Wave-splash impact force measurement method and system based on piezoelectric fiber composites

Abstract

The application discloses a kind of wave splash impact force measurement method and system based on piezoelectric fiber composite material, MFC sensor is fixed on base to constitute impact force measuring device, and the mathematical model of impact force and output voltage is established by water drop free fall impact calibration, multiple MFC sensors are vertically arranged along the surface of structure and the voltage time history signal generated by wave splash is synchronously collected, the impact event identification based on statistical threshold is sequentially carried out to voltage time history signal, the noise is removed based on adjacent sensor correlation coefficient, and the impact type discrimination based on voltage peak value and pulse width combination feature, impact event is divided into single droplet impact, splash water droplet group impact and continuous water film impact and transition type impact four types, finally, according to calibration model, the voltage signal after processing is converted into wave splash impact force value.The application solves the problem that traditional pressure sensor measures wave splash impact force, and stability is poor, impact type cannot be distinguished.

Description

Technical Field

[0001] This invention relates to the field of marine engineering monitoring technology, specifically to a method and system for measuring wave splash impact force based on piezoelectric fiber composite materials. Background Technology

[0002] Impact refers to the phenomenon where an object strikes another object at a certain velocity, resulting in a rapid energy conversion at the moment of impact. The impact contact process is a highly complex nonlinear motion process, influenced by factors such as the material characteristics, structure, and impact velocity of the object. A key characteristic of impact is its short contact time, typically on the order of milliseconds or microseconds, requiring the release of a high-intensity load within this extremely short period, easily leading to material damage. Impact contact phenomena are prevalent in marine engineering, civil engineering, and aerospace engineering, and the impact problem is receiving increasing attention due to the practical needs of engineering design. Macro Fiber Composites (MFCs) are composed of piezoelectric ceramics and polymers. They combine the excellent properties of piezoelectric crystal materials and polymer matrices, exhibiting good flexibility, high sensitivity, and short response time. Due to the positive piezoelectric properties of piezoelectric materials, upon impact, opposite charges appear on the upper and lower surfaces of the MFC, creating a potential difference between the two electrodes. This charge or potential difference is proportional to the applied stress. Based on this characteristic, MFCs are well-suited for measuring impact contact processes.

[0003] MFC sensors are advanced thin-film sensors that can be embedded into any structural surface and offer high reliability under complex load environments. Therefore, when used as sensors, MFCs are not only suitable for measuring impact contact processes in engineering fields such as construction, automotive, and aerospace, but also for addressing impact problems in marine engineering with complex load environments, such as those experienced by ships, marine pipelines, and offshore platforms.

[0004] Currently, wave splash impact force measurement often relies on traditional water pressure sensors, which suffer from drawbacks such as high cost, slow response, poor stability, and single-point measurement capability. While piezoelectric materials have sensing potential, piezoelectric ceramics are fragile and piezoelectric thin films have low precision. Macrofiber composite materials (MFCs) combine flexibility and high sensitivity, but have not yet been used for wave splash impact force measurement. Summary of the Invention

[0005] This invention proposes a method and system for measuring wave splash impact force based on piezoelectric fiber composite materials, which solves the problem that existing technologies cannot measure wave impact force using traditional pressure sensors.

[0006] To address the aforementioned technical problems, this invention provides a method for measuring wave splash impact force based on piezoelectric fiber composite materials, comprising the following steps: Step S1: Fix the piezoelectric fiber composite material sensor onto the substrate to form an impact force measuring device; Step S2: Control water droplets to fall freely from a preset height to impact the piezoelectric fiber composite material sensor, and establish a calibration model of impact force and output voltage; Step S3: Vertically arrange multiple piezoelectric fiber composite material sensors along the surface of the structure and synchronously collect voltage time history signals generated by wave splash; Step S4: After sequentially performing impact event identification, adjacent sensor correlation noise removal, and impact type discrimination on the voltage time history signal, the processed voltage time history signal is converted into wave splash impact force value according to the calibration model and the correction coefficient of the corresponding impact type.

[0007] Preferably, the piezoelectric fiber composite material sensor in step S1 includes two layers of interdigitated electrodes clamping a rectangular cross-section of piezoelectric ceramic fiber. The gap between the piezoelectric ceramic fiber and the interdigitated electrodes is filled with polymer resin to form a composite structure. The piezoelectric fiber composite material sensor is fixed to the center of the substrate with epoxy resin and is tightly bonded to the substrate. The substrate is set at a preset angle with the horizontal plane. The material of the substrate is one of bakelite board, 1060 pure aluminum plate, H62 brass plate or SUS304 stainless steel plate.

[0008] Preferably, the establishment of the calibration model for impact force and output voltage in step S2 includes the following steps: Step S21: Construct a water droplet impact platform, control water droplets to fall freely from a preset height to impact the piezoelectric fiber composite material sensor, and collect the peak output voltage at different drop heights. ; Step S22: Based on the condition that no splashing occurs during the water droplet impact and the rebound velocity is approximately zero, calculate the maximum impact force according to the impulse relationship: ; In the formula, For maximum impact force; Peak factor; The density of the water droplets; The diameter of the water droplet; This represents the actual collision velocity of the water droplet when it reaches the sensor surface. This is the equivalent collision time; Step S23: Establish a quadratic fitting relationship between the maximum impact pressure and the peak value of the output voltage as the calibration model: ; In the formula, This represents the maximum impact pressure. These are calibration coefficients.

[0009] Preferably, step S3, which involves vertically arranging multiple piezoelectric fiber composite material sensors along the surface of the structure, includes the following steps: setting up an upright plate model in a wave tank, arranging multiple piezoelectric fiber composite material sensors at equal intervals along the vertical center line of the upright plate model, wherein the arrangement positions of the piezoelectric fiber composite material sensors cover the area above, at, and below the still water surface, and the placement direction of the upright plate model is perpendicular to the wave running direction.

[0010] Preferably, the synchronous acquisition of voltage time history signals generated by wave splash in step S3 includes the following steps: for regular wave conditions with different wave heights, acquire the voltage time history signals of each piezoelectric fiber composite material sensor under wave splash impact, filter the voltage time history signals to obtain the impact peak voltage, and take the average value of the results of multiple repeated tests as the representative peak voltage.

[0011] Preferably, the impact event identification in step S4 includes the following steps: acquiring background segment data of the voltage time history signal during the non-impact phase, and calculating the average voltage of the background segment. and standard deviation Define the threshold for identifying impact events: ; In the formula This is the threshold coefficient; When the voltage peak value in the voltage time history signal Greater than the impact event identification threshold At that time, it is determined that a wave splash impact event has occurred.

[0012] Preferably, the adjacent sensor correlation noise removal in step S4 includes the following steps: for vertically adjacent sensors... The and the first For the piezoelectric fiber composite material sensor, the correlation coefficient between the voltage peak sequences of the two sensors is calculated: ; When the correlation coefficient is greater than a preset correlation threshold, the first... The and the first The signals recorded by each piezoelectric fiber composite material sensor represent the same wave splash impact event. The corresponding voltage peak signal is retained for subsequent impact force calculation; otherwise, the corresponding signal is judged as noise and discarded.

[0013] Preferably, the impact type determination in step S4 includes the following steps: The moment when the voltage signal abruptly begins in the voltage time history signal is defined as... The moment when the voltage signal returns to zero is Then the pulse width for: ; Voltage classification boundaries were determined using water droplet calibration experiments and wave tank experiments. , and time classification boundaries , ; According to voltage peak With pulse width The combined characteristics of impact events classify them into the following three types: when Greater than and Less than When the time frame is short, it is determined to be a single droplet impact; when multiple local voltage peaks with similar amplitudes appear within a preset time window, it is determined to be a splashing droplet group impact; when Less than and Greater than If the impact event does not meet the above three criteria, it is determined to be a continuous water film impact; if the impact event does not meet the criteria for the above three types, it is determined to be a transitional impact, and the impact pressure is calculated using the same calibration model as the single droplet impact.

[0014] Preferably, in step S4, when converting the processed voltage time history signal into wave splash impact force values ​​based on the calibration model and the correction coefficients corresponding to the impact type, different conversion strategies are adopted for different impact types: For single-droplet impact, the voltage peak value is directly... Substitute into the calibration model Calculate the impact pressure; For the impact of splashing water droplets, the peak envelope within a preset time window is extracted, and the equivalent voltage of the envelope is substituted into the calibration model to obtain the uncorrected impact pressure. Multiply by the swarm impact correction factor The corrected impact pressure is obtained, where ; For continuous water film impact, substituting the voltage peak value into the calibration model yields the uncorrected impact pressure. Then multiply by the water film correction factor The corrected impact pressure is obtained. ; The group impact correction factor and water film correction factor The following method is used to determine the location: a reference pressure sensor is simultaneously deployed at a position adjacent to the location of the piezoelectric fiber composite material sensor, and the measured pressure value of the reference pressure sensor under the same impact event is used. Alternative theoretical calculations were performed for both droplet swarm impact events and water film impact events. and The mean of the ratios is obtained. and .

[0015] This invention also provides a wave splash impact force measurement system based on piezoelectric fiber composite materials. The system is used to implement the aforementioned wave splash impact force measurement method based on piezoelectric fiber composite materials, comprising: Multiple piezoelectric fiber composite material sensors: Each of the piezoelectric fiber composite material sensors is composed of piezoelectric ceramic fibers with a rectangular cross section sandwiched between two layers of interdigitated electrodes, with the gaps filled with polymer resin; Substrate: Each of the piezoelectric fiber composite material sensors is fixed on the corresponding substrate, which is configured to be installed at a preset angle; Dynamic signal acquisition system: connected to the output end of each piezoelectric fiber composite material sensor via wires, used to synchronously acquire the charge signals output by each piezoelectric fiber composite material sensor; Computer terminal: Connected to the dynamic signal acquisition system via a gigabit network cable, used to receive, store and process voltage signals, and perform impact event identification, noise removal, impact type discrimination and impact force calculation based on the calibration model.

[0016] The advantages of this invention include at least the following: 1. Utilizing the high sensitivity and short response time characteristics of the MFC sensor, it can accurately capture the transient process of wave splash impact. In addition, the MFC sensor has good flexibility and can fit into complex structural surfaces, making it suitable for measurement needs of irregular structures such as ships and offshore platforms. 2. Thin-film MFC sensors can be flexibly deployed at multiple locations on the surface of structures to achieve spatially distributed impact force measurement, overcoming the limitation of traditional sensors that can only measure at a single point. Compared with traditional water pressure sensors, MFC sensors are lower in cost, have a sealed structure, long lifespan, and are moisture-resistant, making them suitable for long-term monitoring in marine engineering. 3. Through Dirac δ The function models the transient impact force generated by water droplet collision, establishes a quantitative relationship between the peak output voltage and the maximum impact force, ensures the accuracy and repeatability of the measurement results, and, based on the characteristic that the piezoelectric effect is only sensitive to transient loads, naturally filters out the interference of hydrostatic pressure, directly obtains the dynamic pressure component of wave splash impact, and simplifies data processing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a water droplet-plate impact testing system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the MFC sensor structure in an embodiment of the present invention; Figure 3 This is a schematic diagram of the connection between the MFC sensor and the substrate according to an embodiment of the present invention, wherein (a) is a top view and (b) is a side view; Figure 4 This is a schematic diagram of the connection between the base and the upright in an embodiment of the present invention; Figure 5 This is a schematic diagram of the connection between the upright and the crossbar according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the connection between the universal clamp and the dropper in an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the impact of water droplets on the MFC sensor and the impact force in an embodiment of the present invention; Figure 8 This is a schematic diagram of the fitting curve between the maximum impact pressure of the water droplet and the peak voltage in an embodiment of the present invention; Figure 9 This is a schematic diagram of measuring wave splash impact by attaching an MFC sensor to a wave tank according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the upright board model and MFC numbering in an embodiment of the present invention; Figure 11 This is a schematic diagram of the MFC voltage time history curve and signal processing parameter definition within the wave cycle in an embodiment of the present invention; Figure 12 This is a schematic diagram of the wave splash impact force distribution on a vertical plate with different incident wave heights in an embodiment of the present invention.

[0018] In the diagram: 1-MFC sensor; 2-substrate; 3-wire; 4-dynamic signal acquisition system; 5-gigabit network cable; 6-computer terminal; 7-interdigital electrode; 8-piezoelectric ceramic fiber; 9-polymer resin; 10-base; 11-upright pole; 12-bolt; 13-universal clamp; 14-dropper; 15-butterfly nut; 16-crossbar; 17-nut; 18-wave trough; 19-upright plate model; 20-wave height meter. Detailed Implementation

[0019] 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 protection scope of the present invention.

[0020] This invention provides a method and system for measuring wave splash impact force based on piezoelectric fiber composite materials. The overall technical solution includes four stages: fabrication of the impact force measurement sensor device, sensor calibration, wave splash impact force measurement, and signal processing and impact feature identification. These four stages will be described in detail below: Step S1: Fix the piezoelectric fiber composite material sensor onto the substrate to form an impact force measuring device.

[0021] like Figure 1 As shown, the impact force measuring device provided in this embodiment includes an MFC sensor 1, a base 2, a wire 3, a dynamic signal acquisition system 4, a gigabit network cable 5, and a computer terminal 6.

[0022] like Figure 2 As shown, the MFC sensor 1 uses piezoelectric fiber composite material. In this embodiment, piezoelectric fiber composite material of model P3-M2814 is selected, with dimensions of 38 mm × 20 mm × 0.32 mm and a Poisson's ratio of 0.30. The MFC sensor 1 consists of two layers of interdigitated electrodes 7 sandwiching rectangular cross-section piezoelectric ceramic fibers 8, with the remaining gaps filled with polymer resin 9 to form a composite structure. The purpose of using rectangular cross-section piezoelectric ceramic fibers 8 is to increase the effective contact area between the electrodes and the fibers, improve the transmission efficiency of the electric field in the composite material, and thus enhance the sensitivity of the electrical signal output under impact load.

[0023] like Figure 3 As shown, the MFC sensor 1 is fixed to the center of the substrate 2 with epoxy resin adhesive, ensuring a tight fit between the sensor and the substrate to reduce interfacial energy loss and improve impact load transfer efficiency. The substrate 2 is installed at a 45-degree angle to the ground to prevent water droplets from accumulating above the MFC sensor 1 and affecting the measurement results. Two wires 3 extend from one side of the sensor, serving as the positive and negative output terminals for transmitting piezoelectric signals.

[0024] The substrate 2 can be made of different materials to change the boundary stiffness conditions, including bakelite board, 1060 pure aluminum plate, H62 brass plate, or SUS304 stainless steel plate, all with dimensions of 100mm × 100mm × 4mm. The elastic moduli of the above four substrate materials are 2.45GPa, 71GPa, 103GPa, and 194.02GPa, respectively, and the Poisson's ratios are 0.36, 0.33, 0.324, and 0.30, respectively. By changing the substrate material, a comparative study of the impact load transmission characteristics can be achieved. In this embodiment, SUS304 stainless steel plate is preferred as the substrate material.

[0025] When an external impactor strikes the MFC sensor 1, the piezoelectric ceramic fibers inside the sensor generate transient strain and output a charge signal proportional to the impact stress through the piezoelectric effect. This charge signal is transmitted to the dynamic signal acquisition system 4 via the wire 3, converted into a voltage signal, and sampled and recorded at high frequency. This embodiment uses a DH5960 dynamic signal acquisition system, which is capable of acquiring data on impact contact processes at the microsecond level, with a sampling frequency set above 100 kHz. The acquisition system transmits the voltage signal in real time to the computer terminal 6 via a gigabit network cable 5, generating an impact voltage time history curve and completing data storage.

[0026] Step S2: Control the water droplets to fall freely from a preset height to impact the piezoelectric fiber composite material sensor, and establish a calibration model of impact force and output voltage.

[0027] The purpose of the calibration phase is to establish a mathematical model of the impact force and output voltage by impacting the MFC sensor with free-falling water droplets. This phase includes building a water droplet impact platform, establishing a water droplet motion model, and using the Dirac delta method. The process involves four steps: modeling the impact force using a function, establishing a calibration and fitting relationship, and so on.

[0028] First, a water droplet-MFC impact force measurement platform was built. For example... Figure 1 As shown, the platform includes a base 10, a vertical pole 11, bolts 12, a universal clamp 13, a dropper 14, a butterfly nut 15, a crossbar 16, and the aforementioned impact force measuring device, all connected in sequence. Figure 4 As shown, the base 10 and the upright 11 are connected by a nut 17. Figure 5 As shown, the height of the crossbar 16 can be freely adjusted along the vertical direction of the upright 11 using bolts 12. Figure 6 As shown, the dropper 14 is fixed to the crossbar 16 by a universal clamp 13 and locked at a specified height by a butterfly nut 15, allowing the water droplet to fall freely from the specified height and impact the MFC sensor 1. In this embodiment, the diameter of the water droplet is... Take a 5mm water droplet density Take 1000 kg / m 3 .

[0029] After setting up the impact platform, control the water droplets from a height. The MFC sensor was subjected to free fall impact within the range of 0.05~0.5m, and the peak output voltage was collected. To calculate the maximum impact force generated when a water droplet impacts the MFC sensor. A model of the water droplet's motion in the air needs to be established. When a water droplet falls through the air, it is subject to three dominant external forces: gravity... ,buoyancy and air resistance The expressions for each force are as follows: ; ; ; In the formula, It is the acceleration due to gravity; The diameter of the water droplet; The density of the water droplets; air density; This refers to the air drag coefficient; Let be the projected area of ​​the water droplet on a plane perpendicular to the direction of motion. ; The velocity of the water droplet.

[0030] The value of the air resistance coefficient is based on the Reynolds number during the movement of the water droplet. Confirmed, among which , For aerodynamic viscosity, when the water droplet is approximately spherical and in the low to medium Reynolds number range, the air drag coefficient is calculated using an empirical formula. When the Reynolds number is large, We approximate it to be a constant of 0.44.

[0031] air density With air temperature The relationship is: ; A water droplet undergoes two states of motion during free fall: first acceleration, then uniform motion. During the acceleration phase, the equation of motion for the water droplet is: ; When the water droplet reaches a uniform velocity, the net force is zero, and its force equation becomes: Substituting the expressions for each force into the above equations of motion, we obtain the final velocity of the accelerated downward segment as: ; The terminal velocity during uniform motion is: ; In the formula The drop height is the falling height. According to the formula above, it can be calculated that within the ten falling heights of 0.05~0.5m selected in this embodiment, the water droplets are always in the variable acceleration phase and have not yet reached the terminal velocity.

[0032] Because the contact time between the water droplet and the MFC sensor is extremely short, ranging from milliseconds to microseconds, this embodiment of the invention employs Dirac. Describing the transient impact force of water droplets on the MFC sensor using a functional form is a key modeling technique for achieving accurate calibration. It should be noted that Dirac... The function here describes the temporal concentration of the impact force, i.e., the impact force is released in a concentrated manner within a very short time; while the calculation of the impact force amplitude is based on the fluid momentum flux model, i.e., the rate at which fluid momentum is transferred to the impacted surface per unit time. Both describe the temporal characteristics of the impact process and the magnitude of the force, respectively.

[0033] Specifically, the impact force of a water droplet on an MFC sensor is defined. for: when hour, ;when hour, .

[0034] In the formula This represents the maximum impact force generated by the water droplet during its collision with the MFC sensor. This represents the moment when the water droplet collides with the sensor.

[0035] like Figure 7 As shown, the complete process of a water droplet impacting an MFC sensor can be divided into three stages: contact, spreading, and adhesion. Upon contact with a typical wet surface, the water droplet undergoes significant deformation due to inertia and spreads along the sensor surface. Its momentum is converted into an impact force acting on the MFC sensor in a very short time, causing transient bending deformation, which is then converted into a voltage signal output through the piezoelectric effect. As the water droplet's kinetic energy gradually dissipates, the spreading process ends, and the output voltage reaches its peak. Subsequently, under the influence of surface tension, the spread water droplet rebounds to a certain extent, reducing its spreading diameter and increasing its height. Finally, under the combined action of gravity and surface tension, the water droplet completely adheres to and deposits on the MFC sensor surface, completing a full impact response process.

[0036] During the aforementioned impact process, the water droplet does not splash and its rebound velocity is approximately zero. For single-droplet impacts, an impact force model is established using the impulse theorem.

[0037] Diameter The mass of the spherical water droplet is With speed After impacting the sensor surface, it fully adhered, and the speed increased from... When the momentum becomes zero, according to the impulse theorem, the time integral of the force during the impact process equals the change in momentum. .

[0038] In actual collisions, the impact force is not a constant value, but rather rises rapidly to its peak in the initial stage, then gradually decays to zero as the droplets spread and kinetic energy dissipates. For ease of engineering calculations, the aforementioned continuous force pulse is equivalent to a duration of... Amplitude A rectangular pulse that makes the impulses of the two pulses equal: ; Due to the peak value of the actual force pulse Amplitude higher than the equivalent rectangular pulse Introducing peak factor ( Describe the sharpness of the actual force pulse waveform: ; In the formula, The peak factor reflects the degree to which the actual impact force waveform deviates from a rectangular pulse; its value depends on the wetting characteristics of the droplet and the surface, as well as the collision dynamics. For the positive impact of low-velocity water droplets on a typical wetted surface, the peak factor... Typically, it ranges from 1.5 to 3. In this embodiment, due to the use of Dirac... The function models the impact force, and the contact time between the water droplets is extremely short. Under the condition of impulse conservation, the actual peak force is... It will not be significantly higher than the equivalent rectangular pulse amplitude. ,therefore Take 1.5. The maximum impact force corresponding to each height in Table 1 is based on... =1.5 is calculated. To determine the equivalent collision time, a high-speed camera is used to capture the process of a water droplet colliding with the sensor surface, recording the time from initial contact to complete spread of the water droplet.

[0039] It should be noted that the purpose of the above single-droplet impulse model is to provide a theoretical estimate of the impact force as a reference benchmark during the calibration process. The final calibration model... It is by using the theoretical impact pressure value Compared with the measured peak voltage The accuracy of empirical relationships obtained through regression fitting depends on the goodness of fit rather than the precision of the theoretical formula. This represents the equivalent contact area of ​​the droplet. .

[0040] The maximum contact area of ​​a water droplet during its spreading phase can be estimated using empirical relationships, and the maximum spreading diameter of the droplet after impacting the surface is also considered. With Weber number related: .

[0041] ; In the formula, The surface tension of water.

[0042] In this embodiment, 10 different drop heights were set, ranging from 0.05m to 0.5m, with a step size of 0.05m. The DH5960 dynamic signal acquisition system was used to collect the peak voltage generated by the water droplets impacting the MFC sensor at each height. And calculate the corresponding maximum impact force according to the above formula. and maximum impact pressure The calibration test parameters are shown in Table 1.

[0043] Table 1. MFC sensor water droplet calibration test parameters The maximum impact pressure in the above calibration test data With the corresponding peak voltage By performing a fitting, the maximum impact pressure is established. With peak output voltage The quadratic fitting relationship: ; in These are calibration coefficients. In this embodiment, the specific calibration formula for the P3-M2814 MFC sensor is as follows: .

[0044] It should be noted that the calibration formula above is the optimal regression curve obtained by performing a second-order fit on all 10 sets of experimental data points in Table 1 using the least squares method, rather than a calculation formula that corresponds precisely to each point. There is a certain deviation between the calculated values ​​obtained by substituting each peak voltage in Table 1 into this fitting formula and the theoretical impact pressure values ​​in the table. This is an inherent characteristic of regression fitting, and the fitting curve reflects the overall trend of data change.

[0045] like Figure 8 As shown, the goodness of fit between the two is... The result of 0.9912 indicates a strong quadratic correlation between the maximum impact pressure of the water droplet and the square of the peak output voltage of the MFC, verifying the effectiveness of using the Dirac delta method. The rationality and effectiveness of function modeling methods.

[0046] Step S3: Vertically deploy multiple piezoelectric fiber composite material sensors along the surface of the structure and synchronously collect voltage time history signals generated by wave splash.

[0047] After calibration, the MFC sensor is deployed on the surface of the marine structure to collect voltage signals generated by wave splash impact. This embodiment uses a vertical plate model in a wave tank as the measurement object, and the specific implementation process is as follows.

[0048] like Figure 9As shown, a vertical plate model 19 is set up on one side of the wave tank 18. The wave tank is 31.08 m long, of which the test section is 21.07 m long. The tank is 1.08~1.42 m high and 3 m wide. The minimum working water depth is 0.2 m and the maximum working water depth is 0.8 m. In this embodiment, the test water depth d is set to 0.7 m.

[0049] like Figure 10 As shown, the upright plate model 19 is 2.8 m long, 1 m high, and 2 cm thick, with a wave-facing surface of 2.8 m × 1 m. To study the vertical distribution of wave splash impact force, seven MFC sensors 1 were numbered 1 to 7 from top to bottom along the vertical centerline of the upright plate model, with equal spacing of 5 cm between each sensor. The sensors were placed in the center of the plate rather than at the edge to avoid the measurement values ​​being affected by other factors when the left and right sides were close to the tank wall. Among them, MFC sensor 4 was located at the still water surface, sensors 1 to 3 were located above the still water surface at distances of 0.15 m, 0.10 m, and 0.05 m respectively, and sensors 5 to 7 were located below the still water surface at distances of -0.05 m, -0.10 m, and -0.15 m respectively. A wave height meter 20 with a measuring length of 0.5 m was used to measure the wave height.

[0050] During the experiment, the upright plate was placed perpendicular to the direction of wave movement, i.e., the regular wave was incident in the forward direction. In this embodiment, five regular waves with different wave heights were selected for measurement, with wave heights H of 0.03 m, 0.06 m, 0.09 m, 0.12 m, and 0.15 m, respectively, a period T of 1 s for all waves, and a wavelength L of 1.4 m for all waves.

[0051] When a regular wave is incident forward onto a vertical plate, the grid structure positioned in front of the plate locally obstructs and disturbs the incident wave, causing a rapid redistribution of wave momentum under the combined action of the grid and the plate. The obstructed water accelerates vertically at the plate's leading edge, causing the free surface to rise significantly and forming a steep wavefront. As the local wave height and velocity further increase, the uprushing water forms a high-speed water jet on the surface of the plate and grid. This water jet, under conditions where inertial forces dominate and surface tension and viscous constraints are insufficient, undergoes unstable breakup and, under the shearing and dispersing action of the grid structure, splits into a group of water droplets with a certain initial velocity—the wave splash phenomenon. The splashed droplets then impact an MFC sensor positioned above the still water surface, generating a typical transient impact load signal.

[0052] Under each operating condition, the voltage time history signal of each sensor during the impact process is collected, and the peak impact voltage is read after filtering. To improve the reliability of the measurement results, each sensor is subjected to multiple repeated tests under the same operating condition, and the average of the five peak values ​​is taken as the representative peak voltage under that operating condition.

[0053] Step S4: After sequentially performing impact event identification, adjacent sensor correlation noise removal, and impact type discrimination on the voltage time history signal, the processed voltage time history signal is converted into wave splash impact force value according to the calibration model.

[0054] Before converting the voltage signal into an impact force value, the voltage time history signals collected by each sensor need to undergo three signal processing steps: impact event identification, noise removal, and impact type determination. For example... Figure 11 As shown, the moment at which the voltage signal abruptly begins in the MFC voltage time history curve is defined as... The time of voltage peak is Peak voltage is The time when the voltage signal returns to zero is Then the pulse width is: .

[0055] Because the MFC sensor continuously outputs a voltage signal during wave tank testing, it is necessary to accurately identify wave splash impact events from the continuous voltage time history curve. The specific method is as follows: During the non-impact phase, i.e., before the wave reaches the sensor location, a segment of background voltage data is collected, and the average voltage value of this segment is calculated. and standard deviation : ; ; Define the threshold for identifying impact events: ; in The threshold coefficient is taken in this embodiment. , corresponding to 3 The principle is that a voltage signal exceeding three standard deviations from the mean is considered a valid impulse event. This applies when the voltage peak value in the voltage time-history signal... satisfy At that moment, it was determined that a wave splash impact event had occurred, and the corresponding event was recorded. , , and .

[0056] In actual wave tank tests, factors such as electromagnetic interference and mechanical vibration may cause false impact signals from individual sensors. Since the same wave splash event should act simultaneously on multiple vertically adjacent MFC sensors, the spatial correlation of signals from adjacent sensors can effectively distinguish between real impact events and noise.

[0057] For the vertically adjacent first The and the first Two sensors were used to extract the voltage peak sequence identified by both sensors within the same wave cycle. and The following signal similarity index is defined as the correlation coefficient: ; In this embodiment, the correlation threshold is set to 0.7. When At that time, the judgment of the first The and the first The signals recorded by each sensor represent the response to the same wave splash impact event, and the corresponding peak voltage signal is retained for subsequent impact force calculation. When When the signal is detected, it is identified as noise and removed. The threshold of 0.7 is selected based on the following: In the wave tank test of this embodiment, statistical analysis showed that the correlation coefficient of real wave splash events between adjacent sensors was greater than 0.75, while the correlation coefficient of noise signals such as electromagnetic interference was usually lower than 0.3. 0.7 can be used as a dividing value to effectively distinguish between them.

[0058] When waves splash and impact structures, the impact events can be categorized into three types based on the morphology of the impacting water: single-droplet impact, splash droplet swarm impact, and continuous water film impact. These three impact types exhibit different waveform characteristics on the voltage-time history curve of the MFC sensor, which can be identified by the voltage peak value. With pulse width The combined features are used for discrimination. Voltage classification boundaries are determined through water droplet calibration experiments and wave tank experiments. , and time classification boundaries , .

[0059] The method for determining the classification boundary is as follows: (1) In the water droplet calibration experiment, the distribution range of voltage peak values ​​and the corresponding pulse duration distribution range generated by the impact of a single droplet at different falling heights were statistically analyzed, and the lower limit of the voltage peak value distribution was taken as the standard value. Take the upper limit of the pulse duration as ; (2) In the wave tank experiment, the distribution range of voltage peak value and pulse duration corresponding to continuous water film impact were statistically analyzed, and the upper limit of the voltage peak value distribution was taken as the upper limit of the voltage peak value distribution. Take the lower limit of the pulse duration as .

[0060] In this embodiment, based on the water droplet calibration experiment results, the peak value of the single droplet impact voltage is mainly distributed above 500mV, and the pulse duration is concentrated in the range of 1~2ms; based on the wave tank experiment results, the peak value of the continuous water film impact voltage is mainly below 200mV, and the pulse duration is usually greater than 20ms. Therefore, this embodiment takes... =500mV, =2ms, =200mV, =20ms.

[0061] The specific judgment rules are as follows: (1) Single droplet impact: High voltage peak and short pulse width, i.e., satisfying and Single droplet impact corresponds to a single water droplet striking the sensor surface at a high speed, generating a sharp, high-amplitude, short-pulse voltage signal.

[0062] (2) Impact of splashing water droplets: Within a preset time window, which is 10ms in this embodiment, three or more local voltage peaks with similar amplitudes appear. The amplitude difference between each peak does not exceed 30% of the maximum peak value. The impact of the splashing water droplets corresponds to multiple water droplets formed after the wave breaks, which hit the sensor surface one after another in a short period of time.

[0063] (3) Continuous water film impact: low voltage peak and long pulse width, i.e., satisfying and The continuous water film impact corresponds to the continuous water film formed by the upward movement of waves covering the sensor surface, generating a low-amplitude, long-duration voltage signal.

[0064] For impact events that do not meet the above three criteria, such as voltage peaks > But pulse width > The situation is classified as a transitional impact. This type of signal typically corresponds to complex wave action states such as droplet fusion impact, water film entrainment splash, or localized continuous impact, and its characteristics are between those of single droplet impact and continuous water film impact. For transitional impacts, the same calibration model as for single droplet impacts is used. Perform impact pressure calculation.

[0065] By using the above four-step signal processing method chain, reliable impact force data can be extracted from complex wave splash voltage signals, and impact type distribution information can be obtained, providing quantitative basis for the study of wave splash impact mechanism.

[0066] After identifying the impact type, the calibration model is directly applied to single droplet impacts. Transformation; for the impact of splashing water droplets, introduce a group impact correction coefficient. ( Substituting the equivalent voltage of the peak envelope into the calibration model and multiplying by For continuous water film impact, since the water film coverage alters the sensor's boundary conditions, a water film correction coefficient is introduced. ( The water film impact pressure is obtained after correction. The group impact correction coefficient is... and water film correction factor The following method was used to determine the location: a reference pressure sensor was simultaneously deployed at a location adjacent to the location of the piezoelectric fiber composite material sensor, and the measured pressure value of the reference pressure sensor under the same impact event was used. Alternative theoretical calculations were performed for both droplet swarm impact events and water film impact events. and The mean of the ratios is obtained. and The converted data is summarized in Table 2.

[0067] Table 2 Summary of wave splash impact force (kPa) measured at various sensors at different wave heights To verify the rationality of the MFC sensor measurement results, the measured values ​​were compared and analyzed with the theoretical calculation values ​​of classical wave pressure empirical formulas commonly used in marine engineering. The selected empirical formulas included the Sainnflou formula, the Goda formula, and relevant calculation methods from the Chinese "Harbor Hydrology Code". It should be noted that these empirical formulas are mainly used to describe the wave pressure distribution under continuous water body action and do not consider the discrete impact of splashed water droplets formed after wave breakup on structures. Therefore, the comparative analysis aims to verify the MFC sensor's response capability to the overall wave impact trend and magnitude, rather than directly calculating the impact force of splashed water droplets.

[0068] like Figure 12 As shown, comparative analysis reveals the following conclusions: there is a good linear relationship between the water droplet impact force on the MFC sensor and the square of its peak voltage, and a mathematical model of the two can be established using calibration experiments. The experimental results are in good agreement with the calculation results in Chinese standards, with a small overall average error, indicating that the experimental conditions are close to the applicable range of Chinese standards. This further demonstrates that, according to Chinese standards, measuring wave splash impact force with an MFC sensor is feasible and applicable, and it can serve as an alternative to traditional pressure sensors. From the experimental measurements and empirical formula calculations, the wave splash impact force distribution on the upright plate shows a pattern of maximum at the still water surface and gradually decreasing upwards or downwards along the water surface. The consistency of multiple MFC measurements at the same height is good, further proving the reliability of this method.

[0069] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0070] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for measuring wave splash impact force based on piezoelectric fiber composite materials, characterized in that, Includes the following steps: Step S1: Fix the piezoelectric fiber composite material sensor onto the substrate to form an impact force measuring device; Step S2: Control water droplets to fall freely from a preset height to impact the piezoelectric fiber composite material sensor, and establish a calibration model of impact force and output voltage; Step S3: Vertically arrange multiple piezoelectric fiber composite material sensors along the surface of the structure and synchronously collect voltage time history signals generated by wave splash; Step S4: After sequentially performing impact event identification, adjacent sensor correlation noise removal, and impact type discrimination on the voltage time history signal, the processed voltage time history signal is converted into wave splash impact force value according to the calibration model and the correction coefficient of the corresponding impact type. The adjacent sensor correlation noise removal includes the following steps: for vertically adjacent sensors... The and the first For the piezoelectric fiber composite material sensor, the correlation coefficient between the voltage peak sequences of the two sensors is calculated: ； When the correlation coefficient is greater than a preset correlation threshold, the first... The and the first If the signals recorded by the piezoelectric fiber composite material sensor are from the same wave splash impact event, the corresponding voltage peak signal is retained for subsequent impact force calculation; otherwise, the corresponding signal is judged as noise and discarded. The impact type determination includes the following steps: The moment when the voltage signal abruptly begins in the voltage time history signal is defined as... The moment when the voltage signal returns to zero is Then the pulse width for: ； Voltage classification boundaries were determined using water droplet calibration experiments and wave tank experiments. , and time classification boundaries , ; According to voltage peak With pulse width The combined characteristics of impact events classify them into the following three types: when Greater than and Less than When the time frame is short, it is determined to be a single droplet impact; when multiple local voltage peaks with similar amplitudes appear within a preset time window, it is determined to be a splashing droplet group impact; when Less than and Greater than If the impact event does not meet the above three criteria, it is determined to be a continuous water film impact; if the impact event does not meet the criteria for the above three types, it is determined to be a transitional impact, and the impact pressure is calculated using the same calibration model as the single droplet impact. Based on the calibration model and the correction coefficients corresponding to the impact type, when converting the processed voltage time history signal into wave splash impact force values, different conversion strategies are adopted for different impact types: For single-droplet impact, the voltage peak value is directly... Substitute into the calibration model Calculate the impact pressure; where For maximum impact pressure, These are calibration coefficients; For the impact of splashing water droplets, the peak envelope within a preset time window is extracted, and the equivalent voltage of the envelope is substituted into the calibration model to obtain the uncorrected impact pressure. Then multiply by the swarm impact correction factor The corrected impact pressure is obtained, where ; For continuous water film impact, the voltage peak value is substituted into the calibration model to obtain the uncorrected impact pressure. Then multiply by the water film correction factor The corrected impact pressure is obtained, where ; For transient surges, the peak voltage is directly... Substitute into the calibration model Calculate the impact pressure; The group impact correction factor and water film correction factor The following method is used to determine the location: a reference pressure sensor is simultaneously deployed at a position adjacent to the location of the piezoelectric fiber composite material sensor, and the measured pressure value of the reference pressure sensor under the same impact event is used. Alternative theoretical calculations were performed for both droplet swarm impact events and water film impact events. and The mean of the ratios is obtained. and .

2. The wave splash impact force measurement method based on piezoelectric fiber composite material according to claim 1, characterized in that: The piezoelectric fiber composite sensor in step S1 includes two layers of interdigitated electrodes clamping a rectangular cross-section of piezoelectric ceramic fiber. The gap between the piezoelectric ceramic fiber and the interdigitated electrodes is filled with polymer resin to form a composite structure. The piezoelectric fiber composite sensor is fixed to the center of the substrate with epoxy resin and is tightly bonded to the substrate. The substrate is set at a preset angle with the horizontal plane. The material of the substrate is one of bakelite board, 1060 pure aluminum plate, H62 brass plate or SUS304 stainless steel plate.

3. The wave splash impact force measurement method based on piezoelectric fiber composite material according to claim 1, characterized in that: Step S2, which establishes the calibration model for impact force and output voltage, includes the following steps: Step S21: Construct a water droplet impact platform, control water droplets to fall freely from a preset height to impact the piezoelectric fiber composite material sensor, and collect the peak output voltage at different drop heights. ; Step S22: Based on the condition that no splashing occurs during the water droplet impact and the rebound velocity is approximately zero, calculate the maximum impact force according to the impulse relationship: ； In the formula, For maximum impact force; Peak factor; The density of the water droplet; The diameter of the water droplet; This represents the actual collision velocity of the water droplet when it reaches the sensor surface. This is the equivalent collision time; Step S23: Establish a quadratic fitting relationship between the maximum impact pressure and the peak value of the output voltage as the calibration model: ； In the formula, This represents the maximum impact pressure. These are calibration coefficients.

4. The wave splash impact force measurement method based on piezoelectric fiber composite material according to claim 1, characterized in that: The step S3 of vertically arranging multiple piezoelectric fiber composite material sensors along the surface of the structure includes the following steps: setting up an upright plate model in the wave tank, arranging multiple piezoelectric fiber composite material sensors at equal intervals along the vertical center line of the upright plate model, the arrangement positions of the piezoelectric fiber composite material sensors covering the area above, at, and below the still water surface, and the placement direction of the upright plate model being perpendicular to the wave running direction.

5. The wave splash impact force measurement method based on piezoelectric fiber composite material according to claim 4, characterized in that: The synchronous acquisition of voltage time history signals generated by wave splash in step S3 includes the following steps: for regular wave conditions with different wave heights, acquire the voltage time history signals of each piezoelectric fiber composite material sensor under wave splash impact, filter the voltage time history signals to obtain the impact peak voltage, and take the average value of the results of multiple repeated tests as the representative peak voltage.

6. The wave splash impact force measurement method based on piezoelectric fiber composite material according to claim 1, characterized in that: The impact event identification in step S4 includes the following steps: acquiring background segment data of the voltage time history signal during the non-impact phase, and calculating the average voltage of the background segment. and standard deviation Define the threshold for identifying impact events: ； In the formula This is the threshold coefficient; When the voltage peak value in the voltage time history signal Greater than the impact event identification threshold At that time, it is determined that a wave splash impact event has occurred.

7. A wave splash impact force measurement system based on piezoelectric fiber composite material, said system being used to implement the wave splash impact force measurement method based on piezoelectric fiber composite material according to any one of claims 1 to 6, characterized in that, include: Multiple piezoelectric fiber composite material sensors: Each of the piezoelectric fiber composite material sensors is composed of piezoelectric ceramic fibers with a rectangular cross section sandwiched between two layers of interdigitated electrodes, with the gaps filled with polymer resin; Substrate: Each of the piezoelectric fiber composite material sensors is fixed on the corresponding substrate, which is configured to be installed at a preset angle; Dynamic signal acquisition system: connected to the output end of each of the piezoelectric fiber composite material sensors via wires, used to synchronously acquire the charge signals output by each of the piezoelectric fiber composite material sensors; Computer terminal: Connected to the dynamic signal acquisition system via a gigabit network cable, used to receive, store and process voltage signals, and perform impact event identification, noise removal, impact type discrimination and impact force calculation based on the calibration model.

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