Sandy Day

Rotor Scaling Methodologies for Small Scale Testing of Floating Wind Turbine Systems

Two scaling methodologies are presented to address the dissimilitude normally experienced when attempting to measure global aerodynamic loads on a small scale wind turbine rotor from a full scale reference. The first, termed direct aerofoil replacement (DAR), redesigns the profile of the blade using a multipoint aerofoil optimisation algorithm, which couples a genetic algorithm (GA) and XFOIL, such that the local non-dimensional lift force is similar to the full scale. Correcting for the reduced Reynolds number in this manner allows for the non-dimensional chord and twist distributions to be maintained at small scale increasing the similitude of the unsteady aerodynamic response; an inherent consideration in the study of the aerodynamic response of floating wind turbine rotors. The second, the geometrically free rotor design (GFRD) methodology, which utilises the Python based multi-objective GA DEAP and blade-element momentum (BEM) code CCBlade, results in a more simplistic but less accurate design. Numerical simulations of two rotors, produced using the defined scaling methodologies, show an excellent level of similarity of the thrust and reasonably good torque matching for the DAR rotor to the full scale reference. The GFRD rotor design is more simplistic, and hence more readily manufacturable, than the DAR, however the aerodynamic performance match to the full scale turbine is relatively poor.

Optimum Distance Between Two Advancing Ships Arranged Side by Side

The hydrodynamic interaction between two advancing ships is very important. Because of the hydrodynamic interactions, even relatively small waves can induce large motions of the smaller ship due to the proximity of the larger ship. The aim of this paper is to develop a method to optimize the spacing between two advancing ships, in order to minimize the hydrodynamic interactions. The optimization method is based on the far-field wave patterns produced by a translating and oscillating source point. For values of the parameter τ > 0.25 ( τ = ωeu/g) there is a fan-shaped quiescent region in front of the vessel. As τ increases, the range of the fan-shaped quiescent region will be expanded. It can be supposed that if the two ships are located in each other’s fan-shaped quiescent region, the hydrodynamic interactions can be minimized. This assumption was validated through the numerical simulation, which was based on a 3-D Rankine source panel method. We calculated and compared the wave exciting forces and wave patterns of two Wigley hulls advancing in waves side by side. The numerical results were consistent with our theoretical assumption.

Numerical Studies on Added Resistance and Ship Motions of KVLCC2 in Waves

In this study, numerical simulations for the prediction of added resistance and ship motions at various ship speed for the KVLCC2 vessel are presented. These simulations are conducted using a Computational Fluid Dynamics (CFD) method and a 3-D potential method, both in regular head seas. Numerical analysis is focused on the added resistance and the vertical ship motions (heave and pitch motions) for a wide range of wave conditions at stationary, operating and design speeds. Firstly, the characteristics of the CFD and the 3-D potential flow method are presented. Simulations of various wave conditions at design speed are used as a validation study, and then simulations are carried out at stationary condition and at operating speed. Secondly, unsteady wave patterns and time history results of the added resistance and the ship motions are simulated and analysed at each ship speed using the CFD tool. Thirdly, the relationship between the added resistance and the vertical ship motions and the non-linear effects such as green water on deck, and non-linear ship motions are investigated. Systematic studies of the numerical computations against the available Experimental Fluid Dynamics (EFD) data are conducted as well as grid convergence tests, to show that the numerical results have a reasonable agreement with the EFD results in the prediction of added resistance and ship motions in waves.