bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Turbulence Models With Experiment for Heat Transfer in a Cooling Channel With Dimples
Authors: Guntur Krishna , Amano R. S. , Lucci Jose Martinez
Published: May 2012

Turbine blade cooling is one of the most important developments in gas turbine history. Development of blade cooling enabled increase in firing temperature and in turn improving the efficiency. Different cooling channel geometries have been tested for improving the heat transfer efficiency. Smooth channels, channels with sharp bends, channels with ribs and other such tabulators were used to improve the turbulence and thereby increasing the efficiency. In the recent developments, hemi-spherical dimples are being considered instead of ribs as dimples have less pressure loss. This paper compares numerical computations of the heat transfer characteristics of a dimpled rectangular channel with published experimental values. Reynolds number ranges from 5000 to 40,000. For the numerical computations two different turbulence models, k-ε and k-ω models are used, the software for the simulation was Fluent and grid generation was achieved by Ansys workbench. The dimpled channel results are normalized with the smooth channel results.
Determining the Computational Domain Length to Obtain Closure for VAT Based Modeling by 3D Numerical Simulation and Field Synergy Analysis
Authors: Zhou Feng , Hansen Nicholas , Catton Ivan
Published: May 2012

Volume Averaging Theory (VAT) has been used to rigorously cast the point-wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of heat exchanger channel morphology. Closure terms in the VAT equations are related to a local friction factor and a heat transfer coefficient of the REV, which could be evaluated using scaling suggested by VAT from the output of a CFD code. To get reasonable lower scale flow field and heat transfer solutions, the length of computational domain must be determined in advance. There-dimensional numerical simulations for laminar heat transfer and fluid flow characteristics of plain finned tube heat exchangers were performed. The effects of two factors, Reynolds number and tube row number, were examined. The Reynolds number based on the fin collar outside diameter varied from 500 to 6000 and the corresponding air frontal velocity was ranged from 0.38m/s to 4.6m/s. The cases with tube row number varying from 1 to 9 were tested numerically. Field synergy principle analysis was performed for the results, including the in-depth analysis of every REV, which gave a clear perspective of the variation of heat transfer performance with the tube rows. It is found that when the number of tube row N>4, the increasing trend of the intersection angle decreases and almost keep constant when N>6, which leads to the heat transfer approaching fully developed conditions. Simulations over the computational domain with a length of 5+2+2 REVs were recommended to obtain a reasonable local flow and heat transfer field, and then the VAT based closure formulas for drag resistance coefficient and heat transfer coefficient were integrated over the sixth and seventh REV to close the heat exchanger modeling based volume averaging theory.
Minimization of Errors in a Calibration-Surface-Derived Scanning Probe Microscope Model
Authors: Okorafor M. K. , Clayton G. M.
Published: May 2012

In this paper, we present a method to choose operating parameters to minimize intrinsic error in a newly developed scanning probe microscope (SPM) modeling method. This modeling method uses the probe-sample interaction signal to develop a model for the SPM dynamics — it is noted that this is especially advantageous when sensor information is either unavailable or unreliable. Despite the method’s advantages, the choice of operating parameters affect the accuracy of the model. The main contribution of this paper is a complete error analysis of the modeling method and the application of multi-objective optimization to determine SPM operating parameters that minimize this error.
Numerical Studies of Stretching Liquid Bridges Between Two Spherical Solid Particles With Different Contact Angles
Authors: Darabi Pirooz , Pougatch Konstantin , Salcudean Martha , Grecov Dana
Published: May 2012

Numerical simulations of the governing Navier-Stokes equations are used to predict the rupture and liquid distribution of stretching liquid bridges between two equal-sized solid spherical particles with different liquid-solid contact angles. A commercial computational fluid dynamics (CFD) tool — FLUENT — is used. The effects of the capillary number and contact angle on the rupture distance and liquid transfer fraction are studied. The simulation results show that for particles with different contact angles, the rupture distance increases as the capillary number is increased; this is similar to the case of particles with identical contact angles. Also, it is shown that for quasi-static conditions, the rupture distance decreases as the difference between the contact angles is increased. Plots of the variations of the liquid transfer fraction with respect to the capillary number show three zones: (1) for high capillary numbers, liquid is almost equally distributed (dynamic zone); (2) for low capillary numbers, the liquid transfer fraction depends on the contact angles and more liquid is transferred to the particle with the smaller contact angle (quasi-static zone); (3) at intermediate capillary numbers, the curve connecting the above limiting conditions resembles an S-shape (transition zone), showing the dependency of the liquid distribution on both capillary number and contact angles. The trends are consistent with the experimental findings published in the literature.
Analysis of Wheel-Tissue Interaction for In Vivo Robotic Mobility
Authors: Wang Xin , Qi H. Jerry , Rentschler Mark E.
Published: May 2012

Providing mobility of miniature, in vivo surgical robots under a variety of changing in vivo conditions is necessary to help expand the application of minimally invasive surgery. Analytical and finite element analysis results of wheeled mobility on tissue inside abdominal cavity are presented here, as a preliminary step towards further improved mobility performance. Results indicate that the mobility of a wheeled robot on tissue is influenced by factors including wheel torque application rate and material relaxation time. While using a viscoelastic standard linear solid material tissue model, the steady state translation speed of the wheel decreases with the increase of material relaxation time given a constant torque application time. Interestingly, at a relaxation time threshold value, the wheel’s steady-state speed no longer decreases, but abruptly undergoes continuous acceleration. Results also indicate that for very small and very large relaxation times the viscoelastic material can be approximated as an elastic material.
Analysis of Embedded Blade Root Carrot and T-Bolt Connections Subject to Cold Weather Conditions Using a Finite Element Model
Authors: Lillo Patricio , Crawford Curran
Published: May 2012

Canada has aggressive targets for introducing wind energy across the country, but also faces challenges in achieving these goals due to the harsh Canadian climate. One issue which has received little attention in other countries not experiencing these extremes is the behavior of the composite blades in winter conditions. The scope of this work is to determine and analyze the static stresses on the blade root during operational conditions at extreme cold temperatures. The paper analyses the stresses in the root of the composite blades, specifically two blade-hub connection methods: embedded root carrots and T-bolts. Finite element models of the root are proposed to properly simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. Finally, it is shown that the blade root is strongly affected by the thermal stresses caused by the mismatch and orthotrophy of the coefficients of thermal expansion of the blade root constituents.
Computational Fluid Dynamics for Atherosclerosis and Aneurysm Diagnostics
Authors: Al-Rawi M. A. , Al-Jumaily A. M. , Lowe A.
Published: May 2012

Non-invasive diagnosis of cardiovascular diseases is a valuable tool to reduce patient’s risk and discomfort. The main aim of this work is to investigate the possibilities of using computational fluid dynamics as a tool to investigate the biomechanical characteristics of the aorta under different medical conditions. These conditions include an aorta with healthy conditions, atherosclerosis and aneurysm. A three dimensional pulsatile flow model for an elastic aorta is developed and constructed in ANSYS® CFX 12. Abnormalities are simulated as diameter changes at the root of the ascending aorta. The computational model shows the reflection of these diseases on the blood flow and the artery wall at other locations downstream along the aorta. This 3D model has several advantages over previously published 1D and 2D models by giving more realistic results as compared with clinical trials.
Study on a Novel SFOC/GT Hybrid Cycle System With CO2 Capture
Authors: Duan Liqiang , Yang Yongping , He Binbin , Xu Gang
Published: May 2012

A novel SOFC/GT hybrid cycle system with CO2 capture is proposed based on the typical topping cycle SOFC/GT hybrid system. The H2 gas is separated from the mixed gas of SOFC anode outlet by employing the advanced ceramics proton membrane technology, and then it is injected into the afterburner. The combustion production gas of the afterburner expands in the turbine. The SOFC anode outlet gas employs the oxy-fuel combustion mode in another burner after H2 gas is separated. Then, the oxy-fuel combustion production gas expands in another micro turbine. In order to ensure the flue gas temperature not exceed the maximum allowed temperature of the micro turbine, steam is injected into the oxy-fuel burner. The outlet gas of the oxy-fuel burner contains all the CO2 gas of the system. When the steam is removed by condensation, the CO2 gas can be captured. The steam generated by waste heat boiler is used to drive refrigerator and make CO2 gas liquefied at a lower temperature. The performance of the novel quasi-zero CO2 emission SOFC/GT hybrid cycle system is studied with a case study. The effect of CO2 liquefaction temperature and the oxygen production energy consumption on the new hybrid cycle system performance are investigated. Compared with the other quasi-zero CO2 emission power systems, the new system has the highest efficiency. The research achievements will provide the valuable reference for further study of quasi-zero CO2 emission power system with high efficiency.
Heat Transfer Enhancement by Helium Gas Filled in a Hard Disk Drive Enclosure
Authors: Yang Jiaping , Tan Cheng Peng , Ong Eng Hong
Published: May 2012

Heat transfer issue has become a challenging task in designing a high power density data center. As power consumption (Watts) of the data center continues to increase, effective thermal management of computing clusters, servers and data storage systems in data center will become more and more demanding. Hard disk drive (HDD) as a key power consumption device in high-end data storage system, its heat transfer issue has attracted more research attentions due to its complexity in nature of enclosure air flow driven by spinning disks. Among various thermal management solutions, one promising approach is to enclose helium rather than air in the hermetically-sealed hard disk drive as to reduce windage loss and flow disturbance. This paper investigates the thermal performances of disk drives where their enclosures have been filled up with helium and various helium-air gas mixtures using FEM simulations and experimental validations. Windage loss and heat convection of the disk drives being filled up with helium or helium-air mixtures are compared and analysed. The results show that helium-filled HDD provides heat transfer enhancement capability than the air-filled HDD by achieving up to 41% reduction of average temperature rise. Furthermore, 40% reduction of magnetic transducer position error signals (PES) was experimentally observed in helium filled HDD. Enhancing heat transfer and better PES quality via helium gas will greatly improve HDD read/write reliability and increase track density capability for data storage systems in data center.
Experimental Study on Oblique Collisions of Water Droplets With Hot Solid
Authors: Fujimoto Hitoshi , Doi Ryota , Ogihara Tomohiro , Hama Takayuki , Takuda Hirohiko
Published: May 2012

The oblique collision of single water droplets with a hot Inconel 625 alloy surface has been investigated by means of a two-directional flash photography technique that uses two digital still cameras and three flash units. The experiments were conducted under the following conditions. The pre-impact diameter of the droplets was approximately 0.6 mm, the impact velocity was 1.9–3.0 m/s, and the temperature of the Inconel 625 alloy surface ranged from 170 °C to 500 °C. The impact angle of the horizontal line to the tilted solid surface was 30°. When a droplet impacts a solid at a temperature of 200 °C with an impact velocity of approximately 2.0 m/s, many boiling vapor bubbles are formed at the liquid/solid interface. The droplet deforms into an asymmetric disk and moves downward along the tilted surface. Numerous secondary droplets jet upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. At a surface temperature of 500 °C, no secondary droplets are observed. The droplet rebounds off the solid without disintegration. The shape of the droplet is almost axisymmetric during the collision. Experiments using 2.5-mm-diameter droplets at an impact velocity of approximately 1.0 m/s were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At a surface temperature of 500 °C, the two dimensionless deformation behaviors of the droplets are similar to each other. The hydrodynamics and boiling phenomena of the droplets were investigated in detail.
Mechanical Properties and Microfabrication Study of Injection Molding on Ultra-High Molecular Weight Polyethylene Polymer
Authors: Kuo Hsien-Chang , Jeng Ming-Chang
Published: May 2012

In this study, the experiments were divided into three categories: tensile strength experiments, wear test experiments and microstructure molding experiments. Firstly, as the tensile strength of UHMWPE being concerned, the experimental results indicate that the effect of process parameters is relatively smaller than weld line on the tensile strength of specimens. The frictional heating could enhance the molecular bonding and self-diffusion in the frozen layer of both sides on the weld line region during the experimental observations. Secondly, as the wear behavior being concerned, the experimental results show that the friction coefficient increase linearly with the increase of sliding frequency. The results also indicate that the wear resistance in the sliding direction perpendicular to the melt flow direction is stronger than that in the sliding direction parallel with the melt flow direction. The main wear mechanisms in dry sliding conditions were plastic deformations and wrinkled formations observed by optical microscopy. Thirdly, as the micro-fabrication being concerned, replication accuracy was examined for injection molding and injection compression molding. Both the injection molding parts and the injection compression molding parts were observed under microscope to compare their replication accuracy. The experimental results show that the micro-structures can be filled with UHMWPE by injection molding and injection compression molding technology. The height and shape of microstructure were affected by process parameters. Thus for better replication accuracy, both injection molding and injection compression molding processes will be in need of a parametric optimization.
Mechatronic Design for a Fail-Safe Catheter Guide System
Authors: Che Zakaria Noor Ayuni , Komeda Takashi , Low Cheng Yee
Published: May 2012

Interventional Radiology (IVR) is one of the Minimally Invasive Surgery (MIS) methodologies. The operation of the IVR procedures are guided by image guidance Digital Subtraction Angiography (DSA) device which transmits continuous x-rays to detect the position of catheter. Catheter is a small tube inserted in blood vessel or body cavity, used in IVR procedures for diagnosing or treatment purposes. Recently, there has been considerable interest in developing remote-control system for catheter guide to prevent the surgeons from the risk of x-rays exposure. This paper describes the mechatronic design for a fail-safe catheter guide system used in blood circulatory system for IVR procedures. Several aspects of the catheter guide system are described, i.e. requirements, functions, environment, active structure, and behavior. There are close interplay between these aspects. Such a representation forms the basis for the subsequent design concretion. The prototype development of a key module for the catheter guide system, i.e. the slave system, is exemplified.
A Review of Cooling Systems in Electric/Hybrid Vehicles
Authors: Lin Wamei , Sunde´n Bengt
Published: May 2012

Due to increasing oil demand and serious global warming, a green power generation system is urgently requested in transportation. Electric/hybrid vehicles (EV/HEV) have been considered as a potential solution with great promise in achieving high energy/power efficiency and a low environmental impact. The important electric and electronic equipment in EV/HEV are the battery, inverter and motor. However, because of the high power density in the inverters or the low working temperature of batteries, the cooling problems affect significantly the working performance or the lifetime of electric and electronic equipment in EV/HEV. This paper views different cooling systems including the battery cooling system, inverter cooling system and motor cooling system. A general introduction to the EV/HEV and the electric and electronic equipment working processes are briefly presented at first. Then different methods for the battery cooling system, the inverter cooling system and the motor cooling system are outlined and discussed in this paper. Among other things, the means of using phase change material, or electro-thermal modules are significant for the battery cooling system. Finally, some conclusions or recommendations are presented for the cooling systems, in order to promote the EV/HEV development.
Adaptive Sliding Mode Control of Piezoelectric Tube Actuator With Hysteresis, Creep and Coupling Effect
Authors: Chung S. H. , Fung Eric H. K.
Published: May 2012

The piezoelectric tube actuator of Atomic Force Microscope (AFM) realizes rapid scanning in nano-scale. However, hysteresis, creep and coupling effect of piezoelectric tube actuator significantly limit the precision of AFM. In this paper, an adaptive sliding mode controller is proposed to minimize the tracking error due to the adverse effects. The piezoelectric tube actuator is characterized as a multiple-input-multiple-output (MIMO) nonlinear time-varying system because of hysteresis and creep. The controller is designed based on the reduced order nonlinear finite element (FE) model. Hysteresis is divided into a linear part and a bounded time-varying unknown part to reduce the bound of the uncertainties. The latter part together with creep and electrode dislocation is considered as bounded uncertainty. The controller gains of the equivalent control part are estimated through adaptive laws. The sliding mode observer is designed based on Walcott Zak observer for estimating the unmeasurable states. Lyapunov criterion is stated to guarantee the stability of the closed loop system. The simulation of the piezoelectric tube actuator with the adaptive sliding mode controller is performed under scanning operation. The result shows that the tracking errors are bounded in small values. Finally, the performance of the adaptive sliding mode controller is compared with the output feedback controller and the proportional-integral (PI) controller which is commonly adopted in AFM.
Recent Advancement on Liquid Metal Cooling for Thermal Management of Computer Chip
Authors: Liu Jing , Deng Yue-Guang , Deng Zhong-Shan
Published: May 2012

Efficient cooling of a high performance computer chip has been an extremely important however becoming more and more tough issue. The recently invented liquid metal cooling method is expected to pave the way for high flux heat dissipation which is hard to tackle otherwise by many existing conventional cooling strategies. However, as a new thermal management method, its application also raised quite a few challenging fundamental and practical issues for solving. To illustrate the development of the new technology, this talk is dedicated to present an overview on the latest advancements made in the author’s lab in developing the new generation chip cooling device based on the liquid metal coolant with melting point around room temperature. The designing and optimization of the cooling device and component will be discussed. Several major barriers to prevent the new method from practical application such as erosion between liquid metal coolant and its substrate material will be outlined with good solutions clarified. Performance comparison between the new chip cooling method with commercially available products with highest quality such as air cooling, water cooling and heat pipe cooling devices were evaluated. Typical examples of using liquid metal cooling for the thermal management of a real PC or even super computer will be demonstrated. Further, miniaturizations on the prototype device by extending it as a MEMS cooling device or mini/micro channel liquid metal cooling device will also be explained. Along with the development of the hardware, some fundamental heat transfer issues in characterizing the liquid metal cooling device will be discussed through numerical or analytical model. Future challenging issues in pushing the new technology into large scale practices will be raised. From all the outputs obtained so far, it can be clearly seen that the new cooling strategy will find very promising and significant applications in a wide variety of engineering situations whenever thermal managements or heat transport are needed.
Reduction of Flow Induced Vibration in Hard Disk Drive
Authors: Mou J. Q. , Zhang Q. D. , Sundaravadivelu K. , Liu N. Y. , Ong E. H.
Published: May 2012

In this paper, system level analysis is carried out for a functional HDD with two disks and four sliders operating at spindle speed of 15000 rpm. Full numerical models both for computational fluid dynamics (CFD) analysis and structural Finite Element Analysis (FEA) are developed. The flow induced vibrations of the sliders in all three directions, namely, off-track (X), down-track (Y) and out-of-plane direction (Z) are examined respectively. The numerical simulation results are compared and validated with the experimental results measured with a 3D laser Doppler vibrometer (LDV). Good agreements are observed for the vibrations in the three directions. The airflow patterns and characteristics of the flow induced vibration in HDD for three critical positions of the head gimbal assembly (HGA) parked at the disks identified as ID, MD and OD are investigated. The results reveal that the first slider from top has the highest flow induced vibrations in all the three directions due to the higher turbulent flow close to the top disk surface. Moreover, the results indicate that the slider vibration is interacted with the disk flutter in the HDD. Optimal designs of the HDD disk and air shroud are carried out to reduce the flow induced vibration of the slider, by suppressing the disk flutter and improving the turbulent flow in the HDD. It is demonstrated that significant reduction of flow induced slider vibration could be achieved with the optimal designs of the HDD.
Structural Health Monitoring Using PZT Transducer Network and Lamb Waves
Authors: Mou J. Q. , Martua L. , Yu Y. Q. , He Z. M. , Du C. L. , Zhang J. L. , Ong E. H.
Published: May 2012

Structure health monitoring (SHM) using ultrasonic waves is an emerging technology that can be applied to real-time detect, locate and quantify the structural damages in aircraft structures. In this paper, the monitoring of crack growth at rivet holes in an aluminum test plate using a PZT transducer network and Lamb waves is investigated. The thin disc PZT transducers surface mounted at the test plate are used as actuators to transmit the windowed sinewave bursts and sensors to receive the ultrasonic Lamb waves. The symmetrical S0 mode and antisymmetrical A0 mode of the Lamb waves in the structures are studied with correlated theoretical, experimental and numerical analysis. The optimal excitation frequency is determined for the test plate. Finite element method (FEM) numerical models for simulations of the wave propagations and interactions with the holes and cracks in the plate are developed and verified with the experimental results. The wave responses modes and characteristics for detection of the cracks at the rivet holes are analyzed. The Lamb wave signals in the PZT transducer network are processed with the short time Fourier transform (STFT). It is demonstrated that the time of flight and the energy transmission ratio of the S0 wave are sensitive to the cracks in the structure.
Unsteady Numerical Analysis on PCCI Combustion Affected by Intentional Initial Fuel Concentration Distribution
Authors: Yoshida Kenji , Yamada Kenichi , Matsuo Naoshige , Tanimura Toshinobu , Takayama Takemori , Kataoka Isao
Published: May 2012

Unsteady numerical analyses were carried out for the PCCI combustion realization on the next generation diesel engine. The effects of intentional initial fuel concentration distribution on the ignition timing and the expansion of the operable range were focused. The numerical code was originally developed to analyze the unsteady combustion behavior of premixed gas with intentional initial fuel concentration distribution in the combustion chamber of PCCI engine. The fundamental equations for the numerical analysis are the Euler’s equations for compressible fluid, that consist of the conservation equation of mass, momentum, energy and chemical species. The equations are expressed in axisymmetric cylindrical (r-z) coordinate system. The time variation of the internal cylinder volume of the reciprocating crank-piston movement is expressed by the volume change rate, which is substituting the convection term in axial direction of the Euler’s equations. By using this technique, we can reduce the spatial dimension of the equations with keeping the consideration of volume change of the combustion chamber of reciprocating engine. The radial direction corresponds to the bore of the engine cylinder. By solving this equation system, we can consider the radial distribution in combustion chamber during the PCCI combustion such as temperature, mass fraction of chemical species, pressure, and so on. Detailed chemical kinetics with elementary reactions and multi-component diffusion for n-heptane system as fuel, ERC-mechanism, were considered. The NOx emission can be also considered by using the part of GRI-Mech3.0 for generation of thermal NOx. Totally, the 34 chemical species and 61 elementary reactions were considered. This code has a high resolution for time and space to capture the dynamic behavior in PCCI combustion such as a generation and propagation of shockwave causing detonation. A series of unsteady events on PCCI combustion can be simulated by considering the time variation of volume of combustion chamber varied with crank angle; such as the charged compression and auto-ignition of premixed gas, the flame propagation and the detonation with shockwave.
Possibility of a Hyperflexion Neck Injury in a Rear Impact Accident for a Rear Middle Seat Passenger
Authors: Thorbole Chandrashekhar K. , Renfroe David A. , Andrews Stan B. , Partain Mark M. , Tanwar Digvijay S.
Published: May 2012

Rear impact accidents primarily involve neck extension injury. The sudden forward motion of the lower torso causes the head to lag the body. This results in the extension injury or whiplash injury, depending on the rate at which the struck vehicle moves forward. The front seat passengers are equipped with various technologies to help prevent the neck injuries in a rear impact scenario. A range of research has been conducted to investigate the effect of various seat design characteristics on the neck injury during a rear impact. The head restraint on the seat limits the backward movement of the head, thus preventing the serious injury. The neck injury is still a major problem for a rear seat passenger. However, very little effort has been made to improve the rear seat crashworthiness performance relating to a rear impact. Surprisingly, the middle rear seat is not required to comply with the FMVSS 202 standard. This paper demonstrates the possibility of a neck hyper-flexion during a rear impact and the mechanism of a facet dislocation injury for a rear middle seat adult passenger. A biodynamic computational model is utilized to simulate the rear impact accident of an adult male. A MADYMO standard Hybrid III 50th percentile ATD is used to simulate a real world rear impact accident. The accident reconstruction is conducted using PC CRASH to analyze the impact orientation and the change in velocity of the struck vehicle. This information along with the crush on the vehicle is used to develop an acceleration pulse to be applied on the occupant. The rear compartment of the subject vehicle was digitized using a FARO arm to recreate the exact seat structure and interior features for the simulation. This study investigates the inadequate performance of the lap belt in conjunction with roof to seat clearance for the middle seat passenger in reducing the injury severity during a rear impact.
Improving the Performance of a PEMFC by Means of Achieving Uniform Flow Distribution
Authors: Ramos-Alvarado Bladimir , Hernandez-Guerrero Abel , Elizalde-Blancas Francisco , Rubio-Arana Cuauhtemoc
Published: May 2012

A performance analysis of a proton exchange membrane fuel cell is reported in this work. Two different flow patterns are modeled as gas distributors and current collectors of a PEM fuel cell. Both flow patterns have the same active area with similar channel distribution over the membrane electrode assembly. Three dimensional models are used in order to simulate the performance of the fuel cells. The Navier-Stokes equations as well as potential fields (potentiostatic and galvanostatic) are solved using computational fluid dynamics techniques. Two dimensionless parameters were computed to quantify and compare the uniformity of the flow over the reaction area. The present analysis shows that achieving a good flow distribution is a key parameter in the PEMFC performance. The reduction of the concentration losses is the main result when a parallel channel configuration operates with uniform reactants distribution. In this study is demonstrated that the conventional parallel channels flow pattern does not achieve similar flow conditions in each sub-stream and therefore, irregular energy generation is obtained.
Real Shear Forces and Moment Generated by Tyre During Pure Lateral Slip
Authors: Kie´bre´ Rimyalegdo , Anstett-Collin Floriane , Basset Michel
Published: May 2012

This study takes an interest in the tyre/road interface characteristics modelling during steady-state pure cornering. In the literature, it is mostly assumed zero longitudinal force during pure cornering of tyres. However, in the present study, longitudinal force data recorded during pure lateral slip of a civil aircraft tyre have shown relative significant magnitudes when they are compared with the corresponding lateral force magnitudes. Thus, for this type of tyres, neglecting longitudinal force during pure lateral slip might lead to an inaccurate representation of the real tyre behaviour. The Poisson ratio, which describes the contraction of an incompressible material when it is stretched in one direction, is taken into account in a comprehensive physical approach to describe the generation of this force. Moreover, it has been possible to exhaustively describe the generation of the self-aligning moment by decomposing it into contributions of the induced longitudinal force and of the lateral force. Relative simple models are proposed for the induced longitudinal force and for the self-aligning moment and finally, they are validated using the measurements data.
Compression and Flexural Response of Carbon/Epoxy-Nanoclay Nanocomposites Subjected to UV Radiation and Condensation
Authors: Tcherbi-Narteh Alfred , Hosur Mahesh V. , Zainuddin Shaik , Jeelani Shaik
Published: May 2012

Compressive and flexural properties of carbon fiber reinforced composites (CFRC) infused with montmorillonite nanoclay exposed to UV radiation and condensation was examined in this study. Nanoclay contents in samples used in this study were 0 (control), 1, 2 and 3 wt%. Samples were exposed to 15 days UV radiation and condensation using QUV/SE accelerated weathering system. Compressive properties were characterized using quasi-static and dynamic loadings before and after exposure. Flexural properties were also characterized through three point bending test according to ASTM standards. Compressive and flexural properties were monitored every 5 days of exposure in each conditioning. UV exposed samples with nanoclay showed a different trend after 5 days compared to neat samples, showing an increase in strength and modulus after 10 days of exposure. Samples exposed to condensation did not follow any specific pattern, although there was a decrease in mechanical properties in all samples.
On the Transition From Creeping to Inertial Flow in Arrays of Cylinders
Authors: Yazdchi K. , Srivastava S. , Luding S.
Published: May 2012

Many important natural processes involving flow through porous media are characterized by large filtration velocity. Therefore, it is important to know when the transition from viscous to the inertial flow regime actually occurs in order to obtain accurate models for these processes. In this paper, a detailed computational study of laminar and inertial, incompressible, Newtonian fluid flow across an array of cylinders is presented. Due to the non-linear contribution of inertia to the transport of momentum at the pore scale, we observe a typical departure from Darcy’s law at sufficiently high Reynolds number (Re). Our numerical results show that the weak inertia correction to Darcy’s law is not a square or a cubic term in velocity, as it is in the Forchheimer equation. Best fitted functions for the macroscopic properties of porous media in terms of microstructure and porosity are derived and comparisons are made to the Ergun and Forchheimer relations to examine their relevance in the given porosity and Re range. The results from this study can be used for verification and validation of more advanced models for particle fluid interaction and for the coupling of the discrete element method (DEM) with finite element method (FEM).
Lattice Boltzmann Modeling of Phonon Heat Conduction in Superlattice Structures
Authors: San Marti´n Cristian J. , Guzma´n Amador M. , Escobar Rodrigo A.
Published: May 2012

The results of temperature prediction and determination of effective thermal conductivity in periodic Si-Ge superlattice in one dimension, at length scale comparable to the mean free path are presented. Classical heat transfer models such as Fourier’s law do not represent what actually happens within electronic devices at these length scales. Phonon-border and phonon-interface scattering effects provide discontinuous jumps in temperature distribution when the mean free path is comparable with the device’s characteristic length, a relation given by the Knudsen number (Kn). For predicting the temperature within the periodic Si-Ge superlattice use is made of the lattice Boltzmann method in one dimension, using Debye’s model in the phonon dispersion relation. The predictions show that as Kn increases, so do the jumps at the borders, the same as at the interfaces. The prediction also shows that the effective conductivity of the Si-Ge superlattice decreases as Kn and the number of layers of material increase, and that keff decreases as the magnitude of p increases, a factor that allows heat flow between one layer and another. Use of gray LBM leads to good approximations of the actual temperature field and thermal conductivity values for the superlattice materials model when the physics of phonons established by Debye’s model is used.
Gas Evolution of Corn Kernels and Paper Sludge From Biomass Gasification and Pyrolysis
Authors: Ulstad James , Ratner Albert , Dochtermann Jean , Sulak Brian , Hennigan John
Published: May 2012

Gasification of biomass has become an area of key interest as it is a reasonably quick and direct way of converting the material into a fuel source that works directly in many industrial systems. The purpose of the present work is to explore gasification and pyrolysis behavior of corn kernels and paper sludge. For both corn kernels and paper sludge, low temperature gasification behavior was studied. Due to corn’s low ash fusion temperature, ∼1400 C, gasification is typically undertaken at temperatures near 1000 C, and most of the chemical mechanisms are similar down to ∼500 C. Here, tests were performed with pyrolysis temperatures from 400–800°C, at 1 atm and a rapid heating rate. The evolution of CO and CO2 were measured throughout the pyrolysis process. Results show a direct correlation between temperature and equivalence ratios and the composition of the gas byproduct for both biomasses. CO production increases with an increase in temperature while CO2 shows no temperature correlation. No hydrogen was observed, as would be expected for the short experimental residence time (0.2 seconds).
Size Specific Immunofluorescence of Mycobacterium Tuberculosis Cells by Using a Microtip-Sensor
Authors: Yeo Woon-Hong , Chou Fong-Li , Gao Dayong , Shen Amy Q. , Chung Jae-Hyun , Lee Kyong-Hoon
Published: May 2012

The size-specific capturing mechanism for Mycobacterium tuberculosis (MTB) cells is presented using a microtip-sensor. When a microtip is withdrawn from a solution drop, enriched cells by an alternating current (AC) electric field are selectively captured onto the tip due to capillary- and viscous forces. The size-specificity on the 50 μm-diameter tip is studied by using polystyrene microspheres. The size-specific capturing mechanism is applied to capture MTB cells from a sample mixture containing MTB and Drosophila S2 cells. Under the competition between capillary- and viscous forces, MTB cells are captured onto the microtip by the viscous force, while Drosophila S2 cells are removed from the tip by the capillary force. The microtip-sensor yields the detection limit of 800 cells/mL for MTB cells, which is one of the highest-sensitivity immunosensors.
Thermal Analysis of the Particle Critical Velocity on Bonding Efficiency in Cold Gas Dynamics Spray Process
Authors: Jen Tien-Chien , Wong Sung-Cheng , Yen Yi-Hsin , Chen Qinghua , Liao Quan
Published: May 2012

This paper presents a numerical analysis of the particle critical velocity on the bonding efficiency in Cold Gas Dynamic Spray (CGDS) process by using ABAQUS/CAE 6.9-EF1. The particle impact temperature in CGDS is one of the most important factors that can determine the properties of the bonding strength to the substrate. In the CGDS process, bonding occurs when the impact velocity of particles exceed a critical velocity [1], which can reach minimum interface temperature of 60% of melting temperature in °C [2]. The critical velocity depends not only on the particle size, but also the particle material. Therefore, critical velocity should have a strong effect on the coating quality. In the present numerical analysis, impact velocities were increased in steps of 100 m/s from the lowest simulated impact velocity of 300 m/s. This study illustrates the substrate deformations and the transient impact temperature distribution between particle(s) and substrate. In this paper, an explicit numerical scheme was used to investigate the critical velocity of different sizes of particle during the bonding process. Finally, the computed results are compared with the experimental data. Copper particles (Cu) and Aluminum substrate (Al) were chosen as the materials of simulation.
Principles of Development and Foundations of Dynamical Analysis of Optimal Brake Leverage Systems of Passenger Carriages
Authors: Sharashenidze Guri , Gelashvili Otar , Kurtanidze Pavle , Dolidze Mamuka
Published: May 2012

The safety movement of rolling stock is depended on the parameters of “carriage-rail” dynamical system as well as on the automatic brake’s reliability. The automatic brake provides the full brake effect at which the brake force transfer to the brake shoes is executed by linkage mechanical system. The linkage mechanical system will transfer the brake force with minimal force losses is characterized by simple structure and reliability operation. Hence the development of such system is very topical and problematic task. Nowadays the brakes systems consist from number of levers therefore are characterized by force great losses in the hinge junctions on the friction overcoming, great material capacity and making costs. In the work are developed perspective passenger car mechanical system, in which are overcoming the noted problems-they have simple structure, better condition for brake and force transfer, minimal economical costs. For brake mechanical systems optimal design due developed in the dynamic model are solved the dynamic analysis tasks. Due the carried out theoretical researches and according computational experiment is achieved the topical task solution. Carried out in the work research is acceptable for other kinds of brake mechanical systems optimization task solution as well as is possible fore application at development and research of arbitrary complexity lever mechanical system.
Threat Assessment and Control Decision for Automated Lane Change Maneuver
Authors: Lee Jin-Woo , Chen Xingping
Published: May 2012

Automated vehicle steering control has been actively researched in the automotive industries and academia over a decade. While several automotive companies and suppliers have recently demonstrated autonomous parking, lane keeping control, and lane centering control systems, automated lane change and obstacle avoidance maneuvering have not been as well demonstrated with the same level of maturity. This paper describes an algorithm that assesses environment and situation around the subject vehicle and makes a proper decision when an automated lane change or obstacle avoidance maneuvering is needed. The algorithm continuously monitors the surrounding traffic and lane markings using various types of sensors, and makes judgments along the vehicle future motion. Collision threat is evaluated by comparing the future path of the vehicle and the surrounding traffics in temporal-spatial plane. Typical driving behavior patterns are modeled to ensure safety under various scenarios. This algorithm has been implemented on a test vehicle and validated on straight and curved roads for various speeds of up to 110km/h. Several test cases have been completed and the results are provided.
Non-Contacting Seal for Rail Freight Applications
Authors: Lattime Scott B. , Borowski Richard
Published: May 2012

Due to increasing energy costs and emissions restrictions, many industries are paying closer attention to the energy required to keep their equipment operating. Parasitic losses in power such as those due to the drag produced by contacting lip seals that are found in a variety of rotating equipment can significantly add to the total operating costs of that equipment. In mobile industries (railroad, heavy truck, and automotive), these losses can significantly affect the amount of fuel consumed and emissions produced. Power losses due to seal drag are also accompanied with frictional heat and wear which can degrade components and lead to maintenance costs to service or replace these components. To address these issues for the railroad industry, Timken has developed a non-contacting seal for use in railroad bearings. A review is given of the design and development of a non-contacting labyrinth seal for railroad bearing applications. The seal has been qualified by the Association of American Railroads (AAR) for use in North America freight car service and is currently the only non-contacting seal in operation for this market. The unique design of the labyrinth pathway allows for zero seal drag with exceptional grease retention and contaminant exclusion capabilities as compared to contacting elastomer lip seals that are typical for this industry. Experimental test performance of this seal will be compared to other seals that are currently used in this industry. Operating torque reductions of 10–30 in-lb per seal achieved through this technology can lead to fuel savings on the order of hundreds of thousands of gallons per year corresponding to the elimination of thousands of tons of emissions due to the reduced fuel usage in the U.S. alone. These savings can be passed directly to railroads and freight car owners as well as the general population with lower operating costs, increased reliability, longer service life, and reduced emissions.
Estimating the Performance of Sound Restoration Hearing Protectors by Using the Speech Intelligibility Index
Authors: Azman Amanda S. , Yantek David S.
Published: May 2012

Despite advances in engineering noise controls and the use of administrative controls, miners are still dependent on hearing protection devices for prevention of noise-induced hearing loss. However, miners often raise concerns about the audibility of spoken communication when wearing conventional hearing protectors. Electronic technologies that selectively process and restore sounds from outside of hearing protectors have been suggested as a partial remedy to the audibility problem. To assess the potential benefits of this technology for miners, NIOSH tested the impact of nine electronic sound restoration hearing protectors on speech intelligibility in selected mining background noises. Because of the number of devices and potential settings of those devices, it was necessary to narrow the choices before conducting human subject testing. This was done by testing the nine devices on an acoustic test fixture (ATF) to acquire one-third-octave-band data, and then calculating the speech intelligibility index (SII) to determine estimates of performance across device, noise and setting. The estimates of speech intelligibility obtained with the SII are highly correlated with the intelligibility of speech under adverse listening conditions such as noise, reverberation, and filtering. The results of fixture based testing indicate that performance varies little between most devices, with few showing exceptionally good or poor estimated speech intelligibility. The most significant differences in estimated performance using the devices were between the different noise sources used, regardless of device or setting. The findings of this research were used to select the devices and settings for subsequent human subject based speech intelligibility testing. The human subject testing results largely concurred with the findings from the acoustic test fixture testing and calculation of speech intelligibility index. Specifically, variations in background noise led to the greatest differences in speech intelligibility.