A Design Analysis Method for the Mooring System of a Floating Structure Applicable to Shallow Water Conditions

Abstract

The present invention provides a design and analysis method for a mooring system of a floating structure applicable to shallow water conditions, specifically belonging to the technical field of mooring of floating equipment. In the present invention, first, the deformation energy requirement of the platform is calculated according to the platform structure type, the residual deformation energy of the mooring line configuration scheme is calculated based on the deformation energy principle, and the mooring scheme with the maximum residual deformation energy is preferably selected; then, based on the numerical method of viscous flow theory, the overlapping grid method is applied to couple the dynamic simulation method of the mooring cable to check the motion response and mooring safety factor of the floating structure of the preferred scheme. The present invention determines the layout scheme of the mooring system through the process of scheme design and safety check. The entire design process is scientific, logically rigorous, highly feasible, and has guiding significance for practical engineering applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of mooring of floating equipment, and particularly relates to a design and analysis method for an anchoring system of a floating structure applicable to shallow water conditions. Background Art

[0002] The mooring technology of offshore engineering floating equipment mainly includes mooring positioning and dynamic positioning. Mooring positioning is a traditional passive platform positioning method (such as catenary type, etc.), which is usually applied in medium and deep waters. With the continuous development and innovation of the research and development and construction technologies of offshore platforms, the challenges faced by mooring systems are getting higher and higher. Especially in shallow water environments, it is difficult for mooring positioning methods to ensure the motion safety of the platform relying on its own gravity, and new anchoring system design schemes are extremely important.

[0003] Regarding the design problem of the anchoring system, in the prior art, various solutions have been proposed from the perspectives of the design scheme of the anchoring system and the design method of the anchoring system. One is to propose a design scheme for a shallow water anchoring system including anchor chain, counterweight, buoyancy block and anchoring foundation, which can meet the requirements of mooring restoring force and anchor chain tension; the other is to consider the influence of the pitch second-order steady wave moment on the anchoring system, and by analyzing parameters such as the peak value of the pitch second-order steady wave moment transfer function in the frequency domain, the maximum pitch motion angle, etc., and optimizing through the genetic algorithm to obtain the anchoring system parameters that meet the target motion requirements.

[0004] Since mooring in shallow water environments is more easily affected by waves and ocean currents, resulting in a more complex marine environment for mooring in shallow water conditions, the above-mentioned schemes in the prior art cannot truly fit the actual shallow water marine environment, making the final scheme unable to meet the safety and reliability of shallow water mooring. Summary of the Invention

[0005] Aiming at the technical problem of low reliability existing in the design scheme of the anchoring system under shallow water conditions in the prior art, the present invention provides a design and analysis method for an anchoring system of a floating structure applicable to shallow water conditions, and gives design ideas from the structural type and design process respectively, forming a set of design and analysis methods for the anchoring system applicable to shallow water conditions, and solving the technical problems existing in the anchoring system scheme under shallow water conditions in the prior art.

[0006] In the first aspect of the present invention, the present invention provides a design and analysis method for an anchoring system of a floating structure applicable to shallow water conditions, characterized by including:

[0007] Step S1, according to the structural type of the floating equipment, the location of the service sea area and the hydrogeological conditions, obtain the environmental load value received by the floating equipment;

[0008] Step S2: Calculate the horizontal tension at the static equilibrium position based on the environmental load value acting on the floating equipment, and calculate the hydrodynamic parameters of the platform based on the frequency-domain wave radiation / diffraction theory under the framework of potential flow theory;

[0009] Step S3: Calculate the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform according to the hydrodynamic parameters of the platform and the stiffness range of the shallow water mooring system;

[0010] Step S4: Determine multiple groups of different anchor chain parameters, calculate the functional relationship between the horizontal tension and the horizontal displacement according to the selected anchor chain parameters, and obtain the stiffness and residual deformation energy of the mooring system at the static equilibrium position based on the functional relationship between the horizontal tension and the horizontal displacement and the horizontal tension at the static equilibrium position;

[0011] Step S5: Obtain the deformation energy requirement of the platform according to the stiffness of the mooring system at the static equilibrium position and the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform, calculate the safety factor according to the platform energy requirement and the residual deformation energy, and select the mooring system with the safety factor meeting the preset conditions as the system design scheme.

[0012] Furthermore, step S1 further includes: The environmental load value acting on the floating equipment includes wind load and current load, and the calculation formula for the wind load is: where C w 、C s 、C h 、A, V w are the wind force coefficient, platform shape coefficient, platform height coefficient, vertical projection area of the platform's windward side, and wind speed respectively; the current load where C ss 、C d 、A c 、A f 、V c are the current force coefficient, drag force coefficient, total projected area of cylindrical members below the waterline, total projected area of flat members below the waterline, and flow velocity respectively.

[0013] Furthermore, step S2 further includes:

[0014] The numerical value of the horizontal tension at the static equilibrium position calculated according to the environmental load value acting on the floating equipment, that is, T 0 = F H = F w + F cs ; Calculate the hydrodynamic parameters of the platform based on the frequency-domain wave radiation / diffraction theory under the framework of potential flow theory, including the added mass A, radiation damping B, and wave exciting force F.

[0015] Furthermore, step S3 further includes:

[0016] Step S31: Calculate the amplitude of the surge motion response of the platform according to the environmental load value received by the floating equipment and the stiffness range of the shallow water mooring system.

[0017] Step S32: Calculate the energy spectrum of the surge motion based on the surge motion response value in combination with the wave action conditions, and then obtain the significant value of the surge motion response.

[0018] Step S33: Calculate the deformation energy requirement of the floating equipment under different mooring stiffnesses based on the principle of deformation energy, and obtain the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform.

[0019] Further, step S3 further includes:

[0020] Step S31: Considering that the system stiffness K of the shallow water mooring is below 2000 kN / m, calculate the amplitude of the surge motion response RAO of the platform in the range of mooring stiffness from 0 to 2000 kN / m according to the formula That is, the component of X in the surge direction, where M is the platform mass and X is the motion response of the platform. surge

[0021] Step S32: Calculate the energy spectrum S of the surge motion according to the surge motion response value in combination with the incident wave spectrum S w (ω) Calculate the energy spectrum S of the surge motion surge (ω)=(RAO surge ) 2 S w (ω), and obtain the 1 / 10 significant value corresponding to the surge motion Where

[0022] Step S33: Calculate the deformation energy requirement of the floating structure based on the principle of deformation energy Calculate the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform under the action of irregular waves.

[0023] Further, step S4 further includes:

[0024] Select multiple groups of anchor chain parameters, and calculate the functional relationship between the horizontal tension and the horizontal displacement as T H =f(x) respectively according to the selected multiple groups of anchor chain parameters, and calculate the mooring stiffness of the mooring system based on the horizontal tension at the static equilibrium position and the residual deformation energy Where, x 0 、T 0 are the deformation amount and the horizontal tension of the mooring system at the static equilibrium position respectively, and x m is the deformation amount of the mooring system at the limit position.

[0025] Further, step S5 further includes:

[0026] Based on the mooring stiffness parameter K obtained in step S4 and the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform in step 2, the platform energy requirement E is calculated P , and according to the platform energy requirement and the residual deformation energy, the safety factor κ = E M / E P is calculated, where κ = 1.4. If κ > 1.4, the corresponding mooring scheme is used as the alternative mooring system design scheme

[0027] Furthermore, the method of the present invention further includes:

[0028] Step S6, based on the numerical solver of the viscous flow theory, applying the overlapping grid method to couple the dynamic simulation method of the mooring cable, checking the motion response of the floating structure and the mooring safety factor of the selected scheme. Based on computational fluid dynamics and the lumped mass method, the platform motion response and the anchor chain force are analyzed to quickly analyze the platform motion and the anchor chain force under the action, and the optimal mooring scheme is determined

[0029] Furthermore, step S6 further includes:

[0030] Step S61, using the model building software to build a model of the floating structure and export the model file; importing the model file into the built computational model, performing grid division, assigning relevant physical parameters to the imported floating structure model, and designing relevant water depth and wave conditions according to the service sea area location and hydrogeological conditions in step S1, and verifying the accuracy and convergence of the model

[0031] Step S62, based on the verified numerical model and the water depth and wave conditions, for the number of anchor chains and the connection positions adopted in the design of the target mooring structure, using the lumped mass method to analyze the anchor chain force

[0032] Step S63, analyzing the maximum force of each anchor chain, finding out the mooring structure and the number of mooring that meet the requirements of the mooring force safety factor, and obtaining the optimal mooring scheme

[0033] Furthermore, the specific contents of assigning relevant physical parameters to the imported floating structure model in step S61 include:

[0034] Respectively assign the corresponding physical parameters to the floating platform and the anchor chain, and assign the corresponding boundary conditions; use the VOF method to express the gas and liquid phases: ρ = (1 - α i )ρ g + α i ρ l , μ = (1 - α i )μ g + α i μ l , where αi is the fluid volume fraction of the i-th item, ρ g is the gas density, ρ l is the liquid density, μ g is the gas viscosity, μ l is the liquid dynamic viscosity.

[0035] Furthermore, the analysis of the anchor chain force using the lumped mass method in step S62 includes:

[0036] The lumped mass method divides the anchor chain into multiple mass nodes, and the nodes are connected by massless springs. The tension in the i-th segment caused by the axial stiffness where E is the elastic modulus, d is the diameter of the anchor chain, r i+1 and r i are the global position vectors of node i + 1 and node i, the direction is from node i to node i + 1, ε i+1 / 2 is the strain value of the anchor chain; the internal damping force where C int is the internal damping coefficient, is the strain rate; the interaction between the mooring cable and the seabed where, l is the tensile length of the anchor chain, d is the diameter of the anchor chain, k b is the seabed stiffness coefficient, c b is the seabed damping coefficient, z b is the seabed elevation, z i is the node coordinate, is z i take the differential, is the unit vector in the z direction; the transverse drag force where, ρ is the water density, is the node velocity, d is the diameter of the anchor chain, C dn is the transverse drag coefficient; the tangential drag force where C dt is the tangential drag coefficient; after solving the anchor chain force, construct the motion equations of each node where, T i+1 / 2 and T i-1 / 2 represent the tensions caused by the segments on both sides of the node, C i+1 / 2 and C i-1 / 2 represent the internal damping forces caused by the segments on both sides of the node, W i is the underwater weight, m i is the mass of the anchor chain at node i, I is the identity matrix, a i is the added mass matrix, is the acceleration of node i, and the motion of the floating structure platform and the forces on each anchor chain are obtained by solving.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: For the problem of shallow water mooring, the present invention first calculates the platform deformation energy requirement according to the platform structure type, calculates the residual deformation energy of the mooring line configuration scheme based on the deformation energy principle, and optimizes the mooring scheme with the largest residual deformation energy; then, based on the numerical method of viscous flow theory, the overlapping grid method is applied to couple the dynamic simulation method of mooring cables to check the motion response of the floating structure and the mooring safety factor of the optimized scheme, ensuring the safety of the final mooring system scheme; the present invention determines the layout scheme of the mooring system through the scheme design and safety check process. The entire design process is scientific, logically rigorous, highly executable, and has guiding significance for practical engineering applications. Description of the Drawings

[0038] Figure 1 Flow chart of the design method for the mooring system of a floating structure under shallow water conditions;

[0039] Figure 2 Principle diagram for calculating the mooring stiffness and residual deformation energy of the mooring system. Detailed Embodiments

[0040] The description of the embodiments of this specification should be combined with the corresponding drawings, and the drawings should be part of the complete specification. In the drawings, the shape or thickness of the embodiments can be enlarged and simplified or conveniently marked. Furthermore, the parts of each structure in the drawings will be described separately. It should be noted that the elements not shown or described in words in the drawings are in the forms known to those of ordinary skill in the art.

[0041] Any reference to directions and orientations in the description of the embodiments herein is for convenience of description only and should not be construed as any limitation on the protection scope of the present invention. The following description of the preferred embodiments will involve combinations of features, which may exist independently or in combination. The present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0042] As Figure 1 shown, in the first embodiment of the present invention, the present invention provides a design and analysis method for the mooring system of a floating structure applicable to shallow water conditions, which is characterized by including:

[0043] Step S1, obtaining the environmental load values received by the floating equipment according to the floating equipment structure type, service sea area location, and hydrogeological conditions;

[0044] Step S2, calculating the horizontal tension at the static equilibrium position according to the environmental load values received by the floating equipment, and the platform hydrodynamic parameters calculated based on the frequency-domain wave radiation / diffraction theory under the framework of potential flow theory;

[0045] Step S3: Calculate the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform according to the platform hydrodynamic parameters and the shallow water mooring system stiffness range;

[0046] Step S4: Determine multiple groups of different anchor chain parameters, calculate the functional relationship between the horizontal tension and the horizontal displacement according to the selected anchor chain parameters, and obtain the stiffness and residual deformation energy of the mooring system at the static equilibrium position based on the functional relationship between the horizontal tension and the horizontal displacement and the horizontal tension at the static equilibrium position;

[0047] Step S5: Obtain the deformation energy requirement of the platform according to the stiffness of the mooring system at the static equilibrium position and the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform, calculate the safety factor according to the platform energy requirement and the residual deformation energy, and select the mooring system with the safety factor meeting the preset conditions as the system design scheme.

[0048] Further, step S3 further includes:

[0049] Step S31: Calculate the amplitude of the surge motion response of the platform according to the environmental load value received by the floating equipment and the shallow water mooring system stiffness range;

[0050] Step S32: Calculate the energy spectrum of the surge motion according to the surge motion response value combined with the wave action conditions, and further obtain the significant value of the surge motion response;

[0051] Step S33: Calculate the deformation energy requirement of the floating equipment under different mooring stiffnesses based on the deformation energy principle, and calculate the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform.

[0052] Further, the method of the present invention further includes:

[0053] Step S6: Based on the numerical solver of the viscous flow theory, apply the overlapping grid method to couple the mooring cable dynamic simulation method to check the motion response of the floating structure and the mooring safety factor of the selected scheme. Complete the platform motion response and anchor chain force analysis based on computational fluid dynamics and the lumped mass method, quickly analyze the platform motion and anchor chain force under the action of viscous force, and determine the optimal mooring scheme.

[0054] Further, step S6 further includes:

[0055] Step S61: Use the model building software to build a model of the floating structure and export the model file; import the model file into the built computational model, perform mesh division, assign relevant physical parameters to the imported floating structure model, and design relevant water depths and wave conditions according to the service sea area location and hydrogeological conditions in step S1, and verify the accuracy and convergence of the model;

[0056] Step S62: Based on the validated numerical model, water depth, and wave conditions, determine the number and connection positions of the anchor chains for the target mooring structure, and analyze the forces on the anchor chains using the lumped mass method.

[0057] Step S63: Analyze the maximum forces on each anchor chain, determine the mooring structure and number of anchor chains that meet the requirements of the mooring force safety factor, and obtain the optimal mooring plan.

[0058] The following further details the design process of the mooring system for a floating platform under shallow water conditions.

[0059] Process 1. Scheme design of the mooring system under shallow water conditions.

[0060] Step 1: Take a floating platform as an example. Consider the environmental loads in the working state as: wind speed V w ; flow velocity V c ; the wave is an irregular wave, the wave spectrum is the JONSWAP spectrum, the spectral peak elevation factor is γ, the spectral peak frequency is ω p , the significant wave height is H s . Based on the structural type and scale parameters of the platform, calculate the wind load according to the formula where C w , C s , C h , and A are the wind force coefficient, platform shape coefficient, platform height coefficient, and the vertical projected area of the platform's windward side respectively; the flow load where C ss , C d , A c , and A f are the flow force coefficient, drag force coefficient, the total projected area of cylindrical members below the waterline, and the total projected area of flat members below the waterline respectively; calculate the hydrodynamic parameters of the platform based on the frequency-domain wave radiation / diffraction theory under the framework of potential flow theory, including the added mass A, radiation damping B, and wave exciting force F.

[0061] Step 2: Considering that the system stiffness K of the shallow water mooring is generally below 2000 kN / m, calculate the amplitude of the surge motion response RAO of the platform in the range of 0 - 2000 kN / m of mooring stiffness (i.e., the component of X in the first direction), where M is the platform mass and X is the motion response of the platform. Combine with the wave action condition S surge (ω) to calculate the energy spectrum S w (ω) of the surge motion = (RAO surge ) surge S 2 (ω), and obtain the 1 / 10 significant value corresponding to the surge motion w where where Calculating the deformation energy demand of a floating structure based on the principle of deformation energy Obtain the relationship curve between the mooring stiffness and the deformation energy demand of the floating platform under the action of irregular waves.

[0062] Step 3: According to the horizontal tension value at the static equilibrium position calculated in Step 1, mainly the wind load and current load, i.e., T 0 = F H = F w + F cs , design an anchor mooring system with impact resistance. Select anchor chains of different specifications and materials, and plot the functional relationship between the horizontal tension and the horizontal displacement as T H = f(x). According to different anchor chain parameters (diameter, length, wet weight, axial stiffness, breaking force), plot the relationship curve between the horizontal tension of the anchor chain and the horizontal displacement. Obtain the mooring stiffness and the residual deformation energy ( Figure 2 ) of the anchor mooring system based on the static analysis method of the mooring line. Where, x 0 , T 0 are respectively the deformation amount and the horizontal tension of the anchor mooring system at the static equilibrium position, and x m is the deformation amount of the anchor mooring system at the limit position.

[0063] Step 4: Refer to the mooring stiffness parameter K in Step 3, and combine it with the relationship curve between the mooring stiffness and the deformation energy demand of the floating platform in Step 2, then the platform energy demand E P can be obtained. Calculate the safety factor κ = E M / E P , (κ is the safety factor, the most dangerous working condition of the anchor mooring system is the longitudinal motion problem of the floating structure. By analogy with the large-angle dynamic stability problem of the rolling of the floating structure, referring to the CCS marine platform stability specification, take κ = 1.4). If κ > 1.4, it meets the design requirements of the anchor mooring system. If not, redesign the anchor chain parameters in Step 3, calculate the safety factor until the design requirements are met, and determine the design scheme of the anchor mooring system.

[0064] Process 2. Platform motion response and anchor chain force analysis.

[0065] Step 1: Verify the accuracy of the established numerical model using classical examples. After verification, export the STL model file using 3D model construction software according to the parameters of the floating platform. Simulate the rigid body motion using the overlapping grid technique (which can avoid problems such as negative volume caused by the movement of dynamic grids). Import the STL model file into the overlapping grid region and perform grid division on the overlapping grid region and the background grid region. Assign the corresponding physical parameters (mass of the floating structure, mass of the anchor chain, position of the anchoring point, length of the anchor chain, axial stiffness, etc.) to the floating platform and the anchor chain respectively, and assign the corresponding boundary conditions; Use the VOF method to express the gas and liquid phases: ρ=(1-α i )ρ g +α i ρ l 、μ=(1-α i )μ g +α i μ l (where α i is the volume fraction of the i-th fluid, ρ g is the gas density, ρ l is the liquid density, μ g is the gas viscosity, μ l is the liquid dynamic viscosity). After setting all the parameters of the model, select the working conditions that can describe the typical characteristics of the dynamic response of the floating structure-anchoring system, and set multiple grid sizes to verify the grid convergence of the numerical model (ensuring that the grid size has little impact on the results).

[0066] Step 2: Based on the verified numerical model, adopt the water depth, wave and other conditions in Step 1, and analyze the force on the anchor chain for the anchor chain quantity and connection position adopted in the design of a specific target mooring structure. The lumped mass method divides the anchor chain into multiple nodes with mass, and the nodes are connected by massless springs. The tension in the i-th segment caused by the axial stiffness where E is the elastic modulus, d is the diameter of the anchor chain, the internal damping force where C int is the internal damping coefficient, is the strain rate, the interaction between the mooring cable and the seabed where, k b is the seabed stiffness coefficient, c b is the seabed damping coefficient, z b is the seabed elevation, z i is the node coordinate, the lateral drag force where, C dn is the lateral resistance coefficient, the tangential drag force where C dt is the tangential resistance coefficient. After solving the force on the anchor chain as above, construct the motion equation Among them, T i+1 / 2 and T i-1 / 2 represent the tensions caused by the segments on both sides of the node, C i+1 / 2 and C i-1 / 2 represent the internal damping forces caused by the segments on both sides of the node, W i is the underwater weight, m i is the mass of the anchor chain at node i, I is the identity matrix, a i is the added mass matrix, is the acceleration of node i, and the motion of the floating structure platform and the forces on each anchor chain are obtained by solving.

[0067] Step 3: According to the loads on each anchor chain obtained in Step 2, analyze whether the forces on each anchor chain meet the requirements of the mooring force safety factor (the ratio of the mooring cable breaking strength to the maximum tension received). If not, return to Step 2 to re - design the anchor chain. If the requirements are met, the target mooring plan is obtained.

[0068] For the problem of shallow - water mooring, the present invention first calculates the platform deformation energy requirement according to the platform structure type, calculates the residual deformation energy of the mooring line configuration plan based on the deformation energy principle, and optimizes the mooring plan with the maximum residual deformation energy; then, based on the numerical method of the viscous flow theory, applying the overlapping grid method to couple the dynamic simulation method of the mooring cable, checks the motion response of the floating structure and the mooring safety factor of the optimized plan, ensuring the safety of the final mooring system plan; the present invention determines the layout plan of the mooring system through the process of plan design and safety check. The entire design process is scientific, logically rigorous, highly executable, and has guiding significance for practical engineering applications.

Claims

1. A design and analysis method for a floating structure mooring system suitable for shallow water conditions, characterized in that: include: Step S1, obtaining the environmental load value of the floating equipment according to the structure type of the floating equipment, the service sea area location and the hydrogeological conditions; Step S2, calculating the horizontal tension at the static equilibrium position according to the environmental load value of the floating equipment, and the hydrodynamic parameters of the platform calculated based on the frequency domain wave radiation / diffraction theory under the potential flow theory framework; Step S3, calculating the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform according to the platform hydrodynamic parameters and the stiffness range of the shallow water mooring system; The step S3 further comprises: Step S31: Since the system stiffness K of the shallow water mooring is below 2000 kN / m, according to the formula Calculate the surging motion response amplitude RAO of the platform with mooring stiffness ranging from 0 to 2000 kN / m surge , that is, the component of X in the longitudinal direction, where A is the additional mass, B is the radiation damping, F is the wave excitation force, M is the platform mass, and X is the motion response of the platform. Differentiate X, To find the second order differential; Step S32, based on the surging motion response value combined with the incident wave spectrum S w (ω) Calculate the energy spectrum S of the longitudinal motion surge (ω)=(RAO surge ) 2 S w (ω), obtain the 1 / 10 meaningful value corresponding to the longitudinal motion in Step S33, calculating the deformation energy requirement of the floating structure based on the deformation energy principle The functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform under the action of irregular waves is calculated; Step S4, determining a plurality of different anchor chain parameters, calculating the functional relationship between horizontal tension and horizontal displacement according to the selected anchor chain parameters, and obtaining the stiffness and residual deformation energy of the mooring system at the static equilibrium position based on the functional relationship between horizontal tension and horizontal displacement and the horizontal tension at the static equilibrium position; said step S4 further comprises: Select multiple groups of anchor chain parameters, and calculate the functional relationship between horizontal tension and horizontal displacement according to the selected multiple groups of anchor chain parameters as T H =f(x), the mooring stiffness of the mooring system is obtained by calculating the horizontal tension at the static equilibrium position and residual deformation energy Among them, x0 and T0 are the deformation and horizontal tension of the mooring system at the static equilibrium position, respectively. m is the deformation of the mooring system at the extreme position; Step S5, obtaining the deformation energy requirement of the platform according to the stiffness of the mooring system at the static equilibrium position and the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform, calculating the safety factor according to the platform energy requirement and the residual deformation energy, and selecting the mooring system whose safety factor meets the preset conditions as the system design scheme.

2. A design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 1, characterized in that: The step S1 further includes: the environmental load value of the floating equipment includes wind load and flow load, wherein the calculation formula of the wind load is: Among them C w , C s , C h , A, V w They are wind force coefficient, platform shape coefficient, platform height coefficient, vertical projection area of ​​the platform windward surface and wind speed; flow load Among them C ss , C d , A c , A f 、V c They are the flow coefficient, drag coefficient, the total projected area of ​​cylindrical components under the waterline, the total projected area of ​​flat plate components under the waterline and the flow velocity.

3. A design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 2, characterized in that: The step S2 further comprises: The horizontal tension value at the static equilibrium position calculated according to the environmental load value of the floating equipment, that is, T0 = F H =F w +F cs ; The platform hydrodynamic parameters, including added mass A, radiation damping B and wave excitation force F, are calculated based on the frequency domain wave radiation / diffraction theory under the framework of potential flow theory.

4. A design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 1, characterized in that: The step S5 further comprises: According to the mooring stiffness parameter K obtained in step S4 and the functional relationship between the mooring stiffness and the deformation energy requirement of the floating platform in step 2, the platform deformation energy requirement E is calculated. P , calculate the safety factor κ=E according to the platform deformation energy requirement and residual deformation energy M / E P , where κ=1.

4. If κ>1.4, the corresponding mooring scheme will be taken as the alternative mooring system design scheme.

5. The design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 1 is characterized in that: The method further comprises: Step S6, based on the numerical solver of viscous flow theory, the overlapping grid method is applied to couple the dynamic simulation method of the mooring cable to check the motion response of the floating structure and the safety factor of the anchoring of the selected scheme, complete the platform motion response and anchor chain force analysis, quickly analyze the platform motion and anchor chain force under the action, and determine the optimal anchoring scheme.

6. A design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 5, characterized in that: The step S6 further comprises: Step S61, using model building software to build a floating structure model and export the model file; importing the model file into the constructed calculation model, and performing grid division, assigning relevant physical parameters to the imported floating structure model, and designing relevant water depth and wave conditions according to the service sea area location and hydrogeological conditions in step S1, and verifying the accuracy and convergence of the model; Step S62, based on the verified numerical model and the water depth and wave conditions, the anchor chain forces are analyzed using the concentrated mass method for the number of anchor chains and the connection positions used in the target mooring structure design; Step S63, analyzing the maximum force of each anchor chain, finding the mooring structure and the number of anchors that meet the requirements of the mooring force safety factor, and obtaining the optimal mooring solution.

7. A design and analysis method for a floating structure mooring system suitable for shallow water conditions according to claim 6, characterized in that: The analysis of the anchor chain stress by using the concentrated mass method in step S62 includes: The concentrated mass method divides the anchor chain into multiple nodes with mass, and each node is connected by a massless spring. The tension in the i-th segment caused by the axial stiffness is Where E is the elastic modulus, d is the diameter of the anchor chain, r i+1 and r i is the global position vector of node i+1 and node i, The direction is from node i to node i+1, ε i+1 / 2 is the anchor chain strain value; internal damping force Among them C int is the internal damping coefficient, is the strain rate; the interaction between the mooring line and the seabed Where l is the stretched length of the anchor chain, d is the diameter of the anchor chain, and k b is the seabed stiffness coefficient, c b is the seabed damping coefficient, z b is the seafloor elevation, z i is the node coordinate, For z i Find the differential, is the unit vector in the z direction; the lateral drag force Where ρ is the water density, is the node speed, d is the anchor chain diameter, C dn is the lateral drag coefficient; tangential drag Among them C dt is the tangential resistance coefficient; after solving the anchor chain force, the motion equation of each node is constructed Among them, T i+1 / 2 and T i-1 / 2 represents the tension caused by the segments on both sides of the node, C i+1 / 2 and C i-1 / 2 represents the internal damping force caused by the segments on both sides of the node, W i is the underwater weight, m i is the mass of the anchor chain at node i, I is the unit matrix, a i is the additional mass matrix, is the acceleration of node i, and the motion equation is solved to obtain the motion of the floating structure platform and the forces on each anchor chain.

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