bluuebunny/crossref_metadata_2025 huggingface dataset:
Rigid-Plastic Deformation of a Ring-Stiffened Shell Under Blast Loading
Authors: Hoo Fatt M. S.
Published: February 2008

An approximate solution for the plastic deformation of a ring-stiffened cylindrical shell in response to a nonaxisymmetric, exponentially decaying pressure load, is presented. The analogy between the ring-stiffened cylindrical shell and a rigid-plastic string-on-foundation with discrete plastic resisting elements is used to find closed-form solutions for the transient and final deformations of the shell. Dynamic equilibrium of the central bay of the shell and the adjacent ring-stiffeners results in an inhomogeneous wave equation with inhomogeneous boundary conditions for the string. The initial-boundary value problem is solved by the method of eigenfunction expansion and a suitable orthogonality condition. The zeroth mode for the string describes rigid-body motion of the bay due to the remaining inertia of adjacent stiffeners. Permanent deformations are obtained using a plastic unloading criterion whereby the velocity and strain rate for each eigenmode vanish simultaneously. In the example problem, higher eigenmodes decay and vanish rapidly and final shell deformations are primarily governed by lower eigenmodes. The structural model gives qualitatively correct transient deflections and would be amenable to fine-tuning with numerical analysis and experimental evidence.
Technical Basis for Flawed Cylinder Test Specification to Assure Adequate Fracture Resistance of ISO High-Strength Steel Cylinder
Authors: Rana M. D. , Smith J. H. , Tribolet R. O.
Published: February 2008

High-pressure industrial gases (such as oxygen, nitrogen, argon, hydrogen, etc.) are stored and transported in portable cylinders. ISO TC58 SC3 has developed a draft specification 9809 for design and fabrication of high-pressure cylinders with maximum tensile strength limitation of 1100 N/mm2. In order to extend the ISO 9809 rules for higher than 1100 N/mm2 strength level cylinders, a working group WG14 was formed in 1989 to develop new rules to assure adequate fracture resistance. In 1994, WG14 recommended a simple, but unique flawed cylinder test method for design qualification of the cylinder and acceptance criteria to assure adequate fracture resistance. WG14 also recommended Charpy-V-notch impact tests to control the required fracture resistance on production cylinders. This paper presents the technical basis that was employed in developing the flawed cylinder test method and acceptance criteria. The specification was developed for seamless steel cylinders having actual strength in the range of 1100 to 1400 N/mm2 and cylindrical section wall thickness in the range of 3 to 10 mm. Flawed cylinder tests were conducted on several hundred cylinders of varying sizes and strength levels. The specification requires to demonstrate LEAK-BEFORE-BREAK performance of the cylinder having flaw length equal to 1.6 (o.d. × tdesign)0.5 at failure pressure = (tdesign/tactual) × Design Pressure.
Dynamic Response of a Hemispherical Foundation Embedded in an Elastic Half-Space
Authors: Yeh C.-S. , Teng T.-J. , Liao W.-I.
Published: February 2008

The dynamic response of a massless rigid hemispherical foundation embedded in a uniform homogeneous elastic half-space is considered in this study. The foundation is subjected to external forces, moments, plane harmonic P and SH waves, respectively. The series solutions are constructed by three sequences of Lamb’s singular solutions which satisfy the traction-free conditions on ground surface and radiation conditions at infinity, automatically, and their coefficients are determined by the boundary conditions along the soil-foundation interface in the least square sense. The fictitious eigen-frequencies, which arise in integral equation method, will not appear in the numerical calculation by the proposed method. The impedance functions which characterize the response of the foundation to external harmonic forces and moments at low and intermediate frequencies are calculated and the translational and rocking responses of the foundation when subjected to plane P and SH waves are also presented and discussed in detail.
Effects of Flaw Sizing Errors on the Reliability of Vessels and Piping
Authors: Simonen F. A. , Khaleel M. A.
Published: February 2008

This paper describes probabilistic fracture mechanics calculations that simulate fatigue crack growth, flaw detection, flaw sizing accuracy, and the impacts of flaw acceptance criteria. The numerical implementation of the model is based on a Latin hypercube approach. Calculations have been performed for a range of parameters. For representative values of flaw detection probability, flaw sizing errors, and flaw acceptance criteria, detection capability is the most limiting factor with regard to the ability of the inservice inspections to reduce leak probabilities. However, gross sizing errors or significant relaxations of current flaw acceptance standards could negate the benefits of outstanding probability of detection capabilities.
A Sensitive Ultrasonic Approach to NDE of Tightly Closed Small Cracks
Authors: Ahmed S. R. , Saka M.
Published: February 2008

A sensitive ultrasonic technique for the quantitative nondestructive evaluation of small closed cracks is developed. The use of an oblique longitudinal wave with small angle of incidence upon the specimen surface is emphasized. Firstly, ultrasonic testing is performed with open cracks in order to predict the optimum angle of evaluation, and an empirical calibration equation is then derived for the same as a basis to deal with the analysis of closed cracks. From the measurement on real fatigue cracks, the parameters of interest, specifically the crack size and the closure stress, are determined simultaneously by analyzing the inverse problem. The method developed here is fully automated and computer-controlled. Evaluated results are found to be in good conformity with the destructive measurements, and the corresponding superiority of the method is realized, especially for tightly closed small fatigue cracks, when compared with the method using a beam of longitudinal wave incident normally and/or with a large angle.
J-R Curves From Circumferentially Through-Wall-Cracked Pipe Tests Subjected to Combined Bending and Tension—Part I: Theory and Numerical Simulation
Authors: Miura N. , Wilkowski G. M.
Published: February 2008

One of the key aspects in leak-before-break analyses is to predict the maximum load-carrying capacity of a circumferentially cracked pipe. Such analyses require the fracture resistance of the material using the J-integral parameter, typically using small-scale laboratory specimens, such as compact tension, C(T), or three-point bend specimens. To evaluate the similitude between the laboratory specimens and a circumferentially through-wall-cracked pipe, the toughness can be evaluated directly from the pipe using an analysis typically called an η-factor approach. The fracture resistance from the pipe tests can then be compared to laboratory specimen toughness values to assess similitude issues. Additionally, several analysis methods (i.e., LBB.NRC, LBB.ENG, LBB.GE, etc.) that predict maximum load capability of through-wall-cracked pipes have η-factor analyses embedded in them. Hence, the evaluation of the J-R curve accuracy or consistency with small-scale specimens is a verification of one step in such predictive analyses. This paper presents extensions to the earlier η-factor solutions for circumferentially through-wall-cracked pipes where the previous analyses were for cracks in pipes under either pure bending or pure tension. The improvements investigated account for loading under combined bending and tension due to internal pressure. The application of these methods to full-scale pipe tests is presented in Part II (Miura and Wilkowski, 1998) of this paper.
J-Estimation Schemes for Internal Circumferential and Axial Surface Cracks in Pipe Elbows
Authors: Mohan R. , Krishna A. , Brust F. W. , Wilkowski G. M.
Published: February 2008

In the spirit of GE/EPRI fracture mechanics procedure, estimation schemes for the crack driving force for circumferentially and axially surface-cracked pressurized elbows subjected to bending are developed. These schemes are based on the results of line-spring/shell model. The line-spring/shell model offers an attractive and inexpensive alternative to performing a large number of analyses of surface-cracked structures. This model has been shown to provide accurate predictions in comparison with the more involved three-dimensional model by Mohan (1998). Using the results of this model and following the GE/EPRI procedure, the coefficient functions, F1 and h1, which provide the necessary information for predicting the crack driving force in cracked elbows, for several elbow and crack geometries are tabulated.
Dome Reversal of Metal Beverage Containers
Authors: Corona E.
Published: February 2008

Dome reversal in metal beverage containers refers to the event when the dome at the bottom of the containers snaps through due to overpressurization. This paper presents a combined experimental and numerical investigation of the problem. The response of the bottom of the containers considered is primarily axisymmetric prior to buckling and is characterized by a limit pressure instability. Under volume-controlled loading, collapse in an asymmetric mode occurs shortly after the limit pressure is achieved. An axisymmetric model of the problem was sufficient to calculate the limit pressure for the case considered. Results from a nonaxisymmetric model indicated that asymmetric modes became dominant after the limit pressure had been achieved.
The Functional Basis of Steady-State Thermal Energy Use in Air-Side HVAC Equipment
Authors: Reddy T. A. , Katipamula S. , Kissock J. K. , Claridge D. E.
Published: February 2008

A proper understanding of the functional basis of energy use in residences has been crucial in spurring energy conservation in such building stock. In commercial buildings, however, such understanding is lacking, partly because there are numerous possible HVAC system types and control strategies, and partly because the detailed algorithms available to simulate energy use in various types of HVAC systems provide little insight into identifying ways of saving energy in existing buildings. The objective of this paper is to derive closed-form steady-state functional relations for air-side cooling and heating thermal energy use for four of the most widespread HVAC system types, namely terminal reheat and dual-duct, both under constant air volume and under variable air volume operation. Expressions are derived for hourly energy use as a function of climatic variables, building characteristics, and system parameters. The effects of economizer cycle and deck reset schedules are also treated. The expressions derived could be utilized to develop functionally accurate regression models of monitored energy use for retrofit savings determination and to ascertain whether the HVAC system is operating properly, as well as for parameter estimation from either short-term or long-term monitoring and for sensitivity analyses of how various physical and operating parameters affect energy use.
On the Use of the Parabolic Concentration Profile Assumption for a Rotary Desiccant Dehumidifier
Authors: Chant E. E. , Jeter S. M.
Published: February 2008

The current work describes a model for a desiccant dehumidifier which uses a parabolic concentration profile assumption to model the diffusion resistance inside the desiccant particle. The relative merits of the parabolic concentration profile model compared widely utilized rotary desiccant wheel models are discussed. The periodic steady-state parabolic concentration profile model developed is efficient and can accommodate a variety of materials. These features make it an excellent tool for design studies requiring repetitive desiccant wheel simulations. A quartic concentration profile assumption was also investigated which yielded a 2.8 percent average improvement in prediction error over the parabolic model.
Thermal Fatigue Failure at the White Cliffs Solar Thermal Power Plant
Authors: Bannister P.
Published: February 2008

The failure of receivers has been one of the main operating problems at the White Cliffs solar thermal power plant. This Technical Note reports the results of an initial investigation that identifies the cause as having been the thermal fatiguing of the tube walls. The fatigue appears to be caused by unstable heat transfer at vapor qualities below the point where critical heat flux is generally exceeded. Methods for avoiding this problem are tested.
A Strong, Low-Cost Mount for Parabolic Dish Solar Collectors
Authors: Cordy C.
Published: February 2008

This paper presents the design of a cradle for mounting solar energy concentrator dishes. The cradle is strong and provides unobstructed space to mount a well braced dish. It will survive high winds without being driven to a stow position. The axes of rotation of the dish pass near the plane of the edge of the dish to reduce wind-induced torques in the drive system. Large radius tracks are attached to both the dish and cradle so the gear train on the drive motors can be simple and inexpensive. The cradle is a strong gimbal mount built of 12 structural members in the form of three tetrahedra. It provides a polar axis mount for the concentrator dish. All forces parallel to the polar axis are delivered to the earth at the end of the cradle closest to the equator.
Nonisothermal Receivers
Authors: Ries H. , Kribus A. , Karni J.
Published: February 2008

The reradiation losses, inherent to every thermal receiver, can be significantly reduced by exposing the working fluid to monotonously increasing irradiance and preventing energy exchange between parts of the receiver that are at different temperatures. In this way the highest temperatures are reached only near the end of the working fluid’s path. The improvement is much more pronounced for nonuniform as compared to uniform irradiance. For a Gaussian distribution of irradiance we calculate improvements exceeding a factor of two for the efficiency at a given temperature (0.8 of the peak stagnation temperature), and for the temperature at a given efficiency of 0.8. These results are independent of the peak irradiance and of the width of the distribution. Even a coarse partitioning into two mutually isothermal parts can already produce a significant improvement over the totally isothermal receiver.
Advanced Solar Dynamic Space Power Systems, Part I: Efficiency and Surface Optimization
Authors: Agazzani A. , Massardo A.
Published: February 2008

The aim of this work is the proposal and the analysis of advanced solar dynamic space power systems for electrical space power generation. The detailed thermodynamic analysis of SDCC (Solar Dynamic Combined Cycle) and SDBC (Solar Dynamic Bynary Cycle) systems is carried out. The analysis is completed with an optimization procedure that allows the maximum efficiency and minimum surface conditions to be obtained. The calculation is carried out for the orbital conditions of the NASA-Freedom Space Station. The results are presented, compared with the data already published for a reference CBC (Closed Brayton Cycle) plant (Massardo, 1993b), and discussed in depth.
Advanced Solar Dynamic Space Power Systems, Part II: Detailed Design and Specific Parameters Optimization
Authors: Agazzani A. , Massardo A.
Published: February 2008

The aim of this work is the proposal and the analysis of advanced solar dynamic space power systems for electrical space power generation. In the first part of this work (Agazzani and Massardo, 1995) a performance optimization procedure for a SDCC (Solar Dynamic Combined Cycle) and a SDBC (Solar Dynamic Binary Cycle) was presented. Results have pointed out improvements obtainable in terms of conversion efficiency and specific area (m2/kWe), this last estimated in a simplified way. Nevertheless, before drawing conclusions about the superiority of these advanced systems, it is necessary to verify the constructive possibility of the single components of the systems, estimating weights and surfaces, the most significant parameters in space applications. In this second part the design procedures of some components will be discussed in detail; a complete optimization procedure (thermodynamic analysis and detailed design) will be presented with the purpose of minimizing specific area (m2/kWe) and specific mass (kg/kWe). The results obtained are presented, discussed, and compared with the data of a reference optimized CBC system (Massardo, 1993b).
Natural Convection in a Corrugated Enclosure With Mixed Boundary Conditions
Authors: Noorshahi S. , Hall C. A. , Glakpe E. K.
Published: February 2008

Numerical solutions to the two-dimensional equations governing natural convective flow of air (Prandtl number = 0.71) contained in an enclosure with varying angles of inclination to the horizontal axis have been obtained. The air layer is bounded by a corrugated surface under uniform heat flux conditions, a flat isothermal cooled surface and around the edges by flat adiabatic surfaces. The numerical solutions are obtained in a transformed coordinate system in which the boundaries of the enclosure coincide with coordinate surfaces. The coordinate system is generated with simple algebraic expressions. The numerical scheme is employed in performing parametric heat transfer calculations. The range of parameters investigated include: modified Rayleigh numbers up to 106, amplitude aspect ratio from 0 to 0.4, inclination angles of 30, 60, and 90 degrees, and number of cycles per unit length of enclosure values of 4/5 and 4. All parameters investigated have varying degrees of influence on the heat transfer and fluid flow. In addition to the usual influence of the modified Rayleigh number on natural convective flows, the region of pseudo-conduction is increased as the enclosure amplitude ratio is increased. The distributions of temperature along the corrugated surface suggest that correlations obtained under isothermal conditions cannot be employed in the design or analysis of the energy transfer system investigated.
The Thermal Performance of Residential Electric Water Heaters Subjected to Various Off-Peak Schedules
Authors: Fanney A. H. , Dougherty B. P.
Published: February 2008

An increasing number of utilities control the supply of power to residential water heaters as one means of reducing peak electrical demand. Water heaters operated in this manner are referred to as off-peak water heaters. Several utilities are also considering the use of solar domestic water heaters as an additional means of limiting power demand during times of greatest electrical usage. The research described within this paper quantifies the variation in thermal efficiency attributable to subjecting residential electrical water heaters to various off-peak and water removal schedules and, thus, forms a basis of comparison to which the thermal efficiency of solar water heaters or other water heating technologies may be compared. Laboratory tests, where the off-peak period and hot water draw schedule were varied, were conducted on two residential storage water heaters. A computer model of an electric water heater was developed and validated. The laboratory tests and the model were used to quantify the effect that various off-peak and hot water draw schedules have on water heater thermal efficiency. Thermal efficiency was found to vary up to seven percent for water heaters which meet the present minimum efficiency standards as specified within the National Appliance Energy Conservation Act. The energy factor, as measured using the Department of Energy Test Procedure for Water Heaters, is shown to be independent of the off-peak schedule because of a “normalizing” that occurs as part of the calculation procedure.
Exergy Analysis of Thermal Energy Storage With Specific Remarks on the Variation of the Environmental Temperature
Authors: Bisio G.
Published: February 2008

Energy storage is a key technology for many purposes and in particular for air conditioning plants and a successful exploitation of solar energy. Thermal storage devices are usually classified as either variable temperature (“sensible heat”) or constant temperature (“latent heat”) devices. For both models a basic question is to determine the efficiency suitably: Only exergy efficiency appears a proper way. The aim of this paper is to examine exergy efficiency in both variable and constant temperature systems. From a general statement of exergy efficiency by the present author, two types of actual definitions are proposed, depending on the fact that the exergy of the fluid leaving the thermal storage during the charge phase can be either totally lost or utilized elsewhere. In addition, specific remarks are made about the exergy of a system in a periodically varying temperature environment.
Analytical Model to Predict Nonhomogeneous Soil Temperature Variation
Authors: Krarti M. , Claridge D. E. , Kreider J. F.
Published: February 2008

This paper presents an analytical model to predict the temperature variation within a multilayered soil. The soil surface temperature is assumed to have a sinusoidal time variation for both daily and annual time scales. The soil thermal properties in each layer are assumed to be uniform. The model is applied to two-layered, three-layered, and to nonhomogeneous soils. In case of two-layered soil, a detailed analysis of the thermal behavior of each layer is presented. It was found that as long as the order of magnitude of the thermal diffusivity of soil surface does not exceed three times that of deep soil; the soil temperature variation with depth can be predicted accurately by a simplified model that assumes that the soil has constant thermal properties.
Airflow and Air Quality in a Large Enclosure
Authors: Jiang Z. , Chen Qingyan , Haghighat F.
Published: February 2008

Knowledge of air flow patterns and thermal parameters are essential in the design of a ventilation system for large enclosures. The objective of this paper is to evaluate the possibility of using computer simulation to predict the airflow pattern and removal effectiveness of ventilation systems in large enclosures. The quality of air and thermal comfort in a three-floor shopping center are studied by the computational fluid dynamics (CFD) method. Two ventilation systems are selected. In System 1, rooms are ventilated by two ceiling slot diffusers, supplying air downward into the rooms. The halls are equipped with wall jet diffusers delivering air in a horizontal direction. Airflow and air quality, under both summer and winter conditions, are investigated. In System 2, the air in each room is supplied in a radial manner by four ceiling rectangular diffusers. The hall and balconies have jet diffusers which supply air vertically downward. Different ventilation rates, outdoor air ratios and supply air temperatures are studied. Occupants are simulated by heat and CO2 sources without aerodynamic blockages. It was found that the summer and winter air temperature differences in the shopping center differ by approximately 2°C. The rectangular air diffusers should he used in the rooms and the jet diffusers in the halls and balconies. Both the variable air volume and the constant air volume methods, with an adjusted supply air temperature, can be used for air conditioning control in a large enclosure.
Gradient-Zone Erosion by Extraction in Solar Ponds
Authors: Estevadeordal J. , Kleis S. J.
Published: February 2008

The erosion the dynamically stable gradient zone of a salinity-gradient solar pond, due to the extraction of fluid from the storage zone, is numerically investigated. The effects of fluid withdrawal rate, density stratification level, pond and diffuser geometries, and diffuser placement are considered. It is found, for a typical salinity-gradient solar pond with uniform salinity in the storage zone and a continuous salinity gradient above that a finite amount of fluid entrainment from the gradient zone is inevitable. That is, a finite density difference across the interface is always required for a finite extraction rate under steady-state conditions. The magnitude of the density difference is predicted as function of the geometric and flow parameters. From the results, it is possible to predict the total amount of fluid entrained from the gradient zone as the pond reaches steady-state for prescribed operating conditions.
The Measured Energy Impact of Infiltration in an Outdoor Test Cell
Authors: Claridge D. E. , Liu Mingsheng
Published: February 2008

Air infiltration energy consumption was investigated in an outdoor test cell with different leakage configurations and air flow rates under both infiltration and exfiltration. Measurements showed that under heating conditions, the air infiltration energy consumption ranged from 55 percent less than to 15 percent greater than the classically calculated values, depending on the air flow rate and direction (infiltration or exfiltration), solar radiation, and air leakage configuration.
Heat and Mass Transfer From a Streaming Hot Saline Water in an Enclosure Partitioned by an Active Baffle
Authors: Njomo D. , Tchinda R. , Kaptouom E.
Published: February 2008

Equations describing heat and mass exchanges in a closed cavity with hot saline water streaming on its base and partitioned by an externally cooled flat heat exchanger are numerically solved. The results obtained show that an increase of inlet saline water temperature or mass flow rate increases the heat and mass transfer between evaporation and condensation surfaces. Furthermore, external cooling of the condensation surface contributes significantly to the increase of these exchanges. Our theoretical analysis is in reasonably good agreement with experimental results published in the literature for the practical heat exchange fluxes encountered in solar stills.
Performance of Wind-Electric and Solar-PV Water Pumping Systems for Watering Livestock
Authors: Vick B. D. , Clark R. N.
Published: February 2008

The water pumping performance of two wind-electric systems is compared to the water pumping performance of two solar-PV systems. The wind-electric systems were rated at 1.0 kW and 1.5 kW at a wind speed of about 12 m/s, and the rotor diameters were 2.75 m and 3.05 m, respectively. The solar-PV systems were rated at 0.1 kW and 0.9 kW at a radiation level of about 1000 W/m2, and the total solar panel surface areas were 1 and 17 m2, respectively. Both wind-electric systems powered three-phase 230 V a-c induction motors with centrifugal pumps. The smaller of the solar-PV systems powered a d-c motor with a diaphragm pump, and the larger one powered a single phase 230 V a-c induction motor with a centrifugal pump. Only a well pumping depth of 30 m was evaluated for both wind-electric and solar-PV water pumping systems. The 0.1 kW and the 0.9 kW solar water pumping systems can provide enough water for 25 and 75 cattle, respectively, if the incident solar radiation is similar to that of Bushland, TX. The 1.0 kW and 1.5 kW wind-electric water pumping systems can provide enough water for 300 and 400 cattle, respectively, if the wind regime is similar to that of Bushland, TX.
Effects of Blade Bending on Aerodynamic Control of Fluctuating Loads on Teetered HAWT Rotors
Authors: Eggers A. J. , Ashley H. , Rock S. M. , Chaney K. , Digumarthi R.
Published: February 2008

Active aerodynamic control, in the form of closed-loop actuation of blade-tip ailerons or all-moveable blades, is investigated as a means of increasing the structural fatigue life of HAWT rotors. The rotor considered is upwind and teetered, with two blades of diameter 29.2 m., fiberglass construction and other properties representative of modern light-weight construction. The paper begins with a review of prior work which studied the problem for an essentially rigid structure. For that and the present research, two loading conditions were invoked: exposure to a Rayleigh distribution of operating winds with vertical shear and a 15 percent superimposed spectrum of turbulence; and occasional exposure to 62 m/s hurricanes. Accounted for herein is the effect of flatwise bending flexibility on the loads spectra of root flatwise bending moment, thrust, and torque (both open loop and closed loop). Using Miner’s rule, the moments are converted to fatigue lives. With aerodynamic control, RMS flatwise moments for the flexible blade in turbulence are found to be less than 1/2 of those without control. At a fixed blade weight of 540 kg when hurricane loads are added, the aileron-controlled blade is “designed” by that limit-load condition. In contrast, the all-moveable blade can be feather controlled in the high wind so that its life is dominated by turbulent loads. Simplified fatigue analysis permits weight reductions to be estimated which yield controlled blades capable of 30 years’ operation with a safety factor of 11. The resulting weights are about 400 kg for the aileron-controlled blade, and 230 kg for the all-moveable blade. However, such light-weight rotors require attention to other design considerations, such as start-stop cycles. Apart from limit loads, the methods of analysis in this paper are linearized (locally for aerodynamic loads). It follows that the results are more likely to be meaningful in terms of comparative, rather than absolute, values of fatigue life and weight.
Using a Collision Model to Design Safer Wind Turbine Rotors for Birds
Authors: Tucker V. A.
Published: February 2008

A mathematical model for collisions between birds and propellor-type turbine rotors identifies the variables that can be manipulated to reduce the probability that birds will collide with the rotor. This study defines a safety index—the “clearance power density”—that allows rotors of different sizes and designs to be compared in terms of the amount of wind energy converted to electrical energy per bird collision. The collision model accounts for variations in wind speed during the year and shows that for model rotors with simple, one-dimensional blades, the safety index increases in proportion to rotor diameter, and variable speed rotors have higher safety indexes than constant speed rotors. The safety index can also be increased by enlarging the region near the center of the rotor hub where the blades move slowly enough for birds to avoid them. Painting the blades to make them more visible might have this effect. Model rotors with practical designs can have safety indexes an order of magnitude higher that those for model rotors typical of the constant speed rotors in common use today. This finding suggests that redesigned rotors could have collision rates with birds perhaps an order of magnitude lower than today’s rotors, with no reduction in the production of wind power. The empirical data that exist for collisions between raptors, such as hawks and eagles, and rotors are consistent with the model: the numbers of raptor carcasses found beneath large variable speed rotors, relative to the numbers found under small constant speed rotors, are in the proportions predicted by the collision model rather than in proportion to the areas swept by the rotor blades. However, uncontrolled variables associated with these data prevent a stronger claim of support for the model.
The Effect of Using a Heat Recovery Absorber on the Performance and Operating Cost of the Solar Ammonia Absorption Cycles
Authors: Saghiruddin  , Siddiqui M. Altamush
Published: February 2008

Economic analysis of ordinary and evacuated tubular type flat-plate collectors have been carried out for operating absorption cycles with and without heat recovery absorber. Water-ammonia, NaSCN-NH3 and LiNO3-NH3 have been selected as the working fluids in the cycles. Use of a heat recovery absorber, in addition to the primary absorber in the conventional absorption cycles, lead to improvement in the system performances by about 20–30 percent in the H2O-NH3 and 33–36 percent in the NaSCN-NH3 and LiNO3-NH3 mixtures. Subsequently, there is a considerable amount of reduction in the cost of the solar collector required to operate them. For the set of operating conditions, in this theoretical study, the cost reduces to about 25 percent in the H2O-NH3 and 30 percent in the NaSCN and LiNO3-NH3 cycles.
Gradient-Zone Erosion in Seawater Solar Ponds
Authors: Shi J. , Hart R. A. , Kleis S. J. , Bannerot R. B.
Published: February 2008

An experimental program has been conducted to examine the feasibility of using seawater solar ponds in mariculture operations along the Texas gulf coast to protect fish crops from the potentially lethal, cold temperatures experienced in outdoor ponds. Seawater solar ponds in the form of floating thermal refuge areas are proposed as a method for reducing the loss of heat from small sections of a pond. Gradient zone erosion under various ambient and operating conditions is examined. Comparisons with previous laboratory studies show a much lower entrainment rate in the natural environment. For conditions which are typical of those encountered in mariculture pond operation, the entrainment rate was found to depend only weakly on the Richardson number. For these conditions, a simple (linear) correlation of entrainment rate with wind speed was developed.
Feedforward Control of Solar Thermal Power Plants
Authors: Meaburn A. , Hughes F. M.
Published: February 2008

In recent years the problem of controlling the temperature of oil leaving an array of parabolic trough collectors has received much attention. The control schemes developed have in general utilized a feedback control loop combined with feedforward compensation. The majority of the published papers place the emphasis almost entirely on the design of the feedback control loop. Little or no attention has been paid to issues involved in the design of the feedforward controller. This paper seeks to redress this imbalance by concentrating upon the design and development of a feedforward controller for the ACUREX distributed solar collector field at the Plataforma Solar de Almeria. Different methods of combining feedback and feedforward will be assessed and experimental results will be presented in order to support any theoretical observations made.
The Effect of Irradiation Directional Distribution on Absorption in Volumetric Solar Receivers
Authors: Doron P. , Kribus A.
Published: February 2008

Volumetric solar absorbers are designed to enable the penetration of radiation deep into the absorber in order to improve the efficiency of the energy transfer from incoming radiation to the working fluid. The design of such absorbers is usually based on the irradiation energy flux distribution. We show that the directional features of the irradiation also affect the absorption characteristics of volumetric absorbers, present criteria for the characterization of directional attributes, and describe a method for their calculation. The significance of the directional data is demonstrated for two types of volumetric absorbers. Receiver design and modeling guidelines are presented.
The DIAPR: A High-Pressure, High-Temperature Solar Receiver
Authors: Karni J. , Kribus A. , Doron P. , Rubin R. , Fiterman A. , Sagie D.
Published: February 2008

A solar central receiver absorbs concentrated sunlight and transfers its energy to a working medium (gas, liquid or solid particles), either in a thermal or a thermochemical process. Various attractive high-performance applications require the solar receiver to supply the working fluid at high temperature (900–1500°C) and high pressure (10–35 bar). As the inner receiver temperature may be well over 1000°C, sunlight concentration at its aperture must be high (4–8 MW/m2), to minimize aperture size and reradiation losses. The Directly Irradiated Annular Pressurized Receiver (DIAPR) is a volumetric (directly irradiated), windowed cavity receiver that operates at aperture flux of up to 10 MW/m2. It is capable of supplying hot gas at a pressure of 10–30 bar and exit temperature of up to 1300°C. The three main innovative components of this receiver are: • a Porcupine absorber, made of a high-temperature ceramic (e.g., alumina); • a Frustum-Like High-Pressure (FLHIP) window, made of fused silica; • a two-stage secondary concentrator followed by the KohinOr light extractor. This paper presents the design principles of the DIAPR, its structure and main components, and examples of experimental and computational results.
Stress in Shaped Glass Evacuated Collectors
Authors: Garrison J. D. , Fischer-Cripps A.
Published: February 2008

Shaped glass evacuated collectors have the lower vacuum envelope formed with a CPC shape. The internal surface is silvered. This surface concentrates solar radiation onto an internal absorbing tube. The upper part of the vacuum envelope is a window to pass the solar radiation in to the absorbing tube. A computer program using analytical equations is used to design these collectors while keeping the glass tensile stress arising from evacuation below acceptable limits. A finite element computer program is used to test the accuracy of the stress calculated analytically. The calculations agree within about 1 MPa. Wind and thermal stresses in the glass are lower than the stresses caused by evacuation.
Photocatalytic Disinfection of Indoor Air
Authors: Goswami D. Y. , Trivedi D. M. , Block S. S.
Published: February 2008

The present study demonstrated the antibacterial effect of photocatalytic oxidation in indoor air using titanium dioxide as the catalyst. Through a series of experiments, it was determined that titanium dioxide did enhance the inactivation rate of the microorganisms under certain conditions. In these experiments the air velocity, relative humidity, and UV (350 nm) intensity were varied. It was found that higher velocities retarded the destruction rate due to the low retention time in the reactor. TiO2 also did not accelerate the reaction at low humidities (30 percent). At a relative humidity of 50 percent, there was complete inactivation of the organisms, but at higher humidities (85 percent), 10 percent of the organisms were still viable. The experiments showed that at higher UV intensities, most of the inactivation was done by the UV photons. However, the photons were not able to completely inactivate the microorganisms. In the photocatalysis experiments there was complete inactivation of the bacteria.
Transient Dynamic Response of Arbitrary Stiffened Shells by the Finite Element Method
Authors: Sinha G. , Mukhopadhyay M.
Published: February 2008

Stiffened plates and shells often find wide application in bridge engineering, aircraft, ship and allied industries owing to its high strength to weight ratios. They are often subjected to dynamic loading such as air blast loading, for which detailed dynamic analysis is required to study the structure under these conditions. In the present approach, the dynamic response of stiffened plates and shells has been investigated by the finite element method employing a high precision arbitrary-shaped triangular shell element in which stiffeners may lie in any arbitrary direction within the element. This provides greater flexibility in the mesh generation. The governing undamped equations of motion have been solved by Newmark’s method for direct time integration. The dynamic response of plates and shells with or without stiffeners, subjected to different kinds of load-history have been studied and results are compared with the published analytical results.
Dynamic Characteristics of TEHD Tilt Pad Journal Bearing Simulation Including Multiple Mode Pad Flexibility Model
Authors: Kim J. , Palazzolo A. , Gadangi R.
Published: February 2008

An approach for incorporating the heat transfer and elastic deformation effects into dynamic coefficient calculation is presented. A global analysis method is used, which finds the equilibrium pad tilt angles at each eccentricity position and includes cross-film variable viscosity, heat transfer effects in the lubricant, elastic deformation, heat conduction effects in the pads, and elastic deformation effect in the pivots. Deflection modes are used to approximate deformation of the top surface of the pads. The dynamic coefficients of a single pad are calculated at the equilibrium state of the bearing, based on numerical perturbation with respect to the bearing degrees of freedom. These include journal position, pad rotation, pivot deformation, and modal coordinates. The stiffness and damping coefficients are calculated and show very good agreement with experimental and numerical results from the existing literature.
A Time-Domain Impedance Element for FEA of Axisymmetric Exterior Structural Acoustics
Authors: Kallivokas L. F. , Bielak J.
Published: February 2008

A finite element (FE)-based procedure is presented for the solution directly in the time-domain of transient problems involving axisymmetric three-dimensional structures submerged in an infinite acoustic fluid. The central component of the procedure is a novel impedance element that is used to render the computational domain finite. The element is local in both time and space, and is completely defined by a pair of stiffness and damping matrices. It is shown that the exterior structural acoustics problem can be solved accurately and efficiently by using the same tools as those used for interior problems. The method is illustrated with numerical results for a submerged shell.
A Formulation for Mean Flow Effects on Sound Radiation from Rectangular Baffled Plates with Arbitrary Boundary Conditions
Authors: Atalla N. , Nicolas J.
Published: February 2008

A general formulation of the sound radiation from fluid-loaded rectangular baffled plates with arbitrary boundary conditions has been developed by Berry et al. (JASA, Vol. 90, No. 4, Pt. 2, 1991). In this paper, an extension of this formulation to inviscid, uniform subsonic flow is considered. The analysis is based on a variational formulation for the transverse vibrations of the plate and the use of the extended, to uniformly moving media, form of the Helmholtz integral equation. The formulation shows explicitly the effect of the flow in terms of added mass, and radiation resistance. Furthermore, it avoids the difficult problem of integration in the complex domain, typical of the wavenumber transform approaches to fluid-loading problems. Comparison of the acoustic radiation impedance with existing studies supports the validity of the approach. The details of the formulation and its numerical implementation is exposed and a discussion of the flow effects on the radiation impedance of a rectangular piston is presented. It is shown that subsonic mean flow increases the modal radiation resistance at low frequencies and affects added mass more strongly than it affects radiation resistance.
Dynamic Characteristics of Specialty Composite Structures with Embedded Damping Layers
Authors: Saravanos D. A. , Pereira J. M.
Published: February 2008

Damping mechanics for predicting the damped dynamic characteristics in specialty composite structures with compliant interlaminar damping layers are presented. Finite-element based mechanics incorporating a discrete layer (or layer-wise) laminate damping theory are utilized to represent general laminate configurations in terms of lay-up and fiber orientation angles, cross-sectional thickness, shape and boundary conditions. Evaluations of the method with exact solutions and experimental data illustrate its accuracy. Additional parametric studies demonstrate the unique capability of angle-ply composite laminates with cocured interlaminar damping layers to significantly enhance structural damping.
Simple Modeling and Analysis for Crankshaft Three-Dimensional Vibrations, Part 2: Application to an Operating Engine Crankshaft
Authors: Morita T. , Okamura H.
Published: February 2008

The modeling and analysis procedures with the dynamic stiffness matrix method described in Part 1 were applied to a crankshaft system, consisting of crankshaft, front pulley, flywheel, piston, and connecting rod, under firing conditions. For firing conditions, (7) one half of the reciprocating masses consisting of the piston, piston pin, and connecting rod small end, and (2) rotating masses of the connecting rod big end mass, were attached to the two ends of the crankpin, taking account of the rigidity of the connecting rod. The excitation forces were calculated from the gas force and the inertia force due to the reciprocating masses. By solving the equations of motion derived in the form of the dynamic stiffness matrix, we calculated the three-dimensional steady-state vibrations of the crankshaft system under firing conditions. A crankshaft system for a four-cylinder in-line automobile engine was used for the analysis. We calculated the influence of the mass and moments of inertia of the front pulley on the behavior of the crankshaft vibrations and the excitation induced at the crankjournal bearings. Calculated values were compared with experimental results.
Nonlinear Normal Modes of a Continuous System With Quadratic Nonlinearities
Authors: Nayfeh A. H. , Nayfeh S. A.
Published: February 2008

We use two approaches to determine the nonlinear modes and natural frequencies of a simply supported Euler-Bernoulli beam resting on an elastic foundation with distributed quadratic and cubic nonlinearities. In the first approach, we use the method of multiple scales to treat the governing partial-differential equation and boundary conditions directly. In the second approach, we use a Galerkin procedure to discretize the system and then determine the normal modes from the discretized equations by using the method of multiple scales and the invariant manifold approach. Whereas one- and two-mode discretizations produce erroneous results for continuous systems with quadratic and cubic nonlinearities, all methods, in the present case, produce the same results because the discretization is carried out by using a complete set of basis functions that satisfy the boundary conditions.
Unsteady Isentropic Flow through Ducts with Prescribed Sound Pressure Level Distribution
Authors: Cherng J. G. , Na Tsung-Yen
Published: February 2008

An analytical method for the determination of the required shape of a duct for a prescribed sound pressure level distribution is presented in this paper. The physical model involves a sound wave propagating in an unsteady flow of compressible fluids through ducts. Two cases are considered. In the first case, the channel shape, F(X), is given as either an exponential function or a linear function of the distance along the axis with an unknown parameter in the expression for F(X). The unknown parameter is determined by the prescribed ratio of the sound pressure level at the exit section of the duct to that at the entrance. In the second case, the sound pressure level is specified at every point along the length of the duct, and the duct shape, F(X), is sought. The governing differential equations of the model are presented. The method of complex superposition is used to separate the real and the imaginary parts of the perturbation quantities. The results show that the cross-sectional area is sensitive to the flow speed and the frequency of the sound source. Furthermore, a convergent/divergent duct has to be used to achieve a linear sound pressure level distribution.
Decomposition of Gear Motion Signals and Its Application to Gearbox Diagnostics
Authors: Wang W. J. , McFadden P. D.
Published: February 2008

The decomposition of gear motion and the related dynamic measurements for the condition monitoring and fault diagnosis of gearboxes are described. The motion error signal is separated according to fundamental frequencies into the harmonic error and the residual error, which are used to quantify the gear condition. High-order accelerations, such as jerk, are considered and shown to be more sensitive to some classes of early damage to gear teeth. Analysis of the time domain average of a gearbox casing vibration signal enables early detection of gear damage. Several methods to represent and enhance the fault information in the signal are introduced, based on the representation of different forms of the motion errors.