bluuebunny/crossref_metadata_2025 huggingface dataset:
A High-Pressure Window for Volumetric Solar Receivers
Authors: Karni J. , Kribus A. , Ostraich B. , Kochavi E.
Published: February 2008

The absorbing matrix of a volumetric (directly irradiated) solar receiver must be exposed to the concentrated incoming sunlight. Most applications require that the receiver operates at an elevated pressure and in many cases the working fluid is not air. These requirements can be met only if the receiver is equipped with a transparent window. A novel frustum-like high-pressure (FLHiP) window, made of fused silica, is presented. Optical, mechanical, and thermal analyses, over 1,000 hours of accelerated life-time tests and several hundred hours of tests in a solar receiver, show that this window satisfies the required criteria for operation in a volumetric solar receiver, whose operating pressure and peak absorber temperature reach 30 bar and 1700°C, respectively.
New Airfoils for Small Horizontal Axis Wind Turbines
Authors: Gigue`re P. , Selig M. S.
Published: February 2008

In a continuing effort to enhance the performance of small wind energy systems, one root airfoil and three primary airfoils were specifically designed for small horizontal axis wind turbines. These airfoils are intended primarily for 1–5 kW variable-speed wind turbines for both conventional (tapered/twisted) or pultruded blades. The four airfoils were wind-tunnel tested at Reynolds numbers between 100,000 and 500,000. Tests with simulated leading-edge roughness were also conducted. The results indicate that small variable-speed wind turbines should benefit from the use of the new airfoils which provide enhanced lift-to-drag ratio performance as compared with previously existing airfoils.
Use of Calibrated HVAC System Models to Optimize System Operation
Authors: Liu Mingsheng , Claridge D. E.
Published: February 2008

A calibrated simplified engineering modeling method has been developed to optimize HVAC system operation. This method can be used to optimize operating strategies and control schedules. It has also served to identify malfunctioning components on occasion. This method has been successfully applied to 18 LoanSTAR buildings where over $2.0 million per year in potential savings have been identified, and over $1.4 million per year have been implemented. The method is described in the context of a case study.
On the Thermodynamic Optimization of Power Plants With Heat Transfer and Fluid Flow Irreversibilities
Authors: Ikegami Y. , Bejan A.
Published: February 2008

This note addresses the current debate on the correctness of power plant models and analyses of the type published by Curzon and Ahlborn (1975) among others. Such models are based on the highly questionable assumption that the heat input is freely available, i.e., a degree-of-freedom for steady-state operation. This modeling assumption is wrong when the heat input (e.g., fuel) is in limited supply. On the other hand, it is shown that a model with freely varying heat input is possible if the roles of heat source and heat sink are played by two streams pumped from fluid reservoirs of different temperatures, as in geothermal and ocean thermal energy conversion systems, for example. The simplified model has both heat transfer and fluid flow irreversibilities, however, it neglects other possible sources. Several new results are developed. There exist optimal flow rates of hot fluid and cold fluid such that the net power output is maximized. As an alternative to power maximization, the model can be optimized for maximum efficiencies (net, first law, or second law). The note illustrates the importance of separating the questioned modeling assumption (e.g., Curzon and Ahlborn, 1975) from the generally applicable method of modeling and optimization (entropy generation minimization, EGM).
On the Stability of Solar Chemical Particle Receivers
Authors: Ries H. , Tschudi H. R. , Spirkl W.
Published: February 2008

We model the decomposition reaction of a solid powder into a solid plus gas in a mixed homogeneous open solar reactor and derive criteria for stability. Instability may occur via a feedback mechanism whereby gas produced in the decomposition reaction reduces the inflow, which leads to even higher reaction rate. For a variety of reactions proposed for solar application, we list the limits of stable operation as the maximum fraction of solid educt in the input carrier gas both for complete as well as for partial decomposition.
Development of Graphical Indices for Viewing Building Energy Data: Part II
Authors: Haberl J. S. , Abbas M.
Published: February 2008

Graphs are an effective way of displaying quantitative and statistical information. Unfortunately, only a few studies have systematically looked at presenting building energy data in forms which are both informative, visually efficient, and easy to comprehend. Recent advancements in computing, including the development of sophisticated graphing packages and powerful desktop computers have made the concept of graphical displays or graphical indices more timely than ever before. In this two part paper, graphical displays or indices are reviewed and discussed that can be used to analyze several years of hourly data (20,000 to 30,000 data points). Part I reviewed the literature on graphical presentations of building energy me data and graphical perception and presents two graphical indices. Part II provides four additional graphical indices and a discussion about their effectiveness.
Procedures for Calibrating Hourly Simulation Models to Measured Building Energy and Environmental Data
Authors: Haberl J. S. , Bou-Saada T. E.
Published: February 2008

This paper discusses procedures for creating calibrated building energy simulation programs. It begins with reviews of the calibration techniques that have been reported in the previous literature and presents new hourly calibration methods including a temperature bin analysis to improve hourly x−y scatter plots, a 24-hour weather-daytype bin analysis to allow for the evaluation of hourly temperature and schedule dependent comparisons, and a 52-week bin analysis to facilitate the evaluation of long-term trends. In addition, architectural rendering is reviewed as a means of verifying the dimensions of the building envelope and external shading placement as seen by the simulation program. Several statistical methods are also presented that provide goodness-of-fit indicators, including percent difference calculations, mean bias error (MBE), and the coefficient of variation of the root mean squared error (CV(RMSE)). The procedures are applied to a case study building located in Washington, D. C. where nine months of hourly whole-building electricity data and sitespecific weather data were measured and used with the DOE-2.1D building energy simulation program to test the new techniques. Simulations that used the new calibration procedures were able to produce an hourly MBE of –0.7% and a CV(RMSE) of 23.1% which compare favorably with the most accurate hourly neural network models (Kreider and Haberl, 1994a, b).
Application of an End-Use Disaggregation Algorithm for Obtaining Building Energy-Use Data
Authors: Akbari H. , Konopacki S. J.
Published: February 2008

Metered end-use data for most Department of Defense (DoD) facilities are scarce. We discuss the application of a method (end-use disaggregation algorithm, EDA) to disaggregate short-interval (hourly) whole-facility electrical load into major end uses. Hourly load data, hourly load-temperature regression coefficients, and simulated end-use data comprise the algorithm input. The algorithm produces hourly load profiles for air conditioning, lighting, fans and pumps, and miscellaneous loads. In previous studies, the EDA has been applied to both individual and prototypical buildings to estimate energy use by end use for two major California utilities. In this study, we have refined the EDA for application to DoD facilities where typically only the hourly electricity use data are available for the entire facility.
Estimation of Energy Savings for Building Retrofits Using Neural Networks
Authors: Krarti M. , Kreider J. F. , Cohen D. , Curtiss P.
Published: February 2008

This paper overviews some applications of neural networks (NNs) to estimate energy and demand savings from retrofits of commercial buildings. First, a brief background information on NNs is provided. Then, three specific case studies are described to illustrate how and when NNs can be used successfully to determine energy savings due to the implementation of various energy conservation measures in existing commercial buildings.
Instrumentation for High Performance Nonintrusive Electrical Load Monitoring
Authors: Shaw S. R. , Abler C. B. , Lepard R. F. , Luo D. , Leeb S. B. , Norford L. K.
Published: February 2008

This paper reviews the design and implementation of hardware and software tools for nonintrusive electrical load monitoring. Estimates of spectral content in measured waveforms can be used to determine in real time the operating schedule of loads at a target site. Techniques for transient event detection are reviewed. These techniques can detect the turn-on and turn-off transients of individual loads, and can be used to easily determine the energy usage of loads that draw constant power in steady-state operation. Techniques for monitoring the power consumption of smoothly varying loads (e.g., variable speed drives) using spectral estimates are also discussed.
Performance Limits of Heliostat Fields
Authors: Kribus A. , Krupkin V. , Yogev A. , Spirkl W.
Published: February 2008

Geometric and thermodynamic arguments are used to derive upper limits on the performance of a solar energy collection system, consisting of an axisymmetric heliostat field, a solar tower, secondary optics and a black receiver. Performance limits on collected power, concentration, and work output are presented. Performance of tower systems with several secondary optics options is compared: tower-top Compound Parabolic Concentrator (CPC), Tailored Edge-Ray Concentrator (TERC) approximated by a cone, and Cassegrainian with ground-level CPC or Compound Elliptic Concentrator (CEC). Optimized ray tracing is used to generate the design parameters of the secondary concentrators that yield the highest optical efficiency. The results show that the tower-top Cone provides the best performance regarding both concentration and efficiency, except for very large fields. The Cassegrainian designs come in second, but become equal and even better than the Cone for large fields. The results for the Cassegrainian are sensitive to the value of the reflectivity, due to the additional reflections incurred. The choice of a CEC is better than a CPC for the terminal concentration in a Cassegrainian system, but the difference is small. The suitability of the different design options for high-temperature solar applications is discussed. The recommendations regarding optical configuration depend on field size, as well as on application-specific constraints.
Ice Storage System Controls for the Reduction of Operating Cost and Energy Use
Authors: Henze G. P. , Krarti M.
Published: February 2008

Ice storage systems have the reputation of saving cost for operating building cooling plants by appropriately recognizing time-of-use incentives in the utility rate structure. However, many systems can consume more electrical energy than a conventional cooling plant without ice storage. This excess energy problem is illustrated in this paper by a simplified cooling plant model employed in a simulation environment that allows the assessment of the control performance of various conventional and optimal strategies. The optimal control strategy of minimizing operating cost only is introduced and subsequently is modified to allow the simultaneous consideration of operating cost and energy consumption. This proposed optimal control strategy could be valuable if ice storage systems are to stand on their own merits in a deregulated utility environment. Due to the lack of demand charges under real-time pricing, even small energy penalties and their associated excess energy cost may jeopardize the feasibility of the ice storage system.
Solar Collectors with Tubes Partially Filled with Porous Substrates
Authors: Alkam M. K. , Al-Nimr M. A.
Published: February 2008

In this work, the thermal performance of a conventional collector is improved by inserting porous substrates at the inner walls of the collector tubes. The porous substrates improve the convective heat transfer coefficient between the tube wall and the fluid. This improvement is investigated numerically and its effects on the efficiency and the useful gain of the collector are evaluated. It is found that inserting the porous substrate may raise the collector efficiency considerably, especially at high values of the overall heat loss coefficient.
Surface Hardening of Steel Using Highly Concentrated Solar Energy Process
Authors: Ferriere A. , Faillat C. , Galasso S. , Barrallier L. , Masse J-E.
Published: February 2008

A recent French contribution in the field of surface hardening of steel using concentrated solar energy is presented. Single spot and continuous scanning processes have been investigated in a small-scale solar furnace. Hardened regions of 0.5–1.5 mm in thickness have been obtained on specimens of carbon steel, resulting from the transformation hardening process. Compressive stresses are induced in the thermally affected layer, without tensile peak in the bulk.
Development of an Inverse Method to Estimate Overall Building and Ventilation Parameters of Large Commercial Buildings
Authors: Reddy T. A. , Deng S. , Claridge D. E.
Published: February 2008

We propose an inverse method to estimate building and ventilation parameters from non-intrusive monitoring of heating and cooling thermal energy use of large commercial buildings. The procedure involves first deducing the loads of an ideal one-zone building from the monitored data, and then in the framework of a mechanistic macro-model, using a multistep linear regression approach to determine the regression coefficients (along with their standard errors) which can be finally translated into estimates of the physical parameters (along with the associated errors). Several different identification schemes have been evaluated using heating and cooling data generated from a detailed building simulation program for two different building geometries and building mass at two different climatic locations. A multistep identification scheme has been found to yield very accurate results, and an explanation as to why it should be so is also given. This approach has been shown to remove much of the bias introduced in multiple linear regression approach with correlated regressor variables. We have found that the parameter identification process is very accurate when daily data over an entire year are used. Parameter identification accuracy using twelve monthly data points and daily data over three months of the year was also investigated. Identification with twelve monthly data points seems to be fairly accurate while that using daily data over a season does not yield very good results. This latter issue needs to be investigated further because of its practical relevance.
A Fourier Series Model to Predict Hourly Heating and Cooling Energy Use in Commercial Buildings With Outdoor Temperature as the Only Weather Variable
Authors: Dhar A. , Reddy T. A. , Claridge D. E.
Published: February 2008

Accurate modeling of hourly heating and cooling energy use in commercial buildings can be achieved by a Generalized Fourier Series (GFS) approach involving weather variables such as dry-bulb temperature, specific humidity and horizontal solar flux. However, there are situations when only temperature data is available. The objective of this paper is to (i) describe development of a variant of the GFS approach which allows modeling both heating and cooling hourly energy use in commercial buildings with outdoor temperature as the only weather variable and (ii) illustrate its application with monitored hourly data from several buildings in Texas. It is found that the new Temperature based Fourier Series (TFS) approach (i) provides better approximation to heating energy use than the existing GFS approach, ((ii) can indirectly account for humidity and solar effects in the cooling energy use, (iii) offers physical insight into the operating pattern of a building HVAC system and (iv) can be used for diagnostic purposes.
Generalization of the Fourier Series Approach to Model Hourly Energy Use in Commercial Buildings
Authors: Dhar A. , Reddy T. A. , Claridge D. E.
Published: February 2008

Development of the accurate models for hourly energy use in commercial buildings has important ramifications for (I) retrofit savings analysis, (ii) diagnostics, (iii) on-line control and (iv) acquiring physical insights into the operating patterns of the buildings. Electric and thermal energy uses in commercial buildings, being strongly periodic, are eminently suitable for Fourier series analysis. Earlier studies assumed trigonometric polynomials with the hour of the day as the primary variable and one week as the period. This model, though suitable on the whole, was poor during certain weekday periods and during weekends. This paper presents a generalized Fourier series approach which, while ensuring a wider range of applicability, also yields superior regression fits partly because of the care taken to separate days of the year during which commercial buildings are operated differently and partly because of the rational functional form of regression model proposed. The validity of the approach is verified with year-long data of twenty-two monitored buildings.
Numerical Simulation of Dynamic Stall Around an Airfoil in Darrieus Motion
Authors: Allet A. , Halle´ S. , Paraschivoiu I.
Published: February 2008

The objective of this study is to investigate the two-dimensional unsteady flow around an airfoil undergoing a Darrieus motion in dynamic stall conditions. For this purpose, a numerical solver based on the solution of the Reynolds-averaged Navier-Stokes equations expressed in a streamfunction-vorticity formulation in a non-inertial frame of reference was developed. The governing equations are solved by the streamline upwind Petrov-Galerkin finite element method (FEM). Temporal discretization is achieved by second-order-accurate finite differences. The resulting global matrix system is linearized by the Newton method and solved by the generalized minimum residual method (GMRES) with an incomplete triangular factorization preconditioning (ILU). Turbulence effects are introduced in the solver by an eddy viscosity model. Our investigation centers on an evaluation of the algebraic Cebeci-Smith model (CSM) and the nonequilibrium Johnson-King model (JKM). In an effort to predict dynamic stall features on rotating airfoils, first we present some testing results concerning the performance of both turbulence models for the flat plate case. Then, computed flow structure together with aerodynamic coefficients for a NACA 0015 airfoil in Darrieus motion under dynamic stall conditions are presented.
A New High-Flux Solar Furnace for High-Temperature Thermochemical Research
Authors: Haueter P. , Seitz T. , Steinfeld A.
Published: February 2008

A new high-flux solar furnace, capable of delivering up to 40kW at peak concentration ratios exceeding 5000, is operational at PSI. Its optical design characteristics, main engineering features, and operating performance are described. This solar concentrating facility will be used principally for investigating the thermochemical processing of solar fuels at temperatures as high as 2500 K.
Frequency Domain Analysis of an Electrical Substitution Radiometer
Authors: Oliveira A. , Lobo P. C. , Deep G. S. , Freire R. C. S. , da Rocha Neto J. S.
Published: February 2008

A small signal analysis of a feedback radiation meter circuit is presented with a view to estimate its effective response time, taking into account parameters of a practical operational amplifier: The amplifier input offset voltage is shown to considerably influence the stable operation of the circuit. Numerical examples and simulation results are included.
The SCATMES Device for Measurement of Concentrated Solar Radiation
Authors: Neumann A. , Schmitz A.
Published: February 2008

Video camera systems monitoring a diffuse reflecting target for measuring the flux distribution of concentrated solar radiation are quite common. This technique cannot be used if parts of the experimental setup screen the surface of the target. The development of a new measurement system with a compact geometry and a new optical design is described. With this system it is possible to measure the flux distribution behind parts of an experiment and at any position of the plane of measurement, without any alteration of the setup. The sources of error, especially those of the target and the camera, are described and discussed, and finally a comparison to the existing FATMES-System, which has been performed at the solar furnace of the DLR in Cologne, is presented. Due to its measurement principle the new system is called ’Scanning Camera and Target Measurement System‘ (acronym: SCATMES).
Influence of the Meteorology Mast on a Cup Anemometer
Authors: Hansen M. O. L. , Pedersen B. M.
Published: February 2008

The actuator disc model is applied on lattice-type meteorological masts to estimate the influence of the tower on the accuracy of the measured wind speed. Combining the results with corrections for the boom, on which the anemometer is mounted, good agreement is found for measurements made on the mast at Tjœcereborg. Iso-speed plots are computed to estimate the influence of different solidities. Depending on the distance from the mast and the solidity the influence from a typical mast is normally less than 3%.
Analysis of a New Thermodynamic Cycle for Combined Power and Cooling Using Low and Mid Temperature Solar Collectors
Authors: Goswami D. Yogi , Xu Feng
Published: February 2008

A combined thermal power and cooling cycle is proposed which combines the Rankine and absorption refrigeration cycles. It can provide power output as well as refrigeration with power generation as a primary goal. Ammonia-water mixture is used as a working fluid. The boiling temperature of the ammonia-water mixture increases as the boiling process proceeds until all liquid is vaporized, so that a better thermal match is obtained in the boiler. The proposed cycle takes advantage of the low boiling temperature of ammonia vapor so that it can be expanded to a low temperature while it is still in a vapor state or a high quality two phase state. This cycle is ideally suited for solar thermal power using low cost concentrating collectors, with the potential to reduce the capital cost of a solar thermal power plant. The cycle can also be used as a bottoming cycle for any thermal power plant. This paper presents a parametric analysis of the proposed cycle.
Heat Transfer in Vertically Aligned Phase Change Energy Storage Systems
Authors: El-Dessouky H. T. , Bouhamra W. S. , Ettouney H. M. , Akbar M.
Published: February 2008

Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data is used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.
A Second Law Approach to Characterising Thermally Stratified Hot Water Storage With Application to Solar Water Heaters
Authors: Rosengarten G. , Morrison G. , Behnia M.
Published: February 2008

This paper presents a method of characterising and evaluating the performance of hot water storage systems in terms of their temperature distribution. The change in exergy from the stratified state to the delivery state depends on the stored energy and the stratification. It can thus he used to define the storage efficiency for sensible heat storage devices. A new parameter that isolates the stratification component of the exergy is defined and called the stratification efficiency. The effect of temperature distribution, delivery temperature and tank cross-section on exergy and stratification efficiency is investigated. The advantage that stratification offers over a mixed tank is examined in terms of the storage efficiency and overall solar water heating system performance. Exergy is used to assess the operation of mantle heat exchangers in solar water heating systems and it is shown that exergy and stratification efficiency, as well as energy, should be used to ascertain the performance of such heat exchangers.
The Feasibility of Using a Septic Tank as a Heat Source for Geothermal Heat Pumps
Authors: Hanegan T. , DenBraven K.
Published: February 2008

A geothermal heat pump (GHP) system with three ground coils was installed in a residence in northern Idaho with a portion of the ground heat exchanger wrapped around the residential septic tank. The septic coil provided a significant portion of the heating for the residence over the heating season. There was no evidence of the septic tank freezing up or failing to properly function. Utilizing a septic tank as a heat source for GHP systems is feasible design option if the septic tank is used on a full-time basis. However, the tank should be surrounded on all sides by a large amount of soil and/or insulated from the ground surface to ensure that ground temperatures near the tank remain warm during the winter.
Acoustical Resonance of Tube-in-Shell Units
Authors: Smoglie C.
Published: February 2008

Severe noise emission due to acoustical resonance can occur in conduits or chambers containing large tube arrays subjected to fluid cross flow, as is the case in many heat exchangers and steam generators. A theoretical basis obtained from updated literature is used to assess excitation and damping forces. Whether acoustical resonance is to be expected or not depends upon the relative magnitude of both forces. A calculation method is proposed for the prediction of acoustical resonance and its frequency. The method has been checked by using geometrical and experimental data for Moisture Separator Reheaters of two different power plants. Results show reasonable agreement between predictions and measurements. Two methods are suggested for the suppression of existing resonance.
A Method for Calculating the Dynamics of Rotating Flexible Structures, Part 1: Derivation
Authors: Segalman D. J. , Dohrmann C. R.
Published: February 2008

The problem of calculating the vibrations of rotating structures has challenged analysts since it was observed that the use of traditional modal approaches may incorrectly lead to the prediction of infinite deformation when rotation rates exceed the first natural frequency. Much recently published work on beams has shown that such predictions are artifacts of incorporating incomplete kinematics into the analysis, but only simple structures such as individual beams and plates are addressed. The authors present a new approach to analyzing rotating flexible structures that applies to the rotation of general linear (unjointed) structures, using a system of nonlinearly coupled deformation modes. This technique, tentatively named a Method of Quadratic Components, utilizes a nonlinear configuration space in which all kinematic constraints are satisfied up to second order.
An Impedance-Based System Modeling Approach for Induced Strain Actuator-Driven Structures
Authors: Zhou Su-Wei , Liang Chen , Rogers C. A.
Published: February 2008

This paper presents the theoretical development and experimental verification of a system model of piezoelectric (PZT) patch actuators for induced strain actuation of two-dimensional active structures. The model includes the dynamic interaction between PZT actuators and their host structures. Analytical solutions of the output behavior of the PZT actuators have been developed based upon the actuator input impedance and the mechanical impedance of the host structures. The impedance-based model was then applied to thin plates and thin shells, and to beams. The case studies demonstrate the generality and utility of the impedance modeling approach. A simply-supported thin plate with surface-bonded PZT patches was built and tested so that the ability of the impedance model to accurately predict the dynamic performance of the actuator and the host structure has been verified. When compared with conventional static models, the impedance modeling method offers insight into the dynamic coupling of the integrated PZT/substrate systems.
On Nonlinear Normal Modes of Systems With Internal Resonance
Authors: Nayfeh A. H. , Chin C. , Nayfeh S. A.
Published: February 2008

A complex-variable invariant-manifold approach is used to construct the normal modes of weakly nonlinear discrete systems with cubic geometric nonlinearities and either a one-to-one or a three-to-one internal resonance. The nonlinear mode shapes are assumed to be slightly curved four-dimensional manifolds tangent to the linear eigenspaces of the two modes involved in the internal resonance at the equilibrium position. The dynamics on these manifolds is governed by three first-order autonomous equations. In contrast with the case of no internal resonance, the number of nonlinear normal modes may be more than the number of linear normal modes. Bifurcations of the calculated nonlinear normal modes are investigated.
On the Spectral Signature of Weakly Bilinear Oscillators
Authors: Bayly P. V.
Published: February 2008

An analytical relationship is derived between the strength of a weak stiffness discontinuity and the magnitudes of superharmonic peaks in the Fourier spectrum of a bilinear oscillator. Expressions are obtained for three ranges of forcing frequencies: far from resonances, and near primary and superharmonic resonances. The difference between the two linear stiffness coefficients is used as the small parameter, ε, in a modified perturbation analysis. Closed-form expressions for the extra harmonic components in the spectrum are obtained as functions of the strength of the stiffness discontinuity. These results are relevant to the problem of detecting small cracks in structures and shafts; they suggest that greater sensitivity to small cracks can be obtained by exploiting superharmonic resonance.
Torsional Instabilities in a System Incorporating a Hooke’s Joint
Authors: Asokanthan S. F. , Hwang Ming-Chang
Published: February 2008

Dynamic stability analysis of a driveline which incorporates a Hooke’s joint is presented in this paper. In particular, torsional instabilities due to fluctuating angular velocity ratio across the joint are examined. The method of averaging is used to establish the critical speed ranges by considering the linearized equations which govern the torsional motion of the system. Within these ranges, parametric instability characterized by exponential build up of response amplitudes of the torsional modes occur. Closed form conditions for onset of sub-harmonic as well as sum-type combination resonance have been established. The significance of the sum-type combination resonance in a typical diesel hydraulic locomotive driveline has been demonstrated. Difference-type combination resonance has been shown to be absent. The instability conditions indicate the range of driveshaft speeds to be avoided during the design of a driveline which employs a Hooke’s joint.
On the Vibration of Coupled Traveling String and Air Bearing Systems
Authors: Lakshmikumaran A. V. , Wickert J. A.
Published: February 2008

Air bearings are used to position and guide such axially-moving materials as high speed magnetic tapes, paper sheets, and webs. In each case, vibration of the moving medium couples with the air bearing’s dynamics, and techniques are developed here to reduce the computational effort that is required to predict the natural frequencies, damping ratios, and vibration modes of the prototypical traveling string and self-pressurized air bearing model. Automatic nodal point allocation reduces the number of nonlinear equations that arise in finding the equilibrium string displacement and air pressure, and in subsequent vibration analysis, the response is obtained in closed form by using the Green’s function for the traveling string. Global discretization of the air pressure alone then yields a matrix eigenvalue problem which is simpler than that obtained through previous methods which required discretization of both displacement and pressure. Overall, essentially a five-fold increase in computational speed is achieved, thus facilitating design and parameter studies. Changes in the natural frequencies, damping ratios, and coupled displacement-pressure mode shapes with respect to several design variables are discussed and compared with experiments.
Free Vibration of Serpentine Belt Drive Systems
Authors: Beikmann R. S. , Perkins N. C. , Ulsoy A. G.
Published: February 2008

The vibration of an automotive serpentine belt drive system greatly affects the perceived quality and the reliability of the system. Accessory drives with unfavorable vibration characteristics transmit excessive noise and vibration to other vehicle structures, to the vehicle occupants, and may also promote the fatigue and failure of system components. Moreover, these characteristics are a consequence of decisions made early on in the design and arrangement of the accessory drive system. The present paper focuses on fundamental modeling issues that are central to predicting accessory drive vibration. To this end, a prototypical drive is evaluated, which is composed of a driven pulley, a driving pulley, and a dynamic tensioner. The coupled equations of free response governing the discrete and continuous elements are presented herein. A closed-form solution method is used to evaluate the natural frequencies and modeshapes. Attention focuses on a key linear mechanism that couples tensioner arm rotation and transverse vibration of the adjacent belt spans. Modal tests on an experimental drive confirm the theoretical predictions.
Threaded Components Under Axial Harmonic Vibration, Part 1: Experiments
Authors: Hess D. P. , Davis K.
Published: February 2008

Threaded components have found ubiquitous use in many systems and structures. Although frequently overlooked, they represent a complex and often critical design element. One can identify numerous instances where such elements are subjected to vibratory conditions, yet their behavior in such an environment is still poorly understood. In this paper, we report on a series of experiments that were run to examine the motions of threaded fasteners subjected to axial harmonic vibration. The components are loaded by gravity and excited over a broad range of conditions. It is found that significant relative twisting motion can occur both with and against the load. This indicates that threaded components may loosen or tighten in the presence of vibration. It is shown that the direction of twist depends on the frequency and amplitude of the vibratory input as well as various physical parameters. Previous theoretical analyses of threaded components under vibration are based on static equilibrium conditions, and only predict a loosening action, i.e., twist with load. In Part 2 of this paper, a kinematic model is developed which predicts twisting both with and against load as observed in the experiments.
Self-Sensing Active Suppression of Vibration of Flexible Steel Sheet
Authors: Matsuda Ken-ichi , Yoshihashi Masahiro , Okada Yohji , Tan Andy C. C.
Published: February 2008

In rolling processes, flexible steel sheet is supported by rollers and is bound to produce structural vibration. This vibration can cause severe problems to surface finish and affect the quality of the product. To overcome these problems, active vibration control has been proposed. This usually requires both sensors and actuators. The location of sensors and actuators plays a very important role in active vibration control. Moreover, a reliable sensor can be very expensive. This paper proposes a self-sensing vibration control using a push-pull type electromagnet to control the transverse vibration of the steel plate. The construction of the electromagnet has two types of coils, namely the bias coil and the control coil. Vibration displacement is estimated by using the mutual inductance change between the bias and the control coils. The estimated signal is proportional to the gap displacement. The proportional and derivative signals are fed back to the control coil to reduce the transverse vibration of the steel sheet. The proposed method is applied to a simple test rig to confirm the capability of the device. The results obtained are showing high possibility for reducing steel sheet vibration.
Perturbation Stability of Frictional Sliding With Varying Normal Force
Authors: Dupont P. E. , Bapna D.
Published: February 2008

In many systems, the normal force at friction contacts is not constant, but is instead a function of the system’s state variables. Examples include machine tools, friction dampers, brake systems and robotic contact with the environment. Friction at these contacts has been shown to possess dynamics associated with changes in normal force. In an earlier paper, the authors derived a critical value of system stiffness for stability based on a linearized analysis of constant velocity sliding (Dupont and Bapna, 1994). In this paper, the domain of attraction for the steady sliding equilibrium point is characterized for a system in which normal force is coupled to tangential displacement. Perturbations consisting of sudden changes in the displacement and velocity of the loading point are considered. These perturbations can be viewed as either actuator disturbances or changes in control input. The effect and interaction of the frictional and geometric parameters are elucidated. The results are applicable to the design and analysis of systems in which steady motion without friction-induced limit cycles is desired.
Dispersion of Flexural Waves on Shells
Authors: Rebinsky D. A. , Norris A. N.
Published: February 2008

Simple and accurate approximations are given for the dispersion properties of flexural waves on curved shells in vacuo. The results apply to shells of arbitrary double curvature, and are valid over the full frequency range of interest, from very high down to values below the generalized ring frequency.
Pendulum as Vibration Absorber for Flexible Structures: Experiments and Theory
Authors: Cuvalci O. , Ertas A.
Published: February 2008

The dynamic response of a beam-tip mass-pendulum system subjected to a sinusoidal excitation is investigated. A simple pendulum mounted to a tip mass of a beam is used as a vibration absorber. The nonlinear equations of motion are developed to investigate the autoparametric interaction between the first two modes of the system. The nonlinear terms appear due to the curvature of the beam and the coupling effect between the beam and pendulum. Complete energy transfer between modes is shown to occur when the beam frequency is twice the pendulum frequency. Experimental results are compared with a theoretical solution obtained using numerical integration. The experimental results are in qualitative agreement with the theory.
Determination of Far-Field Pattern of Rigid Scatterers Using Independent Finite Element Method and Eigenfunction Expansion, Part 1: Axisymmetric Scattering
Authors: Vendhan C. P. , Prabavathi C.
Published: February 2008

The near-field steady state scattered potential around a rigid scatterer subjected to plane incident wave is computed using the finite element method with radiation boundary dampers on a finite truncation boundary. Then the solution in the outer domain is sought in the form of an eigenfunction expansion and the expansion coefficients are obtained using the finite element solution on the truncation boundary as Dirichlet boundary condition. The scattered far-field pattern is derived from this solution for prolate spheroid and hemispherically capped cylinder problems.
Minimization of Acoustic Potential Energy in Irregularly Shaped Cavities
Authors: Yang T. C. , Tseng C. H. , Ling S. F.
Published: February 2008

This study presents a software design tool for solving active noise control problems in irregularly shaped cavities with continuous and noncontinuous design variables and appropriate constraints. The optimum amplitude, phase, and location of the secondary source were simultaneously determined by minimizing the total acoustic potential energy of the control volume in the cavity. The boundary element method was utilized for computing the sound field in the cavity. An optimizer based on sequential quadratic programming was selected for its accuracy, efficiency, and reliability. In order to cope with noncontinuous design variables, the optimizer was linked with a modified branch and bound procedure for practical applications. Simulations indicated that the optimal secondary source in an irregularly shaped car cabin could always be positioned in a region close to the primary source if the primary source was located in a corner of the cavity and the excitation frequency was not a resonance. However, different findings were obtained if the primary source was not located in a corner and the excitation frequency was a resonance. Optimal secondary source locations could appear at antinodal points of the dominant mode not necessarily near the primary source.
Performance of Particle Dampers Under Random Excitation
Authors: Papalou A. , Masri S. F.
Published: February 2008

An experimental and analytical study is made of the performance of particle dampers under wide-band random excitation. A small model, provided with a nonlinear auxiliary mass damper, was used to investigate the major system parameters that influence the performance of particle dampers: total auxiliary mass ratio, particle size, container dimension, and the intensity and direction of the excitation. It is shown that properly designed particle dampers, even with a relatively small mass ratio, can considerably reduce the response of lightly damped structures. An approximate analytical solution, which is based on the concept of an equivalent single unit-impact damper, is presented. It is shown that the approximate solution can provide an adequate estimate of the root-mean-square response of the randomly excited primary system when provided with a particle damper that is operating in the vicinity of its optimum range of parameters.
Practical Limitations in Achieving Shaped Modal Sensors With Induced Strain Materials
Authors: Clark R. L. , Burke S. E.
Published: February 2008

The purpose of this work is to explore practical limitations associated with the design of distributed modal sensors from induced strain materials for two-dimensional structures and illuminate difficulties associated with positioning sensors on structures in general. Results from this study indicate that a true modal sensor cannot be realized on a two-dimensional structure unless the boundary conditions are all pinned. This result stems from the fact that the sensor aperture must be orthogonal with respect to the structural mode (eigenfunction) and the curvature of the structural mode to render a distributed modal filter. The only class of functions satisfying this condition are sinusoidal functions. In addition, positioning of distributed strain sensing material is shown to be critical to the performance of the sensor over a specified bandwidth, specifically in the vicinity of structural resonances.
Thermodynamic Analysis of Space Solar Dynamic Heat Receivers with Cyclic Phase Change
Authors: Hall C. A. , Glakpe E. K. , Cannon J. N. , Kerslake T. W.
Published: February 2008

A physical and thermodynamic model of space solar dynamic heat receivers employing solid-liquid phase change storage is developed. Generalized first and second law efficiencies are defined for cyclic operation. The solar heat receiver of NASA Glenn Research Center’s Solar Dynamic Ground Test Demonstration System is used to generate numerical results from startup through balanced-orbit (asymptotic) conditions. In addition, a parametric study is performed to assess changes in receiver first and second law efficiencies due to changes in various system measurable parameters. Results show that parametric changes in system parameters result in maximum deviations of the asymptotic first law efficiency of less than 5 percentage points. The maximum departures of the asymptotic second law efficiency are less than 4 percentage points. Although the NASA receiver configuration is not optimized for cyclic thermodynamic performance, the cycle-integrated first and second law efficiencies compare favorably with steady-state numerical and experimental first and second law efficiencies.
Dynamic Stall and Aerodynamic Damping
Authors: Rasmussen F. , Petersen J. T. , Madsen H. A.
Published: February 2008

Riso̸ has developed a dynamic stall model that is used to analyze and reproduce open air blade section measurements as well as wind tunnel measurements. The dynamic stall model takes variations in both angle of attack and flow velocity into account. The paper gives a brief description of the dynamic stall model and presents results from analyses of dynamic stall measurements for a variety of experiments with different airfoils in wind tunnel and on operating rotors. The wind tunnel experiments comprises pitching as well as plunging motion of the airfoils. The dynamic stall model is applied for derivation of aerodynamic damping characteristics for cyclic motion of the airfoils in flapwise and edgewise direction combined with pitching. The investigation reveals that the airfoil dynamic stall characteristics depend on the airfoil shape, and the type of motion (pitch, plunge). The aerodynamic damping characteristics, and thus the sensitivity to stall induced vibrations, depend highly on the relative motion of the airfoil in flapwise and edgewise direction, and on a possibly coupled pitch variation, which is determined by the structural characteristics of the blade.