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Numerical Calculation of the Hydrodynamic Forces on a Ship in Pure Sway Motion in Restricted Waters

Author: LouPengYu
Tutor: ZouZaoJian
School: Shanghai Jiaotong University
Course: Naval Architecture and Ocean Engineering
Keywords: ship maneuverability restricted waters pure sway viscous flow hydrodynamics forces hydrodynamic derivatives numerical calculation
CLC: U661.33
Type: Master's thesis
Year: 2012
Downloads: 96
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Abstract

Ship maneuverability is one of the most important hydrodynamic performances related to the navigation safety. With the continuous development of shipbuilding industry and shipping business, the ship size becomes larger and the waterways become crowded. As a result, it becomes more difficult to steering ships and the risk of marine accidents such as collision increases. According to the“Standards for Ship Maneuverability”promulgated by the International Maritime Organization, it is required to predict the ship maneuverability during the ship design stage. At present, the most practical and effective method to predict ship maneuverability is the method of computer simulation by using the mathematical model (equations of ship maneuvering motion). The key to using this method is to determine the hydrodynamic derivatives in the mathematical model. Among the methods for determining the hydrodynamic derivatives, the most reliable one recognized is the method of captive model tests; among them the planar motion mechanism (PMM) test is a mature and powerful one which can be used to determine various velocity derivatives, acceleration derivatives as well as the coupling derivatives. It has an important position in the captive model tests.With the rapid development of computer technique, computational fluid dynamic (CFD) technique is becoming an important tool in research on ship hydrodynamics. During the last years, numerical methods using CFD technique to numerically simulate the viscous flow of captive model test and to determine the hydrodynamic forces and hydrodynamic derivatives of ship maneuvering motion already have significant development. They have provided a new way for predicting ship maneuverability. These methods can overcome the shortcomings of the captive model tests such as long test period and high costs. In addition, with these numerical methods it is convenient to optimize ship maneuverability by changing the hull form and conducting series of calculations; the efficiency and accuracy of determining the hydrodynamic derivatives can be enhanced by combining these numerical methods with captive model tests.In this thesis, the general CFD package FLUENT which is based on finite volume method is used to numerically simulate the viscous flow around a KVLCC1 model in pure sway motion in restricted waters by solving the unsteady RANS equations in conjunction with the moving mesh technique. The hydrodynamics forces acting on the hull and the corresponding hydrodynamic derivatives are calculated.The main work carried out in this thesis includes three parts. Firstly, the viscous flow around the ship model undergoing pure sway motion of small amplitude in deep and shallow water is numerically simulated, and the sway force, the yaw moment acting on the model are calculated. By comparing the numerical results with the test results by the Italian Ship Model Basin (INSEAN), the numerical modeling and the numerical method is validated. Secondly, the viscous flow around the ship model in PMM pure sway test is numerical simulated. A series of calculations are conducted for different tank widths and different water depths, and the sway force and yaw moment acting on the model are calculated. From the calculated hydrodynamic forces, the corresponding hydrodynamic derivatives are obtained. By analyzing and comparing the numerical results, the influences of tank width and water depth on the hydrodynamic forces and hydrodynamic derivatives are identified. The smallest ratio of tank width to ship breadth and the smallest ratio of water depth to draft, under which the influences of tank width and water depth on the test results can be neglected, are determined. Thirdly, the viscous flow around the ship model sailing along the channel bank and simultaneously undergoing a pure sway motion is numerically simulated. The hydrodynamic forces and the corresponding hydrodynamic derivatives are obtained at different ship-bank distance. The influence of the bank on the hydrodynamic forces and hydrodynamic derivatives are analyzedThe research work carried out in this thesis can provide some references for choosing reasonable model scale and water depth when doing PMM pure sway tests in ship model basin. By analyzing the influence of water depth and bank on the hydrodynamic forces and ship maneuverability, some guidance on safely steering a ship sailing in restricted water may be gained.

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