Tow-out Forces and Motion during Installation of a Complete Assembled Wind Turbine.

Abstract

Uttauingskrefter og bevegelser av en komplett vindturbin under installasjon har blitt aanalysert.

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Towing forces and motions due to selected weather conditions during installation of the gravity stabilised wind turbine concept, developed by Dr.Techn. Olav Olsen a.s and Vici Ventus, has been analysed. Today, an extensive search for the most suitable foundation concepts for offshore wind turbines is taking place as huge offshore wind farms are being planned and engineered mainly in Europe, North America and China. As the different concepts are being evaluated, characteristics of crucial importance include the concept’s potential for efficient, cheap and reliable installation in terms of their tolerance for rough weather during the tow-out and installation operation. The purpose of the analyses in this thesis is to attempt to quantify for what sea states and weather conditions the concept can be installed, and to calculate the towing force needed for relevant towing velocities. Towing forces have been investigated, and a towing speed of 3-4 knots appears to be realistic with the suggested combination of tugs with the towing capacity of 300 tonnes. The structure response for a “summer storm” during the “unrestricted” towing phase shows acceptable values at significant wave height of 7.5 meters. Partly due to exponentially increasing damping as the structure approaches the sea bed, the installation analyses show relatively low response in surge, heave and pitch even in significant wave heights up to 4 meters. However, before model tests have been executed and based on this thesis, significant wave height of 3 meters is the recommended upper limit for the installation phase. The point of the structure where impact with the sea bed will occur, has received extra attention.