Effective consideration of soil characteristics in time domain simulations of bottom fixed offshore wind turbines

An effective consideration of the soil characteristics is challenging. Sophisticated soil-structure interaction models have many degrees of freedom and are highly non-linear. Hence, they are not applicable for transient calculations of the design stage due to high computing times. Therefore in a first step, a six-directional, linear approach to consider soil effects is presented which assumes the turbine connected to the soil by inertial and elastic coupling terms. Results of jackets with piles and suction buckets are presented and show significant shifts of the eigenfrequencies compared to approaches with substructures clamped to the seabed. In a second step, a piecewise defined response surface has been developed in order to take the operating point into account. It correlates the previously known environmental conditions with the loads required for calculating the interaction matrices. This approximation has been proven to be accurate enough in this context and led to a further shift of the eigenfrequencies compared to results with no loads applied.