A semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device and method

Abstract

A semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device comprises a negative stiffness mechanism that can move axially relative to the propulsion shaft, an automatic equilibrium position adjustment mechanism that adjusts the position of the negative stiffness mechanism, a positive stiffness mechanism, and a semi-active vibration control system; the negative stiffness mechanism comprises a mobile steel frame, a radial damper, a radial spring, and a thrust plate, a thrust bearing, and a thrust flange arranged on the propulsion shaft; the outer cover of the negative stiffness mechanism is provided with a submarine skeleton, the submarine skeleton is fixedly connected to the submarine shell, a plurality of automatic equilibrium position adjustment mechanisms are arranged circumferentially between the submarine skeleton and the outer periphery of the negative stiffness mechanism, and a positive stiffness mechanism is arranged between the submarine skeleton and the two ends of the negative stiffness mechanism; the positive stiffness mechanism comprises a plurality of longitudinal springs and a switch-controllable damper; the automatic equilibrium position adjustment mechanism comprises a swinging oil cylinder, a gear, and a rack. The present invention reduces the natural frequency of the system while having radial and axial vibration isolation effects.

Description

Technical Field

[0001] The invention relates to the field of submarine vibration control, and in particular to a semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device and method. Background Art

[0002] When a submarine is sailing underwater, the propulsion shaft system is directly driven by the power unit or motor to rotate, and the propeller connected to the end of the transmission shaft rotates in the water, thereby providing the submarine with the power required for forward or reverse movement. When a submarine moves in the water, an uneven wake field will be generated at the stern. The propeller at the end of the propulsion shaft will generate pulsating thrust when moving in the wake field. Relevant research shows that 90% of the pulsating excitation force will be transmitted to the hull through the propulsion shaft system, which is the main source of vibration of the submarine hull and thus the generation of acoustic radiation. Reducing the transmission of the excitation force along the shaft system can reduce the vibration of the hull, thereby effectively improving the stealth performance of the submarine during navigation.

[0003] From the classical vibration isolation theory, it is known that the natural frequency of the vibration isolation system must be lower than the excitation frequency to work. The natural frequency of the system can be reduced by reducing the stiffness of the system. However, reducing the stiffness of the vibration isolation system will lead to problems such as reduced system load-bearing capacity, excessive deformation, and easy instability. The contradiction between high load-bearing capacity and low natural frequency has become a bottleneck in the development of vibration isolation technology. The introduction of quasi-zero stiffness vibration isolation technology can better solve the contradiction between high load-bearing capacity and low natural frequency.

[0004] The quasi-zero stiffness system has a high static load-bearing capacity and extremely low dynamic stiffness near the equilibrium position, so that a very low natural frequency can be obtained. The application of the quasi-zero stiffness system to submarine propulsion shaft system vibration isolation is expected to greatly improve the vibration isolation effect. However, there are two new problems: (1) The submarine propulsion system is a variable load system. The change in the magnitude and direction of the axial force will cause the quasi-zero stiffness vibration isolation system to deviate from the equilibrium position, thereby causing the natural frequency of the vibration isolation system to increase significantly, and it no longer has the quasi-zero stiffness characteristics, and the vibration isolation effect is greatly reduced; (2) Under the low-frequency excitation generated by the low-speed operation of the shaft system, when the excitation frequency is close to the natural frequency, the system will inevitably produce resonance. Summary of the invention

[0005] In order to overcome the above problems, the present invention provides a semi-active control system for quasi-zero stiffness vibration isolation of a submarine propulsion shaft system.

[0006] The first aspect of the present invention provides a semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device, comprising a negative stiffness mechanism that can move axially relative to the propulsion shaft, an automatic equilibrium position adjustment mechanism that adjusts the position of the negative stiffness mechanism, a positive stiffness mechanism, and a vibration semi-active control system; the direction parallel to the central axis of the propulsion shaft is the axial direction, the diameter direction of the cross section of the propulsion shaft is the radial direction, and the direction of rotation around the central axis of the propulsion shaft is the circumferential direction;

[0007] The negative stiffness mechanism comprises a movable steel frame, a radial damper, a radial spring, and a thrust plate, a thrust bearing and a thrust flange arranged on the propulsion shaft; a thrust bearing is arranged at each end of the thrust plate, and a thrust flange is arranged at each end of the two thrust bearings away from the thrust plate; a movable steel frame is commonly covered on the outer sides of the thrust plate, the thrust bearing and the thrust flange, a plurality of radial dampers and radial springs are connected between the thrust plate and the movable steel frame, the plurality of radial dampers and radial springs are arranged at intervals in the circumferential direction, and the two ends of the radial damper and the radial spring are respectively hinged to the thrust plate and the movable steel frame; the thrust plate is stationary relative to the propulsion shaft system, the position of the movable steel frame can be moved axially relative to the position of the propulsion shaft system, and the entire propulsion shaft system is in a static balance state;

[0008] The outer cover of the negative stiffness mechanism is provided with a submarine frame, the submarine frame is fixedly connected to the submarine shell, a plurality of automatic equilibrium position adjustment mechanisms are provided at intervals along the circumferential direction between the submarine frame and the outer periphery of the negative stiffness mechanism, and a positive stiffness mechanism is provided between the submarine frame and both ends of the negative stiffness mechanism;

[0009] The positive stiffness mechanism includes a plurality of longitudinal springs and a switch-controllable damper. The switch-controllable damper has two states: on and off. When powered, it is in a high damping state, and the damping value is C on When power is off, the damping is low, and the damping value is C off ; Multiple longitudinal springs and switch-controllable dampers are respectively connected between the two ends of the mobile steel frame and the submarine frame, and the multiple longitudinal springs and switch-controllable dampers are arranged at intervals along the circumferential direction, and a single longitudinal spring and switch-controllable damper are arranged along the axial direction; when the thrust plate deviates from the static equilibrium position along the axial direction and reciprocates near the static equilibrium position, the multiple radial springs jointly provide a longitudinal negative stiffness, and the longitudinal spring provides a longitudinal positive stiffness, and the quasi-zero stiffness vibration isolation device has a quasi-zero stiffness characteristic;

[0010] The automatic adjustment mechanism for the equilibrium position includes a swing cylinder, a gear and a rack. A plurality of racks distributed in the circumferential direction are arranged on the outer wall of the mobile steel frame, and each rack extends in the axial direction. The rack is meshed with the gear, and the gear is installed on the output shaft of the swing cylinder. The gear and the swing cylinder are fixed to the submarine frame through a mounting frame. When the thrust plate deviates from the equilibrium position, the swing cylinder drives the gear to rotate, and the rack matched with the gear moves in the axial direction, thereby controlling the position of the mobile steel frame to change, so that the thrust plate can always be in the equilibrium position, and the quasi-zero stiffness vibration isolation device still meets the quasi-zero stiffness condition.

[0011] The vibration semi-active control system includes an encoder, an acceleration sensor, a force sensor, a solenoid valve, a relay, and an industrial computer; the encoder is arranged on a mobile steel frame, the encoder is electrically connected to the industrial computer, and the encoder transmits the relative displacement between the negative stiffness mechanism and the propulsion shaft to the industrial computer; the swing cylinder is connected to the industrial computer through a solenoid valve, and the industrial computer controls the opening and closing of the solenoid valve according to the relative displacement between the negative stiffness mechanism and the propulsion shaft, thereby controlling the oil in and out of the swing cylinder, and under the action of the hydraulic oil, the swing cylinder swings an angle, driving the gear to rotate an angle; the acceleration sensor is arranged on the thrust plate, and the force sensor is arranged on the thrust flange, the acceleration sensor and the force sensor are electrically connected to the industrial computer respectively, and the switch-controllable damper is connected to the industrial computer through a relay; the acceleration sensor and the force sensor transmit the collected data to the industrial computer, and the industrial computer controls the switch of the relay according to the switch control algorithm to realize the switching of the switch-controllable damper between the energized state and the de-energized state, and changes the damping characteristics of the quasi-zero stiffness vibration isolation device in real time, thereby changing the frequency response characteristics of the quasi-zero stiffness vibration isolation device.

[0012] A second aspect of the present invention provides a switch control algorithm, comprising the following steps:

[0013] (1) When the velocity direction of the thrust plate is the same as the direction of the exciting force, the switch-controllable damper is turned on; otherwise, the switch-controllable damper is turned off; the mathematical expression is as follows:

[0014]

[0015] In the formula, c is the damping value of the switch-controllable damper, v is the velocity of the thrust plate, and F is the value of the exciting force.

[0016] (2) When the frequency of the exciting force is high, the control algorithm will not work because the switch-controlled damper has a certain response time. At this time, the damper should be turned off to put the system in a low damping state.

[0017] The design idea of ​​the present invention is: to address the two new problems raised in the background technology,

[0018] (1) The equilibrium position of the quasi-zero stiffness vibration isolation system of the submarine propulsion shaft system depends on the axial position of the negative stiffness mechanism in the system relative to the propulsion shaft. To this end, this problem is solved by designing an "automatic equilibrium position adjustment mechanism" that automatically adjusts the position of the negative stiffness mechanism. When the magnitude and direction of the axial force change, the propulsion shaft will be displaced in the axial direction. At this time, the "automatic equilibrium position adjustment mechanism" can automatically adjust the position of the negative stiffness mechanism in the quasi-zero stiffness vibration isolation system so that its axial position relative to the propulsion shaft remains unchanged. That is, when the magnitude and direction of the axial force change, the equilibrium position of the quasi-zero stiffness vibration isolation system of the submarine propulsion shaft system always remains unchanged.

[0019] (2) The quasi-zero stiffness vibration isolation system of the submarine propulsion shaft system may produce resonance problems under low-frequency excitation. The semi-active control technology is introduced to effectively suppress the low-frequency resonance phenomenon. Its essence is variable damping control. The vibration signal is tested by the sensor, and the control strategy is given according to the vibration signal to control the switch controllable damper to achieve semi-active control of the system.

[0020] The quasi-zero stiffness system is applied to the vibration isolation of the propulsion shaft system, and the natural frequency of the system is greatly reduced, so as to achieve the purpose of greatly improving the vibration isolation effect of the system. At the same time, by introducing the "balance position automatic adjustment mechanism", it is ensured that when the axial force size and direction of the propulsion shaft change, the balance position of the quasi-zero stiffness vibration isolation system remains unchanged, that is, the quasi-zero stiffness vibration isolation system is at the working point with the minimum natural frequency; by introducing the variable damping semi-active control technology, the possible low-frequency resonance phenomenon is suppressed. It can make the submarine propulsion shaft system have excellent vibration isolation effect and reliability in a wider frequency range, and has a good application prospect.

[0021] The beneficial effects of the present invention are:

[0022] 1. Introducing quasi-zero stiffness into the propulsion shaft isolation system reduces the natural frequency of the system while having better static load-bearing capacity.

[0023] 2. The designed "automatic adjustment mechanism for the equilibrium position" has a simple and reliable structure. The quasi-zero stiffness vibration isolation system can realize automatic adjustment of the equilibrium position. The vibration isolation system is always at the working point with the minimum natural frequency. The system has good vibration isolation effect and has both radial and axial vibration isolation effects.

[0024] 3. The energy transfer to the foundation is reduced, the vibration isolation effect in the mid- and high-frequency bands is greatly improved, the resonance amplitude of the vibration isolation system in the low-frequency band is suppressed, and the vibration isolation frequency band is greatly expanded to the low frequency.

[0025] 4. It has the characteristics of low energy consumption, simple and reliable system and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] Figure 2 yes Figure 1 Sectional view along AA direction.

[0028] Figure 3 It is the output power-frequency image of the present invention.

[0029] Figure 4 It is a structural diagram of the vibration semi-active control system of the present invention.

[0030] Explanation of the reference numerals: propeller 1, housing 2, propulsion shaft 3, submarine frame 4, longitudinal spring 5, switch-controllable damper 6, thrust flange 7, thrust bearing 8, thrust plate 9, radial damper 10, radial spring 11, mounting frame 12, gear 13, swing cylinder 14, movable steel frame 15, rack 16. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be noted that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] Referring to the accompanying drawings, the first aspect of the present invention provides a semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device, comprising a negative stiffness mechanism that can move axially relative to the propulsion shaft 3, an automatic equilibrium position adjustment mechanism that adjusts the position of the negative stiffness mechanism, a positive stiffness mechanism, and a vibration semi-active control system; the direction parallel to the central axis of the propulsion shaft 3 is the axial direction, the diameter direction of the cross section of the propulsion shaft 3 is the radial direction, and the direction of rotation around the central axis of the propulsion shaft 3 is the circumferential direction;

[0035] The negative stiffness mechanism comprises a movable steel frame 15, a radial damper 10, a radial spring 11, and a thrust plate 9, a thrust bearing 8 and a thrust flange 7 arranged on the propulsion shaft 3; a thrust bearing 8 is arranged at each end of the thrust plate 9, and a thrust flange 7 is arranged at each end of the two thrust bearings 8 away from the thrust plate 9; a movable steel frame 15 is commonly provided on the outer sides of the thrust plate 9, the thrust bearing 8 and the thrust flange 7, a plurality of radial dampers 10 and radial springs 11 are connected between the thrust plate 9 and the movable steel frame 15, the plurality of radial dampers 10 and radial springs 11 are arranged at intervals along the circumferential direction, and the two ends of the radial damper 10 and the radial spring 11 are respectively hinged to the thrust plate 9 and the movable steel frame 15; the thrust plate 9 is stationary relative to the propulsion shaft system, the position of the movable steel frame 5 can be moved axially relative to the position of the propulsion shaft system, and the stiffness of a single radial spring is K p , the entire propulsion shaft system is in a state of static equilibrium;

[0036] The outer cover of the negative stiffness mechanism is provided with a submarine frame 4, the submarine frame 4 is fixedly connected to the submarine hull 2, a plurality of automatic equilibrium position adjustment mechanisms are provided at intervals along the circumferential direction between the submarine frame 4 and the outer periphery of the negative stiffness mechanism, and a positive stiffness mechanism is provided between the submarine frame 4 and both ends of the negative stiffness mechanism;

[0037] The positive stiffness mechanism includes multiple longitudinal springs 5 ​​and switch-controllable dampers 6. Multiple longitudinal springs 5 ​​and switch-controllable dampers 6 are connected between the two ends of the mobile steel frame 15 and the submarine skeleton 4. Multiple longitudinal springs 5 ​​and switch-controllable dampers 6 are arranged at intervals along the circumference, and a single longitudinal spring 5 and switch-controllable damper 6 are arranged along the axial direction. To ensure that the propulsion shaft has axially symmetrical mechanical properties, multiple switch-controllable dampers 6 and longitudinal springs 5 ​​are symmetrically arranged along the circumferential direction of the propulsion shaft, and multiple switch dampers are synchronized in control. Adjusting the number of longitudinal springs 5 ​​can adjust the total longitudinal stiffness of the shaft system. After adjustment, the total stiffness of multiple longitudinal springs along the longitudinal direction is K s .

[0038] When the thrust plate 9 deviates from the static equilibrium position in the axial direction and reciprocates near the static equilibrium position, the plurality of radial springs 11 jointly provide a longitudinal negative stiffness, the longitudinal spring 5 provides a longitudinal positive stiffness, and the quasi-zero stiffness vibration isolation device has a quasi-zero stiffness characteristic;

[0039] The condition for the vibration isolation device to have zero stiffness characteristics is to satisfy the relationship: Where n is the number of radial springs, K p is the total stiffness of the radial spring in the radial direction, K s is the total stiffness of the longitudinal spring, δ is the initial pre-compression of the radial spring when the thrust plate is in static equilibrium, and L is the length of the radial spring after initial compression. s Slightly larger than When , the vibration isolation system will have quasi-zero stiffness.

[0040] The automatic adjustment mechanism of the equilibrium position includes a swing cylinder 14, a gear 13 and a rack 16. The outer wall of the mobile steel frame 15 is provided with a plurality of axial racks 16 distributed in the circumferential direction, and each rack 16 extends in the axial direction; the rack 16 meshes with the gear 13, and the gear 13 is installed on the output shaft of the swing cylinder 14. The gear 13 and the swing cylinder 14 are fixed on the submarine frame 4 through the mounting frame 12; when the submarine is sailing underwater, there are usually two working conditions: forward and reverse. When the two working conditions are switched quickly, the load of the propulsion shaft system will change greatly in a short time, the thrust plate 9 will deviate from the equilibrium position, the negative stiffness mechanism cannot play an ideal negative stiffness role, the overall stiffness of the vibration isolation system increases, the natural frequency increases, and the vibration isolation effect deteriorates. At this time, the swing angle of the swing cylinder 14 can be controlled by controlling the inlet and outlet oil of the swing cylinder 14, thereby driving the gear 13 to rotate, and the rack 16 matched with the gear 13 moves axially, thereby controlling the position of the mobile steel frame 15 to change. The thrust plate 9 can be always in a balanced position after adjustment, and the entire device still meets the quasi-zero stiffness condition.

[0041] The semi-active vibration control system includes an encoder, an acceleration sensor, a force sensor, a solenoid valve, a relay, and an industrial computer; the encoder is arranged on a mobile steel frame 15, the encoder is electrically connected to the industrial computer, and the encoder transmits the relative displacement between the negative stiffness mechanism and the propulsion shaft to the industrial computer; the swing cylinder 14 is connected to the industrial computer through a solenoid valve, and the industrial computer controls the opening and closing of the solenoid valve according to the relative displacement between the negative stiffness mechanism and the propulsion shaft 3, and then controls the oil in and out of the swing cylinder 14. Under the action of the hydraulic oil, the swing cylinder 14 swings an angle, driving the gear 13 to rotate The acceleration sensor is arranged on the thrust plate 9, and the force sensor is arranged on the thrust flange 7. The acceleration sensor and the force sensor are electrically connected to the industrial computer respectively, and the switch controllable damper 6 is connected to the industrial computer through a relay. The acceleration sensor and the force sensor transmit the collected data to the industrial computer, and the industrial computer controls the switch of the relay according to the switch control algorithm to realize the switching of the switch controllable damper 6 between the power-on state and the power-off state, and change the damping characteristics of the quasi-zero stiffness vibration isolation device in real time, thereby changing the frequency response characteristics of the quasi-zero stiffness vibration isolation device.

[0042] The core is a switch controllable damper. The switch controllable damper 6 described in the present invention has two states: switch and power. When powered, it is in a high damping state, and the damping value is C on When power is off, the damping is low, and the damping value is C off, the industrial computer can control the relay to realize the switching of the switch damper between power on and power off. For the switch controllable damper, a suitable control strategy and algorithm must be proposed. The present invention performs calculations based on the thrust plate speed and excitation force in the vibration isolation system, switches the switch controllable damper on or off according to the calculation results, and puts the switch controllable damper in a powered or de-powered state, thereby adjusting the damping parameters of the vibration isolation system, thereby reducing the vibration transmitted from the shaft system to the hull.

[0043] The evaluation of vibration isolation effect mainly includes displacement response, force transmission rate, vibration level drop and power flow. The transmission of vibration is actually the transmission of energy. The power flow evaluation can more comprehensively evaluate the vibration isolation effect. Based on the purpose of reducing energy transfer, the present invention proposes a switch control algorithm for the switch damper of the present invention.

[0044] The control strategy based on the switch control algorithm used in the present invention is as follows. The exciting force is transmitted to the thrust plate, and there is a phase difference between the speed of the thrust plate and the direction of the exciting force. When the directions of the two are the same, the switch-controlled damper is turned on; if the directions of the two are opposite, the switch-controlled damper is turned off. When the frequency of the exciting force is high, the control algorithm will not work because the switch-controlled damper has a certain response time. At this time, the damper should be turned off to put the system in a low damping state.

[0045] The mathematical expression of the switch control algorithm of the present invention is as follows:

[0046]

[0047] In the above formula, c is the damping value of the switch-controllable damper, v is the velocity of the thrust plate, and F is the value of the exciting force.

[0048] The use of this switch control strategy reduces the transmission of vibration energy, suppresses the resonance peak in the low-frequency band, and also achieves a good vibration isolation effect in the high-frequency band.

[0049] The key points of the present invention are: by introducing quasi-zero stiffness, the natural frequency of the system is made to be an extremely low value, which can effectively play the role of the vibration isolation system, with reliable control effect and high static stiffness load capacity; through ingenious design, not only the automatic adjustment of the quasi-zero stiffness equilibrium position is realized, but also vibration isolation in both longitudinal and radial directions is achieved; the resonance phenomenon of the vibration isolation system causes its vibration isolation effect in the low frequency band to be poor, and increasing the system damping can suppress the resonance in the low frequency band, but at the same time it will cause the vibration isolation effect in the high frequency band to deteriorate. Applying the control strategy of the present invention to the vibration isolation system can achieve better vibration isolation effect in the high frequency band while suppressing the resonance in the low frequency band.

[0050] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device, characterized in that: It comprises a negative stiffness mechanism that can move axially relative to the propulsion shaft (3), an automatic equilibrium position adjustment mechanism that adjusts the position of the negative stiffness mechanism, a positive stiffness mechanism, and a vibration semi-active control system; the direction parallel to the central axis of the propulsion shaft (3) is the axial direction, the diameter direction of the cross section of the propulsion shaft (3) is the radial direction, and the direction of rotation around the central axis of the propulsion shaft (3) is the circumferential direction; The negative stiffness mechanism comprises a movable steel frame (15), a radial damper (10), a radial spring (11), and a thrust plate (9), a thrust bearing (8) and a thrust flange (7) arranged on the propulsion shaft (3); a thrust bearing (8) is arranged at each end of the thrust plate (9), and a thrust flange (7) is arranged at each end of the two thrust bearings (8) away from the thrust plate (9); the outer sides of the thrust plate (9), the thrust bearing (8) and the thrust flange (7) are jointly covered with a movable steel frame (15). A plurality of radial dampers (10) and radial springs (11) are connected between the thrust plate (9) and the movable steel frame (15); the plurality of radial dampers (10) and radial springs (11) are arranged at intervals in the circumferential direction; two ends of the radial dampers (10) and radial springs (11) are respectively hinged to the thrust plate (9) and the movable steel frame (15); the thrust plate (9) is stationary relative to the propulsion shaft system; the position of the movable steel frame (15) is movable axially relative to the position of the propulsion shaft system; and the entire propulsion shaft system is in a statically balanced state; The outer cover of the negative stiffness mechanism is provided with a submarine frame (4), the submarine frame (4) is fixedly connected to the submarine hull (2), a plurality of automatic equilibrium position adjustment mechanisms are provided at intervals along the circumferential direction between the submarine frame (4) and the outer periphery of the negative stiffness mechanism, and a positive stiffness mechanism is provided between the submarine frame (4) and both ends of the negative stiffness mechanism; The positive stiffness mechanism comprises a plurality of longitudinal springs (5) and a switch-controllable damper (6). The switch-controllable damper (6) has two states: a switch state and a high damping state when powered on. The damping value is ; Low damping when power is off, the damping value is ; A plurality of longitudinal springs (5) and switch-controllable dampers (6) are respectively connected between the two ends of the movable steel frame (15) and the submarine frame (4); the plurality of longitudinal springs (5) and switch-controllable dampers (6) are arranged at intervals along the circumferential direction, and a single longitudinal spring (5) and switch-controllable damper (6) are arranged along the axial direction; when the thrust plate (9) deviates from the static equilibrium position along the axial direction and reciprocates near the static equilibrium position, the plurality of radial springs (11) jointly provide a longitudinal negative stiffness, the longitudinal spring (5) provides a longitudinal positive stiffness, and the quasi-zero stiffness vibration isolation device has a quasi-zero stiffness characteristic; The automatic adjustment mechanism for the equilibrium position comprises a swing cylinder (14), a gear (13) and a rack (16); a plurality of racks (16) distributed in the circumferential direction are provided on the outer wall of the movable steel frame (15); each rack (16) extends in the axial direction; the rack (16) meshes with the gear (13); the gear (13) is mounted on the output shaft of the swing cylinder (14); the gear (13) and the swing cylinder (14) are fixed to the submarine frame (4) via a mounting frame (12); when the thrust plate (9) deviates from the equilibrium position, the swing cylinder (14) drives the gear (13) to rotate, and the rack (16) matched with the gear (13) moves in the axial direction, thereby controlling the position of the movable steel frame (15) to change, so that the thrust plate (9) can always be in the equilibrium position, and the quasi-zero stiffness vibration isolation device still meets the quasi-zero stiffness condition; The semi-active vibration control system comprises an encoder, an acceleration sensor, a force sensor, a solenoid valve, a relay, and an industrial computer; the encoder is arranged on a movable steel frame (15), the encoder is electrically connected to the industrial computer, and the encoder transmits the relative displacement between the negative stiffness mechanism and the propulsion shaft to the industrial computer; the swing cylinder (14) is connected to the industrial computer via a solenoid valve, and the industrial computer controls the opening and closing of the solenoid valve according to the relative displacement between the negative stiffness mechanism and the propulsion shaft (3), thereby controlling the oil inlet and outlet of the swing cylinder (14); under the action of the hydraulic oil, the swing cylinder (14) swings at an angle, driving the gear (13) ) rotates an angle; an acceleration sensor is arranged on the thrust plate (9), a force sensor is arranged on the thrust flange (7), the acceleration sensor and the force sensor are electrically connected to the industrial computer respectively, and the switch controllable damper (6) is connected to the industrial computer via a relay; the acceleration sensor and the force sensor transmit the collected data to the industrial computer, and the industrial computer controls the switch of the relay according to the switch control algorithm to realize the switching of the switch controllable damper (6) between the power-on state and the power-off state, thereby changing the damping characteristics of the quasi-zero stiffness vibration isolation device in real time, and then changing the frequency response characteristics of the quasi-zero stiffness vibration isolation device.

2. The switch control algorithm of the semi-actively controlled submarine propulsion shaft system quasi-zero stiffness vibration isolation device according to claim 1 is characterized in that: The following steps are involved: (1) When the velocity direction of the thrust plate is the same as the direction of the exciting force, the switch-controllable damper is opened; Otherwise, the switch controllable damper is closed; the mathematical expression is as follows: (1) Wherein c is the damping value of the switch controllable damper, v is the velocity of the thrust plate, and F is the value of the exciting force; (2) When the frequency of the exciting force is high, the control algorithm will not work because the switch-controlled damper has a certain response time. At this time, the damper should be turned off to put the system in a low damping state.

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