Calculation method for horizontal bearing capacity of wind power installation vessel under symmetrical loading condition

Abstract

The invention provides a method for calculating the horizontal bearing capacity of a wind power installation ship under the condition of symmetrical load, which comprises the following steps of: according to the direction of the horizontal load borne by the wind power installation ship, dividing a pile shoe on one side of the wind power installation ship into a loading pile shoe and an unloading pile shoe on the other side of the wind power installation ship; according to the method, unloading pile shoes in a sand site and loading pile shoes in a clay site are defined as characteristic pile shoes for calculating the horizontal bearing capacity of a wind power installation ship; calculating a V-H damage envelope surface of the characteristic pile shoe through a pre-pressing load of the wind power installation vessel; the load path slope of the characteristic pile shoe on the V-H plane is calculated in a fitting mode through the distance between the pile legs on the two sides and the length of the pile legs; obtaining a load path equation of the characteristic pile shoe on a V-H plane; calculating an intersection point of the load path of the characteristic pile shoe and the damage envelope surface, wherein the abscissa of the intersection point is the horizontal load borne by the characteristic pile shoe when the wind power installation vessel reaches the horizontal bearing capacity; and calculating the horizontal bearing capacity of the wind power installation vessel under the symmetrical load condition.

Description

Technical Field

[0001] This invention belongs to the technical field of marine engineering, specifically relating to a method for calculating the horizontal bearing capacity of a wind turbine installation vessel under symmetrical loading conditions. Background Technology

[0002] As a key piece of equipment in the construction of offshore wind farms, wind turbine installation vessels are primarily responsible for the transportation and hoisting of wind turbine foundations, towers, nacelles, and blades. Their operational performance, especially the stability of the pile foundations under complex sea conditions, directly affects construction safety, efficiency, and the overall cost of the wind power project.

[0003] Wind turbine installation vessels typically employ self-elevating platforms with multiple legs. During operation, the legs are lowered to the seabed and preloaded to support the hull, elevating it above the sea surface to form a stable working platform. In this process, the legs and their bottom shoe form the foundation of the entire structure, and their horizontal bearing capacity is a key indicator for assessing the platform's resistance to wind, current, and wave loads—that is, its overall stability.

[0004] Currently, the main methods for analyzing and calculating the horizontal load-bearing capacity of wind turbine installation vessels are as follows: 1. Formula-based method based on standards: Traditional shipbuilding and marine engineering standards provide simplified calculation formulas for estimating the horizontal bearing capacity of shallow foundations. These methods typically rely on the verification results of horizontal anti-sliding safety factors and overturning safety factors to determine the stability of the pile shoe foundation of a wind turbine installation vessel under horizontal loads. However, this method has problems: while the calculation process is simple, it fails to fully consider the coupling effect between vertical loads, horizontal loads, and bending moments under combined loads. The accuracy of the calculation results is limited, often leaning towards conservatism, leading to excessive redundancy in structural design, or, in extreme cases, insufficient estimation resulting in safety hazards.

[0005] 2. Single-Foundation VHM Failure Envelope Method: This method treats the pile shoes of a wind turbine installation vessel as an independent shallow foundation. It assesses the ultimate bearing capacity by constructing a three-dimensional failure envelope that considers the coupling effects of vertical loads (V), horizontal loads (H), and bending moments (M). This method goes a step further than purely empirical formulas, taking into account the influence of composite loads to some extent. However, the core of this method is to analyze the failure of a single foundation. For wind turbine installation vessels with four or more pile legs, it cannot consider the synergistic effect of the pile legs interconnected through the hull under load, nor can it reflect the redistribution of loads and coupling failure mechanisms of the pile shoes in the event of overall instability.

[0006] 3. Finite Element Numerical Simulation Method: With the development of computer technology, using large-scale general-purpose finite element software to establish a refined "pile-soil coupling" model including the hull, pile legs, pile shoes, and seabed soil for nonlinear static or dynamic analysis has become an important method. Theoretically, this method can obtain relatively accurate results. However, this method involves complex modeling and high computational costs. Nonlinear contact and complex soil constitutive models may lead to difficulties in computational convergence, requiring high-performance computers and computation time measured in hours or even days. Furthermore, the accuracy of the analysis results heavily depends on the engineer's understanding of the software, the selection of model parameters (such as soil parameters), and the setting of boundary conditions, making it highly subjective and difficult to standardize.

[0007] In summary, existing technologies face a dilemma when calculating the horizontal bearing capacity of wind turbine installation vessels, a specific engineering problem: while empirical formulas and the single-foundation VHM envelope method are relatively simple, the former lacks accuracy, and the latter cannot accurately reflect the mechanical nature of the coordinated operation of multiple pile legs. Finite element numerical simulation, on the other hand, is too complex and time-consuming to meet the needs of rapid, iterative evaluation during the engineering design phase.

[0008] Therefore, there is an urgent need in this field for a dedicated calculation method that combines engineering accuracy and computational efficiency, capable of quickly and accurately assessing the overall horizontal load-bearing capacity of wind turbine installation vessels under symmetrical loading conditions from a system-level perspective, providing a reliable basis for vessel design optimization and operational safety assessment. Summary of the Invention

[0009] The purpose of this invention is to propose a new calculation method that, by considering the mutual influence between multiple foundations and combining the load path of each foundation under load and the failure envelope of a single foundation, provides a simple and quick evaluation method for the horizontal bearing capacity of wind turbine installation vessels under symmetrical loading conditions, thus providing assistance for practical engineering design.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for calculating the horizontal bearing capacity of a wind turbine installation vessel under symmetrical loading conditions, characterized by the following steps: Step 1: Based on the direction of the horizontal load on the wind turbine installation vessel, divide the pile shoes on one side of the wind turbine installation vessel into loading pile shoes and the other side into unloading pile shoes. Step 2: Define the unloading pile shoes in the sandy soil site and the loading pile shoes in the clay soil site as characteristic pile shoes, and use them to calculate the horizontal bearing capacity of the wind turbine installation vessel. Step 3: Calculate the VH failure envelope of the characteristic pile shoe using the preload of the wind turbine installation vessel; Step 4: Determine the influencing factors of the load path slope. By using the distance between the pile legs on both sides and the length of the pile legs, calculate the load path slope of the characteristic pile shoe in the VH plane. Step 5: Based on the ballast ratio of the wind turbine installation vessel and the slope of the load path of the characteristic pile shoe in the VH plane, obtain the load path equation of the characteristic pile shoe in the VH plane. Step 6: Calculate the intersection of the load path and the failure envelope of the characteristic pile shoe using the load path equation and the failure envelope equation of the characteristic pile shoe. The x-coordinate of this intersection point is the horizontal load on the characteristic pile shoe when the wind turbine installation vessel reaches its horizontal bearing capacity. Step 7: Calculate the horizontal bearing capacity of the wind turbine installation vessel under symmetrical load conditions based on the number of pile legs on the vessel.

[0011] Furthermore, in step three, the formula for calculating the VH failure envelope of the characteristic pile shoe is as follows: In the formula, H The horizontal load on a single pile shoe; V The vertical load on a single pile shoe; V 0 represents the preload of a single pile shoe; w The insertion depth during the preloading and penetration stage of the pile shoe; B The width of the pile shoe is denoted by ; the rest are fitting parameters. h 0 is a parameter that determines the size of the failure envelope of a single pile shoe in a clay site; β 1, β 2 represents the shape parameters of the single pile shoe failure envelope in clay sites; χ Characterizes the tensile strength of the pile shoe in clay sites; α The shape parameters of the single pile shoe failure envelope in sandy soil sites; Furthermore, in step three, h 0 is 0.127; β 1 is 0.764. β 2 is 0.882; χ Take 0.24; α Take 0.95.

[0012] Furthermore, in step four, the formula for fitting and calculating the slope of the load path of the characteristic pile shoe in the VH plane is as follows: ; In the formula, s The distance between the two pile legs; l This refers to the length of the pile leg.

[0013] Furthermore, in step five, the load path equation for the characteristic pile shoe in the VH plane is as follows: In the formula, v Ballast ratio for wind turbine installation vessels k The characteristic pile shoe represents the slope of the load path in the VH plane.

[0014] Furthermore, the horizontal load on the characteristic pile shoe when the wind turbine installation vessel reaches its horizontal bearing capacity is denoted as... H cs In step seven, the formula for calculating the horizontal bearing capacity of the wind turbine installation vessel under symmetrical load conditions is: In the formula, H ult Horizontal load-bearing capacity of wind turbine installation vessels; n The number of pile legs for a wind turbine installation vessel.

[0015] Compared with existing technologies, the method for calculating the horizontal bearing capacity of wind turbine installation vessels under symmetrical loading conditions provided by this invention has the following significant advantages: 1. A novel calculation method is proposed: Existing technologies (such as the single-foundation VHM envelope method) treat pile shoes as isolated individuals, completely ignoring the mutual influence between pile shoes. This invention distinguishes between loaded and unloaded pile shoes to differentiate the stress characteristics of different loading paths; by identifying characteristic pile shoes, an appropriate loading path is selected for calculating the horizontal bearing capacity, thereby accurately characterizing the load transfer and redistribution mechanism among pile legs under symmetrical loads in a simplified analysis method.

[0016] 2. High computational accuracy and more reliable results: The analysis accuracy approaches that of complex finite element methods within a simplified framework. The limit state is solved by combining the overall mechanical response of the system (load path slope) with the bearing characteristics of a single foundation (VH failure envelope). This method considers both the nonlinear characteristics of the soil through the failure envelope and the geometric constraints of the structural system through pile leg spacing and length, resulting in significantly better reliability of the calculation results at the system level compared to the single foundation envelope method that neglects load redistribution.

[0017] 4. High computational efficiency: Enables rapid assessment within minutes, meeting real-time engineering needs. This invention transforms the complex coupled nonlinear finite element analysis of the "pile-soil-hull" system into a series of well-defined algebraic equations. The entire calculation process requires no complex modeling or iteration; engineers, after mastering the basic parameters, can complete the calculation within minutes through manual calculation or by writing a simple program. It is suitable for applications in scenarios requiring extensive and repeated calculations, such as scheme design, rapid on-site safety assessments, and parameter sensitivity analysis and optimization.

[0018] 5. Provides direct and crucial quantitative basis for engineering design. This invention ultimately provides a clear ultimate limit value for horizontal bearing capacity. H ult This value can be directly used to assess the operational safety of wind turbine installation vessels under specific working conditions, determine whether they meet the design wind and wave conditions, and provide key and reliable data support for the structural design of the vessel, the formulation of ballast schemes, and the decision-making on the operational window, thereby effectively reducing engineering risks and ensuring the safety of personnel and assets.

[0019] In summary, this invention proposes a simple and fast calculation method that considers both system coupling effects, providing an evaluation approach for the design and safe operation of wind turbine installation vessels. Attached Figure Description

[0020] Figure 1 Composite bearing capacity test and fitted failure envelope of a single pile shoe in clay site Figure 2 Composite bearing capacity test and fitted failure envelope of a single pile shoe in a sandy soil site Figure 3 The measured characteristic pile shoe's load path slope in the VH plane. k and s / l Relationship Figure 4 The relationship between the predicted horizontal bearing capacity of the wind turbine installation vessel and the measured value. Figure 5 This is a schematic diagram of the structural dimensions, preload, and soil conditions of the wind turbine installation vessel in the embodiment. Figure 6 The single pile shoe failure envelope is determined based on the single pile shoe preload in the embodiment. Table 1 shows the unstable pile shoes of the wind turbine installation vessel when it reaches horizontal bearing capacity. Detailed Implementation

[0021] The following section, with reference to the accompanying drawings, presents a specific method for calculating the horizontal bearing capacity of the wind turbine installation vessel of the present invention under symmetrical loading conditions: Step 1: Based on the direction of the horizontal load on the wind turbine installation vessel, divide the pile shoes on one side of the wind turbine installation vessel into loading pile shoes and unloading pile shoes on the other side.

[0022] Step 2: Based on the centrifuge test results in Table 1, the unloaded pile shoe in the sandy soil site and the loaded pile shoe in the clay soil site are defined as characteristic pile shoes, which are used to calculate the horizontal bearing capacity of the wind turbine installation vessel.

[0023] Table 1. Instability of pile shoes when the wind turbine installation vessel reaches horizontal bearing capacity.

[0024] Step 3: Calculate the VH failure envelope of the characteristic pile shoe using the preload of the wind turbine installation vessel. This formula is applicable to calculating the combined bearing capacity of a single pile shoe in clay and sandy soil sites. Where, H The horizontal load on a single pile shoe; V The vertical load on a single pile shoe; V 0 represents the preload of a single pile shoe; w The insertion depth during the preloading and penetration stage of the pile shoe; B This represents the width of the pile shoe. The rest are fitting parameters, based on the composite bearing capacity test of a single pile shoe in clay and sandy soil sites (results are shown in...). Figure 1 ), h 0 is 0.127; β 1 is 0.764. β 2 is 0.882; χ Take 0.24; α Take 0.95.

[0025] Step 4, based on theoretical analysis and model experiments (see...) Figure 3 The factors influencing the load path slope, and the formula for calculating the load path slope of the characteristic pile shoe in the VH plane using the distance between the pile legs and the length of the pile legs on both sides, are as follows: In the formula, s The distance between the two pile legs; l This refers to the length of the pile leg.

[0026] Step 5: Based on the ballast ratio of the wind turbine installation vessel and the slope of the load path of the characteristic pile shoe in the VH plane, calculate the load path of the characteristic pile shoe in the VH plane: In the formula, v Ballast ratio for wind turbine installation vessels k The load path of the characteristic pile shoe in the VH plane is determined by step four.

[0027] Step Six: Using the load path equation and failure envelope equation of the characteristic pile shoe, calculate the intersection point of the load path and failure envelope of the characteristic pile shoe. The x-coordinate of this intersection point represents the horizontal load on the characteristic pile shoe when the wind turbine installation vessel reaches its horizontal bearing capacity, denoted as... H cs .

[0028] Step 7: Calculate the horizontal bearing capacity of the wind turbine installation vessel under symmetrical load conditions based on the number of pile legs: In the formula,H ult Horizontal load-bearing capacity of wind turbine installation vessels; n This refers to the number of pile legs on the wind turbine installation vessel. The verification relationship between the predicted horizontal bearing capacity of the wind turbine installation vessel and the measured value, based on centrifuge testing, is shown in the appendix. Figure 4 .

[0029] This method can be used to calculate the horizontal bearing capacity of wind turbine installation vessels under symmetrical load conditions, providing a scientific basis for the design and construction of wind turbine installation vessels and for the safe construction and maintenance of wind turbine units.

[0030] Step 2 identifies the characteristic pile shoe as the core factor affecting the horizontal bearing capacity of the wind turbine installation vessel, simplifying the calculation process and improving calculation efficiency.

[0031] Step four calculates the slope of the load path of the characteristic pile shoe using the hull structure dimensions, taking into account the influence of geometric constraints on the mechanical response of the characteristic pile shoe.

[0032] Step 5 provides the horizontal bearing capacity of the characteristic pile shoe within the multi-foundation system, avoiding the view of each pile shoe as an isolated individual.

[0033] The present invention will be further described below with reference to embodiments: In this embodiment of the invention, the method for calculating the horizontal bearing capacity of a wind turbine installation vessel under symmetrical loading conditions includes the following steps: Step 1: Determine the loading and unloading pile shoes of the wind turbine installation vessel according to the load direction, see Appendix. Figure 5 .

[0034] Step 2: Determine the characteristic pile shoes for the wind turbine installation vessel based on soil conditions, see appendix. Figure 5 .

[0035] Step 3: Determine the failure envelope of the characteristic pile shoe based on the preload of the pile shoe, see Appendix. Figure 6 .

[0036] Step 4: Based on the ship's structural dimensions (see appendix) Figure 5 ), calculate the slope of the characteristic pile shoe load path: Step 5: Based on the ballast ratio of the wind turbine installation vessel (see appendix) Figure 5 ), calculate the load path equation for the characteristic pile shoe: Step 6: Using the load path equation and failure envelope equation of the characteristic pile shoe, calculate the intersection point of the load path and failure envelope of the characteristic pile shoe, and obtain the x-coordinate of the intersection point. H cs =6.04MN.

[0037] Step 7: Determine the horizontal bearing capacity of the wind turbine installation vessel based on the number of its pile legs. Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings and specific embodiments, the present invention is not limited to the specific functions and working processes described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these are within the protection scope of the present invention.

Claims

1. A method for calculating the horizontal bearing capacity of a wind farm installation vessel under symmetric loading conditions, characterized in that, The method comprises the following steps: Step one, according to the direction of the horizontal load on the wind power installation ship, the spudcan on one side of the wind power installation ship is divided into a loaded spudcan, and the spudcan on the other side is an unloaded spudcan; Step two, the unloaded spudcan in the sand field and the loaded spudcan in the clay field are defined as characteristic spudcans to calculate the horizontal bearing capacity of the wind power installation ship; Step three, the V-H failure envelope surface of the characteristic spudcan is calculated through the preloading load of the wind power installation ship; Step four, the influencing factors of the load path slope are determined, and the load path slope of the characteristic spudcan in the V-H plane is fitted and calculated through the distance between the two spudcans and the length of the spudcan; Step five, the load path equation of the characteristic spudcan in the V-H plane is obtained according to the ballast ratio of the wind power installation ship and the load path slope of the characteristic spudcan in the V-H plane; Step six, the intersection of the load path of the characteristic spudcan and the failure envelope surface of the characteristic spudcan is calculated through the load path equation of the characteristic spudcan and the failure envelope surface equation of the characteristic spudcan, and the horizontal load on the characteristic spudcan when the wind power installation ship reaches the horizontal bearing capacity is the horizontal coordinate of the intersection; Step seven, the horizontal bearing capacity of the wind power installation ship under the symmetric load condition is calculated according to the number of spudcans of the wind power installation ship.

2. The method of claim 1, wherein, In step three, the formula for calculating the V-H failure envelope surface of the characteristic spudcan is as follows: where, H is the horizontal load on the single pile shoe; V is the vertical load on the single pile shoe; V 0is the preloading load on the single pile shoe; w is the penetration depth of the preloading and penetration stage of the pile shoe; B is the width of the pile shoe; and the rest are fitting parameters, h 0is a parameter that determines the size of the failure envelope surface of the single pile shoe in clay sites; β 1, β 2is a shape parameter of the failure envelope surface of the single pile shoe in clay sites; In step four, the formula for fitting and calculating the load path slope of the characteristic spudcan in the V-H plane is as follows: characterizes the tensile capacity of the pile shoe in clay sites; α is a shape parameter of the failure envelope surface of the single pile shoe in sand sites.

3. The method of claim 2, wherein, In step three, h 0 take 0.127; β 1 take 0.764, β 2 take 0.882; In step five, the load path equation of the characteristic spudcan in the V-H plane is as follows: Take 0.24; α Take 0.

95.

4. The method of claim 1, wherein, ​ ； wherein s is the distance between the legs; l is the leg length.

5. The method of claim 1, wherein, ​ wherein v is the ballast ratio of the wind turbine installation vessel, k is the load path slope of the characteristic spud shoe in the V-H plane.

6. The method of claim 1, wherein, The horizontal load on the characteristic spud shoe when the wind turbine installation vessel reaches the horizontal bearing capacity is denoted by H cs In step seven, the formula for calculating the horizontal bearing capacity of the wind turbine installation vessel under symmetric load conditions is In the formula, H ult is the horizontal bearing capacity of the wind turbine installation vessel; n is the number of legs of the wind turbine installation vessel.

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