| The hydrodynamic performance of damaged ship will deteriorate seriously. At the same sea condition, the damaged ship does not sail normally as a intact ship. To lessen the loss of ship function, life, property, and pollution of rivers or seas, domestic experts and foreign scholars have attached importance to the study of damaged ship hydrodynamics. Sea keeping and maneuverability of damaged ship have been researched, but the study of its maneuverability is few. However, the maneuverability is one of the most important ship hydrodynamic performances which have a close relationship with navigation safety. Therefore, it is urgent to study the damaged ship maneuverability, while it has great significance and engineering meaning to predict the maneuverability of damaged ship exactly. At present, this research is becoming one of the new hot topics in the field of ship hydrodynamics.During the last decade, with the rapid development of computer science and technology, the performance of computer has been improved. This has provided the necessary hardware condition for the development and practical application of Computational Fluid Dynamics (CFD) in ship hydrodynamics, and made it possible to simulate the complicated flow fields around a maneuvering ship and calculate the hydrodynamic forces on the ship. In this thesis, the hydrodynamic forces of damaged ship in oblique motion are studied based on numerical simulation which is by solving the Reynolds-Averaged Navier-Stokes (RANS) equation, and tests. On the other hand, the maneuverability experiments and comprehensive evaluations for the damaged ship maneuverability are carried out.(1) The viscous flow theories and numerical calculation methods applied widely in the study of ship hydrodynamic forces are introduced. Five two-equation turbulence models are introduced, and some numerical technology, for example, some discretization methods, and pressure-velocity coupling algorithm, and grid construction are analyzed.(2) In this thesis, the statistical analysis about the damaged ship models is carried out. In order to construct the damaged ship model, a lot of maritime casualties in the last tens years have been collected. Then the probability and statistical theory is applied to analyze these casualties It is obtained that the bow, waist, and stern of ship are usually damaged. Then a 29000 ton oil tanker is selected in the study. The damaged models, which have two kinds of damaged sizes, three damaged positions (bow cabin, waist cabin, and stern cabin) are set up based on the statistical analysis. The three kinds of damaged ship floatation in full load conditions are computed based on ship theory.(3) The velocity decomposition method is applied to study the viscous hydrodynamics forces acting on the 29000 ton oil tanker model in oblique motion through comparison of two kinds of numerical results. In the process of numerical calculation of maneuvering hydrodynamic forces, suitable turbulence model and high qualified grids are the key to a successful simulation. The numerical results of viscous hydrodynamic forces of intact ship are obtained respectively with five two-equation turbulence models, which are widely used in calculation, are compared with measurements, and then the SSTk-ωturbulent model is selected. The accuracy of the numerical results with the number of different grids is analyzed by comparing the numerical results with experimental ones. Based on the analysis of turbulent models and grids, and so on, the turbulent model and structed grids and unstructed grids, and other numerical methods, are applied in prediction of the total resistance, transverse force, yaw moment of the 29000 ton oil tanker ship model sailing at different drift angle. The numerical results agreed with the experiment values. In order to analyze furtherly the errors between ship model experiment and numerical calculation, the least squares method is adopted to fit the transverse force equation and bow wag moment equation.(4) Both experiment and numerical calculation are applied in study on maneuvering hydrodynamic forces of damaged ship. The geometric model of the damaged ship is constructed firstly.Regular grids are adopted in the damaged compartment. The study of hydrodynamic forces of damaged ship includes three steps as follows:Firstly, In the damaged ship upright condition, the maneuvering hydrodynamic forces of damaged ship and viscous flow fields are simulated respectively in three different damaged cabins (bow cabin, waist cabin, and stern cabin) at the velocity of 0.81m/s (Fr=0.1296). The hydrodynamic forces of waist cabin are also calculated in three different velocities of 0.81m/s (Fr=0.1296),0.73m/s (Fr=0.1168),0.63m/s (Fr=0.1008). The relation between viscous hydrodynamic forces and different damaged cabin is explored. Secondly, maneuvering hydrodynamic forces of damaged waist cabin are simulated respectively at three different velocities and 9 kinds of drift angles. The numerical results of total resistance coefficient, transverse force coefficient, and yaw moment coefficient between the intact ship model and the damaged one are compared. In the thesis, the characteristics of the viscous flow around the manoeuring ships are captured. By analyzing the flow information, one can get deep insight into the changing mechanism of the hydrodynamic forces of damaged ship in oblique motion. The relations of hydrodynamic forces and viscous flow fields being among to damage sizes are explored. Thirdly, The maneuvering hydrodynamic forces of damaged ship and viscous flow fields around the damaged ship in heel condition are simulated too. The relation between hydrodynamics and drift angle is explored. By analyzing the numerical results, it verifies that the numerical method based on RANS equations applied in study on the damaged ship maneuverability hydrodynamic performance is feasible and effective.(5)Turning tests and zig-zag tests of both the intact ship and its damaged ship have been carried out. The maneuvering tests of the damaged ship are analyzed, and the maneuverability changes are explored. At the same time, the turning and zig-zag of the intact 29000ton oil tanker are simulated based on MMG mathematical model and empirical hydrodynamic derivatives formulas.(6) Comprehensive evaluation factors of damaged ship maneuverability are determined according to the practical navigation and the principles of evaluation factor selection in system-engineering. Then, with AHP, gray relation theory, and Fuzzy mathematical theory, two integrated assessment models both AHPGR and AHPFC are constructed, and applied in comprehensive assessment of 29000 ton damaged ship maneuverability. The evaluation result agrees with the practice. In the fuzzy assessment, every factor subordinate degree function of damaged ship maneuverability is established based on every assessment faction criterion and one kind of generalize-bell-shape membership function. In this thesis, numerical and experimental study on the maneuverability for the damaged ship is carried out innovatively in the domestic. Moreover, the numerical method can accurately predict the viscous hydrodynamic forces of damaged maneuvering ship in oblique motion. The relations between the damaged ship maneuverability and the damaged positions or damaged sizes of damaged cabins are explored.The characteristics of the flow in the damaged cabins are captured. The experiments and comprehensive assessment of the damaged ship maneuverability are carried out. The research in this thesis reveals the change regularity of damaged ship maneuverability and lays a foundation for study on the damaged ship maneuverability in the future. |
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