Ice loading on Danish wind turbines: Part 1: Dynamic model tests

Abstract

An extensive model test program has been carried out to investigate the key ice load issues on offshore wind turbines in Danish waters. Tests were performed using a compliant structure that had scaled structural characteristics. The test program investigated seven configurations of model structures and dynamic characteristics. Both first- and second-mode vibration issues were investigated. Forty-one ice sheets were used giving information on 144 different experimental set-ups. The parameters that were changed in the tests included the ice velocity, ice thickness, shape of the structure, water level on the structure, structure stiffness and the natural frequency of the structure. Measurements were made of forces, accelerations and displacement of the model during the interaction with ice. Four different ice failure modes were identified—flexure, crushing, mixed mode, and lock-in. The results gave information on the anticipated ice loads and the likelihood of ice-induced vibrations for both the first-mode and second-mode vibration frequencies. They also provided guidance on the optimum angle and cone-size for a protective ice collar for the wind turbines. This paper provides the results of the model tests. A companion paper [Cold Reg. Sci. Technol., (2004)], provides information on the application of the results to the design of an offshore wind turbine farm.