Structure-Sensing Integrated Prefabricated Transition Connection Components and Monitoring Methods for Offshore Wind Turbine Steel-Concrete Towers

Abstract

This invention discloses a structure-sensor integrated prefabricated transition connection component and monitoring method for offshore wind turbine steel-concrete towers. It relates to the field of building structural component technology, and includes: a lower flange and an upper flange respectively provided on the upper and lower ends of the transition connection component body; a sliding decoupling interface layer on the lower end face of the lower flange and an upper sliding decoupling interface layer on the upper end face of the upper flange; an inner ring bolt assembly for connecting the lower flange to the lower concrete section ring body; and an outer ring bolt assembly for connecting the upper flange to the upper steel tower section; an FBG sensing channel is disposed within the wall of the transition connection component body. This invention, a structure-sensor integrated prefabricated transition connection component and monitoring method for offshore wind turbine steel-concrete towers, can serve as a load-bearing structural component, and simultaneously integrates strain self-sensing, interface slip self-detection, bolt axial force self-monitoring, and preload active hydraulic-semi-passive SMA combined self-compensation functions within the component body.

Description

Technical Field

[0001] This invention relates to the technical field of offshore wind power support structure and structural health monitoring, and more specifically to a structure-sensor integrated prefabricated transition connection component and monitoring method for offshore wind power steel-concrete towers. Background Technology

[0002] With the development of offshore wind power towards larger capacity and deeper waters, steel-concrete hybrid towers have become the preferred support form for 10MW and above units due to their economy, fatigue resistance, and adaptability to varying heights. The lower part of the hybrid tower is a prestressed concrete section, and the upper part is a steel tower section, with load transfer achieved through a transition connection. This transition section bears enormous vertical compressive forces over long periods, as well as the combined effects of cyclic bending moments and shear forces caused by wind, waves, and earthquakes. The clamping state, interface cracking, and relative slippage at its connection interface directly determine the overall stiffness, fatigue life, and service safety of the turbine.

[0003] I. Regarding the transition connection components for steel-concrete hybrid towers, there is already a considerable amount of existing technology. For example, CN207715298U (Beijing Wanyuan Industrial Co., Ltd., 2017) discloses a transition section connection device for hybrid wind turbine towers, comprising a lower flange, a cylinder wall, stiffening ribs, and an upper flange. The upper flange is connected to the steel tower section with high-strength friction bolts, and the lower flange is connected to the concrete section with prestressed steel strands. CN202047421U discloses a transition section for offshore wind turbine tower foundations, with a pre-embedded steel flange at the top connecting to the upper tower section. Foreign patents such as US9243418B2, EP2807317A1, and WO2023287401A1 disclose transition adapter schemes made by integrally casting annular concrete and steel components. CN108266330A discloses a prestressed steel-concrete tower and its concrete tower transition section. However, the above solutions are all purely load-bearing structural components, with no integrated sensing or actuation elements within the component itself. Their health status relies entirely on externally installed sensors such as strain gauges and accelerometers for monitoring. In the high-salt-fog and high-humidity environment of the ocean, external sensors have inherent defects such as easy corrosion, easy debonding, and easy failure. Moreover, the internal space of the offshore tower is narrow, making the subsequent installation, wiring, and maintenance costs of the sensors extremely high.

[0004] II. Regarding intelligent bolt connection monitoring, existing technologies mainly include two branches: preload monitoring based on piezoresistive impedance (EMI) and preload recovery based on shape memory alloys (SMA). In the area of ​​EMI smart washers, CN103644997A (Wuhan University of Science and Technology, 2013) discloses a bolt preload sensor based on piezoelectric smart materials, embedding a ring-shaped piezoelectric ceramic in concentric annular grooves on the end faces of two metal washers. Huo Linsheng, Song Gangbing, et al. published a sandwich-type piezoelectric smart washer in Smart Materials and Structures in 2017, sandwiching a PZT sheet between two planar metal rings to quantify preload changes through impedance scanning above 30 kHz and RMSD indicators. However, these smart washers use ordinary steel substrates and only possess sensing functions, lacking active preload recovery capabilities. Regarding SMA preload compensation, Park G, Muntges DE, and Inman DJ published a concept for self-healing bolt connections based on binary NiTi cylindrical SMA washers and external heaters in the JOM in 2003; Antonios, Bouzid, and others subsequently reported similar experiments with Ni-55.7%Ti SMA ring actuators. However, the above-mentioned schemes based on binary NiTi alloys have two fundamental limitations: First, the austenitic phase transformation completion temperature Af of binary NiTi is low (usually below or close to room temperature), and it must be kept at low temperature after pre-deformation, otherwise spontaneous recovery will occur, which is extremely inconvenient for the construction process of offshore wind turbine towers that are installed first and then activated; Second, during the cooling process after activation, due to the narrow thermal hysteresis (typically less than 30°C), the alloy tends to recover along the original phase transformation path, requiring continuous external heating to maintain the recovery stress, resulting in high energy consumption. Furthermore, in Park 2003 and other literature, the PZT sensor chip and SMA washer were installed on the screw as two independent components, each occupying the bolt clamping length, thus failing to achieve structural integration of sensing and execution functions within a single component.

[0005] III. Regarding the structural health monitoring of wind turbine towers, CN202158867U discloses a scheme for pre-embedding fiber optic grating sensors in wind turbine pile foundations, abutments, and tower bodies for health diagnosis; Bremer K et al. (Sensors, 2018) pre-embedded FBG strain sensors in wind turbine concrete foundations and configured them with dedicated temperature-compensated gratings; Bang HJ et al. (IJPEM, 2012) installed a 6-channel FBG array on the inner wall of a 1.5 MW wind turbine tower. However, in these schemes, the sensing channels exist only as independent monitoring devices, without integrated design with the load-bearing structure of the transition connection components, without coordinated integration with bolt preload monitoring and compensation mechanisms, and without utilizing FBG temperature grating data to provide temperature compensation for the piezoresistive impedance spectrum.

[0006] IV. Regarding slip control at the steel-concrete interface, PTFE sliding bearings in traditional bridge engineering allow for free sliding of large displacements ranging from tens to hundreds of millimeters between the steel plate and the concrete, with the sliding direction being isotropic. In the field of tribology, there has been some research on the directional frictional differences generated by laser-directed microtextures (Lu et al., Tribology Letters, 2018), but this is limited to fundamental research under lubrication and sliding conditions in mechanical engineering and has not been applied to flange connection interfaces in structural engineering.

[0007] In summary, the existing technology has the following shortcomings and needs improvement: Firstly, existing transition connection components are purely load-bearing structural components, and no sensing or actuation elements are integrated inside the component body, so component-level integrated self-sensing and self-maintenance cannot be achieved. Secondly, the rigid mating surface of steel-concrete flanges generates significant shear stress concentration under material stiffness mismatch conditions. Existing technologies lack effective means to introduce controlled micro-slip in the transition section to release this stress concentration. Third, the inner and outer ring bolts of the existing steel-concrete flange connection are regarded as a single pre-tightening system, and differential pre-tightening control is not carried out for the functional differences between the inner ring (mainly shear force transmission) and the outer ring (mainly tensile force and bending moment transmission). Fourth, the SMA self-compensation scheme based on binary NiTi requires continuous low-temperature storage or continuous heating due to its narrow thermal hysteresis loop, which is not suitable for the construction logic of offshore wind turbine towers being installed first and then activated. Fifth, existing piezoelectric smart washers and SMA compensation washers are independent components, each occupying the bolt clamping length, and have not achieved true structural integration of sensing and execution functions within a single component. Sixth, the internal space of offshore towers is narrow, and existing external hydraulic tensioning tools are difficult to operate and have extremely high maintenance costs. There is a lack of hydraulic retensioning methods that can be permanently built into the component itself. Seventh, the existing solutions' sensing channels, SMA compensation, hydraulic compensation, and interface slip monitoring are isolated from each other, failing to form a closed-loop monitoring-compensation system with synergistic effects.

[0008] Therefore, how to provide a structural-sensor integrated offshore wind power steel-concrete tower prefabricated transition connection component and monitoring method that can serve as a structural component to bear load transfer, and integrates strain self-sensing, interface slip self-detection, bolt axial force self-monitoring, and preload active hydraulic-semi-passive SMA combined self-compensation functions within the component body, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] In view of this, the present invention provides a structure-sensor integrated prefabricated transition connection component and monitoring method for offshore wind power steel-concrete towers, which aims to solve the problems in the background art mentioned above. At the same time, the component body integrates strain self-sensing, interface slip self-detection, bolt axial force self-monitoring, and preload active hydraulic-semi-passive SMA combined self-compensation functions.

[0010] To achieve the above objectives, in one respect, the present invention provides: A prefabricated transition connection component for a structure-sensor integrated offshore wind turbine steel-concrete tower includes: The transition connection component body has multiple pre-embedded strain sensors inside. The upper and lower end faces of the transition connection component body are respectively provided with a lower flange and an upper flange. The lower end face of the lower flange and the upper end face of the upper flange are respectively provided with a sliding decoupling interface layer and an upper sliding decoupling interface layer. Both the sliding decoupling interface layer and the upper sliding decoupling interface layer are provided with interface displacement sensors inside. The system comprises an inner ring screw assembly and an outer ring screw assembly. The inner ring screw assembly connects the lower flange to the lower concrete section ring, while the outer ring screw assembly connects the upper flange to the upper steel tower section. Each of the inner and outer ring screw assemblies is equipped with an independent hydraulic pre-tightening circuit. SMA gasket assemblies are provided at the connection points between the inner ring screw assembly and the lower flange, as well as at the contact points between the outer ring screw assembly and the upper sliding decoupling interface layer. Both the inner ring screw assembly and the lower concrete section ring are mounted on a bottom mounting base plate. An FBG sensing channel is disposed within the wall of the transition connection member body, and a fiber Bragg grating sensing fiber is inserted inside the FBG sensing channel. A data acquisition and control unit is used to receive signals from various sensors in real time.

[0011] Furthermore, the SMA gasket assembly is provided with a heating element on its outer periphery.

[0012] Furthermore, the wall of the transition connecting member body is provided with a hydraulic microchannel. The hydraulic microchannel is configured as a hydraulic passage with an inner diameter of 3 to 8 mm machined in the wall of the transition connecting member body. The hydraulic microchannel is connected circumferentially to the hydraulic tensioning chambers at each screw position. The hydraulic microchannel is provided with a zone control valve.

[0013] Furthermore, both the sliding decoupling interface layer and the upper sliding decoupling interface layer include two layers of micro-textured metal sheets and a PTFE composite friction-reducing layer sandwiched between them. The surface of the micro-textured metal sheets is provided with directional microgrooves with a depth of 0.1 to 0.3 mm and a spacing of 2 to 5 mm.

[0014] Furthermore, the interface displacement sensor is configured as an LVDT miniature displacement sensor, and multiple interface displacement sensors are symmetrically arranged on both sides along the loading direction.

[0015] Furthermore, the SMA gasket assembly includes a lower SMA gasket and an upper SMA gasket. The lower SMA gasket is located at the connection position between the inner ring screw assembly and the lower flange, and the upper SMA gasket is located at the contact position between the outer ring screw assembly and the upper sliding decoupling interface layer. Both the lower and upper SMA gaskets are embedded with piezoelectric ceramic sensing sheets.

[0016] Furthermore, the target preload of the inner ring screw assembly is 0.6 to 0.8 times the yield strength of the corresponding screw, and the target preload of the outer ring screw assembly is 0.3 to 0.5 times the yield strength of the corresponding screw.

[0017] On the other hand, the present invention provides a method for in-service monitoring of offshore wind turbine reinforced concrete towers. The monitoring method, based on the aforementioned integrated structure-sensor prefabricated transition connection component for offshore wind turbine reinforced concrete towers, specifically includes the following steps: S1, Prefabrication of the transition connection component body and sensor integration: The transition connection component body is formed in a factory environment, and the FBG sensing channel, strain sensor, hydraulic microchannel and interface displacement sensor mounting slot are pre-embedded simultaneously. S2, On-site installation and system calibration: The prefabricated transition connection component body is hoisted into place on-site, the sliding decoupling interface layer, screw assembly and SMA gasket assembly are installed, the data acquisition and control unit is connected and zero-point calibration is completed; S3, Inner and outer double ring differential preload: Differential preload is applied to the inner ring screw assembly and the outer ring screw assembly through their respective independent hydraulic circuits; S4, Service Load Monitoring Start-up: After the tower is installed and put into operation, the data acquisition and control unit continuously collects data from each sensor channel at a preset sampling frequency. S5, Multi-source data synchronous acquisition and fusion: Synchronously acquire strain signals from the FBG sensing channel and strain sensor, slip signals from the interface displacement sensor, and impedance spectrum signals from the piezoresistive impedance sensing chip, and perform effective frequency shift temperature compensation on the impedance spectrum based on the ambient temperature acquired by the FBG temperature grating, and perform multi-source data fusion analysis. S6, Preload Deviation Judgment: When the screw shaft force measured by the piezoresistive impedance sensor chip deviates from the target value by more than 3% to 10% of the set threshold, or when the cumulative slip of the interface measured by the interface displacement sensor exceeds 50% of the design allowable value, an early warning is triggered. S7, Closed-loop compensation execution: Active hydraulic compensation, injects hydraulic oil into the hydraulic tensioning chamber corresponding to the screw with reduced preload through hydraulic microchannel, re-tensions the screw to the target preload, and provides short-term compensation with a fast response in seconds; SMA thermal activation compensation uses heating elements on the outer periphery of the SMA washer assembly to heat the corresponding SMA washer to a temperature not lower than its austenitic phase transformation completion temperature Af, triggering the constrained reverse phase transformation recovery of NiTiNb alloy, generating axial recovery stress of 150-300 MPa to maintain screw preload for a long time, providing semi-passive long-term compensation. Active hydraulic compensation and SMA thermal activation compensation work together to form a closed-loop self-compensation system with short-term response and long-term maintenance. S8, Data Recording and Health Assessment: Stores time history data, compensation event records and damage index calculation results of each channel in the data acquisition and control unit, and generates structural health assessment reports periodically; S9, Early Warning Output and Maintenance Decision: When the strain of the transition connection component reaches the design allowable value, the cumulative slippage of the interface exceeds the limit, or the number of preload compensations exceeds the set threshold, an early warning signal is output and maintenance suggestions are provided.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a prefabricated transition connection component and monitoring method for an integrated structure-sensor offshore wind power steel-concrete tower, the beneficial effects of which are: 1) By directly integrating sensing channels, strain sensors, hydraulic microchannels, etc. into the interior of the wall during the component manufacturing stage, a prefabricated transition connection component integrating structure and sensing is realized. The component itself has both load-bearing and sensing functions, overcoming the limitation of sensors being only external accessories in the existing technology. 2) Through the independent hydraulic differential preload of the inner and outer double-ring screws, the preload level can be optimized for two different functions: shear force transmission and tensile / bending moment transmission, thereby improving connection performance and fatigue durability; 3) By setting a sliding decoupling interface layer at the connection interface, a controllable mechanical channel is provided for the micro-slippage of the interface, and a mounting carrier is provided for the interface displacement sensor, thus realizing the early detection of the interface degradation state; 4) Through the dual mechanism of active hydraulic compensation and semi-passive SMA thermal activation compensation, the preload can be maintained autonomously for a long time without human intervention, significantly reducing the cost of offshore operation and maintenance. 5) This component is suitable not only for offshore wind power steel-concrete towers, but can also be extended to large-scale prefabricated ring connection scenarios such as bridges, tunnels and nuclear power containment structures. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 A cross-sectional view of the prefabricated transition connection component for the structure-sensor integrated offshore wind power steel-concrete tower provided by the present invention; Figure 2 A top view schematic diagram of the arrangement of the double-turn differential preload screw provided by the present invention; Figure 3 A schematic diagram illustrating the embedding of the sliding decoupling interface layer and the sensor provided by the present invention; Figure 4 This is a schematic diagram of the SMA self-recovering preload compensation mechanism provided by the present invention; Figure 5 This is a schematic diagram of the closed-loop preload self-compensation control principle provided by the present invention; Figure 6 The flowchart of the method for in-service monitoring of offshore wind turbine steel-concrete towers provided by the present invention.

[0021] The components are as follows: 1 is the bottom mounting base plate; 2 is the lower concrete section ring; 3 is the transition connection component body; 4 is the lower flange; 5 is the upper flange; 6 is the upper steel tower section; 7 is the inner ring screw assembly; 8 is the outer ring screw assembly; 9 is the sliding decoupling interface layer; 10 is the upper sliding decoupling interface layer; 11 is the FBG sensing channel; 12 is the pre-embedded strain sensor; 13 is the SMA gasket assembly; 131 is the lower SMA gasket; 132 is the upper SMA gasket; 14 is the hydraulic microchannel; 15 is the interface displacement sensor; 16 is the piezoelectric ceramic sensor; 17 is the data acquisition and control unit; 18 is the heating element; and 19 is the zone control valve. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] See Figure 1-4 This invention discloses an integrated structure-sensor prefabricated transition connection component and monitoring method for offshore wind power reinforced concrete towers, comprising: The transition connection component body 3 has multiple pre-embedded strain sensors 12 inside. The upper and lower ends of the transition connection component body 3 are respectively provided with a lower flange 4 and an upper flange 5. The lower end of the lower flange 4 and the upper end of the upper flange 5 are respectively provided with a sliding decoupling interface layer 9 and an upper sliding decoupling interface layer 10. Both the sliding decoupling interface layer 9 and the upper sliding decoupling interface layer 10 are provided with interface displacement sensors 15 inside. The transition connection component body 3 is set as an annular steel shell. The pre-embedded strain sensors 12 are set as resistance or vibrating wire strain gauges that are directly embedded in the wall during the casting process of the transition connection component body 3. The lead wires of the pre-embedded strain sensors 12 are led to the wiring terminals at the end of the transition connection component body 3 through pre-embedded conduits. The inner ring screw assembly 7 and the outer ring screw assembly 8 are configured. The inner ring screw assembly 7 is used to connect the lower flange 4 to the lower concrete section ring 2, and the outer ring screw assembly 8 is used to connect the upper flange 5 to the upper steel tower section 6. The inner ring screw assembly 7 and the outer ring screw assembly 8 are each equipped with an independent hydraulic preload circuit. The hydraulic preload circuit is used to apply differential preload forces of different target values ​​to the two screw rings. SMA gasket assemblies 13 are provided at the connection position between the inner ring screw assembly 7 and the lower flange 4, and at the contact position between the outer ring screw assembly 8 and the upper sliding decoupling interface layer 10. The inner ring screw assembly 7 and the lower concrete section ring 2 are both mounted on the bottom mounting base plate 1. The SMA washer assembly 13 is made of NiTiNb wide hysteresis shape memory alloy, with an austenite completion temperature Af of 60-80°C and an As-Af thermal hysteresis width greater than 150°C. The SMA washer assembly 13 is provided with a heating element 18 on its outer periphery. The heating element 18 is used to actively heat and activate the SMA washer assembly 13 when the screw preload decay exceeds a set threshold. It also includes a piezoresistive impedance sensor chip, which is directly embedded inside the SMA washer assembly 13, forming a structural integration of sensing and execution functions within a single component. The FBG sensing channel 11 is disposed within the wall of the transition connecting component body 3, and a fiber Bragg grating sensing fiber is inserted inside the FBG sensing channel 11. Specifically, the FBG sensing channel 11 is configured as a fiber Bragg grating FBG sensing channel 11, which is an axially extending channel reserved during the casting or processing of the wall of the transition connecting component body 3. The FBG sensing channel 11 extends along the wall thickness direction of the transition connecting component body 3 or extends circumferentially, and the grating nodes are uniformly distributed along the circumferential and axial directions of the FBG sensing channel 11, for real-time monitoring of the strain field distribution of the transition connecting component body 3.

[0024] In this embodiment, a data acquisition and control unit 17 is also included. The data acquisition and control unit 17 is used to receive signals from each sensor in real time. When the screw shaft force is detected to deviate from the target value by more than the threshold, active compensation is performed through the hydraulic microchannel 14 to achieve dual preload self-maintenance by combining active hydraulic compensation and passive SMA phase change compensation.

[0025] In this embodiment, a hydraulic microchannel 14 is provided in the wall of the transition connecting member body 3. The hydraulic microchannel 14 is configured as a hydraulic passage with an inner diameter of 3 to 8 mm machined in the wall of the transition connecting member body 3. The hydraulic microchannel 14 is connected to the hydraulic tensioning chamber at each screw position in the circumferential direction. A partition control valve 19 is provided in the hydraulic microchannel 14. The hydraulic microchannel 14 extends through the wall thickness direction of the transition connecting member body 3 or extends in the circumferential direction. The partition control valve 19 is used to realize full-circle synchronous or local sector differential compensation.

[0026] In this embodiment, both the sliding decoupling interface layer 9 and the upper sliding decoupling interface layer 10 include two layers of micro-textured metal sheets and a PTFE composite friction-reducing layer sandwiched between them. The surface of the micro-textured metal sheets is provided with directional microgrooves with a depth of 0.1 to 0.3 mm and a spacing of 2 to 5 mm. The directional microgrooves are used to allow controllable interface micro-slip. The upper sliding decoupling interface layer 10 and the lower sliding decoupling interface layer 9 allow a controlled micro-slip of 0.5 to 2 mm in the loading direction to release the interface shear stress concentration caused by the material stiffness difference between the upper steel tower section and the lower concrete ring 2, and provide high friction constraint in the vertical loading direction.

[0027] In this embodiment, the interface displacement sensor 15 is set as an LVDT miniature displacement sensor. Multiple interface displacement sensors 15 are symmetrically arranged on both sides along the loading direction, specifically at least three. The interface translational sliding component is obtained by averaging, and the interface opening angle component is obtained by calculating the difference and combining it with the distance between measuring points. The interface displacement sensor 15 can also be set as a capacitive displacement sensor.

[0028] In this embodiment, the SMA gasket assembly 13 includes a lower SMA gasket 131 and an upper SMA gasket 132. The lower SMA gasket 131 is located at the connection position between the inner ring screw assembly 7 and the lower flange 4, and the upper SMA gasket 132 is located at the contact position between the outer ring screw assembly 8 and the upper sliding decoupling interface layer 10. Both the lower SMA gasket 131 and the upper SMA gasket 132 are embedded with piezoelectric ceramic sensing elements 16. The piezoelectric ceramic sensing elements 16 obtain the change in screw axial force in real time through impedance spectroscopy analysis.

[0029] In this embodiment, the target preload of the inner screw assembly 7 is 0.6 to 0.8 times the yield strength of the corresponding screw, and the target preload of the outer screw assembly 8 is 0.3 to 0.5 times the yield strength of the corresponding screw.

[0030] In addition, in this embodiment, the outer wall of the transition connection member body 3 is provided with stiffening ribs.

[0031] like Figure 2 As shown, in a top-down view, the outer ring screw assembly 8 includes 24 high-strength screws, evenly distributed along a distribution circle near the outer wall of the transition connecting component body 3; the inner ring screw assembly 7 includes 12 high-strength screws, evenly distributed along a distribution circle near the inner wall of the transition connecting component body 3; each ring of screws is equipped with an independent hydraulic preload circuit, wherein the target preload of the inner ring screw assembly 7 is set to 0.7 times the yield strength of the corresponding screw (taking an M36 grade 10.9 grade screw as an example, the target preload of a single screw is approximately 510kN), used to optimize the shear force transmission at the steel-concrete interface; the target preload of the outer ring screw assembly 8 is set to the yield strength of the corresponding screw. The preload is 0.4 times the strength of the bolt (taking an M27 grade 10.9 grade screw as an example, the single target preload is about 225kN) to extend the fatigue life under bending moment. Six FBG grating nodes and four pre-embedded strain sensors 12 are set in the circumferential direction of the FBG sensing channel 11. Five FBG grating nodes are set in each FBG sensing channel 11, and a total of 30 measuring points are evenly distributed along the circumference and axial direction of the transition connection component body 3. A temperature-sensitive grating is also set in the FBG sensing channel 11 for measuring the ambient temperature. The temperature data of the temperature-sensitive grating is used to perform temperature compensation on the impedance spectrum of the piezoresistive impedance sensing chip. The hydraulic microchannel 14 connects the screw positions circumferentially within the wall of the transition connecting component body 3, and is equipped with four zone control valves 19.

[0032] like Figure 3 As shown, the upper sliding decoupling interface layer 10 and the lower sliding decoupling interface layer 9 have the same structure. Each layer includes a three-layer structure: an upper metal sheet, a PTFE composite friction-reducing layer, and a lower metal sheet. The metal sheet is 1-2 mm thick, and its surface is laser-processed to form oriented microgrooves with a depth of 0.1-0.3 mm and a spacing of 2-5 mm. The microgrooves are oriented along the loading direction, allowing controllable micro-slippage to occur at the interface in this direction. The PTFE composite friction-reducing layer is 0.5-1.0 mm thick, providing low... The friction coefficient is a sliding medium, and the interface displacement sensor 15 is embedded in the reserved mounting groove in the sliding decoupling interface layer, with no less than three symmetrically arranged on each side of the loading direction; the base material of the PTFE composite friction reducing layer is polytetrafluoroethylene, with glass fiber, bronze powder or molybdenum disulfide added to improve the pressure bearing capacity and wear resistance; the function of the PTFE composite friction reducing layer is to provide a low friction coefficient (typically 0.04 to 0.08) sliding medium between the micro-textured metal sheets, forming a directionally controllable composite friction behavior with the microtexture; Typical laser processing parameters are: laser wavelength 1064 nm, average power 20-50 W, scanning speed 100-500 mm / s, and multiple scans to reach the target depth; the directional geometry of the microgrooves gives the interface low sliding resistance along the groove direction, allowing controlled micro-slippage of 0.5-2 mm; while the groove sidewalls form mechanical embedding in the direction perpendicular to the groove, providing high frictional constraint.

[0033] like Figure 4 As shown, the SMA washer assembly 13 is installed between the nut and the flange plate. The SMA washer assembly 13 is made of NiTiNb wide hysteresis shape memory alloy, and its martensitic reverse phase transformation completion temperature Af is set to 60~80℃. During initial installation, the SMA washer assembly 13 is pre-compressed and deformed to the design compression amount in the martensitic state. During service, when the screw preload decreases, causing the constraint force on the SMA washer assembly 13 to decrease and the temperature rises above Af due to solar radiation or internal heating coil, the SMA washer assembly 13 undergoes a martensitic reverse phase transformation to generate axial restoring force, passively compensating for the preload loss. The piezoelectric ceramic sensor 16 is embedded in the SMA washer body and obtains the screw axial force change in real time through impedance spectroscopy analysis. The preparation process of NiTiNb alloy includes: vacuum melting into ingots → hot rolling or forging → machining into gasket blanks → pre-deformation treatment at liquid nitrogen temperature (typical pre-deformation amount 8%~16%) → storage at room temperature. The pre-deformation treatment significantly increases the Af temperature of the NiTiNb alloy from approximately -10°C to 60~80°C, and creates a wide hysteresis characteristic, allowing the gaskets to be stored stably at room temperature for a long time without spontaneous phase transformation recovery. The key technological advantages of choosing NiTiNb alloy instead of binary NiTi are: First, the wide hysteresis characteristic allows the pre-deformed alloy to be stored and installed stably in a normal temperature environment for a long time without spontaneous recovery, which is crucial for the pre-installation and post-activation processes in offshore wind power construction; Second, due to the wide hysteresis characteristic, the alloy will not recover along the original phase transformation path during the cooling process after activation. Therefore, even if the power is cut off and the temperature is cooled to ambient temperature after one heating activation, the gasket will still stably maintain the axial compression state after recovery, realizing a semi-passive compensation mechanism that is effective for a long time after one heating, which is different from the active compensation mechanism of the binary NiTi scheme that requires continuous heating.

[0034] Regarding the activation mechanism of the SMA gasket: Since the actual operating environment temperature of offshore wind turbine towers is typically -10°C to +35°C, which is far lower than the Af temperature (60-80°C) of NiTiNb alloy after pre-deformation treatment, simply relying on changes in ambient temperature cannot trigger the reverse phase transition recovery of the SMA gasket. Therefore, this invention provides a heating element 18 on the outer periphery of each SMA gasket assembly 13. The heating element 18 can be a ring-shaped resistance heating film (e.g., a mica thin-film heater wound with nickel-chromium alloy resistance wire, with a power density of 2-5 W / cm²), or alternatively, an electromagnetic induction heating coil. The active thermal activation process is as follows: When the data acquisition and control unit 17 determines, based on the impedance spectrum monitoring results of the piezoelectric ceramic sensor 16, that the preload of a certain screw has decreased beyond a set threshold (e.g., 10% of the initial preload), the control system energizes the heating element 18 at the corresponding position, heating the SMA washer to above the Af temperature (target heating temperature 80–100°C), triggering the reverse martensitic phase transformation of the NiTiNb alloy, generating constrained recovery stress (150–300 MPa), thereby compensating for the decrease in bolt preload. The duration of the heating process depends on the washer quality and environmental heat dissipation conditions, typically ranging from 3 to 10 minutes. After heating is completed, the power is turned off. Due to the wide hysteresis characteristics of the NiTiNb alloy (As-Af hysteresis width greater than 150°C), the SMA washer remains in its recovered axial compression state after cooling to ambient temperature, achieving a long-term effective semi-passive compensation effect from a single heating process.

[0035] like Figure 5 As shown, the data acquisition and control unit 17 receives three types of sensing signals in real time: strain signals from the FBG sensing channel 11 and the pre-embedded strain sensor 12, sliding signals from the interface displacement sensor 15, and axial force signals from the piezoelectric ceramic sensing sheet 16. The control unit is equipped with a preload deviation judgment module. When the average axial force of a certain screw assembly deviates from the target value by more than 3% to 10% of the preset threshold, the hydraulic actuator is driven to perform active hydraulic compensation on the corresponding sector or the entire turn through the hydraulic microchannel 14. For cases where the axial force deviation does not reach the active compensation threshold but exceeds the passive compensation triggering condition, the SMA washer assembly 13 automatically provides restoring force for passive compensation. The two compensation mechanisms work together to form an active + passive dual closed-loop self-maintaining system. When the average axial force of a certain screw assembly deviates from the target value by more than 3% to 10% of the preset threshold, the hydraulic actuator is first driven to perform active hydraulic compensation (second-level rapid response) on the corresponding sector or the entire screw assembly through the hydraulic microchannel 14; at the same time, the SMA gasket heating program (semi-passive long-term compensation) is started, and the SMA gasket is thermally activated by the heating element 18 at the corresponding position; the two work together to form a closed-loop self-compensation system with short-term rapid response and long-term stable maintenance. When the cumulative slippage of the interface exceeds 50% of the design allowable value, an early warning is triggered and a manual on-site inspection is prompted. The specific collaborative relationship is as follows: slip decoupling interface layer → differential preload requirement → independent hydraulic circuits for inner and outer rings → embedded hydraulic microchannels → SMA gasket zonal arrangement → piezoelectric ceramic impedance sensing → closed-loop compensation decision → joint execution of active hydraulics (second-level response) and semi-passive SMA thermal activation (long-term stability) → global strain verification of the embedded fiber optic sensing field → LVDT interface state confirmation. The absence of any link in this closed-loop chain will lead to a significant decrease in the overall technical performance. The piezoelectric ceramic sensor 16 is directly embedded inside the SMA gasket assembly 13. The specific integration process is as follows: during the machining stage of the SMA gasket blank, a circular receiving cavity with a depth of 2-3 mm and a diameter of 8-15 mm is milled along the end face or side of the gasket; the PZT-5A type piezoelectric ceramic sheet (thickness 0.5 mm) together with the temperature compensation electrode is installed into a pre-prepared ceramic or polyimide thin-walled encapsulation shell (wall thickness 0.2-0.3 mm); the encapsulated PZT chip is placed into the receiving cavity and filled and sealed with high-temperature ceramic glue (temperature resistance ≥200°C); the signal lead is led out to the external terminal through the radially pre-drilled micro-hole (diameter 0.8-1.2 mm) of the SMA gasket assembly 13. The purpose of the encapsulation shell is to isolate the effects of microscopic lattice distortion and internal stress fluctuations during the SMA phase transition on the brittle PZT ceramic, while ensuring good mechanical coupling between PZT and the SMA substrate. This allows the electrical impedance characteristics of PZT to accurately reflect the local mechanical impedance changes of the screw-washer-flange assembly. Experimental verification shows that the encapsulated PZT chip maintains stable impedance characteristics even after the SMA washer undergoes multiple heating-cooling cycles (more than 50 cycles at 80–100°C), without exhibiting brittleness or bonding failure. The piezoelectric ceramic sensor 16 acquires real-time information on screw axial force changes through electromagnetic impedance spectroscopy (EMI) analysis. The specific analysis method is as follows: impedance measurement employs a frequency scanning method, with a scanning frequency range of 30 kHz to 400 kHz and a frequency step of 100 Hz. Within this frequency range, the electrical impedance characteristics of the PZT are coupled with the local mechanical impedance of the screw-washer-flange assembly, resulting in multiple resonance peaks on the impedance spectrum curve. Screw axial force changes are characterized by the following two quantitative indicators: First, the resonant frequency offset method: Select the resonant peak with the highest sensitivity (usually the first or second order resonant peak in the range of 50–200 kHz) and record its resonant frequency fn. Increased screw axial force leads to increased contact stiffness and a higher resonant frequency; decreased axial force leads to a lower resonant frequency. A calibration curve of fn-F (resonant frequency - axial force) is established through graded loading calibration experiments during the installation phase, which can be fitted as... F = a·f n 2 + b·f n The quadratic polynomial form of + c, where the coefficients a, b, and c are determined by regression of the calibration data.

[0036] Second, the root mean square deviation index (RMSD) method: using the impedance spectrum under the initial healthy state as the reference spectrum, the RMSD value between the current impedance spectrum and the reference spectrum is calculated. The formula is RMSD = √[Σ(Zi - Zi0)]. 2 / Σ(Zi0) 2 ], where Zi is the real part of the current impedance and Zi0 is the real part of the reference impedance, and the summation range covers the entire scanning frequency range. The RMSD value and the change in axial force have an approximately linear relationship, and the RMSD-ΔF mapping relationship can be established through calibration.

[0037] Temperature Compensation Method: Due to the wide temperature range at sea (-10°C to +35°C), the impedance spectrum is significantly affected by temperature. This invention employs the Effective Frequency Shift (EFS) algorithm for temperature compensation. During each measurement, the ambient temperature is simultaneously acquired (measured by a temperature-sensitive grating in a pre-embedded FBG sensing fiber). The current impedance spectrum is then frequency-axis corrected using the reference spectrum at the reference temperature and the temperature-frequency shift coefficient before calculating the RMSD value, thereby eliminating the interference of temperature changes on axial force interpretation.

[0038] On the other hand, the present invention provides a method for in-service monitoring of offshore wind turbine reinforced concrete towers. This monitoring method, based on the aforementioned integrated structure-sensor prefabricated transition connection component for offshore wind turbine reinforced concrete towers, specifically includes the following steps: Figure 6 As shown: S1, Prefabrication of transition connection component body 3 and sensor integration: The transition connection component body 3 is formed in a factory environment, and the mounting slots of FBG sensing channel 11, strain sensor, hydraulic microchannel 14 and interface displacement sensor 15 are pre-embedded simultaneously. S2, On-site installation and system calibration: The prefabricated transition connection component 3 is hoisted into place on-site, the sliding decoupling interface layer, screw assembly and SMA washer assembly 13 are installed, the data acquisition and control unit 17 is connected and zero-point calibration is completed. S3, Inner and outer double ring differential preload: Differential preload force is applied to the inner ring screw assembly 7 and the outer ring screw assembly 8 through their respective independent hydraulic circuits; S4, Service load monitoring starts: After the tower is installed and put into operation, the data acquisition and control unit 17 continuously collects data from each sensor channel at a preset sampling frequency. S5, Multi-source data synchronous acquisition and fusion: Synchronously acquire strain signals from FBG sensing channel 11 and strain sensor, slip signal from interface displacement sensor 15 and impedance spectrum signal from piezoresistive impedance sensing chip, and perform effective frequency shift temperature compensation on impedance spectrum based on ambient temperature acquired by FBG temperature grating, and perform multi-source data fusion analysis. S6, Preload deviation judgment: When the screw shaft force measured by the piezoresistive impedance sensor chip deviates from the target value by more than 3% to 10% of the set threshold, or when the cumulative slip of the interface measured by the interface displacement sensor 15 exceeds 50% of the design allowable value, an early warning is triggered. S7, Closed-loop compensation execution: Active hydraulic compensation, hydraulic oil is injected into the hydraulic tensioning chamber corresponding to the screw with reduced preload through the hydraulic microchannel 14, and the screw is re-tensioned to the target preload, providing short-term compensation with a fast response in seconds; SMA thermal activation compensation involves heating the corresponding SMA gasket to a temperature not lower than its austenitic phase transformation completion temperature Af using the heating element on the outer periphery of the SMA gasket assembly 13, triggering the constrained reverse phase transformation recovery of the NiTiNb alloy, generating an axial recovery stress of 150-300 MPa to maintain the screw preload for a long time, and providing semi-passive long-term compensation. Active hydraulic compensation and SMA thermal activation compensation work together to form a closed-loop self-compensation system with short-term response and long-term maintenance. S8, Data Recording and Health Assessment: Store the time history data of each channel, compensation event records and damage index calculation results in the data acquisition and control unit 17, and generate structural health assessment reports periodically; S9, Early Warning Output and Maintenance Decision: When the strain of the transition connection component body reaches the design allowable value, the cumulative slippage of the interface exceeds the limit, or the number of preload compensations exceeds the set threshold, an early warning signal is output and maintenance suggestions are provided.

[0039] In this embodiment, in step S3, the inner ring screw assembly 7 is pre-tightened to 0.6 to 0.8 times the corresponding screw yield strength, and the outer ring screw assembly 8 is pre-tightened to 0.3 to 0.5 times the corresponding screw yield strength.

[0040] In a preferred application scenario, the transition connection component body 3 of the present invention is applied to a 10MW offshore wind power steel-concrete hybrid tower. The outer diameter of the transition connection component body 3 is 6.0m, the wall thickness is 60mm, and the height is 1.5m. The inner ring screw group 7 uses 12 M36 grade 10.9 grade high-strength screws, the outer ring screw group 8 uses 24 M27 grade 10.9 grade high-strength screws, there are 6 FBG sensing channels 11, each with 5 FBG grating nodes, for a total of 30 measuring points, and 8 pre-embedded strain sensors 12. Six LVDT miniature displacement sensors are installed in each sliding decoupling interface layer. SMA washers are installed on four representative screws in the inner ring and eight in the outer ring. The hydraulic microchannel 14 is divided into four independent sectors. This configuration enables self-monitoring, self-diagnosis and self-maintenance of the transition connection component body 3 throughout its entire life cycle.

[0041] The heating element 18 is set as a resistance heating film or an electromagnetic induction heating coil. The power density of the resistance heating film is 2 to 5 W / cm². The target heating temperature of the SMA gasket assembly 13 is 80 to 100°C, and the heating duration is 3 to 10 minutes. After heating is completed, the power is turned off. Due to the wide hysteresis characteristics of NiTiNb alloy, the SMA gasket assembly 13 maintains the recovered axial compression state after cooling to the ambient temperature, realizing long-term effective semi-passive compensation with a single heating.

[0042] The piezoresistive impedance sensor chip obtains information on the screw axial force variation through electromagnetic impedance spectroscopy analysis. The frequency scanning range is 30 kHz to 400 kHz, with a frequency step of 100 Hz. The screw axial force variation is quantitatively characterized by two methods: the resonant frequency shift method and the root mean square deviation (RMSD) method.

[0043] The slip-decoupling interface layer in this invention differs fundamentally from traditional PTFE slip bearings in bridge engineering in three key ways: First, the former is a microtextured composite structure with directional microgrooves, while the latter is an isotropic continuous PTFE sliding surface; second, the former only allows a small amount of controllable slip along the loading direction (typically 0.5–2 mm), aiming to release shear stress concentration at the steel-concrete interface, while the latter allows free sliding with large displacements (typically tens to hundreds of millimeters), aiming to compensate for temperature deformation and seismic displacement; third, the two differ in their functional purpose, mechanical action, and design parameters. The slip-decoupling interface layer of this invention cannot be directly replaced by any existing bridge bearing product.

[0044] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A prefabricated transition connection component for a structure-sensor integrated offshore wind power steel-concrete tower, characterized in that, include: The transition connection component body has multiple pre-embedded strain sensors inside. The upper and lower end faces of the transition connection component body are respectively provided with a lower flange and an upper flange. The lower end face of the lower flange and the upper end face of the upper flange are respectively provided with a sliding decoupling interface layer and an upper sliding decoupling interface layer. Both the sliding decoupling interface layer and the upper sliding decoupling interface layer are provided with interface displacement sensors inside. The system comprises an inner ring screw assembly and an outer ring screw assembly. The inner ring screw assembly connects the lower flange to the lower concrete section ring, while the outer ring screw assembly connects the upper flange to the upper steel tower section. Each of the inner and outer ring screw assemblies is equipped with an independent hydraulic pre-tightening circuit. SMA gasket assemblies are provided at the connection points between the inner ring screw assembly and the lower flange, as well as at the contact points between the outer ring screw assembly and the upper sliding decoupling interface layer. Both the inner ring screw assembly and the lower concrete section ring are mounted on a bottom mounting base plate. An FBG sensing channel is disposed within the wall of the transition connection member body, and a fiber Bragg grating sensing fiber is inserted inside the FBG sensing channel. A data acquisition and control unit is used to receive signals from various sensors in real time.

2. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, The SMA gasket assembly has a heating element on its outer periphery.

3. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, The wall of the transition connecting component body is provided with a hydraulic microchannel. The hydraulic microchannel is configured as a hydraulic passage with an inner diameter of 3 to 8 mm machined in the wall of the transition connecting component body. The hydraulic microchannel is connected to the hydraulic tensioning cavity at each screw position in the circumferential direction. The hydraulic microchannel is provided with a zone control valve.

4. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, Both the sliding decoupling interface layer and the upper sliding decoupling interface layer include two layers of micro-textured metal sheets and a PTFE composite friction-reducing layer sandwiched between them. The surface of the micro-textured metal sheets is provided with directional microgrooves with a depth of 0.1 to 0.3 mm and a spacing of 2 to 5 mm.

5. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, The interface displacement sensor is configured as an LVDT miniature displacement sensor, and multiple interface displacement sensors are symmetrically arranged on both sides along the loading direction.

6. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, The SMA gasket assembly includes a lower SMA gasket and an upper SMA gasket. The lower SMA gasket is located at the connection position between the inner ring screw assembly and the lower flange. The upper SMA gasket is located at the contact position between the outer ring screw assembly and the upper sliding decoupling interface layer. Both the lower and upper SMA gaskets are embedded with piezoelectric ceramic sensing sheets.

7. The prefabricated transition connection component for an integrated structure-sensor offshore wind power steel-concrete tower according to claim 1, characterized in that, The target preload of the inner screw assembly is 0.6 to 0.8 times the yield strength of the corresponding screw, and the target preload of the outer screw assembly is 0.3 to 0.5 times the yield strength of the corresponding screw.

8. A method for in-service monitoring of offshore wind turbine reinforced concrete towers, based on the prefabricated transition connection component for offshore wind turbine reinforced concrete towers integrating structure and sensing as described in any one of claims 1-7, characterized in that, Specifically, the following steps are included: S1, Prefabrication of the transition connection component body and sensor integration: The transition connection component body is formed in a factory environment, and the FBG sensing channel, strain sensor, hydraulic microchannel and interface displacement sensor mounting slot are pre-embedded simultaneously. S2, On-site installation and system calibration: The prefabricated transition connection component body is hoisted into place on-site, the sliding decoupling interface layer, screw assembly and SMA gasket assembly are installed, the data acquisition and control unit is connected and zero-point calibration is completed; S3, Inner and outer double ring differential preload: Differential preload is applied to the inner ring screw assembly and the outer ring screw assembly through their respective independent hydraulic circuits; S4, Service Load Monitoring Start-up: After the tower is installed and put into operation, the data acquisition and control unit continuously collects data from each sensor channel at a preset sampling frequency. S5, Multi-source data synchronous acquisition and fusion: Synchronously acquire strain signals from the FBG sensing channel and strain sensor, slip signals from the interface displacement sensor, and impedance spectrum signals from the piezoresistive impedance sensing chip, and perform effective frequency shift temperature compensation on the impedance spectrum based on the ambient temperature acquired by the FBG temperature grating, and perform multi-source data fusion analysis. S6, Preload Deviation Judgment: When the screw shaft force measured by the piezoresistive impedance sensor chip deviates from the target value by more than 3% to 10% of the set threshold, or when the cumulative slip of the interface measured by the interface displacement sensor exceeds 50% of the design allowable value, an early warning is triggered. S7, Closed-loop compensation execution: Active hydraulic compensation, injects hydraulic oil into the hydraulic tensioning chamber corresponding to the screw with reduced preload through hydraulic microchannel, re-tensions the screw to the target preload, and provides short-term compensation with a fast response in seconds; SMA thermal activation compensation uses heating elements on the outer periphery of the SMA washer assembly to heat the corresponding SMA washer to a temperature not lower than its austenitic phase transformation completion temperature Af, triggering the constrained reverse phase transformation recovery of NiTiNb alloy, generating axial recovery stress of 150-300 MPa to maintain screw preload for a long time, providing semi-passive long-term compensation. Active hydraulic compensation and SMA thermal activation compensation work together to form a closed-loop self-compensation system with short-term response and long-term maintenance. S8, Data Recording and Health Assessment: Stores time history data, compensation event records and damage index calculation results of each channel in the data acquisition and control unit, and generates structural health assessment reports periodically; S9, Early Warning Output and Maintenance Decision: When the strain of the transition connection component reaches the design allowable value, the cumulative slippage of the interface exceeds the limit, or the number of preload compensations exceeds the set threshold, an early warning signal is output and maintenance suggestions are provided.

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