CN116127627A - Method for checking structural strength of upper module of cylindrical FPSO (FPSO) based on SACS (secure storage and retrieval) - Google Patents

Abstract

The invention discloses a method for checking structural strength of a cylindrical FPSO upper module based on SACS, and relates to the technical field of offshore oil engineering. Comprises a cylindrical FPSO upper module, a wave wall and a ship body main deck, wherein, the upper module of the cylindrical FPSO comprises a cylindrical FPSO module double deck plate, a cylindrical FPSO module process deck plate and cylindrical FPSO module leg columns, and comprises the following steps of: and according to the SACS software model element numbering rule and the model simulation method, the number of the upper modules of the cylindrical FPSO is combined, and the upper modules of the cylindrical FPSO are named. The invention can directly account for the mutual influence between the modules at the upper part and between the modules and the breakwater due to the fact that the process deck is an integral deck, so that the calculation simulation of the modules at the upper part is more in line with the actual situation, and the calculation result is more accurate. The difficulty that the coupling influence of other modules on the module cannot be considered at the boundary of the module process deck when the bit strength is calculated by the sub-modules is avoided.

Description

Method for checking structural strength of upper module of cylindrical FPSO (FPSO) based on SACS (secure storage and retrieval)

Technical Field

The invention relates to the technical field of offshore oil engineering, in particular to a cylindrical FPSO upper module structure strength checking method based on SACS.

Background

The FPSO is a short term for floating production and storage platform, which is a comprehensive offshore oil production base integrating the functions of personnel living, production, oil storage, external transportation and the like, and is usually a ship type. Most of the mooring units are moored at a single point, have the effect of wind vane, and the ship body can rotate around the single point under the effect of wind and waves, so that the ship body always keeps a windward state. The ship-type FPSO upper modules are space frame structures mainly composed of pipe, beam and plate members, as shown in figure 1, ship-type FPSO module double deck plates and ship-type FPSO module process deck plates between the ship-type FPSO upper modules are not connected with each other, and are independent. The upper module of the ship-type FPSO is designed and built in a modularized mode and is integrally installed on the main deck of the ship body through a gantry crane or a floating crane. The leg columns of part of the ship-shaped FPSO modules between the upper module of the ship-shaped FPSO and the ship body are designed to be in sliding connection, so that the influence of the total longitudinal deformation of the ship body on the module structure is reduced. Because each module is independent of each other, the module deck does not have lateral support, and lateral load is born mainly by the ship-type FPSO module leg post, so ship-type FPSO module diagonal bracing structure is installed to ship-type FPSO module leg post.

The cylindrical FPSO is a novel floating type oil storage device, the hull of the novel floating type oil storage device is cylindrical, and a multipoint mooring mode is adopted. The economic advantage is obvious in deep water sea development, especially in isolated oil fields and small remote oil fields. Different from the upper modules of the ship-shaped FPSO, the cylindrical FPSO module two decks of all the upper modules of the cylindrical FPSO and the cylindrical FPSO module process deck are connected to form an integral deck, and the process deck is connected with the main deck of the ship through the lower upright post of the deck and the ship body breakwater around the deck to form an integral platform structure.

Because the upper modules are independent, the upper module structure of the ship-type FPSO checks in-place working conditions, two modules symmetrically distributed on two sides of the main axis of the ship body are generally modeled together according to the characteristic that the port and the starboard of the ship body are symmetrical, and ship movement and ship deformation data are loaded in a load mode to carry out simulation operation. For a cylindrical FPSO, because the process deck is an integral deck, the stress among the modules is mutually influenced, for example, the coupling influence of the modules at the joint of the process deck can not be accurately simulated by referring to a method for modeling and calculating the upper module of the ship-shaped FPSO.

Aiming at the structural characteristics of the upper module of the cylindrical FPSO, the invention provides an in-place working condition structural strength analysis method which is used for modeling according to module partitioning, then integrating the module into an integral model for analysis and check, and selecting a re-split model for detailed calculation according to requirements.

Disclosure of Invention

The invention aims to provide a method for checking the structural strength of a cylindrical FPSO upper module based on SACS, which aims to solve the problems in the prior art.

In order to achieve the above purpose, the present invention provides the following technical solutions: the method for checking structural strength of the upper module of the cylindrical FPSO based on SACS comprises the upper module of the cylindrical FPSO, a breakwater wall and a main deck of a ship body, wherein the upper module of the cylindrical FPSO comprises a double deck of the cylindrical FPSO module, a process deck of the cylindrical FPSO module and leg columns of the cylindrical FPSO module, and comprises the following steps:

step one: according to SACS software model element numbering rules and model simulation methods, combining the number of cylindrical FPSO upper modules, the naming of the cylindrical FPSO upper modules, the number of layers of cylindrical FPSO module decks and cylindrical FPSO module process decks, the names of the cylindrical FPSO module decks and cylindrical FPSO module process decks and load working conditions, and formulating sub-module modeling according to unified rules;

step two: according to the unified rule formulated in the first step, respectively establishing three-dimensional structure models of all upper modules of the cylindrical FPSO and the ship body wave wall, loading professional weights, and generating SACS model files corresponding to all the upper modules of the cylindrical FPSO and all the block models of the ship body wave wall;

step three: importing the block model files of each upper module built in the second step into the same module model, completing the connection of the bulk connection structure rods between the modules and between each cylindrical FPSO upper module and the breakwater, combining the weights of each specialty such as machinery, piping, electricity and the like in each module into the integral weight of the specialty in the cylindrical FPSO platform, forming an integral model, and generating a SACS model file of the integral model;

step four: calculating the gravity load, wind load and inertial force load caused by the overall motion of the platform by using the integrated integral model in the step three, and superposing the loads to obtain the overall stress of the integral model to generate a SACS combined solving file;

step five: solving the stress of the whole model structure under the least adverse stress obtained in the step four, checking the structural strength of the upper module, and generating detailed results of the stress of the rod piece and the deformation of the node;

step six: and (3) an analysis module, namely applying the force or the node displacement of the module boundary rod piece extracted from the step (V) at the module boundary, superposing the force or the node displacement with the gravity, wind load and motion load of the module to obtain the integral stress of the module, and carrying out detailed stress calculation and check of the module.

In the step one, a unified rule of block modeling is formulated, meaning is given by continuous number segmentation using and multi-bit character number segmentation under the SACS software model element numbering rule, model elements which need to be distinguished according to modules, or distinguished according to the layers of the armor plates where the model elements are positioned, or distinguished according to professional distinguishing or working conditions are distinguished and numbered, wherein the model element distinguishing and numbering comprises node numbering, plate numbering, wind area numbering, basic weight/load and combined weight/load, and model elements which need all modules to be kept consistent are numbered uniformly.

Furthermore, in the second step, the block models of the upper module of each cylindrical FPSO and the breakwater of the ship body can be established by multiple persons at the same time, each person is responsible for one or more modules, each block model is reasonably arranged according to project plans and professional manpower conditions, each block model correspondingly generates a respective SACS model file, and all block models are defined by using the same coordinate direction and coordinate origin.

In the third step, each module model integrates an integral analysis model, comprising two parts of finite element model integration and professional weight combination, wherein the integration of the finite element model is based on one of the upper module of each cylindrical FPSO and the three-dimensional structure model of the breakwater of the ship body, other upper module models are imported, and the connection between the upper modules of each cylindrical FPSO and between the upper modules of the cylindrical FPSO and the breakwater is completed;

and combining the weights of the professions according to the combination of the modules to form the total weight of each module, combining the weights of the modules according to the combination of the professions to form the total weight of each specialty, and finally combining to obtain the total weight of all the upper modules.

In the fourth step, the wind load of each module is not considered to be reduced due to the shielding of the upstream module in the wind direction;

calculating inertial force load caused by motion, and adopting six-degree-of-freedom combination of translational acceleration and rotational acceleration at corresponding reference points to account for the influence of acceleration differences of the modules at different platform positions, wherein superposition of wind load, weight load and inertial force load is required to be superposed according to the same direction so as to obtain the most adverse stress condition of the modules.

Further, while calculating the structural stress, calculating and outputting detailed results report of the rod internal force and node deformation of the boundary of the upper module of the cylindrical FPSO and the boundary position of the upper module of the cylindrical FPSO and the upper module of the cylindrical FPSO.

Furthermore, the step six is an optional step, modeling is performed in a blocking manner, analysis and check of the integrated overall model can be completed in-situ calculation and analysis, the overall model can be selectively split into a plurality of single-module models again according to project requirements, and more detailed calculation and evaluation of each module are performed;

and step six, extracting rod stress or node deformation at the boundary of the module in the step five to serve as boundary constraint of the sub-module model to perform detailed calculation analysis of the single-module model.

Compared with the prior art, the invention has the beneficial effects that:

the method for checking the structural strength of the upper module of the cylindrical FPSO based on the SACS can directly account for the mutual influence between the upper modules and the breakwater due to the fact that the process deck is an integral deck, so that the calculation simulation of the upper modules is more in line with the actual situation, and the calculation result is more accurate. The difficulty that the coupling influence of other modules on the module cannot be considered at the boundary of the module process deck when the bit strength is calculated by the sub-modules is avoided.

Drawings

FIG. 1 is a schematic diagram of the upper module structure of a boat-type FPSO of the present invention;

FIG. 2 is a schematic diagram of the upper module structure of the cylindrical FPSO of the present invention;

FIG. 3 is a schematic diagram of a typical block SACS model of an upper module of a cylindrical FPSO according to the present invention;

FIG. 4 is a schematic view of a cylindrical FPSO breakwater model according to the present invention;

FIG. 5 is a schematic view of the overall model of the integration of all the upper modules with the breakwater model of the present invention;

FIG. 6 is a schematic diagram of a re-splitting single module model according to the present invention;

FIG. 7 is a schematic flow chart of the present invention;

FIG. 8 is a schematic diagram of a plate number in step one of the present invention;

FIG. 9 is a schematic diagram of basic weight/load nomenclature in step one of the present invention;

FIG. 10 is a schematic diagram of the naming of the combined weight/load in step one of the present invention;

FIG. 11 is a schematic diagram of the cross-sectional numbering of the round tube and the cross-sectional numbering of the welded I-beam in step one of the present invention;

FIG. 12 is a numbered schematic representation of the cross-sectional groups in step one of the present invention.

In the figure: 1. a ship-type FPSO upper module; 11. a ship-type FPSO module deck; 12. a ship-type FPSO module process deck; 13. boat-shaped FPSO module leg columns; 14. a ship-type FPSO module diagonal bracing; 2. a cylindrical FPSO upper module; 21. cylindrical FPSO module deck; 22. a cylindrical FPSO module process deck; 23. cylindrical FPSO module leg posts; 3. a breakwater; 4. and a main deck of the hull.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It should be noted that, in the description of the present invention, the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or elements to be referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.

Furthermore, it should be understood that the dimensions of the various elements shown in the figures are not drawn to actual scale, e.g., the thickness or width of some layers may be exaggerated relative to other layers for ease of description.

It should be noted that like reference numerals and letters refer to like items in the following figures, and thus once an item is defined or illustrated in one figure, no further detailed discussion or description thereof will be necessary in the following description of the figures.

As shown in fig. 3-6, the present invention provides a technical solution: the utility model provides a method for checking structural strength of a cylindrical FPSO upper module based on SACS, which comprises a cylindrical FPSO upper module 2, a breakwater 3 and a hull main deck 4, wherein the cylindrical FPSO upper module 2 comprises a cylindrical FPSO module double deck 21, a cylindrical FPSO module process deck 22 and a cylindrical FPSO module leg column 23, and comprises the following steps:

step one: according to SACS software model element numbering rules and model simulation methods, the number of cylindrical FPSO upper modules 2, the naming of the cylindrical FPSO upper modules 2, the number of layers of the cylindrical FPSO module double deck 21 and the cylindrical FPSO module process deck 22, the names and load working conditions of the cylindrical FPSO module double deck 21 and the cylindrical FPSO module process deck 22 are combined, and a unified rule is formulated for modeling the split modules according to unified rules, wherein under the SACS software model element numbering rules, the split modules are distinguished according to the modules, or distinguished according to the layers of the positioned plates, or distinguished according to the expertise, or distinguished according to the working conditions, model element distinguishing numbers comprising node numbers, plate numbers, wind area numbers, basic weight/load and combined weight/load are formulated, and the model elements which need all modules to be kept consistent are uniformly numbered are given meaning modes.

The specific method comprises the following steps:

(1) The model elements (node number, plate number, wind area number, basis weight/load and combined weight/load) which are required to be distinguished according to modules, or respectively according to the layers of the armor plates, or respectively according to professions or working conditions are distinguished and numbered in a mode of continuous number segmentation use, multi-character number field assignment meaning and the like:

(1) for example, the node number can be four digits "0001", and the number is assigned to different upper modules and the ship breakwater models according to the number size, so that each model has a special node number section, for example, 0001-1000 thousands of node numbers are assigned to the first module for use, and 1001-2999 number sections are assigned to the second module for use. The size of the segmentation limit is determined by estimating the size of each module.

(2) The plate number can be a first letter plus three-digit continuous number P001, the first letter respectively represents different modules, the three-digit continuous number distinguishes different deck layers according to the blocks, for example, P represents a first module and Q represents a second module. The three digits after the letters are assigned to different deck layers according to the segments, for example, the 001-200 segments are assigned to the two deck layers, and the 201-500 segments are assigned to the process deck layers. The deck boards numbered in the sections P001 to P200 are the first deck boards of the module, and the deck boards numbered in the sections Q201 to Q500 are the second process deck boards of the module. The size of the segmentation limit is determined by estimating the size of each module. The large size of the module may be assigned two letters as the initial numbers, e.g., the plate numbers at the beginning of Q and R each represent module two.

(3) The basis weight/load may be named using a four-bit string. The first two characters represent the module to which the weight belongs, the third character represents the specialty to which the weight belongs, and the fourth character represents the working condition to which the weight belongs. For example, the dry weight of the device on the PR-I module may be designated as P1MD, where P1 represents the PR-I module, M represents the mechanical specialty, and D represents the dry weight of the device.

(4) The combined weight/load may be named using a four-bit string. The first three characters represent the module to which the weight belongs, and the fourth character represents the working condition to which the weight belongs. For example, the unstructured dry weight loadings of PR-I modules may be combined and designated PR1D, where D represents dry weight and PR1 represents process module one; the operating loads of all modules are combined to define a DWTO, the extreme loads of all modules are combined to define a DWTE, where the letter O represents the operating condition, the letter E represents the extreme condition, and the DWT represents all upper modules.

(2) Model elements (rod sections, rod sets) that require all modules to remain identical are numbered in unison, for example:

(1) in all model files, rods with the same size are uniformly defined with the same Section (SECT), the section number of a round tube is uniformly in a six-or seven-bit character string type with the external diameter value plus X plus the wall thickness value, for example, the section number of a phi 914X38 tube (914 diameter and 38 wall thickness) is defined as 914X38; the cross section of the welding I-beam is uniformly in a seven-bit character string type of 'H' +beam height value+beam width value, and the cross section number of H120400 represents all I-beams with the beam height 1200 and the flange width 400. The section of the finished I-steel can be directly selected from the section of the SACS model library without additional definition.

(2) In all the model files, rods with the same section are uniformly defined as a section group, the numbers of the section group, the round tubes are uniformly defined as 'T' +two digits, and the I-steel is uniformly defined as 'H' or 'P' +two digits. The two digits are sequential numbers determined according to the number of specifications of round tubes and I-steel used in the model, or can represent a specific diameter wall thickness combination or beam height and beam width combination, for example, all tubes with sections 914X38 are defined as a group with the number T93, and all I-shaped Liang Dingyi with sections H120400 are defined as a group with the number H12.

(3) All decks of the same thickness are defined as unified PLATE GROUP, e.g., 8 mm boards are defined as PL8.

(3) The modeling range, the modeling method, the main technical requirements and the like of each upper module are subjected to unified requirements, for example:

(1) modeling all the main structures and the secondary structures comprising upright posts, inclined struts, deck beams, decks and other structural members contributing to the overall rigidity of the module, and applying a tertiary structure or an auxiliary structure and the like to the structural model through a load pattern;

(2) the JOINT is built at the theoretical elevation of the deck of the drawing, and the JOINT eccentricity and the OFFSET of the structural members are properly simulated in the model to investigate the local bending moment and shearing action, such as the pipe JOINT diagonal bracing, and the JOINT diagonal bracing is required to be OFFSET to the chord surface according to the actual dimension (OFFSET).

The weight of the profession, both mechanical and electrical, etc. was uniformly simulated using WEIGHT SKID and LIVE LOAD (LIVE LOAD) was uniformly loaded using AREA LOAD.

Step two: according to the unified rule formulated in the first step, as shown in fig. 3 and fig. 4, three-dimensional structure models of each upper module 2 of the cylindrical FPSO and each breakwater 3 of the ship are respectively built, each professional weight is loaded, SACS model files corresponding to each upper module 2 of the cylindrical FPSO and each block model of each breakwater 3 of the ship are generated, specifically, the block models of each upper module 2 of the cylindrical FPSO and each block model of each breakwater 3 of the ship can be built by multiple persons at the same time, each person is responsible for one or more modules, reasonable arrangement is carried out according to project plans and professional manpower conditions, each block model correspondingly generates each SACS model file, and all the block models are defined by using the same coordinate direction and coordinate origin.

The specific method comprises the following steps:

(1) According to project planning and professional manpower conditions, modeling work can be performed by multiple persons simultaneously, and each person is responsible for one or more modules;

(2) All blocking models are defined using the same coordinate direction and origin of coordinates. The X-axis positive direction is the bow direction, the Y-axis positive direction points to the port, and the Z-axis vertical direction is positive. The X-axis Y-axis origin of coordinates is located at the center of the circular ship body, and the Z-axis origin of coordinates is located on the surface of the keel of the ship body.

(3) FIG. 3 is a schematic diagram of PR-I module model. A three-dimensional bar analysis calculation model of the breakwater structure was separately built as a boundary condition model as shown in fig. 4. Each block model correspondingly generates a respective SACS model file (SACINP file).

Step three: as shown in fig. 5, the block model file of each upper module built in the second step is imported into the same module model, so as to complete the connection of the bulk connection structure rods between each module and between each cylindrical FPSO upper module and the breakwater, combine the weights of each module in the mechanical, piping, electrical and other professions as the whole weight of each specialty on the cylindrical FPSO platform, form an integral model, generate a SACS model file of the integral model, integrate the integral analysis model of each module model, and comprise two parts of finite element model integration and each professional weight combination, wherein the integration of the finite element model is based on one of the three-dimensional structure models of each cylindrical FPSO upper module 2 and the breakwater 3 of the ship body, import other upper module models, and complete the connection between each cylindrical FPSO upper module 2 and the breakwater 3; combining the specialized weights according to the modules to form the respective total weights of the modules, combining the weights of the modules according to the specialized weights to form the respective total weights of the specialized weights, and finally combining to obtain the overall weights of all the upper modules;

the specific method comprises the following steps:

(1) Finite element model integration

(1) The IMPORT function of the SACS software PRECDE function module is used for importing SACS model files of other upper modules based on a ship breakwater model;

(2) manually completing modeling of the un-simulated bulk connection members in the block models between the upper modules and the breakwater through a user interaction interface of the SACS software PRECDE functional module, and automatically merging the nodes or the rods modeled by the modules at the same position by a program;

(2) Each professional weight combination

(1) Copying and editing text contents of a user interaction interface or a model file of the SACS software PRECDE functional module, and combining the professional weights of the modules according to the modules to form the total weight of each module;

(2) copying and editing text contents of a user interaction interface or a model file of the PRECDE function module of SACS software, and combining the professional weights of the modules according to the professions to form respective total weights of the professions;

(3) and combining to obtain the total weight of the upper module of the whole platform on the basis of professional combination or module combination.

Step four: calculating the gravity load, wind load and inertial force load caused by the overall motion of a platform by using the integrated integral model in the step three, superposing the loads to obtain the overall stress of the integral model, and generating a SACS combined solving file (COMBINED SOLUTION FILE), wherein the wind load of each module does not consider the wind speed reduction caused by the shielding of an upstream module in the wind direction; calculating inertial force load caused by motion, and adopting six-degree-of-freedom combination of translational acceleration and rotational acceleration at corresponding reference points to account for the influence of acceleration differences of the modules at different platform positions, wherein superposition of wind load, weight load and inertial force load is required to be superposed according to the same direction so as to obtain the most adverse stress condition of the modules.

The specific method comprises the following steps:

(1) And solving the gravity load, and solving the DEAD weight of the structure by using DEAD. Solving the professional weight and weight combination of each module in the step three by utilizing the function combination (INCWGT command) of applying the vertical acceleration ACCL, the whole weight load of each module, the whole weight load of all modules and the like;

(2) And combining the same professional load of each module into the professional integral load of the platform. Meanwhile, the single professional gravity output of a single module is still reserved;

(3) The wind load calculation considers eight wind direction conditions, with 45 degrees of wind direction spacing. For a certain wind direction, the wind area of the windward side of each module is calculated by the wind load, namely the wind load of each module is not considered to be reduced due to the shielding of the upstream module in the wind direction;

(4) And calculating inertial force load caused by motion by adopting six-degree-of-freedom combination of translational acceleration and rotational acceleration at corresponding reference points so as to account for different acceleration difference influences of the module at the platform position. The translational acceleration at the center of gravity of the module is not converted. The phase difference of the accelerations with different degrees of freedom is considered, and for a certain specific wave direction, 64 combination conditions are provided for positive and negative combination of the accelerations with six degrees of freedom.

(5) And (5) utilizing a load superposition function (COMBINE SOLUTION FILE) of SACS software, taking a solving file generated by wind load calculation as a main file, taking a weight load solving file as a second input file, taking an inertia force load solving file as a third input file, and combining to generate an upper module integral load combination solving file.

(6) When stacking, the module equipment facility gravity load, wind load and inertial force load should be combined according to the least adverse condition to ensure that the least adverse stress condition of the module is covered.

Step five: the method comprises the steps of solving the structural stress of the whole model under the least adverse stress obtained in the step four, checking the structural strength of an upper module, and generating detailed results of rod stress and node deformation.

(1) The bar intensity checking is carried out by adopting the CODE CHECK of the SACS software POST PROCESSING module;

(2) TUBULAR CONNECTION CHECK of a POST PROCESSING module of SACS software POST PROCESSING is adopted to check the punching shear strength of the pipe node;

(3) Checking, namely COMBINED SOLUTION FILE generated in the step S4 is needed to be used for inputting the file COMMON SOLUTION FILE;

(4) Detailed results reports of the rod internal FORCE (MEMBER FORCE) and node deformation (JOINT deformation) of the upper module boundary and the module interface position are selectively output.

6. Step six: the analysis module, as shown in fig. 6, applies the module boundary rod force or node displacement extracted from the step five at the module boundary, and overlaps with the gravity, wind load and motion load of the module to obtain the overall stress of the module, and performs detailed stress calculation and check of the module.

(1) Analyzing the model;

(2) Extracting the gravity and wind area of other modules in the single-module model working condition combination;

(3) Applying the extracted boundary node deformation;

(4) Combining the loads;

(5) And checking the module.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (7)

1. The utility model provides a cylindrical FPSO upper module structural strength check method based on SACS, includes cylindrical FPSO upper module (2), breakwater (3) and hull main deck (4), and wherein, cylindrical FPSO upper module (2) include cylindrical FPSO module double deck (21), cylindrical FPSO module technology deck (22) and cylindrical FPSO module leg post (23), its characterized in that: the method comprises the following steps:

step one: according to SACS software model element numbering rules and model simulation methods, the number of cylindrical FPSO upper modules (2), the naming of the cylindrical FPSO upper modules (2), the number of layers of cylindrical FPSO module decks (21) and cylindrical FPSO module process decks (22), the names of the cylindrical FPSO module decks (21) and cylindrical FPSO module process decks (22) and load working conditions are combined, and unified rules are followed to make sub-module modeling;

step two: according to the unified rule formulated in the first step, respectively establishing three-dimensional structure models of all upper modules (2) of the cylindrical FPSO and the ship body breakwater wall (3), loading professional weights, and generating SACS model files corresponding to all the block models of all the upper modules (2) of the cylindrical FPSO and the ship body breakwater wall (3);

step three: importing the block model files of each upper module built in the second step into the same module model to finish the connection of the bulk connection structure rods between the modules and between each cylindrical FPSO upper module (2) and the breakwater wall (3), combining the weight of each specialty such as machinery, piping, electricity and the like in each module into the integral weight of the specialty in the cylindrical FPSO platform to form an integral model, and generating the SACS model file of the integral model;

step four: calculating the gravity load, wind load and inertial force load caused by the overall motion of the platform by using the integrated integral model in the step three, and superposing the loads to obtain the overall stress of the integral model to generate a SACS combined solving file;

step five: solving the stress of the whole model structure under the least adverse stress obtained in the step four, checking the structural strength of the upper module, and generating detailed results of the stress of the rod piece and the deformation of the node;

step six: and (3) an analysis module, namely applying the force or the node displacement of the module boundary rod piece extracted from the step (V) at the module boundary, superposing the force or the node displacement with the gravity, wind load and motion load of the module to obtain the integral stress of the module, and carrying out detailed stress calculation and check of the module.

2. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: in the first step, a unified rule of block modeling is formulated, meaning is given to model elements which need to be distinguished according to modules, or distinguished according to the layers of the armor plates where the model elements are located, or distinguished according to professions or working conditions by using continuous number segmentation and multi-character number segmentation under the rule of SACS software model element numbering, wherein the model element distinguishing numbers comprise node numbers, plate numbers, wind area numbers, basic weight/load and combined weight/load, and model elements which need to keep the consistency of all the modules are unified numbered.

3. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: in the second step, the block models of the upper module (2) of each cylindrical FPSO and the breakwater wall (3) of the ship body can be established by multiple persons at the same time, each person is responsible for one or more modules, the block models are reasonably arranged according to project plans and professional manpower conditions, each block model correspondingly generates a respective SACS model file, and all the block models are defined by using the same coordinate direction and coordinate origin.

4. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: in the third step, each module model integrates an integral analysis model, and comprises two parts of finite element model integration and professional weight combination, wherein the integration of the finite element model is based on one of three-dimensional structure models of each cylindrical FPSO upper module (2) and a breakwater wall (3) of a ship body, other upper module models are imported, and connection between each cylindrical FPSO upper module (2) and the breakwater wall (3) are completed;

and combining the weights of the professions according to the combination of the modules to form the total weight of each module, combining the weights of the modules according to the combination of the professions to form the total weight of each specialty, and finally combining to obtain the total weight of all the upper modules.

5. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: in the fourth step, the wind load of each module is not considered to be reduced due to the shielding of the upstream module in the wind direction;

calculating inertial force load caused by motion, and adopting six-degree-of-freedom combination of translational acceleration and rotational acceleration at corresponding reference points to account for the influence of acceleration differences of the modules at different platform positions, wherein superposition of wind load, weight load and inertial force load is required to be superposed according to the same direction so as to obtain the most adverse stress condition of the modules.

6. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: in the fifth step, the load superposition function of SACS software in the fourth step is adopted, structural stress is calculated, and meanwhile, the boundary of the cylindrical FPSO upper module (2) and a detailed result report of the rod internal force and node deformation at the boundary position of the cylindrical FPSO upper module (2) and the cylindrical FPSO upper module (2) are calculated and output.

7. The SACS-based upper module structural strength checking method of a cylindrical FPSO according to claim 1, wherein the method comprises the following steps: step six is an optional step, modeling in a blocking way, integrating the whole model to analyze and check to finish all in-place calculation and analysis, and according to project requirements, the whole model can be selectively split into a plurality of single-module models again to carry out more detailed calculation and evaluation of each module; and step six, extracting rod stress or node deformation at the boundary of the module in the step five to serve as boundary constraint of the sub-module model to perform detailed calculation analysis of the single-module model.

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