Wind Engineering

Since energy requirements for desalination processes are large, the energy supply in remote areas is a problem, especially if electricity is required. The status and perspectives of development of wind-powered desalination are reviewed in this paper. Desalination processes suitable for coupling to wind turbines are reverse osmosis (RO), mechanical vapour compression (MVC) and electrodialysis (ED). Wind-powered RO is the most mature technology whereas there are very few pilot plants of wind-driving MVC and ED.

The analytical formulae are proposed to estimate the maximum value for along-wind load and across-wind load on the wind turbine towers by using the quasi-steady analysis. The critical parameters in the standard deviation such as the mode correction factors, aerodynamic damping ratios, size reduction factors and wind load ratios are investigated to identify their directional characteristics. A non-Gaussian peak factor is necessary for the along-wind load, while a Gaussian peak factor is acceptable for the across-wind load. A loads combination formula is proposed in order to consider the correlation of along-wind load and across-wind load. The proposed formulae show the favorable agreements with the full dynamic simulation.

A site specific model of avian-turbine collision risk is an important component of assessing environmental impacts from wind power projects. Existing models assume, however, that avian flight paths are either parallel or perpendicular to the turbine orientation and that other orientations do not significantly affect the predicted collision probability. We describe a mathematical model which estimates the probability of a collision between a bird passing through a wind turbine and one of the turbine components. Our model improves significantly upon the reference “Tucker Model”, and Band model, by accounting for different angles of avian approach other than perpendicular or parallel to the turbine rotor plane. We demonstrate, using a case study of fall raptor migration data, that the angle of approach between the flight path and the turbine orientation has a significant effect on the collision probability and resulting mortality estimates. We conclude that the angle of approach should be considered when estimating avian-turbine collision risk.

Despite having been used for a long time, tubular lattice towers with three or four legs have not been systematically analysed for use with small wind turbines. We present a design procedure based on modelling the towers as either tripods or quadrapods to allow analytic approximations to the tower stresses. Following the IEC standard for small wind turbine design, the critical load occurs at the 50-year extreme wind speed acting on a stationary turbine and tower. To avoid buckling in the downwind leg, three separate methods of estimating the critical buckling resistance are shown to give very similar results. The analytic models also allow the tower-top deflection to be simply approximated. We use an arbitrary limit on deflection as 5% of the tower height, to ensure linear, static behaviour for extreme wind loads. Two example tower designs are considered: an 18 m tower for a 5 kW turbine and a 12 m tower for a 500 W turbine.

The present paper discusses wind and wind power characteristics in a region north of 40° S (North Patagonia, Argentina) as well as wind power projects sustainability. Extreme wind episodes influence most economic and social regional activities. Mean flow pattern was studied in three North Patagonia sites: Neuquén, Mari Menuco and Cutral-Có, by sampling analysis of wind direction and intensity during a year. Gusts were quantified and strong winds were studied. Available meteorological power was also estimated. It was observed that North Patagonia is a place of great wind power potential. However, the energy available, which is related to prevailing strong winds, is also associated to high gust occurrence which certainly restricts exploitation.

Small wind turbines have the potential to provide a significant amount of useful electricity; particularly in urban areas where it is necessary to use self-supporting monopole towers. Their take-up can be increased by reducing tower costs. The numerical optimisation technique called differential evolution (DE) was used to design a minimal mass self-supporting tower for a 5 kW wind turbine, whilst retaining the required strength and stability. The main problem in the optimisation was the limited availability of appropriate simple equations for buckling analysis of the chosen octagonal geometry as required for design certification to the appropriate international standards. Performing linear buckling analysis (which is unsuitable for global optimisation) on towers designed to meet the available buckling equations showed that the buckling strength was significantly overestimated for low wall thicknesses. A correction factor was formulated and applied to the existing buckling equations to remove this inconsistency. DE was then used to design a tower that was 7% lighter and 20% more resistant to buckling than the current reference design.

A standard design procedure is to optimise wind turbine rotors for maximum power coefficient within a specified range of wind speeds, up to the rated wind speed. The downwind thrust force upon the rotor is greatest at this design condition. Reacting large forces using cantilever beams necessitates high material costs for the blades, tower and foundations. This paper shows that limiting the maximum allowable downwind thrust can lower the capital expenditure (CAPEX) of a wind farm per MW installed. This saving is made at the expense of sacrificing power coefficient over the small range of wind speeds at which the thrust limit is enforced. We describe this concept as ‘force-capping’. For small reductions in the maximum allowable force, the effect on annual energy production (AEP) is minor. This paper outlines a parametric analysis procedure to evaluate how reducing the material content of a wind turbine affects the energy production. Dynamic forces and fatigue life are considered. For small reductions in turbine material, we show that the change in CAPEX is first order, whereas the loss of AEP is second order. We therefore conclude that force-capping must be beneficial in every case to at least some extent. Our analysis shows that the cost of energy can reduce by approximately 0.2% through imposing a force-cap of ∼90% upon the maximum thrust force for a 5MW machine. The case for force-capping strengthens further as the cost of borrowing and cost of material rises.

This preliminary research examined the applicability of Mini Doppler SODAR (MDS – sonic detection and ranging) for wind characteristics assessment of a potential wind farm. The wind characteristics obtained from the MDS were compared with those from standard anemometers on a 70 m high observation tower located near the MDS on relatively flat terrain. The wind speed and direction data recorded from the MDS were in general agreement with those from the tower at each height except for Z = 30 m. The wind speed profiles measured by these two methods at night agreed well. However, in the daytime the MDS underestimated the wind speed due to the effects of acoustic noise from surrounding activities, to turbulence caused by the wake of windbreaks and to convective instability. These results showed that the MDS might serve as useful equipment for the wind characteristics investigation after some improvement.