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# FINITE ELEMENT MODELING AND JACKET LAUCH ANALYSIS USING A BARGE

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### FINITE ELEMENT MODELING AND JACKET LAUCH ANALYSIS USING A BARGE

1. 1. Tiểu ban Năng lượng, Kỹ thuật công trình, Vận tải và Công nghệ Biển 163 FINITE ELEMENT MODELING AND JACKET LAUCH ANALYSIS USING A BARGE Dinh Quang Cuong (1); Ngo Tuan Dung (2) (1) Institute of Construction for Offshore Engineering (ICOFFSHORE) University of Civil Engineering - 55 Giai Phong Street - Hanoi (2) PetroVietnam Marine Shipyard J/S Company (PVshipyard), No. 65A2, 30/4 Street, Vung Tau; Email: dqc@hn.vnn.vn Abstract: There jacket - barge system models can be using Software system, which have currently on the world and in Vietnam to calculating: StruCAD*3D; StabCAD; NEPTUNE Developed by Zentech USA; MOSES (Multi Operational Structural Engineering Simulation) and SACS (Structural Analysis Computer System), ProgramManual- Engineering Dynamic, Inc. USA, but their use often by foreigners. The most important problem is the system simulation includes barge and jacket. This paper presents method numerically simulate the barge - jacket system for calculating the jacket launch process using a barge by finite elements software, desire to affirm the ability of our engineers in the calculation of the problems mentioned above. PHƯƠNG PHÁP PHẦN TỬ HỮU HẠN GIẢI BÀI TOÁN VẬN CHUYỂN, ĐÁNH CHÌM KHỐI CHÂN ĐẾ CÔNG TRÌNH BIỂN TỪ SÀ LAN Tóm tắt: Có thể dùng các chương trình phần mềm theo phương pháp phần tử hữu hạn để giải bài toán vận chuyển, đánh chìm khối chân đế từ xà lan. Các chương trình phần mềm nói trên là: StruCAD*3D; StrabCAD; SASC,… đã được trang bị tại Việt Nam, tuy nhiên hầu như vẫn chỉ do người nước ngoài sử dụng. Vấn đề quan trọng nhất khi thực hiện bài toán là sự thống nhất về mặt phương pháp mô phỏng hệ thống kết cấu khối chân đế và sà lan trong quá trình vận chuyển, đánh chìm. Báo cáo này trình bầy việc mô phỏng hệ thống kết cấu theo phương pháp phần tử hữu hạn và một số kết quả ban đầu khi tính toán vận chuyển, đánh chìm khối chân đế công trình biển bằng thép từ sà lan bằng chương trình phần mềm theo phương pháp phần tử hữu hạn, với mong muốn khẳng định khả năng của các kỹ sư của chúng ta có thể giải các bài toán nêu trên đây. 1. Introduction The launch process is broadly divided into four dynamically distinct phases: Phase 1: Jacket sliding over the launch-way of the barge towards the rocker arm
2. 2. Hội nghị Khoa học và Công nghệ Biển toàn quốc lần thứ V164 Phase 2: Jacket sliding on the rocker arm and rotating with respect to the rocker pin Phase 3: Jacket tipping on one side of the barge Phase 4: Separation of the jacket from the barge During each phase, the equations of motion are developed and solved using a powerful variable time step algorithm [1] [2]. In the launch formulation, the barge-jacket interaction effect is incorporated and barge and jacket motions (including displacement, velocity, and acceleration) are computed for each time step, and the reaction forces and hydrodynamic forces are summarized. Bottom clearance for the jacket can also be checked during the launch process. Currently, the program assumes the lateral symmetry of the barge-jacket system, and thus only Phase 1, Phase 2, and Phase 4 are simulated by the program. Although the first two phases of jacket motion are constrained to the vertical plane of the barge, the hydrodynamic forces of the barge and jacket are considered in three dimensions. 2. Simulate the system 2.1. Coordinate Systems: There are five major coordinate systems: 2.1.1.The input coordinate system The input coordinate system is the coordinate system used to generate barge and jacket models and to enter launch data. In general, the input coordinate system is also known as the structural global system when generating the jacket structural model. The x-axis of the input coordinate system should be parallel to water surface and run along the center of the barge toward the rocker arm, i.e., the launch direction. It is recommended that the x-axis of the input coordinate system be chosen along the keel of the launch barge. 2.1.2. The barge body coordinate system The barge body coordinate systems are fixed in the body with the origin located at the barge Center of Gravity (C.G.), respectively (Figure 2). The barge body coordinate system is also used to describe relative motions between jacket and barge during the first two phases of the launch process. 2.1.3. The jacket body coordinate system The jacket body coordinate systems are fixed in the body with the origin located at the jacket Center of Gravity respectively (Figure 2). 2.1.4. The rocker arm coordinate system The rocker arm coordinate system is fixed in the rocker arm, with its origin at the rocker pin (Figure 3). The rocker arm coordinate system is mainly used to describe phase 2 motion and jacket-barge interaction forces. 2.1.5. The global (water surface) coordinate system The global coordinate system, which is an inertial system fixed in space, that the origin is at the water surface directly above the barge center of gravity before the launch process begins. The global coordinate system has the same positive directions (X, Y, and Z) as the
3. 3. Tiểu ban Năng lượng, Kỹ thuật công trình, Vận tải và Công nghệ Biển 165 input coordinate system (Figure 1). The barge and jacket motions and hydrodynamic forces are described in the global coordinate system. Originally, all the x-axes are in the direction of the barge bow to stern (i.e., in the launch direction), and all z-axes are vertical upward. The y-axis is determined by the right-hand rule. By specifying the jacket leading points, trailing points, and trailing edge distance, the program automatically puts the jacket on the top of the launch runner based the the assumption that the launch runner is parallel to the barge keel. 2.2. Mathematical Formulation The forces acting on the jacket-barge system due to inertial, gravitational, frictional, and hydrostatic and hydrodynamic forces are evaluated, and the equations of motion in the form )(tFKXXCXM   are established. (1) M: Total mass matrix of the global coordinate system; C: Damping matrix; K: Structural stiffness matrix; F(t): Force vector; XXX ;;  : Vector of accelerations, velocities and displacements. Thus the equations of motion are non-linear and the time domain method of analysis is inevitable.
4. 4. Hội nghị Khoa học và Công nghệ Biển toàn quốc lần thứ V166 2.3. Model Generation Other typical input which includes the barge C.G., simulation time and time step, jacket initial position relative to launch runner, and rocker arm data. The barge geometry is modeled by 'PANEL' cards. Each panel is a flat area described by connecting lines of up to 8 points. All the joints in the panel must be in the same plane. The order of the connecting nodes, whether clockwise or counter-clockwise, will determine the direction of the panel in accordance with the right hand rule. All the panels must have inward normal (i.e., the direction of the panel) to form a complete enclosed body, i.e., the hull of the launch barge. The jacket model can be generated in any orientation in the input coordinate system (Figure 4). By defining the contacting surface of the jacket on the barge, the program will re-orient the jacket. The initial position of the jacket can be determined by further specifying the initial trailing edge position and the height of rocker pin and rocker arm in the input coordinate system. Since it is assumed that the barge-jacket system is laterally symmetric, it is not necessary to specify the relative position in the y-direction. The contacting surface of the jacket on the barge is defined by specifying four typical points, i.e., the leading starboard point, the leading port point, the trailing starboard point, and the trailing port point (Figure 1). These points are used to determine the coordinate system associated with the contacting surface, and the contacting length of jacket structure members on the launch runner. Therefore, the trailing points should be the aft-most points of the jacket structure members that contact the barge launch runner. 2.4. Initial Equilibrium Position The barge-jacket system is assumed to be in static equilibrium under the effect of gravity and hydrostatic forces when the launch simulation begins. The initial equilibrium position can be obtained by the program based upon mass matrices, geometry, and the relative