Per Vølund - Academia.edu (original) (raw)

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Papers by Per Vølund

Journal of Wind Engineering and Industrial Aerodynamics, 1992

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Wind Energy, Apr 1, 2005

Detailed knowledge of mean wind speed profiles is essential for properly assessing the power outp... more Detailed knowledge of mean wind speed profiles is essential for properly assessing the power output of a potential wind farm. Since atmospheric stratification plays a crucial role in affecting wind speed profiles, obtaining a detailed picture of the climatology of stability conditions at a given site is very important. In the present study, long time series from offshore measurement sites around Denmark are analysed, with the aim of quantifying the role of atmospheric stability in wind speed profiles and in our ability to model them. A simple method for evaluating stability is applied, and the resulting statistics of the atmospheric stratification is thoroughly studied. A significant improvement in the mean wind speed profile prediction is obtained by applying a stability correction to the logarithmic profiles suitable for neutral conditions. These results are finally used to estimate power densities at different heights. Copyright

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Cold Reg Sci Technol, 2005

An extensive model test program has been carried out to investigate the key ice load issues on of... more 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.

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