Short cable real-time cable force identification method based on corrected effective vibration length

Abstract

The invention discloses a short cable real-time cable force identification method based on a corrected effective vibration length. The method comprises the following steps: A) fitting a vibration mode function of a short cable; b) calculating cable force T and flexural rigidity EI under various working conditions; c) recording the effective vibration length Ly and the cable force value Tx under the working conditions, and fitting a Tx-Ly curve; d) monitoring an acceleration signal of a sensor to obtain a real-time frequency; e) calculating the cable force, calculating the cable force by combining the real-time frequency with the effective vibration length and the flexural rigidity at the previous moment, substituting the cable force value back to the Tx-Ly curve, and obtaining the updated effective vibration length, F) verifying the cable force value, comparing the cable force value with the cable force value at the previous moment, if the difference between the cable force value and the cable force value at the previous moment is within the error range, outputting the cable force value, and if the difference is within the error range, outputting the cable force value. Otherwise, repeating the step E) through the updated effective vibration length to calculate the cable force value. The short cable real-time cable force identification method based on the corrected effective vibration length is high in calculation precision and can be used for real-time cable force identification.

Description

Technical Field

[0001] The invention relates to the technical field of bridge cable force monitoring, and in particular to a short cable real-time force identification method based on correcting effective vibration length. Background Art

[0002] At present, most frequency methods for real-time cable force identification estimate time-varying cable force by combining real-time frequency with the frequency-tension relationship of tensioned string or simply supported beam. The cable force calculation methods in the prior art include obtaining real-time frequency by short-time Fourier transform and improved S transform, and substituting the real-time frequency into the frequency-tension relationship of tensioned string or simply supported beam to obtain real-time cable force. The above frequency-based real-time cable force identification methods achieve good results on long cables, but real-time cable force identification methods suitable for short cables are rare because the frequency method has poor accuracy in identifying short cables. This is because the frequency method usually identifies cable force based on the frequency-tension relationship of tensioned string or simply supported beam, which is very suitable for long cables. In fact, the anchoring condition of the cable is between fixed support and hinged, and the vibration reduction device can be regarded as a constraint of the adjacent anchor point. For long cables, the anchoring conditions at both ends and the vibration reduction device can be simplified to hinged boundary conditions, which can meet the basic assumptions of tensioned string or simply supported beam, so the frequency method can accurately identify the cable force of long cables.

[0003] However, the short cable is short and its boundary conditions have a significant impact on the modal characteristics. It cannot be simplified as a hinge like a long cable and cannot meet the basic assumptions of the frequency method. In addition, the boundary conditions are uncertain, which limits the application of the frequency method in the identification of short cable forces. There are some solutions to this problem in the prior art. For example, Chinese patent CN117113289A discloses a method for identifying the force of a short cable, which obtains the acceleration signal of the short cable when there is no additional mass by installing an acceleration sensor on the low side of the short cable, and then obtains the acceleration signal of the short cable when there is additional mass by installing an additional mass block on the low side of the short cable; based on the acceleration signal, the frequency value and amplitude of the short cable with or without additional mass are obtained; the sine function obtained by fitting the obtained amplitude value is used to obtain the virtual hinge position of the equivalent cable model; based on the frequency-cable force relationship of the equivalent cable, the short cable length and the frequency value without additional mass are substituted, and the least squares linear regression method is used to obtain the initial cable force and bending stiffness. Based on the obtained, the finite element frequency value is obtained by using the equivalent cable finite element model with the short cable length as the initial length; the difference between the obtained finite element frequency value and the frequency value when the mass is added is used as the objective function, and the optimal equivalent cable length is optimized using the least squares trust region reflection algorithm to optimize and improve the accuracy of cable force identification.

[0004] In the above-mentioned prior art, the steps for calculating the effective vibration length are relatively complicated, and an additional mass block needs to be added to the cable. It can only be used for average cable force identification, and cannot be used for real-time cable force identification. Summary of the invention

[0005] In view of the above problems, the present invention provides a real-time cable force identification method for a short cable based on a modified effective vibration length, aiming to solve the problem that the prior art cannot be used for real-time cable force identification.

[0006] The present invention adopts the following technical solutions to achieve the above purpose:

[0007] The method for real-time cable force identification of short cables based on corrected effective vibration length includes the following steps:

[0008] A) Fitting the vibration mode function of the short cable: Install three or more sensors on the short cable, the sensors are used to measure the vibration information of the short cable under at least two working conditions of gravity load, temperature load or vehicle static load, process the acceleration signal of the vibration information, and obtain the amplitude Ψ of the sensor ki and the frequency f of the short cable k , the fitting function of the short cable vibration mode is:

[0009]

[0010] Among them, x i is the distance from the sensor to the anchor point, L k is the effective vibration length, d k Bias coefficient, a k is the amplitude coefficient, k is the order of the mode;

[0011] B) Calculate the cable force T and bending stiffness EI under the above working conditions. The calculation formula is:

[0012]

[0013] in, is the mass per unit length of the short cable;

[0014] C) Fitting the empirical relationship curve of Tx-Ly: Record the effective vibration length Ly and cable force value Tx under the above working conditions, and fit the empirical relationship curve of Tx-Ly;

[0015] D) Vibration information processing, monitoring the vibration information of one of the sensors and processing the acceleration signal to obtain the real-time frequency;

[0016] E) Cable force calculation, combining the real-time frequency and the effective vibration length Ly at the previous moment i-1 Substituting the bending stiffness EI into formula (2), the cable force Tx is calculated. i , will cable force Tx i Substitute back to the Tx-Ly curve to obtain the updated effective vibration length Ly i , where, at the initial moment, Ly0 selects the effective vibration length value corresponding to any one of the above working conditions;

[0017] F) Cable force verification, when (Ly i -Ly i-1 ) / Ly i When within the error range, the output Tx i is the current real-time cable force, Ly i As the effective vibration length at the next moment, calculate the cable force value at the next moment; when (Ly i -Ly i-1 ) / Ly i When the error range is exceeded, Ly i As the updated effective vibration length Ly at the last moment i-1 Repeat step E).

[0018] In this technical solution, more than three sensors are used to fit the vibration mode function of the short cable, so as to obtain the effective vibration length of the short cable under different working conditions, and linear regression is used to calculate the cable force value and bending stiffness of the short cable under each working condition. By recording the cable force value and effective vibration length corresponding to each working condition, the empirical relationship curve of Tx-Ly is fitted, and the empirical relationship curve is used to correct the real-time effective vibration length during cable force measurement to improve the measurement accuracy of the cable force value. Specifically, on the one hand, the concept of effective vibration length is introduced into the identification method of the real-time cable force of the short cable, so that the frequency method is applied to the short cable without the influence of complex boundary conditions, thereby improving the accuracy of the cable force identification of the short cable; on the other hand, the empirical relationship curve of cable force-effective vibration length is used to correct the effective vibration length when the cable force changes, further improving the identification accuracy of the real-time cable force.

[0019] A further technical solution is that the sensor in step A) is a displacement sensor, a velocity sensor or an acceleration sensor. In this technical solution, sensors can be arranged on both the upper and lower sides of the short rope, and the sensors can adopt a contact or non-contact measurement method.

[0020] A further technical solution is that the temperature load condition in step A) includes two or more load conditions at different temperatures. In this technical solution, the measurement accuracy can be improved by using data under multiple different temperature conditions.

[0021] A further technical solution is that the fitting method described in step C) is a spline function interpolation method.

[0022] A further technical solution is to use a characteristic system to implement an algorithm for processing the acceleration signal of the vibration information.

[0023] The beneficial effects of the present invention are:

[0024] The present invention provides a method for identifying the real-time cable force of a short cable based on correcting the effective vibration length. The concept of the effective vibration length is introduced into the method for identifying the real-time cable force of a short cable, so that the influence of complex boundary conditions is not required when the frequency method is applied to the short cable, thereby improving the accuracy of identifying the cable force of the short cable. The cable force value and the effective vibration length of the short cable under different working conditions are calculated by combining the short cable vibration mode fitting function and linear regression, and an empirical relationship curve of the cable force-effective vibration length is fitted. The effective vibration length when the cable force changes is corrected by the empirical relationship curve, thereby further improving the identification accuracy of the real-time cable force. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of a short rope for implementing the rope force identification method of the short rope described in the present invention.

[0026] Figure 2 : The empirical relationship curve diagram of the cable force-effective vibration length described in the present invention.

[0027] Figure 3 : An acceleration signal diagram when the short cable force changes in an embodiment of the present invention.

[0028] Figure 4 for: Figure 3 Real-time frequency extraction plot of the acceleration signal.

[0029] Figure 5 for: Figure 4 Cable force identification diagram corresponding to real-time frequency.

[0030] Figure 6 The present invention is a flowchart of the method for identifying the cable force of a short cable.

[0031] In the figure:

[0032] 1. Short rope; 21. First damper; 22. Second damper; 31. First anchor point; 32. Second anchor point. DETAILED DESCRIPTION

[0033] The following is combined with Figures 1 to 6 The present invention is described in detail with specific implementation modes. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0034] like Figure 6 As shown, this embodiment provides a method for identifying the real-time cable force of a short cable based on correcting the effective vibration length, comprising the following steps:

[0035] A) Fitting the vibration mode function of the short cable: Install three or more sensors on the short cable, the sensors are used to measure the vibration information of the short cable under at least two working conditions of gravity load, temperature load or vehicle static load, process the acceleration signal of the vibration information, and obtain the amplitude Ψ of the sensorki and the frequency f of the short cable k , the short cable vibration mode fitting function is:

[0036]

[0037] Among them, x i is the distance from the sensor to the anchor point, L k is the effective vibration length, d k Bias coefficient, a k is the amplitude coefficient, k is the order of the mode; thus the effective vibration length of the short cable under different working conditions is obtained;

[0038] Specifically, in step A), an acceleration sensor is installed and arranged on the left side, the middle part and the right side of the short cable respectively, and the specific positions are shown in Table 1, which is used to obtain the vibration information of the short cable, wherein the temperature load condition is a condition containing temperature load in addition to gravity, including a normal temperature load condition and a low temperature load condition, the gravity load condition is a condition without other obvious external loads in addition to gravity, and the vehicle static load condition is a condition containing static loads such as vehicles in addition to gravity. The characteristic system realization algorithm (ERA algorithm) or other spectrum analysis methods can be used to process the acceleration signal of the acceleration sensor;

[0039] B) Calculate the cable force T and bending stiffness EI under the above working conditions. The calculation formula is:

[0040]

[0041] in, is the mass per unit length of the short cable;

[0042] C) Fitting the empirical relationship curve of Tx-Ly: recording the effective vibration length Ly and the cable force value Tx under the above working conditions, and fitting the empirical relationship curve of Tx-Ly; specifically, recording the effective vibration length Ly and the cable force value Tx under each working condition in the above steps A) and B), and fitting the empirical relationship curve of Tx-Ly by using the spline function interpolation method;

[0043] D) Vibration information processing, monitoring the vibration information of one of the sensors and processing the acceleration signal to obtain the real-time frequency; specifically, in actual working conditions, the other two sensors can be removed, and only one acceleration sensor is included on the cable. In order to facilitate installation and maintenance, the acceleration sensor on the side of the short cable can be retained, and the synchronous compression transformation method is used to process the acceleration signal to obtain the real-time frequency;

[0044] E) Cable force calculation, combining the real-time frequency and the effective vibration length Ly at the previous moment i-1 Substituting the bending stiffness EI into formula (2), the cable force Tx is calculated. i , will cable force Tx iSubstituting back to the Tx-Ly curve, the cable force Tx i The corresponding Ly i As the updated effective vibration length value, wherein, at the initial moment, Ly0 selects the effective vibration length value corresponding to any one of the above working conditions; specifically, at the initial moment, the effective vibration length Ly0 corresponding to the normal temperature working condition is selected;

[0045] F) Cable force verification, when (Ly i -Ly i-1 ) / Ly i When it is less than 0.001, the output Tx i is the current real-time cable force, Ly i As the effective vibration length at the next moment, calculate the cable force value at the next moment; when (Ly i -Ly i-1 ) / Ly i Greater than 0.001, Ly i As an updated Ly i-1 Repeat step E). In this embodiment, the error range is within 1‰. In practical applications, the error range can be limited according to specific projects.

[0046] Specifically, Figure 1 As shown in FIG. 1 , the specific parameters of the short cable 1 are as follows: the total length is 29.3 m, the first damper 21 and the second damper 22 are respectively provided on the left and right sides, the distance from the first damper 21 to the first anchor point on the left side is 3.5 m, the distance from the second damper 22 to the second anchor point on the right side is 2.7 m, the unit length mass is 61.3 kg / m, the bending stiffness is 7.31×10 5 N·m 2 , the damper stiffness is 5×10 5 N·m 2 , the reference cable force is 2.56×10 6 N. In this embodiment, three sensors are used to fit the vibration function of the short cable, and their installation positions and measured amplitudes are shown in Table 1. Through the measurement results in Table 1, combined with formula (1), the effective vibration length under the first working condition (gravity load condition) is obtained to be approximately 23.1m, and the bias coefficient and amplitude coefficient do not need to be used in subsequent calculations. Based on the effective vibration length, formula (2) is used to identify the cable force, and its error is only 0.05%, as shown in Table 2, which is far superior to the frequency method of the traditional string / beam theory.

[0047] Table 1 Sensor positions and corresponding order amplitudes

[0048]

[0049] Table 2 Average cable force identification results

[0050]

[0051] Repeating the above steps A) and B) can measure the effective vibration length of the short cable under different working conditions (temperature load conditions and vehicle static load conditions), and use linear regression to calculate the cable force and bending stiffness of the short cable under each working condition. The above steps are within the scope of average cable force identification. By recording the cable force and effective vibration length corresponding to each working condition, the empirical relationship curve of Tx-Ly is fitted, such as Figure 2 As shown, the empirical relationship curve can be used to correct the real-time effective vibration length when measuring the cable force to improve the measurement accuracy of the cable force value. Specifically, on the one hand, the concept of effective vibration length is introduced into the identification method of the real-time cable force of the short cable, so that the frequency method is applied to the short cable without the influence of complex boundary conditions, thereby improving the accuracy of the short cable identification cable force; on the other hand, the empirical relationship curve of cable force-effective vibration length is used to correct the effective vibration length when the cable force changes, thereby further improving the identification accuracy of the real-time cable force.

[0052] like Figures 1 to 5 As shown, the cable force identification method of this embodiment is compared with the frequency method based on string theory and the frequency method based on beam theory in the prior art. In the cable force identification process described in this embodiment, the empirical relationship curve of fitting Tx-Ly obtained in step C) is as follows: Figure 2 As shown, Figure 2 In addition to the four working conditions described in this embodiment, the fitting curves of two working conditions and three working conditions are shown, among which the fitting curves of the four working conditions have the highest accuracy. When an external force is applied to change the short cable force, the acceleration signal monitored is as follows: Figure 3 As shown, the real-time frequency obtained by processing the acceleration signal using the synchronous compression transformation method in step D) is as follows: Figure 4 As shown, the cable force value calculated through step E) and step F) is as follows Figure 5 As shown, Figure 5 Shows Figure 2 The measurement results of the fitting curves of two working conditions, three working conditions, and four working conditions and the cable force identification results without updating the effective vibration length (i.e., the effective vibration length adopts a fixed value) are shown. The results show that the cable force identification accuracy of updating the effective vibration length is higher than the identification result of not updating the effective vibration length. The cable force is calculated using the frequency method based on string theory, the frequency method based on beam theory, and the cable force identification method of this embodiment, and the following results are obtained:

[0053] The frequency method based on the total length of the cable overestimates the effective vibration length, thereby overestimating the cable force value. The relative error of cable force identification is as high as 60%, and the identification method of the prior art can only measure the average cable force. The frequency method of the effective vibration length accurately measured by the above-mentioned implementation method has a relative error of about 0.05% in cable force identification, which is much more accurate than traditional methods and can measure real-time cable force.

[0054] The present invention provides a method for identifying the real-time cable force of a short cable based on correcting the effective vibration length. The concept of the effective vibration length is introduced into the method for identifying the real-time cable force of a short cable, so that the influence of complex boundary conditions is not required when the frequency method is applied to the short cable, thereby improving the accuracy of identifying the cable force of the short cable. The cable force value and the effective vibration length of the short cable under different working conditions are calculated by combining the short cable vibration mode fitting function and linear regression, and an empirical relationship curve of the cable force-effective vibration length is fitted. The effective vibration length when the cable force changes is corrected by the empirical relationship curve, thereby further improving the identification accuracy of the real-time cable force.

Claims

1. A short cable real-time cable force identification method based on corrected effective vibration length, characterized in that: The following steps are involved: A) Fitting the vibration mode function of the short cable: Install three or more sensors on the short cable, the sensors are used to measure the vibration information of the short cable under at least two working conditions of gravity load, temperature load or vehicle static load, process the acceleration signal of the vibration information, and obtain the amplitude Ψ of the sensor ki and the frequency f of the short cable k , the short cable vibration mode fitting function is: Among them, x i is the distance from the sensor to the anchor point, L k is the effective vibration length, d k Bias coefficient, a k is the amplitude coefficient, k is the order of the mode; B) Calculate the cable force T and bending stiffness EI under the above working conditions. The calculation formula is: in, is the mass per unit length of the short cable; C) Fitting the empirical relationship curve of Tx-Ly: Record the effective vibration length Ly and cable force value Tx under the above working conditions, and fit the empirical relationship curve of Tx-Ly; D) Vibration information processing, monitoring the vibration information of one of the sensors and processing the acceleration signal to obtain the real-time frequency; E) Cable force calculation, combining the real-time frequency and the effective vibration length Ly at the previous moment i-1 Substituting the bending stiffness EI into formula (2), the cable force Tx is calculated. i , will cable force Tx i Substitute back to the Tx-Ly curve to obtain the updated effective vibration length Ly i , where, at the initial moment, Ly0 selects the effective vibration length value corresponding to any one of the above working conditions; F) Cable force verification, when (Ly i -Ly i-1 ) / Ly i When within the error range, the output Tx i is the current real-time cable force, Ly i As the effective vibration length at the next moment, calculate the cable force value at the next moment; when (Ly i -Ly i-1 ) / Ly i When the error range is exceeded, Ly i As the updated effective vibration length Ly at the last moment i-1 Repeat step E).

2. The method for real-time short-cable force identification based on corrected effective vibration length according to claim 1 is characterized in that: The sensor described in step A) is a displacement sensor, a velocity sensor or an acceleration sensor.

3. The method for real-time short-cable force identification based on corrected effective vibration length according to claim 1 is characterized in that: The temperature load conditions in step A) include more than two load conditions with different temperatures.

4. The method for real-time short-cable force identification based on corrected effective vibration length according to claim 1 is characterized in that: The fitting method described in step C) is a spline function interpolation method.

5. The method for real-time short-cable force identification based on corrected effective vibration length according to claim 1 is characterized in that: The acceleration signal for processing vibration information adopts the characteristic system implementation algorithm.

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