bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-Parameter Estimation in Hyperthermia Problem by Using an Optimal Choice of Descent Parameters in Iterative Methods
Authors: Loulou Tahar , Scott Elaine P.
Published: May 2008

This paper describes a numerical procedure conducted to estimate thermo-physical properties of the human tissue during hyperthermia treatment of a cancerous region. The estimation algorithm is based on the solution of an inverse heat conduction problem. The Gauss-Newton method is used to estimate simultaneously the volumetric heat capacity, the thermal conductivity, and the volumetric blood rate (blood perfusion) in the bio-heat transfer equation during a hyperthermia treatment cycle. The treatment quality of hyperthermia is analyzed by the computation of the thermal dose which is obtained from the resulting temperature field in the tissue. The importance of an accurate estimation of the thermo-physical properties of the tissue lies in that they are the most important factors for achieving a high precision heating cycle which results in an optimized treatment. The inverse analysis is based on the temperature measurements taken inside the cancerous tissue region during the transient heating process. An experimental optimization procedure is conducted to make the estimated parameters as accurate as possible. Several numerical tests were performed and show that the developed method provides an accurate estimation of thermo-physical properties in a very short practical time. As the blood perfusion is very sensitive to the temperature variation in the tissue, this estimation tool can be implemented during one cycle treatment which results in an on-line thermo-physical parameter correction while the treatment is performed.
Closed Loop Impingement Cooling System for High Power Density Electronic Devices
Authors: Bhunia Avijit , Chen Chung-Lung
Published: May 2008

Liquid jet and droplet impingement cooling of the 1cm2 base plate area of a 1mm2 Silicon carbide diode is reported. DI water flowing from a single or two-orifice injection port of diameter 118–130μm at a rate of 4.5–15ml/min, impinges on the diode base plate and undergoes phase change. For practical implementation of liquid impingement cooled electronic devices, a closed loop system with a recovery scheme for the vapor and the excess liquid is developed. Boiling of the thin liquid film on the base plate surface is observed at a superheat of 10°C, measured at a location 3.2mm away from the diode footprint area on the base plate, and a maximum phase change heat transfer effectiveness of 39%. The effects of liquid flow rate, and injection pattern (single or two-orifice) on the heat transfer and the diode current-voltage characteristics are investigated.
An Experimental Investigation of Flow Past a Smooth Circular Cylinder at the Sub-Critical Region
Authors: He Chuan , Long Tianyu , Xin Mingdao , Chung Benjamin T. F.
Published: May 2008

An experimental investigation for the incompressible flow past a smooth circular cylinder at the sub-critical region is presented in detail. A smooth circular cylinder is placed in a wind tunnel and the local pressure distribution on the cylinder surface is measured subtly. The Reynolds Number ranges from 104 to 8 × 104. The experimental data show that there exists a nadir point of the surface pressure in the front the across section of the cylinder and the pressure nadir position varies with the Reynolds number. It is found that this point tends to move forward of the cylinder as Reynolds number increases. Based on the present experimental findings, a simple algebraic expression describing the relationship between the location of the pressure’s nadir and Reynolds number is proposed.
The Effect of Convective Heat Transfer Instabilities on the Diameter of Polymer Optical Fiber
Authors: Reeve Hayden M. , Mescher Ann M. , Emery Ashley F.
Published: May 2008

The effect of various natural convection regimes on the diameter of drawn polymer fiber was studied experimentally. Results indicate that as the buoyant potential of air within a cylindrical furnace enclosure is increased the natural convection regime transitions from laminar to oscillatory, and finally, to chaotic flow. The time-dependent heating caused by the oscillatory and chaotic regimes alters the rheology of the elongating polymer preform, causing detrimental time-dependent variations in the fiber diameter. The gas-phase temperature oscillations recorded on opposite sides of the necking perform were not identically in-phase indicating the convective flow is asymmetric in nature. The period of the recorded oscillations was found to be a function of the driving temperature difference, consistent with prior investigations. Furthermore, near the transition to chaotic flow sub-harmonics were observed within the recorded oscillations. When subjected to oscillatory and chaotic natural convection the standard deviation of the fiber diameter variations was up to 2.5 to 10 times greater, respectively, than that measured under laminar heating conditions. This represents a significant instability mechanism, one that has not been investigated within the context of the fiber drawing process to date.
Validation of Twin-Screw Polymer Extruder Modeling
Authors: Jaluria Yogesh
Published: May 2008

The mathematical and numerical modeling of twin-screw polymer extruders is examined with respect to accuracy of results and validity of the simulation. A numerical model is developed incorporating the translation region, which is similar to a single-screw extruder channel, and the intermeshing, or nip, region. The numerical modeling is carried out for steady and time-dependent operation, considering various polymeric materials like polyethylene and corn meal. A range of design parameters and operating conditions are considered. The results are evaluated in terms of the expected physical behavior of the system and compared with experimental results available in the literature to determine the accuracy of the predictions. In many cases, only qualitative comparisons are possible since the operating conditions and design parameters are not explicitly known. However, the basic trends are as expected and good quantitative comparisons with experimental data is used to validate the model. Validated numerical models can extend the domain of relevant inputs for process design and optimization.
Hydrodynamics of Rotating Bubble Flow
Authors: Borisov I. , Khalatov A. , Wang T.
Published: May 2008

This paper presents a new set of experimental data on the hydrodynamics of rotating bubble flow and is a continuation of previous gas-liquid rotating flow studies. The new data include the surface friction on both end walls of the vortex chamber, and static pressure distributions at the exit of swirl generator slots and on the inner surface of vortex chamber. The corotating disk technique was used to determine the friction momentum measured by the dynamometer. The air-liquid velocity was registered by the blade-anemometer with a light modulator fixed on its axis. The friction coefficient was found based on the conservation of rotational momentum and the assumption of constant air-liquid rotational velocity throughout the two-phase flow field. The ‘jump-like’ reductions in static pressure were registered on the border between the incoming jets and the bubble flow. A new correlation describing linear gas-liquid rotating velocity is given. The static pressure measurements are in reasonable agreement with the data predicted from the theoretical model.
Computer Simulations of Non-Newtonian Fluid Flow in Rectangular Cavity
Authors: Bakhtiyarova Ayten S.
Published: May 2008

In this paper we present the results of the CFD simulations of the non-Newtonian fluid flow in rectangular cavity. FLOW-3D commercial software (Flow-Simulations, Inc.) has been used to predict flow velocity distributions and pressure losses when non-Newtonian fluid flows through the square cavity.
Run-Time Three-Dimensional Blend-Path Generation for Cobot Constraint Surfaces
Authors: Faulring Eric L. , Colgate J. Edward
Published: May 2008

During human-cobot interaction, transitions often occur between free mode operation and constraint surface following. This paper considers the following typical scenario: an operator of a three-dimensional (e.g. x-y-z or x-y-θ) cobot commands a “join” from free mode to a one-dimensional constraint path. To ensure that this transition is smooth and responsive, a “blend path” is computed that joins the cobot’s initial location to a location on the constraint path. The blend path must match tangency and curvature at each end, and must also exhibit continuous curvature. A novel “triple-clothoid” algorithm is developed that meets these requirements. In addition, we demonstrate that the triple-clothoid is particularly amenable to x-y-θ systems via implementation on a planar cobot.
The Design and Development of 3DP Cobotic Manipulator
Authors: Wannasuphoprasit Witaya , Sirikasemsuk Sirisak
Published: May 2008

This paper describes development of a 3-Dimensional Workspace Passive Cobotic Manipulator. The cobot has 3 dimensional workspace (x,y,z). Inspired by previous works of Scooter1 and Extreme Joystick2 cobots, the 3DP Cobotic Manipulator consists of a spherical ball and three steering Cobotic joints and mechanical links. The sphere-rotating axis is constraint to rotate about its own center. The ball has 3 C-space, roll, pitch, and yaw (φ, α, β˜) There is a two-link manipulator attached on top of the ball. The function of this links is to transform a spherical C-space, (φ, α, β) to the end-effector’s C-space (x-y-z).
Turbulent Friction Factor for a Rod Bundle in Consideration of a Subchannel Geometry
Authors: Park Joo Hwan , Jeong Chang Joon , Yang Myung Seung , Oh Dong Suk
Published: May 2008

A generalized turbulent friction factor for a rod bundle was developed based on “Law of the Wall” for a tube. It was included two parameters which are one parameter of hydraulic diameter and flow area of a subchannel and rod bundle and another parameter (called geometry parameter hereinafter) of subchannel configuration and pitch-to-diameter ratio (P/D) for a single subchannel. The turbulent geometry parameter for a single subchannel has been used as a constant on the previous works but it was found to be dependent on subchannel shapes and P/D from the present work. Hence, it was modeled as a function of the subchannel shapes and P/D from 1.0 to 1.5. The turbulent geometry parameters for single subchannels were validated by the theoretical derivation of a triangular and square subchannel. Those are compared and agreed well with the previous measurement data for 4 kinds of subchannel types such as a triangular, a square, a wall and a corner subchannel. The present model of turbulent friction factor for a rod bundle included the turbulent geometry parameter has been compared with the various experimental results for circular tubes and hexagonal tubes with various rod numbers. The predicted turbulent friction factors for those rod bundles were agreed excellently with experimental results.
Nanostructuring With Scanning Probe Microscope Tip Irradiated With Femtosecond Laser
Authors: Chimmalgi Anant , Choi Taeyoul , Grigoropoulos Costas P.
Published: May 2008

Nanostructures, which have characteristic dimensions that are difficult to achieve by conventional optical lithography techniques, are finding ever-increasing applications in a variety of fields. High resolution, reliability and throughput fabrication of these nanostructures is essential if applications incorporating nanodevices are to gain widespread acceptance. Owing to the minimal thermal and mechanical damage, ultra-short pulsed laser radiation has been shown to be effective for precision material processing and surface micro-modification. In this work, nanostructuring based on local field enhancement in the near field of a Scanning Probe Microscope (SPM) probe tip irradiated with femtosecond laser pulses has been studied. High spatial resolution (~10–12nm), flexibility in the choice of the substrate material and possibility of massive integration of the tips make this method highly attractive for nanomodification. We report results of nanostructuring of gold thin film utilizing an 800nm femtosecond laser system in conjunction with a commercial SPM in ambient air. Further, Finite Difference Time Domain (FDTD) simulation results for the spatial distribution of the laser field intensity beneath the tip are presented. Potential applications of this method include nanolithography, nanodeposition, high-density data storage, as well as various biotechnology related applications.
Numerical Solution of Melting Processes for Unfixed Phase Change Material in the Presence of Electromagnetic Field: Simulation of Low Gravity Environment
Authors: Gonc¸alves Eduardo , Faghri Mohammad , Asako Yutaka , Charmchi Majid
Published: May 2008

Electromagnetic simulation of low-gravity environment has been numerically investigated to study the transport phenomena associated with melting of an electrically conducting Phase Change Material (PCM) inside a rectangular enclosure. Electromagnetic fields are configured in such a way that the resulting Lorentz force can be used to damp and/or counteract the natural convection as well as the flow induced by sedimentation and/or floatation, and thereby simulating the low gravity environment of outer space. The governing equations are discretized using a control-volume-based finite difference scheme. Numerical solutions are obtained for true low-gravity environment as well as for the simulated-low-gravity conditions due to electromagnetic forces. The results show that when the Lorentz force is caused by the presence of magnetic field alone, the low-gravity condition is simulated by the damping effect, which is shown to have a profound effect on the flow field. On the other hand, it is shown that under electromagnetic field simulation, where the Lorentz force is caused by the transverse electric and magnetic fields, it is possible to minimize the flow field distortion caused by the high magnetic field and therefore achieving a much better simulation of low-gravity.
Application of the Cumulative Wavenumber Approach for Modeling Radiative Transfer in H2O Under Non-Isothermal and Non-Homogeneous Conditions
Authors: Solovjov Vladimir P. , Webb Brent W.
Published: May 2008

Recently, the cumulative wavenumber approach was formulated and its viability demonstrated in predictions of radiative heat transfer in high temperature CO2. The approach allows for local spectrum correlation, rather than full-spectrum correlation as commonly done previously. This work reports on the generation of cumulative wavenumber data for H2O, and explores solutions using the cumulative wavenumber approach for water vapor (balance nitrogen) in homogeneous/non-isothermal media, and extends the technique to non-homogeneous/non-isothermal scenarios. Model predictions are compared with rigorous line-by-line benchmark integration of the Radiative Transfer Equation, with the same spectral database (HITEMP) used in both model and line-by-line benchmark predictions.
Modeling of Radiation Heat Transfer in Glass Melts
Authors: Golchert B. , Chang S. L. , Zhou C. Q.
Published: May 2008

Glass furnaces combust fuels and oxidizers so that the batch will be melted and the molten glass refined. The heat generated from the combustion space is mainly transmitted to the glass melt by radiation. This radiation is strongly wavelength dependent due to the nature of soot and carbon dioxide/water emission. Conventional wisdom indicates that the transport of radiation in molten glass can be modeled using a diffusion approximation. However, for many glass compositions, this approximation may not be justified since there is appreciable transmission of thermal energy at lower wavelengths. To account for the detailed transmission of radiation in the glass melt, a recently developed radiation model was incorporated into a glass melt simulation. This spectral model rigorously conserves emitted and absorbed energy throughout the melt and the surrounding walls. The glass melt flow simulation is a multi-phase reacting flow computational fluid dynamic code that accounts for the solid batch material, liquid glass, and gas bubble. This paper presents details of the radiation model along with results depicting the effect of the detailed radiation transmission on the glass melt flow field.
Mathematical Modeling of the Geothermal Reservoir With Multi-Borehole Circulating System
Authors: Fomin Sergei , Chugunov Vladimir , Yoshida Kei , Hashida Toshiyuki
Published: May 2008

A three-dimensional model (FRACSIM-3D) developed in Tohoku University for numerical simulation of heat and fluid flow within the fractured media is used in the analysis of geothermal reservoir performance. The model effectively simulates two main stages of the geothermal reservoir exploitation, namely, (i) hydraulic stimulation of the existing natural fractures within the Hot Dry Rock (HDR) reservoir and (ii) forced convection through the fractured media when the filtrating fluid extracts the heat from the hot rock and delivers it to the production well. Since the heat accumulated by the fluid within the system of injection boreholes can constitute a substantial fraction of the total thermal output of the geothermal power plant, the model of heat and mass transfer in the fractured media at the heat extraction stage should be coupled with the equations which describe the heat transport in the system of injection and production wells. Mathematical modeling of heat flow within the multi-borehole circulating system is proposed in this study. On the basis of this model the major parameters that affect the thermal productivity of the geothermal power plant are analyzed. The effective regimes of the fluid circulation and optimal geometry of the multi-borehole system are proposed.
Numerical Modeling of a Lifted Laminar Coflow Methane Diffusion Jet Flames Using Detailed Chemistry and Non-Grey Gas Radiation Models
Authors: Liu Fengshan , Guo Hongsheng , Smallwood Gregory J.
Published: May 2008

Two lifted laminar coflow non-sooting methane diffusion jet flames, one diluted by nitrogen and the other diluted by carbon dioxide, at atmospheric pressure were calculated using detailed chemistry and complex thermal and transport properties. Chemical reactions were modeled using the GRI-Mech 3.0 mechanism with species and reactions related to NOx formation removed. Radiation heat transfer by CO, CO2, and H2O was calculated using the discrete-ordinates method coupled with a statistical narrow-band correlated-k based band model. Calculations of each flame were performed with and without radiation absorption term in the radiative transfer equation in order to provide a quantitative evaluation of the importance of radiation absorption in these two lifted flames. Numerical results show that radiation absorption is relatively unimportant in the nitrogen diluted flame but becomes important in the carbon dioxide diluted flame.
Product Strength and Orientation Manipulation via Vibration-Assisted Injection Molding
Authors: Angstadt David C. , Coulter John P.
Published: May 2008

This investigation focuses on determining why polystyrene ASTM specimens exhibit an increase in tensile strength when processed by vibration assisted injection molding (VAIM) while polycarbonate parts do not. VAIM is one of several polymer processing methods that attempt to improve product properties via manipulation of the polymer melt. Observation of birefringence patterns in VAIM processed polystyrene samples show a significant impact on molecular orientation. The same studies were conducted on opaque polycarbonate and were unable to determine the degree of molecular orientation via birefringence measurement. It was theorized that VAIM did not produce significant orientation due to its higher thermal conductivity and stiffer backbone. It has been determined by this investigation that VAIM processing does impart significant molecular orientation in polycarbonate specimens but still does not increase its UTS. It is proposed that increased molecular orientation induced by VAIM processing inhibits crazes from growing into cracks. VAIM therefore favors polymers that fail by crazing (e.g., polystyrene) rather than those that fail by shear yielding (e.g., polycarbonate).
Modeling of Annular Plate With Piezoelectric Actuators for Active Vibration Control
Authors: Sekouri El Mostafa , Hu Yan-Ru , Ngo Anh Dung
Published: May 2008

This paper presents an analytical approach for modeling the mechanical-electrical response of annular plate components of space structures containing distributed piezoelectric under static as well as dynamic mechanical or electrical loadings. The analytical approach used in this paper is based on the Kirchhoff plate model. The equations governing the dynamics of the plate, relating the strains in the piezoelectric elements to the strain induced in the system, are derived for annular plate using the partial differential equation. The natural frequencies and mode shapes of the structures were determined by modal analysis. In addition, the harmonic analysis is performed for analyzing the steady-state behavior of the structures subjected to cyclic sinusoidal loads. Numerical simulation results are obtained using finite element approach. Experiments using a thin circular aluminum plate structure with distributed piezoelectric actuators were also conducted to verify the analysis and the computer simulations. Relatively good agreements between the results of these three approaches are observed. Finally, the results show that the model can predict natural frequencies and modes shapes of the plate very accurately.
Micro-Signals and Modal Potentials of Nonlinear Deep and Shallow Conical Shells
Authors: Chai W. K. , Smithmaitrie P. , Tzou H. S.
Published: May 2008

Conventional sensors, such as proximeters and accelerometers, are add-on devices usually adding additional weights to structures and machines. Health monitoring of flexible structures by electroactive smart materials has been investigated over the years. Thin-film piezoelectric material, e.g., polyvinylidene fluoride (PVDF) polymeric material, is a lightweight and dynamic sensitive material appearing to be a perfect candidate in monitoring structure’s dynamic state and health status of flexible shell structures with complex geometries. The complexity of shell structures has thwarted the progress in studying the distributed sensing of shell structures. Linear distributed sensing of various structures have been studied, like beam, plate, cylindrical shell, conical shell, spherical shell, paraboloidal shell and toroidal shell. However, distributed sensing control of nonlinear shell structures has not been carried out rigorously. This study is to present the microscopic signals, modal voltages and distributed micro-sensing components of truncated nonlinear conical shells laminated with distributed infinitesimal piezoelectric neurons. Signal generation of distributed neuron sensors laminated on conical shells is defined first. The dynamic signal of truncated nonlinear conical shell consists of microscopic linear and nonlinear membrane strain components and linear bending strain component based on the von Karman geometric nonlinearity. Micro-signals, modal voltages and distributed sensing components of two different truncated nonlinear conical shells are investigated and their sensitivities discussed.
On an Iterative General-Order Perturbation Method for Multiple Structural Damage Detection
Authors: Wong C. N. , Zhu W. D. , Xu G. Y.
Published: May 2008

A general-order perturbation method involving multiple perturbation parameters is developed for eigenvalue problems with changes in the stiffness parameters. The perturbation solutions and eigenparameter sensitivities of all orders are derived explicitly. The perturbation method is used iteratively in conjunction with an optimization method in a robust damage detection algorithm. The generalized inverse method is used efficiently with the first order perturbations, and the gradient and quasi-Newton methods are used with the higher-order perturbations. Numerical simulations demonstrated the effectiveness of the algorithm in detecting the locations and extents of small to large levels of damage.
An Experimental Investigation of Soot Formation During Nonpremixed Turbulent Combustion of Hydrocarbon Fuels
Authors: Yang Bo , Koylu Umit O.
Published: May 2008

Although practical combustion devices involve turbulent conditions, crucial soot investigations have generally been based on the data obtained from laminar flames with relatively limited number of studies in the literature on turbulent flames. Motivated by the need for data that can allow proper characterization of soot properties within the fuel-rich regions of turbulent flames, optical experiments were carried out within hydrocarbon-fueled nonpremixed turbulent jet flames. Specifically, two gaseous fuels, ethylene and acetylene, were burned at relatively high Reynolds numbers in air at atmospheric pressure. In-situ diagnostics included laser scattering and extinction techniques to determine the soot field at various axial and radial positions in these flames. The findings are relevant not only to developing advanced computational models for accurate predictions of radiative transfer but also to controlling and predicting performance and pollutant emissions in combustion systems.
Passive Damping Augmentation Using Macro-Fiber Composite Actuators
Authors: Adachi Kazuhiko , Park Gyuhae , Inman Daniel J.
Published: May 2008

This paper aims at presenting the structural vibration-suppression capability of the recently developed Macro-Fiber Composite (MFC) actuator as a passive piezoelectric absorber using an inductive resonant shunt circuit. The resistance and inductance of the series RL shunt circuit are designed by the analogy with the single-degree-of-freedom mechanical damped vibration absorber and by using the maximum power transfer theorem of the electric network. Experimental test of a simple cantilevered beam demonstrates that the MFC actuator has excellent capability of improving the dynamic response of the beam as a piezoelectric damping system. The damping enhancement performance of the MFC actuator is superior to that of the conventional monolithic PZT actuator.
Mechanical Deformation of Field-Coupled Materials
Authors: Chaplya Pavel M. , McKnight Geoffrey P. , Carman Gregory P.
Published: May 2008

This article describes remarkable similarities in the nonlinear mechanical response of different active/smart materials despite fundamental differences in the underlying mechanisms associated with each material. Active/smart materials (i.e., piezoelectric (PZT-5H), magnetostrictive (Terfenol-D), and shape memory alloys (NiTi)) exhibit strong non-linear mechanical behavior produced by changing non-mechanical internal states such as polarization, magnetization, and phase/twin configuration. In active/smart materials the initial deformation proceeds linearly followed by a jump in strain associated with the transformation of an internal non-mechanical state. After the transformation, the mechanical response returns to linear elastic. Upon unloading, a residual strain is observed which can be recovered with the application of a corresponding external field (i.e., electric, magnetic, or thermal). Due to coupling between applied fields and non-mechanical internal states, mechanical deformation is also a function of applied external fields. At a critical applied field, the residual strain is eliminated, providing repeatable cyclic characteristics that can be used in passive damping applications. Even though different intrinsic processes (i.e., polarization, magnetization, and phase/twin variant composition) govern the deformation of each material, their macroscopic behavior is explained using a unified volume fraction concept. That is, the deformation of piezoelectric material is described in terms of the volume fraction of ferroelectric domains with polarization parallel or orthogonal to the applied load; the deformation of magnetostrictive materials is described in terms of the volume fraction of magnetic domains with magnetization parallel or orthogonal to the applied load; and the deformation of shape memory material is described in terms of the volume fraction of twin variants that are oriented favorably to the applied load. Although the qualitative behavior of each material is similar, the average magnitude of stress required to induce non-linearity varies from ~10 MPa for Terfenol-D to ~65 MPa for PZT-5H to ~300 MPa for NiTi shape memory alloy. It is hypothesized that a composite material made of these materials connected in series would exhibit passive damping over a wide range of applied stress.
Effect of Centrifugal Force Effect on Magneto-Rheological Fluid Clutches
Authors: Neelakantan Vijay A. , Washington Gregory N.
Published: May 2008

The property of magnetorheological fluids to change their yield stress depending on applied magnetic fields can be employed to develop many controllable devices one of them being MR fluid based clutches. One major problem however with MR fluid based clutches is that at high rotational speeds, the iron/ferrous particles in the MR fluid centrifuge due to very high centrifugal forces. Thus the particles move outward as the speed increases thereby making the fluid non-homogeneous. Many times however the initial analysis assumes fluid homogeneity, which is really not the case. In this paper this problem is addressed by assuming various volume fraction profiles describing the fluid particle orientation. Two cases, one with a linear profile and the other with an exponential profile are discussed. Expressions for the torque transmitted are derived at for both disc shaped and cylindrical shaped clutches. In addition, the use of a MR sponge based clutch that may indeed reduce the effect of centrifugal forces significantly is described. The design methodology and configuration for the sponge clutch are also discussed. An experimental set up used to test the clutch is also described.
Micro Combustion Research for Micro Thermophotovoltaic Systems
Authors: Yang W. M. , Chou S. K. , Shu C. , Xue H.
Published: May 2008

A research program is currently underway with the purpose of developing a novel, MEMS-sized thermophotovoltaic (TPV) system, which would use hydrogen as fuel and would be capable of delivering power on the order of watts in a package less than one cubic centimeter in volume. High surface to volume ratio is very favorable to the output power density per unit volume, though it tends to suppress ignition and quench the reaction in micro devices. This is the most attractive feature of micro TPV system. As part of an effort to develop such a micro power system, numerical and experimental works are carried to test feasibility of combustion in micro devices and determine relevant factors affecting micro combustion. Results indicate micro flame tube combustor is favorable in keeping the uniform of temperature along the wall, and stable combustion could be achieved in a tube with a sudden step within wider flow rate and wider hydrogen/air ratio than in straight tube. High and uniform temperature has been achieved along the wall of flame tube, which is very important to the efficiency of micro TPV system.
Modified Stewart Platform for Spacecraft Thruster Vector Control
Authors: Ghasemi-Nejhad Mehrdad N. , Doherty Kathleen M.
Published: May 2008

Adaptive or intelligent structures which have the capability for sensing and responding to their environment promise a novel approach to satisfying the stringent performance requirements of future space missions. This paper introduces an intelligent modified Stewart platform as an adaptive thruster mount structure with precision positioning and active vibration suppression capabilities for use in space satellites as an intelligent thruster vector control platform. The intelligent thruster mount would utilize piezoelectric sensors and actuators for precision positioning and active vibration suppression to provide fine-tuning of position tolerance for thruster alignment and low transmissibility of vibration to the satellite structure. Similar intelligent platform, introduced here, may be used for sensitive equipment aboard of the spacecraft to suppress the vibration that resonates throughout the spacecraft structure during a thruster firing, solar panel boom opening/reorientation, etc. This vibration renders sensitive optical or measurement equipment non-operational until the disturbance has dissipated. This intelligent system approach would greatly enhance mission performance by fine tuning attitude control, potentially eliminating the non-operational period as well as minimizing fuel consumption utilized for position correction. The configuration of the intelligent thruster mount system is that of a modified Stewart platform. This system is an intelligent tripod with two in-plane rotational degrees of freedom (2-DOF) for the top device-plate. Precision positioning of this structure is achieved using active members that extend or contract to tilt the upper device-plate where the thruster is mounted. An inverse analysis of a modified Stewart platform is employed to determine the required axial displacement of the active struts for the desired angular tilt of the upper device-plate. The active struts can participate in precision positioning as well as vibration suppression of the upper device-plate where the thruster, i.e., the source of the unwanted vibrations and misalignment, is mounted. The proposed Thruster Vector Control (TVC) intelligent platform offers a promising method for achieving fine tuning of positioning tolerances of a thruster as well as minimizing the effects of the disturbances generated during thruster firing in spacecraft such as a satellite.
Effect of Thermodynamic Conditions on Droplet Size in Diesel Engines: Importance of an Advanced Surface Tension Model
Authors: Delplanque J.-P. , Labs J. , Lengsfeld C. S. , Parker T. E.
Published: May 2008

The effort described in this extended abstract aims at elucidating how droplet secondary breakup is affected by surface tension behavior at thermodynamic conditions relevant to diesel engine operation. The droplet surface tension coefficient is calculated using the method of MacLeod and Sugden, which takes into account mixture and high-pressure phase equilibrium effects. To this end, high-pressure binary phase equilibrium is computed for prescribed droplet interface conditions using a Peng-Robinson equation of state. Finally, droplet propensity to secondary breakup is estimated based on recently developed criteria. The model thus obtained is compared to spray sizing data acquired in a Diesel Engine Simulator for dodecane.
Flame Blowoff Limit Phenomenon of Turbulent Jet Diffusion Flames With Annular Counterflow
Authors: Torii Shuichi , Chan Sze Man Simon , Yano Toshiaki
Published: May 2008

The present study deals with the transport phenomena of turbulent jet diffusion flames with air-suction flow and the possibility of extending the flame blow-off limits through the shear stress augmentation using the annular counterflow technique. The experimental apparatus employed here comprises a fuel nozzle placed at the center of a concentric annulus with an outer cylinder adopted to encompass the nozzle. Fuel jet is allowed to eject upwards and turbulent jet diffusion flames are formed by igniting the jet and by increasing the volume flow rates of fuel. It is found that (1) the augmentation of turbulent shear effect exerted on the shear layer formed between the jet flames and the opposed flow of air causes an extension of flame blowoff limits, (2) by using the annular counterflow technique, the flame lift-off height is suppressed than the normal diffusion flame, and (3) its height is correlated using the effective air-suction momentum flux proposed here.
Boiling Heat Transfer to Subcooled Nitrogen From Thin Wire in Narrow Space
Authors: Takata Y. , Kubota H. , Ito T.
Published: May 2008

Boiling heat transfer characteristic of liquid nitrogen was investigated to obtain the basic information on cooling design of high-TC superconducting transformer which is cooled by subcooled nitrogen to avoid bubble formation. Thin wire of platinum-30%/rodium in diameter of 50μm was used as heater and thermometer. The wire was covered outside with acrylic tube to simulate the practical winding condition and we examined the effect of space restriction on boiling heat transfer characteristics. The subcooling of nitrogen tested was between 0 and 10.4K. The results show that the CHF and MHF increase considerably with the degree of subcooling.
The Simulation of Mechanical Systems Kinematics and Dynamics
Authors: Yuan Q. K.
Published: May 2008

The Kinematics and dynamics is the important properties of a mechanical system or a mechanical product. In this paper, a describing method by the symbol sets, motion equations auto-building method and auto-solving method are discussed, a software system MSKDSP (Mechanical System Kinematics and Dynamics Simulation Program) is developed, and an example is given.
Thermal Assessment of a Power Amplifier Module in Wireless Handsets
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom
Published: May 2008

Increased functionality of microelectronic packages for commercial applications leads to the necessity of identifying packaging solutions with high standards for thermal performance. A detailed numerical analysis examines the thermal characteristics of a power amplifier module for time division multiple access (TDMA), using commercially available software. The increasing trend in power levels and densities leads to the need of design thermal optimization, either at the module level or at the system (module board stack-up) level. Several designs are investigated for thermal performance and the best thermal design is identified. Initial study focuses on assessing the thermal performance of a baseline design. The peak temperature reaches 144°C, about 60°C temperature increase over the reference temperature. The peak temperature value is slightly below the limit of 150°C, and is calculated based on the optimal (temperature constant) heat sink scenario attached to the bottom face of the module. Several alternatives are investigated, by modifying the thermal via array structure and Cu plating thickness. The increase in copper plating from 0.025 mm to 0.05 mm (1 to 2 mils) has the largest impact on module’s thermal performance. The addition of solder material and radio board increases by almost 50% the overall thermal resistance, hence the estimated peak temperatures reached by the heat stages would exceed the limit. A detailed sensitivity study was completed to assess the importance of each element in the module-board stack-up. Finally, a comprehensive experimental study was completed to validate the numerical simulation. The results indicate that the error between measurements and simulation range between 5–8%.
A Multi-Level Superelement Technique for Damage Analysis
Authors: Fan J. P. , Tang C. Y. , Chow C. L.
Published: May 2008

A multi-level superelement technique is applied to model the effects of circular voids on the effective elastic properties of a material. A two-dimensional representative volume element with a circular void in its center is initially modeled by a superelement. Using this superelement, a thin planar material with circular voids is constructed. The finite element computation is then conducted to estimate the effective Young’s modulus, Poisson’s ratio and the shear modulus of the material using the ABAQUS code for different void sizes. The values of the isotropic damage variables, DE and DG, under various degree of damage are hence determined. These values are compared with those calculated by using a conventional micromechanics damage model. A new isotropic damage model is proposed based on the results of this analysis. To demonstrate the applicability of this damage model, an example case of a notched cylindrical bar under tensile loading is investigated.
Cooldown Simulation for the Compact Ignition Tokamak (CIT), Poloidal Field (PF) Coils
Authors: Mottahed Behzad , Kyto¨maa Harri
Published: May 2008

An experimental investigation was conducted to study the cooldown behavior of the Poloidal Field (PF) magnets. A full-scale model of a section of the cooling passages was built for this purpose. LN2, was used as the coolant in the vertical passages at mass fluxes ranging between 42 to 140 Kg/m2-s and heat fluxes from 17000 to 75000 W/m2 with nearly saturated liquid at the inlet. The heat flux was controlled with resistive heaters. Two distinct boiling regimes were observed. The first, Type I consists of film-boiling throughout the passage. Type II has nucleate boiling at the inlet, and is followed, in a short distance, to film-boiling. The equilibrium quality at the burnout point was calculated and was found to increase slightly with decreasing heat flux. The Leidenfrost temperature at which liquid Nitrogen wets the wall was measured to be about 180–200 K. Heat transfer coefficients in the order of 200–500 W/m2-K for film boiling and 5000 to 10000 W/m2-k for nucleate boiling in the type II regime were attained. Higher heat flux and mass flow rates resulted in higher heat transfer coefficients. Empirical correlations were obtained for the nucleate region of the type II regime.
Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
Authors: Garimella Srinivas , Killion Jesse D. , Coleman John W.
Published: May 2008

This paper reports the development of an experimentally validated model for pressure drop during intermittent flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2s and 750 kg/m2s. Results from previous work by the authors were used to select the data that correspond to the intermittent flow regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. The model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubbles and slugs. Slug frequency was estimated using a simple correlation for non-dimensional unit-cell length. The model predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.
Application of Blind Source Separation Method in Mechanical Sound Signal Analysis
Authors: Wu J. B. , Chen J. , Zhong Z. M. , Zhong P.
Published: May 2008

As the result of vibration emission in air, the mechanical noise signal carries affluent information about the working condition of machinery and it can be used in mechanical fault diagnosis. But in practice, the measured sound signal is usually the mixing of condition signal and other uncorrelated signals. And the signal received is usually of very low SNR. Therefore, to obtain the features of original signals, the mixed signals have to be separated and the uncorrelated signals have to be removed by means of the blind source separation technique. The BSS is a class of signal processing method that can recover the original signals according to the observed mixing signals. In application of BSS algorithms, it is generally supposed that the number of sources is known. But unfortunately, this is not the case in application. Then, before applying the BSS method, the singular-value analysis method is introduced to estimate the number of sound sources at first. On the other hand, to avoid the ill-conditioned problem caused by environment noise and/or measuring noise in applying BSS method, the partial singular-value analysis method is employed to select those signals with maximum information entropy from mixed signals. This method significantly reduces the distortion of separated signals. Afterward, the second order blind identification (SOBI) algorithm, one of the BSS methods, which only relies on the second order statistics of measuring signals, is utilized and it is modified, in this paper, especially for purpose of spectra separation. Finally, the spectra separation results obtained from the mixed signals measured in a semi-anechoic chamber demonstrate the availability of the presented method.
Structural/Acoustic Sensitivity Analysis of a Panel With Manufacturing Variability
Authors: Mulani Sameer B. , Allen Michael J.
Published: May 2008

Sensitivity analysis is an essential component in the design of structural/acoustic systems. Current structural/acoustic sensitivity algorithms assume deterministic system design parameters and therefore predict changes in the deterministic response of the system. Due to variability associated with manufacturing tolerances most structural/acoustic systems consist of random and deterministic structural design parameters and therefore produce a probabilistic acoustic response. In this work, a structural/acoustic sensitivity algorithm is presented that considers systems comprised of random and deterministic design parameters. The new sensitivity algorithm calculates the change in the probabilistic vibro-acoustic response of a system due to a change in a deterministic design parameter. The new algorithm uses boundary element analysis, finite element analysis, and an advanced mean value method. An elastically supported panel subject to a non-uniform load is used to illustrate the algorithm. Variability is considered in the elastic support while structural sizing parameters are taken to be deterministic. The response of the panel is defined in terms of probabilistic radiated sound power. Probabilistic sound power sensitivity results are calculated and used to predict new sound power values via finite difference analysis. These results are compared successfully to results obtained through re-analysis.
On Double Frequency Vibration of a Generator-Bearing System With Asymmetrical Stiffness
Authors: Huang Senlin , Liu Zhansheng , Su Jiexian
Published: May 2008

A finite element model for a generator-bearing system with asymmetrical stiffness is developed for investigation of the double frequency vibration. The modal reduction method is used for reducing the degrees of freedom system to improve computing efficiency, and the Newmark direct integration method is employed to solve the reduced motion equations. The two-modal interaction vibration is induced when the rotation speed is half a critical speed of the system due to asymmetry and gravity force of the generator. Such a phenomena is observed in the practical test.
Modeling of Forced Convection in an Electronic Device Heat Sink as Porous Media Flow
Authors: Horvat Andrej , Catton Ivan
Published: May 2008

An algorithm for simulation of conjugate heat transfer used to find the most suitable geometry for an electronic chip heat sink is described. Applying Volume Averaging Theory (VAT) to a system of transport equations, a heat exchanger structure was modeled as a homogeneous porous media. The interaction between the fluid and the structure, the VAT equation closure requirement, was accomplished with drag and heat transfer coefficients, which were taken from the available literature and inserted into a computer code. The example calculations were performed for an aluminum heat sink exposed to force convection airflow. The geometry of the simulation domain and boundary conditions followed the geometry of the experimental test section. The comparison of the whole-section drag coefficient and Nusselt number as functions of Reynolds number shows a good agreement with the experimental data. The calculated temperature fields reveal the local heat flow distribution and enable further improvements of the heat sink geometry.