| Summary: | Wind turbine noise is a re-emerging issue in the wind industry. As the competition for sites with good wind potential on land is rising, offshore projects in coastal areas seem as a reasonable alternative to onshore. In this context offshore sound propagation is gaining more importance considering that sound will travel over longer distances on water, especially with regard to lower frequencies. Moreover different meteorological conditions that occur on sea may attenuate or enhance sound propagation on water. The prediction tools commonly used by developers are only partially taking these parameters into account. This will be investigated in this thesis. Hence, different methods for predicting offshore wind turbine noise are going to be assessed. These methods can be divided in two approaches namely algebraic and Partial Differential Equation (PDE) based. The methods evaluated are the ISO 9613-2 standard for outdoor noise prediction, the Danish method and the Swedish method for wind turbines noise estimation over water. For the PDE based approach, the Helmholtz Equation will be employed in order to examine different meteorological conditions and phenomena occurring over a flat reflecting surface. The experiments with the PDE include the simulation of meteorological conditions with different levels of refraction and changing ground impedance in order to take into account the effect of a shoreline. In addition a meteorological phenomenon called the low-level jet is investigated which is characterised by strong winds at relatively low altitude. Noise prediction tools used by developers need to be able to consider these effects in order to allow for thorough planning of wind energy projects. Nonetheless, relatively more complex models such as the Helmholtz Equation require experienced users and significant computing time. Further research and development needs to be made in order to promote the wider use of noise prediction methods like the Helmholtz Equation in the wind industry.
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