bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum Energy-Efficiency Compliant Mechanism Design for Piezoelectric Stack Actuators
Authors: Abdalla Mostafa M. , Frecker Mary , Gu¨rdal Zafer , Johnson Terrence , Lindner Douglas K.
Published: May 2008

Combined optimization of a compliant mechanism and a piezoelectric stack actuator for maximum energy conversion efficiency is considered. The paper presents a system level analysis in which the actuator and the compliant mechanism are mathematically described as linear two-port systems. The combination of stack and compliant mechanism is used to drive a structure, modeled as a mass-spring system. The analysis assumes all components to be free from dissipation, and the piezoelectric stack is driven by an ideal voltage source. Energy conversion efficiency is defined as the ratio of the output mechanical energy to the input electric energy. Theoretical bounds on the system efficiency are obtained. It is shown that the stack actuator can be optimized separately and matched to the specified structure and an optimally designed complaint mechanism. The optimization problem for the compliant mechanism is formulated to maximize a weighted objective function of energy efficiency and stroke amplification. Optimization results are presented for ground structures modeled using frame elements.
Time-Dependent Simulations of Sub-Continuum Heat Generation Effects in Electronic Devices Using the Lattice Boltzmann Method
Authors: Escobar Rodrigo A. , Ghai Sartaj S. , Amon Cristina H. , Jhon Myung S.
Published: May 2008

The lattice Boltzmann method (LBM), which accounts for electron-phonon scattering, is used to investigate heat generation effects on silicon-on-insulator (SOI) transistors. The wave nature of the LBM is shown and its influence on subcontinuum dynamics is discussed. The implementation of boundary conditions for constant temperature and constant heat flux is described. SOI devices are modeled as thin films in one dimension. The LBM simulation results for diffusive, transitional, and ballistic regimes are compared with Fourier equation solutions and literature results. For transitional and ballistic regimes, Fourier equation results underpredict the temperature levels obtained by the LBM, which is consistent with the findings previously reported by different authors.
A Compact, Easily Assembled Micromirror With Liquid Metal Pivot
Authors: Zeng Hongjun , Feinerman Alan , Wan Zhiliang
Published: May 2008

We have developed a new approach to achieve a high-speed micromirror, which can rapidly tilt large angles with a low voltage and a compact footprint. In our approach we use a liquid metal drop with a low vapor pressure as the pivot, and the micromirror is tilted by an electrostatic torque. Micromirrors (1 mm x 1 mm) and the actuating circuit are microfabricated with a centralized wetting area surrounded by a non-wetting Parylene area to confine the drop. The frequency response curve shows that the mirror has 78V snap-down voltage and resonant frequency at 165Hz, and has a potential resonant frequency more than 3k Hz if the size of the mirror and liquid metal pivot is reduced. A micromirror with a liquid metal pivot is expected to have significantly higher reliability since a liquid drop does not suffer from mechanical fatigue. Due to the single point support, the micromirror can be tilted in an arbitrary direction, and the fabrication process is simpler than those required to create solid torsional weak links.
An Algorithm for the Selection of Physical System Model Order Based on Desired State Accuracy and Computational Efficiency
Authors: Sendur Polat , Stein Jeffrey L. , Peng Huei , Louca Loucas S.
Published: May 2008

In recent years, algorithms have been developed to help automate the production of dynamic system models. The focus of this development has been to create procedures and algorithms that use modeling metrics for generating minimum complexity models with physically meaningful parameters of dynamic systems (proper models). Existing algorithms, however, do not explicitly address the accuracy of the system variables, and validity of system models. The objective of this paper is to integrate a previously published accuracy and validation algorithm [9] with an energy based (activity index) reduction algorithm [2] to quantify model accuracy as a function of model complexity. In addition, a new metric for selecting the best model based on model accuracy and computational efficiency is introduced. A model of a Class VI International 4700 series delivery truck is used as an illustrative example. The results demonstrate that the proposed model assessment procedure not only provides the means for identifying the proper model based on accuracy and computational constraints, but also provides further evidence that practical systematic tools for improving the modeling process can be developed.
A Cellular Motor Based Micro Pump: Integration of Cellular Motors With Micro Channels
Authors: Pooran Ryan , Kim Jin-Woo , Tung Steve , Malshe Ajay P. , Lee Chuen Cheak
Published: May 2008

To achieve a high degree of functional density and efficiency, some of the micro actuators in MEMS can be replaced by active biological elements. An example of this is the cellular motor micro pump (CMMP) currently under development at the University of Arkansas. The CMMP is realized through the tethering of a harmless strain of Escherichia coli cells to a MEMS-based micro fluidic channel. In a free moving state, an E.coli cell ‘swims’ by rotating its’ flagella, driven at the base by a rotary motor. When a cell is attached to a surface by a single shortened flagellar filament (∼0.5 micron long), the motor turns the entire cell body at a high rotational speed. The CMMP utilizes this mechanism to transport liquid in a micro fluidic channel through viscous pumping. This paper describes two important areas in the CMMP development process: cell tethering in micro channels fabricated from various substrate materials and visualization of tethered cell behavior through fluorescent microscopy.
Analysis of Vibration and Wave Propagation in Cylindrical Grid-Like Structures
Authors: Jeong Sang Min , Ruzzene Massimo
Published: May 2008

The wave propagation in and the vibration of cylindrical grid structures are analyzed. The considered grids are composed of a sequence of identical elementary cells repeating along the axial and circumferential directions to form a two-dimensional (2D) periodic structure. Two-dimensional periodic structures are characterized by wave propagation patterns that are strongly frequency dependent and highly directional. Such unique characteristics can be utilized to design structures able to confine external perturbations to specified regions. The wave propagation characteristics of 2D periodic structures are determined through the analysis of the dynamic properties of the unit cell, which is described by its Finite Element mass and stiffness matrices. The cell is composed of curved beams to form a cylindrical grid. The combined application of the Finite Element formulation and the theory of 2D periodic structures yields the phase constant surfaces, which define, for the considered cell lay-out, the directions of wave propagation for assigned frequency values. The predictions from the phase constant surfaces analysis are verified by estimating the forced harmonic response of the complete grid. The results demonstrate the unique characteristics of this class of grid structures, and suggest how they may be designed to enhance attenuation capabilities of shell structures commonly used in aerospace or naval applications. Design configurations can be identified so that the transmission of vibrations towards specified locations and at certain frequencies is minimized. The study can be extended to include the optimization of the geometry and topology of the unit cell to achieve desired transmissibility levels in specified directions and for given excitation frequencies.
Vibration and Sound Radiation of Sandwich Beams With Honeycomb Truss Core
Authors: Ruzzene M.
Published: May 2008

The vibrations of and the sound radiation from sandwich beams with truss core are here analyzed. The structure of the core is composed of a sequence of identical unit cells repeating along the beam length and across the core thickness. Each cell is composed of beam elements assembled to form a frame structure. Layouts with honeycomb patterns arranged through the thickness of the core are considered. This design represents an alternative with respect to the traditional application of honeycombs in sandwich construction. The proposed configuration provides sandwich beams with interesting structural as well as acoustic characteristics. A spectral finite element model is developed to evaluate the structural and the acoustic behavior of the considered class of sandwich beams. The spectral model can be easily coupled with a Fourier Transform based analysis of the sound radiated by the fluidloaded structure. The model predicts the performance of beams with various core configurations. The comparison is carried out in terms of vibration and sound radiation in an unbounded acoustic half-plane. Hexagonal and re-entrant honeycomb configurations are considered to study the effects of core geometry on structural response and acoustic radiation.
Characterization of Collagen and Elastin Remodeling in Engineered Arteries
Authors: Nichol Jason W. , Gooch Keith J.
Published: May 2008

We have shown that elongation of arteries perfused ex vivo is possible by applying moderate axial strain (∼8%) daily. In 9 days we were able to elongate porcine carotid arteries 48 ± 3% while being perfused under subphysiological conditions, retaining a 20 ± 3% increase when removed from the system and unloaded (p < 0.005). General appearance, viability and vasoactive function were similar to fresh and control (perfused but not elongated) arteries. Mechanical properties (ultimate stress and strain, elastic modulus) were insignificantly different than fresh arteries. To investigate the effects of pressure and flow rate on elongation and remodeling, we elongated arteries under the same elongation protocol, but with physiological flow, pressure and viscosity. Arteries were able to elongate 50 ± 1% in the system, but only retained an 8 ± 1% length increase when unloaded (p < 0.005). The increase in wet weight (29 ± 13%) was similar to that seen in previous elongation experiments (40 ± 18%), as was the increase in the total collagen content 30% vs. 34% previously). Data are also presented on mechanical properties, and elastin arrangement.
Mixing Enhancement in Simple Geometry Microchannels
Authors: Glasgow Ian K. , Aubry Nadine
Published: May 2008

Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems is typically difficult. Instead of using complex geometries and/or relatively long channels, we demonstrate the merits of flow rate time dependency through periodic forcing. We illustrate the technique by studying mixing in three different simple channel intersection geometries (“⊢”, “Y”, and “T”) by means of computational fluid dynamics (CFD) as well as physically mixing two aqueous reagents. In these geometries, both inlet channel segments (upstream of the confluence) and the outlet channel segment (downstream from the confluence) are 200 μm wide by 120 μm deep, a practical scale for mass-produced disposable devices. The flow rate and average velocity after the confluence of the two reagents are 48 nl s−1 and 2 mm s−1 respectively, which, for aqueous solutions at room temperature, corresponds to a Reynolds number of 0.3. We use a mass diffusion constant of 10−10 m2 s−1, typical of many BioMEMS applications, and vary the flow rates of the reagents such that the inlet time-averaged flow rate remains unchanged but the instantaneous flow rate is sinusoidal (with a DC bias) with respect to time. We analyze the effect of pulsing the flow rate in both inlets at 90 and 180 degrees out of phase in all three geometries. While mixing is good in all six cases, we demonstrate that the best results occur when both inlets are pulsed 90 degrees out of phase in the “T” geometry. In all six cases, the interface is shown to stretch, retain two folds, and sweep through the confluence zone, leading to good mixing within 2 mm downstream of the confluence, i.e. about 1 s of contact. From a practical viewpoint, the case where the inlet pulsing is 180 degrees out of phase is of particular interest as the outflow is constant.
Nanofluidic Channel Fabrication and Characterization by Micromachining
Authors: Kim Wan-Sik , Lee Junghoon , Ruoff Rodney S.
Published: May 2008

The well-established microfabrication techniques of complementary metallic oxide silicon (CMOS) selective oxidation and wafer-wafer fusion bonding were used to fabricate sub-micrometer silicon fluidic channels as small as 30 nm between extremely thin SiO2 top and bottom layers of 30 nm thicknesses. Trenches a few tens of nanometer deep were patterned in 10-cm diameter Si wafers by selective oxidation and their depth measured by atomic force microscopy (AFM); the AFM measured depths showed that the trench depth could be controlled to nanometer resolution. The resolution of the photolithography employed determined the trench width resolution. Nanochannels were formed with direct wafer-wafer fusion bonding. Channels of 30-nm depth or greater between the bonded wafer pair were nondestructively detected by a simple infrared (IR) image system; channels less than this depth collapsed for the overall channel geometry employed. Thus the nanofluidic structures survived the pressure and high temperature anneal of wafer bonding. Experimental results agree well with a theoretical prediction for which depths nanochannels would collapse.
Modeling and Disturbance Rejection Control of a Nanopositioner With Application to Beam Steering
Authors: Gorman Jason J. , Dagalakis Nicholas G.
Published: May 2008

This paper discusses the modeling and control of a nanopositioning flexure hinge mechanism with a piezoelectric actuator. A complete dynamic model for the mechanism is presented along with experimentally determined system parameters. The control design concentrates on the problem of controlling the nanopositioner when a base excitation is injected into the system. The effects of the base excitation are overcome using two approaches. The first is a robust tracking controller which is developed to cancel the excitation effect on the tracking error. The second is an inertial compensator which is designed to update the desired trajectory using base motion measurements, such that the nanopositioner performs the desired trajectory in an inertial frame. This approach is demonstrated through simulation results. These principals are being developed for use in beam steering applications which require nanoradian resolution and very low beam jitter.
Fuzzy Control of a Resonant Vibration Dryer
Authors: Sudera V. , Liu G. , Yu S. D.
Published: May 2008

This paper presents a fuzzy control method for a resonant vibration grain dryer. The proposed control method identifies and maintains the resonant condition for the dynamical system having constant linear stiffness, varying mass and varying damping. Both simulation results and experimental results show that the amplitude-based fuzzy control approach proposed in this paper are reliable and efficient.
Micro Ultrasonic Machining of Ceramic MEMS With Micro Metallic Dies
Authors: Yang Yong , Li Xiaochun
Published: May 2008

Micro ultrasonic Machining (MUSM) is useful for producing micro parts in brittle materials, especially ceramics. By use of suitable micro metallic dies, the efficiency of fabrication can be significantly enhanced. In this study, the LIGA process was used to generate micro nickel dies, which also served as microelectrodes in Die-sinking Electrical Discharge Machining (EDM) to produce micro tungsten dies for MUSM. With these micro metallic dies, micro ceramic components were fabricated.
Bearing Damping: A Simple, Inexpensive Experiment in System Dynamics
Authors: Murray William R. , Garbini Joseph L.
Published: May 2008

Bearings commonly are modeled as a linear viscous element. This behavior is easily confirmed with a simple, inexpensive experiment using only a wristwatch and a bicycle equipped with a speedometer. With the bicycle inverted so that its rear wheel is free to spin, this experiment involves observing and recording the variation of the angular velocity of the rear wheel as it decelerates from some initial speed. This experiment is a group activity, requiring teamwork to record the data by hand. From the data recorded and an estimate of the moment of inertia of the wheel, students determine the time constant of the system, the degree to which first-order response is exhibited by the system, and the equivalent damping coefficient for the bearings that support the rear wheel. Because of the familiarity of the components of the system being examined, the simplicity of the experiment, the teamwork required in the experiment, and the high degree of agreement between the analytical predictions and the experimental results, this experiment is an excellent experiment in system dynamics.
Modeling and Identification of Feed Drive Kinematics and Cycle Time Calculation
Authors: Wang Wencai , Yip-Hoi Derek M.
Published: May 2008

Cycle time calculation plays a major role in the design of manufacturing systems. Accurate estimates are needed to correctly determine the capacity of a line in terms of the number of machines that must be purchased. Over estimation results in excess capacity and under estimation leads to unsatisfied demand. Due to the high automation and cutting speeds of modern machining processes, cycle time calculation must consider both the timing of various machining actions and the kinematics of feed motions. This paper presents a cycle time calculation algorithm that gives accurate cycle time results by considering the effects of jerk and acceleration of the machine tool drives. The kinematic model for axis motion is based on trapezoidal acceleration profiles along the toolpaths. Based on this model, an algorithm for identifying the kinematic parameters has been developed. This algorithm has the advantage of utilizing a minimal set of axis motion data thus reducing the amount of data that must be collected from experiments by the machine tool vendor or the machine tool’s enduser. The proposed cycle time calculation algorithm has been verified in machining a V6 cylinder head on a four axis CNC machine.
Ambulatory Rehabilitation Suspension System
Authors: Shetty Devdas , Campana Claudio , Fast Avital
Published: May 2008

This paper provides a new technique to assist patients during gait rehabilitation and safety support during exercise. The device can also be used by patients who have experienced physical trauma, and in need of assistance so that they can regain the strength needed to support them during rehabilitation. The procedure results in an adjustable gait rehabilitation lifting system and has the ability to support the weight of the user. The apparatus can lift a patient from a sitting position in a wheel chair to a standing position and has the provisions to remove a percentage of the patient’s body weight and recognize subtle changes in elevation. The patient requiring gait rehabilitation would be free to traverse a flat plane and climb a number of stairs and at the same time does not impede free walking and prevents sudden fall of the patient.
3D CFD Analysis of an Industrial Gas Turbine Compartment Ventilation System
Authors: Ponnuraj Balakrishnan , Sultanian Bijay K. , Novori Alessio , Pecchi Paolo
Published: May 2008

The proper design of the compartment ventilation system is an important requirement in the gas turbine industry. A poor ventilation system not only causes a circumferentially nonuniform casing temperature distribution, but also allows the formation of dangerous gas pockets inside the enclosure. Further, the presence of a circumferential casing temperature gradient has a negative impact on the operational efficiency of the turbine. Keeping the above design objectives in mind, a three-dimensional CFD analysis has been carried out using a leading commercial code to analyze the effectiveness of GE MS5002E ventilation system. A detailed geometric model is developed by including the entire turbine casing, various pipelines, surfaces of inlet and exhaust plenums, roof (with ventilation air inlets and outlet) and walls. Surfaces of all the components in the auxiliary compartment are also captured in the model. For easy meshing, the gas turbine compartment is divided into five regions: 1) inlet plenum and inlet case, 2) compressor, 3) compressor discharge case, 4) HPT and LPT, and 5) exhaust plenum. After meshing, these regions and the auxiliary compartment are combined using arbitray interfaces. A steady incompressible, high Reynolds number k-ε turbulence model is used in the present analysis. Except the casing external surfaces, temperatures are specified on the surfaces of various components, pipes, enclosure inside walls and roof. The casing temperature is determined using conjugate heat transfer modeling in which convective boundary conditions are stipulated on the casing interior surfaces and conduction through casing walls is solved as a part of the CFD solution. Radiation boundary conditions are applied on the casing external surfaces, enclosure walls and roof. Most of the pipes are included in the model. Small regions are modeled as porous media. Buoyancy effects are accounted in the model. The present CFD results will be used in conjunction with prototype testing to optimize the ventilation layout.
Development of an Ideal Project Law
Authors: Hall David C. , Kohl Ron , Graves Roger
Published: May 2008

Our research collaboration has begun a project to develop an Ideal Project Law (IPL). What we are trying to accomplish is the development of some equation with a mathematical underpinning that can usefully relate Functionality, Cost, Schedule and Risk which can then be graphed, and this graph then becomes a decision making and communications aid. For some of us, the current contention is that a possible IPL is analogous to the Ideal Gas Law (IGL), which relates Pressure (P), Volume (V) and Temperature (T) for reasonably well-behaved gases. (P*V)/T = Constant (where the constant has very much to do with the nature of the gas under discussion). This is due to our belief that the IPL will represent some form of a relationship (inverse or direct) between Cost (C), Schedule (S), Functionality (F) and Risk (R) much like the IGL represents relationships between P, V and T for a given gas. We also expect that at least some of the factors will change based on the type of project, so we might have to develop a range of factors and constants. The Ideal Gas Law informs us, for example, that if you keep V fixed and increase P, then you can expect T to also increase. So “keep this one factor fixed, and change that other factor and then watch the third factor move one way or the other” relationships can be described via the Ideal Gas Law. We believe that this “push on one factor and see what happens to the other factors” feature of the Ideal Gas Law seems to be very analogous to project and operation Cost, Schedule, Functionality and Risk relationships. This law, or some such function, is absolutely essential. Having such a Law that is proven valid will introduce (or rather tactfully enforce) some systematic thinking in the project and operational management set-up. Otherwise, no matter how elaborate a case is made for project or operational risks, the risk decisions will be left to the whims, fancies and moods of the key decision-making person(s) in the organization or project — we are working towards reducing this subjectivity in decision-making. We may determine that it is impossible to have a 100% scientific outlook on project or operational factors simply because human beings are involved, but if that is the case, we may be able to be at least 80% scientific about it.
Comparison of Steady State and Asymptotic Transient Thermal-Mechanical Simulations of Optoelectronic Laser Processing
Authors: Ting Ben , Manno Vincent P.
Published: May 2008

Traditional optoelectronic manufacturing of butterfly packages involves laser welding of a fiber mount followed by a tedious realignment procedure to reverse thermally induced distortions commonly referred to as Post Weld Shift (PWS). An alternative PWS compensation technique, Laser Hammering, entails manipulation of the fiber to light alignment through deformation of the fiber housing with high precision laser beams. The goal of this study is to predict and understand fiber displacements for butterfly packages subjected to the laser hammering process using finite element analysis. A standardized, two-dimensional fiber mounting/ferrule geometry is employed in a simulation case study. Various laser waveforms are applied to focus spot diameters of 50 and 200 μm over a range of applied heat fluxes (10 to 1000 W/mm2). The primary investigation focused on the degree to which a steady state (SS) model can predict the final state of a transient response (asymptotic steady state) subjected to a periodic laser excitation. Effects of laser energy deposition location and resolution, as well as the use of multiple lasers were also studied. The results obtained to date show that the steady state solution is in good agreement with the asymptotic transient response (ATR) for the center horizontal fiber displacement and the center fiber temperature. The focus spot region surface temperature predictions of steady state and asymptotic transient simulations were also found to be in reasonable agreement. However, the vertical fiber displacement tends to be over predicted by the steady state solution, sometimes by as much as an order of magnitude. The causes, both physical and computational, of this disagreement are discussed in the paper.
Design and Evaluation of a Pneumatic Gantry Robot for the Grinding of Steel Blanks
Authors: Raoufi Ashar , Surgenor Brian
Published: May 2008

This paper describes the design and evaluation of a pneumatic gantry robot that is used to grind the edges of steel blanks as part of a finishing operation prior to being stamped. The objective of this research project is to automate the grinding process in order to reduce the frequency of cracking. The required force and degree of precision needed were thought to be within the capabilities of a pneumatically actuated robot. This would keep the cost of the apparatus down, which was important given the low capital cost of the manual operation. Furthermore, given that manipulation of the air pressure is the mechanism used to move a pneumatic actuator, the combined control of force and position is inherent to the system. A number of different pneumatic circuit configurations were examined before adopting a design that uses a combination of directional solenoid and flow control valves controlled by a Programmable Logic Controller (PLC). Pressure transducers and analog linear potentiometers are used for data acquisition. Laboratory test results are presented as well as a discussion of additional work that must be completed with the pneumatic gantry robot before field tests are conducted.
Comparison Between MCFC/Gas Turbine and MCFC/Steam Turbine Combined Power Plants
Authors: Bove Roberto , Lunghi Piero
Published: May 2008

Worldwide, the main power source to produce electric energy is represented by fossil fuels, principally used at the present time in large combustion power plants. The main environmental impacts of fossil fuel-fired power plants are the use of non-renewable resources and pollutants emissions. An improvement in electric efficiency would yield a reduction in emissions and resources depletion. In fact, if efficiency is raised, in order to produce an amount unit of electric energy, less fuel is required and consequently less pollutants are released. Moreover, higher efficiency leads to economic savings in operating costs. A generally accepted way of improving efficiency is to combine power plants’ cycles. If one of the combined plants is represented by a fuel cell, both thermodynamic efficiency and emissions level are improved. Fuel cells, in fact, are ultra-clean high efficiency energy conversion devices because no combustion occurs in energy production, but only electrochemical reactions and consequently no NOx and CO are produced inside the cell. Moreover, the final product of the reaction is water that can be released into the atmosphere without particular problems. Second generation fuel cells (Solid Oxide FC and Molten Carbonate FC) are particularly suitable for combining cycles, due to their high operating temperature. In previous works, the authors had analyzed the possibility of combining Molten Carbonate Fuel Cell (MCFC) plant with a Gas Turbine and then a MCFC with a Steam Turbine Plant. Results obtained show that both these configurations allow to obtain high conversion efficiencies and reduced emissions. In the present work, a comparison between MCFC-Gas Turbine and MCFC-Steam Turbine is conducted in order to evaluate the main advantages and disadvantages in adopting one solution instead of the other one.
Application of SISO and MIMO Modal Analysis Techniques on a Membrane Mirror Satellite
Authors: Ruggiero Eric J. , Bonnema Garret T. , Inman Daniel J.
Published: May 2008

The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures orders of magnitude greater in size than current satellite technology. Such large craft will increase current communication and imaging capabilities from orbit. To get ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e. on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. However, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC®) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results. These piezoelectric-based devices possess a superior electromechanical coupling coefficient making them superb sensors and actuators in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultralarge structures. Based on the matrix formulation and postprocessing techniques recently developed, the current work applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5 – 200 Hz). MIMO modal testing techniques are ideal for large, inflated structure applications. The nature of the structure requires the use of multiple sensors and actuators for worthwhile dynamic analysis and control. Therefore, in the future, the results of this work will form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration—all while on-orbit.
Modeling the Transport Phenomena During Hybrid Laser-MIG Welding Process
Authors: Zhou Z. , Zhang W. H. , Tsai H. L. , Marin S. P. , Wang P. C. , Menassa R.
Published: May 2008

Hybrid laser-MIG welding technology has several advantages over laser welding alone or MIG welding alone. These include the possibility of modifying weld bead shape including the elimination of undercut, the change of weld compositions, and the reduction of porosity formation in the weld. Although the hybrid laser-MIG welding method is becoming popular in industry, its development has been based on the trial-and-error procedure. In this paper, mathematical models and the associated numerical techniques were developed to calculate the heat and mass transfer and fluid flow during the laser-MIG welding process. The continuum formulation was used to handle solid phase, liquid phase, and mushy zone during the melting and solidification processes. The volume-of-fluid (VOF) method was employed to handle free surfaces, and the enthalpy method was used for latent heat. The absorption (Inverse Bremsstrahlung and Fresnel absorption) and the thermal radiation by the plasma in the keyhole, and multiple reflections at the keyhole wall were all considered in the models. The transient keyhole dynamics, interactions between droplets and weld pool, and the shape and composition of the solidified weld bead were all predicted for both the pulsed laser-MIG welding and three-dimensional moving laser-MIG welding. Computer animations showing the fluid flow, weld pool dynamics, and the interaction between droplets and weld pool will be shown in the presentation.
Ultrasonic Testing for Vulcanization Inspection of Natural Rubber
Authors: Seenawat Mongkol , Prateepasen Asa , Jomdecha Cherdpong
Published: May 2008

This paper presents a novel method to inspect the levels of vulcanization of natural rubber by ultrasonic testing. In the research, test specimens are natural rubbers of type ‘cis-1,4-polyisoprene’ vulcanized at different durations. Piezoelectric contact transducers were used to transmit and receive ultrasonic to/from each sample. Longitudinal waves at nominal frequency of 2, 2.25 and 5 MHz were used to investigate the samples. Experiments were conducted using two techniques: pulse echo and through transmission. The pulse echo technique was applied to inspect the ultrasonic attenuation and the velocity of longitudinal wave of natural rubber. The through transmission technique was implemented to identify the shape and amplitude of the frequency spectrum. The results from both time and frequency domains can be employed to classify the levels of the vulcanization. From the experiments, this ultrasonic testing provides an effective way to inspect the vulcanization of natural rubber with repeatability and allows faster inspection rate than other methods.
Natural Convection in Square Cavities Heating From Below: Investigation of Three Different Values of the Heat Source Length
Authors: Paroncini Massimo , Calcagni Barbara , Marsili Federico
Published: May 2008

The objective of the present study is to gain some insight into fluid motion and heat transfer phenomena in the case of a square enclosure heated from below and symmetrically cooled from the sides; the effects of different values of the heat source is experimentally investigated. The localized heating is a centrally located heat source on the bottom wall; three different values of the heat source length (1/5, 2/5, 3/5 of the wall) are considered. The test cell is a square enclosure filled with air with isothermal side walls at equal temperatures Tc; the remaining vertical walls are realized with glass to allow optical access to the cavity. The top and bottom surfaces of the enclosure are made of plexiglass and, except for the heated section, are considered to be adiabatic. The located heat source is assumed to be isothermal at a temperature Th. The temperature distribution is experimentally measured by real-time and double-exposure holographic interferometry. The real-time technique is used in order to reveal the presence of plume oscillations while the double-exposure technique is used for steady-state measurements. Holographic interferometry shows the typical advantages over the classical optical techniques, such as high precision and sensitivity, very low noise level, and the possibility of displaying the temperature distribution across the whole investigated region. The objective of the heat transfer analysis is the experimental investigation of the Nusselt number distribution around the cavity at various Rayleigh numbers and several dimensions of the heat source. Different convection forms were obtained depending on Ra and on the heat source length. The Nusselt number was evaluated on the heat source surface and it showed a symmetrical form rising near the heat source borders.
Nanotube-Based Actuator and Sensor Paradigm: Conceptual Design and Challenges
Authors: Jalili Nader
Published: May 2008

With the widespread application of mechatronic concepts to dynamic systems in recent years, interest has been focused on the substitution of piezoelectric ceramic (PZT) fibers for conventional electrical motors and actuators. Piezoelectricity effects in elongated and poled PVDF as well as the ferroelectric properties have been observed for a number of decades. Although PVDF copolymers have found diverse uses in industrial applications, such as ultrasonic transducers and vibration damping, their low stiffness and electromechanical coupling coefficients have limited their use. To improve the performance and capability of future automated systems, the development of next generation actuator subsystems utilizing nanotubes is presented. Specifically, the actuation mechanism associated with carbon and boron nitride (BN) nanotube-based actuators, and ultimately manufacturing macro-level actuators compromised of functional nanotubes are discussed in this paper. This exciting area of research is motivated by discovery of bond extension in charged nanotubes. Termed “artificial muscles”, such actuators provide wonderful opportunities in MEMS due to their incredible strength and stiffness, with relatively low (∼10 V) driving voltage. The proposed nanotube-based actuator configuration could be utilized for many applications such as miniature motors, vibration control of flexible structures, micro scale robotic systems, biomedical (drug delivery and tumor removal), and power generation applications.
Teaching and Learning “Green Engineering” in a Multidisciplinary Seminar
Authors: Sisson Richard D. , Weir William C. S. , O’Shaughnessy James C.
Published: May 2008

This paper presents the recent experience of teaching and learning “Green Engineering” in a multidisciplinary seminar. The instructors who organized the seminar included an environmental engineer and a mechanical/manufacturing engineer. The student population included both graduate and undergraduate students majoring in civil/environmental, mechanical, manufacturing and aerospace engineering as well as several biology majors. The course was organized as a semester long seminar with many guest speakers from industry, government, academia and law firms. In addition to assigned reading and literature searches/reviews, the main learning experiences were provided by two large team projects. The first multidisciplinary team project was a “game” that required the students to develop a facility to provide a variety of products that utilized materials that are toxic, hazardous and radioactive. The students were assigned various roles in the company including bidding, manufacturing, environmental and purchasing responsibilities. The teams were judged on both the financial and environmental success of their company. The second multidisciplinary major team project focused on the creation of a green product including, the design and manufacturing processes, as well as the business plan. The student interest in this project was enhanced by a competition with cash prizes that was financed and judged by WPI’s Entrepreneurship program’s faculty and staff.
DSMC Simulation of Ion Generation in Atmospheric Air
Authors: Zhang W. , Fisher T. S. , Schilitz D. J. , Garimella S. V.
Published: May 2008

The generation of ions in air has several useful applications, such as electrohydrodynamic (EHD) pumping, air purification and isolation breakdown prevention. In this paper, ion generation processes in atmospheric air are simulated using a Direct Simulation Monte Carlo (DSMC) method. Details of the collision model are discussed. A C++ code is developed to implement the Monte Carlo method with cross-section data compiled from the literature. Self-sustaining discharge and ionization can be reproduced in the simulation under sufficient voltage bias, and the associated trends obtained are similar to those predicted by Paschen’s curve for a parallel-plate configuration.
Comparison of Analytical and Numerical Simulations for Variable Spindle Speed Turning
Authors: Insperger Tama´s , Schmitz Tony L. , Burns Timothy J. , Ste´pa´n Ga´bor
Published: May 2008

The turning process with varying spindle speed is investigated. The well-known single degree of freedom turning model is presented and the governing delay-differential equation with time varying delay is analyzed. Three different numerical techniques are used to solve the governing equation: (1) direct Euler simulation with linear interpolation of the delayed term, (2) Taylor expansion of the time delay variation combined with Euler integration and (3) semi-discretization method. The results of the three method are compared. Stability charts are constructed, and some improvements in the process stability is shown, especially for low spindle speed domains.
Diffusion Modeling of the Radiative Transfer in a Non-Absorbing Foam Layer
Authors: Jones Matthew R. , Solovjov Vladimir P. , Webb Brent W.
Published: May 2008

Techniques for determining the properties foam are of interest due to the number of industrial process in which they play a significant role. A technique known as diffusing-wave spectroscopy has shown promise as a method for determining the radiative properties of foam. In diffusing-wave spectroscopy, an amplitude modulated laser beam is injected into the foam layer, and the reflected flux and the phase shift between the incident and the reflected beams are measured. Relationships between these measurable quantities and the radiative properties of the foam are derived using the diffusion approximation. The objective of this paper is to investigate the conditions for which the diffusion approximation accurately predicts the time dependent reflectance of a laser pulse from the surface of a non-absorbing from layer. The accuracy of the diffusion approximation is assessed by comparison with Monte Carlo simulations.
Fixed Abrasive Diamond Wire Saw Slicing of Single Crystal SiC Wafers
Authors: Hardin Craig W. , Qu Jun , Shih Albert J.
Published: May 2008

This paper investigates the slicing of single crystal SiC with a fixed abrasive diamond wire. A spool-to-spool rocking motion diamond wire saw machine using a 0.22 mm nominal diameter diamond wire with electroplated bond and 20 μm average size diamond grit is used. The effect of wire downfeed speed on wafer surface roughness and subsurface damage is first investigated. The surface marks due to the loose diamond and stagnation of the wire during the change in wire cutting direction are studied. A scanning acoustic microscope is explored as a non-destructive evaluation method to identify the level of subsurface damage. Another set of tests investigates the effects of using a new diamond wire on the cutting forces and surface roughness. Scanning electron microscopy (SEM) is applied to examine the machined surfaces and the diamond wire wear. This study demonstrated the feasibility of fixed abrasive diamond wire cutting of SiC wafers and the usage of a scanning acoustic microscope to study the machining subsurface damage.
An Efficient Lane Change Maneuver for Platoons of Vehicles in an Automated Highway System
Authors: Sun Xiaotian , Horowitz Roberto , Tan Chin-Woo
Published: May 2008

The current lane change maneuver for vehicles in a platoon under the California PATH automated highway system (AHS) architecture is inefficient, because the follower has to split from the rest of the platoon before making a lane change. In this paper, we propose to add a lane change within platoons maneuver that allows a follower to change lanes and be inserted into another platoon directly without splitting either platoon. This maneuver is performed by aligning and locking the longitudinal positions of the two platoons in adjacent lanes. The estimated improvement in the AHS utilization, in term of the space-time, is approximately 4342 m.s. The longitudinal controller for the lane changing follower is designed and proved to maintain the string stability of the platoons. The leader law is modified for the common leader of the two locked platoons. An intra-platoon spacing adjustment procedure is also designed for the purpose of the proposed maneuver.
Safety Guarantees for Lanekeeping Assistance Systems With Time-Varying Disturbances: A Lyapunov Approach
Authors: Rossetter Eric J. , Gerdes J. Christian
Published: May 2008

Active lanekeeping assistance systems have the potential of saving thousands of lives every year. These systems must provide some level of increased safety while working cooperatively with the driver. Our approach passively couples the vehicle to the environment using the paradigm of ‘artificial’ potential fields. Since this control scheme does not attempt to track a desired trajectory, disturbances encountered during normal driving (such as road curvature) will alter the path of the vehicle. In order to ensure nominal safety of this system, a Lyapunov based bound is developed that handles general time-varying disturbances. This technique provides excellent bounds on the lateral motion of the vehicle. Experimental results verify that this bound works extremely well in practice.
Emission Characteristics of NO and NO2 in Rich-Lean Combustion of Hydrogen
Authors: Shudo T. , Omori K. , Hiyama O.
Published: May 2008

Hydrogen is expected as a clean and renewable alternative to the conventional hydrocarbon fuels. Because the only possible pollutants from the hydrogen combustion are nitrogen oxides (NOx), it is crucial to reduce the NOx emission in the hydrogen utilization. The rich-lean combustion is well known as a technique to reduce the emission of the Zel’dovich NO from the continuous combustion burners for such as gas turbines and boilers. Because the Zel’dovich NO occupies a large part of the total NOx emission, the rich-lean combustion is quite effective to reduce the NOx emission. However, the NOx reduction effect of the rich-lean combustion has not yet been proven for the hydrogen fuel, while the effect has been demonstrated for the hydrocarbon fuels. On the other hand, the prompt NO is emitted from the hydrocarbon combustion especially under the fuel-rich conditions. Though the amount of the prompt NO is quite small for premixed or diffusion combustion, it could be a relatively significant part in the total NO emission from the rich-lean combustion due to the decreased Zel’dovich NO. The authors estimate that hydrogen is more suitable for the rich-lean combustion compared with hydrocarbons, because hydrogen does not emit the prompt NO even under the fuel-rich conditions which necessarily exist in the rich-lean combustion. This research proposes the rich-lean combustion as a method to reduce the NOx emission from hydrogen combustion and experimentally analyzes the characteristics using a coaxial rich-lean burner with varying the mixture conditions.
Bond Graph Binary Encoding Method for Genetic Algorithms Applications
Authors: Di´az-Cuevas Germa´n L. , Ngwompo Roger F.
Published: May 2008

A binary encoding method for bond graphs that can be used for genetic algorithms (GAs) applications is presented. The originality of the proposed coding is that it encompasses causal information. This ensures that causal analysis is taken into account in assessing the fitness of topologies generated in GA operations and the suitability of design candidates to meet performance specifications can be tested directly from the binary code as the model equations can be derived from it. The code is suitable for GAs applications on bond graphs (BG) for topology and parameter optimisation in automated synthesis of dynamic systems. The coding method and its possible applications are illustrated through worked examples.