bluuebunny/crossref_metadata_2025 huggingface dataset:
A Co-Reduction Process for Plating Ionic Polymer Transducers With Precious and Non-Precious Metal Electrodes
Authors: Bennett Matthew D. , Leo Donald J.
Published: May 2008

A co-reduction process is developed for plating ionic polymer materials with precious and non-precious metal electrodes. The purpose is to develop a process that reduces the use of expensive precious metals such as platinum and gold in the development of ionic polymer transducers. Previous results by Bennett and Leo (1) have demonstrated that oxidation is the key issue associated with the use of non-precious metal electrodes. The present work overcomes this problem through the use of a co-reduction process in which an alloy of platinum and copper is deposited in an impregnation/reduction process. A thin (~50 nm) layer of gold is then deposited to increase the surface conductivity of the electrode. Actuators developed using this process are tested for longevity for approximately 250,000 cycles. The results demonstrate the stability of the electrode, although multiple tests reveal that variations in the process produce variations in the electrode stability.
Modeling of Electromechanical Transduction in Ionic Polymer Materials
Authors: Newbury Kenneth , Leo Donald J.
Published: May 2008

A coupled, linear electromechanical model is developed for ionic polymer transducers. The model is based on the linear equations for a piezoelectric material. Integrating the equations over the geometry of the transducer produces a model of the electromechanical coupling of the polymer transducers as a function of fundamental material parameters and geometry. Explicit modeling of electromechanical coupling produces a model that is useful for analyzing sensing or actuation using ionic polymer transducers. Experiments on polymer samples verify the scaling of the model parameters as a function of sample length and width. The results also demonstrate the reciprocity of the electromechanical coupling. The symmetric model is expressed as a linear transformer which can be incorporated into system-level models for design of devices that utilize ionic polymer materials. The model is limited to linear operation at low-voltage with constant levels of material hydration.
Buckling Induced Nonlinear Phenomenon in a Micro-Electromechanical Resonator
Authors: Li He , Balachandran B.
Published: May 2008

Oscillations of micro-electromechanical resonators constructed from clamped-clamped beam structures are studied in this effort. Piezoelectric actuation is used to excite these structures on the input side and piezoelectric sensing is carried out on the output side. Although axial loads in clamped-clamped beam based on micro-electromechanical systems (MEMS) have been considered before, the relevance of buckling to this problem has not studied before in such “small” scale systems. In this work, possibilities for buckling are examined, and it is shown that for resonance excitations, consideration of buckling may help explain associated experimentally observed spatial patterns as a nonlinear phenomenon.
Independent Modal Sliding Mode Shape and Vibration Control Using a Stereophotogrammetric Measurement System
Authors: Manthram Sivasubramaniam , Washington Gregory N.
Published: May 2008

The last decade has seen the advent of active aperture antennas and other large distributed parameter systems. These antennas have the capability to change their shape to resemble a desired radiation pattern. In this study a method to simultaneously achieve active shape and vibration control of distributed parameter systems is presented. The optimal actuator location is computed for a desired profile using non-linear optimal programming techniques. For most shape control applications the actuator and sensor dynamics are much faster than the structural dynamics and slow shape changes are sufficient, thus quasi-static analysis is sufficient. The quasi-static actuation forces for the desired profile are then calculated by using independent modal space control (IMSC) principles. Quasi-static shape control is then implemented in a closed loop control using a 3-D photogrammetry sensing system. A sliding mode controller is designed for each dominant mode such that it drives the error between the required and actual modal contribution to zero. Conventional sliding mode controllers are discontinuous in nature and they might cause “control spillover”. This is avoided by using an “observer-based” solution.
Embedded-Ultrasonics Structural Radar for Nondestructive Evaluation of Thin-Wall Structures
Authors: Giurgiutiu Victor , Bao Jingjing
Published: May 2008

Embedded-Ultrasonics Structural Radar (EUSR) is a new concept and methodology for in-situ nondestructive evaluation (NDE) of thin-wall structures. EUSR utilizes (a) a Piezo Wafer Active Sensors (PWAS) array embedded onto the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. The EUSR methodology is developed as an extension of our previous work on the Lamb wave propagation NDE. Based on the study of the Lamb wave characteristic, the excitation signal is optimized to obtain good signal to noise ratio. Lamb wave speed-frequency curve is plotted to obtain the wave speed of the excitation signal. This wave speed is then used to map the EUSR data from time domain to distance domain, thus the locations of the reflectors can be visually displayed. The EUSR algorithm is adopted from the beamforming process currently used in phased-array radar applications. Each element in the PWAS array plays the role of both transmitter and receiver. A circuit is designed to change the role of the PWAS in a round robin fashion. The responses of the structure to all the excitation signals are collected. By applying the EUSR algorithm, an appropriate delay is applied to each signal in the data set to make them all focus on a direction denoted by angle φ. When this angle φ is changed from 0 to 180 degrees, a virtual scanning beam is formed and a large area of the structure can be interrogated. The EUSR algorithm is explained in this paper. Experimental results from a proof-of-concept EUSR system are also presented.
Positive Position Feedback Vibration Control of a Composite I-Beam With Fuzzy Gain Tuning
Authors: Gu H. , Song G.
Published: May 2008

Positive position feedback (PPF) control is widely used in active vibration control of flexible structures. To ensure the vibration is quickly suppressed, a large PPF scalar gain is often applied in a PPF controller. However, PPF control with a large scalar gain causes initial overshoot, which is undesirable in many situations. In this paper, a fuzzy gain tuner is proposed to tune the gain in the positive position feedback control to reduce the initial overshoot while still maintaining a quick vibration suppression. The fuzzy system is trained by the desired input-output data sets by batch least squares algorithm so that the trained fuzzy system can behave like the training data. A 3.35 meter long I-beam with piezoceramic patch sensors and actuators is used as the experimental object. The experiments include the standard PPF control, standard PPF control with traditional fuzzy gain tuning, and PPF control with batch least squares fuzzy gain tuning. Experimental results clearly demonstrate that PPF control with batch least squares fuzzy gain tuner behaves much better than the other two in terms of successfully reducing the initial overshoot and quickly suppressing vibration.
Pole Placement Control of a Smart Flexible Beam
Authors: Sethi V. , Song G.
Published: May 2008

This paper concerns active vibration control of a 3.35 meter long composite I-beam that is used in civil structures in a cantilevered configuration by using peizoceramics materials, in particular the PZT (Lead Zirconate Titanate), in the form of patches. These PZT patches are surface-bonded on the I-beam and perform as actuators and sensors. A real-time data acquisition and control system is used to record the experimental data and to implement controllers. To assist control system design, open loop testing and system identification are conducted. A Pole Placement controller is designed and is simulated using the identified model. Simulations show the dramatic increase in damping of the beams which when implemented experimentally corroborates the simulation results. Experimental results verify the simulated results and demonstrate the effectiveness of active control of a civil structure using smart materials.
Optimal Design of a Smart Conformable Rotor Airfoil
Authors: Sarjeant Roberto A. , Frecker Mary , Gandhi Farhan S.
Published: May 2008

An optimization method has been developed for the design of a smart conformable rotor airfoil with distributed piezoelectric actuators. A conformable airfoil is proposed as a substitute for trailing edge flaps used for helicopter vibration reduction by achieving high frequency camber variations. A topology optimization approach is used where the objective is to maximize trailing edge deflection while minimizing airfoil deformations due to aerodynamic loads. Solutions of the design problem are obtained using Sequential Linear Programming coupled with a Finite Element Analysis procedure. Results show good algorithm convergence and satisfactory airfoil deformations. A study of the effects of different active material resources, skin thickness and aerodynamic loads is performed. Changes in lift coefficient are found to be lower than those obtained for an equivalent flap at similar deflection angles, suggesting that larger deflections might be required for vibration reduction purposes.
Parametric Study and Experimental Correlation of an SMA Based Damping and Passive Vibration Isolation Device
Authors: Lagoudas Dimitris C. , Khan Mughees M. , Mayes John J. , Henderson Benjamin K.
Published: May 2008

In this work, the effect of pseudoelastic response of shape memory alloys (SMAs) on damping and passive vibration isolation will be presented. This study has been conducted by developing and utilizing a shape memory alloy (SMA) model (a physically based SMA model) to perform extensive parametric studies on a non-linear hysteretic dynamic system, representing an actual SMA damping and passive vibration isolation prototype device. The prototype device consists of SMA tubes undergoing pseudoelastic transformations under transverse loading. To accurately model the non-linear hysteretic response of SMA tubes present in the prototype device, a Preisach model (an empirical model based on system identification) has also been modified to simulate the response of the prototype device. Both the simplified SMA model and the Preisach model have been utilized to perform experimental correlations with the results obtained from actual testing of the prototype device. The investigations show that variable damping and tunable isolation response are major benefits of SMA pseudoelasticity. Correlation of numerical simulations and experimental results has shown that large amplitude displacements causing phase transformations of SMA components are necessary for an SMA based vibration isolation device to be effective in reducing the transmissibility of a dynamic system. It has also been shown that SMA based devices can overcome performance trade-offs inherent in a typical softening spring-damper vibration isolation system. In terms of modeling, the Preisach model gave relatively accurate results due to close proximity in predicting actual SMA component behavior. However, for a generic parametric study, the simplified SMA model has been found to be more useful as it is motivated from the constitutive response of SMAs and hence, could easily incorporate different changes in system conditions.
Electrically Controllable Deformations in Ionic Polymer Metal Composite Actuators
Authors: Shahinpoor Mohsen
Published: May 2008

Ionic polymer metal composites (IPMC’s) exhibit spectacular coupling between electrical and mechanical domains. Sensing and actuation properties of these materials and the force and displacement characteristics have been investigated as a means of determining the electromechanical coupling coefficients of the material. An electric field applied across the thickness of the polymer causes electrophoretic ionic migration within the material. Electro-osmotic drag induces solvent migration in addition to the ion motion, and a stress is generated within the material causing the material to deform. This phenomenon is also reversible, making it possible to use ionic polymer materials as sensors, transducers and power generators. The salient feature of ionic polymeric materials, as compared to other electromechanical transducers such as piezoelectrics, is the large deformations that are achievable with low electric fields. Cantilever samples of ionic polymer material exhibit tip displacements on the order of their length with applied electric fields of the order of 10 volts per mm. Recent measurements of the motion of cantilever samples of ionic polymers have demonstrated a controllable, repeatable deformation in which the zero force position of the ionic polymer changes depending on the amplitude of the applied electric field. This effect appears to be controllable in the sense that the change in the zero force position of the polymer is a function of the amplitude of the applied electric field. It is also reversible to a degree because a step change in the voltage with the opposite polarity will change the shape of the ionic polymer strip back to a position that is close to the original position before cycling of the material. Thus, there is a potential to use this effect as a deformation memory mechanism within the polymer material. These observations and subsequent interpretations are reported in this presentation.
Trace Gas Adsorption Within Gas-Sorbent Suspensions in the Presence of O2 and Water Vapor
Authors: Narasimhan Uttam , Clack Herek L.
Published: May 2008

New federal regulations will soon limit total mercury emissions from coal-fired electric power plants, which supply half of the electric power and are responsible for one-third of the anthropogenic mercury emissions in the U.S [1]. This presents a significant challenge to the electric power industry because of variability in mercury concentration and speciation (both within a single facility and between different facilities) and a lack of proven continuous emissions monitor (CEM) and mercury control technologies. Although wet flue gas desulfurization (WFGD) has demonstrated effectiveness in removing oxidized forms of mercury (Hg2+, nominally in the form HgCl2), elemental mercury (Hg0) generally passes unaffected through such processes.
Vegetable Oils as Fuel for Diesel Engines: An Overview
Authors: Babu A. K. , Devaradjane G.
Published: May 2008

The intent of this paper is to summarize the state of knowledge on use of vegetable oils as diesel fuels. Fuel related properties are reviewed and compared with conventional diesel fuel. The use of neat vegetable oil (edible and/or nonedible), biodiesel and its blends in a diesel engine has been discussed. Performance and emission characteristics are highlighted. Suitability of different combustion chambers for diesel engine operation with vegetable oils is outlined. Techniques to decrease viscosities are discussed. An overview on current developments on the use of vegetable oils directly and indirectly in diesel engines is presented.
Effect of Engine Variables on Combustion Performance of Lean Burn Spark Ignition Engine: An Overview
Authors: Manivannan A. , Ramprabhu R.
Published: May 2008

In the development of internal combustion engines, there has been a continuous effort to reduce fuel consumption and exhaust emissions. Lean combustion is a preferred concept for reducing exhaust emissions for meeting stringent emission standards. However lean combustion is associated with increased cycle-by-cycle combustion variation due to combustion instability. The combustion stability under lean mixture conditions could be improved through enhancement of flow characteristics. Effect of engine variables on lean combustion of Spark Ignition (SI) engine is presented, including combustion chamber and inlet port configuration, and ignition system. Use of pre-chamber for lean combustion is one of the feasible method to achieve stable ignition and quick flame propagation. This paper highlights and compares status of various research works carried out in the area of lean burn engines. A critical analysis of reported experimental data is presented in order to substantiate use of lean combustion in SI engine.
Real-Time Monitoring of Dynamical State Changes in Staged Combustion
Authors: Daw C. S. , Finney C. E. A. , Bailey R. T. , Flynn T. J. , Fuller T. A.
Published: May 2008

We describe techniques for diagnosing the state of coal-fired utility burners using dynamic characteristics of the output of optical flame scanner signals. The analysis techniques are optimized for targeting dynamical features associated with nonlinear instabilities that develop as burner operating parameters are changed. Various specific instability indicators are used, including shifts in probability distributions, temporal asymmetry and coarsed-grained descriptions of unstable periodicities. We show that careful application of such methods can accurately characterize a range of different flame states. Specifically, transitions through bifurcation points between attached and lifted flames are targeted, giving insight into causes of instability such as stoichiometry or feed and flow variations. We demonstrate results from the application of these methods to utility-scale staged pulverized-coal burners in a real-time software package. The Flame Doctor™ burner-monitoring software is presently undergoing plant-implementation trials in a program sponsored by the Electric Power Research Institute and participating utilities. In a practical application, we show how real-time monitoring and intervention can significantly mitigate adverse combustion conditions.
Control of Nonpremixed Flames Using Microjets
Authors: Ganguly R. , Mukhopadhyay A. , Puri I. K.
Published: May 2008

Control of the shape of a non-premixed flame in a quiescent environment by injection of a high-velocity central micro-jet has been investigated experimentally. The flame height and shape change significantly as the central co-flow micro-jet is introduced. The flame also becomes free from the buoyancy-induced flickering. We hypothesize that the narrow, strong central jet enhances the entrainment of the surrounding air leading to a larger oxidizer influx and results in a reduction of soot emission.
Effect of Microgravity on Laminar Diffusion Flames
Authors: Ganguly R. , Mukhopadhyay A. , Datta A.
Published: May 2008

A numerical model has been developed to predict the effect of microgravity on a laminar diffusion flame. Transition of the flame from 1-g to the zero-g condition is also studied. Results show that the flame, upon sudden withdrawal of gravity, require some relaxation-time before attaining a steady state profile characterized by a larger width and almost unchanged height.
Simulation and Analysis of Combustion and Heat Transfer in Low Heat Rejection Diesel Engine Using Two Zone Combustion Model and Different Heat Transfer Models
Authors: Tamilporai P. , Chandrasekaran S. , Baluswamy N.
Published: May 2008

The quest for increasing the efficiency of internal combustion engines has been going on ever since the invention of this reliable workhorse. In recent times much attention has been focused on achieving higher thermal efficiency by reducing the heat loss to the surroundings by the application of “Low heat rejection” concept using ceramic coating for engine components or ceramic components itself. In this direction, the present analysis focused towards the formulation and development of a two-zone combustion model for the prediction of combustion, heat release and performance of the conventional and low heat rejection engines.
Photographic Study of Orientation Effects on Near-Saturated Flow Boiling
Authors: Zhang Hui , Mudawar Issam , Hassan Mohammad M.
Published: May 2008

Experiments were performed to examine the effects of body force on flow boiling CHF. FC-72 was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface just prior to CHF. High-speed video imaging techniques were used to identify dominant CHF mechanisms. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed significant sensitivity to orientation for flow velocities under 0.2 m/s, where extremely low CHF values where measured, especially with a downward-facing heated wall and downflow orientations. High flow velocities dampened the effects of orientation considerably. The CHF data were used to assess the suitability of previous CHF models and correlations for different orientations and velocities. It is shown the Interfacial Lift-off Model is very effective at predicting CHF for high velocities at all orientations. The flooding limit, on the other hand, is useful at estimating CHF at low velocities and downflow orientations.
An Experimental Study of Microscopic Explosive Boiling Induced by Pulsed-Laser Irradiation
Authors: Huai Xiulan , Dong Zhaoyi , Liu Dengying , Wang G.-X.
Published: May 2008

Microscopic explosive boiling due to rapid heating has found many applications in modern technologies such as thermal ink jet printing, laser cleaning, and laser surgery. It is a nonequilibrium process involving an extremely high liquid superheating. This paper presents an experimental study of such an explosive vaporization process induced by firing a microsecond pulsed laser beam on a thin Pt film deposited on a quartz substrate. The temperature variation of the Pt film is measured by recording the electric resistance of the film during laser heating and subsequent cooling. A high-speed photographic technique is employed to visualize the bubble formation and the explosive evaporation process. Explosive boiling experiments have been carried out in either a pool of acetone liquid or a thin acetone film covering the Pt film. The heating rate achieved ranges from 8.0×106 K/s to 9.0×107 K/s. Violent explosive boiling was observed in the case of a liquid film and the vapor bubbles together with liquid droplets were expelled from the Pt film. While in the case of a liquid pool, only a large cluster of bubbles was formed on the Pt film during laser heating. A close examination of the temperature curves reveals a sudden reduction in the heating rate during laser heating, and an apparent bubble nucleation temperature can be defined. Experimental data show that this apparent bubble nucleation temperature is a strong function of the heating rate. It is close to the equilibrium boiling point at low heating rates while approaches the homogeneous nucleation temperature at high heating rates.
Hybrid Neural Network-First Principles Modeling of Critical Heat Flux in a Thin Annular Channel
Authors: Xie T. , Ghiaasiaan S. M. , Karrila S. , McDonough T.
Published: May 2008

The hybrid artificial neural network-first principle modeling (ANN-FPM) is a powerful and flexible methodology that can be particularly useful for complex multi-phase flow processes. In this method the flow state variables are obtained from the solution of conservative equations using first principle-based closure relations whenever possible, and using trained artificial neural networks for poorly-understood rate processes. The ANN-FPM methodology is applied to a set of experimental data representing critical heat flux in a uniformly heated horizontal annular test section cooled with water. The first principle method is based on numerical solution of one-dimensional two-phase equilibrium conservation equations with velocity slip represented by an algebraic slip ratio correlation. The critical heat flux is predicted using trained neural networks that use local hydrodynamic parameters estimated by the first principle method. It is shown that the methodology works well for the studied data.
A Simplified Thermodynamic Analysis of a LiBr-H2O Vertical Tube Absorber
Authors: Rogdakis E. D. , Papaefthimiou V. D.
Published: May 2008

One of the most important components of an absorption air-conditioning/heat pump system is the absorber, where the refrigerant water vapour is absorbed into the liquid solution. While absorption systems have been in use for several years, the complex transport phenomena occurring in the absorber are not fully elucidated yet. Thus, an attempt is made to model the absorption process of water vapour in aqueous solutions of lithium bromide considering a falling-film, vertical-tube absorber. The proposed analysis is based on the formulation of four differential equations describing the spatial variation (parallel to the tube-axis) of solution mass, temperature, mass fraction and coolant temperature. The system of ordinary differential equations is numerically solved using a non-stiff numerical method. Thermophysical properties and especially, heat and mass transfer coefficients are calculated using widely-accepted and reliable relationships, which are extracted from the literature using recently published information on wavy-laminar flows. In the present study, the questionable assumption of treating the water vapour as an ideal gas is heavily modified utilizing. Consequently, the hypothesis of saturated water vapour at the steam-solution interaction surface is revised by introducing an energy difference between the superheated steam and the liquid water within the binary solution. The last correction encouraged us to compare theoretical results for solution temperature, mass fraction and mass flow rate, which were obtained using both assumptions. It was proved that the initial treatment causes an underestimation of the absorbed steam mass and correspondingly, an underestimation of solution temperature and mass fraction at the mass exchange interface. An attempt is made also to identify the effect of mass transfer coefficient on the effectiveness of the absorption process and on the energy differences between the superheated steam and the liquid water either as pure substance or as component of the binary mixture. It was shown that the increase of mass transfer coefficient leads to an increase of steam mass transfer rate and to a corresponding decrease of solution temperature slope at the entrance of a tube. Correspondingly, the increase of mass transfer coefficient results in an increase of heat of absorption and heat of dilution at the same variation range of the solution mass fraction.
Slow Passage Through Resonance in Mathieu’s Equation
Authors: Ng Leslie , Rand Richard , O’Neil Michael
Published: May 2008

We investigate slow passage through the 2:1 resonance tongue in Mathieu’s equation. Using numerical integration, we find that amplification or de-amplification can occur. The amount of amplification (or de-amplification) depends on the speed travelling through the tongue and the initial conditions. We use the method of multiple scales to obtain a slow flow approximation. The WKB method is then applied to the slow flow equations to get an analytic approximation.
Periodic Behavior of a Nonlinear Third Order Vibrating System
Authors: Jazar Gholamreza Nakhaie , Alimi Mohammad H. , Mahinfalah Mohammad , Khazaei Ali
Published: May 2008

In modeling of dynamical systems, differential equations, either ordinary or partial, are a common outcome of the modeling process. The basic problem becomes the existence of solution of these deferential equations. In the early days of the solution of deferential equations at the beginning of the eighteenth century the methods for determining the existence of nontrivial solution were so limited and developed very much on an ad hoc basis. Most of the efforts on dynamical system are related to the second order systems, derived by applying Newton equation of motion to dynamical systems. But, behavior of some dynamical systems is governed by equations falling down in the general nonlinear third order differential equation x″′+f(t,x,x′,x″)=0, sometimes as a result of combination of a first and a second order system. It is shown in this paper that these equations could have nontrivial solutions, if x, x′, x″, and f(t,x,x′,x″) are bounded. Furthermore, it is shown that the third order differential equation has a τ-periodic solution if f(t,x,x′,x″) is an even function with respect to x′. For this purpose, the concept of Green’s function and the Schauder’s fixed-point theorem has been used.
Computer Simulation of the Response of a Railway Vehicle Carbody
Authors: Kumar M. Senthil , Jawahar P. M.
Published: May 2008

In this paper, a nonlinear mathematical model has been constructed by deriving the equations of motion of a Rail Vehicle carbody using Newton’s law. The nonlinear formula is used to evaluate the wheel rail contact forces. The nonlinear profile of wheel and rail are taken into account. Also the lateral stiffness of the track is taken into consideration. The equations of motion are derived for (a) Carbody with conventional wheelset (b) Carbody with unconventional wheelset (independently rotating wheels). For lateral vibration, 17 degrees of freedom are considered. The degrees of freedom represent lateral and yaw movements of 4 wheelsets and lateral, yaw and roll movements of the bogie and carbody. These equations of motion are transformed into a form suitable for numerical differential equation by Runge Kutta method. In the interest of computing economy, certain approximations have been introduced for calculating the creep forces. Sample results are given for a model of a typical railway vehicle used by the Indian Railways. The lateral dynamic response of the railway vehicle carbody for both conventional and unconventional wheelset has been analysed.
Development and Experimental Evaluation of a Vehicle Rear Suspension Vibration Model
Authors: Sung Shung H. , Nefske Donald J. , Feldmaier Douglas A. , Doggett Spencer J.
Published: May 2008

A finite-element model of a vehicle rear suspension is developed and experimentally evaluated for predicting the vibration response of the rear suspension to 300 Hz. The suspension model is developed from ten major component finite-element models that were individually correlated to 300 Hz prior to assembly. The bushing and isolator connections between the components are represented using measured dynamic stiffness and damping rates, and a modal tire model is used to represent the tire-wheel assembly. Shaker excitation tests were conducted with the rear suspension supported in a specially designed test fixture to obtain the measured vibration response of the suspension. Comparisons are made of the predicted and measured frequency response functions (FRFs) and modes to experimentally assess the accuracy of the suspension model to 300 Hz. The accuracy of a traditional rigid-link rear suspension model is also assessed.
An Accurate Incremental Bekker Equation for Computational Tire-Soil Modeling
Authors: Han Ray P. S. , Mao S. G.
Published: May 2008

In this paper, an accurate computational model for analyzing tire-soil interaction is presented. In the traditional approach, Bekker equation is written in a global form and a quasi-static analysis is done to iteratively model the interaction of the tire and soil. This is due to the nonlinear relationship between soil sinkage and pressure and the unknown loading and unloading status of soil as they are dependent on past loading histories. In this work, an incremental form of Bekker model is proposed. The resulting tire-soil interaction problem is described by a set of nonlinear complementarity equations, which are easier to solve compared to the iterative approach required in the traditional Bekker model. Two numerical examples are presented to demonstrate the effectiveness of the algorithm presented in this work.
Detecting Backlash and Crack in Torsional Vibration of a Gear Train System
Authors: Ghassabzadeh Saryazdi M. , Ghaffari Saadat M. H.
Published: May 2008

Torsional vibration of a two-stage gear train system is investigated, considering backlash and crack. Two criteria are used to detect backlash and crack for the purpose of vibration monitoring. A discretized model is considered which consists of a servomotor, a two-stage gearbox and a brake. It is shown that second moment of acceleration increases, increasing backlash. Kurtosis number diagnoses the tooth crack. Abrupt change in Kurtosis number shows that crack has been developed.
Investigations on the Behavior of the Body in Response to Vertical Vibration
Authors: Hoviattalab Maryam , Varziri Mohammad S.
Published: May 2008

In this paper a lumped mass model was used to simulate the behavior of the human body during vertical vibration. Force method has been used to obtain the differential equations of the model, which were solved using simulink toolbox of Matlab software the appropriate damping and stiffness coefficients of shoes were chosen by comparing the results with the experimental data. The model has been used to produce a useful package, which has various abilities. We obtained the kinematics characteristics for each links of the model, in response of sine wave stimulation. This package has also the ability of comparing results by changing the damping and stiffness coefficients for the contact point (shoe) of the model. One of the important specifications of this package is its flexibility. With a little change in the codes of the program we can obtain the curves in response of other kinds of stimulations like noises and pulses.
Mathematical and Experimental Investigation of Liquid-Gas Interfaces in Porous Wicks
Authors: Yang Yuelei , Gerner Frank M. , Henderson H. Thurman
Published: May 2008

This paper focuses on the investigation of the liquid-gas (or vapor) interface, which occurs in very small diameter pores. A mathematical model is built to formulate the movements of a liquid column trapped in a capillary pore. The Navier-Stokes equations are applied to the liquid side with assumed no-slip conditions, while the Young-Laplace equation is used to formulate the shape of the interface. This theoretical model calculates both velocity profiles in the liquid side and transient profiles of the interface itself; and of particular interest, it predicts the pressure difference, oscillation frequency and amplitude required to burst this interface. These predicted parameters are examined by the experiments with both oscillating Coherent Porous Silicon (CPS) wicks and porous plastic wicks. This research helps better understanding the phenomena such as multiphase flow in porous media or de-watering process that happens in vibro-separators.
Enhancing the Power Handling Capacity of Micro Mirrors: An Experimental and Numerical Investigation
Authors: Shao D. , Panchawagh H. , Mahajan R. L.
Published: May 2008

In this paper we present three techniques to improve optical power handling capacity of micro-mirrors: (a) improving flexure conduction, (b) improving reflectivity of micro-mirrors and (c) using silicon carbide as MEMS structural material. Mirrors fabricated in Multi-User MEMS Processes (MUMPs) are used as prototype models. It is shown numerically that these three techniques can improve the power handling capacity of the mirrors by factors of 1.25, 4–13 and 7 respectively. Further enhancement can be achieved by using the combination of these methods. Numerical work in this paper was done using Coventorware® while experiments were carried out using an 808 nm center wavelength laser diode with maximum power of 1 W.
The Connection Between Microstructural Damage Modeling and Continuum Damage Modeling for Eutectic Sn-Pb Solder Alloys
Authors: Sharma Pradeep , Dasgupta Abhijit
Published: May 2008

Researchers resort to a wide range of simplified representations at the continuum scale, to model creep-fatigue damage in viscoplastic heterogeneous materials such as Sn-Pb eutectic solders, caused by thermo-mechanical and mechanical cyclic loading (e.g. due to power cycling, environmental temperature cycling, vibration, etc). Typically, in macroscale phenomenological damage models, the cyclic damage is assumed to depend on some loading parameter such as cyclic strain range, work dissipation per cycle, partitioned strain range, partitioned work dissipation per cycle, cyclic entropy changes, cyclic stress range, integrated matrix creep, etc. In many instances, some of these variables are weighted with a factor to account for rate-dependent effects. The task of finding the best damage metric is difficult because of complex microstructural interactions between cyclic creep and cyclic plasticity due to the high homologous temperature under operating conditions. In this study we use insights obtained from microstructural and more mechanistic modeling to identify the most appropriate macro-scale damage metrics. The microstructural models are based on such phenomena as grain boundary sliding, blocking of grain boundary sliding by second-phase particles, grain boundary, volumetric and surface diffusion, void nucleation, void growth and plastic collapse of cavitating grain boundaries. As has been demonstrated in the literature, microstructural models suggest that fatigue damage caused by cyclic plasticity should correlate well with the two most commonly used damage indicators: both cyclic strain range and plastic work dissipation per cycle. This study, however, demonstrates that in the case of damage dominated by cyclic creep, microstructural models developed by the authors indicate closer correlation with creep work dissipation per cycle, than with cyclic creep strain range.
Constitutive Model for Sn-Pb Solder Under Fatigue Loading
Authors: Wei Y. , Chow C. L. , Nielsen M. K. , Fang H. E.
Published: May 2008

The paper presents a constitutive model for Sn-Pb solder which captures the response of this complex material subject to a variety of load paths including fatigue loading. Internal state variables are established to characterize grain coarsening and material degradation observed experimentally. A damage-coupled viscoplastic constitutive model is formulated to take into account the effects of temperature and loading rates on mechanical response. The influence of fatigue loading frequency or strain rate, hold time and temperature on mechanical behavior and fatigue life for 63Sn-37Pb solder alloy is examined. The fatigue failure predictions are compared with those obtained experimentally and found to be satisfactory.
A Finite Element Analysis of Void Evolution in 2-D Machining
Authors: Cao Q. , Ee K. C. , Dillon O. W. , Jawahir I. S.
Published: May 2008

The objective of this paper is to study void evolution and its effects on material failure during the machining process. The influence of cutting conditions on void nucleation, growth and coalescence is studied. The ultimate goal of this approach, as applied to machining, is to predict chip breakage and surface conditions via damage mechanics. A damage mechanics model proposed by Komori [1] is chosen to study the evolution of the void volume fraction in the chip and workpiece being machined with a grooved tool. A Thomason [2] type criterion as modified by Dhar et al. [3], that uses the variables calculated by FEM analysis, is used to predict void coalescence (failure). The distribution of the variables, such as effective strain-rate, nondimensional hydrostatic stress, and effective strain are obtained using the FEM methodology described by Zhang [4]. It is found that void coalescence always occurs in the newly machined surface below the flank face of the tool and in the chip flowing around the chip-groove region near the upper end of the face land. On the other hand, whether void coalescence occurs inside the chip or not, depends on the complex interactions between the machining parameters and chip geometry.
Silicon Spaced Wafer Stack Thermoacoustic Refrigerator Design and Testing
Authors: Holmberg D. G. , Tsai S. Y. , Wo A. M.
Published: May 2008

The design of a new, small-scale thermoacoustic refrigerator stack and heat exchanger test platform is presented. A special silicon (Si) stack is fabricated to encourage anisotropic heat conduction — good heat conduction along the plane of the Si wafer (normal to the direction of acoustic propagation) and poor conduction across it (along the direction of acoustic propagation). This is accomplished by separating two wafer pieces with an insulator in between. The aim of this paper is to quantify the performance of this stack arrangement. The apparatus utilizes a modified piston engine with a motor running the piston (max 300 Hz) as an acoustic source. Comparison of results show that the a slight performance degradation for the Si stack compared with that of the ceramic stack. It is believed that advantages gain by suppressing heat conduction along the stack is offset by increased losses due to viscous effect and flow streaming within the Si stack.
Thermochemical Design of a Micro Liquid Monopropellant Rocket With Catalytic Reaction of Hydrogen Peroxide
Authors: Lee Dae Hoon , Kwon Sejin , Hwang Jin Soo , Park Sang-Eon
Published: May 2008

A theoretical and experimental investigation on a design of catalytic reactor of submilimeter scale to be used as a micro propulsion device is described. A micro reactor was fabricated on an aluminum plate and catalyst was prepared on the anodized internal surface of the reactor. The reactor has a height of 1mm and width of 10mm. The height of the reactor is the major constraint when a prototype device is to be fabricated on a wafer by MEMS processing. Thermodynamic properties of product gases from the decomposition process of hydrogen peroxide in contact with perovskite based redox cycling catalyst were measured. A theoretical model was developed to predict the heat and gaseous mass generated from the decomposition process of hydrogen peroxide by using asymptotic approximation of reacting flow in 1-D channel with height of 1mm or less in order to approximate the actual operating condition of propulsion device on a chip. The measured heat transfer coefficients and thermodynamic properties were used in the calculation. As the monopropellant decomposes into water and oxygen, the reaction products are heated. The enhanced heat loss due to the small size of the chamber, however, adversely affected the thermochemical process of decomposition.
Pressure Drop Characteristics of R134a Two-Phase Flow in a Horizontal Rectangular Microchannel
Authors: Tu X. , Hrnjak P.
Published: May 2008

Adiabatic two-phase flow pressure drop of R134a have been investigated experimentally in a rectangular channel with hydraulic diameter of 0.14 mm. Single-phase flow experiments were also conducted with liquid and vapor R134a, and an empirical correlation was developed for the turbulent flow regime. The parameter ranges examined for two-phase flow are: mass flux from 158 to 785 kg m−2 s−1; vapor quality from 0.01 to 0.95; and saturation temperature at about 24 ~ 32°C. The experimental data were compared with twelve existing correlations. The homogeneous model and the Mishima and Hibiki (1996) correlation give better predictions than any other correlations.
Evaporation, Condensation, and Flow in an Idealized Micro Heat Pipe
Authors: Zhang Jin , Wong Harris
Published: May 2008

Micro heat pipes have been used in cooling micro electronic components. However their effective thermal conductivity is low compared with that of conventional heat pipes. Due to the complexity of the coupled heat and mass transport, and to the complicated three-dimensional bubble geometry inside micro heat pipes, there is a lack of rigorous analysis. As a result, the relatively low effective thermal conductivity remains unexplained. We have conceptualized an idealized micro heat pipe that eliminates the complicated geometry, but retains the essential physics. Given the simplified geometry, many effects can be studied, such as thermocapillary flow, and evaporation and condensation physics. In this talk, we will present the flow field induced by evaporation.
Thermocapillary Effect in Heterogeneously-Formed Bubbles in Microsystems
Authors: Akbar M. K. , Chedester R. C. , Ghiaasiaan S. M.
Published: May 2008

Bubble nucleation and growth in microsystems, and in microchannels supporting subcooled nucleate boiling, occur within liquids with extremely large temperature gradients. Non-uniform bubble-liquid interfacial temperatures may occur, leading to important thermocapillary effects. This analytical investigation is an attempt to demonstrate the potential impact of the thermocapillary effects on heterogeneously-generated micro-bubbles. Quasi-steady bubbles occupying heated microtubes are first modeled. It is shown that the temperature of the liquid-vapor interphase in these bubbles can be non-uniform. This temperature non-uniformity increases with increasing the heat transfer rate, and depends on the microtube size. A method for the prediction of liquid-vapor interphase geometry resulting from non-uniform bubble surface temperature is developed. It is shown that the aforementioned bubbles can be distorted from spherical geometry rather significantly. Quasi-steady bubbles attached to a heated microchannel surface supporting subcooled nucleate boiling are also modeled. The bubble-liquid interfacial temperature distribution is estimated based on assuming equal evaporation and condensation mass fluxes at the bubble base and top, and using the simple gas kinetic theory methods. The result shows that the thermocapillary effect tends to slightly distort and elongate the bubbles in the direction perpendicular to the heated surface, and leads to a thermocapillary force that resists bubble detachment. The geometric distortion of the bubble leads to an increase in drag force in comparison with a chopped-spherical bubble with equal volume.
A Robust Semi-Active Tuned Vibration Absorber for Reducing Vibrations in Force-Excited Structures
Authors: Koo Jeong-Hoi , Ahmadian Mehdi , Setareh Mehdi , Murray Thomas M.
Published: May 2008

A passive TVA is only effective when it is tuned properly; otherwise, it can magnify the vibration levels. Often, inevitable off-tuning of a TVA occurs due to changes in the primary structure mass and stiffness for force-excited structural systems such as a floor. The main purpose of this study is to evaluate the robustness of semi-active groundhook TVAs to structure mass and stiffness off-tuning. In the case of floor systems, adding external mass to an existing floor, such as people and furniture, will increase the floor mass, and reduce the mass ratio. Theses changes result in off-tuning of the frequency ratio, which is defined by the ratio of the natural frequency of the TVA to the primary structure natural frequency. In order to study the effect of off-tuning, a force-excited equivalent model of a groundhook TVA is developed and its closed-form solutions are obtained for dynamic analysis of such systems. Moreover, the optimal design parameters of both passive and groundhook equivalent semiactive TVA models are obtained based on minimization of peak transmissibility. The two optimally tuned models are compared as the primary mass and primary structure stiffness changes. The results indicate that the peak transmissibility of the groundhook TVA is lower than that of passive, implying that the groundhook TVA is more effective in reducing vibration levels. The results further indicate that the groundhook TVA is more robust to changes in primary structure mass and stiffness.