). The polymers are synthesized by the direct polymerization of sulfonated monomers. This synthetic scheme affords precise control of the amount and the location of ionic groups along the polymar backbone. These polymers differ from Nafion™ in two major ways. First, the concentration of ionic groups on a mass basis is almost double that of standard Nafion™, 1.51 meq/g for BPSH-30 versus 0.91 meq/g for Nafion™ 1100. Also, the backbone of the BPSH copolymers is much stiffer than Nafion, which affords a higher modulus material. Both of these factors, ion content and modulus, are expected to affect the performance of polymer-based actuators. Another ionomer characterized is the PATS (poly(arylene thiother sulfone)s) which is similar to BPSH. For both polymers we are varying the ionic concentration, stiffness, and water content. Those variations are fostering the understanding of operating concepts of ionic transducers, especially the correlation between ionic transducers, especially the correlation between ionic concentration and performance. Experiments on BPSH-35 demonstrate improved performance as compared to Nafion™ They provide larger strain per unit volt, larger force generated, and larger bandwidth. The novel polymers are characterized as sensors and actuators.
Methodology and Model to Determine Key Process Parameters for Tailor Welded Blank Forming
Authors: Kinsey Brad , Bravar Matt , Cao Jian
Published: May 2008

Tailor Welded Blanks (TWBs) offer several notable benefits compared to traditional sheet metal parts including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers must overcome formability concerns related to stamping TWBs and be able to accurately predict unique characteristics related to the forming of this blank type. In this research, an analytical model using a 2D cross-sectional approach was devised and implemented to predict the weld line movement and forming height for a uniform binder force TWB application. The inputs into the analytical model are the desired strain at the weld line location, the geometry of the 2D cross-section, material properties, and the frictional condition. From this information, the model predicts the stress and strain at several key locations on the 2D cross-section as well as the movement of the material in the binder area and in the formed walls.
On Hot Metal Gas Forming Process
Authors: Smith Philip E. , Fang Que-Tsang , Wu Xin
Published: May 2008

Hot Metal Gas Forming (HMGF) is a new metal forming process jointly developed by 15 automotive/aerospace companies/suppliers and one university under NIST-Advanced Technology Program [1, 2]. The primary goals of this program are (1) to achieve enhanced formability for automotive steels and aluminum alloys at high speeds, and (2) to reduce manufacturing cost. The technical approach is to develop a gas forming process that forms tubular components at elevated temperatures inside ceramic dies. During the forming, 1) a tubular workpiece is placed into the ceramic die cavity, then is rapidly heated to above 0.6Tm (melting temperature in K) by a set of induction coils that are embedded behind the ceramic die outer surfaces; 2) The two tube ends are sealed and a gas pressure is applied inside the bube; and 3) The metal fill the die cavity under combined internal gas pressure and optional axial feeding. After forming the workpiece is transferred to a cooling station for possible on-line heat treatment. For many steels and heat-treatable aluminum alloys the mechanical properties can be improved through controlled cooling rate after forming. In this presentation, the results on the elevated-temperature tensile behaviors and formability of several commonly used automotive aluminum alloys and steels will be presented. The microstructural evolution and its effect on the formability and post-forming properties will also be discussed. Two types of tube in-die forming 0processes have been studied: (1)tube expansion from 2 inche to 3 inch in diameter; (2) tube forming from round to squared sections. Based on laboratory that can perform continuous operation at a cycle time less than 30 seconds. Current activities in implementation of this new metal forming method for manufacturing vehicle chassis components will be described.
Computer Simulation on a Thermally Activated Tube Forming Process
Authors: Krishnamurthy Ramnath K. , Wu Xin
Published: May 2008

Under thermally activated deformation condition extensive formability may be obtained. In this paper, elevated-temprature formability and tube forming process [1] were analyzed. Two most typical tube forming process, tube free expansion and in-die bulge forming, were simulated by FEA with the use of Abaqus/Standard code. An empirical material equation was used that takes into account bothe starain handening and strain rate heardening effects, to reflects, to reflect material characteristics at high strain rates and at elevated tempratures. For tube free expansion forming, the deformation path was varied by changing the end velocity with respect to internal gas pressure, thus providing an assessment of material forming limit at various strain path. Falure to may occur due to necking and bucking, which are related tko the ratio of internal pressure and end-load. The deformation process and limit strain were obtained for various meterial parameters, including n-value and m-value, as well as the tempreture distribution. The effect of tube gemetry (diameter, thickness and heating length) on the process is also investigated. For in-die tube forming process, the effect of die friction on the material flow and strain distribution was analyzed, and the thickness distributions in the longitudinal direction (for axi-symmetrical tube forming) and in the circumferential direction (for round-to-squared tube forming) were predicted as function of forming parameters. A comparison between prediction and experiment was provided.
Free Asymmetric Vibrations of Composite Full Circular Cylindrical Shells With a Bonded Central Lap Joint
Authors: O¨zerciyes V. , Yuceoglu U.
Published: May 2008

In this study, the problem of the free asymmetric vibrations of composite “full” circular cylindrical shells with a bonded single lap joint is considered. The “full” circular cylindrical shell adherends to be made of dissimilar and orthotropic materials are connected by relatively very thin, yet flexible and linearly elastic adhesive layer. The bonded single lap joint is a centrally located in the composite shell system. The analysis is based on a “Timoshenko-Mindlin (and Reissner) Type Shell Theory” which is a “First Order Shear Deformation Shell Theory (FSDST)”. In the formulation, the set of governing differential equations is reduced to a system of first order ordinary differential equations in the “state vector” form. Then, they are integrated by means of a numerical procedure, that is, the “Modified Transfer Matrix Method (with Chebyshev Polynomials)”. The mode shapes and the natural frequencies of the “full” cylindrical shell lap joint system are investigated for various boundary conditions. Also, the effects, on the modes and natural frequencies, of the “hard” (or rather relatively stiff) and the “soft” (or relatively very flexible) adhesive layer cases are considered and presented. Some of the numerical results of the important parametric studies are computed and plotted.
Three-Dimensional Finite Element Analysis of Melting in an Alloy Irradiated With a High Energy Laser Beam
Authors: Kasula Bhavani , Majumdar Pradip
Published: May 2008

Lasers are being widely used in the material processing industry lately. In this work, study is performed on the resluting temperature and stress distribution, the width and depth of the melt pool in the heat-affected zone during material processing with a high energy Gussian laser beam. A three-dimensional enthalphy-based mathematical model is developed to study the effect of high energy laser beam on the formation of molten pool. The mathematical model is based on a three-dimensional transient heat equation taking into consideration the power intensity of the Gussian laser beam and phase diagram of the material. A computational algorithm is implemented to evaluate the temperature distributions as well as shape and size of molten pool. The numerical solution with the applied heat flux and convective boundary conditions is obtained usign a 3-D finite element code.
Characterization of Chaotic Motion of DNA in Linear Shear Flows
Authors: Walker D. G. , Stremler M. A.
Published: May 2008

Motion of macromolecules in flows is important to several disciplines such as DNA hybridization studies, self assembly of nanostructures, and transport of suspensions. The present study simulates the motion of macromolecular structures in linear shear flows. A molecular chain is modeled as a coarse-grained series of beads and springs. For a wide range flow conditions, the flow appears chaotic, where quasi-stable limit cycles are observed for several smaller ranges of flow conditions.
Basic Limitations on the Performance of Stirling Engines
Authors: de Boer P. C. T.
Published: May 2008

The performance of Stirling engines is subject to limitations resulting from power dissipation in the regenerator. The dissipation is caused by pressure gradients in the regenerator to generate flow. Without this flow the power output would by zero. Hence the dissipation is an essential element of the operation of the engine. Using linearized theory, the equation for pressure in the regenerator is solved for the case of a linear temperature distribution. The regenerator is taken to be thermally perfect. All various are taken to be sinusoidal in time. Expressions are derived for the net power output and the thermal efficiency. The net power output is optimized under various constraints. The constraint yielding the best results is fixed piston amplitude in the compression chamber. Upper bounds on the dimensionless power output are found as function of regenerator void volume and regenerator temperature. These bounds are derived in the limit of zero frequency, and ae independent of the conductance of the regenerator. Both power output and thermal efficiency decrease decreases as frequency and regenerator void volume increase.
Transient Analysis of a Line of Valves With Camshaft Flexibility and Valve-Spring Surge Effects
Authors: Teodorescu M. , Kushwaha M. , Rahnejat H. , Taraza D.
Published: May 2008

The paper presents analysis of a line of inlet valves in a 4-cylinder, 4-stroke diesel engine. The combined dynamics and tribological investigation provides important data that can be used in the design or design evaluation of automotive valvetrain systems, inlcluding vibration signature of the system, as well as prevailing contact conditions, including friction and lubrication data.
Gas-Displacement of Oldroyd-B Liquids in Capillary Tubes
Authors: Quintella Erick Fabri´zio , de Souza Mendes Paulo Roberto , da Silveira Carvalho Ma´rcio
Published: May 2008

Displacement of a liquid in a capillary tube by gas injection occurs in many situations, like enhanced oil recovery, coating of catalytic converters and gas-assisted injection molding. Generally the liquid being displaced is a polymeric solution or dispersion, that are not Newtonian. Viscoelastic forces alter the force balance in various parts of the flow and consequently change the amount of liquid left attached to the capillary wall. In order to model the effect of the rheological properties in this important flow, the mechanical behavior of the flowing liquid has to be well described by an appropriate constitutive model. Here, the Oldroyd-B differential constitutive equation that approximate viscoelastic behavior of dilute polymer solutions was used, together with momentum and continuity equation, to model the two-dimensional free surface flow near the gas-liquid interface. The equation system was solved with the Finite Element Method. The resulting nonlinear system of algebraic equations was solved by Newton’s method. The results show the effect of the viscoelastic character of the liquid on the free surface shape and the film thickness attached to the capillary wall.
Optimum Management of Cogeneration Power Plants With Thermal Storage in Day-Ahead Electricity Markets
Authors: Carraretto Cristian
Published: May 2008

The development of proper tools for power plants production planning is becoming crucial to profitably compete in a deregulated market scenario. Two numerical techniques, the former based on the dynamic programming, the latter on an original real-coded genetic algorithm, are suggested in this paper to optimize the management of cogeneration power plants with thermal storage. Detailed mathematical models are required to simulate plant part-load performance in order to evaluate possible operation plans profitability. Electricity price trends, forecasted from market analyses, are used as input data. Technical constrains and those derived from the market characteristics are included in the optimization problem. The suggested approaches are applied to some possible market situations, typical of different seasons and competition intensities. Results obtained are compared in terms of accuracy and resolution time. Iterative analyses are also performed to assess possible management flexibility improvements resulting from different design choices of the cogeneration system.
Energy Optimal Control of a Residential Space-Conditioning System Based on Sensible Heat Transfer Modeling
Authors: Hong Feng , Kulkarni Manohar
Published: May 2008

Nowadays most HVAC systems for residential building in the Unites States use a single-zone, two-position control system which is simple and easy to manage. However, this two-position control system has its disadvantage due to its unsatisfactory thermal comfort and energy inefficiency. This paper presents a proportional control system for the residential building by setting up the dynamic simulation for the building and the control system. The state-space method is used to model the building system and the simulation code is implemented on MATLAB™. Under this model, optimization of the controller is possible and implemented. The thermal comfort and energy efficiency are compared under the different schemes. It has been found that proportional control is advantageous to the two-position control for the thermal comfort while there is not much different in energy consumption between two control schemes. In this work, the furnace was operated without any minimum run time and under continuous data sampling.
Advances in Farm Tractor Modelling and Simulation
Authors: Mastinu G. , Gobbi M. , Previati G. , Ribaldone M.
Published: May 2008

The paper deals with the modelling of the dynamics of farm tractors in order to simulate their motion on smooth or rough surface, on road or off road and in different loading situations. The aim is to develop reliable models to speed-up the design and development activities. The derived farm tractor models can simulate the working conditions of the farm tractor while hauling a plough or running at relatively high speed on a rough soil, or steering soil, or steering on a sloped, soft surface. Two models of farm tractors have been developed and experimentally validated. The first model is based on a proprietary software. able to quickly simulate the motion of a vehicle on smooth or rough soil. The second model has been developed with the software ADAMS/Car® which allows to model complicated transmission and suspension systems. In both of the models, the tires, the transmission system, the suspension system, the steering system, the engine and the body inertia are carefully described mathematically. Particular attention has been devoted to the measurements of the tire characteristic and of the inertia parameters of the farm tractor body. Both of the models are defined in a parametric way. Parameters sensitivity analysis a strong influence of the transmission system on the tractor dynamic response in all of the considered working conditions. Experimental tests have realized to validate the two models.
Simulation-Based Parametric Reliability Modeling Using Covariate Theory
Authors: Wallace Jon M. , Mavris Dimitri N.
Published: May 2008

Reliability analysis methods used for preliminary safety assessments of complex systems typically assume a predetermined and invariant set of input variable statistical properties. However, during the product development phase of the system and especially during in service operation, the characteristics of the random variables can themselves be subject to variation. Thus, the resulting failure probability distribution can vary greatly from early predictions. The objective of this paper is to explore a technique used to create a general parametric failure probability distribution as a function of key variables. This technique is constructed around covariate theory which is the basis of the familiar Accelerated Life Testing and Proportional Hazards Modeling approaches. Where these approaches have traditionally been used with physical experiments, they are applied within this study to Monte Carlo simulation data generated using an available component modeling and simulation environment of a gas turbine airfoil limited by a single failure mode. Necessary modifications to the traditional from of the covariate approach are identified for application to controlled Monte Carlo simulation data. Implications to potential safety improvements early on in the product development phase are discussed.
Design for Assembly Versus Design for Disassembly: A Comparison of Guidelines
Authors: Tavakoli Massoud S. , Mariappan Jawaharlal , Huang Jin
Published: May 2008

As key issues in product life-cycle investigations. Design for Assembly (DFA) and Design for Disassembly (DFD) have received increasingly more attention. While some DFA techniques have reached a reasonable level of maturity, DFD methodology is still in its early stages of development. There has been little research on the relationship between DFA and DFD, especially as it pertains to their implementation. in this paper, the relationship between DFA and DFD rules is explored through a case study, where assemble and disassembly time data are collected for a commercial device. Then, a DFA and a DFD tool are applied to this device, and the results are examined to gauge the degree of overlap between DFA and DFD rules.
Steady-State Operation of a Loop Heat Pipe: Network Thermofluid Model and Results
Authors: Atabaki Nima , Baliga B. Rabi
Published: May 2008

A network thermofluid model of a loop heat pipe (LHP) operating under steady-state conditions is presented. Attention is focused on a simple LHP, with one evaporator, a vapor transport line, a single condenser, a liquid transport line, and a compensation chamber. The evaporator is an internally grooved circular pipe, with a cylindrical wick installed on its inner surface. The wick is made of a sintered metal. The condenser is a horizontal tube covered with a high-thermal-conductivity sleeve, and the outer temperature of the sleeve is maintained at a constant sink temperature. Quasi one-dimensional mathematical models of the fluid flow and heat transfer in each of the elements of the LHP, and collectively of the entire LHP, are proposed and discussed. The working fluid considered in this work is ammonia, but the proposed model can work with any suitable fluid. Results pertaining to the LHP performance for a range of operating conditions are presented, compared (qualitatively) to corresponding results of an earlier experimental investigation in the literature, and discussed.
Time-Mean Wall Static Pressure Distributions and Module Friction Factors for Fully Developed Flows in a Rectangular Duct With Spatially Periodic Interrupted-Plate Inserts
Authors: Candanedo Jose´ A. , Aboumansour Emile , Baliga B. Rabi
Published: May 2008

An experimental study of fully developed flows of air in straight rectangular ducts with interrupted-plate inserts is presented. These flows have features akin to those produced in the cores of plate-fin compact heat exchangers. In all, flows in one plain duct and six different ducts with interrupted-plate inserts were studied. Values of the dimensionless geometric parameters of the interrupted-plate ducts, normalized with respect to its half-height, are the following: width of the duct cross-section between 19.68 and 23.58; plate length between 3.286 and 3.938; plate thickness of 0.062, 0.115, and 0.205; and inter-plate spacing between 3.264 and 7.815. Values of the Reynolds number, based on a nominal average velocity and hydraulic diameter, ranged from 1663 to 30993. The results include graphical and tabular presentations of time-mean static pressure distributions along the axial centerline of the top wall of the duct, and module friction factor versus Reynolds number data, all in the periodic fully developed region.
Design and Fabrication of Silica Nanotube Arrays and Nanofluidic Devices
Authors: Li Deyu , Yue Min , Majumdar Arun , Fan Rong , Wu Yiying , Yang Peidong
Published: May 2008

Silica nanotube arrays have been fabricated from vertical silicon nanowire templates prepared by Vapor-Liquid-Solid (VLS) epitaxial growth. The silicon nonowire arrays are uniformly oxidized by a dry oxidation process in a tube furnace heated to 1000 °C and filled with pure O2, which gives SiO2 sheaths with continuous silicon wire cores inside. A dry etch process with XeF2 as etchant removes the silicon cores, thus silica nanotube arrays are obtained. The resulting silica nanotubes are more than 10 μm long with an inner diameter range from 10 to 200 nm. A nonofluidic device has been fabricated based on individual silica nanotubes. The nanotube is drop-casted onto a silica substrate from a solution and after the solution is dried out, a 200 nm thick chrome layer is sputter deposited. A 3 μm wide Cr gate structure is patterned across the silica nanotube. Photoresist is patterned to define the hydrophilic (silica) and hydrophobic (photoresist) regions. The hydrophilic regions form a reservoir at each side of the nanotube, thus giving us a nanofluidic device. Ion current flow through the nanotube has been measured in 1 M KCl solution and the measured current matches the theoretical estimation reasonably well.
A Mathematical Model for the Cranking Period in the Cold Start of Diesel Engines
Authors: Zhong Lurun , Henein Naeim A. , Liu Hengqing , Bryzik Walter
Published: May 2008

A mathematical model is developed to predict the length of the cranking period of direct injection diesel engines at low ambient temperatures. The model takes into consideration the physical and chemical process that develop in the cylinder over the whole cranking period. The model accounts for the variation in the following: (a) fuel accumulated in the cylinder in both the liquid and the vapor phases, (b) gas temperature and pressure, (c) wall temperature and (d) the autoignition reactions rate. An “Autoignition Index” (AI) is developed to account for the combined effects of fuel volatility and its Cetane Number. The model considers that autoignition starts in the cycle where AI reaches a critical value at the end of the cranking period. The model predictions are compared with the experimental data obtained on a single cylinder diesel engine tested in a cold room using four distillate fuels having different volatilities and Cetane numbers.
Robust, Adaptive Q-Parameterization for Feedback Control of Vibro-Acoustic Systems
Authors: McEver Mark A. , Cole Daniel G. , Clark Robert L.
Published: May 2008

An adaptive, single-mode feedback controller for vibroacoustic applications is developed based on the IMC form Q-parameterization. By structuring the Q-parameter as a third-order filter with fixed dynamics and an adaptable gain, the resulting controller is robust to changes in plant natural frequency variation. Analysis shows the advantages of using a highly-damped plant model in terms of increased stability and performance robustness, and was proven by closed-loop simulations on a single-mode plant with a time-varying natural frequency. Even with a natural frequency variation of ±50%, the adaptive-Q controller was able to decrease the squared plant output response to white noise disturbance by an order of magnitude, outperforming an optimally-tuned positive position feedback controller.
Natural Frequencies in Pipes With Orifice Terminations
Authors: Peng Mark M. , Moody Fred J.
Published: May 2008

Acoustic resonance frequencies help identify which pipe segments in a complex piping system are likely to undergo forced vibration. This study focuses on a pipe with a sinusoidal pressure disturbance imposed at one end on an otherwise steady flow, with the other end of the pipe terminating at an orifice. In order to determine the natural acoustic frequencies of this scenario, it is not obvious whether to model the boundary condition at the orifice as an open or closed pipe, or somewhere in between. The results of this study show how the natural frequencies in a pipe segment are related to the loss coefficient K in three different categories. First, when K is less than C/V, where C is the speed of sound and V is the mean fluid velocity, the natural acoustic frequency resembles that of an open pipe, with the amplitude that grows to a limiting value. Second, when K is greater than C/V, the natural frequency corresponds to a closed pipe, and the amplitude also grows to a limiting value. Lastly, when K is equal to C/V, disturbance will propagate to the orifice without exciting a resonance as if pipe were infinitely long.
Modeling Tire Blow-Out in Roadside Hardware Simulations Using LS-DYNA
Authors: Orengo Fabio , Ray Malcolm H. , Plaxico Chuck A.
Published: May 2008

Often when vehicles interact with roadside hardware like guardrails, bridge rails and curbs, the interaction between the roadside hardware and the tire causes the tire to lose its air seal and “blow-out”. Once the seal between the rim and rubber tire is lost, the tire deflates. The behavior of the deflated tire is much different than the behavior of an inflated tire such that when this behavior is observed in real world crashes or in full-scale crash tests, the vehicle kinematics are strongly coupled to the behavior of the deflated tire. Accounting for this behavior in LS-DYNA models is crucial in many types of roadside hardware simulations since the forces generated by the deflated tire often introduce instability into the vehicle that can cause rollover or spinout. This paper will present a method for accounting for tire deflation during LS-DYNA simulations and will present examples of the use of this type of improved model.
Shear Deformation of High Density Aluminum Honeycombs
Authors: Lu Wei-Yang , Korellis John , Hinnerichs Terry
Published: May 2008

The orthotropic crush model has commonly been used to describe the constitutive behavior of honeycomb [1]. To completely define the model parameters of a honeycomb, experimental data of axial crushes in T, L, and W principal directions as well as shear stress-strain curves in TL, TW, and LW planes are required. The axial crushes of high-density aluminum honeycombs, e.g., 38 pcf (pound per cubic foot), under various loading speeds and temperatures have been investigated and reported [2]. This paper describes experiments and model simulations of the shear deformation of the same high-density aluminum honeycomb. Results of plate shear test, beam flexure test, and off-axis compression are presented and discussed.
Development of a Stochastic Approach for Vehicle FE Models
Authors: Riha David , Hassan Joseph , Forrest Marlon , Ding Ke
Published: May 2008

This paper describes the development of a mathematical model capable of providing realistic simulations of vehicle crashes by accounting for uncertainty in the model input parameters. The approach taken was to couple advanced and efficient probabilistic and reliability analysis methods with well-established, high fidelity finite element and occupant modeling software. Southwest Research Institute has developed probabilistic analysis software called NESSUS. This code was used as the framework for a stochastic crashworthiness FE model. The LS-DYNA finite element model of vehicle frontal offset impact and the MADYMO model of a 50th percentile male Hybrid III dummy were integrated with NESSUS to comprise the crashworthiness characteristics. The system reliability of the vehicle is computed by defining ten acceptance criteria performance functions; four occupant injury criteria and six compartment intrusion criteria. The reliability for each acceptance criteria was computed using NESSUS to identify the dominant acceptance criteria of the original design. The femur axial load acceptance criteria event has the lowest reliability (46%) followed by the HIC event (58%) and the door aperture closure event (73%). One approach to improve the reliability is to change vehicle parameters to improve the reliability for the dominant criteria. However, a parameter change such as vehicle strength/stiffness may have a beneficial effect on certain acceptance criteria but be detrimental to others. A system reliability analysis was used to include the contribution of all acceptance criteria to correctly quantify the vehicle reliability and identify important parameters. A redesign analysis was performed using the computed probabilistic sensitivity factors. These sensitivities were used to identify the most effective changes in model parameters to improve the reliability. A redesign using 11 design modifications was performed that increased the original reliability from 23% to 86%. Several of the design changes include increasing the rail material yield strength and reducing its variation, reducing the variation of the bumper and rail installation tolerances, and increasing the rail weld stiffness and reducing its variation. The results show that major reliability improvements for occupant injury and compartment intrusion can be realized by certain specific modifications to the model input parameters. A traditional (deterministic) method of analysis would not have suggested these modifications.
Interactive Failure in High Velocity Impact of Two Box Beams
Authors: Xue Liang , Zheng Li , Wierzbicki Tomasz
Published: May 2008

The research reported in the present paper has been motivated mainly by the need of reconstructing the airplane impact damage of the WTC Towers. The initial phase of this catastrophic event was dominated by fracture, leading to breakup and fragmentation of the airplane and severance of a large number of external columns. However, the role of fracture has been de-emphasized in the recent attempt to reconstruct the 9/11 attack [1–3]. The objective of this paper is to raise the phenomenon of ductile fracture to the level of a main factor controlling the initial phase of the September 11th event. Our philosophy is similar to that employed by Lawver et al [4], but we are treating ductile fracture in a much more comprehensive way including the topics of material testing, calibration, validation and finite element implementation. A particular scenario considered is the impact of a corresponding section of the wing of the Boeing 767 into one external box column of a Twin Tower. Real dimensions are taken for the WTC column and the wing section is represented as a thin-walled box beam. Both members undergo extensive plastic deformation and fracture. In developing computer models, special attention was paid to the choice of the element type (shell vs. solid), contact algorithm, element removal (erosion) option, and above all the fracture criterion. Most calculations were done using LS-DYNA for several combinations of the equivalent strain to fracture of the aluminum alloy wing and the steel columns. In addition five ABAQUS runs were made with a newly developed criterion for ductile fracture with a cut-off value for negative triaxialities. Impact velocities considered ranged from 120 to 480 m/sec where 240 m/sec was the actual impact speed of the Boeing 767. It was found that the damage process is localized in the immediate velocity of the impact area. The fracture process initiates at the impacting flanges in the Mode III out-of-plane shear, continues down the webs as a combined shear/tension (tearing) and finally ends up as a tensile fracture of the rear flanges. While the airplane wing box was almost always completely cut, the WTC column was often partially penetrated for a wide range of the equivalent strain to fracture. It was also found that introducing a modified fracture locus changes the sequence of failure pattern as well as the mode of fracture.
2002-2003 Report of Survey Committee: Progress in Passenger Rail Vehicles, Components and Systems
Authors: Hesser Kenneth R.
Published: May 2008

This annual ASME committee report covers selected worldwide developments in passenger rail vehicles, components and systems. The information contained herein was obtained from responses to survey letters sent to the manufacturers of passenger rail vehicles and components, and from review of trade and technical publications.
Processing Considerations for Salicylic Acid-Based Polymers
Authors: Wagner Eva , Uhrich Kathryn , Twardowski Thomas
Published: May 2008

This paper describes some of the processing issues for extruding salicylic acid-based polymer prodrugs into fibers for medical devices. Polymeric prodrugs, in which a drug is polymerized in a degradable polymer that delivers controlled quantity of the drug to a targeted site in the body as the device degrades, are a new approach to controlled release. Hollow fibers were produced by solution spinning. Solid fibers were formed by melt processing. The salicylic acid polymers exhibited shear-thinning behavior. The viscosity exhibited pronounced temperature dependence.
Approximate Explicit Calculation of First Vibration Frequencies of an Unsymmetrical High Speed Rotor
Authors: Antoine J. F. , Abba G. , Sauvey C.
Published: May 2008

In order to easily predict and optimize the dynamic behavior of a high speed switched reluctance motor, a full analytic model, that gives directly and quickly the three first eigenfrequencies of the rotor, is proposed. The rotor is modelled as a 3 DOF Timoshenko’s beam model. The stiffness matrix is calculated with the Castigliano’s second theorem in structural analysis, which allows to obtain explicitly the eigenfrequencies expression and prevents to use classical finite element analysis. The influence of design and material modifications is studied and the dynamic behavior quickly predicted. The calculation time needed for testing a geometry is strongly smaller than with a finite element analysis.
Electron Transport in Gas Diffusion Layer of Polymer Electrolyte Fuel Cells
Authors: Meng Hua , Wang Chao-Yang
Published: May 2008

A three-dimensional, single-phase, isothermal numerical model of polymer electrolyte fuel cell (PEFC) is employed to investigate effects of lateral electron transport in gas diffusion layer (GDL) for the first time. An additional electron transport equation is solved in the catalyst and gas diffusion layers, and in the current collector. It is found that the lateral electronic resistance plays a critical role in determining the current distribution and cell performance. With reduced GDL thickness, the effect of the lateral electronic resistance becomes even stronger, because the cross-sectional area of GDL for lateral electron transport is smaller. Inclusion of GDL electron transport enables the thickness of GDL and widths of the gas channel and current collecting land to be optimized for better current distribution and cell performance. In addition, the present model enables: (1) direct incorporation of contact resistances emerging from GDL/catalyzed membrane and GDL/land interfaces in the solution process, (2) natural implementation of the total current as the more useful boundary condition than the cell voltage, and (3) stack modeling with cells connected in series and hence having the identical total current.
Effects of Inlet Flow Field Conditions on the Stall Onset of Centrifugal Compressor Vaned Diffusers
Authors: Deniz Sabri
Published: May 2008

This paper considers the performance and operating range of vaned diffusers for use in high performance centrifugal compressors. An experimental and numerical investigation is performed to determine the effects of inlet flow field conditions on pressure recovery and stall onset of different type vaned diffusers, such as discrete-passage and straight-channel diffusers. Diffuser inlet flow conditions examined include Mach number, flow angle, blockage, and axial flow non-uniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. Unsteady pressure measurements showed the operating range of a compressor stage was limited by the onset of rotating stall, triggered by the loss of stability in the vaned diffuser, independent of the impeller operating point. For both diffusers investigated, loss of flow stability in the diffuser occurred at a critical value of the momentum-averaged flow angle into the diffuser. To provide additional information on diffuser flow development and to complement previous experimental work performed on straight-channel type diffuser, a computational investigation has been undertaken and important results are presented.