Estimating extreme level ice and ridge thickness for offshore wind turbine design: Case study Kriegers Flak

Abstract

When designing offshore wind turbines in ice‐covered seas, site‐specific ice conditions present crucial input for the structural design. In this study, methods of estimating the maximum level ice thickness occurring once in 50 years and parameters of a design ice ridge in an area where no direct ice thickness measurements exists are presented. The site of Kriegers Flak at the Southern Baltic Sea is taken as a case study. Rather than just applying basic equations found from the standards, the method gives more detailed estimates by utilizing available ice chart information, ice reports and atlases together with measured air temperature data to estimate the starting and ending date of ice growth. The maximum level ice thickness occurring once in 50 years at the site of Kriegers Flak wind farm was estimated to be between 0.26 and 0.44 m depending on the assumptions. The effect of the studied history length, the utilized weather station and the use of snow thicknesses to the 50‐year ice thickness estimates are compared and discussed. Interaction with ice ridges was found to be a relevant but infrequent, load scenario for the site of Kriegers Flak. For this reason, a representative ridge for determining ice ridge loads is presented. The most important parameter in a ridge, the thickness of the consolidated layer, was found based on scenario analyses to be in a range between 0.43 and 0.67 m can be used to calculate ice loads against the wind turbine substructures.

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