A hierarchical redundancy optimization method for improving ice belt structure of a ship against ice load

Abstract

The application relates to a ship ice belt structure grading redundancy optimization method for improving ice load capacity, which comprises the following steps: determining the floating ice collision load of the ship ice belt according to the ship ice grade and design parameters; performing finite element modeling on the ship body structure and dividing the structure levels of each side ice belt; the components of each structure level form the plate grid, the plate frame structure or the component part of the transverse frame structure; when encountering external floating ice collision load, the stress is first transmitted among the components of each level and then is extended to the components of the higher level; the structure residual strength analysis is carried out based on the finite element technology, the redundancy of the side ice belt structure is evaluated through the key component grading iterative damage method; the side ice belt structure is optimized, the optimization target is to ensure that the structure damage cannot be transmitted from the low-level component to the high-level component under the load working condition; and the residual strength analysis and the structure redundancy analysis are carried out on the optimized structure.

Description

Technical Field

[0001] This invention relates to the field of ship design, construction, and reliability analysis, and in particular to a method for optimizing the ice zone structure of ships to improve their ability to resist repeated collisions with floating ice in ice-covered areas under conditions of localized damage. Background Technology

[0002] For ice-covered vessels, the harsh environment of ice floes in polar shipping routes places high demands on ship structures. In addition to wave loads, vertical bending moments, and corrosion effects, ice-covered vessels navigating in polar waters are highly likely to encounter continuous collisions of ice floes with the bow and side ice structures, potentially causing localized damage and failure of the hull structure. To ensure the safety of ice-covered vessels in the event of localized structural failure, redundancy analysis and structural grading optimization of the hull side structure should be performed to ensure sufficient safety margins even under collision damage conditions.

[0003] Currently, in response to the problem of residual strength under localized structural damage, structural redundancy theory is gradually being introduced into ship structural design. The SOLAS code, promulgated in 2009, provides a qualitative description and requirements for the structural strength and redundancy of bulk carriers. Furthermore, the IMO MSC circular specifies structural redundancy, requiring that ships be designed and built with redundancy so that localized damage to any stiffened structural member does not immediately lead to the collapse of the entire stiffened hull. Currently, domestic research mainly analyzes the overall and local structural redundancy of conventional ship types (such as bulk carriers and oil tankers) under hazardous conditions using methods such as redundancy criterion calculations and failure path analysis. However, looking at current research, no specific quantitative standards have been established, either domestically or internationally, for the structural redundancy of key areas of ships in ice-covered areas under continuous collisions with floating ice. At the same time, research on redundancy assessment systems for different structural levels of ships is limited, and the corresponding structural assessment and design methods are still incomplete.

[0004] Therefore, to ensure the reliability of ships in ice zones under localized damage from ice collisions, structural redundancy theory should be adopted, and components at different structural levels should be classified and analyzed to establish a graded optimization method for the collision resistance of ship ice zone structures. Summary of the Invention

[0005] The purpose of this invention is to provide a graded redundancy optimization method for ship ice belt structures that can improve their resistance to ice loads. This method effectively assesses the structural redundancy of ship ice belt structures under continuous collisions with floating ice, and iteratively optimizes structural components at different levels based on their stress conditions. Finally, the changes in the overall structural mass after optimization under different schemes are analyzed to derive the optimal structural optimization scheme, ensuring the safety and reliability of the ice belt structure under extreme sea conditions.

[0006] The technical solution is as follows:

[0007] A graded redundancy optimization method for ship ice zone structures to improve ice load resistance includes the following steps:

[0008] Step 1: Determine the collision load of floating ice in the side ice zone based on the ship's ice class and design parameters;

[0009] To simulate extreme load conditions when a ship navigates in an ice zone, three regions of the ice zone—the bow, middle, and stern—are assumed to be subjected to floating ice collision loads along their entire length. The floating ice collision load conditions on the side of the ice zone are set as follows: the equivalent load of the floating ice is p, the load height is 1m, and it is evenly distributed in the bow, middle, and stern regions of the ice zone. The direction of the load is perpendicular to the hull plating.

[0010] Step 2: Perform finite element modeling of the hull structure and divide the structural layers of the side of the ship into different levels;

[0011] The mechanical response of the side ice zone structure under ice floe collision was analyzed using the finite element method. Based on the ship design parameters and structural form, the hull structure was modeled and meshed using finite element methods. In order to simulate the stress transfer and failure modes of the side ice zone structural components, the side model mesh was generated using hexahedral or tetrahedral elements.

[0012] For different ship structural forms, the ship is divided into various structural levels on the side to conduct strength assessment and optimization at each level. The components of each structural level form a plate grid, plate frame structure or are part of the transverse frame structure within their respective levels. When encountering external ice collision loads, the stress is first transferred between the internal components of each level and then extended to higher-level components.

[0013] Step 3: Perform structural residual strength analysis based on finite element technology, and evaluate the redundancy of the side structure through the "critical component graded iterative damage method";

[0014] Numerical simulation analysis was performed using the finite element model of the hull structure established in the second step. The boundary conditions were set as follows: symmetrical constraints were applied to the transverse bulkhead end, that is, the displacement in the x direction and the rotation angles in the y and z directions were constrained; the hull side ice belt collision load determined in the first step was applied to obtain the structural stress distribution, and on this basis, the ultimate strength analysis and structural redundancy assessment were carried out.

[0015] To ensure the safety of ships under extreme repeated collision loads, a standard for measuring ultimate strength, σ, is determined. accept The ultimate strength criterion is expressed as:

[0016]

[0017] Among them, R eL R is the yield strength of the material.m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. m This is a nonlinear correction factor for structural materials;

[0018] The structural redundancy is assessed using a critical component hierarchical iterative damage method, with the following steps:

[0019] 1) Perform finite element analysis of the structure based on the load conditions for ice collision, and select the component with the highest stress in the current structure, denoting its stress value as σ. max If σ max Less than σ accept If σ satisfies the structural requirements, the analysis terminates; max Greater than σ accept If so, then this component will be considered a key component of the current structure, and further analysis will continue.

[0020] 2) Determine the structural level of the critical component; if the critical component appears in the first level structure, perform damage simulation on the critical component, and then repeat step 1); if the critical component appears in the second level structure, it means that the damage risk has shifted from the first level component to the second level component, perform damage simulation on the critical component, and then repeat step 1); if the critical component appears in the third level structure, it means that the damage risk has shifted to the third level component, and the analysis terminates.

[0021] 3) After the analysis is terminated, the structural redundancy is rated. If the complete structure meets the requirements in the finite element analysis, the structural redundancy is considered to be very high, and no optimization or reinforcement is required. If only the first-level components are damaged after iterative damage analysis, the structural redundancy is rated as R1, and the structure is considered to have sufficient redundancy and no optimization is required. If the second-level components are damaged, the structural redundancy is rated as R2, and the structural redundancy is considered to be insufficient, and the first-level components need to be optimized. If the third-level components are damaged, the structural redundancy is rated as R3, and the structural redundancy is considered to be severely insufficient, and the first and second-level components need to be optimized.

[0022] For the damage simulation of the key component in step 2), the damage mode is the most unfavorable case, that is, the component ends break. Accordingly, the constraint conditions of the key component in the finite element model are modified to be simply supported at one end and fixed at the other end to simulate its damage mode.

[0023] Step 4: Side ice zone structure optimization design: Based on the structural redundancy analysis results in Step 3, the corresponding components are optimized in stages. The optimization goal is to ensure that under load conditions, structural damage will not be transmitted from lower-level components to higher-level components.

[0024] Step 5: Perform residual strength analysis and structural redundancy analysis on the optimized structure. If the optimized scheme meets the requirements, calculate and analyze the structural mass change caused by the scheme. If the optimized scheme does not meet the requirements or the structural mass change is too large, exceeding 3%, continue to step 4 until the structure meets the strength and structural redundancy requirements in step 3.

[0025] Step 6: Determine the final redundancy optimization scheme for the ice zone structure.

[0026] Furthermore, in the first step,

[0027] The equivalent load of a ship colliding with ice floes is:

[0028]

[0029] The value of k is related to the ship's displacement and the output power of the ship's engine, and is expressed as:

[0030]

[0031] Δ represents the ship's displacement when operating under the highest designed ice class conditions;

[0032] P represents the actual continuous output power of the ship's engine, in kW;

[0033] a and b are related to the value of k and the area affected by the ice load;

[0034] c1 represents the probability that ice loads will appear in the head, middle, and tail regions of the ice belt under different ice classes.

[0035] Furthermore, in the second step, the structural levels on the hull side are divided as follows:

[0036] Level 1:

[0037] 1) Side longitudinal ribs;

[0038] 2) The rib structure includes ordinary ribs, intermediate ribs, and interplate ribs;

[0039] Level 2:

[0040] 1) Side longitudinal girder;

[0041] 2) Strengthen the ribs;

[0042] Level 3:

[0043] 1) Deck sideboards;

[0044] 2) Elbow plate structure including bilge elbow plate and beam elbow plate;

[0045] 3) A bulkhead structure comprising horizontal bulkhead girders, vertical bulkhead girders, and bulkhead panels.

[0046] In the third step, the ultimate strength measurement standard σ is determined. accept :

[0047]

[0048] Among them, R eL R is the yield strength of the material. m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. m This is the nonlinear correction coefficient for the structural material.

[0049] Furthermore, the optimization methods in the fourth step include: improving the structural strength of key components, i.e., increasing the size of the components or improving the steel used in the components; and increasing the force transmission path of key components, i.e., adjusting the structural form of the components or increasing the number of components within the structural level to be optimized.

[0050] The proposed method for graded redundancy optimization of ship structures in ice zones to improve ice load resistance has the following advantages compared to existing technologies:

[0051] 1) This invention proposes a graded redundancy optimization method for the side ice zone structure under ice floe collision, which can quantitatively evaluate the remaining strength and redundancy of the structure at low cost and high efficiency, and perform targeted optimization for each level of the structure;

[0052] 2) The key component hierarchical iterative damage method proposed in this invention can efficiently evaluate the structural redundancy under collision damage conditions, provide a basis for structural optimization, and supplement existing specifications;

[0053] 3) The structural hierarchical optimization method proposed in this invention can improve the residual strength under local damage and optimize the structural reliability by targeting key components at different levels during the structural stress process, while ensuring that the overall structural quality remains basically unchanged. Attached Figure Description

[0054] Figure 1 Flowchart for implementing the graded iterative damage method for key components;

[0055] Figure 2 The finite element model and mesh diagram are examples of this invention;

[0056] Figure 3 This is a schematic diagram of the ice floe collision load in the finite element model of an example of the present invention;

[0057] Figure 4 This is the first analysis of the structural stress cloud diagram in the example of the present invention;

[0058] Figure 5 This is the second structural stress cloud diagram for an example of the present invention;

[0059] Figure 6 This is the third structural stress cloud diagram of an example of the present invention;

[0060] Figure 7 This is the fourth analysis structural stress cloud diagram of an example of the present invention;

[0061] Figure 8 This is the fifth structural stress cloud diagram analyzed in this invention example;

[0062] Figure 9 This is the sixth structural stress cloud diagram of an example of the present invention;

[0063] Figure 10 The stress cloud diagram is an optimized structural scheme of an example of the present invention.

[0064] Figure 11 This is a comparison diagram of the stress of key components in the optimized scheme and the original scheme of the present invention. Detailed Implementation

[0065] The technical solution of the present invention, which is a graded redundancy optimization method for improving the ice load resistance of ship ice zone structures, is first introduced below, including the following steps:

[0066] Step 1: Determine the collision load of floating ice in the side ice zone based on the ship's ice class and design parameters.

[0067] The equivalent load of a ship colliding with ice floes is:

[0068]

[0069] The value of k is related to the ship's displacement and the output power of the ship's engine, and can be expressed as:

[0070]

[0071] Δ represents the ship's displacement when operating under the highest designed ice class conditions;

[0072] P represents the actual continuous output power of the ship's engine, in kW;

[0073] a and b are related to the value of k and the area affected by the ice load, and the specific values ​​are shown in Table 1.

[0074] Table 1 Values ​​of a and b for different areas of the ship

[0075]

[0076] c1 represents the probability that ice loads will appear in the head region, middle region, and tail region of the ice belt under different ice classes. The specific values ​​are shown in Table 2.

[0077] Table 2. Values ​​of c1 in different regions of the ice zone for each ice class.

[0078]

[0079] p0 is the nominal ice pressure, which is taken as 5.6 MPa in actual calculations.

[0080] To simulate extreme load conditions when a ship navigates in ice-covered areas, the analysis assumes that three regions of the ice zone are subjected to ice collision loads along their entire length. The load conditions are set as follows: the equivalent ice load is p, the load height is 1m, and it is evenly distributed in the bow, midsection, and stern regions of the ice zone, with the load direction perpendicular to the hull plating.

[0081] The second step is to perform finite element modeling of the hull structure and divide it into various structural layers on the hull side.

[0082] The mechanical response of the hull side ice zone structure under ice floe collision was analyzed using the finite element method. Based on the ship's design parameters and structural form, finite element modeling and meshing were performed on the hull structure. To accurately simulate the stress transfer and failure modes of the hull side ice zone structural components, hexahedral or tetrahedral elements were used for the meshing of the hull side model.

[0083] For different ship structural forms such as longitudinal frame, transverse frame and hybrid frame, the structure is divided into three levels for strength assessment and optimization at each level. The specific classification is as follows.

[0084] Level 1:

[0085] 1) Side longitudinal ribs;

[0086] 2) The rib structure includes ordinary ribs, intermediate ribs, and interplate ribs;

[0087] Level 2:

[0088] 1) Side longitudinal girder;

[0089] 2) Strengthen the ribs;

[0090] Level 3:

[0091] 1) Deck sideboards;

[0092] 2) Elbow plate structure including bilge elbow plate and beam elbow plate;

[0093] 3) A bulkhead structure comprising horizontal bulkhead girders, vertical bulkhead girders, and bulkhead panels.

[0094] Each structural member at each level forms a lattice, a frame structure, or is part of a transverse frame structure within its own level. When encountering external ice collision loads, stress is first transferred between the internal members at each level, and then extends to higher-level members.

[0095] Step 3: Perform residual strength analysis of the structure based on finite element method, and evaluate the redundancy of the side structure using the "critical component graded iterative damage method".

[0096] Numerical simulation analysis was performed using the finite element model of the hull structure established in the second step. Boundary conditions were set as follows: symmetrical constraints were applied to the transverse bulkhead ends (i.e., constraints on displacement in the x-direction and rotation in the y and z directions). Loading was performed according to the load conditions described in the first step to obtain the structural stress distribution. Based on this, ultimate strength analysis and structural redundancy assessment were conducted.

[0097] To ensure the safety of ships under extreme repeated collision loads, the ultimate strength criterion is expressed as:

[0098]

[0099] Among them, R eL R is the yield strength of the material. m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. m This is the nonlinear correction coefficient for the structural material.

[0100] The structural redundancy is evaluated using the critical component hierarchical iterative damage method. The analysis steps are as follows:

[0101] 1) Perform finite element analysis of the structure based on the loading conditions for ice floe collision. Select the component with the highest stress in the structure and denote its stress value as σ. max If σ max Less than σ accept If σ satisfies the structural requirements, the analysis terminates; max Greater than σ accept If so, then this component will be considered a key component of the current structure, and further analysis will continue.

[0102] 2) Determine the structural level of the critical component. If the critical component appears in the first level structure, perform damage simulation on the critical component and then repeat step 1); if the critical component appears in the second level structure, it means that the damage risk has shifted from the first level component to the second level component, perform damage simulation on the critical component and then repeat step 1); if the critical component appears in the third level structure, it means that the damage risk has shifted to the third level component, and the analysis terminates.

[0103] 3) After the analysis is terminated, the structural redundancy is rated. If the complete structure meets the requirements in the finite element analysis, the structural redundancy is considered to be high, and no optimization or reinforcement is required. If only the first-level components are damaged after iterative damage analysis, the structural redundancy is rated as R1, indicating that the structure has sufficient redundancy and no optimization is required. If the second-level components are damaged, the structural redundancy is rated as R2, indicating that the structural redundancy is insufficient and the first-level components need to be optimized. If the third-level components are damaged, the structural redundancy is rated as R3, indicating that the structural redundancy is severely insufficient and the first and second-level components need to be optimized.

[0104] For the damage simulation of the critical component in step 2), the most unfavorable damage mode is taken, i.e., fracture occurs at the end of the component. Accordingly, the constraint conditions of the critical component in the finite element model are modified to be simply supported at one end and fixed at the other end to simulate its damage mode.

[0105] Step 4: Optimization design of the side ice zone structure

[0106] Based on the structural redundancy analysis results from the third step, the corresponding components are optimized in a hierarchical manner. The optimization objective is to ensure that under load conditions, structural damage does not transfer from lower-level components to higher-level components. The optimization methods mainly include: improving the structural strength of key components, i.e., increasing component size or improving component steel; and increasing the force transmission paths of key components, i.e., adjusting the structural form of components or increasing the number of components within the structural level to be optimized.

[0107] Step 5: Perform residual strength analysis and structural redundancy analysis on the optimized structure. If the optimized scheme meets the requirements, calculate and analyze the structural mass change caused by the scheme. If the optimized scheme does not meet the requirements or the structural mass change is too large, such as exceeding 3%, continue to Step 4 until the structure meets the strength and structural redundancy requirements in Step 3.

[0108] Step 6: Determine the final redundancy optimization scheme for the ice zone structure.

[0109] The following example, using the structural optimization of the side ice belt structure of a PC6-class ice-covered vessel under ice floe collision, illustrates the specific implementation of this invention.

[0110] First, the collision load of floating ice on the side ice zone structure is determined based on the ship's ice class, design parameters, and navigation conditions. The side structure uses AH36 steel. Using the equivalent load calculation formula, the load condition is set as follows: load magnitude 2.55 MPa, load height 1 m, evenly distributed in the bow area of ​​the ship's ice zone (sub-regions 1 to 25), with the load direction perpendicular to the hull plating.

[0111] Finite element modeling was performed on the hull structure, and the various structural layers on the hull sides were divided. Based on the structural form of the bow region in the ice zone, finite element modeling and mesh generation of the hull were performed, see [link to documentation]. Figure 1 Apply an equivalent load of floating ice to the structure, see Figure 2 .

[0112] In the structural hierarchy classification, the structure is divided into three levels so that strength assessment and optimization can be carried out at each level.

[0113] Level 1:

[0114] 1) Side longitudinal ribs;

[0115] 2) The rib structure includes ordinary ribs, intermediate ribs, and interplate ribs;

[0116] Level 2:

[0117] 1) Side longitudinal girder;

[0118] 2) Strengthen the ribs;

[0119] Level 3:

[0120] 1) Deck sideboards;

[0121] 2) Elbow plate structure including bilge elbow plate and beam elbow plate;

[0122] 3) A bulkhead structure comprising horizontal bulkhead girders, vertical bulkhead girders, and bulkhead panels.

[0123] Each structural member at each level forms a lattice, a frame structure, or is part of a transverse frame structure within its own level. When encountering external ice collision loads, stress is first transferred between the internal members at each level, and then extends to higher-level members.

[0124] Residual strength analysis of the structure was performed using finite element method (FEM), and the redundancy of the side structure was assessed using the "critical component graded iterative damage method." In the FEM model setup, boundary conditions were set to apply symmetrical constraints to the transverse bulkhead ends (i.e., constraining displacement in the x-direction and rotation in the y and z directions). Loading was performed according to the load conditions described in the first step to obtain the structural stress distribution. Based on this, ultimate strength analysis and structural redundancy assessment were conducted.

[0125] To ensure the safety of ships under extreme repeated collision loads, the ultimate strength criterion is expressed as:

[0126]

[0127] Among them, R eL R is the yield strength of the material. m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. mThis is the nonlinear correction factor for the structural materials. Calculations show that σ is... for this ship. accept It is 309.75 MPa.

[0128] The structural redundancy is assessed using a critical component hierarchical iterative damage method. The flowchart for the method implementation is shown below. Figure 3 The specific analysis steps are as follows:

[0129] 1) Perform finite element analysis of the structure based on the loading conditions for ice floe collision. Select the component with the highest stress in the structure and denote its stress value as σ. max If σ max Less than σ accept If σ satisfies the structural requirements, the analysis terminates; max Greater than σ accept If so, then this component will be considered a key component of the current structure, and further analysis will continue.

[0130] 2) Determine the structural level of the critical component. If the critical component appears in the first level structure, perform damage simulation on the critical component, and then repeat step 1); if the critical component appears in the second level structure, it means that the damage risk has shifted from the first level component to the second level component, perform damage simulation on the critical component, and then repeat step 1); if the critical component appears in the third level structure, it means that the damage risk has shifted to the third level component, and the analysis terminates.

[0131] 3) After the analysis is terminated, the structural redundancy is rated. If the complete structure meets the requirements in the finite element analysis, the structural redundancy is considered to be high, and no optimization or reinforcement is required. If only the first-level components are damaged after iterative damage analysis, the structural redundancy is rated as R1, indicating that the structure has sufficient redundancy and no optimization is required. If the second-level components are damaged, the structural redundancy is rated as R2, indicating that the structural redundancy is insufficient and the first-level components need to be optimized. If the third-level components are damaged, the structural redundancy is rated as R3, indicating that the structural redundancy is severely insufficient and the first and second-level components need to be optimized.

[0132] For the damage simulation of the critical component in step 2), the most unfavorable damage mode is taken, i.e., fracture occurs at the end of the component. Accordingly, the constraint conditions of the critical component in the finite element model are modified to be simply supported at one end and fixed at the other end to simulate its damage mode.

[0133] Analysis shows that the ice zone structure on the ship's side underwent six iterative damage simulations. The results of each simulation are shown in Table 3, and the stress cloud diagrams of the structure for each analysis are shown in [the table below]. Figures 4-9 Based on the analysis results, two components in the first-level structure and four components in the second-level structure were damaged, ultimately leading to damage to the transverse bulkhead in the third-level structure. Therefore, the structural redundancy is assessed as R3, requiring optimization of the first and second-level components.

[0134] Table 3. Analysis process of critical component graded iterative damage method

[0135]

[0136] Based on the structural redundancy analysis results, key components were optimized in stages. By comparing and analyzing various optimization methods, the structural reinforcement scheme was determined as follows: increase the size of the side longitudinal girder of key component 1-1 in the load area, and change the ball flat steel from type 10 (100×6) to type 14a (140×7); increase the size of the side longitudinal girder of key component 2-1 in the load area, and change the ball flat steel from type 14a (140×7) to type 16a (160×8).

[0137] Finite element analysis was performed again on the optimized structure, and the stress cloud diagram of the side structure is shown below. Figure 10 The results show that the maximum stress value σ max It appears at key components 1-2 of the original structure, and σ max Less than σ accept This indicates that the structure has sufficient redundancy. Under the complete structural condition, compared to the original design, the stress values ​​of each key component are reduced, indicating a significant improvement in the remaining strength of the structure. (See...) Figure 11 Furthermore, the structural mass changes caused by the optimization scheme were calculated and analyzed. The results show that the change in hull structural mass before and after optimization does not exceed 3%. Therefore, the optimization scheme meets the requirements, and the final ice zone structure graded optimization scheme for the ship is formed.

Claims

1. A graded redundancy optimization method for ship ice zone structures to improve ice load resistance, comprising the following steps: Step 1: Determine the collision load of floating ice in the side ice zone based on the ship's ice class and design parameters; Step 2: Perform finite element modeling of the hull structure and divide the structural layers of the side of the ship into different levels; Step 3: Perform structural residual strength analysis based on finite element technology, and evaluate the redundancy of the side structure using the "critical component graded iterative damage method"; To ensure the safety of ships under extreme repeated collision loads, a standard for measuring ultimate strength, σ, is determined. accept The ultimate strength criterion is expressed as: in, R eL R is the yield strength of the material. m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. m This is a nonlinear correction factor for structural materials; The structural redundancy is assessed using a critical component hierarchical iterative damage method, with the following steps: 1) Perform finite element analysis of the structure based on the load conditions for ice collision, and select the component with the highest stress in the current structure, denoting its stress value as σ. max If σ max Less than σ accept If σ satisfies the structural requirements, the analysis terminates; max Greater than σ accept If so, then this component will be considered a key component of the current structure, and further analysis will continue. 2) Determine the structural level of the critical component; If a critical component appears in the first-level structure, then perform a damage simulation on the critical component, and then repeat step 1). If the critical component appears in the second-level structure, it indicates that the damage risk has shifted from the first-level component to the second-level component. Perform a damage simulation on the critical component and then repeat step 1). If the critical component appears in the third-level structure, it indicates that the risk of damage has been transferred to the third-level component, and the analysis is terminated. 3) After the analysis is terminated, the structural redundancy is rated; If the complete structure meets the requirements in the finite element analysis, the structural redundancy is considered to be high, and no optimization or reinforcement is needed. If, after iterative damage analysis, only the first-level components are damaged, the structural redundancy is rated as R1, indicating that the structure has sufficient redundancy and no optimization is needed. If the second-level components are damaged, the structural redundancy is rated as R2, indicating that the structural redundancy is insufficient and the first-level components need to be optimized. If the third-level components are damaged, the structural redundancy is rated as R3, indicating that the structural redundancy is severely insufficient and the first and second-level components need to be optimized. For the damage simulation of the key component in step 2), the damage mode is the most unfavorable case, that is, the component ends fracture. Accordingly, the constraint conditions of the key component in the finite element model are modified to be simply supported at one end and fixed at the other end to simulate its damage mode. Step 4: Side ice zone structure optimization design: Based on the structural redundancy analysis results in Step 3, the corresponding components are optimized in stages. The optimization goal is to ensure that under load conditions, structural damage will not be transmitted from lower-level components to higher-level components. Step 5: Perform residual strength analysis and structural redundancy analysis on the optimized structure. If the optimized scheme meets the requirements, calculate and analyze the structural mass change caused by the scheme. If the optimized scheme does not meet the requirements or the structural mass change is too large, exceeding 3%, continue to step 4 until the structure meets the strength and structural redundancy requirements in step 3. Step 6: Determine the final redundancy optimization scheme for the ice zone structure.

2. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, In the first step, the equivalent load of the ice floe collision on the side of the hull is: The value of k is related to the ship's displacement and the output power of the ship's engine, and is expressed as: Δ represents the ship's displacement when operating under the highest designed ice class conditions; P represents the actual continuous output power of the ship's engine, in kW; a and b are related to the value of k and the area affected by the ice load; c1 represents the probability that ice loads will appear in the head, middle, and tail regions of the ice belt under different ice classes.

3. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, The first step is as follows: To simulate the extreme load conditions when a ship is navigating in an ice zone, three regions of the ice zone—the bow region, the middle region, and the stern region—are assumed to be subjected to floating ice collision loads along their entire length. The floating ice collision load conditions on the side of the ice zone are set as follows: the equivalent load of the floating ice is p, the load height is 1m, and it is evenly distributed in the bow, middle, and stern regions of the ice zone. The direction of the load is perpendicular to the hull plating.

4. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, In the second step, the structural levels of the hull side are divided as follows: Level 1: 1) Side longitudinal ribs; 2) The rib structure includes ordinary ribs, intermediate ribs, and interplate ribs; Level 2: 1) Side longitudinal girder; 2) Strengthen the ribs; Level 3: 1) Deck side panels; 2) Elbow plate structure including bilge elbow plate and beam elbow plate; 3) A bulkhead structure comprising horizontal bulkhead girders, vertical bulkhead girders, and bulkhead plates; In the third step, the ultimate strength measurement standard σ is determined. accept : Among them, R eL R is the yield strength of the material. m Let C be the tensile strength of the material, λ be the load safety factor under the calculated working condition, and C be the tensile strength of the material. m This is the nonlinear correction coefficient for the structural material.

5. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, The second step involves analyzing the mechanical response of the side ice belt structure under ice floe collision using the finite element method. Based on the ship's design parameters and structural form, the hull structure is modeled and meshed using finite element methods. To simulate the stress transfer and failure modes of the side ice belt structure components, the side model mesh uses hexahedral or tetrahedral elements. For different ship structural forms, the side structure is divided into various levels to facilitate strength assessment and optimization at each level. Components at each structural level form plate grids, plate frames, or are part of the transverse frame structure within their respective levels. When encountering external ice floe collision loads, stress is first transferred between the internal components of each level and then extends to higher-level components.

6. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, The third step includes: using the finite element model of the hull structure established in the second step to perform numerical simulation analysis, with boundary conditions set as follows: applying symmetrical constraints to the transverse bulkhead ends, i.e. constraining displacement in the x direction and rotation in the y and z directions; loading according to the ice collision load of the side ice belt determined in the first step to obtain the structural stress distribution, and on this basis, performing ultimate strength analysis and structural redundancy assessment.

7. The method for hierarchical redundancy optimization of ship ice zone structure according to claim 1, characterized in that, The fourth step of the optimization method includes: improving the structural strength of key components, i.e., increasing the size of the components or improving the steel used in the components; and increasing the force transmission path of key components, i.e., adjusting the structural form of the components or increasing the number of components within the structural level to be optimized.

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