With the growing energy needs of the world and the sustainable nature of wind energy this sector is a highly innovative growth industry. The past years have seen the industry develop and test not only more efficient, but also much larger wind turbines than those that are in current use. The next generation of wind turbines that are on the drawing boards are gigantic in size. These huge dimensions of the proposed wind turbines will put large demands on the foundations. As an increasing number of wind farms are being planned offshore in water depths of over 40 m, the combination of water depth and the increased windmill tower heights and rotor blade diameters create loads that make foundation design very complex. Moreover, offshore foundations are exposed to additional loads such as ocean currents, storm wave loading, ice loads and potential ship impact loads. All of these factors pose significant challenges in the design and construction of wind turbine foundations. This paper presents the various issues facing the designer in designing and constructing wind turbine tower foundations. Current practices are summarized to assist developers in foundation type selection and design.
Important aspects of the combustion instability phenomenon are not addressed in any of the presently developing programs for nonlinear combustion instability analysis. The irregular burning effect, characterized by a sometimes very large mean pressure increase is of particular concern. There can be little confidence in any analytical tool if it does not incorporate the necessary fundamental physical/chemical interactions that lead to these fundamental aspects of combustion instability. This paper describes the known characteristics of the DC shift effect, the several mechanisms that have been proposed for its origin, and new insights, which come from inclusion of physical elements that have either not been included before or have been incorrectly evaluated. Of key importance is the role of vorticity in the nonlinear interactions in the burning zone. Its inclusion yields second order corrections to the gas motions in the burning zone that are much larger than those that have been suggested in models based on irrotational flow. Of great importance is that the geometrical features of these corrections matches the observed pattern of increased burning. Both longitudinal and transverse wave motions can produce a DC shift, but the new theory shows that the transverse case yields a significantly larger increase in local burning rate.
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