Minimizing the displacement of integrated system of wind and tidal turbines based on the soil types under cyclic loads

Abstract

Hybrid offshore platforms are complex structures that need to tolerate cyclic loads. These loads occur when the turbine is working between cut-in and cut-out speeds and depend on the turbine's rotational speeds. However, selecting a proper soil for the structure to be secured in is very important for the stability of the hybrid system. This study aimed to calculate the displacement of an integrated offshore structure capable of supporting a hybrid assembly of one wind plus two tidal turbines under cyclic loads. The monopile has been found to be a suitable foundation type, as the most inexpensive solution in water depths less than 30 meters, for integrating both types of turbines. The deflection of the structure was compared for different types of soil with finite element analysis. Several simulations were conducted using OPTUM G3 software for calculating the stability of each type of soil in the rotational speed range of turbines. The results enable determining the amount of deflection for each soil type. The displacement range for soft clay is 0.0052 to 0.0098 m, and displacement is between 0.007 and 0.0158 m for medium sand. The minimum displacement of firm clay, which is 0.0115 meters at 5 rpm, is higher than all minima of other soil types. Thus, soft clay and medium sand show more stability, and firm clay is less stable in the rotational speed range of the turbines.