Post-combustion effect simulation method introducing chemical reaction analysis

Abstract

The invention discloses a post-combustion effect simulation method introducing chemical reaction analysis. The post-combustion effect simulation method comprises the steps that detonation energy, detonation products, mass fraction and related thermodynamic parameters are obtained according to the detonation process of explosives; obtaining an energy release parameter containing a chemical reaction source item; establishing a combustion analysis and calculation model introduced with a chemical reaction source item after the explosion of the closed space; solving the initial temperature and initial pressure of the equivalent gas mass of the explosive; inputting related parameters into a combustion analysis and calculation model after explosion in a closed space in which chemical reaction is introduced, and solving to obtain an energy release rate; and the specific heat energy of the post-combustion effect is obtained through calculation, the JWL state equation is modified, and the implosion response of the closed space considering the post-combustion effect is simulated. The method has the advantages that the calculation model including the chemical reaction source item is introduced, the explosive initiation process can be accurately and effectively simulated, the post-combustion reaction starting and ending time and the energy release rate are obtained, and the simulation result is accurate.

Description

Technical Field

[0001] The invention relates to the technical field of implosion post-combustion effect evaluation, and in particular to a post-combustion effect simulation method introducing chemical reaction analysis. Background Art

[0002] When explosives explode in a confined space, a high temperature and high pressure environment will be formed in the confined space. The combustible detonation products will continue to burn and release energy after mixing with oxygen, which is called the afterburning effect. When there is sufficient oxygen in the confined space, the detonation products of oxygen-enriched explosives will react completely. At this time, the afterburning effect is more significant, and there is a significant enhancement effect on the quasi-static pressure load in the confined space, thereby increasing the degree of structural deformation under the explosion.

[0003] Ships may face threats of extreme loads such as anti-ship missiles and explosions in enclosed spaces during their missions. Therefore, accurately assessing the damage and vulnerability level of ships after encountering extreme loads has become an inevitable requirement for taking effective measures to deal with the attack. However, the current economic cost of test evaluation and many other issues such as military capability guarantee make it difficult to carry out damage tests on real ships. Therefore, using simulation software to carry out finite element calculation simulation is currently a generally accepted solution, and considering the post-implosion combustion effect in finite element calculation has become a prerequisite for accurately evaluating the effect of explosives.

[0004] The method of considering the afterburning effect in the current mainstream finite element software (Autodyn, Abaqus and Ls-Dyna) is based on the JWL state equation, adding an additional energy at a specific energy release rate in the time period set by the user. Therefore, the start and end time of the afterburning effect (that is, the start and end time of the time period in the previous text) and the energy release rate become the key factors for accurately describing the afterburning effect. However, the existing method does not have relevant theories to guide users on how to correctly calculate and select the start and end time and energy release rate. It can only reversely infer the two simulation parameters of the afterburning effect start and end time and energy release rate under specific working conditions through the changes in cabin pressure in the test. Therefore, the main defect of the existing mainstream method is its dependence on specific test results. Specifically, this method cannot obtain the simulation parameters of the afterburning effect outside the test conditions, and the simulation results are not accurate enough. Therefore, it is impossible to reasonably characterize the afterburning effects of different explosive types and different enclosed space sizes contained in the research and design space, and it does not have the versatility required by professionals. Summary of the invention

[0005] The purpose of the present invention is to provide a post-combustion effect simulation method introducing chemical reaction analysis to improve the accuracy of simulation results in view of the deficiencies of the prior art.

[0006] The technical solution adopted by the present invention is: a method for simulating post-combustion effects by introducing chemical reaction analysis, comprising the following steps: According to the detonation process of explosives, the detonation energy and detonation products, as well as the mass fraction of each detonation product and related thermodynamic parameters are obtained; Based on the composition of detonation products, the chemical reactions that further occur during the afterburning of explosives are clarified, and the energy release parameters including the chemical reaction source terms are obtained; Calculate and obtain the source term including chemical reaction, and establish the closed space explosion combustion analysis and calculation model with the introduction of chemical reaction source term; The explosion process in a closed space is divided into three stages: detonation stage, adiabatic expansion stage and post-combustion reaction stage; Based on the characteristics of the detonation stage, the initial temperature and initial pressure of the equivalent gas mass of the explosive are solved; The relevant parameters obtained by calculation are input into the closed space explosion after-combustion analysis calculation model for chemical reaction, and the diffusion rate, energy release and pressure of each detonation product in the adiabatic expansion stage and the after-combustion reaction stage are solved as the explosion time changes, and then the start and end time of the after-combustion is determined, and the energy release is calculated to obtain the energy release rate; The specific heat energy of the afterburning effect is calculated by using the start and end time of the afterburning effect and the energy release rate. The JWL state equation is modified and solved by the Euler-Lagrangian coupling solver to simulate the implosion response of the enclosed space considering the afterburning effect.

[0007] According to the above scheme, the closed space explosion post-combustion analysis and calculation model with the introduction of chemical reaction source terms includes the modified reaction fluid control equation, the modified component mass fraction conservation equation, and the modified chemical kinetic energy and reaction component transport model. The three modified equations are all obtained by introducing the corresponding chemical reaction source terms into the original initial equations. (1) Introducing specified source terms including chemical reactions into the initial continuity equation S u , the modified continuity equation obtained is: ; in, t is time, unit is s; V is the volume, in m 3 ; a is the area vector, unit is m 2 ; r is the density, in kg / m 3 ; v is the speed, unit is m / s; S u is the specified source term related to mass, and its value is 0; (2) Introducing the specified source term including the chemical reaction into the initial momentum equation Su , the modified momentum equation is obtained as: ; in, p is the pressure, unit MPa; T is the viscous stress tensor, unit MPa; f b is the resultant force, in N; I is the impulse, in N·s; S u is the specified source term related to mass, and its value is 0; (3) Introducing energy source terms including chemical reactions into the initial energy equation S E , the corrected energy equation is obtained as: ; in, E is the total energy per unit mass, in J; σ is the fluid dynamic stress, in MPa; q is the heat flux, in J; S E is the energy source term including chemical reactions, is the total combustion heat of each detonation product; (4) Introducing the mass fraction source term including chemical reaction into the conservation equation of the initial component mass fraction S Yi , the modified component mass fraction conservation equation is obtained as: ; in, i is the component serial number; Y i For components i Quality score: r is the density, in kg / m 3 ; U is the total internal energy, unit J; J i is the molecular diffusion flux, unit: mol / (m²·s); m t is the turbulent dynamic viscosity, unit: Pa·s; s t is the turbulent Schmidt number, which is a dimensionless number; S Yi is the mass fraction source term from chemical reaction, and its specific value is the mass fraction of each mixed gas.

[0008] According to the above scheme, S E The solution is: S EIt is the sum of the combustion heat of all detonation products, but it changes with the degree of reaction; the combustion heat of a single detonation product is the product of the combustion heat of the detonation product per unit molar mass and the number of moles of the detonation product in the reaction process. Since a chemical reaction is an incomplete reaction process, the number of moles of the reaction detonation product can be obtained according to the reaction rate; Overall reaction rate constant k Usually the Arrhenius equation is used to determine the specific formula: ; in, R is the universal gas constant, with the unit of J / (kg·K); A is the pre-exponential factor; T is the temperature, in K; β is the temperature index; E a is the activation energy, in J / mol; The sum of the heat of combustion of the detonation products per unit molar mass considering the reaction rate is calculated according to the following formula : ; in, is the formation enthalpy of the corresponding component, that is, the combustion heat of the detonation product per unit molar mass, in KJ / mol; Calculate the sum of the unit molar mass heat of combustion of a certain detonation product taking into account the reaction rate , multiplied by the amount of substance in the detonation product, the combustion heat of the detonation product can be obtained; then the combustion heat of all detonation products is summed up to obtain S E , which is the sum of the heat of combustion of all detonation products.

[0009] According to the above scheme, the modified JWL state equation is: ; In the formula, λQ is the specific heat of the afterburning effect, in J / (kg·K), which is the product of the afterburning energy release rate and the duration; P is the pressure, in MPa; R 1. R 2. A , B , oh All are constants related to explosive materials; V is the volume of the enclosed space, in m 3 , E is the specific heat energy, and its unit is J / (kg·K).

[0010] According to the above scheme, the specific method of dividing the explosion process in the closed space into three stages is: The detonation stage is simplified according to the instantaneous detonation assumption, that is, it is assumed that the detonation process of the explosive is completed instantaneously, and the explosive is completely converted into detonation products at the moment of detonation, and the size of the air mass is the same as the initial size of the charge; during the adiabatic expansion stage, the air and detonation products are not fully mixed, that is, they are in a restricted mixing state, and the energy released by the detonation products is very limited. It is assumed that no chemical reaction occurs in this process until the restricted mixing state ends; in the post-combustion reaction stage, the reflected shock wave enhances the mixing degree of the detonation products and oxygen, and the restricted mixing state ends. In the calculation, the start time of the post-combustion reaction stage is taken as the time when the shock wave first contacts the near wall of the enclosed space.

[0011] According to the above scheme, the calculation method of the initial temperature of the explosive equivalent air mass is: Use thermodynamic polynomial data to define the properties of the detonation products involved in the detonation process, and convert the specific heat of each detonation product into C p Fitting was performed with a polynomial of 5 coefficients; ; in the formula All are fitting coefficients; C p is the specific heat capacity, in J / (kg·K); R is the universal gas constant, taken as 8.314 J / (mol·K); The specific heat of each detonation product is fitted C p Convert to specific heat at constant volume C V : ; The constant volume specific heat of the mixed gas is obtained by weighting the mass of each detonation product component C vm : ; in, C vm It represents the constant volume specific heat of the mixed gas, in J / (kg·K); i is the type of detonation product in the mixed gas; y i Detonation products in mixed gas i The quality score of C v ( i ) represents the detonation products in the mixed gas i The unit of specific heat at constant volume is J / (kg·K); N Indicates the total number of components in the mixed gas; Obtaining the temperature of the mixed gas in the air mass through thermodynamic relations T m : ; In the formula, W is the charge mass, in g; Q is the detonation energy of the fuel-rich explosive, in MJ / kg; n is the amount of substance in the mixed gas, mol; T 0 is room temperature, unit is K; T m is the initial temperature of the detonation products to be solved, in K; By integrating the change curve of the constant volume specific heat of the mixture, the initial temperature of the detonation product is finally obtained. T m .

[0012] According to the above scheme, the initial pressure of the explosive equivalent air mass is p 0 is calculated by the following formula: ; In the formula, n is the amount of substance in the air mass, in mol; R is the universal gas constant; V TNT is the volume of the air mass, in m 3 .

[0013] The beneficial effects of the present invention are: 1. The present invention can accurately and effectively simulate the detonation process of explosives and obtain the start and end time and energy release rate of the afterburning reaction by introducing a calculation model including a chemical reaction source term into the afterburning effect, thereby solving the defect that the mainstream solution method relies on test results and cannot reasonably obtain the action time and energy release rate of the afterburning effect; compared with the prior art, the simulation result of the afterburning effect obtained by the present invention is more accurate, can simulate the afterburning effect of different explosive types and different enclosed space sizes, has strong versatility, and can provide support for accurately evaluating the damage effect of explosives.

[0014] 2. The present invention divides the process of implosion in a closed space based on the physical characteristics of different stages. The model provides a theoretical basis and support for the simulation of the after-combustion effect, and improves the defect that the existing mainstream solution method completely relies on test data and cannot predict the after-combustion effect under non-test conditions.

[0015] 3. The simulation of the explosive detonation process of the present invention is completely determined by the thermodynamic properties of the explosive detonation products and is not completely dependent on the specific explosive characteristics. The solution and analysis of the afterburning effect is applicable to all explosion problems with known detonation products and detonation energy. It has extremely high versatility and a very wide range of application and has great engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the process of the present invention.

[0017] Figure 2 Schematic diagram of closed space grid division in this embodiment.

[0018] Figure 3 Schematic diagram of the energy release process of detonation products in a closed space in this embodiment.

[0019] Figure 4 Schematic diagram of the amount change process of each detonation product substance in the closed space in this embodiment.

[0020] Figure 5 Schematic diagram for comparing the experimental and numerically calculated pressure history in this embodiment. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0022] like Figure 1 A post-combustion effect simulation method for introducing chemical reaction analysis is shown, comprising the following steps: S1. According to the detonation process of explosives, the detonation energy and detonation products, as well as the mass fraction of each detonation product and related thermodynamic parameters, including pre-exponential factor and activation energy, are obtained.

[0023] In the present invention, both the pre-exponential factor and the activation energy Ea can be obtained by using existing methods.

[0024] S2. Based on the composition of the detonation products, the chemical reactions that further occur during the post-combustion process of the explosive are clarified to obtain the energy release parameters including the chemical reaction source term. The energy release parameters include the reaction temperature, the amount of substance of the detonation products released by the chemical reaction combustion per unit of TNT, and the combustion heat of the detonation products per unit molar mass.

[0025] The reaction temperature, the amount of substance of the detonation product released per unit TNT chemical reaction combustion, and the combustion heat of the detonation product per unit molar mass can all be obtained by existing techniques.

[0026] S3. The source term including the chemical reaction is calculated based on the relevant energy release parameters, and a closed space post-explosion combustion analysis and calculation model is established by introducing the chemical reaction source term.

[0027] In the present invention, the closed space refers to the physical space where the explosion occurs; the closed space explosion post-combustion analysis calculation model introducing the chemical reaction source term includes a modified reaction fluid control equation, a modified component mass fraction conservation equation, and a modified chemical kinetic energy and reaction component transport model. The three modified equations are all obtained by introducing the corresponding chemical reaction source term into the original initial equation.

[0028] (1) Introducing specified source terms including chemical reactions into the initial continuity equation S u , the modified continuity equation obtained is: (1); In formula (1), t is time, unit is s; V is the volume, unit is m 3 ; a is the area vector, unit is m 2 ; r is the density, in kg / m 3 ; v is the speed, unit is m / s; S u is the specified source term related to mass, and its value is 0.

[0029] (2) Introducing the specified source term including the chemical reaction into the initial momentum equation S u , the modified momentum equation is obtained as: (2); In formula (2), p is the pressure, unit MPa; T is the viscous stress tensor, unit MPa; f b is the resultant force, in N; I is the impulse, in N·s; S u is the specified source term related to mass, and its value is 0; t is time, unit is s; V is the volume, in m 3 ; a is the area vector, unit is m 2 ; r is the density, in kg / m 3 ; v is the speed, unit is m / s; For formula (1) and formula (2), S u In order to include the mass source term of chemical reaction, the explosion process is in a closed space and does not involve the inflow and outflow of substances. Su The value is 0.

[0030] (3) Introducing energy source terms including chemical reactions into the initial energy equation S E , the corrected energy equation is obtained as: (3); In formula (3), E is the total energy per unit mass, in J; σ is the fluid dynamic stress, in MPa; q is the heat flux, in J; S E is the energy source term including chemical reactions, and is the total combustion heat of each detonation product in S2.

[0031] (4) Introducing the mass fraction source term including chemical reaction into the conservation equation of the initial component mass fraction S Yi , the modified component mass fraction conservation equation is obtained as: (4); In formula (4), i is the component serial number; Y i For components i The quality score of r is the density, in kg / m 3 ; U is the total internal energy, unit J; J i is the molecular diffusion flux, in mol / (m²·s); m t is the turbulent dynamic viscosity, in Pa·s; s t is the turbulent Schmidt number, which is a dimensionless number; S Yi is the mass fraction source term from the chemical reaction, and its specific value is the mass fraction of each mixed gas (i.e., detonation product) in step S1.

[0032] For formula (3) S E Solution description: S E It is the sum of the heat of combustion of all detonation products, but it changes with the degree of reaction. The heat of combustion of a single detonation product is the product of the heat of combustion of the detonation product per unit molar mass and the number of moles of the detonation product during the reaction. Since a chemical reaction is an incomplete reaction process, the number of moles of the detonation product can be obtained based on the reaction rate.

[0033] Chemical kinetics involves the reaction mechanisms and reaction rates of chemical components at the molecular level. When modeling the transport of reacting components, providing source terms for the transport equations requires calculating the reaction rates of all reactions in the chemical mechanism. Any elementary chemical reaction can be represented by the following general equation: (5); In formula (5), u represents the stoichiometric coefficient, A , B Represent the reactants, , Respectively, reactants A , B The stoichiometric coefficient of C , D Respectively represent the products, , are the stoichiometric coefficients of the products, respectively; k f is the forward reaction rate constant, k b is the reverse reaction rate constant.

[0034] According to the stoichiometric coefficient u ij Give a reaction j Components produced or consumed i Total number of moles: (6); In formula (6), j Indicates reaction, i Indicates the component number; Indicates the components in the product i The stoichiometric coefficient of Represents the components in the reactants i The stoichiometric coefficient of Reaction j Middle component i The net chemical calculation coefficient of the reaction j Components produced or consumed i The total number of moles; k is the overall reaction rate constant.

[0035] The reaction can proceed in the forward or reverse direction. k f is the forward reaction rate constant, k b is the reverse reaction rate constant. k To consider at the same time k f and k b The overall reaction rate constant (7); Overall reaction rate constant k It is usually determined using the Arrhenius equation, where the rate is nonlinearly related to temperature, as given by: (8); In formula (8), R is the universal gas constant, with the unit of J / (kg·K); A is the pre-exponential factor; T is the temperature, in K; β is the temperature index; E a is the activation energy, and its unit is J / mol.

[0036] The sum of the heat of combustion of the detonation products per unit molar mass considering the reaction rate is calculated according to the following formula (also known as chemical heat release rate): (9); In formula (9), is the formation enthalpy of the corresponding component (that is, the combustion heat of the detonation product per unit mole, which can be directly found), and the unit is KJ / mol.

[0037] According to the above formula, the sum of the unit molar mass combustion heat of a certain detonation product considering the reaction rate is calculated. , multiplied by the amount of the detonation product in step 2, the combustion heat of the detonation product can be obtained; and then the combustion heat of all detonation products is summed to obtain S E , which is the sum of the heat of combustion of all detonation products.

[0038] S4. Divide the explosion process in a closed space into three stages: detonation stage, adiabatic expansion stage and post-combustion reaction stage.

[0039] The division method of the explosion process in a closed space is mainly based on the physical characteristics of each stage. The detonation stage can be simplified according to the instantaneous detonation assumption, that is, it is assumed that the detonation process of the explosive is completed instantaneously, and the TNT explosive is completely converted into detonation products at the moment of detonation. The explosive can be equivalent to a high-temperature and high-pressure air mass (the temperature of the air mass exceeds the reaction temperature of the detonation products), and the size of the air mass is the same as the initial size of the charge. During the adiabatic expansion stage, the air and the detonation products are not fully mixed, that is, they are in a restricted mixing state, and the energy released by the detonation products is very limited. It is assumed that no chemical reaction occurs in this process until the restricted mixing state ends. In the post-combustion reaction stage, the reflected shock wave enhances the mixing degree of the detonation products and oxygen, and the restricted mixing state ends. In the calculation, the start time of the post-combustion reaction stage is taken as the time when the shock wave first contacts the near wall of the closed space.

[0040] S5. Based on the characteristics of the detonation stage, solve the initial temperature and initial pressure of the equivalent gas mass of the explosive.

[0041] Use thermodynamic polynomial data to define the properties of the detonation products involved in the detonation process, and convert the specific heat of each detonation product into C p Fitting was performed with a polynomial of 5 coefficients; R is the universal gas constant, which is taken as 8.314 J / (mol·K).

[0042] (10); In formula (10), All are fitting coefficients; C p is the specific heat capacity, and its unit is J / (kg·K).

[0043] Furthermore, since the explosion in the closed space of the test is a constant volume explosion, the specific heat of each detonation product is fitted by the following formula: C p Convert to specific heat at constant volume C V (Unit: J / (kg·K)): (11); In formula (11), R is the universal gas constant.

[0044] Furthermore, the constant volume specific heat of the mixed gas is obtained by weighting the mass of each detonation product component C vm , as shown below: (12); In formula (12), C vm It represents the constant volume specific heat of the mixed gas, in J / (kg·K); i is the type of detonation product in the mixed gas; y i Detonation products in mixed gas i The quality score of C v ( i ) represents the detonation products in the mixed gas i The unit of specific heat at constant volume is J / (kg·K). N Indicates the total number of components in the mixed gas.

[0045] Furthermore, the temperature of the mixed gas in the air mass is obtained through thermodynamic relations T m , the relevant expressions are as follows: (13); In formula (13), W is the charge mass, in g; Q is the detonation energy of the fuel-rich explosive, in MJ / kg; n is the amount of substance in the mixed gas, mol; T 0 is room temperature (in K), T m In order to solve the initial temperature of the detonation product (in K), the initial temperature of the detonation product is obtained by integrating the change curve of the constant volume specific heat of the mixture. T m .

[0046] The initial pressure p0 of the air mass is calculated by the following formula: (14); In formula (14), n is the amount of substance in the air mass, in mol; R is the universal gas constant; V TNT is the volume of the air mass, in m 3 .

[0047] In the present invention, for explosives of a specific composition, the ratio of detonation products can be considered to be relatively stable, which means that the initial temperature and pressure parameters of the high-pressure air mass under the explosion of any amount of the specific explosive are also relatively fixed.

[0048] S6. The relevant parameters obtained by calculation are input into the closed space explosion post-combustion analysis calculation model for chemical reactions. The Euler solver is used to solve the diffusion rate, energy release and pressure changes of each detonation product in the adiabatic expansion stage and the post-combustion reaction stage as the explosion time changes. Then the start and end time of the post-combustion is determined, and the energy release is calculated to obtain the energy release rate.

[0049] In the present invention, the input related parameters specifically include the closed space structure size, the initial temperature and initial pressure of the environment, the initial temperature and initial pressure of the high-pressure air mass, the type of substance produced by the detonation, and the amount of the substance, which are obtained through the above steps.

[0050] The modified continuity equation, momentum equation and energy equation in the calculation model are placed in the Euler solver. After inputting the relevant parameters, the changes in diffusion rate, energy release and pressure with explosion time can be solved. The start and end time of afterburning are determined according to the diffusion rate and pressure change of the detonation products, and the energy release amount is obtained through the energy change of the detonation products; energy release amount / time = energy release rate.

[0051] In the present invention, the Euler solver is used to calculate the modified continuity equation, momentum equation and energy equation to simulate the diffusion process of high-pressure air masses in a closed space, which is a prior art and will not be described in detail here.

[0052] S7. The specific heat energy of the afterburning effect is calculated using the start and end time of the afterburning effect and the energy release rate. The JWL state equation is modified and solved by the Euler-Lagrangian coupling solver to simulate the implosion response of the enclosed space considering the afterburning effect.

[0053] The JWL state equation is modified using the parameters such as the start and end time of the afterburning effect and the energy release rate. Combined with the geometric characteristics and material properties of the explosive, the Euler-Lagrangian coupling solver is used to accurately simulate the implosion response process in a closed space considering the afterburning effect.

[0054] The difference between the modified JWL state equation and the original JWL state equation is that the former introduces the specific heat energy λQ of the afterburning effect. The modified JWL state equation is: (15); In formula (15), λQ is the specific heat of the afterburning effect, in J / (kg·K), which is the afterburning energy release rate Q With duration l The product of . P is the pressure, in MPa; R 1 、R 2 、A、B、ω is a constant related to explosive materials (which can be obtained by fitting experimental data); V is the volume of the enclosed space, in m 3 ; E is the specific heat energy, and its unit is J / (kg·K).

[0055] In the present invention, the use of the Euler-Lagrange coupling solver to calculate the JWL state equation and simulate the implosion response process in a closed space is a prior art and will not be described in detail here.

[0056] Example Taking a cylindrical TNT explosive with a height of 36 mm, a diameter of 25.2 mm and a mass of 28 g as an example, the detonation process of the explosive is explained.

[0057] S1. According to the detonation process of explosives, the detonation energy and detonation products, as well as the mass fraction of each detonation product and related thermodynamic parameters, including pre-exponential factor and activation energy, are obtained.

[0058] The chemical reaction of TNT detonation is shown in formula 1. The types of detonation products produced in the detonation process and their corresponding mass fractions are shown in Table 1. After calculation, the total mass of the detonation is 1.2895 mol. T When 0=298 K (room temperature), the unit mass detonation energy is 4.495 MJ / kg. The pre-exponential factor and activation energy Ea of the detonation product are shown in Table 2. The pre-exponential factor and activation energy Ea can be obtained by existing methods.

[0059] C7H5N3O6→ 2.2CO+1.6H2O+1.5N2+1.1CO2+0.36H2+0.27CH4+3.43C(1).

[0060] Table 1 Mass fraction of each detonation product in the detonation product mixture

[0061] Table 2 Thermodynamic parameters of detonation products

[0062] S2. Based on the composition of detonation products, the chemical reactions that further occur during the post-combustion process of the explosive are clarified to obtain the energy release parameters including the chemical reaction source term, including the reaction temperature, the amount of substance of the detonation products released per unit TNT chemical reaction combustion, and the combustion heat of the detonation products per unit molar mass.

[0063] In this embodiment, it can be seen from formula (1) in S1 that the components of the detonation products mainly include C, CO, H2O, N2, CO2, H2 and CH4. Among them, CO, H2, CH4 and C are all combustible products, which will further release energy after mixing with sufficient oxygen in a high temperature environment. The chemical reactions that further occur in the post-combustion process of the specific detonation products and the combustion energy release parameters are shown in Table 3. The reaction temperature, the amount of the detonation product released by the chemical reaction combustion of a unit of TNT and the combustion heat of the detonation product per unit molar mass can all be obtained by existing technologies.

[0064] Table 3 Energy parameters released by chemical reaction and combustion of detonation products

[0065] S3. According to the energy release parameters including the chemical reaction source term obtained in S2, a closed space explosion post-combustion analysis and calculation model introducing the chemical reaction source term is established; S u In order to include the mass source term of chemical reaction, the explosion process is in a closed space and does not involve the inflow and outflow of substances. S u The value is 0; S Eis the energy source term including chemical reactions, is the total combustion heat of each detonation product in S2; S Yi is the mass fraction source term from the chemical reaction, and its specific value is the mass fraction of each mixed gas in Table 1 in step S1.

[0066] S4. Divide the explosion process in a closed space into three stages: detonation stage, adiabatic expansion stage and post-combustion reaction stage.

[0067] S5. Based on the characteristics of the detonation stage, solve the initial temperature and initial pressure of the equivalent gas mass of the explosive.

[0068] W is the charge mass, which is 28 g; Q is the detonation energy of the fuel-rich explosive, which is 4.495 MJ / kg; T m is the initial temperature of the detonation product to be solved (in K), calculated to be 3366 K; the initial pressure of the high-pressure air mass p 0 is 2016Mpa.

[0069] S6. The relevant parameters obtained by calculation are input into the closed space explosion post-combustion analysis calculation model for chemical reactions. The Euler solver is used to solve the diffusion rate, energy release and pressure changes of each detonation product in the adiabatic expansion stage and the post-combustion reaction stage as the explosion time changes. The start and end time of the post-combustion is determined, the energy release amount is calculated, and the energy release rate is obtained.

[0070] This example is a TNT explosion environment in a closed space. The structural characteristics of the closed space include the length, width, height, wall thickness, material properties, etc. The closed space structure size is 900mm×400mm×400mm, the initial temperature is 298K (room temperature), and the initial pressure is 0.101MPa (atmospheric pressure). The TNT explosion environment in the test closed space is modeled, and the initial fluid domain mesh is divided as follows: Figure 2 As shown; the energy release process of the detonation products obtained by the Euler solver Star-CCM is shown in Figure 3 As shown in the figure, the amount of each detonation product changes as follows: Figure 4 According to step S6, the starting time of the afterburning effect is 0.1 ms, the duration is 2 ms, the stabilization time is 2.1 ms, the energy release is 6.5 MJ / kg, and the energy release rate is calculated to be 3.25 MJ / (kg•ms).

[0071] S7. The specific heat energy of the afterburning effect is calculated using the start and end time of the afterburning effect and the energy release rate, and the JWL state equation is modified. The Euler-Lagrangian coupling solver is used to simulate the implosion response of the enclosed space considering the afterburning effect.

[0072] Based on the above parameters, the Euler-Lagrangian coupling solver Autodyn is used to solve the 28 g charge considering the combustion of detonation products. The pressure change history at the measuring point obtained by numerical calculation is compared with the experimental test data. Figure 5 As shown in the figure, it can be found that the pressure change history considering the afterburning process of detonation products is in good agreement with the test results, especially in the capture of the initial pressure peak and oscillation changes. This shows that the established afterburning effect simulation method introducing chemical reaction analysis can better reflect the test pressure changes and can be used for the analysis of explosion load characteristics in closed spaces.

[0073] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for simulating post-combustion effects by introducing chemical reaction analysis, characterized in that: The following steps are involved: According to the detonation process of explosives, the detonation energy and detonation products, as well as the mass fraction of each detonation product and related thermodynamic parameters are obtained; Based on the composition of detonation products, the chemical reactions that further occur during the afterburning of explosives are clarified, and the energy release parameters including the chemical reaction source terms are obtained; Calculate and obtain the source term including chemical reaction, and establish the closed space explosion combustion analysis and calculation model with the introduction of chemical reaction source term; The explosion process in a closed space is divided into three stages: detonation stage, adiabatic expansion stage and post-combustion reaction stage; Based on the characteristics of the detonation stage, the initial temperature and initial pressure of the equivalent gas mass of the explosive are solved; The relevant parameters obtained by calculation are input into the closed space explosion after-combustion analysis calculation model for chemical reaction, and the diffusion rate, energy release and pressure of each detonation product in the adiabatic expansion stage and the after-combustion reaction stage are solved as the explosion time changes, and then the start and end time of the after-combustion is determined, and the energy release is calculated to obtain the energy release rate; The specific heat energy of the afterburning effect is calculated, the JWL state equation is modified and solved, and the implosion response of the enclosed space considering the afterburning effect is simulated.

2. The post-combustion effect simulation method for introducing chemical reaction analysis as claimed in claim 1, characterized in that: The closed space explosion post-combustion analysis and calculation model with the introduction of chemical reaction source terms includes the modified reaction fluid control equation, the modified component mass fraction conservation equation, and the modified chemical kinetic energy and reaction component transport model. The three modified equations are all obtained by introducing the corresponding chemical reaction source terms into the original initial equations. (1) Introducing specified source terms including chemical reactions into the initial continuity equation S u , the modified continuity equation obtained is: ； in, t is time, unit is s; V is the volume, in m 3 ; a is the area vector, unit is m 2 ; ρ is the density, in kg / m 3 ; v is the speed, unit is m / s; S u is the specified source term related to mass, and its value is 0; (2) Introduce the specified source term S including chemical reaction into the initial momentum equation u , the modified momentum equation is obtained as: ； in, p is the pressure, unit MPa; T is the viscous stress tensor, unit MPa; f b is the resultant force, in N; I is the impulse, in N·s; S u is the specified source term related to mass, and its value is 0; (3) Introducing energy source terms including chemical reactions into the initial energy equation S E , the corrected energy equation is obtained as: ； in, E is the total energy per unit mass, in J; σ is the fluid dynamic stress, in MPa; q is the heat flux, in J; S E is the energy source term including chemical reactions, is the total combustion heat of each detonation product; (4) Introducing the mass fraction source term including chemical reaction into the conservation equation of the initial component mass fraction S Yi , the modified component mass fraction conservation equation is obtained as: ； in, i is the component serial number; Y i For components i Quality score: ρ is the density, in kg / m 3 ; U is the total internal energy, unit J; J i is the molecular diffusion flux, in mol / (m²·s); μ t is the turbulent dynamic viscosity, in Pa·s; σ t is the turbulent Schmidt number, which is a dimensionless number; S Yi is the mass fraction source term from chemical reactions, and its specific value is the mass fraction of each detonation product.

3. The post-combustion effect simulation method for introducing chemical reaction analysis as claimed in claim 2, characterized in that: S E The solution is: S E It is the sum of the combustion heat of all detonation products, but it changes with the degree of reaction; the combustion heat of a single detonation product is the product of the combustion heat of the detonation product per unit molar mass and the number of moles of the detonation product in the reaction process. Since a chemical reaction is an incomplete reaction process, the number of moles of the reaction detonation product can be obtained according to the reaction rate; Overall reaction rate constant k Usually the Arrhenius equation is used to determine the specific formula: ； in, R is the universal gas constant, with the unit of J / (kg·K); A is the pre-exponential factor; T is the temperature, in K; β is the temperature index; E a is the activation energy, in J / mol; The sum of the heat of combustion of the detonation products per unit molar mass considering the reaction rate is calculated according to the following formula : ； in, is the formation enthalpy of the corresponding component, that is, the combustion heat of the detonation product per unit molar mass, in KJ / mol; Calculate the sum of the unit molar mass heat of combustion of the detonation products taking into account the reaction rate , multiplied by the amount of substance in the detonation product, the combustion heat of the detonation product can be obtained; then the combustion heat of all detonation products is summed up to obtain S E , which is the sum of the heat of combustion of all detonation products.

4. The post-combustion effect simulation method of introducing chemical reaction analysis as claimed in claim 2 or 3, characterized in that: The modified JWL state equation is: ； In the formula, λQ is the specific heat of the afterburning effect, in J / (kg·K), which is the product of the afterburning energy release rate and the duration; P is the pressure, in MPa; R 1. R 2. A , B , ω All are constants related to explosive materials; V is the volume of the enclosed space, in m 3 , E is the specific heat energy, and its unit is J / (kg·K).

5. The post-combustion effect simulation method of introducing chemical reaction analysis as claimed in claim 4, characterized in that: The specific method of dividing the explosion process in a closed space into three stages is: The detonation stage is simplified according to the instantaneous detonation assumption, that is, it is assumed that the detonation process of the explosive is completed instantaneously, and the explosive is completely converted into detonation products at the moment of detonation, and the size of the equivalent air mass of the explosive is the same as the initial size of the charge; during the adiabatic expansion stage, the air and detonation products are not fully mixed, that is, they are in a restricted mixing state, and the energy released by the detonation products is very limited. It is assumed that no chemical reaction occurs in this process until the restricted mixing state ends; in the post-combustion reaction stage, the reflected shock wave enhances the mixing degree of the detonation products and oxygen, and the restricted mixing state ends. In the calculation, the time when the shock wave first contacts the near wall of the enclosed space is taken as the starting time of the post-combustion reaction stage.

6. The post-combustion effect simulation method of introducing chemical reaction analysis as claimed in claim 4, characterized in that: The calculation method of the initial temperature of the explosive equivalent air mass is: Use thermodynamic polynomial data to define the properties of the detonation products involved in the detonation process, and convert the specific heat of each detonation product into C p Fitting was performed with a polynomial of 5 coefficients; ； in the formula All are fitting coefficients; C p is the specific heat capacity, in J / (kg·K); R is the universal gas constant, taken as 8.314 J / (mol·K); The specific heat of each detonation product is fitted C p Convert to specific heat at constant volume C V : ； The constant volume specific heat of the mixed gas is obtained by weighting the mass of each detonation product component C vm : ； in, C vm It represents the constant volume specific heat of the mixed gas, in J / (kg·K); i is the type of detonation product in the mixed gas; y i Detonation products in mixed gas i The quality score of C v ( i ) represents the detonation products in the mixed gas i The unit of specific heat at constant volume is J / (kg·K); N Indicates the total number of components in the mixed gas; Obtaining the temperature of the mixed gas in the air mass through thermodynamic relations T m : ； In the formula, W is the charge mass, in g; Q is the detonation energy of the fuel-rich explosive, in MJ / kg; n is the amount of substance in the mixed gas, mol; T 0 is room temperature, unit is K; T m is the initial temperature of the detonation products to be solved, in K; By integrating the change curve of the constant volume specific heat of the mixture, the initial temperature of the detonation product is finally obtained. T m .

7. The post-combustion effect simulation method of introducing chemical reaction analysis as claimed in claim 4, characterized in that: Initial pressure of explosive equivalent gas mass p 0 is calculated by the following formula: ； In the formula, n is the amount of substance in the air mass, in mol; R is the universal gas constant; V TNT is the volume of the air mass, in m 3 .

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