bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Some Integrated Cooling Mechanisms for an Active IPEM
Authors: Pang Y. , Scott E. , van Wyk J. D. , Liang Z.
Published: April 2008

With the growing demands on the performance, cost, and advances in packaging and interconnection technology, three-dimensional (3D) packaging provides higher density packaging. On the other hand, thermal management of the 3D package becomes a very important issue. This paper assesses the various possibilities of integrated thermal management for integrated power electronics modules (IPEMs).
Control of Adiabatic Liquid/Vapor Flow Utilizing EHD Conduction Pumping Mechanism
Authors: Feng Yinshan , Seyed-Yagoobi Jamal
Published: April 2008

Unlike the electrohydrodynamic (EHD) induction and iondrag pumping, the conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes which are based on the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The conduction term here represents a mechanism for electric current flow in which charged carriers are produced not by injection from electrodes, but by dissociation of molecules within the fluid. This paper presents the control of adiabatic two-phase (liquid/vapor) flow distribution with EHD conduction pumping mechanism at two mass flux levels, Gtotal = 50 kg/m2s and Gtotal = 100 kg/m2s. The effects of the vapor quality, ranging from 0 to 26%, on the EHD conduction pumping have also been experimentally investigated. The measured pressure data show that the EHD conduction pumping can significantly decrease the pressure drop of the two-phase flow. It is also found that the performances of the EHD conduction pump are related to the mass flux and quality of two-phase flow.
Scattering of Phonons by Nano and Micro Particles
Authors: Prasher Ravi S.
Published: April 2008

Scattering theory for the scattering of phonons by particulate scatterers is developed in this paper. Recently the author introduced the generalized equation of phonon radiative transport (GEPRT) in particulate media which included a phase function to account for the anisotropic scattering of phonons by particulate scatterer. Solution of the GEPRT showed that scattering cross section is different than the thermal transport cross section. In this paper formulations for the scattering and transport cross section for horizontally shear (SH) wave phonon or transverse wave phonon without mode conversion is developed. The development of the theory of scattering and the transport cross section is exactly analogous to the Mie scattering theory for photon transport in particulate media. Results show that transport cross section is very different than the scattering cross section. It is also shown that for SH (horizontally shear) phonons the scattering and transport cross sections are proportional to ω8 rather than the well accepted value of ω4 in the Rayleigh regime where ω is the frequency of the SH phonons. The theory of phonon scattering developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems such as nano composites, nano-micro particle laden systems and etc.
Measurement of Kinetic Zone Temperature and Heat Transfer Coefficient in the Lost Foam Casting Process
Authors: Liu X. J. , Bhavnani S. H. , Overfelt R. A.
Published: April 2008

A thermometric technique has been developed to study the thermal characteristics of the foam-metal interaction in the lost foam casting process. A cylindrical foam pattern and heated steel block have been used to estimate the endothermic losses associated with the thermal degradation of the expanded polystyrene at the metal front. Thermocouple readings have been analyzed to determine the temperature of the kinetic zone between the advancing metal front and the receding foam pattern. The heat transfer coefficient between the metal front and the foam pattern has been calculated from the thermal data at the simulated metal front. The results confirmed that the endothermic degradation of the polystyrene pattern at the metal front introduced a steep thermal gradient in the metal and a consistently increasing heat flux. It is found that the heat transfer coefficient, initially 150 W/m2·K increases to 220 ~ 300 W/m2·K during the process. Foam density has marginal effect on the heat flux and heat transfer coefficient, whereas the increase of simulated metal front velocity enhances the heat transfer at the metal front. The kinetic zone temperature is measured to be in the range of 150 to 290°C with an average of 200°C and a gaseous gap size of 1 to 4 cm.
Design of a Haptic Arm Exoskeleton for Training and Rehabilitation
Authors: Gupta Abhishek , O’Malley Marcia K.
Published: April 2008

A high-quality haptic interface is typically characterized by low apparent inertia and damping, high structural stiffness, minimal backlash and absence of mechanical singularities in the workspace. In addition to these specifications, exoskeleton haptic interface design involves consideration of additional parameters and constraints including space and weight limitations, workspace requirements and the kinematic constraints placed on the device by the human arm. In this context, we present the design of a five degree-of-freedom haptic arm exoskeleton for training and rehabilitation in virtual environments. The design of the device, including actuator and sensor selection, is discussed. Limitations of the device that result from the above selections are also presented. The device is capable of providing kinesthetic feedback to the joints of the lower arm and wrist of the operator, and will be used in future work for robot-assisted rehabilitation and training.
Comparative Computational Fluid Dynamics and Experimental Phase-Contrast MRI: Evaluations of In-Stent Restenosis
Authors: Holton Andrea D. , Brott Brigitta C. , Walsh Edward G. , Venugopalan Ramakrishna , Shih Alan M. , Koomullil Roy , Ito Yasushi , Anayiotos Andreas S.
Published: April 2008

While angiography and other translesional catheter-based assessments of stented peripheral vasculature are currently used in clinical applications, a quantitative non-invasive imaging modality would improve the treatment of intermediate levels of in-stent restenosis (ISR). The use of magnetic resonance imaging (MRI), in metal stents has been limited due to magnetic susceptibility artifacts and radiofrequency shielding effects. However, MRI compatible materials such as nickel-titanium alloys used in stents have shown superior lumen visibility. In this study, we used phase contrast MRI in a flow phantom of three different geometries of stenosis: a) 90% axisymmetric, b) 75% axisymmetric and c) 50% asymmetric. The velocity distribution was obtained at 3 different locations inside the stent. This was compared with an equivalent computational fluid dynamics (CFD) model of the same stenotic geometries.
Evaluation of Processing Effects in Injection Molded Thermoplastics Using Excimer Laser
Authors: Sancaktar E. , Negandhi N. , Adwani S.
Published: April 2008

The ablation behavior of amorphous (polystyrene (PS), and polycarbonate (PC)) and crystalline (poly(ethylene terephthalate) (PET), and glass filled poly(butylenes terephthalate) (PBT)) polymers by 248 nm KrF excimer laser irradiation were investigated for different injection molding conditions namely, injection flow rate, injection pressure, and mold temperature, as a possible method to evaluate the processing effects in the specimens. For this purpose, dumb-bell shaped samples were injection molded at different sets of processing conditions, and weight loss measurements were carried out for the different injection molding conditions. Some of the crystalline (PET) samples were annealed at different annealing time and temperature. For PET, weight loss decreased with increasing mold temperature and remained insensitive to injection flow rate. Annealing time and temperature significantly reduced weight loss in PET. For PBT, the weight loss due to laser ablation reduced with increase in material packing due to pressure, and also showed some sensitivity to flow rate variation. The major effect was seen with glass filled PBT samples. The weight loss decreased drastically with increasing glass fiber content. Laser ablation allowed observation of process induced fiber orientation by SEM in PBT samples. For PS and PC, the weight loss increased with increases in the injection flow rate and mold temperature, and decreased with increasing injection pressure. Position near the gate showed higher ablation than the position at the end for all the conditions. A decrease in the material orientation, with injection speed and mold temperature, led to increase in the weight loss, while increase in the injection pressure, and consequently orientation, led to lower weight loss for PS and PC. Higher residual stress samples showed higher weight loss.
Analysis of Enthalpy Approximation for Compressed Liquid Water
Authors: Kostic M.
Published: April 2008

It is custom to approximate solid and liquid thermodynamic properties as being function of temperature only, since they are virtually incompressible, and Pdv compression work may be neglected. Furthermore, in classical literature, for isothermal compression processes, a general improvement and correction for liquid enthalpy approximation is given by adding the “pumping” work, vdP, to the corresponding saturation value. Analysis of water real properties shows that such a correction is unnecessary for intermediate pressures and temperatures, and it is even erroneous for higher temperatures and pressures, and thus counterproductive and misleading.
Thermal Model and Experimental Validation of the Re-Design of High Temperature Superconducting Leads for X-Ray Spectrometer Applications
Authors: Marrero Vi´ctor L. , Panek John S. , Couti´n Sandra
Published: April 2008

The thermal modeling for the redesign of an X-Ray Spectrometer (XRS) High Tc Superconducting Current (HTSC) lead assembly was the objective of this research work. In order to achieve a 2.5-year lifetime for the XRS, low thermal conductance leads were redesign to supply electric current to the Adiabatic Demagnetization Refrigerator (ADR) magnet and the cryostat valve motors with a minimal heat load. This research work consisted of the development of a mockup of the HTSC lead assembly and a computer model to simulate the thermal behavior of the system. Experimental data of the mockup was used to validate the thermal model, which was employed in the optimization of the design to minimize the heat load. The thermal model development and validation of the new HTSC lead design is discussed, with emphasis on thermal test results.
Flow-Independent Viscoelastic Response of Bovine Articular Cartilage Under Dynamic Tensile Loading
Authors: Park Seonghun , Ateshian Gerard A.
Published: April 2008

The objective of the current study was to characterize the mechanical response of bovine articular cartilage under dynamic tensile loading. Testing was performed under an applied stress magnitude of 1.3 MPa and frequencies from 10−4 Hz to 10 Hz. The dynamic tensile modulus ranged from 20.1±7.0 MPa at 10−4 Hz to 64.0±9.7 MPa at 10 Hz. The phase angle derived from the area under the stress-strain hysteresis loop changed from 21.4±6.9° at 10−4 Hz to 1.1±0.2° at 10 Hz. Based on earlier theoretical predictions, the observed viscoelastic response in tension may be attributed to the intrinsic viscoelasticity of the collagen-proteoglycan matrix.
Sensitivity Coefficients for Analyzing Interstitial Properties During Phase Change in Porous Media
Authors: Nnanna A. G. Agwa , Haji-Sheikh A.
Published: April 2008

The sensitivity coefficients for analyzing the interstitial properties during phase change in porous media are presented. Computation of the sensitivity coefficients is the main objective of this study. Experimentally measured temperature data provide an estimate of the phase front locations used as the state variable for this study. The derivations are based on the assumption that the phase front, X, at a given time, t, is a function of interstitial properties τt and τq with all other parameters remaining constant. The properties τt and τq are the lag-time in temperature and heat flux, respectively. The analysis includes two types of boundary conditions: prescribed temperature of phase change materials and prescribed temperature for solid matrix. Results for the first case show that for any given ratio τt/τq, the sensitivity coefficient decreases asymptotically to zero at large times. Furthermore, the sum of the sensitivity coefficients St + Sq = 0 when τt/τq ≈ 1. This is significant information because the variables St and Sq have the same magnitude with opposite signs. This implies that these two sensitivity coefficients become linearly dependent and it will be difficult to predict the values of τt and τq in the neighborhood of τt/τq ≈ 1. A similar trend but with different sensitivity values are reported for the second case.
Ultrasonic Signal Attenuation in Syntactic Foams Filled With Rubber Particles
Authors: Mylavarapu Phani , Li Guoqiang , Gupta Nikhil , Maharsia Rahul , Woldesenbet Eyassu
Published: April 2008

Ultrasonic imaging is a non-destructive evaluation technique, which is used to obtain density profile, phase distribution and three-dimensional profiles of cracks and defects in a material. Although this technique is used for a variety of metals and non-metals, it is difficult to use it for testing of porous materials and foams due to high attenuation of ultrasonic waves in these materials. Syntactic foams are hollow particle filled composites that have recently emerged as attractive material for use in applications requiring low weight, low moisture absorption and high insulation properties. The present paper focuses on determining the attenuation coefficient in syntactic foams and its correlation with porosity distribution. Eight types of foam samples are tested in the study. A combination of four types of microballoons and two types of rubber particles is used. Volume fractions of microballoons and rubber particles are maintained at 0.63 and 0.02, respectively, in all samples. Pulse Echo ultrasonic test method is used and results are compared to determine the effect of constituent particles on the ultrasound signal attenuation. Coefficient of attenuation is observed to increase with decrease in density of foam samples and with decrease in size of rubber particles.
Numerical Simulation of Two-Phase Fluid Flow and Heat Transfer With or Without Phase Change Using a Volume-of-Fluid Model
Authors: Wang Lieke , Sunde´n Bengt
Published: April 2008

Numerical simulations of two-phase fluid flow and heat transfer with or without phase change have been carried out. The Volume-of-Fluid (VOF) model was used in the simulations, and a procedure for considering the phase change process was developed. The Piecewise Linear Interface Calculation (PLIC) method is employed for the interface reconstruction, to keep the sharp interface. The coupling between pressure and velocity is treated by the SIMPLEC algorithm. The surface tension is modeled by the Continuum Surface Force (CSF) model. An in-house code has been developed, and two examples are presented in this paper, i.e., dam-break case and a falling water droplet in a steam bath. The calculation results are compared with corresponding experimental data, and good agreement is obtained.
Plane Poiseuille Flow of Two Compatible Polymers: Influence of the Interphase on the Flow Stability
Authors: Rousset Franc¸ois , Bourgin Patrick , Palade Liviu-Iulian
Published: April 2008

This paper deals with coextrusion flows of two compatible polymers which are known to be generally more stable than the same flows of incompatible systems. We show that the weak response to disturbance of such flows can be predicted by considering an interphase of non-zero thickness (corresponding to an interdiffusion zone) instead of a purely geometrical interface between the two layers. As a first step we try to explain the weak sensibility to disturbance of compatible systems by the sole presence of this intermediate layer. For that purpose we study the linear stability response to very long waves of a three-layer plane Poiseuille flow with an inner thin layer which represents the interphase. This first approach (corresponding to a reduction in the effective viscosity ratio) is shown to explain the diminished growth rates but not the reduction in the size of the unstable region. As a second step, we formulate an energetic approach of the problem. We evaluate the energy dissipated during the interdiffusion process and the variation of kinetic energy of the global system. A modified growth rate is then determined by taking into account the energy dissipated by the interdiffusion process. This lower growth rate enables us to explain the increase of the stable domain in the case of compatible polymeric systems.
Stress Distributions Along the Inner Wall of the Femoropopliteal Bypass Graft Anastomoses
Authors: Campbell Triona , Cole Reena , Davies Mark , O’Donnell Michael
Published: April 2008

The distal junction of a femoral or femoropopliteal artery bypass graft has a predilection for failure due to restenosis. However neither the initiation nor proliferation process of atherosclerotic plaque is completely understood. Presently it is hypothesized that the process of atherosclerosis initiates as a result of damage or ‘insult’ to the endothelium. The cause of this initial damage is unknown, although it is widely believed that wall shear stresses are a contributing factor. The primary cause of plaque proliferation has not yet been identified, however it is our belief that intramural pressure plays a significant role. In this study numerical models of the proximal and distal junctions were used to determine both the location and magnitude of the stresses caused by intramural pressure. The simulated artery bypass graft was examined under both static and dynamic conditions.
Routes to Chaos in Squeeze-Film Dampers
Authors: Inayat-Hussain Jawaid I. , Mureithi Njuki W.
Published: April 2008

This work reports on a numerical study undertaken to investigate the imbalance response of a rigid rotor supported by squeeze-film dampers. Two types of damper configurations were considered, namely, dampers without centering springs, and eccentrically operated dampers with centering springs. For a rotor fitted with squeeze-film dampers without centering springs, the study revealed the existence of three regimes of chaotic motion. The route to chaos in the first regime was attributed to a sequence of period-doubling bifurcations of the period-1 (synchronous) rotor response. A period-3 (one-third subharmonic) rotor whirl orbit, which was born from a saddle-node bifurcation, was found to co-exist with the chaotic attractor. The period-3 orbit was also observed to undergo a sequence of period-doubling bifurcations resulting in chaotic vibrations of the rotor. The route to chaos in the third regime of chaotic rotor response, which occurred immediately after the disappearance of the period-3 orbit due to a saddle-node bifurcation, was attributed to a possible boundary crisis. The transitions to chaotic vibrations in the rotor supported by eccentric squeeze-film dampers with centering springs were via the period-doubling cascade and type 3 intermittency routes. The type 3 intermittency transition to chaos was due to an inverse period-doubling bifurcation of the period-2 (one-half subharmonic) rotor response. The unbalance response of the squeeze-film-damper supported rotor presented in this work leads to unique non-synchronous and chaotic vibration signatures. The latter provide some useful insights into the design and development of fault diagnostic tools for rotating machinery that operate in highly nonlinear regimes.
Effect of Modeling Assumptions in the Plantar Pressure Distribution of the Diabetic Foot Using the p-Version of the Finite Element Method
Authors: Actis Ricardo L. , Ventura Liliana B. , Szabo Barna A. , Smith Kirk E. , Commean Paul K. , Mueller Michael J.
Published: April 2008

This paper summarizes the modeling work performed by our research group in the last year utilizing the p-version of the finite element method for the simulation of the mechanical behavior of the human foot in regard to the plantar pressure distribution during push-off.
A Study of a New Ceramic Membrane for Use in Hemodialysis
Authors: Huang Zhongping , Zhang Weiming , Tang Sonja M. , Yu Jianping , Lai-Fook Stephen J. , Gao Dayong
Published: April 2008

The non-uniformity of pore size and pore distribution of the current hemodialysis membrane results in low efficiency of uremic solute removal as well as the loss of albumin. By using nano technology, an anodic alumina membrane (ceramic membrane) with self-organized nano-pore structure was produced. The objective of this study was to investigate the correlation between various anodization conditions and the pore characteristics of the ceramic membrane as a potential use in artificial kidney / hemodialysis. An aluminum thin film was oxidized in two electrolytes consisting of 3% and 5% sulfuric acid and 2.7% oxalic acid. The applied voltages were 12.5, 15, 17.5 and 20 (V) for sulfuric acid and 20, 30, 40 and 50 (V) for oxalic acid. Pore size and porosity were determined by analyzing scanning electron microscopy (SEM) images and hydraulic conductivity was measured. Pore size increased linearly with voltage. Acid concentration affected pore formation but not pore size and pore distribution. Hydraulic conductivity of the ceramic membrane was higher than that of polymer dialysis membrane. The optimal formation conditions for self-organized nano-pore structure of ceramic membrane were 12.5–17.5V in 3–5% sulfuric acid at 0 °C. These conditions produced ceramic membranes with pores of ~ 10 nm diameter. Conclusion: Anodic alumina technology reliably produced in quantity structures with pore sizes in the 10–50 nm diameter range. Because of more uniform pore size, high porosity, high hydraulic conductivity and resistance to high temperature, the ceramic membrane has potential for future application as a hemodialysis membrane.
Nonlinear Dynamics of Axially Moving Systems
Authors: Pellicano Francesco
Published: April 2008

The object of the present paper is a deep analysis of some recent numerical and experimental results regarding the complex dynamics of axially moving systems. Such important mechanical systems exhibit interesting dynamic behaviors: homoclinic orbits; sub-harmonic responses; amplitude modulations and chaos. These dynamics have been obtained numerically and in some case have been experimentally observed. Using recent techniques of the Nonlinear Time Series analysis, the response of axially moving systems is studied for a large variety of test cases. The correlation dimension of the time series, which is deeply related to the minimal dimension of a system able to reproduce the dynamics, is estimated. Lyapunov exponents are evaluated in order to quantify the response regularity. The present work give a contribution in understanding complex dynamics observed both in conservative and dissipative systems. The dynamical phenomena are analyzed within the unified framework fo the Nonlinear Time Series Analysis. In the case of experimental data the new nonlinear filtering techniques, based on the embedding techniques, have been applied to reduce high noise when classical techniques give bad results.
Hierarchical Optimal Contour-Position Control of Motion Control Systems
Authors: Landers Robert G. , Balakrishnan S. N.
Published: April 2008

Contour control is critical in many motion control systems (e.g., manufacturing, robotics). A contour control algorithm is implemented in many applications to drive the contour error to zero; however, the additional algorithm significantly increases the complexity of the overall control system. In this paper, a hierarchical optimal control methodology is developed to design a single servomechanism control system capable of simultaneously driving contour error and individual servomechanism position errors to zero. The designer can systematically trade-off the importance of contour error and servomechanism position errors without the increased complexity of an additional algorithm. The methodology is applied to a two-axis motion control system and simulation studies are conducted for linear, circular, and elliptical contours. The results demonstrate the excellent tracking ability of the proposed motion control methodology and its utility for complex contours.
Direct Measurements of Transverse Piezoelectric Coefficient e31 of PZT Thin Films
Authors: Wu Chia-Che , Lee Cheng-Chun , Cao G. Z. , Shen I. Y.
Published: April 2008

The purpose of this paper is to develop a direct method to measure e31 of PZT thin films regardless of the boundary conditions of the specimens. The experimental setup consists of a silicon beam with a PZT film excited by a tiny shaker. A charge amplifier detects the charge accumulated in the PZT film. A spectrum analyzer processes the charge amplifier’s output to obtain a frequency spectrum. In addition, three calibration points are defined along the PZT film as 1, 2, and 3. These points are evenly spaced with distance Δx. A laser Doppler vibrometer (LDV) measures the deflection w1, w2, and w3 of the calibration points 1, 2, and 3. According to Euler-Bernoulli beam theory, the normal strain is ε ≈ 0.5h(w1 – 2w2 + w3)/(Δx)2, where h is the thickness of the cantilever. Finally, the ratio of the charge to the strain ε gives e31. Note that this approach does not depend on the boundary conditions of the specimen. Therefore, the boundary conditions do not affect the accuracy of the measurements. To demonstrate the direct measurement method, we fabricate a silicon cantilever beam with a PZT film using sol-gel processes. The dimensions of the silicon canteliver and the PZT thin film are 30 mm × 7.5 mm × 0.4 mm and 4 mm × 4 mm × 1 μm, respectively. Using the resonance amplitude of the first bending mode at 520 Hz, we obtain e31 to be 0.24 C/m2.
Validation of CFD Model for Hot Metal Flow and Heat Transfer Simulation in a Blast Furnace
Authors: Yan Fang , Zhou Chenn Q. , Huang D. , Chaubal Pinakin
Published: April 2008

Hearth wearing is the key limit of a blast furnace campaign life. Hot metal flow pattern and temperature distributions are the two key variables to determine the rate and style of the hearth wearing. And the shape, structure and position of the deadman are the three major variables to assign the fluid flow pattern and temperature profile in the hearth. In this paper, a comprehensive computational fluid dynamics (CFD) program which was developed specifically for the simulation of blast furnace hearth was extensively evaluated using actual industrial operation data. That program can predict the liquid flow patterns and temperature distributions of the hot metal as well as temperature profiles in the hearth refractory materials under different conditions. Sensitivity study has also been performed to investigate the effect of the production rate on refractory temperature distribution.
Design Considerations for an Articulated Leg-Wheel Locomotion Subsystem
Authors: Jun Seung Kook , Krovi Venkat N.
Published: April 2008

In this paper, we examine and evaluate candidate articulated leg-wheel subsystem designs for use in vehicle systems with enhanced uneven-terrain locomotion capabilities. The leg-wheel subsystem designs under consideration consist of disk wheels attached to the chassis through an articulated linkage containing multiple lower-pair joints. Our emphasis is on creating a design that permits the greatest motion flexibility between the chassis and wheel while maintaining the smallest degree-of-freedom (d.o.f.) within the articulated chain. In particular, we focus our attention on achieving two goals: (i) obtaining adequate ground clearance by designing the desired/feasible motions of the wheel axle, relative to the chassis, using methods from kinematic synthesis; and (ii) reducing overall actuation requirements by a judicious mix of structural equilibration design and spring assist. We examine this process in the context of two candidate designs — a coupled-serial-chain configuration and four-bar-configuration — for the articulated-leg-wheel subsystem. The performance of planar variants of these designs, operating in the sagittal plane, is evaluated and representative results are presented to highlight the process.
Design and Fabrication of a Novel MEMS Device for High Resolution Force and Displacement Measurement
Authors: Desai A. V. , Haque M. A.
Published: April 2008

We present the design and fabrication of a MEMS device for high resolution force and displacement measurements. Both quantitative and qualitative measurements can be performed in-situ in scanning, transmission and tunneling electron microcopy (SEM, TEM and STM), where the small chamber size makes it challenging to integrate conventional force-displacement sensors. The device exploits the amplification of displacement and attenuation of structural stiffness due to buckling of slender silicon beams to obtain pico-Newton force and nanometer displacement resolution. The design uses buckling of two sets of beams of slightly different lengths to create a loading device. The amplification of the specimen deformation into the micron range enables measurement by visual inspection (optical microscope) without using complex displacement sensing mechanism. Co-fabrication of the specimen with the device is possible, thus eliminating the problems associated with alignment and positioning. The device can be used for characterization of materials such as carbon nanotube-polymer interfaces, nanoscale thin films and mechanical testing of single biological cells.
Lattice Boltzmann Simulation of Two-Phase Flow and Heat Transfer in a Rectangular Channel
Authors: Yuan Peng , Schaefer Laura
Published: April 2008

The lattice Boltzmann method (LBM) is a kinetic approach, which assumes that a fluid consists of mesoscopic fluid particles with repeating collision and streaming patterns and is used to solve for the hydrodynamic phenomena of various systems In this work, we employ the LBM to investigate two-phase flow and heat transfer problems in a rectangular channel. First, the validity of the LBM is shown through some benchmark tests. Next, we use a single component multi-phase lattice Boltzmann model proposed by Shan and Chen to simulate two-phase flow in the channel. The two-phase interface is reproduced by interaction between different kinds of particles. The temperature field is simulated using the passive scalar approach, i.e. modeling the density field of an extra component, which evolves according to the advection-diffusion equation. Fluid-solid interaction, gravity, and the pressure gradient are also incorporated into the model. The dynamic behavior of the bubble under different conditions is investigated.
Algorithm Development for Determination of Species Concentrations in Post-Combustion Gases
Authors: Mei Anhua , Aung Kendrick
Published: April 2008

This paper describes the development of algorithms to determine the species concentration in Post-Combustion gases by absorption spectroscopy. Absorption spectroscopy using tunable diode lasers provides a cost-effective and non-intrusive way to determine the concentration of H2O, CO, CO2 and NO in the exhaust gas streams [1,2]. For each species, wavelength suitable for absorption spectroscopy is determined using the spectra distributions of the species provided in the HITRAN database. Inverse method is used to determine the concentration profile of each species from absorption measurements. The results of the paper provide the foundation to develop dynamic diagnostic instrument to measure the concentration of gaseous species in hostile environments such as furnaces, industrial burners, and stacks.
Fast MRI Flow Imaging by Sparse Sampling and Segmentation
Authors: Hershey Bradley L. , More Rohan A. , Doyle Mark , Kortright Eduardo , Anayiotos Andreas S.
Published: April 2008

Clinical use of cardiac synchronized Magnetic Resonance Imaging has been limited because of long unacceptable acquisition times. BRISK (Block Regional Interpolation Scheme for k-space) is a rapid MRI technique, which employs temporal sparse sampling scheme that varies the sampling rate as a function of distance from the k-space center. Using combination of conventional segmentation and BRISK approach, a new rapid phase contrast cine approach named FAST was investigated. FAST technique samples contiguous regions of k-space using a segmentation factor, just as in conventional segmentation, with the difference that the segmentation factor (SF) is varied as a function of distance from the k-space center. FAST and BRISK can be performed in nearly equally scan times. Both retained excellent axial-velocity accuracy. However secondary velocities, which were two orders of magnitude lower than the primary, suffered from comparable inaccuracies and distortion in conventional segmentation, BRISK and FAST.
Effects of Thoracic Ramping on Whiplash Kinematics
Authors: Stemper Brian D. , Yoganandan Narayan , Pintar Frank A.
Published: April 2008

Whiplash injuries result from differential motion between the head and thorax. Experimental investigations using human volunteers and full body cadavers have described thoracic ramping due to interaction with the seatback and straightening of the thoracic spine. The effect of this motion on cervical kinematics has not been investigated. A head-neck computer model was used to determine the effects of thoracic ramping on whiplash kinematics. The model consisted of skull, cervical spine, first thoracic vertebra, intervertebral discs, spinal ligaments, facet joints, and passive musculature, and was subjected to 2.7 m/sec rear impact velocity. Vertical acceleration of T1 was prescribed according to literature. Segmental angulations and region dependent facet joint capsular ligament distractions were obtained from levels C2-C3 through C7-T1 during the time of cervical S-curvature. Maximum capsular ligament distractions during this time occurred in the dorsal region at the C2-C3 level and in the lateral region at the C3-C4 through C7-T1 levels. Increasing magnitudes of T1 ramping decreased segmental angulations and ligament distractions by less than 20% in most cases. Results of the present investigation demonstrated that thoracic ramping may play a secondary role in whiplash kinematics.
Inverse Design of Solidification Processes
Authors: Okamoto Kei , Li Ben Q.
Published: April 2008

An inverse algorithm is developed for the design of the solidification processing systems. The algorithm entails the use of the Tikhonov regularization method, along with an appropriately selected regularization parameter. Both the direct solution of moving boundary problems and the inverse design formulation are presented, along with the L-curve to select an optimal regularization parameter for inverse design calculations. The design algorithm is applied to determine the appropriate boundary heat flux distribution in order to obtain a unidirectional solidification front in a 2-D cavity by eliminating the effect of natural convection. Inverse calculation is also performed for the case in which the solid-liquid interface is prescribed to vary linearly. The L-curve based regularization method is found to be reasonably accurate for the purpose of designing solidification processing systems.
Fuzzy Logic Control of Projectile Fin Angle Using Piezoelectric Beam Actuator
Authors: Trabia Mohamed B. , Yim Woosoon , Parimi Surya Kiran
Published: April 2008

Fin of a subsonic projectile produce maneuvering force and moment that control the rotation angle of a projectile fin during flight. The objective of this paper is to study the feasibility of using piezoelectric actuator and fuzzy logic control to create a smart fin. The fin is rotated by a beam-based piezoelectric actuator, which has an end fixed to the rotation axle of the fine while the other end is pinned at the tip of the fin. A model of the dynamics of the system is obtained using the finite element approach. A fuzzy logic controller for the fin is designed. The membership functions of the fuzzy variables for this controller are determined using a hybrid genetic algorithm. Simulation results show that the proposed controller worked satisfactorily.
Thermodynamic and Phase Behavior of Supercritical Water: Environmentally Significant Organic Chemical Mixtures
Authors: Artemenko S. , Mazur V.
Published: April 2008

The importance of equation of state models is fundamental to new technologies such as supercritical water oxidation for the destruction of organic pollutants. In order to be able to perform hazard and risk assessments, the parameters ofthermodynamic models are considered as information characteristics of chemicals that store the knowledge on their thermodynamic, phase and environmental behavior. Considering the extremely large number of existing chemicals, it is obvious that there is need for developing theoretically sound methods for the prompt estimation of their phase behavior in aquatic media at supercritical conditions. Recent developments of the global phase equilibria studies of binary mixtures provide some basic ideas of how the required methods can be developed based on global phase diagrams for visualization of the phase behavior of mixtures. The mapping of the global equilibrium surface in the parameter space of the equation of state (EoS) model provides the most comprehensive system of criteria for predicting binary mixture phase behavior. The main types of phase behavior for environmentally significant organic chemicals in aqueous environments are considered using structure-property correlations for the critical parameters of substances. Analytic expressions for azeotropy prediction for cubic EoS are derived. A local mapping concept is introduced to describe thermodynamically consistently the saturation curve of water. The classes of environmentally significant chemicals (polycyclic aromatic hydrocarbons - PAH, polychlorinated biphenyls - PCB, polychlorinated dibenzo-p-dioxins and furans, and selected pesticides) are considered and main sources of the property data are examined. Vapor pressure, heat of vaporization, and critical parameter estimations for pure components were chosen for seeking a correlation between the octanol–water partition coefficients KOW and the EoS binary interaction parameters - k12. The assessment of thermodynamic and phase behavior of representatives for different pollutants is given.
Prediction of Mechanical Behavior of Balloon-Expandable Stents
Authors: Yu Mei , Grosse Ian
Published: April 2008

Coronary heart disease is a major health threat for people in the developed countries. Narrowing of the coronary arteries is one of the most common types of coronary heart diseases and is often treated by percutaneous transluminal coronary angioplasty (PTCA) and recently by stenting. A stenting procedure involves inserting a slotted metal tube or coil into the artery and expanding it to help achieve a sufficient luminal size. To optimize the design of stents, we have developed a finite element model of the stenting procedure. The results showed the distal ends of the stent could damage arteries due to non-uniform expansion of the stent. Our model also showed that inclusion of the plaque and artery is important for predicting the final stent shape and diameter. A response surface of the stent hoop stiffness is proposed to help designers quickly decide the stiffness of the stent for a given design. Results show that contact stresses are inversely proportional to stent stiffness and a minimum stent hoop stiffness is needed to prevent stent collapse after balloon removal.
Geometry of Elastase-Induced Aneurysms in Rabbits
Authors: Onizuka M. , Miskolczi L. , Gounis M. J. , Seong J. , Lieber B. B. , Wakhloo A. K.
Published: April 2008

Thirty New Zealand White rabbits were used in the study. The diameter of the origin of the CCA measured immediately after elastase incubation correlated positively to the aneurysm neck at three week follow up. Moreover, the aneurysm neck both after creation and three week follow-up had a positive correlation with the final dome height. Finally, the dome height was found to be related to the angle between the innominate artery and the aneurysm centerline for dome diameter/neck ratio of <1.5. These results indicate that neck width immediately after creation and the curvature of the parent artery are linked to aneurysm dimensions.
Grazing and Chaos in a Periodically Forced, Piecewise Linear System
Authors: Luo Albert C. J.
Published: April 2008

The criteria for the grazing bifurcation of a periodically forced, piecewise linear system are developed and the initial grazing manifolds are obtained. The grazing flows are illustrated. The mechanism for the fragmentation of the strange attractors caused by the grazing is discussed and the strange attractor fragmentized by grazing is illustrated through the Poincare mapping. This fragmentation phenomenon extensively exists in non-smooth dynamical systems.
Compliant Silicone Elastomer Models of Elastase-Induced Aneurysms in the Rabbit: Model Construction and Hemodynamics
Authors: Seong Jaehoon , Lieber Baruch B. , Wakhloo Ajay K.
Published: April 2008

An elastase-induced saccular aneurysm in the rabbit right common carotid artery was developed as a model of human cerebrovascular aneurysm, and used for testing various endovascular devices and therapies. The carotid artery of the rabbit approximates the size of the human middle cerebral artery. Therefore, the created aneurysm is similar to those found in humans around the main branches of the circle of Willis. To minimize the use of animals and gain more insight into the hemodynamics of this model, in addition to the ability to perform early testing of endovascular devices in vitro, we have developed a rapid prototyping technique to produce compliant elastomer replicas of such aneurysms. In this implementation, the geometry of the constructed aneurysm is a representative average. The rapid prototyping system reliably reproduces as many copies of the lumen of the arterial bed out of Polyacrylonitrile-butadiene-styrene (ABS). The ABS output of the prototyping system can be used as a core that is dipped a silicone elastomer and then spin coated until cured. Thereafter, the core is melted away to yield the elastomer replica of the arterial bed. This replica was included in a mock circulation loop for detailed hemodynamic investigation using particle image velocimetry (PIV).
End Point Position Control of Multi-Link Flexible Manipulators Using SDRE Method
Authors: Renno Jamil M. , Yim Woosoon , Singh Sahjendra N.
Published: April 2008

This paper treats end point regulation of multi-link light-weight flexible manipulators using the State Dependent Riccati Equation: SDRE method. It is well known that end point trajectory control using widely used feedback linearization techniques is not possible when the equilibrium state of the zero dynamics of the system is unstable or weakly stable. Furthermore, control saturation is a major problem in controlling nonlinear systems. In this paper, an optimal control problem is formulated for the derivation of control law with and without control constraints on the joint torques for a multi-link flexible manipulator and suboptimal control laws are designed using the SDRE method. For the purpose of control, pseudo joint angles and elastic modes of each link are regulated to their equilibrium values which correspond to the target end point. Weighting matrices in the quadratic performance index provide flexibility in shaping the pseudo angles and elastic modes trajectories. In the closed-loop system, the equilibrium state is asymptotically stable, and vibration is suppressed. Simulation results are presented for a two-link flexible manipulator, which show that in the closed-loop system, end point trajectory tracking is accomplished even with constraints on the control torque. Results also show that the transient characteristics of the pseudo angles and elastic modes can be easily shaped by the choice of the performance criterion.
Image-Based Control of Dynamic Effects in Scanning Tunneling Microscopes
Authors: Clayton G. M. , Devasia S.
Published: April 2008

In this article, we present an image-based control scheme to address the problem of low operating speed in scanning tunneling microscopes (STMs). Low operating speeds are used because dynamic effects cause error in positioning the STM probe over the sample. The STM’s low operating speed limits its capability to investigate fast surface phenomena and its throughput during nanofabrication. The proposed image-based approach to achieve high speed operation exploits the extant imaging capabilities of STMs. In practice, distortions in high-speed images are used to identify and correct errors in the STM probe position. The approach is applied to an STM and experimental results are presented.
Competitive Designs of Evaporator Top Cap of the Micro Loop Heat Pipe
Authors: Arragattu Praveen Kumar , Gerner Frank M. , Ponugoti Priyanka , Henderson H. T.
Published: April 2008

The Micro Loop Heat Pipe (LHP) is a two phase device that may be used to cool electronics, solar collectors and other devices in space applications. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference developed between the evaporator and condenser and capillary forces developed inside its wicked evaporator to circulate a working fluid through a closed loop. While previous experiments have shown reduction in chip temperature, maximum heat flux was less than theoretically predicted. This paper addresses the main problem with the past designs of top cap which has been the conduction of heat from the heat source to the primary wick. The new top cap design provides conduction pathways which enables the uniform distribution of heat to the wick. The provision of conduction pathways in the top cap increases the pressure losses and decreases the temperature drop. The feasible competitive designs of the top cap with conduction pathways from the fabrication point of view were discussed in detail. Calculation of pressure drop and temperature drop is essential for the determination of optimal solutions of the top cap. Approximate pressure drop was calculated for the top cap designs using simple 2-D microchannel principles. Finite element modeling was performed to determine the temperature drop in the conduction pathways. The conditions used for arriving at the optimal design solutions are discussed. A trapezoidal slot top cap design was chosen for fabrication as it was relatively easy to fabricate with available MEMS fabrication technologies. The exact pressure drop calculation was performed on the fabricated top cap using commercial flow solver FLUENT 6.1 with appropriate boundary conditions. The temperature drop calculation was performed by finite element modeling in ANSYS 6.1. Obtained values of pressure drop and temperature drop for fabricated trapezoidal slot top cap was found to be within the optimal limits.
Dynamic Responses of a Cracked Gas-Bearing Spindle
Authors: Huang Bo-Wun , Kuang Jao-Hwa
Published: April 2008

The dynamic response of a cracked gas-bearing spindle system is studied in this work. A round Euler-Bernoulli beam is used to approximate the spindle system. The stiffness effect of the gas bearing spindle is considered as massless springs and the Hamilton principle is employed to derive the equation of motion for the spindle system. The effects of crack depth, rotation speed and air applied pressure on the dynamic characteristics of a rotating gas-bearing spindle system are studied.