A connection optimization design method for double-layer cryogenic structures

Abstract

The present invention discloses a method for optimizing the connection design of a double-layer cryogenic structure, comprising the following steps: (1) calculating the axial and radial cryogenic shrinkage of a tank; (2) determining the installation angle and length of tie rods based on the axial and radial cryogenic shrinkage of the tank; and (3) establishing an optimized model of the connection structure between the tank and the fuselage based on the installation angle and length of the tie rods. The present invention can solve the problem of connection matching between the cryogenic tank and the fuselage while also meeting the strength, stiffness, and structural stability requirements of the structure under different loads.

Description

Technical Field

[0001] The present invention belongs to the technical field of lift-type reusable vehicles with double-layer structures, and in particular relates to a connection optimization design method for a double-layer cryogenic structure. Background Art

[0002] Traditional launch vehicles have a single-layer structure, with the tank serving as the outer shell, eliminating the need for temperature-induced deformation and coordination issues. However, lift-type reusable launch vehicles have a double-layer structure, with an outer fuselage and an inner tank. The tank, which uses cryogenic fuel, can reach temperatures below -170°C after refueling, creating a significant temperature difference with the outer structure. This can lead to serious challenges in terms of matching, connection, and deformation compensation between the tank and the outer structure. Summary of the Invention

[0003] Tanks undergo significant deformation under the combined effects of temperature, internal pressure, and overload. This deformation influences the connection scheme between the tank and the fuselage, and thus the load-bearing capacity of the two. Conversely, the stiffness matching between the tank and fuselage affects the deformation of the tank, meaning that tank deformation and the load-bearing capacity of the two are coupled. Therefore, exploring the interplay between tank deformation and stiffness matching between the tank and fuselage is a key issue in selecting the optimal connection scheme and designing the tank and fuselage structure.

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and provide a connection optimization design method for a double-layer cryogenic structure, which can not only solve the connection matching problem between the cryogenic tank and the fuselage, but also meet the strength, stiffness and structural stability requirements of the structure under different loads. It is suitable for double-layer structure carriers using cryogenic propellants.

[0005] The object of the present invention is achieved by the following technical solution: a connection optimization design method for a double-layer low-temperature structure, the method comprising the following steps: (1) calculating the axial and radial low-temperature shrinkage of the tank; (2) obtaining the installation angle and length of the tie rod based on the axial and radial low-temperature shrinkage of the tank; (3) establishing an optimization model of the connection structure between the tank and the fuselage based on the installation angle and length of the tie rod.

[0006] In the above-mentioned connection optimization design method of the double-layer cryogenic structure, in step (1), the axial cryogenic shrinkage of the tank is obtained based on the tank length, the thermal expansion coefficient of the tank material, the propellant temperature and the room temperature; and the radial cryogenic shrinkage of the tank is obtained based on the tank diameter, the thermal expansion coefficient of the tank material, the propellant temperature and the room temperature.

[0007] In the above-mentioned connection optimization design method of the double-layer cryogenic structure, the axial cryogenic shrinkage of the tank is d1 = L × α × (T-T0); the radial cryogenic shrinkage of the tank is d2 = D × α × (T-T0); wherein, d1 is the axial cryogenic shrinkage of the tank; d2 is the radial cryogenic shrinkage of the tank; L is the tank length; D is the tank diameter; α is the thermal expansion coefficient of the tank material; T is the propellant temperature; and T0 is the room temperature.

[0008] In the above-mentioned connection optimization design method of the double-layer cryogenic structure, in step (2), the connection point between the tie rod and one end of the tank under normal temperature is point A. After the tank is filled with cryogenic propellant, point A will deform to point A'; the connection point between the tie rod and one end of the fuselage is point B. After the tank is deformed, the connection length BA between point B and point A must be equal to the length BA' of the line segment connecting point B and point A'. From this, the length and installation angle of the tie rod can be calculated.

[0009] In the above-mentioned connection optimization design method of the double-layer low-temperature structure, in step (3), the goal of the optimization model of the connection structure between the tank and the fuselage is to minimize the total weight; the design variables of the optimization model of the connection structure between the tank and the fuselage are the tank thickness, the fuselage structure thickness, the number of tie rods, and the size of the tie rods; the constraints of the optimization model of the connection structure between the tank and the fuselage are strength constraints, stiffness constraints, stability constraints, and frequency constraints.

[0010] In the above-mentioned connection optimization design method for the double-layer cryogenic structure, the strength constraint processing includes the following steps:

[0011] The optimized model of the connection between the tank and the fuselage is meshed with finite element units. The maximum values ​​of the corresponding stresses in the three directions of tension, compression, and shear of each unit are selected respectively. The unit stress ratio is calculated by comparing it with the allowable stress, thereby obtaining the maximum stress ratio of the unit. The strength constraint of the unit is then obtained as follows:

[0012]

[0013] Where g1 is the strength constraint; X t 、X c 、X s are the tensile, compressive and shear stresses of the element respectively; σ η is the allowable stress.

[0014] In the above-mentioned connection optimization design method for the double-layer cryogenic structure, the stiffness constraint processing includes the following steps:

[0015] Read the maximum displacement of each element node and compare it with the allowable displacement to obtain the stiffness constraint:

[0016]

[0017] Where g2 is the stiffness constraint; wmax is the maximum displacement of the unit; w 许用 is the allowable displacement.

[0018] In the above-mentioned connection optimization design method for the double-layer cryogenic structure, the stability constraint processing includes the following steps:

[0019] Read the buckling factor of the optimized model of the connection between the tank and the fuselage and compare it with 1 to obtain the stability constraint:

[0020]

[0021] Among them, g3 is the stability constraint; factorbuckling is the buckling factor.

[0022] In the above-mentioned connection optimization design method for the double-layer cryogenic structure, the frequency constraint processing includes the following steps:

[0023] Read the first-order frequency of the connection optimization model and compare it with the allowed frequency to obtain the frequency constraint:

[0024]

[0025] Among them, g4 is the frequency constraint; f is the first-order frequency; f 许用 is the first-order permissible frequency.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention can not only solve the problem of connection matching between the cryogenic storage tank and the fuselage, but also meet the requirements of strength, rigidity, structural stability, etc. under different load conditions;

[0028] (2) The present invention provides a connection structure with minimal weight that meets performance requirements;

[0029] (3) The present invention regularizes the constraints of strength, stiffness, structural stability, etc., automatically compares the criteria with the results, and can intuitively and conveniently judge whether the constraints are met from the positive and negative values ​​of the results. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0031] Figure 1 is a schematic diagram of a connection structure provided by an embodiment of the present invention;

[0032] Figure 2It is a schematic diagram of the pull rod structure provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] Figure 1 is a schematic diagram of a connection structure provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the pull rod structure provided by an embodiment of the present invention.

[0035] The present invention considers the strength, stiffness, structural stability and frequency constraints of the tank and fuselage, and adopts an optimization algorithm to perform multi-constraint optimization design on the design variables of the connection scheme to obtain the optimal parameter matching of the connection structure, so that the connection structure has high load-bearing reliability throughout the entire service life.

[0036] First, the tank's axial and radial cryogenic deformations are calculated based on the tank's dimensions, material, and cryogenic propellant temperature. The length and installation angle of the connecting rods are then calculated based on these deformations. A preliminary connection design is then developed, specifying the number and dimensions (diameter and wall thickness) of the connecting rods, as well as the structural thickness of the fuselage and tank at the junction. Finally, an optimized design of the connection structure is performed.

[0037] like Figure 1 and Figure 2 As shown, this embodiment provides a connection optimization design method for a double-layer low-temperature structure, which includes the following steps: (1) calculating the axial and radial low-temperature shrinkage of the tank; (2) obtaining the installation angle and length of the tie rod based on the axial and radial low-temperature shrinkage of the tank; (3) establishing an optimization model of the connection structure between the tank and the fuselage based on the installation angle and length of the tie rod.

[0038] (1) Calculate the axial and radial low-temperature shrinkage of the tank

[0039] Calculate the tank's low-temperature shrinkage based on the propellant temperature, tank dimensions, and the thermal expansion coefficient of the tank material:

[0040]

[0041] Where d1 is the axial shrinkage of the tank; d2 is the radial shrinkage of the tank; L is the length of the tank; D is the diameter of the tank; α is the thermal expansion coefficient of the tank material; T is the propellant temperature; and T0 is the room temperature.

[0042] (2) Calculate the tie rod installation angle and length

[0043] like Figure 1 As shown, the tie rod connects to one end of the tank at point A (at room temperature). After the tank is filled with cryogenic propellant, this connection point A will deform to point A'. The tie rod connects to one end of the fuselage at point B. After the tank is deformed, the length BA connecting point B and point A must be equal to the length BA' of the line segment connecting point B and point A'. This allows the calculation of the tie rod's length and mounting angle.

[0044] (3) Establish an optimization model for the connection structure between the tank and the fuselage

[0045] Preliminary design of the connection scheme, given the number and size of the connecting rods, the structural parameters of the fuselage and tank at the connection, and established the optimization model:

[0046] Goal: Minimum total weight;

[0047] Design variables: tank thickness, fuselage structure thickness, number of connecting rods, connecting rod dimensions (diameter, wall thickness);

[0048] Constraints: strength constraints, stiffness constraints, stability constraints, and frequency constraints on the tank, connecting rods, and fuselage as a whole;

[0049] 1) Handling of strength constraints

[0050] The optimized model of the connection between the tank and the fuselage is meshed with finite element units. The maximum values ​​of the corresponding stresses in the three directions of tension, compression, and shear of each unit are selected respectively. The unit stress ratio is calculated by comparing it with the allowable stress, thereby obtaining the maximum stress ratio of the unit. The strength constraint of the unit is then obtained as follows:

[0051]

[0052] Where g1 is the strength constraint; X t 、X c 、X s are the tensile, compressive and shear stresses of the element, respectively;

[0053] σ η is the allowable stress.

[0054] 2) Processing of stiffness constraints

[0055] Read the maximum displacement of each element node and compare it with the allowable displacement to obtain the stiffness constraint:

[0056]

[0057] Where g2 is the stiffness constraint; w max is the maximum displacement of the unit; w 许用 is the allowable displacement.

[0058] 3) Handling of stability constraints

[0059] In this structural optimization, the structure should not buckle, that is, the minimum buckling factor should be no less than 1. Read the buckling factor of the connection optimization model and compare it with 1 to obtain the stability constraint:

[0060]

[0061] Where g3 is the stability constraint and factorbuckling is the buckling factor.

[0062] 4) Processing of frequency constraints

[0063] Read the first-order frequency of the connection optimization model and compare it with the allowed frequency to obtain the frequency constraint:

[0064]

[0065] Where g4 is the frequency constraint; f is the first-order frequency; f 许用 is the first-order permissible frequency.

[0066] (4) Perform optimization calculations

[0067] With the minimum total weight of the connecting structure as the design goal and the strength, stiffness, stability and frequency of the tank, connecting rod and fuselage as the constraints, iterative optimization calculations are performed on design variables such as tank thickness, fuselage structure thickness, number of connecting rods, and connecting rod size (diameter, wall thickness) until a connecting structure that meets the requirements is obtained.

[0068] The present invention can not only solve the connection matching problem between the cryogenic storage tank and the fuselage, but also meet the strength, stiffness, structural stability and other requirements of the structure under different load conditions; the present invention obtains a connection structure with the minimum weight that meets the performance requirements; the present invention regularizes constraints such as strength, stiffness, and structural stability, automatically compares the criteria with the results, and can intuitively and conveniently judge whether the constraints are met based on the positive and negative values ​​of the results.

[0069] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications 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 scope of protection of the technical solutions of the present invention.

Claims

1. A connection optimization design method for a double-layer low-temperature structure, characterized in that: The method comprises the following steps: (1) Calculate the axial and radial low-temperature shrinkage of the tank; (2) Obtain the installation angle and length of the tie rod based on the axial and radial low-temperature shrinkage of the tank; (3) Establish an optimization model for the connection structure between the tank and the fuselage based on the installation angle and length of the tie rod; In step (2), the connection point between the tie rod and one end of the tank at room temperature is point A. After the tank is filled with cryogenic propellant, point A will deform to point A'; the connection point between the tie rod and one end of the fuselage is point B. After the tank is deformed, the connection length BA between point B and point A must be equal to the length BA' of the line segment connecting point B and point A'. From this, the length and installation angle of the tie rod can be calculated. In step (3), the goal of the optimization model of the tank-to-fuselage connection structure is to minimize the total weight; The design variables of the optimization model of the tank-fuselage connection structure are tank thickness, fuselage structure thickness, number of tie rods, and tie rod size; The constraints of the optimization model of the tank-to-fuselage connection structure are strength constraints, stiffness constraints, stability constraints, and frequency constraints.

2. The connection optimization design method of a double-layer low-temperature structure according to claim 1, characterized in that: In step (1), the axial low-temperature shrinkage of the tank is obtained based on the tank length, the thermal expansion coefficient of the tank material, the propellant temperature and the room temperature; The radial low-temperature shrinkage of the tank is obtained based on the tank diameter, the thermal expansion coefficient of the tank material, the propellant temperature and the room temperature.

3. The connection optimization design method of a double-layer low-temperature structure according to claim 2, characterized in that: The axial low-temperature shrinkage of the tank is d1 = L × α × (T-T0); the radial low-temperature shrinkage of the tank is d2 = D × α × (T-T0); among them, d1 is the axial low-temperature shrinkage of the tank; d2 is the radial low-temperature shrinkage of the tank; L is the length of the tank; D is the diameter of the tank; α is the thermal expansion coefficient of the tank material; T is the propellant temperature; T0 is the room temperature.

4. The connection optimization design method of a double-layer low-temperature structure according to claim 1, characterized in that: Strength constraint processing includes the following steps: The optimized model of the connection between the tank and the fuselage is meshed with finite element units. The maximum values ​​of the corresponding stresses in the three directions of tension, compression, and shear of each unit are selected respectively. The unit stress ratio is calculated by comparing it with the allowable stress, thereby obtaining the maximum stress ratio of the unit. The strength constraint of the unit is then obtained as follows: Where g1 is the strength constraint; X t 、X c 、X s are the tensile, compressive and shear stresses of the element respectively; σ η is the allowable stress.

5. The connection optimization design method of a double-layer low-temperature structure according to claim 4, characterized in that: The stiffness constraint processing includes the following steps: Read the maximum displacement of each element node and compare it with the allowable displacement to obtain the stiffness constraint: Where g2 is the stiffness constraint; w max is the maximum displacement of the unit; w 许用 is the allowable displacement.

6. The connection optimization design method of a double-layer low-temperature structure according to claim 1, characterized in that: Stability constraint processing includes the following steps: Read the buckling factor of the optimized model of the connection between the tank and the fuselage and compare it with 1 to obtain the stability constraint: Among them, g3 is the stability constraint; factorbuckling is the buckling factor.

7. The connection optimization design method of a double-layer low-temperature structure according to claim 1, characterized in that: Frequency constraint processing includes the following steps: Read the first-order frequency of the connection optimization model and compare it with the allowed frequency to obtain the frequency constraint: Among them, g4 is the frequency constraint; f is the first-order frequency; f 许用 is the first-order permissible frequency.

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