bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanics of cuticular elastic energy storage in leg joints lacking extensor muscles in arachnids
Authors: Sensenig Andrew T. , Shultz Jeffrey W.
Published: January 2003

Certain leg joints in arachnids lack extensor muscles and have elastically deformable transarticular sclerites spanning their arthrodial membranes, an arrangement consistent with a model in which flexor muscles load transarticular sclerites during flexion and energy from elastic recoil is used for extension. This study quantifies the potential contribution of elastic recoil to extension torque at joints of the fourth leg of representative arachnids. Extension torques of isolated joints with and without transarticular sclerites were measured as the joint was rotated through angles and at angular velocities comparable with those used by walking animals. The procedure was repeated with the joint subjected to different internal fluid pressures in order to assess the potential role of hydraulically induced extension.

The efficiency of elastic energy storage (resilience) in the absence of internal fluid pressure was 70-90% for joints with well-developed transarticular sclerites, and the magnitude of torque was similar to those produced by different joint extension mechanisms in other arthropods. Increased internal fluid pressure acted synergistically with transarticular sclerites in some joints but had little or no effect in others. Joints that lacked both extensor muscles and transarticular sclerites appeared to be specialized for hydraulic extension, and joints operated by antagonistic muscles lacked apparent specializations for either elastic or hydraulic extension. It is well known that elastic energy storage is a significant contributor to propulsion in running vertebrates and certain arthropods, where elastic elements are loaded as the center of mass falls during one phase of the locomotor cycle. However, transarticular sclerites are apparently loaded by contraction of flexor muscles when the leg is not in contact with the substratum. Hence the mechanism of a transarticular sclerite is more similar to the flight and jumping mechanisms of other arthropods than to running vertebrates. The evolutionary significance and potential mechanical advantages of the transarticular elastic mechanism are discussed.
Measuring wing kinematics, flight trajectory and body attitude during forward flight and turning maneuvers in dragonflies
Authors: Wang Hao , Zeng Lijiang , Liu Hao , Yin Chunyong
Published: January 2003

A robust technique for determining the wing kinematics, body position and attitude of a free-flight dragonfly is described. The new method is based on a projected comb-fringe technique combined with the natural landmarks on a dragonfly, allowing us to establish the local body-centered coordinate system with high accuracy, and to measure the body attitude at any instant. The kinematic parameters, including wingbeat frequency, flapping angle, angle of attack, torsional angle and camber deformation, required no assumptions to be made with respect to wing geometry, deformability (except the assumption of rigid leading edges) or bilateral wing symmetry. Two typical flight behaviors,forward flight and turning maneuvers, of dragonflies Polycanthagyna melanictera Selys were measured and analyzed.
Numerical analysis of fretting contacts of dissimilar isotropic and anisotropic materials
Authors: Rajeev P. T , Farris T. N
Published: January 2003

A numerical method is presented to obtain the contact tractions when two dissimilar isotropic or anisotropic bodies are in partial slip contact. The solution to the governing coupled singular integral equations (SIEs) is obtained by incorporating the appropriate singular behaviour for the contact pressure and the shear traction. The edges of the contact zone and the stick zone are determined by iteration such that the constant multipliers of the singular functions vanish. For anisotropic materials the out-of-plane shear traction is assumed to be very small and hence neglected. The solution method has been successfully verified by comparing its results to solutions available in the literature and to the results obtained by the finite element method (FEM). By modifying the slip function to take into account the remote stress on the half-space, the SIE method can be used to analyse fretting contact problems. The resulting technique efficiently accounts for the effect of load history on the contact tractions and the contact and stick zone sizes. The pronounced effect that load history has on the stick zone size is illustrated.
Effects of process variables on fretting fatigue crack initiation in Ti-6A1-4V
Authors: Namjoshi S A , Mall S , Jain V K , Jin O
Published: January 2003

A fretting fatigue crack initiation mechanism (number of cycles, location and orientation angle) using critical plane based parameters has been addressed by several researchers. There are several process variables that can affect these parameters and thereby the prediction of fretting fatigue crack initiation behaviour. Effects of two such parameters, viz. process volume and the coefficient of friction, were investigated in this work. Fretting fatigue experiments with a titanium alloy were conducted with different contact pad geometries. Finite element analysis (FEA) was used to obtain a stress state in specimens for the experimental conditions used during fretting fatigue tests. Analysis was carried out for two values of the coefficient of friction, thereby providing a framework for calculation of several critical plane based multiaxial fatigue parameters for different process volumes. A program was developed to compute these multiaxial fatigue parameters from the FEA data for different values of process variables. It was observed that parameters for cylindrical pad geometries with no singularity-type behaviour were inversely proportional to the size of process volume and directly proportional to the coefficient of friction. There was no change in the predicted orientation of the primary crack for this geometry, due to variations in these process variables. Parameters for flat-pad geometries with behaviour approaching that of a singularity were also inversely proportional to the size of process volume, but the coefficient of friction had a minimal effect on their values. Predicted orientation of the primary crack for these geometries changed slightly when the process volume increased from that of a grain size of the tested material to a larger size, and then did not change with the increase of process volume size. Overall, the effect of these process variables on the critical plane based parameters was similar in all five contact geometries used in this study, when the scatter in fatigue data is kept in mind. Finally, the modified shear stress range parameter satisfactorily predicted the crack initiation location, orientation angle and number of cycles to fretting fatigue crack initiation independent of the contact geometry for a given process volume size and coefficient of friction.
Torsional loading of a finite shrink-fit shaft
Authors: Truman C E , Sackfield A , Hills D A
Published: January 2003

This paper treats the problem of a shaft of finite depth, shrink-fitted into a cavity and subject to remote torsion. The evolution of slip regions along the curved surface of the shaft is discussed and the effect of finite depth is investigated. The end face of the shaft is traction-free, which is achieved by distributing special axisymmetric dislocations giving a relative twist displacement over the end plane. This permits the conditions for no-slip along the curved surface to be found explicitly.
Three component velocity measurements of an isothermal confined swirling flow
Authors: Ahmed S A
Published: January 2003

A two-component fibre-optic laser Doppler velocimeter (LDV) system has been employed to measure the flowfield characteristics of a confined, isothermal strongly swirling flow in a combustor model. The primary objectives are to understand such complex flowfields and to provide complete benchmark data for comparisons with numerical predictions based on practical models for turbulent swirling flows, and thereby guide the development of such models. For this confined strongly swirling flow, the measurements show the radial velocity component (close to the swirler exit) to be of the same order as the axial and swirl components. Comprehensive and detailed data show a large central recirculation region close to the dump plane which extends beyond the last measurement station. High velocity gradients and high turbulence activities are common for this type of flow and the current set of data confirms these previous findings. Generally speaking, most of the mixing takes place in the shear layer between the annular swirling jet and the corner recirculation region due to the sudden expansion.
Airworthiness aspects of new technologies: Interaction between aircraft structural dynamics and control systems
Authors: Hockenhull M
Published: January 2003

The application of electrical flight control systems to civil transport aircraft has directed attention to the need for improved airworthiness regulation. In this paper, the scope and interpretation of a new FAR/JAR Part 25 regulation in preparation is discussed, applicable to aircraft that have closed-loop control systems for flight control, load alleviation or stability augmentation, and have the potential to interact with the aircraft's structural dynamics.
Vibration and control of aircraft wings
Authors: Whalley R , Ebrahimi M
Published: January 2003

The analysis and control of an aircraft, non-linear, variable parameter wing model is considered. Simple procedures using established techniques related to wing vibrational problems are outlined. Frequency response methods are employed to accommodate analysis methods wherein both the poles and zeros of the system model vary with velocity. A simple control strategy is invoked enabling regulation. The transient behaviour of the system is computed for the operational speeds of interest. The effectiveness of the control strategy is commented upon.
Characteristics of combustion and radiation heat transfer of an oxygen-enhanced flame burner
Authors: Hwang S. S. , Gore J. P.
Published: January 2003

The spectral and total radiation intensities of a methane/oxygen flame were investigated experimentally and compared with those of a methane/air flame. Different combinations of central and annular fuel-oxygen supplies were studied to find the best combination for increasing the radiation intensity. A fast infrared array spectrometer was used to measure the spectral radiation intensity in the mid-infrared range (1.3–4.8 μm). A laser-induced incandescence technique was utilized to visualize the instantaneous and average soot distribution in the flames. The results show that an oxygen-enhanced inverse diffusion flame is very effective in increasing the thermal radiation compared to a normal oxygen diffusion flame. The power spectral densities (PSD) of spectral radiation intensity in the wavelength region corresponding to soot show a Gaussian shape in the methane/oxygen flames, in contrast to a log-normal shape in the methane/air flames. The difference in the probability density functions (PDFs) is caused by a more uniform spatial distribution of soot in the methane/oxygen flames compared to that in the methane/air flames. The PSDs of the spectral radiation intensities for methane/air flames show buoyant flickering while those of methane/oxygen flames do not for the present operating conditions.
Influence of blade tip clearance shapes on aerodynamic performance of an axial flow compressor stator
Authors: Wang Z , Jia X , Cai R
Published: January 2003

The influence of different tip clearance shapes on aerodynamic performance of an axial-flow compressor stator under the condition of both stationary and rotating hub was investigated by a numerical method. In this paper, the calculations are based on the three-dimensional Navier-Stokes equations expressed with non-orthogonal curvilinear coordinates and corresponding non-orthogonal velocity components, and the explicit time marching algorithm and Baldwin-Lomax turbulence model are adopted. The clearance shapes considered in this paper include large and small uniform tip clearance, expanding and shrinking tip clearance from the blade leading edge to the trailing edge along the axial direction. The analysis of computed results shows, at least for the test cases in this paper, that tip leakage vortex was found to be generated earlier for stationary hub cases than for rotating hub cases. On the same working conditions and within a certain range of clearance scale, the blade row with smaller tip clearance height can attain higher efficiency, and for the same circumferential leakage area, the blade row with expanding tip clearance was found to have higher efficiency.
Optimum stage design in axial-flow gas turbines
Authors: Rao K V J , Kolla S , Penchalayya Ch , Rao M Ananda , Srinivas J
Published: January 2003

This paper proposes the formulation and solution procedures in the stage optimization of the effective dimensions of an axial-flow gas turbine. Increasing the stage efficiency and minimizing the overall mass of components per stage are the common objectives in gas turbine design. This multiple objective function, with important constraints like natural frequency limits, root stress values, and tip deflection in blades, constitutes the overall optimization problem. The problem is solved by using a modified nonlinear simplex method with a built-in user interactive program that helps in on-line modifications of parameters other than variables in the problem. Results are presented with single objective and multiple objective criteria, including sensitivity analyses about the optimum point.
The heating value of gas obtained from biomass gasification: A new method for its calculation or prediction
Authors: Bomprezzi L , Pierpaoli P , Raffaelli R
Published: January 2003

An empirical correlation is presented for calculating the lower heating value (LHV) of gases obtained from the gasification of the most common types of biomass. Four types of equation are considered (polynomial, power, exponential, and logarithmic), all containing the process temperature (maximum) parameter; they were obtained by interpolating experimental data available in the literature on the volumetric composition of the gas discharged by gasifiers. On the strength of a statistical analysis, it emerged that although all four were valid within the temperature range considered, the polynomial correlation was the one that came closest to the experimental values.
Design of a prototype fuel cell/composite cycle power station
Authors: Fry M R , Watson H , Hatchman J C
Published: January 2003

The aspiration for fuel cells, in a public utility context, is that they are envisaged in the developed world as a means of significantly increasing the overall efficiency of power plants and of utilizing poor-quality fuel supplies. The thermodynamic and practical aspects in the design of a prototype power station consisting of a composite cycle of fuel cells, a gas turbine expander and a steam plant, or a steam plant only, are reported. The design was based on tubular fuel cell development. Overall efficiencies are estimated and limiting factors in the design are identified. Performance and emission characteristics are compared with existing plant.
The influences of turbine blade mean temperature and component efficiencies on coolant optimization in the gas turbine
Authors: Martin B W , Brown A , Finnis M
Published: January 2003

This paper continues the computational invcstigalion of optimum performance of a gas turbine configuration incorporating a gas generator, previously reported by the authors. Even for contemporary pressure ratios not previously considered, there appears to be no advantage in prebleeding the coolant air, and within the range considered, as previously found, the amount of coolant preheating has only a secondary effect on maximum engine efficiency. This is also true of the influence of allowable mean blade temperature on maximum engine efficiency, but both factors do have a pronounced effect on the optimum coolant and where maximum cycle efficiency is primarily determined by compressor pressure ratio and component isen-tropic efficiencies. The specific work output is confirmed under optimum conditions to be an almost linear function of the compressor turbine inlet temperature.
An optimum set of loss models for performance prediction of centrifugal compressors
Authors: Oh H W , Yoon E S , Chung M K
Published: January 2003

The present study has tested most of the loss models previously published in the open literature and found an optimum set of empirical loss models for a reliable performance prediction of centrifugal compressors. In order to improve the prediction of efficiency curves, this paper recommends a modified parasitic loss model. The performance analyses by using various empirical loss models are also compared with those by the two-zone modelling. Predicted performance curves by the proposed optimum set agree fairly well with experimental data for a variety of centrifugal compressors. The prediction method developed through this study can serve as a tool for preliminary design and assist the understanding of the operational characteristics of general purpose centrifugal compressors.
Oligonuclear Metal-Assembly of Antiferromagnetic Ni4 and Ferromagnetic Ni6 Clusters with Non-Schiff-Base Tetradentate Ligand
Authors: Mikuriya Masahiro , Tanaka Kumiko , Inoue Nozomi , Yoshioka Daisuke , Lim Jong-Wan
Published: January 2003

Tetranuclear and hexanuclear nickel(II) complexes with N,N′-bis(2-hydroxy-3,5-dimethylbenzyl)-N,N′-dimethyl-1,2-ethanediamine (H2L), [Ni4L2(CH3COO)4]·4THF and [Ni6L3(OH)4(NO3)2(H2O)2]·2DMF, have been synthesized and characterized by X-ray crystallography, electronic spectroscopy and magnetic susceptibility measurement.
Bones, Bombs, and Break Points: The Geography of Economic Activity
Authors: Davis Donald R , Weinstein David E
Published: January 2003

We consider the distribution of economic activity within a country in light of three leading theories—increasing returns, random growth, and locational fundamentals. To do so, we examine the distribution of regional population in Japan from the Stone Age to the modern era. We also consider the Allied bombing of Japanese cities in WWII as a shock to relative city sizes. Our results support a hybrid theory in which locational fundamentals establish the spatial pattern of relative regional densities, but increasing returns help to determine the degree of spatial differentiation. Long-run city size is robust even to large temporary shocks.
Property Rights and Finance
Authors: Johnson Simon , McMillan John , Woodruff Christopher
Published: January 2003

Which is the tighter constraint on private sector investment: weak property rights or limited access to external finance? From a survey of new firms in post-communist countries, we find that weak property rights discourage firms from reinvesting their profits, even when bank loans are available. Where property rights are relatively strong, firms reinvest their profits; where they are relatively weak, entrepreneurs do not want to invest from retained earnings.
Measuring Market Inefficiencies in California's Restructured Wholesale Electricity Market
Authors: Borenstein Severin , Bushnell James B , Wolak Frank A
Published: January 2003

We present a method for decomposing wholesale electricity payments into production costs, inframarginal competitive rents, and payments resulting from the exercise of market power. Using data from June 1998 to October 2000 in California, we find significant departures from competitive pricing during the high-demand summer months and near-competitive pricing during the lower-demand months of the first two years. In summer 2000, wholesale electricity expenditures were $8.98 billion up from $2.04 billion in summer 1999. We find that 21 percent of this increase was due to production costs, 20 percent to competitive rents, and 59 percent to market power.
Racial Profiling, Fairness, and Effectiveness of Policing
Authors: Persico Nicola
Published: January 2003

Citizens of two groups may engage in crime, depending on their legal earning opportunities and on the probability of being audited. Police audit citizens. Police behavior is fair if both groups are policed with the same intensity. We provide exact conditions under which forcing the police to behave more fairly reduces the total amount of crime. These conditions are expressed as constraints on the quantile-quantile plot of the distributions of legal earning opportunities in the two groups. We also investigate the definition of fairness when the cost of being searched reflects the stigma of being singled out by police.
Learning-by-Doing as a Propagation Mechanism
Authors: Chang Yongsung , Gomes Joao F , Schorfheide Frank
Published: January 2003

This paper suggests that skill accumulation through past work experience, or “learning-by-doing” (LBD), can provide an important propagation mechanism in a dynamic stochastic general-equilibrium model, as the current labor supply affects future productivity. Our econometric analysis uses a Bayesian approach to combine micro-level panel data with aggregate time series. Formal model evaluation shows that the introduction of the LBD mechanism improves the model's ability to fit the dynamics of aggregate output and hours.
How Vouchers Could Change the Market for Education
Authors: Neal Derek
Published: January 2003

As vouchers become a more significant part of education policy debates, the time is right to consider what we know and do not know about the likely effects of adopting various voucher schemes. In the balance of this paper, the author describes both empirical and theoretical work on education that speaks to this topic. He argues that we cannot confidently predict the outcomes that would result from various voucher schemes, and he also stresses that debates over vouchers per se are not informative. Details concerning funding, targeting and discretion in the use of vouchers should greatly affect the outcomes associated with any
Productivity Growth in World Agriculture: Sources and Constraints
Authors: Ruttan Vernon W
Published: January 2003

During the last half-century, advances in crop production came from expansion in areas irrigated from more intensive application of fertilizers and crop protection chemicals, and from crop varieties that were more responsive to technical inputs and management. Advances in animal production came from genetic improvements and advances in animal nutrition. Differences among developed and developing countries in output per hectare and per worker have widened. If these gaps are to be narrowed agricultural research capacity in developing countries will have to be substantially strengthened.
Retrospectives: Economists and the Fed: Beginnings
Authors: Mehrling Perry
Published: January 2003

As usually understood, the significant debate over the founding of the Fed was between advocates of the real bills doctrine and advocates of the quantity theory of money. This understanding however conflates two different distinctions: one between the banking principle and the currency principle, and one between self-regulation and active management. It also fails to take seriously both the context of practical experience with the national banking system and the developing practical experience inside the Fed. I propose a new interpretation focused mainly on the contributions of four economists: J. Laurence Laughlin, Irving Fisher, Paul Warburg and Benjamin Strong.
Recommendations for Further Reading
Authors: Saffran Bernard
Published: January 2003

This section will list readings that may be especially useful to teachers of undergraduate economics, as well as other articles that are of broader cultural interest. In general, the articles chosen will be expository or integrative and not focus on original research. They may include survey articles, discussion of related subjects in which economists might have an interest or analyses of economics from other perspectives. If you write or read an appropriate article, please send a copy of the article (and possibly a few sentences describing it) to Bernard Saffran, c/o Journal of Economic Perspectives, Department of Economics, Swarthmore College, Swarthmore, PA 19081.
Conductive hearing loss: investigation of possible inner ear origin in three cases studies
Authors: Muhaimeed Hamad Al , Sayed Yousry El , Rabah Abdulrahman , Al-Essa Abdulrahman
Published: January 2003

This is a report of three cases of mixed hearing loss that resulted from inner ear disorders. Two cases were unilateral and the third was bilateral. The diagnosis was based on the findings of normal middle and external ears in association with the absence of round window reflexes. The contralateral stapedial reflex was present in the two unilateral cases. This is the first documentation of conductive deafness due to inner ear abnormality. This diagnosis should be considered in cases of conductive hearing loss if the middle and external ears are normal. More studies are needed to establish the pathophysiology of this entity.
Spontaneous orbital haematoma
Authors: Martinez Devesa P.
Published: January 2003

Spontaneous orbital haematoma is uncommon in ENT practice. The sudden presentation of proptosis and diplopia may guide the differential diagnosis towards more common pathologies such as an intraorbital complication of acute sinusitis or neoplasm of the orbit. The diagnosis by computed tomography (CT) scan, the management of this orbital disease and the literature in this field are discussed.
Haemangiopericytoma of the submental region
Authors: Constantinides H. , Toh C. , Warfield A. T. , Johnson A. P.
Published: January 2003

Haemangiopericytoma refers to an uncommon vascular/perivascular neoplasm of which a minority of cases arise in the head and neck. It comprises a group of lesions with marked clinical and pathological heterogeneity and a lack of positive criteria by which to make a definitive diagnosis.

We describe an unusual case of such a tumour in the submental region, review its pathological features and discuss issues in management and prognosis.
A World-Wide Perspective of Gas in the 21st Century
Authors: Lerche I.
Published: January 2003

Current availability of gas and current distribution of gas are examined in relation to potential gas discoveries, their likely worldwide distributions, and the present-day markets for gas. Current demands for gas in relation to future likely demands are also evaluated in respect of traditional gas uses. Strategies for evaluating likely new disciplines for gas usage are related to government policies and national security interests. The economic concerns of well-head price, pipelines, and liquefaction are considered in relation to evolving technologies for extracting known reserves, predicting the discoverability of unknown fields, and setting trends for exploration beyond the year 2000. The relation of gas to oil is also considered. The up-shot of all of these factors, evaluated in an integrated manner, would seem to imply that, through about the first third of this century, adequate proven and potential supplies of gas will be available; by the middle of the century there are likely to be local to regional shortages of both reserves of gas as well as supplies of gas in relation to domestic and industrial consumption. By the last third of the century it would appear that gas will not be a dominant energy source in relation to oil, solar, nuclear fusion or other alternatives. Continued industrialization of nations will shorten these lifetime estimates as well as raise significantly the price of gas on a competitive market demand basis.
Gas Export Potential of Russia's East: Will it Match Asia-Pacific Markets?
Authors: Khartukov Eugene , Starostina Ellen
Published: January 2003

Russia's Far East and East Siberia are emerging as new major sources of gas supplies for East Asian energy markets. Thanks to ongoing and earmarked resource and infrastructure developments in Sakhalin, Yakutia (Sakha) and Irkutsk, by around 2020 these poorly developed but naturally endowed areas of the country's East can provide between 50 and 70 Bcm/yr (5–7 Bcfd) of natural gas, including up to 10 Mt/yr of LNG, available for exports to neighbouring Pacific countries (primarily to the PRC, Japan, South Korea as well as to Taiwan and the U.S. West Coast). This can noticeably reshape today's matrix of the Asia-Pacific energy flows and even destabilize the regional gas market.
Natural Gas for Europe — Present State and Prediction for a Stable Supply in the Future
Authors: Rempel Hilmar
Published: January 2003

Natural gas provides 21% of the primary energy supply of Europe. According to EU predictions, this share will increase to approximately 28% in 2020 and dependence on natural gas imports will increase. The question arises how the increasing demand for gas can be assured? This will be analysed in this paper focussing on the resource base, technical viability, as well as contract security. As far as the resource base for natural gas is concerned, Western Europe's situation is quite favourable. Despite little resources of its own, Western Europe is surrounded by countries and regions with high gas potential (Russia, North Africa, the Caspian region and the Middle East). In addition to a sufficient resource base, production and transport play an important role, especially if there are long distances between producer and consumer countries. Transport costs are a decisive factor, due to the lower energy density of natural gas than that of oil and coal, which limits the distance for transport of gas. Therefore, natural gas markets are mainly regional. Only large gas fields (especially supergiants) are suitable for natural gas supply over long distances despite high infrastructure costs. An extensive pipeline network exists for the gas supply in Europe. This network has to be expanded in the future, however. The price of natural gas is coupled to the price of crude oil. Sizeable fluctuations in the oil price are a factor of uncertainty for capital investment decisions. In order to secure the future gas supply and to take advantage of this environmentally friendly energy source in competition with other primary fuels, all cost-reducing measures must be taken. Political measures must be taken to safeguard the very long-term capital investments.
The Role of Gas Resources in Mexico: Opportunities for the 21st Century
Authors: Rocha-Legorreta F.
Published: January 2003

The Mexican gas basins have played an important role in the energy industry as well as providing strategic investment opportunities. In 1999 Mexico produced about 1.29 Tcf of natural gas, consuming 1.26 Tcf. Pemex had the exclusive function for the transportation and storage of natural gas. With the new reforms, new laws permit private participation in these activities. Considerable increases in production can be observed in different fields of the northern region, making this the most important gas province in Mexico. Pemex is planning to improve the production in all its facilities for the next 10 years with new technology and strategic procedures, and is contemplating exploration and development in Sabinas, Burgos, exploration offshore Burgos, exploration at Sierra Madre, and exploration and development in Veracruz and southern basins.
A Certificate-Based Approach to Marketing Green Power and Constructing New Wind Energy Facilities
Authors: Blank Eric , Bird Lori , Swezey Blair
Published: January 2003

The availability of wind energy certificates in Pennsylvania's retail electricity market has made a critical difference in the economic feasibility of developing 140 MW of new wind energy projects in the region. Certificates offer important benefits to both green power suppliers and buyers by reducing transaction barriers. They thus lower the cost of renewable energy. Buyers also benefit through the increased flexibility offered by certificate products. The experience described in this paper offers important insights for selling green power certificates and achieving new wind energy development in other areas of the country.
Generic Vortex Modelling for Horizontal-Axis Wind Turbines
Authors: Wood D. H.
Published: January 2003

This paper describes a generic free-wake calculation of wind turbine wakes. The expanding, helical, tip vortices are represented by a sequence of straight segments, the blades are modelled as lines of constant bound vorticity, and the hub vortices lie along the axis of rotation. It is shown that this model is consistent with the one-dimensional analysis that leads to the Lanchester-Betz limit, in that the velocity in the far-wake is uniform with radius. Particular attention is paid to turbines operating above the Lanchester-Betz limit. It is shown that the usual relationship between the velocity through the blades and in the far-wake breaks down when there is significant wake expansion, and an empirical modification to that relation is presented. For highly expanding wakes, the dynamics of the turbine depend sensitively on the behaviour of the tip vortices.
Variable-Speed Wind Turbines with Doubly-Fed Induction Generators
Authors: Akhmatov Vladislav
Published: January 2003

Variable-speed pitch-controlled wind turbines with doubly-fed induction generators (DFIG) are modelled for power system dynamic stability. The model is explained and the parts of the model are verified. The model is implemented in the simulation tool PSS/E and created as a modular structure. This means that it is possible easily to add other control loops, as other modules, to the existing model code for ad-hoc investigations. This article is the first part of a large work dealing with investigation of dynamic interaction between the variable-speed wind turbines equipped with DFIG and the power grid.
Promoting Renewables through Market Mechanisms
Authors: Agerholm Bent , Kristoffersen Hans-Erik , Morthorst Poul Erik , Nybroe Malene Hein , Mortensen Bjarne Crone
Published: January 2003

Section 1 gives an introduction explaining the need for a separate promotion scheme for renewables. In section 2, the so far successful promotion of renewables in Denmark is described, as is the background for introducing a certificate-based system. Section 3 describes a model national certificate market, followed by a description in section 4 of the proposed Danish system and the necessary administrative set-up. Section 5 deals with the perspectives and problems of trading certificates internationally based on a three-country case study performed by Risø National Laboratory. The last section presents the conclusions from the paper.
Acoustic Barriers: Analytical Methods, Boundary Element Method and Experimental Verification
Authors: Gerges Samir N. Y. , Calza Arlinton João
Published: January 2003

The use of acoustic barriers has become a common solution to control and reduce the nuisance caused by transportation noise (e.g. highways, railroads, and aircraft). Acoustic barriers can be defined as any solid obstacle that blocks the straight line between sound source and receptor creating an acoustic shadow region behind. The precise prediction of acoustic barrier behaviour has been the goal of researchers, but the complexity of the phenomenon prevents generality. Many theoretical models are available but they are limited to particular cases. The main objective of this work is to carry out comparisons between the results obtained for the insertion loss using analytical methods of prediction, numerical methods using the Finite Elements Method (FEM) and Boundary Elements Method (BEM) and experimental measurements in the laboratory.
A Tentative Noise Control Method for Buildings above Railway Tunnels
Authors: Hassan O. A. B.
Published: January 2003

In this paper, a design method to reduce the transmission of structure-borne sound in buildings to be built above railway tunnels is studied. The case studied is similar to the one studied previously by the author in the sense that the building is founded on rock. However, in the present case, the load-bearing columns on the first floor are not placed above other load-bearing columns or walls. Analytical models for the propagation of structure-borne sound upward in the buildings are derived. The models are based on the assumption that the initial vibrational energy that propagates from the foundation is in the form of quasi-longitudinal waves. The propagation of bending and quasi-longitudinal waves in the load-bearing columns is considered. A finite ground impedance is taken into account as well as the wave reflection from the roof. A parametric survey is conducted to investigate the influence of certain important geometrical properties of the first floor on the sound transmission. Finally, the results are compared with previous results for a “normal” building and it is shown that the relocation of the columns can considerably reduce the sound transmission upward in the building.
Modelling of Scattering from Balcony Fronts
Authors: Chan T. M. , To W. M.
Published: January 2003

Balconies are normally used in large auditoria such as concert halls or opera houses, to increase seating capacity or to give better view for a distinguished group of the audience. When ray-tracing based computer models are applied to study the acoustical quality of these auditoria, the alteration of the sound field due to balcony fronts is normally unobservable, because of the relative small size of the balcony fronts in the auditorium. Furthermore, most diffuse reflection ray-tracing methods are not based on direct wave acoustics but on an approximation of the scattering effect. In practice, experience shows that balcony fronts give additional warmth to music. This effect is more prominent when singers perform in traditional horseshoe shaped opera houses with multi-levels balconies. This paper describes modelling of scattering from balcony fronts using a theoretical wave approach, in which the incident wave front is not plane but spherical. A computer simulation illustrates the scattering of sound that takes place when the wavefront impinges on the surface of the balcony fronts.
The Effect of the Urban Street Canyon on the Noise from Low Flying Aircraft
Authors: Ismail M. R. , Oldham D. J.
Published: January 2003

The effect of urban streets on the noise from a low-flying aircraft has been investigated. The study first involved the development of a prediction method based on geometrical acoustics with the assumption of specular reflections. The effect of a variety of street configurations on the transmission gain was investigated and analysed in terms of changes in street geometry. The relative Effective Perceived Noise Level was also predicted. The predictions show that for specular reflections the relative Effective Perceived Noise Level increases in proportion to the ratio of building height to flying altitude, however, changing the street width has only a minor effect. The effect of mixed specular and diffuse reflections was investigated using a commercial acoustical modelling package and it was shown that although the effect on the transmission gain was small, the scattering of sound energy out of the street channel resulted in a decrease in the value of the relative Effective Perceived Noise Level with the ratio of building height to flying altitude resulting in a value of the relative Effective Perceived Noise Level which was negative for most street configurations examined. It can be concluded that although simple specular models can predict the transmission gain with reasonable accuracy, more complex models involving the effects of diffuse reflections are required for noise units involving integration over time.
Vibration Isolation on Lightweight Floor Structures
Authors: Hammer P , Brunskog J
Published: January 2003

A theoretical and experimental study of vibration isolation for a source on a lightweight floor structure is presented. The effectiveness of one-stage and two-stage isolator systems is studied. Approximate formulae are presented for both low and high frequency for the receiver, the floor structure. For the mobility, a comparison between approximate formulae, numerical exact results and experimental results are presented. The low frequency asymptote for the approximate mobility is valid up to l/λp ≈ 1/4. The high frequency asymptote is valid from l/λp ≈ 1/2. A straight line can be drawn between these two points for the intermediate range 1/4 < l/λp < 1/2. Finally, a case study is presented. A fan is mounted on a wooden joist floor. The effect of both one and two stage isolation is demonstrated. It is clearly seen that the high mobility situation for the receiver is increased by adding a rigid body to the mount. Hence, in the frequency range of interest, the ‘receiver’ acts more or less as a blocked termination. A two-stage isolator almost completely eliminates the structure borne sound and compared to a one-stage isolator it reduces the sound by 20 dB at the rpm for the fan.
Acoustics of Apulian-Romanesque Churches: An Experimental Survey
Authors: Cirillo Ettore , Martellotta Francesco
Published: January 2003

A detailed acoustic survey was carried out of nine Romanesque churches built in Apulia, in Southern Italy. Despite the common architectural style the churches show specific features and have volumes ranging from 1500 m3 to 32000 m3. In each church both monaural and binaural acoustic parameters were measured according to the ISO 3382 standard. The results of the measurements are discussed in this paper, analysing both the distribution of the acoustic parameters inside each church, and how that distribution depends on specific characteristics. Finally, a discussion of the results as a whole is given. In a later paper the whole set of data will be used in order to investigate the correlations between architectural features, such as dimensions and materials, and acoustic characteristics.
Case Study: Predicted Effect of Station Design Changes on High Speed Train Noise
Authors: Haan Chan-Hoon
Published: January 2003

The present study investigates the effects of design changes on high-speed train noise in railway stations. Noise barriers alongside the tracks and various absorptive materials applied to interior station surfaces are considered. TGV noise level data was used to predict the sound power levels of the high-speed trains. Computer simulations were used to predict noise levels on platforms during a high-speed train pass, and the expected noise reductions for various interior absorptive materials. It was found that a minimum barrier height of 1.8m, which is equivalent to the height from the rail floor to the bottom of the cabin window, is required to prevent noise diffraction. It was also found that any structures over the tracks could increase the noise levels up to 2.5dB in the platform area. The main station ceiling is the most effective area to control reverberation and improve the clarity of sound from broadcast systems.
Church Acoustics and the Influence of Occupancy
Authors: Desarnaulds Victor , Carvalho António P.O. , Monay Gilbert
Published: January 2003

Speech intelligibility is usually evaluated, by the use of objective parameters, in unoccupied rooms, due to practical considerations. However, under normal conditions, the room occupancy can increase or decrease the values of speech intelligibility by the effect of the additional sound absorption present in the room or by the change in S/N ratio. Measurements were carried out in six churches, with and without occupancy. The results show that occupancy induces a mean increase for the speech intelligibility of ΔSTI ( STIoccup–STIunoccup) of 0.050 with the use of a public address system (PA) and 0.035 without a PA. This increase is caused mainly by the reduction of the room reverberation time, due to the increased sound absorption and by the reduction of the additional RT induced by the PA (using loudspeakers with strong directivity oriented towards the congregation area). The variations in the speech intelligibility values with occupancy can be predicted in churches by employing new empirical formulations. The decrease in S/N ratio (due to the background sound level augmentation by the presence of people and by sound level decrease with distance in the congregation area), or the poor directivity and orientation of the sound sources, could reduce the speech intelligibility gain in particular cases. Other effects induced by the congregation, such as the variations of humidity and temperature, generally have negligible effect on speech intelligibility.
Technical Note: Test Procedure and User Interface for Determination of the Acoustic Properties of Materials Using the Two-Microphone Transfer Function Method
Authors: Ryu Yunseon
Published: January 2003

There are many different methods to determine the acoustic properties of materials by exposing them to sound fields and measuring the effects caused by their presence. Test methods have to be executed according to the appropriate Standards, which specify well-defined acoustical conditions and specific instrumentation, to ensure a high and known degree of repeatability and reproducibility. In this technical note, the two-microphone transfer method, based on the standing wave impedance tube method, is described as a procedure for determining the absorption coefficient, reflection coefficient, surface impedance and surface admittance of materials. This method provides a simple and convenient procedure for determining the acoustic properties materials at normal incidence. It is both a fast and accurate method applicable over a large frequency range. The theoretical background of the method, based on the transfer function between two microphones is discussed. To check the reliability of the measurement results, tests were conducted on a sample of typical acoustic material.
Problems in the Current Seismic Designs and Questions Regarding the Structural Damages by Earthquakes
Authors: Toma Shouji
Published: January 2003

The paper presents an overview of topics in recent seismic designs in Japan and the United States. New trends in seismic designs are first discussed including limit state design, isolation of structures from seismic motion, performance-based design, displacement ductility design, capacity design, etc. Then, questions are raised by describing some typical structural damages in the Kobe Earthquake; namely, the collapse of old wooden houses that killed most people, the effect of axial force and shock motion that was significant, steel structures exhibited good ductility even when damaged severely, and the damages of railway bridges showed the importance of structural details in seismic design. Finally, special topics which lead to a hypothesis on the seismic wave records are discussed.
New European Design Concepts for Beam Columns
Authors: Lindner Joachim , Rusch Andreas
Published: January 2003

The load carrying capacity of steel structures is in many cases limited by the stability check. In general, two types of overall stability failure can occur: Lateral torsional buckling. and in the case of restrained torsional deformations flexural buckling. Therefore, the rules for buckling are one of the most used important issues and therefore are of great interest for design in practice. For the conversion of Eurocode 3 (ENV 1992-1-1: 1993) to an EN code, extensive works were especially done by several researchers for flexural buckling. This paper gives an overview of the new European flexural buckling design concept and other proposals taken into account in the evaluation. Test results and extensive ultimate load calculations are considered for a statistical analysis. Comparisons between ultimate load calculations are discussed with respect to an easy formulation of the design concept.