bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Study of Lead-Free Wave Soldering Using SAC 305 and No-Clean Flux
Authors: Subbarayan Guhan , Warnock Buck , Damodaran Purushothaman , Srihari Krishnaswami , Arellano Jorge
Published: April 2008

The transition to lead-free assembly will have a significant effect on wave soldering operations. Since the wetting ability of lead-free solder is usually less than that of tin-lead solder, it can result in unacceptable hole fills and inconsistent top side wetting - especially in the case of thick Printed Circuit Boards (PCBs). Presently, there is very little data available on lead-free wave soldering with tin-silver-copper (SnAgCu or SAC) alloy and no-clean flux chemistry. Although some researchers and consortia recommend tin-copper (SnCu) for lead-free wave soldering, demonstrating the feasibility of using the SAC alloy for wave soldering operation can aid manufacturers to use the same alloy for both reflow and wave soldering operations. In this study, SAC 305 alloy and no-clean flux were evaluated in terms of percentage of hole fill and solderability on a 93 mil thick test vehicle with Immersion Silver (ImmAg) surface finish. The evaluation was performed on a nitrogen equipped wave soldering equipment. It has 4 preheating zones (3 convection bottom heaters and 1 infrared top heater) that provides good control to develop the required preheat profile. A partial factorial experiment was conducted to study the main effects of solder pot temperature, topside preheat temperature and conveyor speed on wave soldering performance. Wave soldering was performed after two reflow cycles. A 100% visual inspection was done for all the through hole components using a 10X microscope to determine top side wetting, percentage of hole fill, bridging, flux residue and solder balling. Thickness of the hole fill was also measured using digital X-Ray equipment. The data generated from this experiment was used to determine the 'optimum' lead-free process parameters for wave soldering using a SAC 305 alloy with a no-clean flux chemistry. The 'optimized' process parameters were then used to evaluate boards with Organic Solderability Protective (OSP) and Electroless Nickel Immersion Gold (ENIG) surface finishes. The designed experiments approach adopted to determine the optimum process settings and the research findings are explained in detail.
Feasibility Study of Smart PZT Thin-Film Microresonators
Authors: Wu Chia-Che , Lee Cheng-Chun , Cao G. Z. , Shen I. Y.
Published: April 2008

The quality factor of MEMS-based microresonators is often limited due to damping of the resonator structure and the surrounding air. A possible avenue to enhance the quality factor is to incorporate a negative damping feedback to reduce the damping of the resonator for those vibration modes of interest. This method is particularly easy to implement for piezoelectric based microresonators, because piezoelectric materials can serve as a sensor and an actuator simultaneously. This paper first demonstrates the concept on a silicon cantilever with a PZT thin-film actuator and a laser Doppler vibrometer as an external sensing element. Then the paper describes a design of PZT thin-film actuator consisting of a diaphragm suspension and multiple electrodes. Some of the electrodes serve as the sensors and others as actuators to reduce resonator damping. This design can potentially be used for microresonators without using external sensing elements.
Non-Contact Mechanical Testing and Characterization of Micro-Scale Structures
Authors: Chen Jian , Subramanian Ganesh , Ricci Justin , Ban Liang , Cetinkaya Cetin
Published: April 2008

A non-contact testing and characterization method based on air-coupled acoustic excitation and interferometric displacement measurements of micro-scale MEMS structures at room conditions is introduced. In demonstrating its potential uses in testing and characterization, the present non-contact approach is applied to (i) micro-cantilever beams and (ii) rotational disk oscillators. Air-coupled multi-mode excitation of micromechanical cantilever-type oscillators under a pulsed acoustic field generated by an air-coupled transducer is demonstrated and reported. Also, the testing and characterization of a micro-scale rotational disk oscillator developed for a new class of sensor platform is demonstrated. The main design objective of the rotational disk oscillator class is to overcome the out-of-plane motion related sensitivity limitations of the cantilever-based sensors at high frequency operations. The dynamics of the rotational disk oscillators is more complex than micro-cantilever beams due to its in-plane motion in addition to its various out-of-plane modes of vibration. The fabrication of a rotational disk oscillator requires a suspended disk whose underside is visibly inaccessible due to a narrow micro-gap. In addition to the dynamic characterization of the cantilever beams and rotational disk oscillators, the current investigation demonstrates that the presented approach can address unique structural concerns such as the verification of a gap separation of the rotational oscillator from the underlying silicon substrate. Utilizing the proposed technique, the resonant frequencies of the oscillator structures are obtained and its potential uses in the testing and characterization of micro-scale structures are discussed. The major specific advantages of the introduced approach include that (i) its noncontact nature can eliminate testing problems associated with stiction and adhesion, and (ii) it allows direct mechanical characterization and testing of components and sub-components of a micro-scale devices.
Intelligent Control of Energy Usage in Commercial Buildings
Authors: Shoureshi Rahmat A. , Permana Virdiansyah , Khayani Mohammad B.
Published: April 2008

Distributed energy resources hold great potential for meeting future energy needs. When operated in an optimized combined heat and power (CHP) mode distributed generation (DG) devices provide many operational and economic advantages over conventional energy supply options. This paper presents results of our research which has been focused on intelligent control of energy usage in commercial buildings by utilizing CHP systems. Operation of the CHP system is optimized through applications of Artificial Intelligence and advanced control systems. Energy usage in a commercial building, performance of a CHP system, and desiccant storage are mathematically modeled by using a neuro-fuzzy inference engine. Two commercial buildings are being used as testbeds to identify and analyze the technical issues associated with the deployment and operation of the CHP. Results from the energy control in these buildings are presented in this paper.
Smart Diagnostic System for High Voltage Electric Transmission Lines
Authors: Shoureshi Rahmat A. , Lim Su-Wook , Sarusi Benny
Published: April 2008

Overhead electric transmission lines are subjected to many natural hazards. Presently, the strength and remaining life of the transmission lines have primarily been determined by visual inspection. This paper presents results of our research, which has been focused on the feasibility analysis, and the development of an intelligent monitoring and integrity assessment system without the need for de-energizing or disassembly of transmission lines. This mechatronic system combines advances in electronics, mechanical system design, embedded signal processing and neural networks for signature analysis and feature extraction to create a smart diagnostic system for real-time operation. This paper also presents results from the actual field-testing of the Electromagnetic-Acoustic-Transducer (EMAT) monitoring system from utility companies. The utility companies are currently utilizing the EMAT to identify status of the overhead transmission lines without de-energizing and disassembly of their tower structures.
A Generalized Model of a Class of Interconnected Hydro-Pneumatic Suspensions and Analysis of Pitch Properties
Authors: Cao Dongpu , Rakheja Subhash , Su Chun-Yi
Published: April 2008

The static and dynamic properties of pitch-interconnected hydro-pneumatic vehicle suspensions are derived using a generalized analytical model. The suspensions incorporate two compact struts with integrated gas chambers and damping valves within each unit. The struts provide superior flexibility in realizing fluidic couplings, while offering large effective working area. The proposed suspension configurations consist of hydraulic, pneumatic or hybrid fluidic couplings between the front and rear suspension struts. The coupling effects due to different interconnected suspensions are established through the mathematical formulations. A generalized model of the hydro-pneumatic suspensions is developed that could be applied for either the roll or pitch plane of the vehicle, permitting analyses of suspension forces in a very simple manner. The 7-DOF pitch plane model of a heavy vehicle is analyzed to derive the relative vertical and pitch properties of different suspension configurations, in terms of suspension rates, pitch stiffness, bounce and pitch mode damping properties. The results suggest that the use of fluidic interconnections could yield considerable design flexibility and reduced coupling between the bounce and pitch stiffness properties, while the hydraulic and hybrid fluidic couplings offer added flexibility in tuning the bounce and pitch damping characteristics. The influence of load distribution on the bounce and pitch stiffness properties is also explored.
Effect of Selected Manufacturing Variables on Reliability of Lead Free Solder Joints
Authors: Ladani Leila Jannesari , Dasgupta Abhijit , Cardoso Idelcio , Monlevade Eduardo
Published: April 2008

This paper presents a systematic approach to study the effect of manufacturing variables on the creation of defects and the effect of those defects on the durability of lead free solder joints. An experiment was designed to systematically vary the reflow and printing process variables in order to fabricate error-seeded test assemblies. The error-seeded samples were then inspected visually and with x-rays, to identify different types of defects, and tested for electrical performance. The specimens were put under accelerated thermal cycling test to characterize the durability of specimens and to study the effect of each manufacturing variable on the durability of solder joints. Thus, the response variable for the design of experiments is the thermal cycling durability of the solder joints. Pre-test micro-structural analysis shows that specimens produced under inadequate reflow profiles suffer from insufficient wetting and insufficient intermetallic formation. Statistical analysis of the response variable shows that waiting time, heating ramp, peak temperature and cooling rate have non-linear effects on the response variable. Two variables, in particular (the heating ramp time and the waiting time), appear to have optimum values within the ranges investigated.
Numerical Simulation of Welding Induced Residual Stresses in a Circular Hollow Section T-Joint
Authors: Joshi Suraj , Semetay Cumali , Price John W. H. , Nied Herman
Published: April 2008

Heavily welded circular hollow cross sections (CHS) are a common feature in civil structures such as draglines used in the mining industry and other off-shore structures. The sheer mass of the weldment and the application of intense heat generated during the welding process give birth to significant residual stresses in the structure. Often, residual stresses are high enough to act to accelerate factors such as corrosion, crack growth and fatigue. The objective of this research investigation was to predict welding generated residual stresses in a typical CHS T-Joint using Sysweld+, a welding Finite Element Analysis software. The T-joint is the first of the four lacings welded on to the main chord of a BE 1370 mining dragline cluster (designated All) of a type which is often used in the mining industry in Australia. This work examines a massive 3-dimensional geometry, which is on a much larger scale than those examined in existing studies. The paper presents the results of the simulation of residual stresses generated during the welding process in a single weld pass and compares them with the approach used in the commonly used document R6-Revision 4, Assessment of the Integrity of Structures Containing Defects.
Hardware-Based Simulation of a Fuel Cell Turbine Hybrid Response to Imposed Fuel Cell Load Transients
Authors: Smith Thomas P. , Haynes Comas L. , Wepfer William J. , Tucker David , Liese Eric A.
Published: April 2008

Electrical load transients imposed on the cell stack of a solid oxide fuel cell/gas turbine hybrid power system are studied using the Hybrid Performance (HyPer) project. The hardware simulation facility is located at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). A computational fuel cell model capable of operating in real time is integrated with operating gas turbine hardware. The thermal output of a modeled 350 kW solid oxide fuel cell stack is replicated in the facility by a natural gas fired burner in a direct fired hybrid configuration. Pressure vessels are used to represent a fuel cell stack's cathode flow and post combustion volume and flow impedance. This hardware is used to simulate the fuel cell stack and is incorporated with a modified turbine, compressor, and 120 kW generator on a single shaft. For this study, a simulation was started with a simulated current demand of 307 A on the fuel cell at approximately 0.75 V and an actual 45 kW electrical load on the gas turbine. An open loop response, allowing the turbine rotational speed to respond to thermal transients, was successfully evaluated for a 5% current reduction on the fuel cell followed by a 5% current increase. The impact of the fuel cell load change on system process variables is presented. The test results demonstrate the capabilities of the hardware-in-the-loop simulation approach in evaluating hybrid fuel cell turbine dynamics and performance.
Online Measurement of Viscosity of HDPE-Wood Flour Composites Compunded in Different Processing Condition
Authors: Zhang Jing-Jing , Huang Han-Xiong , Wang Yu-Huan
Published: April 2008

In this study, the viscosity of high-density polyethylene (HDPE)-wood flour composites compounded in different processing condition was measured using the Hakke online rheometer (Hakke Proflow). Composites were prepared in an intermeshing co-rotating twin-screw extruder. Influence of HDPE melt index on the melt shear viscosities of the composites was studied. To investigate the viscosity in different processing condition, two screw configurations and three screw speeds were considered. The results showed that the effect of wood on increasing the viscosity was more pronounced in higher melt index HDPE composites. The viscosity decreased with increasing screw speed from 100rpm to 300rpm. In terms of screw configuration, both small-pitch conveying screw element and kneading elements with wide disks and large staggering angle were benefit to the flow of HDPE-wood composites. Medium shear should be selected to optimize the flow. Higher HDPE melt index wood composites processed in shear and longitudinal mixing flow field presented more shear-thinning behavior.
Dynamics of Variable-Geometry Electrostatic Microactuators
Authors: Najar F. , Choura S. , Abdel-Rahman E. M. , El-Borgi S. , Nayfeh A. H.
Published: April 2008

This paper investigates the dynamic behavior of a microbeam-based electrostatic microactuator. The cross-section of the microbeam under consideration varies along its length. A mathematical model, accounting for the system nonlinearities due to mid-plane stretching and electrostatic forcing, is adopted and used to examine the microbeam dynamics. The Differential Quadrature Method (DQM) and Finite Difference Method (FDM) are used to discretize the partial-differential-integral equation representing the microbeam dynamics. The resulting nonlinear algebraic system is solved for the limit cycles of various microstructure geometries under combined DC-AC loads and the stability of these limit cycles is examined using Floquet theory. Results are presented to show the effect of variations in the geometry on the frequency-response curves of the microactuator. We examine the effect of varying the gap size and the microbeam thickness and width on the frequency-response curves for hardening-type and softening-type behaviors. We found that it is possible to tune the geometry of the microactuator to eliminate dynamic pull-in.
Improved Control of a Steering Wheel Vibration Simulator
Authors: Mynderse James A. , Chiu George T.-C.
Published: April 2008

The improved control of a steering wheel vibration simulator capable of reproducing a set of desired vibration/acceleration signals is presented. The simulator is to be used in characterizing human perception of vibration as transmitted to the hand through the steering wheel. Accelerometers are used to record the acceleration at the top of the steering wheel in both the up-down (z) and side-to-side (y) directions. The plant is modeled by frequency response measurements including an uncertainty model generated from measured changes in system frequency response due to variations in subject grip force. The simulator control problem is formulated as a 2-input, 1-output tracking control of the z-axis while minimizing the y-axis response. A two degree-of-freedom controller is synthesized with a stabilizing feedback controller and a zero phase error tracking feedforward controller. The feedback controller is designed using linear matrix inequality techniques and ensures robust stability of the coupled closed-loop system with uncertainty due to subject grip force. Simulation and experimental results to verify the effectiveness of the simulator are presented.
Optimization Design of Vibration and Shock Isolation System
Authors: Zhao Cun-Sheng , Zhu Shi-Jian , Zhang Zhen-Zhong
Published: April 2008

The combination optimization design problem of vibration isolation and shock resistance system is studied in consideration of acoustical concealment performance and lifeforce of ships. The weakness of design method based on continuity is pointed out and combination optimal design method is brought forward. Then the limiting performance of shock isolation system is analyzed and two realization methods are discussed. One method is to adopt linear stiffness component with large damping. The other method is to use multiple linear stiffness components without damping. Amplitude of steady excitation is much smaller than that of shock input during experiment. Experimental results showed that the optimal loss factor is still 0.4 when the stiffness of shock bumper is much larger than that of vibration isolator, just the same with that suffered from only shock loads. Experimental results also showed that limiting performance can be achieved by configuration optimal design using multiple linear components. The two discussed methods can be used to direct engineering application.
Optimal Wheel Diameter Design for a Water-Vapor (R-718), Axial, Compressor
Authors: Holden Nathan , Mu¨ller Norbert
Published: April 2008

There is an interest to phase out environmentally harmful refrigerants (ie: HCFC-12, HCFC-22, but also HCFC-134A and other). Theoretical analysis coupled with mostly European research has proven that water-vapor (R-718) technology can be comparable to and even more efficient than other modern chiller technology using conventional refrigerants. The crucial component to succeed with water-vapor as refrigerant is the compressor. European compressor designs already introduced and commercialized have shown that with the currently available mechanics of using water-vapor, energy consumption can be reduced by as much as 20% over conventional technology utilizing refrigerants like HCFC134A. However, currently these compressor designs are physically large and the chillers can be as much as five (5) times more expensive to manufacture and install. Often for this reason they are often deemed to be insufficient. Much more reasonably priced compressors of possibly smaller size are desired now to developed water-vapor into an economically viable refrigerant, that may also be applicable for smaller cooling capacities. The presented work looks at the preliminary design considerations to determine the minimum impeller-wheel diameter with respect to the pre-determined operating parameters (ie: limiting relative critical Mach number, rotational speed, total fluid temperature, total fluid density, etc....). The results need then to be further refined in subsequent steps leading to a final design not discussed here. With the preliminary optimal impeller-wheel diameter of a water-vapor (R-718) compressor as established here, industry can easily perform a critical first step in developing a workable water-vapor (R-718) refrigeration system.
Dynamics of Multilayer Microplates Considering Nonlinear Squeeze Film Damping
Authors: Ahmadian M. T. , Zand M. Moghimi , Borhan H.
Published: April 2008

This paper presents a model to analyze pull-in phenomenon and dynamics of multi layer microplates using coupled finite element and finite difference methods. First-order shear deformation theory is used to model dynamical system using finite element method, while Finite difference method is applied to solve the nonlinear Reynolds equation of squeeze film damping. Using this model, Pull-in analysis of single layer and multi layer microplates are studied. The results of pull-in analysis are in good agreement with literature. Validating our model by pull-in results, an algorithm is presented to study dynamics of microplates. These simulations have many applications in designing multi layer microplates.
Effect of High Coolant Velocity on Heat Transfer in Compact Heat Exchangers
Authors: Sathyanarayanan P. L. , Venkateswaran N. , Ramprabhu R.
Published: April 2008

Compact Heat Exchangers were developed to have very high efficiency in transfer of heat within a very small space or volume and are being used in the automotive, aircraft and space applications. In order to obtain much higher heat transfer, these Heat Exchangers uses closely packed fins, narrow or small diameter passages and turbulators or turbulence promoters. Though these arrangements result in much higher pressure drop for the fluids, this disadvantage is expected to be off-set with a larger increase in heat transfer capability. Generally it is known that turbulence enables better mixing of the fluid and results in enhancing the heat being transferred. However in practice it has been observed that there is a limit to this enhancement and the heat transfer does not improve beyond certain turbulence levels. The higher turbulence level probably results in carrying the heat away along with the fluid without transferring all the heat to the cooling medium. The presence of turbulence promoters was found to be beneficial at a lower fluid velocity level, where they conduct the heat away more by surface conduction than by convection in the fluid. Detailed experimental investigation and findings of this phenomenon using a compact heat exchanger for a military vehicle is described in this paper.
A New Method of Motion Coordination of a Group of Mobile Agents
Authors: Lal Mayank , Sethuraman Swaminathan , Jayasuriya Suhada , Rojas J. Maurice
Published: April 2008

This paper presents a new method for coordinated motion planning of multiple mobile agents. The position in 2-D of each mobile agent is mapped to a complex number and a time varying polynomial contains information regarding the current positions of all mobile agents, the degree of the polynomial being the number of mobile agents and the roots of the polynomial representing the position in 2-D of the mobile agents at a given time. This polynomial is constructed by finding a path parameterized in time from the initial to the goal polynomial which represent the initial and goal positions of the mobile agents so that the discriminant variety or the set of polynomials with multiple roots is avoided in polynomial space. This is equivalent to saying that there is no collision between any two agents in going from initial position to goal position.
Wind-Generated Electrical Energy Using Flexible Piezoelectric Mateials
Authors: Robbins William P. , Morris Dustin , Marusic Ivan , Novak Todd O.
Published: April 2008

Electrical energy can be harvested from the wind using flag-like membranes (termed piezoelements or bimorphs) composed of flexible piezoelectric materials. The flapping of the membrane caused by the wind induces bending stresses that generate a voltage across electrodes positioned on the surfaces of the material via the piezoelectric properties of the material. The best results to date using PVDF (polyvinyledene fluoride) as the piezoelectric material are 10 mW of dc power (50 Vdc across 250 kΩ) obtained from a single bimorph element (size about 8"X11"X 0.02") flapping a frequency of 5 Hz in a wind speed of 15 mph. The overall efficiency was low (estimated at 0.1%) and to improve this figure, three specific areas of improvement are targeted. The efficiency of the piezoelement in converting wind energy into stored elastic energy will be optimized by determining the best geometry and dimensions for the element in conjunction with upwind bluff bodies using wind tunnel tests. A novel circuit, termed a quasi-resonant rectifier, for extracting the electric energy from the piezoelectric has been developed which can extract several times more power from the piezoelement than a conventional full-wave rectifier. A number of piezoelectric and electrostrictive materials including PZT fibers embedded in an epoxy matrix (termed active fiber composites or macro fiber composites) which may have higher generation efficiencies than PVDF will be examined for this application.
Experimental Design and Analysis of Bimorphs as Synthetic Jet Diaphragms
Authors: Mane Poorna P. , Mossi Karla M. , Bryant Robert G.
Published: April 2008

Synthetic jet actuators are promising Active Flow Control (AFC) devices which could lead to saving millions of dollars in fuel consumption each year. The Bimorph piezoelectric actuators are an attractive alternative to other type of actuators as active diaphragms and are the focus of this work. Among the properties of a Bimorph actuator, a number of geometrical and physical external factors may have an effect on its performance as a synthetic jet actuator. Using statistical tools some of the physical and geometrical factors are evaluated as independent variables that may have an effect on the synthetic jet peak velocity, the dependent variable. Among the factors studied are the geometry of the synthetic jet cavity, the driving signal used to operate the active diaphragm, and the effect of a pressure gradient on the device. Among the six factors considered, the driving signal was found to have the highest effect on the peak jet velocity, and the factor of frequency proved to have a smaller effect. The cavity geometrical parameters were also relevant, a smaller orifice and a smaller cavity produce higher peak jet velocities. An adverse pressure gradient was also found to have a significant effect on peak jet velocity, diminishing its magnitude with increasing pressure.
Bifurcation Behavior of a Supercavitating Vehicle
Authors: Lin Guojian , Balachandran Balakumar , Abed Eyad H.
Published: April 2008

In this effort, a numerical study of the bifurcation behavior of a supercavitating vehicle is conducted. The nonsmoothness of this system is due to the planing force acting on the vehicle. With a focus on dive-plane dynamics, bifurcations with respect to a quasi-static variation of the cavitation number are studied. The system is found to exhibit rich and complex dynamics including nonsmooth bifurcations such as the grazing bifurcation and smooth bifurcations such as Hopf bifurcations, cyclic-fold bifurcations, and period-doubling bifurcations, chaotic attractors, transient chaotic motions, and crises. The tailslap phenomenon of the supercavitating vehicle is identified as a consequence of the Hopf bifurcation followed by a grazing event. It is shown that the occurrence of these bifurcations can be delayed or triggered earlier by using dynamic linear feedback control aided by washout filters.
Investigation of Locking Force of Stay Cable Vibration Control Using Magneto-Rheological Fluid Damper
Authors: Min Liu , Sethi Vineet , Song Gangbing , Li Hui
Published: April 2008

This paper analyzes the locking force of a stay cable equipped with a Magneto-rheological (MR) damper. For the single mode vibration of the stay cable, the formula of the locking force is derived and the important factors that affect the locking force are analyzed. The experimental investigations of the locking force of the stay cable vibration control are carried out on a cable-stayed bridge model equipped with an MR damper to verify of the computational locking force in the Smart Materials and Structures Laboratory at University of Houston. For the multi-mode vibration of the stay cable, the modal shapes of the stay cable vibration are estimated by utilizing a pole placement observer using the acceleration values at selected locations of the stay cable and the locking forces of the stay cable in multi-mode vibration are numerically obtained. In all experimental cases, the locking forces based on the analytical and numerical formulas approximately match the experimental results.
Novel Friction Test Structures for Microelectromechanical Systems
Authors: Currano Luke J. , Yu Miao , Balachandran Balakumar
Published: April 2008

Novel friction test structures that are suitable for determining the friction coefficient of vertical surfaces in microelectromechanical systems (MEMS) devices are fabricated and used to carry out friction measurements on smooth and rough deep reactive ion etched (DRIE) silicon surfaces. The results obtained for rough surfaces show that the friction coefficient decreases as the sliding contact is put through the first eight to ten cycles, before it reaches a steady-state value that closely matches the friction coefficient of the smooth surface.
Influence of Clearance on the Dynamics of Chain CVT Drives
Authors: Srivastava Nilabh , Miao Yi , Haque Imtiaz U.
Published: April 2008

A continuously variable transmission (CVT) is an emerging automotive transmission technology that offers a continuum of gear ratios between desired limits. The present research focuses on developing models to understand the influence of clearance on the dynamic performance of a chain CVT drive. Clearances may arise in such a CVT during the assembly process or during extensive continual operation of the system, which further leads to wear and failure of the system. A detailed planar multibody model of a chain CVT is developed in order to accurately capture the dynamics characterized by the discrete structure of the chain, which causes polygonal excitations in the system. A suitable model for clearance between the chain links is embedded into this multibody model of the chain CVT. Friction between the chain link and the pulley sheaves is modeled using continuous Coulomb approximation theory. The mathematical models, the computational scheme, and the results corresponding to different loading scenarios are discussed. The results discuss the influence of clearance parameters on the dynamic performance, the axial force requirements, and the torque transmitting capacity of a chain CVT drive.
Artificial Neural Network Military Impulse Noise Classifier
Authors: Bucci Brian , Vipperman Jeffrey
Published: April 2008

Civilian noise complaints and damage claims have created the need for stations to monitor the production of military impulse noise. However, these stations suffer from numerous false positive detections (due to wind noise) of impulse events and often miss many events of interest. There is also interest in identifying specific noise sources, such different types of ordinance or different types of aircraft. To improve the accuracy of military impulse noise monitoring and make and initial effort to specifically classify noise source, an algorithm based upon an artificial neural network with inputs of conventional and custom acoustic metrics was proposed. To train and evaluate the noise classifier approximately 1,000 waveforms were field collected (110 military aircraft noise, 330 military impulse noise, and 560 non-impulse noise). The final noise classifier used kurtosis and crest factor and the custom metrics spectral slope and weighted square error as inputs. The classifier was able to achieve 99.7% accuracy on the training data set and 99.4% accuracy on the validation data set.
Real Time Prognostic Strategies With Application to Stationary Gas Turbines
Authors: Sekhon Rajat , Bassily Hany , Wagner John
Published: April 2008

Stationary gas turbines are increasingly deployed throughout the world to provide electrical and mechanical power in consumer and industrial sectors. The efficiency of these complex multi-domain systems is dependent on the turbine's design, established operating envelope, environmental conditions, and maintenance schedule. A real time health management strategy can enhance overall plant reliability through the continual monitoring of transient and steady-state system operations. The availability of sensory information for control system needs often allow diagnostic/prognostic algorithms to be executed in a parallel fashion which warn of impending system degradations. Specifically, prognostic strategies estimate the future plant behavior which leads to minimized maintenance costs through timely repairs, and hence, improved reliability. In this paper, statistical and wavelet prognostic methods are presented to forecast system health. For the statistical approach, a multi-dimensional empirical description reveals dominant data trends and estimates future behavior. The wavelet approach uses second order Daubechies wavelet coefficients to generate signal approximations that forecast future plant operation. Experimental data has been collected on a Solar Mercury 50 stationary gas turbine. The monitored plant signals were analyzed to identify prognostic information for preventative action recommendations. Representative results are presented and discussed to compare the overall performance of each prognostic algorithm.
Thermal Management Analysis of On-Board High-Pressure Metal Hydride Systems
Authors: Zheng Yuan , Velagapudi Varsha , Pourpoint Timothee , Fisher Timothy S. , Mudawar Issam , Gore Jay P.
Published: April 2008

Reversible metal hydrides are ideal vehicular hydrogen storage materials for the realization of on-board filling. Systems utilizing metal hydrides with high hydrogen release pressure (> 3 bar at -30 °C) can provide excellent cold-start capability. Although the required hydrogen filling pressure will also be high accordingly (> 100 bar), high-pressure (HP) metal hydride (MH) systems can store 20% to 50% more hydrogen in the void space between hydride particles in addition to the hydrogen absorbed by the metal alloys. To maintain a sufficiently high hydriding driving force during filling, it is very important to keep the MH temperature below a desirable level (85 °C). This issue becomes more important when the systems operate at high pressures, because the stress limits of materials for the container and other components decrease with increasing temperature. Efficient thermal management is needed to dissipate the large amount of heat produced during the initial rapid compression process (< 20 seconds) and the subsequent fast hydriding process (< 5 minutes). In this paper, thermal management design and analysis of a bench-scale rectangular-shaped HPMH module is reported. This module is approximately 1/70 of a vehicle-scale hydrogen storage tank. The modular approach provides flexibility to apply the knowledge obtained in this study to vehicle-scale designs. A typical AB2 HPMH is used as the hydrogen storage material. During the hydrogen filling process, the time-averaged volumetric heat release rate is approximately 3 MW/m3. Inner coolant passages are adopted to remove the heat. Through a scaling analysis of the energy conservation equation, the results indicate that thermal conduction in the metal hydride bed and convection in the coolant passages are both important factors. For the test module under development, finned tubes in conjunction with two-phase convection have been designed to meet the cooling requirements. Fin designs (material, thickness and spacing) have been evaluated using 3D numerical analysis. The knowledge learned from theoretical and numerical analyses is used to guide the construction of the HPME module, and hydrogen filling tests will be conducted soon.
Viscoelastic Effects on Fatigue Behavior of Braided Composites
Authors: Tate Jitendra S. , Kelkar Ajit D. , Beall Gary
Published: April 2008

Textile composites include woven, braided, and knitted fabrics. Textile composites are considered when out-of-plane properties are also important. Textile composites generally have better dimensional stability, out-of-plane properties, and impact and delamination resistance. The natural conformability of biaxial braids makes them more cost competitive than woven fabric. These material systems are gaining popularity, in particular for the small business jets, where FAA requires take off weights of 5670 kgf or less. The vacuum assisted resin transfer molding (VARTM) process has proven to be low in cost compared to resin transfer molding (RTM). Thus, the combination of biaxial braids and the VARTM process is likely to considerably reduce overall costs. Before the braids can be confidently used in the primary structures, it is necessary to understand the performance of biaxial braided composites under various loading conditions and especially under fatigue. This will reduce uncertainty and hence reduce the factor of safety in the design This research addresses viscoelastic effects on fatigue behavior of carbon/epoxy braided composites. It is observed that braided composites exhibit creep and stress relaxation. Further it is observed that frequency in axial fatigue loading plays dominant role in fatigue life, but very little role in fatigue failure mechanisms. Rate of stiffness degradation is greatly affected by frequency. These entire phenomena such as creep, stress relaxation, frequency effect, and dependency of stiffness on rate of loading indicate the viscoelastic behavior of braided composites. In this research different tests were performed to confirm viscoelastic behavior of braided composites. Axial tension-tension fatigue tests were conducted at different frequencies and stiffness degradation was studied.
Model Reduction of Modal Representations
Authors: Louca Loucas S. , Xydas Evagoras
Published: April 2008

Dynamic analysis is extensively used to study the behavior of continuous and lumped parameter linear systems. In addition to the physical space, analyses can also be performed in the modal space where useful frequency information of the system can be extracted. More specifically, modal analysis can be used for the analysis and controller design of dynamic systems, where reduction of model complexity without degrading the accuracy is often required for the efficient use of the model. The reduction of modal models has been extensively studied and many reduction techniques are available. The majority of these techniques use frequency as the metric to determine the reduced model. This paper describes a new method for calculating the modal power of lumped parameter systems with the use of the bond graph representation, which is developed through a power conserving modal decomposition. This method is then used to reduce the size of the model. This technique is based on the previously developed Model Order Reduction Algorithm (MORA), which uses an energy-based metric to generate a series of proper reduced models. An example is provided to demonstrate the calculation of the modal power and the elimination of unimportant modes or modal elements using MORA.
Vibration Characteristics of the Vocal Folds
Authors: Hai L. , Al-Jumaily A. M. , Mirnajafi A.
Published: April 2008

The vibration characteristics of the vocal folds are investigated using a finite element model which incorporates the in-homogeneity and anisotropy of the materials and the irregularity of the geometry. The model employs the cover and body theory to build the structure of the vocal folds and implements measured viscoelastic properties of the mucosa and the transverse isotropic elastic properties of the muscles. It has the potential to simulate some vocal-fold disorders and determine the change in characteristics. To determine the oscillation characteristics of the folds, the eigenfrequency and eigenmodes of the finite element model are determined using the ABAQUS software. The model results compare well with some experiments performed on a silicon vocal fold. It is anticipated that the model will help to identify voice disorders such as vocal-fold paralysis and vocal-fold nodules.
Particle Transport In Microchannels
Authors: Yap Y. F. , Chai J. C. , Wong T. N. , Nguyen N. T. , Toh K. C. , Zheng H. Y.
Published: April 2008

A numerical model for particle transport in microchannel is presented. This article focuses on situations where the sizes of the particles are comparable to the sizes of the channels. The present approach is validated against (1) flow around stationary, (2) flow around forced rotating, (3) flow around freely rotating cylinders and (4) sedimentation of a circular cylinder under gravity. With the present model, the motion of particles carried by an incompressible fluid in a microchannel system is studied.
Substructuring Developments in the Energy Finite Element Formulation
Authors: Zhang Geng , Vlahopoulos Nickolas , Sun Jiulong
Published: April 2008

In Naval applications of the Energy Finite Element Analysis (EFEA) there is an increasing need for developing comprehensive models with a large number of elements which include both structural and interior fluid elements, while certain parts of the structure are considered to be exposed to an external heavy fluid loading. In order to accommodate efficient computations when using simulation models with a large number of elements, joints, and domains, a substructuring computational capability has been developed. The new algorithm is based on dividing the EFEA model into substructures with internal and interface degrees of freedom. The system of equations for each substructure is assembled and solved separately and the information is condensed to the interface degrees of freedom. The condensed systems of equations from each substructure are assembled in a reduced global system of equations. Once the global system of equations has been solved the solution for each substructure is pursued. Important issues which have been considered in the new development originate from the necessity to define substructure interfaces along joint locations. The discontinuity of the energy density variables and the proper formulation of the joints across substructure interfaces have been considered in the new algorithm. In order to demonstrate the validity of the developments and the computational savings a set of previous applications where simulation results were compared to test data is repeated using the substructuring algorithm.
Computationally Efficient Approaches to Simulate the Dynamics of Microbeams Under Mechanical Shock
Authors: Younis Mohammad I. , Jordy Danial , Pitarresi James M.
Published: April 2008

We present computationally efficient models and approaches and utilize them to investigate the dynamics of microbeams under mechanical shock. We explore using a hybrid approach utilizing a beam model combined with the shock spectrum of a spring-mass-damper model. We conclude that this approach is computationally efficient and yields accurate results in both quasi-static and dynamic loading conditions. We utilize a reduced-order model based on the nonlinear Euler-Bernoulli beam model. We demonstrate that this model is capable of capturing accurately the dynamic behavior of microbeams under shock pulses of various amplitudes (low-g and high-g), in various damping conditions, structural boundaries (clamped-clamped and clamped-free), and can capture both linear and nonlinear behavior. We investigate high-g loading cases. We report significant increase in the computational cost of simulations when using traditional nonlinear finite-element models because of the activation of higher-order modes. We demonstrate that the developed reduced-order model can be very efficient in such cases.
Electrophoretic Motion of Particles in a Microsystem
Authors: Yap Y. F. , Chai J. C. , Wong T. N. , Nguyen N. T. , Toh K. C. , Zheng H. Y.
Published: April 2008

Electrophoresis is the motion of a charged particle relative to the surrounding liquid due to an imposed external electric field1. Its applications include but are not limited to characterization and manipulation of organic and inorganic particles. In particular, electrophoresis has been applied to a variety of analytical separation problems involving nucleic acids, proteins and drugs. For electrophoresis on various Lab-on-a-chip platforms, the particles are of sizes comparable to the microchannel in which they flow. As such, particle-particle and particle-wall interactions are no longer negligible. Therefore, the electric field, the flow field and the particles motion are strongly coupled together. Numerical models based on a moving-grid method2 have been employed to investigate the related phenomena. Mesh regeneration as the particles move is an extra computational complication. To circumvent the complexity of mesh regeneration, a level-set based fixed-grid method3 is presented for electrophoretic motion of particles in this article. The particles are assumed to be a highly viscous liquid constraint to move with rigid body motion. A distance function is employed to represent the liquid-particle interfaces. The electric field, the flow field and the particles motion are governed respectively by the Poisson, the Navier-Stokes and the Euler-Newton equations. The effect of the electric field on the particle motion is accounted for by incorporating slip boundary conditions on the particles surfaces. The nonlinear governing equations are discretized and solved using a finite volume method4. The model is used to investigate electrophoretic motion of non-conducting circular and elliptical particles in a microsystem. Figure 1 shows the electrophoretic motion of a single circular particle in a microchannel. The induced electroosmotic flow is from the left to the right. The thick circles are the particle at t = 0. The direction of the particle movement is indicated by the arrows. The motions of the particle if neutral, positively or negatively charged are obviously different. Basically, a positively charged particle move faster than the main flow. However, a negatively charged particle flows slower. When the particle is highly charged negative, it can even flow against the streamwise direction toward upstream (+V) as in Fig. 1c. This suggests that there would be a situation where the particle can be kept static. Figure 2 shows the electrophoretic motion of multiple particles. The initial locations of the particles are shown in Fig. 2a. In the case of charged particles, particle 1, 2 and 3 are respectively negatively, neutral and positively charged. Particle 1 which is elliptical undergoes obvious rotational motion when charged (Fig. 2c). The case of the neutral particles (Fig. 2b) is included for comparison.