Energy saving within shipping is gaining more attention due to environmental awareness, financial incentives, and, most importantly, new regional and international rules, which limit the acceptable emission from the ships considerably. One of the measures is installation of energy saving devices (ESD). One type of such a device, known as pre-swirl stator (PSS), consists of a number (usually 3 to 5) of fins, which are mounted right in front of the propeller. By modifying the inflow and swirl into the propeller, the fins of a PSS have the possibility to increase the total propulsion efficiency. However, at the same time, they may introduce additional resistance either due to changes in pressure distribution over the aft ship or due to its own resistance of fins. In this paper, the authors present experimental and numerical investigation of a PSS for a chemical tanker. Numerical analysis of the vessel with and without PSS is performed in the model and full scale. Model testing is performed with and without PSS to verify the power savings predicted numerically. Among other quantities, 3D wake field behind the hull is densely measured at different planes, starting from the PSS plane to the rudder stock plane. 3D wake measurements are also conducted with a running propeller. The measurements show considerable improvement in the performance of the vessel fitted with PSS. On the numerical side, analyses show that scale effect plays an important role in the ESD performance. Investigation of the scale effect on the vessel equipped with an ESD provides new insight for the community, which is investing more into the development of energy saving devices, and it offers valuable information for the elaboration of scaling procedures for such vessels.
This paper presents numerical simulations of Green Water events and wave impact on a FPSO. The simulations are performed at model scale and the results are compared against experimental model test results. The commercial Star-CCM+ CFD software is used in the simulations. The incoming waves are modeled using 5th order Stokes theory, as implemented in the CFD software. Both fixed and free floating FPSO are considered. The moving FPSO are modeled using Chimera overset mesh technology. The vessels is free to move in heave and pitch at 180 (head sea), roll and heave at 270 (beam sea), while roll, pitch and heave is released at 225 (quartering sea). The computed water height on the deck and the relative wave height in vicinity the vessel are compared against model test results at several positions. Also the impact force on load cells blocks located at the deck of the vessel is computed and compared against model test results. The comparison of the time histories of the water elevation and load histories are in reasonable agreement with the measured time series. The number of grid cells range from 7M for the simulations at head sea, where flow is assumed to be symmetric, to 21M for the simulations at quartering sea. Total wall clock simulation time was about 10days for the most computationally demanding cases, which are the quartering sea simulations. This includes simulation of 12 wave periods with the ship fixed, and thereafter 8 wave periods of the free floating vessel. The computations show that CFD tools can be used as a research tool when studying the physics of green water and wave impact events. However, due to time CPU demanding simulations, this type of CFD analysis are not yet a practical tool for parametric design studies and deck structure optimizations. This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.
Results of the fluid-structure co-simulations that were carried out as part of the FleksProp project are presented. The FleksProp project aims to establish better design procedures that take into account the hydroelastic behavior of marine propellers and thrusters. Part of the project is devoted to establishing good validation cases for fluid-structure interaction (FSI) simulations. More specifically, this paper describes the comparison of the numerical computations carried out on three propeller designs that were produced in both a metal and resin variant. The metal version could practically be considered rigid in model scale, while the resin variant would show measurable deformations. Both variants were then tested in open water condition at SINTEF Ocean’s towing tank. The tests were carried out at different propeller rotational speeds, advance coefficients, and pitch settings. The computations were carried out using the commercial software STAR-CCM+ and Abaqus. This paper describes briefly the experimental setup and focuses on the numerical setup and the discussion of the results. The simulations agreed well with the experiments; hence, the computational approach has been validated.
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