Experimental Study of Wave Run-Up on Tripod Offshore Wind-Turbine Foundations

For the design of offshore wind turbines, the airgap height of a service platform above still water level (SWL) is dependent on the maximum level of wave run-up in seas. A number of laboratory model tests were carried out in a wave flume to evaluate and predict the wave run-up on a tripod foundation in regular and irregular waves. Comparison of the measured data with the predictions by existing methods revealed that the empirical formulae for wave run-up on monopile foundations cannot straightforwardly be applied to the tripod foundation for the sake of more complex structural geometry and associated hydrodynamics. Hence, the run-up coefficients m for measured regular and irregular wave run-ups are derived with the velocity stagnation head theory and then fitted against wave steepness. The hindcast results using the fitted m show good agreement with measurement, thus enabling fast prediction of wave run-ups on tripod foundations in practice. In addition, an exceptionally large wave-up has been recorded in the irregular wave tests, which affirms the occurrence of a similar phenomenon in Horns Reef 1 wind farm some years ago.