Numerical simulation method for calculating collapse critical pressure reduction rate of IV-type hydrogen storage container lining

Abstract

The invention provides a numerical simulation method for calculating the collapse critical pressure reduction rate of an IV-type hydrogen storage container lining. The method comprises the following steps: determining the size of a cavity defect generated by sinking of a container lining, establishing a finite element model of a container straight tube section with the cavity defect, establishing two closed fluid cavity models representing the volume of the cavity defect and the internal volume of the container, and the like. According to the method, through a fluid cavity gas modeling method based on an ideal gas state equation, a finite element model capable of reflecting the collapse of the IV-type hydrogen storage container lining in the rapid pressure reduction process is established, and a corresponding critical pressure difference and a critical pressure reduction rate are obtained through calculation; therefore, rapid prediction and safe design of the pressure reduction rate of the IV-type hydrogen storage container in practice are realized.

Description

Technical Field

[0001] The invention relates to the field of fluid-solid coupling numerical simulation, and in particular to a numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container. Background Art

[0002] Compared with traditional hydrogen storage containers, non-metallic liner fiber fully wrapped (Type IV) hydrogen storage containers have the advantages of light weight and high hydrogen storage density, making them widely used in new energy vehicles and aerospace fields. Small molecule hydrogen inevitably dissolves and diffuses through the polymer container lining, and accumulates in the cavity defects existing at the interface between the container lining and the carbon fiber reinforced composite material layer, which is equivalent to introducing a pressure equal to the external pressure at the interface. During the decompression process of the container, since the hydrogen diffusion rate at the interface is lower than the decompression rate of hydrogen, a pressure difference is immediately generated on the interface. When the pressure difference at the interface exceeds the critical value, it leads to the buckling and collapse of the polymer container lining, greatly shortening its service life. In this case, the liner collapse problem that occurs during rapid decompression becomes an issue that cannot be ignored, affecting the life and safe operation of Type IV hydrogen storage containers.

[0003] Although the collapse of polymer liners in Type IV hydrogen storage vessels has been studied experimentally and numerically, questions remain regarding the key parameters that affect the liner collapse behavior during rapid decompression and how they work. Most importantly, there is an inherent coupling relationship between hydrogen exhaust and the mechanical behavior of composite vessels.

[0004] Therefore, it is important and necessary to develop a fluid-solid coupling numerical simulation method for the collapse of the lining of type IV hydrogen storage containers and further determine the critical decompression rate. Summary of the invention

[0005] The purpose of the present invention is to provide a numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container, so as to solve the problems existing in the prior art.

[0006] The technical solution adopted to achieve the purpose of the present invention is as follows: a numerical simulation method for calculating the critical decompression rate of the liner collapse of a type IV hydrogen storage container, wherein the type IV hydrogen storage container includes a rotationally molded bottle body and a bottle mouth. The bottle body includes a container liner, a carbon fiber reinforced composite material winding layer and an outer protective layer from the inside to the outside. The following steps are included:

[0007] 1) Determine the size of the cavity defect caused by the depression of the container lining and establish a finite element model of the straight section of the container with the cavity defect.

[0008] 2) Based on the established finite element model, two closed fluid cavity models representing the cavity defect volume and the internal volume of the container are established.

[0009] 3) Based on the ideal gas state equation, the hydrogen in the fluid cavity is characterized to establish a fluid-solid coupling model. The model is used to calculate the mechanical response of the container during the decompression process at different decompression rates and obtain the critical pressure difference for the collapse of the container lining.

[0010] 4) The critical decompression rate of container lining collapse is calculated based on the calculated critical pressure difference.

[0011] Further, step 1) specifically includes the following sub-steps:

[0012] 1.1) Determine the cavity defect size of the container lining. The cavity defect control equation is:

[0013]

[0014] In the formula, r, z, are three parameters of the cylindrical coordinate system, a and b represent half of the length and width of the cavity defect, respectively, d is the depth of the cavity defect, and R is the radius of the straight section of the container.

[0015] 1.2) A finite element model of the straight section of the container with the cavity defect is established according to the defect size of the container lining.

[0016] 1.3) Define the interface mechanical behavior between the outer carbon fiber composite material and the inner lining of the model.

[0017] Further, in step 2), a fluid cavity I representing the volume of the defective cavity and a fluid cavity II representing the internal volume of the container are established. All nodes on the inner surface of the carbon fiber reinforced composite winding layer and the outer surface of the container liner are extracted, and the common nodes are processed at the ends to form a closed domain of the fluid cavity I. Two zero-thickness mesh surfaces are generated at both ends of the container liner, and then they are integrated with the inner surface mesh of the container liner through the common nodes at the ends to form a closed domain of the fluid cavity II.

[0018] Further, each surface normal of the fluid cavity is arranged to point outwards.

[0019] Further, step 3) specifically includes the following sub-steps:

[0020] 3.1) The ideal gas state equation is used to characterize the hydrogen in the fluid cavity to establish a fluid-solid coupling model. The ideal gas state equation is:

[0021]

[0022] Where P is the gas pressure, V g is the volume of gas, T g is the gas temperature. M is the mass of the gas, M mol is the molar mass of the gas, is the universal gas constant.

[0023] 3.2) The new finite element model is used to calculate the mechanical response of the container during the decompression process at different decompression rates. The decompression rate can be expressed as:

[0024]

[0025] Where k is the decompression rate, P ini and P final is the initial pressure in fluid chamber II and the pressure at the end of decompression, t total is the total time of decompression.

[0026] The container decompression process can be expressed by the reduction of the gas mass in the fluid cavity as:

[0027]

[0028] In the formula, is the total mass change of hydrogen per unit time, and It is the mass of hydrogen entering and exiting the fluid cavity per unit time.

[0029] 3.3) Calculate the critical pressure difference for the collapse of the container lining. The pressure difference is defined as:

[0030] ΔP=P int -P ext

[0031] Where ΔP is the equivalent pressure difference, P int and P ext Represent the pressure values ​​of fluid chamber I and fluid chamber II respectively. As the decompression process proceeds, at a certain moment, when the volume of the liner suddenly increases and then the pressure difference decreases, the pressure difference is the critical pressure difference ΔP cr Among them, P ext It can be expressed as:

[0032] P ext = k·t

[0033] P int Combining Henry's law with the decompression time, the hydrogen concentration in the fluid cavity caused by hydrogen diffusion at any time t can be expressed as:

[0034]

[0035] Where, t l is the lining thickness, D is the diffusion coefficient, S is the solubility of hydrogen, and C is the hydrogen concentration.

[0036] Henry's law is:

[0037]

[0038] The P int Under the combined effect of hydrogen diffusion and decompression, it can be finally expressed as:

[0039]

[0040] Where k is the decompression rate and t is the decompression time.

[0041] Further, in step 4), the critical pressure difference of the container liner collapse is calculated based on the calculated critical pressure difference. Based on the proposed fluid-solid coupling method and the established finite element model, the critical pressure difference ΔP of any initial cavity defect container is obtained. cr . Critical pressure difference ΔP cr The critical decompression rate k is calculated by combining the following formula: cr :

[0042]

[0043] The technical effect of the present invention is unquestionable: based on a new fluid-solid coupling model, a numerical simulation method is established that can reflect the physical process of the evolution law of the liner collapse of the type IV hydrogen storage container during the decompression process, thereby achieving the purpose of quickly predicting the critical decompression rate of the container. The realization of fluid-solid coupling numerical simulation of the liner collapse process of the type IV hydrogen storage container is helpful for in-depth research on the evolution law and structural response characteristics of the liner collapse problem of the type IV hydrogen storage container during the decompression process, which can be applied to the design and manufacturing field of the type IV hydrogen storage container and can solve related engineering problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the structural diagram of the Type IV hydrogen storage container;

[0045] Figure 2 Flowchart of the numerical simulation method.

[0046] In the figure: container lining 1, carbon fiber reinforced composite material wrapping layer 2, outer protective layer 3, bottle mouth 4. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0048] Embodiment 1:

[0049] See also Figure 1The type IV hydrogen storage container includes a rotationally molded bottle body and a bottle mouth 4. The bottle body includes a container liner 1, a carbon fiber reinforced composite material winding layer 2 and an outer protective layer 3 from the inside to the outside. The container liner is responsible for air tightness, while the outer carbon fiber composite material winding layer is responsible for the strength and deformation of the hydrogen storage bottle.

[0050] See also Figure 2 This embodiment provides a numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container, comprising the following steps:

[0051] 1) Determine the size of the cavity defect caused by the depression of the container lining 1, and establish a finite element model of the straight section of the container with the cavity defect. Step 1) specifically includes the following sub-steps:

[0052] 1.1) Determine the cavity defect size of the container lining 1. The cavity defect control equation is:

[0053]

[0054] In the formula, r, z, are three parameters of the cylindrical coordinate system, a and b represent half of the length and width of the cavity defect, respectively, d is the depth of the cavity defect, and R is the radius of the straight section of the container.

[0055] 1.2) A finite element model of the straight section of the container with the cavity defect is established according to the defect size of the container lining.

[0056] 1.3) Define the interface mechanical behavior between the outer carbon fiber composite material and the inner lining of the model.

[0057] 2) Two closed fluid cavity models representing the defect volume of the cavity and the internal volume of the container are established based on the established finite element model. Fluid cavity I representing the defect cavity volume and fluid cavity II representing the internal volume of the container are established. All nodes on the inner surface of the carbon fiber reinforced composite winding layer 2 and the outer surface of the container liner 1 are extracted, and common nodes are processed at the ends to form a closed domain of fluid cavity I. Two zero-thickness mesh surfaces are generated at both ends of the container liner 1, and then they are integrated with the inner surface mesh of the container liner 1 through the end common nodes to form a closed domain of fluid cavity II. Each surface normal of the fluid cavity is set to face outward.

[0058] 3) Based on the ideal gas state equation, the hydrogen in the fluid cavity is characterized to establish a fluid-solid coupling model, and the model is used to calculate the mechanical response of the container during the decompression process at different decompression rates and obtain the critical pressure difference for the collapse of the container liner. Step 3) specifically includes the following sub-steps:

[0059] 3.1) The ideal gas state equation is used to characterize the hydrogen in the fluid cavity to establish a fluid-solid coupling model. The ideal gas state equation is:

[0060]

[0061] Where P is the gas pressure, V g is the volume of gas, T g is the gas temperature. M is the mass of the gas, M mol is the molar mass of the gas, is the universal gas constant.

[0062] 3.2) The new finite element model is used to calculate the mechanical response of the container during the decompression process at different decompression rates. The decompression rate can be expressed as:

[0063]

[0064] Where k is the decompression rate, P ini and P final is the initial pressure in fluid chamber II and the pressure at the end of decompression, t total is the total time of decompression.

[0065] The container decompression process can be expressed by the reduction of the gas mass in the fluid cavity as:

[0066]

[0067] In the formula, is the total mass change of hydrogen per unit time, and It is the mass of hydrogen entering and exiting the fluid cavity per unit time.

[0068] 3.3) Calculate the critical pressure difference for the collapse of the container lining. The pressure difference is defined as:

[0069] ΔP=P int -P ext

[0070] Where ΔP is the equivalent pressure difference, P int and P ext Represent the pressure values ​​of fluid chamber I and fluid chamber II respectively. As the decompression process proceeds, at a certain moment, when the volume of the liner suddenly increases and then the pressure difference decreases, the pressure difference is the critical pressure difference ΔP cr Among them, P ext It can be expressed as:

[0071] P ext = k·t

[0072] P intCombining Henry's law with the decompression time, the hydrogen concentration in the fluid cavity caused by hydrogen diffusion at any time t can be expressed as:

[0073]

[0074] In the formula, t l is the lining thickness, D is the diffusion coefficient, S is the solubility of hydrogen, and C is the hydrogen concentration.

[0075] Henry's law is:

[0076]

[0077] The P int Under the combined effect of hydrogen diffusion and decompression, it can be finally expressed as:

[0078]

[0079] Where k is the decompression rate and t is the decompression time.

[0080] 4) The critical pressure difference of the container liner collapse is calculated based on the calculated critical pressure difference. The critical pressure difference of the container liner collapse is calculated based on the calculated critical pressure difference. Based on the proposed fluid-solid coupling method and the established finite element model, the critical pressure difference ΔP of the container with any initial cavity defect is obtained. cr . Critical pressure difference ΔP cr The critical decompression rate k is calculated by combining the following formula: cr :

[0081]

[0082] Embodiment 2:

[0083] The main contents of this embodiment are the same as those of Embodiment 1, wherein, in step 3.1), two fluid cavity surface units are selected and established, and the relevant properties of hydrogen (molar mass, etc.) are first applied to them respectively, and then the state of hydrogen is described using the ideal gas state equation, so that the relationship between the hydrogen pressure and the fluid cavity volume at any time can be obtained and acted on the solid structure of the container.

[0084] Embodiment 3:

[0085] The main contents of this embodiment are the same as those of embodiment 1, wherein, in step 3.2), the outer surface of the model is first completely constrained, and hydrogen pressure is applied in the two fluid cavities, specifically: in the initial stage, the pressure value in the two fluid cavities is equal to the maximum working pressure. Once the decompression process begins, the pressure in the fluid cavity 2 decreases linearly with the decompression rate, and the pressure in the fluid cavity 1 also decreases accordingly. The pressure change in the fluid cavity is controlled by controlling the hydrogen mass flow rate, and the mechanical response of the container is obtained by finite element calculation. Software such as Abaqus, Anasys, and Hypermesh can be used to solve the model.

Claims

1. A numerical simulation method for calculating the critical decompression rate of collapse of the liner of a type IV hydrogen storage container, wherein the type IV hydrogen storage container comprises a rotationally molded bottle body and a bottle mouth (4); the bottle body comprises, from inside to outside, a container liner (1), a carbon fiber reinforced composite material winding layer (2) and an outer protective layer (3); characterized in that: The following steps are involved: 1) determining the size of the cavity defect caused by the depression of the container lining (1), and establishing a finite element model of the straight section of the container with the cavity defect; 2) Two closed fluid cavity models representing the cavity defect volume and the internal volume of the container are established based on the established finite element model; 3) Based on the ideal gas state equation, the hydrogen in the fluid cavity is characterized to establish a fluid-solid coupling model. The model is used to calculate the mechanical response of the container during the decompression process at different decompression rates and obtain the critical pressure difference for the collapse of the container liner; 4) The critical decompression rate of the container lining collapse is calculated based on the calculated critical pressure difference.

2. The numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container according to claim 1, characterized in that: Step 1) specifically includes the following sub-steps: 1.1) Determine the cavity defect size of the container lining (1); the cavity defect control equation is: In the formula, r, z, are three parameters of the cylindrical coordinate system, a and b represent half of the length and width of the cavity defect, d is the depth of the cavity defect, and R is the radius of the straight section of the container; 1.2) establishing a finite element model of the straight section of the container with the cavity defect according to the defect size of the container lining; 1.3) Define the interface mechanical behavior between the outer carbon fiber composite material and the inner lining of the model.

3. The numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container according to claim 1, characterized in that: In step 2), a fluid cavity I representing the volume of the defect cavity and a fluid cavity II representing the internal volume of the container are established; All nodes on the inner surface of the carbon fiber reinforced composite material winding layer (2) and the outer surface of the container liner (1) are extracted, and common nodes are processed at the ends to form a closed domain of the fluid cavity I; two zero-thickness mesh surfaces are generated at both ends of the container liner (1), and then they are integrated with the inner surface mesh of the container liner (1) through the common nodes at the ends to form a closed domain of the fluid cavity II.

4. The numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container according to claim 3, characterized in that: Each surface normal of the fluid cavity is set to point outwards.

5. The numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container according to claim 3, characterized in that: Step 3) specifically includes the following sub-steps: 3.1) The ideal gas state equation is used to characterize the hydrogen in the fluid cavity to establish a fluid-solid coupling model; the ideal gas state equation is: Where P is the gas pressure, V g is the volume of gas, T g is the gas temperature. M is the mass of the gas, M mol is the molar mass of the gas, is the universal gas constant; 3.2) The new finite element model is used to calculate the mechanical response of the container during the decompression process at different decompression rates; the decompression rate can be expressed as: Where k is the decompression rate, P ini and P final is the initial pressure in fluid chamber II and the pressure at the end of decompression, t total is the total time of decompression; The container decompression process can be expressed by the reduction of the gas mass in the fluid cavity as: In the formula, is the total mass change of hydrogen per unit time, and is the mass of hydrogen entering and exiting the fluid cavity per unit time; 3.3) Calculate the critical pressure difference for the collapse of the container liner; the pressure difference is defined as: ΔP=P int -P ext Where ΔP is the equivalent pressure difference, P int and P ext Respectively represent the pressure values ​​of fluid chamber I and fluid chamber II; As the decompression process proceeds, at a certain moment, the volume of the liner increases suddenly and then the pressure difference decreases. This pressure difference is the critical pressure difference ΔP cr ; Among them, P ext It can be expressed as: P ext =k·t P int Combining Henry's law with the decompression time, the hydrogen concentration in the fluid cavity caused by hydrogen diffusion at any time t can be expressed as: Where, t l is the lining thickness, D is the diffusion coefficient, S is the solubility of hydrogen, and C is the hydrogen concentration; Henry's law is: The P int Under the combined effect of hydrogen diffusion and decompression, it can be finally expressed as: Where k is the decompression rate and t is the decompression time.

6. The numerical simulation method for calculating the critical decompression rate of liner collapse of a type IV hydrogen storage container according to claim 1, characterized in that: In step 4), the critical decompression rate of the container liner collapse is calculated based on the calculated critical pressure difference; the critical pressure difference ΔP of any initial cavity defect container is obtained based on the proposed fluid-solid coupling method combined with the established finite element model cr ; Critical pressure difference ΔP cr The critical decompression rate k is calculated by combining the following formula: cr :

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