10:30
Ship hydromechanics resistance IV
Chair: José Miguel Fonfach
10:30
30 mins
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AN ANALYSIS METHOD TO EVALUATE THE ADDED RESISTANCE IN SHORT WAVES CONSIDERING BOW WAVE BREAKING
BongJun Choi, Rene H.M. Huijsmans
Abstract: A bow wave breaking is one of the most prominent factors to be considered regarding the nonlinearity of added resistance for a ship. Considering the stability of the bow wave breaking, which is mostly influenced by the ship speed and the waterline entrance angle, can enhance understanding of the nonlinearity. Understanding of the nonlinearity can be improved by considering the stability of the bow wave breaking, which is mostly influenced by the ship speed and the waterline entrance angle. New transfer function containing the ship speed is proposed to make a better representative of the nonlinearity. This method is evaluated with the model test data of the Fast Displacement Ship (FDS) under the short waves condition (λ/L= 0.4). This study has shown that new transfer function can be an efficient analysis method of the ship performance prediction offering intuitive consistency with proposed residual resistance concept. The findings lead to better understanding the nonlinearity considering bow wave breaking.
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11:00
30 mins
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INVESTIGATION ON PROPULSION AND FLOW FIELD OF SHIPS WITH ENERGY SAVING DEVICES USING CFD PREDITIONS AND MODEL TESTS
Jingpu Chen, Jia Su, Wujie Jiang, Li Yang
Abstract: Recently, International Maritime Organization put forward various new regulations related to air pollution and ship safety, and the Energy Efficiency Design Index(EEDI) inspires shipyards and ship owners to install Energy Saving Devices(ESDs) for the control of CO2 emission from ships and fuel consumption.
From the scope of hydrodynamics, lines optimization, high-efficiency propellers and ESDS are widely adopted to reduce the fuel consumption of ships. The optimization and prediction of ESDs are very important topics related to hydrodynamics. The design and validation of ESDs can be carried out by model tests, while this method will be time costly and expensive, the design method based on CFD predictions is the best choice.
XCHAP module which is a steady state solver using structured, overlapping grids, is adopted in this paper. The EASM turbulence model was used and no-slip conditions were applied on the hull surface.
At first, the CFD predictions should be verified and validated carefully for the reliable design of ESDs. In this paper, CFD predictions on the Benchmark test of the JAPAN Bulk Carrier (JBC) with and without an energy saving device (ESD) are performed. The comparison of CFD predictions results of the resistance, self-propulsion with that of model tests, shows that the present method could predict the delivered power tendency of ESD.
Then this method is used for the design and optimization the ESD of an oil tanker. In order to obtain the best ESD, about five parameters are selected based on SOBOL algorithm, series CFD predictions are performed to assess delivered power of different variants. The best ESD with 2.95% reduction of delivered power are obtained for the oil tanker. The model tests of resistance and self-propulsion were conducted for the validation the effects of ESD, the results shows that about 3.45% delivered power reduction from model test. The comparison of experimental and computed wake field at propeller plane shows that good agreement.
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11:30
30 mins
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COUPLED TIME DOMAIN METHOD FOR SHIP DYNAMICS AND SLOSHING FLOWS
José Miguel Fonfach, Marcelo Neves
Abstract: In the present contribution, a numerical study of the coupling effect between the sloshing flows and ship sway motion under beam regular waves is carried out employing a coupled time domain method. The lateral ship dynamics is solved using an “Instantaneous Update” algorithm. Sequentially, sloshing Y-forces are obtained by the I-MPS (Improved Moving Particle Semi-Implicit) method. The “Instantaneous Update” algorithm is a 6DOF (six degrees of freedom) seakeeping simulator, where a frequency-domain calculation of the radiation and diffraction coefficients is required as input data, which is performed by a panel method. Furthermore, non-linear effects are incorporated to calculate the instantaneous position of the ship, and the external wave excitation forces are calculated at each time step, considering the relative positon between the excitation waves and ship surfaces. The sloshing flow solver is a 2D (two dimension) robust method based on particle interactions in a Lagrangian coordinate system. Sloshing simulations are performed within a closed domain in which the free surface is modelled as a deformable surface for a single-phase flow. For the coupled process, the sloshing-induced forces are included into the external wave-excitation forces, and then the corresponding position of the ship is actualized. At the same time, the sloshing flow is consequence of the instantaneous ship motion. In order to assess the numerical method, the coupled time domain method is validated for the sway motion of a barge with two identical rectangular tanks with length 25% of the barge length, according with Rognebakke & Faltinsen (2001) experiments. The study takes into account one or two tank filled and several amounts of water in the tank for a range of excitation wave frequencies near to the eigenfrequency of the fluid motion in the tanks.
REFERENCES
[1] Rognebakke, O. R. and Faltinsen, O. M., (2001), “Effect of sloshing on ship motions”, 16th International Workshop on Water Waves and Floating Bodies, Hiroshima, Japan
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