bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model for the Onset of Tearing at Slits in Stressed Coated Woven Fabrics
Authors: Godfrey T. A. , Rossettos J. N. , Bosselman S. E.
Published: April 2008

Coated woven fabrics are often used as stressed membranes in inflatable and tension structures. When the stressed fabrics in such structures are damaged locally, the damage site often provides a starting point for the propagation of a tear. In this paper, a micromechanical model is developed for predicting the onset of tearing at slit-like damage sites in biaxially stressed coated woven fabrics. The stress concentration in the first intact yarn adjacent to the slit is determined as a function of increasing remote stress, and predictions for tearing onset are made assuming that tearing initiates through the rupture of the first intact yarn when the maximum tension in the yarn reaches the yarn ultimate breaking load. A crucial aspect of the model is the treatment of inelastic deformation involving yielding and/or separation of the coating and relative slip between interlaced yarns near the slit tip. Inelastic deformation near the slit tip leads to significant reduction in the stress concentration compared with the elastic deformation case and, therefore, acts to inhibit the onset of tearing. A single dimensionless parameter is shown to govern the stress concentration at tearing versus slit length behavior of particular fabrics. The parameter may be interpreted as a measure of the slit damage tolerance of coated fabrics and shows how particular microstructural properties of the fabric (coating yield stress, coating shear stiffness, yarn axial stiffness, etc.) affect tearing onset. A series of experiments on various coated nylon and polyester fabrics are conducted using slit-damaged cruciform specimens in a simple biaxial test frame. Initial slit lengths in these tests ranged from five to 61 consecutive yarn breaks. The model is shown to capture the onset of tearing in these fabrics over a range of slit lengths quite well.
Predictive Intelligent Filter Design in Signal Processing Using AR and ARMA Models
Authors: Schoen Marco P. , Kaur Bhag Singh Kelwant , Chinvorarat Sinchai , Kuo Chien-Hsun
Published: April 2008

The design of filters for the prediction of signals has been a widely studied field. For some of the applications, more accurate and further reaching algorithms are necessary. For example, in the prediction of irregular waves for wave energy converters, an accurate prediction of wave height and velocity are important in order to maximize the converter’s efficiency. This paper presents three prediction filters for such an application. The first algorithm is based on a simple autoregressive (AR) model and a standard least-squares estimation scheme. The second proposed filter is based on an autoregressive moving average (ARMA) model. The third filter is a fixed horizon predictive filter based on an AR structure, using a Genetic Algorithm to estimate its prediction parameters. All proposed algorithms are simulated using a Pierson-Moskowitz spectrum representing wind speeds of 30 knot.
Neural Network Based Intelligent Learning of Fuzzy Logic Controller Parameters
Authors: Kumar Manish , Garg Devendra P.
Published: April 2008

Design of an efficient fuzzy logic controller involves the optimization of parameters of fuzzy sets and proper choice of rule base. There are several techniques reported in recent literature that use neural network architecture and genetic algorithms to learn and optimize a fuzzy logic controller. This paper presents methodologies to learn and optimize fuzzy logic controller parameters that use learning capabilities of neural network. Concepts of model predictive control (MPC) have been used to obtain optimal signal to train the neural network via backpropagation. The strategies developed have been applied to control an inverted pendulum and results have been compared for two different fuzzy logic controllers developed with the help of neural networks. The first neural network emulates a PD controller, while the second controller is developed based on MPC. The proposed approach can be applied to learn fuzzy logic controller parameter online via the use of dynamic backpropagation. The results show that the Neuro-Fuzzy approaches were able to learn rule base and identify membership function parameters accurately.
Using the Milliken Moment Method and Dynamic Simulation to Evaluate Vehicle Stability and Controllability
Authors: Hoffman Robert C. , Stein Jeffrey L. , Louca Loucas S. , Huh Kunsoo
Published: April 2008

The Milliken Moment Method (MMM) is a way of efficiently organizing the results from a kinematically constrained vehicle test. Using the MMM and closed-loop dynamic simulation, the authors present a new method for evaluating vehicle handling, where the MMM assesses the overall performance capability of the vehicle, and the simulation determines how much of that performance is used for a closed-loop maneuver. By mapping the simulation data onto the yaw moment - lateral acceleration diagram from the MMM, this method allows a design engineer to explicitly quantify the tradeoff between the controllability and stability of a vehicle. Results from a design case study and comparison of the stability measure to phase plane analysis show that this method captures the tradeoff in design, and clearly represents the overall capability of the driver-vehicle system.
Dynamic Characteristics of a Free Piston Compressor
Authors: Barth Eric J. , Riofrio Jose
Published: April 2008

The design and dynamic characterization of a free piston compressor is presented in this paper. The free piston compressor is a proposed device that utilizes combustion to compress air into a high-pressure supply tank. The device is configured such that the transduction from thermal energy to stored energy, in the form of compressed gas, is efficient relative to other small-scale portable power supply systems. This efficiency is achieved by matching the dynamic load of the compressor to the ideal adiabatic expansion of the hot gas combustion products. It is shown that a load that is dominantly inertial provides a nearly ideally matched load for achieving high thermodynamic efficiency in a heat engine. The device proposed exploits this fact by converting thermal energy first into kinetic energy of the free piston, and then compressing air during a separate compressor phase. The proposed technology is intended to provide a compact pneumatic power supply source appropriate for human-scale robots. The combined factors of a high-energy density fuel, the efficiency of the device, the compactness and low weight of the device, and the use of the device to drive lightweight linear pneumatic actuators (lightweight as compared with power comparable electric motors) is projected to provide at least an order of magnitude greater total system energy density (power supply and actuation) than state of the art power supply (batteries) and actuators (electric motors) appropriate for human-scale power output. A thermodynamic analysis reveals relationships between key design variables with regard to efficiency. A dynamic model of the proposed device is developed and simulation results are discussed. This model shows the potential of the proposed device.
Design, Fabrication, and Mixing Characteristics of an Electrostatically Activated Resonant Micropump-Mixer
Authors: Tsao Chia-Wen , Mohseni Kamran
Published: April 2008

An active mixing and pumping strategy is proposed to enhance mixing of two fluids through vortex accumulation by a resonant plate actuation. A resonant micropump-mixer is designed and fabricated, where an electrostatically activated plate is placed at or in close vicinity of the interface between the two incoming streams at the junction of a Y-shaped microchannel. Mixing is enhanced by increased interface area between the two fluids during the vortex formation at the tip of the resonant plate. Fabrication of the micropump-mixer is achieved in two steps. Commercial PolyMUMPs process is initially used to fabricate a resonant plate, where it is eventually packaged into a Y-shaped microchannel. The resonant plate, in this study, has a length of 300 μm, thickness of 1.5 μm, and it is activated by an AC power source, which results in significant oscillation amplitude at the tip of the plate. The Laser Induced Fluorescence (LIF) technique is used for flow visualization and characterization, where effective mixing and pumping capabilities of the micropump-mixer are demonstrated.
Experimental Analysis of Pediatric Brain Injury Causation Utilizing Scientifically Proven Quantitative Measures
Authors: Rintalan Christopher J. , Liptai Laura L.
Published: April 2008

On February 19, 2003, a 3-year-old child was sent downstairs to retrieve a toy. Shortly after, her guardian heard a noise and ran to find her lying at the bottom of the split-foyer stairs. She was rushed to the hospital immediately by paramedics. She died five days later and the cause of death determined was brain herniation due to anoxic/ischemic brain injury. The objective of this research was to determine which fall scenario(s) matched the trauma sustained utilizing scientifically proven quantitative measures.
Radial Heat Transfer Dynamics During Cryogen Spray Cooling
Authors: Franco Walfre , Wang Guo-Xiang , Nelson J. Stuart , Aguilar Guillermo
Published: April 2008

Cryogen spray cooling (CSC) is a heat extraction process that protects the epidermal layer during skin laser surgery of port wine stain (PWS) birthmarks and other specific dermatoses. The objective of the present work is to investigate temporal and radial variations on the heat transferred at the surface of a skin model during CSC. A fast-response thermal sensor is used to measure temperature across the radius of the sprayed surface of a skin model. These interior measurements along with an inverse heat conduction algorithm are used to determine the heat transferred at the surface. Results show that radial and temporal variations of the boundary conditions have a strong influence on the homogeneity of heat extraction from skin. However, there are subregions of uniform cooling. It is also observed that the surface heat flux undergoes a marked dynamic variation, with a maximum heat flux occurring at the center of the sprayed surface early in the spurt followed by a quick decrease. The study shows that external conditions must be taken into account and ideally controlled to guarantee uniform protection during CSC.
Evaluation of Anatomical Effects Using Laboratory +Gz Impact Tests
Authors: Hamlin David B. , Manteufel Randall D.
Published: April 2008

A number of recent studies have been conducted to determine if gender and/or anatomy significantly contribute to the probability of spinal injury of military pilots during the initial stages of an in-flight ejection. These studies have been prompted by the introduction of females into combat aircrew positions, and the concern that they may be at higher risk of spinal injury than males, especially considering most ejection tests and evaluations were conducted for an all-male pilot population [1]. Although some studies have suggested that no statistically significant difference exists in experimentally measured acceleration response between males and females [2, 3], the anatomical difference between the genders is clearly significant. The female body, on average, has 30% less mass, 25% less vertebral cross-sectional area (CSA), 20% less vertebral breaking strength, 10% less muscle mass and 10% shorter spine than the avearge male [4, 5].
Modulating Stiffness in DNA-Crosslinked Polyacrylamide Gels
Authors: Lin David C. , Langrana Noshir A. , Yurke Bernard
Published: April 2008

At Rutgers, we have developed a new class of DNA-crosslinked hydrogels that promise to have a wide range of applications ranging from drug delivery to prosthetics. Advantages of using DNA in place of more common crosslinkers such as bis(acrylamide) include thermoreversibility and the ability to engineer the crosslink length. We have shown previously that gel stiffness is a function of the DNA crosslink density [1], and demonstrated a second method whereby stiffness was enhanced by generating tensegrity within the gel network [2]. In this study, controlled procedures were employed to monitor the extent to which gel compression during electrophoresis influences the stiffness of the gel. The effects of DNA “fuel” and counter-fuel (removal) strands were investigated. A nearly four-fold increase in elastic modulus was reversibly attained by the introduction of fuel strands to stiffen the crosslinks and create a tensegrity microstructure.
E. Coli Inspired Propulsion for Swimming Microrobots
Authors: Behkam Bahareh , Sitti Metin
Published: April 2008

Medical applications are among the most fascinating areas of microrobotics. For long, scientists have dreamed of miniature smart devices that can travel inside the human body and carry out a host of complex operations such as minimally invasive surgery (MIS), highly localized drug delivery, and screening for diseases that are in their very early stages. Still a distant dream, significant progress in micro and nanotechnology brings us closer to materializing it. For such a miniature device to be injected into the body, it has to be 800 μm or smaller in diameter. Miniature, safe and energy efficient propulsion systems hold the key to maturing this technology but they pose significant challenges. Scaling the macroscale natation mechanisms to micro/nano length scales is unfeasible. It has been estimated that a vibrating-fin driven swimming robot shorter than 6 mm can not overcome the viscous drag forces in water. In this paper, the authors propose a new type of propulsion inspired by the motility mechanism of bacteria with peritrichous flagellation, such as Escherichia coli, Salmonella typhimurium and Serratia marcescens. The perfomance of the propulsive mechanism is estimated by modeling the dynamics of the motion. The motion of the moving organelle is simulated and key parameters such as velocity, distribution of force and power requirments for different configurations of the tail are determined theoretically. In order to validate the theoretical result, a scaled up model of the swimming robot is fabricated and characterized in silicone oil using the Buckingham PI theorem for scaling. The results are compared with the theoretically computed values. These robots are intended to swim in stagnation/low velocity biofluid and reach currently inaccessible areas of the human body for disease inspection and possibly treatment. Potential target regions to use these robots include eyeball cavity, cerebrospinal fluid and the urinary system.
A Micro Helico-Kinematic Platform via Spherical Crank Sliders
Authors: Lusk Craig P. , Howell Larry L.
Published: April 2008

A novel surface micromachined mechanism, the Micro Helico-Kinematic Platform (MHKP), is presented. The MHKP achieves a combination of vertical out-of-plane translation and in-plane rotation (helical motion) of a platform with an in-plane rotational input. The motion achieved requires specialized analysis techniques in spherical kinematics and introduces the micro spherical crank-slider. Spherical kinematic concepts are reviewed to aid in describing the motion and conveying the scope of the device’s design freedom. The force and displacement relations for the mechanism are derived using virtual work techniques. A surface micromachined prototype was fabricated and tested. Testing indicates that the sliding interface between the spherical crank sliders and the platform results in some stick-slip friction and that the mechanism is able to achieve its full range of motion. The vertical motion of the platform can be advantageous in micro manipulation applications such as the positioning of micro-optical components.
Thermal Defocussing Criteria for a Laser Welding Process
Authors: Kowalski Gregory J. , Whalen Richard A.
Published: April 2008

A numerical simulation code is developed to study the significance of refraction effects (beam self-focussing or defocussing) of a laser during a laser welding process. Relationships between the size of the heat affected zone (HAZ), the melt zone and the laser beam parameters are investigated for a short pulsed laser welding process. The solution method includes the thermally stimulated nonlinear optical effects caused by the temperature dependent index of refraction, as well as the step change in surface reflection that occurs due to the liquid and solid phase change. The interaction of these parameters is investigated to better control the laser manufacturing processes. Difficulties of numerical modeling and the tradeoff between using small nodes to reduce the sawtooth behavior in the phase change model and computer run times that are consistent with real time control are discussed. The results indicate that there are no significant refraction affects of the laser beam and that the heat affected zone is approximately 6% larger for a collimated beam input as compared to a gaussian beam input. Peak temperatures are lower for the collimated beam.
Thermal Performance Evaluation of New Power QFN (Quad Flat No Lead) Packages for Automotive Applications
Authors: Chiriac Victor , Lee Tien-Yu Tom
Published: April 2008

An extensive 3-D conjugate numerical study is conducted to assess the thermal performance of the novel Power Quad Flat No Lead (PQFN) packages for automotive applications. Several PQFN packages are investigated, ranging from smaller die/flag size to larger ones, single or multiple heat sources, operating under various powering and boundary conditions. The steady state and transient thermal performance are compared to those of the classical packages, and the impact of the thicker lead frame and die attach material on the overall thermal behavior is also evaluated. Under one steady state (1W) operating scenario, the PQFN package reaches a peak temperature of ~106.3°C, while under 37W@40ms of transient powering, the peak temperature reached by the corner FET is ~260.8°C. With an isothermal boundary (85°C) attached to the board backside, the junction temperature does not change, as the PCB has no significant thermal impact. However, when the isothermal boundary is attached to package bottom, it leads to a drop in by almost 20% after 40 ms. Additional transient cases are evaluated, with an emphasis on the superior thermal performance of this new class of power packages for automotive applications.
Analysis of Tiplock Phenomenon in Extension Ladders
Authors: Morse John S. , Rasnic C. Russ
Published: April 2008

Extension ladder accidents injure thousands of people each year in the U.S. One cause of these accidents is false lock of the flylocks. Flylocks are the devices that support the upper or fly section of an extended ladder. False locked flylocks are not fully locked, but nevertheless support a load. False lock is not stable and may release under disturbance of the ladder, e.g. from climbing. False lock modes include tiplock, flipperlock, and camlock. If a false lock releases the ladder will telescope, and may cause serious injury. One false lock mode is tiplock, where the tip of the flylock is resting on the rung of the ladder in a metastable position. The tiplock may be held in place by mechanical locking, or by friction between the tip and the rung. Tiplock may occur when the ladder is being extended and the fly section is not raised enough to fully engage the flylocks. Ladder labels usually instruct “Securely engage ladder locks before climbing,” but typically do not instuct a user how to do this. Ladder users employ various methods to securely engage flylocks. These methods do not always prevent false lock. No gravity or spring actuated flylock design is known which will completely eliminate tiplock, but various designs have different ranges of fly section travel over which tiplock can occur (tiplock “window”). A mathematical expression defines the conditions under which friction tiplock can occur. Two methods of evaluating the tiplock window are discussed: geometric analysis and physical measurement. Tiplock propensity during random ladder extension is calculated. A geometric analysis is made of two flylocks with different tip radii. The flylock with the smaller tip radius is observed to have a smaller tiplock window.
Experimental Study of the Effect of Channel Orientation and Flow Oscillations on Critical Heat Flux
Authors: Hayes Benjamin Z. , Warrier Gopinath R. , Dhir Vijay K.
Published: April 2008

Limited studies reported in the literature show that oscillatory flows can reduce critical heat flux (CHF) in boiling channels. In this study the effect of oscillatory flow on the CHF in a rectangular channel is investigated. Oscillation amplitude, average mass flux, and gravity vector orientation were systematically varied in this low-pressure, low-flow study using PF-5060 as the test liquid. The tests were conducted on a test section with a 2 × 2 cm2 cross sectional area and a Hastelloy B-2 ribbon heater mounted flush on one side. The ribbon was 0.406 mm thick and 28.0 cm in length, and was heated using DC power. Oscillations in flow were created by sending a sine wave control signal to a proportional control, solenoid valve. The experiments show that CHF decreases when oscillations are introduced into the flow for vertical upflow (90°) and horizontal flow with the heater surface facing up (0°). CHF values decreased with increasing liquid subcooling, and were nearly insensitive to oscillations at low liquid subcoolings. For horizontal flow, with the heater facing down (180°). CHF was found to be enhanced by the flow oscillations, when the liquid was near saturation temperature.
Localization of Anatomical Landmarks of the Foot by Surface Curvature
Authors: Liu Xiang , Kim Wangdo , Drerup Burkhard
Published: April 2008

The anatomical landmarks on the body surface are important to shape and motion analysis. This paper presents a method for extracting anatomical landmarks on the foot from scattered 3D surface points collected by FastSCAN (Polhemus, Colchester, Vermont, USA). By least squares surface fitting, the surface is reconstructed from the scattered points and the Gaussian curvature and mean curvature are calculated. The landmarks formed by underlying muscles and skeletal structures distinguish themselves clearly on the Koenderink shape index maps. The loci of landmarks avail possible statistical shape analysis and medical applications such as tibial torsion measurement.
A Semi-Empirical Evaluation for Effective Thermal Conductivity of Diamond-Coated Silicon Heat Spreaders
Authors: Wu M. C. , Lin T. W. , Chen P. L. , Peng C. H. , Hung Y. H.
Published: April 2008

An effective and time-saving method for precisely evaluating the effective thermal conductivities of diamond-coated silicon heat spreader is presented. For the present two-layer (diamond/silicon) composite material, by using both a numerical thermal network method and an experimental measurement together with a statistical least-square technique, the parallel and normal effective thermal conductivities of the anisotropic testing diamond film with a thickness of 6.93 micro-meters are semi-empirically determined as 141W/mK and 1700W/mK, respectively. Furthermore, the present results also show that an isotropic model using the geometric mean of the parallel and normal effective thermal conductivities (489.5W/mK) predicts the local temperature distribution on the diamond-coated surface with a satisfactory agreement.
Boundary/Finite Edge Element Modeling of 3-D Microwave Thermal Food Processing
Authors: Huo Y. , Li B. Q. , Tang Ju.
Published: April 2008

An integrated numerical model is developed for the modeling of microwave thermal processing of food packages in industrial MW applicators for the purpose of food sterilization. The model employs a hybrid boundary/finite element method for the solution of 3-D Maxwell equations and the finite element method for thermal calculations. The coupling of the electromagnetic and thermal models is made by the use of an iterative procedure. The integrated model is applied to study the microwave distribution in industrial scale microwave applicators and the absorbed power and the temperature field within the packaged foods. Calculated results are compared with experimental measurements. Results show that the temperature distribution in food packages immersed in water differs significantly from that in air.
Analysis of Deformation Process of a Bubble in a Cell Model by Shock Wave for Developing Drug Delivery Systems
Authors: Tamagawa Masaaki , Yamanoi Ichiro
Published: April 2008

This paper describes the trial of making microcapsules and deformation analysis of a bubble near the curved elastic wall using macro 2d model and plane shock wave. The prototype microcapsules are made by using micromanipulation systems. It is found that by controlling the initial position of a bubble from the wall and the curvature of the wall there is a point to have large deformation, which tends to be collapsed easily. This is one of the results to aid design of DDS or bioprocess for cell-integration.
Swirling Flow of a Viscoelastic Fluid With Free Surface: Part II — Numerical Analysis With Extended Marker-and-Cell Method
Authors: Yu Bo , Wei Jinjia , Kawaguchi Yasuo
Published: April 2008

In Part I [1], we presented the experimental results for swirling flows of water and cetyltrimethyl ammonium chloride (CTAC) surfactant solution in a cylindrical vessel with a rotating disk located at the bottom for a Reynolds number of around 4.3 × 104 based on the viscosity of solvent. For the large Reynolds number, violent irregular instantaneous secondary flows at the meridional plane were observed by use of a PIV system. Because of the limitations of our computer resources, we did not carry out DNS simulation for such a large Reynolds number. The LES and turbulence model are alternative methods, but a viscoelastic LES/turbulence model has not yet been developed for the surfactant solution. In this study, therefore, we limited our simulations to a laminar flow. The Marker-and-Cell (MAC) method proposed for Newtonian flow was extended to the viscoelastic flow to track the free surface, and the effects of Weissenberg number and Froude number on the flow pattern and surface shape were studied. Although the Reynolds number is much smaller than that of the experiment, the major experimental observations such as the inhibition of primary and secondary flows and the decrease of the dip of the free surface by the elasticity of the solution, were qualitatively reproduced in the numerical simulations.
Unconstrained and Constrained Control for a Tentacle Manipulator
Authors: Ivanescu Mircea
Published: April 2008

The control problem of the spatial tentacle manipulator is presented. In order to avoid the difficulties generated by the complexity of the nonlinear integral - differential model, the control problem is based by the artificial potential method. It is shown that the control of a tentacle robot to a desired position it is possible if the artificial potential is a potential functional whose point of minimum is attractor of this dissipative controlled system. Then, the method is used for constrained motion in an environment with obstacles. Numerical simulations for spatial and planar tentacle models are presented in order to illustrate the efficiency of the method.
Evaluation of Possible Stress Distributions in Abdominal Aorta on the Basis of Physiologically Loading Data
Authors: Yamada Hiroshi , Momii Shinya
Published: April 2008

It is highly desired to establish a method of estimating the stress state and mechanical properties in blood vessels numerically using diagnosis data. To obtain the mechanical state, it is necessary to evaluate the reliability of results from numerical simulation. In the current study, we investigate the possibility of stress distribution in a circular cylindrical shape of vascular wall based on the pressure-diameter relationship in the physiological pressure range with assumptions of a hyperelastic material and no residual stress. As another case, we simulate wall stress in an axisymmetric vessel at a mean pressure level. Results form the former case show that one has many solutions which reproduce the pressure-diameter (p-d) relationship and that more information is required to determine the mechanical properties. Results form the latter case show that a pair of Laplace equation and force equilibrium in the axial direction provides a wall stress for an axisymmetric shape of vessel.
Alarming the Population Using SMS
Authors: Sillem S. , Wiersma J. W. F. , Ale B. J. M.
Published: April 2008

Alarming a community in case of an emergency is not always perfect, as recent incidents in the Netherlands have shown. The audibility of the current siren is too low, especially for people indoors, and the public often does not know how to behave in an emergency situation. This paper describes the evaluation study of a project that investigates the possibilities of using Short Message Services (SMS) as an addition to the siren. The study describes a pilot project in the Netherlands, where an SMS service was used to inform and give instructions to the population of the city of Vlaardingen in case of an emergency. The pilot study has been carried out in the first half of 2004. The objective of this pilot study was to determine the effectiveness and efficiency of the service. At this moment (April 2004) the pilot study is still ongoing. This paper presents the first results of this pilot.
Applying Proper Orthogonal Decomposition Tools for Modal Identification of Coupled Structural-Acoustic Dynamic Fields
Authors: Georgiou Ioannis T. , Papadopoulos Christos I. , Servis Dimitris P.
Published: April 2008

To characterize the modal structure of the interaction dynamics of plate-like structures functioning as sound reducing systems, we apply the method of Proper Orthogonal Decomposition (POD) to analyze the dynamics of a room-plate-room coupled system. Given the finite element simulation as information on the dynamic response of this coupled system, it is shown that the POD technique identifies unique, optimum spatial patterns (modes) for all dynamic fields such as the sound pressure in the rooms and especially the vibration response of the plate. The Proper Orthogonal Decomposition (POD) technique proves to be a very effective identification tool for structural-acoustical systems.
Mode Decoupling Controller for Feedback Model Updating
Authors: Jung Hunsang , Park Youngjin , Park K. C.
Published: April 2008

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed-loop frequency information for parameter modifications to overcome the problems associated with the conventional methods employing the modal sensitivity matrix. To obtain new modal information from the closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of the closed-loop system. The present paper proposes a mode-decoupling controller that can alter a target mode while guaranteeing the stability of the closed-loop, and that can be constructed by using the measured open-loop, mode shapes. A simulation based on time domain input/output data is performed to evaluate the feasibility of the proposed control method, which is subsequently corroborated via experiments. Experimental data obtained on a beam via the proposed mode-decoupling controller have been applied to estimate thicknesses of a beam. The results show that the proposed approach outperforms conventional methods with a far less number of data set for the estimation of system parameters.
Study of Electrical Breakdown Phenomena on Silicon With Micron Separations
Authors: Wang P. J. , Chen C. H.
Published: April 2008

Although Paschen’s Law has been thoroughly studied and experimentally verified on the electric breakdown of various metallic materials with millimeter gaps in the last century, today’s microelectromechanical systems (abbreviated as MEMS) are still facing the challenges of electric breakdown problems with micron-scale insulation gaps fabricated on silicon wafers. Apparently, the breakdown problems are possibly attributed to the misinterpretation of Paschen’s Law for the micron gaps between electrodes typically adopted for circuit insulation purposes. In this paper, breakdown-voltages were measured on various configurations of electrode fabricated on silicon-on-insulator wafers together with insulation gaps carefully made between 2 and 21 microns. In addition, most common configurations, such as plane-plane and comb-shape electrodes, are cautiously fabricated for illustrative comparisons. As a result, empirical curves different from the one predicted by Paschen’s Law for describing the electric breakdown phenomenon on MEMS devices with small insulation gaps are shown for reinstating the design criterion of electrical insulation gap in MEMS devices.
Open-Loop Active Control of Combustion Dynamics on a Gas Turbine Engine
Authors: Richards Geo. A. , Thornton Jimmy D. , Robey Edward H. , Arellano Leonell
Published: April 2008

Combustion dynamics is a prominent problem in the design and operation of low-emission gas turbine engines. Even modest changes in fuel composition, or operating conditions can lead to damaging vibrations in a combustor that was otherwise stable. For this reason, active control has been sought to stabilize combustors that must accommodate fuel variability, new operating conditions, etc. Active control of combustion dynamics has been demonstrated in a number of laboratories, single-nozzle test combustors, and even on a fielded engine. In most of these tests, active control was implemented with closed-loop feedback between the observed pressure signal and the phase and gain of imposed fuel perturbations. In contrast, a number of recent papers have shown that open-loop fuel perturbations can disrupt the feedback between acoustics and heat release that drives the oscillation. Compared to the closed-loop case, this approach has some advantages because it may not require high-fidelity fuel actuators, and could be easier to implement. This paper reports experimental tests of open-loop fuel perturbations to control combustion dynamics in a complete gas turbine engine. Results demonstrate the technique was very successful on the test engine, and had minimal effect on pollutant emissions.
Radiative Heat Transfer Using Isotropic Scaling Approximation: Application to Fibrous Medium
Authors: Kamdem Tagne Herve´ T. , Doermann Baillis Dominique
Published: April 2008

The applicability of the isotropic scaling approximation to heat transfer analysis in fibrous medium is discussed. The isotropic scaling model allows the transformation of an anisotropic scattering problem to an isotropic one. The scaled parameters are derived for general anisotropic scattering and for radiative properties dependent of the incidence direction such as for fibrous medium. The fibers are randomly oriented either in space or parallel to the boundaries of the medium. The radiative transfer equation is solved with the discrete ordinate method and comparisons between the exact and the isotropic scaling problems for several Gauss quadrature are studied.
Redundancy of Vital Systems for Merchant Ships
Authors: Kozˇuh Mitja , Petelin Stojan , Perkovicˇ Marko
Published: April 2008

When we talk about redundancy we have to compare risks of different options that compete for the same final result and for this result we have to decide what our goal is. Most of the time everything is fine but a ship can experience an event that surpasses its abilities. Either propulsion is lost and the ship cannot control its behavior during a storm, resulting in lost lives or even the loss of the ship, or a polluted environment causes a loss. Most ships are not equipped with a redundant parallel propulsion system. The most common reason is that any redundancy is a cost which burdens the operating company. Even safety costs are not really defined since the compensation for the lost lives is negotiable and also depends on the skills of lawyers. Therefore only the business costs can be defined with relative accuracy.
Bone Mineral Density of Cervical Spine Vertebrae Using Quantitative Computed Tomography
Authors: Yoganandan Narayan , Pintar Frank A. , Aktay Recai , Paskoff Glenn , Shender Barry S.
Published: April 2008

While numerous studies exist quantifying the bone mineral content of the human lumber vertebrae, such information is not available for the cervical spine. This study determined the bone mineral densities of cervical vertebrae. Adult healthy human volunteers, ages ranging from 18 to 40 years, underwent quantitative computed tomography scanning of the neck. BMD data were divided according to subject weight (above and below 50th percentile, termed low and heavy mass) and gender. Low-mass subjects did not consistently have higher bone mineral density at all levels of the cervical column. Bone mineral were higher (259 ± 6 mg/cc) for females than males (247 ± 8 mg/cc); for the entire ensemble the mean density was 253 ± 9 mg/cc. Altered strength of cervical vertebrae coupled with the increased mobility of the disc at the inferior levels of the neck may explain regional biomechanical differences and subsequent physiologic effects secondary to aging. This study quantifies BMD of the human neck vertebrae and offers explanations to the biomechanical behaviors of the human cervical spine.
Modulation Frequency Analysis of 1-D Semi-Transparent Medium
Authors: Boulanger Joan , Charette Andre´ , Liu Fengshan
Published: April 2008

Frequency analysis is an interesting alternative to the full transient optical probing due to its relatively simpler frame of investigation. Both frequency analysis and the full transient probing are superior to the steady-state tomography because of more information gathered per measurement point. The study of the systematic response of a semi-transparent slab to a harmonic excitation through a power modulated laser is therefore of interest and is conducted to investigate its optical properties using an accurate algorithm to solve the Radiative Transfer Equation in the frequency domain. It is found that a semi-transparent slab behaves like a low-pass filter for the power modulated light and this behaviour is mainly controlled by the scattering events occurring on the light path (dispersion). The results found are consistent with those in the literature obtained from experiments or simpler analysis models.
Study on Unstable Brittle Crack Arrest Toughness of Extremely-Low Carbon Bainitic Steel Plates
Authors: Handa Tsunehisa , Kubo Takahiro , Amano Keniti , Okatsu Mitsuhiro , Miyamoto Kazunori , Satoh Michio
Published: April 2008

The extremely-low carbon bainitic steel (ELCB steel) is a high strength steel with about 0.02 mass% or less carbon. In this research, unstable brittle crack arrest toughness of ELCB steel plates was investigated by temperature-gradient ESSO tests, compared with that of conventional TMCP steel plates. Both of ELCB and TMCP steel plates without pre-straining had sufficient crack-arrest toughness at 0°C. After 10% prestraining, the TMCP steel plate had not sufficient crack-arrest toughness at 0 °C . The ELCB steel plates, however, maintained high crack arrest toughness at 0°C. even after 10% pre-straining. ELCB steel were also different from TMCP steels in the correlation between transition temperature of crack arrest toughness and fracture appearance transition temperature (vTrs) obtained by Charpy impact test. When the vTrs of an ELCB steel and that of a TMCP steel were the same value, crack arrest toughness of an ELCB steel was higher than that of a TMCP steel. In the cross section of the ESSO test piece of the ELCB steels, many sub-cracks and micro-crack branching were observed. However, in the cross section of the ESSO test piece of the conventional TMCP steels, there were few subcracks and branching. Initiation of sub-cracks and branching around the main crack tip reduces the stress intensity factor of the main crack. It was considered that the above features of the ELCB steel were caused by initiation of sub-cracks and branching at the tip of the main brittle crack.
Measurement of Stress/Charge Coefficients of a Thin Polyvinylidene Fluoride Film
Authors: Zahui Marcellin
Published: April 2008

An experimental/analytical approach is used to detemine the piezoelectric coefficients of PolyVinyliDene Fluoride (PDVF). PVDF manufacturers usually publish the values of the charge coefficients in the 1 or 3 directions of the piezoelectric film. However; some applications, such as the use of volume displacement sensors for vibrating plates in active noise control, require the knowledge of the PVDF charge coefficients in the 2 direction. The objective of this work is to determine experimentally and numerically the stress/charge coefficient of a PVDF film in the 2 direction. The method is based on volume displacement measurement of a vibrating beam. Two PVDF volume displacement sensors are fabricated with two different piezoelectric 1 and 2 directions respectively. An accelerometer is used to measure the volume displacement of the vibrating beam. The values are compared with the output charge of the PVDF sensors to determine the unknown stress/charge coefficient. Results obtained at room temperature are presented and compare favorably with existing similar data.
Numerical Investigation of a Transient Operation of a Heat Pipe With Experimental Validation
Authors: Gutierrez Gustavo , Catan˜o Juan , Jen Tien-Chien
Published: April 2008

In this paper, a full transient analysis of the performance of a heat pipe with a wick structure is performed. For the vapor flow, the conventional Navier-Stokes equations are used. For the liquid flow in the wick structure, which is modeled as a porous media, volume averaged Navier-Stokes equation are adopted. The energy equation is solved for the solid wall and wick structure of the heat pipe. The energy and momentum equations are coupled through the heat flux at the liquid-vapor interface that defines the suction and blowing velocities for the liquid and vapor flow. The evolution of the vapor-liquid interface temperature is coupled through the heat flux at this interface that defines the mass flux to the vapor and the new saturation conditions to maintain a fully saturation vapor all the time. A control volume approach is used in the development of the numerical scheme. A parametric study is conducted to study the effect of different parameters that affect the thermal performance of the heat pipe. And experimental setup is developed and numerical results are validated with experimental data. The results of this study will be useful for the heat pipe design and implementation in processes that are essentially transient and steady state conditions are not reached like for example drilling applications.
The Effects of Post-Weld Cold Working Processes on the Fatigue Strength of Low Carbon Steel Resistance Spot Welds
Authors: Spitsen R. , Kim D. , Flinn B. , Ramulu M. , Easterbrook E. T.
Published: April 2008

The investigation on the use of a post-weld cold working process to improve fatigue strength of low carbon steel resistance spot welds is presented. The cold working process generates uniform and consistent large zones of compressive residual stresses in resistance spot-welded low carbon steel structures using a specially designed indentation device. The effect of the indentation process parameters on the mechanical properties of the resistance spot-weld was investigated. Comparisons of the mechanical properties and qualitative results between the as-resistance spot-welded specimens and the post-weld cold worked resistance spot-welded specimens have been made in this investigation. Fatigue testing was also conducted to evaluate the effect of post-weld cold working process on the fatigue characteristics of resistance spot welds. Preliminary results showed that a significant improvement in the fatigue endurance limit has been achieved through the post-weld cold working process.
Improved Sensor Data Utility Through Receptance Coupling Modeling
Authors: Schmitz Tony L.
Published: April 2008

This paper describes compensation for scaling and frequency distortion errors arising from non-ideal sensor placement on mechanical structures. The mathematical approach is based on receptance coupling techniques for assembly dynamics prediction and offers a hybrid method where measured and modeled component frequency response functions, or receptances, are analytically coupled using rigid, flexible, or flexible/damped compatibility conditions to predict the assembly response at any spatial location. This method offers an alternative to existing finite element analysis packages that can accurately describe natural frequencies and mode shapes, but are generally less successful at predicting properly-scaled assembly dynamic responses. The ability to accurately predict assembly dynamics allows sensor data recorded at one location on the structure to be compensted for the structural dynamics between the measurement point and actual location of interest. Additionally, knowledge of the response at any location on the structure enables mode shape prediction and, therefore, selection of high signal-to-noise ratio sensor locations.
An Experimental Investigation of a High Flux Heat Pipe Heat Sink
Authors: Ma H. B. , Lofgreen K. P. , Peterson G. P.
Published: April 2008

An experimental investigation on a highly efficient heat pipe heat sink was investigated, in which the interline region was optimized using sintered particles. The effects of condenser size, sintered particles, and forced air flow on the heat transfer performance were investigated experimentally. The experimental results indicated that the thin film evaporation could significantly increase the evaporating heat transfer coefficient and remove heat fluxes up to 800 kW/m2. In addition, a theoretical model capable of predicting the temperature drop occurring in the device was developed. The predicted performance was in good agreement with the experimental data. The resulting model can be used to assist in the design of high heat flux, heat pipe heat sinks for applications to both ground based and spacecraft applications.
Modeling Stable and Unstable Crack Growth Observed in Quasi-Static Adhesively Bonded Beam Tests
Authors: Kapania Rakesh K. , Makhecha Dhaval P. , Johnson Eric R. , Simon Josh , Dillard David A.
Published: April 2008

An experimental and computational study of an adhesively bonded, double cantilevered beam (DCB) under quasi-static loading is presented. The polymeric adhesives are either an acrylic or an epoxy, and the adherends are 6061 aluminum alloy. DCB tests bonded with the acrylic exhibited stable crack growth, while the DCB tests bonded with the epoxy exhibited unstable crack growth. The responses of the DCB test speciments were modeled in the ABAQUS/Standard® software package. Interface finite elements were located between bulk elements to model crack initiation and crack growth in the adhesive. These interface elements are implemented as user-defined elements in ABAQUS®, and the material law relating the interfacial tractions to the separation displacements is based on a cohesive zone model (CZM). Using interface elements only to model the acrylic adhesive, the simulation correlates very well to the test. Good correlation between the simulation and the test for the epoxy adhesive is achieved if both bulk modeling of the adhesive and inertia of the specimen are included.