bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer in Rotating Serpentine Passages With Selected Model Orientations for Smooth or Skewed Trip Walls
Authors: Johnson B. V. , Wagner J. H. , Steuber G. D. , Yeh F. C.
Published: June 2008

Experiments were conducted to determine the effects of model orientation as well as buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. Turbine blades have internal coolant passage surfaces at the leading and trailing edges of the airfoil with surfaces at angles that are as large as ±50 to 60 deg to the axis of rotation. Most of the previously presented, multiple-passage, rotating heat transfer experiments have focused on radial passages aligned with the axis of rotation. The present work compares results from serpentine passages with orientations 0 and 45 deg to the axis of rotation, which simulate the coolant passages for the midchord and trailing edge regions of the rotating airfoil. The experiments were conducted with rotation in both directions to simulate serpentine coolant passages with the rearward flow of coolant or with the forward flow of coolant. The experiments were conducted for passages with smooth surfaces and with 45 deg trips adjacent to airfoil surfaces for the radial portion of the serpentine passages. At a typical flow condition, the heat transfer on the leading surfaces for flow outward in the first passage with smooth walls was twice as much for the model at 45 deg compared to the model at 0 deg. However, the differences for the other passages and with trips were less. In addition, the effects of buoyancy and Coriolis forces on heat transfer in the rotating passage were decreased with the model at 45 deg, compared to the results at 0 deg. The heat transfer in the turn regions and immediately downstream of the turns in the second passage with flow inward and in the third passage with flow outward was also a function of model orientation with differences as large as 40 to 50 percent occurring between the model orientations with forward flow and rearward flow of coolant.
Calculation of Transitional Boundary Layers With an Improved Low-Reynolds-Number Version of the k–ε Turbulence Model
Authors: Biswas D. , Fukuyama Y.
Published: June 2008

Several well-known low-Reynolds-number versions of the k–ε models are analyzed critically for laminar to turbulent transitional flows as well as near-wall turbulent flows from a theoretical and numerical standpoint. After examining apparent problems associated with the modeling of low-Reynolds-number wall damping functions used in these models, an improved version of the k–ε model is proposed by defining the wall damping factors as a function of some quantity (turbulence Reynolds number Ret) that is only a rather general indicator of the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering the wall limiting behavior, the free-stream asymptotic behavior, and the balance between production and destruction of turbulence. This new model is applied to the prediction of (1) transitional boundary layers influenced by the free-stream turbulence, pressure gradient, and heat transfer; (2) external heat transfer distribution on the gas turbine rotor and stator blade under different inlet Reynolds number and free-stream turbulence conditions. It is demonstrated that the present model yields improved predictions.
An Experimental Investigation of Solid-State Phase-Change Materials for Solar Thermal Storage
Authors: Son Chang H. , Morehouse Jeffrey H.
Published: June 2008

The goal of this study is to determine and produce the thermal properties of solid-state phase-change materials appropriate for solar system space heating storage (transition temperatures in the 40 to 60°C range). A major effort is directed toward improving the overall heat storage characteristics of solid-state phase-change materials by increasing the materials’ thermal conductivities. The solid-state phase change materials focused on in this study are neopentyl glycol and pentaglycerine. The results from testing various materials are reported as thermophysical property values. The results from a constant heat flux, thermal storage charging experiment are reported for both the solid-state materials and the enhanced conductivity materials. The storage system modeled is a tube bank with hot fluid inside the tubes transferring heat to the solid-solid phase-change material outside the tubes.
Thermophysical Property Measurements Using an Encapsulated Bead Thermistor: Applications to Liquids and Insulation Materials
Authors: Dougherty Brian P. , Thomas William C.
Published: June 2008

A technique for simultaneously measuring thermal conductivity and thermal diffusivity was evaluated for applications with insulation materials and liquids. The thermophysical properties are determined from a single, transient measurement. The measurement apparatus employs an encapsulated bead thermistor as the sensing probe. The results from using a glass-encapsulated and a teflon-encapsulated bead thermistor are described.
Natural Convection and Conduction in Porous Wall, Solar Collector Systems Without Vents
Authors: Mbaye M. , Bilgen E.
Published: June 2008

Steady natural convection heat transfer has been studied in porous wall, solar collector systems. The boundary conditions were: two isothermal walls at different temperatures, two horizontal bounding adiabatic walls, and either uniform or nonuniform heat generating porous layer without vents. The aspect ratio A was from 0.5 to 1.4. The Rayleigh number varied from 103 to 108. The Darcy number was from 10−8 to 10−2 but the detailed studies were carried out only for 10−4, an optimum value. The results are presented in terms of thermal parameters (θ, θmax, Nu) as a function of Ra and other nondimensional parameters (A=H/L, B=1/L, F=d/L, kr). The isotherms and streamlines within the system are also produced. The overall results indicate that geometrical parameters are the most important parameters affecting the system performance.
Design Optimization of a Two-Phase Solar Water Heater Using R-123
Authors: Davidson J. H. , Walker H. A.
Published: June 2008

Design of a vapor transport solar water heater using R-123 is optimized to maximize thermal performance and minimize life cycle cost. Optimal systems for one and two-story homes are identified in a parametric study of collector area, condenser heat transfer area, water storage tank volume and circulating refrigerant volume for the Solar Rating and Certification Corporation rating procedure. Selection of collector and heat exchanger areas is critical to performance. With warm and cloudless ambient conditions, the most economic system is a large collector area, low efficiency system capable of meeting nearly 100 percent of the load. Under more realistic operating conditions, the best design will place more emphasis on efficiency. The condenser should have sufficient surface area to avoid significant increases in collector operating temperatures. Thermal performance is relatively insensitive to either refrigerant or water storage volume.
Analysis of Catalytically Enhanced Solar Absorption Chemical Reactors: Part I—Basic Concepts and Numerical Model Description
Authors: Hogan R. E. , Skocypec R. D.
Published: June 2008

A detailed numerical model is presented for high-temperature, catalytically enhanced, solar absorption chemical reactors. In these reactors, concentrated solar energy is volumetrically absorbed throughout a porous absorber matrix impregnated with a catalyst. The catalyst promotes heterogeneous reactions with fluid-phase reactant species flowing through the absorber. This paper presents a description of a numerical model and the basic concepts of reactor operation. The numerical model of the absorber includes solar and infrared radiation, heterogeneous chemical reactions, conduction in the solid phase, and convection between the fluid and solid phases. The model is nonlinear primarily due to both the radiative transfer and the heterogeneous chemistry occurring in the absorber. The nonlinear two-point boundary value problem is solved using superposition with orthonormalization and an adaptive solution point scheme. This technique preserves accuracy throughout the domain. The model can be modified for other chemical reactions and can be simplified to model volumetric air-heating receivers.
Thermodynamic Analysis of Latent Heat Storage in a Shell-and-Tube Heat Exchanger
Authors: Charach Ch. , Zemel A.
Published: June 2008

This work addresses the entropy generation aspects of a latent heat storage in which the energy delivered by a hot gas flowing through a cylindrical tube induces melting of the material surrounding the tube. The heat transfer for conduction-dominated melting is analyzed, taking into account the two-dimensional effects. The storage process irreversibilities associated with both the gas flow and the heat transfer (including entropy generation in the melted layer) are considered. The number of entropy generation units, which is a measure of the thermodynamic imperfection of the energy storage process, is expressed as a function of the main design parameters of the system. Analytic bounds and simplified asymptotic expressions for this quantity are derived. The results are compared with earlier one-dimensional studies.
Experimental Investigation of an Atmospheric-Open Cyclone Solar Reactor for Solid-Gas Thermochemical Reactions
Authors: Steinfeld A. , Imhof A. , Mischler D.
Published: June 2008

A solar receiver-reactor has been designed to conduct solid-gas chemical reactions, using concentrated solar radiation as the energy source of high-temperature process heat. It consists of a conical cyclone gas-particle separator that has been modified to let concentrated solar energy enter the cavity through a windowless (atmospheric-open) aperture. It combines the advantages of cavity receivers and volumetric reactors, and permits continuous mode of operation. A small-scale prototype reactor to conduct the thermal decomposition of calcium carbonate at 1300 K was experimentally investigated in a solar furnace. Its thermal performance was evaluated. The mean energy absorption efficiency, based on the optically measured power incident on the receiver aperture, was 43 percent. Reaction products showed high degree of calcination.
Transient Natural Convection in Enclosures With Application to Solar Thermal Storage Tanks
Authors: Reindl D. T. , Beckman W. A. , Mitchell J. W.
Published: June 2008

Many previously studied natural convection enclosure problems in the literature have the bounding walls of the enclosure responsible for driving the flow. A number of relevant applications contain sources within the enclosure which drive the fluid flow and heat transfer. The motivation for this work is found in solar thermal storage tanks with immersed coil heat exchangers. The heat exchangers provide a means to charge and discharge the thermal energy in the tank. The enclosure is cylindrical and well insulated. Initially the interior fluid is isothermal and quiescent. At time zero, a step change in the source temperature begins to influence the flow. The final condition is a quiescent isothermal fluid field at the source temperature. The governing time-dependent Navier-Stokes and energy equations for this configuration are solved by a finite element method. Solutions are obtained for 103≤RaD≤106. Scale analysis is used to obtain time duration estimates of three distinct heat transfer regimes. The transient heat transfer during these regimes are compared with limiting cases. Correlations are presented for the three regimes.
Chemical Energy Storage System for Solar Electric Generating System (SEGS) Solar Thermal Power Plant
Authors: Brown D. R. , La Marche J. L. , Spanner G. E.
Published: June 2008

The Pacific Northwest Laboratory evaluated the potential feasibility of using chemical energy storage at the Solar Electric Generating System (SEGS) power plants developed by Luz International. Like sensible or latent heat energy storage systems, chemical energy storage can be beneficially applied to solar thermal power plants to dampen the impact of cloud transients, extend the daily operating period, and/or allow a higher fraction of power production to occur during high-valued peak demand periods. Higher energy storage densities make chemical energy storage a potentially attractive option. The results of the evaluation indicated that a system based on the reversible reaction, CaO + H2O = Ca(OH)2, could be technically and economically feasible for this application, but many technical and economic issues must be resolved.
Impact of Component Selection and Operation on Thermal Ratings of Drain-Back Solar Water Heaters
Authors: Davidson J. H. , Carlson W. T. , Duff W. S.
Published: June 2008

A half-factorial, two-level experimental design is used to determine the effects of changes in collector area, storage tank volume, collector flow rate, recirculation flow rate, and storage tank design on thermal rating of a solar drain-back water heating system. Experimental ratings are determined in accordance with the Solar Rating and Certification Corporation guidelines. Storage tank design is varied by using a stratification manifold in place of the standard drop tube. Variations in other component sizes and operating factors are based on current industry standards. Statistical analyses indicate that a change in collector area accounts for nearly 90 percent of the variation in heat output. Doubling collector area from 2.78 m2 to 5.56 m2 increases delivered solar energy by 31 percent. Use of a stratification manifold increases the delivery of solar energy by six percent. Doubling collector flow rate from 0.057 to 0.114 1/s increases solar output by approximately three percent; however, the increase in pumping energy outweighs the benefits of increasing collector flow rate. The effects of recirculation flow rate and tank volume are obscured by experimental error.
Experiments on Oxygen Desorption From Surface Warm Seawater Under Open-Cycle Ocean Thermal Energy Conversion
Authors: Pesaran Ahmad A.
Published: June 2008

This paper presents the results of scoping deaeration experiments conducted with warm surface seawater under open-cycle ocean thermal energy conversion (OC-OTEC) conditions. Concentrations of dissolved oxygen in seawater at three locations (in the supply water, water leaving the predeaerator, and discharge water from an evaporator) were measured and used to estimate oxygen desorption levels. The results suggest that 7 percent to 60 percent of the dissolved oxygen in the supply water was desorbed from seawater in the predeaerator for pressures ranging from 35 to 9 kPa. Bubble injection in the upcomer increased the oxygen desorption rate by 20 percent to 60 percent. The data also indicated that at typical OC-OTEC evaporator pressures, when flash evaporation in the evaporator occurred, 75 percent to 95 percent of the dissolved oxygen was desorbed overall from the warm seawater. The results were used to find the impact of a single-stage predeaeration scheme on the power to remove noncondensable gases in an OC-OTEC plant.
Sunshape and Its Influence on the Flux Distribution in Imaging Solar Concentrators
Authors: Schubnell M.
Published: June 2008

Imaging solar concentrators, such as a parabolic dish, image the sun to their focal plane. Thus, the flux distribution is basically an image of the angular distribution of the direct incident solar radiation. This distribution, referred to as sunshape, is determined by solar limb darkening and by small angle scattering in the atmosphere. In this paper we present measurements of the sunshape and investigate its influence on the flux distribution in the solar furnace at Paul Scherrer Institute (PSI) and in parabolic concentrators, both experimentally and by a ray tracing procedure. Analyzing the influence of the spectral dependence of the sunshape we find that the characteristic width of the focal spot increases with longer wavelengths. In contrary, the mean concentration ratio is higher at shorter wavelengths. Although these effects are rather small, they can be important in radiometric measurement techniques to determine the emissivity and the temperature distribution of an irradiated sample as well as in designing solar pumped lasers. Comparing various sunshapes with the corresponding flux distributions in the two-stage solar furnace at PSI, we show that the influence of the circumsolar radiation on the flux distribution is usually negligible as compared to the distortion due to astigmatism. However, in more accurate optical systems, such as highly concentrating parabolic dishes, the flux distribution is a fairly accurate image of the sunshape. We find, that due to sunshape, the mean concentration ratio in a parabolic dish is decreased by about ten percent. As an example we subsequently estimate the mean annual conversion efficiency of an ideal solar converter operated in the Swiss mountains.
Energy Monitoring of a Thermally Massive Passive Solar Residence by the PSTAR Approach
Authors: Chun Wongee , Jeon Myung Seok , Kim Hyung Taek
Published: June 2008

This paper reports the application of the PSTAR (Primary and Secondary Terms Analysis and Renormalization) method to a thermally massive passive solar house located in Daejeon, Korea. The house has approximately 156 m2 of living area with three bedrooms and a living room, which embodies many passive solar features for energy conservation. The primary concern of this work was to properly evaluate the thermal behavior of a thermally massive building structure using the PSTAR method. Results show close agreements between the measured and renormalized values reflecting the effects of heavy thermal mass, whereas the simulation results from the audit description of the house deviate somewhat considerably.
Development of Nondimensional Cycling Model for Estimating the Seasonal Performance of Air Conditioners
Authors: O’Neal D. L. , Katipamula S.
Published: June 2008

A nondimensional cycling model for estimating the seasonal performance of conventional air conditioners and heat pumps was developed. Starting with a simple time-constant model of the startup of an air conditioner, a nondimensional time variable was developed which captures three important influences of on-off cycling performance degradation: response of the system, fraction on-time of the system, and cycling rate. Experimental data from three air conditioners and one heat pump provided excellent agreement with the model. The model should be applicable to any cooling technology that has similar on-off characteristics to conventional air conditioners and heat pumps.
Unglazed Transpired Solar Collectors: Heat Loss Theory
Authors: Kutscher C. F. , Christensen C. B. , Barker G. M.
Published: June 2008

Unglazed transpired solar collectors offer a potentially low cost, high-efficiency option for once-through applications such as preheating air for ventilation, crop drying, and desiccant regeneration. This paper examines the major heat loss mechanisms associated with this concept. Radiation heat loss is determined by considering losses to both the sky and the ground. Convective heat losses are obtained by integrating the product of the temperature and velocity profiles in the boundary layer at the downwind edge of the collector. This convective heat loss is then expressed in terms of the thermal equivalent length of irradiated absorber, and analysis shows that this loss can be very low for large collectors even under windy conditions. These results are incorporated into a simple computer model which predicts collector efficiency as a function of suction velocity, wind speed, ambient temperature, and radiation. Remaining research issues are discussed.
High-Efficiency Solar Dynamic Space Power Generation System
Authors: Massardo Aristide
Published: June 2008

Space power technologies have undergone significant advances over the past few years, and great emphasis is being placed on the development of dynamic power systems at this time. A design study has been conducted to evaluate the applicability of a combined cycle concept—closed Brayton cycle and organic Rankine cycle coupling—for solar dynamic space power generation systems. In the concept presented here (solar dynamic combined cycle), the waste heat rejected by the closed Brayton cycle working fluid is utilized to heat the organic working fluid of an organic Rankine cycle system. This allows the solar dynamic combined cycle efficiency to be increased compared to the efficiencies of two subsystems (closed Brayton cycle and organic fluid cycle). Also, for small-size space power systems (up to 50 kW), the efficiency of the solar dynamic combined cycle can be comparable with Stirling engine performance. The closed Brayton cycle and organic Rankine cycle designs are based on a great deal of maturity assessed in much previous work on terrestrial and solar dynamic power systems. This is not yet true for the Stirling cycles. The purpose of this paper is to analyze the performance of the new space power generation system (solar dynamic combined cycle). The significant benefits of the solar dynamic combined cycle concept such as efficiency increase, mass reduction, specific area—collector and radiator—reduction, are presented and discussed for a low earth orbit space station application.
A Second-Law Study on Packed Bed Energy Storage Systems Utilizing Phase-Change Materials
Authors: Adebiyi George A.
Published: June 2008

Thermal modeling of packed bed, thermal energy storage systems has traditionally been limited to first-law considerations. The exceptions include a few second-law studies, noted in the Introduction, of sensible heat storage systems and the latent heat storage systems. The cited second-law studies treat the storage and removal processes essentially as “batch” heating and cooling. The approximation effectively ignores the significant temperature gradient, especially in the axial direction, in the storage medium over a substantial portion of both the storage and removal processes. The results presented in this paper are for a more comprehensive model of the packed bed storage system utilizing encapsulated phase-change materials. The fundamental equations for the system are similar to those of Schumann, except that a transient conduction equation is included for intraparticle conduction in each pellet. The equations are solved numerically, and the media temperatures obtained are used for the determination of the exergy (or availability) disposition in complete storage-removal cycles. One major conclusion of the study from both the first-law and second-law perspectives is that the principal advantage in the use of phase-change storage material is the enhanced storage capacity, compared with the same size of packed bed utilizing a sensible heat storage material. Thermodynamically, however, it does not appear that the system employing phase-change storage material will always, or necessarily, be superior to that using a sensible heat-storage material. The latter conclusion is reached only on the basis of the second-law evaluation.
A Nonlinear Steady-State Characteristic Performance Curve for Medium-Temperature Solar Energy Collectors
Authors: Eames P. C. , Norton B.
Published: June 2008

A numerical simulation model was employed to investigate the effects of ambient temperature and insolation of the efficiency of compound parabolic concentrating solar energy collectors. The limitations of presently used collector performance characterization curves were investigated and a new approach proposed. The major advantage of the new procedure over those employed previously is that different solar collector performance characteristics can now be readily normalized to a common set of environmental conditions. Thus, an equitable comparison may be made, in the context of the application conditions, of rating characteristics for disparate collectors which were obtained initially under different conditions.
Analysis and Design of Two Stretched-Membrane Parabolic Dish Concentrators
Authors: Mancini Thomas R.
Published: June 2008

The state-of-the-art of parabolic dish solar concentrators is the faceted, glass-metal dish. The mass production costs of glass-metal dishes may be high because they do not incorporate the innovations of design and materials developed over the last eight years. Therefore, Sandia National Laboratories has undertaken to develop two stretched-membrane parabolic dish concentrators for the Department of Energy’s Solar Thermal Program. These solar concentrators are being designed for integration with an advanced solar receiver and a Stirling engine/generator in a 25-kWe power production unit. The first dish, which builds on the successful design of the stretched-membrane heliostats, is to be a low risk, near-term commercial solar concentrator. This solar concentrator comprises 12 large, 3.6-m diameter, stretched-membrane facets that are formed into parabolic shapes either with a large vacuum or by performing the thin membranes plastically. The focal length-to-diameter ratios (f/Ds) for the facets are about 3.0, relatively large for a dish but much lower than heliostats where they typically range from 50 to 100. Two contractors are currently fabricating facets for this dish, and a third contractor is designing the facet support structure and pedestal for the dish. The second stretched-membrane concentrator is a single-element monolithic dish with an f/D of 0.6. The dish is shaped into a parabola by plastically yielding the membrane using a combination of uniform and nonuniform loading. Initial measurements of the dish indicate that it has a slope error of 2.6 milliradians (one standard deviation) relative to a perfect parabola. In this paper, the designs of the two stretched-membrane dishes are analyzed using the computer code CIRCE to model the optical performance of the concentrators and a thermal model, which includes conduction, convection, and radiation heat transfer, to calculate the thermal losses from the cavity solar receivers. The solar collector efficiency, defined as the product of the optical efficiency of the collector and the thermal efficiency of the receiver, is optimized for comparing the performance of several solar concentrator configurations. Ten facet arrangements for the faceted stretched-membrane dish and the single-element stretched-membrane dish are modeled and their performances compared with that of a state-of-the-art glass-metal dish. Last, the initial designs of these two stretched-membrane dishes are described along with the results of preliminary performance measurements on their respective optical elements.
Numerical Study of Laminar Natural Convection From a Plate to its Cylindrical Enclosure
Authors: Elshamy M. M. , Ozisik M. N.
Published: June 2008

The steady-state laminar natural convection for air bounded by a hot plate and a cold cylindrical enclosure has been studied numerically for the case of cold isothermal cylinder and hot isothermal plate. A correlation is presented for the average Nusselt number over the range of Rayleigh number from 105 to 106 for different values of the width-aspect ratio Sw and thickness aspect-ratio St of the plate. It is found that the average Nusselt number increases with increasing Sw and Rayleigh number. A two-cell pattern is observed for Sw=1.5 and less. The effect of Sw on the average Nusselt number is found to be stronger than that of St.
Rapid Swing-Free Transport of Nonlinear Payloads Using Dynamic Programming
Authors: Zameroski Daniel , Starr Gregory , Wood John , Lumia Ron
Published: June 2008

Residual vibration suppression in freely suspended payload transports has been the focus of extensive work in the past. Many methods have been used to address this problem, including both open-loop motion planning and closed-loop control techniques. However, to be effective, most of these methods require linearization of the system and, in turn, have been restricted in their maneuver speeds. The inherent nonlinearity of suspended payload systems suggests the need for a more rigorous method, where the complete dynamic description can be retained throughout the optimization. Dynamic programming (DP) is such a method. This paper will outline the development of the DP algorithm for a discrete time system as well as its application to the rapid transport of a doubly suspended payload, a nonlinear system. The system consists of a long slender payload, suspended by a cable at each end. The two cables are each held by an independent robot manipulator. We will show that DP is effective at reducing residual oscillations for nonlinear systems, as demonstrated by both simulations and experimental validation. Residual oscillations were suppressed to less than 5% of their original magnitudes.
MIMO Active Vibration Control of Magnetically Suspended Flywheels for Satellite IPAC Service
Authors: Park Junyoung , Palazzolo Alan , Beach Raymond
Published: June 2008

Theory and simulation results have demonstrated that four, variable speed flywheels could potentially provide the energy storage and attitude control functions of existing batteries and control moment gyros on a satellite. Past modeling and control algorithms were based on the assumption of rigidity in the flywheel’s bearings and the satellite structure. This paper provides simulation results and theory, which eliminates this assumption utilizing control algorithms for active vibration control (AVC), flywheel shaft levitation, and integrated power transfer and attitude control (IPAC), that are effective even with low stiffness active magnetic bearings (AMBs) and flexible satellite appendages. The flywheel AVC and levitation tasks are provided by a multiple input–multiple output control law that enhances stability by reducing the dependence of the forward and backward gyroscopic poles with changes in flywheel speed. The control law is shown to be effective even for (1) large polar to transverse inertia ratios, which increases the stored energy density while causing the poles to become more speed dependent, and for (2) low bandwidth controllers shaped to suppress high frequency noise. Passive vibration dampers are designed to reduce the vibrations of flexible appendages of the satellite. Notch, low-pass, and bandpass filters are implemented in the AMB system to reduce and cancel high frequency, dynamic bearing forces and motor torques due to flywheel mass imbalance. Successful IPAC simulation results are presented with a 12% initial attitude error, large polar to transverse inertia ratio (IP∕IT), structural flexibility, and unbalance mass disturbance.
Characterization of the Dynamical Response of a Micromachined G-Sensor to Mechanical Shock Loading
Authors: Jordy Daniel , Younis Mohammad I.
Published: June 2008

Squeeze film damping has a significant effect on the dynamic response of microelectromechanical system (MEMS) devices that employ perforated microstructures with large planar areas and small gap widths separating them from the substrate. Perforations can alter the effect of squeeze film damping by allowing the gas underneath the device to easily escape, thereby lowering damping. By decreasing the size of the holes, damping increases and the squeeze film damping effect increases. This can be used to minimize the out-of-plane motion of the microstructures toward the substrate, thereby minimizing the possibility of contact and stiction. This paper aims to explore the use of the squeeze film damping phenomenon as a way to mitigate shock and minimize the possibility of stiction and failure in this class of MEMS devices. As a case study, the performance of a G-sensor (threshold accelerometer) employed in an arming and fusing chip is investigated. The effect of changing the size of the perforation holes and the gap width separating the microstructure from the substrate are studied. A multiphysics finite-element model built using the software ANSYS is utilized for the fluidic and transient structural analysis. A squeeze film damping model, for both the air underneath the structure and the flow of the air through the perforations, is developed. Results are shown for various models of squeeze film damping assuming no holes, large holes, and assuming a finite pressure drop across the holes, which is the most accurate way of modeling. It is found that the threshold of shock that causes the G-sensor to contact the substrate has increased significantly when decreasing the holes size or the gap width, which is very promising to help mitigate stiction in this class of devices, thereby improving their reliability.
H
∞
Fuzzy Tracking Control Design for Nonlinear Active Fault Tolerant Control Systems
Authors: Wu Huai-Ning , Bai Ming-Zhen
Published: June 2008

This paper studies the problem of H∞ fuzzy tracking control design for nonlinear active fault tolerant control systems based on the Takagi and Sugeno fuzzy model. Two random processes with Markovian transition characteristics are introduced to model the system component fault process and the fault detection and isolation decision process used to reconfigure the control law, respectively. The random behavior of the FDI process is conditioned on the fault process state. The parallel distributed compensation scheme is employed for the control design. As a result, a closed-loop fuzzy system with two Markovian jump parameters is obtained. Based on a stochastic Lyapunov function, a sufficient condition for stochastic stability of the closed-loop fuzzy system with a guaranteed H∞ model reference tracking performance is first derived. A linear matrix inequality approach to the control design is then developed to reduce the effect of the external disturbance and reference input on tracking error as small as possible. Finally, a simulation example is presented to illustrate the effectiveness of the proposed design method.
Parametric Resonance of Hopf Bifurcation
Authors: Rand Richard , Barcilon Albert , Morrison Tina
Published: June 2008

We investigate the dynamics of a system consisting of a simple, harmonic oscillator with small nonlinearity, small damping and small parametric forcing in the neighborhood of 2:1 resonance. We assume that the unforced system exhibits the birth of a stable limit cycle as the damping changes sign from positive to negative (a supercritical Hopf bifurcation). Using perturbation methods and numerical integration, we investigate the changes which occur in long-time behavior as the damping parameter is varied. We show that for large positive damping, the origin is stable, whereas for large negative damping a quasiperiodic behavior occurs. These two steady states are connected by a complicated series of bifurcations which occur as the damping is varied.
Frequency Locking in a Forced Mathieu-van der Pol System
Authors: Pandey Manoj , Rand Richard , Zehnder Alan
Published: June 2008

In this paper we investigate the dynamics of a Mathieu-van der Pol equation, which is forced both parametrically and nonparametrically. It is shown that the steady state response can consist of either 1:1 frequency locking, or 2:1 subharmonic locking, or quasiperiodic motion. The system displays hysteresis when the forcing frequency is slowly varied. We use perturbations to obtain a slow flow, which is then studied using the bifurcation software package AUTO. This study was motivated by an application to a MEMS device.
Buckling Analysis of Circular FGM Plate Having Variable Thickness Under Uniform Compression by Finite Element Method
Authors: Shamekhi Abazar , Naei Mohammad H.
Published: June 2008

This study presents the buckling analysis of radially-loaded circular plate with variable thickness made of functionally-graded material. The boundary conditions of the plate is either simply supported or clamped. The stability equations were obtained using energy method based on Love-Kichhoff hypothesis and Sander’s non-linear strain-displacement relation for thin plates. The finite element method is used to determine the critical buckling load. The results obtained show good agreement with known analytical and numerical data. The effects of thickness variation and Poisson’s ratio are investigated by calculating the buckling load. These effects are found not to be the same for simply supported and clamped plates.
Free Vibration Analysis of Circular FGM Plate Having Variable Thickness Under Axisymmetric Condition by Finite Element Method
Authors: Nikkhah-Bahrami M. , Shamekhi Abazar
Published: June 2008

This study presents the free vibration analysis of circular plate having variable thickness made of functionally-graded material. The boundary conditions of the plate is either simply supported or clamped. Dynamic equations were obtained using energy method based on Love-Kichhoff hypothesis and Sander’s non-linear strain-displacement relation for thin plates. The finite element method is used to determine the natural frequencies. The results obtained show good agreement with known analytical data. The effects of thickness variation and Poisson’s ratio are investigated by calculating the natural frequencies. These effects are found not to be the same for simply supported and clamped plates.
Sensitivity Analysis of the Extended Bouc-Wen Model of Hysteresis
Authors: Ma F. , Imam A.
Published: June 2008

The extended Bouc-Wen differential model is one of the most widely accepted phenomenological models of hysteresis in random vibration. It is routinely used in the characterization of nonlinear damping and in system identification. In this paper, the differential model of hysteresis is carefully re-examined and two significant issues are uncovered. First, it is found that the unspecified parameters of the model are functionally redundant. One of the parameters can be eliminated through suitable transformations in the parameter space. Second, local and global sensitivity analyses are conducted to assess the relative sensitivity of each model parameter. Through extensive Monte Carlo simulations, it is found that some parameters of the hysteretic model are rather insensitive. If the values of these insensitive parameters are fixed, a greatly simplified model is obtained.
Prediction of Clamp Load Loss Under Fully Reversed Cyclic Loads in Bolted Joints
Authors: Matin Payam H. , Nassar Sayed A.
Published: June 2008

The amount of clamp load loss due to a fully reversed cyclic service load is determined for a bolted assembly in which both the fastener and the joint were initially tightened beyond their respective proportional limits. After the initial tightening of the fastener, the joint is subsequently subjected to a fully reversed cyclic load that acts as a tensile separating force in the first half cycle, and as a compressive force on the joints during the second half cycle of the loading. During the first quarter cycle, the separating force would increase the fastener tensile stress further into the non-linear range. Such separating force would simultaneously reduce the clamping force in the bolted joint. At the end of the following quarter of the cycle, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the clamp load is reduced from its initial value, due to the plastic elongation of the fastener. In the third quarter of the cycle, the compressive service load would increase the joint compressive stress into the non-linear range. Similarly, the clamp load loss would be increased at the end of the second half cycle, due to the plastic compression in the joint. The total clamp load loss may significantly lead to joint leakage, loosening, or fatigue failure. A non-linear strain hardening model is implemented in order to determine the clamp load loss due to accumulative effect of the permanent set in the fastener and the joint after the service load had been removed. Various rates of strain hardening are used for modeling the behavior of the fastener and joint materials. The effect of three non-dimensional variables on the amount of clamp load loss is investigated. The variables include the joint-to-fastener stiffness ratio, the ratio of the initial fastener tension to its elastic limit, and the ratio of the external force to its maximum tensile value that would cause joint separation to start.
Effect of Bolt Tightening and Joint Material on the Strength and Behavior of Composite Joints
Authors: Nassar Sayed A. , Virupaksha Vinayshankar L.
Published: June 2008

This experimental study investigates the effect of the various combinations of bolt tightening and joint material on the strength and behavior of single lap, double bolted composite joints. The strength of the bolted joint is determined from a load-displacement test in which the joint members are pulled in the transverse direction relative to the bolts axis. Additionally, damage assessment is performed on the bearing surface between the shank of each bolt and the members of the joint. The bearing surface damage is examined using a Motic Microscope. Four tightening configurations are used in the testing of each joint. These configurations permit each bolt to be in either tight or loose conditions. The effect of joint material is also investigated, as well. Tested joints include composite-to-composite and composite-to-aluminum joint combination. The metric M8x1.25 bolts; Class 8.8 bolts are used in this study. Experimental results, data analysis, and conclusions are presented.
Constrained Motion of Tethered Satellites
Authors: Schutte Aaron , Dooley Brian
Published: June 2008

The orbital motion of tethered satellites is a highly complex nonlinear problem. This investigation sets out to formulate a new method that significantly simplifies the dynamic analysis of tethered satellite systems. This is accomplished using the fundamental equation for constrained dynamic systems, which was formulated by Udwadia and Kalaba. As a result of this new method, a study of the periodicity of tethered satellite motion is conducted and an extension to formation flying satellites is made. With varying fixed tether lengths, the system motion seems to transition from periodic to quasi-periodic. The simplified method is also applied to the computation of the control force required for formation flight.
Vibration Suppression of Rotating Machinery Utilizing Discontinuous Spring Characteristics
Authors: Ishida Yukio , Liu Jun
Published: June 2008

In rotating machinery, resonance phenomena occur with large amplitude in the vicinities of the major critical speeds. In this paper, a new vibration suppression method utilizing a discontinuous spring characteristic is proposed. This spring characteristic is made by additional springs with preload. This method has the following advantages: In designing these additional springs, we need not adjust their parameter values to the rotor stiffness and the system damping. The amplitude of vibration can be suppressed to any desired level. Although this method has a disadvantage that an almost periodic motion occurs above the major critical speed, two countermeasures are proposed to diminish it. We clarified these phenomena theoretically and experimentally.
Oscillator in a Clearance: Asymptotic Approaches and Nonlinear Effects
Authors: Fidlin Alexander
Published: June 2008

Averaging combined with non-smooth unfolding transformations is used in this paper for investigating of the basic properties of an oscillator in a clearance. The classical stereo-mechanical approach is used in order to describe collisions between the mass and the limits. Energy dissipation during collision events is taken into account. The analysis is concentrated on the oscillation regimes with alternating collisions with both sides of the clearance. The self-excited friction oscillator in a clearance is considered as the first example. It is shown that applying the unfolding transformation the oscillator can be converted to an almost conservative pendulum rotating in a limited, non-smooth periodical potential field. Analytic predictions are obtained for the total energy of the pendulum which is the natural measure for the oscillations intensity. It is shown that the oscillation frequency can be controlled by changing the negative slope of the friction characteristics, by alternating the normal force and varying the length of the clearance. The classical externally excited oscillator in the clearance is considered as the second example. Applying the same approach the problem of the resonant oscillations can be reduces to the analysis of the rotation of the harmonically excited pendulum in the same potential field as in the first example. The main attention is paid to the high-energy resonances. The perturbation analysis in the vicinity of the resonant surfaces enables to dissociate slow, semi-slow and fast motions and to obtain very accurate analytic predictions for the energies of stationary resonant regimes. It is demonstrated that different high-energy regimes exist alongside with low-energy oscillations. The last case is typical for relative strong energy losses during collision events, so that the system needs several collision-free oscillations in order to increase the amplitude and reach the limits of the clearance.
Dynamics of Roller Coasters
Authors: Pfeiffer Friedrich
Published: June 2008

Roller coasters are dynamically multibody systems with unilateral contacts due to the usual raceway design including straight parts and bends. In running down such tracks and passing parts of the track with changing curvature impacts with friction are generated in the track-wheel contacts. The impacts are always connected with large overloads of the wheels sometimes leading to damages. To investigate these problems the roller coaster carriages are modelled as a non-smooth multibody system with impacts and stick-slip processes. The results in terms of wheel loads are used to improve wheel design.
A Predictive Tool for Remaining Useful Life Estimation of Rotating Machinery Components
Authors: Liao Haitao , Qiu Hai , Lee Jay , Lin Daming , Banjevic Dragan , Jardine Andrew
Published: June 2008

This paper introduces a model for multiple degradation features of an individual component. The maximum likelihood approach is employed to estimate the model parameters. Afterwards, a proportional hazards model is presented, which considers hard failures and multiple degradation features simultaneously. The integrated model enables us to predict the mean remaining useful life of a component based on on-line degradation information. An example for bearing prognostic is provided to demonstrate the proposed models in practical use.
Quantization of a Free Particle in a Dissipative Medium: Interaction of Charged Particles With Matter
Authors: Rabei Eqab M. , Ajlouni Abdul-Wali , Ghassib Humam B.
Published: June 2008

Following our work on the quantization of nonconservative systems using fractional calculus, the canonical quantization of a system of free particles in a dissipative medium is carried out according to the Dirac method. A suitable Schro¨dinger equation is set up and solved for the Lagrangian representing this system. The wave function is plotted and the damping effect manifests itself very clearly. This formalism is then applied to the problem of energy loss of charged particles when passing through matter. The results are plotted and the relation between the energy loss and the range agrees qualitatively with experimental results.
A Probabilistic Theory of Random Maps
Authors: Elbeyli Ozer , Sun J. Q.
Published: June 2008

We present a probabilistic theory of random maps with discrete time and continuous state. The forward and backward Kolmogorov equations as well as the FPK equation governing the evolution of the probability density function of the system are derived. The moment equations, the reliability and first passage time problem are studied. The present work compliments the existing theory of continuous time stochastic processes.