Detachable mooring apparatus for floating offshore wind turbine and structural design method thereof

Abstract

A detachable mooring device for a floating offshore wind turbine and a method for designing the structure thereof are disclosed. The detachable mooring device comprises a housing fixedly coupled to a floating body, an arm rotatably coupled to the housing, a chain stopper arranged along the arm and supporting a mooring chain, an upper chain stopper arranged on the housing side to receive a load in a towing state, a chain wheel that induces movement of the chain when installing and dismantling the mooring chain, and a pin coupling structure rotatably connecting the housing, the arm, the chain stopper, and the upper chain stopper, wherein in a mooring state, the tensile load of the mooring chain is mainly transmitted through the arm and the chain stopper, and in a towing state, the towing load is mainly transmitted to the housing through the upper chain stopper.

Description

Technology Field

[0001] The present invention relates to a detachable mooring device for a floating offshore wind turbine and a method for designing the structure thereof. Background Technology

[0002] Floating offshore wind turbines require the repeated connection and disconnection of mooring lines during the offshore installation and maintenance process.

[0003] Existing mooring systems are often designed based on a permanently fixed structure, which results in slow release during typhoon avoidance, large-scale maintenance, or emergency transport, as well as increased installation and operating costs due to the increased weight of the mooring devices.

[0004] In particular, while very large tensile loads are applied by the mooring chains in the moored state, a different load transfer path is formed by the towing force rather than the mooring chains in the towing state; therefore, structural design based solely on a single load condition has limitations in terms of safety or weight efficiency.

[0005] This invention is the result of the 2025 Mokpo National University Glocal College Grant Project, which was funded by the Ministry of Education and supported by the National Research Foundation of Korea. Prior art literature

[0006] Korean Patent Publication No. 10-2025-0015409 (February 3, 2025) The problem to be solved

[0007] The present invention is intended to provide a detachable mooring device capable of stably accommodating different load transfer characteristics in mooring and towing states.

[0008] In addition, it is intended to provide a structural design philosophy that can suppress unnecessary weight increase while ensuring structural safety.

[0009] In addition, the purpose is to provide a structural design method for a mooring device that can improve design efficiency without repetitive structural analysis. means of solving the problem

[0010] According to one aspect of the present invention, a detachable mooring device is disclosed that is installed on a floating body of a floating offshore wind turbine and enables the connection and disconnection of a mooring line.

[0011] A detachable mooring device according to an embodiment of the present invention comprises a housing fixedly coupled to a floating body, an arm rotatably coupled to the housing, a chain stopper disposed along the arm and supporting a mooring chain, an upper chain stopper disposed on the side of the housing to receive a load in a towing state, a chain wheel that induces movement of the chain when installing and dismantling the mooring chain, and a pin coupling structure rotatably connecting the housing, the arm, the chain stopper, and the upper chain stopper, wherein in a mooring state, the tensile load of the mooring chain is mainly transmitted through the arm and the chain stopper, and in a towing state, the towing load is mainly transmitted to the housing through the upper chain stopper.

[0012] The above arm is a member that exerts a dominant influence on the structural response to the load occurring in the above mooring state, and is formed to be relatively larger than the thickness of the housing to ensure structural safety in the above mooring state.

[0013] The above housing is a member that exerts a dominant influence on the structural response to the load occurring in the above towing state, and is formed with a thickness range different from that of the arm to ensure structural safety in the above towing state.

[0014] The above chain stopper and upper chain stopper include a curved contact portion that contacts the mooring chain or towing load to transmit the load.

[0015] The above-described pin coupling structure is configured to allow rotational degrees of freedom in an axial direction orthogonal to the load transfer direction while restricting translational movement.

[0016] The above chain wheel includes a plurality of pockets to stably guide the path of the chain during the installation and dismantling process of the mooring chain.

[0017] The above arm, chain stopper, and upper chain stopper are formed of a high-strength metal material and configured to repeatedly accommodate design loads occurring in the mooring and towing states.

[0018] According to another aspect of the present invention, a method for designing the structure of a detachable mooring device for a floating offshore wind turbine is disclosed.

[0019] A structural design method for a detachable mooring device according to an embodiment of the present invention comprises the steps of: defining design load conditions for a mooring state and a towing state, respectively; evaluating the structural response of the detachable mooring device according to the design load conditions; deriving a member that has a dominant influence on the structural response for each of the mooring state and the towing state; and ensuring structural safety by preferentially adjusting the dimensions of the derived member.

[0020] Design parameters are selected such that in the above mooring state, the arm series members exert a dominant influence on the structural response, and in the above towing state, the housing series members exert a dominant influence on the structural response.

[0021] The above structural response includes at least one of weight and maximum stress. Effects of the invention

[0022] The detachable mooring device for a floating offshore wind turbine and the structural design method according to an embodiment of the present invention can stably accommodate different load characteristics occurring in the mooring state and the towing state.

[0023] In addition, by selectively reinforcing only the dominant members according to load conditions, the increase in weight of the mooring device can be minimized.

[0024] In addition, the easy-to-detach structure can improve the efficiency of installation, maintenance, and emergency transport of floating offshore wind turbines.

[0025] In addition, design time and costs can be reduced by decreasing the burden of repetitive structural analysis. Brief explanation of the drawing

[0026] FIGS. 1 to 9 are drawings for explaining a detachable mooring device for a floating offshore wind turbine and a structural design method thereof according to an embodiment of the present invention. FIG. 10 is a flowchart schematically illustrating a structural design method for a detachable mooring device for a floating offshore wind turbine according to an embodiment of the present invention. Specific details for implementing the invention

[0027] As used in this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "composed" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be excluded, or that additional components or steps may be included. Furthermore, terms such as "...part," "module," etc., as used in the specification refer to a unit that processes at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

[0028] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings.

[0029] FIGS. 1 to 9 are drawings for explaining a detachable mooring device for a floating offshore wind turbine and a structural design method thereof according to an embodiment of the present invention.

[0030] In the present invention, the Fairlead Chain Stopper (FCS) is a detachable device used during the transportation process to the installation site and during mooring of a floating offshore wind turbine, and is designed to facilitate easy connection and separation between the floating platform and the mooring line. In particular, it has functional characteristics that enable rapid transfer of the floating platform in emergency situations or when large-scale maintenance is required. The 10MW class floating offshore wind turbine that is the subject of the present invention is designed as a semi-submersible Floating Offshore Wind Turbine (SFOWT) having three floating platforms as a substructure, and FIG. 1 illustrates the configuration in which the FCS is installed on the said SFOWT.

[0031] The design shape of the FCS and the configuration of its main components are schematically illustrated in Fig. 2. As shown in Fig. 2, the FCS is designed to ensure structural safety even under the Minimum Breaking Load (MBL) conditions of the mooring line by connecting to the mooring chain above the sea surface. The FCS is largely composed of two parts: the Arm and the Housing. Among these, the 5 Pocket Chain Wheel guides the movement of the chain during installation and dismantling, while the Arm guides the chain's path and performs the function of transferring the load transmitted to the Chain Stopper to the entire FCS structure. The Chain Stopper and Upper Chain Stopper serve to support the loads generated during the installation, operation, and dismantling of the mooring chain. The Housing is a fixed structure that connects the entire FCS to the substructure of the floating body, and the Hydraulic Cylinder Support is a component to which a hydraulic device controlling the operation of the Upper Chain Stopper is attached. All these main components are connected by a pin joint structure to enable rotational operation.

[0032] To obtain design certification for mooring systems such as FCS, a structural performance review must be performed to determine whether the design load conditions for mooring conditions defined by classification society regulations are satisfied. In addition, design load conditions for towing conditions considered during actual operation must also be evaluated. The design load conditions for the structural performance evaluation were established based on the DNV classification society regulations. Since the FCS is a device directly connected to the SFOWT platform, the Design Working Range (DWR) in the horizontal plane relative to sea level and the Design Inlet Angle (DIA) in the vertical plane must be set within the ranges defined according to the classification society standards for offshore structure design. The ranges of DWR and DIA specified in the DNV classification society regulations are presented in Fig. 3.

[0033] As shown in Fig. 3, the DWR was set to 0°, and the DIA of the vertical plane was defined as 10° and 29° based on the angle of the mooring line of the FCS where the maximum tensile force occurs in extreme environment mooring conditions, referencing the results calculated under the condition where the SFOWT is subjected to the EWM (Extreme Wind Speed ​​Model) and ESS (Extreme Sea State) in the integrated load analysis, and utilized for structural performance review. The design load acting on the chain stopper of the FCS in the mooring state must be applied based on the MBL, and in this invention, a studless chain with a diameter of 147 mm suitable for a 10 MW class floating offshore wind turbine was applied. The MBL of the chain was confirmed to be 21,179 kN. In the towing state, a direct traction force acts on the FCS connected to the SFOWT, and the load applied to the Upper Stopper and Chain Wheel of the FCS at this time was calculated to be 3,434 kN based on the results of the integrated load analysis. The overall design load conditions applied to the FCS structural performance evaluation are comprehensively summarized in Table 1.

[0034]

[0035] As shown in Table 1, the design load conditions for evaluating the structural performance of the FCS consist of a total of three load combinations: LC1, LC2, and LC3. Among these, LC1 and LC2 are conditions for reviewing structural safety in mooring conditions, and LC3 is a condition set to evaluate structural safety in towing conditions.

[0036] Finite Element Analysis (FEA) modeling and pre- and post-processing were performed using Altair's HyperWorks. As shown in Figure 4, the FEA model of the FCS was composed of a total of 496,472 elements and 384,305 nodes using an element size of 25 mm. Major components were modeled using both Shell and Solid elements, and contact conditions were set on surfaces where contact occurred between components.

[0037] The characteristics of the design materials for the FCS are summarized in Table 2. As shown in Table 2, SCM440 high-strength alloy steel was applied to the Stopper and Pin components, OILESS500-ABR material was used for the solid Bushing, and A148 series steel was used for the Chain Wheel on which the mooring line is mounted. For other major components, DH36 and A694F70 materials were applied, respectively. This material selection was made considering the high yield strength characteristics capable of withstanding high-load conditions in the marine environment; while it provides superior mechanical performance compared to general structural steel, the material cost is high.

[0038]

[0039] The degrees of freedom of motion and boundary conditions of the contact part for structural analysis are shown in Fig. 5. As shown in Fig. 5, the boundary conditions of the FCS were set based on the fixed part of the Main pin connected to the SFOWT, and all degrees of freedom of motion were constrained except for the rotational degree of freedom of the gravity axis. Since the Main pin has a solid axis structure and design tolerances were applied to prevent translational movement, only the rotational degree of freedom of the gravity axis was considered to occur.

[0040] Contact boundary conditions were applied to the contact surface between the main pin and the flange bushing, and the details of the contact conditions are shown in Table 3. By setting symmetric boundary conditions for the entire FEA model, the costs of modeling and numerical analysis were effectively reduced.

[0041]

[0042] As shown in Fig. 5, the boundary conditions of the FCS were set based on the fixed part of the Main pin connected to the SFOWT, and all degrees of freedom of motion were constrained except for the rotational degrees of freedom along the gravity axis. In addition, contact boundary conditions were applied to the contact surface between the Main pin and the flange bushing. By setting symmetric boundary conditions for the entire FEA model, the costs of modeling and numerical analysis were effectively reduced.

[0043] The design load conditions presented in Table 1 were applied as load conditions to the FEA model as shown in Figure 6, and structural analysis was performed.

[0044] As shown in Fig. 6, the design load in the mooring state is transmitted through the curved contact surface between the mooring chain and the chain stopper. To realize the load transmitted when the chain contacts the stopper, the load was implemented in the form of a bearing load. In the towing state, since the traction force acts directly on the upper stopper and chain wheel of the FCS, the design load was applied as a distributed load to these areas. Structural analysis was performed using the general-purpose finite element analysis software ABAQUS, and the analysis results are summarized in Table 3. The von-Mises stress combination was applied for stress evaluation. The safety evaluation of the structural design was based on the criteria set by the DNV classification society, with the allowable stress of the material set at 90% of the yield strength. Accordingly, the values ​​were calculated as 436.5 MPa for A694F70, 279 MPa for DH36, 750.6 MPa for SCM440, 526.5 MPa for A148, and 555.3 MPa for OILESS500-ABR.

[0045]

[0046] As shown in Table 4, the structural performance evaluation of the FCS was performed based on whether the component where the maximum stress occurred met the allowable stress of the corresponding material for each design load condition. As a result, it was found that structural safety was ensured, as the maximum stress derived under all load conditions did not exceed the allowable stress specified in the DNV classification regulations. The highest stress occurred under the LC2 condition, and the maximum stress generated in the DH36 component was closest to the allowable stress. The stress distribution characteristics of the FCS for the LC2 condition are presented representatively in Figure 7. As shown in Figure 7, the highest stress concentration occurred at the chain stopper in the moored state of the FCS, followed by relatively high stresses in the arm pin bearing plate and arm wall plate.

[0047] In the structural design sensitivity analysis, the influence of each design factor on the structural performance and weight of the FCS was analyzed using the orthogonal array experiment technique. The orthogonal array experiment method is an experimental design method capable of analyzing not only the principal influence between design factors and response functions but also the interactions between design factors. It is characterized by the ability to efficiently reduce the total number of experiments by eliminating interactions and higher-order interaction effects of factors with low influence. In this invention, utilizing these characteristics, an orthogonal array experiment was performed based on three-level design factors as shown in the following mathematical formula.

[0048]

[0049] Here, m is an integer greater than or equal to 2, and 3 m is the size of the experiment, (3 m -1) / 2 represents the number of columns in the orthogonal array experiment. To evaluate the structural design influence of the FCS, six major components with high stress and weight were selected as shown in Fig. 8. DF#1~3 are major components constituting the Arm; the Wall plate and Arm pin plate are connected to the Housing and operate according to the behavior of the mooring line, and are components that transmit the load transferred from the Chain stopper, while the Guide plate plays a role in stabilizing the path of the mooring rope connected to the FCS. DF#4~6 are major components constituting the Housing and serve as the connection structure between the Arm and SFOWT, playing a role in supporting the load generated during mooring and installation operations.

[0050] The thickness dimensions of the main components were defined as discrete three-level design factors (DF) considering the actual steel thickness produced and the feasibility of actual production, and the maximum stress and weight for each design load condition shown in Table 1 were set as response functions.

[0051] A total of 128 design matrices were constructed as shown in Table 5 through the application of 3-level orthogonal array experiments.

[0052]

[0053] Sensitivity analysis was performed from the design matrix results in Table 5, and the quantitative main effect on the response function of weight and structural performance for each design factor is shown in Figure 9.

[0054] As shown in Figure 9(a), the results of the main influence diagram on the weight response showed that the order of sensitivity was DF#4 (Housing wall plate), DF#3 (Arm pin plate), DF#1 (Wall plate), DF#5 (Top plate), DF#6 (Base plate), and DF#2 (Guide plate), and it was found that variations in design variables had a proportional effect on the response function.

[0055] The results of the analysis of the major influences on the maximum stress for each design load condition from LC1 to LC3 are presented in Figures 9(b) through (d), respectively. For LC1, the sensitivity of DF#1 was the highest at 62%, while the sensitivities of DF#4 and DF#3 were relatively high at 12% each. For LC2, the sensitivity of DF#1 was the most prominent at 70%, followed by DF#3 at 19%. This similar trend is attributed to the fact that both LC1 and LC2 are design load conditions under mooring conditions, and the only difference between the two conditions is the DIA. For LC3, the sensitivity of DF#4 was the highest at 95%, whereas the influence of other design factors was negligible. This is analyzed as a result of LC3 being a load condition considering the towing state, where the traction load transmitted through the upper chain stopper is concentrated on DF#4, causing high stress concentration.

[0056] Metamodels are generally generated based on Design of Experiments (DEs), such as orthogonal array experiments. Accordingly, the accuracy of a metamodel is significantly influenced by the number of experiments set in the DOE, the level of design factors, and the suitability of the experimental design theory. Therefore, the validity of the applied DOE methodology can be verified by evaluating the predictive accuracy of the generated metamodel.

[0057] Meanwhile, securing a metamodel suitable for a design problem enables effective application to nonlinear optimization analysis, robustness analysis, and reliability-based design optimization, which require extensive iterative calculations for solution convergence; this, in turn, can significantly reduce the overall cost of numerical analysis. Therefore, the generation of a metamodel with high accuracy is considered a key element in design space exploration research. In this invention, based on the results of orthogonal array experiments conducted on the structural design of FCS, a total of four metamodels—RSM, Kriging, COP, and RBFN—were constructed. To improve the accuracy of the constructed metamodels and reduce the possibility of overfitting, leave-p-out cross-validation was performed. This method is a technique that evaluates model performance by excluding p random samples from the entire dataset for validation and using the remainder for training, then repeating this process for all possible combinations. By ensuring that data is utilized evenly for both training and validation, it enables highly reliable performance verification.

[0058] Subsequently, the predictive performance of each model was compared and analyzed to examine the fit of the orthogonal array experimental results and the reliability of the metamodel.

[0059] RSM is expressed as a regression model in the form of a quadratic polynomial, as shown in the following mathematical equation, using the least squares method.

[0060]

[0061] Given a response vector g from n experimental points and a matrix Z defined by k basis variables, the unknown RSM approximation coefficient vector A is obtained by minimizing the random error vector e from the relationship between g and Z. r It is calculated from the following mathematical formula.

[0062]

[0063]

[0064] By applying the approximation coefficients calculated from the above equation, an RSM metamodel can be generated.

[0065] Kriging is defined as the sum of a global model, which represents the entire domain characteristics of the actual design space to be approximated, and a local model, which is the difference between the actual function and the global model.

[0066]

[0067] Here, A K is an unknown coefficient vector. E(x) is defined as the spatial correlation of design data and is a Gaussian correlation function.

[0068] COP is an orthogonal polynomial commonly used in polynomial regression models at regular sampling intervals.

[0069]

[0070] Here, is the mean of the design variable, a is the number of levels, and h is the level interval coefficient. b is an approximation coefficient and can be expressed by the following formula.

[0071]

[0072] RBFN was developed to approximate scattered multivariate data with high accuracy. To approximate the response function, RBFN uses a linear combination of radially symmetric functions utilizing Euclidean distance. The set of nodes in a neural network Given this, the basis functions of RBFN are defined as follows.

[0073]

[0074] Here, is a power spline basis function, and is the Euclidean distance. Power spline basis functions are defined as follows.

[0075]

[0076] Here, c is a variable of the shape function with a positive constant value. Input data Data to approximate for Given , RBFN is defined as follows.

[0077]

[0078] Here, is an unknown approximation coefficient.

[0079] A second-order polynomial was applied to RSM. Kriging used a Gaussian Kernel, applied a correlation distance of 5.0E-4 for each input variable, and set the maximum number of iterations for model optimization to 1,000. The fitting parameters for COP were set as sequential orthogonal polynomials. For RBFN, a learning rate of 0.7, 1 to 3 hidden layers, and weights ranging from -0.25 to 0.25 were applied.

[0080] The accuracy of the metamodel is R in Equation 11 2 It is determined by the value.

[0081]

[0082] In the above equation, t i is the actual result, y i is the prediction result estimated from the metamodel, represents the average of the actual results, and R 2 A value closer to 1.0 indicates that the prediction results estimated by the metamodel match the entire design space. The accuracy analysis results for each response function derived from each metamodel are shown in Table 6.

[0083]

[0084] As presented in Table 6, R for the response function of each metamodel 2 As a result of comparing prediction accuracy based on [the criterion], COP showed the lowest accuracy overall. On the other hand, RSM had an average R of 0.9 or higher 2 The value was maintained, but exceptionally low predictive performance was observed under the LC1 condition. In the case of Kriging and RBFN, R² under all conditions 2 It showed high prediction accuracy with a value converging to 1.0, and through this, it was proven that the orthogonal array experiment method applied in the present invention is suitable for approximating the FCS design space. Therefore, among the metamodels constructed in the present invention, Kriging and RBFN are judged to be the most effective metamodels for expressing the FCS structural design space with high precision.

[0085] Among the constructed metamodels, Kriging and RBFN were identified as the most effective for representing the FCS structure design space with high precision. Kriging provides stable predictive performance in cases involving complex nonlinearities and distinct interactions between variables, while RBFN smoothly interpolates response changes for multidimensional design variables to deliver excellent approximation results even with relatively small training data. Therefore, Kriging is suitable for identifying global response trends in the early design stages, while RBFN is appropriate when data is limited and rapid approximation is required.

[0086] In the case of conventional FEA analysis, the analysis time for each design load condition took 900 seconds using an analysis server with specifications of a 16-core CPU and 96 GB RAM, requiring a total of 2,700 seconds to execute all levels from LC1 to LC3. In contrast, the training time required to build the metamodel was only about 10 seconds, and the prediction time for design modifications or optimizations utilizing it is within a few seconds. This corresponds to a time reduction effect of more than 270 times compared to conventional FEA, and the total design time can be drastically shortened when performing iterative design or multiple optimization scenarios. This quantitative comparison demonstrates that the proposed method provides very high efficiency in actual design practice.

[0087] It is believed that these models can be applied in the future in fields requiring high-cost numerical analysis, such as optimization analysis, robust design, and reliability analysis, thereby improving analysis efficiency.

[0088] FIG. 10 is a flowchart schematically illustrating a structural design method for a detachable mooring device for a floating offshore wind turbine according to an embodiment of the present invention.

[0089] In step S110, design load conditions for mooring and towing conditions are defined, respectively.

[0090] In step S120, the structural response of the detachable mooring device is evaluated according to the design load conditions.

[0091] Here, the structural response includes at least one of weight and maximum stress.

[0092] In step S130, the member having a dominant influence on the structural response is identified for the mooring state and the towing state, respectively.

[0093] Here, design parameters are selected such that in the mooring state, the arm series members exert a dominant influence on the structural response, and in the towing state, the housing series members exert a dominant influence on the structural response.

[0094] In step S140, structural safety is ensured by first adjusting the dimensions of the derived member.

[0095] The embodiments of the present invention described above are disclosed for illustrative purposes only, and those skilled in the art with ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions should be considered to fall within the scope of the following claims.

Claims

Claim 1 A detachable mooring device installed on a floating body of a floating offshore wind turbine to enable the connection and disconnection of a mooring line, comprising: a housing fixedly coupled to the floating body; an arm rotatably coupled to the housing; a chain stopper disposed along the arm and supporting a mooring chain; an upper chain stopper disposed on the side of the housing to receive a load in a towing state; a chain wheel that induces movement of the chain when installing and dismantling the mooring chain; and a pin coupling structure rotatably connecting the housing, the arm, the chain stopper, and the upper chain stopper, wherein in a mooring state, the tensile load of the mooring chain is transmitted through the arm and the chain stopper, and in a towing state, the towing load is transmitted to the housing through the upper chain stopper. Claim 2 A detachable mooring device according to claim 1, wherein the arm is a member that has a dominant influence on the structural response to a load occurring in the mooring state, and is formed to be relatively larger than the thickness of the housing to ensure structural safety in the mooring state. Claim 3 A detachable mooring device according to claim 1, wherein the housing is a member that has a dominant influence on the structural response to the load occurring in the towing state, and is formed with a thickness range different from that of the arm to ensure structural safety in the towing state. Claim 4 A detachable mooring device according to claim 1, characterized in that the chain stopper and the upper chain stopper include a curved contact portion that contacts the mooring chain or towing load to transmit the load. Claim 5 A detachable mooring device according to claim 1, characterized in that the pin coupling structure is configured to allow rotational freedom in an axial direction orthogonal to the load transfer direction while restricting translational movement. Claim 6 A detachable mooring device according to claim 1, characterized in that the chain wheel includes a plurality of pockets to stably guide the path of the chain during the installation and dismantling process of the mooring chain. Claim 7 A detachable mooring device according to claim 1, characterized in that the arm, chain stopper, and upper chain stopper are formed of a high-strength metal material and configured to repeatedly accommodate design loads occurring in the mooring state and towing state. Claim 8 A method for designing the structure of a detachable mooring device for a floating offshore wind turbine, comprising: a step of defining design load conditions for a mooring state and a towing state, respectively; a step of evaluating the structural response of the detachable mooring device according to the design load conditions; a step of deriving a member that has a dominant influence on the structural response for each of the mooring state and the towing state; and a step of ensuring structural safety by preferentially adjusting the dimensions of the derived member. Claim 9 A structural design method for a detachable mooring device according to claim 8, characterized by selecting design factors such that in the mooring state, the arm series member has a dominant influence on the structural response, and in the towing state, the housing series member has a dominant influence on the structural response. Claim 10 A method for designing the structure of a detachable mooring device according to claim 8, wherein the structural response comprises at least one of weight and maximum stress.

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