Numerical Modeling and Analysis of the Combined Wind and Wave Energy Concept SFC

This thesis work primarily aims to achieve a good understanding of the basic principle of the frequency domain and time domain analysis methods for response analysis of combined wind and wave energy concept SFC. SFC is a semi-submersible floating wind turbine concept with 3 wave energy converter units on each pontoon. However, this work is intended to investigate the motion RAOs of the whole platform and internal load RAOs in the floater s pontoon of the SFC at a particular position for the aligned condition. Besides, the comparison between numerical and experimental results are also performed for motion RAOs. Finally, the response analysis of the SFC in the irregular sea is performed. In time domain analysis, the motion responses of surge, heave and pitch are carried out. Besides, the response analysis of tower base bending moment at the base of the tower is also carried out. When performing a comparative study it is important to ascertain that the numerical model is as much close as the physical model. But, it is important to mention that there are some differences between the experimental model and the numerical model. In frequency domain analysis the basic difference is the absence of mooring lines and the assumption of the WECs to be rigidly connected to the pontoons. So it is to be kept in mind while comparing the numerical motion RAOs of the numerical model and the experimental model. The numerical frequency domain analysis is performed in HydroD which uses the 1st order potential theory along with the Morison s drag for viscous forces. The differences could be the reason for discrepancies in surge and pitch motion RAOs specially. However, the physical model is modelled as 1:50 using Froude s scaling law for performing the experimental analysis. But, all of the results are provided in full scale. Besides the sectional load analysis is performed for two wave directions (00 and 1200) for investigating the dominating criteria. Finally, the fully coupled time domain numerical analysis is performed in SRA (SIMORIFLEX-Aerodyn). Here, both of the wind and wave conditions are considered. The first step is to build the model with the import of hydrodynamic coefficients from HydroD into SIMO. This is an important step, as this may affect the accuracy of the result if there is any mistake. However, the main focus in this section is to perform the decay test of the SFC for verification. Again, there was some discrepancy specially for pitch natural period. The final task intends to perform numerical analysis in extreme and operational environmental conditions. The aligned condition is considered in TD analysis in terms of both wind and wave direction