Simplified analysis method for seismic response of offshore jacket platform

Abstract

A simplified analysis method for seismic response of an offshore jacket platform comprises the steps that firstly, a three-dimensional structure finite element model of the jacket platform is established, the model comprises a jacket and main components of an upper module, the influence of secondary components on the structural rigidity is ignored, and the secondary components are loaded into the model in the mode of modifying the material density; the equipment weight is loaded to a corresponding gravity center position in a mass point form, meanwhile, the mass of attached water and the mass of attached marine organisms are considered in the model, and then the model is constrained by adopting an equivalent build-in pile boundary condition. And performing modal analysis on the model to obtain first-order and second-order total vibration frequencies of the model, and querying a corresponding seismic acceleration in a given seismic response spectrum according to the two-order vibration frequencies of the platform. And then loading the two horizontal seismic accelerations obtained by calculation in the previous step into the model, solving and analyzing by using finite element software, and finally evaluating. The method is simple in process and low in analysis time consumption, and about 5 hours of modeling time can be saved.

Description

Technical Field

[0001] The invention belongs to the field of offshore ship design and construction, and in particular relates to a simplified analysis method for seismic response of an offshore jacket platform. Background Art

[0002] The offshore jacket platform is a structure widely used in the field of marine engineering. It has the characteristics of simple design, convenient construction and obvious economic benefits. It is widely used in the development of marine resources in shallow and medium sea areas. According to research, seismic conditions are the restrictive conditions for the design of jacket platforms. In addition, there are frequent seismic activities in my country's coastal waters, especially in the Bohai Sea area. Therefore, the influence of seismic loads must be considered when designing jacket platforms. The response spectrum method is mostly used in engineering to analyze and calculate seismic responses. This method first requires the establishment of a pile-soil model. During the analysis, the pile-soil nonlinear system needs to be converted into a linear system, and then the response is calculated for each direction of the load and each order of the structure. This method requires accurate soil information, and the pile foundation conversion process needs to be iterated repeatedly. It is not suitable for the initial scheme design stage, and the calculation of the pile-soil system needs to be completed with the help of professional software. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a simplified analysis method for seismic response of an offshore jacket platform, and the technical solution adopted is: A simplified analysis method for seismic response of an offshore jacket platform, the specific analysis method is as follows: S1: Obtain the structural drawings of the target platform, and use finite element numerical simulation technology to establish a three-dimensional structural model of the platform based on the full platform structural drawings. The three-dimensional structural model includes steel pipe piles, jacket structure, upper modules and equipment in the platform.

[0004] S2: The three-dimensional structural model is constrained by using equivalent embedded pile boundary conditions, retaining part of the steel pipe pile below the mud surface, and applying rigid fixed boundary conditions to the pile bottom. The length of the steel pipe pile below the mud surface, ha, can be obtained from the relationship curve between the ratio of the embedded length to the pile diameter and the foundation reaction coefficient according to the soil type. The larger value is taken for soft soil and the smaller value is taken for hard soil. When there is no soil data, 6 times the pile diameter is taken.

[0005] S3: Perform modal analysis on the three-dimensional structural model to obtain its first-order and second-order overall vibration frequencies, and query the corresponding seismic acceleration according to the two-order vibration frequencies of the platform in a given seismic response spectrum.

[0006] S4: The calculated two horizontal earthquake accelerations are then loaded into the three-dimensional structural model and solved and analyzed using finite element software.

[0007] S5: Evaluate the components and nodes of the jacket platform according to the specifications.

[0008] The simplified analysis method for seismic response of an offshore jacket platform described above, further, uses Genie software to model the entire ship, and the main structures of the steel pipe piles, jacket structure, and upper module are simulated using BEAM units, and other secondary structures are taken into account in the model by modifying the material density in the finite element software.

[0009] The method of the present invention has a simple process, takes less time to analyze, and can save about 5 hours of modeling time. In addition, the method of the present invention does not require professional software and can be completed by relying on general finite element software. The accuracy of the calculation results meets the requirements of the preliminary design stage. No accurate soil data or professional analysis software is required to calculate the pile-soil interaction force, thereby reducing modeling and analysis time. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the three-dimensional structural model of the platform; Figure 2 is a schematic diagram of equivalent embedded piles; Figure 3 It is a schematic diagram of the rigid fixed boundary conditions in the model; Figure 4 It is a curve diagram showing the relationship between the ratio of the embedment length to the pile diameter and the foundation reaction coefficient; Figure 5 is the acceleration spectrum curve; Among them, 11-steel pipe piles, 12-jacket structure, 13-upper assembly, 14-equipment in the platform, 31-rigid fixed boundary conditions. DETAILED DESCRIPTION

[0011] The present invention will be further described in conjunction with the accompanying drawings.

[0012] A simplified analysis method for seismic response of an offshore jacket platform is provided. The structural drawings of the target platform are obtained, and a three-dimensional structural model of the entire platform is established according to the structural drawings of the platform. The model includes upper modules, jackets, and major platform equipment. The major platform equipment includes converter valve towers, transformers, emergency generators, etc.

[0013] The entire ship was modeled using Genie software. The main structures of the steel pipe piles, jacket and upper modules were simulated using BEAM units, the platform equipment was simulated using EQUIPMENT, and other secondary structures were taken into account in the model by modifying the material density.

[0014] According to the soil characteristics of the working area Figure 4 The embedded length ha is obtained. In this embodiment, ha is 4.88 times the pile diameter, ha=13.2 meters, and then a rigid fixed boundary condition is applied to the bottom of the pile.

[0015] Modal analysis was performed on the above model. The overall vibration period of the platform in the X direction was 1.77s and the overall vibration period in the Y direction was 1.48s. According to the vibration period in the X direction of the platform in the given operating area seismic acceleration spectrum curve, Figure 5 As shown, the horizontal earthquake acceleration in the X direction when the platform is subjected to an earthquake is 1.32 m / s 2 Similarly, the horizontal earthquake acceleration of the platform in the Y direction is 1.48m / s 2 .

[0016] Add four analysis conditions in the Genie software, and add the accelerations obtained above to the analysis conditions respectively, that is, the acceleration field of condition one is set to (1.32, 1.48, 0), the acceleration field of condition two is set to (1.32, -1.48, 0), the acceleration field of condition three is set to (-1.32, 1.48, 0), and the acceleration field of condition four is set to (-1.32, -1.48, 0), and then use the software to perform static solutions for the above four conditions.

[0017] The components and nodes of the jacket platform are evaluated according to the specifications, and the components that do not meet the requirements are modified until they meet the specifications.

Claims

1. A simplified analysis method for seismic response of an offshore jacket platform, characterized in that: The specific analysis method is as follows: S1: Obtaining the structural drawings of the target platform, and establishing a three-dimensional structural model of the platform using finite element numerical simulation technology according to the structural drawings of the entire platform, wherein the three-dimensional structural model includes steel pipe piles (11), a jacket structure (12), an upper assembly (13), and equipment (14) in the platform; S2: The three-dimensional structural model is constrained by using the equivalent embedded pile boundary condition, retaining the steel pipe pile below the mud surface, and applying the rigid fixed boundary condition (31) to the pile bottom. The length of the steel pipe pile below the mud surface, ha, can be obtained from the relationship curve between the ratio of the embedded length to the pile diameter and the foundation reaction coefficient according to the soil type. The larger value is taken for soft soil and the smaller value is taken for hard soil. When there is no soil data, 6 times the pile diameter is taken. S3: Perform modal analysis on the three-dimensional structural model to obtain its first-order and second-order overall vibration frequencies, and query the corresponding seismic acceleration according to the two-order vibration frequencies of the platform in a given seismic response spectrum; S4: Then the calculated two horizontal earthquake accelerations are loaded into the three-dimensional structural model and solved and analyzed using finite element software; S5: Evaluate the components and nodes of the jacket platform according to the specifications.

2. A simplified analysis method for seismic response of an offshore jacket platform according to claim 1, characterized in that: The entire ship was modeled using Genie software. The main structures of the steel pipe piles, jacket structure, and upper modules were simulated using BEAM units, and other secondary structures were taken into account in the model by modifying the material density in the finite element software.

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