Rocket interstage pressure building separation method and simulation method

Abstract

The invention discloses a rocket interstage pressure building separation method and a simulation method.The pressure building separation method comprises the steps that a rocket interstage pressure building separation structure without an initiating explosive device is designed, specifically, a weakening groove is designed in an interstage section structure, and initial crack starts from a longitudinal groove; after the longitudinal groove cracks, the annular grooves at the two ends are driven to crack from the crack initiation groove, and finally the separation process is achieved; the simulation method comprises the following steps: calculating a pneumatic pressure-time curve of interstage pressure building after ignition of a secondary engine by using an engineering algorithm, simulating a damage separation process of an interstage structure, and preliminarily verifying the feasibility of damage separation of the interstage section structure under the pressure building condition; carrying out interstage section fluid-solid coupling simulation based on LS-DYNA, and further verifying that the interstage section can still be completely destroyed and separated after weakening groove pressure relief after longitudinal groove crack initiation; according to the inter-stage separation structure design without the initiating explosive device, the design load requirement during first-stage flight can be met, it can be guaranteed that the inter-stage sections are completely damaged and separated, and the problem that traditional design is high in cost is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-stage rocket design, and in particular relates to a method for separating rocket stages by pressure holding and a simulation method. Background Art

[0002] In the design and development process of multi-stage rockets, separation technology is one of the core technologies of each model. There are two main ways to separate the stages of a tandem rocket: hot separation and cold separation. Domestic and foreign research on rocket stage separation has shown that the use of hot separation can significantly improve the stability and maneuverability of the upper stage. The hot separation process includes three stages: ignition and pressure building of the upper stage engine, shutdown of the lower stage engine, and shearing or explosion of the coupling. Figure 1 shown.

[0003] There are two main types of separation devices at the interstage separation site: point type and line type. Linear separation has the advantages of continuous stiffness, high load-bearing capacity, and high separation reliability [3,4]. Foreign rockets generally use linear separation devices. Domestic large rockets also often use linear separation due to the large forces on the interstage. Regardless of the separation device used, traditional rocket separation cannot be separated from pyrotechnics. The pyrotechnic separation device cannot be functionally checked before ignition, has a short duration, and has impact load and safety issues. In addition, there are few engineering methods or national standards that can be used or referenced in the application of pyrotechnics. The existing specifications for conventional power sources cannot be applied to pyrotechnics. There is a lack of test methods and theoretical systems to characterize the functional margin of pyrotechnic devices. This means that the estimation of device reliability can only rely on the number of successful tests, and examples of pyrotechnic application failures have occurred repeatedly [5]. With the rapid development of aerospace technology, higher requirements have been placed on the design of separation devices. The development of light-weight, highly reliable, low-impact separation, and pollution-free separation separation devices is a general trend and a necessity of development.

[0004] The traditional interstage structure design method is to determine the separation structure and size based on engineering design experience and material static strength theory during the development cycle of the spacecraft, and then verify and correct the plan through multiple ground experiments. This design method cannot quantify the relationship between design parameters and structural dynamic strength performance, so it cannot explain the material dynamic strength characteristics of the structure under the impact of explosions. It requires repeated testing, modification and redesign, resulting in long development cycles and high costs.

[0005] Recently, through ground separation tests, it was found that after the upper stage engine was ignited, the enclosed space formed by the interstage compartment structure and the upper and lower tank bottoms was rapidly pressurized under the action of the engine jet. When the connection unlocking device had not yet been detonated and unlocked, the interstage structure was damaged at the weakening groove of the linear separation surface, resulting in separation not being carried out according to the established sequence. This phenomenon gave us inspiration, whether it is possible to use the gas pressure generated by the upper stage engine to cause the failure and damage of the preset weakening groove material without pyrotechnics, so as to achieve interstage separation. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention proposes a rocket interstage pressure holding separation method and a simulation method. The first purpose is to solve the problems that the pyrotechnic separation device cannot be functionally checked before ignition, the duration is short, and there are impact loads and safety risks; the second purpose is to solve the traditional interstage structure design method, which determines the separation structure and size based on engineering design experience and material static strength theory, and then verifies and corrects the plan through multiple ground experiments. This method cannot quantify the relationship between design parameters and structural dynamic strength performance, and cannot explain the material dynamic strength characteristics of the structure under the impact of explosion. It requires repeated experiments, modifications and redesign, resulting in problems such as long development cycle and high cost.

[0007] The present invention proposes the following technical solutions to solve the technical problems:

[0008] A method for separating rocket stages by holding pressure, characterized in that the method comprises the following steps:

[0009] Step 1, designing a rocket interstage pressure holding and separation structure, which does not use pyrotechnics, and designs a weakening groove in the interstage structure. During the thermal separation process, after the upper stage engine is ignited, its jet is pressure held in the interstage. When the pressure reaches a predetermined design range, the rocket interstage structure is disconnected from the designed weakening groove, thereby achieving interstage separation; the weakening groove of the pressure holding and separation structure refers to the thickness of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove; the initial cracking starts from the longitudinal groove;

[0010] Step 2: After the longitudinal groove is cracked, the annular grooves at both ends are driven to crack from the cracking groove, and finally the separation process is completed.

[0011] Furthermore, the calculation process of the pressure holding separation structure in step 1 is as follows:

[0012] 1) The load specialist gives the design load of the interstage during the first stage flight;

[0013] 2) Preliminarily determine the thickness h of the ring 1 weakening groove and the ring 2 weakening groove by the design load of the separation section during the first stage flight;

[0014] 3) Calculate the thickness h' of the longitudinal groove weakening groove according to the pressure range at the time of destruction required for pressure holding separation.

[0015] Furthermore, the specific steps of process 1) and process 2) of step 1 are as follows:

[0016] A. Give the design loads of the rocket at the first stage of separation: axial force T, shear force Q, bending moment M, and outer diameter D of the rocket;

[0017] B. Calculate the maximum equivalent tension, which is generated by the axial force T and the bending moment M. The maximum equivalent tension is:

[0018]

[0019] C. Calculate the axial stress generated by the tension. The axial stress generated by the tension is:

[0020]

[0021] Where h is the thickness of the ring groove, σ b is the material strength;

[0022] D. Preliminarily determine the thickness h of the weakening groove of ring 1 and the weakening groove of ring 2 by using formula (1) and formula (2).

[0023] Furthermore, the specific steps are as follows:

[0024] ① Obtain the pressure range P (1.5MPa~1.6MPa) during pressure holding and separation;

[0025] ② Calculate the longitudinal groove thickness h' according to the pressure range P (1.5MPa~1.6MPa) required for pressure separation:

[0026]

[0027] ③ After preliminarily obtaining the weakening groove thickness, a three-dimensional model is established and finite element calculations are carried out to ensure that the interstage section will not be damaged under the first-stage flight load.

[0028] Furthermore, the pressure-holding separation structure initially cracks from the longitudinal groove, and its specific structure is: when the separation structure is subject to the constraints that the total mass does not exceed 80kg and the shell thickness of the interstage section cannot exceed 5mm, and when the thicknesses of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove are 4mm, 2.5mm, and 4mm respectively, the longitudinal groove weakening groove cracks first, and after cracking, the ring 1 weakening groove and the ring 2 weakening groove at both ends are driven to crack from the crack initiation groove, thereby finally realizing the separation process.

[0029] A method for simulating pressure holding and separation between rocket stages, characterized in that it comprises the following steps:

[0030] Step 1: Use engineering algorithms or FLUENT to calculate the aerodynamic pressure-time curve of the interstage pressure after the second-stage engine is ignited. This curve does not consider the separation pressure relief.

[0031] Step 2: A three-dimensional finite element model of the interstage structure is established based on ABAQUS. The aerodynamic-pressure curve calculated in step 1 is applied to the inner wall surface as a boundary condition to perform transient calculations to simulate the destruction and separation process of the interstage structure, and preliminarily verify the feasibility of the destruction and separation of the interstage structure under pressure holding conditions.

[0032] Step 3: Based on LS-DYNA, fluid-solid coupling simulation of the interstage section was carried out to further verify that after the longitudinal groove cracks, the weakening groove is destroyed and the pressure is released at the same time, and the interstage section can still achieve complete destruction and separation;

[0033] Step 4: Compare the calculation results of ABAQUS and LS-DYNA. The comparison proves that the longitudinal groove crack initiation pressures calculated by different modeling methods in different software should be consistent. If the crack initiation pressures are consistent, it can be inferred that the fluid-solid coupling simulation results after pressure relief calculated by LS-DYNA are credible.

[0034] Furthermore, the calculation results of ABAQUS and LS-DYNA are compared in step 4, and the comparison includes:

[0035] Longitudinal groove cracking time / s, internal pressure corresponding to longitudinal groove cracking / MPa, pressure corresponding to complete fracture of annular groove 1 / MPa.

[0036] Furthermore, the comparison of calculation results between ABAQUS and LS-DYNA in step 4 includes the following comparison of calculation results:

[0037] ① The peak pressure of LS-DYNA at the time of crack initiation is basically consistent with the corresponding value of ABAQUS;

[0038] ② In the case of complete destruction, the pressure calculated by LS-DYNA is smaller than that by ABAQUS because the effect of pressure relief is taken into account.

[0039] Advantages and effects of the present invention

[0040] 1. The present invention adopts a method for separating rocket stages by pressure holding without using pyrotechnics. The method can not only meet the design load requirement during the first stage flight, but also ensure the complete destruction and separation of the interstage, thereby solving the problems that the traditional interstage structure design cannot quantify the relationship between the design parameters and the dynamic strength performance of the structure, cannot explain the material dynamic strength characteristics of the structure under the impact of explosion, requires repeated experiments, modifications and redesigns, resulting in long development cycles and high costs.

[0041] 2. The present invention adopts a method of combined verification of two simulation softwares to verify that the pressure holding separation method can achieve complete destruction and separation of the interstage. The feasibility of the destruction and separation of the interstage structure under pressure holding is preliminarily verified by the simulation software based on ABAQUS, and further verified by the simulation software based on LS-DYNA that after the longitudinal groove starts to crack, the weakening groove is destroyed while releasing pressure, and the interstage can still achieve complete destruction and separation. Through combined verification, it is proved that the rocket interstage pressure holding separation structure of the present invention is feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of interstage heat separation;

[0043] Figure 2 Interstage and internal structure;

[0044] Figure 3 The pressure-time curve of the inner surface of the interstage;

[0045] Figure 4 Damage constitutive curve of ductile materials;

[0046] Figure 5 Interstage structure 1 / 2 model;

[0047] Figure 6 The present invention weakens the groove details;

[0048] Figure 7 a is the longitudinal groove crack initiation calculated by ABAQUS simulation software (0.0687s, internal pressure 1.541225MPa);

[0049] Figure 7 b is Figure 7 A partial enlargement of a;

[0050] Figure 8 a is the crack initiation of ring groove 1 calculated by ABAQUS simulation software (0.0692s);

[0051] Figure 8 b is Figure 8 A partial enlargement of a;

[0052] Fig. 9 The complete fracture of the ring groove 2 calculated by ABAQUS simulation software (0.07s);

[0053] Fig.10 The ring groove 1 calculated by ABAQUS simulation software is completely broken (0.0711s, pressure 1.59425MPa);

[0054] Fig.11a This is the Z-direction displacement cloud diagram at the moment of complete separation calculated by ABAQUS simulation software;

[0055] Fig.11b The Y-direction displacement cloud diagram at the moment of complete separation calculated by ABAQUS simulation software;

[0056] Fig.12 a is the stress cloud diagram at 0.06765s calculated by ABAQUS simulation software;

[0057] Fig.12 b is the stress cloud diagram at 0.06785s calculated by ABAQUS simulation software;

[0058] Fig.12 c is the stress cloud diagram at 0.06805s calculated by ABAQUS simulation software;

[0059] Fig.12 d is the stress cloud diagram at 0.0705s calculated by ABAQUS simulation software;

[0060] Fig.13a The longitudinal groove crack initiation time calculated by LS-DYNA software is 0.085499s (corresponding to an internal pressure of 1.58MPa);

[0061] Fig.13b for Fig.13a A partial enlarged view of

[0062] Fig.14 The time for complete fracture of the ring groove 1 calculated by LS-DYNA software is 0.086999s (corresponding to the internal pressure of 1.39MPa after pressure relief).

[0063] Fig.15 The internal pressure-time curve of the interstage separation process calculated by LS-DYNA software;

[0064] Fig.16a The separation process of the gas particles at the first moment calculated by LS-DYNA software is not displayed;

[0065] Fig.16b The separation process of gas particles at the second moment calculated by LS-DYNA software is not displayed;

[0066] Fig.16c The separation process of gas particles at the third moment calculated by LS-DYNA software is not displayed;

[0067] Fig.16d The separation process of gas particles at the fourth moment calculated by LS-DYNA software is not displayed;

[0068] Fig.16e The separation process of gas particles at the 5th moment calculated by LS-DYNA software is not displayed;

[0069] Fig.16f The separation process of gas particles at the 6th moment calculated by LS-DYNA software is not displayed;

[0070] Fig.17a The first moment of separation of gas particles calculated by LS-DYNA software;

[0071] Fig.17b The second moment separation process of gas particles calculated by LS-DYNA software;

[0072] Fig.17c The LS-DYNA software calculates the separation process of gas particles at the third moment;

[0073] Fig.17d The LS-DYNA software calculates the separation process of gas particles at the fourth moment;

[0074] Fig.18 Table 1 Comparison of calculation results between ABAQUS and LS-DYNA;

[0075] Fig.19 The present invention is a flow chart of a method for separating rocket stages by holding pressure. DETAILED DESCRIPTION

[0076] Design principle of the present invention

[0077] 1. Innovation of the present invention: One of the innovations is that a method for separating rocket stages by holding pressure without using explosives is adopted. The method can meet the design load requirement of the first stage flight and ensure that the interstage can achieve complete destruction and separation through the optimization design of the interstage structure. The structural optimization design is to design the thickness of each weakening groove so that the initial cracking starts from the longitudinal groove. After the longitudinal groove is cracked, the cracking of the annular grooves at both ends is driven from the cracking groove to finally achieve the separation process. The second innovation is that the combined verification method of ABAQUS and LS-DYNA simulation software is used to prove that the pressure-holding separation method is feasible. Specifically, a three-dimensional finite element model of the interstage structure is established based on the ABAQUS simulation software, and the calculated monotonically increasing aerodynamic-pressure curve is applied to the inner wall as a boundary condition to perform transient calculations to simulate the destruction and separation process of the interstage structure, and preliminarily verify the feasibility of the destruction and separation of the interstage section structure under pressure holding conditions; the interstage section fluid-solid coupling simulation is carried out based on the LS-DYNA simulation software to further verify that after the longitudinal groove cracks, the weakening groove is destroyed while releasing pressure, and the interstage section can still achieve complete destruction and separation; the comparison of the calculation results of the two simulation softwares, ABAQUS and LS-DYNA, proves that the longitudinal groove cracking pressures calculated by different modeling methods in different software are consistent. When the cracking pressures are consistent, it is inferred that the fluid-solid coupling simulation results after pressure release calculated by LS-DYNA are credible.

[0078] 2. Design difficulties and solutions of the present invention: The difficulty lies in that the interstage structure must not only meet the design load requirements during the first stage flight, but also ensure that complete destructive separation can be achieved during separation. The solution of the present invention is as follows: ① Specifically, under the constraint that the total mass does not exceed 80kg and the maximum shell thickness of the interstage section cannot exceed 5mm, based on the stress characteristics of the cylindrical pressure vessel, the circumferential stress of the column section shell is twice the longitudinal stress. Since the longitudinal groove cracks under the circumferential stress, and the annular groove cracks under the longitudinal stress, if the longitudinal weakening groove and the annular weakening groove are desired to be destroyed at the same time, the wall thickness of the longitudinal weakening groove should be twice the wall thickness of the annular weakening groove. If the wall thickness of the longitudinal groove is 3mm, the wall thickness of the annular groove 1 should be 1.5mm. However, since the annular groove 1 and the annular groove 2 surround the interstage section for a full 360 degrees, they are mainly destroyed under the longitudinal stress. The main load axial force and bending moment during the first-stage flight will generate large longitudinal stress. The design load requirement during the first-stage flight is: during the first-stage flight, the ring 1, the ring 2, and the longitudinal groove are required to exist. If the annular groove is destroyed during the first-stage flight, the consequences will be disastrous. The stress environment of the longitudinal groove during the first-stage flight is much better, with almost no annular stress. Therefore, considering the first stage flight stress, the shell thickness of the ring groove cannot be too small, that is, the ring-to-vertical groove thickness ratio is greater than 1:2, which causes the longitudinal groove to crack first during separation, and then drives the ring groove to crack. Figure 7 a_ Fig.10 As shown, the longitudinal groove cracks first, and the annular groove 1 and annular groove 2 crack later; ② Ensure that the interstage can be completely destroyed and separated. The method of first cracking the longitudinal groove and then driving the annular grooves at both ends to crack from the cracking groove meets the design load requirements during the first-stage flight, but it is also accompanied by risks. The risk is that after the longitudinal groove cracks, pressure relief occurs at the gap. Whether it can still ensure complete destruction and separation under pressure relief is a serious study. If the internal pressure is insufficient due to pressure relief to ensure that the interstage is completely destroyed and separated, but only partially separated, the consequences will be even more unimaginable. Therefore, the difficulty lies in being able to achieve complete destruction and separation of the interstage under pressure relief, which involves the structural design of the interstage. The structural design refers to the design of the thickness of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove. The present invention designs the thickness of the weakening groove of ring 1 / longitudinal groove / ring 2 to be 4mm / 2.5mm / 4mm respectively. This interstage structural design can not only ensure that the structure of the interstage is intact during the first stage flight, but also can achieve complete separation by driving the cracking of the annular groove through the cracking of the longitudinal groove during the interstage pressure separation. ③ Two simulation software are used to verify in combination that the pressure separation method of the present invention can completely destroy and separate the interstage. The first simulation software (based on ABAQUS simulation) simulates the process of structural destruction and separation of the interstage under a given monotonically increasing pressure-time load, preliminarily verifies the feasibility of pressure separation, and because it is only a structural simulation, the calculation speed is fast, and the structure can be quickly iterated and optimized; the second simulation software (based on LS-DYNA simulation) simulates the whole process of interstage pressure, longitudinal groove cracking, pressure relief, longitudinal groove driving the cracking of the annular groove, and complete destruction of the annular groove by establishing a fluid-solid coupling simulation model. The influence of pressure relief after longitudinal cracking on the destruction and separation is taken into consideration. From the calculation results, it can be seen that the design can still enable the interstage section to be completely destroyed and separated under the condition of pressure relief. The feasibility of the pressure holding and separation method of the present invention is ensured by the complementary advantages of the two simulation software and the mutual verification of the results.

[0079] Based on the above invention principle, the present invention relates to a method for separating rocket stages by holding pressure, such as Figure 1-19 As shown, it is characterized in that: the method comprises the following steps:

[0080] Step 1, designing a rocket interstage pressure holding and separation structure, which does not use pyrotechnics, and designs a weakening groove in the interstage structure. During the thermal separation process, after the upper stage engine is ignited, its jet is pressure held in the interstage. When the pressure reaches a predetermined design range, the rocket interstage structure is disconnected from the designed weakening groove, thereby achieving interstage separation; the weakening groove of the pressure holding and separation structure refers to the thickness of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove; the initial cracking starts from the longitudinal groove;

[0081] like Figure 1Shown is the separation structure of the two-stage rocket. The upper stage is the part that continues to fly after separation, and the lower stage is the part that is discarded after separation.

[0082] like Figure 2 As shown, the pressure buildup comes from the nozzle, and the gas produced by the nozzle generates pressure buildup in the interstage section.

[0083] Step 2: After the longitudinal groove is cracked, the annular grooves at both ends are driven to crack from the cracking groove, and finally the separation process is completed.

[0084] Supplementary Note 1:

[0085] i. The longitudinal groove cracks are as follows Figure 7 As shown in a-7b;

[0086] ii. The cracking of the annular grooves at both ends is that the annular groove 1 cracks first (upper level) and the annular groove 2 (lower level) cracks later; the annular groove 1 is at the upper level and the annular groove 2 is at the lower level, or, Figure 5 As shown, ring groove 1 is on the left (upper stage) and ring groove 2 is on the right (lower stage)

[0087] iii. Figure 8 a is the crack initiation (0.0692s) of the ring groove 1 calculated by ABAQUS simulation software; Fig.10 This is the case where the ring groove 1 is completely broken (0.0711s, pressure 1.59425MPa);

[0088] iv. Fig. 9 This is the case where the ring groove 2 is completely broken. When it is completely broken, the crack runs through the top and bottom, such as Fig. 9 The crack on the right side runs from top to bottom;

[0089] v. Figure 4 As shown in the figure, the failure process of ductile metal materials under external loads will successively go through the elastic deformation stage with stress level lower than the material yield strength σ0, the stress level between the yield strength and the strength limit σ y0 The plastic hardening stage between and the stiffness degradation stage after exceeding the strength limit.

[0090] Furthermore, the calculation process of the pressure holding separation structure in step 1 is as follows:

[0091] 1) The load specialist gives the design load of the interstage during the first stage flight;

[0092] 2) Preliminarily determine the thickness h of the ring 1 weakening groove and the ring 2 weakening groove by the design load of the separation section during the first stage flight;

[0093] 3) Calculate the thickness h' of the longitudinal groove weakening groove according to the pressure range at the time of destruction required for pressure holding separation.

[0094] Furthermore, the specific steps of process 1) and process 2) of step 1 are as follows:

[0095] A. Give the design loads of the rocket at the first stage of separation: axial force T, shear force Q, bending moment M, and outer diameter D of the rocket;

[0096] B. Calculate the maximum equivalent tension, which is generated by the axial force T and the bending moment M. The maximum equivalent tension is:

[0097]

[0098] C. Calculate the axial stress generated by the tension. The axial stress generated by the tension is:

[0099]

[0100] Where h is the thickness of the ring groove, σ b is the material strength;

[0101] D. Preliminarily determine the thickness h of the weakening groove of ring 1 and the weakening groove of ring 2 by using formula (1) and formula (2).

[0102] Furthermore, the specific steps are as follows:

[0103] ① Obtain the pressure range P (1.5MPa~1.6MPa) during pressure holding and separation;

[0104] ② Calculate the longitudinal groove thickness h' according to the pressure range P (1.5MPa~1.6MPa) required for pressure separation:

[0105]

[0106] ③ After preliminarily obtaining the weakening groove thickness, a three-dimensional model is established and finite element calculations are carried out to ensure that the interstage section will not be damaged under the first-stage flight load.

[0107] Furthermore, the pressure-holding separation structure initially cracks from the longitudinal groove, and its specific structure is: when the separation structure is subject to the constraints that the total mass does not exceed 80kg and the shell thickness of the interstage section cannot exceed 5mm, and when the thicknesses of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove are 4mm, 2.5mm, and 4mm respectively, the longitudinal groove weakening groove cracks first, and after cracking, the ring 1 weakening groove and the ring 2 weakening groove at both ends are driven to crack from the crack initiation groove, thereby finally realizing the separation process.

[0108] A method for simulating pressure holding and separation between rocket stages, characterized in that it comprises the following steps:

[0109] Step 1: Use engineering algorithms or FLUENT to calculate the aerodynamic pressure-time curve of the interstage pressure after the second-stage engine is ignited. Figure 3As shown, this curve does not take separation pressure relief into account;

[0110] Step 2: A three-dimensional finite element model of the interstage structure is established based on ABAQUS. The aerodynamic-pressure curve calculated in step 1 is applied to the inner wall surface as a boundary condition to perform transient calculations to simulate the destruction and separation process of the interstage structure, and preliminarily verify the feasibility of the destruction and separation of the interstage structure under pressure holding conditions.

[0111] Step 3: Based on LS-DYNA, fluid-solid coupling simulation of the interstage section was carried out to further verify that after the longitudinal groove cracks, the weakening groove is destroyed and the pressure is released at the same time, and the interstage section can still achieve complete destruction and separation;

[0112] Step 4: Compare the calculation results of ABAQUS and LS-DYNA. The comparison proves that the longitudinal groove crack initiation pressures calculated by different modeling methods in different software should be consistent. If the crack initiation pressures are consistent, it can be inferred that the fluid-solid coupling simulation results after pressure relief calculated by LS-DYNA are credible.

[0113] Furthermore, the calculation results of ABAQUS and LS-DYNA in step 4 are compared, and the comparison content includes: longitudinal groove cracking time / s, internal pressure corresponding to longitudinal groove cracking / MPa, and pressure corresponding to complete fracture of annular groove 1 / MPa.

[0114] Furthermore, the comparison of calculation results between ABAQUS and LS-DYNA in step 4 includes the following comparison of calculation results:

[0115] ① The peak pressure of LS-DYNA at the time of crack initiation is basically consistent with the corresponding value of ABAQUS;

[0116] ② In the case of complete destruction, the pressure calculated by LS-DYNA is smaller than that by ABAQUS because the effect of pressure relief is taken into account.

[0117] Example 1: Separation simulation of interstage structure

[0118] like Figure 7 As shown in a-12d, in order to preliminarily verify the feasibility of the stage section structure to destroy the separation under the condition of pressure holding, ABAQUS explicit calculation is used to simulate the nonlinear dynamic response of the stage section structure under the given internal pressure-time curve; at the same time, the size and structure form are quickly iterated and optimized according to the design requirements, so that the stage section structure can be separated under the given pressure load. Specifically, the iterative design can be carried out based on the weakening groove thickness preliminarily calculated by the engineering algorithm, such as 4 / 2.5 / 4, and the total skin thickness shall not exceed 5mm (mass limit).

[0119] In order to improve the computational efficiency, Figure 5As shown in the figure, the calculation model uses the 1 / 2 model. The first stage front skirt, the second stage rear skirt and the interstage are connected by screws in the actual structure, which is defined as bound contact in ABAQUS; the second stage engine rear skirt section adopts fixed support constraint, and the first stage engine front skirt section constrains the in-plane displacement, that is, only axial displacement is allowed; the out-of-plane displacement is constrained on the symmetry plane. The pressure-time curve applied to the inner surface of the entire interstage structure is shown in Figure 3 As shown, the pressure value is 0 at t=0, and the designed separation breaking pressure is 1.5MPa~1.6MPa.

[0120] Example 2: Fluid-Solid Coupling Simulation of Interstage Separation

[0121] like Figure 13a-18 As shown in the figure, ABAQUS was used to build a model of the structure and perform dynamic separation calculations on the structure. The impact of uneven pressure distribution during the ignition and pressure building process of the previous engine was not considered, nor was the pressure relief condition simulated to see whether the structure could be completely destroyed and finally separated. Therefore, LS-DYNA is also needed to simulate the fluid-solid coupling phenomenon during the interstage separation process, so as to simulate the interstage separation process more realistically and verify the feasibility of the pressure holding separation scheme. After many calculation tests and debugging, when using LS-DYNA to simulate and analyze the fluid-solid coupling problem of interstage separation, establishing a shell model of the entire interstage structure can better simulate the structural pressure holding destruction, as well as the gas inflation and pressure relief process. The internal nozzle and tank bottom use a rigid shell model.

[0122] In order to compare with the calculation results of ABAQUS, the material failure model should be basically consistent. In the *MAT keyword, select 024-PIECEWISE_LINEAR_PLASTICITY to define the elastic-plastic parameters of the interstage and the first and second tank structure materials; define 020-RIGID as the rigid material properties of the internal nozzle and tank bottom, the nozzle is fixedly constrained, and the first tank bottom can move axially; define 000-ADD_EROSION as the failure model of the interstage and the first and second tank structure materials, and select the GISSMO failure model. The nozzle and the second stage rear skirt end face share a node, so it is equivalent to the fixed constraint on the second stage engine rear skirt end face in ABAQUS. The first stage tank bottom and the first stage front skirt section share a node, so it is equivalent to the in-plane constraint on the first stage engine front skirt end face in ABAQUS.

[0123] The entire interstage structure is regarded as a closed cavity, and the Corpuscular Particle Method for Airbag Simulation is used to simulate the rapid inflation flow field. The gas flow rate at the nozzle mouth is defined as a function of time, the gas temperature and composition, and the fluid-solid coupling calculation is carried out. The results are as follows:

[0124] The comparison between the interstage fluid-solid coupling simulation results of LS-DYNA and the structural dynamic separation simulation results of ABAQUS is shown in Table 1. Considering the fluid-solid coupling, the interstage structure begins to break at an internal pressure of about 1.58 MPa and is completely broken after 1.5 ms. The pressure inside the interstage cavity is 1.39 MPa when the interstage cavity is completely broken. Fig.15 .

[0125] Compared with the results of ABAQUS structural dynamic simulation, the cracking time is delayed by about 17ms. This can be seen from the interstage pressure curve. The real inflation process simulated by LS-DYNA takes a longer time to reach the pressure required for cracking. The peak pressure at the time of cracking is basically consistent with the corresponding value of ABAQUS. The pressure at the time of complete destruction is smaller because the influence of pressure relief is considered. It takes a long time for the structure to go from cracking to complete destruction in ABAQUS simulation, which takes 2.4ms. In addition, the distance between the longitudinal seam and the annular seam at complete destruction is very large. This is because in ABAQUS, the pressure load acts vertically on the inner surface of the interstage. As the longitudinal seam breaks and the annular seam is opened, the vertical and unattenuated pressure will cause the structures on both sides of the separated longitudinal seam to produce a large displacement perpendicular to the longitudinal seam surface. Since ABAQUS uses solid elements and divides 4 layers of solid elements in the thickness direction, while LS-DYNA uses shell elements and only one layer of shell elements in the thickness direction, the duration of the destruction and fracture process in ABAQUS is slightly longer than that in LS-DYNA.

[0126] It should be emphasized that the above specific embodiments are merely explanations of the present invention, and they are not limitations of the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without any creative contribution as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for separating rocket stages by holding pressure, characterized in that: The method comprises the following steps: Step 1, designing a rocket interstage pressure holding and separation structure, which does not use pyrotechnics, and designs a weakening groove in the interstage structure. During the thermal separation process, after the upper stage engine is ignited, its jet is pressure held in the interstage. When the pressure reaches a predetermined design range, the rocket interstage structure is disconnected from the designed weakening groove, thereby achieving interstage separation; the weakening groove of the pressure holding and separation structure refers to the thickness of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove; the initial cracking starts from the longitudinal groove; Step 2: After the longitudinal groove is cracked, the annular grooves at both ends are driven to crack from the cracking groove, and finally the separation process is completed.

2. A rocket stage separation method according to claim 1, characterized in that: The calculation process of the pressure holding and separation structure in step 1 is as follows: 1) The load specialist gives the design load of the interstage during the first stage flight; 2) Preliminarily determine the thickness h of the ring 1 weakening groove and the ring 2 weakening groove by the design load of the separation section during the first stage flight; 3) Calculate the thickness h' of the longitudinal groove weakening groove according to the pressure range at the time of destruction required for pressure holding separation.

3. A rocket stage separation method according to claim 2, characterized in that: The specific steps of process 1) and process 2) of step 1 are as follows: A. Give the design loads of the rocket at the first stage of separation: axial force T, shear force Q, bending moment M, and outer diameter D of the rocket; B. Calculate the maximum equivalent tension, which is generated by the axial force T and the bending moment M. The maximum equivalent tension is: C. Calculate the axial stress generated by the tension. The axial stress generated by the tension is: Where h is the thickness of the ring groove, σ b is the material strength; D. Preliminarily determine the thickness h of the weakening groove of ring 1 and the weakening groove of ring 2 by using formula (1) and formula (2).

4. A rocket stage separation method according to claim 2, characterized in that: The process 3) of step 1, the specific steps are as follows: ① Obtain the pressure range P (1.5MPa~1.6MPa) during pressure holding and separation; ② Calculate the longitudinal groove thickness h' according to the pressure range P (1.5MPa~1.6MPa) required for pressure separation: ③ After preliminarily obtaining the weakening groove thickness, a three-dimensional model is established and finite element calculations are carried out to ensure that the interstage section will not be damaged under the first-stage flight load.

5. A rocket stage separation method according to claim 1, characterized in that: The pressure-holding separation structure initially cracks from the longitudinal groove, and its specific structure is: when the separation structure is subject to the constraints that the total mass does not exceed 80kg and the shell thickness of the interstage section cannot exceed 5mm, and when the thicknesses of the ring 1 weakening groove, the longitudinal groove weakening groove, and the ring 2 weakening groove are 4mm, 2.5mm, and 4mm respectively, the longitudinal groove weakening groove cracks first, and after cracking, the ring 1 weakening groove and the ring 2 weakening groove at both ends are driven to crack from the crack initiation groove, thereby finally realizing the separation process.

6. A rocket interstage pressure holding and separation simulation method for a rocket interstage pressure holding and separation method as described in any one of claims 1-5, characterized in that: The following steps are involved: Step 1: Use engineering algorithms or FLUENT to calculate the aerodynamic pressure-time curve of the interstage pressure after the second-stage engine is ignited. This curve does not consider the separation pressure relief. Step 2: A three-dimensional finite element model of the interstage structure is established based on ABAQUS. The aerodynamic-pressure curve calculated in step 1 is applied to the inner wall surface as a boundary condition to perform transient calculations to simulate the destruction and separation process of the interstage structure, and preliminarily verify the feasibility of the destruction and separation of the interstage structure under pressure holding conditions. Step 3: Based on LS-DYNA, fluid-solid coupling simulation of the interstage section was carried out to further verify that after the longitudinal groove cracks, the weakening groove is destroyed and the pressure is released at the same time, and the interstage section can still achieve complete destruction and separation; Step 4: Compare the calculation results of ABAQUS and LS-DYNA. The comparison proves that the longitudinal groove crack initiation pressures calculated by different modeling methods in different software should be consistent. If the crack initiation pressures are consistent, it can be inferred that the fluid-solid coupling simulation results after pressure relief calculated by LS-DYNA are credible.

7. A rocket stage separation simulation method according to claim 6, characterized in that: The fourth step is to compare the calculation results of ABAQUS and LS-DYNA, and the comparison includes: Longitudinal groove cracking time / s, internal pressure corresponding to longitudinal groove cracking / MPa, pressure corresponding to complete fracture of annular groove 1 / MPa.

8. A rocket stage separation simulation method according to claim 6, characterized in that: The step 4 of comparing the calculation results of ABAQUS and LS-DYNA includes the following calculation results comparison: ① The peak pressure of LS-DYNA at the time of crack initiation is basically consistent with the corresponding value of ABAQUS; ② In the case of complete destruction, the pressure calculated by LS-DYNA is smaller than that by ABAQUS because the effect of pressure relief is taken into account.

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