Liquid multimodal rotational sloshing experimental device and method based on six-degree-of-freedom platform

Abstract

The present application relates to the field of complex spacecraft coupling dynamics and control technology, in particular to a liquid multimode rotational sloshing experimental device and method based on a six-degree-of-freedom platform, comprising: a six-degree-of-freedom platform, a load support frame (4), an ellipsoidal Cassini tank (5), a pressure acquisition system and a three-dimensional depth camera (7); wherein the six-degree-of-freedom platform is used to control the load support frame (4) on it to simulate the six-degree-of-freedom motion attitude of the rocket in space, and the ellipsoidal Cassini tank (5) is fixed inside the load support frame (4) and moves together with the load support frame (4); the present application simulates the multidimensional vibration effect of the rocket under the influence of high-altitude aerodynamic disturbance force and the changing thrust of the liquid engine; not only the experimental phenomenon is closer to the actual situation, but also it can provide reference for actual engineering as a ground preliminary research project.

Description

Technical Field

[0001] This invention relates to the field of coupled dynamics and control technology for complex spacecraft, and in particular to an experimental apparatus and method for liquid multimodal rotational swaying based on a six-degree-of-freedom platform. Background Technology

[0002] In modern aerospace, launch vehicles typically carry a large amount of liquid propellant, which accounts for about 90% of the total launch mass, such as China's Long March series launch vehicles and SpaceX's Falcon 9 series rockets. During flight, rockets are affected by high-altitude aerodynamic disturbances, varying engine thrust, and weightlessness, which can easily induce small-amplitude / nonlinear sloshing of the liquid propellant in the rocket's tanks. This causes low-frequency coupled vibrations between the liquid propellant and the rocket's rigid body, directly affecting the rocket's flight attitude and payload orbital accuracy. Furthermore, under weightlessness, low-frequency coupled vibrations can cause the liquid propellant to exhibit low-speed rotational sloshing, causing it to deviate from the fuel outlet at the bottom of the tank. In this case, some pressurized gas enters the liquid engine piping, leading to gas-liquid mixing and causing malfunctions in the liquid engine, sometimes even resulting in the failure of the entire launch mission. Therefore, liquid propellant management has always been a critical issue in modern aerospace, and in recent years, numerous scholars both domestically and internationally have made progress in addressing the problem of liquid propellant sloshing.

[0003] Currently, ground-based experiments are a cost-effective and widely used research method for studying liquid propellant sloshing. Relevant references are as follows:

[0004] Reference [1] (Abramson H N. The dynamic behavior of liquids in moving containers [R]. NASA SP-106. NASA Special Publication, 1966.) conducted a system experiment on small-amplitude shaking of various regular tank structures such as cylindrical and rectangular tanks under normal ground weight conditions, and obtained the relationship between the excitation frequency f and some experimental phenomena, as well as the parameters of the anti-sway baffle.

[0005] Reference [2] (Li Xu. Mechanical performance analysis of float-type anti-sloshing structure in fuel tank [D]. Harbin: Harbin Institute of Technology, 2016.) explored the effect of covering the free liquid surface of a cylindrical tank with a layer of various floats on the suppression of liquid sloshing from the perspective of passive control of liquid sloshing through a ground scale model experiment.

[0006] Reference [3] (Jin Yulin. Dynamics analysis of liquid sloshing in a storage tank with a novel anti-sloshing structure [D]. Harbin: Harbin Institute of Technology, 2013.) used a ground horizontal vibrator to apply sinusoidal excitation to a flat rectangular storage tank and explored the anti-sloshing effect of a novel "cross-shaped" blade structure that can rotate around a fixed axis.

[0007] Reference [4] (Wu Wenjun, Gao Chaonan, Yue Baozeng, et al. Experiment and dynamic characteristics analysis of nonlinear steady-state sloshing of liquid in cylindrical tank [J]. Journal of Astronautics, 2021, 42(09): 1078-1089.) designed an experimental device for accurate measurement of dynamic sloshing force and sloshing torque of liquid in cylindrical tank. The device uses a horizontal exciter to apply excitation to the cylindrical tank and explores the numerical values ​​of dynamic sloshing force and sloshing torque of liquid under two states: non-rotational sloshing and rotational sloshing.

[0008] Reference [5] (Zhang Haitao, Sun Beibei, Chen Jiandong, et al. Experimental study on large-scale nonlinear sloshing of liquid in moving container [J]. Journal of Southeast University (Natural Science Edition), 2017, 47(01): 33-37.) By applying transverse harmonic excitation to a rectangular liquid-filled tank using a horizontal exciter, the experiment investigated the slapping and resonance phenomena of the liquid in the tank, and measured the liquid pressure time history at a certain point on the side wall of the container using a pressure sensor.

[0009] Reference [6] (Berry RL, Tegart J R. Experimental study of transient liquidmotion in orbiting spacecraft[R]. NASA final Report, NASA-CR-144213, 1976.) proposed using a drop tower experiment to suddenly apply a constant horizontal acceleration excitation to a small Cassini tank falling at a constant acceleration, observe the sloshing law of the liquid in the tank, and conduct a reasonable analysis.

[0010] While many scholars have made good progress in addressing the problem of liquid sloshing, few have conducted systematic research on the issue of low-speed rotational sloshing of liquid propellant deviating from the central fuel outlet. For ground-based scaled-down model experiments, existing research largely utilizes horizontal exciters to apply sinusoidal excitation to regular propellant tanks (cubic prisms, cylinders, etc.) to observe some experimental phenomena and data. However, in actual engineering, propellant tanks are typically ellipsoidal Cassini tank structures, meaning the middle section is cylindrical and the ends are semi-ellipsoidal. Furthermore, current technology using horizontal exciters can only achieve two-dimensional vibration effects of the propellant liquid, such as traveling waves and standing waves, and cannot simulate the actual conditions during rocket flight. Summary of the Invention

[0011] The purpose of this invention is to overcome the problem that existing technologies can only achieve two-dimensional vibration effects of liquid in a storage tank and cannot simulate the real situation during rocket flight. Therefore, this invention proposes a liquid multimodal rotational swaying experimental device and method based on a six-degree-of-freedom platform.

[0012] To address the various shortcomings of the existing technologies, the present invention aims to provide a liquid multimodal rotational sloshing experimental device and method based on a six-degree-of-freedom platform. This invention can effectively simulate the multimodal rotational sloshing phenomenon of real liquid propellants. By changing the input peak value D, frequency f, and phase angle θ of the six electric cylinders through the six-degree-of-freedom platform control cabinet 9, the six-degree-of-freedom servo electric cylinder component 3 can drive the liquid to exhibit multimodal rotational sloshing phenomena. This allows for the acquisition of important parameter information such as the peak value of the liquid surface rotational sloshing and the fixed-point dynamic pressure on the inner wall of the tank. This fills the research gap in the existing technology regarding liquid rotational sloshing and addresses the complex parameter problem of obtaining the sloshing law of liquid within the tank, aiming to provide a reference for practical engineering applications.

[0013] This invention provides a liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform, comprising: a six-degree-of-freedom platform, a load support frame 4, an ellipsoidal Cassini tank 5, a pressure acquisition system, and a three-dimensional depth camera 7; wherein,

[0014] The six-degree-of-freedom platform is used to control the load support frame 4 on it to simulate the six-degree-of-freedom motion attitude of the rocket in space. The ellipsoidal Cassini tank 5 is fixed inside the load support frame 4 and moves together with the load support frame 4. The six-degree-of-freedom motion attitude in space includes: the rocket's lateral, longitudinal, vertical, pitch, yaw and roll motion attitudes.

[0015] The pressure acquisition system is used to acquire the pressure value of the liquid in the ellipsoidal Cassini tank 5 in real time; and

[0016] The three-dimensional depth camera 7 is used to collect the height of the liquid surface rotation and sloshing through the camera observation hole 58 set on the top of the ellipsoidal Cassini tank 5.

[0017] As an improvement to the aforementioned device, the six-degree-of-freedom platform includes: a worktable 1, a parallel pressure plate 2, a six-degree-of-freedom servo electric cylinder component 3, and a six-degree-of-freedom platform control cabinet 9; wherein,

[0018] The six-degree-of-freedom servo electric cylinder component 3 is fixed to the worktable 1 by a parallel pressure plate 2;

[0019] The load support frame 4 is fixed on the load platform 35 of the six-degree-of-freedom servo electric cylinder component 3, so that its motion posture is the same as that of the load platform 35.

[0020] The six-degree-of-freedom servo electric cylinder component 3, under the control of the six-degree-of-freedom platform control cabinet 9, is used to simulate the six-degree-of-freedom motion posture in space; the ellipsoidal Cassini tank 5, driven by the load support frame 4, maintains the same motion posture as the load platform 35.

[0021] As an improvement to the above-mentioned device, the six-degree-of-freedom platform control cabinet 9 is used to set the vibration peak value D, vibration frequency f and phase angle θ of each servo electric cylinder 32 in the six-degree-of-freedom servo electric cylinder component 3, so that the six-degree-of-freedom servo electric cylinder component 3 can simulate the motion posture of six degrees of freedom in space.

[0022] As an improvement to the aforementioned device, the six-degree-of-freedom servo electric cylinder component includes: a lower base 31, six servo electric cylinders 32, an upper universal joint 33, a lower universal joint 34, and a load platform 35; wherein...

[0023] The lower base 31 is fixedly connected to the workbench 1 via a parallel pressure plate 2;

[0024] The six servo electric cylinders 32 are configured as three groups of servo electric cylinders 32 spaced 120 degrees apart. Each group consists of two closely adjacent servo electric cylinders 32, which are arranged together above the lower base 31. Their lower ends are connected to the lower base 31 through the lower universal joint 34, and their upper ends are connected to the load platform 35 through the upper universal joint 33.

[0025] As an improvement to the above-mentioned device, the load support frame 4 includes: a support plate 41, a plurality of support profiles 42, four arc-shaped connectors 44, and a support plate-load platform fixing assembly 45;

[0026] The support plate 41 is fixed above the load platform 35 by the support plate-load platform fixing assembly 45;

[0027] The plurality of supporting profiles 42 form an inner and outer square frame; the outer square frame is used to bind the power cable and signal cable of the three-dimensional depth camera 7; the inner square frame is fixed on the support plate 41.

[0028] The four arc-shaped connectors 44 are arranged in a cross shape and fixed to the inner side of the horizontal beam of the inner square frame. They are used to clamp the ellipsoidal Cassini tank 5, so that the ellipsoidal Cassini tank 5 maintains the same motion posture as the load platform 35 under the drive of the load support frame 4, and keeps the bottom of the ellipsoidal Cassini tank 5 in a suspended state.

[0029] As an improvement to the above-mentioned device, the arc-shaped connector 44 is composed of an arc-shaped support base 441, a telescopic screw 442, and an arc-shaped fitting piece 443. The telescopic screw 442 has a threaded structure and is screwed onto the axis of the arc-shaped support base 441 and the arc-shaped fitting piece 443. The arc-shaped support base 441 is fixed to the inner side of the horizontal beam of the inner square frame. By adjusting the nut on the telescopic screw 442, the arc-shaped fitting piece 443 and the ellipsoidal Cassini tank 5 are fitted together.

[0030] As an improvement to the above-mentioned device, the ellipsoidal Cassini tank 5 includes: an upper cover and a lower tank; wherein, the upper cover and the lower tank are connected by a flange ring 51, and the flange ring 51 has a plurality of evenly distributed through holes 52, and the upper cover and the lower tank structure of the ellipsoidal Cassini tank 5 are assembled together by bolt assemblies passing through the through holes 52.

[0031] The ellipsoidal Cassini tank 5 has two pressure holes 53 on its side wall, and the probe part of the pressure sensor 61 of the pressure acquisition system is installed in the two pressure holes 53.

[0032] The top of the ellipsoidal Cassini tank 5 is provided with a camera observation hole 58 and several bolt through holes. The three-dimensional depth camera 7 is fixed to the top of the ellipsoidal Cassini tank 5 by bolt assembly and bolt through holes, and acquires images of the liquid level inside the ellipsoidal Cassini tank 5 through the camera observation hole 58.

[0033] As an improvement to the above-mentioned device, the device further includes: an annular baffle 54, a vertical through groove 55, a chain 56, and a membrane float 57; wherein...

[0034] The annular baffle 54 is perpendicular to the axial direction of the ellipsoidal Cassini tank 5 and is fixed to the lower inner side of the ellipsoidal Cassini tank 5; wherein, the outer edge of the annular baffle 54 is fixed to the inner wall of the cylindrical section of the ellipsoidal Cassini tank 5.

[0035] The inner wall of the ellipsoidal Cassini tank 5 is provided with vertical through grooves 55 at 90° intervals; the height of the vertical through grooves 55 is less than or equal to the height of the cylindrical section of the ellipsoidal Cassini tank 5.

[0036] One end of the ring chain 56 is fitted into the vertical through groove 55 and moves freely up and down along the axis of the ellipsoidal Cassini tank 5; the other end of the ring chain 56 is connected to the membrane float 57 through a through hole.

[0037] The thin-film float 57 floats on the liquid surface inside the ellipsoidal Cassini tank 5 and moves together with the liquid surface.

[0038] As an improvement to the aforementioned device, the pressure acquisition system includes: a pressure sensor 61 and an intelligent data acquisition unit 62; wherein,

[0039] The pressure sensor 61 is a piezoresistive pressure sensor, and its probe is installed in the pressure hole 53 on the side wall of the ellipsoidal Cassini tank 5.

[0040] The pressure sensor 61 transmits the liquid pressure value to the computer 8 via the intelligent data acquisition instrument 62.

[0041] To achieve another objective of the present invention, the present invention also provides a method for conducting a liquid multimodal rotational swaying experiment based on a six-degree-of-freedom platform, implemented using the aforementioned liquid multimodal rotational swaying experiment apparatus based on a six-degree-of-freedom platform, comprising the following steps:

[0042] Step 1) Reset the six-degree-of-freedom servo electric cylinder component 3;

[0043] Step 2) Based on the motion posture requirements of the experimental platform, set the simulation parameters of the six-degree-of-freedom servo electric cylinder component 3, wherein the simulation parameters include: vibration peak value D, vibration frequency f and phase angle θ of each servo electric cylinder 32;

[0044] Step 3) Determine whether the simulation parameters exceed the system range of the six-degree-of-freedom servo electric cylinder component 3. If yes, reset the simulation parameters. If no, control the six-degree-of-freedom servo electric cylinder component 3 to work based on the simulation parameters through the six-degree-of-freedom platform control cabinet 9.

[0045] Step 4) After the liquid movement pattern in the ellipsoidal Cassini tank 5 becomes obvious, the three-dimensional depth camera 7 is used to measure the rotational sloshing distance of the liquid to obtain the rotational sloshing height of the liquid surface, and the pressure value of the liquid in the ellipsoidal Cassini tank 5 is measured using a pressure acquisition system.

[0046] The liquid multimodal rotational swaying experimental device and method based on a six-degree-of-freedom platform described in this invention has the following advantages compared with the prior art:

[0047] 1) The present invention provides a liquid multimodal rotational swaying experimental device and method based on a six-degree-of-freedom platform. The experimental excitation device adopts a six-degree-of-freedom servo electric cylinder component 3. Compared with the use of a horizontal exciter to realize the two-dimensional small-amplitude swaying of the liquid in the tank, the present invention can better simulate the multi-dimensional (lateral, longitudinal, vertical, pitch, yaw, roll) vibration effects of a rocket under the influence of high-altitude aerodynamic interference forces and the changing thrust of the liquid engine.

[0048] 2) The experimental device and method for liquid multimodal rotation and swaying based on a six-degree-of-freedom platform described in this invention uses a scaled-down ellipsoidal Cassini tank 5. Compared with flat rectangular and cylindrical tanks, this invention is closer to the liquid propellant tanks used in actual engineering. Not only are the experimental phenomena closer to the real situation, but it can also serve as a ground-based preliminary research project to provide reference for actual engineering.

[0049] 3) The liquid multimodal rotational sloshing experimental device and method based on a six-degree-of-freedom platform described in this invention adopts a combination of a six-degree-of-freedom servo electric cylinder component 3 and an ellipsoidal Cassini tank 5. The six-degree-of-freedom platform control cabinet 9 sets the vibration peak value D, vibration frequency f and six independent phase angles θ of the six-degree-of-freedom servo electric cylinder component 3, so that the liquid in the tank exhibits a multimodal rotational sloshing phenomenon, which solves the problem that it is difficult to simulate this sloshing phenomenon in ground experiments.

[0050] 4) The liquid multimodal rotational sloshing experimental device and method based on a six-degree-of-freedom platform described in this invention utilizes a three-dimensional depth camera 7 to measure the peak value h of the rotational sloshing of the liquid surface in the tank, and two pressure sensors 61 to measure the fixed point dynamic pressure P during the liquid sloshing process in the tank, thereby fully acquiring experimental data during the liquid sloshing process in the tank. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of a liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform in an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram showing the overall system operation of the experimental apparatus in this embodiment of the invention;

[0053] Figure 3 This is a schematic diagram of the structure of the six-degree-of-freedom servo electric cylinder in an embodiment of the present invention;

[0054] Figure 4 This is a schematic diagram of the load support (arc-shaped connector) structure in an embodiment of the present invention;

[0055] Figure 5(a) is a schematic diagram of the ellipsoidal Cassini tank structure in an embodiment of the present invention;

[0056] Figure 5(b) is a cross-sectional view of the ellipsoidal Cassini tank along AA in Figure 5(a);

[0057] Figure 6(a) is a schematic diagram of the ellipsoidal Cassini tank with annular baffle structure in an embodiment of the present invention;

[0058] Figure 6(b) is a cross-sectional view of the ellipsoidal Cassini tank with an annular baffle along AA in Figure 6(a);

[0059] Figure 7(a) is a schematic diagram of the ellipsoidal Cassini tank structure with a thin-film float in an embodiment of the present invention;

[0060] Figure 7(b) is a cross-sectional view of the ellipsoidal Cassini tank structure with a thin-film float along AA in Figure 7(a);

[0061] Figure 7(c) is a cross-sectional view of the ellipsoidal Cassini tank structure with a thin-film float along BB in Figure 7(a);

[0062] Figure 8 This is a flowchart of the liquid multimodal rotation and shaking experiment operation in an embodiment of the present invention;

[0063] Figure 9 This is a graph showing the relationship between the excitation frequency of the liquid multimodal rotational sloshing and the peak value of the liquid surface in an embodiment of the present invention.

[0064] Figure 10(a) is a first schematic diagram of the six-degree-of-freedom platform control cabinet in an embodiment of the present invention;

[0065] Figure 10(b) is a second schematic diagram of the six-degree-of-freedom platform control cabinet in an embodiment of the present invention.

[0066] Attached Figure Labels

[0067] 1. Workbench; 2. Parallel pressure plate; 3. Six-DOF servo electric cylinder component; 31. Lower base; 32. Servo electric cylinder; 33. Upper universal joint; 34. Lower universal joint; 35. Load platform; 4. Load support frame; 41. Support plate; 42. Support profile; 43. Fixed angle bracket; 44. Arc-shaped connector; 441. Arc-shaped support base; 442. Telescopic screw; 443. Arc-shaped fitting; 45. Support plate and load platform fixing assembly; 5. Ellipsoidal Cassini tank; 51. Flange; 52. Through hole; 53. Pressure hole; 54. Annular baffle; 55. Vertical through groove; 56. Chain; 57. Thin-film float; 58. Camera observation hole; 61. Pressure sensor; 62. Intelligent data acquisition instrument; 7. Three-dimensional depth camera; 8. Computer; 9. Six-DOF platform control cabinet. Detailed Implementation

[0068] The technical solutions provided by the present invention will be further illustrated below with reference to the embodiments.

[0069] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0070] Example 1

[0071] The present invention provides a liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform. The experimental device includes: a six-degree-of-freedom platform control cabinet, a six-degree-of-freedom servo electric cylinder component, a load platform tank structure system, a liquid level height and depth measurement system, and a liquid dynamic pressure measurement system.

[0072] Hereinafter, specific embodiments will be described with reference to the accompanying drawings. Furthermore, the specific embodiments shown below do not limit the scope of the invention as described in the claims. Additionally, the entirety of the configurations represented in the following specific embodiments is not limited to those necessary for the solution of the invention described in the claims.

[0073] like Figures 1-7(c) As shown, the liquid multimodal rotational shaking experimental device based on a six-degree-of-freedom platform provided in this embodiment includes a worktable 1 for supporting a six-degree-of-freedom servo electric cylinder component 3, a load support frame 4, and an ellipsoidal Cassini tank 5. The worktable 1 plays a role in increasing the weight and fixing the entire experimental device, preventing the experimental device from shifting due to the excessively fast vibration frequency of the six-degree-of-freedom servo electric cylinder component 3 during the experiment. The worktable 1 is provided with several T-slots. The six-degree-of-freedom servo electric cylinder component 3 is fixedly connected to the T-slot worktable 1 by a parallel pressure plate 2. The lower base 31 of the six-degree-of-freedom servo electric cylinder component 3 is in contact with the surface of the T-slot worktable 1. The parallel pressure plate 2 has a through groove in the middle, and a bolt assembly is located in the through groove. The top of the bolt is set in the T-slot of the T-slot worktable 1. One end of the parallel pressure plate 2 presses against the surface of the lower base 31. The bolt is fitted into the through groove in the middle of the parallel pressure plate 2 and is tightened with a nut. There is a support bolt at the rear end of the through groove to keep the rear end and front end of the parallel pressure plate 2 horizontal, ensuring that the structure between the lower base 31 and the T-slot worktable 1 is firm. Figure 3As shown, the servo electric cylinder 32 is located above the lower base 31 and consists of six independent servo electric cylinders. The lower base 31 is connected to each servo electric cylinder 32 through six lower universal joints 34, and the other end of each servo electric cylinder 32 is connected to the load platform 35 through an upper universal joint 33. The six-degree-of-freedom platform control cabinet 9 is connected to the six-degree-of-freedom servo electric cylinder component 3 and is used to set the vibration peak value D, vibration frequency f, and phase angle θ of each servo electric cylinder 32 in the six-degree-of-freedom servo electric cylinder component 3, so that the six-degree-of-freedom servo electric cylinder component 3 simulates the motion posture of six degrees of freedom in space. The servo electric cylinder in this invention is a servo electric cylinder known in the art. The servo electric cylinder model used in this embodiment is DH50-S100-T-R5-M3-C1, and the AC servo motor included in the servo electric cylinder part is model 60CB020C-500000. However, other servo electric cylinders that can meet the technical effects of this invention can also be used in this invention, such as DI95-S200-T-R10-M1-C1-P2. The six-degree-of-freedom platform control cabinet 9 includes various electrical devices, such as an integrated controller: MD-NV3020EV4, a Delta Electronics power supply: EOE11010006, and an Ethernet switch: TL-SF1005 industrial grade. Using the six-degree-of-freedom platform control cabinet 9 to input the vibration peak value D, vibration frequency f, and phase angle θ of each servo electric cylinder 32 in the six-degree-of-freedom servo electric cylinder component 3 are also well-known techniques in the art. Figures 10(a)-10(b) This is a schematic diagram of the exterior and interior of the six-degree-of-freedom platform control cabinet 9.

[0074] Above the load platform 35 are mainly the load support frame 4, the ellipsoidal Cassini tank 5, the pressure sensor 61, and the three-dimensional depth camera 7. The support plate 41 is above the load platform 35 and is firmly fixed to the load platform 35 by the support plate-load platform fixing assembly 45. The support plate-load platform fixing assembly 45 consists of 8 bolt assemblies. There are 8 through holes arranged in a cross shape on the support plate 41 and the load platform 35. The above 8 bolts are used in conjunction with these 8 through holes to firmly fix the two together. On both sides of the support plate 41, there are 5 profile-support plate fixing assemblies. Each profile-support plate fixing assembly includes a through hole and a T-bolt. The through hole corresponds exactly to the slot of the profile 42. The T-bolt assembly is used to fix the profile 42 to the support plate 41. Several support profiles 42 form an inner and outer square frame. The outer square frame is mainly used to bind the power line and signal line of the 3D depth camera 7 to prevent the transmission line of the 3D depth camera 7 from bending and affecting its use. The inner square frame is mainly used to support the ellipsoidal Cassini tank 5. The shape and size of the support plate 41 are the same as the top view area of ​​the inner square frame. The profile-support plate fixing assembly is also installed on the inner square frame. Both the outer and inner square frames have 4 profiles (beams) at the top, 4 profiles (columns) in the middle, and 4 profiles (bases) at the bottom. The profiles at the intersection of the spaces are fixed by several fixing brackets 43, so that the profiles are stably built into a cuboid shape.

[0075] Inside each of the four horizontal and mutually perpendicular beams of the small cuboid profile 42, there is an arc-shaped connector 44, all located in the middle of the beam. The spatial arrangement of the four arc-shaped connectors 44 is cross-shaped, as shown below. Figure 4 As shown, the arc-shaped connector 44 consists of an arc-shaped support base 441, a telescopic screw 442, and an arc-shaped fitting part 443. The telescopic screw 442 has a threaded structure and is screwed onto the axis of the arc-shaped support base 441 and the arc-shaped fitting part 443. The arc-shaped support base 441 is fixed to the inner side of the horizontal beam of the profile 42. By tightening and loosening the nut on the telescopic screw 442, the arc-shaped fitting part 443 and the ellipsoidal Cassini tank 5 are seamlessly fitted together, and the ellipsoidal Cassini tank 5 is in a suspended state, with its bottom not in contact with any experimental device. In this embodiment, the arc of the arc-shaped fitting part 443 is 60 degrees, which can firmly clamp the ellipsoidal Cassini tank 5. It should be noted that the arc-shaped connector 44 is not limited to the form of this embodiment. As long as it can firmly fix the ellipsoidal Cassini tank 5 through some clamping device, ensuring that the ellipsoidal Cassini tank 5 moves in the same posture as the entire platform, it is acceptable. Furthermore, the size of the ellipsoidal Cassini tank 5 can be changed according to actual needs, and the required tank can be clamped by adjusting the telescopic screw 442 and its nut.

[0076] like Figures 5(a)-5(b)As shown, the ellipsoidal Cassini tank 5 is a modular structure, consisting of an upper cover and a lower tank. A flange ring 51 connects the upper cover and the lower tank, each with eight evenly distributed through holes 52. Bolts are used to assemble the upper cover and lower tank of the ellipsoidal Cassini tank 5 together through the through holes 52. On one side of the ellipsoidal Cassini tank 5, there are two pressure holes 53, one upper and one lower. A pressure sensor 61 is installed in each of the two pressure holes 53, with its probe portion inside each hole. The other side of the pressure sensor 61 is connected to a smart device via a transmission line. The intelligent data acquisition device 62 is connected to the computer 8 via a transmission line. A large camera observation hole 58 and four bolt holes are provided on the top of the ellipsoidal Cassini tank 5. A three-dimensional depth camera 7 is fixed to the top of the ellipsoidal Cassini tank 5 using bolt assemblies and the four bolt holes. The lens of the three-dimensional depth camera 7 observes the changes in the liquid level inside the ellipsoidal Cassini tank 5 through the camera observation hole 58. One output terminal of the three-dimensional depth camera 7 is connected to a power cable, and the other is connected to the computer 8. Furthermore, as... Figures 6(a)-7(c) As shown, this invention also explores the design experiment of the anti-sway baffle by modifying the internal structure of the ellipsoidal Cassini tank 5, namely: 1) adding an annular baffle 54 inside the ellipsoidal Cassini tank 5, the annular baffle 54 being fixed to the lower inner side of the ellipsoidal Cassini tank 5, with a thickness of about 5 mm and a width of about 10 mm, and surrounding the cylindrical section of the ellipsoidal Cassini tank 5; 2) installing four vertical through grooves 55 at 90° intervals on the inner wall of the ellipsoidal Cassini tank 5, the vertical through grooves 55 and... The cylindrical sections of the ellipsoidal Cassini tank 5 have the same or slightly smaller height. The chain 56 can pass through the vertical through groove 55 and move freely up and down along the axis of the ellipsoidal Cassini tank 5. The other end of the chain 56 is connected to the membrane float 57 through a through hole. The membrane float 57 is very thin and its size is smaller than the diameter of the inner wall of the tank. That is, when water is added to the tank, the membrane float can move upward as the liquid filling height increases. Experiment 2 is mainly to investigate the effect of the membrane float 2 on the suppression of liquid surface sloshing when the liquid sloshes.

[0077] like Figure 2 As shown, computer 8 is connected to three devices: intelligent data acquisition instrument 62, 3D depth camera 7, and six-degree-of-freedom platform control cabinet 9.

[0078] Example 2

[0079] This embodiment provides a method for conducting a liquid multimodal rotational swaying experiment based on a six-degree-of-freedom platform, implemented using the liquid multimodal rotational swaying experimental apparatus based on a six-degree-of-freedom platform as described in Embodiment 1. Figure 8 As shown, it includes the following steps:

[0080] 1) First, turn on the main power switch of the intelligent data acquisition instrument 62, the three-dimensional depth camera 7 and the six-degree-of-freedom platform control cabinet 9. Then, the six-degree-of-freedom servo electric cylinder component 3 will be reset. Then, the computer 8 will be turned on and the six-degree-of-freedom platform control software, such as the six-degree-of-freedom platform motion control system, will be opened. The interface of the "sine test" module will be entered. This interface includes the setting of vibration peak value D, vibration frequency f and phase angle θ. If the platform is not reset after the six-degree-of-freedom servo electric cylinder component 3 is powered on, click the "Platform Reset" button in the "sine test" interface to reset it.

[0081] 2) Subsequently, according to the motion posture requirements of the experimental platform, set the parameters of "peak value D", "frequency f" and "phase angle θ" of the six independent electric cylinders, and press the "sine start" button. If the experimental parameters exceed the system range, the system will prompt an error and re-enter the parameters. 3) If the parameter settings are reasonable and safe, the six-degree-of-freedom servo electric cylinder component 3 will start working. After the liquid motion law in the ellipsoidal Cassini tank 5 becomes obvious, observe the experimental phenomenon, use the three-dimensional depth camera 7 to measure the liquid rotation and sloshing distance, and obtain the rotation and sloshing height of the liquid surface; use the pressure acquisition system to measure the liquid dynamic pressure in the ellipsoidal Cassini tank 5. Finally, both the three-dimensional depth camera 7 and the pressure acquisition system are monitored by visualization in the corresponding control software of the computer 8.

[0082] 4) After the data recording is completed, press the "Sine Stop" button to pause the operation of the six-DOF servo electric cylinder component 3. If you need to conduct experimental research under different input parameters, you can click the "Clear Screen" and "Platform Reset" buttons to restore the platform to its initial state and continue the relevant experiments.

[0083] 5) After the experiment, close all software, exit the operating system and disconnect the main power supply.

[0084] In this embodiment, the six-degree-of-freedom servo electric cylinder component 3 operates based on the input peak value, frequency, and the independent phase angles of the six electric cylinders. Figure 9 This paper presents a graph illustrating the relationship between the excitation frequency and the peak liquid level of the liquid multimodal rotational sloshing in an embodiment of the present invention. The liquid in the ellipsoidal Cassini tank 5 exhibits different experimental phenomena under different parameters, displaying multimodal rotational sloshing phenomena (large-amplitude left-right swaying, low-speed bottom-exposed rotational sloshing, rapid rotational sloshing, and high-frequency sloshing with bulging liquid surface). Finally, pressure sensor 61 and 3D depth camera 7 are used to measure the height of the liquid rotational sloshing and the dynamic pressure value of the liquid inside the ellipsoidal Cassini tank 5, respectively, to measure various parameter information inside the ellipsoidal Cassini tank 5 in ground experiments as much as possible, aiming to provide reference for practical engineering applications.

[0085] As can be seen from the above description, the liquid multimodal rotational swaying experimental apparatus and method based on a six-degree-of-freedom platform provided by the present invention have the following advantages:

[0086] 1) The scaled-down model of the ellipsoidal Cassini tank 5 structure. The design of this structure is quite difficult in actual processing. Therefore, many scholars only conduct ground experiments on cuboid and cylindrical tanks with simple structure and processing. However, the ellipsoidal Cassini tank 5 is the most commonly used tank structure in actual engineering.

[0087] 2) The arc-shaped connector 44 structure is one of the products independently conceived and designed in this invention. It can not only achieve a perfect and seamless fit with the ellipsoidal Cassini tank 5, but also lock ellipsoidal Cassini tanks 5 of different sizes by tightening and loosening the nut on the telescopic screw 442, making it more versatile.

[0088] 3) The six-degree-of-freedom servo electric cylinder component 3 operates based on the input peak value D, frequency f and the independent phase angle θ of the six electric cylinders, driving the sinusoidal vibration of the entire load platform 35, thereby causing the liquid in the ellipsoidal Cassini tank 5 to exhibit a multimodal rotational swaying phenomenon.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform, characterized in that, include: The system consists of a six-degree-of-freedom platform, a load support frame (4), an ellipsoidal Cassini tank (5), a pressure acquisition system, and a three-dimensional depth camera (7); among which, The six-degree-of-freedom platform is used to control the load support frame (4) on it to simulate the six-degree-of-freedom motion attitude of the rocket in space. The ellipsoidal Cassini tank (5) is fixed inside the load support frame (4) and moves together with the load support frame (4). The six-degree-of-freedom motion attitude in space includes: the rocket's lateral, longitudinal, vertical, pitch, yaw and roll motion attitudes. The pressure acquisition system is used to acquire the pressure value of the liquid in the ellipsoidal Cassini tank (5) in real time; and The three-dimensional depth camera (7) is used to collect the height of the liquid surface rotation and sloshing through the camera observation hole (58) set on the top of the ellipsoidal Cassini tank (5); The six-degree-of-freedom platform includes: a worktable (1), a parallel pressure plate (2), a six-degree-of-freedom servo electric cylinder component (3), and a six-degree-of-freedom platform control cabinet (9); wherein, The six-degree-of-freedom servo electric cylinder component (3) is fixed on the worktable (1) by a parallel pressure plate (2); The load support frame (4) is fixed on the load platform (35) of the six-degree-of-freedom servo electric cylinder component (3) so that it has the same motion posture as the load platform (35); The six-degree-of-freedom servo electric cylinder component (3) is used to simulate the motion posture of six degrees of freedom in space under the control of the six-degree-of-freedom platform control cabinet (9); the ellipsoidal Cassini tank (5) maintains the same motion posture as the load platform (35) under the drive of the load support frame (4); The six-degree-of-freedom platform control cabinet (9) is used to set the vibration peak value D and vibration frequency of the six-degree-of-freedom servo electric cylinder component (3). f and the phase angle of each servo electric cylinder (32) in the six-degree-of-freedom servo electric cylinder component (3) θ This allows the six-degree-of-freedom servo electric cylinder component (3) to simulate the motion posture of six degrees of freedom in space; The six-degree-of-freedom servo electric cylinder component includes: a lower base (31), six servo electric cylinders (32), an upper universal joint (33), a lower universal joint (34), and a load platform (35); wherein, The lower base (31) is fixedly connected to the workbench (1) via a parallel pressure plate (2); The six servo electric cylinders (32) are configured as three groups of servo electric cylinders (32) spaced 120 degrees apart in the circumferential direction. Each group consists of two closely adjacent servo electric cylinders (32), which are set together above the lower base (31). Their lower ends are connected to the lower base (31) through the lower universal joint (34), and their upper ends are connected to the load platform (35) through the upper universal joint (33). The load support frame (4) includes: a support plate (41), several support profiles (42), four arc-shaped connectors (44), and a support plate-load platform fixing assembly (45). The support plate (41) is fixed above the load platform (35) by the support plate-load platform fixing assembly (45); The aforementioned support profiles (42) form an inner and outer square frame; the outer square frame is used to bind the power line and signal line of the three-dimensional depth camera (7); the inner square frame is fixed on the support plate (41). The four arc-shaped connectors (44) are arranged in a cross shape and fixed to the inner side of the horizontal beam of the inner square frame. They are used to clamp the ellipsoidal Cassini tank (5), so that the ellipsoidal Cassini tank (5) maintains the same motion posture as the load platform (35) under the drive of the load support frame (4), and the bottom of the ellipsoidal Cassini tank (5) is suspended.

2. The liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform according to claim 1, characterized in that, The arc-shaped connector (44) consists of an arc-shaped support base (441), a telescopic screw (442), and an arc-shaped fitting piece (443). The telescopic screw (442) is a threaded structure, which is screwed on the axis of the arc-shaped support base (441) and the arc-shaped fitting piece (443). The arc-shaped support base (441) is fixed inside the horizontal beam of the inner square frame. By adjusting the nut on the telescopic screw (442), the arc-shaped fitting piece (443) and the ellipsoidal Cassini tank (5) are fitted together.

3. The liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform according to claim 1, characterized in that, The ellipsoidal Cassini tank (5) includes: an upper cover and a lower tank; wherein, the upper cover and the lower tank are connected by a flange ring (51), and the flange ring (51) has several evenly distributed through holes (52), and the upper cover and the lower tank of the ellipsoidal Cassini tank (5) are assembled together by bolt assemblies passing through the through holes (52); The ellipsoidal Cassini tank (5) has two pressure holes (53) on its side wall, and the probe part of the pressure sensor (61) of the pressure acquisition system is installed in the two pressure holes (53). The top of the ellipsoidal Cassini tank (5) is provided with a camera observation hole (58) and several bolt through holes. The three-dimensional depth camera (7) is fixed to the top of the ellipsoidal Cassini tank (5) by bolt assembly and bolt through holes, and collects the height image of the liquid level inside the ellipsoidal Cassini tank (5) through the camera observation hole (58).

4. The liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform according to claim 1, characterized in that, The device further includes: an annular baffle (54), a vertical through groove (55), a chain (56), and a membrane float (57); wherein, The annular baffle (54) is perpendicular to the axial direction of the ellipsoidal Cassini tank (5) and is secured to the lower inner side of the ellipsoidal Cassini tank (5); wherein, the outer edge of the annular baffle (54) is secured to the inner wall of the cylindrical section of the ellipsoidal Cassini tank (5); The inner wall of the ellipsoidal Cassini tank (5) is provided with vertical through grooves (55) at 90° intervals; the height of the vertical through grooves (55) is less than or equal to the height of the cylindrical section of the ellipsoidal Cassini tank (5); One end of the ring chain (56) is fitted into the vertical through groove (55) and moves freely up and down along the axis of the ellipsoidal Cassini tank (5); the other end of the ring chain (56) is connected to the membrane float (57) through a through hole; The thin film float (57) floats on the liquid surface inside the ellipsoidal Cassini tank (5) and moves together with the liquid surface.

5. The liquid multimodal rotational swaying experimental device based on a six-degree-of-freedom platform according to claim 1, characterized in that, The pressure acquisition system includes: a pressure sensor (61) and an intelligent data acquisition unit (62); wherein, The pressure sensor (61) is a piezoresistive pressure sensor, and its probe is installed in the pressure hole (53) on the side wall of the ellipsoidal Cassini tank (5); The pressure sensor (61) transmits the liquid pressure value to the computer (8) via the intelligent data acquisition instrument (62).

6. A method for conducting a liquid multimodal rotational swaying experiment based on a six-degree-of-freedom platform, implemented using the liquid multimodal rotational swaying experiment apparatus based on a six-degree-of-freedom platform as described in any one of claims 1-5, comprising the following steps: Step 1) Reset the six-degree-of-freedom servo electric cylinder component (3); Step 2) Based on the motion posture requirements of the experimental platform, set the simulation parameters of the six-degree-of-freedom servo electric cylinder component (3), wherein the simulation parameters include: vibration peak value D, vibration frequency f and phase angle θ of each servo electric cylinder (32); Step 3) Determine whether the simulation parameters exceed the system range of the six-degree-of-freedom servo electric cylinder component (3). If yes, reset the simulation parameters. If no, control the six-degree-of-freedom servo electric cylinder component (3) to work based on the simulation parameters through the six-degree-of-freedom platform control cabinet (9). Step 4) After the liquid movement pattern in the ellipsoidal Cassini tank (5) becomes obvious, a three-dimensional depth camera (7) is used to measure the rotational sloshing distance of the liquid to obtain the rotational sloshing height of the liquid surface, and a pressure acquisition system is used to measure the pressure value of the liquid in the ellipsoidal Cassini tank (5).

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