CN-122021205-A - Floating fan foundation structure fatigue life calculation method under multi-field coupling

CN122021205ACN 122021205 ACN122021205 ACN 122021205ACN-122021205-A

Abstract

The invention provides a method for calculating fatigue life of a floating fan foundation structure under multi-field coupling, which relates to the technical field of fan structure fatigue life calculation, and the method realizes quantitative description of the corrosion depth of a coating along with the change of time and environmental parameters by establishing a corrosion attenuation model, and reflects the corrosion behavior of mooring lines in a complex sea area environment; based on historical sea state data decomposition and time sequence analysis, accurate environmental load time sequence input is obtained, a first fatigue life which does not consider corrosion influence is obtained by utilizing finite element simulation and combining a rain flow counting method and a fatigue accumulated damage theory, and then a correction factor is constructed based on the corrosion action of a mooring line so as to correct the first fatigue life and obtain a second fatigue life which considers the corrosion influence, so that the influence of the corrosion action on the fatigue life of the mooring line is effectively reflected, the deviation of corrosion influence estimation in the traditional method is reduced, and the accuracy and reliability of fatigue life prediction of a floating fan foundation structure are improved.

Inventors

ZHOU CHENYAN
CHEN LING
LI XIAOQUAN
LIU WEITING
YANG FENG
ZHU XINYAN
GAO YU

Assignees

南通理工学院

Dates

Publication Date: 20260512
Application Date: 20260414

Claims (9)

1. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling is characterized by comprising the following specific steps: S1, collecting environmental parameters of a sea area where a floating fan is located, constructing a plurality of salt water environments with different environmental parameters by adopting an orthogonal test method, respectively setting mooring lines in each salt water environment to perform an accelerated corrosion test, and simultaneously generating an acceleration ratio of the test in time; S2, collecting coating parameters of the mooring line changing along with the test time, combining the acceleration ratio and the test time to obtain the actual service time of the mooring line, generating influence factors of the service time and environmental parameters on the coating parameters, and constructing a corrosion attenuation model according to the influence factors to calculate the coating parameters under any service time and environmental parameter combination; S3, collecting historical sea state parameters of the sea area, decomposing the historical sea state parameters into long-term uniform components and short-term random components, carrying out time sequence analysis on the long-term uniform components and the short-term random components by adopting different models, and then coupling the long-term uniform components and the short-term random components to obtain time sequence sea state parameters of the sea area; s4, establishing a three-dimensional model for the floating fan, carrying out finite element analysis, taking the time sequence sea state parameters as the load input of the model, solving based on a structural dynamics equation to obtain the time sequence stress parameters of each mooring line on the floating fan, and jointly generating the first fatigue life of each mooring line by combining a rain flow counting method and an S-N fatigue curve; And S5, obtaining coating parameters in a corresponding state of the mooring line based on the environmental parameters of the sea area, the first fatigue life and the corrosion attenuation model, correcting the first fatigue life according to the coating parameters and generating the second fatigue life, and completing the fatigue life calculation of the floating fan foundation structure.
2. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 1, wherein the environmental parameters comprise environmental temperature, salinity and oxygen content, and the coating parameter is the maximum corrosion depth; When the accelerated corrosion test is carried out on the mooring line, an electrochemical acceleration method is adopted to accelerate the corrosion process, and the specific logic of the corrosion test is as follows: Determining environmental parameters related to corrosion of the mooring line coating, and based on the types of the environmental parameters and preset level values, jointly configuring a plurality of groups of brine environments by combining corresponding orthogonal test tables, and simultaneously configuring a group of brine environments with the same environmental parameters as the sea area as a reference group; Immersing a mooring line serving as a working electrode, an auxiliary electrode and a reference electrode in a corresponding saline water environment together, accelerating the corrosion process by adopting a constant potential polarization method, setting an open circuit potential between 0.2V and 0.5V, and setting the current density between 1mA/cm 2 ~5mA/cm 2 ; Taking out the mooring line regularly, carrying out microscopic appearance detection on the surface of the mooring line, measuring the corrosion depth of all corrosion areas on the mooring line, and calibrating the maximum value of the corrosion depth as the maximum corrosion depth.
3. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 2, wherein the actual service time of the mooring line is defined as the product of test time and acceleration ratio, and the logic for determining the acceleration ratio of the accelerated corrosion test is as follows: collecting mooring lines which work in the sea for a preset time period, performing microscopic morphology detection on the surfaces of the mooring lines to obtain the total area and the average corrosion depth of all corrosion areas of the mooring lines, and respectively calibrating the total area and the average corrosion depth as a reference corrosion area and a reference corrosion depth; For a reference group in the accelerated corrosion test, periodically measuring the total area and the average corrosion depth of all corrosion areas of a mooring line of the reference group, respectively comparing the total area and the average corrosion depth with the reference corrosion area and the reference corrosion depth until a preset similarity condition is met, and dividing the preset duration by the test duration when the reference group meets the similarity condition to obtain the accelerated corrosion ratio; The similarity condition is that the relative error between the total area of all corrosion areas of the mooring lines in the reference group and the reference corrosion area, the relative error between the average corrosion depth and the reference corrosion depth is not higher than 10%.
4. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 2, wherein the corrosion attenuation model is constructed based on a Logistic differential equation and satisfies a nonlinear differential equation form, specifically, after a corrosion factor is integrally added to the right side of the Logistic differential equation as an exponential term, the corrosion factor is multiplied by an influence factor of service time and environmental parameters on coating parameters, wherein: the influence factors are obtained by fitting by adopting a multiple regression method or a machine learning method; The Logistic differential equation converges to a preset limiting corrosion depth.
5. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 1, wherein the sea state parameters are wave load and wind load, and the logic for generating the time-sequence sea state parameters in the step S3 is as follows: s301, performing fast Fourier transform on historical sea state data, and converting the historical sea state data into frequency domain signals; S302, constructing a low-pass filter according to the sea-area period, and decomposing a frequency domain signal into a low-frequency component spectrum and a high-frequency component spectrum by using the low-pass filter; s303, respectively carrying out inverse Fourier transform on the low-frequency component spectrum and the high-frequency component spectrum to obtain a long-term uniform component and a short-term random component which are respectively used for reflecting a long-term trend caused by the seasonal change of the sea area and a short-term trend caused by the environmental change; s304, respectively adopting a seasonal ARIMA model and an ARMA model to perform time sequence fitting on the long-term uniform component and the short-term random component, and outputting the superimposed fitting results as time sequence sea state parameters of the sea area.
6. The method for calculating the fatigue life of the floating fan foundation structure under multi-field coupling according to claim 1, wherein the step S4 comprises the following steps: S401, establishing a three-dimensional model for the floating fan, and respectively defining the material properties, boundary conditions and connection relations between the fan body and the mooring line; S402, taking the time sequence sea state parameters as load input of a three-dimensional model, solving a structural dynamics equation by utilizing a numerical integration method to obtain equivalent stress of each mooring line on the floating fan, and arranging the equivalent stress according to a time sequence to obtain time sequence stress parameters; S403, circularly dividing the time sequence stress parameters by adopting a rain flow counting method to obtain a plurality of groups of stress circulation with different stress amplitudes and corresponding actual circulation times, combining the stress circulation with the S-N fatigue curve of the mooring line, and calculating the first fatigue life of each mooring line by adopting a Miners linear accumulated damage method.
7. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 6, wherein the first fatigue life calculating logic is as follows: Based on the S-N fatigue curve of the mooring line and the stress amplitude under each group of stress circulation, obtaining the maximum circulation times corresponding to each group of stress circulation; And calculating accumulated damage caused by all stress cycles together based on Miners linear accumulated damage method, wherein when the accumulated damage is equal to 1, the mooring line is considered to generate fatigue damage, and the first fatigue life is the ratio of the collection duration corresponding to the time sequence sea state parameter to the accumulated damage.
8. The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling of claim 4, wherein the second fatigue life generating logic is as follows: Substituting the first fatigue life as theoretical maximum service time, and substituting the maximum service time and environmental parameters of the sea area into a corrosion attenuation model to obtain coating parameters of the mooring line in the maximum service time; Constructing a correction factor based on the coating parameters, wherein the correction factor is a piecewise function, the function value is monotonically decreasing along with the coating parameters, and the method satisfies the following conditions: when the coating parameter is lower than the critical value, the piecewise function is in an exponential form, the base number term is natural logarithm, and the exponential term comprises the ratio of the coating parameter to the limiting corrosion depth; when the coating parameter is not lower than the critical value, the piecewise function is in the form of a power function, the base number item comprises the ratio of the coating parameter to the limiting corrosion depth, and the index item is a control coefficient larger than zero; The first fatigue life is multiplied by a correction factor to obtain a second fatigue life reflecting the effect of sea corrosion on the theoretical maximum length of service of the mooring line.
9. The method of claim 8, wherein the threshold value of the piecewise function is set to 0.7-0.8 times the limiting corrosion depth.

Description

Floating fan foundation structure fatigue life calculation method under multi-field coupling Technical Field The invention relates to the technical field of fan structure fatigue life calculation, in particular to a floating fan foundation structure fatigue life calculation method under multi-field coupling. Background With the rapid development of the marine wind power industry, the fatigue life of a basic structure of a floating fan serving as key technical equipment suitable for deep water sea areas becomes a core problem for guaranteeing operation safety and economy. The floating fan mooring system is exposed to complex and changeable sea environments for a long time, and is subjected to comprehensive influence of various environmental factors such as temperature, salinity, oxygen content and the like, so that the mooring wire material is corroded and degenerated, and further fatigue performance of the mooring wire material is influenced. However, existing fatigue life assessment methods mostly ignore or simply handle corrosion effects and fail to adequately incorporate the multi-field coupling effects of environmental parameters, resulting in large uncertainties and deviations in fatigue life predictions. In the prior art, publication number CN113283125A discloses a fatigue analysis method of a turret mooring system based on measured data, which relates to the field of mooring system design and safety evaluation, and comprises the steps of data acquisition, fatigue analysis and evaluation result update of the turret mooring system according to fatigue damage calculation results. However, although this scheme can perform life analysis of the mooring line, depending on an empirical formula and static load interpolation, the influence of corrosion on life is not considered, resulting in limited accuracy and applicability of fatigue life prediction. The above information disclosed in the background section is only for enhancement of understanding of the background of the disclosure and therefore it may include information that does not form the prior art that is already known to a person of ordinary skill in the art. Disclosure of Invention The invention aims to provide a method for calculating the fatigue life of a floating fan foundation structure under multi-field coupling, so as to solve the problems in the background technology. In order to achieve the above purpose, the present invention provides the following technical solutions: The method for calculating the fatigue life of the floating fan foundation structure under the multi-field coupling comprises the following specific steps: S1, collecting environmental parameters of a sea area where a floating fan is located, constructing a plurality of salt water environments with different environmental parameters by adopting an orthogonal test method, respectively setting mooring lines in each salt water environment to perform an accelerated corrosion test, and simultaneously generating an acceleration ratio of the test in time; S2, collecting coating parameters of the mooring line changing along with the test time, combining the acceleration ratio and the test time to obtain the actual service time of the mooring line, generating influence factors of the service time and environmental parameters on the coating parameters, and constructing a corrosion attenuation model according to the influence factors to calculate the coating parameters under any service time and environmental parameter combination; S3, collecting historical sea state parameters of the sea area, decomposing the historical sea state parameters into long-term uniform components and short-term random components, carrying out time sequence analysis on the long-term uniform components and the short-term random components by adopting different models, and then coupling the long-term uniform components and the short-term random components to obtain time sequence sea state parameters of the sea area; s4, establishing a three-dimensional model for the floating fan, carrying out finite element analysis, taking the time sequence sea state parameters as the load input of the model, solving based on a structural dynamics equation to obtain the time sequence stress parameters of each mooring line on the floating fan, and jointly generating the first fatigue life of each mooring line by combining a rain flow counting method and an S-N fatigue curve; And S5, obtaining coating parameters in a corresponding state of the mooring line based on the environmental parameters of the sea area, the first fatigue life and the corrosion attenuation model, correcting the first fatigue life according to the coating parameters and generating the second fatigue life, and completing the fatigue life calculation of the floating fan foundation structure. Preferably, the environmental parameters include environmental temperature, salinity, oxygen content, and the coating parameter is maximum corrosion depth; When the acc