In the shallow seas that are the favoured locations for offshore wind farms, the limited water depths can result in highly non-linear waves. The determination of the design wave loads involves the selection of appropriate models of wave kinematics as well as force and structural dynamics models. Each selection will involve a compromise between accuracy and usability (speed, ease of use and comprehension of the results). Currently, the offshore oil and gas industry is focusing on ever deeper waters as much of the available hydrocarbon resource in accessible medium depth waters is already being exploited. In contrast, offshore wind energy is being developed in shallower waters, though often at sites exposed to extreme weather such as the European North Sea. The approach needed here will be subtly different but equally demanding, with economic reasons being more prominent. Electricity is a low-value commodity in a highly competitive market and the costs of generation using offshore wind farms are approaching the costs of conventional generation. It is vitally important that inappropriate and excessively conservative design approaches do not sabotage this trend. Although existing offshore design methods can undoubtedly result in a durable structure, there may be excessive cost penalties. On the other hand, non-linear and breaking waves experienced in shallow waters may mean that the design methods based on experience in deeper water are unconservative. The coastal engineering branch does have substantial experience in designing in shallow water conditions, albeit again to much more stringent durability criteria than are appropriate here.
This paper gives a final report on the work undertaken on this subject within the OWTES ‘‘Design Methods for Offshore Wind Turbines at Exposed Sites’ research project and examines the following aspects: ·
different recommendations for slender (monopiles) structures
the affect of the shallow water on wave climate,
