Dynamic Model Test of Monopile for Offshore Wind Turbines

In current practice, the most common foundation type for Offshore Wind Turbine generators (OWT’s) at moderate water depths is the monopile. A model pile in scale 1:20 of a typical monopile foundation for offshore wind turbine has undergone lateral vibration testing in dry laboratory sand. Eigen-frequencies are determined based on acceleration measurements. The aim of the tests is to provide benchmark results for validation of different calculation methods for offshore wind monopile foundations. The stiffness contribution from the sand is evaluated on behalf of measuring the first natural frequency of the pile-soil interaction system. Preliminary results from back-calculations of the model tests using both 3D -FEM and a simple beam on elastic foundation model indicate that strain-dependent soil stiffness plays an important role for determining the system stiffness. In this paper, the model tests and their results are presented, along with the preliminary results from the back-calculation.