Horizontal Large Amplitude Easily Tiltable Frequency Absolute Displacement Sensor and Method without Reference Point

Abstract

This invention discloses a horizontal, large-amplitude, easily adjustable frequency absolute displacement sensor and method that requires no reference point, comprising a track unit, a connecting unit, an elastic telescopic shaft unit, and a displacement monitoring unit. This invention applies the principle of quasi-zero stiffness and optimizes geometric parameters to design a quasi-zero stiffness absolute displacement sensor that combines large displacement and low natural frequency. Based on this characteristic, the horizontal absolute displacement of a floating wind turbine base can be characterized by the relative displacement measured by the displacement monitoring unit. This invention directly monitors the absolute displacement of the wind turbine base through the quasi-zero stiffness principle, overcoming the drawbacks of traditional methods that require a fixed reference point for absolute displacement monitoring. Furthermore, the simple and easily implemented method of adjusting the natural frequency by changing the mass allows for displacement monitoring of floating wind turbine bases under different wave environments and vibration frequencies. The monitoring frequency band is easily adjustable, the displacement monitoring range is large, and it can be used for long-term displacement monitoring.

Description

Technical Field

[0001] This invention belongs to the field of marine floating wind turbine structural displacement monitoring technology, specifically relating to a horizontal large amplitude easily adjustable frequency absolute displacement sensor and method that does not require a reference point. Background Technology

[0002] Offshore floating wind turbines typically consist of the turbine body, floating foundation, mooring system, and dynamic cable. Unlike stationary offshore wind turbines, the floating foundation is not rigidly fixed to the seabed but floats on the surface due to buoyancy, with the mooring system limiting its overall drift. Under the combined effects of wind, waves, currents, and turbine operating loads, the floating foundation exhibits significant low-frequency, large-amplitude movements, with horizontal sway, transverse sway, and drift displacements being particularly pronounced. This horizontal floating displacement not only alters the turbine's operating attitude but also affects mooring line tension, dynamic cable stress, tower fatigue load, and overall turbine stability. Therefore, monitoring large horizontal displacements of offshore floating wind turbines is a crucial technical means to ensure their safe operation and condition assessment.

[0003] However, accurate monitoring of the absolute horizontal displacement of offshore floating wind turbines faces a fundamental challenge: in the marine environment, it is often difficult to establish a stable, absolute static spatial reference point. This challenge limits the application of many traditional sensing technologies that rely on fixed reference frames, such as LVDTs (Linear Variable Differential Transformers) that require installation at both ends. Furthermore, methods using acceleration or velocity integration are prone to integral drift during low-frequency displacement reconstruction, making it difficult to obtain accurate low-frequency vibration displacement data of the platform over long periods. Therefore, current displacement monitoring of offshore floating wind turbines primarily relies on non-contact measurement methods, with Geographic Information Systems (GNSS) and computer vision being the main approaches. The literature [Lian Jijian, Xu Wenliang, Liang Chao. Research on motion response monitoring of floating photovoltaic islands at sea based on computer vision. Journal of Tianjin University (Natural Science and Engineering Technology Edition), 2024, 57(11): 1211-1220] uses a telephoto camera to track natural landmarks on the offshore platform and calculates the vertical displacement of the platform using the scale factor method. However, the visual method has poor accuracy in monitoring horizontal displacement. In the long-term actual monitoring process, factors such as light intensity, air humidity, fog and rain, and camera equipment vibration may cause large errors in computer vision displacement monitoring. The Chinese invention patent technology with authorization announcement number CN116518019B uses two pairs of obliquely placed compression springs connected in parallel with positive stiffness springs to obtain a horizontal quasi-zero stiffness vibration isolator. However, because it uses linear positive stiffness to compensate for negative stiffness, its quasi-zero stiffness region design has poor flexibility and the quasi-zero stiffness stroke is narrow, which is not suitable for monitoring large vibration displacements of offshore floating structures.

[0004] In summary, existing technologies cannot simultaneously meet the comprehensive requirements of "low-frequency wide amplitude response, high sensitivity, long-term stability, and adaptability to complex sea conditions" in the horizontal displacement monitoring of offshore floating wind turbines. Therefore, developing a new method that does not rely on fixed external reference points, has high accuracy in low-frequency monitoring, monitors large displacements, is highly adaptable to the environment, and is suitable for long-term monitoring is of great significance for promoting the development of displacement measurement technology for offshore floating wind turbines. Summary of the Invention

[0005] In view of the above, the present invention provides a horizontal large amplitude easily adjustable frequency absolute displacement sensor and method without reference point. The sensor has a quasi-zero stiffness characteristic with a long stroke and is symmetrical with respect to the equilibrium position. Therefore, it can provide a stable vibration-free point over a large displacement range. In addition, the device is simple, the natural frequency is easy to adjust, it has strong environmental adaptability, is easy to replace, and has high accuracy, which can meet the needs of long-term monitoring.

[0006] A horizontal, large-amplitude, easily adjustable frequency absolute displacement sensor without a reference point is fixedly mounted on a floating offshore wind turbine base via a base plate to monitor its horizontal vibration displacement. The sensor includes an inner track unit, an outer track unit, a connecting unit, an elastic telescopic shaft unit, a displacement monitoring unit, and a self-powered unit. Both the outer and inner track units employ a sliding rail and slider configuration. The outer track unit is located on both sides of the base plate, while the inner track unit is located in the middle. The sliding rails of both the outer and inner track units are fixed to the base plate and can move with it. The connecting unit uses a connecting plate as the connection medium between the inner and outer track units, with a mass block supported on its top. The elastic telescopic shaft unit uses a spring-loaded telescopic shaft to connect the sliders in the outer and inner track units. The displacement monitoring unit uses laser and force sensing methods to collect relevant displacement data and calculates the vibration displacement of the floating offshore wind turbine base through correction. The self-powered unit supplies power to the displacement monitoring unit.

[0007] Furthermore, the outer track unit includes two parallel outer slide rails, which are fixed to both sides of the base plate respectively. Three outer sliders are provided on the outer slide rails. For the outer sliders located on both sides of the outer slide rail, limit blocks are provided on their outer sides. For the outer slider located in the middle of the outer slide rail, limit blocks are provided on both sides to restrict its movement. The side extension of the outer slider has an outer slider connecting groove, and a through connecting hole is provided on the groove wall. The inner track unit includes one inner slide rail, which is parallel to the outer slide rail and fixed in the middle of the base plate. An inner slider is provided on the inner slide rail.

[0008] Furthermore, the connecting unit is a rigid and hollow connecting plate, which is fixed to the top of the inner slider. The connecting plate has three telescopic shaft connecting slots on both sides parallel to the inner slide rail, which correspond to the three outer sliders on the outer slide rail respectively. The groove walls of the telescopic shaft connecting slots have through connecting holes.

[0009] Since the preload springs of this absolute displacement sensor are all horizontally suspended, they are prone to buckling and failure due to deviation from the centerline under the influence of gravity if no limiting measures are taken. Therefore, a supporting inner core is required. To ensure that the springs deflect and deform normally during movement, the supporting inner core must not only have a certain strength, but also be able to smoothly extend, contract, and rotate to change its length. Furthermore, the elastic telescopic shaft unit includes six telescopic shafts (four on the outer side and two on the inner side) for connecting the outer and inner sliders. Springs are fitted onto the telescopic shafts. Each telescopic shaft includes an outer sleeve, a piston rod, a linear bearing, a left connector, and a right connector. The left connector is threaded onto one end of the outer sleeve and connects to the corresponding outer slider. One end of the piston rod is inserted into the outer sleeve from the other end via a linear bearing, and the other end is threaded onto the right connector, which connects to the corresponding telescopic shaft connecting groove. One end of the outer sleeve has an external thread for installing a left spring stop, and the other end of the piston rod also has an external thread for installing a right spring stop. The outer sleeve has vent holes to reduce additional resistance caused by air pressure during movement due to the sealed outer sleeve. The main purpose of these features is to ensure smooth movement and reduce the impact of unnecessary friction on accuracy.

[0010] Furthermore, ball bearings are press-fitted onto the left and right connectors with an interference fit. The inner ring of the ball bearings is fitted with a central shaft with an internal thread. The central shaft is coaxial with the connecting hole of the outer slider connecting groove or the telescopic shaft connecting groove. The connection between the telescopic shaft and the outer slider and the inner slider is achieved by fastening the bolt through the central shaft and the connecting hole and locking it with the fastening nut.

[0011] Furthermore, the displacement monitoring unit includes two sets of laser displacement gauges, two baffles, a force sensor, and a processor. The two sets of laser displacement gauges are respectively installed on two sides of the connecting plate perpendicular to the direction of movement. The two baffles are set on the base plate and face the two sets of laser displacement gauges respectively. The distance between the baffles and the laser displacement gauges is adjusted through the holes on the base plate. The laser displacement gauges measure the relative displacement between the inner slider and the base plate based on the reflected light formed by the emitted laser hitting the baffle. The force sensor is set between the left spring baffle and the spring. It calculates the displacement of the base plate in the direction of movement by converting the change of spring force during movement through geometric relationships. The processor combines the displacement data provided by the laser displacement gauges and the force sensor to perform algorithm self-correction to obtain the vibration displacement of the offshore floating wind turbine base.

[0012] Furthermore, the processor calculates the vibration displacement of the offshore floating wind turbine base using the following formula:

[0013]

[0014]

[0015] in: This refers to the absolute displacement of the base plate, i.e., the vibration displacement of the offshore floating wind turbine foundation. and The relative displacement between the inner slider and the base plate was measured by two sets of laser displacement gauges. The displacement of the base plate in the direction of motion is calculated based on the spring force on the outer telescopic shaft. The displacement of the base plate in the direction of motion is calculated based on the spring force on the inner telescopic shaft. The change in spring force on the outer telescopic shaft, as measured by a force sensor. The change in spring force on the inner telescopic shaft, as measured by a force sensor. The stiffness of the spring on the outer telescopic shaft. The stiffness of the spring on the inner telescopic shaft. and These are the lengths of the outer and inner telescopic axes, respectively, in their initial equilibrium state. a It is half the length of the absolute displacement sensor (the distance between the connecting holes of the connecting slots of the outer sliders corresponding to the two outer telescopic shafts on the same side). b It is half the width of the absolute displacement sensor (the distance between the connecting holes of the connecting slots of the outer sliders corresponding to the two inner telescopic shafts). c It is half the distance between the connecting holes of the corresponding telescopic shaft connecting slots of the two inner telescopic shafts. d It is half the distance between the connecting holes of the connecting slots of the two outer telescopic shafts on the same side.

[0016] Furthermore, the self-powered unit includes two sets of electromagnetic generators, respectively installed at the ends of two outer slide rails. The self-powered unit includes a generator housing, a top cover, an electromagnetic coil, a rotating hinge support, two side wall permanent magnets, and a pendulum permanent magnet. The rotating hinge support is connected to the bottom of the top cover and is connected to the pendulum permanent magnet via a swing arm. The generator housing is fixedly connected to the outer slide rails. The electromagnetic coil is wound on a cylinder inside the generator housing. The two side wall permanent magnets are fixed inside the generator housing and are arranged opposite each other. When the base plate vibrates with the offshore floating wind turbine foundation, it drives the generator housing to move together. The pendulum permanent magnet and the two opposite side wall permanent magnets have the same magnetic poles, thereby generating a repulsive force that allows the pendulum permanent magnet to maintain relative motion with the electromagnetic coil. Since the pendulum permanent magnet and the electromagnetic coil move asynchronously, the electromagnetic coil cuts the magnetic lines of force of the pendulum permanent magnet to generate an electromotive force, which in turn generates current to power the displacement monitoring unit.

[0017] When the absolute displacement sensor is in equilibrium, due to its quasi-zero stiffness characteristics, the stiffness of the inner slider, the connecting plate fixed on it, and the mass block is almost zero. Therefore, the inner slider, the connecting plate fixed on it, and the mass block create a vibration-free point inside the absolute displacement sensor. Within this range, the inner slider and the corresponding structure do not undergo displacement. By changing the size of the mass block mounted on the connecting plate, the natural frequency of the absolute displacement sensor can be changed to meet the monitoring range requirements of different frequencies.

[0018] The design method for the aforementioned horizontal large-amplitude easily tunable frequency absolute displacement sensor includes the following steps: (1) The motion equation of the absolute displacement sensor is optimized by using a genetic algorithm to obtain the parameter combination with the largest quasi-zero stiffness range, including the width-to-length ratio of the absolute displacement sensor, the stiffness ratio of the inner and outer springs, and the original length coefficient of the inner and outer springs (the ratio of the original length of the spring to the length of the spring in the initial equilibrium state); and then the corresponding dimensionless force-displacement curve and dimensionless stiffness-displacement curve are obtained. (2) Determine the maximum allowable horizontal displacement amplitude of the offshore floating wind turbine base and the minimum vibration frequency that vibrates with the waves. Based on the displacement amplitude and the dimensionless stiffness-displacement curve, determine the actual size of the absolute displacement sensor and then calculate the length of the inner and outer springs. (3) Determine the stiffness of the inner and outer springs, the overall stiffness of the absolute displacement sensor, and the weight of the mass block; (4) Determine the initial installation position of the absolute displacement sensor according to the size parameters of the absolute displacement sensor and move the inner and outer sliders to the corresponding positions. Install the telescopic shaft between the outer slider and the connecting plate, and adjust the position of the spring baffle to ensure that the spring is exactly at its free length. (5) Move the outer slider to the design balance position of the outer slide rail in sequence so that the spring reaches the pre-compression design amount, and fix it with the limit block to prevent the outer slider from moving when the absolute displacement sensor is working.

[0019] Further, in step (3), the weight of the mass block at the design frequency is calculated and determined using the following expression:

[0020] in: m Let be the weight of the mass block. f The lowest vibration frequency of the offshore floating wind turbine base as it vibrates with the waves. K The overall stiffness of the absolute displacement sensor and , Let be the dimensionless stiffness of the absolute displacement sensor in its initial equilibrium state. The stiffness of the outer spring. This is the monitoring accuracy coefficient (generally taken as 10). To adapt to the needs of different monitoring frequencies, the monitoring frequency band of the absolute displacement sensor needs to be adjusted. This is achieved by increasing or decreasing the weight of the mass block to change the natural frequency of the absolute displacement sensor, thereby realizing flexible frequency tuning: increasing the weight of the mass block lowers the natural frequency of the absolute displacement sensor and increases the monitoring frequency band; decreasing the weight of the mass block increases the natural frequency of the absolute displacement sensor and decreases the monitoring frequency band.

[0021] A method for monitoring the horizontal vibration displacement of an offshore floating wind turbine base is as follows: First, the aforementioned horizontal large-amplitude easily adjustable frequency absolute displacement sensor is installed on the offshore floating wind turbine base via a base plate. When the offshore floating wind turbine vibrates horizontally due to the action of waves and its own operation, the base plate drives the inner and outer slide rails to move together. Due to the quasi-zero stiffness, the inner slider and the connecting plate and mass block above it are created as a vibration-free point. Therefore, within the quasi-zero stiffness range, the inner slider and the connecting plate and mass block above it will not displace. At this time, the relative displacement between the slider and the baffle monitored by the displacement monitoring unit is the absolute displacement of the base plate. Since the base plate is fixedly connected to the offshore floating wind turbine base, the absolute displacement of the base plate at this time is the vibration displacement of the offshore floating wind turbine base.

[0022] Based on the above technical solution, the inventiveness of this invention is mainly reflected in the following aspects: 1. Unlike traditional methods that use linear positive stiffness to compensate for nonlinear negative stiffness to obtain quasi-zero stiffness, this invention directly achieves symmetrical quasi-zero stiffness by pre-compressing three pairs of linear springs. Compared to existing quasi-zero stiffness structures that combine nonlinear negative stiffness with linear positive stiffness, this invention achieves a wider range of symmetrical quasi-zero stiffness and stronger stability. Since the force-displacement relationship of the three spring pairs in the same direction is nonlinear, and no linear positive stiffness element is used for compensation, it possesses richer mechanical characteristics and greater freedom in stiffness design.

[0023] 2. This invention can adjust the inherent frequency of the sensor by changing the size of the mass block. The entire adjustment process is simple and easy to implement, and does not require additional disassembly. Therefore, it can be applied to the horizontal absolute displacement monitoring of floating wind turbines in various marine wind and wave environments.

[0024] 3. This invention integrates multiple displacement monitoring systems within the same sensor system. The displacement correction algorithm inside the sensor can self-correct the obtained displacement data, which is convenient and fast, and eliminates the need to set up multiple monitoring points.

[0025] 4. This invention creatively designs an elastic telescopic shaft that can freely change its length and angle with movement. The length can be continuously changed during the movement of the sensor. By adding bearings to parts that are prone to friction, friction is minimized to improve the monitoring accuracy of absolute displacement.

[0026] Therefore, compared with the prior art, the present invention has at least the following beneficial technical effects: 1. This invention utilizes the quasi-zero stiffness characteristic to create a large range of vibration-free points (inner slider + connecting plate + mass block) around the equilibrium point by the sensor itself as fixed reference points, thus eliminating the need for external additional reference points, making installation convenient and reducing constraints; while visual measurement of absolute displacement often requires external fixed reference points.

[0027] 2. The sensor of this invention is assembled with a spring-loaded telescopic structure and a slider, which is simple to package and has low sensitivity to environmental weather conditions, exhibiting strong robustness. In contrast, existing horizontal displacement monitoring technologies for floating wind turbine bases are often susceptible to limitations imposed by marine weather and environmental conditions.

[0028] 3. Compared with GNSS technology, which requires the deployment of base stations and access to satellites, this invention does not require base station and satellite support for the horizontal absolute displacement monitoring of floating wind turbine bases. It only requires fixing the sensor base plate to the wind turbine base to perform absolute displacement monitoring, which not only reduces long-term monitoring costs, but also ensures high measurement accuracy.

[0029] 4. The sensor of this invention has a built-in displacement monitoring unit, which can obtain high-precision absolute displacement results through self-calibration. Compared with the existing technology that relies on external multi-point calibration, the solution of this invention significantly simplifies the process and has a greater cost advantage. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the absolute displacement sensor in an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the planar structure of the absolute displacement sensor in an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the connection structure between the connecting plate and the inner slider in an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of the telescopic shaft in an embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram of the structure of the outer slider in an embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram of the structure of the telescopic shaft connection end in an embodiment of the present invention.

[0036] Figure 7 This is a schematic diagram of the structure of the electromagnetic generator in an embodiment of the present invention.

[0037] Figure 8 This is a schematic diagram showing the dimensional parameters of the absolute displacement sensor in an embodiment of the present invention.

[0038] Figure 9 This is a schematic diagram of the dimensionless force-displacement curve monitored by the absolute displacement sensor in an embodiment of the present invention.

[0039] Figure 10 This is a schematic diagram of the dimensionless stiffness-displacement curve monitored by the absolute displacement sensor in an embodiment of the present invention.

[0040] Figure 11 This is a schematic diagram comparing the relative displacement and absolute displacement monitored by the absolute displacement sensor in an embodiment of the present invention.

[0041] In the diagram: 1—Outer slide rail, 2-1—First outer slider, 2-2—Second outer slider, 2-3—Outer slider connecting groove, 2-4—Outer telescopic shaft connecting hole, 3—Second limit block, 4—First limit block, 5—Fastening bolt, 5-1—Central shaft, 5-2—Fastening nut, 6—Telescopic shaft, 6-1—Left connector, 6-2—Outer sleeve external thread, 6-3—Left spring stop, 6-4—Outer sleeve, 6-5—Linear bearing, 6-6—Piston rod, 6-7—Right spring stop, 6-8—Piston rod external thread, 6-9—Right connector, 6-10—Ball bearing, 6-11—Exhaust hole, 7—First spring, 8—Second spring, 9— 10—Inner slide rail, 10-1—Top connecting hole, 11—Connecting plate, 11-1—Fixing hole, 11-2—Inner telescopic shaft connecting hole, 11-3—Connecting bolt, 11-4—Outer connecting groove of telescopic shaft, 11-5—Middle connecting groove of telescopic shaft, 12—Mass block, 13—Laser displacement gauge, 14—Insertion hole, 15—Baffle, 16—Base plate, 17—Force sensor, 18—Electromagnetic generator, 18-1—Top cover, 18-2—Generator housing, 18-3—Electromagnetic coil, 18-4—Side wall permanent magnet, 18-5—Rotating hinge support, 18-6—Swing arm, 18-7—Pendulum permanent magnet, 19—Mass rod. Detailed Implementation

[0042] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] like Figure 1 and Figure 2 As shown in the figure, this embodiment provides a horizontal large-amplitude easily adjustable frequency absolute displacement sensor that does not require a reference point. It mainly includes a track unit, a connecting unit, an elastic telescopic shaft unit, a displacement monitoring unit, and a self-powered unit, wherein: The track unit includes an outer track unit and an inner track unit. The outer track unit includes two symmetrical outer slide rails 1, the bottom of which is fixedly connected to the base plate 16 and can move synchronously with the base plate 16 during operation. Three outer sliders are symmetrically arranged along the track direction on each side of the outer slide rail 1. Before the sensor operates, the three outer sliders need to be moved along the outer slide rail 1 to the equilibrium position of the sensor and fixed to restrict its movement. For the first outer slider 2-1 located on the outer side of the outer slide rail 1, a first limiting block 4 needs to be set on its outer side; for the second outer slider 2-2 located on the inner side of the outer slide rail 1, second limiting blocks 3 need to be set on both sides to restrict its movement.

[0044] The inner track unit includes an inner slide rail 9 arranged parallel to the outer slide rail 1, and an inner slider 10 is provided on the inner slide rail 9. The bottom of the inner slide rail 9 is fixedly connected to the base plate 16, and can move synchronously with the base plate 16 during operation; the inner slider 10 is located in the center of the inner slide rail 9 during the installation stage and is in a free movement state without any limiting measures.

[0045] like Figure 1 and Figure 3 As shown, the connecting unit is a rigid connecting plate 11 with a telescopic shaft connecting groove, used to connect the inner and outer track units and support the top mass block 12. The connecting plate 11 is connected to the top connecting hole 10-1 of the inner slider 10 through fixing holes 11-1 and connecting bolts 11-3 to form a whole. Two parallel mass rods 19 are vertically provided on the top of the connecting plate 11 to fix the mass block 12. The counterweight can be adjusted by adding or removing the mass block 12 by inserting it through the mass rods 19. The two ends of the connecting plate 11 parallel to the inner slide rail 9 are respectively provided with three telescopic shaft connecting grooves (the outer telescopic shaft connecting grooves 11-4 on both sides and the middle telescopic shaft connecting groove 11-5) and an inner telescopic shaft connecting hole 11-2, used to connect the right connector 6-9 of the telescopic shaft.

[0046] The elastic telescopic shaft unit mainly consists of an internal telescopic shaft 6 and springs sleeved on the outside of the telescopic shaft 6. The telescopic shaft 6, equipped with the first spring 7, is connected at both ends to the first outer slider 2-1 and the telescopic shaft outer connecting groove 11-4 of the connecting plate 11, with one spring on each side arranged symmetrically. The telescopic shaft 6, equipped with the second spring 8, is connected at both ends to the second outer slider 2-2 and the telescopic shaft middle connecting groove 11-5 of the connecting plate 11. The left connector 6-1 and right connector 6-9 of the telescopic shaft 6 are press-fitted with ball bearings 6-10 using an interference fit to ensure that the telescopic shaft 6 can rotate flexibly to change angles during sensor operation, reducing friction caused by rotation. To reduce corrosion and high-stress damage in marine environments, the first spring 7 and the second spring 8 are made of corrosion-resistant materials such as molybdenum-containing 316 / 316L stainless steel, and are coated with an anti-corrosion coating.

[0047] like Figure 4 As shown, to ensure smooth extension and retraction of the telescopic shaft during operation and minimize deformation resistance, the telescopic shaft 6 requires specific design. The telescopic shaft includes an outer sleeve 6-4, a piston rod 6-6, a linear bearing 6-5, a left connector 6-1, and a right connector 6-9. To ensure the telescopic shaft 6 maintains a straight line and moves smoothly, a linear bearing 6-5 with a diameter matching the inner diameter of the outer sleeve 6-4 is installed inside the outer sleeve 6-4. To reduce additional resistance caused by air pressure during movement due to the sealed outer sleeve 6-4, an exhaust port 6-11 is provided on the outer sleeve 6-4. The piston rod 6-6 is a smooth shaft with a diameter matching the inner diameter of the linear bearing 6-5. During initial installation, the piston rod 6-6 is inserted into the outer sleeve 6-4 with a partial overlap, the overlap length being greater than or equal to the length of the linear bearing. Internal threads are machined at the ends of the outer sleeve 6-4 and the piston rod 6-6 for installing the left connector 6-1 and the right connector 6-9. Meanwhile, the outer sleeve 6-4 and the piston rod 6-6 are respectively machined with outer sleeve external threads 6-2 and piston rod external threads 6-8. Their function is to adjust the positions of the left spring stop 6-3 and the right spring stop 6-7 to ensure that the first spring 7 and the second spring 8 are limited during the initial installation stage, and that the first spring 7 and the second spring 8 are exactly at their free length. With this design, when external displacement excitation acts on the base plate 16 to move the outer slide rail 1 and the inner slide rail 9, the telescopic shaft 6 will change length with the movement. Due to the presence of the left spring stop 6-3 and the right spring stop 6-7, the first spring 7 and the second spring 8 will be compressed to the same degree. In this embodiment, the outer sleeve 6-4 uses a seamless oil pipe to reduce friction, and the piston rod 6-6 uses a solid metal shaft. The surface of the metal shaft is coated with anti-corrosion paint to extend its service life in the marine environment.

[0048] For displacement monitoring of the moving parts, when manufacturing the telescopic shaft 6, the force sensor 17 is fixedly installed between the left spring stop 6-3 and the first spring 7 or the second spring 8, ensuring that the force is 0 during initial installation. When the first outer slider 2-1 and the second outer slider 2-2 are moved from the initial installation position to the equilibrium position, the force sensor 17 will generate an initial force reading due to the pre-compression of the spring.

[0049] like Figure 5 As shown, in order to connect the inner and outer track units into a whole and to ensure a reliable connection between the outer slider and the elastic telescopic shaft unit, an outer slider connecting groove 2-3 extends inward through an L-shaped steel on the outer slider for connecting the left connector 6-1 of the telescopic shaft 6.

[0050] like Figure 6As shown, the left connector 6-1 and right connector 6-9 of the telescopic shaft 6 are connected to the telescopic shaft connecting groove of the outer slider and the connecting plate 11 using fastening bolts 5 and fastening nuts 5-2, as follows: The inner ring of the ball bearing 6-10 is interference-fitted with a central shaft 5-1. The central shaft 5-1 has internal threads machined inside. The center of the central shaft 5-1 is coaxial with the outer telescopic shaft connection hole 2-4 of the outer slider and the inner telescopic shaft connection hole 11-2 on the connecting plate 11. A fastening bolt 5 passes through the internal thread of the central shaft and extends to the other side of the outer telescopic shaft connection hole 2-4 and the inner telescopic shaft connection hole 11-2. It is fixed with a fastening nut 5-2 to ensure that the central shaft 5-1 remains stationary during movement.

[0051] After the main structure is installed, laser displacement gauges 13 are installed on the two sides of the connecting plate 11 perpendicular to the direction of movement. A baffle 15 is positioned in front of and behind the laser displacement gauges 13, allowing the laser spot to fall on the baffle 15 to obtain displacement data. In this embodiment, the baffle 15 is made of opaque matte white plastic or matte white paint to obtain a clear and high-quality laser reflectivity, thus improving monitoring accuracy.

[0052] To enable long-term monitoring, the sensor is equipped with a self-powered unit, such as... Figure 7 As shown, the self-powered unit consists of two centrally symmetrical electromagnetic generators 18. Each electromagnetic generator 18 comprises a generator housing 18-2, a top cover 18-1, an electromagnetic coil 18-3, two sidewall permanent magnets 18-4, and a pendulum permanent magnet 18-7 connected to a rotating hinge support 18-5 below the top cover 18-1. The rotating hinge support 18-5 and the pendulum permanent magnet 18-7 are connected by a cylindrical swing arm 18-6. The generator housing 18-2 is fixedly connected to the outside of the first outer slider 2-1 of the outer slide rail 1. The electromagnetic coil 18-3 is wound around a cylinder inside the generator housing 18-2 and moves with it. When the sensor's base plate 16 vibrates with the offshore wind turbine foundation, it causes the generator housing 18-2 to move together. Because the pendulum permanent magnet 18-7 is hinged to the top cover 18-1, the pendulum permanent magnet 18-7 and the electromagnetic coil 18-3 move asynchronously, resulting in relative motion. The electromagnetic coil 18-3 cuts the magnetic lines of force of the pendulum permanent magnet 18-7 to generate an electromotive force, producing current to power the sensor. The opposing side wall permanent magnets 18-4 on both sides of the electromagnetic generator 18 have the same magnetization direction, and the two opposing sides are at different magnetic poles. The pendulum permanent magnet 18-7, connected to the rotating hinge support 18-5 below the top cover 18-1 of the electromagnetic generator, has the same magnetic poles as the opposing side wall permanent magnets 18-4. This generates a repulsive force, allowing the pendulum permanent magnet 18-7 to maintain relative motion with the electromagnetic coil 18-3, thereby generating current to supply power.

[0053] This embodiment also provides a design method for the absolute displacement sensor and an absolute displacement monitoring method, the specific implementation process of which is as follows: First, the motion equations of the sensor are optimized using a genetic algorithm to obtain the parameter combination that maximizes the quasi-zero stiffness range, such as... Figure 8 As shown, the parameters include the sensor's aspect ratio. The stiffness ratio of the second spring 8 to the first spring 7 The original length coefficient of the first spring 7 (Spring's original length and spring's length at equilibrium position) The ratio of the two springs and the original length coefficient of the second spring 8. (Spring's original length and spring's length at equilibrium position) The ratio of the length of the sensor to the length of the sensor is 2. a The distance between the centers of the connecting slots of the two outermost outer sliders on the same outer slide rail, and the width of the sensor is 2. b Let this be the distance between the centers of the connecting grooves of two opposing outer sliders on different outer slide rails; thus, the corresponding dimensionless force-displacement curves and dimensionless stiffness-displacement curves can be obtained, as shown below. Figure 9 and Figure 10 As shown.

[0054] Determine the maximum permissible horizontal displacement amplitude A of the target floating wind turbine foundation and the minimum vibration frequency that vibrates with the waves. f And based on the displacement amplitude and the dimensionless stiffness-displacement curve, the actual size of the sensor at the equilibrium position (length 2) is determined. a Width 2 b Accordingly, the required lengths of the first spring 7 and the second spring 8 can be calculated. The determination process is as follows: Combination Figure 8 It can be seen that: the length of the sensor is defined as the distance between the centers of the outer telescopic shaft connecting holes 2-4 of the two outermost first outer sliders 2-1 on the same outer slide rail 1; the width is defined as the distance between the centers of the outer telescopic shaft connecting holes 2-4 of two opposite first outer sliders 2-1 on different outer slide rails 1. From... Figure 8 It can be seen that the quasi-zero stiffness interval is in Between, therefore the length can be expressed by the formula: get, Based on geometric relationships, the equilibrium position can be determined to be the length of the first spring 7. The length of the second spring 8 .in This is a dimensionless displacement.

[0055] Determine the appropriate stiffness of the first spring 7 The stiffness of the second spring 8 The stiffness can be multiplied by the stiffness ratio of the first spring. The overall stiffness of the device can be obtained by... Obtained. Among them. Let be the dimensionless stiffness of the sensor at its equilibrium position (operating origin). The stiffness of the first spring 7.

[0056] Determine the weight of mass block 12: the weight of mass block 12 m The following formula is used to calculate the frequency of horizontal vibration of the floating wind turbine base:

[0057] To ensure monitoring accuracy, Generally, 10 is chosen. To adapt to the needs of different monitoring frequencies and broaden the application range of the sensor, it is necessary to easily change the sensor's natural frequency. In this embodiment, two parallel mass rods 19 are vertically provided at the top of the connecting plate 11 to fix the mass block 12. By inserting or removing the mass block 12 through the mass rods 19, the counterweight can be adjusted to change the natural frequency of the system, thereby achieving flexible frequency tuning. That is, increasing the weight of the mass block lowers the sensor's natural frequency and increases the monitoring frequency bandwidth, and vice versa.

[0058] Determine the initial installation position of the sensor based on the determined sensor size parameters, such as... Figure 2 As shown, the inner and outer sliders are moved to their respective initial positions, the elastic telescopic shaft is installed between the outer slider and the connecting plate 11, and the positions of the left spring stop 6-3 and the right spring stop 6-7 are adjusted to ensure that the first spring 7 and the second spring 8 are just at their free length.

[0059] Following the sequence of first the second outer slider 2-2, then the first outer slider 2-1, the outer sliders are moved sequentially to the designed equilibrium position of the outer slide rail 1, so that the first spring 7 and the second spring 8 reach the pre-compression design amount, and are fixed with limit blocks to prevent the outer sliders from moving during sensor operation, which would cause additional deformation of the springs and affect the monitoring results. The positions of the two first outer sliders 2-1 are symmetrically distributed with respect to the central axis of the second outer slider 2-2.

[0060] In the actual design process, the calculation of the width-to-length ratio should take into account the dimension between the centers of the inner telescopic shaft connecting holes 11-2 on the corresponding connecting plate 11. .

[0061] The specific process for monitoring the horizontal vibration displacement of the floating wind turbine base using the aforementioned absolute displacement sensor is as follows: First, the absolute displacement sensor is installed at the corresponding position on the offshore floating wind turbine base via the base plate 16. When the base vibrates horizontally, the base plate 16 drives the inner and outer slide rails to move together. At this time, the two displacement monitoring systems will monitor the displacement data respectively. Among them, the laser displacement gauges 13 installed on both sides of the connecting plate 11 will monitor the relative displacement of the vibration-free points (inner slider 10, connecting plate 11, and mass block 12) relative to the base plate 16. , The force sensor installed at one end of the telescopic shaft 6 will generate additional force changes due to the deformation of the spring during movement. Based on the force-displacement relationship of the spring and geometric relationships, the displacement of the moving part, i.e., the base plate 16, in the direction of movement can be calculated. , The displacement calculation formula is as follows: For the first spring 7, the displacement For the second spring 8, the displacement .

[0062] By calculating in the processor , , , mean Thus, the internal self-correcting measurement value is achieved. Since the quasi-zero stiffness creates a vibration-free point, the inner slider 10, its connecting plate 11, and the mass block 12 will not displace within this range. Therefore, the absolute displacement of the base plate 16, i.e., the floating wind turbine base, can be characterized by the corrected relative displacement.

[0063] After optimizing the design according to the above design process, the comparison between the relative displacement data monitored by the displacement monitoring system and the absolute displacement data of the base plate 16 is as follows: Figure 11 As shown, the error between the two is small, indicating the effectiveness of the present invention for monitoring horizontal absolute displacement.

[0064] Unlike traditional horizontal quasi-zero stiffness devices that use linear positive stiffness elements to compensate for negative stiffness, the springs used in this invention are all linear springs. However, the first spring 7 and the second spring 8 generate nonlinear elastic forces in the y-direction. Therefore, the sensor of this invention achieves quasi-zero stiffness characteristics in the working direction through the combined action of nonlinear restoring forces. This is achieved by introducing different spring length coefficients. and This invention not only expands the design forms of quasi-zero stiffness structures and enhances the flexibility of parameter design, but also provides a quasi-zero stiffness range approximately twice that of existing horizontal quasi-zero stiffness devices. This allows the sensor to adopt a more compact structural size under the same displacement amplitude requirements, thereby achieving weight reduction. By fixing the mass rod 19 on the connecting plate 11, the natural frequency of the sensor can be easily adjusted by inserting or removing the mass blocks 12, thereby changing the sensor's monitoring bandwidth to adapt to the monitoring frequency requirements under different vibration frequencies.

[0065] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A horizontal, large-amplitude, easily adjustable frequency absolute displacement sensor that requires no reference point, fixedly mounted on the base of an offshore floating wind turbine via a base plate for monitoring its horizontal vibration displacement, characterized in that... The system includes an inner track unit, an outer track unit, a connecting unit, an elastic telescopic shaft unit, a displacement monitoring unit, and a self-powered unit. Both the outer and inner track units utilize a sliding rail and slider configuration. The outer track unit is located on both sides of the base plate, while the inner track unit is located in the middle. The sliding rails of both the outer and inner track units are fixed to the base plate and can move with it. The connecting unit uses a connecting plate as the connection medium between the inner and outer track units, with a mass block supported on its top. The elastic telescopic shaft unit uses a telescopic shaft equipped with a spring to connect the sliders in the outer and inner track units. The displacement monitoring unit uses laser and force sensing methods to collect relevant displacement data and calculates the vibration displacement of the offshore floating wind turbine base through correction. The self-powered unit supplies power to the displacement monitoring unit.

2. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points as described in claim 1, characterized in that: The outer track unit includes two parallel outer slide rails, which are fixed on both sides of the base plate. Three outer sliders are provided on the outer slide rails. For the outer sliders located on both sides of the outer slide rail, limit blocks are provided on their outer sides. For the outer slider located in the middle of the outer slide rail, limit blocks are provided on both sides to restrict its movement. The outer slider has an outer slider connecting groove on its side extension, and a through connecting hole is provided on the groove wall. The inner track unit includes one inner slide rail, which is parallel to the outer slide rail and fixed in the middle of the base plate. An inner slider is provided on the inner slide rail.

3. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points as described in claim 2, characterized in that: The connecting unit is a rigid and hollow connecting plate, which is fixed to the top of the inner slider. The connecting plate has three telescopic shaft connecting slots on both sides parallel to the inner slide rail, which correspond to the three outer sliders on the outer slide rail respectively. The groove walls of the telescopic shaft connecting slots have through connecting holes.

4. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points according to claim 3, characterized in that: The elastic telescopic shaft unit includes six telescopic shafts for connecting the outer slider and the inner slider. Springs are fitted onto the telescopic shafts. Each telescopic shaft includes an outer sleeve, a piston rod, a linear bearing, a left connector, and a right connector. The left connector is threaded onto one end of the outer sleeve and connects to the corresponding outer slider. One end of the piston rod is inserted into the outer sleeve from the other end via a linear bearing, and the other end of the piston rod is threaded onto the right connector, which connects to the corresponding telescopic shaft connecting groove. One end of the outer sleeve has an external thread for installing a left spring stop, and the other end of the piston rod also has an external thread for installing a right spring stop. An exhaust hole is provided on the outer sleeve.

5. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points according to claim 4, characterized in that: The left and right connectors are press-fitted with ball bearings in an interference fit. The inner ring of the ball bearing is fitted with a central shaft with internal threads. The central shaft is coaxial with the connecting hole of the outer slider connecting groove or the telescopic shaft connecting groove. The connection between the telescopic shaft and the outer slider and the inner slider is achieved by fastening the bolt through the central shaft and the connecting hole and locking it with the fastening nut.

6. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points according to claim 4, characterized in that: The displacement monitoring unit includes two sets of laser displacement gauges, two baffles, a force sensor, and a processor. The two sets of laser displacement gauges are respectively installed on two sides of the connecting plate perpendicular to the direction of movement. The two baffles are set on the base plate and face the two sets of laser displacement gauges respectively. The distance between the baffles and the laser displacement gauges is adjusted through the holes on the base plate. The laser displacement gauges measure the relative displacement between the inner slider and the base plate based on the reflected light formed by the emitted laser hitting the baffle. The force sensor is set between the left spring baffle and the spring. It calculates the displacement of the base plate in the direction of movement by converting the change of spring force during movement through geometric relationships. The processor combines the displacement data provided by the laser displacement gauges and the force sensor to perform algorithm self-correction to obtain the vibration displacement of the offshore floating wind turbine base.

7. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points as described in claim 6, characterized in that, The processor calculates the vibration displacement of the offshore floating wind turbine base using the following formula: ; ; ; in: This refers to the absolute displacement of the base plate, i.e., the vibration displacement of the offshore floating wind turbine foundation. and The relative displacement between the inner slider and the base plate was measured by two sets of laser displacement gauges. The displacement of the base plate in the direction of motion is calculated based on the spring force on the outer telescopic shaft. The displacement of the base plate in the direction of motion is calculated based on the spring force on the inner telescopic shaft. The change in spring force on the outer telescopic shaft, as measured by a force sensor. The change in spring force on the inner telescopic shaft, as measured by a force sensor. The stiffness of the spring on the outer telescopic shaft. The stiffness of the spring on the inner telescopic shaft. and These are the lengths of the outer and inner telescopic axes, respectively, in their initial equilibrium state. a Half the length of the absolute displacement sensor. b It is half the width of the absolute displacement sensor. c It is half the distance between the connecting holes of the corresponding telescopic shaft connecting slots of the two inner telescopic shafts. d It is half the distance between the connecting holes of the connecting slots of the two outer telescopic shafts on the same side.

8. The horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points according to claim 2, characterized in that: The self-powered unit includes two sets of electromagnetic generators, respectively installed at the ends of two outer slide rails. The self-powered unit includes a generator housing, a top cover, an electromagnetic coil, a rotating hinge support, two side wall permanent magnets, and a pendulum permanent magnet. The rotating hinge support is connected to the bottom of the top cover and is connected to the pendulum permanent magnet via a swing arm. The generator housing is fixedly connected to the outer slide rails. The electromagnetic coil is wound on a cylinder inside the generator housing. The two side wall permanent magnets are fixed inside the generator housing and are arranged opposite each other. When the base plate vibrates with the offshore floating wind turbine foundation, it drives the generator housing to move together. The pendulum permanent magnet and the two opposite side wall permanent magnets have the same magnetic poles, thereby generating a repulsive force that allows the pendulum permanent magnet to maintain relative motion with the electromagnetic coil. Since the pendulum permanent magnet and the electromagnetic coil move asynchronously, the electromagnetic coil cuts the magnetic lines of force of the pendulum permanent magnet to generate an electromotive force, which in turn generates current to power the displacement monitoring unit.

9. The design method of a horizontal large-amplitude easily adjustable frequency absolute displacement sensor without reference points as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) The motion equation of the absolute displacement sensor is optimized by using a genetic algorithm to obtain the parameter combination with the largest quasi-zero stiffness range, including the width-to-length ratio of the absolute displacement sensor, the stiffness ratio of the inner and outer springs, and the original length coefficient of the inner and outer springs; and then the corresponding dimensionless force-displacement curve and dimensionless stiffness-displacement curve are obtained. (2) Determine the maximum allowable horizontal displacement amplitude of the offshore floating wind turbine base and the minimum vibration frequency that vibrates with the waves. Based on the displacement amplitude and the dimensionless stiffness-displacement curve, determine the actual size of the absolute displacement sensor and then calculate the length of the inner and outer springs. (3) Determine the stiffness of the inner and outer springs, the overall stiffness of the absolute displacement sensor, and the weight of the mass block; (4) Determine the initial installation position of the absolute displacement sensor according to the size parameters of the absolute displacement sensor and move the inner and outer sliders to the corresponding positions. Install the telescopic shaft between the outer slider and the connecting plate, and adjust the position of the spring baffle to ensure that the spring is exactly at its free length. (5) Move the outer slider to the design balance position of the outer slide rail in sequence so that the spring reaches the pre-compression design amount, and fix it with the limit block to prevent the outer slider from moving when the absolute displacement sensor is working.

10. The design method according to claim 9, characterized in that, In step (3), the weight of the mass block at the design frequency is calculated and determined using the following expression: ; in: m Let be the weight of the mass block. f The lowest vibration frequency of the offshore floating wind turbine base as it vibrates with the waves. K The overall stiffness of the absolute displacement sensor and , Let be the dimensionless stiffness of the absolute displacement sensor in its initial equilibrium state. The stiffness of the outer spring. To monitor accuracy coefficients, and to adapt to different monitoring frequency requirements, the monitoring frequency band of the absolute displacement sensor needs to be adjusted. This is achieved by increasing or decreasing the weight of the mass block to change the natural frequency of the absolute displacement sensor: increasing the weight of the mass block decreases the natural frequency of the absolute displacement sensor and increases the monitoring frequency band; decreasing the weight of the mass block increases the natural frequency of the absolute displacement sensor and decreases the monitoring frequency band.

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