Comparison of laboratory wave generation techniques on response of a large monopile in irregular sea

As the offshore wind industry moves toward larger monopile turbines, model testing and validation of hydrodynamic load models become more important for new designs of turbines. Wave generation is an important aspect of hydrodynamic model testing. When generating irregular waves with a piston-type wavemaker, first order wavemaker theory is commonly used. This leads to generating spurious free waves in the tank. Using second order wavemaker theory reduces the generation of these spurious waves. In this study, the two wave generation techniques have been used in the measurement of the dynamic responses of a monopile with (full-scale) natural period of 5 sec. The effect of superharmonic spurious waves on the response statistics was minor. A marginal improvement in experimental repeatability of the second mode response in large wave events was observed by using second order wavemaker theory