A liquid-filled tank liquid-solid coupling refined dynamic modeling method

Abstract

The application provides a liquid-filled tank liquid-solid coupling fine dynamics modeling method, and belongs to the field of spacecraft dynamics modeling analysis. The application is based on ANSYS APDL modeling language, and a "shell+liquid" three-dimensional finite element model of the liquid-filled tank is established through a parameterized modeling method. The three-dimensional finite element model established by the method can realize liquid-solid coupling operation of the shell model and the liquid model, and obtain the liquid-solid coupling mode of the liquid-filled tank. According to actual needs, the liquid top surface can be set as a free liquid surface, and the liquid-filled tank liquid-solid coupling mode and the liquid shaking mode in the liquid-filled tank can be obtained. The liquid model established by the application perfectly simulates the liquid in the tank, so that a more actual liquid-filled tank finite element model is established, and more real modal data of the liquid-filled tank is obtained.

Description

Technical Field

[0001] This invention belongs to the field of spacecraft dynamics modeling and analysis, and relates to a coupled modeling method for tanks and liquid propellants, and more particularly to a refined dynamics modeling method for liquid-solid coupling of liquid-filled tanks. Background Technology

[0002] With increasing demands on the carrying capacity of liquid-propelled rockets, the on-orbit time of satellites, and their maneuverability, the proportion of propellant in the structure of rockets and satellites is constantly increasing. The coupled vibration of liquid propellant and its tank has a growing impact on the normal operation of rockets and satellites. Modern launch vehicles have a large propellant mass and a low sloshing frequency, which is close to the low-order frequencies of the structure. Therefore, the sloshing of liquid propellant within the tank has a significant impact on the motion stability of rockets and satellites.

[0003] Therefore, inventing a modeling method that can accurately reflect the coupling vibration between the liquid propellant and the tank and the sloshing of the liquid propellant within the tank is of great significance for the flight performance and flight safety of rockets and satellites. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a refined dynamic modeling method for liquid-solid coupling of liquid-filled tanks, which can construct a finite element model that accurately reflects the coupling vibration of liquid propellant and tank and the swaying of liquid propellant in tank, and perform dynamic analysis on it to obtain more realistic frequencies and mode shapes of liquid-filled tanks.

[0005] This invention, based on the ANSYS APDL modeling language, establishes a three-dimensional finite element model of a liquid-filled tank using a parametric modeling method, consisting of a shell and liquid. The 3D finite element model established using this method allows for liquid-solid coupling operations on the shell and liquid models to obtain the liquid-solid coupling modes of the liquid-filled tank. Alternatively, a free liquid surface can be set on the top of the liquid surface according to actual needs, simultaneously obtaining the liquid-solid coupling modes and the internal liquid sloshing modes of the liquid-filled tank. The liquid model established by this invention perfectly simulates the liquid inside the tank, thus creating a more realistic finite element model of the liquid-filled tank and obtaining more accurate modal data.

[0006] To achieve the above objectives, the technical solution of this invention is to establish a three-dimensional finite element model of a liquid-filled storage tank that conforms to actual conditions, specifically including the following steps:

[0007] Step 2: Determine the cell type;

[0008] Step 3: Define the element real constants;

[0009] Step 4: Establish the geometric model of the storage tank shell;

[0010] Step 5: Establish the geometric model of the liquid;

[0011] Step 6: Set the number of units and unit attributes, and divide the tank shell and liquid into units respectively;

[0012] Step 7: Set up the liquid-solid contact interface;

[0013] Step 8: Perform liquid-solid node coupling;

[0014] Step 9: Configure the free interface as needed.

[0015] Step 10: Read the APDL modeling command stream file using ANSYS software to achieve refined dynamic modeling of the liquid-solid coupling of the liquid-filled tank.

[0016] Further, step 1 includes: defining the geometric parameters and physical parameters of the model in the / PREP7 preprocessing module of the ANSYS APDL modeling software. The geometric parameters include: the radius and thickness of the tank, the height of each section, and the height of the liquid inside. The physical parameters include: the elastic modulus, Poisson's ratio, and density of the tank, and the density and acoustic properties of the liquid.

[0017] Furthermore, step 2 includes: setting up a rocket propellant tank using a SHELL 281 unit; and using a FLUID 220 unit to simulate the liquid inside the propellant tank.

[0018] Furthermore, step 3 includes: the unit real constants include the wall thickness of the shell and the liquid pressure of the FLUID 220 unit.

[0019] Furthermore, step 4 includes: establishing a point, line, and surface geometric model of the storage tank structure according to the geometric dimensions of the storage tank. The points are established at the middle position of the storage tank wall thickness, and the lines connect the points at the middle position. Then, the surface of the storage tank is established based on the lines. This surface is the outer shell of the storage tank, thereby establishing a closed storage tank geometric model.

[0020] Furthermore, step 5 includes: establishing a geometric model of the liquid inside the tank. The nodes on the periphery of the liquid model need to coincide with the nodes of the previously established tank shell to ensure that when the liquid and the tank are coupled in a liquid-solid manner, the nodes at the contact point between the shell model and the liquid model coincide.

[0021] Furthermore, step 6 includes: setting the number of elements and element attributes for the lines constituting the tank shell and the internal liquid, respectively, to perform mesh generation. At the contact points, the number of elements for the tank shell and the number of elements for the liquid need to be consistent, so as to ensure that the nodes at the contact points of the shell model and the liquid model coincide after mesh generation.

[0022] Furthermore, step 7 includes: for the contact surfaces where the liquid model and the shell model are in contact, selecting the face of the liquid model, then selecting the nodes on these faces, and using the "FSI" command of the "SF" command on these faces to set these faces as the contact interfaces in contact with the solid phase.

[0023] Furthermore, step 8 includes: for the contact surfaces where the liquid model and the shell model come into contact, both types of surfaces are selected. Using the method used in the previous modeling, the nodes on these surfaces are overlapping. Therefore, the nodes on these surfaces are selected, and the nodes on both types of surfaces are coupled together using the "CP" command to establish the liquid-solid coupling model of the liquid-filled tank.

[0024] Furthermore, step 9 includes: For the top of the liquid, except in the case where the liquid completely fills the tank, the top of the liquid surface can sway freely. Therefore, when it is necessary to analyze the liquid swaying mode, the "FREE" command of the "SF" command can be used to set the top surface of the liquid as a free interface.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) This invention proposes a refined dynamic modeling method for liquid-solid coupling of a "shell + liquid" filled tank, which can accurately reflect the coupling vibration of the liquid propellant and the tank and the swaying of the liquid propellant in the tank, and obtain the frequency and mode shape of the filled tank that are more in line with reality.

[0027] (2) This invention establishes an accurate liquid propellant model, which accurately simulates the dynamic characteristics of the propellant and improves the accuracy of rocket structural dynamic characteristic analysis. By coupling the liquid propellant with the tank shell unit, it realizes the simultaneous simulation of different effects of the propellant in lateral, longitudinal and torsional motions, laying the foundation for realizing integrated longitudinal, lateral and torsional modeling of rockets, and can be further extended to the calculation of longitudinal and lateral loads of launch vehicles, improving the efficiency of modeling and analysis.

[0028] (3) In this invention, FLUID 220 elements are used to simulate the liquid propellant in the launch vehicle's propellant tank for liquid-solid coupling modal analysis. Previously, liquid-solid coupling modal analysis in ANSYS software typically used FLUID 80 elements to simulate the liquid. There are significant differences between the simulation method using FLUID 220 elements and the simulation method using FLUID 80 elements in handling the liquid-solid interface and the liquid-free interface; the latter is easier. However, current versions of ANSYS software no longer support the use of FLUID 80 elements for liquid-solid coupling modal analysis. Therefore, the method of this invention can be used in all current versions of ANSYS software. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the refined dynamic modeling method for liquid-solid coupling in a liquid-filled tank according to the present invention.

[0030] Figure 2 This is a TXT text file in command stream format for shell and liquid elements defined using the ANSYS APDL language.

[0031] Figure 3 A geometric model diagram of the storage tank shell;

[0032] Figure 4 A geometric model diagram of the liquid being constructed;

[0033] Figure 5 A TXT text file in command stream format for setting up the liquid-solid interface, defined using the ANSYS APDL language.

[0034] Figure 6 This is a TXT text file in the command stream format defined using the ANSYS APDL language for coupling between liquid and solid nodes.

[0035] Figure 7 A three-dimensional model diagram showing the coupling of the tank shell and the liquid.

[0036] Figure 8 A TXT text file in the command stream format for setting up a liquid free interface, defined using the ANSYS APDL language.

[0037] Figure 9 The mode shapes are shown for the first, second, and third bending modes of the fluid-solid coupling model.

[0038] Figure 10 The mode shape of the liquid sloshing mode is captured after setting a free interface for the model. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0040] To obtain more realistic modal and dynamic response predictions for liquid-filled tanks, this invention discloses a refined dynamic modeling method for liquid-solid coupling in liquid-filled tanks based on the ANSYS APDL modeling language. First, in the preprocessing stage, the geometric and physical parameters of the model are defined. Then, the element type is determined, and real constants are defined. Next, geometric models of the tank shell and the liquid are established, and element meshing is performed on the tank shell and the liquid respectively. Then, the liquid-solid contact interface is set, and liquid-solid node coupling is performed. Free interfaces are then set as needed. Finally, the APDL modeling command stream file is read by ANSYS software to achieve refined dynamic modeling of the liquid-solid coupling in the liquid-filled tank.

[0041] The method of the present invention specifically includes the following steps:

[0042] Step 1: Define the geometric and physical parameters of the model.

[0043] Step 1 includes: in the / PREP7 preprocessing module of the ANSYS APDL modeling software, defining the material's property parameters using the "MP" command. The property parameters include: the elastic modulus, Poisson's ratio, and density of the tank, and the density and acoustic properties of the liquid.

[0044] Step 2: Determine the cell type.

[0045] Step 2 includes: using the “ET” command to determine the cell type, using the SHELL 281 cell to simulate the rocket's propellant tank, and using the FLUID 220 cell to simulate the liquid inside the propellant tank.

[0046] Considering that the liquid has a free surface and a small sloshing speed, the liquid can be assumed to be an incompressible fluid. That is, by setting the KEYOPT(6) of the FLUID 220 unit to 1, it is indicated that the sound speed is equivalent to an incompressible fluid with an infinite velocity, thus determining that the liquid is an incompressible fluid.

[0047] Step 3: Define the element real constants;

[0048] Step 3 includes defining the cell real constants using the “R” command. The cell real constants include the wall thickness of the tank shell represented by the SHELL 281 cell and the liquid pressure of the liquid represented by the FLUID 220 cell.

[0049] Step 4: Establish the geometric model of the tank shell.

[0050] Step 4 includes: using the "K" command to establish key points, determining the bottom, height, and points on a boundary line of the tank. Since the tank has a wall thickness, the key points are established at the middle of the wall thickness.

[0051] Furthermore, the keypoints are connected to generate lines using the "L" command. Connecting these keypoints in sequence yields a boundary line for the tank.

[0052] Furthermore, by using the "AROTAT" command, these lines are rotated around the central axis of the tank to obtain surfaces, which constitute the shell of the tank.

[0053] Step 5: Establish the geometric model of the liquid.

[0054] Step 5 includes: similar to step 3, establishing the liquid inside the tank using the "K" command, "L" command, "A" command, and "VROTAT" command.

[0055] The key point of the liquid established by the "K" command is also established at the midpoint of the tank wall thickness, that is, the key point of the liquid coincides with the key point of the tank shell, and the key point of the liquid top is established according to the actual height of the liquid.

[0056] Step 6: Set the number of units and unit attributes for the tank and liquid, and divide the tank shell and liquid into units respectively.

[0057] Step 6 includes: using the "LSEL" command to select the lines representing the tank and the liquid respectively; using the "LESIZE" and "LATT" commands to set the number of elements and element properties for the tank shell and the liquid respectively; using the "MSHAPE" command to determine the element shape of the mesh, defining the tank shell as a 2D model and the liquid as a 3D model; and finally using the "MSHKEY" command to determine the type of mesh generation, thus completing the mesh generation. It is important to note that at the contact point between the tank and the liquid, the number of elements in the tank shell and the liquid mesh must be consistent, ensuring that the nodes at the contact point of the outer shell model and the liquid model coincide.

[0058] Step 7: Set up the liquid-solid contact interface.

[0059] Step 7 includes: For the contact surfaces where the liquid model and the shell model are in contact, use the "ASEL" command to select the faces of the liquid model, then use the "NSLA" command to select the nodes on these faces, and use the "SF" command's "FSI" command on these faces to set these faces as the contact interfaces with the solid phase.

[0060] Step 8: Perform liquid-solid node coupling.

[0061] Step 8 includes: For the contact surfaces where the liquid model and the shell model come into contact, use the "ASEL" command to select both types of surfaces. Since the nodes on these surfaces overlap using the method used in the previous modeling, use the "NSLA" command to select the nodes on these surfaces together. Use the "CP" command to couple the nodes on both types of surfaces to establish the liquid-solid coupling model of the liquid-filled tank.

[0062] Step 9: Configure the free interface as needed.

[0063] Step 9 includes: For the top of the liquid, except when the liquid is completely filled in the tank, the top of the liquid surface can sway freely. Therefore, when it is necessary to analyze the liquid sway mode, the "NSEL" command can be used to select the nodes on the top surface of the liquid, and then the "SF" command's "FREE" command can be used on these nodes to set the top surface of the liquid as a free interface.

[0064] Step 10: Read the APDL modeling command stream file using ANSYS software to achieve refined dynamic modeling of the liquid-solid coupling in the liquid-filled tank.

[0065] The finite element modeling method implemented in steps 1 to 10 is applied to the structural dynamics of liquid-filled tanks to construct a finite element model that can accurately reflect the coupling vibration between the liquid propellant and the tank and the swaying of the liquid propellant inside the tank. Dynamic analysis is then performed on the model to obtain frequencies and mode shapes of the liquid-filled tank that are more consistent with actual conditions.

[0066] The following describes the solution of the present invention with specific examples.

[0067] Example 1

[0068] like Figure 1 As shown in the figure, this embodiment provides a refined dynamic modeling method for liquid-solid coupling in a liquid-filled tank, including the following steps:

[0069] Step 1: Define the geometric and physical parameters of the model.

[0070] Enter the / PREP7 preprocessing module of the ANSYS APDL modeling software and define the material's property parameters using the "MP" command. These property parameters include: the tank's elastic modulus, Poisson's ratio, density, the liquid's density, and acoustic properties.

[0071] The defined geometric and physical parameters are as follows:

[0072] The storage tank has a radius of 1.9m, a total height of 20m, a hemispherical height of 1.3m at the bottom and top, a length of 17.4m in the middle, a shell thickness of 0.03m, and a liquid height of 18.7m inside the tank.

[0073] The tank material has an elastic modulus E = 71 GPa, a Poisson's ratio υ = 0.33, and a density ρ = 2810 kg / m³. 3 ;

[0074] The density of the liquid material is ρ = 800 kg / m³ 3 The speed of sound in this material is v = 1324 m / s;

[0075] Step 2: Determine the cell type.

[0076] like Figure 2 As shown, the unit types for the tank shell and the liquid are established using the "ET" command. The SHELL 281 unit is used to simulate the launch vehicle tank; the FLUID 220 unit is used to simulate the liquid inside the tank. By setting the KEYOPT(6) of the FLUID 220 unit to 1, it is determined that the liquid is an incompressible fluid with an equivalent sound speed approaching infinity.

[0077] Step 3: Define the unit real constants.

[0078] The cell real constants are defined using the “R” command. The cell real constants include the wall thickness of the tank shell represented by the SHELL 281 cell and the liquid pressure represented by the FLUID 220 cell.

[0079] The thickness of the tank, 0.03 m, is defined as real constant 1. The pressure of the liquid is limited to between 0.00002 Pa and 101325 Pa, and this number is defined as real constant 2.

[0080] Step 4: Establish the geometric model of the tank shell.

[0081] Step 4 includes: using the "K" command to create key points on the bottom, height, and one of the boundary lines of the tank. Since the tank shell has thickness, the key points are created in the middle of the tank shell.

[0082] Furthermore, the keypoints are connected to generate lines using the "L" command. Connecting these keypoints in sequence yields a boundary line for the tank.

[0083] Furthermore, by using the "AROTAT" command to rotate these lines around the central axis of the tank, surfaces are obtained; these surfaces form the shell of the tank, such as... Figure 3 As shown.

[0084] Step 5: Establish the geometric model of the liquid.

[0085] Similar to step 3, use the "K" command to create key points for the liquid model, use the "L" command to connect these key points in sequence, use the "A" command to create a face on one side of the tank's central axis, and finally use the "VROTAT" command to rotate this face around the model's central axis to create the liquid model inside the tank. Figure 4 As shown.

[0086] The key point of the liquid established by the "K" command is also established at the midpoint of the tank shell, that is, the key point of the liquid coincides with the key point of the tank shell, and the height of the key point at the top of the liquid is 18.7m.

[0087] Step 6: Set the number of units and unit attributes for the tank and liquid, and divide the tank shell and liquid into units respectively.

[0088] The mesh is created by selecting the lines representing the tank and the liquid using the "LSEL" command, setting the number of elements and element properties for the tank shell and liquid using the "LESIZE" and "LATT" commands respectively, determining the element shape of the mesh using the "MSHAPE" command, defining the tank shell as a "2D" model and the liquid as a "3D" model, and finally determining the mesh type using the "MSHKEY" command. It is crucial that the number of elements in the tank shell and liquid meshes at their contact points be consistent, ensuring that the nodes at the contact points of the shell and liquid models coincide.

[0089] Step 7: Set up the liquid-solid contact interface.

[0090] like Figure 5 As shown, for the contact surfaces where the liquid model and the shell model come into contact, use the "ASEL" command to select the faces of the liquid model, then use the "NSLA" command to select the nodes on these faces, and use the "SF" command's "FSI" command on these faces to set these faces as the contact interfaces with the solid phase.

[0091] Step 8: Perform liquid-solid node coupling.

[0092] like Figure 6 As shown, for the contact surfaces where the liquid model and the shell model meet, the "ASEL" command is used to select both types of surfaces. Using the method from the previous modeling, the nodes on these surfaces overlap, so the "NSLA" command is used to select all the nodes on these surfaces together. Then, the "CP" command is used to couple the nodes on both types of surfaces, thus establishing the liquid-solid coupling model of the liquid-filled tank. Figure 7This is a model diagram showing the coupling of the tank shell and the liquid together.

[0093] Step 9: Configure the free interface as needed.

[0094] Except when the tank is completely filled, the top of the liquid surface can move freely. Therefore, when analyzing the liquid sloshing mode, such as... Figure 8 As shown, you can use the "NSEL" command to select nodes on the top surface of the liquid, and then use the "FREE" command of the "SF" command on these nodes to set the top surface of the liquid as a free interface.

[0095] Step 10: Use ANSYS software to read the command stream file of the above APDL modeling to realize the modeling of the refined dynamic model of the liquid-solid coupling of the liquid-filled tank.

[0096] Then, modal analysis was performed on the model to obtain the mode shape and frequency of the liquid-filled tank. Figure 9 The vibration mode diagrams are for the first, second, and third bending modes of the fluid-solid coupling model.

[0097] If it is necessary to obtain the sloshing modes of the liquid inside the tank, a free interface can be set for the liquid as described in step 9, and then modal analysis can be performed. This will yield a large number of liquid sloshing modes. Of course, the mode shapes obtained at the corresponding frequencies are still those obtained without setting a free interface, which are liquid-solid coupling mode shapes. Figure 10 The image shows the mode shape of the extracted liquid sloshing mode.

[0098] Although embodiments of the invention have been described, it will be understood by those skilled in the art that various modifications, variations, substitutions, and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0099] This invention provides a refined dynamic modeling method for liquid-solid coupling in a liquid-filled tank. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A refined dynamic modeling method for liquid-solid coupling in a liquid-filled storage tank, characterized in that, The method is as follows: Step 1: Define the geometric and physical parameters of the model; Step 1 specifically includes: in the / PREP7 preprocessing module of the ANSYS APDL modeling software, defining the geometric and physical parameters of the model. The geometric parameters include: the radius and thickness of the tank, the height of each section, and the height of the liquid inside; the physical parameters include: the elastic modulus, Poisson's ratio, and density of the tank, and the density and acoustic properties of the liquid. Step 2: Determine the cell type; Step 2 specifically includes: setting the rocket's propellant tank to use a SHELL 281 cell; and using a FLUID 220 cell to simulate the liquid inside the propellant tank. Step 3: Define the unit real constants; in Step 3, the unit real constants include the wall thickness of the shell and the liquid pressure of the FLUID 220 unit; Step 4: Establish the geometric model of the storage tank shell; Step 5: Establish the geometric model of the liquid; Step 6: Set the number of units and unit attributes for the meshing, and perform unit meshing on the tank shell and the liquid respectively; Step 6 specifically includes: setting the number of units and unit attributes for the lines that constitute the tank shell and the internal liquid respectively, thereby performing meshing, and at the contact position, the number of units for the tank shell and the liquid need to be consistent, that is, to ensure that after the shell model and the liquid model are meshed, the nodes at the contact position coincide together; Step 7: Set the liquid-solid contact interface; Step 7 specifically includes: for the contact surface between the liquid model and the shell model, select the face of the liquid model, then select the nodes on the face, and use the FSI command of the SF command on these nodes to set these faces as the contact interface with the solid phase. Step 8: Perform liquid-solid node coupling; Step 8 specifically includes: For the contact surfaces where the liquid model and the shell model come into contact, select both types of surfaces. Using the method used in the previous modeling, the nodes on these surfaces are overlapping. Therefore, select the nodes on these surfaces and use the CP command to couple the nodes on both types of surfaces to establish the liquid-solid coupling model of the liquid-filled tank. Step 9: Set the free interface as needed; Step 9 specifically includes: For the top of the liquid, except when the liquid is completely filled in the tank, the top of the liquid surface can sway freely. When it is necessary to analyze the liquid swaying mode, use the FREE command of the SF command to set the top surface of the liquid as a free interface. Step 10: Read the APDL modeling command stream file using ANSYS software to achieve refined dynamic modeling of the liquid-solid coupling of the liquid-filled tank.

2. The refined dynamic modeling method for liquid-solid coupling in a liquid-filled storage tank according to claim 1, characterized in that, Step 4 specifically includes: establishing a point, line, and surface geometric model of the storage tank structure according to the geometric dimensions of the storage tank. The points are established at the middle position of the storage tank wall thickness, and the lines connect the points at the middle position. Then, the surface of the storage tank is established based on the lines. This surface is the outer shell of the storage tank, thereby establishing a closed storage tank geometric model.

3. The refined dynamic modeling method for liquid-solid coupling in a liquid-filled storage tank according to claim 1, characterized in that, Step 5 specifically includes: establishing a geometric model of the liquid inside the tank. The nodes on the periphery of the liquid model need to coincide with the nodes on the previously established tank shell to ensure that when the liquid and the tank are coupled in a liquid-solid manner, the nodes at the contact point between the shell model and the liquid model coincide.

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