A method and device for predicting submarine cable burial depth based on multi-source data fusion

Abstract

The present invention discloses a method and device for predicting the buried depth of a submarine cable based on multi-source data fusion. The method comprises: constructing a finite element model of a submarine cable, and performing a temperature field analysis of the submarine cable based on the finite element method; analyzing the influence of the current carrying capacity and the buried depth of the submarine cable on the cable core temperature, and analyzing the influence of the ambient temperature and the buried depth of the submarine cable on the cable core temperature; constructing a general formula of a third relationship equation of current carrying capacity, ambient temperature, buried depth and cable core temperature; substituting the cable core temperature, ambient temperature and current carrying capacity of the known submarine cable into the third relationship equation, and obtaining the buried depth of the submarine cable. The method uses finite element simulation to fit the general formula of the relationship equation between the buried depth of the submarine cable and the cable core temperature, soil temperature and current carrying capacity. It is achieved that the purpose of monitoring the buried depth of the entire submarine cable can be achieved by real-time monitoring of the cable core temperature, ambient temperature and current carrying capacity of the submarine cable without the aid of external hardware equipment.

Description

Technical Field

[0001] The present invention relates to the field of submarine cable burial depth monitoring, and in particular to a method and device for predicting submarine cable burial depth based on multi-source data fusion, and specifically to predicting submarine cable burial depth by using multi-source data such as submarine cable core temperature, ambient temperature and current carrying capacity. Background Art

[0002] With the acceleration of the development of marine renewable energy and island development, the role of submarine cables is becoming increasingly important. Submarine cables are transmission lines that transmit electricity between islands or between islands and the mainland. In long-distance submarine cable transmission projects, the laying methods of submarine cables vary with the changes in the environment, mainly including burying, laying and pipe laying.

[0003] For submarine cables buried under the seabed, the depth of their burial will be affected by factors such as meteorological disasters, hydrology, geological movements, and human activities. When the submarine cable is buried too deep, the probability of external damage to the submarine cable increases greatly, such as seawater erosion, marine animal bites, and anchor damage; when the submarine cable is buried too deep, the decrease in the heat dissipation capacity of the environment will lead to a decrease in the ultimate load capacity of the submarine cable, and when the submarine cable is abnormal or fails, it will block maintenance work and deployment, further increasing the risk of accidents and losses. Therefore, understanding the actual burial depth of the submarine cable can not only effectively prevent the submarine cable from being damaged by the outside, but also ensure the normal operation of the submarine cable.

[0004] In the actual laying of submarine cables, they are generally buried 0.3 to 2.5 meters below the seabed. At present, the detection of submarine cable burial depth mainly relies on external hardware equipment. The commonly used external instruments mainly include: pipeline detectors, ocean magnetometers, side-scan sonars and underwater ROV integrated equipment.

[0005] In the related technologies, Document 1: Huang Chunhui. Submarine power cable detection method and practical application [J]. Electric Power Technology, 2010, 19(Z3): 20-26 points out that although the ocean detector can detect the buried depth of submarine cables, the detection accuracy needs to be improved, and it is not suitable for power cable buried depth detection in some special environments. Document 2: Pei Yanliang, Liang Ruicai, Zheng Yanpeng, et al. Magnetic detection method and practice of submarine cables [J]. Progress in Geophysics, 2012, 27(05): 2226-2232 points out that although the ocean magnetometer is not affected by the buried state of the submarine cable, when the magnetometer is dragged more than 10m from the seabed, the magnetometer cannot detect the magnetic field of the submarine cable, and its detection range is limited by the water depth. Reference 3: Zhao Jianhu, Wang Aixue, Guo Jun. Research on the method of fusion of multi-beam and side-scan sonar image block information [J]. Journal of Wuhan University (Information Science Edition), 2013, 38(03): 287-290. High-resolution seabed topography images can be obtained by towing side-scan sonar, but the position accuracy is poor, and it cannot detect the position information of submarine cables laid in the seabed. Reference 4: Xu Pengfei, Hu Zhen, Cui Weicheng, et al. Application of optical vision in underwater pipeline inspection [J]. China Shipbuilding, 2010, 51(03): 91-100. The submarine cable images detected by underwater ROV integrated equipment are clearer, but manual operation is required, and the inspection task is lengthy and easily affected by the underwater environment.

[0006] In summary, the existing external detection methods have problems such as high labor costs and long detection time periods, and the detection effect is also limited by various factors, so it is impossible to effectively monitor the changes in the buried depth of submarine cables in the long term. Summary of the invention

[0007] The purpose of the present invention is to provide a method and device for predicting the buried depth of submarine cables based on multi-source data fusion, which can predict the buried depth of submarine cables by using multi-source data such as the temperature of submarine cable core, ambient temperature and current carrying capacity, thereby solving various problems in submarine cable buried depth monitoring, such as high labor cost, long time period and lengthy inspection tasks.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] In a first aspect, an embodiment of the present invention provides a method for predicting the buried depth of a submarine cable based on multi-source data fusion, comprising the following steps:

[0010] Construct a finite element model of the submarine cable and conduct temperature field analysis of the submarine cable based on the finite element method;

[0011] Analyze the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature, and construct a general formula of the first relationship equation of three variables;

[0012] Analyze the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature, and construct a general formula of the second relational equation of three variables;

[0013] According to the first general formula of the relational equation and the second general formula of the relational equation, construct a third general formula of the relational equation of current carrying capacity, ambient temperature, burial depth and cable core temperature;

[0014] According to the general formula of the third relationship equation, the cable core temperature, ambient temperature and current carrying capacity of the known submarine cable are substituted to obtain the buried depth of the submarine cable.

[0015] Furthermore, a finite element model of the submarine cable is constructed, and the temperature field analysis of the submarine cable based on the finite element method is performed, including:

[0016] The structural layers with similar thermal conductivity and contacting each other in the submarine cable are merged and simplified to construct the finite element model of the submarine cable;

[0017] The boundary distances around the submarine cable are all set to preset distances to construct boundary conditions;

[0018] Dense grid division is performed on the temperature field area within a preset range of the submarine cable and its vicinity, and relatively coarse grid division is performed on the temperature field area outside the preset range to realize integral calculation of the finite element method.

[0019] Furthermore, the boundary distances around the submarine cable are all set to preset distances, and boundary conditions are constructed, including:

[0020] The deep soil temperature at the lower boundary of the submarine cable is set to a fixed value as a first-class boundary condition;

[0021] The temperature gradient in the horizontal direction of the submarine cable is approximately 0, that is, the normal heat flux density of the left and right boundaries is 0, and the left and right boundaries are set as the second type of boundary conditions;

[0022] There is solid-liquid convection heat exchange between the soil and seawater at the upper boundary of the submarine cable, and the upper boundary is set as a third-type boundary condition.

[0023] Furthermore, the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature is analyzed, and a general formula of the first relational equation of three variables is constructed; including:

[0024] The ambient temperature, the convection heat transfer coefficient between soil and seawater, and the thermal conductivity of soil are set, and multiple sets of rated current carrying capacity with different data are applied to the submarine cable. Experiments are also conducted at multiple sets of different burial depths to obtain multiple sets of corresponding cable core temperatures.

[0025] Perform curve fitting on multiple sets of different data of rated current carrying capacity, corresponding to multiple sets of different burial depths, and corresponding multiple sets of cable core temperatures;

[0026] The cable core temperature and burial depth under different current carrying capacity are nonlinearly fitted by the least square method, and a plurality of first relational expressions between the cable core temperature and burial depth under the same ambient temperature and different current carrying capacity are obtained;

[0027] The first relational expression is a logarithmic function, including a bending coefficient and a mean coefficient; extracting two coefficients from all the first relational expressions, and constructing a relationship between the two coefficients and the current carrying capacity;

[0028] The least square method is used to perform nonlinear fitting on the bending coefficient and the current carrying capacity percentage, and the mean coefficient and the current carrying capacity percentage, and two second relationship equations are obtained;

[0029] Based on a plurality of the first relational expressions and two of the second relational expressions, a general formula of a first relational equation for three variables, namely, current carrying capacity, burial depth and cable core temperature, is constructed.

[0030] Furthermore, the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature is analyzed, and a general formula of a second relational equation of three variables is constructed; including:

[0031] The convection heat transfer coefficient between soil and seawater and the thermal conductivity of soil were set, 100% of the rated current was applied to the submarine cable, and experiments were conducted at multiple different ambient temperatures and different burial depths to obtain multiple corresponding cable core temperatures.

[0032] Perform curve fitting on multiple groups of different ambient temperatures, different burial depths and corresponding multiple groups of cable core temperatures;

[0033] The cable core temperature and burial depth under different ambient temperatures are nonlinearly fitted by the least square method, and multiple third relational equations between the cable core temperature and burial depth under the same current carrying capacity and different ambient temperatures are obtained;

[0034] The third relational expression is a logarithmic function, including a bending coefficient and a mean coefficient; according to the influence of ambient temperature on the mean coefficient and multiple third relational expressions, a general formula of the second relational equation of three variables, ambient temperature, burial depth and cable core temperature, is constructed.

[0035] Furthermore, the third relationship equation is generally expressed as:

[0036]

[0037] In the formula, D represents the burial depth; T represents the cable core temperature; t represents the ambient temperature; y1 represents the bending coefficient of the plurality of the first relational expressions; y2 represents the mean coefficient of the plurality of the first relational expressions; and e represents a constant.

[0038] In a second aspect, an embodiment of the present invention further provides a submarine cable burial depth prediction device based on multi-source data fusion, comprising:

[0039] Finite element analysis module, used to construct the finite element model of the submarine cable and conduct temperature field analysis of the submarine cable based on the finite element method;

[0040] An analysis and construction module, used for analyzing the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature, and constructing a first general formula of a relational equation of three variables; and used for analyzing the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature, and constructing a second general formula of a relational equation of three variables; and constructing a third general formula of a relational equation of current carrying capacity, ambient temperature, burial depth and cable core temperature according to the first general formula of the relational equation and the second general formula of the relational equation;

[0041] The prediction module is used to substitute the known cable core temperature, ambient temperature and current carrying capacity of the submarine cable into the general formula of the third relationship equation to obtain the buried depth of the submarine cable.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The embodiment of the present invention provides a method for predicting the buried depth of submarine cables based on multi-source data fusion, which is different from the traditional method for monitoring the buried depth of submarine cables. It uses finite element simulation to fit the general equation of the relationship between the buried depth of submarine cables and the cable core temperature, soil temperature, and current carrying capacity. It achieves the purpose of monitoring the buried depth of the entire submarine cable by real-time monitoring of the cable core temperature, ambient temperature, and current carrying capacity without the help of external hardware equipment, and solves the problems of high labor cost, long time period, and lengthy inspection tasks in the monitoring of the buried depth of submarine cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flowchart of a method for predicting submarine cable burial depth based on multi-source data fusion provided by an embodiment of the present invention;

[0045] Figure 2a This is a schematic diagram of the cross-sectional structure of an optical fiber composite submarine cable;

[0046] Figure 2b A simplified schematic diagram of the physical model of submarine cables;

[0047] Figure 2c Schematic diagram of the structural parameters and physical parameters of each layer of the submarine cable contained in Table 1;

[0048] Figure 2d This is a simplified schematic diagram of a submarine cable model laid under the seabed;

[0049] Figure 3aThis is the grid effect diagram of the submarine cable body;

[0050] Figure 3b This is the grid effect diagram of the entire temperature field area;

[0051] Figure 3c Schematic diagram of temperature distribution inside the submarine cable;

[0052] Figure 3d It is a schematic diagram of the overall temperature distribution;

[0053] Figure 4a Schematic diagram of the core temperature parameters of the submarine cable at 10% to 50% of the rated current carrying capacity contained in Table 2;

[0054] Figure 4b Schematic diagram of the structural parameters and physical parameters of each layer of the submarine cable contained in Table 3;

[0055] Figure 4c It is a schematic diagram of the relationship curve between cable core temperature, burial depth and current carrying capacity;

[0056] Figure 5a It is a schematic diagram of the relationship between the bending factor and the current carrying capacity percentage;

[0057] Figure 5b It is a schematic diagram of the relationship curve between the mean coefficient and the current carrying capacity percentage;

[0058] Figure 6a The core temperature of the submarine cable is between 8℃ and 16℃;

[0059] Figure 6b The core temperature of the submarine cable is between 18℃ and 26℃;

[0060] Figure 7 It is a schematic diagram of the relationship curve between the cable core temperature, the burial depth and the ambient temperature;

[0061] Figure 8 It is a schematic diagram of the comparison data between the calculated value and the simulated value of the buried depth of the submarine cable under different operating conditions contained in Table 6;

[0062] Fig. 9 A block diagram of a submarine cable burial depth prediction device based on multi-source data fusion provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0064] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0065] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0066] Reference Figure 1 As shown, the present invention provides a method for predicting the buried depth of a submarine cable based on multi-source data fusion, comprising the following steps:

[0067] S1. Construct a finite element model of the submarine cable and conduct a temperature field analysis of the submarine cable based on the finite element method;

[0068] S2. Analyze the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature, and construct a general formula of the first relational equation of three variables;

[0069] S3, analyzing the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature, and constructing a general formula of a second relational equation of three variables;

[0070] S4. Constructing a third relationship equation formula of current carrying capacity, ambient temperature, burial depth and cable core temperature according to the first relationship equation formula and the second relationship equation formula;

[0071] S5. According to the general formula of the third relationship equation, substitute the known cable core temperature, ambient temperature and current carrying capacity of the submarine cable to obtain the buried depth of the submarine cable.

[0072] The serial numbers of the above steps do not limit the order of executing the steps of this method, but are only for the convenience of clear viewing. This method uses finite element simulation to fit the general equation of the relationship between the buried depth of the submarine cable and the cable core temperature, soil temperature, and current carrying capacity. It is achieved that without the help of external hardware equipment, the purpose of monitoring the buried depth of the entire submarine cable can be achieved by real-time monitoring of the submarine cable core temperature, ambient temperature and current carrying capacity, solving many problems in the monitoring of the buried depth of the submarine cable, such as high labor costs, long time periods, and lengthy inspection tasks.

[0073] The following is a detailed description of each of the above steps:

[0074] (1) Analysis of submarine cable temperature field based on finite element method:

[0075] In step S1, the present invention takes the HYJQF41-F type 35kV XLPE insulated optical fiber composite submarine cable as an example to establish a submarine cable finite element model. The cross-sectional structure of the 35kV high voltage three-core cross-linked polyethylene optical fiber composite submarine cable is as follows: Figure 2a As shown. The structure of the submarine cable is complex. In order to reduce the amount of finite element analysis calculations and the calculation time, without affecting the calculation accuracy, this embodiment merges and simplifies the structural layers in the submarine cable with similar thermal conductivity and in contact with each other. The optical fiber, stainless steel pipe, and steel wire reinforcement are merged and collectively referred to as the optical unit steel pipe; the wrapping tape and the PE outer sheath are merged and collectively referred to as the optical unit sheath; the cable core shielding layer, the XLPE insulation layer, and the insulation shielding layer are merged and collectively referred to as the insulation layer; the wrapping tape and the PP inner cushion layer are merged and collectively referred to as the inner cushion layer; the asphalt and the PP outer sheath are merged and collectively referred to as the outer sheath. The physical model of the submarine cable after the merger and simplification is shown as follows: Figure 2b As shown in Figure 2, the structural parameters and physical parameters of each layer of the submarine cable are as follows: Figure 2c As shown in Table 1.

[0076] In order to meet the actual situation as much as possible, the submarine cable is laid at a preset distance under the seabed, such as a depth of about 2m. Since the impact of the submarine cable on the surrounding environment is limited, the boundary distance around the submarine cable in the simulation is taken as 2m. Figure 2d shown.

[0077] The deep soil temperature at the lower boundary is a fixed value and is set as the first type of boundary condition; the horizontal temperature gradient is approximately 0, that is, the normal heat flux density of the left and right boundaries is 0, so the left and right boundaries are set as the second type of boundary conditions; there is convective heat exchange between solid and liquid between the upper boundary soil and seawater, so the upper boundary is set as the third type of boundary condition. The integral calculation of the finite element method is performed in each grid unit. The higher the grid density, the more accurate the calculation, but it will increase the calculation time. Since the submarine cable and its surrounding areas are the key analysis areas, dense grid division is performed, while relatively coarse grid division is performed for areas farther away to ensure that the calculation accuracy is improved without increasing the number of units and nodes. The grid division of the submarine cable body is as follows: Figure 3a As shown in Figure 2, the grid division of the entire temperature field area is as follows: Figure 3b shown.

[0078] The rated current carrying capacity of the submarine cable is 585A. The seawater temperature in August is 26℃. The deep soil temperature is considered to be approximately equal to the seawater temperature and is taken as the ambient temperature. The convection heat transfer coefficient between soil and seawater is 600W / m2·℃, the soil thermal conductivity is 1.5W / m·℃, and the submarine cable is buried at a depth of 2m. Finite element simulation is performed to obtain the temperature distribution results in the submarine cable. Figure 3c The overall temperature distribution results are shown in Figure 3d shown.

[0079] Depend on Figure 3c It can be seen that after the rated current carrying capacity is applied to the three-core submarine cable model, the final temperature of the submarine cable core is 89.79°C, which is only 0.21°C different from the maximum operating temperature of the copper cable core. In the modeling process, in order to improve the calculation efficiency, this embodiment reasonably simplifies the three-core submarine cable model and the external environment. Therefore, errors are inevitable in the simulation process, but they are within an acceptable range, and the steady-state solution results also prove the correctness of the model built by the present invention.

[0080] (2) The influence of current carrying capacity and burial depth on cable core temperature:

[0081] In step S2, the current carrying capacity is one of the important factors affecting the temperature change of the submarine cable core, and the temperature of the submarine cable core will also vary greatly under the same current carrying capacity and different burial depths, so here we will first discuss the influence of current carrying capacity and burial depth on the cable core temperature. Set the ambient temperature to 26°C, the convection heat transfer coefficient between soil and seawater to 600W / m2·℃, and the thermal conductivity of soil to 1.5W / m·℃. Apply 10% to 100% of the rated current carrying capacity to the three-core submarine cable, and gradually reduce the burial depth from 2m to 0.2m at 0.2m / time. The final temperature data of the submarine cable core is as follows: Figure 4a Table 2 and Figure 4b As shown in Table 3.

[0082] according to Figure 4a Table 2 and Figure 4b The data in Table 3 are fitted to obtain the relationship curve between the cable core temperature, burial depth and current carrying capacity, as shown in Figure 4c shown.

[0083] Depend on Figure 4c It can be obtained that, when the burial depth remains unchanged, the cable core temperature of the submarine cable increases with the increase of the current carrying capacity; when the current carrying capacity remains unchanged, the cable core temperature of the submarine cable increases with the increase of the burial depth. The least square method is used to perform nonlinear fitting on the cable core temperature and burial depth under different current carrying capacities, and the relationship between the cable core temperature and burial depth under the same ambient temperature and different current carrying capacities (multiple first relationship) is obtained.

[0084] T 100％ =8.817lnD+83.939 (2-1)

[0085] T 90％ =7.145lnD+72.943 (2-2)

[0086] T 80％ =5.645lnD+63.104 (2-3)

[0087] T 70％ =4.3254lnD+54.424 (2-4)

[0088] T 60％ =3.1819lnD+46.9 (2-5)

[0089] T 50％ =2.211lnD+40.534 (2-6)

[0090] T 40％ =1.4205lnD+35.325 (2-7)

[0091] T 30％ =0.8015lnD+31.274 (2-8)

[0092] T 20％ =0.3637lnD+28.381 (2-9)

[0093] T 10％ =0.0999lnD+26.644 (2-10)

[0094] Where, T 100％ 、T 90％ 、T 80％ 、T 70％ 、T 60％ 、T50％ 、T 40％ 、T 30％ 、T 20％ 、T 10％ They are the core temperatures of the submarine cable at 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% and 10% of the rated current carrying capacity respectively; D represents the burial depth of the submarine cable.

[0095] In statistics, when linear regression analysis is performed on variables and the least squares method is used for parameter estimation, the coefficient of determination R 2 It is the ratio of the regression sum of squares to the total deviation sum of squares. The larger the ratio, the better. The more accurate the model is and the more significant the regression effect is. 2 All are greater than 0.99, indicating that the degree of fit is very high and the reliability of the trend line is very high. Since the fitted relationship is a logarithmic function, the logarithmic function has two coefficients, which correspond to the curvature and mean of the curve respectively. Figure 3d It can be seen that as the current carrying capacity changes, the curvature and mean value of the fitting curve also change accordingly, so the curvature coefficient and mean coefficient in the curve relationship will naturally change. Now extract the coefficients of the relationship (2-1) to (2-10) and establish the relationship between the two coefficients and the current carrying capacity. The fitted relationship curve is as follows: Figure 5a and Figure 5b shown.

[0096] Depend on Figure 5a and Figure 5b It can be seen that both the bending coefficient and the mean coefficient increase with the increase of the current carrying capacity percentage. The bending coefficient and the current carrying capacity percentage, the mean coefficient and the current carrying capacity percentage are nonlinearly fitted by the least square method, and the following relationship (two second relationship) is obtained.

[0097] y1=8.8117I 2 -0.0065I+0.0121 (2-11)

[0098] y2=57.873I 2 +0.0003I+26.065 (2-12)

[0099] In the formula, y1 and y2 are the bending coefficient and mean coefficient respectively; is the current carrying capacity percentage of the current entering the submarine cable. The determination coefficient R of the relationship (2-11) to (2-12) 2 All are equal to 1, indicating that the degree of fit is very high and the reliability of the trend line is very high. Combining equations (2-1) to (2-12), a general first relationship equation for the three variables of comprehensive current carrying capacity I, burial depth D and cable core temperature T can be combined as shown below.

[0100] T=y1lnD+y2 (2-13)

[0101] (3) The influence of ambient temperature and burial depth on cable core temperature:

[0102] In step S3, the ambient temperature is also one of the important factors affecting the temperature of the submarine cable core, so here we continue to explore the influence of ambient temperature and burial depth on the cable core temperature. The ambient temperature of the actual sea area where the submarine cable is laid varies with the seasons, ranging from 8°C to 26°C. A total of 10 ambient temperature points of 8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C and 26°C are selected for simulation calculations. Similarly, the convective heat transfer coefficient between soil and seawater is set to 600W / m2·℃600W / m2·℃, the thermal conductivity of the soil is 1.5W / m·℃, and 100% of the rated current is applied to the three-core submarine cable. At the same time, the burial depth is gradually reduced from 2m to 0.2m at 0.2m / time. The final temperature data of the submarine cable core is obtained as follows Figure 6a Table 4 and Figure 6b As shown in Table 5.

[0103] according to Figure 6a Table 4 and Figure 6b The data in Table 5 are fitted to obtain the relationship curve between the cable core temperature, burial depth and ambient temperature, as shown in Figure 7 shown.

[0104] Depend on Figure 7 It can be seen that when the burial depth remains unchanged, the cable core temperature of the submarine cable increases with the increase of the ambient temperature; when the ambient temperature remains unchanged, the cable core temperature of the submarine cable increases with the increase of the burial depth. The least square method is used to perform nonlinear fitting on the cable core temperature and burial depth at different ambient temperatures, and multiple third relationship equations between the cable core temperature and burial depth at the same current carrying capacity and different ambient temperatures are obtained.

[0105] T 26 =8.817lnD+83.939 (3-1)

[0106] T 24 =8.817lnD+81.939 (3-2)

[0107] T 22 =8.817lnD+79.939 (3-3)

[0108] T 20 =8.817lnD+77.939 (3-4)

[0109] T 18 =8.817lnD+75.939 (3-5)

[0110] T 16 =8.817lnD+73.939 (3-6)

[0111] T 14 =8.817lnD+71.939 (3-7)

[0112] T 12 =8.817lnD+69.939 (3-8)

[0113] T 10 =8.817lnD+67.939 (3-9)

[0114] T8=8.817lnD+65.939 (3-10)

[0115] Where, T 26 、T 24 、T 22 、T 20 、T 18 、T 16 、T 14 、T 12 、T 10 , T8 are the cable core temperatures at 26℃, 24℃, 22℃, 20℃, 18℃, 16℃, 14℃, 12℃, 18℃, and 8℃ respectively; D is the buried depth of the cable. The determination coefficient R of equations (3-1) to (3-10) 2 All are greater than 0.99, indicating that the degree of fit is very high and the reliability of the trend line is very high. Figure 5b It can be seen that the ambient temperature only affects the mean value of the fitting curve and does not change the curvature of the fitting curve. Similarly, this embodiment can combine a second relationship equation general formula of the three variables of the comprehensive ambient temperature t, the burial depth D and the cable core temperature T as shown below.

[0116] T=8.817lnD+83.939+t-26 (3-11)

[0117] (4) Prediction of submarine cable burial depth based on multi-source data fusion:

[0118] In steps S4 to S5, the core temperature of the submarine cable is affected by two aspects: 1) current carrying capacity; 2) environmental conditions. Environmental conditions include ambient temperature and heat dissipation materials. As a heat source, the submarine cable has limited impact on the surrounding environment. At the beginning, only the soil is responsible for heat dissipation. As the burial depth becomes shallower, the soil and seawater jointly bear the heat dissipation, and the heat dissipation ratio of the soil gradually decreases, while the heat dissipation ratio of seawater gradually increases. Since the heat dissipation of seawater is better than that of soil, even at the same current carrying capacity and the same ambient temperature, the corresponding core temperature of the submarine cable at different burial depths is different. Combining the two parts of the influence of current carrying capacity and burial depth on the core temperature of the submarine cable and the influence of ambient temperature and burial depth on the core temperature of the submarine cable discussed above, the two general equations (2-13) and (3-11) are obtained to integrate a general equation for the comprehensive current carrying capacity I, ambient temperature t, burial depth D and cable core temperature T.

[0119] T=y1lnD+y2+t-26 (4-1)

[0120] This general formula is now transformed to obtain a third relationship equation general formula with the submarine cable burial depth D as the dependent variable and the cable core temperature T, ambient temperature t and current carrying capacity I as the independent variables.

[0121]

[0122] Since submarine cables are laid in an extremely complex marine environment, their operating conditions must be fully considered both in the actual operation process and in the finite element simulation analysis. In addition to the submarine cable burial depth, ambient temperature and current carrying capacity discussed above, the convection heat transfer coefficient between soil and seawater and the thermal conductivity of soil will also affect the cable core temperature of the submarine cable. The analysis is as follows:

[0123] (a) The convective heat transfer coefficient between soil and seawater will affect the speed and amount of heat dissipation from soil to seawater, thereby affecting the cable core temperature and the temperature distribution around the cable. However, in general, the convective heat transfer coefficient between soil and seawater varies in the range of 200 to 1000 W / m2·℃ due to the influence of wind speed and temperature difference, so the impact on the cable core temperature is very small, so an average value of 600 W / m2·℃ can be taken in simulation.

[0124] (b) Although the soil thermal conductivity of the same submarine cable in different sections is different, and the soil thermal conductivity of the same submarine cable at different buried depths in the same section is also different, the variation is very small, so it can be unified as a fixed value of 1.5 W / m·℃ during simulation.

[0125] Now, different operating conditions are imposed on the submarine cable, and the numerical values ​​between the calculated value and the simulated value of the submarine cable burial depth are compared. Figure 8As shown in Table 6, the degree of fit between the general relationship equation (4-2) and the submarine cable simulation situation is analyzed.

[0126] Depend on Figure 8 As shown in Table 6, under various operating conditions, the error between the calculated value and the simulated value of the buried depth of the submarine cable is less than 0.05m, indicating that the general formula of the relationship equation fitted by the embodiment of the present invention is highly consistent with the submarine cable simulation situation, and the general formula of the relationship equation (the third general formula of the relationship equation) can accurately replace the submarine cable simulation situation. Then, when the core temperature, ambient temperature and current carrying capacity of the submarine cable are known, the general formula of the relationship equation can be used to calculate the buried depth of the current submarine cable.

[0127] The accuracy and reliability of the general formula of the relationship equation fitted by the embodiment of the present invention are very high, and it has certain practicality. It provides a theoretical basis for predicting the burial depth of the submarine cable based on the use of distributed optical fiber temperature sensing technology to monitor the temperature of the submarine cable core, combined with many factors such as ambient temperature, current carrying capacity, convective heat transfer coefficient between soil and seawater, and thermal conductivity of soil.

[0128] In the specific implementation, the specific steps are as follows:

[0129] (1) Determine the model of the submarine cable, obtain its structural schematic diagram, structural dimension table and physical parameters of each layer, use ANSYS simulation software to build a finite element model of the submarine cable, set boundary conditions and divide the mesh for the model.

[0130] (2) Apply the rated current carrying capacity to the submarine cable model and set the correct working conditions to obtain the final temperature data of the submarine cable core, which is compared with the maximum working temperature of the copper cable core of 90°C. If the difference between the two is not much, the model is correct.

[0131] (3) A rated current carrying capacity of 10% to 100% was applied to the three-core submarine cable, and the burial depth was gradually reduced from 2 m to 0.2 m at a rate of 0.2 m / time to obtain the final temperature data of the submarine cable core. The least squares method was used to fit the relationship between the cable core temperature and burial depth under the same ambient temperature and different current carrying capacities. Finally, a general formula of the first relationship equation was integrated to integrate the three variables of current carrying capacity, burial depth and cable core temperature.

[0132] (4) Ambient temperature points between 8°C and 26°C were selected for simulation calculation. At the same time, the burial depth was gradually reduced from 2 m to 0.2 m at a rate of 0.2 m / time to obtain the final temperature data of the submarine cable core. The least squares method was used to fit the relationship between the cable core temperature and burial depth at the same current carrying capacity and different ambient temperatures. Finally, a general formula of the second relationship equation was integrated that combined the three variables of ambient temperature, burial depth and cable core temperature.

[0133] (5) Combining the two general formulas of the above integrated relationship equations, we finally get a third general formula of the relationship equation with the cable burial depth as the dependent variable and the cable core temperature, ambient temperature and current carrying capacity as the independent variables. Finally, different operating conditions are applied to the submarine cable, and the numerical values ​​between the calculated value and the simulated value of the cable burial depth are compared to verify the fit and reliability of the general formula of the relationship equation.

[0134] By using finite element simulation, the relationship equation between the buried depth of submarine cables and the cable core temperature, soil temperature and current carrying capacity was fitted. This achieved the purpose of monitoring the buried depth of the entire submarine cable by real-time monitoring of the cable core temperature, ambient temperature and current carrying capacity without the help of external hardware equipment, solving the problems of high labor costs, long time cycles and lengthy inspection tasks in submarine cable buried depth monitoring.

[0135] Based on the same inventive concept, an embodiment of the present invention also provides a submarine cable burial depth prediction device based on multi-source data fusion. Since the principle of the problem solved by the device is similar to the aforementioned submarine cable burial depth prediction method based on multi-source data fusion, the implementation of the device can refer to the implementation of the aforementioned method, and the repeated parts will not be repeated.

[0136] The embodiment of the present invention also provides a submarine cable burial depth prediction device based on multi-source data fusion, referring to Fig. 9 As shown, including:

[0137] Finite element analysis module, used to construct the finite element model of the submarine cable and conduct temperature field analysis of the submarine cable based on the finite element method;

[0138] An analysis and construction module, used for analyzing the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature, and constructing a first general formula of a relational equation of three variables; and used for analyzing the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature, and constructing a second general formula of a relational equation of three variables; and constructing a third general formula of a relational equation of current carrying capacity, ambient temperature, burial depth and cable core temperature according to the first general formula of the relational equation and the second general formula of the relational equation;

[0139] The prediction module is used to substitute the known cable core temperature, ambient temperature and current carrying capacity of the submarine cable into the general formula of the third relationship equation to obtain the buried depth of the submarine cable.

[0140] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for predicting submarine cable burial depth based on multi-source data fusion, characterized in that: The following steps are involved: Construct a finite element model of the submarine cable and conduct temperature field analysis of the submarine cable based on the finite element method; The influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature is analyzed, and the general formula of the first relationship equation of three variables is constructed; including: setting the ambient temperature, the convective heat transfer coefficient between soil and seawater, and the thermal conductivity of soil, applying multiple sets of rated current carrying capacity of different data to the submarine cable, and conducting experiments corresponding to multiple sets of different burial depths to obtain multiple sets of corresponding cable core temperatures; curve fitting is performed on the rated current carrying capacity of multiple sets of different data, the corresponding multiple sets of different burial depths, and the corresponding multiple sets of cable core temperatures; nonlinear fitting is performed on the cable core temperature and burial depth under different current carrying capacity by using the least squares method. Combined, multiple first relationship expressions between the cable core temperature and the buried depth under the same ambient temperature and different current carrying capacity are obtained; the first relationship expression is a logarithmic function, including a bending coefficient and a mean coefficient; extract two coefficients from all the first relationship expressions, and construct the relationship between the two coefficients and the current carrying capacity; use the least squares method to perform nonlinear fitting on the bending coefficient and the current carrying capacity percentage, and the mean coefficient and the current carrying capacity percentage, respectively, to obtain two second relationship expressions; based on multiple first relationship expressions and two second relationship expressions, construct a general formula of the first relationship equation for the three variables of current carrying capacity, burial depth and cable core temperature; The influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature is analyzed, and a general formula of the second relationship equation of three variables is constructed; including: setting the convective heat transfer coefficient between soil and seawater and the thermal conductivity of soil, applying 100% of the rated current carrying capacity to the submarine cable respectively, and conducting experiments corresponding to multiple groups of different ambient temperatures and different burial depths to obtain multiple groups of corresponding cable core temperatures; performing curve fitting on multiple groups of different ambient temperatures, different burial depths and corresponding multiple groups of cable core temperatures; performing nonlinear fitting on the cable core temperature and burial depth under different ambient temperatures by using the least squares method to obtain multiple third relationship equations between the same current carrying capacity, the cable core temperature under different ambient temperatures and the burial depth; the third relationship equation is a logarithmic function, including a bending coefficient and a mean coefficient; according to the influence of ambient temperature on the mean coefficient, and multiple third relationship equations, a general formula of the second relationship equation of three variables of ambient temperature, burial depth and cable core temperature is constructed; According to the first relational equation and the second relational equation, a third relational equation of current carrying capacity, ambient temperature, burial depth and cable core temperature is constructed; the third relational equation is: In the formula, D represents the burial depth; T represents the cable core temperature; t represents the ambient temperature; y1 represents the bending coefficient of the plurality of the first relational expressions; y2 represents the mean coefficient of the plurality of the first relational expressions; e represents a constant; According to the general formula of the third relationship equation, the cable core temperature, ambient temperature and current carrying capacity of the known submarine cable are substituted to obtain the buried depth of the submarine cable.

2. A method for predicting submarine cable burial depth based on multi-source data fusion according to claim 1, characterized in that: Construct a finite element model of the submarine cable and conduct a finite element method-based analysis of the submarine cable temperature field, including: The structural layers with similar thermal conductivity and contacting each other in the submarine cable are merged and simplified to construct the finite element model of the submarine cable; The boundary distances around the submarine cable are all set to preset distances to construct boundary conditions; Dense grid division is performed on the temperature field area within a preset range of the submarine cable and its vicinity, and relatively coarse grid division is performed on the temperature field area outside the preset range to realize integral calculation of the finite element method.

3. The method for predicting submarine cable burial depth based on multi-source data fusion according to claim 2 is characterized in that: The boundary distances around the submarine cable are all set to preset distances, and boundary conditions are constructed, including: The deep soil temperature at the lower boundary of the submarine cable is set to a fixed value as a first-class boundary condition; The temperature gradient in the horizontal direction of the submarine cable is approximately 0, that is, the normal heat flux density of the left and right boundaries is 0, and the left and right boundaries are set as the second type of boundary conditions; There is solid-liquid convection heat exchange between the soil and seawater at the upper boundary of the submarine cable, and the upper boundary is set as a third-type boundary condition.

4. A submarine cable burial depth prediction device based on multi-source data fusion, characterized in that: A method for predicting the buried depth of a submarine cable based on multi-source data fusion as claimed in any one of claims 1 to 3; comprising: Finite element analysis module, used to construct the finite element model of the submarine cable and conduct temperature field analysis of the submarine cable based on the finite element method; An analysis and construction module, used for analyzing the influence of the current carrying capacity and burial depth of the submarine cable on the cable core temperature, and constructing a first general formula of a relational equation of three variables; and used for analyzing the influence of the ambient temperature and burial depth of the submarine cable on the cable core temperature, and constructing a second general formula of a relational equation of three variables; and constructing a third general formula of a relational equation of current carrying capacity, ambient temperature, burial depth and cable core temperature according to the first general formula of the relational equation and the second general formula of the relational equation; The prediction module is used to substitute the known cable core temperature, ambient temperature and current carrying capacity of the submarine cable into the general formula of the third relationship equation to obtain the buried depth of the submarine cable.

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