Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free-decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid-fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertainties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge-decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction-type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid-fidelity models.

In recent years, electrical vehicle (EV) starts showing its unique advantages that the conventional combustion vehicles do not have. Together with the increasing interests on EV, the motor drive with higher efficiency and lighter weight also becomes more attractive. A promising solution is to apply the wide band gap (WBG) components including gallium nitride (GaN) and silicon carbide (SiC) in the motor drive. Thus, the performance of the GaN, SiC and Si based motor drive in this application are compared. Besides, as the current maximum current rating of the GaN and SiC MOSFET is limited and insufficient to satisfy the large phase current in the acceleration and braking process, the inverter topology that adds the parallel MOSFETs in one position is considered. To reduce the time and cost for the development, this paper proposes the modelling of the motor drive, with which the voltage and current stress, power loss, thermal and electromagnetic performance can all be evaluated. The modelling to be introduced consists of the 1-D power loss, simplified thermal modelling of the motor drive and the 3-D modelling of the electromagnetic performance, detailed thermal performance of the motor drive. In the 3-D modelling, to make the heat transfer simulation closer to the realistic, computational fluid dynamic (CFD) is used to evaluated the heat transfer coefficient on the surface with forced air-cooling.