Protective device for submarine pipeline anti-scour and its size calculation method

Abstract

The present invention discloses a protective device for preventing scouring of submarine pipelines and a method for calculating its size. The device comprises a plurality of protective structures arranged at equal intervals along the axis of the pipeline, the protective structure comprising at least two protective layers fixed together in an upper and lower stacking manner, the bottom protective layer comprising a first geotextile and a plurality of first protective blocks, the bottom protective layer weighing more than the weight of the protective layers of other layers, the other protective layers comprising a second geotextile, a plurality of second protective blocks and a plurality of third protective blocks, the second protective blocks and the third protective blocks differ in at least their height dimensions, the second protective blocks and the third protective blocks being fixed on the second geotextile in an alternating arrangement, the gaps between the protective blocks in the upper and lower protective layers being staggered, the protective structure designed by the present invention can increase the resistance of ocean currents flowing through pipelines in deep sea areas, slow down the flow rate of the water flow when the water flows through the protective structure and form a local backflow vortex, reduce the scouring effect of the water flow and have good silt-promoting ability.

Description

Technical Field

[0001] The present invention relates to the technical field of submarine pipeline scour protection, and in particular to a protective device for submarine pipeline scour protection suitable for deep water and a size calculation method thereof. Background Art

[0002] Subsea pipelines are a crucial component of marine oil and gas transportation equipment. Maintaining their safety is crucial for ensuring the development of marine gas fields and protecting the marine environment. Although currents in deepwater areas are relatively slow, the soft soil in shallow water layers and the presence of numerous uneven seabed areas make deepwater submarine pipelines susceptible to overhangs due to the scouring effects of currents. When currents flow through overhanging pipelines, vortex shedding occurs in the wake. When the frequency of vortex shedding approaches the natural frequency of the pipeline, vortex-induced vibrations (VIVs) can occur, leading to fatigue failure and potentially causing marine oil and gas leaks.

[0003] Existing pipeline scour protection methods mainly include spoiler method, bionic seaweed method, riprap method, and concrete soft drainage method. The spoiler method achieves scour protection by self-burying the pipeline. However, since deepwater areas are mostly soft clay, this method is not suitable for deepwater areas. The bionic seaweed method uses bionic seaweed to slow down the scour of the seabed. This method is time-consuming and expensive to invest in, making it unsuitable for scour protection of deepwater, long-distance submarine pipelines. The riprap method reduces the scour of the seabed soil by covering it with a layer of gravel. However, this method has stone stability issues, and the cost of deepwater riprap increases sharply with increasing water depth. The concrete soft drainage method protects the pipeline through concrete interlocking plates and geotextiles, but the gaps between the concrete blocks are large, and the lower part of the soft drainage will experience secondary scour after silting.

[0004] Therefore, there is an urgent need for a protective device for anti-scouring of submarine pipelines suitable for deep water and a size calculation method thereof to solve the above technical problems. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem that existing submarine pipelines in deep water areas may span under the scouring action of ocean currents, and that spanning pipelines are prone to fatigue damage, while the current pipeline scouring protection methods are not suitable for pipeline scouring protection in deep water areas.

[0006] To this end, in a first aspect, the present invention provides a protective device for preventing scour of a submarine pipeline, comprising a plurality of protective structures arranged at equal intervals along the axial direction of the submarine pipeline, the protective structure comprising at least two protective layers fixed together in an upper and lower stacking manner, the bottom protective layer comprising a first geotextile and a plurality of first protective blocks fixed on the first geotextile, the weight of the bottom protective layer being greater than the weight of the protective layers of other layers, the protective layers of other layers comprising a second geotextile, a plurality of second protective blocks and a plurality of third protective blocks, the second protective blocks and the third protective blocks having different dimensions at least in height, and the second protective blocks and the third protective blocks being fixed on the second geotextile in an alternating arrangement.

[0007] In a specific embodiment of the above-mentioned protective device for preventing submarine pipeline scour, multiple first protective blocks are fixed on the first geotextile in a closely arranged manner, and the second protective blocks and the third protective blocks are fixed on the second geotextile in an alternating closely arranged manner.

[0008] In a specific embodiment of the above-mentioned protective device for preventing scour of submarine pipelines, the size of the first protective block is larger than that of the second protective block and the third protective block.

[0009] In a specific embodiment of the above-mentioned protective device for submarine pipeline anti-scouring, the shape of the first protective block is a quadrangular pyramid or a pentagonal pyramid.

[0010] In a specific embodiment of the above-mentioned protective device for submarine pipeline anti-scouring, the second protective block and the third protective block are both in the shape of a quadrangular pyramid or a pentagonal pyramid.

[0011] In a specific embodiment of the above-mentioned protective device for preventing submarine pipeline scour, the first protective block is made of concrete, and the second protective block and the third protective block are both made of asphalt.

[0012] In a specific embodiment of the above-mentioned protective device for preventing scour of submarine pipelines, the protective structure includes three protective layers fixed together in a stacked manner, the size of the second protective block in the upper protective layer is less than or equal to the size of the second protective block in the lower protective layer, and the size of the third protective block in the upper protective layer is less than or equal to the size of the third protective block in the lower protective layer.

[0013] In a second aspect, the present invention further provides a method for calculating the size of a submarine pipeline anti-scour protection device according to any one of the first aspects, wherein the submarine pipeline anti-scour protection device is a device for calculating the size of a submarine pipeline, and the method comprises the following steps:

[0014] S1, using a scour calculation numerical model to calculate scour parameters corresponding to multiple sets of data parameters, and grouping some of the data parameters and the corresponding scour parameters as training set parameters, and grouping the remaining parameters as test set parameters; wherein each set of data parameters includes the size parameters of the first protection block, the second protection block, and the third protection block, and the spacing parameters between two adjacent protection structures, and the scour parameters include scour velocity, scour area, and scour area;

[0015] S2, training a neural network based on the training set parameters to obtain neural network parameters;

[0016] S3, building a neural network model based on neural network parameters;

[0017] S4, inputting the data parameters in the test set parameters obtained by the scour calculation numerical model into the neural network model to obtain the corresponding predicted scour velocity, predicted scour depth and predicted scour area;

[0018] S5, obtaining the error values ​​between the scour velocity, scour depth and scour area in the test set parameters and the corresponding predicted scour velocity, predicted scour depth and predicted scour area;

[0019] S6, determining the difference between the error value and a preset difference value;

[0020] S7, determining an approximate proxy model based on a determination result between the error value and a preset difference value;

[0021] S8, taking the minimum values ​​of scour area, scour depth and total cost as the optimization objectives;

[0022] S9, establishing a multi-objective optimization mathematical model based on the set constraints and the optimization objectives;

[0023] S10, using the approximate proxy model and the NSGA-Ⅱ algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution, and comparing different solutions in the Pareto front, finally obtaining the size parameters of the first protection block, the second protection block and the third protection block that meet the requirements and the spacing parameters between two adjacent protection structures.

[0024] In a specific embodiment of the above-mentioned method for calculating the size of a protective device for submarine pipeline scour prevention, the step of "using an approximate proxy model and the NSGA-II algorithm to solve the Pareto front of the multi-objective optimization mathematical model under a set ocean current velocity probability distribution" specifically includes:

[0025] Using the approximate proxy model, a mapping relationship between the scour area and the scour depth and the size parameters of the first protection block, the second protection block, and the third protection block, as well as the spacing parameters between two adjacent protection structures is obtained;

[0026] A mapping relationship between the total cost and the size parameters of the first protection block, the second protection block, and the third protection block, as well as the spacing parameters between two adjacent protection structures, is established using a total cost calculation formula;

[0027] These mapping relationships are substituted into the NSGA-Ⅱ algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution.

[0028] In a specific embodiment of the above-mentioned method for calculating the size of a protective device for preventing scour of a submarine pipeline, the step of "determining an approximate proxy model based on a determination result of the error value and a preset difference value" specifically includes:

[0029] If the error value is less than or equal to the preset difference value, the neural network model is selected as the approximate proxy model;

[0030] If the error value is greater than the preset difference value, steps S2 to S6 are repeated until the error value is less than or equal to the preset difference value.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The bottom protective layer is designed to be heavier than the upper protective layer, which can ensure the overall stability of the protective structure, and the upper protective layer is designed to be lighter in weight to reduce the difficulty of transportation and installation; second protective blocks and third protective blocks of different sizes are set in the other protective layers except the bottom layer, and are arranged in an alternating manner, which increases the resistance of the ocean current flowing through the submarine pipeline. When the water flows through the protective structure, the water flow rate will be slowed down and a local backflow vortex will be formed, which can effectively reduce the scouring effect of the water flow and has a better siltation-promoting ability. Compared with the existing protection method, the present invention has low construction difficulty and low cost, is suitable for scouring protection of deep-water and long-distance submarine pipelines, and can avoid secondary scouring after siltation promotion.

[0033] 2. This scour protection device has many dimensional parameters, and it is difficult to establish a mapping relationship between the scour area, scour depth, and the dimensional parameters of the first, second, and third protective blocks, as well as the spacing parameters between two adjacent protective structures. This dimensional calculation method uses a machine learning method to establish an approximate proxy model to describe the mapping relationship between the scour area, scour depth, and the dimensional parameters of the first, second, and third protective blocks, as well as the spacing parameters between two adjacent protective structures. A multi-objective optimization mathematical model for dimensional parameters is established with the minimum scour area, scour depth, and total cost as the optimization objectives, and the NSGA-Ⅱ algorithm is used to solve it. The optimal dimensional parameters of the protective device finally obtained take into account the minimum scour area, minimum scour depth, and minimum total cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0035] Figure 1 This is a schematic structural diagram of a protective device for submarine pipeline anti-scouring provided by the present invention;

[0036] Figure 2 yes Figure 1 A magnified view of the middle protective structure;

[0037] Figure 3 is a dimension parameter marking diagram of the first guard block;

[0038] Figure 4 is a diagram showing the size parameters of the second guard block;

[0039] Figure 5 This is a diagram showing the size parameters of the third protective block.

[0040] List of reference numerals:

[0041] 1. Submarine pipeline; 2. First protection block; 3. Second protection block; 4. Third protection block. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the present invention. They are not intended to indicate or imply that the systems or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the use of terms such as "first" and "second" to define components is intended solely to facilitate distinction between such components. Unless otherwise stated, these terms have no special meanings and should not be construed as indicating or implying relative importance.

[0044] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "installed," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0045] The present invention relates to the technical field of submarine pipeline scouring protection, and in particular to a protective device for submarine pipeline scouring protection and a method for calculating its dimensions. The purpose is to solve the problem that submarine pipelines in existing deep-water areas will span under the scouring action of ocean currents, and spanning pipelines are prone to fatigue damage, while the current submarine pipeline scouring protection methods are not suitable for pipeline scouring protection in deep-water areas. To this end, the present invention provides a protective device for submarine pipeline scouring protection, comprising a plurality of protective structures arranged at equal intervals along the axis of the submarine pipeline, the protective structure comprising at least two layers of protective layers fixed together in an upper and lower stacking manner, the bottom protective layer comprising a first geotextile and a plurality of first protective blocks fixed on the first geotextile, the bottom protective layer weighing more than the other layers, the other layers of protective layers comprising a second geotextile, a plurality of second protective blocks and a plurality of third protective blocks, the second protective blocks and the third protective blocks having at least a different height dimension, and the second protective blocks and the third protective blocks having different height dimensions. The three protective blocks are fixed on the second geotextile in an alternating arrangement. The weight of the bottom protective layer is designed to be heavier than that of the upper protective layer, which can ensure the overall stability of the protective structure. The upper protective layer is designed to be lighter in weight to reduce the difficulty of transportation and installation. Second protective blocks and third protective blocks of different sizes are set in the other protective layers except the bottom layer, and are arranged in an alternating manner, which increases the resistance of the ocean current through the submarine pipeline. When the water flows through the protective structure, it will slow down the water flow rate and form a local backflow vortex, which can effectively reduce the scouring effect of the water flow and has a good silt-promoting ability.

[0046] Hereinafter, a submarine pipeline anti-scour protection device and a size calculation method thereof provided by an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0047] See Figure 1-2The present invention provides an anti-scour protection device for a submarine pipeline 1, comprising a plurality of protection structures arranged at equal intervals along the axial direction of the submarine pipeline 1, the protection structure comprising at least two protective layers fixed together in an upper and lower stacking manner, the bottom protective layer comprising a first geotextile and a plurality of first protection blocks 2 fixed on the first geotextile, the weight of the bottom protective layer being greater than the weight of the protection layers of other layers, the protection layers of other layers comprising a second geotextile, a plurality of second protection blocks 3 and a plurality of third protection blocks 4, the dimensions of the second protection blocks 3 and the third protection blocks 4 being different in at least the height dimension, the second protection blocks 3 and the third protection blocks 4 being fixed on the second geotextile in an alternating arrangement.

[0048] Specifically, a plurality of first protective blocks 2 are fixed on the first geotextile in a closely arranged manner, and the second protective blocks 3 and the third protective blocks 4 are fixed on the second geotextile in an alternating closely arranged manner. When installing on the seabed, the entire protective structure can be laid on the submarine pipeline 1. Since the second protective blocks 3 and the third protective blocks 4 are arranged alternately, when the ocean current flows through the submarine pipeline 1, the resistance of the ocean current flowing through the submarine pipeline 1 is increased, the flow rate of the water flow is slowed down and a local backflow vortex is formed, which reduces the scouring effect of the water flow, and can promote the silt in the ocean current to settle on the protective structure, and has a good silt-promoting ability. The upper protective layer and the lower protective layer are fixed by bonding. For example, Figure 1 As shown, the protective layer consists of two layers, and the second geotextile on the upper layer is fixed to the top of the first protective block 2 on the lower layer by bonding.

[0049] In the above embodiment, the second protective block 3 and the third protective block 4 may differ in size only in height, such as Figure 1 As shown, the height and one or two other dimensional parameters may also be different. This is not specifically limited in this application and can be flexibly set according to actual circumstances without departing from the basic principles of the present invention. Using different sizes for the second and third protective blocks can increase the surface friction coefficient, thereby increasing the frictional force, and thus increasing the resistance of the ocean current flowing through the submarine pipeline, slowing the water flow rate, while also improving the ability to promote sedimentation.

[0050] In one embodiment, see Figure 2 The size of the first protective block 2 is larger than that of the second protective block 3 and the third protective block 4. This helps to increase the weight of the bottom protective layer and ensure the stability of the overall protective structure on the submarine pipeline 1.

[0051] In this application, see Figure 2 , the gaps between the protective blocks in the upper and lower protective layers are in a staggered state.

[0052] In one embodiment, the first protection block 2 is in the shape of a quadrangular pyramid or a pentagonal pyramid, or may be in the shape of a hexagonal pyramid or a triangular pyramid.

[0053] In one embodiment, the second protection block 3 and the third protection block 4 are both in the shape of a quadrangular pyramid or a pentagonal pyramid, or in the shape of a hexagonal pyramid or a triangular pyramid.

[0054] In one embodiment, the first protective block 2 is made of concrete, and the second and third protective blocks 3 and 4 are both made of asphalt. Concrete, a high density material, ensures the stability of the protective structure, while the upper second and third protective blocks 3 and 4 are made of asphalt, a low density material that reduces the difficulty of transportation and installation.

[0055] In one embodiment, the protective structure includes three protective layers fixed together in an upper and lower stacking manner, the size of the second protective block 3 in the upper protective layer is less than or equal to the size of the second protective block 3 in the lower protective layer, and the size of the third protective block 4 in the upper protective layer is less than or equal to the size of the third protective block 4 in the lower protective layer.

[0056] In another embodiment, the present invention further provides a method for calculating the size of a submarine pipeline anti-scour protection device, wherein the submarine pipeline anti-scour protection device is the submarine pipeline anti-scour protection device described in the various embodiments above. The size calculation method includes the following steps:

[0057] S1, using a scour calculation numerical model to calculate scour parameters corresponding to multiple sets of data parameters, and grouping some of the data parameters and the corresponding scour parameters as training set parameters, and grouping the remaining parameters as test set parameters; wherein each set of data parameters includes the size parameters of the first protection block, the second protection block, and the third protection block, and the spacing parameters between two adjacent protection structures, and the scour parameters include the scour velocity, the scour area, and the scour area; wherein, data with different values ​​are taken to form multiple sets of data parameters;

[0058] S2, training the neural network based on the training set parameters to obtain neural network parameters, where the neural network parameters include at least weights and thresholds;

[0059] S3, building a neural network model based on neural network parameters;

[0060] S4, inputting the data parameters in the test set parameters into the neural network model to obtain the corresponding predicted scour velocity, predicted scour depth and predicted scour area;

[0061] S5, obtaining the error values ​​between the scour velocity, scour depth, and scour area in the test set parameters and the corresponding predicted scour velocity, predicted scour depth, and predicted scour area;

[0062] S6, determining the difference between the error value and the preset difference value;

[0063] S7, determining an approximate proxy model based on a determination result of the error value and a preset difference value;

[0064] S8, taking the minimum values ​​of scour area, scour depth and total cost as the optimization objectives;

[0065] S9, establishing a multi-objective optimization mathematical model based on the set constraints and optimization objectives;

[0066] In S10, an approximate surrogate model and the NSGA-II algorithm were used to solve the Pareto front of the multi-objective optimization mathematical model under a given ocean current velocity probability distribution. Different solutions on the Pareto front were compared and selected, ultimately obtaining the size parameters of the first, second, and third protection blocks, as well as the spacing parameters between adjacent protection structures, that met the requirements. Because the Pareto front obtained contains a series of solutions for size and spacing parameters, representing a set of solutions, some of which are extreme, it is necessary to screen them to obtain size and spacing parameters that meet the expected scour area, scour depth, and total cost.

[0067] In step S1, the specific method of obtaining the scour calculation numerical model is to establish the scour calculation numerical model based on the fluid dynamics analysis software FLUENT or FLOW-3D, and then build a pipeline scour test platform, carry out pipeline scour tests and verify the accuracy of the numerical model from at least the perspectives of scour velocity, scour depth, scour area, and scour pit shape. Through the scour test platform, multiple sets of experimental data on the perspectives of scour velocity, scour depth, scour area, and scour pit shape are obtained, and these data are compared with the data obtained by numerical simulation. The final required scour calculation numerical model can be obtained within the required error range.

[0068] Specifically, step S7 of “determining the approximate proxy model based on the judgment result between the error value and the preset difference value” specifically includes:

[0069] If the error value is less than or equal to the preset difference, the neural network model is selected as the approximate proxy model;

[0070] If the error value is greater than the preset difference, steps S2-S6 are repeated until the error value is less than or equal to the preset difference. The preset difference may be set to 1%.

[0071] In step S10, the step of "using the approximate agent model and the NSGA-II algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution" specifically includes:

[0072] The mapping relationship between the scour area and the scour depth and the size parameters of the first protection block, the second protection block and the third protection block and the spacing parameters between two adjacent protection structures is obtained by using an approximate proxy model;

[0073] A mapping relationship between the total cost and the size parameters of the first protection block, the second protection block, and the third protection block, as well as the spacing parameters between two adjacent protection structures, is established using a total cost calculation formula;

[0074] These mapping relationships are substituted into the NSGA-Ⅱ algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution.

[0075] Specifically, the total cost calculation formula is: the total cost is the sum of manufacturing cost and installation cost, where the installation cost is the manufacturing cost multiplied by a coefficient, which is less than one, and the manufacturing cost is the product of the total volume, the unit volume cost and the total number of protective structures. The total volume is obtained according to the size parameters, and the total number of protective structures is obtained according to the spacing parameters between two adjacent protective structures and the pipeline length.

[0076] Below Figure 1 The protective layer shown in the figure is two layers. The first protective block in the lower layer is made of concrete, and the second and third protective blocks in the upper layer are made of asphalt. The first, second and third protective blocks are all in the shape of a quadrangular pyramid. The second and third protective blocks have different heights, but the bottom length and bottom width are the same. Figure 1 and Figure 3-5 As shown, the size parameters of the first protective block include the bottom length , bottom width , top side length , top edge width ,high The size parameters of the second protective block include the bottom length , bottom width , top side length , top edge width ,high , The size parameters of the third protective block include the bottom length , bottom width ,high , the spacing between adjacent protective layers is Execute step S1, take multiple sets of different data to form multiple sets of data parameters, calculate the corresponding scour parameters based on these data parameters, and then execute steps S2-S7. Let the scour area be S, the scour depth be h, and the total cost of the protective structure be C. At this time, the lowest value of S, h, and C is used as the optimization goal. Since the manufacturing result is related to the mass, and the mass is the product of the volume and density, the manufacturing result is also related to the size parameters and spacing. Therefore, the optimization goal is as follows:

[0077] .

[0078] The constraints set are as follows:

[0079] .

[0080] A multi-objective optimization mathematical model is established based on the set constraints and optimization objectives. After executing steps S8 and S9, step S10 is executed. The NSGA-II algorithm used in step S10 to solve the multi-objective optimization mathematical model is known to those skilled in the art and is therefore not described in detail here, as it does not affect the sufficiency of the disclosure of this application.

[0081] In this application, there are many dimensional parameters for the protective structure, and it is difficult to establish a mapping relationship between the scour area, scour depth, and the dimensional parameters of the first protective block, the second protective block, and the third protective block, as well as the spacing parameters between two adjacent protective structures. This size calculation method uses a machine learning method to establish an approximate proxy model to describe the mapping relationship between the scour area, scour depth, and the dimensional parameters of the first protective block, the second protective block, and the third protective block, as well as the spacing parameters between two adjacent protective structures. A multi-objective optimization mathematical model for dimensional parameters is established with the minimum scour area, scour depth, and total cost as the optimization objectives, and the NSGA-Ⅱ algorithm is used to solve it. The optimal dimensional parameters of the protective device finally obtained take into account the minimum scour area, the minimum scour depth, and the minimum total cost.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the protection scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A protective device for submarine pipeline anti-scouring, characterized in that: The invention comprises a plurality of protective structures arranged at equal intervals along the axis direction of the submarine pipeline, wherein the protective structure comprises at least two protective layers fixed together in an upper and lower stacking manner, the bottom protective layer comprises a first geotextile and a plurality of first protective blocks fixed on the first geotextile, the weight of the bottom protective layer is greater than the weight of the protective layers of other layers, the protective layers of other layers all comprise a second geotextile, a plurality of second protective blocks and a plurality of third protective blocks, the dimensions of the second protective blocks and the third protective blocks differ at least in height, the second protective blocks and the third protective blocks are fixed on the second geotextile in an alternating arrangement, the plurality of first protective blocks are fixed on the first geotextile in a closely adjacent arrangement, the second protective blocks and the third protective blocks are fixed on the second geotextile in an alternating closely adjacent arrangement, the size of the first protective block is greater than the size of the second protective block and the third protective block, the shape of the first protective block is a quadrangular pyramid or a pentagonal pyramid, the shapes of the second protective block and the third protective block are both quadrangular pyramid or a pentagonal pyramid.

2. The protective device for submarine pipeline anti-scouring according to claim 1, characterized in that: The first protection block is made of concrete, and the second protection block and the third protection block are both made of asphalt.

3. The protective device for submarine pipeline anti-scouring according to claim 1, characterized in that: The protective structure includes three protective layers fixed together in a stacked manner, the size of the second protective block in the upper protective layer is less than or equal to the size of the second protective block in the lower protective layer, and the size of the third protective block in the upper protective layer is less than or equal to the size of the third protective block in the lower protective layer.

4. A method for calculating the size of a submarine pipeline anti-scour protection device according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, using a scour calculation numerical model to calculate scour parameters corresponding to multiple sets of data parameters, and grouping some of the data parameters and the corresponding scour parameters as training set parameters, and grouping the remaining parameters as test set parameters; wherein each set of data parameters includes the size parameters of the first protection block, the second protection block, and the third protection block, and the spacing parameters between two adjacent protection structures; the scour parameters include scour velocity, scour depth, and scour area; S2, training a neural network based on the training set parameters to obtain neural network parameters; S3, building a neural network model based on neural network parameters; S4, inputting the data parameters in the test set parameters into the neural network model to obtain corresponding predicted scour velocity, predicted scour depth and predicted scour area; S5, obtaining the error values ​​between the scour velocity, scour depth and scour area calculated by the scour calculation numerical model in the test set parameters and the corresponding predicted scour velocity, predicted scour depth and predicted scour area; S6, determining the difference between the error value and a preset difference value; S7, determining an approximate proxy model based on a determination result between the error value and a preset difference value; S8, taking the minimum values ​​of scour area, scour depth and total cost as the optimization objectives; S9, establishing a multi-objective optimization mathematical model based on the set constraints and the optimization objectives; S10, using the approximate proxy model and the NSGA-Ⅱ algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution, and comparing different solutions in the Pareto front, finally obtaining the size parameters of the first protection block, the second protection block and the third protection block that meet the requirements and the spacing parameters between two adjacent protection structures.

5. The method for calculating the size of a submarine pipeline anti-scour protection device according to claim 4, characterized in that: The steps of "using the approximate proxy model and the NSGA-II algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution" specifically include: Using the approximate proxy model, a mapping relationship between the scour area and the scour depth and the size parameters of the first protection block, the second protection block, and the third protection block, as well as the spacing parameters between two adjacent protection structures is obtained; A mapping relationship between the total cost and the size parameters of the first protection block, the second protection block, and the third protection block, as well as the spacing parameters between two adjacent protection structures, is established using a total cost calculation formula; These mapping relationships are substituted into the NSGA-Ⅱ algorithm to solve the Pareto front of the multi-objective optimization mathematical model under the set ocean current velocity probability distribution.

6. The method for calculating the size of a submarine pipeline anti-scour protection device according to claim 4, characterized in that: The step of “determining an approximate proxy model based on a determination result between the error value and a preset difference value” specifically includes: If the error value is less than or equal to the preset difference value, the neural network model is selected as the approximate proxy model; If the error value is greater than the preset difference value, steps S2 to S6 are repeated until the error value is less than or equal to the preset difference value.

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