Fatigue analysis method for offshore tall platform

Abstract

The invention discloses a fatigue analysis method for an offshore towering platform. The fatigue analysis method for the offshore towering platform comprises wave-induced fatigue and wind-induced fatigue, and the service life of the platform is evaluated through superposition of wave-induced fatigue damage and wind-induced fatigue damage. A tall platform integral finite element model is established in ocean engineering structure analysis software, and wave spectrum fatigue analysis is performed on the tall platform based on a PM spectrum through a fatigue analysis module in the analysis software according to an in-service sea area wave scatter diagram, a node stress concentration coefficient and an S-N curve of the tall platform to obtain a wave-induced fatigue damage value of each node of the tall platform; the distribution probability of the wind speed and the wind direction of the in-service sea area of the towering platform is analyzed through an ocean engineering structure analysis software fatigue analysis module, Weibull distribution of the average wind speed is obtained, spectrum wind fatigue analysis is carried out based on the dynamic response characteristic of the towering structure, and the wind-induced fatigue damage value of each node of the towering platform is obtained; and obtaining a total damage value of each node of the high-rise structure according to a fatigue damage superposition theory, and evaluating the fatigue life of the high-rise platform.

Description

Technical Field

[0001] The invention belongs to the field of marine steel structure engineering, and in particular relates to a fatigue analysis method for an offshore high-rise platform. Background Art

[0002] At present, the conventional jacket-type fixed platform consists of a jacket and an upper module, with a service life of 20 years. During the design, fatigue analysis only considers the impact of wave loads on the jacket. The wind tower on the top of the towering platform is a slender and flexible steel structure with an altitude of 100 meters and a service life of 30 years. The service area is located in the East China Sea and is often hit by typhoons. The wind load has a greater impact on the overall structure, and the damage caused by wind fatigue cannot be ignored.

[0003] For high-rise offshore platforms, the wave-induced fatigue of the jacket and the wind-induced fatigue of the top wind tower act on the platform structure at the same time, which belongs to the time domain. This requires the collection of a large amount of environmental data to obtain the wave spectrum and wind time-history load of the wind tower, and the input conditions are extremely harsh. For engineering projects, seeking a fatigue analysis method that can transform difficult time-domain problems into highly operational and reliable methods is the key to solving engineering problems.

[0004] Therefore, it is urgent to design a fatigue analysis method for tall offshore platforms to solve the problem of calculating the damage value caused by fatigue under the simultaneous action of waves and wind mentioned above. Summary of the invention

[0005] In order to solve the technical problem that the wave-induced fatigue of the jacket and the wind-induced fatigue of the top wind tower mentioned in the background technology act on the platform structure at the same time, it is necessary to collect a large amount of environmental data, obtain the wave spectrum and the wind time-history load of the wind tower, and the input conditions are extremely harsh. The present invention provides a fatigue analysis method for an offshore high-rise platform to solve the problem of calculating the damage value caused by fatigue under the simultaneous action of waves and wind.

[0006] To achieve the above purpose, the specific technical scheme of the fatigue analysis method of offshore high-rise platform of the present invention is as follows: A fatigue analysis method for high-rise offshore platforms is a combined fatigue analysis method that evaluates the fatigue of the entire platform, including wave-induced fatigue and wind-induced fatigue. The platform life is evaluated by superimposing the wave-induced fatigue and wind-induced fatigue damage. The overall finite element model of the tall platform is established in the offshore engineering structure analysis software. Through the fatigue analysis module in the analysis software, the wave scatter diagram of the in-service sea area of ​​the tall platform, the node stress concentration factor and the SN curve are analyzed, and the spectral fatigue analysis of the tall platform is carried out based on the PM spectrum to obtain the wave-induced fatigue damage value of each node of the tall platform. The fatigue analysis module of the offshore engineering structure analysis software is used to obtain the Weibull distribution of the average wind speed based on the distribution probability of wind speed and wind direction in the sea area where the tall platform is in service. Based on the dynamic response characteristics of the tall structure, a spectral wind fatigue analysis is performed on it to obtain the wind-induced fatigue damage value of each node of the tall platform. According to the fatigue damage superposition theory, the total damage value of each node of the tall structure is obtained, so as to evaluate the fatigue life of the tall platform.

[0007] Furthermore, based on the probability distribution of waves in different directions in the sea area where the tall platform is in service, the maximum wave height and maximum wave period at the damage center are obtained, and the dynamic response characteristic value of the tall platform is obtained through the modal analysis module.

[0008] Furthermore, based on AIRY linear wave theory, the transfer functions under different wave periods are obtained through software wave response analysis.

[0009] Furthermore, the SCF values ​​of different nodes are determined based on the node form and welding form, and the PM spectrum is subjected to spectral fatigue analysis to obtain the wave-induced fatigue damage value of each point on the platform and the platform life.

[0010] Furthermore, the dynamic response characteristics of the tall platform are obtained through the modal analysis module, the SCF values ​​of different nodes are determined according to the node form and welding form, and the spectral wind fatigue analysis is performed based on the Harris wind spectrum to obtain the wind-induced fatigue damage value of each node of the tall platform and the platform life.

[0011] Furthermore, wave-induced fatigue is PM spectrum fatigue, and wind-induced fatigue is Harris wind spectrum fatigue. According to fatigue damage superposition theory, the total damage value of high-rise structures is: D= = .

[0012] in, is the wind-induced fatigue damage value; is the wave-induced fatigue damage value; m is the steepness of the selected SN curve.

[0013] Furthermore, the SCF value of the TKYX node of the high-rise platform is obtained using the Efthymiou formula; the SCF of inline butt welds, girth welds, double-sided welds with cone transitions, or single-sided welds are all obtained using the DNV fatigue standard built into the program.

[0014] Furthermore, the SCF value of the Kink point on the wind tower was obtained using the DNV fatigue standard; the SCF values ​​of the connection nodes between the skirt sleeve and the conductor frame, and between the module and the wind tower were obtained using finite element analysis.

[0015] Furthermore, the SN curve of the TKYX node of the towering platform adopts the API WJ curve in the program; the SN curve of the double-sided weld of inline butt weld, girth weld and cone transition adopts the DNV D curve; the SN curve of the single-sided weld of inline butt weld, girth weld and cone transition adopts the DNV F3 curve.

[0016] Furthermore, the SN curve of the Kink point on the wind tower adopts the DNV D curve; the connection nodes between the skirt sleeve and the conductor frame, and between the module and the wind tower adopt the DNV D curve.

[0017] The fatigue analysis method of the offshore high-rise platform of the present invention has the following advantages: The fatigue life of the high-rise structure was obtained by fatigue analysis of the whole structure. Compared with conventional offshore platforms that only perform fatigue analysis on the jacket, the overall reliability of the high-rise structure during service is better ensured. This application conducts a combined fatigue analysis of waves and wind on the high-rise structure. Compared with conventional offshore platforms that only consider wave-induced fatigue damage, it more comprehensively considers the comprehensive impact of multiple environmental conditions on the high-rise platform, ensuring overall safety during service. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The process flow chart of the fatigue analysis method of the offshore high-rise platform of the present invention is as follows; Figure 2 It is a schematic diagram of the overall structure of a tall offshore platform according to the method for fatigue analysis of the tall offshore platform of the present invention; Figure 3 The diagram is a connection diagram of a wind tower and an upper assembly block in a fatigue analysis method for a tall offshore platform according to the present invention.

[0019] Description of the markings in the figure: 1. Towering platform; 2. Wind tower; 3. Upper assembly; 4. Conductor frame. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0021] Those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and form different embodiments. For example, in the claims, any one of the claimed embodiments may be used in any combination.

[0022] Please refer to the attached Figure 1 To Attachment Figure 3 The fatigue analysis method of a tall offshore platform of the present invention is described.

[0023] like Figure 1 As shown, the fatigue analysis method of the offshore tall platform in the present invention is a combined fatigue analysis, which performs fatigue assessment on the entire platform, including wave-induced fatigue and wind-induced fatigue, and the platform life is assessed by superimposing wave-induced fatigue and wind-induced fatigue damage; an overall finite element model of the tall platform is established in the marine engineering structure analysis software, and a fatigue analysis module in the analysis software is used to perform spectral fatigue analysis on the tall platform based on the PM spectrum according to the wave scatter diagram of the in-service sea area of ​​the tall platform, the node stress concentration factor and the SN curve, to obtain the wave-induced fatigue damage value of each node of the tall platform; The fatigue analysis module of the marine engineering structure analysis software is used to obtain the Weibull distribution of the average wind speed according to the distribution probability of wind speed and wind direction in the sea area where the tall platform is in service. Based on the dynamic response characteristics of the tall structure, a spectral wind fatigue analysis is performed to obtain the wind-induced fatigue damage value of each node of the tall platform. According to the fatigue damage superposition theory, the total damage value of each node of the tall structure is obtained, thereby evaluating the fatigue life of the tall platform.

[0024] Preferably, an overall finite element model of the tall platform 1 is established in the marine engineering structure analysis software, and the fatigue analysis module provided by the software is used to perform spectral fatigue analysis on the tall platform based on the Pierson-Moskowitz spectrum according to the wave scatter diagram of the in-service sea area of ​​the tall platform, the node stress concentration factor (SCF) and the SN curve, and obtain the wave-induced fatigue damage value of each node of the tall platform. The specific process is as follows:

[0025] The “Damage Center” module provided by the software was used to obtain the maximum wave height and maximum wave period of the damage center according to the probability distribution of waves in different directions in the sea area where the tall platform 1 is in service. The modal analysis module was used to obtain the characteristic value of the dynamic response of the tall platform. According to the AIRY linear wave theory, the software wave response analysis was used to obtain the transfer function under different wave periods, that is, the structural stress distribution. The SCF values ​​of different nodes were determined according to the node form and welding form, and spectral fatigue analysis was performed based on the PM spectrum to obtain the wave-induced fatigue damage value of each point on the platform and the platform life.

[0026] Further, if Figure 2 and Figure 3 As shown, the tall platform 1 is an offshore fixed platform structure composed of a conductor pipe frame 4, an upper assembly block 3 and a wind tower 2; preferably, the wind tower 2 is a tall, slender truss structure, the cross-section of the entire tower body gradually decreases from bottom to top, and different cross-sections are connected by a trapezoidal truss structure. A flange-type plug tip is provided at the bottom of the wind tower 2, and the flange-type plug tip is welded to the top column short section of the upper assembly block 3 as a whole.

[0027] The overall finite element model of the tall platform 1 is constructed by using the fatigue analysis module of the marine engineering structure analysis software. According to the distribution probability of wind speed and wind direction in the sea area where the tall platform is in service, the Weibull distribution of the average wind speed is obtained. The dynamic response characteristics of the tall platform are obtained by the modal analysis module. The SCF values ​​of different nodes are determined according to the node form and welding form. The spectral wind fatigue analysis is performed based on the Harris wind spectrum to obtain the wind-induced fatigue damage value of each node of the tall platform and the platform life.

[0028] As a preferred embodiment, the wave-induced fatigue is PM spectrum fatigue, and the wind-induced fatigue is Harris wind spectrum fatigue. According to the fatigue damage superposition theory, the total damage value of the high-rise structure is: D= = in: is the wind-induced fatigue damage value; is the wave-induced fatigue damage value; m is the steepness of the selected SN curve.

[0029] Preferably, the marine engineering structural analysis software used is SACS. The SACS software system developed by Engineering Dynamics is a structural finite element analysis software system used for marine platforms and general land structural engineering design, and includes multiple program modules. In addition to using the basic structural analysis module, the present invention also uses DYNPAC, DynamicResponse, Wave Response and Fatigue Pro modules.

[0030] Preferably, when performing calculations, eight wave directions are selected, including incident directions of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and wave periods range from 1.5 to 20s, for dynamic response analysis. Environmental loads are applied in the same direction to obtain dangerous working conditions, and eight wind directions are also selected, including 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, for fatigue analysis.

[0031] Furthermore, for the tall platform 1, the SCF value of the conventional TKYX node is obtained using the Efthymiou formula; the SCF of inline butt welds, girth welds, double-sided welds or single-sided welds of cone transition can be automatically obtained through the DNV fatigue standard built into the program; the SCF value of the Kink point on the wind tower needs to be obtained through the DNV fatigue standard; the SCF value of the connection node between the skirt sleeve and the conductor frame, and between the module and the wind tower can be obtained through finite element analysis.

[0032] For the tall platform 1, the conventional TKYX node SN curve adopts the API WJ curve in the program; the SN curves of inline butt joints, girth welds, and double-sided welds of cone transition adopt the DNV D curve; the SN curves of inline butt joints, girth welds, and single-sided welds of cone transition adopt the DNV F3 curve; the SN curve of the Kink point on the wind tower adopts the DNV D curve; the DNV D curve is used for the connection nodes between the skirt sleeve and the conductor frame, and between the module and the wind tower.

[0033] Based on the fatigue analysis method of offshore tall platforms, fatigue analysis of the entire tall structure is performed to obtain the fatigue life. Compared with conventional offshore platforms that only perform fatigue analysis on the jacket, the overall reliability of the tall structure during service is better ensured. This application performs a combined fatigue analysis of waves and wind on the tall structure. Compared with conventional offshore platforms that only consider wave-induced fatigue damage, it more comprehensively considers the comprehensive impact of multiple environmental conditions on the tall platform 1, ensuring overall safety during service.

[0034] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A fatigue analysis method for a tall offshore platform, which is a combined fatigue analysis and performs fatigue assessment on the entire platform, characterized in that: Including wave-induced fatigue and wind-induced fatigue, wave-induced fatigue and wind-induced fatigue damage superposition to evaluate platform life; The overall finite element model of the tall platform is established in the offshore engineering structure analysis software. Through the fatigue analysis module in the analysis software, the wave scatter diagram of the in-service sea area of ​​the tall platform, the node stress concentration factor and the SN curve are analyzed, and the spectral fatigue analysis of the tall platform is carried out based on the PM spectrum to obtain the wave-induced fatigue damage value of each node of the tall platform. The fatigue analysis module of the offshore engineering structure analysis software is used to obtain the Weibull distribution of the average wind speed based on the distribution probability of wind speed and wind direction in the sea area where the tall platform is in service. Based on the dynamic response characteristics of the tall structure, a spectral wind fatigue analysis is performed on it to obtain the wind-induced fatigue damage value of each node of the tall platform. According to the fatigue damage superposition theory, the total damage value of each node of the tall structure is obtained, so as to evaluate the fatigue life of the tall platform.

2. The fatigue analysis method for a high-rise offshore platform according to claim 1, characterized in that: Based on the probability distribution of waves in different directions in the sea area where the tall platform is in service, the maximum wave height and maximum wave period at the damage center are obtained, and the dynamic response characteristic value of the tall platform is obtained through the modal analysis module.

3. The fatigue analysis method for a tall offshore platform according to claim 2 is characterized in that: According to AIRY linear wave theory, the transfer function under different wave periods is obtained through software wave response analysis.

4. The fatigue analysis method for a tall offshore platform according to claim 3 is characterized in that: The SCF values ​​of different nodes are determined based on the node form and welding form, and the PM spectrum is subjected to spectral fatigue analysis to obtain the wave-induced fatigue damage value of each point on the platform and the platform life.

5. The fatigue analysis method for a tall offshore platform according to claim 1, characterized in that: The dynamic response characteristics of the tall platform are obtained through the modal analysis module. The SCF values ​​of different nodes are determined according to the node form and welding form. Spectral wind fatigue analysis is performed based on the Harris wind spectrum to obtain the wind-induced fatigue damage value of each node of the tall platform and the platform life.

6. The fatigue analysis method for a tall offshore platform according to claim 5, characterized in that: Wave-induced fatigue is PM spectrum fatigue, and wind-induced fatigue is Harris wind spectrum fatigue. According to fatigue damage superposition theory, the total damage value of high-rise structures is: in, is the wind-induced fatigue damage value; is the wave-induced fatigue damage value; m is the steepness of the selected SN curve.

7. The offshore high-rise platform fatigue analysis method according to claim 1, characterized in that: The SCF value of the TKYX node of the high-rise platform is calculated using the Efthymiou formula; the SCF of inline butt welds, girth welds, double-sided welds with cone transitions, or single-sided welds are all calculated using the DNV fatigue standard built into the program.

8. The fatigue analysis method for a tall offshore platform according to claim 7, characterized in that: The SCF value of the Kink point on the wind tower is obtained by DNV fatigue standard; the SCF value of the connection node between the skirt sleeve and the conductor frame, and between the module and the wind tower is obtained by finite element method.

9. The fatigue analysis method for a tall offshore platform according to claim 1, characterized in that: The SN curve of the TKYX node of the towering platform adopts the API WJ curve in the program; the SN curve of the double-sided weld of inline butt weld, girth weld and cone transition adopts the DNV D curve; the SN curve of the single-sided weld of inline butt weld, girth weld and cone transition adopts the DNV F3 curve.

10. The fatigue analysis method for a tall offshore platform according to claim 9, characterized in that: The SN curve of the Kink point on the wind tower adopts the DNV D curve; the connection nodes between the skirt sleeve and the conductor frame, and between the module and the wind tower adopt the DNV D curve.

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