Method for measuring force and posture of aquatic vegetation

Abstract

The present application relates to the technical field of aquatic vegetation observation, and aims to provide a force and posture measurement method for aquatic vegetation, so as to solve the problem that the existing method can only measure force in a single direction and the posture of vegetation is difficult to observe in a complex environment, and provide more detailed, comprehensive and basic data support for the production research of aquatic plants, artificial vegetation restoration and water ecological restoration. The technical scheme comprises the following measurement steps: first, select a six-component sensor with a suitable range and the size of a fixing clamp; second, vertically insert and tighten a threaded long rod in the soil at the edge of the measured vegetation, fix the six-component sensor through the side screw hole and the upper part of the threaded long rod, and fix the acceleration sensor to the upper trunk of the vegetation through a thin tie; third, electrically connect the six-component sensor and the acceleration sensor to a high-frequency acquisition card and an edge computing DTU respectively, start data acquisition, obtain a three-dimensional force component sequence of the force measurement point, and calculate the resultant force F; fourth, data processing.

Description

Technical Field

[0001] This invention relates to the field of aquatic vegetation observation technology, specifically a method for measuring the force and attitude of aquatic vegetation. Background Technology

[0002] Various aquatic vegetation is distributed along the riverbanks and the seawall front, which is of great significance for the aquatic ecology and for stabilizing the dikes and preventing erosion.

[0003] Currently, there are two main methods for studying the stress on aquatic vegetation: prototype observation and laboratory simulation. Prototype observation has been extensively studied, as exemplified by "CN104764583 B," which uses a two-dimensional measuring instrument combined with a string to analyze and measure the stress on the vegetation. Model-based measurement, such as "CN 102901614A," simulates the stress environment of vegetation in a scaled-down water tank and uses pressure sensors for stress measurement. However, these methods can only measure the stress on vegetation in a single direction and cannot measure the comprehensive stress situation in a real environment. In reality, vegetation experiences comprehensive and multi-directional stress, leading to limitations in the measured data. Furthermore, the use of strings and pressure sensors is prone to entanglement or interference from other obstacles during measurement, resulting in poor data accuracy and stability. Due to the complexity of the vegetation's growth environment, it is difficult to observe the posture of vegetation under stress; currently, there are no research results on the dynamic posture data of aquatic vegetation under stress. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a method for measuring the force and posture of aquatic vegetation. This method solves the problems that existing methods can only measure force in one direction and that the posture of vegetation in complex environments is difficult to observe. It provides more detailed, comprehensive and basic data support for aquatic plant production research, artificial vegetation restoration and aquatic ecological restoration.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for measuring the stress and attitude of aquatic vegetation includes the following measurement steps:

[0007] Step 1: Initially determine the magnitude of the force on the plant under hydrodynamic conditions and the diameter of the plant roots, and select a six-component sensor with an appropriate range and the size of the fixing fixture.

[0008] Step 2: Tighten the threaded rod at a vertical point about 2cm from the edge of the vegetation being measured. The six-component sensor is vertically fixed to the threaded rod through the side screw hole. The front clamp of the fixing clamp is clamped to the root of the vegetation, and the tail end is rigidly fixed to the six-component measurement area. The accelerometer is fixed to the upper part of the vegetation trunk with a thin cable tie.

[0009] Step 3: Connect the high-frequency acquisition card and edge computing DTU to start data acquisition and obtain the (Fx, Fy, Fz) sequence and the three-dimensional torque (Tx, Ty, Tz) sequence for the force measurement point. The formula for calculating the resultant force F is:

[0010]

[0011] The direction F is the angle between the F direction and the horizontal direction.

[0012] Angle with the vertical direction

[0013] Step 4: Simultaneously obtain the acceleration (Axt, Ayt, Azt) sequence, and use a double integral and polynomial compensation algorithm to obtain displacement information. The specific algorithm is as follows: Taking Axt calculation as an example, first perform a double integral...

[0014]

[0015]

[0016] In the formula: α(t) is the acceleration, v(t) is the velocity after the integral of acceleration, s(t) is the displacement after the integral of acceleration, s(t0) is the initial displacement, and ε is the initial acceleration offset;

[0017] The velocity and displacement signals are obtained by numerical integration using the trapezoidal rule.

[0018]

[0019] Since the initial velocity and initial displacement are unknown, the obtained displacement data requires integration and summation, divided by the trend term, to obtain more accurate values. A polynomial fitting algorithm is used, assuming the existence of a polynomial ym(t) that minimizes the sum of squared interpolations between v and s. The least squares method is used to fit the trend term error.

[0020]

[0021] Where m is the number of the highest degree term, pk is the polynomial coefficient, and Φ is the set of polynomials whose highest degree term does not exceed m, we obtain the following equation.

[0022]

[0023] Find y m (t) yields the corrected velocity and displacement.

[0024] v(t)=∫a(t)dt-y 1m (t)

[0025] Sx(t)=∫v(t)dt-y2m (t)

[0026] This gives us the displacement time series Sx(t) in the X direction. Similarly, we obtain Sy(t) and Sz(t). After calculation, we can obtain the final trajectory time series S(t):

[0027]

[0028] S(t) is the centroid trajectory of vegetation movement;

[0029] Arrange S(t) in ascending order, and the maximum value is the maximum movement amplitude of the vegetation.

[0030] The period of vegetation swing and the time of swing and reset can be obtained by using the upper zero-point method and the lower zero-point method on S(t).

[0031] Preferably, the six-component sensor is used to measure the force data of the vegetation, including a spatial three-dimensional force component (Fx, Fy, Fz) sequence and a three-dimensional torque (Tx, Ty, Tz) sequence; the six-component sensor has a detachable threaded long rod on its side to fix the six-component sensor to the bottom of the water, and a fixing clamp on the top of the six-component sensor for connecting the vegetation to the six-component sensor; the analog signals of the six-component sensor and the accelerometer are acquired and converted into digital signals by a high-frequency acquisition card; the high-frequency acquisition card is connected to an edge computing DTU, and the edge computing DTU wirelessly uploads the data to a client computer or the cloud.

[0032] Preferably, an accelerometer is used to measure the attitude data of the vegetation after it is subjected to force. The directly measured data is a three-dimensional acceleration (Ax, Ay, Az) sequence, and the calculated data includes attitude data such as swing amplitude, center of mass trajectory, swing period, and reset time.

[0033] The beneficial effects of this invention are:

[0034] This invention solves the problem of only being able to measure forces in one direction. The measurement process has no moving parts, avoiding problems such as vegetation entanglement and obstacle interference. Furthermore, it uses an accelerometer to indirectly measure vegetation posture, overcoming the problem of difficulty in observing vegetation posture in complex environments. At the same time, it adopts a high-frequency acquisition mode, which can capture more transient information, providing more detailed, comprehensive and basic data support for aquatic plant production research, artificial vegetation restoration and aquatic ecological restoration. Attached Figure Description

[0035] Figure 1 This diagram illustrates the fixing method used in the stress test of aquatic vegetation according to the present invention.

[0036] Figure 2 This is a diagram showing the displacement trajectory of the aquatic vegetation in the X-axis direction during a stress test.

[0037] Figure 3 This is a force analysis diagram of the aquatic vegetation of the present invention in the X, Y and Z axis directions during the force test.

[0038] The diagram is labeled as follows: 1. Accelerometer sensor; 2. Vegetation under test; 3. Fixture; 4. Six-component sensor; 5. Threaded rod. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0040] Example 1

[0041] The attached diagram shows a method for measuring the force and attitude of aquatic vegetation, including a six-component sensor 4, an accelerometer 1, and a high-frequency data acquisition device (omitted in the diagram). The six-component sensor is used to measure the force data of the vegetation, which includes a spatial three-dimensional force component (Fx, Fy, Fz) sequence and a three-dimensional torque (Tx, Ty, Tz) sequence. The six-component sensor has a detachable threaded rod on its side to fix it to the bottom of the water. The top of the six-component sensor has a fixing clamp for connecting the vegetation to the six-component sensor. The analog signals from the six-component sensor and the accelerometer are acquired and converted into digital signals by a high-frequency data acquisition card. The high-frequency data acquisition device is connected to an edge computing DTU (omitted in the diagram), and the DTU wirelessly uploads the data to a client computer or the cloud.

[0042] Specifically, a six-component sensor is used to measure the forces acting on the vegetation. The measured forces include three-dimensional forces (Fx, Fy, Fz) and three-dimensional torques (Tx, Ty, Tz) to obtain the dynamic force process and maximum force of the vegetation. The six-component sensor has a square structure, with the preferred dimensions being 10cm in length, 10cm in width, and 3cm in thickness. It is made of 316L stainless steel, and the interface and bridge circuit are sealed with soft silicone for waterproofing.

[0043] In addition, the threaded rod 5 is deeply inserted into the bottom of the water to fix the six-component sensor. The six-component sensor has threaded holes on its side for installing the detachable threaded rod. The force measuring area of ​​the six-component sensor is located on its upper part. There is a set of four threaded holes in the center of the force measuring area for connecting the fixing clamp 3. The fixing clamp (existing technology) is used to connect the plant roots and the six-component sensor. The clamp has two semi-circular structures with hard rubber pads on the inner side of the semi-circles to reduce damage to the plant roots.

[0044] Meanwhile, the high-frequency data acquisition instrument is connected to the edge computing DTU (data transmission unit) via a serial port. The high-frequency data acquisition instrument transmits data to the edge computing DTU, and the processing and calculation of force data and acceleration data are completed in the DTU. The DTU uploads the calculated data to the client computer or cloud via 4G. If there is no network coverage or fixed antenna on site, the data can be stored in the DTU and retrieved from the device after the data acquisition is completed, and then exported via a data cable.

[0045] Furthermore, accelerometers are used to measure the attitude data of the vegetation after it is subjected to force. The directly measured data is a three-dimensional acceleration (Ax, Ay, Az) sequence, and after calculation, attitude data including swing amplitude, center of mass trajectory, swing period, and reset time are obtained.

[0046] Specifically, the accelerometer measures the attitude parameters of the vegetation after it is subjected to force. The accelerometer uses MEM technology and has dimensions of 0.8cm in length and width and 0.3cm in thickness. The signal line uses a 6-core wire with a diameter of 1mm². The directly measured data is three-dimensional acceleration (Ax, Ay, Az). After double integration of the acceleration, spatial trajectory data is obtained. Analyzing the trajectory data can obtain attitude parameters including swing amplitude, center of mass trajectory, swing period, and reset time.

[0047] The analog signals output by the six-component sensor and the accelerometer are acquired and converted into digital information by a high-frequency acquisition card, with a sampling frequency of up to 100 Hz.

[0048] Furthermore, the following measurement steps are included:

[0049] Step 1: Initially determine the magnitude of the force on the plant under hydrodynamic conditions and the diameter of the plant roots, and select a six-component sensor with an appropriate range and the size of the fixing fixture.

[0050] Specifically, the DTU and data acquisition unit are placed in a waterproof box. The DTU's radio frequency antenna is extended through a signal line and inserted into an area that does not affect the movement of vegetation. The upper end of the radio frequency antenna is placed above the water surface.

[0051] Step 2: After determining the vegetation to be measured in the measurement area, select a six-component sensor with an appropriate range and a fixing fixture (see...). Figure 1 This example uses a common seaside reed community as an example. The maximum force on a single reed under the influence of wind, waves, and currents is less than 10N, and the root diameter is less than 1cm. Therefore, a six-component sensor with a range of 10N for both XYZ is selected, along with a clamp with an inner diameter of 6-12mm.

[0052] Tighten the threaded rod 2cm behind the main stress direction of the reed and insert it into the ground to reduce the influence of the measuring equipment on the flow field. The length of the threaded rod is determined according to the underwater soil. For silty bottom, the rod can be 1.5m long, and for harder soil, the rod can be 1m long. In this case, the growing substrate of the reed community is generally silty, so a 1.5m rod is selected.

[0053] After the six-component sensor is waterproofed, it is fixed to the top of the threaded rod through the side threaded hole. One end of the fixing clamp is connected to the four threaded holes in the measurement area of ​​the six-component sensor, and the other end is clamped to the roots of the vegetation for fixation. The accelerometer is fixed in the middle and upper part of the vegetation with thin cable ties. The high-frequency acquisition instrument and the edge computing DTU are put into the waterproof box. The analog signal line of the sensor is connected to the high-frequency acquisition instrument. The acquisition instrument is connected to the edge computing DTU through the serial port. The RF antenna of the DTU is extended above the water surface through the wire.

[0054] After installing the sensors and data acquisition equipment, a pre-test is conducted first. This mainly involves measuring whether the sensors and communication are functioning properly. The reeds are manually shaken and pulled using a force gauge, and the force count and pulling distance are recorded. If the sensors and communication are working properly, the force values ​​and the amplitude of the reed's sway can be read in the cloud or on the client computer. The read data is compared with the recorded force count and pulling distance. If it is working properly, measurements can begin. Generally, data is measured under conditions of astronomical tides and strong winds and waves. The force and posture of the reeds under these conditions are of significant research value for studying the growth of the vegetation itself and its interaction with wind and wave currents.

[0055] Step 3: Connect the high-frequency acquisition card and edge computing DTU to start data acquisition and obtain the (Fx, Fy, Fz) sequence and the three-dimensional torque (Tx, Ty, Tz) sequence for the force measurement point. The formula for calculating the resultant force F is:

[0056]

[0057] The formula for calculating the resultant torque is as follows:

[0058]

[0059] The angle between direction F and the horizontal direction:

[0060] The angle between direction F and the vertical direction

[0061] Taking the force data in Table 1 as an example, the magnitudes of the three-dimensional forces at a certain moment are: Fx = -3.06 N, Fy = 5.3 N, and Fz = 0.72 N. According to the formula... The net force is 6.45 N, and the angle with the horizontal direction is based on... The horizontal angle is 35.2°, and the angle with the vertical direction is 6.3°.

[0062] Step 4: Simultaneously obtain the acceleration (Axt, Ayt, Azt) sequence, and use a double integral and polynomial compensation algorithm to obtain displacement information. The specific algorithm is as follows: Taking Axt calculation as an example, first perform a double integral...

[0063]

[0064]

[0065] The velocity and displacement signals are obtained by numerical integration using the trapezoidal rule.

[0066]

[0067] Since the initial velocity and initial displacement are unknown, the obtained displacement data needs to be integrated, accumulated, and divided by the trend term to obtain more accurate values. A polynomial fitting algorithm is used, assuming the existence of a polynomial ym(t) that minimizes the sum of squared interpolations between v and s. The least squares method is used to fit the trend term error.

[0068]

[0069] Where m is the number of the highest degree term, pk is the polynomial coefficient, and Φ is the set of polynomials whose highest degree term does not exceed m, we obtain the following equation.

[0070]

[0071] Find y m (t) yields the corrected velocity and displacement.

[0072] v(t)=∫a(t)dt-y 1m (t)

[0073] Sx(t)=∫v(t)dt-y 2m (t)

[0074] This yields the displacement time series Sx(t) in the X direction; similarly, Sy(t) and Sz(t) are obtained, and after calculation, the final trajectory time series S(t) can be obtained:

[0075]

[0076] S(t) is the centroid trajectory of vegetation movement;

[0077] Arrange S(t) in ascending order, and the maximum value is the maximum movement amplitude of the vegetation.

[0078] The period of vegetation swing and the time of swing and reset can be obtained by using the upper zero-point method and the lower zero-point method on S(t).

[0079] Taking the data in Table 2 as an example, we first perform double integration to obtain the maximum displacement of 15.22cm, the polynomial constant of 1.51cm, and the time difference between the two peaks of 1.3s. It can be seen that the oscillation period is 1.3s, the maximum oscillation amplitude is 13.71cm, and the reset time is about 0.65s.

[0080] Table 1

[0081]

[0082] Table 2

[0083]

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the stress and attitude of aquatic vegetation, comprising the following measurement steps: Step 1: Initially determine the magnitude of the force on the vegetation under hydrodynamic conditions and the diameter of the plant roots, and select a six-component sensor with an appropriate range and the size of the fixing fixture. Step 2: Vertically insert and tighten the threaded rod into the soil at the edge of the vegetation to be measured. The six-component sensor is fixed to the upper part of the threaded rod through the side screw hole. The front clamp of the fixing clamp clamps the root of the vegetation, and the tail end of the fixing clamp is rigidly fixed to the measuring end of the six-component sensor. In addition, the accelerometer is fixed to the upper part of the vegetation trunk with a thin cable tie. Step 3: The six-component sensor and accelerometer are electrically connected to the high-frequency acquisition card and the edge computing DTU respectively to start data acquisition and obtain the three-dimensional force component sequence of the force measurement point. Then, the resultant force F is calculated according to the following formula. In the formula: Fx, Fy, and Fz are the components of the resultant force F in the x, y, and z directions, respectively; θ is the angle between the resultant force F and the horizontal direction. α is the angle between the resultant force F and the vertical direction; Step 4: Data processing; The data processing in the fourth step is as follows: (1) For the three-dimensional acceleration sequence obtained simultaneously at the force measurement point, the displacement information of each dimension is obtained by using a double integral and polynomial compensation algorithm; as follows: ① For the acceleration in each dimension, first perform a double integral to obtain the displacement in each dimension; In the formula: α(t) is the acceleration, v(t) is the velocity after the integral of acceleration, s(t) is the displacement after the integral of velocity, and s(t) is the velocity after the integral of velocity. t 0) represents the initial displacement, and ε represents the initial acceleration offset. ② Numerical integration using the trapezoidal rule is used to obtain the velocity and displacement signals: ③ For the obtained displacement data, the trend term error is fitted using the least squares method: in: y m (t) is a polynomial, m is the highest degree term, and p k For polynomial coefficients, For the set of polynomials whose highest degree term does not exceed m, we obtain the following equation. Find The corrected velocity and displacement are obtained. This yields the displacement time series for each dimension; The above process yields three dimensions: Sx(t), Sy(t), and Sz(t). (2) The final trajectory time series S(t) can be obtained through calculation: S(t) is the centroid trajectory of vegetation movement; (3) Arrange S(t) in ascending order, and the maximum value is the maximum movement amplitude of the vegetation; The period of vegetation swing and the time of swing and reset can be obtained by using the upper zero-point method and the lower zero-point method on S(t).

2. The method for measuring the force and attitude of aquatic vegetation according to claim 1, characterized in that: The six-component sensor is used to measure the force data of the vegetation, including a spatial three-dimensional force component sequence and a three-dimensional torque sequence. The analog signals of the six-component sensor and the accelerometer are acquired and converted into digital signals by a high-frequency acquisition instrument. The high-frequency acquisition instrument is electrically connected to the edge computing DTU, which wirelessly uploads the data to the client computer or the cloud.

3. The method for measuring the force and attitude of aquatic vegetation according to claim 2, characterized in that: The data directly measured by the accelerometer is a three-dimensional acceleration sequence. The calculated data includes attitude data such as swing amplitude, center of mass trajectory, swing period, and reset time.

4. The method for measuring the force and attitude of aquatic vegetation according to claim 3, characterized in that: In the second step, the edge of the vegetation being measured refers to the area 2.0 ± 0.5 cm away from the edge of the vegetation being measured.

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