Method and system for calculating scour fatigue damage of submarine cable of pile foundation landing section and storage medium

Abstract

The application relates to the technical field of ocean engineering monitoring, and discloses a pile foundation landing section submarine cable scouring fatigue damage calculation method and system and a storage medium. The method comprises the following steps: collecting phase changes of optical fibers in a submarine cable and extracting submarine cable energy values; extracting main vibration frequencies of submarine cable swinging; establishing a mapping relationship between optical fiber equivalent stress amplitudes and armored equivalent stress amplitudes; performing data processing on the optical fiber equivalent stress amplitudes, the submarine cable swinging energy values and the submarine cable vibration frequencies to obtain a relationship among the energy values, the armored steel wire equivalent stress amplitudes and the submarine cable vibration frequencies; and based on the relationship among the three and in combination with a linear cumulative damage theory, an environment coupling life model of the submarine cable is established. The method is good in real-time performance and small in detection blind area.

Description

Technical Field

[0001] This application relates to the technical field of marine engineering monitoring, and in particular to a method, system, and storage medium for calculating fatigue damage caused by scour of submarine cables in the landing section of a pile foundation. Background Technology

[0002] In the field of transoceanic power transmission and communication, submarine cables are irreplaceable critical infrastructure, shouldering the important mission of connecting energy and information networks in separated sea areas. Whether it is the transmission of electricity from offshore wind power to land or the transmission of communication data between continents, both depend on the stable operation of submarine cables.

[0003] In a submarine cable system, the landing pile section is the core link connecting the seabed and the land, and its structural design and performance directly affect the reliability of the entire submarine cable system. This section is located in the sea-land interaction zone and must withstand multiple natural factors such as tidal erosion, seawater corrosion, and geological changes over a long period of time, which can easily lead to the submarine cable being suspended and causing fatigue damage.

[0004] Currently, traditional methods for monitoring the condition of submarine cable pile foundation landing sections mainly rely on periodic underwater inspections or localized sensor monitoring. Underwater inspections are mostly carried out by divers or remotely operated vehicles (ROVs) and must be conducted on a fixed schedule. They allow for direct observation of structural damage, but are limited by environmental factors such as water flow and visibility, resulting in low efficiency and high cost. Localized sensor monitoring involves deploying sensors at key locations to collect data on stress, corrosion, etc., in real time. However, the sensor coverage is limited, leading to blind spots and making it difficult to comprehensively reflect the overall condition of the landing section. In particular, it is difficult to detect sudden damage and cannot meet the safety requirements in complex environments.

[0005] There is a need for a detection method for the landing section of the pile foundation with good real-time performance and small detection blind zone, so as to improve the detection effect of the existing condition detection of the landing section of the submarine cable pile foundation. Summary of the Invention

[0006] To achieve real-time detection with a small blind zone, this application provides a method, system, and storage medium for calculating fatigue damage caused by scour of submarine cables in the landing section of a pile foundation.

[0007] Firstly, this application provides a method for calculating the fatigue damage caused by scour of submarine cables in the landing section of a pile foundation, employing the following technical solution:

[0008] A method for calculating fatigue damage caused by scour of submarine cables in the landing section of a pile foundation includes the following steps:

[0009] Phase changes of optical fibers inside submarine cables under scouring conditions Where t is a time variable, representing the dynamic change of phase over time, the energy value of the submarine cable is extracted through a phase correspondence algorithm between energy value and phase change. ;

[0010] The main vibration frequency of the submarine cable oscillation was extracted using the power spectrum estimation method. ;

[0011] Establish the mapping relationship between the equivalent stress amplitude of optical fiber and the equivalent stress amplitude of armor;

[0012] Data processing was performed on the equivalent stress amplitude of the optical fiber, the swing energy value of the submarine cable, and the vibration frequency of the submarine cable to obtain the relationship between the energy value, the equivalent stress amplitude of the armored steel wire, and the vibration frequency of the submarine cable.

[0013] Based on the relationship among the three factors and combined with the linear cumulative damage theory, an environmental coupled lifetime model for submarine cables is established: ;in, For time variables, For environmental parameter serial numbers, For the first Duration of environment parameters For the first Fatigue life of armored steel wire under similar environmental parameters, wind speed For the first Wind speed level parameters, ocean currents For the first Seawater current velocity level parameters, This represents the stress influence coefficient corresponding to the seawater flow velocity.

[0014] By adopting the above technical solution, a kilometer-level continuous monitoring can be achieved using a distributed optical fiber acoustic detection device to obtain phase change data of the optical fiber inside the submarine cable in the landing section under scouring. With the help of corresponding data processing and analysis algorithms, various parameters that can be used for fatigue assessment can be extracted. Finally, through analysis, fatigue assessment and life prediction of the submarine cable in the pile foundation landing section can be achieved. Long-term online real-time assessment can be carried out, reducing costs and providing reliable early warning.

[0015] Optionally, the method further includes the following steps:

[0016] Acquire the phase change caused by fiber strain at the monitoring point The energy value of the optical fiber is obtained using an energy phase correspondence algorithm, and the square root of the optical fiber energy value is used as the energy value of the submarine cable. .

[0017] By adopting the above technical solution, the fiber energy value is obtained from the average of the square of the actual phase of the monitoring point. Taking the square root of the fiber energy value as the submarine cable energy value can reduce the difference in the magnitude of the energy value.

[0018] Optionally, the method further includes the following steps:

[0019] The vibration frequency at the flare end of the submarine cable is used as the vibration frequency of the submarine cable.

[0020] Acquire phase data at the horn mouth sampling frequency Collection time If the time is seconds, then the total number of data points collected is... ;

[0021] Phase data at the horn mouth A low-pass filter is used to remove high-frequency noise while retaining a preset oscillation frequency band, resulting in filtered phase data. ;

[0022] Filtered phase data Using the power spectrum estimation method, Segment the data and calculate the power spectral density PSD(f): ;in, Let L be the number of segments, N be the segment length, and O be the total number of data points. Indicates rounding down. For the window function normalization factor, For the first Phase data of the segment, is the window function, and FFT is the Fast Fourier Transform algorithm;

[0023] Find the frequency point in PSD(f) where the amplitude is the largest. , which serves as the main vibration frequency of the submarine cable's oscillation; Let be the frequency value at the k-th frequency point.

[0024] By adopting the above technical solutions, fatigue damage in submarine cables is mostly concentrated in stress concentration areas. The cable flare end, due to structural abrupt changes, is a high-incidence area for fatigue cracks. Furthermore, data monitoring at the cable flare end is more stable. Therefore, the vibration frequency at the flare end is used instead of the overall vibration frequency of the submarine cable. The setting of the acquisition duration can ensure the stability of the frequency domain analysis. Since PSD reflects the degree of energy concentration of different frequency components of the signal, if the PSD amplitude corresponding to a certain frequency component is larger, it indicates that the vibration energy of the signal at that frequency is the most concentrated and is the dominant component driving the cable oscillation.

[0025] Optionally, the method further includes the following steps:

[0026] Model the submarine cable with different suspended sections, and set the suspension height of the submarine cable with different suspended sections to be the same;

[0027] To obtain asymmetric cyclic stress data of armored steel wires and internal optical fibers of submarine cables in different suspended sections under different seawater flow velocities;

[0028] Based on the Goodman linear model: This transforms asymmetric cyclic stress into equivalent symmetric cyclic stress, where... The stress amplitude is equivalent to a symmetrical cycle. The stress amplitude for asymmetric cycles, The average stress of the asymmetric cycle, The tensile strength of the material;

[0029] Based on the equivalent symmetrical cyclic stress amplitudes of the armored steel wire and optical fiber under different seawater flow velocities, the equivalent stress amplitude of the optical fiber is established. Equivalent force amplitude of armor Linear mapping relationship between , where a and b are fitting coefficients related to the suspended length of the submarine cable.

[0030] Optionally, the method further includes the following steps:

[0031] Based on the fact that the optical fiber is subjected to symmetrical cyclic alternating stress, the equivalent stress amplitude of the optical fiber is determined as the maximum stress value. ; through Hooke's Law Obtain the maximum strain of the optical fiber ;

[0032] According to the formula relating phase change and strain: ;

[0033] Maximum dependent variable Convert to phase change ,in, , , , These are the effective refractive index of the optical fiber, the coefficient of refractive index variation with strain, the total length of the optical fiber, and the wavelength.

[0034] Based on the sampling rate and submarine cable vibration frequency. Calculate the number of samplings required for the submarine cable to complete one-quarter of a vibration. ;

[0035] Assuming the phase of the submarine cable vibrates approximately uniformly within 1 / 4 of its cycle, the phase change amount... Divide by the number of samples Calculate the phase change for each sample. ;

[0036] Based on the submarine cable energy value and the preset quantitative standards for data acquisition, an energy value system is established. Equivalent force amplitude of armored steel wire submarine cable vibration frequency A model of the energy relationship among the three: ; This is the equivalent vibration energy value of the submarine cable, used to quantify the cumulative energy generated during the cable's oscillation.

[0037] in, According to the mapping relationship get.

[0038] Optionally, the method further includes the following steps:

[0039] Establish a stress-life curve model for armored steel wire ,in, In order to achieve the equivalent stress amplitude The fatigue life under load is determined by the fatigue performance parameters of the armored steel wire, where a is the fatigue life constant and m is the fatigue strength exponent. The fatigue limit is then determined. ;

[0040] Obtain the energy value and vibration frequency of the armored steel wires of the submarine cable under corresponding wind speed and seawater current speed. The equivalent stress amplitude of the armored steel wires of the submarine cable was calculated using an energy relationship model. ;

[0041] like This indicates that the armor steel wire layer of the submarine cable has suffered irreversible damage. Calculate the number of cycles the armor steel wire can withstand under the current environmental parameters. ;

[0042] Calculate the number of fatigue-damage vibrations experienced by the submarine cable within a preset time period under conditions corresponding to wind speed and seawater current velocity. ;

[0043] in, This indicates the duration during which the wind speed or seawater current speed reaches the preset set speed within a set time period;

[0044] Calculate the total damage life of the armored steel wire under the corresponding wind speed and seawater flow velocity: ;

[0045] Establish a set of wind speeds or seawater current velocities within a preset total time period that allow the submarine cable to exceed its fatigue limit σ-1. ,in, For wind speed or seawater current speed to reach Duration;

[0046] Wind speed or seawater current speed reaches Fatigue life set of submarine cables , of which elements For wind speed or seawater current speed to reach The fatigue life is below, Environmental parameters The total damage life of the lower armored steel wire, of which: ;

[0047] Based on the linear cumulative damage algorithm, the sum of the cumulative damage values ​​of the armored steel wires of the submarine cable is: Calculate the lifespan of the submarine cable: .

[0048] By adopting the above technical solution, finite element simulation software is used to simulate the suspended section of the submarine cable to obtain the stress distribution of each structural node inside the cable. The armor steel wire is the decisive factor affecting the service life of the submarine cable, and the fatigue life of the armor steel wire is used as the service life evaluation index of the submarine cable. By calculating the sum of the cumulative damage values ​​of the armor steel wire of the submarine cable, the service life of the submarine cable can be further estimated. The actual service life of the submarine cable can be evaluated, avoiding the waste of resources caused by relying entirely on the fixed service life of the submarine cable, while reducing operation and maintenance costs and realizing real-time monitoring of the fatigue damage status of the submarine cable.

[0049] Optionally, the quantization criteria include: in phase change At that time, the corresponding numerical value in radians is 256.

[0050] Optionally, the oscillation frequency band is 0.1Hz-20Hz, the set time is one day, and the total time period is one year.

[0051] Secondly, this application provides a calculation system for fatigue damage caused by scour of submarine cables in the landing section of a pile foundation, which adopts the following technical solution:

[0052] A method, system, and storage medium for calculating fatigue damage from scour of submarine cables in the landing section of a pile foundation are disclosed, including a processor in which the steps of the method for calculating fatigue damage from scour of submarine cables in the landing section of a pile foundation as described above are executed.

[0053] Thirdly, this application provides a storage medium, which adopts the following technical solution:

[0054] A storage medium storing a program, which, when executed by a processor, implements the steps of the above-mentioned method for calculating the fatigue damage of submarine cables during pile foundation landing.

[0055] In summary, this application includes at least one of the following beneficial technical effects: It utilizes a distributed optical fiber acoustic wave detection device to achieve kilometer-level continuous monitoring, acquiring phase change data of the optical fiber inside the submarine cable during scouring. Supplemented by corresponding data processing and analysis algorithms, it extracts various parameters suitable for fatigue assessment. Finally, through analysis, it achieves fatigue assessment and life prediction of the submarine cable in the pile foundation landing section, enabling long-term online real-time assessment, reducing costs, and providing reliable early warning. It cleverly combines finite element analysis technology with distributed acoustic wave sensing technology, establishing a dynamic stress mapping relationship between the optical fiber and armored steel wire through finite element analysis, proposing a model with energy value as the core parameter for damage assessment, and introducing environmental parameter statistics to improve the accuracy of life prediction. This makes it more valuable for engineering applications in long-term health monitoring scenarios. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the method for calculating the fatigue damage caused by scouring of submarine cables in the landing section of the pile foundation.

[0057] Figure 2 This is a schematic diagram of the simulation results of the internal structure of a 10-meter suspended section of the submarine cable. Detailed Implementation

[0058] The embodiments of this application are described in detail below, and examples of the embodiments are shown in the accompanying drawings.

[0059] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with an embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] This application discloses a method for calculating fatigue damage caused by scour of submarine cables in the landing section of a pile foundation, referring to... Figure 1 It includes the following steps:

[0061] Step 1: Obtain the dynamic phase change of optical fibers inside the submarine cable under scouring effect using a distributed optical fiber acoustic detection device. Energy value is extracted by the relationship between energy value and phase change. Distributed optical fiber acoustic wave detection equipment (DAS) is a new type of monitoring device based on optical fiber sensing technology. It achieves long-distance, distributed acoustic wave and vibration detection through optical fibers. DAS utilizes the Rayleigh scattering effect when laser light propagates in optical fibers. By analyzing the phase changes of the scattered light, it reconstructs the vibration signals at various points along the path, essentially transforming the optical fiber into countless virtual sensors. DAS features wide coverage, high sensitivity, real-time response, and strong anti-interference capabilities, and can reuse existing communication optical fibers to reduce costs. It is widely used in oil and gas pipeline monitoring, earthquake early warning, perimeter security, and traffic facility inspection, and can identify signals such as leaks, intrusions, and geological activity. With technological advancements, it is evolving towards higher resolution, longer distances, and multi-parameter fusion, becoming a crucial technological support for large-scale dynamic monitoring. Step 1 also includes the following sub-steps:

[0062] Sub-step 1: Obtain the phase change caused by fiber strain at the monitoring point based on the DAS system. Since the fiber optic energy value is essentially the average of the squares of the actual phases at each monitoring point, the square root of this value is used as the submarine cable's energy value to reduce variability. In this example, 2000 monitoring points are distributed every 10km, accumulating 1024 pulses transmitted. Therefore, the energy value formula in this example is: [Energy Value] ;in, For the first fiber optic cable The monitoring point at the 1st The actual phase under each pulse.

[0063] Step 2: Use the Welch method, i.e., the power spectrum estimation method, to extract the principal vibration frequency of the submarine cable oscillation. The Welch method is a classic signal processing technique for estimating the power spectral density (PSD) of random signals. Proposed by American statistician Peter Welch in 1967, it is an improvement on the traditional periodogram method. By reducing the variance of the spectral estimation, it improves the stability and accuracy of power spectral estimation, becoming one of the most widely used methods in modern spectral analysis. Step 2 also includes the following sub-steps:

[0064] Sub-step 21: Fatigue damage in submarine cables is mostly concentrated in stress concentration areas. The flared end of the submarine cable is a high-incidence area for fatigue cracks due to structural abrupt changes. Furthermore, data monitoring at the flared end of the submarine cable is more stable. Therefore, the vibration frequency at the flared end is used instead of the overall vibration frequency of the submarine cable.

[0065] Sub-step 22: Acquire phase data at the cable funnel opening using the DAS system. sampling frequency The DAS system uses a sampling interval of 0.1ms and a data acquisition duration of T=1 second. Therefore, the total number of data points acquired is... .

[0066] Sub-step 23: Phase data at the horn opening A Butterworth filter was used to remove high-frequency noise, retaining the 0.1Hz-20Hz oscillation frequency band as the core frequency of the submarine cable oscillation, and the filtered data was obtained. .

[0067] Sub-step 24: Process the filtered phase data Using the Welch method, Divide the data into segments, where data points can overlap between adjacent segments, and calculate PSD(f): ;

[0068] Among them, the number of segments =19, take the largest integer not greater than the value in parentheses, adjust the segment length L=1000, the total number of data points N=10000, and the overlap length between adjacent segments O=500, thus calculating K=19; L is the segment length, N is the total number of data points, and O is the overlap length between adjacent segments. This indicates rounding down. For the window function normalization factor, For the first Phase data of the segment; Here, is the window function, and FFT is the Fast Fourier Transform. When the Hanning window is used in the Welch method, its core function is to reduce spectral leakage caused by signal segmentation, and at the same time, it further optimizes the stability of power spectrum estimation in conjunction with segmented averaging.

[0069] Step 3: Establish the mapping relationship between the equivalent stress amplitude of the optical fiber and the equivalent stress amplitude of the armor. Step 3 also includes the following sub-steps:

[0070] Sub-step 31: Use finite element software such as Abaqus to model different suspended sections of the submarine cable. Set the suspension height of different suspended sections of the submarine cable to be the same, with the suspended section of the submarine cable set to 10 meters and the suspension height set to 4 meters.

[0071] Sub-step 32: Based on simulation software, obtain the asymmetric cyclic stress data of armored steel wires and internal optical fibers of submarine cables in different suspended sections under different seawater flow velocities. In this example, seawater flow velocity values ​​between 0.2 m / s and 0.5 m / s are selected for software simulation, and the direction of seawater flow is also considered.

[0072] Sub-step 33: Based on the Goodman linear model This transforms asymmetric cyclic stress into equivalent symmetric cyclic stress, where... The stress amplitude is equivalent to a symmetrical cycle. The stress amplitude for asymmetric cycles, The average stress of the asymmetric cycle, This represents the tensile strength of the material. In this example, the tensile strength of the armored steel wire is 345 MPa.

[0073] Sub-step 34: Based on the equivalent symmetrical cycle stress amplitude data of the armored steel wire and optical fiber under different seawater flow velocities, the equivalent symmetrical cycle stress amplitude of the armored steel wire and optical fiber of the 10-meter suspended section of the submarine cable at a suspension height of 4 meters is shown in Table 1:

[0074]

[0075] Table 1 Equivalent stress amplitude conversion between armored steel wire and optical fiber

[0076] The equivalent stress amplitude of the optical fiber was established based on the data in Table 1. Equivalent force amplitude of armor The linear mapping relationship between them is: .

[0077] Step 4: Process the stress amplitude, energy value, and submarine cable vibration frequency to obtain the relationship between the energy value, the equivalent stress amplitude of the armored steel wire, and the submarine cable vibration frequency. Step 4 also includes the following sub-steps:

[0078] Sub-step 41: Assuming the optical fiber is subjected to symmetrical cyclic alternating stress, determine the equivalent stress amplitude of the optical fiber as the maximum stress value. .

[0079] Sub-step 42: Using Hooke's Law Obtain the maximum strain of the optical fiber In this example .

[0080] Sub-step 43: Based on the formula relating phase change and strain: .

[0081] Maximum dependent variable Convert to phase change ,in , , , These represent the effective refractive index of the optical fiber, the coefficient of refractive index variation with strain, the total length of the optical fiber, and the wavelength. In this example, we take... , , , Calculate the phase change. .

[0082] Sub-step 44: Sampling rate and submarine cable vibration frequency based on DAS system Calculate the number of samplings required for the submarine cable to complete one-quarter of a vibration. The sampling rate is 10kHz, which means sampling once every 0.1ms.

[0083] Sub-step 45: Assuming the phase of the submarine cable vibrates approximately uniformly within 1 / 4 of its cycle, the phase change amount... Divide by the number of samples Calculate the phase change for each sample. .

[0084] Sub-step 46: Based on the submarine cable energy value and the quantification standard of the DAS system, derive and establish the energy value. Equivalent force amplitude of armored steel wire submarine cable vibration frequency A model of the energy relationship among the three: The energy value of the submarine cable is determined by taking the square root of the mean square of the phase change. The quantization standard for the DAS system is based on the phase change... The hourly radian corresponds to a numerical value of 256.

[0085] Step 5: Establish an environmental coupled lifetime model for the submarine cable based on the energy relationship model and the linear cumulative damage theory. It should be noted that wind speed is used as the environmental parameter in this example. Step 5 also includes the following sub-steps:

[0086] Sub-step 51: Establish a simplified structural model of the submarine cable. The simplified structure and material properties of the submarine cable are shown in Table 2.

[0087]

[0088] Table 2 Simplified Structure and Material Properties of Submarine Cables

[0089] The outermost layer of the submarine cable is a PP outer sheath, followed by a steel wire armor layer. As it is a three-core submarine cable, it contains three copper conductors and three optical fibers, with the remaining portion being a filler layer. Abaqus was used to simulate a 10-meter suspended section of the submarine cable, with the suspension height set to 2.4 meters. The final simulation results are as follows: Figure 2 As shown in the figure, the results indicate that the nodal stress at the armored steel wire is the greatest, which is the decisive factor affecting the life of the submarine cable. The fatigue life of the armored steel wire is used as the evaluation index of the life of the submarine cable.

[0090] Sub-step 52: Establish the stress-life curve model of the armored steel wire. ,in, In order to achieve the equivalent stress amplitude The fatigue life under the action is the number of cycles, which is set in this example. , , And determine its fatigue limit. .

[0091] Sub-step 53: Based on step 1, obtain the vibration frequency experienced by the armored steel wires of the submarine cable at the current wind speed. The energy values ​​are obtained from the left and right bell-shaped openings of the wind turbines at a wind speed of 7 m / s using the DAS system, and combined with the energy values. Equivalent force amplitude of armored steel wire submarine cable vibration frequency The relationship model among the three factors calculates the equivalent stress amplitude experienced by the armored steel wires of the submarine cable at the current wind speed. The equivalent stress amplitude data of the armored steel wires of the submarine cable at the left and right flare ends under a wind speed of 7 m / s are shown in Tables 3 and 4:

[0092]

[0093] Table 3. Equivalent stress amplitude of the armored steel wire of the submarine cable at the left flare end under a wind speed of 7 m / s.

[0094]

[0095] Table 4. Equivalent stress amplitude of the armored steel wire of the submarine cable at the right flare end under a wind speed of 7 m / s.

[0096] Sub-step 54: If If the cable armor steel wire layer is considered to have suffered irreversible damage, calculate the number of cycles the armor steel wire can withstand at the current wind speed. .

[0097] Sub-step 55: Calculate the number of fatigue-damaging vibrations experienced by the submarine cable in a day at the current wind speed: .in, This indicates the average duration (in seconds) of wind speed reaching that level within one day.

[0098] Sub-step 56: Calculate the total damage life (in days) of the armored steel wire at the current wind speed: Taking fan #6 as an example, at a wind speed of 7 m / s, the equivalent stress amplitude is... The submarine cable at the right-side flared section suffered fatigue damage, with a vibration frequency of 4.88 Hz. Wind speed observations from May 27th to 28th, 2024, showed that the wind speed only reached 7 m / s at 17:00 on May 27th. Since wind speed data was collected every 3 hours, assuming the wind speed reached 7 m / s for the following three hours, the average daily wind speed reached 7 m / s for 1 hour. Therefore, the average duration of this wind speed within a day is 1 hour. Substituting this into the formula for the total damage life of the armored steel wire, the right-side suspended section of the submarine cable can withstand a wind speed of 7 m / s for approximately 1793 days.

[0099] Sub-step 57: Establish a system to push the submarine cable past its fatigue limit within a year. Collection of different wind speed durations (hours) ,in, Wind speed The annual duration of wind speeds is such that some submarine cables will exceed their fatigue limit at 7 m / s. Assuming that the fatigue limit is exceeded when the wind speed is greater than 7 m / s, meteorological data for Lübei Township from June 1, 2023 to June 1, 2024 were exported from a meteorological website. The duration of wind speeds of 7 m / s and above in a year can be obtained in Table 5.

[0100]

[0101] Table 5. Statistical results of the duration of wind speeds of 7 m / s and above throughout the year.

[0102] Sub-step 58: Establish different wind speeds from step 6 The following fatigue life (hours) set , of which elements Wind speed The fatigue life is below, Wind speed The total damage life (days) of the underarmored steel wire, of which: .

[0103] Taking pile foundation No. 6 as an example, its fatigue life statistics under different wind speeds are shown in Table 6:

[0104]

[0105] Table 6. Fatigue life statistics of submarine cable for pile #6

[0106] Sub-step 59: Based on the linear cumulative damage theory, sum the cumulative damage values ​​of the submarine cable armor steel wires. Calculate the lifespan (in years) of the submarine cable: .

[0107] Taking pile foundation No. 6 as an example, its lifespan is calculated to be 27.55 years according to the submarine cable lifespan formula. This value meets the expected lifespan of submarine cables in actual engineering and has certain reference significance.

[0108] This application also discloses a system for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section, including a processor, wherein the processor executes the steps of the method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section as described in any of the above embodiments.

[0109] This application also discloses a storage medium storing a program, which, when executed by a processor, implements the steps of the above-described method for calculating the fatigue damage of submarine cables during pile foundation landing sections.

[0110] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for calculating fatigue damage caused by scour of submarine cables in the landing section of a pile foundation, characterized in that, Includes the following steps: Phase changes of optical fibers inside submarine cables under scouring conditions Where t is a time variable, representing the dynamic change of phase over time, the energy value of the submarine cable is extracted through a phase correspondence algorithm between energy value and phase change. ; The main vibration frequency of the submarine cable oscillation was extracted using the power spectrum estimation method. ; Establish the mapping relationship between the equivalent stress amplitude of optical fiber and the equivalent stress amplitude of armor; Data processing was performed on the equivalent stress amplitude of the optical fiber, the swing energy value of the submarine cable, and the vibration frequency of the submarine cable to obtain the relationship between the energy value, the equivalent stress amplitude of the armored steel wire, and the vibration frequency of the submarine cable. Based on the relationship among the three factors and combined with the linear cumulative damage theory, an environmental coupled lifetime model for submarine cables is established: ;in, For time variables, For environmental parameter serial numbers, For the first Duration of class environment parameters For the first Fatigue life of armored steel wire under similar environmental parameters, wind speed For the first Wind speed level parameters, ocean currents For the first Seawater current velocity level parameters, This is the stress influence coefficient corresponding to the seawater flow velocity; Establish a stress-life curve model for armored steel wire ,in, In order to achieve the equivalent stress amplitude The fatigue life under load is determined by the fatigue performance parameters of the armored steel wire, where a is the fatigue life constant and m is the fatigue strength exponent. The fatigue limit is then determined. ; Obtain the energy value and vibration frequency of the armored steel wires of the submarine cable under corresponding wind speed and seawater current speed. The equivalent stress amplitude of the armored steel wires of the submarine cable was calculated using an energy relationship model. ; like This indicates that the armor steel wire layer of the submarine cable has suffered irreversible damage. Calculate the number of cycles the armor steel wire can withstand under the current environmental parameters. ; Calculate the number of fatigue-damage vibrations experienced by the submarine cable within a preset time period under conditions corresponding to wind speed and seawater current velocity. ; in, This indicates the duration during which the wind speed or seawater current speed reaches the preset set speed within a set time period; Calculate the total damage life of the armored steel wire under the corresponding wind speed and seawater flow velocity: ; Establish a set of wind speeds or seawater current velocities within a preset total time period that allow the submarine cable to exceed its fatigue limit σ-1. ,in, For wind speed or seawater current speed to reach Duration; Wind speed or seawater current speed reaches Fatigue life set of submarine cables , where element For wind speed or seawater current speed to reach The fatigue life is below, Environmental parameters The total damage life of the lower armored steel wire, of which: ; Based on the linear cumulative damage algorithm, the sum of the cumulative damage values ​​of the armored steel wires of the submarine cable is: Calculate the lifespan of the submarine cable: .

2. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 1, characterized in that, The method also includes the following steps: Acquire the phase change caused by fiber strain at the monitoring point The energy value of the optical fiber is obtained using an energy phase correspondence algorithm, and the square root of the optical fiber energy value is used as the energy value of the submarine cable. .

3. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 2, characterized in that, The method also includes the following steps: The vibration frequency at the flared end of the submarine cable is used as the vibration frequency of the submarine cable. Acquire phase data at the horn mouth sampling frequency Collection time If the time is seconds, then the total number of data points collected is... ; Phase data at the horn mouth A low-pass filter is used to remove high-frequency noise while retaining a preset oscillation frequency band, resulting in filtered phase data. ; Filtered phase data Using the power spectrum estimation method, Segment the data and calculate the power spectral density PSD(f): ;in, Let L be the number of segments, N be the segment length, and O be the total number of data points. This indicates rounding down. For the window function normalization factor, For the first Phase data of the segment, is the window function, and FFT is the Fast Fourier Transform algorithm; Find the frequency point in PSD(f) where the amplitude is the largest. , which serves as the main vibration frequency of the submarine cable's oscillation; Let be the frequency value at the k-th frequency point.

4. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 3, characterized in that, The method also includes the following steps: Model the submarine cable with different suspended sections, and set the suspension height of the submarine cable with different suspended sections to be the same; To obtain asymmetric cyclic stress data of armored steel wires and internal optical fibers of submarine cables in different suspended sections under different seawater flow velocities; Based on the Goodman linear model: This transforms asymmetric cyclic stress into equivalent symmetric cyclic stress, where... The stress amplitude is equivalent to a symmetrical cycle. The stress amplitude for asymmetric cycles, The average stress of the asymmetric cycle, The tensile strength of the material; Based on the equivalent symmetrical cyclic stress amplitudes of the armored steel wire and optical fiber under different seawater flow velocities, the equivalent stress amplitude of the optical fiber is established. Equivalent force amplitude of armor Linear mapping relationship between , where a and b are fitting coefficients related to the suspended length of the submarine cable.

5. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 4, characterized in that, The method also includes the following steps: Based on the fact that the optical fiber is subjected to symmetrical cyclic alternating stress, the equivalent stress amplitude of the optical fiber is determined as the maximum stress value. ; through Hooke's Law Obtain the maximum strain of the optical fiber ; According to the formula relating phase change and strain: ; Maximum dependent variable Convert to phase change ,in, , , , These are the effective refractive index of the optical fiber, the coefficient of refractive index variation with strain, the total length of the optical fiber, and the wavelength. Based on the sampling rate and submarine cable vibration frequency. Calculate the number of samplings required for the submarine cable to complete one-quarter of a vibration. ; Assuming the phase of the submarine cable vibrates approximately uniformly within 1 / 4 of its cycle, the phase change amount... Divide by the number of samples Calculate the phase change for each sample. ; Based on the submarine cable energy value and the preset quantitative standards for data acquisition, an energy value system is established. Equivalent force amplitude of armored steel wire submarine cable vibration frequency A model of the energy relationship among the three: ; This is the equivalent vibration energy value of the submarine cable, used to quantify the cumulative energy generated during the cable's oscillation. in, According to the mapping relationship get.

6. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 5, characterized in that, Quantization criteria include: in phase change At that time, the numerical value corresponding to radians is 256.

7. The method for calculating fatigue damage caused by scour of submarine cables in the pile foundation landing section according to claim 6, characterized in that, The oscillation frequency range is 0.1Hz-20Hz, the set time is one day, and the total time period is one year.

8. A calculation system for fatigue damage caused by scour of submarine cables in the landing section of a pile foundation, characterized in that, The device includes a processor that performs the steps of the method for calculating the fatigue damage of submarine cable scour in the pile foundation landing section as described in any one of claims 1-7.

9. A storage medium, characterized in that, The storage medium stores a program, which, when executed by a processor, implements the steps of the method for calculating the fatigue damage of submarine cable scour in the pile foundation landing section as described in any one of claims 1-7.

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