the nation's energy supply, and thus play an important role in securing our energy future. Distributed wind electric systems represent an opportunity for some nations in particular. This study aims: (i) to investigate the efficiency differences between three bladed glass reinforced plastics (GRP) rigid hubs, three bladed steel rigid hubs and twelve bladed steel rigid hubs experimentally, and (ii) to improve the performance of the small wind turbine system (SWTSs) installed at the Solar Energy Institute of Ege University (latitude 38.24°N, longitude 27.50°E), Izmir, Turkey. NACA 4415 (National Advisory Committee for Aeronautics) series blades are preferred to others in this experiment, because of the fact that this profile has shown excellent properties for small wind turbine blades and their average power coefficients are higher than those of other blades. In this study, the performance parameters of the SWTSs are given first. An experimental study is then presented. Finally, the results obtained from the present study are discussed.

05/00737 Analysis of height variations of sodar-derived wind speeds in Northern Spain P6rez, I. A. et al. Journal o f Wind Engineering and Industrial Aerodynamics, 2004, 92, (10), 875-894. The Weibull distribution has been widely used in wind speed analysis. Ten-minute averages from a sodar placed in an extensive plateau in the North of Spain were considered. The measuring period was April 2001. Daily wind speed evolution has been analysed and a sharp contrast between day and night has been obtained. Contrasting behaviour between surface and more distant levels has also been seen. The strong convection during the day and the stratification stability during the night were responsible for this well-defined pattern. Four wind speed intervals for a typical wind turbine were considered. Low wind speeds showed no directional character, although moderate winds came from two prevailing directions due to the synoptic weather systems affecting the Iberian Peninsula with a 5-6-day period. Ground influence was present only at lowest levels. As a result, the behaviour of wind speed derived from surface data must be avoided. Although moderate winds were frequent, a persistence analysis revealed the low number of lasting runs. The wind speed power law was also analysed and the usual one-seventh expression was proved not to be valid. The Weibull parameters were calculated by four methods: linear regression by cumulative frequency, moments, maximum likelihood and quartiles. The equivalence was in general clear. Finally, height analysis revealed that the shape parameter was around two whereas major differences were reached for the scale factor. A successful fit with the height was proved for the latter. Finally, a well-defined daily evolution was obtained, indicating that selection of a site for energy generation purposes must be preceded by a temporal study based on direct height measurements.

05/00738 Efficient models for wind turbine extreme loads using inverse reliability Saranyasoontorn, K. and Manuel, L. Journal o f Wind Engineering and Industrial Aerodynamics, 2004, 92, (10), 789-804. The reliability of wind turbines against extreme loads is the focus of this study. A procedure to establish nominal loads for use in a conventional load-and-resistance-factor-design format is presented. The procedure, based on an inverse reliability approach, permits inclusion of randomness in the gross wind environment as well as in the extreme response given wind conditions. A detailed example is presented where three alternative nominal load definitions are used to estimate extreme bending loads for a 600 kW three-bladed horizontal-axis wind turbine. Only operating loads - here, flapwise (out-of-plane) bending moments - at a blade root are considered but the procedure described may be applied to estimate other loads and response measures of interest in wind turbine design. Results suggest that a full random characterization of both wind conditions and short- term maximum response (given wind conditions) will yield extreme design loads that might be approximated reasonably well by simpler models that include only the randomness in the wind environment but that account for response variability by employing appropriately derived 'higher-than-median' fractiles of the extreme bending load conditional on inflow parameter values.

05100739 Enhancement of convective heat transfer in the developing region of circular tubes using corona wind Molki, M. and Bhamidipati, K. L. International Journal of Heat and Mass Transfer, 2004, 47, (19-20), 4301-4314. An experimental research was conducted to investigate the level of heat transfer enhancement that can be achieved by corona wind in the developing region of circular tubes. The study was focused on transitional and lower range of turbulent flows with Reynolds number and voltage ranging from 2500 to 13 000 and 0 to 10.5 kV, respectively. The maximum enhancements of the local and average heat transfer coefficients were 14-23% and 6-8%, respectively. These values indicate the level of enhancement beyond the convenfionai values in the developing region of the circular tubes.

07 Alternative energy sources (wind energy)

05•00740 HystereUc flow characteristics of biplane Wells turbine Mamun, M. et al. Ocean Engineering, 2004, 31, (11-12), 1423-1435. In order to investigate the hysteretic flow characteristics of the biplane Wells turbine in detail, an incompressible unsteady three-dimensional numerical simulation was carried out with LES model. For the monoplane Wells turbine, the hysteretic loop is opposite to the well- known dynamic stall of an airfoil. For the biplane Wells turbine, the hysteretic behaviour was similar to the monoplane at lower attack angles. But the hysteretic loop similar to the dynamic stall was observed at higher attack angles, which was attributed to the unsteady flow separation near the hub and the trailing edge of the suction surface of the upstream blade.

05/00741 Implementation of wind energy in the Netherlands: the importance of the social-institutional setting Agterbosch, S. et al. Energy Policy, 2004, 32, (18), 2049-2066. This paper analyses the differences in performance of the different types of wind power entrepreneurs now active on the wind power supply market in the Netherlands. The development of the market is divided into three successive market periods: monopoly powers (1989- 1995), interbellum (1996-1997) and free market (1998-2002). For each of these periods, the interdependency between various systemic conditions - technical, economic, institutional and social conditions - is analysed, with the focus on the relative importance of the institutional and social settings for market development. This inter- dependency is analysed using the implementation capacity concept. Implementation capacity is defined as the total of those systemic conditions and mutual interdependencies that influence the behaviour of wind power entrepreneurs. It indicates the feasibility for wind power entrepreneurs to adopt wind turbines. From the analysis it was concluded that no overall implementation capacity exists, and implementation capacities differ for entrepreneurial groups with different entrepreneurial features. With respect to the relative importance of institutional and social conditions, it became clear, that it is mainly these conditions that differentiate between the various entrepreneurial groups. The dynamic configuration of institutional and social conditions facilitates some and hinders other types of wind power entrepreneurs, and as a result determines the development and composition of the market. Finally, the analysis explains the changing roles of entrepreneurial groups throughout the 1990s.

05100742 Importance of thermal effects and sea surface roughness for offshore wind resource assessment Lange, B. et al. Journal o f Wind Engineering and Industrial Aero- dynamics, 2004, 92, (11), 959-988. The economic feasibility of offshore wind power utilization depends on the favourable wind conditions offshore as compared to sites on land. The higher wind speeds have to compensate the additional cost of offshore developments. However, not only is the mean wind speed different, but the whole flow regime, as can, for example, be seen in the vertical wind speed profile. The commonly used models to describe this profile have been developed mainly for land sites. Their applicability for wind power prediction at offshore sites is investigated using data from the measurement program R0dsand, located in the Danish Baltic Sea. Monin-Obukhov theory is often used for the description of the wind speed profile. From a given wind speed at one height, the profile is predicted using two parameters, Obukhov length and sea surface roughness. Different methods to estimate these parameters are discussed and compared. Significant deviations to the Monin-Obukhov theory are found for near-neutral and stable conditions when warmer air is advected from land with a fetch of more than 30 km. The measured wind shear is larger than predicted. As a test application, the wind speed measured at 10 m height is extrapolated to 50 m height and the power production of a wind turbine at this height is predicted with the different models. The predicted wind speed is compared to the measured one and the predicted power output to the one using the measured wind speed. To be able to quantify the importance of the deviations from Monin-Obukhov theory, a simple correction method to account for this effect has been developed and is tested in the same way. The models for the estimation of the sea surface roughness were found to lead only to small differences. For the purpose of wind resource assessment, even the assumption of a constant roughness was found to be sufficient. The different methods used to derive the Obukhov length L were found to differ significantly for near-neutral and stable atmospheric stratification. Here again the simplest method using only bulk measurements was found to be sufficient. For situations with near-neutral and stable atmospheric stratification and long ( > 30 kin) fetch, the wind speed increase with height is larger than what is predicted from Monin-Obukhov theory for all methods to estimate L and z0. It is also found that this deviation occurs at wind speeds important for wind power utilization, mainly at 5-9 m s -1. The power output estimation has also been compared with the method of the resource estimation program WASP. For the Rodsand data set the

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