A liquid carrier rocket lateral vibration analysis method considering sway effect

Abstract

The application provides a liquid-carrying rocket transverse vibration analysis method considering sloshing effect, characterized in that the liquid in the tank has the sloshing effect, and the method comprises the following steps: 1, establishing a finite element model for the transverse vibration analysis of the whole rocket; 2, collecting the structure size of each tank of the liquid-carrying rocket and the liquid parameters in the tank; 3, equivalently taking the first-order sloshing liquid in the tank as a transverse spring oscillator model; 4, recalculating the liquid level height; 5, establishing a mass unit of the sloshing liquid in the tank; 6, establishing a spring connection node of the mass unit of the sloshing liquid in the tank; 7, connecting the reference node and the spring connection node through a spring unit; 8, simulating the remaining liquid in the tank by using a virtual mass method; 9, repeating; and 10, submitting a finite element analysis software to complete the calculation. The application can effectively simulate the influence of the sloshing effect of the liquid in the tank on the transverse vibration characteristics of the whole rocket, and is convenient for obtaining more accurate transverse vibration characteristics of the whole rocket.

Description

Technical Field

[0001] This invention belongs to the field of finite element modeling and analysis technology for launch vehicles, and relates to a method for analyzing the lateral vibration of launch vehicles, particularly a method for analyzing the lateral vibration of liquid launch vehicles that considers swaying effects. Background Technology

[0002] Liquid-propellant launch vehicles are widely used in the aerospace transportation field due to their advantages such as high engine specific impulse and strong operational adaptability. Liquid-propellant rockets account for more than half of the current launch vehicle types both domestically and internationally. The overall dynamic characteristics of liquid-propellant launch vehicles, especially their lateral vibration characteristics, are important inputs for key design stages such as overall payload design, environmental condition design, and stability system design. Therefore, obtaining the most accurate overall dynamic characteristics possible is of paramount importance.

[0003] The finite element method (FEM) is a widely used and effective numerical calculation method for obtaining the overall rocket dynamics. With increasing reliability requirements for launch vehicles, the accuracy requirements of FEM calculations also increase. Traditional finite element models for liquid-propellant launch vehicles primarily use a combination of beam elements and lumped mass elements, simplifying the liquid within the propellant tank into lumped mass elements. In recent years, combined modeling methods using three-dimensional modeling and the liquid virtual mass method have become increasingly popular, effectively improving model accuracy. However, during launch vehicle flight, external disturbances cause sloshing effects in the propellant tank, which significantly impact the overall rocket frequency characteristics, particularly the first-order bending mode frequency. Neither of the above two modeling methods considers the impact of sloshing effects on the overall rocket dynamics. Therefore, this invention develops a finite element modeling and analysis method for liquid-propellant launch vehicles that considers sloshing effects. Summary of the Invention

[0004] The purpose of this invention is to provide a method for analyzing the lateral vibration of a liquid-fueled launch vehicle that considers the swaying effect, effectively simulating the influence of the swaying effect on the overall dynamic characteristics of the rocket, thereby improving the accuracy of finite element analysis and obtaining more accurate lateral vibration characteristics of the entire rocket.

[0005] To achieve the above-mentioned objectives, the present invention is specifically implemented through the following technical solutions:

[0006] A method for analyzing the lateral vibration of a liquid-propellant launch vehicle considering the sloshing effect, characterized in that the liquid-propellant launch vehicle includes a liquid propellant tank, and the liquid in the tank exhibits a sloshing effect, comprising the following steps:

[0007] Step 1: Collect a digital prototype model of the solid structure of the launch vehicle and establish a finite element model for the lateral vibration analysis of the entire rocket;

[0008] Step 2: Collect the structural dimensions of each propellant tank of the launch vehicle and the parameters of the liquid inside the tanks. The structural dimensions of the propellant tanks refer to the inner radius R of the tank cylindrical section.i The liquid parameters in the storage tank refer to the liquid density ρ. i Liquid level height H i First-order swaying mass M i The coordinate X of the first-order wobbling center of mass along the arrow's axis. i First-order oscillation frequency f i , where i is the tank code;

[0009] Step 3: The first-order sloshing liquid in the tank is equivalent to a transverse spring oscillator model, where the mass of the oscillator is equal to the first-order sloshing mass M of the liquid. i Spring stiffness K i The calculation formula is: K i =M i ·(2·π·f i ) 2 ;

[0010] Step 4: Subtract the sloshing portion from the liquid level in step 3, and recalculate the liquid level height. The new liquid level height is h. i The calculation formula is:

[0011] Step 5: Establish a mass element of the sloshing liquid inside the tank in the transverse vibration analysis model of the entire rocket. The position reference node coordinates of the mass element are (X... i ,0,0);

[0012] Step 6: Establish the spring connection node of the sloshing liquid mass element in the tank in the transverse vibration analysis model of the whole rocket, and fix the spring connection node to the adjacent tank structural node.

[0013] Step 7: Connect the reference node of the swaying liquid mass unit in Step 5 to the spring connection node in Step 6 through a spring unit. The stiffness value of the spring unit is the same as that in Step 3.

[0014] Step 8: Based on the new liquid level height h obtained in Step 4 i The virtual mass method was used to simulate the remaining liquid in the tank;

[0015] Step 9: Repeat steps 3 to 8 to treat all the sloshing liquid in the tanks as equivalent to a transverse spring oscillator model;

[0016] Step 10: Set the parameters for the full-arrow modal analysis, including setting the modal extraction method and modal frequency range, and submit the solution to the finite element analysis software.

[0017] Furthermore, the lateral vibration analysis method for liquid launch vehicles that considers the swaying effect, as described above, is characterized in that the lateral vibration refers to the vibration of the launch vehicle that produces bending elastic deformation after being disturbed in a direction perpendicular to the longitudinal direction of the rocket body.

[0018] Furthermore, the lateral vibration analysis method for liquid launch vehicles considering swaying effects, as described above, is characterized in that the digital prototype model in step 1 can accurately describe the actual external dimensions of the solid structure and includes the mechanical property parameters of the materials used, namely, material density, elastic modulus, shear modulus, and Poisson's ratio.

[0019] Furthermore, the lateral vibration analysis method for a liquid launch vehicle considering the swaying effect, as described above, is characterized in that the finite element model for the lateral vibration analysis of the entire rocket in step 1 adopts a hybrid modeling form of three-dimensional solid elements, shell elements, beam elements and mass elements, and the tank structure is simulated using shell elements.

[0020] Furthermore, the method for analyzing the lateral vibration of a liquid launch vehicle considering the swaying effect, as described above, is characterized in that, in step 5, the liquid swaying mass unit in the tank acts only on two orthogonal lateral translational degrees of freedom, where lateral refers to the direction perpendicular to the rocket body axis.

[0021] Furthermore, the lateral vibration analysis method for liquid launch vehicles considering the swaying effect, as described above, is characterized in that the spring connection node in step 6 is established near the center of mass of the swaying, and the number of structural nodes rigidly connected to it should not be too large. The rigid connection refers to the rigid connection form in the finite element modeling method.

[0022] Furthermore, the lateral vibration analysis method for a liquid launch vehicle considering the swaying effect, as described above, is characterized in that the stiffness attribute of the spring unit in step 7 only acts on two orthogonal lateral translational degrees of freedom, where lateral refers to the direction perpendicular to the rocket body axis.

[0023] Furthermore, the lateral vibration analysis method for a liquid launch vehicle considering the swaying effect, as described above, is characterized in that, in step 8, the virtual mass method is used to simulate the remaining liquid in the tank, which requires setting up a wet unit set, liquid density, liquid level height, and liquid level reference coordinate system.

[0024] Furthermore, the lateral vibration analysis method for a liquid launch vehicle considering the swaying effect, as described above, is characterized in that the liquid launch vehicle comprises four liquid propellant tanks.

[0025] Furthermore, the lateral vibration analysis method for liquid launch vehicles considering swaying effects, as described above, is characterized in that, in step 8, a local coordinate system parallel to the global coordinate system is established with the theoretical lowest point of the inner edge of the rear bottom of the tank as the origin, and the new liquid level height is referenced to this local coordinate system. Then, the shell units of the rear bottom of the tank and the cylindrical section are set as single-sided wet units with the inner wall wetted.

[0026] This invention designs a finite element modeling and analysis method for liquid launch vehicles that considers the sloshing effect. It can effectively simulate the influence of the liquid sloshing effect in the propellant tank on the lateral vibration characteristics of the entire rocket, especially its influence on the first-order bending mode frequency of the entire rocket. This is beneficial to improving the accuracy of the dynamic analysis of the entire rocket and facilitating the acquisition of more accurate lateral vibration characteristics of the entire rocket. It is of great significance for improving the design quality of launch vehicles. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the finite element mesh model of the entire structure of the liquid-fueled launch vehicle involved in this invention.

[0028] Figure 2 This is a schematic diagram showing the distribution and numbering of the propellant tanks of the liquid-fueled launch vehicle involved in this invention.

[0029] Figure 3 This is a schematic diagram of the swaying mass unit of a liquid-fueled launch vehicle involved in the present invention.

[0030] Figure 4 This is a schematic diagram of the spring connection node modeling method involved in the present invention.

[0031] Figure 5 This is a schematic diagram of the swaying mass spring oscillator model involved in the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be described in detail below with reference to specific examples and accompanying drawings:

[0033] This invention discloses a method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering the sloshing effect. This method can be used to obtain the lateral vibration modal information of the entire rocket and belongs to the field of finite element modeling and analysis technology for launch vehicles. Based on the finite element model of the entire rocket, this method treats the sloshing liquid inside the propellant tank as an equivalent spring oscillator model, and then uses the virtual mass method to simulate the remaining liquid inside the propellant tank.

[0034] This method can effectively simulate the influence of liquid sloshing in the propellant tank on the overall rocket modes, especially the influence on the first-order bending mode frequency of the entire rocket. It is beneficial to improve the accuracy of the overall rocket dynamics analysis and facilitate the acquisition of more accurate lateral vibration characteristics of the entire rocket, which is of great significance for improving the design quality of launch vehicles.

[0035] In one embodiment, the lateral vibration analysis method for liquid-fueled launch vehicles considering swaying effects of the present invention includes the following steps:

[0036] Step 1: Collect a digital prototype model of the solid structure of the launch vehicle and establish a finite element model for the lateral vibration analysis of the entire rocket. Figure 1 This is a schematic diagram of the finite element mesh model of the entire structure of the liquid-fueled launch vehicle involved in this invention, as shown in the figure. Figure 1As shown, the model adopts a combination of three-dimensional solid elements, shell elements, beam elements and mass elements for modeling.

[0037] Step 2: Figure 2 This is a schematic diagram of the distribution and numbering of the propellant tanks in the liquid-fueled launch vehicle involved in this invention, as shown below. Figure 2 As shown, in this example, the launch vehicle contains four liquid propellant tanks, numbered as Tank 1, Tank 2, Tank 3, and Tank 4, respectively. Figure 2 As shown, the relevant structural dimensions and liquid parameters inside each propellant tank of the launch vehicle were collected. Taking the first propellant tank 1 as an example: R1 = 1.6m, ρ1 = 1000kg / m³ 3 , H1=2.5m, M1=4000kg, X1=9.42m, f1=0.77Hz.

[0038] Step 3: The first-order sloshing liquid in the tank is equivalent to a transverse spring oscillator model, where the mass of the oscillator is equal to the first-order sloshing mass M of the liquid. i Spring stiffness K i The calculation formula is: K i =M i ·(2·π·f i ) 2 Taking the first storage tank 1 as an example: M1 = 4000 kg, K1 = M1·(2·π·f1) 2 =4000×(2×π×0.77) 2 = 9.36E+04N / m.

[0039] Step 4: Subtract the sloshing portion from the liquid level in step 3, and recalculate the liquid level height. The new liquid level height is h. i The calculation formula is: Taking the first storage tank 1 as an example:

[0040] Step 5: Figure 3 This is a schematic diagram of the sloshing mass unit of a liquid-fueled launch vehicle involved in the present invention. Figure 3 As shown, mass elements of the sloshing liquid inside the tank are established in the transverse vibration analysis model of the entire rocket, namely sloshing mass element 5, sloshing mass element 6, sloshing mass element 7, and sloshing mass element 8. The coordinates of the reference nodes for the positions of these mass elements are (X... i The mass element is only effective in the 2nd and 3rd degrees of freedom. Taking the first storage tank 1 as an example: the reference node coordinates of the swaying mass element are (9.42, 0, 0), the swaying mass M1 = 4000 kg is set in the 2nd and 3rd degrees of freedom, and the swaying mass in the other degrees of freedom is zero. That is, the swaying mass is only effective in the Y and Z directions.

[0041] Step 6: Figure 4This is a schematic diagram of the spring connection node modeling method involved in the present invention. For example... Figure 4 As shown, in the transverse vibration analysis model of the whole rocket, a spring connection node of the swaying liquid mass element in the tank is established, and the spring connection node is fixedly connected to the adjacent tank structure node. Taking the first tank 1 as an example: the reference node coordinates of the spring connection node are (9.44, 0, 0), and it is connected to the tank structure node by a rigid connection method.

[0042] Step 7: Figure 5 This is a schematic diagram of the swaying mass spring oscillator model involved in the present invention. Figure 5 As shown, the reference node of the swaying liquid mass unit in step 5 is connected to the spring connection node in step 6 through a spring unit. The reference node is as follows: Figure 5 When the triangle is positioned, the center point below it is the spring connection point. The spring element stiffness value is referenced in step 3. Taking the first storage tank 1 as an example: a transverse spring element is established between the reference node (9.42, 0, 0) of the swaying liquid mass element and the spring connection node (9.44, 0, 0). The spring stiffness K1 = 9.36E+04 N / m only acts on degrees of freedom 2 and 3.

[0043] Step 8: Based on the new liquid level height h obtained in Step 4 i The virtual mass method is used to simulate the remaining liquid in the tank. Taking tank 1 as an example: a local coordinate system parallel to the global coordinate system is established with the theoretical lowest point of the inner edge of the rear bottom of the tank as the origin. The new liquid level height h1 = 2.0m is referenced to this local coordinate system. Then, the shell elements of the rear bottom and cylindrical section of tank 1 are set as single-sided wetted elements with the inner wall wetted, and the liquid density ρ1 = 1000kg / m³. 3 .

[0044] Step 9: Repeat steps 3 to 8, respectively, to treat the swaying liquid in tanks 2, 3 and 4 as equivalent to a transverse spring oscillator model;

[0045] Step 10: Set the parameters for the full-arrow modal analysis, including setting the modal extraction method and modal frequency range, and submit the solution to the finite element analysis software.

[0046] The lateral vibration analysis method for liquid launch vehicles that considers the swaying effect of the present invention has been successfully applied to the development of a new generation of launch vehicles. It accurately predicts the lateral vibration characteristics of the entire rocket and is of great significance to the successful flight test of the new generation of launch vehicles.

[0047] 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 method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects, characterized in that, The liquid-fueled launch vehicle includes a liquid propellant tank, and the liquid inside the tank exhibits a sloshing effect, comprising the following steps: Step 1: Collect a digital prototype model of the solid structure of the launch vehicle and establish a finite element model for the lateral vibration analysis of the entire rocket; Step 2: Collect the structural dimensions of each propellant tank of the launch vehicle and the parameters of the liquid inside the tanks. The structural dimensions of the propellant tanks refer to the inner radius R of the tank cylindrical section. i The liquid parameters in the storage tank refer to the liquid density ρ. i Liquid level height H i First-order swaying mass M i The coordinate X of the first-order wobbling center of mass along the arrow's axis. i First-order oscillation frequency f i , where i is the tank code; Step 3: The first-order sloshing liquid in the tank is equivalent to a transverse spring oscillator model, where the mass of the oscillator is equal to the first-order sloshing mass M of the liquid. i Spring stiffness K i The calculation formula is: K i =M i ·(2·π·f i ) 2 ; Step 4: Subtract the sloshing portion from the liquid level in step 3, and recalculate the liquid level height. The new liquid level height is h. i The calculation formula is: Step 5: Establish a mass element of the sloshing liquid inside the tank in the transverse vibration analysis model of the entire rocket. The position reference node coordinates of the mass element are (X... i ,0,0); Step 6: Establish the spring connection node of the sloshing liquid mass element in the tank in the transverse vibration analysis model of the whole rocket, and fix the spring connection node to the adjacent tank structural node. Step 7: Connect the reference node of the swaying liquid mass unit in Step 5 to the spring connection node in Step 6 through a spring unit. The stiffness value of the spring unit is the same as that in Step 3. Step 8: Based on the new liquid level height h obtained in Step 4 i The virtual mass method was used to simulate the remaining liquid in the tank; Step 9: Repeat steps 3 to 8 to treat all the sloshing liquid in the tanks as equivalent to a transverse spring oscillator model; Step 10: Set the parameters for the full-arrow modal analysis, including setting the modal extraction method and modal frequency range, and submit the solution to the finite element analysis software.

2. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, The lateral vibration refers to the vibration that causes the launch vehicle to bend and deform elastically after being disturbed in a direction perpendicular to the longitudinal direction of the rocket body.

3. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 1, the digital prototype model can accurately describe the actual external dimensions of the solid structure and includes the mechanical property parameters of the materials used, namely material density, elastic modulus, shear modulus and Poisson's ratio.

4. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 1, the finite element model for the transverse vibration analysis of the entire rocket adopts a hybrid modeling approach using three-dimensional solid elements, shell elements, beam elements, and mass elements. The tank structure is simulated using shell elements.

5. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 5, the liquid sloshing mass unit in the tank acts only on two orthogonal transverse translational degrees of freedom, where transverse refers to the direction perpendicular to the arrow body axis.

6. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 6, the spring connection node is established near the center of mass of the swaying object, and the number of structural nodes fixed to it should not be too many. The fixed connection refers to the rigid connection form in the finite element modeling method.

7. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 7, the stiffness property of the spring unit only applies to two orthogonal transverse translational degrees of freedom, where transverse refers to the direction perpendicular to the arrow body axis.

8. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 8, the virtual mass method is used to simulate the remaining liquid in the tank, which requires setting up a wet unit set, liquid density, liquid level height, and liquid level reference coordinate system.

9. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, The liquid-fueled launch vehicle contains four liquid propellant tanks.

10. The method for analyzing the lateral vibration of a liquid-fueled launch vehicle considering swaying effects as described in claim 1, characterized in that, In step 8, a local coordinate system parallel to the global coordinate system is established with the theoretical lowest point of the inner edge of the rear bottom of the tank as the origin. The new liquid level height is referenced to this local coordinate system. Then, the shell unit of the rear bottom of the tank and the cylinder section is set as a single-sided wet unit with the inner wall wetted.

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