bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of a Frontal Rail Structure With Thickness Variation That Performs Under Axial and Oblique Loading
Authors: Nusier Saied Q. , Belwafa Jamel E. , Baccouche Ridha , Mahmood Hikmat F. , Fileta Bahig
Published: August 2009

Progressive crushing of the frontal part of the frame in any collision (frontal, offset and oblique) is one of the factors that determine the safety level that a car or a truck can provide to the occupant. A new approach in frontal rail design will be covered in this paper. The rail thickness will vary along the length of the rail in such away that the compressive strength of a rear section on the compression side of the rail will be greater than or equal to the section in front of it. This design will enable the front rail to collapse in a progressive manner such that the collapse will be transmitted from the front to the rear. Preventing early global bending in the rail will enhance the efficiency of energy absorbed during a crash. Starting with the section with the lowest compressive strength (most forward section of the rail), in a controlled way, the section strength is designed to increase with length. This will help meet the federal regulations such as FMVSS 208 by collapsing the least strong front sections at lower speeds and the strong rear sections at higher speeds. Also, collapsing of the weak frontal sections in a crash can help in compatibility between different vehicles on the road.
Reliability Prediction for a Thermal System Using CFD and FEM Simulations
Authors: Al-Habahbeh O. M. , Aidun D. K. , Marzocca P. , Lee H.
Published: August 2009

A general procedure for reliability prediction is introduced. The procedure is applied to a cylindrical ring and can be used for any similar thermal application. The procedure is classified as a physics-based reliability prediction method. It utilizes different computational tools such as Computational Fluid Dynamics (CFD), Finite Element Method (FEM), and Monte Carlo Simulations (MCS). The process starts with CFD simulation to find the convective terms necessary for the transient FEM thermal analysis. The transient FEM thermal analysis provides values for thermal stress. These values are used in the fatigue life analysis. The end result is the fatigue life of the component. As a result of input parameters uncertainty, the resulting life will be in the form of a Probability Density Function (PDF), which enables the calculation of the reliability of the component.
Resistance Spot Welding (RSW) Process Optimization for Uncoated 1.0 mm Boron to Uncoated 1.0 mm Boron for Automotive Applications
Authors: Koganti Ramakrishna , Angotti Sergio , Wexler Arnon , Maatz Donald F.
Published: August 2009

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with the introduction of new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are gaining popularity due to their superior mechanical properties and weight advantages, as compared to mild steels. These new materials also pose significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application on future vehicle programs. Due to the high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for 1.0 mm uncoated boron to 1.0 mm uncoated boron 2T stack-up combination is discussed. Weld lobes were developed with Mid Frequency Direct Current (MFDC) equipment, ISO type B-16 tip, constant weld force of 3.43 kN (770 lbf), hold time of 5 cycles and the weld times were varied 10, 13 and 16 cycles. Based on the tensile, cross-tension and nugget data, there were no correlations were observed between tensile load and button size and also between cross-tension and button size. Microhardness data assessment found heat affected zone (HAZ) at the weld nugget area and similar HAZ was observed for all the welding cycles. The weld lobes, mechanical properties (tensile shear and cross-tension), cross-section examination, and microhardness of 1.0 mm boron to 1.0 mm boron 2T stack-up results are discussed.
Static and Dynamic Buckling of a Compressed Narrow Rectangular Plate on an Elastic Foundation
Authors: Srubshchik Leonid , Herskowitz Issac , Peckel Irina , Potetyunko Edward
Published: August 2009

In this paper we consider a thin narrow rectangular isotropic plate subjected to a small surface load and supported laterally by a continuous nonlinear elastic foundation. The both short ends of plate are clamped while the longitudinal sides are completely free, so that their points can move along the boundary, along the normal to the boundary, and in a vertical direction. At initial time the uniformly distributed in-plane compressive stresses are suddenly applied to the short ends in the longitudinal direction. Our goal is to find the asymptotic formulas for values of static and dynamic buckling load in the case of the narrow elastic plate and estimate their values as function of the imperfection parameter. We apply the geometrically nonlinear theory for the thin rectangular isotropic plate laterally supported by the continuous softening or stiffening foundation to formulate an associated nonlinear spectral problem for the load parameter. This problem contains a small natural parameter δ - the ratio of the width of the rectangular plate to its length and can be integrated using the asymptotic method developed in the work by Srubshchik, Stolyar and Tsibulin [1]. Accordingly we approximate the solution of the original problem by the leading term of the finite expansion in δ which is described by the motion equations of an axially compressed elastic column on the nonlinear continuous elastic foundation which has only one spatial dimension and can be investigated more comprehensively. The formulas for asymptotic values of the static and dynamic buckling compressive loads are obtained by means of the perturbation theory and by one-term Fourier’s approximation respectively. The specific numerical results for these asymptotic values are presented.
Prediction of Human Neck Injury in Rollovers From Dynamic Tests Using the Hybrid III Dummy
Authors: Friedman Donald , Paver Jacqueline G. , Caplinger Justin , Carlin Fred , Rohde David
Published: August 2009

In the U.S, there are approximately 27,000 occupants seriously injured or killed annually in rollover crashes. This study is part of an ongoing research project aimed at mitigating catastrophic human neck injuries in rollovers using results of dynamic tests, which utilize Hybrid III dummies as human surrogates. A methodology is being developed for replicating, predicting, and differentiating between axial compression and the more predominant neck flexion injuries. This paper presents platen tests, which were performed to determine Hybrid III dummy positioning and instrumentation for use in dynamic rollover tests. In addition, this paper demonstrates the use of the Pintar, et al. logistic regression curves to predict the probability of major flexion neck injury in the human from measured and adjusted Hybrid III dummy neck data. The capability of the Hybrid III dummy neck to realistically evaluate human neck injury potential is discussed.
A Film Boiling Reactor for Chemical Processing
Authors: Choi Sung Ryel , Avedisian C. Thomas , Tsang Wing
Published: August 2009

This paper presents an experimental demonstration of a chemical reactor design based on film boiling, which we term a Film Boiling Reactor (FIBOR). The FIBOR consists of a heated surface coated with a catalyst and immersed in a pool of reactant liquid. Film boiling is established in the liquid and chemical reaction occurs at the surface by reactant gases which evaporate at the liquid/vapor interface and diffuse to the heated surface. In the present study we use a horizontal tube (Inconel 600) immersed in methanol as the means to create the FIBOR. The tube is coated with a platinum catalyst. We show the performance of the reactor concept to produce hydrogen and carbon monoxide. Total flow rates of product gases of approximately 6.5 L/min for a tube surface temperature of around 800°C were measured (product yields depend on catalyst structure). The product gases were measured by gas chromatography which shows a molar ratio of two moles hydrogen to one carbon monoxide as anticipated from the methanol conversion reaction.
Automatic Feature Recognition for Data Interoperability Issues in High-Speed Electronics System Design
Authors: Chen Xiaolin , Zhang Hui , Miller Will
Published: August 2009

Technology trends toward higher speed and density devices have pushed high performance electronic system design to its limits. With fine miniaturization of very-large-scale integrated (VLSI) circuits and rapid increase in the working frequency of system-on-a-chip (SoC), the signal integrity has become a major concern. As the operating frequencies enter the gigahertz range, signal integrity issues such as cross talk, power-ground-plane voltage bounce, and substrate losses can no longer be neglected. In order to design high-performance electronic systems with fast time-to-market, it is often needed to analyze whole or part of the system at one fundamentally deeper level of physics. It has begun to be recognized that electromagnetic (EM) field analysis needs to be rigorously included as an addition to traditional circuit simulation. A common problem in this practice is the lack of efficient tools that enable engineers to easily transfer circuit board design data into EM solvers. To partially solve this problem, ACIS SAT has been introduced as a standard data exchange format and been adopted by many software vendors for data import and export. However, efficient data transfer remains a problem as the geometry created in the design package becomes static and no longer feature-based once imported into the simulation package. In this paper, automatic feature recognition algorithms are implemented to help extract features and parameters from the imported static model in SAT format. Case studies will be provided for some representative high speed electronics designs. This work is supported by Research & Technology Development Grant Program of Washington Technology Center with a goal to achieve improved design process for high-speed electronic systems. The developed tool has a potential to speed up the current design process by eliminating laborious manual preparation of design data for EM simulation and allow what-if analysis to be automated to highlight likely signal integrity issues.
Numerical Study on Cooling Effect of Engine Room Enclosure System
Authors: Bae Yee Seok , Yoo Geun Jong , Choi Hoon Ki
Published: August 2009

In engine room, proper enclosure system is preferable for reducing noise level but the enclosure system in the engine room causes bad influence on cooling performance due to poor ventilation. Cooling efficiency of the enclosure system can be improved by varying fan speed and proper flow path for ventilation. In this study, numerical analysis is performed to assess cooling effect of the enclosure system using finite volume method. The RNG k-ε model is adopted for turbulence model along with heat exchanger model and porous media model for heat exchanger analysis, and moving reference frame model for rotational fan. Cold flow analysis result shows reasonable agreement with experimental data. Analysis results show direct effect of velocity and temperature distribution on cooling ability in the enclosure system. Comparing with analysis result for the engine room which has no enclosure system, the case of total enclosure system which has box hole flow path shows the reasonable cooling capacity with noise reduction effect.
Analysis of Dynamically Loaded Floating Bush Bearing With Flexible Shaft in Flexible Anisotropic Bearing Used in Textile Application
Authors: Patel D. C. , Vakharia D. P.
Published: August 2009

A FLOATING bush bearing is a kind of bearing which has a thin bush floating freely between journal and fixed bush. In recent years considerable attention has been paid to the “vibration suppressing effect” of floating us bearing. It is reported that floating bush bearing are, if properly designed, effective in suppressing both resonant vibrations at the critical speed and self excited vibration call oil whip. This study deal with performance of dynamically loaded floating ring journal bearing and investigates their feasibility for two for one textile machine application. A mathematical model is developed and its analysis for performance of floating bush journal bearing with flexible shat in flexible anisotropic bearing is conducted. The potential contribution of the floating bush journal bearing design concept to reduce vibration is assessed and its compliance with current bearing durability criteria is evaluated. The result indicates that the adoption of floating bush design concept has potential for reducing power loss and vibration in two for one (TFO) textile machine bearing. It is shown that this can be accomplished without violating minimum film thickness constraints currently accepted as criteria for successful machine bearing operation.
Fuel Cell-Based MEMS Power Source
Authors: Moghaddam Saeed , Pengwang Eakkachai , Lin Kevin , Masel Rich , Shannon Mark
Published: August 2009

The increasing demand for high energy density power sources driven by advancements in portable electronics and MEMS devices has generated significant interest in development of micro fuel cells. One of the major challenges in development of hydrogen micro fuel cells is the fabrication and integration of auxiliary systems for generation and delivery of fuel to the membrane electrode assembly (MEA). In this paper, we report the development of a millimeter-scale (3×3×1 mm3) micro fuel cell with on-board fuel and control system. Hydrogen is generated in the device through reaction between water and a metal hydride. The device incorporates a new control mechanism for hydrogen generation that occupies only 50 nL volume (less than 0.5% of the total device volume). More importantly, the control mechanism is self-regulating and does not consume any power, enabling the micro fuel cell to operate passively, similar to a battery.
Assessment of Engineering Solutions for an Oil-Fired Air Preheater Using Numerical Simulations
Authors: Chen Xuelei , Jian Christopher , Smith Jeffrey
Published: August 2009

This paper describes the CFD (Computational Fluid Dynamics) analysis of the combustion chamber of a horizontal oil-fired air preheater. The combustion chamber was originally designed to operate with low excess air at 15%. Upon start-up, it experienced refractory overheating issues on its roof. Following the initial failure, there were questions about the apparent non-uniformity of the shell temperatures with the roof being at higher temperatures. The unknown was whether the “hot-spot” was a combustion related issue or due to refractory failure. The purpose of this project was to determine the root causes of the refractory overheating and develop solutions for the customer. Several cases with different excess air levels were investigated using CFD simulation. The simulations showed that although no flame impingement on the refractory wall was found, the flame shape was short and wide. Since the combustion chamber was operated close to adiabatic condition, the shape of the flame and high overall flue gas temperatures are believed to have contributed to the verheating of the roof refractory. The installations of 8, 12, and 16 bussle pipes around the burner in the firing end were simulated and evaluated based on combustion performance, flame shape, and wall temperature distribution in order to provide a practical solution for the customer. Air supply to the combustion chamber was increased by transferring additional air from a portion of the downstream process. The total air supply was distributed between the main burner and bussle pipes. Several conditions of different air split ratios were also evaluated. Finally, a solution was found that was both satisfactory to the air preheater operation and economical in implementation.
Two Dimensional Oscillatory Flow Analysis in the Pulse Tubes
Authors: Saidi M. H. , Taheri M. , Jahanbakhshi R. , Jafarian A. , Hannani S. K.
Published: August 2009

Recently a great attention has been given to the oscillatory flow modeling in the pulse tube cryocoolers. In this paper multi dimensioning effects of the fluid flow in the pulse tube are investigated. A complete system of governing equations is solved to report the flow field, friction coefficient and Nusselt number in the pulse tube. Harmonic approximation technique is employed to derive an analytical solution. In this respect, mass, momentum and energy balance equations as well as the equation of state for ideal gas are transformed by implementing the harmonic approximation technique. The present model is able to predict the behavior of the two dimensional compressible oscillatory flow in the tube section of the regenerative cryocoolers. Based on the proposed analytical model, friction coefficient and complex Nusselt number is reported.
Control Strategy Study of Colocated GEO Satellites Based on Eccentricity Vector Separation
Authors: Tan Wei , Jen Tien-Chien , Wang Xinfeng , Yang Xiaoqin
Published: August 2009

As the number of geostationary earth orbit (GEO) satellites continues to increase, it is becoming more common for two or more GEO satellites to colocate in the same geographical longitude over the equator. As a consequence, the risk of collision is increased significantly. So various control methods for GEO satellites to colocate are applied in order to ensure the safety of these satellites. This paper mainly focuses on the control strategy study of two colocated GEO satellites based on eccentricity vector separation. In this study, the difference between eccentricity vectors of two colocated GEO satellites is taken into account in order to guarantee that the maximum distance is maintained between two satellites in the same orbital plane. In order to obtain the optimal control strategy, three main control methods concerning eccentricity vector separation are discussed here. In the method of absolute eccentricity vector separation, the eccentricity of one GEO satellite is much larger than that of the other GEO satellite, and the movement region for two satellites does not overlap in the space. The second one is the relative eccentricity vector separation method which means the difference between two eccentricity vectors is very distinct in both the vector direction and vector size, thus one of the two colocated GEO satellites circles around the other. The third method is one kind of joint control method which combines the eccentricity separation and the inclination separation. At the end of this paper, some dynamics simulation results are given to prove the feasibility of these methods.
A Numerical Investigation of Non-Evaporating and Evaporating Diesel Sprays
Authors: Som Sibendu , Aggarwal Suresh K.
Published: August 2009

Fuel injection characteristics, in particular the atomization and penetration of the fuel droplets, are known to affect emission and particulate formation in diesel engines. It is also well established that the primary atomization process is induced by aerodynamics in the near nozzle region, as well as cavitation and turbulence from the injector nozzle. However, most breakup models used to simulate the primary breakup process in diesel engines only consider the aerodynamically induced breakup. In this paper, the standard breakup models in Diesel Engine modeling code called “CONVERGE” are examined in constant volume spray chamber geometry using the available spray data. Since non-evaporating sprays provide a more stringent test for spray models, the x-ray data from Advanced Photon Source is used for detailed validation of the primary breakup model, especially in the region very close to the nozzle. Extensive validation of the spray models is performed under evaporating conditions using liquid length and spray penetration data. Good agreement is observed for global spray characteristics. However, the breakup model could not reproduce some of the experimental trends reported in literature thus identifying the need for a more comprehensive primary breakup model. An attempt is made to statically couple the internal nozzle flow with spray simulations, and examine the effect of nozzle orifice geometry on spray penetration.
A Multibody/Finite Element Non-Linear Formulation of a Two-Ligament Knee Joint
Authors: Weed David , Maqueda Luis G. , Brown Michael A. , Shabana Ahmed A.
Published: August 2009

The focus of this investigation is to study the mechanics of the human knee using a new method that integrates multi-body system and large deformation finite element algorithms. The major bones in the knee joint consisting of the femur, tibia, fibula are modeled as rigid bodies. The ligaments structures are modeled using the large deformation finite element Absolute Nodal Coordinate Formulation (ANCF) with an implementation of a Neo-Hookean constitutive model that allows for large deformations as experienced in knee flexation and rotation. The Neo-Hookean strain energy function used in this study takes into consideration the near incompressibility of the ligaments. The ANCF is used in the formulation of the algebraic equations that define the ligament/bone rigid connection. A unique feature of the ANCF is that it allows for the deformation of the ligament cross-section. At the ligament/bone connection, the ANCF is used to define a fully constrained joint. This aspect of the model reflects the actual structural mechanics of the knee. In addition, this model will reflect the fact that the geometry, placement and attachment of the two collateral ligaments (the LCL and MCL), are significantly different from what has been used in most knee models developed in previous investigations. The approach described in this paper will provide a more realistic model of the knee and thus more applicable to future research studies. The obtained preliminary results of other applications show that the ANCF can be an effective tool for modeling very flexible structures like ligaments subjected to large deformations. In the future, the ANCF models could assist in examining the mechanics of the knee to study knee injuries and possible prevention means, as well as an improved understanding of the role of each individual ligament in the diagnosis and assessment of disease states, aging and potential therapies.
Optimal Behavior of Hot Water Heating Coils at Steady Conditions
Authors: Mahboubi D. , Saidi M. H.
Published: August 2009

Hot water heating coils are key components in air conditioning systems undergo heat transfer. The most widely used exchangers (coils) take the form of fin and tube configuration in association with the application of air conditioning systems. In this research, thermodynamic modeling and mathematical optimization of hot water heating coils at steady conditions, approaching minimum energy consumption are achieved. The modeling procedure for heating coils is done based on the log mean temperature difference (LMTD) method. The objective function for optimization is pressure drop of air crossing coil per heating load of the system. This unction comprises all thermal and geometrical parameters of the coils such as coil surface area, number of rows, fin spacing and air side pressure drop of the coil. The objective function is minimized using Lagrange multipliers method. The optimization results are composed of minimum pressure drop, optimum surface area, optimum number of rows and fin spacing. The effects of varying the heating load, fin efficiency and the surface area of the coils on optimum behavior of them are investigated as well.
Validity of Assessment Procedure in p-M Method for Multiple Volumetric Flaws
Authors: Konosu Shinji , Kano Masato , Mukaimachi Norihiko , Kanamaru Shinichiro
Published: August 2009

General components such as pressure vessels, piping, storage tanks and so on are designed in accordance with the construction codes based on the assumption that there are no flaws in such components. There are, however, numerous instances in which in-service single or multiple volumetric flaws (local thin areas; volumetric flaws) are found in the equipment concerned. Therefore, it is necessary to establish a Fitness for Service (FFS) rule, which is capable of judging these flaws. The procedure for a single flaw or multiple flaws has recently been proposed by Konosu for assessing the flaws in the p–M (pressure-moment) Diagram, which is an easy way to visualize the status of the component with flaws simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. If the assessment point (Mr, pr) lies inside the p–M line, the component with flaws is judged to be safe. In this paper, numerous experiments and FEAs for a cylinder with external multiple volumetric flaws were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic collapse load at volumetric flaws by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are much the same as those calculated under the proposed p–M line based on the measured yield stress.
Stochastic Dynamics of a Variable Inertia System via Lyapunov Exponents
Authors: Asokanthan S. F. , Wang X. H. , Wedig W. V. , Ariaratnam S. T.
Published: August 2009

Torsional instabilities in a single-degree-of-freedom system having variable inertia are investigated by means of Lyapunov exponents. Linearised analytical model is used for the purpose of stability analysis. Numerical schemes for simulating the top Lyapunov exponent for both deterministic and stochastic systems are established. Instabilities associated with the primary and the secondary sub-harmonic resonances have been identified by studying the sign of the top Lyapunov exponent. Predictions for the deterministic and the stochastic cases are compared. Instability conditions have been presented graphically in the excitation frequency-excitation amplitude-top Lyapunov exponent space. The effects of fluctuation density as well as that of damping on the stability behaviour of the system have been examined. Predicted instability conditions are adequate for the design of a variable-inertia system so that a range of critical speeds of operation may be avoided.
Introducing Film Cooling Uniformity Coefficient (CUC)
Authors: Javadi Khodayar , Javadi Aliyar
Published: August 2009

A well performance film cooling implies for a high cooling effectives accompanied with a wide cooling coverage. During the past six decades, film cooling effectiveness has been well defined with a specific relation to quantify it. However, despite of numerous film cooling research, there is not an explicit method to quantify the uniformity of a coolant film spread over the hot surfaces. This work introduces a cooling uniformity coefficient (CUC) to evaluate how well a coolant film spreads over a surface being cooled. Four different cases are computationally studied. In the three cases, a single jet is injected into a hot cross flow with different jet exit shapes (i.e. square, spanwise rectangular, and streamwise rectangular). The fourth case is a novel combined triple jet (CTJ) introduced in our previous work. The cross sections of all the systems are equal to maintain the same coolant mass flow rate injection into the hot cross flow. The CUC’s of the different cases are compared with each other at two blowing ratios of 0.5 and 1.5. It is proposed that in addition to the film cooling effectiveness, the CUC is a necessary parameter to evaluate how well a coolant film is spread over a hot surface.
Highly Efficient Open-Celled Aluminum Foam Heat Sinks With Impinging Axial Fan Flow Cooling
Authors: Lu T. J. , Sui D. , Kim T. , Xu M. L.
Published: August 2009

The challenge in thermal management is the capability to remove heat from the device while maintaining acceptable component operating temperatures. Metal foams with high porosity ε∼0.9 have in recent years emerged as a promising heat dissipation medium, due to high extended surface area densities as well as tortuous flow passages that promote the coolant flow mixing. This study focuses on investigating experimentally the thermal performance of highly porous aluminum foam heat sinks with open cells under the impingement of axial fan flows. While the porosity, foam thickness and axial fan rotation are fixed, three selected pore densities and varying impinging distance are considered. The parameters of overall thermal resistance Rθ and temperature difference ΔT are used to evaluate thermal performance of aluminum foam heat sink which is also compared with that of a conventional fin heat sink. The experimental results represent aluminum foam heat sinks can provide similar or better cooling performance with more compact (a 50% reduction in both the weight and volume) than conventional fin heat sink.
Detailed Analysis of Residual Stress Profile at Micro-Scale in Transmission Laser Bonded Titanium/Polyimide System
Authors: Dhorajiya Ankitkumar P. , Mayeed Mohammed S. , Auner Gregory W. , Baird Ronald J. , Newaz Golam M. , Patwa Rahul , Herfurth Hans
Published: August 2009

Detailed analysis of residual stress profile due to laser micro-joining of two dissimilar biocompatible materials, polyimide (PI) and titanium (Ti), is vital for the long-term application of bio-implants. In this work, a comprehensive three dimensional (3D) transient model for sequentially coupled thermo-mechanical analysis of transmission laser micro-joining of two dissimilar materials has been developed by using the finite element (FE) code ABAQUS, along with a moving Gaussian laser heat source. The laser beam (wavelength of 1100 nm and diameter of 0.2 mm), moving at an optimized velocity, passes through the transparent PI, gets absorbed by the absorbing Ti, and eventually melts the PI to form the bond. The laser bonded joint area is 6.5 mm long by 0.3 mm wide. First the transient heat transfer analysis is performed and the nodal temperature profile has been achieved, and then used as an input for the residual stress analysis. Non-uniform mixed meshes have been used and optimized to formulate the 3D FE model and ensure very refined meshing around the bond area. Heat resistance between the two materials has been modeled by using the thermal surface interaction technique, and melting and solidification issues have been approximated in the residual stress analysis by using the appropriate material properties at corresponding temperature. First the model has been used to observe a good bonding condition with the laser parameters like laser traveling speed, power, and beam diameter (burnout temperature of PI > maximum temperature of PI achieved during heating > melting temperature of PI) and a good combination has been found to be 100 mm/min, 3.14 W and 0.2 mm respectively. Using this combination of parameters in heating, the residual stress profile of the laser-micro-joint has been calculated using FE model after cooling the system down to room temperature of 27 °C and analyzed in detail by plotting the stress profiles on the Ti and PI surfaces. Typically the residual stress profiles on the PI surface show low value in the middle, increase to higher values at about 160 μm from the centerline of the laser travel symmetrically at both sides, and to the contrary, on Ti surface show higher values near the centerline of traveling laser beam. The residual stresses have slowly dropped away on both the surfaces as the distance from the bond region increased further. Maximum residual stresses on both the Ti and PI surfaces are at the end of the laser travel, and are in the orders of the yield stresses of respective materials.
Permeability Measurement Methods in Porous Media: A Review
Authors: Sharma Sanjay , Siginer Dennis A.
Published: August 2009

Accurate measurement of Permeability is critical for fluid flow modeling in porous media. Various experimental methods have been devised that measure permeability as a porous material property. These experiments are based most commonly on Darcy’s law. Liquid flow and gas flow methods of permeability measurement for in-plane and transverse directions are detailed. Issues related to these methods are discussed. Some associated permeability models are discussed. Alternative methods of permeability determination based on cross transport phenomenon are presented.
In Vivo Mechanical Properties of Muscular Bulk Tissue: Mechanical Model Representation of Stress-Relaxation Behavior
Authors: Arıtan Serdar , Oyadiji S. Olutunde , Bartlett Roger M.
Published: August 2009

In Vivo mechanical properties of bulk tissue have not been yet investigated sufficiently. One of the major problems the researchers confront is the lack of agreement for the constitutive models and standardized methodology for experimental studies (1). Despite the fact that the tissue properties are non-linear, many modeling studies preferred to adopt linear isotropic models. The object of this study was to obtain bulk modulus of the upper arm under relax and controlled contraction that was 25% of the maximum voluntary contraction (MVC).
Numerical Study of the Effects of Volumetric Heat Transfer and Emissivity Coefficient and Porosity on Combustion and Pollutants Formation in a Porous Burner
Authors: Hossainpour Siamak , Haddadi Bahman
Published: August 2009

In recent years, more attention has been focused on the use of porous materials to enhance the efficiency of combustion systems and to reduce the emission of pollutants. This is because combustion in inert porous media offers an interesting and promising route towards burner with high-power density, high-power dynamic range, and very low emission of pollutants such as NOx and CO. This work reports one-dimensional combustion in a porous burner using three combustion models: GRI 3.0, GRI 2.11, skeletal mechanism. We conclude that GRI 2.11 mechanism has a good agreement with GRI 3.0 and it costs less. At first, we present a numerical study which shows the effects of these models on temperature, species and pollutant emissions. Then, we investigate the effects of volumetric heat transfer and emissivity coefficient and porosity on combustion and pollutions. It was concluded that NO and CO emission depend mainly on the volumetric and emissivity coefficient. When volumetric heat transfer increased, the difference between gas and solid temperature reduced, therewith NO formation noticeably decreased whereas CO emission didn’t change sensible. On the other hand, the flame peak temperature is increased with the reduction of the solid emissivity coefficient. This important conclusion means that NO and CO emission and velocity increases. Also gas and solid temperature increase and vice versa. The other parameter is Porosity. Increasing in porosity of burner resulted in decreasing gas and solid temperature and subsequently NO and CO emission decreased sensible. Porosity has effected on velocity, too. As porosity decreased, velocity increased. Emissivity effects on the rate of heat flux which issue from burner. As the emissivity increased the efficiency of burner arose. Also these parameters have important roles in decreasing the emission especially on No emission because it has more depend on temperature. In addition the resulted gas and solid temperatures were compared with reported measurements of center line temperature in a cylindrical porous burner. The good agreement with experimental observation upholds that the numerical model is a perfect tool to investigate combustion and pollutants formation in porous media.
A Probabilistic Algorithm in Landing Site Selection of a Distressed Aircraft Including Effects of Failure Rates
Authors: Sarigul-Klijn N. , Rapetti R. , Lopez I. , Jordon A. , Sarigul-Klijn M. , Nespeca P.
Published: August 2009

An algorithm is developed that generates statistically optimal flight trajectory to a best landing site after occurrence of an in-flight distress condition using an abort probability model. The approach developed increases overall survivability by minimizing the expected flight path distance, given the abort probability model. An airport grouping strategy that clumps the airports logically prior to path derivation is also developed. The performance of this newly developed probabilistic trajectory algorithm is evaluated using numerical simulations that include variable failure rates to simulate different in-flight distress conditions, and multiple turns to accommodate realistic trajectories. The results show that it is possible by using this algorithm to increase aircraft survivability.
Static Tensile Strength of Gas Metal Arc Welded (GMAW) Joints of Uncoated Dual Phase 600 (DP600) Steels
Authors: Koganti Ramakrishna , Angotti Sergio , Joaquin Armando , Ziang Cindy , Karas Chris
Published: August 2009

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. These new steels have significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures due to Heat affected Zones (HAZ) at the weld joint. In this study Gas Metal Arc Welding (GMAW) of a lap joint configuration consisting of 1.5 mm uncoated DP600 to itself was investigated. The objective of the study was to understand the wire feed rate and torch speed influence on lap joint strength. A two factor, two level, full factorial design of experiment (DOE) was conducted to understand the wire feed and torch speed influence on tensile strength. In order to understand the curvature effect, center point was also considered in the experiment. Based on the statistical analysis, wire feed rate was the only significant factor on static tensile strength. Metallurgical properties of the lap joints were evaluated using optical microscopy. Significant hardness drop of 40% was observed at the HAZ.
A Novel Assessment Technique for Prosthetic Valve Function: Employing a New Laboratory Approach to Characterize Projected Dynamic Valve Area and Vortex Formation Analysis
Authors: Bartell Jennifer , Pierrakos Olga , Scotten Lawrence
Published: August 2009

The study of heart valve performance (healthy, diseased, and prosthetic) has traditionally involved the examination of transvalvular characteristics, such as pressure gradients and effective and geometric orifice areas. However, recent research has shown that a key downstream flow characteristic, vortex ring formation, should not be overlooked because quantifying this mechanism provides insight into the assessment of valve performance [1]. Vortex ring formation, which is dependent on the valve design [1], is the roll-up of the shear layers shedding past valve leaflets. Governed by a universal time-scale or formation number (FN) that is based on the jet length to diameter ratio (L/D), vortex ring formation provides insight into the kinematics of optimizing effective fluid transport. It has been shown that growth of the leading vortex ring ceases at a FN between 3.5 and 4.5 in various biological systems [2], but most of these studies have assumed a constant or fixed orifice opening. However, incorporating a time-varying jet diameter rather than the constant valve annulus diameter has recently been identified by Dabiri and Gharib as a key factor in the characterization of vortex ring formation and provides a more complete picture of impulse generation and efficiency in vortical flows [2]. This dynamic formation number is governed by the following equation: (L/D)*=∫0tU¯/D¯dt(1) where U is velocity, D is diameter, t is time, and the overbar indicates a time average. Estimating (L/D)* can serve as a powerful evaluation tool in comparison to conventional methods of FN calculation that use either an averaged diameter or the valve annulus diameter. Ideally suited for unsteady flows, such as the opening phase and leaflet motions in heart valves, (L/D)* can provide insight into assessing the performance of natural and prosthetic heart valves (PHVs).
Co-Effect of Chaotic Mixing and Clay on Morphology Development of Polypropylene/Polyamide 6 Blends Along Extruder
Authors: Li Ke , Huang Han-Xiong , Jiang Guo
Published: August 2009

Morphology development of polypropylene (PP)/polyamide 6 (PA6) (60/40 w/w) blends and their nanocomposites with 5 wt% clay along an extruder during compounding was investigated in this work. Two screw geometries were used. One was a conventional geometry, and the other one was a special geometry which was used to induce chaotic mixing. The scanning electron microscopy (SEM) of blends indicated that chaotic mixing facilitated to form thinner laminar layers and co-continuous phase structure. The co-continuous phase structure became uniform as the co-effect of chaotic mixing and clay. Transmission electron microscopy (TEM) results showed that the clay platelets dispersed in the PP phase initially migrated into PA6 phase. In addition, chaotic mixing made a better dispersion of clay in PA6 phase than conventional mixing. Rheological test results showed that the dynamic elastic modulus for the sample with co-continuous phase structure presented a solid-like response at lower frequencies.
Transient Heat Transfer for Carbon Dioxide Flowing Over a Horizontal Plate With Exponentially Increasing Heat Input
Authors: Shibahara Makoto , Liu Qiusheng , Fukuda Katsuya
Published: August 2009

Transient heat transfer coefficients for carbon-dioxide gas flowing over a horizontal plate (ribbon) at various periods of exponentially increasing heat input was experimentally and theoretically studied. In the experimental studies, transient heat transfer coefficients were measured under various velocities and periods. The platinum plate with a thickness of 0.1 mm was used as test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocities ranged from 1 to 3 m/s, the gas temperatures ranged from 313 K to 353 K, and the periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than around 1 s. In the theoretical study, forced convection transient heat transfer was numerically solved based on a conventional turbulent flow model. The temperature within the boundary layer around the heater increases with the increase of the surface temperature. It is understood that the gradient of the temperature distribution near the wall of the plate is higher at a higher surface temperature difference. The values of numerical solutions for the heat fluxes agree well with the experimental data, though the numerical solutions for surface temperatures show some differences with the experimental data.
A Refined Analytical Combustion Model for Evaluating the Effects of EGR Percentage on Improvement of Knock Characteristics of Natural Gas in Spark Ignition Engine
Authors: Ghanbari Mohammad , Safari Hesameddin , Jazayeri Seyed Ali , Ebrahimi Reza
Published: August 2009

Accurate modeling of engine knock onset is needed for control of SI engine combustion and increase of thermal efficiency. This contribution presents a refined model for analysis of engine knock when using natural gas fuel and EGR. The model is used to compare the effectiveness of EGR to other knock suppression methods such as lean-burn combustion, compression ratio reduction, and ignition timing retardation. The model consists of two zones: a burned combustion products region and an unburned reactants comprising the end gas region, separated by a flame front of negligible thickness. A mass burning rate is derived from a turbulent combustion model. FORTRAN code as programming software is used for combustion simulation. Operating conditions which affect an engine’s tendency to knock are discussed. The model was validated by comparison to experimental data. Results show that EGR addition is more effective at suppressing knock, while maintaining high thermal efficiency and output work, compared to other knock suppression techniques such as inlet pressure and temperature, equivalence ratio, spark timing, or compression ratio.
Tubular Nitinol Knit Meshes for External Reinforcement of Saphenous Vein Grafts: A Numerical Design Study
Authors: Franz Thomas , van der Merwe Helena , Zilla Peter , Bezuidenhout Deon , Reddy B. Daya
Published: August 2009

The difference in mechanical properties between grafts and host arteries is a complicating factor for vascular bypass surgery and can cause patho-physiological problems after implantation [1–7]. Diffuse and focal intimal hyperplasia, one of the key factors of vein graft failure, has been attributed to over-distension and diametric irregularities of the veins when exposed to the arterial circulation [8]. The external reinforcement of saphenous vein grafts with open-mesh knitted Nitinol structures is suggested to prevent over-distension, smooth the luminal diameter, and address the mismatch in mechanical properties of vein graft and host vessel. The objectives of this work were: 1) development of Finite Element (FE) models of knitted Nitinol structures to assess mechanical behaviour and structural properties, e.g. vascular compliance, and 2) proof of feasibility of the FE method developed for structural design optimisation of the Nitinol mesh.
Pressure Gradient Prediction in Particle-Liquid Two-Phase Flow
Authors: Aybar Hikmet S¸. , Sharifpur Mohsen , Vaziri Roozbeh
Published: August 2009

The prediction of pressure gradient in two-phase flows is an essential step in the design of a variety of industrial applications. In this study, it is developed the idea that porous media could be a particle-liquid two-phase flow with saturation of the particles. Thus, by setting up an experimental apparatus, it is investigated the behavior of particle-liquid two-phase flow in the cases of dilution of the particles to rich porous media. By using the experimental results an empirical expression is offered for the prediction of pressure gradient of particle-liquid two-phase flow.