bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Studies on Aluminum Honeycomb With Various Cell Specifications Under Impact Loading
Authors: Liu Rongqiang , Luo Changjie , Deng Zongquan , Wang Chuang
Published: August 2009

Through analyzing one Y-shaped cross-section structure of honeycomb cell, the formula for relative density of honeycomb with regular hexagon cell shape is derived. And typical dynamic collapse process of honeycomb is illuminated. Three kinds of aluminum alloy(3003) honeycomb specimens for experiments are got by cutting honeycomb plate using the cutting tool made by ourselves. These specimens’ size specifications are 0.06mm (cell foil thickness t) × 4mm (cell sides length l) × 60mm (specimen height h), 0.06mm (t) × 6mm (l) × 30mm (h) and 0.08mm (t) × 10mm (l) × 50mm (h) respectively. Impact experiment using a drop-hammer apparatus (Instron dynatup 9250HV), whose initial mean impact velocity is 5m/s and mass is 14.6687kg, and the corresponding quasi-static one are also performed. Then the stain-stress curve of these three kinds of specimens under dynamic and quasi-static are recorded. Assuring the same load conditions with experiment and simplifying the honeycomb cell as one Y-shaped cross-section column, numerical simulation for these three kinds of honeycomb’s compression collapse process under impact loading are carried out by using an explicit FEM code LS-DYNA. Then the strain-stress curve is obtained by experiments and compared with numerical simulation. It is shown that the result of numerical simulation well coincide with the experiments. At last, the elastic and plastic collapse stress of theory, experiment and simulation are compared and the result shows that the plastic collapse stress of simulation is fairly well-matched with the experiment while the theory is less than them.
Monitoring and Diagnosis of Steel Reheating Burners
Authors: Thai S. M. , Chong H. S. , Tan C. K. , Wilcox S. J. , Ward J. , Andrews G.
Published: August 2009

This paper describes the development of an intelligent Flame Diagnostic System which is able to monitor the combustion characteristics of individual burners based on direct measurement and analysis of the flame radiation signals. A series of experiments were conducted on a 500 kW pilot-scale furnace fitted with both a single burner and also two burners firing in a regenerative manner. The experiments covered a wide range of burner operating conditions including variations in the burner firing-rate and excess air level. A fibre-optic based optical instrument, incorporating broad ultraviolet, visible and infrared photo diodes was developed and used to acquire the dynamic flame signals through a data acquisition system. These flame signals were then analysed off-line, using simple signal processing methods, to yield a set of flame features. Correlation of these flame features with respect to the excess air level and NOx emissions were made using neural network models. The present work indicates that the measurement of flame radiation characteristics, coupled with advanced data modelling techniques such as neural networks, provides a promising means of monitoring and optimising burner performance.
Numerical Simulation of the Phase Separation of a Polymer-Polymer-Solvent Ternary System on a Heterogeneously Functionalized Substrate
Authors: Shang Yingrui , Kazmer David , Wei Ming , Barry Carol , Mead Joey
Published: August 2009

The spinodal decomposition of a polymer-polymer-solvent ternary system was investigated in a 3-dimensional numerical model. The Cahn-Hilliard equation was employed to describe the free energy profile of the domain. A heterogeneously functionalized substrate was also implemented into the model to simulate the effect of substrate attraction. The mechanism of the morphology evolution was studied quantitatively. The well established linear relationship of the characteristic length, R(t) with t1/3 can be observed in the simulation results. The compatibility of the result pattern and the pattern on the substrate was measured by a scalar, Cs. The influence of the solvent concentration on the refinement of the result pattern was studied in this work. A critical time can be observed from the evolution of the value of Cs. The morphology evolution of a system considering the solvent evaporation was also studied.
Analysis of Machine Tool Failures Using Advanced Reliability Models for Complex Repairable Systems
Authors: Mazzola Marco , Merlo Angelo , Aggogeri Francesco
Published: August 2009

The competitiveness of modern markets has induced machine tool producers to realize high reliability innovative products. Nowadays, machine tool is an integration of extremely advanced technological devices able to perform tasks with high accuracy and flexibility. The main goal must be to guarantee specified performances, but, above all, to maintain them for all the life cycle time. Reliability and maintainability analysis (R&M) of a complex system deals with many opportunities both for the producers and the customers. The analysis permits to understand the behavior of the machine and to obtain useful information in order to base maintenance policies on analytical results. In this paper a structured R&M analysis for repairable systems is applied to a set of lathes. Failure data are collected by the company customer service for thirty months. The whole system is decomposed into main groups and components. Life data analysis is applied and the failure distribution of the repairable groups is described through a non-homogeneous Poisson process. When complex repairable systems are considered, the reliability must be modeled taking into account that it is strictly influenced by maintenance actions that restore/renew system components when they fail. Finally an R&M perspective for the entire machine is shown.
Rate Controlled Constrained-Equilibrium (RCCE) Method Applied to Di-Methyl Ether (DME) Combustion
Authors: Janbozorgi Mohammad , Goldthwaite Donald , Metghalchi Hameed
Published: August 2009

The rate-controlled constrained-equilibrium technique is used to study the ignition characteristics of Di-Methyl Ether (DME) under high pressure, low temperature in a batch reactor. A set of 9 constraints was identified which is able to exactly reproduce the ignition characteristics within the specified range of thermo dynamics conditions. The detailed kinetic scheme involves C1-C2 chemistry and comprises 54 species and 308 reactions without nitrogen chemistry.
Combining Six Sigma With Lean Production to Increase the Performance Level of a Manufacturing System
Authors: Aggogeri Francesco , Mazzola Marco
Published: August 2009

The application of innovative methodologies and problem solving methods to organize and manage manufacturing processes is essential to increase business performance of a company and satisfy customer demand. Specifically, combining Six Sigma quality with Lean Production speed empowers all companies to reach customer satisfaction through continuous improvement and reduction of non added value activities. The goal of this paper is to explain and show the power of Six Sigma and Lean production combination in a manufacturing company that realizes brass extruded and drawn pieces. Lean Six Sigma represents one of more dynamic and innovative program of management to improve quality of products and efficiency of manufacturing. This project focuses on the increase of customer satisfaction and savings by eliminating product defects and reducing scraps and non value added activities of the mechanical manufacturing stream. The authors implemented the DMAIC problem solving method applying different quality management and lean tools. The paper shows a complete roadmap in order to analyze and eliminate defect and waste causes, and improve the performance level of a manufacturing system. The obtained results highlight a reduction of Costs of Poor Quality by 20% and an increase of process cycle efficiency of 6%.
CFD Predictions of Pulsed Film Cooling Heat Flux on a Turbine Blade Leading Edge
Authors: Rutledge James L. , King Paul I. , Rivir Richard
Published: August 2009

Unsteadiness in film cooling jets may arise due to inherent unsteadiness of the blade-vane interaction or may be induced as a means of flow control. A computational study was conducted to determine how leading edge film cooling performance is affected by pulsing the coolant flow. A cylindrical leading edge with a flat afterbody is used to simulate the turbine blade leading edge region. A single coolant hole was located 21.5° from the leading edge, angled 20° to the surface and 90° from the streamwise direction. The leading edge diameter to hole diameter ratio is D/d = 18.7. Time resolved adiabatic effectiveness and heat transfer coefficient are used to calculate the temporally averaged, spatially resolved net heat flux reduction for several pulsing scenarios. The net heat flux reduction with pulsed film cooling is compared to the steady jet with matched average mass flow rate. Steady blowing ratios of M = 0.25 and 0.50 are each compared with two pulsed jet cases with matching averaging blowing ratio, M, at a nondimensional frequency, F = 0.151 and duty cycle, DC = 50%. Simulations were performed at ReD = 60000. Net heat flux is generally increased by pulsing the film coolant, with greater degradation for higher pulsation amplitudes relative to the average blowing ratio.
Natural Frequencies of Centrifugal Compressor Impellers for High Density Gas Applications
Authors: Magara Yohei , Narita Mitsuhiro , Yamaguchi Kazuyuki , Takahashi Naohiko , Kuwano Tetsuya
Published: August 2009

Characteristics of natural frequencies of an impeller and an equivalent disc were investigated in high-density gas to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications. The equivalent disc had outer and inner diameters equal to those of the impeller. We expected that natural frequencies would decrease with increasing the gas density because of the added-mass effect. However, we found experimentally that some natural frequencies of the impeller and the disc in high-density gas decreased but others increased. Moreover, we observed, under high-density condition, some resonance frequencies that we did not observe under low-density condition. These experimental results cannot be explained by only the added-mass effect. For simplicity, we focused on the disc to understand the mechanism of the behavior of natural frequencies. We developed a theoretical analysis of fluid-structure interaction considering not only the mass but also stiffness of gas. The analysis gave a qualitative explanation of the experimental results. In addition, we carried out a fluid-structure interaction analysis using the finite element method. The behavior of natural frequencies of the disc in high-density gas was predicted with errors less than 6%.
Attenuation Coefficients Prediction for Reflection Layers of Solidly Mounted Resonators via Phononic Band Structures
Authors: Liu Chien-Hou , Chou Yuan-Fang
Published: August 2009

The solidly mounted resonator (SMR) is one of the major focuses in filter research because it can be used in the frequency above GHz range. The reflection structure composed of periodic layers is vital to the performance of this type of resonator due to its capability in confining acoustic energy in the piezoelectric layer. Therefore the design of reflection layers is a key issue in the development of SMRs. The performance of reflection layers is revealed by the attenuation coefficient that governs the energy distribution in the periodic structures. The behavior of waves propagate in the finite periodic structures are solved by transfer matrix method while the Hill’s method is employed to find the exact solutions in the corresponding phononic crystal. By comparing their displacement fields, it is observed that the attenuation coefficients of infinite and finite periodic structures are almost identical provided the number of layers is adequate. Therefore referring the design of reflection layers to the band structures of the corresponding phononic crystals is reasonable although the attenuation coefficient of a finite periodic structure can not be calculated directly. For one dimensional phononic crystals, the attenuation coefficient becomes larger as the first band gap gets wider. Moreover, the characteristic impedance ratio and density ratio between two interlaced materials increase simultaneously; the first band gap width also increases. This character can be adopted as a guideline in the design of solidly mounted resonators. Based on this guideline, Al and W are chosen as materials for the reflection structure. By calculating its electric impedance, the resonant frequency is found to be the same as the center frequency of first band gap of the corresponding phononic crystal. It shows that employing this stop band character to design the reflection structure of SMR is adequate and efficient.
A Risk Assessment Method and Safety Plan for a University Research Lab
Authors: Kremer Gregory G. , Ryan Timothy J. , Switzer Shyler
Published: August 2009

Risk management processes follow relatively well established steps, but the hazard identification and risk assessment steps often depend heavily on “experts” with relevant expertise and operating experience. This paper presents a tool developed to help novice researchers identify and assess hazards more efficiently. The hazard identification tool was developed in the form of an updatable algorithm, based initially on previous risk assessments for similar situations as well as checklists and guidelines available from academic texts, Occupational Safety and Health Act (OSHA), and industry. Major risk categories included in the algorithm include: a) Ergonomics and Mechanical, b) Chemical, c) Physical (including Electrical Hazards, Fire Safety, Noise Hazards, and Radiation Hazards), d) Psychological and Organizational, and e) Biological. In the initial test of the algorithm, a team of non-experts used the algorithm to identify risks for two Ohio Coal Research Center (OCRC) projects dealing with solid oxide fuel cell and electrostatic precipitator testing. Their results were comparable to the list of risks generated by a group of “research experts” without the algorithm. Future plans include making the algorithm available on a wiki platform to collaboratively develop it with the combined knowledge, experience and perspectives of all participating researchers. This paper also describes the overall safety plan for the Ohio Coal Research Center (OCRC), which operates within the Institute for Sustainable Energy and the Environment (ISEE) at Ohio University. An OCRC safety flow diagram is presented that has been successfully used to improve the safety of new research projects being led by new researchers.
Analysis of the Idling Start of the Moving Coil Linear Compressor
Authors: Xie Yingbai , Huang Xiuzhi , Lun Liyong , Sun Ganglei
Published: August 2009

The linear compressor is driven by a linear motor. Because it has no crankcase, the piston motion and its control of the linear compressor are differing from that of the conventional reciprocating compressor. For a moving coil linear compressor, mechanical and electromagnetism system are modeled. The open loop and closed loop transfer functions of the system in no-load condition are obtained derived from these equations. The Matlab software is applied to analyze the stability, time domain and frequency domain of the system. Simulation results show that the linear compressor is stable, but the overshoot is relative high, which must be adjusted. This conclusion will be benefit for the design of the idling start of the moving coil linear compressor.
Comparison of the Indoor Climate in Multi-Span and Detached Greenhouses With Various Ventilator Configurations
Authors: Kruger Sunita , Pretorius Leon
Published: August 2009

This paper investigates and compares the indoor climate of detached and connected greenhouses. More specifically, the effect of additional greenhouses on indoor climate of first greenhouse was studied. The indoor velocity and temperature distributions in the greenhouses were numerically analyzed using computation fluid dynamics. The initial two greenhouses were first separated by a distance of 4m between them, and equipped with continuous side ventilators opened at 45°. Secondly, the distance between the first and second four span greenhouse was increased to 8m. Lastly a second row of side ventilators were added above the first row of ventilators. Results found that a connected greenhouse with multiple spans might be detrimental to the spans in the middle, as the air movement is significantly reduced. Adding a separate greenhouse on the leeward side with side ventilators also influences the flow to some extent, especially in the third and fourth spans of the first greenhouse. If this distance is increased, the influence is especially noticeable at the back vents of the first greenhouse, where strong currents of air are sucked in. A second row of side ventilators affects the flow, resulting in an increased heterogeneity in the first two spans. Flow is still homogeneous throughout the third and fourth spans, although the air velocity is slightly lower compared to a greenhouse containing only a singe side ventilator. The presence of a second greenhouse can reduce the advantage double side ventilators might have on the indoor climate of the first four span greenhouse.
Comparing Piezoelectric and Electroosmotic Micropumps for Biomedical Devices
Authors: San Omer , Yalcin Sinan Eren , Baysal Oktay
Published: August 2009

A micropump is an essential component of a microfluidic lab-on-a-chip device, especially for their biomedical applications. Based on their actuation method to drive the fluid flow, pumps may be categorized as mechanical or non-mechanical devices. In our proposed paper, we will report our comparative study of the most promising micropumps in each of these categories: a piezoelectrically-actuated micropump (PAμP) and an electroosmotic micropump (EOμP). A PAμP requires relatively high applied voltage, but provides high flow rates and has emerged to be the dominant type of micropump in biomedical applications. A valveless diffuser-nozzle micropump, driven by an oscillating membrane, has an important advantage, since the fabrication of any additional moving part, such as a check valve, would add significantly to its cost and render a more failure-prone device. The piezoelectrically actuated, valveless micropumps use moving mechanical parts to pump fluid and control the flow with optimized actuation frequency and applied voltage. In the present study, the microflow-structure interaction in the PAμP is modeled using an arbitrary Lagrangian-Eulerian method including a parametric study of applied voltage and frequency. An EOμP consists of multiple micron-scale channels in parallel that are subjected to the electroosmotic effect. However, a major drawback in the conventional design of an EOμP is the need for a high driving voltage to increase the flow rate or to overcome the back pressure. In the present study, a low-voltage EOμP is proposed and computationally modeled. Our simulations are performed in order to study the low-voltage EOμP for its various flow rate and back pressure characteristics. In the proposed paper, we will discuss our comparisons of PAμP and EOμP, with respect to their actuation mechanisms, applied voltages, pump sizes, flow rates and back pressures.
Experimental Validation of Non-Conventional Viscoelastic Models via Equivalent Damping Estimates
Authors: Catania Giuseppe , Sorrentino Silvio
Published: August 2009

Non-conventional rheological models based on non-integer order differential operators can be used to describe the viscoelastic behavior of materials, especially of polymers. These models are usually selected and then validated by means of creep and relaxation tests. However, engineers dealing with structural dynamic problems may need to obtain model identification from vibration measurement data. In this case, however, the direct identification of an optimal set of parameters of a viscoelastic model from time or frequency domain measurements is a difficult task, especially if the structural dissipative contributions are slight. In this paper, an indirect approach is adopted, based on the concept of damping ratio. When dealing with standard linear viscous dissipative models, a damping ratio modal parameter ζn can be analytically defined and experimentally estimated. But this theoretical parameter shows a dependency from the modal frequency that may dramatically fail in fitting the experimental data. On the contrary, it is known that a better agreement between theory and experiments can be achieved by means of non-integer order differential models, even though in this case analytical expressions for ζn are difficult to find. To overcome this difficulty, a method of general validity for viscoelastic models is developed, based on the concept of equivalent damping ratio and on the circle-fit technique. The proposed method is applied to experimental damping estimates from plane flexural vibrations of clamped-free beams, obtained from specimens of different size made of materials such as Polyethylene, Polyvinyl-chloride and Delrin.
Isolating the Role of Nanofillers: A Study on Amorphous Polyamide Nanocomposites
Authors: Reynaud Emmanuelle , Schmidt Daniel , Dorairaju Gowri , Toshniwal Saurabh , Tulsyan Kunal
Published: August 2009

We report the production of transparent, amorphous, partially exfoliated polyamide / nanoclay nanocomposites. Stiffness and yield strength increase with nanoclay content, while work-of-fracture remains constant below an inorganic content of 0.25 vol%.
Design of a Wide-Band Energy Harvester
Authors: Soliman M. S. M. , Abdel-Rahman E. M. , El-Saadany E. F. , Mansour R. R.
Published: August 2009

We propose and validate a new architecture for wide-band vibration-based MPGs. This architecture replaces a linear oscillator with a piecewise-linear oscillator as a vibrations harvesting element. Analytical, numerical, and experimental techniques are used to analyze a prototype of an electromagnetic MPG designed and constructed using the new architecture. The new architecture increases the bandwidth of the MPG during an up-sweep compared to a traditional MPG, while maintaining the same bandwidth in a down-sweep. Closed-form expressions for the response of the piecewise-linear MPG as well as the size of the up-sweep bandwidth are presented and validated experimentally. Simulations show that under a random-frequency base excitations new architecture collects more energy collected by the traditional architecture.
Advanced Testing and Simulation Techniques in Handling Body Deformation
Authors: Miyagawa Kouichi , Maruyama Yoshiyuki , Nasada Masataka , Di Carlo Paolo , Conti Giancarlo , Cibrario Valerio
Published: August 2009

Body reinforcements may have large influence in the handling perception of a professional driver. This paper presents testing and CAE techniques to approach and analyze the phenomena. A full vehicle multi body model correlated against test data was built. The model includes all vehicle subsystems: front and rear suspensions with rotating wheels and tire model in Magic Formula representation, steering line, powertrain mounting system and car body. Flexible components have been implemented for the car trimmed body, the front subframe and the rear twist beam suspension. A special vehicle set-up has been defined for the testing session, including the standard handling equipment and an advanced system measurement based on strain gauges located on the vehicle body. Strain gauge locations have been defined through support of the simulation. Several handling maneuvers (constant radius cornering, step steering at different lateral accelerations, ISO lane change and reverse ISO lane change) have been performed. Results from strain gauges have been obtained and analyzed. Advanced testing equipments are necessary to demonstrate the influence of body flexibility, which standard handling testing equipment does not allow. This represents the first step for understanding the advanced handling perception feeling due to the body deformation and for defining a systematical approach to correlate with objective measurements.
Epoxy/Nickel Conductive Adhesive Rheology During Processing and Cure
Authors: Zhou Jianguo , Sancaktar Erol
Published: August 2009

Epoxy/Ni adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/Ag adhesives with acceptable electrical conductivity. In this work, the effects of preshear history, resin viscosity, temperature, particle size, solid loading, as well as different yield stress determination methods were investigated for moderately filled epoxy/Ni suspensions (10∼60 wt% of Ni). The preshear effect manifests itself from successive shear rate sweeps with the same sample, and one shear rate sweep was employed as the preshear conditioning to obtain reproducible results. Shear thinning generally occurs for epoxy/Ni suspensions. The fractal dimension (Df) can be employed to describe these flocculated structures, and a higher Df value was observed for Epon815C/Ni system as compared to Epon830/Ni system. The Arrhenius equation describes the temperature dependence of suspension viscosity well.
Chatter Vibration Modeling in High Speed Milling Operations
Authors: Catania Giuseppe , Mancinelli Nicolo`
Published: August 2009

High removal rate in milling operations can be limited by chatter occurrence. Several studies on this self-excited vibration can be found in the literature: simple models (1 or 2 dofs) are proposed, i.e. a lumped parameter model of the milling machine being excited by regenerative, time-varying cutting forces. In this study, the machine tool spindle was modeled by a discrete modal approach, based on the continuous beam shape, analytical eigenfunctions, while the eigenvalues were mainly experimentally identified. The regenerative cutting force components lend to a set of Delay Differential Equations (DDEs) with periodic coefficients; DDEs were numerically integrated for different machining conditions. The stability lobe chart was evaluated using the semi-discretization method. Time histories, spectra and Poincare´ maps related to the vibratory behavior of the system were numerically obtained and differences with respect to the bifurcations predicted by the simplest models known in literature are pointed out. Some different behaviors in the shape of the stability lobe charts and in the spectra of the chatter vibrations were also observed.
Thermoelectric Transport in Silicon Germanium Nanocomposite
Authors: Lee Hohyun , Vashaee Daryoosh , Wang Xiaowei , Joshi Giri , Zhu Gaohua , Wang Dezhi , Ren Zhifeng , Bux Sabah , Gogna Pawan , Fleurial Jean-Pierre , Tang Ming Y. , Dresselhaus Mildred S. , Chen Gang
Published: August 2009

Direct energy conversion between heat and electrical energy based on thermoelectric effects is attractive for potential applications in waste heat recovery and environmentally-friendly refrigeration. The energy conversion efficiency depends on the dimensionless figure of merit of thermoelectric materials, ZT, which is proportional to the electrical conductivity, the square of the Seebeck coefficient, and the inverse of the thermal conductivity. Currently, the low ZT values of available materials restrict the applications of this technology. However, significant enhancements in ZT were recently reported in nanostructured materials such as superlattices mainly due to their low thermal conductivities. According to recent studies, the reduced thermal conductivity of nanostructures is attributed to the large number of interfaces at which phonons are scattered. Based on this idea, nanocomposites are expected to have a lower thermal conductivity than their bulk counterparts with low fabrication cost just by mixing nano sized particles. In this work, we will discuss mechanisms of thermoelectric transport via modeling and provide experimental evidence on the enhancement of thermoelectric figure of merit in SiGe-based nanocomposites.
Modeling Nonlinear Motorcycle Dynamical Behavior During Severe Acceleration and Braking
Authors: Catania Giuseppe , Mancinelli Nicolo`
Published: August 2009

The purpose of this work is to study the vibrational behavior, such as wheel bounce or chatter and rear suspension pitch, observed in racing motorcycles during severe acceleration and braking conditions. These vibrations may affect the performances and the safety of the vehicle. A multibody model of the system was implemented using a Newton-Euler approach and an associated linearized model was obtained in symbolic form. Accurate tire modeling was considered, and tire torsional stiffness effects were taken into account, since they may play an important role in transient dynamical vehicle behavior. Several numerical simulations were accomplished with different levels of longitudinal acceleration levels and different values of the tire force characteristic parameters. It was observed that unwanted vibrations may occur, being caused by a loss of stability of the system, and that this phenomenon may exhibit self-excited behavior. A sensitivity analysis was performed on the associated linearized model in order to identify the possible causes of the vehicle instability in severe acceleration and braking conditions.
Lattice Boltzmann Computations of Micro Channel and Micro Orifice Flows
Authors: Yeom Taiho , Zea Caloca Ignacio , Chambers F. W.
Published: August 2009

Filtration in gas micro flows is an important problem complicated by possible slip flow for the filter media and the particles. Slip complicates Navier-Stokes solutions for the flow field. The direct simulation Monte Carlo method and its derivatives can be applied, but they are very complex. The Lattice Boltzmann Method (LBM) appears to offer some advantages for these slip and transitional flows. To evaluate the method, it was used to compute micro channel and micro orifice flows for a range of Knudsen numbers (Kn). The micro orifice simulates an array of micro filter fibers. The Lattice Bhatnagar-Gross-Krook (LBGK) single relaxation time approximation was used with the relaxation parameter accounting for density variations. The effects of different techniques for satisfying slip and no-slip boundary conditions were investigated. Both no-slip bounce-back and slip bounce-back boundary conditions were used. For the slip bounce-back boundary condition, the reflection factor and the accommodation coefficient were applied to improve accuracy. The micro channel computations were performed for conditions matching well-documented compressible slip-flow Navier-Stokes results in the literature. The channel had a length to height ratio of 100 and an inlet to outlet pressure ratio of 2.15. Knudsen numbers of 0.00194, 0.0194, and 0.194 were examined. The bounce-back boundary condition was applied at the top and bottom walls. A reflection factor of 0.85 provided the best agreement with the results in the literature for a Kn = 0.0194. The computed velocity profiles and the nonlinear streamwise pressure profile display excellent agreement with the Navier-Stokes results in the literature at this Knudsen number. At Kn = 0.00194, pure bounce back and bounce back with reflection factor both yield very good results. At Kn = 0.194, the bounce back with reflection factor results exhibit significant deviations from the literature. The accommodation coefficient scheme does not show good results for these micro flows. The reflection factor boundary condition also was applied for the micro orifice flows. The two-dimensional orifice computations were conducted with a 0.6 ratio of the open orifice area to the total area to match results in the literature. The micro orifice LBM results are in good agreement with the literature for Reynolds numbers between 4.8 and 12.5. In summary, the Lattice Boltzmann Method appears promising for micro filter computations, but improvements are needed for larger Knudsen numbers and more sophisticated relaxation time models may be needed for increased compressibility effects at higher Reynolds numbers.
A Hybrid Approach to Investigate Effect of Flip-Chip Packaging on RF MEMS Devices Performance
Authors: Sun Li , Cunningham Shawn , Morris Art , Jang Changsoo , Han Bongtae
Published: August 2009

A hybrid numerical/experimental scheme to investigate the effect of flip-chip packaging, with and without underfill, on MEMS device performance will be described. Finite element analysis (FEA) is used to model the MEMS assembly and is verified with Twyman/Green (T/G) and Moire´ interferometry, and good agreement between FEA and optical measurements is obtained. The die warpage in assemblies with and without underfill are approximately 0.36 μm and 1.1 μm, respectively. The performance of MEMS devices, fixed-fixed beams, in the packages is characterized by Capacitance-Voltage (C-V) measurement sweeping the actuation voltage yielding the “ON” state and “OFF” state capacitances. Beams in packages without underfill exhibit good actuation behavior while beams in packages with underfill are already in the down-position after packaging. Because die warpage of packages with and without underfill are significantly different, beam anchor relative displacement (BARD), which is affected by the warpage, is used to understand the C-V performance. From numerical models, BARD of packages without underfill is 50 nm and 162 nm for packages with underfill. Compared to a simplified critical BARD calculation (BARDcrit = 57 nm), the large BARD of packages with underfill implies that beams may have buckled, which results in the poor C-V performance. Further modeling of varied die thicknesses and coefficients of thermal expansion (CTE) of the underfill shows that the reduction of BARD is limited because of strong underfill-induced coupling between the die and substrate. It is concluded that the MEMS device and package have to be considered as a coupled design problem to minimize the adverse packaging effect on MEMS devices.
Volume Average Turbulence Dissipation Equation for Multiphase Flow
Authors: Schwarzkopf John D. , Crowe Clayton T. , Dutta Prashanta
Published: August 2009

A dissipation transport equation for the carrier phase turbulence in particle-laden flow is derived from fundamental principles. The equation is obtained by volume averaging the same equation used for single phase flows. This process yields three additional terms that reflect the effect of the particles; these terms are evaluated assuming Stokes flow around the particles. Two of the terms reduce to zero and only one term remains which is identified as the production of dissipation due to the particles. The dissipation equation for the standard k-ε model is reformulated to include the additional term. The equation is then applied to the case of particles falling in an initially quiescent fluid and experimental data are used to evaluate the empirical coefficients. The ratio of the coefficient for the production of dissipation (due to the presence of particles) to the coefficient for the dissipation of dissipation is found to correlate well with the relative Reynolds number.
Study of the Bioheat Equation Using Monte Carlo Simulations for Local Magnetic Hyperthermia
Authors: Gutierrez Gustavo , Giordano Mauricio
Published: August 2009

Hyperthermia is a type of cancer treatment in which cancer cells are exposed to high temperatures (up to 44–45°C). Research has shown that high temperatures can damage and kill cancer cells, by a localized and concentrated heating source. By killing cancer cells and damaging proteins and structures within cells, hyperthermia may shrink tumors, with minimal injury to normal tissues. Penne’s bio-heat equation is used to model a heat diffusion process inside a tumor, modeled as a spherical domain with magnetic nanoparticles distributed within the diseased tissue. These magnetic particles are considered as point heat sources. Heat is generated as the result of magnetic relaxation mechanisms (Brownian and Neel relaxation) by the application of alternating magnetic fields. The Bio-Heat equation is solved using Monte Carlo techniques. Monte Carlo simulations are based on departing random walkers from the point where temperature is going to be determined. The probability in each step of the random walk is given by the coefficients of the nodal temperatures after a Finite Difference Discretization of the Penne’s bio-heat diffusion equation. The main advantage of Monte Carlo simulations versus classical numerical methods lies in the possibility of solving the temperature in a specific point without solving for all the points within the domain. This feature and the fact that each random walk is independent from each other results in an easy parallelization of the computer code. Parametric studies of the temperature profiles are carried out to study the effect of different parameters like the heat generation rate, perfusion rate and diameter of the point source on the maximum temperature and on the temperature profile.
Characterization and Estimation of Mass Loss Due to Exfoliation Corrosion From Vibration Spectrum
Authors: Singh Kumar V. , Hamilton Carter , Boehmer Steven
Published: August 2009

Corrosion is a major concern to the aerospace community when evaluating the structural integrity and service-life potential of an airframe. The estimation of corrosion and characterization of material parameters due to such corrosion is of the paramount interest. In this study, corrosion characterization and estimation is considered by using vibration spectrum that can be obtained from non-destructive testing. To that end, aluminum 7075-T6 extrusions were exposed to the exfoliation corrosion environment specified in ASTM G 34 for various times, and the resultant mass loss was measured for each exposure. The corrosion attack was confined to a narrow band centered on the length of a beam specimen by masking the extrusion. Theoretical modeling and lab scale dynamic testing were conducted to establish the correlation between the mass loss and the associated spectral characteristics of the beam (natural frequencies). This research program demonstrates that changes in mass due to exfoliation corrosion may be identified by the measurable change in the spectrum. Estimation/characterization techniques based upon a low dimensional mathematical model as well as based only upon experimental data (natural frequencies) are developed. Successful non-destructive dynamic characterization of aluminum extrusions, therefore, can be the basis of corrosion evaluation and health monitoring of structures operating in corrosive environments.
Comparative Study of Copper Oxidation Schemes and Their Effects on Surface Wettability
Authors: Nam Youngsuk , Ju Y. Sungtaek
Published: August 2009

We present a comparative study of different oxidation methods for Cu, focusing on their effects on surface wettability for potential heat transfer applications. Various Cu2O/CuO nanostructures are formed on copper substrates using thermal and chemical oxidation methods. The morphology and chemical composition of the oxide layers are investigated using atomic force microscopy, scanning electron microscopy, and X-ray diffraction measurements. To evaluate the surface wettability, static contact angles are measured before and after each oxidation process. In thermal oxidation, the contact angle can be tailored from ∼15° to ∼90° by varying heating time (10 min ∼ 4 hrs) and temperature (150–250 °C). Chemical oxidation processes using hot alkali solutions yield stable CuO nanostructures with high roughness factors and unique morphologies, which cause significant changes in wettability. Both superhydrophilic and superhydrophobic surfaces are demonstrated using the chemical oxidation methods.
A High-Performance Flame Fuel Cell Using Ethanol as Fuels
Authors: Wang Kang , Ahn Jeongmin , Shao Zongping
Published: August 2009

A no-chamber solid-oxide fuel cell that operated on a fuel-rich ethanol flame was reported. Heat produced from the combustion of ethanol thermally sustained the fuel cell at a temperature range of 500 ∼ 830 °C. Considerable amounts of hydrogen and carbon monoxide were also produced during the fuel-rich combustion directly providing the fuels for the fuel cell. The location of the fuel cell with respect to the flame was found to have a significant effect on the fuel cell temperature and performance. The highest power density was achieved when the anode was exposed to the inner flame. By modifying the Ni+Sm0.2Ce0.8O1.9 (SDC) anode with a thin Ru/SDC catalytic layer, the fuel cell envisaged not only an increase of the peak power density to ∼ 200 mW/cm2 but also in a significant improvement of the anodic coking resistance.
Investigation Into Bio-Aviation Reaction Mechanisms Using Quantum Mechanical Methods
Authors: Shafagh Ida , Hughes Kevin J. , Pourkashanian Mohamed , Williams Alan
Published: August 2009

Using high level model chemistries the C-C and C-H bond dissociation energies for methyl butanoate molecule (MB) were estimated using the Gaussian 03 program at the CBS-QB3 level of calculations. This consequently located the weaker bonds more likely to break. Thermal decomposition of MB over the temperatures 500 to 2000 K was theoretically studied and the rate constants for these channels were calculated. Crucial reactions in combustion, among which there are reactions of the fuel molecule with flame reactive radicals OH and CH3, were studied and the barrier heights for reactions including different hydrogen atoms transferring to the radicals were evaluated at the B3LYP/6-31+G(d, p) level of theory. The rate constants for these reactions are calculated over the temperatures 500 to 2000 K using the same level.
Friction Stir Welding of T-Joints in Dissimilar Aluminium Alloys
Authors: Tavares S. M. O. , Azevedo P. C. M. , Emi´lio B. , Richter-Trummer V. , Figueiredo M. A. V. , Vilac¸a P. , de Castro P. M. S. T.
Published: August 2009

The T-joint is a common joint type frequently used in transport industries because of the importance of increasing the inertia and strength of thin skins and shells without significant weight increase. This shape can be obtained by different processes as extruding, riveting, welding or others. However, the low weldability of some aluminum alloys, when using traditional welding processes, is an obstacle to the possible full benefit of such reinforced structures. The friction stir welding (FSW) process is suitable to join most aluminum alloys and should be considered as a feasible alternative to the other processes used to produce this type of geometry. This paper reports the results obtained concerning FSW T-joints with a new configuration. These joints simulate a typical reinforcement composed by two materials in order to optimize the damage tolerance. The skin is made of a 6xxx series alloy, and the reinforcement is made of a 7xxx series alloy. Mechanical properties were obtained and micro-structural analyses of the weld zone were performed, and the results were compared with those obtained in base materials and butt joints.
Enhancing the Sensitivity of a Resonant Accelerometer
Authors: Ibrahim Mahmoud I. , Younis Mohammad I.
Published: August 2009

This paper presents an investigation on the sensitivity enhancement of a resonant accelerometer by operating it in the nonlinear regime. The accelerometer is excited by a DC load superimposed to an AC harmonic load. The electric load is tuned such that the accelerometer is driven at primary resonance with a softening-type behavior. Upon the application of a small acceleration, the nonlinear resonance frequency of the accelerometer shifts to a smaller value. This frequency shift is used as an indication for the detected acceleration. This shift is much larger compared to the shift of the resonance frequency of the accelerometer when operating in the linear regime. The concept of the nonlinear excitation is demonstrated by simulation on a commercial capacitive accelerometer. A nonlinear single-degree-of-freedom (SDOF) system is used to model the accelerometer. Several results are shown for the effect of the DC and AC voltages on enhancing the sensitivity of the accelerometer.
A Research Roadmap Toward a Holistic and Structured Top-Down Concept Selection Methodology
Authors: Takai Shun
Published: August 2009

In the field of human cognition, thinking consists of problem-solving and decision-making. In cognitive thinking, top-down processing is an approach used by experts that enables them to solve problems and make decisions efficiently. This paper attempts to apply cognitive top-down thinking process to the concept evaluation of systems and their components. In the top-down concept evaluation approach, engineers first evaluate system concepts. Once a system concept is selected, engineers then identify system components (modules) that they can design independently for the chosen system concept. Engineers generate concepts for system modules and select one concept for each module. The objective of this paper is first to identify characteristics needed for a holistic and structured top-down concept evaluation methodology for a system and its components, and second to propose a research roadmap for establishing the proposed framework.
Milliseconds Microfluidic Bubble Mixer Using Chaotic Advection
Authors: Mao Xiaole , Juluri Bala Krishna , Lapsley Michael Ian , Huang Tony Jun
Published: August 2009

In this work, we report a novel passive micromixer based on the perturbation of chaotic micro-bubbles. The sample flows (ink solution and water) were co-injected with nitrogen in a flow focusing orifice to generate side-by-side laminar flows segmented by monodisperse bubbles. The bubble flow subsequently enters a mixing chamber downstream, upon which the hydrodynamic interactions between two adjacent bubbles result in the stretching and folding of the laminar flow interface, which leads to a rapid chaotic mixing and complete homogenization of two separated streams. Our technique provides a simple, passive, and effective mixing mechanism for sample homogenization in microfluidic devices.
Sequential Transient Numerical Simulation of Inertia Friction Welding Process
Authors: El-Hadek Medhat Awad , Davoud Mohammad S.
Published: August 2009

Inertia friction welding processes often generate substantial residual stresses due to the heterogeneous temperature distribution during the welding process. The residual stresses which are the results of incompatible elastic and plastic deformations in weldment will alter the performance of welded structures. In this study, three-dimensional (3D) finite element analysis has been performed to analyze the coupled thermo-mechanical problem of inertia friction welding of a hollow cylinder. The analyses include the effect of conduction and convection heat transfer in conjunction with the angular velocity and the thrust pressure. The results include joint deformation and a full-field view of the residual stress field and the transient temperature distribution field in the weldment. The shape of deformation matches the experimental results reported in the literature. The residual stresses in the heat-affected zone have a high magnitude but comparatively are smaller than the yield strength of the material.
Biomimetic Microactuator Powered by Polymer Swelling
Authors: Lee Howon , Xia Chunguang , Fang Nicholas Xuanlai
Published: August 2009

We propose novel biomimetic polymer microactuators. The actuation mechanism is inspired by nastic movement of the moving plant, Mimosa pudica, which folds its leaves upon external stimulus by regulating turgor pressure of cells in specific location. Photo-cured poly(ethylene glycol) diacrylate (PEGDA) microactuator is fabricated using projection micro-stereolithography (PμSL) capable of complex 3D micro fabrication. The swelling effect of PEG in water and organic solvent is exploited as an actuation mechanism of the device. Stress relaxation in the structure due to solvent absorption is controlled locally by delivering solvent through microfluidic channels embedded in the actuator, thereby generating a net movement in the device. Timescale of the motion derived from analytical swelling model suggests that actuation speed can be effectively increased by scaling down the actuator because the characteristic swelling time depends on the length as L2, which is verified experimentally.