A design method for internal rotating tower buoy single point load dynamic distribution
By combining SESAM and Orcaflex software with the bubble search algorithm, a dynamic load distribution design for single-point mooring devices with inner turret floats was developed. This solved the problem of the lack of standardized design for single-point mooring devices with inner turret floats, and enabled accurate load prediction and system optimization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- OFFSHORE OIL ENG CO LTD
- Filing Date
- 2024-11-11
- Publication Date
- 2026-06-26
AI Technical Summary
In the existing technology, there is a lack of standardized design methods for internal turret float-type single-point mooring devices, resulting in conservative design structures that cannot identify the most dangerous design conditions and corresponding design parameters.
Hydrodynamic and mooring time-domain analyses were performed using SESAM and Orcaflex software. By combining the bubble search algorithm, dynamic mechanical equilibrium equations were established, forces on mooring connectors were decomposed, and multiphysics coupling parameters and nonlinear coefficients were introduced to perform dynamic load distribution design.
It enables accurate prediction of single-point loads on internal turret floats, identifies weak points, optimizes design, improves system performance, and adapts to complex marine environments.
Smart Images
Figure CN119761230B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of dynamic single-point load distribution technology, and more specifically, to a design method for dynamic single-point load distribution of an inner turret float type. Background Technology
[0002] FPSOs are a major facility for offshore oil and gas field development, especially in areas far from shore and lacking surrounding pipeline networks. As of 2019, there were over 200 FPSOs serving oil fields worldwide. To reduce external loads and improve the facility's maneuverability, FPSOs in harsh environments generally employ single-point mooring, accounting for nearly 50% of all FPSOs. Single-point mooring systems are key equipment in marine engineering; their basic principle is to secure the FPSO to the sea via a 360° rotating mooring point, giving the FPSO a weathervane effect. Internal turret buoy-type single-point mooring is widely used as an economical and practical form of FPSO development.
[0003] The detachable single-point mooring system (FPSO) is designed to detach when environmental conditions exceed design requirements and reconnect in good weather. This characteristic dictates the unique nature of the connection between the single-point mooring system and the FPSO, as well as the complexity of load path transmission. For traditional floating body development devices, such as hull-type FPSOs, specifications provide calculation methods based on the maximum bending moment and shear force at midship. The bending moment and shear force envelope values for each section can be obtained through specifications and calculations for structural design and verification. Similarly, for semi-submersible platforms, relevant specifications provide extreme value calculation conditions under design wave conditions, making structural verification and design simple and feasible. However, there are no specifications or guidelines for the design of detachable single-point mooring systems, necessitating a design method to address this issue.
[0004] FPSOs with internal turret pontoon mooring are anchored in the deep sea via a single-point device. The mooring load changes constantly, and the forces transmitted through the mooring connections to the pontoon turret, bearings, calipers, and hull also vary. Furthermore, the time at which the maximum force occurs differs at each location. Therefore, determining the extreme design load at each location and the corresponding design loads at other locations at the same time becomes the primary task in the design of pontoon-type single-point mooring systems. Previous designs, limited by computational resources, employed simplified methods to handle various loads, often resulting in conservative structural designs that failed to identify alternative design parameters corresponding to the most critical design conditions.
[0005] In summary, a design method for dynamic load distribution at a single point in an internal turret pontoon type is provided. Summary of the Invention
[0006] The purpose of this invention is to provide a design method for dynamic load distribution of a single point in an internal turret pontoon type, in order to solve the problems mentioned in the background art, such as the lack of standards and guidelines for the design of detachable single points and the conservative nature of traditional design structures.
[0007] To achieve the above objectives, the present invention aims to provide a dynamic load distribution design method for a single point load of an internal turret float type, comprising the following steps:
[0008] S1. In the HydroD module of SESAM software, a wetted surface model is established based on the FPSO hull lines, and a mass model is established based on the FPSO loading information. Based on the wetted surface model and the mass model, hydrodynamic analysis is performed to obtain the overall motion response operator RAO of the FPSO.
[0009] S2. In Orcaflex software, a mooring model is established based on the FPSO's aerodynamic force coefficient, mooring cable parameters, mooring arrangement, and key control conditions. At the same time, the motion response operator RAO is imported to perform fully coupled mooring time-domain analysis to obtain dynamic data.
[0010] S3. Consistent with the overall coordinate system of Orcaflex software, the mooring force on the FPSO single-point mooring connector at each moment is decomposed into in-plane and out-of-plane components based on dynamic data, to obtain the in-plane components, the components perpendicular to the plane, and the point of application.
[0011] S4. Based on the relative positions of the single-point mooring connector with the hydraulic caliper, the upper ring of the MCM, the lower ring of the MCM, and the bearing, establish the dynamic mechanical equilibrium equation to obtain the relationship between the design loads R, V, and H of the single-point turret, pontoon, and MCM, as well as the pontoon shape, its in-plane components, its perpendicular components, and its point of application.
[0012] S5. Perform bubble search algorithm to search and sort each R, V and H at each time step in the time domain analysis, obtain the maximum values of R, V and H respectively, and record the values of the components in the plane, the components perpendicular to the plane and the points of action at the corresponding time step, and record other relevant information until the search is completed.
[0013] S6. By using the equivalent simplification method, organize the maximum values of relevant information R, V and H, the in-plane components, the components perpendicular to the plane and their points of application under the working conditions corresponding to the maximum values, the mooring forces on each mooring connection, and the in-plane and out-of-plane angles to obtain the mechanical equations of the complex coupled body. Introduce multi-physics coupling parameters and nonlinear coefficients into the mechanical equations to complete the design and allocation of single-point loads.
[0014] As a further improvement to this technical solution, the step of establishing a wetted surface model based on the FPSO hull lines includes the following steps:
[0015] S1.1 Import the hull line data of the FPSO into the SESAM HydroD module;
[0016] S1.2 Clean and correct the input profile data, and set the grid density, using a finer grid in wet surface areas;
[0017] S1.3 Use the HydroD module to mesh the hull surface and generate corresponding hydrodynamic analysis parameters. Then, use the high-order boundary element method to optimize the generated hydrodynamic analysis parameters, paying special attention to the mesh density of key areas such as the bow, stern, and bilge.
[0018] S1.4. Define boundary conditions and set the location of the free surface according to the expected analysis type.
[0019] As a further improvement to this technical solution, the step of establishing a quality model based on FPSO loading information includes the following steps:
[0020] S1.5 Collect quality information data for each part of the FPSO;
[0021] S1.6 Input mass information data, specifying the mass of each part and its position in the ship's coordinate system;
[0022] S1.7 Define the global coordinate system and define the mass distribution of the FPSO. The mass distribution includes the mass of the hull structure, the weight of the liquid compartments, the mass of equipment and other loads. For each compartment, input the type, density, volume and loading status of the liquid.
[0023] S1.8 Calculate the position of the total center of gravity, the moment of inertia, and the product of inertia to create a mass model.
[0024] As a further improvement to this technical solution, the step of importing the motion response operator RAO for fully coupled mooring time-domain analysis includes the following steps:
[0025] S2.1 Define the time step and duration of the analysis, and set the time window for the analysis;
[0026] S2.2. Import the motion response operator RAO into the mooring analysis software Orcaflex, start the fully coupled mooring time domain analysis, generate the motion response function with six degrees of freedom, and consider the combined effects of waves, wind and water flow, and introduce excitation coefficients to optimize the motion response function.
[0027] S2.3 Record the changes in the tension, position, and shape of the mooring cable over time.
[0028] As a further improvement to this technical solution, the motion response function is:
[0029]
[0030] Considering the combined effects of waves and water flow, the motion response function is optimized as follows:
[0031]
[0032] Among them, AO i1 (g) represents the optimized motion response function; AO i (g) represents the motion response function; X i (g) represents the response magnitude of the system at the i-th degree of freedom; i represents the degree of freedom number; J(g) represents the linear response function; g represents the excitation coefficient; and U represents the frequency. wave (g) represents the amplitude of the wave excitation; U wind (g) indicates the magnitude of wind excitation; U current (g) represents the amplitude of the water flow excitation.
[0033] As a further improvement to this technical solution, the method of decomposing the mooring forces on the FPSO single-point mooring connector at each moment based on dynamic data into in-plane and out-of-plane components includes the following steps:
[0034] S3.1 Extract the mooring force acting on the FPSO single-point mooring connector at each moment from the time-domain analysis results;
[0035] S3.2, The platform where the single-point mooring connector is located is taken as the XY plane;
[0036] S3.3 Decompose the mooring force into a plane component Fxy and a plane-perpendicular component Fz;
[0037] S3.4 Determine the location b of the mooring force's point of application, and project the point of application both in and out of the plane.
[0038] As a further improvement to this technical solution, the dynamic mechanical equilibrium equation is established as follows: based on the characteristics of the inner turret pontoon single-point structure, the force acting on the mooring connector is transmitted and mechanically simplified along the force transmission path of the pontoon turret, the bearing, the cone, and the ship's MCM.
[0039] As a further improvement to this technical solution, the process of obtaining the design loads R, V, and H of the three parts—the single-point turret, the pontoon, and the MCM—and the relationships between the pontoon shape, its in-plane components, its perpendicular-plane components, and its point of application includes the following steps:
[0040] S4.1 For each instant, calculate R, V, and H to determine the location of the mooring force's point of application;
[0041] S4.2 Calculate in-plane and out-of-plane angles;
[0042] S4.3 Record the R, V, H and the position, magnitude, in-plane and out-of-plane angles of the mooring forces at each moment.
[0043] As a further improvement to this technical solution, the bubble search algorithm sorting is specifically performed as follows: the maximum values of R, V and H acting on the single-point coupled body are obtained through the bubble search algorithm, and the design load of the required coupled body is obtained through the load dynamic allocation method in the fully coupled time-domain mooring analysis.
[0044] As a further improvement to this technical solution, the mechanical equations of the complex coupled body are as follows:
[0045] R = α·[Fxy(h1+h2)-b*Fz];
[0046] V=β·[Fxy(h1+h2)-b*Fz]+Fz;
[0047] H=γ·[Fxy(h1+h2)-b*Fz]-Fxy;
[0048] Introducing multiphysics coupling parameters and nonlinear coefficients into the mechanical equations:
[0049] R′=α·[Fxy(h1+h2)-b*Fz]+k non ·Fxy 2 +μ·Ffl;
[0050] V′=β·[Fxy(h1+h2)-b*Fz]+Fz+k non ·Fz 2 +μ·Ffl;
[0051] H′=γ·[Fxy(h1+h2)-b*Fz]-Fxy+k non ·Fxy 2 +μ·Ffl;
[0052] Where h1 is the distance from the upper bearing to the lower bearing, h2 is the distance from the lower bearing to the center of the mooring connection, H is the horizontal force exerted on the buoy by the hull, V is the vertical force exerted on the buoy by the hydraulic caliper, R is the force exerted on the buoy by the lower ring of the hull's MCM, R′ is the force exerted on the buoy by the lower ring of the hull's MCM after introducing multiphysics coupling parameters and nonlinear coefficients, V′ is the vertical force exerted on the buoy by the hydraulic caliper after introducing multiphysics coupling parameters and nonlinear coefficients, H′ is the horizontal force exerted on the buoy by the hull after introducing multiphysics coupling parameters and nonlinear coefficients, α, β, γ are related to the specific single-point shape and friction coefficient, Fxy is the mooring force component in the plane, b is the magnitude of the point of action in the plane, Fz is the mooring force component perpendicular to the plane, and k non is a nonlinear coefficient, μ is a coefficient related to fluid dynamics, and Ffl is the fluid load.
[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0054] 1. This design method for dynamic load distribution at a single point on an inner turret pontoon fully considers the detachable nature of the inner turret pontoon from the hull. It performs a systematic force analysis on multiple coupled structures, decomposes the forces on the mooring connectors along the force transmission path, and establishes dynamic equilibrium equations. Using SESAM and Orcaflex software, hydrodynamic and mooring time-domain analyses are performed respectively, simulating the stress conditions of a single point on the pontoon in deep sea. This enables real-time force analysis of multiple coupled bodies. By reading the results database and employing a bubble search sorting algorithm to filter the extreme design loads of each coupled body, and considering other corresponding design loads under extreme design loads, a numerical analysis model of the single point stress on the inner turret is constructed. This model can accurately predict structural loads, achieving technological innovation and possessing extremely high engineering value.
[0055] 2. In this dynamic load distribution design method for the internal turret-float type, the maximum design load of the three parts—the turret, float, and MCM—is determined through detailed mechanical analysis and a bubble search algorithm. This method helps identify weak points in the system, allowing engineers to strengthen or improve these parts during the design phase, ultimately achieving optimized design of the entire system. Furthermore, the introduction of multiphysics coupling parameters and nonlinear coefficients in the mechanical equations makes the design more closely resemble actual working conditions, further improving the overall system performance. Attached Figure Description
[0056] Figure 1 This is a flowchart illustrating the overall method of the present invention;
[0057] Figure 2 The overall process of dynamic load distribution design method;
[0058] Figure 3It is a single-point coupling structure for the inner turret;
[0059] Figure 4 The equations for the forces and equilibrium of each part of the single-point coupled body of the inner turret are given. Detailed Implementation
[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0061] Example: Please refer to Figure 1 As shown, this embodiment provides a design method for dynamic distribution of single-point load in an internal turret pontoon type, including the following steps:
[0062] S1. In the HydroD module of SESAM software, establish a wetted surface model based on the FPSO hull lines and a mass model based on the FPSO loading information (e.g., Figure 2 Step S7.1) involves hydrodynamic analysis based on the wetted surface model and mass model (e.g., Figure 2 S7.2) yields the FPSO global motion response operator RAO (e.g. Figure 2 (S7.3);
[0063] In this embodiment, a wetted surface model is established based on the FPSO hull lines, including the following steps:
[0064] S1.1 Import the FPSO hull line data into the SESAM HydroD module. The hull line data includes the hull's transverse section, longitudinal section, and waterline.
[0065] S1.2 Clean and correct the input profile data to ensure there are no intersecting lines, overlapping surfaces or other geometric defects, and set the mesh density to use a finer mesh in wet surface areas (i.e., the parts immersed in water).
[0066] S1.3 Use the HydroD module to mesh the hull surface and generate corresponding hydrodynamic analysis parameters (including the FPSO global motion response operator RAO). Use the high-order boundary element method to optimize the generated hydrodynamic analysis parameters, paying special attention to the mesh density of key areas such as the bow, stern and bilge, where the hydrodynamic effects are more complex.
[0067] By using higher-order polynomials to approximate the distribution of physical quantities on the boundary, HOBEM can more accurately simulate real physical phenomena, especially for complex problems that require high-precision analysis, such as the motion of ships in waves and the hydrodynamic response of marine structures.
[0068] S1.4. Based on the expected analysis type (such as hydrostatic pressure, wave effects, etc.), define boundary conditions and set the location of the free surface to simulate different draft depths.
[0069] Furthermore, a quality model is established based on the FPSO loading information, including the following steps:
[0070] S1.5 Collect quality information data for each part of the FPSO, including the hull itself, cargo, equipment, and fuel;
[0071] S1.6 Input mass information data, specifying the mass of each part and its position in the ship's coordinate system;
[0072] S1.7 Define the global coordinate system and define the mass distribution of the FPSO. The mass distribution includes the mass of the hull structure, the weight of the liquid compartments, the mass of equipment and other loads. For each compartment, input the type, density, volume and loading status of the liquid.
[0073] S1.8 Calculate the position of the total center of gravity, the moment of inertia, and the product of inertia to create a mass model.
[0074] S2. In Orcaflex software, establish a mooring model based on the FPSO's aerodynamic coefficient, mooring cable parameters, mooring arrangement, and key control conditions (e.g., Figure 2 Step S7.5) simultaneously imports the motion response operator RAO to perform fully coupled mooring time-domain analysis to obtain dynamic data; (e.g. Figure 2 Step S7.4)
[0075] The dynamic data includes the time history data of the FPSO's six degrees of freedom motion (i.e., roll, pitch, yaw, heave, sway and sway) and the tension of its mooring cables.
[0076] In this embodiment, the motion response operator RAO is imported for fully coupled mooring time-domain analysis, including the following steps:
[0077] S2.1 Define the time step and duration of the analysis, and set the time window for the analysis to ensure coverage of all sea state changes of interest;
[0078] S2.2. Import the motion response operator RAO into the mooring analysis software Orcaflex, start the fully coupled mooring time domain analysis, and generate motion response functions with six degrees of freedom. The motion response includes the response of six degrees of freedom such as drift, sway, heave, roll, pitch, and yaw. Considering the combined effects of waves, wind and water flow, excitation coefficients are introduced to optimize the motion response function.
[0079] Among them, the mooring time-domain analysis records the magnitude of the mooring force on each mooring connector at each moment, the in-plane and out-of-plane angles of the mooring force, as well as the analysis condition number and hull loading information, for subsequent search use;
[0080] Furthermore, the motion response function is:
[0081]
[0082] Waves and currents are two common natural phenomena in the marine environment. They act together on offshore structures, producing complex motion responses. Ignoring the simultaneous influence of these two forces may lead to simulation results deviating from reality. Therefore, considering both comprehensively can improve the accuracy and reliability of the simulation. The combined effect of waves and currents causes structures to experience greater stress and strain than a single factor. By considering the combined effect of these two forces, the safety and stability of the structure can be more comprehensively assessed, ensuring that the structure remains intact even under extreme conditions. The optimized motion response function can more accurately reflect the dynamic behavior of FPSOs in the actual marine environment, especially under the combined effects of multiple environmental loads such as waves, currents, and wind. By introducing excitation coefficients to describe the coupling effects between multiple excitation sources, the various complex environmental conditions that FPSOs may encounter in real sea areas can be better simulated. Considering the combined effect of waves and currents, the motion response function is optimized as follows:
[0083]
[0084] Among them, AO i1 (g) represents the optimized motion response function; AO i (g) represents the motion response function; X i (g) represents the response amplitude of the system in the i-th degree of freedom; i represents the number of the degree of freedom, including six degrees of freedom: drift, sway, heave, roll, pitch, and yaw. U represents the linear response function; J(g) represents the excitation coefficient, used to describe the coupling effect between multiple excitation sources, which quantifies the interaction strength of multiple excitation sources at different frequencies; g represents the frequency; U wave (g) represents the amplitude of the wave excitation; U wind (g) indicates the magnitude of wind excitation; U current(g) represents the amplitude of the water flow excitation;
[0085] S2.3 Record the changes in the tension, position, and shape of the mooring cable over time.
[0086] S3. Consistent with the overall coordinate system of the Orcaflex software, the mooring force on the FPSO single-point mooring connector at each moment is decomposed into in-plane and out-of-plane components based on dynamic data to obtain Fxy (in-plane component), Fz (perpendicular to the plane component), and the point of application b.
[0087] In this embodiment, the mooring forces acting on the single-point mooring connector of the FPSO at each moment are decomposed into in-plane and out-of-plane components based on dynamic data, including the following steps:
[0088] S3.1 Extract the mooring forces acting on the FPSO single-point mooring connector at each moment from the time domain analysis results. These mooring forces are a three-dimensional vector.
[0089] S3.2, The platform where the single-point mooring connector is located is taken as the XY plane;
[0090] S3.3 Decompose the mooring force into a plane component Fxy and a plane-perpendicular component Fz;
[0091] S3.4 Determine the location b of the mooring force's point of application, and project the point of application both in and out of the plane.
[0092] S4. Based on the geometry and relative positions of the single-point mooring connector, hydraulic caliper, MCM upper ring, MCM lower ring, and bearing (e.g., Figure 2 Step S7.6) establishes the dynamic mechanical equilibrium equations (e.g. Figure 2 Step S7.7) yields the relationship between the design loads R (radial), V (vertical), and H (horizontal) of the single-point turret, pontoon, and MCM, and the pontoon shape, Fxy, Fz, and b.
[0093] In this embodiment, the dynamic mechanical equilibrium equation is established as follows: based on the characteristics of the inner turret pontoon single-point structure, the force acting on the mooring connector is transmitted and mechanically simplified along the force transmission path of the pontoon turret, the bearing, the cone, and the ship's MCM.
[0094] Based on the characteristics of the single-point structure of the inner turret pontoon, the force acting on the mooring connection is transmitted and mechanically simplified along the force transmission path of the pontoon turret, bearing, cone, and hull MCM. This simplifies the three-dimensional complex problem into a two-dimensional equivalent problem. The MCM is the connection structure between the hull and the single-point pontoon. The construction form of the inner turret single-point coupling body is as follows: Figure 3 As shown.
[0095] Furthermore, the relationships between the design loads R (radial), V (vertical), and H (horizontal) of the single-point turret, pontoon, and MCM, and the pontoon shape, Fxy, Fz, and b are obtained, including the following steps:
[0096] S4.1 For each instant, calculate R (radial), V (vertical) and H (horizontal) to determine the location of the mooring force's point of application;
[0097] S4.2 Calculate in-plane and out-of-plane angles;
[0098] S4.3 Record the R (radial), V (vertical), H (horizontal) values and the position, magnitude, in-plane and out-of-plane angles of the mooring forces at each moment.
[0099] Furthermore, in the time-domain analysis of mooring, the magnitude of the mooring force on each mooring connector at each moment, as well as the in-plane and out-of-plane angles of the mooring force, are recorded. The in-plane angle is the angle between the mooring chain and the vertical direction, and the out-of-plane angle is the angle between the mooring chain and the horizontal direction. The overall coordinate system is generally based on the platform where the single-point mooring connector is located as the XY plane, the bow of the FPSO as the positive X-axis, the port side as the positive Y-axis, and the centroid of the connector as the center. The positive Z-axis is determined by the right-hand rule. The mooring force on the single-point mooring connector of the FPSO at each moment is decomposed into in-plane and out-of-plane forces to obtain Fxy, Fz, and the point of application b. Fxy is the resultant force of all mooring connectors in the horizontal direction, Fz is the resultant force of all mooring connectors in the vertical direction, and b is the distance of the resultant force of all mooring connectors relative to the central axis.
[0100] S5. Perform a bubble search algorithm to search and sort each R, V, and H at each time step in the time domain analysis, obtaining the maxima of R, V, and H respectively. Simultaneously record the corresponding Fxy, Fz, and b values, along with other relevant information, including the operating conditions at the corresponding time step, the in-plane and out-of-plane angles of the mooring legs, etc., until the search is complete (e.g., ...). Figure 2 Step S7.8);
[0101] In this embodiment, the bubble search algorithm sorting is specifically performed as follows: the maximum values of R, V and H acting on the single-point coupled body are obtained through the bubble search algorithm, and the design load of the required coupled body is obtained through the load dynamic allocation method in the fully coupled time-domain mooring analysis.
[0102] Among them, the bubble search algorithm is a relatively simple sorting algorithm in computer science. It repeatedly visits the column of elements to be sorted, comparing two adjacent elements in turn. If the order (e.g., from largest to smallest, or from Z to A) is incorrect, they are swapped. This process is repeated until no adjacent elements need to be swapped. The bubble search algorithm can be used to obtain the maxima of R, V, and H acting on a single-point coupled body. In fully coupled time-domain mooring analysis, the design load of the required coupled body can be obtained through dynamic load distribution methods.
[0103] S6. By simplifying the information through equivalent methods, the maximum values of R, V, and H are obtained, along with the corresponding maximum values, working conditions, mooring forces on each mooring connector, and in-plane and out-of-plane angles. This yields the mechanical equations of the complex coupled body. Multi-physics coupling parameters and nonlinear coefficients are then introduced into these equations to complete the single-point load design allocation (e.g., ...). Figure 2 Step S7.9), in which the force and equilibrium equations of each part of the single-point coupling body of the inner turret are as follows: Figure 4 As shown;
[0104] In this embodiment, based on the stress characteristics of the pontoon structure, an equivalent simplification method is adopted to obtain the mechanical equations of the complex coupled body. This method simplifies the originally very complex multiphysics coupling problem into a set of simpler equations, which helps reduce computational costs and increase computational speed, making the problem easier to solve. The equivalent simplification method also helps identify key variables and relationships in the system. These relationships allow for the consideration of more uncertainties during the design process, resulting in a more robust design. The specific mechanical equations of the complex coupled body are as follows:
[0105] R = α·[Fxy(h1+h2)-b*Fz];
[0106] V=β·[Fxy(h1+h2)-b*Fz]+Fz;
[0107] H=γ·[Fxy(h1+h2)-b*Fz]-Fxy;
[0108] In practical engineering problems, physical phenomena are often not isolated but rather mutually influential and coupled. Introducing multiphysics coupling parameters aims to more accurately simulate these interactions, thereby improving the model's ability to describe real-world problems. Many physical processes exhibit significant nonlinear characteristics under large deformation or high stress conditions. The introduction of nonlinear coefficients aims to capture these nonlinear effects, thus more realistically reflecting the actual behavior of the system. The introduction of multiphysics coupling parameters and nonlinear coefficients enables the model to more accurately predict the dynamic response of the system, especially under conditions of significant nonlinearity or coupling effects. By introducing multiphysics coupling parameters and nonlinear coefficients, the model can be better adapted to a wider range of working conditions and environmental changes, including behavior under extreme conditions. The multiphysics coupling parameters and nonlinear coefficients introduced into the mechanical equations are as follows:
[0109] R′=α·[Fxy(h1+h2)-b*Fz]+k non ·Fxy 2 +μ·Ffl;
[0110] V′=β·[Fxy(h1+h2)-b*Fz]+Fz+k non ·Fz 2 +μ·Ffl;
[0111] H′=γ·[Fxy(h1+h2)-b*Fz]-Fxy+k non ·Fxy 2 +μ·Ffl;
[0112] Where h1 is the distance from the upper bearing to the lower bearing, h2 is the distance from the lower bearing to the center of the mooring connection, H is the horizontal force exerted on the buoy by the hull, V is the vertical force exerted on the buoy by the hydraulic caliper, R is the force exerted on the buoy by the lower ring of the hull's MCM, R′ is the force exerted on the buoy by the lower ring of the hull's MCM after introducing multiphysics coupling parameters and nonlinear coefficients, V′ is the vertical force exerted on the buoy by the hydraulic caliper after introducing multiphysics coupling parameters and nonlinear coefficients, H′ is the horizontal force exerted on the buoy by the hull after introducing multiphysics coupling parameters and nonlinear coefficients, α, β, γ are related to the specific single-point shape and friction coefficient, Fxy is the mooring force component in the plane, i.e., the magnitude of the mooring force in the xy plane, b is the magnitude of the point of application in the plane, i.e., the distance of the mooring force application point relative to a certain reference point, Fz is the mooring force component perpendicular to the plane, i.e., the magnitude of the mooring force in the z direction, k non is a nonlinear coefficient used to describe nonlinear effects. When the mooring force is large, the nonlinear effects become significant and the nonlinear term needs to be considered. μ is a coefficient related to fluid dynamics and used to describe the influence of fluid load on the system. Ffl is the fluid load, that is, the additional load caused by waves, wind, water flow, etc.
[0113] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A design method for dynamic load distribution at a single point on an internal turret-type pontoon, characterized in that: Includes the following steps: S1. In the HydroD module of SESAM software, a wetted surface model is established based on the FPSO hull lines, and a mass model is established based on the FPSO loading information. Based on the wetted surface model and the mass model, hydrodynamic analysis is performed to obtain the overall motion response operator RAO of the FPSO. S2. In Orcaflex software, a mooring model is established based on the FPSO's aerodynamic force coefficient, mooring cable parameters, mooring arrangement, and key control conditions. At the same time, the motion response operator RAO is imported to perform fully coupled mooring time-domain analysis to obtain dynamic data. S3. Consistent with the overall coordinate system of Orcaflex software, the mooring force on the FPSO single-point mooring connector at each moment is decomposed into in-plane and out-of-plane components based on dynamic data, to obtain the in-plane components, the components perpendicular to the plane, and the point of application. S4. Based on the relative positions of the single-point mooring connector with the hydraulic caliper, the upper ring of the MCM, the lower ring of the MCM, and the bearing, establish the dynamic mechanical equilibrium equation to obtain the relationship between the design loads R, V, and H of the single-point turret, pontoon, and MCM, as well as the pontoon shape, its in-plane components, its perpendicular components, and its point of application. S5. Perform bubble search algorithm to search and sort each R, V and H at each time step in the time domain analysis to obtain the maximum values of R, V and H. At the same time, record the values of the components in the plane, the components perpendicular to the plane and the points of action at the corresponding time step, and record other relevant information until the search is completed. S6. By using the equivalent simplification method, organize the maximum values of relevant information R, V and H, the in-plane components, the components perpendicular to the plane and their points of application under the working conditions corresponding to the maximum values, the mooring forces on each mooring connection, and the in-plane and out-of-plane angles to obtain the mechanical equations of the complex coupled body. Introduce multi-physics coupling parameters and nonlinear coefficients into the mechanical equations to complete the design and allocation of single-point loads. In S4, the dynamic mechanical equilibrium equation is established as follows: based on the characteristics of the inner turret pontoon single-point structure, the force acting on the mooring connector is transmitted and mechanically simplified along the force transmission path of the pontoon turret, the bearing, the cone and the ship's MCM. In step S4, the relationship between the design loads R, V, and H of the single-point turret, pontoon, and MCM, and the pontoon shape, in-plane components, perpendicular-plane components, and points of application is obtained, including the following steps: S4.1 For each instant, calculate R, V, and H to determine the location of the mooring force's point of application; S4.2 Calculate in-plane and out-of-plane angles; S4.3 Record the R, V, H and the position, magnitude, in-plane and out-of-plane angles of the mooring force at each moment.
2. The design method for dynamic distribution of single-point load in an inner turret float type according to claim 1, characterized in that: In step S1, the wetted surface model is established based on the FPSO hull lines, including the following steps: S1.1 Import the hull line data of the FPSO into the SESAM HydroD module; S1.2 Clean and correct the input profile data, and set the grid density, using a finer grid in wet surface areas; S1.3 Use the HydroD module to mesh the hull surface and generate corresponding hydrodynamic analysis parameters. Then, use the high-order boundary element method to optimize the generated hydrodynamic analysis parameters, paying special attention to the mesh density of key areas such as the bow, stern, and bilge. S1.
4. Define boundary conditions and set the location of the free surface according to the expected analysis type.
3. The design method for dynamic distribution of single-point load in an inner turret float type according to claim 2, characterized in that: In step S1, the quality model is established based on the FPSO loading information, including the following steps: S1.5 Collect quality information data for each part of the FPSO; S1.6 Input mass information data, specifying the mass of each part and its position in the ship's coordinate system; S1.7 Define the global coordinate system and define the mass distribution of the FPSO. The mass distribution includes the mass of the hull structure, the weight of the liquid compartments, the mass of equipment and other loads. For each compartment, input the type, density, volume and loading status of the liquid. S1.8 Calculate the position of the total center of gravity, the moment of inertia, and the product of inertia to create a mass model.
4. The design method for dynamic distribution of single-point load in an inner turret float type according to claim 1, characterized in that: In step S2, the motion response operator RAO is imported for fully coupled mooring time-domain analysis, including the following steps: S2.1 Define the time step and duration of the analysis, and set the time window for the analysis; S2.
2. Import the motion response operator RAO into the mooring analysis software Orcaflex, start the fully coupled mooring time domain analysis, generate the motion response function with six degrees of freedom, and consider the combined effects of waves, wind and water flow, and introduce excitation coefficients to optimize the motion response function. S2.3 Record the changes in the tension, position, and shape of the mooring cable over time.
5. The design method for dynamic distribution of single-point load in an inner turret float type according to claim 4, characterized in that: In S2.2, the motion response function is: ； Considering the combined effects of waves and water flow, the motion response function is optimized as follows: ； in, This represents the optimized motion response function; Represents the motion response function; Indicates the system at the 1st Response amplitude over each degree of freedom; The number representing the degree of freedom; Represents a linear response function; Indicates the incentive coefficient; Indicates frequency; Indicates the amplitude of wave excitation; Indicates the magnitude of wind excitation; This indicates the magnitude of the water flow excitation.
6. The design method for dynamic distribution of single-point load of inner turret float type according to claim 5, characterized in that: In step S3, the mooring forces acting on the FPSO single-point mooring connector at each moment are decomposed into in-plane and out-of-plane components based on dynamic data, including the following steps: S3.1 Extract the mooring force acting on the FPSO single-point mooring connector at each moment from the time-domain analysis results; S3.2, The platform where the single-point mooring connector is located is taken as the XY plane; S3.3 Decompose the mooring force into a plane component Fxy and a plane-perpendicular component Fz; S3.4 Determine the location b of the mooring force's point of application, and project the point of application both in and out of the plane.
7. The design method for dynamic single-point load distribution of the inner turret float type according to claim 1, characterized in that: In S5, the bubble search algorithm sorting is specifically performed as follows: the maximum values of R, V and H acting on the single-point coupled body are obtained through the bubble search algorithm, and the design load of the required coupled body is obtained through the load dynamic allocation method in the fully coupled time-domain mooring analysis.
8. The design method for dynamic distribution of single-point load of inner turret float type according to claim 7, characterized in that: In S6, the mechanical equations of the complex coupled body are specifically as follows: ； ； ； Introducing multiphysics coupling parameters and nonlinear coefficients into the mechanical equations: ； ； ； in, This is the distance between the upper and lower bearings. This is the distance from the lower bearing to the center of the mooring connection. The pontoons are subjected to horizontal forces from the ship's hull. The float is subjected to a vertical force from the hydraulic clamps. The buoy is subjected to the force of the lower ring of the MCM on the hull. After introducing multiphysics coupling parameters and nonlinear coefficients, the pontoon is subjected to the force of the lower ring of the ship's MCM. After introducing multiphysics coupling parameters and nonlinear coefficients, the pontoon is subjected to a vertical force from the hydraulic calipers. After introducing multiphysics coupling parameters and nonlinear coefficients, the pontoon is subjected to horizontal forces from the hull. , , It depends on the specific shape of the point and the coefficient of friction. These are the in-plane components of the mooring force. The magnitude of the point of application within the plane. The mooring force component is perpendicular to the plane. These are nonlinear coefficients. For coefficients related to fluid dynamics, For fluid load.