bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Sloshing in Fixed and Vertically Excited Containers
Authors: Frandsen Jannette B. , Borthwick Alistair G. L.
Published: June 2008

Nonlinear effects of standing wave motions in fixed and vertically excited tanks are numerically investigated. The present fully nonlinear model analyses two-dimensional waves in stable and unstable regions of the free-surface flow. Numerical solutions of the governing nonlinear potential flow equations are obtained using a finite-difference time-stepping scheme on adaptively mapped grids. A σ-transformation in the vertical direction that stretches directly between the free-surface and bed boundary is applied to map the moving free surface physical domain onto a fixed computational domain. A horizontal linear mapping is also applied, so that the resulting computational domain is rectangular, and consists of unit square cells. The small-amplitude free-surface predictions in the fixed and vertically excited tanks compare well with 2nd order small perturbation theory. For stable steep waves in the vertically excited tank, the free-surface exhibits nonlinear behaviour. Parametric resonance is evident in the instability zones, as the amplitudes grow exponentially, even for small forcing amplitudes. For steep initial amplitudes the predictions differ considerably from the small perturbation theory solution, demonstrating the importance of nonlinear effects. The present numerical model provides a simple way of simulating steep non-breaking waves. It is computationally quick and accurate, and there is no need for free surface smoothing because of the σ-transformation.
Improving Roll Stability of Vehicles With High Center of Gravity by Using Magneto-Rheological Dampers
Authors: Ahmadian Mehdi , Simon David E.
Published: June 2008

The performance of a new semiactive control method for improving roll stability of sport utility vehicles (SUVs) is discussed, using a series of road tests. The new method augments the conventional skyhook control for semiactive suspensions with steering input, in order to account for the suspension requirements during a lateral maneuver. After discussing the formulation for the steering input augmented (SIA) skyhook control, the paper includes the implementation of a semiactive system with magneto-rheological (MR) dampers on a sport utility vehicle. The vehicle is used for a series of road tests that includes lane change maneuvers, with different types of suspensions. The suspensions that are tested include the stock suspension, the uncontrolled MR dampers, skyhook control, and SIA skyhook. The results of the study show that SIA skyhook can improve the suspension travel and lateral forces at the vehicle body during maneuvers, as compared to other suspensions evaluated on the vehicle.
Modeling the Crushing Response of PMC Tubes Under Quasi-Static and Dynamic Loading Conditions
Authors: Abdel-Haq M. , Newaz G.
Published: June 2008

Non-linear finite element technique was used to predict the crushing response and energy absorption of fiberglass/polyester tubes under quasi-static and dynamic conditions. The major failure modes including axial splitting of the tube wall and delamination were modeled using the available features in LSDYNA and ABAQUS codes for dynamic and quasi-static analysis, respectively. The results show that the finite element models were able to predict the average and peak load levels for the tubes with and without using an external constraint. Finally, it was concluded that modeling the major failure modes in the crushing process in addition to using an appropriate material failure model is essential to capture the load levels and specific energy absorption of the crushed tubes.
The Latest Trends in Reducing Noise and Vibrations in Large Commercial Vehicles
Authors: Ahmadian Mehdi
Published: June 2008

This session-long tutorial will encompass some of the latest research in the area of reducing noise and vibrations in large commercial vehicles, such as railway locomotives, heavy trucks, and transit busses. The tutorial will be conducted by Professor Mehdi Ahmadian, Director, Advanced Vehicle Dynamics Laboratory at Virginia Tech. The session participants will have an opportunity to participate in an open forum about their experience with the methods that are discussed by the presenter.
Time Delay Aeroelastic Feedback Control of 2-D Lifting Surfaces
Authors: Librescu Liviu , Marzocca Piergiovanni , Silva Walter A.
Published: June 2008

Two basic issues related to the open/closed loop aeroelasticity of 2-D lifting surfaces in an incompressible flow field are considered in this paper. These concern the subcritical aeroelastic response to external time-dependent excitations, and the flutter instability of actively controlled airfoils involving a delayed feedback control. Results and comparisons regarding the flutter instability obtained via the first Volterra kernel in conjunction with a frequency eigenvalue analysis are presented. In the same context, the implications of the presence of time delays in the feedback control on the instability boundary and aeroelastic response are investigated and pertinent conclusions are supplied.
Airfoil Vibration Due to Upstream Alternating Vortices Generated by a Circular Cylinder
Authors: Luk K. F. , So R. M. C. , Kot S. C. , Lau Y. L. , Leung R. C. K.
Published: June 2008

An experimental investigation of airfoil vibration due to upstream alternating vortices was carried out in a re-circulating wind tunnel. A circular cylinder with a diameter D = 102mm was positioned upstream of an airfoil (NACA0012), with a chord length c = 200mm and a zero angle of attack placed at a gap distance S, to generate the vortex street. The circular cylinder and airfoil were arranged in tandem and the spacing ratio S/D was varied from 0.5 to 6.5 to investigate the effect of the vortices generated upstream on the vibration of the airfoil. The experiment was carried out in a free stream Re range of 1.6×105 to 2.3×105. The vortex formation region behind a single circular cylinder was measured using a hot wire anemometer and the airfoil dynamic responses were examined using a laser vibrometer. It is found that when S/D is reduced beyond a critical value, there is a rapid drop in vortex shedding frequency and a suppression in airfoil vibration. This critical S/D is found to be the normalized length of the vortex formation region behind the single cylinder. It is hypothesized that the vortex could not be formed at this location within the gap distance in the presence of the airfoil, but instead is formed behind the airfoil. Consequently, as vortex shedding is switched from upstream to downstream of the airfoil, the flow-induced vibration of the airfoil is suppressed at the same time.
Design, Build, and Test of a Permanently Implanted Prosthetic Hand
Authors: Williams Matthew , Walter Wayne
Published: June 2008

The feasibility of a permanently implanted prosthetic hand was evaluated from both an internal biocompatibility and exterior mechanics point of view. A literature review of the issues involved in permanent implantation of a percutanious device was performed in the areas of bone interaction and fixation and neural interface control. A theoretical implant was designed for a 90th percentile male, using a HA-G-Ti composite material to provide a permanent base to which the hand could attach. Using a radial implant length of 1.87 inches and an ulna implant length of 1.32 inches, the simulated implant could withstand a push out force of 10.260 pounds. Using nerve guidance channels and microelectrode arrays, a Regenerative Neural Interface was postulated to control the implant. The use of Laminin-5 was suggested as a method of preventing the lack of wound closure observed in percutanious devices. The exterior portion of a permanent artificial hand was analyzed by the construction of a robotic hand optimized for weight, size, grip force and wrist torque, power consumption and range of motion. Using a novel dual drive system, each finger was equipped with both joint position servos as well as a tendon. Fine grip shape was formed using the servos, while the tendon was pulled taunt when grasping an object. Control of the prosthetic hand was performed using a distributed network of micro-controllers. Each finger’s behavior was governed by a master/slave system where input from a control glove was processed by a master controller with joint servo and tendon instructions passed to lower-level controllers for management of hand actuators. The final weight of the prototype was 3.85 pounds and was approximately 25% larger than the 90th percentile male hand it was based on. Grip force was between 1.25 and 2 pounds per finger, depending on amount of finger flexion with a wrist lifting torque of 1.2 pounds at the center of the palm. The device had an average current draw of 3 amps in both normal operation and tight grasping. Range of motion was similar to that of the human model. Overall feasibility of the device is examined and factors involved in industrial implementation are discussed.
Effect of Tapered Geometry on the Load Transfer of an Idealized Cemented Hip Implant
Authors: Nun˜o N.
Published: June 2008

Implant loosening of cemented hip implants is one of the major causes of failure of the arthroplasty. In cemented hip implants, the polymethyl methacrylate (PMMA), also called bone cement, is used as grouting material between the stem and the surrounding bone. During polymerisation of the cement, residual stresses are generated in the bulk cement. The bone cement does not have a chemical bond with the stem nor the bone; however, it fills completely the space between the two and serves to distribute the load being transferred from the stem to the bone. Numerical analyses on the load transfer of cemented hip implants usually do not include the residual stresses due to cement curing at the stem-cement interface [1–2].
Development and Verification of a Dynamic TKR Model
Authors: Halloran Jason P. , Petrella Anthony J. , Rullkoetter Paul J.
Published: June 2008

The success of current total knee replacement (TKR) devices is contingent on the kinematics and contact mechanics during in vivo activity. Indicators of potential clinical performance of total joint replacement devices include contact stress and area due to articulations, and tibio-femoral and patello-femoral kinematics. An effective way of evaluating these parameters during the design phase or before clinical use is via computationally efficient computer models. Previous finite element (FE) knee models have generally been used to determine contact stresses and/or areas during static or quasi-static loading conditions. The majority of knee models intended to predict relative kinematics have not been able to determine contact mechanics simultaneously. Recently, however, explicit dynamic finite element methods have been used to develop dynamic models of TKR able to efficiently determine joint and contact mechanics during dynamic loading conditions [1,2]. The objective of this research was to develop and validate an explicit FE model of a TKR which includes tibio-femoral and patello-femoral articulations and surrounding soft tissues. The six degree-of-freedom kinematics, kinetics and polyethylene contact mechanics during dynamic loading conditions were then predicted during gait simulation.
Direct Numerical Simulation of Turbulent Flows Using Parallel Computers
Authors: Ai X. , Li B. Q.
Published: June 2008

A parallel computing methodology is presented for the direct numerical simulation of turbulent flows induced by pressure gradients and induction forces in channels. The numerical algorithm is based on the high-order-finite-difference (HOFD) scheme, which has been shown to possess the spectral-like accuracy but with superior computational efficiency and thus is ideally suited for computationally intensive numerical studies such as direct numerical simulation of turbulence. The computational efficiency is further enhanced using parallel computers. The parallel implementation and computational performance are discussed and numerical results using the parallel algorithms for direct numerical simulation of pressure gradient driven in parallel-plate channels and magnetically driven turbulent flows in induction channels are presented.
Method of Fluid-Structure Coupling in Time Domain Using Linearized Aerodynamics for Turbomachineries
Authors: Liauzun Ce´dric , Tran Duc-Minh
Published: June 2008

A fluid-structure coupling method to perform computations in time domain is proposed for turbomachineries. The cyclic symmetry is applied to both structure and embedding fluid. The unsteady aerodynamic forces are linearized and modeled using a minimum state smoothing method. Their determination is uncoupled from the structural computation. The motion equation is projected on the modal basis for a given phase number, and is solved using a Newmark scheme. This method is applied to a compressor row, and the results are compared with those from frequency computations or from direct coupling simulations.
Super Spatio-Temporal Resolution, Digital PIV System for Multi-Phase Flows With Phase Differentiation and Simultaneous Shape and Size Quantification
Authors: Abiven Claude , Vlachos Pavlos P.
Published: June 2008

A unique, super spatio-temporal resolution Digital Particle Image Velocimetry (DPIV) system for the analysis of time-dependent multiphase flows has been developed. The system delivers a sampling frequency between 1KHz and 10KHz, with continuous total acquisition time up to 4 secs and resolution 1Kx1K pixels down to 256×256 pixels. The hardware is integrated with sophisticated image processing algorithms that allow direct image segmentation in order to resolve the multiple phases present in the flow and provides quantitative information about the shape and size of droplets or bubbles present. Finally, the in-plane velocities are measured by a super-resolution, dynamically-adaptive cross-correlation algorithm which is coupled with a particle-tracking scheme. Each individual phase present in the flow is resolved with mean spatial resolution in the order of 3–4 pixels, and accuracy in the order of 0.01–0.1 pixels, while the spatial averaging effects of cross correlation are eliminated.
Evaluation of Drag Coefficient of Coal Ash Particles
Authors: Murphy David , Cherkaduvasala Venkataharibabu , Ban Heng , Harrison Keith , Monroe Larry
Published: June 2008

A type of coal ash particles, fragments of sintered fly ash masses, can travel with flow in the furnace and settle on key places such as catalyst surfaces. Computational fluid dynamics (CFD) models are often used in the design process to prevent the carry over and settling of these particles at key locations. Particle size, density and drag coefficient are the most important hydrodynamic parameters involved in CFD modeling. The objective of this study was to experimentally determine particle size, shape, apparent density, and drag characteristics for sintered fly ash particles from a power plant. Particle size and shape were characterized by digital photography in three orthogonal directions and computer image analysis. Particle apparent density was also determined by volume and mass measurements. Particle terminal velocities in three directions were measured in water and each particle was also weighed in air and in water. The experimental data was analyzed and a method was developed to calculate particle equivalent diameter, equivalent ellipsoid size, apparent density, and drag coefficient distributions. Discussions were focused on developing a practical method that can characterize the aerodynamic properties of porous, sometimes skeletal particles.
Development and Application of Laser Diagnostics for Reacting and Nonreacting Flows at Wright-Patterson AFB
Authors: Carter Campbell D. , Donbar Jeffrey M. , Elliott Gregory S.
Published: June 2008

Over the past few years, we have developed and applied a wide range of laser-diagnostic techniques to an equally wide range of complex flowfields at Wright-Patterson AFB. Our guiding principle in these efforts has been to employ laser-based tools to further our understanding of turbulent flames, so that in the end we improve combustor performance (e.g., thrust, emissions, etc.). We have primarily focused on three areas for development (though our areas of application have been much broader): 1) combined planar laser-induced fluorescence and particle-image velocimetry, 2) planar Doppler velocimetry, and 3) filtered Rayleigh scattering. Each of these is a powerful imaging diagnostic technique that allows the study of complex turbulent flowfields. We discuss these tools in the context of their application to turbulent flows as well as future diagnostic development.
Comparative Study of Established DPIV Algorithms for Planar Velocity Measurements
Authors: Abiven Claude , Vlachos Pavlos P. , Papadopoulos George
Published: June 2008

This paper represents a continuation of our effort to develop a velocity evaluation scheme optimized to resolve multiphase flows. An improved adaptive hybrid scheme that integrates the dynamically adaptive cross-correlation method with a particle tracking velocimetry algorithm is developed, presented and evaluated in this paper. A detailed description of the methodology, error analysis using Monte-Carlo simulations and elaborate comparisons with established schemes and robust commercial packages are presented. Improvements were guided towards increased accuracy for resolving vortical and poly-dispersed multi-phase flows. We introduce a novel iterative scheme that localizes the cross-correlation. We incorporate state of the art elaborate image processing techniques that allow increased particle densities. A new particle pairing method based on an adaptive cross-correlation masking is introduced. Finally, a refined gaussian estimation scheme that involves only four non-saturated pixels for the particle centroid detection is proposed. Overall, the dynamically adaptive hybrid velocity evaluation scheme presented here allows superior resolution of high velocity gradients, minimizes the loss of the rotational motion of the particles, and eliminates the spatial averaging effects inherent from the cross-correlation.
Shattered Rim Wheel Defects and the Effect of Lateral Loads and Brake Heating on Their Growth
Authors: Stone D. H. , Majumder Goutam , Bowaj V. S.
Published: June 2008

This report details studies conducted by Transportation Technology Center, Inc. (TTCI), a subsidiary of the Association of American Railroads (AAR), to determine the causes and behavior of shattered rim defects in wheels. Shattered rim defects are the result of large fatigue cracks that propagate roughly parallel to the wheel tread surface. They form and grow 1/2 to 3/4 inch (12–20 mm) below the tread surface. Once a shattered rim crack is formed it will grow under normal rolling loads. Therefore, the prevention of shattered rims is best accomplished by preventing crack initiation. Shattered rims tend to occur in either relatively new wheels or those that are near their condemning limit. Recent changes have been made to ultrasonic test requirements in AAR Specification M-107/208, “Wheels, Carbon Steel,” to reduce the acceptable size of discontinuities. This will help reduce the occurrence of some shattered rims, but will not prevent the formation of all of them. Ultrasonic testing of returned wheels would be effective in reducing the incidence of shattered rims in wheels with thinner rims.
Some Possible Alternatives for Longer-Life Locomotive Wheels
Authors: Lonsdale Cameron , Stone Daniel
Published: June 2008

An increase in the wear life of locomotive wheels is considered desirable from the locomotive builder and railroad user points of view. If a wheel has a longer service life, economics are improved due to less locomotive out-of-service time, reduced maintenance repair costs and reduced wheel renewal costs. This paper discusses possible alternative materials and microstructures that could be used for longer-life locomotive wheels, and also tires. If locomotive builders and users consider wheel rim hoop compression essential, then microalloying and increased carbon content are perhaps the most likely courses of action to improve wheel life. If rim hoop compression is not considered essential, a wide range of alternatives become possible including bainitic and martensitic microstructure monobloc wheels and tires.
Analysis of Wheel-Rail Elasto-Plastic Contact Problem
Authors: Zhang Jun , Liu Yingxi , Wu Changhua
Published: June 2008

Using the finite element parametric quadratic programming method, computation of Elastic and Elastic-plastic rolling contact problems between wheel and rail is carried out for various cases such as different wheel diameters, different axle loads, different tractive force and different friction factors. The contact states and the contact internal force between wheel and rail are obtained, and their changing laws corresponding with every above-mentioned parameter are analyzed in this paper.
The Advanced Handbrake Actuator System
Authors: Shenhar Joram , Hill John L. , Lombardo Mark A.
Published: June 2008

State-of-the-art freight car handbrakes are manpower intensive. Setting and releasing handbrakes expose operators to safety hazards and the potential for human error exposes train operations for possible time delays, mild to severe maintenance issues and ultimately the potential for major rail accidents. In response to the need to reduce the hazard associated with freight car handbrakes, UTD has developed the Advanced Handbrake Actuator System (AHAS), a fail-safe powered handbrake device, accessible from ground level on either side of the car. The AHAS concept was developed, manufactured and demonstrated under sponsorship of the Federal Railroad Administration (FRA) Small Business Innovation Research (SBIR) program. The system is designed to replace existing handbrake wheels and provide significant improvements by offering new ways of applying or releasing the brake. Remote electronic signal, car mounted hand levered pneumatic valve, and a manual hand crank mechanism, requiring significantly less effort than that required by the state-of-the-art handbrake wheel, constitute three methods of actuation. The AHAS is comprised of a compression coil spring arranged to apply tension to the handbrake chain as its default condition. Two release systems are available. The first uses an air cylinder actuator connected in series with the spring and chain. Applying air pressure by remote or local command will compress the spring and release the handbrake. The spring may also be compressed to release the handbrake by a hand crank mechanism, accessible from ground level on either side of the car. The AHAS is equipped with a dedicated air reservoir charged with compressed air prior to departure via the train’s brake pipe. The AHAS was successfully field tested on a freight car in regular service over a period of three months and was found to be user friendly and safe, logging over 120 successful operations.
Improvement of Prediction Method for Railway Vehicle Natural Frequency With Ride Quality
Authors: Kimura Toshinori , Taguchi Makoto , Kaneda Tetsuo , Oda Mitsuaki
Published: June 2008

Kawasaki has developed a methodology for estimating car body low mode bending and torsion mode natural frequency. These natural frequencies have a significant influence on ride quality. Although it has been believed that the natural frequencies become lower when passengers are present, Kawasaki established that the natural frequency does not change with the number of standing and sitting passengers, and the vibration acceleration amplitude becomes smaller when passengers are present. This has been shown by implementing numerical analyses and experiments using a mock up car. The increased knowledge will enable designing for better ride quality in the future through optimization of more accurate models.
Traditional LRV Side-Load Requirements and Their Applicability to Low Floor Cars
Authors: Madison Wm. Murphy , Lau Jeffrey T.
Published: June 2008

The focus of this paper is to study the application of Light Rail Vehicle (LRV) side-load requirements to Low Floor LRVs (LF LRVs). Although the side-load requirements of LRVs are not completely consistent among different transit authorities, an industry pseudo-standard of 40,000 lbs applied over an 8 foot span at the side sill has emerged. In LF LRVs, this standard may not provide the same level of safety as in High Floor LRVs (HF LRVs). In some US automobiles, the bottom of the bumper is higher than the top of the floor in LF LRVs. Given comparable sidewall construction, when a passenger vehicle impacts the side of an LRV, the opportunity for intrusion/override into the passenger compartment in a LF LRV is higher than that in a HF LRV. The popularity of light trucks, SUVs, minivans and other vehicles with high bumper heights further aggravates this situation.
Evaluating Locomotive Fuel Tank Safety and Crashworthiness
Authors: Kokkins Stephen , Kwok Peter , Punwani S. K. , Tsai N. Tom
Published: June 2008

This paper describes research work sponsored by the Federal Railroad Administration as part of the Train Occupant Protection Program. Locomotive fuel tank strucutural integrity is an extremely important element in providing for crew safety. In the event of train accidents fuel leaks, which can result in a fire, must be prevented. This paper looks at typical train accident scenarios, and deduces the common loading cases that can cause fuel tank penetration. The behavior of a typical fuel tank, compliant with the current AAR RP-506 standard practice, was investigated under these accident loading conditions. Fuel tank wall or plate thickness, material type and strength, corner joint weld size, and baffle support strength were all examined for strength and performance. Using both static and dynamic loading conditions, several parametric design studies were performed to guide the selection of recommended design improvements.
Nonlinear Behavior of a Parametric Resonance-Based Mass Sensor
Authors: Zhang Wenhua , Baskaran Rajashree , Turner Kimberly L.
Published: June 2008

The ability to detect mass change of the order of femtograms (10e-15g) opens up implementations of various precise chemical and biological sensors. Micro-scale oscillator based mass sensors are promising due to their small mass and high sensitivity. Many such sensors detect mass change by measuring the shift of natural frequency. We have reported previous work introducing the idea of using parametric resonance to detect mass change. This method utilizes stability behavior with mass variation as the detection criterion and high sensitivity is expected. This paper presents theoretical and experimental research on nonlinearity effects on the dynamic behavior of a MEMS oscillator, which is the prototype of such a mass sensor. A Duffing equation and a nonlinear Mathieu equation are used to model the behavior of nonlinear harmonic resonance and parametric resonance. Experimental results agree with the theoretical analysis very well. Some bulk equivalent parameters, such as Q factor, cubic stiffness and linear electrostatic stiffness can be estimated by studying the nonlinear behavior. The estimation of the parameters is important for design of the optimal mass sensor. The potential effects of nonlinearity on mass sensor application are discussed.
Predicting the Performance of a Bistable Micro Mechanism Using Design-Stage Uncertainty Analysis
Authors: Wittwer Jonathan W. , Howell Larry L. , Wait Sydney M. , Cherry Michael S.
Published: June 2008

Significant reduction in cost and time to market can be realized by implementing design-stage uncertainty analysis to predict whether a device will meet specified requirements. This paper demonstrates a generalized uncertainty analysis method appropriate for surface micromachined devices and uses a micro linear-displacement bistable mechanism as an example. Dimensional variations, joint clearances, material property uncertainty and friction are included as sources of error. Using matrix notation, the model consists of a system of implicit, nonlinear equations. The analysis is performed at multiple deflections to estimate uncertainty bands around the force-deflection curve of the mechanism. These results can then be used to predict the performance of the mechanism. Applying these techniques resulted in a functional first-time prototype of a bistable mechanism that can be actuated using a non-amplified thermal actuator.
Microlens Fabrication by the Modified LIGA Process and Hot Embossing Process
Authors: Lee Sung-Keun , Lee Hyun Sup , Lee Seung S. , Kwon Tai Hun
Published: June 2008

Microlens and microlens arrays is realized using a novel fabrication technology based on the exposure of a resist, usually PMMA, to deep X-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep X-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. Microlenses were produced with diameters ranging from 30 to 1500 μm. Moreover, fabrication of the microlens through the hot embossing process is studied based upon a microlens mold insert fabricated by the modified LIGA process. A hot embossing machine is designed and manufactured. The hot embossing process follows steps of heating a mold to desired temperature, embossing a mold insert on substrate, cooling the mold to deembossing temperature, and deembossing.
Fabrication and Characterization of Evanescent Microwave Probes Compatible With Atomic Force Microscope for Scanning Near-Field Microscopy
Authors: Wang Yaqiang , Tabib-Azar Massood
Published: June 2008

The design and microfabrication of silicon co-axial evanescent microwave probes (EMP) compatible with atomic force microscope (AFM) imaging was discussed. Scanning EMP (SEMP) imaging is suitable for nondestructive surface and subsurface characterization of materials over a wide frequency range-between 0.1 GHz and 140 GHz. The microfabricated EMP consists of a silicon V-shaped cantilever beam, a co-axial tip, and aluminum co-planar waveguides. The coaxial tip has an apex radius of ∼80 Å. The tip itself is oxidation-sharpened heavily-doped silicon surrounded by an oxide layer that acts as insulator and covered with an aluminum co-axial layer. The tip apex is electrically connected to a strip of aluminum that forms the active part of the waveguide. The design and microfabrication procedure are described. Mechanical and electrical characterizations are discussed. Contact mode and SEMP surface measurement results are reported. The first ever simultaneous contact AFM and scanning near-field microwave microscopy (SNMM) surface imaging are presented. Using the microwave measurement along with the AFM imaging opens up a new window to see inside the materials and sets the stage for hyperspectral imaging of organelles of biological objects as well as electronic devices and structural materials.
Comparison of Piezoresistive and Thermal Detection Approaches to Atomic Force Microscopy Topography Measurement
Authors: King William P. , Kenny Thomas W. , Goodson Kenneth E.
Published: June 2008

Atomic force microscope (AFM) cantilevers with integrated heaters can topographically map a surface with sub-nanometer vertical resolution, and lateral resolution defined by the shape of the tip. As a resistively heated atomic force microscope (AFM) cantilever scans over a surface, the conductance from the cantilever depends upon the distance between the cantilever to the substrate. By measuring the cantilever electrical resitance signal, which is a function of cantilever temperature, it is possible to topographically map surfaces based. This paper models thermal conductance from the cantilever to make predictions of cantilever sensitivity that compare well with data. The model also predicts noise-limited resolution. Comparing the thermal cantilever with an identically-sized piezoresistive cantilever, the thermal cantilever provides two to four orders of magnitude improvement in sensitivity and up to two orders of magnitude resolution improvement over the piezoresistive cantilever.
Design of Mechanically-Latched Micromirror Arrays
Authors: Garcia Ernest J. , Polosky Marc A. , Sleefe Gerard E.
Published: June 2008

This paper describes the design of silicon surface micromachined mirrors that were conceived for operation as part of an extremely large array of mirrors. Such an array has direct application to space-based imaging. For example, in certain spectrometer instrument applications an array of micromirrors is needed to optically switch selected portions of an incoming signal. The mirror array is used to direct selected portions of the signal into the instrument for spectrographic analysis. One technique used to address mirror elements within a large array requires that individual mirror elements can be mechanically latched. This paper will describe the design of a silicon surface micromachined micromirror device with a latching mechanism positioned entirely beneath and within the perimeter of the mirror element.
FEA Modeling of Piezoelectric Clamped-Clamped Beam Microresonators
Authors: Currano Luke J. , Piekarski Brett , DeVoe Donald L.
Published: June 2008

Finite element modeling of MEMS piezoelectric clamped-clamped beam resonators is investigated using a design matrix consisting of beams of varying length and film thickness. Laser Doppler vibrometry was performed on fabricated devices to obtain frequency response, modeshapes, and deflection magnitudes at resonance. The mechanical testing showed an unexpected nonlinearity at resonance in both the frequency response and the modeshapes. Finite element analysis of the beams is presented and the results compared to test data. The model is shown to predict natural frequency well, but the nonlinear modeshapes prevent the accurate prediction of displacement magnitude and modeshape. Evidence is offered from both testing and a finite element buckling model suggesting that the nonlinearity is due to piezoelectrically-induced buckling in the beams.
An Adaptive Feedback Noise Control Approach Using Q-Parameterization
Authors: McEver Mark A. , Cole Daniel G. , Clark Robert L.
Published: June 2008

An algorithm is presented which uses adaptive Q-parameterized compensators for control of sound. All stabilizing feedback compensators can be described in terms of plant coprime factors and a free parameter, Q, which can be any stable function. By generating a feedback signal containing only disturbance information, the parameterized compensator allows Q to be designed in an open-loop fashion. The problem of designing Q to yield desired noise reduction is formulated as an on-line gradient descent-based adaptation process. Coefficient update equations are derived for different forms of Q, including digital finite impulse response (FIR) and lattice infinite impulse response (IIR) filters. Simulations predict good performance for both tonal and broadband disturbances, and a duct feedback noise control experiment results in a 37 dB tonal reduction.
The Theory and Experiments of Recursive Generalized Predictive Control
Authors: Moon Suk-Min , Clark Robert L. , Cole Daniel G.
Published: June 2008

The recursive generalized predictive control algorithm, combining the process of system identification and the process of the controller design, is presented. In the control design process, there are three parameters to be chosen: the prediction horizon, the control horizon, and the input weighting factor. Two new parameters are defined for the practical choice of the prediction horizon and the control horizon. A time varying algorithm for the input weighting factor and a dual-sampling-rate algorithm between system identification and control design are presented. The recursive generalized predictive control algorithm is applied to two different systems: a sound enclosure and an optical jitter suppression testbed.
Thermo-Acoustic Interactions in a Premixed Dump Combuster
Authors: Galvin S. , Fitzpatrick J. A.
Published: June 2008

There is significant interest in the interaction of parameters associated with lean premixed combustion because the demand for reduced emissions has led to an increased usage of this type of system. Thermoacoustic instabilities, which arise as a consequence of unsteady pressure and heat release interactions, are known to occur frequently for these lean premixed configurations. There has been a substantial research effort in the past decade directed at the development of modelling techniques for the prediction and control of these instabilities. Tests have been performed in an optically accessible dump combustor for a range of equivalence ratio with two different dump or expansion ratios and a number of flow rates. Both thermoacoustic and flow/acoustic interactions are observed over a large operating range. The pressure and heat release autospectra and cross-spectra were calculated and their coherence and phase relationships are examined to determine their interaction including the applicability of the Rayleigh criterion.
Flow-Acoustic Interactions in T-Junctions
Authors: Scott A. , Ziada S.
Published: June 2008

The flow-acoustic nature of sharp-edged T-junctions is investigated experimentally. Tests are performed for a Reynolds number range of 54,000 < ReD < 470,000. Four test cases are studied corresponding to: (a) T-junction with flow from the two branches; (b) T-junction with flow from one branch; (c) T-junction with flow into the two branches and (d) T-junction with flow into one branch. It is found that the separation bubble formed when the flow goes around the T-junction corner provides a source of turbulence excitation. For cases (c) and (d) the dimensionless pressure amplitudes of the acoustic modes reach a maximum at a Strouhal number which is in agreement with the broadband peak measured in the separation bubble. Cases (a) and (b) exhibit a different type of flow-acoustic coupling. In both cases, the maximum acoustic pressure is stronger than in Cases (c) and (d) and occurs at a Strouhal number which is different from that observed in the separation bubble. The results are compared to experimental and numerical studies from the literature.
Vibroacoustical Analysis of Flow in Pipe System
Authors: Mohamed Ould Abdallahi , Charley Jacques , Caignaert Guy
Published: June 2008

The present study is devoted to fluid-structure interaction (FSI) within a straight pipe. A non dimensional transfer matrix (dimension 4×4) is defined and links state vectors in two cross-sections of pipe. That matrix formulation, in the frequency domain, has been used as basis for a four transducers intensimetry technique. That method allows for a more accurate determination of a state vector in a given cross section of a straight pipe. All calculations have been done with a control of the conditioning of matrices. A new method is proposed : that one uses pressure, flow velocity, axial displacement and axial strain as variables. The choice leads to a proposal of a non intrusive experimental procedure, which can be useful for the experimental determination of hydroacoustic transfer matrices of complex part of an hydraulic circuit in the low frequencies range. So drilling holes in pipes to insert pressure transducers, for example, will, in many situations, be undesirable or even impossible.
Study of the Acoustic Oscillations of Flow Over Cavities: Part 2 — Sound Reduction
Authors: He´mon Pascal , Amandole`se Xavier , Santi Franc¸oise , Wojciechowski Jan
Published: June 2008

We present experimental results obtained with a deep cavity, like an Helmholtz resonator, excited by an airflow. The resonance under the action of the vortices generated in the shear layer is well described and quantified. The mounting of actuators, based on a few piezo-electric elements, allows to generate a series of two-dimensional vortices forced at a frequency which is different than the natural resonance frequency. The sound level in the cavity is strongly decreased and the broadband noise of the turbulence only remains.
Suppression of Acoustic Waves in Steam Generator and Heat Exchanger Tube Banks
Authors: Eisinger F. L. , Sullivan R. E.
Published: June 2008

Tube banks located in flow channels and exposed to crossflow have a low resistance to acoustic resonance and vibration in general. Such resistance can be increased substantially by placing acoustic baffles inside the tube banks. The locations and the number of baffles play an important role in the degree of their effectiveness of suppressing acoustic waves. One or two baffles placed within a tube bank will raise the threshold to acoustic vibration significantly. Optimum baffle locations suppressing acoustic resonance and vibration or reducing noise levels at resonance can be determined. A general procedure based on acoustic particle velocity mode shape functions is presented for the evaluation of the acoustic baffle effects.
Maglev Linear Actuator for Nanopositioning
Authors: Kim Won-jong , Maheshwari Himanshu , Gu Jie
Published: June 2008

Manufacture of nanoscale structures and atomic-level manipulation is an emerging technology field in the 21st century [1,2]. This paper presents a novel magnetically levitated instrument capable of six-degrees-of-freedom (6-DOF) motion with a single moving part. The applications, where this generic positioning device can be used, are manufacturing of nanoscale structures, assembly and packaging of microparts, vibration isolation for delicate instrumentation and motion/force feedback in telepresence surgery. The key element of this stage is a linear actuator capable of providing forces in both suspension and translation without contact. The total range of motion for the linear actuator is ±250 μm. In this paper, we present the closed-loop control test results and stochastic noise/disturbance analysis and prediction for the linear actuator.
Deep X-Ray Mask With Integrated Actuator for 3D LIGA Process
Authors: Lee Kwang-Cheol , Lee Seung S.
Published: June 2008

We present a noval method of 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a microactuator is integrated. The integrated micro-actuator oscillates the X-ray absorber, which is formed on the shuttle mass of the micro-actuator, during X-ray exposures to modify that absorbed dose profile in X-ray resist, typically PMMA. 3D PMMA microstructures according to the modulated dose controur are revealed after GG development. An X-ray mask with integrated comb drive actuator is fabricated using deep reactive ion etching, absorber electroplating, and bulk micromachining with silicon-on-insulator wafer. 1 mm × 1 mm, 20 μm thick silicon shuttle mass as a mask blank is supported by four 1 mm long suspesnsion beams and is driven by the comb electrodes. A 10 μm thick, 50 μm line and spaced gold absorber pattern is electroplated on the shuttle mass before the release step. The fundamental frequency and arnplitured are around 3.6 kHz and 20 μm, respectively, for a dc bias of 100 V and an ac bias of 20 VP-P (peak-peak). Fabricated PMMA microstructure shows 15.4 μm deep, S-shaped cross section in the case of 1.6 kJ cm−3 surface dose and GG development at 35°C for 40 minutes.
Curvature Study With Application in MEMS Packaging
Authors: Li Gary , McNeil Andrew , Koury Dan , Monk Dave
Published: June 2008

This paper presents a theoretical derivation of curvature equation for a dual stacked structural system whose material properties are temperature dependent. The thickness of the two structural layers are supposed to be in the same magnitude, and the curvature equation for a situation where a thin layer is coated on a thick substrate is given as a special case. The primary goals of this paper are to provide guidance for choosing materials for MEMS sensor packaging and for designing a package aiming at low stress and low deformation.
Fabrication of NdFeB Thin Film and Its Application in MEMS
Authors: Zheng Pan , Kilani Mohammad , Haik Yousef S. , Chen Ching-Jen
Published: June 2008

The paper measures the magnetic properties of NdFeB thin films developed under the effects of magnetic field. The samples exhibited a larger residual inductance, saturation magnetization and energy product than those treated without field or with weaker field. Magnetic MEMS was introduced with application of the NdFeB film to micro device such as pumps and gear transmission system.
Characteristics of Aerodynamic Sound Sources Generated by Coiled Wires in a Uniform Air Flow
Authors: Matsumoto Hiroki , Nishida Kohshi , Saitoh Ken-ichi
Published: June 2008

This study deals experimentally with aerodynamic sounds generated by coiled wires in a uniform air flow. The coiled wire is the model of the hair dryer’s heater. In the experiment, the effects of the outer diameter D, wire diameter d and spacing between coils s of the coiled wire on the aerodynamic sound have been clarified. The results of frequency analyses of the aerodynamic sounds show that an aeolian sound is generated by the coiled wire, when s/d is larger than 1. And the peak frequencies of aeolian sounds generated by the coiled wires are higher than the ones generated by a cylinder having the same diameter d. To clarify the characteristics of the aerodynamic sound sources, the directivity of the aerodynamic sound generated by the coiled wire has been examined. And the coherent function between the velocity fluctuation around the coiled wire and the aerodynamic sound has been measured. Moreover the band overall value of coherent output power between the sound and the velocity fluctuation has been calculated. This method has clarified the sound source region of the aeolian sound generated by the coiled wire. These results show that the aeolian sound is generated by the arc part of the coiled wire which is located in the upper side of the air flow.
Flow-Induced Noise From Short Aspect Ratio Cylinders Inside a Rectangular Duct
Authors: Rodarte Enrique , Miller Norman
Published: June 2008

Flow-induced tonal noise and acoustic resonance problems are found in a variety of applications that range from nuclear power plant heat exchangers to automobile air conditioning evaporators. This tonal component of noise can be associated with the fluctuating forces produced in bluff bodies when subject to flow. Fluctuating forces can be represented as acoustic dipoles [Blake]. An acoustic model based on the inhomogeneous convected Helmholtz equation with a point dipole source term, volumetric damping and damping at the duct walls was used in conjunction with experimental measurements to study the acoustic field produced by short aspect ratio cylinders inside a rectangular duct with flow. The model was able to predict the acoustic field produced by the cylinders once an appropriate fluctuating lift coefficient was estimated and employed. Fluctuating lift coefficients found using the model and an optimization procedure were in reasonable agreement with results reported in the literature.