A Fatigue Strength Analysis Method for Type A Independent Liquid Cargo Tank Based on GeniE

Abstract

The present invention relates to a fatigue strength analysis method for an independent A-type liquid cargo tank based on GeniE, comprising the following steps: S1. Coarse grid modeling: Establish a coarse grid simulation model in GeniE; establish a support coarse grid model in GeniE; construct a coarse grid analysis model; S4. Fatigue analysis: It includes ten analysis conditions, and the fatigue analysis under each analysis condition includes the following steps: S41. Coarse grid analysis: According to the analysis condition, input the corresponding analysis parameters, add the corresponding load conditions; load the condition, and obtain the coarse grid result R file after the analysis; S42. Fine grid modeling: Determine the part to be subjected to fatigue strength analysis as the fatigue analysis node to obtain a fine grid analysis model; S43. Fine grid analysis: Obtain the fine grid result R file after the analysis, and determine the hot spot stress range Δσ in the fatigue analysis node; S5. According to the hot spot stress range Δσ under each analysis condition, calculate the fatigue stress range of fatigue damage under this analysis condition.

Description

Technical Field

[0001] The present invention relates to the field of ship structures, and particularly to a method for analyzing the fatigue strength of Type A independent liquid cargo tanks based on GeniE. Background Art

[0002] Liquefied natural gas and liquefied petroleum gas are flammable, explosive, and easily leakable substances. The safety, transportation, and storage of ships directly affect ship energy consumption and economic benefits. An important issue for LPG / LEG (liquefied petroleum gas / ethylene) and LNG carriers is to evaluate the strength of the connection nodes between independent liquid cargo tanks and the hull. Refer to Figure 2 , a support 3 is provided between the independent liquid cargo tank 3 and the ship's hold 1. For Type A independent liquid cargo tanks, generally, it is not necessary to calculate the fatigue strength of the liquid cargo tank and the support. However, when the design temperature of the liquid cargo is lower than -55 °C, fatigue analysis is required. At present, there is no set of efficient and accurate analysis methods, and there are problems of complex analysis and inaccurate results in the fatigue analysis of independent liquid cargo tanks. Summary of the Invention

[0003] In view of the above-mentioned disadvantages of the prior art, the technical problem to be solved by the present invention is to provide a method for analyzing the fatigue strength of Type A independent liquid cargo tanks based on GeniE, which can quickly and accurately perform fatigue strength analysis, is convenient and fast, accurate and efficient, can effectively reduce the workload, and reduce the labor load.

[0004] To achieve the above object, the present invention provides a method for analyzing the fatigue strength of Type A independent liquid cargo tanks based on GeniE, including the following steps:

[0005] S1. Coarse grid modeling: Establish a coarse grid simulation model in GeniE, including three adjacent cabin sections, and the middle cabin section is the target cabin to be evaluated. The coarse grid simulation model includes the ship's hold part and the liquid tank part. The ship's hold part includes the main components of the hull, the stiffener structure on the main components, and the brackets that support the strength of the main components and usually have a side length greater than the rib pitch. The main components include the main transverse components and the main longitudinal components; and in the coarse grid simulation model, the plate parts are simulated by plate elements, the stiffener structure is simulated by beam elements, and the transverse panel and the vertical web of the T-section are simulated by beam elements and plate elements respectively; the size of the coarse grid in the coarse grid simulation model is the rib pitch multiplied by the rib pitch.

[0006] S2. Support modeling: Establish a support coarse grid model in GeniE, including the support block part and the laminated wood part. Among them, the support block part is simulated by plate elements, and the laminated wood part is simulated by beam elements that can only be compressed, and the attribute is set to "truss-compression only", and the area of the beam element is set according to the size of the laminated wood area, and the axial stiffness is consistent with the actual stiffness of the laminated wood.

[0007] S3. Construct a coarse grid analysis model: Arrange the support coarse grid model in the coarse grid simulation model as required to form a coarse grid analysis model;

[0008] S4. Fatigue analysis: Fatigue analysis includes ten analysis conditions, namely fully loaded HSM, fully loaded FSM, fully loaded BSR, fully loaded BSP, fully loaded OST, ballast HSM, ballast FSM, ballast BSR, ballast BSP, and ballast OST; The corresponding hot spot stress ranges are obtained under the ten analysis conditions respectively. The fatigue analysis under each analysis condition includes the following steps:

[0009] S41. Coarse grid analysis:

[0010] S411. According to the analysis condition, input the corresponding analysis parameters. The analysis parameters include the time proportion of each loading condition, the time proportion of navigation, the draft under the loading state, the initial metacentric height, and the radius of gyration of roll; Add the corresponding load conditions to the condition. The load conditions include the pressure caused by acceleration, hydrodynamic pressure, and the load generated by the deformation of the hull girder; The fatigue load environment is selected as the North Atlantic 10 -2 exceedance probability;

[0011] S412. Load the condition, select the analysis type "Tension / Compression Analysis", and the GeniE program will analyze the three cabin sections of the coarse grid simulation model for the coarse grid analysis model; After the analysis is completed, the coarse grid result R file is obtained. The coarse grid result R file includes the stress results and deformation results of each element and node in the coarse grid analysis model;

[0012] S42. Fine grid modeling: Determine the area to be subjected to fatigue strength analysis as the fatigue analysis nodes. Take the fatigue analysis nodes in the coarse grid analysis model, and extend one strong frame forward and backward in the ship length direction and extend to the adjacent main longitudinal supporting members in the ship width direction for fine meshing to obtain a fine grid analysis model. And the fine grid size at the fatigue nodes is the plate thickness of the parts here, where the main longitudinal supporting members are the longitudinally distributed strong members;

[0013] S43. Fine grid analysis:

[0014] S431. Select "Local Analysis" for analysis. The program will read the boundary conditions and loads of the fine grid analysis model in the coarse grid result R file in step S412 according to the boundary position of the fine grid analysis model and load them into the fine grid analysis model;

[0015] S432. GeniE analyzes the fine grid analysis model. After the analysis is completed, a fine grid result R file is obtained. The fine grid result R file includes the further refined stress results and deformation results of each element and node in the fine grid analysis model. Read the principal stress on the surface of the element and determine the hot spot stress range Δσ of the fatigue analysis node;

[0016] S5. According to the hot spot stress range Δσ under each analysis condition, calculate the fatigue stress range Δσ of the fatigue damage under this analysis condition FS .

[0017] Furthermore, in the step S1, the main longitudinal members include the outer plate, the inner bottom, the inner bottom side plate, and the longitudinal bulkhead, and the main transverse members include the transverse bulkhead, the double bottom and the bilge floor, the deck, and the transverse T-section on the longitudinal bulkhead.

[0018] Furthermore, the step S432 also includes: comparing the fine grid result R file with the group grid result R file to verify the fine grid result R file.

[0019] Furthermore, in the step S5, the fatigue stress range Δσ for calculating the fatigue damage is determined by the following formula FS : Δσ FS = f mean ·f thick ·f material ·f w ·f c ·f e ·Δσ, where f mean is the mean stress adjustment coefficient, f thick is the plate thickness adjustment coefficient; f material is the material adjustment coefficient; f w is the weld treatment adjustment coefficient; f c is the corrosion allowance adjustment coefficient, f e is the environment adjustment coefficient.

[0020] Furthermore, it also includes step S6. Design the fatigue life. The fatigue life is divided into two stages according to the corrosion protection situation. During the corrosion protection stage, the fatigue nodes are calculated according to the S-N curve in the air, and the remaining years T C are calculated according to the corrosion environment, including: S61. Calculate the annual fatigue damage without considering corrosion: Take the maximum value in the fatigue stress range Δσ FS of each analysis condition as the dominant fatigue stress range Δσ FSmax , and calculate the annual fatigue damage under this analysis condition by the following formula: where is the number of stress cycles per year, L is the ship length; N R is the probability of exceedance of 10-2 The stress cycle number at that time; ξ is the Weibull shape parameter; is the complete gamma function; K2 is a constant on the S-N curve; m is the slope of the S-N curve, and μ is an adjustment coefficient when considering the change in the slope of the S-N curve.

[0021] Furthermore, it includes step S62, synthesis fatigue damage calculation: Number the ten analysis working conditions as analysis working conditions 1# to 10# respectively, and record their corresponding annual fatigue damages as D E(1) ~D E(10) , calculate the fatigue damage in the corrosive environment and the fatigue damage without the corrosive environment under each analysis working condition, D j =D E(j) ·(T DF +T C ), wherein, T C is the number of years in the corrosive environment, T C25 is the number of years in the corrosive environment when the design life is 25 years, T D is 25 years, T DF is the fatigue design life, D E(j) is the annual fatigue damage without considering the corrosion condition under the j# analysis working condition, 1≤j≤10.

[0022] Furthermore, it includes step S63, calculate the cumulative fatigue damage of all analysis working conditions: wherein, f0 is the time factor occupied by the navigation state; α j is the proportion of each loading state; D j is the fatigue damage under the j# analysis working condition; n LC =10, which is the number of all analysis working conditions given by the specification.

[0023] Furthermore, it also includes step S64, fatigue life calculation: When When When Wherein

[0024] As described above, the fatigue strength analysis method for the A-type independent liquid cargo tank involved in the present invention has the following beneficial effects:

[0025] By establishing a coarse grid model for fatigue calculation of three tank sections and a fine grid model for fatigue calculation nodes through GeniE software, quickly obtain the hot spot stress range of fatigue nodes under different analysis working conditions, and then calculate the hot spot fatigue damage and fatigue life accordingly. The whole method is convenient, fast, accurate and efficient, can effectively reduce the workload and reduce the labor load. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Schematic flow diagram of the analysis method for the type A independent liquid cargo tank support of the present invention.

[0027] Figure 2 Schematic layout diagram of the support of the present invention between the ship's hold and the liquid cargo tank.

[0028] Description of component labels

[0029] 1 Ship's hold

[0030] 2 Liquid cargo tank

[0031] 3 Support

[0032] 31 Support block

[0033] 32 Laminated wood Specific implementation manner

[0034] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0035] It should be noted that the structures, ratios, sizes, etc. shown in the attached drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have any technical essence. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of description and are not used to limit the scope for the implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope for the implementation of the present invention.

[0036] See Figure 1 , the present invention provides an analysis method for the fatigue strength of the type A independent liquid cargo tank based on GeniE. In the ship structure, multiple supports are provided between the liquid cargo tank 2 and the ship's hold 1. See Figure 2 , the support 3 includes two support blocks 31 and the laminated wood 32 located between the two support blocks. These supports are arranged in multiple areas such as the bottom and side plates of the liquid cargo tank 2. The analysis method for the type A independent liquid cargo tank support of the present invention includes the following steps:

[0037] S1. Coarse grid modeling: Establish a coarse grid simulation model in GeniE, including three adjacent cabin sections, with the middle cabin section being the target cabin to be evaluated. The coarse grid simulation model includes the ship's cabin part and the liquid tank part. The cabin part includes the main components of the hull, the stiffener structures on the main components, and brackets that support the strength of the main components and usually have a side length greater than the rib spacing. The main components include the main transverse components and the main longitudinal components. In the ship's cabin structure, the main longitudinal components refer to the main structural components extending along the ship's length direction, mainly including the outer plate, the inner bottom, the inner bottom side plate, and the longitudinal bulkheads, etc. The main transverse components refer to the main structural components extending along the ship's width direction, mainly including the transverse bulkheads, the double bottom and bilge floors, the deck, and the transverse T-sections on the longitudinal bulkheads, etc. The parts in the ship's cabin structure and the liquid tank structure mainly include plate parts, stiffener structures, and T-sections, etc. In the coarse grid simulation model, the plate parts are simulated by plate elements, the stiffener structures are simulated by beam elements, and the transverse panel and vertical web of the T-section are simulated by beam elements and plate elements respectively. The size of the coarse grid in the coarse grid simulation model is the rib spacing multiplied by the rib spacing, and the rib spacing refers to the distance between two adjacent rib positions in the ship's cabin.

[0038] S2. Support modeling: Establish a support coarse grid model in GeniE, including the support block part and the laminated wood part. See Figure 2 , where the support block part is simulated by plate elements (also known as shell elements), and the laminated wood part is simulated by beam elements that can only be compressed, with the attribute set to "truss-compression only". The laminated wood part can also be called an elastic support unit, and the area of beam element 5 is set according to the size of the laminated wood area, and the axial stiffness is consistent with the actual stiffness of the laminated wood.

[0039] S3. Construct a coarse grid analysis model: Arrange the support coarse grid model in the coarse grid simulation model as required to form a coarse grid analysis model.

[0040] S4. Fatigue analysis:

[0041] The fatigue analysis includes two loading conditions: full load and ballast. The calculation conditions for both loading conditions include the following equivalent design waves: HSM (the maximum and minimum vertical accelerations of the ship's bow in head seas), FSM (the maximum and minimum vertical wave bending moments at the ship's midship in following seas), BSR (the maximum and minimum roll accelerations in beam seas), BSP (the maximum and minimum dynamic pressures at the waterline in beam seas), and OST (the maximum and minimum torsional moments at 0.2L in oblique seas). Therefore, the fatigue analysis includes ten analysis conditions, namely full load HSM, full load FSM, full load BSR, full load BSP, full load OST, ballast HSM, ballast FSM, ballast BSR, ballast BSP, and ballast OST; the corresponding hot spot stress ranges are obtained under the ten analysis conditions respectively. The fatigue analysis under each analysis condition is the same and includes the following steps:

[0042] S41. Coarse grid analysis, including the following steps:

[0043] S411. According to the analysis working conditions, input the corresponding analysis parameters. The analysis parameters include the time ratio α of each loading condition j , the voyage time ratio f0, the draft T in the loading state, the initial metacentric height GM, and the radius of gyration k of rolling r ; Add corresponding load conditions to the working conditions. The load conditions include the pressure caused by acceleration, hydrodynamic pressure, and the load generated by the hull girder deformation; The fatigue load environment selects the 10 -2 exceedance probability in the North Atlantic Ocean;

[0044] S412. Load the working conditions and select the analysis type "Tension / Compression Analysis". The GeniE program performs the analysis on the coarse grid analysis model, and will analyze the three hold sections of the coarse grid simulation model; After the analysis is completed, the coarse grid result R file is obtained. The coarse grid result R file includes the stress results and deformation results of each element and node in the coarse grid analysis model.

[0045] 42. Fine grid modeling: Determine the area to be analyzed for fatigue strength as the fatigue analysis nodes. In addition to the vertical supports for the fatigue calculation of the Type A independent cargo tank, other areas that need to be considered include the end connections of the stiffeners at the bow and stern of the tank, the connections between the stiffeners on the outer shell and the strong frames of the cargo tank, and the high-stress areas inside the cargo tank where there are supports, etc. Take the fatigue analysis nodes in the coarse grid analysis model, and extend one strong frame forward and backward in the ship length direction, and extend to the adjacent main longitudinal supporting members in the ship width direction to perform fine meshing to obtain the fine grid analysis model. And the size of the fine grid at the fatigue nodes is the plate thickness of the parts at this location. That is, in the fine grid analysis model, in addition to including the part of the fatigue analysis nodes, it also includes the partial structures of the cabins and cargo tanks on the front, back, left, and right sides of the fatigue analysis nodes. The main longitudinal supporting members are the strong members longitudinally distributed in the cabins and cargo tanks; In the fine grid analysis model, the boundaries in the front and back directions are located at the strong frame structures, and the boundary positions in the left and right directions are at the main longitudinal supporting members, so as to facilitate reading the boundary conditions at these boundary positions from the coarse grid result R file. In ship structures, the web frame (WEB FRAME), also known as the wide plate rib, is a structure made of T-shaped composite materials with larger dimensions and flanged steel plates. In the fatigue strength analysis of the Type A independent cargo tank, the fatigue nodes to be investigated are located at the plate parts. Therefore, in the fine grid analysis model, the size of the fine grid at the fatigue nodes is the plate thickness of the parts at this location. The grid size of each plate part in the entire fine grid analysis model can be different.

[0046] S43. Fine grid analysis:

[0047] S431. Select "Local Analysis" for analysis. The program will, based on the boundary positions of the fine mesh analysis model, read the boundary conditions and loads of the fine mesh analysis model from the coarse mesh result R file in step S412 and load them into the fine mesh analysis model. Among them, the boundary conditions refer to the displacements and rotations of the nodes on the model boundary in the x, y, and z directions, which are also the deformation results. Since the coarse mesh result R file in the coarse mesh analysis contains the load information of the part of the fine mesh analysis model, the stress conditions in the fine mesh analysis model can be obtained from the boundary positions and loads of the fine mesh analysis model.

[0048] S432. GeniE analyzes the fine mesh analysis model. After the analysis is completed, a fine mesh result R file is obtained. The fine mesh result R file includes the further refined stress results and deformation results of each element and node in the fine mesh analysis model. Read the principal stress on the surface of the element, and determine the hot spot stress range Δσ of the fatigue analysis node. Specifically, from the fine mesh result R file, the principal stress on the surface of the element of the fatigue hot spot can be obtained, and the hot spot stress range is obtained by subtracting the minimum surface principal stress from the maximum surface principal stress.

[0049] In this step, the fine mesh result R file is also compared with the group mesh result R file to verify the fine mesh result R file to ensure whether the fine mesh result R file meets the requirements.

[0050] S5. According to the hot spot stress range Δσ under each analysis condition, calculate the fatigue stress range Δσ of the fatigue damage under this analysis condition FS , and the calculation formula is: Δσ FS = f mean ·f thick ·f material ·f w ·f c ·f e ·Δσ, where f mean is the mean stress adjustment coefficient, reflecting the influence of the stress generated by the static load on the hot spot stress range; f thick is the plate thickness adjustment coefficient, reflecting the influence of the local plate thickness at the weld toe on the hot spot stress range; f material is the material adjustment coefficient, reflecting the influence of the base material; f w is the weld treatment adjustment coefficient, reflecting the influence of grinding on the hot spot stress range; f c is the corrosion allowance adjustment coefficient, reflecting the influence of the corrosion allowance on the hot spot stress range; f e is the environmental adjustment coefficient, reflecting the influence of the sea condition on the hot spot stress range.

[0051] Fatigue stress range Δσ FSIt is important data in fatigue analysis and is used for the design calculation of subsequent fatigue life. Through the above method, the fatigue stress range Δσ under ten analysis conditions can be obtained. FS .

[0052] S6. Design fatigue life. The fatigue life is divided into two stages according to the corrosion protection situation. During the corrosion protection stage, the fatigue nodes are calculated according to the S-N curve in air, and for the remaining years T C are calculated according to the corrosion environment, including:

[0053] S61. Calculate the annual fatigue damage without considering corrosion (i.e., in the corrosion protection stage): Take the maximum value in the fatigue stress range of each analysis condition as the dominant fatigue stress range Δσ FS ; Calculate the annual fatigue damage under this analysis condition by the following formula: where is the number of stress cycles per year, L is the ship length; N R is the number of stress cycles when the exceedance probability is 10 -2 ; ξ is the Weibull shape parameter; is the complete gamma function; K2 is the constant on the S-N curve; m is the slope of the S-N curve, and μ is the adjustment coefficient when considering the change of the S-N curve slope.

[0054] S62. Composite fatigue damage calculation: Number the ten analysis conditions as analysis conditions 1# to 10# respectively, and record the corresponding annual fatigue damages as D E(1) to D E(10) , calculate the fatigue damage in the corrosion environment and the fatigue damage without the corrosion environment under each analysis condition D j =D E(j) ·(T DF +T C ), where, T C is the number of years in the corrosion environment, T C25 is the number of years in the corrosion environment when the design life is 25 years, T D is 25 years, T DF is the fatigue design life, D E(j) is the annual fatigue damage without considering corrosion conditions under the j# analysis condition, 1≤j≤10.

[0055] S63. Calculate the cumulative fatigue damage of all analysis conditions: where, f0 is the time factor occupied by the navigation state; α j is the proportion of each loading state; D j is the fatigue damage under the j# analysis condition; n LC =10, which is the number of all analysis conditions given by the specification.

[0056] S64. Fatigue life calculation: When When

[0057] When Wherein

[0058] The fatigue strength analysis method of the A-type independent liquid cargo tank based on GeniE of the present invention establishes a coarse grid model for fatigue calculation of three tank segments and a fine grid model for fatigue calculation nodes through GeniE software, quickly obtains the hot spot stress range of fatigue nodes under different analysis conditions, and can calculate the hot spot fatigue damage and fatigue life accordingly. The whole method is convenient, fast, accurate and efficient, can effectively reduce the workload and reduce the labor load.

[0059] In summary, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0060] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A fatigue strength analysis method for independent liquid cargo tank of Type A based on GeniE, characterized in that: It includes the following steps: S1. Coarse mesh modeling: Establish a coarse mesh simulation model in GeniE, which includes three adjacent cabin sections, and the middle cabin section is the target cabin to be evaluated. The coarse mesh simulation model includes a ship cabin part and a liquid tank part. The ship cabin part includes the main components of the hull, the stiffener structure on the main components, and the brackets that support the strength of the main components and have a side length greater than the rib spacing. The main components include main transverse components and main longitudinal components. And in the coarse mesh simulation model, the plate parts are simulated by plate elements, the stiffener structure is simulated by beam elements, and the transverse panel and vertical web of the T-section are simulated by beam elements and plate elements respectively; The size of the coarse mesh in the coarse mesh simulation model is the rib spacing multiplied by the rib spacing; S2. Support modeling: Establish a support coarse mesh model in GeniE, which includes a support block part and a laminated wood part. Among them, the support block part is simulated by plate elements, and the laminated wood part is simulated by beam elements that can only be compressed, and the attribute is set to "truss-compression only". And the area of the beam element is set according to the size of the laminated wood area, and the axial stiffness is consistent with the actual stiffness of the laminated wood; S3. Construct a coarse mesh analysis model: Arrange the support coarse mesh model in the coarse mesh simulation model as required to form a coarse mesh analysis model; S4. Fatigue analysis: The fatigue analysis includes ten analysis conditions, namely full load HSM, full load FSM, full load BSR, full load BSP, full load OST, ballast HSM, ballast FSM, ballast BSR, ballast BSP, and ballast OST. The corresponding hot spot stress ranges are obtained under the ten analysis conditions respectively. The fatigue analysis under each analysis condition includes the following steps: S41. Coarse mesh analysis: S411. According to the analysis conditions, input the corresponding analysis parameters, which include the time proportion of each loading condition, the time proportion of the voyage, the draft at the loading state, the initial metacentric height, and the radius of gyration of rolling; add the corresponding load conditions to the conditions, and the load conditions include the pressure caused by acceleration, hydrodynamic pressure, and the load generated by the deformation of the hull girder; select the North Atlantic 10 for the fatigue load environment -2 Exceedance probability; S412. Loading condition, select the analysis type "Tension / Compression Analysis", and the GeniE program analyzes the coarse mesh analysis model, and will analyze the three cabin sections of the coarse mesh simulation model. After the analysis is completed, a coarse mesh result R file is obtained. The coarse mesh result R file includes the stress results and deformation results of each unit and node in the coarse mesh analysis model; S42. Fine mesh modeling: Determine the part to be subjected to fatigue strength analysis as the fatigue analysis node. Take the fatigue analysis node in the coarse mesh analysis model, and extend one strong rib in the fore and aft directions in the ship length direction and extend to the adjacent main longitudinal support member in the ship width direction for fine meshing to obtain a fine mesh analysis model. And the size of the fine mesh at the fatigue node is the plate thickness of the part here, where the main longitudinal support member is a longitudinally distributed strong member; S43. Fine mesh analysis: S431. Select "LocalAnalysis" for analysis. The program will read the boundary conditions and loads of the fine mesh analysis model in the coarse mesh result R file in step S412 according to the boundary position of the fine mesh analysis model and load them into the fine mesh analysis model; S432. GeniE analyzes the fine grid analysis model. After the analysis is completed, a fine grid result R file is obtained. The fine grid result R file includes the further refined stress results and deformation results of each element and node in the fine grid analysis model. Read the principal stress on the surface of the element and determine the hot spot stress range Δσ in the fatigue analysis nodes. S5. Calculate the fatigue stress range Δσ of fatigue damage under this analysis condition according to the hot spot stress range Δσ under each analysis condition. FS .

2. The fatigue strength analysis method of the Type A independent liquid cargo tank according to claim 1, wherein: In step S1, the main longitudinal members include the outer plate, inner bottom, inner bottom side plate, and longitudinal bulkhead. The main transverse members include the transverse bulkhead, double bottom and bilge floor, deck, and transverse T-sections on the longitudinal bulkhead.

3. The fatigue strength analysis method of the Type A independent liquid cargo tank according to claim 1, wherein: Step S432 also includes: comparing the fine grid result R file with the group grid result R file to verify the fine grid result R file.

4. The fatigue strength analysis method of the Type A independent liquid cargo tank according to claim 1, characterized in that: In the step S5, the fatigue stress range Δσ for calculating the fatigue damage is determined by the following formula FS :[[]]END]] Δσ FS = f mean · f thick · f material · f w · f c · f e · Δσ, where f mean is the mean stress adjustment coefficient, f thick is the plate thickness adjustment coefficient; f material is the material adjustment coefficient; f w is the weld treatment adjustment coefficient; f c is the corrosion allowance adjustment coefficient, f e is the environment adjustment coefficient.

5. The fatigue strength analysis method for the Type A independent liquid cargo tank according to claim 1, characterized in that: It also includes step S6 of designing the fatigue life. The fatigue life is divided into two stages according to the corrosion protection situation. During the corrosion protection stage, the fatigue nodes are calculated according to the S-N curve in the air, and for the remaining years T C are calculated according to the corrosion environment, including: S61. Calculate the annual fatigue damage without considering corrosion: Take the maximum value of the fatigue stress range Δσ in each analysis condition as the dominant fatigue stress range Δσ FS , and calculate the annual fatigue damage under this analysis condition using the following formula: FS as the dominant fatigue stress range Δσ FSmax FSmax , and calculate the annual fatigue damage under this analysis condition by the following formula: wherein is the number of stress cycles per year, L is the ship length; N R is the number of stress cycles when the exceedance probability is 10 -2 ; ξ is the Weibull shape parameter; is the complete gamma function; K2 is the constant on the S-N curve; m is the slope of the S-N curve, and μ is the adjustment coefficient when considering the change in the slope of the S-N curve.

6. The fatigue strength analysis method of the Type A independent liquid cargo tank according to claim 5, characterized in that: Including step S62, synthetic fatigue damage calculation: Number the ten analysis conditions as analysis conditions 1# to 10# respectively, and record their corresponding annual fatigue damages as D E(1) ~D E(10) , calculate the fatigue damage in the corrosive environment and the fatigue damage without the corrosive environment under each analysis condition D j =D E(j) ·(T DF +T C ), wherein, T C is the number of years in the corrosive environment, T C25 is the number of years in the corrosive environment when the design life is 25 years, T D is 25 years, T DF is the fatigue design life, D E(j) is the annual fatigue damage without considering the corrosion condition under the j# analysis condition, 1≤j≤10.

7. The fatigue strength analysis method of the Type A independent liquid cargo tank according to claim 6, characterized in that: including step S63, calculating the cumulative fatigue damage of all analysis conditions: wherein, f0 is the time factor occupied by the navigation state; α j is the proportion of each loading state; D j is the fatigue damage under the j# analysis condition; n LC = 10, which is the number of all analysis conditions given by the specification.

8. The fatigue strength analysis method for the Type A independent liquid cargo tank according to claim 7, wherein: It also includes step S64, fatigue life calculation: When When When Among them

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