Assessment and analysis of hook mounted compensation methods for offshore wind turbine blade installation

Abstract

During single-blade offshore wind turbine (OWT) installation, wind disturbance results in blade root motion. The sensitivity to this wind disturbance is more significant for larger blades, reducing the allowable installation weather limit. A potential solution is a Hook Mounted Compensator (HMC) between the crane and the load that can provide high-precision compensation across multiple degree of freedom (DOF), and compensate for the influence of wind on the OWT blade. Several Actuation Method (AM)s have been identified that can be used in a HMC. However, these AMs have not been modelled dynamically and their effectiveness for the desired application is unknown. The aim of this study is to analyse and assess the compensation effectiveness of these AMs in a HMC. For this purpose, the AMs are simulated and analysed in various levels of complexity and DOFs. Initially, the system is considered in a 1DOF. A linear representation is formulated, based on which a Proportional-Integral-Derivative (PID) controller for each AM is formulated. This enables simulation of the Single-Blade Installation System (SBIS) in the time domain. Assessment criteria are used to quantify the compensation effectiveness and actuation input of the AMs. To simulate the SBIS for each AM, 3DOF numerical models are developed that describe the operation of the AMs in their respective operational planes. Six actuation methods are included in the assessment. Based on the assessment results, three AMs are combined in a HMC concept. A XY table is used to control blade root position in the x- and y-directions, gyroscopes for the z-direction, and COG shifting with counterweight to prevent gyroscope saturation. The PID controllers based on the linear 1DOF representation are used, operating in parallel, to control the blade root position in all DOF. The blade root motion is reduced by 96% along the blade axis and 86% radially. The blade root motion is sensitive to the mean wind speed, turbulence intensity, and angle of the incoming wind. The HMC shows robustness to variations in tugger line angle and pretension. The static blade pitch angle affects the magnitude and distribution of the wind-induced moment on the blade. For a pitch angle of -180, the moment around the z-axis is minimal, providing optimal HMC performance. The HMC concept can not directly actuate the blade around the z-axis. Instead, the XY table translates the blade at the COG, resulting in increased cylinder stroke and high power consumption for other pitch angles. Two AMs were assessed to actuate the blade around the z-axis, both showing poor performance. Further exploration of AMS that can directly control the blade rotation around the z-axis could lead to improvement of the HMC concept. Additional improvement can be made in optimization of counterweight and gyroscopes sizes, potentially reducing weight and improving system performance. Further suggestions for future work include; exploring the compensating for the now neglected hub motion using the HMC, examining the stability of the HMC once the blade is mated to the hub, and the impact of sensor noise and delay on the HMC’s performance.