Solid-liquid binding rocket structure simplified modeling method

Abstract

A solid-liquid bundled rocket structure simplified modeling method, comprising: establishing a rocket structure three-dimensional finite element model, the rocket structure three-dimensional finite element model comprising a main structure model and a secondary structure model of a rocket body; for the main structure model of the rocket body, according to the type of the main structure model of the rocket body, simplifying the type of the main structure model of the rocket body into a low-dimensional model; for the secondary structure model of the rocket body, according to the type of the secondary structure model of the rocket body, simplifying the type of the secondary structure model of the rocket body into a particle element model; simplifying each main structure model and each secondary structure model of the rocket body, and connecting the obtained low-dimensional model and particle element model according to the corresponding relationship of the rocket structure three-dimensional finite element model to obtain a rocket structure simplified model.

Description

Technical Field

[0001] This invention belongs to the field of finite element modeling and analysis technology for launch vehicles, and in particular relates to a simplified modeling method for solid-liquid bonded rocket structures, which can improve calculation efficiency while ensuring calculation accuracy and meeting the requirements of high-density launches. Background Technology

[0002] The structural dynamics model of a launch vehicle is mainly used for various dynamic analyses of the rocket, including rocket elastic design, load design, spacecraft-rocket coupling analysis, frequency response analysis, transient analysis, and so on. Each task involves several or even dozens of calculation scenarios, resulting in a large computational workload. Furthermore, China's launch vehicles are entering a period of high-density launches, requiring the shortening of the design cycle as much as possible. Therefore, higher demands are placed on the overall rocket dynamics model, which must not only meet accuracy requirements but also improve efficiency.

[0003] Traditional single-core liquid rockets primarily use point mass and beam elements, with riveted sections and tanks derived from area or volume equivalence to obtain the beam section properties. Traditional single-core rockets assume a perfectly symmetrical structure when conducting structural and attitude control dynamics analyses; therefore, the simplified beam model's bending stiffness is equal in both directions. This simplification is relatively easy to implement and meets the design requirements of traditional single-core liquid rockets.

[0004] Solid-liquid coupled rockets have more complex structures, and attitude control dynamics modeling requires simultaneous provision of elastic correlation data across three channels—pitch, yaw, and roll—for the same mode. Traditional simplified models based on mass-beam elements are no longer suitable, necessitating a comprehensive longitudinal, transverse, and torsional dynamics model. Furthermore, the unique characteristics of solid propellant grains exponentially increase model complexity and the number of degrees of freedom. While meeting accuracy requirements, this model cannot meet the demands for efficient computation. Therefore, it is necessary to simplify the complex three-dimensional refined dynamics model of solid-liquid coupled rockets to obtain a comprehensive longitudinal, transverse, and torsional model capable of rapid computation. Summary of the Invention

[0005] To address the challenge of simplifying complex three-dimensional refined dynamic models of solid-liquid coupled rockets, a simplified integrated longitudinal, transverse, and torsional model capable of rapid computation is required. This invention proposes a simplified modeling method for solid-liquid coupled rocket structures. Based on this simplified finite element modeling, a set of integrated longitudinal, transverse, and torsional dynamic models suitable for efficient computation can be obtained for various dynamic analyses and designs of solid-liquid coupled rockets.

[0006] This invention proposes a simplified modeling method for solid-liquid bonded rocket structures, comprising:

[0007] A three-dimensional finite element model of the rocket structure is established, which includes the main structure model and the secondary structure model of the rocket body.

[0008] For the main structure model of the rocket body, based on the type of the main structure model of the rocket body, the main structure model of the rocket body corresponding to the type is simplified into a low-dimensional model;

[0009] For the substructure model of the rocket body, according to the type of the substructure model of the rocket body, the substructure model of the rocket body corresponding to the type is simplified into a mass element model;

[0010] The main structural models and secondary structural models of the entire rocket body are simplified, and the resulting low-dimensional models and mass element models are connected according to the correspondence of the three-dimensional finite element model of the rocket structure to obtain a simplified rocket structure model.

[0011] Furthermore, the main structural model of the rocket body includes: solid rocket boosters, riveted sections, binding mechanisms, liquid tanks, and satellite fairings.

[0012] Furthermore, based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the solid propellant into a low-dimensional model:

[0013] The three-dimensional model of the solid propellant booster includes a propellant grain, a propellant grain shell, a head cone, and a section connected to the binding mechanism.

[0014] The drug grains were simplified into point mass model units;

[0015] The capsule shell is simplified into a beam element model;

[0016] The head cone and the section connected to the binding mechanism are simplified into a shell element model. The head cone and the binding structure are connected by rigid elements or point connections.

[0017] Furthermore, based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the riveted section into a low-dimensional model:

[0018] Based on the static stiffness equivalence criterion, the riveted section is simplified into a combination of multiple mass element models and beam element models. The combination method is that the mass element models are arranged axially along the central axis of the rocket body, and the mass element models are connected to the element nodes of the beam element models.

[0019] Furthermore, based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the binding mechanism into a low-dimensional model:

[0020] The bundled mechanism shrinkage model is shrinkage-compressed, and during shrinkage-compression, the nodes connecting the bundled mechanism to the core stage and the booster are used as the residual structure of the shrinkage-compression model.

[0021] Furthermore, based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the liquid storage tank into a low-dimensional model:

[0022] The liquid storage tank includes front and rear tank bottoms, cylindrical wall panels and their reinforcing ribs, propellant, conduit, conduit support, and anti-sway fan-shaped plate;

[0023] The cylindrical wall panel is divided into multiple corresponding rib grids according to the distribution of its reinforcing ribs, and each rib grid is simplified into a shell element model; the propellant is simulated using the virtual mass method, and the number of wet elements is determined according to the propellant liquid level.

[0024] The catheter, catheter support, and anti-sway sector plate are simplified into a mass element model, which is connected by rigid elements or directly connected to the nodes of the shell element at the corresponding position of the liquid storage tank.

[0025] Furthermore, based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the riveted compartment into a shell unit.

[0026] Furthermore, the riveting section includes a core-stage inter-cabinet section and a core-stage rear transition section connected to the binding mechanism, and the core-stage inter-cabinet section and the core-stage rear transition section are simplified as shell units.

[0027] Furthermore, based on the type of the rocket body secondary structure model, simplifying the rocket body secondary structure model of that type into a point mass element model specifically includes:

[0028] The secondary structure model of the rocket body includes: duct, support, anti-sway sector plate, thrust rocket, mouth cover, and inertial navigation gyroscope;

[0029] Based on the mass, center of mass, and inertia data of the secondary structure model of the rocket body, a point mass element model with mass and inertia attributes is established at the center of mass. The point mass element model is connected to the beam element model and / or shell element model of the main structure in a common node manner.

[0030] Alternatively, the mass element model can be rigidly connected to the beam element model and / or shell element model of the main structure.

[0031] Furthermore, the obtained low-dimensional model and the mass element model are connected according to the correspondence of the three-dimensional finite element model of the rocket structure to obtain a simplified rocket structure model. Specifically, the connection method includes rigid connection and / or connection by condensation model.

[0032] The simplified modeling method for solid-liquid bundled rocket structure dynamics proposed in this invention can be practically applied to the modeling of next-generation launch vehicles. Using this invention, a simplified modeling of the structural dynamics of a certain solid-liquid bundled rocket was achieved and successfully applied to the rocket's elasticity and space-rocket coupling design. The beneficial effects are mainly reflected in: simplifying the propellant grains and propellant grain shell sections of the solid rocket motor, as well as the riveted compartments such as the second-stage interstage section and interstage section of the core stage rocket, into zero-dimensional mass element models and one-dimensional beam elements, while retaining the front and rear transition sections and tail section connected to the bundling mechanism, and preserving the engine nozzle characteristics. This reduces the solid rocket motor's degrees of freedom to one-tenth of the refined model while retaining the mechanical characteristics of the flexible nozzle. It also reflects: first, fully considering the connection relationship between the main and auxiliary bundling mechanisms to establish a refined model, and then obtaining a condensation model based on static condensation, reducing the degrees of freedom of the bundling mechanism model to one-hundredth of the refined model. Furthermore, it reflects: using the virtual mass method to model the propellant in the tank, improving the propellant modeling accuracy. The final solid-liquid bundled rocket dynamic model meets the accuracy requirements while also improving computational efficiency. Attached Figure Description

[0033] Figure 1 This invention simplifies the process of the solid-liquid bonded rocket structure dynamics model.

[0034] Figure 2 This invention provides a three-dimensional refined structural dynamic model of the solid-liquid bonded rocket.

[0035] Figure 3 This invention provides a refined three-dimensional dynamic model of the solid booster and a simplified model of the mass-beam-shell element.

[0036] Figure 4 This provides a three-dimensional refined dynamic model and a simplified model of the mass beam element for the riveted section of this invention.

[0037] Figure 5 This refers to the residual structure in the three-dimensional refined dynamic model and condensation model of the main force transmission binding mechanism of this invention.

[0038] Figure 6 These are the fine-grid model and coarse-grid model of the storage tank of the present invention.

[0039] Figure 7 This invention provides a simplified three-dimensional structural dynamic model of the solid-liquid bonded rocket. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The present invention proposes a simplified modeling method for solid-liquid bonded rocket structures. Figure 1 This is a flowchart illustrating the simplified modeling method for solid-liquid bonded rocket structure dynamics provided by the present invention. The specific operations are as follows:

[0041] Step 1: Based on the structural design drawings, and fully considering the main and secondary structures of the rocket body, first, establish a three-dimensional finite element model of the rocket structure. This model includes the main structure model and the secondary structure model. It is advisable to simplify the three-dimensional finite element model of the rocket structure into a corresponding low-dimensional model. Here, a low-dimensional model refers to a simplified model with lower dimensions than the original three-dimensional finite element model, including models of point elements, beam elements, shell elements, and condensed elements.

[0042] like Figure 2 As shown, the so-called refined finite element model refers to the representation of all sections in three dimensions, fully considering the local characteristics of secondary structures. Structural design drawings include CAD drawings of the rocket, 3D digital prototypes, and subsystem drawings and prototype models. Secondary structures include pipelines, components, supports, tank sector plates, thrust rockets, hatches, inertial navigation systems, gyroscopes, etc. The type of element used for secondary structures is determined by their contribution to stiffness or mass. The main structure of the rocket body includes the satellite fairing, liquid propellant tanks, riveted sections, binding mechanisms, solid rocket boosters, and other major load-bearing structures. Refined modeling requires high accuracy for the main load-bearing structures to realistically reflect the dynamic characteristics of each load-bearing section. The overall 3D refined finite element model of the rocket refers to a model established during the development of a new launch vehicle that accurately reflects the characteristics of each section and the connections between them. Models developed during the development phase generally have a large degree of freedom and obvious local modal characteristics. In later development stages, combined with frequency domain analysis, it can be concluded that most local modes and some overall modes are not important, which is one of the bases for simplifying the structural dynamics model. Secondly, for the main structure model of the rocket body, based on the type of the main structure model, the corresponding main structure model is simplified into a low-dimensional model. Thirdly, for the secondary structure models of the rocket body, based on the type of the secondary structure model, the corresponding secondary structure model is simplified into a point mass element model. Finally, all the main structure models and secondary structure models of the entire rocket body are simplified, and the resulting low-dimensional models and point mass element models are connected according to the correspondence of the three-dimensional finite element model of the rocket structure to obtain a simplified rocket structure model.

[0043] Step 2: The main structural model of the rocket body includes the solid rocket booster, riveted sections, binding mechanism, liquid propellant tanks, and satellite fairing. The propellant grain section of the solid rocket booster is essentially non-load-bearing; the propellant grain shell bears the load. Therefore, the solid rocket booster propellant grain is simplified to a zero-dimensional point mass element, the propellant grain shell section is simplified to a beam element, and other sections are retained as a three-dimensional model primarily composed of shell elements, such as... Figure 3 As shown.

[0044] Step 3: Simplify the riveted section into a low-dimensional model. Obtain the beam element model of the riveted section by applying static stiffness equivalence to the refined 3D model of the riveted section. Static stiffness equivalence means that the simplified mass beam element model has the same bending stiffness EI, torsional stiffness EJ, and tensile stiffness EA as the refined finite element model before simplification. The beam section properties can be obtained by applying a fixed constraint at one end and a unit force at the other end to the refined 3D model. The riveted section before and after simplification is as follows: Figure 4 As shown. The riveted compartments are simulated using static stiffness equivalence. Compared to the traditional method using equivalent area, the advantage of static stiffness equivalence is that it considers the strength of connections with other compartments and the asymmetry of the compartments, resulting in higher simulation accuracy. Figure 4 As can be seen from this, when implementing static stiffness equivalence, the original refined model of the riveted compartment includes interface constraints.

[0045] Step 4: Simplify the binding mechanism into a low-dimensional model. Obtain the bounding mechanism condensation model by performing static condensation on the binding mechanism. The residual structure after condensation retains the nodes connecting to the core stage and the solid rocket booster. Figure 5 The figures show the finite element models of the main lashing mechanism before and after simplification. The lashing mechanism further includes a main lashing mechanism and an auxiliary lashing mechanism. The main and auxiliary lashing mechanisms are simplified into a residual structure containing only interface connection points. The riveted compartments in the booster and core stage that are connected to the lashing mechanism are rigidly connected through nodes in the residual structure of this simplified model. The nodes in the residual structure of the lashing mechanism are the main nodes of the simplified model, and at least the nodes related to the lashing mechanism connections are retained.

[0046] Step 5: Simplify the liquid tank into a low-dimensional model. For the liquid tank, secondary structures with little impact on stiffness, such as conduits, conduit supports, and anti-sway fan-shaped plates, only consider mass effects, establishing zero-dimensional mass elements at their centers of mass. These mass elements are connected to the tank shell elements through rigid elements or directly established on the nodes of the corresponding shell elements in the tank. For the tank cylinder section, only one shell element is established for the area of ​​one rib grid. The ribs are beam elements, which are not involved in the virtual mass method calculation. This method reduces the number of wet elements in the calculation and improves computational efficiency. The number of wet elements is determined based on the propellant level. Wet elements refer to shell elements located below the tank level during calculation, such as the tank cylinder section in a full state and the shell elements at the rear bottom. The tank models before and after simplification are as follows: Figure 6As shown. The reduction in wet elements is mainly because the mass matrix formed by wet elements is a full-rank matrix. The inversion process of a large-dimensional full-rank matrix is ​​slow, which affects the calculation speed. Therefore, simplifying the process requires reducing the number of wet elements.

[0047] Since beam elements are difficult to accurately simulate in the von Kármán curve section of the satellite fairing, no element type simplification is performed.

[0048] The core-level inter-box section and the core-level rear transition section are connected to the binding mechanism. The local effects near the connection surface are quite obvious. The static stiffness method cannot reflect the local effects near the connection surface, so the element type is not simplified.

[0049] Combining the above steps, a hybrid model of the entire arrow can be obtained, which includes zero-dimensional particle elements, one-dimensional beam elements, and two-dimensional shell elements.

[0050] Specifically, in step 2, the three-dimensional refined finite element model of the solid propellant booster cannot use the virtual mass method of liquid propellant due to the viscoelastic characteristics of the solid propellant grain. Instead, it uses solid elements with a smaller elastic modulus to simulate the characteristics of the propellant grain. A smaller elastic modulus means three orders of magnitude smaller than the elastic modulus of aluminum. Too many solid elements would affect computational efficiency and are not suitable for high-density launches. The simplified model simplifies the propellant grain shell section into beam elements and the propellant grain into point mass model elements. Although this may cause deviations in the torsional and tensile characteristics of the individual booster, the torsional and longitudinal frequencies of the individual booster are relatively high and not within the frequency bands of concern for rocket dynamics and attitude control dynamics.

[0051] Finally, the simplified module models can be connected using elastic or rigid elements based on the connection relationships between the modules, resulting in a simplified structural dynamics model, such as... Figure 7 As shown. Figure 7 In the simplified structural dynamics model, the satellite fairing 1, the riveted section beam and mass model unit 2, the mass unit on the tank 3, the tank 4, the booster shell section and propellant grain 5, and the section connected to the binding structure 6.

[0052] This invention can be applied to the development of dynamics for solid-liquid bonded rocket structures. Compared to the simplified dynamics model of a conventional single-core rocket, the method of this invention better reflects the mechanical characteristics and asymmetries of stiffened propellant tanks, riveted sections, etc. Compared to a fully detailed three-dimensional model, it better meets the requirements of efficient calculation and adapts to high-density launch demands.

[0053] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A simplified modeling method for solid-liquid bonded rocket structures, characterized in that, include: A three-dimensional finite element model of the rocket structure is established, which includes the main structure model and the secondary structure model of the rocket body. The main structural model of the rocket body includes: solid rocket boosters, riveted sections, binding mechanism, liquid tanks, and satellite fairing; For the main structure model of the rocket body, based on the type of the main structure model of the rocket body, the main structure model of the rocket body corresponding to the type is simplified into a low-dimensional model; Based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the solid rocket booster into a low-dimensional model: The three-dimensional model of the solid propellant booster includes a propellant grain, a propellant grain shell, a head cone, and a section connected to the binding mechanism. The drug grain was simplified into a point mass element model; The capsule shell is simplified into a beam element model; The head cone and the section connected to the binding mechanism are simplified into a shell element model. The head cone and the binding mechanism are connected by rigid elements or point connections. Based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the riveted section into a low-dimensional model: Based on the static stiffness equivalence criterion, the riveted section is simplified into a combination of multiple mass element models and beam element models. The combination method is that the mass element models are arranged axially along the central axis of the rocket body, and the mass element models are connected to the element nodes of the beam element models. Based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the binding mechanism into a low-dimensional model: The three-dimensional model of the binding mechanism is condensed, and the nodes connecting the binding mechanism to the core stage and the booster are used as the residual structure of the condensed model during the condensation process. Based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the liquid storage tank into a low-dimensional model: The liquid storage tank includes front and rear tank bottoms, cylindrical wall panels and their reinforcing ribs, propellant, conduit, conduit support, and anti-sway fan-shaped plate; The cylindrical wall panel is divided into multiple stiffener grids according to the distribution of its reinforcing ribs, and each stiffener grid is simplified into a shell element model; the propellant is simulated using the virtual mass method, and the number of wet elements is determined according to the propellant liquid level. The catheter, catheter support, and anti-sway sector plate are simplified into a mass element model, which is connected by rigid elements or directly connected to the nodes of the shell element at the corresponding position of the liquid storage tank. Based on the type of the main structure model of the rocket body, simplifying the main structure model of the rocket body corresponding to the type into a low-dimensional model specifically includes: simplifying the riveted compartment into a shell unit; For the substructure model of the rocket body, according to the type of the substructure model of the rocket body, the substructure model of the rocket body corresponding to the type is simplified into a mass element model; The main structural models and secondary structural models of the entire rocket body are simplified, and the resulting low-dimensional models and mass element models are connected according to the correspondence of the three-dimensional finite element model of the rocket structure to obtain a simplified rocket structure model.

2. The method according to claim 1, characterized in that, The riveting section includes a core-stage inter-cabinet section and a core-stage rear transition section connected to the binding mechanism, and the core-stage inter-cabinet section and the core-stage rear transition section are simplified as shell units.

3. The method according to claim 1, characterized in that, Based on the type of the rocket body secondary structure model, simplifying the rocket body secondary structure model of that type into a point mass element model specifically includes: The secondary structure model of the rocket body includes: duct, support, anti-sway sector plate, thrust rocket, mouth cover, and inertial navigation gyroscope; Based on the mass, center of mass, and inertia data of the secondary structure model of the rocket body, a point mass element model with mass and inertia attributes is established at the center of mass. The point mass element model is connected to the beam element model and / or shell element model of the main structure in a common node manner. Alternatively, the mass element model can be rigidly connected to the beam element model and / or shell element model of the main structure.

4. The method according to claim 1, characterized in that, The obtained low-dimensional model and the mass element model are connected according to the correspondence of the three-dimensional finite element model of the rocket structure to obtain a simplified rocket structure model, specifically including: The connection methods include rigid connection and / or connection using a condensation model.

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