A passive and active composite damping system for a sandwich cylindrical shell structure of an underwater vehicle

Abstract

The application discloses a kind of underwater vehicle sandwich cylindrical shell structure active-passive composite damping systems, including passive damping module, active damping module and feedback control module;The passive damping module is set in the cylindrical shell body of underwater vehicle, passive damping module is used to realize the passive isolation and energy dissipation of broadband vibration;The active damping module is installed in the cylindrical cavity inside the cylindrical shell body, active damping module is installed on the central axis of underwater vehicle, active damping module is used to actively cancel control for specific frequency vibration;The feedback control module is electrically connected with active damping module, for collecting vibration signal and driving active damping module to generate control force.The application can combine the broadband passive vibration isolation characteristics of negative poisson ratio metamaterial and the active precise control ability of piezoelectric stack, form compact and efficient active-passive composite damping system.

Description

Technical Field

[0001] This invention belongs to the field of underwater vehicle vibration control technology, specifically relating to an active-passive composite vibration reduction system for a sandwich cylindrical shell structure of an underwater vehicle, which is particularly suitable for structural vibration reduction and acoustic stealth design of cylindrical shell underwater vehicles. Background Technology

[0002] Vibration and noise control are key technical indicators for evaluating the performance of underwater vehicles. During navigation, the operation of internal mechanical equipment generates broadband vibrations, which are transmitted to the external waters through the hull structure, forming radiated noise and severely affecting the vehicle's stealth and acoustic stealth capabilities. With the continuous advancement of sonar detection technology, higher requirements are being placed on the vibration and noise reduction capabilities of underwater vehicles.

[0003] Traditional cylindrical shell vibration reduction schemes are mainly divided into two categories: passive control and active control. Passive control techniques commonly include applying damping materials to the shell, using a double-shell structure, and installing vibration isolators. Among these, using negative Poisson's ratio metamaterials as the core layer is a novel passive vibration reduction scheme that has emerged in recent years. Negative Poisson's ratio structures undergo lateral contraction rather than expansion under axial compression; this unique deformation mechanism gives them excellent energy absorption and impact buffering performance. However, existing negative Poisson's ratio sandwich structures mostly employ concave hexagonal, star-shaped, or chiral structures, which suffer from poor adaptability and insufficient connection strength when applied to curved cylindrical shell surfaces.

[0004] In active control, piezoelectric ceramic stacks are widely used in precision drive and vibration control due to their advantages such as fast response, large output, and high control precision. However, because the output displacement of piezoelectric ceramics is relatively small, it is difficult to directly meet the actuation stroke required for engineering vibration reduction. Therefore, it needs to be used in conjunction with a displacement amplification mechanism. Existing displacement amplification mechanisms, such as bridge amplification mechanisms and lever amplification mechanisms, can achieve a certain displacement amplification, but they have the problem of balancing amplification factor and output stiffness, and their spatial layout within cylindrical cavities is poorly adaptable.

[0005] Therefore, how to organically combine the broadband passive vibration isolation characteristics of negative Poisson's ratio metamaterials with the active and precise control capabilities of piezoelectric stacks to form a compact and efficient active-passive composite vibration reduction system, and make it well adapted to the curved surface structure of cylindrical shells and the narrow cylindrical cavity inside, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide an active-passive composite vibration reduction system for a sandwich cylindrical shell structure of an underwater vehicle, which can organically combine the broadband passive vibration isolation characteristics of negative Poisson's ratio metamaterials with the active and precise control capabilities of piezoelectric stacks to form a compact and efficient active-passive composite vibration reduction system.

[0007] Technical Solution: The present invention provides a passive-active composite vibration reduction system for a sandwich cylindrical shell structure of an underwater vehicle, comprising a passive vibration reduction module, an active vibration reduction module, and a feedback control module. The passive vibration reduction module is disposed within the cylindrical shell body of the underwater vehicle and is used to passively isolate and dissipate energy from broadband vibrations. The active vibration reduction module is installed in a cylindrical cavity inside the cylindrical shell body and is mounted on the central axis of the underwater vehicle. The active vibration reduction module is used to actively cancel vibrations at specific frequencies. The feedback control module is electrically connected to the active vibration reduction module and is used to collect vibration signals and drive the active vibration reduction module to generate control force.

[0008] Furthermore, the cylindrical shell body adopts a multi-layer composite sandwich structure, which includes an inner load-bearing panel, a negative Poisson's ratio core layer, and an outer compression-resistant panel from the inside out; wherein, the negative Poisson's ratio core layer serves as a passive vibration damping module.

[0009] Furthermore, the negative Poisson's ratio sandwich layer is composed of several periodically arranged negative Poisson's ratio unit cells, each of which includes a star-shaped negative Poisson's ratio structure and a concave hexagonal structure; the curvature of the upper and lower arc-shaped walls of the negative Poisson's ratio unit cells is consistent with the shell surface of the cylindrical shell body, and the negative Poisson's ratio unit cells are spliced ​​together without gaps during installation.

[0010] Furthermore, in the negative Poisson's ratio sandwich layer, by adjusting the angle between the diagonal brace and the horizontal direction, the equivalent Poisson's ratio of the negative Poisson's ratio sandwich layer and the aspect ratio of the unit cell can be flexibly adjusted within a preset range, thereby achieving impedance matching optimization for vibration waves of different frequency bands; the interior of the negative Poisson's ratio sandwich layer is a cavity, without any damping material, and relies on its own geometric nonlinear deformation and friction between the skeletons to dissipate broadband vibration energy into heat energy, thereby achieving passive vibration isolation.

[0011] Furthermore, the active vibration reduction module employs a piezoelectric stacked actuator, which includes a three-stage micro-displacement flexible amplifier, a piezoelectric stacked element, and a base. The base is fixed to the central axis of the underwater vehicle, which extends longitudinally through the cylindrical cavity. The piezoelectric stacked element and the three-stage micro-displacement flexible amplifier are mounted within the cylindrical cavity via the base, and the output end of the piezoelectric stacked element is connected to the three-stage micro-displacement flexible amplifier. The driving direction of the piezoelectric stacked actuator is arranged radially along the cylindrical shell body, used to directly suppress the radial vibration of the cylindrical shell body.

[0012] Furthermore, every four piezoelectric stacked actuators form a group, and two groups of piezoelectric stacked actuators form an active control unit. An active control unit is set at a preset distance on the central axis. The mounting bases of the four piezoelectric stacked actuators in each group are all connected to the same position on the central axis, and the driving directions of the four piezoelectric stacked actuators in each group are distributed at equal angular intervals along the circumference. The axial spacing between the two groups of piezoelectric stacked actuators is 10mm~50mm, and the two groups of piezoelectric stacked actuators are staggered and overlap each other in the circumferential direction.

[0013] Furthermore, the piezoelectric stacked element is composed of multiple layers of piezoelectric ceramic sheets stacked together, and the piezoelectric stacked element elongates along the stacking direction after being energized.

[0014] Furthermore, the three-stage micro-displacement flexible amplifier includes a first-stage bridge amplification structure, a second-stage lever amplification structure, and a third-stage single-bridge amplification structure. The first-stage bridge amplification structure uses a rhomboid frame with flexible hinges, where the short diagonal of the rhomboid frame is the input end and the long diagonal is the output end. When the piezoelectric stack element extends, it pushes the input end of the first-stage bridge amplification structure, causing the rhomboid frame to open, and the output end of the first-stage bridge amplification structure to be displaced in the vertical direction. The output end of the first-stage bridge amplification structure is connected to the short arm end of the second-stage lever amplification structure. The second-stage lever amplification structure is straight-arm shaped, and its fulcrum is connected to the base. The displacement output from the long arm end of the second-stage lever amplification structure is transmitted to the third-stage single-bridge amplification structure. The third-stage single-bridge amplification structure is a simplified bridge amplification unit.

[0015] Furthermore, the ratio of the length of the long and short diagonals of the rhomboid frame in the first-stage bridge amplification structure determines the first-stage amplification factor, and the ratio of the length of the short arm to the long arm in the second-stage lever amplification structure determines the second-stage amplification factor; the geometric design of the input and output arms of the third-stage single-bridge amplification structure enables the third-stage single-bridge amplification structure to have a preset amplification factor; the total amplification factor of the three-stage micro-displacement flexible amplifier reaches tens of times, thereby amplifying the micron-level input displacement of the piezoelectric stacked element to the hundreds of micron or sub-millimeter level, meeting the actuation stroke required for active vibration reduction.

[0016] Furthermore, the output end of the three-stage micro-displacement flexible amplifier is connected to a force transmission rod, which passes through the gap inside the cylindrical cavity of the cylindrical shell body, and the end of the force transmission rod contacts the inner bearing panel of the cylindrical shell body.

[0017] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows:

[0018] (1) Deep integration of active and passive vibration and high space utilization: The active vibration damping module is installed in the cylindrical cavity with the central axis as the base, without occupying the space of the shell wall thickness; the passive vibration damping module is set in the shell sandwich. The two are spatially separated but functionally coordinated, avoiding the problem of mutual interference or encroachment of limited space by active and passive components in traditional solutions.

[0019] (2) Uniform circumferential control and strong multi-mode suppression capability: Two sets of piezoelectric stacked actuators are adopted, with four piezoelectric stacked actuators in each set. The two sets of piezoelectric stacked actuators are staggered in the circumferential direction. The first set is along the orthogonal direction, and the second set is rotated forty-five degrees. The two sets are arranged close to each other with an axial spacing of 10mm~50mm, which ensures that the active control force is uniformly covered in the circumferential direction and can effectively suppress the vibration of multiple circumferential modes of the shell at the same time.

[0020] (3) Output displacement is greatly improved: The three-stage micro-displacement flexible amplifier (bridge-lever-single bridge) achieves high displacement amplification while maintaining a compact size, which significantly enhances the performance of active vibration reduction;

[0021] (4) Lightweight and efficient vibration isolation: The negative Poisson ratio sandwich layer is not filled with any material. It relies on the geometric deformation and friction energy dissipation of the skeleton itself to achieve lightweight structure while ensuring broadband vibration isolation effect, which is conducive to the overall weight control of underwater vehicles. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the negative Poisson's ratio sandwich layer in this invention;

[0024] Figure 3 This is a schematic diagram of the three-stage micro-displacement flexible amplifier in this invention;

[0025] Figure 4 This is a schematic diagram of the overall arrangement of two sets of piezoelectric stacked actuators closely adjacent to each other along the axial direction in this invention;

[0026] Figure 5 This is a schematic diagram of the working process of the active-passive composite vibration control system described in this invention. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0028] like Figure 1-4As shown, the present invention discloses an active-passive composite vibration reduction system for a sandwich cylindrical shell structure of an underwater vehicle, comprising a passive vibration reduction module, an active vibration reduction module, and a feedback control module. Specifically, it involves the following components: an outer pressure-resistant panel 1, a negative Poisson's ratio sandwich layer 2, a concave hexagonal structure 201, a star-shaped negative Poisson's ratio structure 202, an inner load-bearing panel 3, a central shaft 4, a piezoelectric stacked actuator 5, a second-stage lever amplification structure 501, a piezoelectric stacked element 502, a base 503, a third-stage single-bridge amplification structure 504, a first-stage bridge amplification structure 505, and a force transmission rod 506.

[0029] The passive vibration damping module is housed within the cylindrical shell of the underwater vehicle. This module is used to achieve passive isolation and energy dissipation of broadband vibrations. Specifically, such as... Figure 1 As shown, the cylindrical shell body adopts a multi-layer composite sandwich structure, consisting of an inner load-bearing panel 3, a negative Poisson's ratio core layer 2, and an outer pressure-resistant panel 1, from the inside out. Both the inner load-bearing panel 3 and the outer pressure-resistant panel 1 are made of structural materials with good mechanical properties and resistance to seawater corrosion; the panel thickness is determined according to the shell strength requirements. The negative Poisson's ratio core layer 2 serves as a passive vibration damping module.

[0030] like Figure 2 As shown, the thickness of the negative Poisson's ratio sandwich layer 2 is optimized based on vibration reduction requirements and total weight constraints. It consists of periodically arranged negative Poisson's ratio unit cells, each composed of a star-shaped negative Poisson's ratio structure 202 and a concave hexagonal structure 201. Because the curvature of the upper and lower arc-shaped walls of the negative Poisson's ratio unit cells matches the shell surface of the cylindrical shell body, gapless splicing can be achieved between the negative Poisson's ratio unit cells during installation, and they are firmly bonded to the inner and outer panels through welding, diffusion welding, or adhesive bonding processes. In the negative Poisson's ratio sandwich layer 2, by adjusting the angle between the diagonal brace and the horizontal direction, as well as the negative Poisson's ratio and the aspect ratio of the unit cell, the equivalent Poisson's ratio of the negative Poisson's ratio sandwich layer 2 can be flexibly adjusted within a certain range, thereby achieving impedance matching optimization for vibration waves of different frequency bands. The negative Poisson's ratio sandwich layer 2 has a hollow cavity inside and is not filled with any damping material. It dissipates vibration energy by relying on the local buckling and wall friction generated by the negative Poisson's ratio structure under vibration. In other words, the negative Poisson's ratio sandwich layer 2 dissipates broadband vibration energy into heat energy by relying on its own geometric nonlinear deformation and friction between the skeletons, thereby achieving passive vibration isolation while maintaining the lightweight characteristics of the structure.

[0031] like Figure 1 and Figure 3-4As shown, the active vibration damping module is installed in the cylindrical cavity inside the cylindrical shell body. The active vibration damping module is mounted on the central axis 4 of the underwater vehicle and is used to actively cancel vibrations at specific frequencies. Specifically, the active vibration damping module employs a piezoelectric stacked actuator 5, which includes a three-stage micro-displacement flexible amplifier, a piezoelectric stacked element 502, and a base 503. The base 503 is fixed to the central axis 4 of the underwater vehicle, which extends longitudinally through the cylindrical cavity. The piezoelectric stacked element 502 and the three-stage micro-displacement flexible amplifier are positioned within the cylindrical cavity via the base 503. The output end of the piezoelectric stacked element 502 is connected to the three-stage micro-displacement flexible amplifier. The driving direction of the piezoelectric stacked actuator 5 is arranged radially along the cylindrical shell body, directly suppressing the radial vibration of the cylindrical shell body.

[0032] like Figure 4 As shown, in terms of spatial layout, four piezoelectric stacked actuators 5 form a group, and two groups of piezoelectric stacked actuators 5 constitute an active control unit. Each active control unit has a total of eight piezoelectric stacked actuators 5. An active control unit is set at regular intervals on the central axis 4, and the spacing between adjacent active control units is determined according to the wavelength of the main vibration mode of the aircraft. The bases 503 of the four piezoelectric stacked actuators 5 in each group are all connected to the same position on the central axis 4, and the driving directions of the four piezoelectric stacked actuators 5 in each group are distributed at equal angular intervals along the circumference, that is, the included angle between two adjacent piezoelectric stacked actuators 5 is ninety degrees. Two sets of piezoelectric stacked actuators 5 are arranged at intervals, and the two sets of piezoelectric stacked actuators 5 are staggered in the circumferential direction. In this embodiment, the four piezoelectric stacked actuators in the first set are respectively oriented towards the four orthogonal radial directions of the cylindrical shell, namely the four radial directions of up, down, left, and right. The four piezoelectric stacked actuators in the second set are fixed to the central shaft 4 by another base 503. The second set of piezoelectric stacked actuators is arranged adjacent to the first set. However, the driving direction of the four piezoelectric stacked actuators in the second set is rotated 45 degrees relative to the first set as a whole. That is, the driving direction of each actuator in the second set is located on the angle bisector between two adjacent directions in the first set. The two sets of piezoelectric stacked actuators are arranged close together in the axial direction, that is, the axial spacing is kept compact to ensure uniform coverage of the control force in the axial and circumferential directions, forming a complete active control unit. This "double-set staggered" layout makes the active control force more uniformly covered in the circumferential direction of the cylindrical shell, avoids the blind zone of single-direction control, and can effectively suppress the vibration of each mode in the circumferential direction of the shell.

[0033] In this embodiment, the piezoelectric stack element 502 is composed of multiple layers of piezoelectric ceramic sheets stacked together. When energized, the piezoelectric stack element 502 undergoes a slight elongation along the stacking direction. To achieve sufficient active control stroke, the output terminal of each piezoelectric stack element 502 is connected to a three-stage micro-displacement flexible amplifier.

[0034] The three-stage micro-displacement flexible amplifier includes a first-stage bridge amplification structure 505, a second-stage lever amplification structure 501, and a third-stage single-bridge amplification structure 504. Details are as follows:

[0035] The first-stage bridge amplification structure 505 employs a rhomboid frame with flexible hinges. The short diagonal of the rhomboid frame serves as the input end, and the long diagonal as the output end. When the piezoelectric stack element 502 extends, it pushes the input end of the first-stage bridge amplification structure 505, causing the rhomboid frame to open. This results in a vertical displacement at the output end of the first-stage bridge amplification structure 505. The first-stage amplification factor is set by the ratio of the long and short diagonals of the rhomboid frame. The output end of the first-stage bridge amplification structure 505 is connected to the short arm end of the second-stage lever amplification structure 501.

[0036] The second-stage lever amplification structure 501 is in the shape of a straight arm. The fulcrum of the second-stage lever amplification structure 501 is connected to the base 503. The length ratio of the short arm to the long arm determines the amplification factor of the second stage, and this ratio can be designed according to the required total amplification factor. The displacement output from the long arm end of the second-stage lever amplification structure 501 is transmitted to the third-stage single-bridge amplification structure 504.

[0037] The third-stage single-bridge amplifier structure 504 is a simplified bridge amplifier unit. The geometric design of its input and output arms allows this stage to have a preset amplification factor.

[0038] In the three-stage micro-displacement flexible amplifier, the ratio of the length of the long and short diagonals of the rhomboid frame of the first-stage bridge amplification structure 505 determines the first-stage amplification factor. The ratio of the length of the short arm to the long arm of the second-stage lever amplification structure 501 determines the second-stage amplification factor. The geometric design of the input and output arms of the third-stage single-bridge amplification structure 504 enables the third-stage single-bridge amplification structure 504 to have a preset amplification factor. The total amplification factor of the three stages of the three-stage micro-displacement flexible amplifier can reach tens of times, thereby amplifying the micron-level input displacement of the piezoelectric stack element 502 to the hundreds of microns or even sub-millimeter level, meeting the actuation stroke required for active vibration reduction.

[0039] All hinges of the three-stage amplification mechanism employ rounded cuts to reduce stress concentration. The entire assembly is integrally formed from a metal material with good elasticity and fatigue resistance through wire cutting or precision machining. The output end of the three-stage micro-displacement flexible amplifier is connected to a force transmission rod 506. The force transmission rod 506 passes through the gap in the cylindrical cavity inside the cylindrical shell body. The end of the force transmission rod 506 contacts the inner bearing panel 3 of the cylindrical shell body, ensuring precise transmission of power in the radial direction while allowing for minute axial and angular displacements of the shell due to thermal expansion and contraction or changes in water pressure.

[0040] The feedback control module is electrically connected to the active vibration damping module and is used to collect vibration signals and drive the active vibration damping module to generate control force. Specifically, the feedback control module includes an accelerometer, a signal conditioning circuit, a controller, and a power amplifier. The accelerometer is installed on the inner wall of the cylindrical shell or at the base of the mechanical equipment to collect vibration acceleration signals in real time. The signal conditioning circuit includes a charge amplifier and a filter to convert the sensor signal into a standard voltage signal and filter out high-frequency noise. The controller uses a digital signal processor or a field-programmable gate array and has a built-in adaptive filtering control algorithm. The power amplifier amplifies the controller's output signal to drive the piezoelectric stacked actuator 5.

[0041] like Figure 5 The diagram illustrates the system's workflow, showing the transmission of vibrations between internal mechanical equipment and the external environment during normal navigation of the aircraft. First, the star-shaped negative Poisson's ratio structure 202 in the negative Poisson's ratio sandwich layer 2 utilizes friction between its skeletons to dissipate broadband vibration energy into heat, achieving passive vibration isolation. For specific frequency line spectrum vibrations that the negative Poisson's ratio structure fails to effectively suppress, an accelerometer picks up the frequency component, and the controller drives the piezoelectric stacked actuator group in the corresponding direction to generate a reverse action force. Because the two sets of piezoelectric stacked actuators are staggered and overlapped in the circumferential direction, line spectrum vibrations in any direction can be effectively canceled out by at least one piezoelectric stacked actuator.

[0042] The negative Poisson's ratio sandwich layer 2 enables passive vibration isolation. This passive isolation works in conjunction with the active control unit, which provides broadband basic isolation and implements precise line spectrum cancellation. Together, they achieve vibration and noise control of the cylindrical shell structure across the entire frequency band. The entire system is compact, with the active module fully integrated within the cylindrical cavity, without increasing the external dimensions of the shell. The passive module only occupies the original shell sandwich space, and the two do not interfere with each other, achieving an optimal balance between vibration reduction performance and space utilization for the underwater vehicle.

[0043] This invention can solve the technical problems in the prior art, such as poor compatibility between the negative Poisson's ratio sandwich layer and the curved surface of the cylindrical shell, insufficient output displacement of the piezoelectric stack, suboptimal spatial layout of the active vibration damping module in the cylindrical cavity, and low integration of the active and passive vibration damping structures.

Claims

1. A composite active and passive vibration reduction system for a sandwich cylindrical shell structure of an underwater vehicle, characterized in that: It includes a passive vibration damping module, an active vibration damping module, and a feedback control module; The passive vibration damping module is installed in the cylindrical shell of the underwater vehicle. The passive vibration damping module is used to achieve passive isolation and energy dissipation of broadband vibration. The active vibration reduction module is installed in the cylindrical cavity inside the cylindrical shell body. The active vibration reduction module is installed on the central axis (4) of the underwater vehicle. The active vibration reduction module is used to actively cancel vibrations at a specific frequency. The feedback control module is electrically connected to the active vibration damping module and is used to collect vibration signals and drive the active vibration damping module to generate control force.

2. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 1, characterized in that: The cylindrical shell body adopts a multi-layer composite sandwich structure, which includes an inner load-bearing panel (3), a negative Poisson's ratio sandwich layer (2) and an outer pressure-resistant panel (1) from the inside to the outside; wherein, the negative Poisson's ratio sandwich layer (2) serves as a passive vibration reduction module.

3. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 2, characterized in that: The negative Poisson ratio sandwich layer (2) is composed of several periodically arranged negative Poisson ratio units, each negative Poisson ratio unit including a star-shaped negative Poisson ratio structure (202) and a concave hexagonal structure (201). The curvature of the upper and lower arc-shaped walls of the negative Poisson's ratio unit cell is consistent with the shell surface of the cylindrical shell body, and the negative Poisson's ratio unit cells are spliced ​​together without gaps during installation.

4. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 1, characterized in that: In the negative Poisson ratio sandwich layer (2), by adjusting the angle between the diagonal brace and the horizontal direction to achieve a negative Poisson ratio and the aspect ratio of the unit cell, the equivalent Poisson ratio of the negative Poisson ratio sandwich layer (2) can be flexibly adjusted within a preset range, thereby achieving impedance matching optimization for vibration waves of different frequency bands. The negative Poisson's ratio sandwich layer (2) has a cavity inside and is not filled with any damping material. It dissipates broadband vibration energy into heat energy by relying on its own geometric nonlinear deformation and friction between the skeletons, thus achieving passive vibration isolation.

5. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 1, characterized in that: The active vibration reduction module adopts a piezoelectric stacked actuator (5), which includes a three-stage micro-displacement flexible amplifier, a piezoelectric stacked element (502), and a base (503). The base (503) is fixed on the central axis (4) of the underwater vehicle, and the central axis (4) runs through the cylindrical cavity longitudinally along the underwater vehicle. The piezoelectric stack element (502) and the three-stage micro-displacement flexible amplifier are disposed in the cylindrical cavity through the base (503), and the output end of the piezoelectric stack element (502) is connected to the three-stage micro-displacement flexible amplifier. The piezoelectric stacked actuator (5) is driven in a radial direction along the cylindrical shell body, and is used to directly suppress the radial vibration of the cylindrical shell body.

6. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 5, characterized in that: Every four piezoelectric stacked actuators (5) form a group, and two groups of piezoelectric stacked actuators (5) form an active control unit. An active control unit is set on the central axis (4) at a preset distance. The bases (503) of the four piezoelectric stacked actuators (5) in each group are all connected to the same position on the central shaft (4), and the driving directions of the four piezoelectric stacked actuators (5) in each group are distributed at equal angular intervals along the circumferential direction. The axial spacing between the two sets of piezoelectric stacked actuators (5) is 10mm~50mm, and the two sets of piezoelectric stacked actuators (5) are staggered and overlapped in the circumferential direction.

7. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 5, characterized in that: The piezoelectric stack element (502) is composed of multiple layers of piezoelectric ceramic sheets stacked together. When the piezoelectric stack element (502) is energized, it extends along the stacking direction.

8. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 5, characterized in that: The three-stage micro-displacement flexible amplifier includes a first-stage bridge amplification structure (505), a second-stage lever amplification structure (501), and a third-stage single-bridge amplification structure (504). The first-stage bridge amplifier structure (505) adopts a rhomboid frame with flexible hinges. The short diagonal of the rhomboid frame is the input end, and the long diagonal is the output end. When the piezoelectric stack element (502) extends, it pushes the input end of the first-stage bridge amplifier structure (505) to open the rhomboid frame, and the output end of the first-stage bridge amplifier structure (505) is displaced in the vertical direction. The output end of the first-stage bridge amplification structure (505) is connected to the short arm end of the second-stage lever amplification structure (501); The second-stage lever amplification structure (501) is in the shape of a straight arm. The fulcrum of the second-stage lever amplification structure (501) is connected to the base (503). The displacement output from the long arm end of the second-stage lever amplification structure (501) is transmitted to the third-stage single-bridge amplification structure (504). The third-stage single-bridge amplification structure (504) is a simplified bridge amplification unit.

9. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 8, characterized in that: The ratio of the length of the long and short diagonals of the rhomboid frame of the first-stage bridge amplification structure (505) determines the first-stage amplification factor, and the ratio of the length of the short arm to the long arm of the second-stage lever amplification structure (501) determines the second-stage amplification factor. The geometric design of the input and output arms of the third-stage single-bridge amplification structure (504) enables the third-stage single-bridge amplification structure (504) to have a preset amplification factor. The three-stage micro-displacement flexible amplifier has a total amplification factor of tens of times, thereby amplifying the micron-level input displacement of the piezoelectric stack element (502) to the level of hundreds of microns or sub-millimeters, which meets the actuation stroke required for active vibration reduction.

10. The active and passive composite vibration reduction system for the sandwich cylindrical shell structure of an underwater vehicle according to claim 5, characterized in that: The output end of the three-stage micro-displacement flexible amplifier is connected to the force transmission rod (506). The force transmission rod (506) passes through the gap in the cylindrical cavity inside the cylindrical shell body, and the end of the force transmission rod (506) contacts the inner layer bearing panel (3) of the cylindrical shell body.

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