This paper documents the round robin testing campaign carried out on a floating wind turbine as part of the EU H2020 MaRINET2 project. A 1/60th scale model of a 10 MW floating platform was tested in wave basins in four different locations around Europe. The tests carried out in each facility included decay tests, tests in regular and irregular waves with and without wind thrust, and tests to characterise the mooring system as well as the model itself. For the tests in wind, only the thrust of the turbine was considered and it was fixed to pre-selected levels. Hence, this work focuses on the hydrodynamic responses of a semi-submersible floating foundation. It was found that the global surge stiffness was comparable across facilities, except in one case where different azimuth angles were used for the mooring lines. Heave and pitch had the same stiffness coefficient and periods for all basins. Response Amplitude Operators (RAOs) were used to compare the responses in waves from all facilities. The shape of the motion RAOs were globally similar for all basins except around some particular frequencies. As the results were non-linear around the resonance and cancellation frequencies, the differences between facilities were magnified at these frequencies. Surge motions were significantly impacted by reflections leading to large differences in these RAOs between all basins.
Recently, there have been active efforts to investigate the effect of hull roughness on ship resistance using Computational Fluid Dynamics (CFD). Although, several studies demonstrated that the roughness modelling in the CFD simulations can precisely predict the increase in frictional resistance due to the surface roughness, the experimental validations have been made only for flat plates which have zero pressure gradient. This means that the validations cannot necessarily guarantee the validity of this method for other ship resistance components besides the frictional resistance. Therefore, it is worth to demonstrate the validity of the roughness modelling in CFD on the total resistance of a 3D hull. In this study, CFD models of a towed flat plate and a KRISO Container Ship (KCS) model were developed. In order to simulate the roughness effect in the turbulent boundary layer, a previously determined roughness function of a sand-grain surface was employed in the wall-function of the CFD model. Then the result of the CFD simulations was compared with the experimental data. The result showed a good agreement suggesting that the CFD approach can precisely predict the roughness effect on the total resistance of the 3D hull. Finally, the roughness effects on the individual ship resistance components were investigated. Recently, the use of Computational Fluid Dynamics (CFD) is considered as an effective alternative to improve these shortcomings [17]. The merit of using CFD is that the distribution of the local friction velocity, , is dynamically computed for each discretised cell, and therefore the dynamically varying roughness Reynolds number, + , and corresponding roughness function, + , can be considered in the computation. The 3D effects can also be taken into account, and the simulations are free from the scale effects if they are modelled in full-scale. Correspondingly, there have been increasing number of studies utilising CFD modelling to predict the effect of surface roughness on ship resistance [16, 18-20] and propeller performance [21, 22], as well as ship self-propulsion characteristics [23]. These recent studies suggest that the hull roughness does not only increase the ship frictional resistance but also affects the viscous pressure resistance and the wave making resistance.
In this paper, the CFD-DEM coupling numerical method was applied to study the ship resistance of a certain type of ice-strengthened Panama bulk carrier in the brash ice channel. The ship-water interaction is established under Euler framework, and the ship-ice interaction is realized by means of the DEM method under Lagrange framework. The DEM ice particles modelling and the establishment of numerical brash ice channel were firstly carried out with reference to the HSVA ice tank test image and test parameters. Next, the influence of DEM ice particle shape on contact force and ship-ice interaction was studied. After that, the influence of the one-way coupling and two-way coupling computational scheme between fluid and particles on the calculation accuracy and the interaction phenomenon was studied and analyzed. Finally, the ship-ice interaction process and mechanical behavior of ship and particle interaction in the brash ice channel was simulated, and the numerical results were compared with the experiment of HSVA ice tank. The results show that the CFD-DEM coupling numerical method which takes full account of the effect of ship-water and the interaction between fluid and particles, can well simulate the phenomenon and process of ship-ice interaction, and compared with the experimental results, the average error of the numerical prediction is about 5.03~5.23% for ICE-1 case with one-way and two-way coupling.The CFD-DEM coupling numerical method includes water resistance, which improves the prediction accuracy of the alone DEM calculation method. The research work in this paper can provide a reference for the numerical prediction of navigation process of ships in the brash ice channel.
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This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC).Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study.
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