Abstract
Installation of wind-turbine blades on monopile-type offshore wind turbines is a demanding task. Typically, a jack-up crane vessel is used, and blades are individually lifted from the vessel deck and docked with the preinstalled hub. During the process of mating, large relative motions are developed between the hub and root due to combined effects of wind-generated blade-root responses and wave-generated monopile vibrations. This can cause impact loads at the blade root and induce severe damages at the blade-root connection. Such events are highly likely to cause the failure of the mating task, while affecting the subsequent activities, and thus require competent planning. The purpose of this paper is to present a probabilistic response-based methodology for estimating the allowable sea states for planning a wind-turbine blade-mating task, considering impact risks with the hub as the hazardous event. A case study is presented where the installation system consisting of blade-lift and monopile system are modelled using multibody formulations. Time-domain analyses are carried out for various sea states, and impact velocities between root and hub are analyzed. Finally, an extreme value analysis using the Gumbel fitting of response parameters is performed and limiting sea state curves are obtained by comparing characteristic extreme responses with allowable values. It is found that the limiting sea states for blade-root mating tasks are low for aligned wind–wave conditions, and further increase with increased wind–wave misalignment. The results of the study also show that the parameter T p is essential for estimating limiting sea states given that this parameter significantly influences monopile vibrations during the blade-root mating task. Overall, the findings of the study can be used for a safer and more cost-effective mating of wind-turbine blades.
Highlights
The increase in the market share of renewable sources of energy helps in the reduction of carbon content in the environment [1]
One of the key reasons for this is the use of strict weather limits for planning and executing the installation task given that the components of turbines are sensitive and not structurally resistant to handle unexpected loads during the temporary installation phases [6]
We focus on estimating allowable sea states for blade-root mating task on a preassembled hub of a monopile-type offshore wind-turbine (OWT), which is regarded as one of the most critical tasks by the industry [25]
Summary
The increase in the market share of renewable sources of energy helps in the reduction of carbon content in the environment [1]. One of the key reasons for this is the use of strict weather limits for planning and executing the installation task given that the components of turbines are sensitive and not structurally resistant to handle unexpected loads during the temporary installation phases [6]. These weather limits are generally obtained from experiences and lack a methodical basis, which makes the installation tasks restricted to a narrow workable weather window of operation. It can be seen that more than half of the time (53%) is spent waiting on weather, whereas the actual time used for the installation of turbine components is only 15%
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