A method and terminal for evaluating the liner of a type IV hydrogen storage bottle

Abstract

The present invention relates to the field of defect detection technology, and discloses an evaluation method and terminal for the inner liner of a type IV hydrogen storage bottle. The evaluation method comprises: S10. acquiring characteristic information of hole defects; S11. simplifying the hole defects into spherical hole defects, and dividing them into single hole defects, double hole defects and dense hole defects; S12. establishing a three-dimensional model of a hydrogen storage bottle containing different hole defects; S13. predicting the hydrogen concentration in the hole defects during the filling and deflation process; S14. establishing a thermal-fluid-solid coupling model of the hydrogen storage bottle containing hole defects; S15. based on the above model, obtaining the maximum coupling equivalent stress F of the inner liner containing dense hole defects c ; S16. Determine the ultimate stress of liner failure and judge the maximum coupling equivalent stress F c Is it greater than the ultimate stress? S17. Based on the Chaboche fatigue life prediction model, the fatigue life of the inner liner hole defect location, the inner surface of the inner liner, and the outer surface of the inner liner is predicted. The present invention can more comprehensively evaluate the impact of hole defects on the performance of hydrogen storage bottles.

Description

Technical Field

[0001] The present invention relates to the field of defect detection technology, and in particular to a method and terminal for evaluating the inner liner of a type IV hydrogen storage bottle. Background Art

[0002] Large-capacity plastic liner Type IV hydrogen storage bottles have the advantages of being lightweight, corrosion-resistant, and plastic, but there are still many problems in production, stress analysis, and safety assessment.

[0003] Compared with metal liners, the production process of plastic liners is simpler, but there are also some challenges. During the operation of the extruder or injection molding machine, air may be inhaled, causing air to mix into the plastic melt. In addition, if the temperature, pressure, extrusion speed and other parameters are not set correctly, it is easy to cause the flow of the plastic melt to be poor or unstable, resulting in bubbles. Especially in areas with complex structures or uneven wall thickness, bubble problems are more likely to occur. In addition, due to the relatively low mechanical strength of the plastic liner, when the gas cylinder is deflated, the pressure relief speed is much greater than the hydrogen escape speed in the hole, and the bubbles at the edge of the liner are likely to rupture, which may cause leakage of the liner in severe cases. At the same time, the gas cylinder will be subjected to cyclic pressure loads and temperature loads during the filling and deflation process. Under the combined effect of these loads, the presence of hole defects will accelerate the damage process of the hydrogen storage bottle and increase the risk of failure of the hydrogen storage bottle.

[0004] According to the research results on the mechanical properties of materials and components containing holes at home and abroad, the characteristics of hole porosity, size, shape and position distribution will directly affect the key performance indicators of the material or structure, such as strength, stiffness, toughness and fatigue performance. For the evaluation of the sealing of pressure vessels with hole defects, it is necessary to consider the influence of a single hole and pay attention to the coupling mechanism between multiple holes. In fact, the interaction between multiple holes may lead to nonlinear failure. In the study of the influence of periodic array hole defects and dense hole defects on the evolution law of material or structural damage, the existing technology sets the hole size to a fixed value or establishes a two-dimensional model for analysis. Although it simplifies the problem, it ignores the influence of the hole arrangement direction and may not truly reflect the complex situation of holes in actual engineering.

[0005] Although a number of standards and specifications have been promulgated for the assessment of defects in in-service pressure vessels, these standards are mainly applicable to metal pressure vessels. Since the failure mechanism of plastic liner pressure vessels is different from that of metal pressure vessels, the existing evaluation standards cannot be directly applied to the assessment of hole defects in the plastic liner of Type IV hydrogen storage bottles. Although GB / T42612-2023 has made clear requirements on the hole tolerance of automotive compressed hydrogen plastic liner carbon fiber fully wrapped gas cylinders, the maximum volume of the applicable objects of this standard is 450L, and it is not applicable to 1750L large-capacity plastic liner carbon fiber fully wrapped gas cylinders. In addition, due to the lack of experimental data support, some standards are relatively conservative in the assessment of hole defects. Therefore, it is necessary to propose a method and system for evaluating the structural integrity of hydrogen bottles with hole defects. Summary of the invention

[0006] The purpose of the present invention is to provide a method and terminal for evaluating the inner liner of a type IV hydrogen storage bottle, to establish a thermal-fluid-solid coupling model of a hydrogen storage bottle containing hole defects, and to more comprehensively evaluate the impact of the hole defects on the performance of the hydrogen storage bottle.

[0007] In a first aspect, the present invention provides a method for evaluating the inner liner of a type IV hydrogen storage bottle, which is used to evaluate the sealing performance and deformation of the inner liner, comprising the following steps:

[0008] S10. Obtain hole defect characteristic information, the hole defect characteristic information includes at least hole diameter, hole position, and hole spacing;

[0009] S11. Simplify the hole defect into a spherical hole defect, and divide the hole defect into a single hole defect, a double hole defect, and a dense hole defect; among which, the single hole defect is characterized by the hole diameter and hole position; the double hole defect is characterized by the hole diameter, hole position, hole spacing, and arrangement direction; the dense hole defect is characterized by the hole diameter, minimum spacing, and number of holes;

[0010] S12. Establish a three-dimensional model of a hydrogen storage cylinder with different hole defects, specifically including: firstly, determining the dangerous position of the inner tank; secondly, establishing a single hole defect, a double hole defect and a dense hole defect based on the dangerous position;

[0011] S13. Prediction of hydrogen concentration in hole defects during inflation process; Prediction of hydrogen concentration in hole defects during deflation process;

[0012] S14. Establish a thermal-fluid-solid coupling model of a hydrogen storage cylinder with hole defects;

[0013] S15. Based on the thermal-fluid-solid coupling model of hydrogen storage cylinders with pore defects, the maximum coupling equivalent stress F of the inner liner with dense pore defects is obtained c , F c =h×F one, where h is the stress amplification factor of the two-hole defect, obtained by solving the empirical model of h; F one is the maximum coupled equivalent stress of the inner tank containing a single hole defect, which is determined by the single hole defect distribution position and hole diameter through machine learning;

[0014] S16. Determine the ultimate stress of liner failure and determine the maximum coupling equivalent stress F c Is it greater than the limit stress? If so, it is determined that the liner is failed. If not, it jumps to S17;

[0015] S17. Based on the Chaboche fatigue life prediction model, the fatigue life of the inner liner hole defect location, the inner surface of the inner liner, and the outer surface of the inner liner is predicted. If the life of the above three locations is less than the life threshold, it is judged that the inner liner has lost its sealing, otherwise, it is judged that the inner liner can continue to serve.

[0016] As a possible implementation method, the dangerous position of the inner tank is determined by the following steps:

[0017] S120. Establish a three-dimensional model of a hydrogen storage cylinder without hole defects;

[0018] S121. Establish a finite element model of the filling and discharging of the three-dimensional model of the hydrogen storage cylinder, specifically including: configuring boundary conditions, the boundary conditions include ambient temperature, inlet boundary conditions and outlet boundary conditions; wherein the inlet boundary conditions include upper limit pressure, lower limit pressure, filling rate and inlet hydrogen temperature; the outlet boundary conditions include upper limit pressure, lower limit pressure and maximum safe pressure relief rate of the hydrogen storage cylinder;

[0019] S122. Based on the finite element model of gas filling and discharging, simulate the filling and discharging process from the lower limit pressure to the upper limit pressure and from the upper limit pressure to the lower limit pressure, and obtain the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder;

[0020] S123. Import the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder into the structural mechanics calculation module, and then conduct comparative analysis on the three scenarios of thermal-solid coupling, fluid-solid coupling and thermal-fluid-solid coupling, obtain the difference degree of the maximum equivalent stress of the liner under the three scenarios, determine that the temperature field and the pressure field are necessary factors for the maximum equivalent stress, and based on this, use the thermal-fluid-solid coupling analysis method to determine the maximum equivalent stress of the liner;

[0021] S124. Based on the stress cloud diagram obtained from the thermal-fluid-solid coupling analysis, the location of the maximum equivalent stress is determined, which is the dangerous location.

[0022] As a possible implementation method, the maximum safe depressurization rate of the hydrogen storage cylinder is determined by the following method:

[0023] S1210. Based on continuum mechanics and the introduction of the yield stress of the liner material, a blister damage model for the liner of a type IV hydrogen storage bottle is established:

[0024]

[0025] Among them, p Y is the yield pressure of the inner wall of the cylinder, unit: MPa; σ Y is the yield stress of the liner material, in MPa;

[0026] S1211. Establish and solve the cavitation risk assessment model to obtain the maximum safe pressure relief rate; the cavitation risk assessment model is specifically:

[0027]

[0028] Among them, p sat is the initial saturation pressure, unit: MPa; p min is the final minimum pressure, in MPa; D is the diffusion coefficient of the liner material, in m 2 / s; l is the thickness of the liner, unit: mm.

[0029] As a possible implementation method, S14 specifically includes the following steps:

[0030] S140. Mesh the three-dimensional model of the hydrogen storage cylinder with different hole defects, including meshing of the inner tank and the winding layer; the mesh size of the winding layer is larger than the mesh size of the inner tank; the mesh size of the hole surface, the mesh size of the arc test block where the hole is located, the mesh size close to the arc test block, and the mesh size far from the arc test block increase in sequence;

[0031] S141. Configure boundary conditions, which include fixed constraints, inner surface pressure load of the liner, inner surface pressure load of the bottle mouth sealing structure, volume temperature load of each solid domain and hole surface pressure load; wherein, fixed constraints refer to applying fixed support at the bottle mouth of the hydrogen storage cylinder, and the degree of freedom is restricted to 0; the inner surface pressure load of the liner, the inner surface pressure load of the bottle mouth sealing structure, and the volume temperature load of each solid domain are imported into the three-dimensional model of the hydrogen storage cylinder containing different hole defects using the inner surface pressure load and volume temperature load obtained in S123 as mapping loads; the hole surface pressure load is based on the hydrogen concentration in the hole defect predicted during the filling and discharging process, and the hole surface pressure load is obtained by solving Fick's law. At this point, the thermal-fluid-solid coupling model of the hydrogen storage cylinder with hole defects is established.

[0032] As a possible implementation method, the two holes are arranged circumferentially or axially, and the diameters D2 of the two holes are equal. The empirical model of h is:

[0033] h=0.386D2+0.762,H2<0.2mm,D2<0.65mm,at this time, R 2 =0.998;

[0034] h=1, H2<0.2mm, D2≤0.65mm;

[0035] h=1,H2≥0.2mm,0.2mm≤D2≤1.2mm。H2 is the hole spacing, R 2 is the variance.

[0036] As a possible implementation, the two holes are arranged circumferentially or axially, and the diameters of the two holes are D 21 and D 22 Not equal, the empirical model of h is:

[0037] When D 21 ≤0.65mm and D 22 When ≤0.65mm, h=1;

[0038] When H2<0.2mm, D 21 ≤0.65mm and D 22 >0.65mm, or D 21 >0.65mm and D 22 >0.65mm, At this time, R 2 =0.979;

[0039] H2 is the hole spacing, R 2 is the variance.

[0040] As a possible implementation method, the two holes are arranged radially, and the hole diameters D2 are equal. The empirical model of h is:

[0041] When 0.2mm≤D2≤0.4mm, H2<0.2mm, h=1.429D2 0.226 , at this time, R 2 =0.989;

[0042] When D2>0.4mm, 0.2≤H2<0.3mm, h=1.161D2 0.149 , at this time, R 2 =0.993;

[0043] When D2>0.4mm, 0.3≤H2<0.4mm, h=1.059D2 0.066 , at this time, R 2 =0.987;

[0044] When D2≤0.4mm and H2≥0.2mm, or when H2≥0.4mm is any size of two hole defects, h=1. H2 is the hole spacing, R 2 is the variance.

[0045] As a possible implementation, two holes are arranged radially, and the hole diameter D 21 and D 22 Not equal, D 22 >D 21 , h empirical model is:

[0046] When D 22 ≤0.4mm, H2<0.2mm, h=1.469D 22 0.274 , at this time, R 2 =0.993;

[0047] When D 22 >0.4mm, 0.2≤H2<0.3mm, h=1.163D 22 0.169 , at this time, R 2 =0.986;

[0048] When D 22 >0.4mm, 0.3≤H2<0.4mm, h=1.050D 22 0.065 , at this time, R 2 =0.944;

[0049] When D 22 >0.4mm and H2≥0.2mm, or, when there are two holes of any size with H2≥0.4mm, h=1. H2 is the hole spacing, R 2 is the variance.

[0050] As a possible implementation method, the maximum coupling equivalent stress F of the inner liner with a single hole defect is determined by machine learning. one The specific steps include:

[0051] S150. Configure N D1 values, configure M W1 values, and obtain N×M groups of F through simulation one Datasets;

[0052] S151. Combine N×M groups of F one The dataset is split into training and testing sets;

[0053] S152. iForest is used to process the training set and the test set to improve the quality and reliability of the data;

[0054] S153. Use the Bayesian optimization random forest ensemble learning algorithm to train the training set to obtain F one The machine learning prediction model has the following accuracy: mean square error MSE is 0.105, variance R 2 It is 0.9848.

[0055] In a second aspect, the present invention provides a terminal including a processor and a communication interface coupled to the processor, wherein the processor is used to run a computer program or instruction to implement the method for evaluating the inner liner of a type IV hydrogen storage bottle provided in the first aspect.

[0056] Compared with the prior art, the present invention has the following effects:

[0057] 1. The method for evaluating the inner liner of a type IV hydrogen storage bottle provided by the present invention establishes a thermal-fluid-solid coupling model of a type IV hydrogen storage bottle, which can more comprehensively evaluate the impact of hole defects on the performance of the type IV hydrogen storage bottle and has important engineering application value.

[0058] 2. The method for evaluating the inner liner of a type IV hydrogen storage bottle provided by the present invention deeply explores the relevant information between the characteristics such as hole size, distribution position, spacing, arrangement direction and the stress response of the inner liner through the method of numerical simulation, and establishes an empirical model of the stress amplification factor of the inner liner; the dense hole defect problem is simplified to a single hole defect problem for analysis, and the numerical simulation method and machine learning technology are comprehensively applied. Through the empirical model of stress amplification factor and the machine learning model for stress prediction of the inner liner containing a single hole defect, the maximum coupling equivalent stress of the inner liner containing dense hole defects is obtained, which solves the problem of the complex damage mechanism of the inner liner caused by dense hole defects.

[0059] 3. The evaluation method for the inner liner of a type IV hydrogen storage bottle provided by the present invention is based on the inner liner stress prediction model and the Chaboche fatigue life prediction model, and takes the flow stress failure criterion and the fatigue failure criterion of three key parts as the criteria. A type IV hydrogen storage bottle suitable for single-hole defects, two-hole defects and dense hole defects is established, and the nonlinear behavior of the material and the influence of hole defects on the structural strength and fatigue life of the hydrogen storage bottle are comprehensively considered, ensuring that even if a certain degree of deformation occurs in the local area of ​​the hydrogen bottle inner liner, it still has the key performance to ensure its safe use. It is of great significance to improve the efficiency of material use and extend the service life of the hydrogen storage bottle. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0061] Figure 1A flow chart of a method for evaluating the liner of a type IV hydrogen storage bottle provided in an embodiment of the present invention;

[0062] Figure 2 The maximum equivalent stress of the thermal-fluid-solid coupling of the inner tank changes with time during the hydrogen storage bottle filling process, which is calculated by the structural mechanics calculation module in the embodiment of the present invention;

[0063] Figure 3 The maximum equivalent stress of the thermal-fluid-solid coupling of the inner tank changes with time during the degassing of the hydrogen storage bottle, which is calculated by the structural mechanics calculation module in the embodiment of the present invention;

[0064] Figure 4 is a curve showing the relationship between the hole defect stress amplification factor and the hole diameter for holes arranged in an annular direction / axial direction and having the same hole diameter in the embodiment of the present invention;

[0065] Figure 5 is a curve showing the relationship between the hole defect stress amplification factor and the hole diameter of radially arranged holes with the same hole diameter under different hole spacings in the embodiment of the present invention;

[0066] Figure 6 It is an empirical model of the stress amplification factor of radially arranged holes with the same hole diameter when the hole spacing is 0.1 mm in the embodiment of the present invention;

[0067] Figure 7 It is an empirical model of the stress amplification factor of radially arranged holes with the same hole diameter when the hole spacing is 0.2 mm in the embodiment of the present invention;

[0068] Figure 8 It is an empirical model of the stress amplification factor of radially arranged holes with the same hole diameter when the hole spacing is 0.3 mm in the embodiment of the present invention;

[0069] Fig. 9 The hole defect stress amplification factor and hole diameter D of radially arranged holes with different hole spacing in the embodiment of the present invention are shown in FIG. 22 The relationship curve between

[0070] Fig.10 It is an empirical model of the hole defect stress amplification factor of radially arranged holes with different hole diameters when the hole spacing is 0.1 mm in the embodiment of the present invention;

[0071] Fig.11 It is an empirical model of the hole defect stress amplification factor of radially arranged holes with different hole diameters when the hole spacing is 0.2 mm in the embodiment of the present invention;

[0072] Fig.12It is an empirical model of the stress amplification factor of radially arranged holes with different hole diameters when the hole spacing is 0.3 mm in the embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, words such as "first" and "second" are used to distinguish the same items or similar items with basically the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and their order is not limited. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit them to be different.

[0074] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0075] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0076] Large-capacity Type IV hydrogen storage bottles are about to replace traditional hydrogen bottles due to their excellent performance. Due to the size effect and the pressure-temperature coupling effect, hydrogen bottles may suffer from macro-scale structural integrity problems such as collapse and bulging. More importantly, the hole defects in the liner will cause deformation or rupture due to the diffusion behavior of hydrogen, further threatening the overall safety of the hydrogen bottle. Although a number of standards and specifications have been promulgated for the assessment of defects in in-service pressure vessels, these standards are mainly applicable to metal pressure vessels. Since the failure mechanism of plastic liner pressure vessels is different from that of metal pressure vessels, the existing evaluation standards cannot be directly applied to the assessment of hole defects in the plastic liner of Type IV hydrogen storage bottles. In addition, due to the lack of experimental data support, some standards are relatively conservative in the assessment of hole defects.

[0077] To solve the above problems, the present invention provides a method and terminal for evaluating the inner liner of a type IV hydrogen storage bottle, establishes a thermal-fluid-solid coupling model of a hydrogen storage bottle with hole defects, simulates more complex hole conditions in actual engineering, and more comprehensively evaluates the impact of hole defects on the performance of the hydrogen bottle.

[0078] In a first aspect, the present invention provides a method for evaluating the inner liner of a type IV hydrogen storage bottle, for evaluating the sealing and deformation of the inner liner, see Figure 1 , including the following steps:

[0079] S10. Obtain hole defect characteristic information, the hole defect characteristic information includes at least hole diameter, hole position, and hole spacing;

[0080] As an example, industrial eddy current testing and computerized tomography (CT) non-destructive testing technology are used to identify hole defects in the inner tank of a hydrogen storage bottle, and characteristic information such as hole diameter, hole position, and hole spacing are extracted.

[0081] S11. Simplify the hole defect into a spherical hole defect, and divide the hole defect into a single hole defect, a double hole defect, and a dense hole defect; among which, the single hole defect is characterized by the hole diameter and hole position; the double hole defect is characterized by the hole diameter, hole position, hole spacing, and arrangement direction; the dense hole defect is characterized by the hole diameter, minimum spacing, and number of holes;

[0082] As an example, based on the definition and characterization method of defects in GB / T 35013-2018 "Evaluation of fitness for use of pressure equipment" and GB / T19624-2019 "Safety assessment of in-use pressure vessels containing defects", combined with the characteristic information of hole defects extracted from S10, the hole defects are simplified to spherical hole defects and divided into three types: single hole defects, double hole defects and dense hole defects.

[0083] S12. Establish a three-dimensional model of a hydrogen storage cylinder with different hole defects, specifically including: firstly, determining the dangerous position of the inner tank; secondly, establishing a single hole defect, a double hole defect and a dense hole defect based on the dangerous position;

[0084] As a possible implementation method, the dangerous position of the inner tank is determined by the following steps:

[0085] S120. Establish a three-dimensional model of a hydrogen storage cylinder without hole defects;

[0086] As an example, according to the national standard GB-T 42612-20 and engineering practice, based on the given inner liner size and load-bearing conditions of large-capacity hydrogen storage bottles, the plastic liner material is PA6, the BOSS structural material is 316L stainless steel, and the fiber winding layer material is T700S / epoxy resin composite material. The carbon fiber composite material of the IV hydrogen storage cylinder with a working pressure of 70MPa is laid up to complete the establishment of a three-dimensional model of the hydrogen storage cylinder without hole defects. The total length of the hydrogen storage cylinder is 5354mm, the inner wall diameter of the inner liner is 664mm, and the outer wall diameter is 676mm. The diameter of the BOSS structure entrance is 100mm, the outer diameter is 140mm, and the total length of the BOSS structure is 167mm.

[0087] S121. Establish a finite element model of the filling and discharging of the three-dimensional model of the hydrogen storage cylinder, specifically including: configuring boundary conditions, the boundary conditions include ambient temperature, inlet boundary conditions and outlet boundary conditions; wherein the inlet boundary conditions include upper limit pressure, lower limit pressure, filling rate and inlet hydrogen temperature; the outlet boundary conditions include upper limit pressure, lower limit pressure and maximum safe pressure relief rate of the hydrogen storage cylinder;

[0088] As an example, the ambient temperature is configured to 23°C; the upper limit pressure of the inlet boundary condition is configured to 87.5MPa, the lower limit pressure is configured to 2MPa, the inflation rate is 0.0406MPa / s, and the inlet hydrogen temperature is -40°C; the upper limit pressure of the outlet boundary condition is configured to 87.5MPa, the lower limit pressure is configured to 2MPa, and the maximum safe pressure relief rate of the hydrogen storage cylinder is 0.00676MPa / s.

[0089] As a possible implementation method, the maximum safe depressurization rate of the hydrogen storage cylinder is determined by the following method:

[0090] S1210. Based on continuum mechanics and the introduction of the yield stress of the liner material, a blister damage model for the liner of a type IV hydrogen storage bottle is established:

[0091]

[0092] Among them, p Y is the yield pressure of the inner wall of the cylinder, unit: MPa; σ Y is the yield stress of the liner material, in MPa;

[0093] S1211. Establish and solve the cavitation risk assessment model to obtain the maximum safe pressure relief rate; the cavitation risk assessment model is specifically:

[0094]

[0095] Among them, p sat is the upper limit pressure, unit: MPa; p minis the lower limit pressure, unit MPa; D is the diffusion coefficient of the liner material, unit m 2 / s, the diffusion coefficient of PA6 is 3×10 ―10 m 2 / s; l is the thickness of the liner, unit: mm.

[0096] S122. Based on the finite element model of gas filling and discharging, simulate the filling and discharging process from the lower limit pressure to the upper limit pressure and from the upper limit pressure to the lower limit pressure, and obtain the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder;

[0097] S123. Import the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder into the structural mechanics calculation module, and then conduct comparative analysis on the three scenarios of thermal-solid coupling, fluid-solid coupling and thermal-fluid-solid coupling, obtain the difference degree of the maximum equivalent stress of the liner under the three scenarios, determine that the temperature field and the pressure field are necessary factors for the maximum equivalent stress, and based on this, use the thermal-fluid-solid coupling analysis method to determine the maximum equivalent stress of the liner;

[0098] As an example, the stress differences under the three scenarios are shown in Table 1:

[0099] Table 1 Differences in the maximum equivalent stress of the liner under three scenarios

[0100]

[0101]

[0102] S124. Based on the stress cloud diagram obtained from the thermal-fluid-solid coupling analysis, the location of the maximum equivalent stress is determined, which is the dangerous location.

[0103] As an example, see Figures 2 to 3 , which is the curve of the maximum equivalent stress of the thermal-fluid-solid coupling of the inner liner changing with time during the filling and degassing process of the hydrogen storage bottle obtained by the structural mechanics calculation module. It can be seen that the maximum coupling equivalent stress of the inner liner increases with time during the inflation process; during the degassing process, the maximum coupling equivalent stress of the inner liner gradually decreases with time. Therefore, in a complete filling and degassing process, the maximum stress of the inner liner of the hydrogen storage bottle occurs at the initial moment of degassing. Combined with Table 1, it can be seen that at this time, the weak link of the inner liner is located in the annular area where the bottle mouth head and the barrel are connected; when considering the influence of temperature load, due to the uneven temperature distribution, the weak link of the inner liner is reduced from the annular area to a node below the area, that is, below the connection between the bottle mouth head and the barrel.

[0104] In actual applications, manufacturing defects inside the gas cylinder cause stress concentration at the defective part of the liner. When the stress reaches a certain level, the liner will fail due to local stress. In addition, the gas cylinder will be subjected to cyclic loads during operation. As the damage accumulates, low-cycle fatigue failure may occur. If the hole defect also appears at the weak link of the liner of the known defect-free hydrogen storage cylinder, the possibility of failure of the gas cylinder will be greater. Therefore, this point is a dangerous position.

[0105] S13. Prediction of hydrogen concentration in hole defects during inflation process; Prediction of hydrogen concentration in hole defects during deflation process;

[0106] As an example, during the filling process of a hydrogen storage cylinder, the hydrogen concentration in the hole defect is solved by the following formula:

[0107]

[0108] Where x is the distance between the hole defect and the inner surface of the liner, in m, t f is the time the liner is exposed to hydrogen environment, in seconds, C f0 is the initial concentration of hydrogen in the hole, in kg / m 3 , C f The concentration of hydrogen in the liner at the end of inflation, in kg / m 3 , D is the diffusion coefficient of hydrogen, in m 2 / s.

[0109] In the above formula, the expression of erf(x) is:

[0110]

[0111] It is known that the pressure on the surface of the inner liner and the hole in the initial state of inflation is 2MPa, the final inflation pressure is 87.5MPa, and D is 3E-10m 2 / s, and each parameter is brought into the above hydrogen concentration solution formula to obtain the hydrogen concentration change curve in the inner liner hole defect. The hydrogen concentration gradually increases with the increase of the time the inner liner is exposed to the hydrogen environment, and the concentration growth rate is large in the initial stage, and then becomes smaller and smaller. The closer the hole is to the inner surface of the inner liner, the greater the hydrogen concentration, that is, the hydrogen inside the hole close to the inner side of the inner liner can reach equilibrium with the hydrogen concentration inside the inner liner faster.

[0112] During the degassing process of the hydrogen storage cylinder, the hydrogen concentration in the hole defect is solved by the following formula:

[0113]

[0114] Where, t cis the time the liner is exposed to hydrogen, y is the distance between the hole defect and the inner surface of the liner, c(y, t c ) represents t c The hydrogen concentration inside the hole at time y, C c0 is the hydrogen concentration at the initial time of degassing, C c is the hydrogen concentration when the gas is deflated to the target pressure, t cz is the total time of deflation, L is the thickness of the liner, and D is the diffusion coefficient of hydrogen. It is known that the initial deflation pressure of the gas cylinder is 87.5MPa, the final pressure is 2MPa, and the total pressure relief time is 13000s. Substitute each parameter into the above hydrogen concentration solution formula to obtain the hydrogen concentration change curve in the liner hole defect. As the deflation time increases, the hydrogen concentration in the holes at various positions gradually decreases. And the rate of decrease of hydrogen concentration in the holes far away from the inner surface of the liner is greater than the rate of decrease of hydrogen concentration in the holes close to the inside of the liner. This is because when the pressure is relieved, the hydrogen in the holes diffuses from the outside to the inside along the thickness of the liner, and the hydrogen diffused from the outside will pass through the internal holes and then fill the internal holes.

[0115] S14. Establish a thermal-fluid-solid coupling model of a hydrogen storage cylinder with hole defects;

[0116] As a possible implementation method, S14 specifically includes the following steps:

[0117] S140. Mesh the three-dimensional model of the hydrogen storage cylinder with different hole defects, including meshing of the inner tank and the winding layer; the mesh size of the winding layer is larger than the mesh size of the inner tank; the mesh size of the hole surface, the mesh size of the arc test block where the hole is located, the mesh size close to the arc test block, and the mesh size far from the arc test block increase in sequence;

[0118] As an example, the grid division scheme is: the grid size away from the arc test block is 10mm, the grid size close to the arc test block is 5mm, the grid size of the arc test block where the hole is located is 0.5mm, and the grid size on the hole surface is 0.03mm; the grid size of the winding layer is 20mm.

[0119] S141. Configure boundary conditions, which include fixed constraints, inner surface pressure load of the liner, inner surface pressure load of the bottle mouth sealing structure, volume temperature load of each solid domain and hole surface pressure load; wherein, fixed constraints refer to applying fixed support at the bottle mouth of the hydrogen storage cylinder, and the degree of freedom is restricted to 0; the inner surface pressure load of the liner, the inner surface pressure load of the bottle mouth sealing structure, and the volume temperature load of each solid domain are imported into the three-dimensional model of the hydrogen storage cylinder containing different hole defects using the inner surface pressure load and volume temperature load obtained in S123 as mapping loads; the hole surface pressure load is based on the hydrogen concentration in the hole defect predicted during the filling and discharging process, and the hole surface pressure load is obtained by solving Fick's law. At this point, the thermal-fluid-solid coupling model of the hydrogen storage cylinder with hole defects is established.

[0120] S15. Based on the thermal-fluid-solid coupling model of hydrogen storage cylinders with pore defects, the maximum coupling equivalent stress F of the inner liner with dense pore defects is obtained c , F c =h×F one , where h is the stress amplification factor of the two-hole defect, obtained by solving the empirical model of h; F one is the maximum coupled equivalent stress of the inner liner with a single hole defect, which is determined by the single hole defect distribution position and hole diameter through machine learning;

[0121] When the two holes are independent of each other, the maximum coupling equivalent stress of the liner depends on the hole with a larger size. At this time, it can be regarded as a single hole defect problem for study. When the spacing between the two hole defects is less than the minimum independent spacing, due to the coupling effect between the holes, the maximum coupling equivalent stress of the two holes in the liner is greater than the maximum coupling equivalent stress when a single hole exists. At this time, it is necessary to solve the stress amplification factor of the two-hole defect to describe the relationship between the maximum coupling equivalent stress of the two-hole defect and the single-hole defect liner. Two hole defects arranged circumferentially, axially and radially are established inside the liner of the hydrogen storage cylinder to simulate the maximum coupling equivalent stress of the liner of the hydrogen storage cylinder.

[0122] As a possible implementation method, the two holes are arranged circumferentially or axially, and the diameters D2 of the two holes are equal. The empirical model of h is:

[0123] h=0.386D2+0.762,H2<0.2mm,D2>0.65mm,at this time, R 2 =0.998;

[0124] h=1, H2<0.2mm, D2≤0.65mm;

[0125] h=1, H2≥0.2mm, 0.2mm≤D2≤1.2mm;

[0126] H2 is the hole spacing, R2 is the variance.

[0127] As an example, the simulated data is shown in Table 2, where W2 is the minimum distance between the hole surface and the inner side of the liner; the two-hole defect stress amplification factor h is the ratio of the maximum coupled equivalent stress of the hydrogen storage cylinder liner containing two holes to the maximum coupled equivalent stress of the hydrogen storage cylinder liner when a single hole with a diameter of D2 exists. It can be seen from Table 2 that the two-hole defect stress amplification factor h does not change with the change of W2, but increases with the increase of D2.

[0128] Table 2 Stress amplification factor h of defects containing two holes with equal diameters arranged circumferentially and axially

[0129]

[0130] See also Figure 4 , is the relationship curve between the defect stress amplification factor h of two holes with the same aperture arranged in the circumferential / axial direction and the hole diameter D2. It can be seen that there is an obvious linear relationship between the defect stress amplification factor h of the two holes and the hole diameter D2. The average stress amplification factor h in Table 2 is a Perform a linear fit with D2 to obtain the variance R 2 The empirical model h=0.386D2+0.762 is 0.998, which is applicable to two hole defects with D2 greater than 0.65mm, circumferential or axial arrangement, equal aperture and H2 less than 0.2mm. When H2 is greater than or equal to 0.2mm, D2 is greater than or equal to 0.2mm and less than or equal to 1.2mm, or H2 is less than 0.2mm, D2 is less than or equal to 0.65mm, the two holes are independent of each other, and h is 1 at this time.

[0131] As a possible implementation, the two holes are arranged circumferentially or axially, and the diameters of the two holes are D 21 and D 22 Not equal, the empirical model of h is:

[0132] When D 21 ≤0.65mm and D 22 When ≤0.65mm, h=1;

[0133] When H2<0.2mm, D 21 ≤0.65mm and D 22 >0.65mm, or D 21 >0.65mm and D 22 >0.65mm, At this time, R 2 =0.979;

[0134] H2 is the hole spacing, R 2 is the variance.

[0135] As an example, suppose D 21 Less than D 22 From the above, it can be seen that the stress amplification factor h of the two hole defects does not change with the change of W2. Therefore, when the diameters of the two holes are not equal, only the two hole defects with W2 of 1 can be simulated and analyzed. The simulation data is shown in Table 3, which is the maximum coupling equivalent stress F of the inner liner when the two holes with unequal diameters are arranged in the circumferential direction and axial direction. two , and the maximum coupling equivalent stress F of the liner when the large diameter hole exists alone D22 From Table 3, we can see that under the combined action of two holes with unequal diameters, the maximum coupling equivalent stress F of the inner liner is two is greater than the result when holes of the same diameter act together, and as D 21 Get smaller, D 22 Get bigger, D 22 With D 21 As the difference between the two holes increases, the defect amplification factor h of the two holes also increases.

[0136] Table 3 Stress amplification factor h of defects containing two holes with unequal diameters arranged circumferentially and axially

[0137]

[0138]

[0139] Therefore, D 21 , D 22 and D 22 / D 21 As a variable, establish the ternary function as follows:

[0140]

[0141] Among them, A, B, C, and F are coefficients, and the empirical model is obtained through multivariate linear fitting:

[0142]

[0143] The fitting results are shown in Table 4. The variance R 2 It is 0.979.

[0144] Table 4 Ternary function fitting results

[0145]

[0146] This model is suitable for H2 less than 0.2mm, D 21 Less than or equal to 0.65mm and D 22 When the diameter of the two holes is greater than 0.65mm, or the diameter of both holes is greater than 0.65mm; when D 21 and D 22When both holes are less than or equal to 0.65 mm and the two hole defects are arranged axially or radially in the inner tank, the two holes are always independent of each other, and h is 1.

[0147] As a possible implementation method, the two holes are arranged radially, and the hole diameters D2 are equal. The empirical model of h is:

[0148] When 0.2mm≤D2≤0.4mm, H2<0.2mm, h=1.429D2 0.226 , at this time, R 2 =0.989;

[0149] When D2>0.4mm, 0.2≤H2<0.3mm, h=1.161D2 0.149 , at this time, R 2 =0.993;

[0150] When D2>0.4mm, 0.3≤H2<0.4mm, h=1.059D2 0.066 , at this time, R 2 =0.987;

[0151] When D2≤0.4mm and H2≥0.2mm, or when there are two holes of any size and H2≥0.4mm, h=1;

[0152] H2 is the hole spacing, R 2 is the variance.

[0153] As an example, see Figure 5 The three curves in the figure represent the relationship between the defect stress amplification factor h and D2 of two holes with equal hole diameters D2 and radial arrangement when the hole spacing H2 is 0.1mm, 0.2mm and 0.3mm respectively. Figure 5 It can be seen that the stress amplification factor h of the two-hole defect shows a nonlinear growth trend with the increase of D2, and the smaller the hole spacing H2, the larger the stress amplification factor h of the two-hole defect. The nonlinear fitting of the stress amplification factor h of the two-hole defect under different conditions of hole spacing H2 of 0.1mm, 0.2mm and 0.3mm is performed with the hole diameter D2 as the variable, see Figures 6 to 8 , we get the empirical model h = 1.429D2 0.226 , applicable when the hole diameter D2 is greater than or equal to 0.2mm and less than or equal to 0.4mm and the hole spacing H2 is less than 0.2mm; h = 1.161D2 0.149 , applicable when the hole diameter D2 is greater than 0.4mm, the hole spacing H2 is greater than or equal to 0.2mm and less than 0.3mm; h = 1.059D2 0.066, applicable when the hole diameter D2 is greater than 0.4mm and the hole spacing H2 is greater than or equal to 0.3mm and less than 0.4mm. When two holes are independent, that is, two hole defects with a hole diameter D2 less than or equal to 0.4mm and a hole spacing H2 greater than or equal to 0.2mm, or two hole defects of any size with a hole spacing H2 greater than or equal to 0.4mm, h = 1.

[0154] As a possible implementation, two holes are arranged radially, and the hole diameter D 21 and D 22 Not equal, D 22 >D 21 , h empirical model is:

[0155] When D 22 ≤0.4mm, H2<0.2mm, h=1.469D 22 0.274 , at this time, R 2 =0.993;

[0156] When D 22 >0.4mm, 0.2≤H2<0.3mm, h=1.163D 22 0.169 , at this time, R 2 =0.986;

[0157] When D 22 >0.4mm, 0.3≤H2<0.4mm, h=1.050D 22 0.065 , at this time, R 2 =0.944;

[0158] When D 22 ≤0.4mm and H2≥0.2mm, or, for any two hole defects of any size with H2≥0.4mm, h=1;

[0159] H2 is the hole spacing, R 2 is the variance.

[0160] As an example, see Tables 5 to 7, which are the stress amplification factors h of two hole defects with different hole diameters and radial arrangement with hole spacing H2 of 0.1mm, 0.2mm, and 0.3mm. It can be seen from the data in the table that when the two hole defects act together, when D is fixed 22 Change D 21 When the inner liner F two No significant changes occurred; however, with the 22 Increased, inner liner F two Therefore, when the inner tank contains two holes with different diameters and arranged radially, its stress amplification factor h is proportional to D 22There is a close connection between them.

[0161] Table 5 Defect stress amplification factor h of two holes with different diameters arranged radially with hole spacing H2 of 0.1 mm

[0162]

[0163] Table 6 Defect stress amplification factor h of two holes with different diameters arranged radially with hole spacing H2 of 0.2 mm

[0164]

[0165] Table 7 Defect stress amplification factor h of two holes with different radial diameters and hole spacing H2 of 0.3 mm

[0166]

[0167]

[0168] See also Fig. 9 The three curves in the figure represent the stress amplification factor h and D of two holes with different diameters and radial arrangement when the hole spacing H2 is 0.1mm, 0.2mm and 0.3mm respectively. 22 As can be seen from the figure, under different H2, the hole defect stress amplification factor h shows a nonlinear growth trend as D2 increases, and the smaller H2 is, the larger h is. 22 Nonlinear fitting of h for different H2 conditions for variables, see Figures 10 to 12 , we get the empirical model h=1.469D 22 0.274 , suitable for hole diameter D 22 When the hole spacing H2 is less than 0.2mm, h=1.163D 22 0.169 , suitable for hole diameter D 22 When the hole spacing H2 is greater than or equal to 0.2mm and less than 0.3mm, h=1.050D 22 0.065 , suitable for hole diameter D 22 When the hole spacing H2 is greater than or equal to 0.3mm and less than 0.4mm. When the two holes are independent, that is, the hole diameter D 22 When there are two hole defects of any size less than or equal to 0.4 mm and the hole spacing H2 is greater than or equal to 0.2 mm, or when the hole spacing H2 is greater than or equal to 0.4 mm, h=1.

[0169] As a possible implementation method, the maximum coupling equivalent stress F of the inner liner with a single hole defect is determined by machine learning. oneThe specific steps include:

[0170] S150. Configure N D1 values, configure M W1 values, and obtain N×M groups of F through simulation one Datasets;

[0171] As an example, configure 11 D1 values, configure 11 W1 values, and obtain 121 groups of F through simulation. one Datasets;

[0172] S151. Combine N×M groups of F one The dataset is split into training and testing sets;

[0173] As an example, 121 sets of F one The data set is divided into a training set and a test set, with 97 sets of training set data and 24 sets of test set data.

[0174] S152. iForest is used to process the training set and the test set to improve the quality and reliability of the data;

[0175] As an example, iForest is used to process the data of the training set and the test set, including the following sub-steps:

[0176] S1520. Build a tree: Randomly select n sample points from the training data and put them into the root node of the tree. Randomly select an attribute and randomly select a value of this attribute (between the maximum and minimum) as the cut value of the sample. When the training sample is divided, data less than the cut value is assigned to the left branch, and data greater than or equal to the cut value is assigned to the right branch. Then, repeat the above steps in the left and right branch data until the data is no longer divisible or the binary tree reaches a finite height.

[0177] S1521. Determine outliers: For each data point, the path length in each tree is used to measure its degree of isolation in iForest. The smaller the path length, the easier it is for the sample to be isolated and the more likely it is an outlier. The path length in each tree is the number of edges from the root node to the leaf node where it is located, defined as h(x). The outlier score is:

[0178]

[0179] In the above formula, E(h(x)) is the average path length in all trees, and c(n) is the average value of h(x) for a data set of size n, which can be calculated as:

[0180]

[0181] S1522. Bayesian Optimization: Based on Bayes’ theorem and Gaussian process principle, the objective functions of various machine learning models are modeled by continuously using prior information and actual observation data, so as to find the hyperparameter combination that makes the objective function achieve the optimal value.

[0182] First, define the prior distribution of the surrogate function, combine the existing observation data, update the prior knowledge to obtain the posterior model, and then use a certain sampling strategy to select the next most promising hyperparameter value based on the posterior model, and use the selected hyperparameter value to evaluate the performance of the objective function. Finally, add the new observation data to the existing data set, and then continuously update and iterate, and terminate the iteration when the specified number of iterations is reached or certain convergence conditions are met. The formula of Bayes' theorem is as follows:

[0183]

[0184] Where A is the objective function, B is the observation value, p(A) is the prior distribution of A, i.e., the proxy model, p(B) is the boundary likelihood distribution of A, p(B│A) is the distribution of observed data B given the proxy model, and p(A│B) is the posterior distribution, i.e., the new distribution of the proxy model after given observed data B.

[0185] In Bayesian optimization, the objective function is assumed to be an unknown random function, and an appropriate prior model needs to be selected to describe the probability distribution of this random function. GPR is usually used as the prior model. A Gaussian process consists of a mean function m:x→R and a covariance k:x×x→R, and the generative model is:

[0186] f(x)~gp(m(x)),k(x,x);

[0187] Where m(x) is the mean and k(x,x) is the covariance. The mean and variance of the posterior distribution of the random variable X under the influence of the observed data are:

[0188] μ n (x) = μ0(x) + k(x) T (k+σ 2 ) ―1 (y-m);

[0189]

[0190] Select Expected Improvement (EI) as the acquisition function.

[0191] S153. Use the Bayesian optimization random forest ensemble learning algorithm to train the training set to obtain F oneMachine learning prediction model. The accuracy of the machine learning prediction model is: mean-square error (MSE) 0.105, variance R 2 It is 0.9848.

[0192] S16. Determine the ultimate stress of liner failure and determine the maximum coupling equivalent stress F c Is it greater than the limit stress? If so, it is determined that the liner is failed. If not, it jumps to S17;

[0193] S17. Based on the Chaboche fatigue life prediction model, the fatigue life of the inner liner hole defect location, the inner surface of the inner liner, and the outer surface of the inner liner is predicted. If the life of the above three locations is less than the life threshold, it is judged that the inner liner has lost its sealing, otherwise, it is judged that the inner liner can continue to serve.

[0194] As an example, under stress-controlled conditions, a typical model of fatigue damage is:

[0195]

[0196] In the above formula, D f is the fatigue damage variable, N is the fatigue life under the current load, S max is the maximum stress, S m is the average stress, β is the temperature correlation coefficient, α and M are the temperature and stress correlation functions, expressed as:

[0197]

[0198] M=M0(1―bS m );

[0199] In the above formula, S l0 is the fatigue endurance limit, S u is the ultimate tensile strength, a, b, M0 are constants related to temperature. <> is the Macaulay bracket:

[0200]

[0201] By integrating the typical fatigue damage model, the number of failure cycles N can be obtained: f and fatigue damage D f They are:

[0202]

[0203]

[0204] Therefore, the fatigue life prediction model can be expressed as:

[0205]

[0206] In a second aspect, the present invention provides a terminal including a processor and a communication interface coupled to the processor, wherein the processor is used to run a computer program or instruction to implement the method for evaluating the inner liner of a type IV hydrogen storage bottle provided in the first aspect.

[0207] Compared with the prior art, the present invention has the following technical effects:

[0208] 1. The method for evaluating the inner liner of a type IV hydrogen storage bottle provided by the present invention establishes a thermal-fluid-solid coupling model of a type IV hydrogen storage bottle, which can more comprehensively evaluate the impact of hole defects on the performance of the type IV hydrogen storage bottle and has important engineering application value.

[0209] 2. The provided method for evaluating the inner liner of a type IV hydrogen storage bottle uses numerical simulation methods to deeply explore the relevant information between the characteristics of hole size, distribution position, spacing, arrangement direction and the stress response of the inner liner, and establishes an empirical model of the stress amplification factor of the inner liner; the dense hole defect problem is simplified to a single hole defect problem for analysis, and numerical simulation methods and machine learning techniques are comprehensively applied. Through the empirical model of stress amplification factor and the machine learning model for stress prediction of the inner liner containing a single hole defect, the maximum coupled equivalent stress of the inner liner containing dense hole defects is obtained, which solves the problem of the complex damage mechanism of the inner liner caused by dense hole defects.

[0210] 3. The evaluation method for the inner liner of a type IV hydrogen storage bottle provided by the present invention is based on the inner liner stress prediction model and the Chaboche fatigue life prediction model, and takes the flow stress failure criterion and the fatigue failure criterion of three key parts as the criteria. A type IV hydrogen storage bottle suitable for single-hole defects, two-hole defects and dense hole defects is established, and the nonlinear behavior of the material and the influence of hole defects on the structural strength and fatigue life of the hydrogen storage bottle are comprehensively considered, ensuring that even if a certain degree of deformation occurs in the local area of ​​the hydrogen bottle inner liner, it still has the key performance to ensure its safe use. It is of great significance to improve the efficiency of material use and extend the service life of the hydrogen storage bottle.

[0211] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the drawings, etc. In the specification, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit can implement several functions listed in the specification. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0212] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is obvious that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the technical solutions recorded in the embodiments of the present invention, the present invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating the inner liner of a type IV hydrogen storage bottle, characterized in that: The evaluation method is used to evaluate the sealing and deformation of the liner; the evaluation method comprises the following steps: S10. Obtain hole defect characteristic information, wherein the hole defect characteristic information includes at least hole diameter, hole position, and hole spacing; S11. Simplify the hole defect into a spherical hole defect, and divide the hole defect into a single hole defect, a double hole defect and a dense hole defect; wherein the single hole defect is characterized by the hole diameter and the hole position; the double hole defect is characterized by the hole diameter, the hole position, the hole spacing and the arrangement direction; the dense hole defect is characterized by the hole diameter, the minimum spacing and the number of holes; S12. Establishing a three-dimensional model of a hydrogen storage cylinder containing different hole defects, specifically comprising: firstly determining the dangerous position of the liner; secondly, establishing a single hole defect, a double hole defect and a dense hole defect based on the dangerous position; S13. Prediction of hydrogen concentration in hole defects during inflation process; Prediction of hydrogen concentration in hole defects during deflation process; S14. Establish a thermal-fluid-solid coupling model of a hydrogen storage cylinder with hole defects; S15. Based on the thermal-fluid-solid coupling model of hydrogen storage cylinders with pore defects, the maximum coupling equivalent stress F of the inner liner with dense pore defects is obtained c , F c =h×F one , where h is the stress amplification factor of the two-hole defect, obtained by solving the empirical model of h; F one is the maximum coupled equivalent stress of the inner tank containing a single hole defect, which is determined by the single hole defect distribution position and hole diameter through machine learning; S16. Determine the ultimate stress of liner failure and determine the maximum coupling equivalent stress F c Is it greater than the limit stress? If so, it is determined that the liner is failed. If not, it jumps to S17; S17. Based on the Chaboche fatigue life prediction model, the fatigue life of the inner liner hole defect location, the inner surface of the inner liner, and the outer surface of the inner liner is predicted. If the life of the above three locations is less than the life threshold, it is judged that the inner liner has lost its sealing, otherwise, it is judged that the inner liner can continue to serve.

2. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: Determine the dangerous position of the inner tank by following the steps below: S120. Establish a three-dimensional model of a hydrogen storage cylinder without hole defects; S121. Establish a finite element model of the filling and discharging of the three-dimensional model of the hydrogen storage cylinder, specifically including: configuring boundary conditions, the boundary conditions including ambient temperature, inlet boundary conditions and outlet boundary conditions; wherein the inlet boundary conditions include upper limit pressure, lower limit pressure, filling rate and inlet hydrogen temperature; the outlet boundary conditions include upper limit pressure, lower limit pressure and maximum safe pressure relief rate of the hydrogen storage cylinder; S122. Based on the finite element model of gas filling and discharging, simulate the filling and discharging process from the lower limit pressure to the upper limit pressure and from the upper limit pressure to the lower limit pressure, and obtain the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder; S123. Import the temperature field of the solid domain and the pressure field on the inner surface of the gas cylinder into the structural mechanics calculation module, and then conduct comparative analysis on the three scenarios of thermal-solid coupling, fluid-solid coupling and thermal-fluid-solid coupling, obtain the difference degree of the maximum equivalent stress of the liner under the three scenarios, determine that the temperature field and the pressure field are necessary factors for the maximum equivalent stress, and based on this, use the thermal-fluid-solid coupling analysis method to determine the maximum equivalent stress of the liner; S124. Determine the location of the maximum equivalent stress based on the stress cloud map obtained based on the thermal-fluid-solid coupling analysis, which is the dangerous location.

3. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 2, characterized in that: The maximum safe depressurization rate of the hydrogen storage cylinder is determined as follows: S1210. Based on continuum mechanics and the introduction of the yield stress of the liner material, a blister damage model for the liner of a type IV hydrogen storage bottle is established: Among them, p Y is the yield pressure of the inner wall of the cylinder, unit: MPa; σ Y is the yield stress of the liner material, in MPa; S1211. Establish and solve a cavitation risk assessment model to obtain the maximum safe pressure relief rate; the cavitation risk assessment model is specifically: Δp=p sat ―p min # Among them, p sat is the initial saturation pressure, unit: MPa; p min is the final minimum pressure, in MPa; D is the diffusion coefficient of the liner material, in m 2 / s; l is the thickness of the liner, unit: mm.

4. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 2, characterized in that: The S14 specifically includes the following steps: S140. Mesh the three-dimensional model of the hydrogen storage cylinder with different hole defects, including meshing of the inner tank and the winding layer; the mesh size of the winding layer is larger than the mesh size of the inner tank; the mesh size of the hole surface, the mesh size of the arc test block where the hole is located, the mesh size close to the arc test block, and the mesh size far from the arc test block increase in sequence; S141. Configure boundary conditions, which include fixed constraints, inner surface pressure load of the liner, inner surface pressure load of the bottle mouth sealing structure, volume temperature load of each solid domain and hole surface pressure load; wherein, the fixed constraint condition refers to applying a fixed support at the bottle mouth of the hydrogen storage cylinder, and the degree of freedom is limited to 0; the inner surface pressure load of the liner, the inner surface pressure load of the bottle mouth sealing structure, and the volume temperature load of each solid domain are imported into the three-dimensional model of the hydrogen storage cylinder containing different hole defects using the inner surface pressure load and volume temperature load obtained in S123 as mapping loads; the hole surface pressure load is based on the hydrogen concentration in the hole defect predicted during the filling and discharging process, and the hole surface pressure load is obtained by solving Fick's law. At this point, a thermal-fluid-solid coupling model of the hydrogen storage cylinder with hole defects is established.

5. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: The two holes are arranged circumferentially or axially, and the diameters D2 of the two holes are equal. The empirical model of h is: h=0.386D2+0.762,H2<0.2mm,D2>0.65mm,at this time, R 2 =0.998; h=1, H2<0.2mm, D2≤0.65mm; h=1, H2≥0.2mm, 0.2mm≤D2≤1.2mm; H2 is the hole spacing, R 2 is the variance.

6. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: The two holes are arranged circumferentially or axially, and the diameter of the two holes is D 21 and D 22 Not equal, the empirical model of h is: When D 21 ≤0.65mm and D 22 When ≤0.65mm, h=1; When H2<0.2mm, D 21 ≤0.65mm and D 22 >0.65mm, or D 21 >0.65mm and D 22 >0.65mm, At this time, R 2 =0.979; H2 is the hole spacing, R 2 is the variance.

7. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: The two holes are arranged radially and the hole diameters D2 are equal. The empirical model of h is: When 0.2mm≤D2≤0.4mm, H2<0.2mm, h=1.429D2 0.226 , at this time, R 2 =0.989; When D2>0.4mm, 0.2≤H2<0.3mm, h=1.161D2 0.149 , at this time, R 2 =0.993; When D2>0.4mm, 0.3≤H2<0.4mm, h=1.059D2 0.066 , at this time, R 2 =0.987; When D2≤0.4mm and H2≥0.2mm, or two holes of any size with H2≥0.4mm, h=1; H2 is the hole spacing, R 2 is the variance.

8. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: The two holes are arranged radially, and the hole diameter D 21 and D 22 Not equal, D 22 >D 21 , h empirical model is: When D 22 ≤0.4mm, H2<0.2mm, h=1.469D 22 0.274 , at this time, R 2 =0.993; When D 22 >0.4mm, 0.2≤H2<0.3mm, h=1.163D 22 0.169 , at this time, R 2 =0.986; When D 22 >0.4mm, 0.3≤H2<0.4mm, h=1.050D 22 0.065 , at this time, R 2 =0.944; When D 22 ≤0.4mm and H2≥0.2mm, or, for any two hole defects of any size with H2≥0.4mm, h=1; H2 is the hole spacing, R 2 is the variance.

9. The method for evaluating the inner liner of a type IV hydrogen storage bottle according to claim 1, characterized in that: Determination of the maximum coupled equivalent stress F of a liner with a single hole defect by machine learning one The specific steps include: S150. Configure N D1 values, configure M W1 values, and obtain N×M groups of F through simulation one Datasets; S151. Combine N×M groups of F one The dataset is split into training and testing sets; S152. iForest is used to process the training set and the test set to improve the quality and reliability of the data; S153. Use the Bayesian optimization random forest ensemble learning algorithm to train the training set to obtain F one The machine learning prediction model has the following accuracy: mean square error MSE is 0.105, variance R 2 It is 0.9848.

10. A terminal, characterized in that: It includes a processor and a communication interface coupled to the processor, and the processor is used to run a computer program or instruction to implement the method for evaluating the inner liner of a Type IV hydrogen storage bottle as described in claims 1 to 9.

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