Posters

Abstract

As turbines are increasing in size and new companies are entering the offshore wind market, the installation phase of offshore windfarms is becoming a critical period where teething problems can have a large impact on windfarm lifetime. The variability of this period can have a large impact on the lifetime damage accumulated in the foundation due to a reduction in system damping contribution from the absence of an operating rotor. The contribution from aerodynamic damping is a critical assumption made in the design process load calculations. The damage accumulated in the foundation can be very sensitive to the total non-operational time of the turbine. The period before commissioning the turbine is a significant portion of the total non-operational time in a project. However, even an idling rotor contributes some damping to the system response. A rotor with fewer than three blades installed will contribute even less to damping, and the system frequency will also shift. If there is an installed passive damper device, the frequency shift of the system may result in a reduced damping effect from the device. A delay in the complete installation of the rotor's blades, could lead to a significant increase in accumulated damage. Therefore, it is critical to evaluate the effect of this scenario on the calculated damage and fatigue lifetime of a fatigue-driven monopile foundation design. The impact of an extended period without blade installation on the lifetime fatigue damage accumulation in the foundation is quantified. The contribution of a passive damper is also investigated, considering varying system frequency bands. A base case is established assuming no delay in blade installation. Sensitivities to the duration of blade installation delay and the number of blades installed are investigated on the resulting additional fatigue damage accumulated in comparison to original assumptions.