CN115096494A - Online monitoring system for cable force of large cable-stayed bridge - Google Patents
Online monitoring system for cable force of large cable-stayed bridge Download PDFInfo
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Abstract
A large-scale cable-stayed bridge cable force on-line monitoring system comprises an acceleration sensor, a field acquisition station and a remote monitoring center, wherein the acceleration sensor is installed on a cable of a cable-stayed bridge, a cable force acquisition industrial personal computer and a data integration industrial personal computer are arranged in the field acquisition station, the cable force acquisition industrial personal computer is connected with the acceleration sensor, and the cable force acquisition industrial personal computer and the data integration industrial personal computer are respectively connected with the remote monitoring center; and load the cable force acquisition program that is used for gathering the acceleration signal on the industrial computer is gathered to the cable force, remote monitoring center is provided with WEB server and database server, the cable force acquisition program gathers acceleration signal and sends the bridge acquisition client program that the data integration industrial computer loaded in batches, gathers client program by the bridge and handles acceleration signal and solve the cable force in real time, and the calculating speed is fast, and can realize full-bridge cable force dynamic distribution's visualization, provides convenience for cable-stay bridge's cable force monitoring.
Description
Technical Field
The invention relates to the technical field of cable force monitoring, in particular to a large cable-stayed bridge cable force online monitoring system.
Background
With the continuous improvement of the traffic infrastructure in China, more and more large cable-stayed bridges are put into operation. Large cable-stayed bridges typically contain hundreds of stay cables, and measurement and evaluation of cable force are important contents for bridge health monitoring. Different from the monitoring of physical quantities such as temperature, displacement, wind speed, strain and the like, the on-line monitoring of the cable force is more complex in design and implementation. In the operation process of the bridge, dynamic changes of cable force can be caused no matter the structure is concentrated in stress, corroded, fatigued and damaged, or external wind, frost, rain, snow and vehicles pass through, and the changes are expressed by the vibration mode of the cable. Because the vibration mode of the cable is dynamic change, the real-time requirement of bridge health monitoring is difficult to meet through manual analysis, and therefore, the on-line monitoring has important significance.
The currently used cable force measuring methods comprise an oil pressure method, a magnetic flux method, a vibration frequency method and the like, wherein the magnetic flux method and the vibration frequency method are applied to the field of cable force dynamic monitoring, and the vibration frequency method is one of the most widely applied cable force measuring technologies because the implementation is simple and the precision basically meets the application requirements.
However, the cable force measurement based on the vibration frequency method has several difficulties:
(1) the method is characterized in that the data volume is huge, a vibration frequency method is to analyze cable force by picking up high-frequency vibration signals of the stay cables, the acquisition frequency of the signals is at least over 50Hz, generally, the stay cables of a large-scale cable-stayed bridge are dozens of stay cables in small quantity, and are hundreds of the stay cables in large quantity, the generated data volume is huge, and the traditional processing method is difficult to meet the requirements;
(2) the vibration mode is complex, the vibration frequency spectrum of the stay cable comprises a fundamental frequency and a high-order natural vibration frequency, wherein the fundamental frequency is an intermediate value for calculating the cable force, but for different stay cables, the positions, amplitudes and forms of the vibration fundamental frequency and the high-order natural vibration frequency are different, and great difficulty is brought to the vibration mode analysis;
(3) the identification accuracy of the fundamental frequency is low, and the fundamental frequency in the frequency spectrum is often submerged by noise due to the influence of factors such as environment, installation conditions and the like, so that the fundamental frequency cannot be directly identified; meanwhile, because the high-order natural vibration frequency may have serious deletion or distortion, the fundamental frequency can be calculated only by depending on the limited high-order natural vibration frequency, and the success rate is low, the manual identification is generally taken as the main point at present;
(4) the cable force calculation result is not visual, and after the cable forces of all the cables are calculated respectively, the cable forces are only a series of numerical values and cannot visually reflect the full-bridge cable force distribution state, particularly the cable forces need to be calculated dynamically, and the cable force distribution visualization requirement is higher.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an online monitoring system for cable force of a large cable-stayed bridge, so as to solve the problems in the background art.
The technical problem solved by the invention is realized by adopting the following technical scheme:
a large-scale cable-stayed bridge cable force on-line monitoring system comprises an acceleration sensor, a field acquisition station and a remote monitoring center, wherein the acceleration sensor is installed on a cable of a cable-stayed bridge, a cable force acquisition industrial personal computer and a data integration industrial personal computer are arranged in the field acquisition station, the cable force acquisition industrial personal computer is connected with the acceleration sensor, and the cable force acquisition industrial personal computer and the data integration industrial personal computer are respectively connected with the remote monitoring center; and a cable force acquisition program for acquiring acceleration signals is loaded on the cable force acquisition industrial personal computer, the remote monitoring center is provided with a WEB server and a database server, the cable force acquisition program acquires the acceleration signals and sends the acceleration signals to a bridge acquisition client program of the data integration industrial personal computer in batches, and the bridge acquisition client program processes the acceleration signals to calculate the cable force in real time so as to monitor the cable force of the cable-stayed bridge.
In the invention, the acceleration sensor is connected with a cable force acquisition industrial personal computer through a signal conditioner.
In the invention, the cable force acquisition industrial personal computer and the data integration industrial personal computer are connected with a central switch of a remote monitoring center through a field switch.
In the invention, the acceleration sensor adopts a CA-YD-188 piezoelectric acceleration sensor.
In the invention, a data server program is loaded in the WEB server.
The utility model provides a large-scale cable-stay bridge cable-stay force on-line monitoring system, carries out on-line monitoring to cable-stay bridge cable-stay force, and the concrete implementation step is as follows:
the first step is as follows: build an online monitoring system
The method comprises the following steps of building an acceleration sensor, a field acquisition station and a remote monitoring center, wherein the acceleration sensor is installed on a stay cable of a cable-stayed bridge so as to acquire the vibration condition of the stay cable at a high speed in real time; the acceleration vibration signal is accessed to a signal conditioner of a field acquisition station nearby by a cable and then transmitted to a cable force acquisition industrial personal computer, a cable force acquisition program is loaded on the cable force acquisition industrial personal computer, the program acquires acceleration signals and sends the acceleration signals to a bridge acquisition client program of a data integration industrial personal computer in batches, and the bridge acquisition client program processes the acceleration signals and calculates the cable force in real time; the acceleration original data is locally stored and periodically cleaned by a data integration industrial personal computer, and the cable force data is sent to a database server of a remote monitoring center for permanent storage;
the second step is that: development software platform
(1) The software platform consists of a cable force acquisition program, a bridge acquisition client program, a data server program and a WEB display platform, wherein the first three are realized by adopting a WPF technology of a NET Framework platform, and the WEB display platform is realized by adopting a Java EE technology;
(2) this on-line monitoring system design has two collection ends: one is a cable force acquisition program and the other is a bridge acquisition client program;
the third step: design data processing flow
(I) Acquiring data, namely acquiring vibration signals of the inhaul cable at a high speed in real time by a cable force acquisition program through an API (application program interface), wherein the acquired data is a packaged two-dimensional matrix structure analog waveform < double >, the structure comprises a channel number, a voltage value and acquisition time, the cable force acquisition program traverses the matrix, establishes a mapping relation between the channel number and the serial number of the acceleration sensor, and then transmits the data to a bridge acquisition client program through a TCP (transmission control protocol), and the bridge acquisition client program receives the data and then processes the data;
(II) data caching, wherein the data caching is important content of data preprocessing, data caching control is carried out in a bridge acquisition client program, and meanwhile, in order to avoid access conflict, a caching space is realized by adopting a ConcurrentQueue object with thread safety;
(III) performing spectrum analysis, namely detecting the data volume in the cache space, starting to perform multi-thread spectrum analysis after the cache space is filled, timing by a timer, triggering callback every timing time T, finishing spectrum analysis by a thread at the moment and outputting a cable value;
the fourth step: fundamental frequency extraction
According to the principle, a natural vibration frequency search algorithm based on frequency spectrum grouping is designed, and then the fundamental frequency is obtained according to the searched natural vibration frequency, wherein the specific steps are as follows:
1) data acquisition, supposing that M groups of inhaul cable vibration time domain signals are provided, wherein each group of signals comprises N sampling points (N is 2) n ) Expressed by matrix a:
2) performing frequency spectrum transformation, namely performing FFT transformation on the vibration time domain signals of each group of inhaul cables to obtain M groups containing 2 n The discrete spectrum sequence of data points is only a half of discrete spectrum sequence B, i.e. the spectrum has symmetry
3) And (3) performing window-shifting grouping, namely grouping each group of frequency spectrums of the discrete frequency spectrum sequence B again, wherein the number of points in each group is p, and the value of p is required to be an integral power of 2, for example, p is 2,4,8,16,32 and 64 … …, so that each group of frequency spectrums can obtain 2 n-1 P groups of sub-vectors, where the number of elements of the last sub-vector may be less than p, i.e.
4) Extracting peak values, and solving the maximum value of each group of subvectors in the step 3), wherein the maximum values of all groups form a new vector C'
Wherein, c 11 ＝max{b 11 b 12 b 13 … b 1p }，c 12 ＝max{b 1(p+1) b 1(p+2) b 1(p+3) … b 1(2p) }, and so on;
5) eliminating DC, and eliminating to obtain peak value vector C as the first column in C' is DC and near DC components in frequency spectrum sequence
6) Identifying the main amplitude, and taking the global maximum value of the peak vector C matrix in the step 5), namely the amplitude of the main vibration frequency:
E＝max(max(C)) (6)
7) extracting effective amplitude, screening vectors of the peak value vector C, and only keeping values larger than m × E, wherein m is a constant between [0 and 1], so as to obtain a new vector G:
8) extracting the natural frequency, and obtaining the frequency corresponding to each element value in the new vector G to obtain a natural frequency vector F, namely the natural frequency of each order:
F＝{f 1 f 2 f 3 … f k } (8)
9) assuming that k elements exist in the natural frequency vector F and k > is 2, subtracting the previous natural frequency from the extracted 2 nd natural frequency to obtain a frequency difference vector D
D＝diff(F)＝{d 1 d 2 d 3 … d k-1 }，d i ＝f j -f j-1 ，j＝2，3，4…k (9)
10) Extracting fundamental frequency, and comparing the frequency difference vector of the step 9)D is the mode, i.e. the fundamental frequency f 1
f 1 ＝mode(D) (10)
11) Calculating the cable force T
The vibration frequency method is derived according to a string vibration theory, and the free vibration equation of the stay cable is solved to obtain the cable force:
wherein T is cable force, K is 4Wl 2 G is a proportionality coefficient, W is the gravity of the unit cable length, l is the cable length, g is the acceleration of gravity, f n For the nth order natural frequency of the cable, it is obvious that the key to find the cable force is to find the fundamental frequency f 1 According to a formula, each peak value on the power spectrum of the stay cable is equal to the distance theoretically, and the value of the distance is the fundamental frequency f of the stay cable 1 The higher order frequencies are integer multiples of the fundamental frequency, so:
T＝K(f 1 ) 2 ；
the fifth step: result visualization
Extracting fundamental frequencies of all guys, calculating full-bridge guy force according to the extracted fundamental frequencies, and performing visual display monitoring by a WEB display platform.
Has the advantages that:
(1) according to the invention, through the design of a high-performance acquisition system and an acquisition program, the high-efficiency acquisition and transmission of mass acceleration data can be completed;
(2) the invention adopts the multithread programming technology, and improves the calculation speed of the cable force on the basis of not increasing the hardware cost;
(3) the self-vibration frequency search algorithm based on the frequency spectrum grouping enables the self-vibration frequency search to be simple, and can accurately and quickly complete the fundamental frequency extraction only by adjusting two parameters;
(4) the invention realizes the visualization of the dynamic distribution of the full-bridge cable force and provides convenience for the cable force monitoring of the cable-stayed bridge.
Drawings
FIG. 1 is an overall architecture diagram of an embodiment of the present invention.
FIG. 2 is a diagram illustrating system software and data flow according to an embodiment of the present invention.
FIG. 3 is a flow chart of multi-threaded spectral analysis according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of a maximum packet pickup value in the process of the fundamental frequency extraction algorithm according to the embodiment of the present invention.
FIG. 5 is a schematic diagram of the screening vibration frequency in the process of the fundamental frequency extraction algorithm in the embodiment of the present invention.
FIG. 6 is a schematic diagram of a inhaul cable time domain vibration signal in the embodiment of the present invention.
Fig. 7 is a schematic diagram of a cable signal spectrum distribution in the embodiment of the present invention.
Fig. 8 is a schematic diagram of cable signal spectrum analysis natural vibration frequency extraction in the embodiment of the present invention.
Fig. 9 is a schematic diagram of fundamental frequency distribution of the stay cable in the embodiment of the present invention.
Fig. 10 is a schematic view illustrating cable force distribution of a stay cable according to an embodiment of the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below by combining the specific drawings.
The utility model provides a large-scale cable-stay bridge cable-stay force on-line monitoring system, carries out on-line monitoring to cable-stay bridge cable-stay force, and the concrete implementation step is as follows:
the first step is as follows: build an online monitoring system
The on-line monitoring system comprises an acceleration sensor, an on-site acquisition station and a remote monitoring center, as shown in figure 1, the acceleration sensor of the system adopts a CA-YD-188 piezoelectric acceleration sensor (IEPE), a low-noise IEPE is arranged in the acceleration sensor, the IEPE adopts a constant current source excitation of 12-24 VDC/2-10 mA, the constant current source adopts a YE3826 multi-channel IEPE constant current adjuster and is connected with the sensor through a BNC connector, an acceleration signal is acquired by an NI 9205 acquisition board card, the acquisition board card is provided with 32 channels, a rated input voltage +/-0.2- +/-10V can be matched, the acquisition board card is directly inserted into a card slot of an NI cDAQ-9139 controller of a cable force acquisition industrial personal computer through a detachable spring terminal connector, the NI cDAQ-9139 controller is internally provided with an Intel Core i7 dual-Core processor, and is provided with a USB high-speed interface, a gigabit Ethernet interface and a serial interface, and is provided with a WES7 and LabEW Real-Time operation system, the signal acquisition of the acceleration sensor can be independently finished, but because the capacity of a hard disk configured by the NI cDAQ-9139 controller is small and difficult to expand, the controller is only used as an acquisition platform in the embodiment, and the acquired data is transmitted to a data integration industrial personal computer for processing through a local area network;
the acceleration sensor is arranged on a stay cable of the cable-stayed bridge so as to acquire the vibration condition of the stay cable at a high speed in real time; the acceleration vibration signal is accessed to a signal conditioner of a field acquisition station nearby by a cable and then transmitted to a cable force acquisition industrial personal computer, a cable force acquisition program is loaded on the cable force acquisition industrial personal computer, the program acquires acceleration signals and sends the acceleration signals to a bridge acquisition client program of a data integration industrial personal computer in batches, and the bridge acquisition client program processes the acceleration signals and calculates the cable force in real time; the acceleration original data is locally stored and periodically cleaned by a data integration industrial personal computer, and the cable force data is sent to a database server of a remote monitoring center for permanent storage;
the second step: development software platform
(1) The software platform consists of a cable force acquisition program, a bridge acquisition client program, a data server program and a WEB display platform, wherein the first three are realized by adopting the WPF technology of the NET Framework platform, the WEB display platform is realized by adopting the Java EE technology, and the structure of the software system is shown in figure 2;
(2) this on-line monitoring system design has two collection ends: the system mainly considers that an NI acquisition system is an independent platform, and independent acquisition programs are developed to avoid the coupling between the NI acquisition system and a bridge acquisition client program, so that the program development and the later operation and maintenance are facilitated;
the third step: design data processing flow
(I) The method comprises the steps that data are collected, vibration signals of a stay cable are collected in real time at a high speed through an API (application program interface) provided by an NI (network interface) company by a cable force collection program, the obtained data are a packaged two-dimensional matrix structure analog waveform < double >, the structure comprises information such as a channel number, a voltage value and collection time, the cable force collection program traverses the matrix and establishes a mapping relation between the channel number and the number of an acceleration sensor, then the data are sent to a bridge collection client program through a TCP (transmission control protocol), the bridge collection client program receives the data and then carries out subsequent processing such as denoising, spectrum analysis and cable force calculation, and finally the data are sent to a data server program to complete higher-level data analysis work such as statistics, early warning and storage;
(II) data caching, wherein data preprocessing work is performed in a bridge acquisition client program, the content of the preprocessing is mainly data caching control, and because FFT conversion is required for subsequent spectrum analysis work, in order to improve efficiency and precision, a radix-2 FFT algorithm is adopted in the embodiment, and a time domain signal of an acceleration sensor is required to have 2 n The program is used as input data of FFT (fast Fourier transform) conversion by establishing a cache and limiting the cache space to a fixed length, although the capacity of the cache space is fixed, the data in the cache is dynamically updated, and new data can cover old data; considering the requirement that a plurality of threads access the data cache space, simultaneously meeting the data first-in first-out principle, and avoiding access conflict, the cache space is realized by adopting a ConcurrentQueue object with thread safety;
(III) performing spectrum analysis, namely detecting data volume in a cache space, starting to perform spectrum analysis after the cache space is filled, and realizing multi-thread spectrum analysis by software programming, wherein as shown in fig. 3, assuming that the number of stay cables is M, the number of FFT (fast Fourier transform) calculation points is N, a timing operation interval is T, after a program is started, M working threads are directly opened up, each thread is responsible for calculating the cable force of one stay cable, and the M threads work in parallel to improve the utilization rate of a CPU (Central processing Unit) and realize real-time calculation and online monitoring of the cable force; opening up 3 sub-threads in each working thread, wherein the thread a is responsible for data cache control, the thread b is responsible for spectrum analysis, and the thread c is responsible for timing trigger operation; the spectrum analysis function in the thread b is a callback function of the thread c, the timer is used for timing, the callback is triggered every timing time T, the thread b completes spectrum analysis once and outputs a cable force value;
the fourth step: fundamental frequency extraction
According to the principle, a natural vibration frequency search algorithm based on frequency spectrum grouping is designed, and then the fundamental frequency is obtained according to the searched natural vibration frequency, wherein the specific steps are as follows:
1) data acquisition, as shown in fig. 6, assume that M groups of stay cable vibration time domain signals are provided, and each group of signals includes N sampling points (N ═ 2) n ) Expressed by matrix a:
2) performing frequency spectrum transformation, namely performing FFT transformation on the vibration time domain signals of each group of inhaul cables to obtain M groups containing 2 n Since the spectrum has symmetry, the present embodiment only takes a half of discrete spectrum sequence B as shown in FIG. 7, i.e. the discrete spectrum sequence of data points
3) And (4) performing window-shifting grouping, namely grouping each group of frequency spectrums of the discrete frequency spectrum sequence B again, wherein the number of points in each group is p, and the value of p is required to be an integral power of 2, for example, p is 2,4,8,16,32 and 64 … …, so that each group of frequency spectrums can obtain 2 n-1 A/p sets of sub-vectors, wherein the number of elements of the last sub-vector may be less than p, i.e.
4) Extracting peak values, and solving the maximum value of each group of subvectors in the step 3), wherein the maximum value of each group forms a new vector C'
Wherein, c 11 ＝max{b 11 b 12 b 13 … b 1p }，c 12 ＝max{b 1(p+1) b 1(p+2) b 1(p+3) … b 1(2p) And so on, as shown in fig. 4;
5) eliminating direct current, because the first column in C' is the direct current and near direct current components in the frequency spectrum sequence, eliminating to obtain a peak value vector C
6) Identifying the main amplitude, and taking the global maximum value of the peak vector C matrix in the step 5), namely the amplitude of the main vibration frequency:
E＝max(max(C)) (6)
7) extracting effective amplitude, screening vectors of the peak value vector C, and only keeping values larger than m × E, wherein m is a constant between [0 and 1], so as to obtain a new vector G:
8) extracting the natural frequency, and obtaining the frequency corresponding to each element value in the new vector G to obtain a natural frequency vector F, namely the natural frequency of each order:
F＝{f 1 f 2 f 3 … f k } (8)
as shown in fig. 5, F ═ 3.1250,4.6875,5.4688,6.2500,7.0313,7.6563,8.2813,9.0625,10.4688,11.2500,12.1875,12.9688,13.7500,14.5313,15.3125,16.2500,17.0313}
9) Assuming that k elements exist in the natural frequency vector F and k > is 2, subtracting the previous natural frequency from the extracted 2 nd natural frequency to obtain a frequency difference vector D
D＝diff(F)＝{d 1 d 2 d 3 … d k-1 }，d i ＝f j -f j-1 ，j＝2，3，4…k (9)
Calculated D ═ 1.5625,0.7813,0.7813,0.7813,0.6250,0.6250,0.7813,1.4063,0.7813,0.9375,0.7813,0.7813,0.7813,0.7813,0.9375,0.7813}
10) Extracting fundamental frequency, and solving the mode of the frequency difference vector D in the step 9) to obtain the fundamental frequency f 1
f 1 ＝mode(D) (10)
Calculating the fundamental frequency f1, f 1 ＝0.7813(Hz)
11) Calculating the cable force T
The vibration frequency method is derived according to a string vibration theory, and the free vibration equation of the stay cable is solved to obtain the cable force:
wherein T is cable force, K is 4Wl 2 G is a proportionality coefficient, W is the gravity of the unit cable length, l is the cable length, g is the acceleration of gravity, f n For the nth order natural frequency of the cable, it is obvious that the key to find the cable force is to find the fundamental frequency f 1 According to a formula, all peak values on the power spectrum of the inhaul cable are equal intervals theoretically, and the value of the intervals is the fundamental frequency f of the inhaul cable 1 The high-order frequency is an integer multiple of the fundamental frequency, and the scale factor K of the cable is 5630 according to engineering data, so:
T＝K(f 1 ) 2 ＝5630×(0.7813) 2 ＝3437；
the fifth step: result visualization
According to the flow shown in fig. 3, the fundamental frequencies of all the guys are extracted, as shown in fig. 9, the full-bridge guy force is calculated according to the extracted fundamental frequencies, then the visual display monitoring is carried out by the WEB display platform, as shown in fig. 10, the full-bridge guy force distribution is clear at a glance.
Claims (10)
1. A large-scale cable-stayed bridge cable force on-line monitoring system comprises an acceleration sensor, a field acquisition station and a remote monitoring center, and is characterized in that the acceleration sensor is installed on a cable of a cable-stayed bridge, a cable force acquisition industrial personal computer and a data integration industrial personal computer are arranged in the field acquisition station, the cable force acquisition industrial personal computer is connected with the acceleration sensor, and the cable force acquisition industrial personal computer and the data integration industrial personal computer are respectively connected with the remote monitoring center; and a cable force acquisition program for acquiring acceleration signals is loaded on the cable force acquisition industrial personal computer, the remote monitoring center is provided with a WEB server and a database server, the cable force acquisition program acquires the acceleration signals and sends the acceleration signals to a bridge acquisition client program loaded by the data integration industrial personal computer in batches, and the bridge acquisition client program processes the acceleration signals to calculate the cable force in real time so as to monitor the cable force of the cable-stayed bridge.
2. The large cable-stayed bridge cable force on-line monitoring system according to claim 1, characterized in that the acceleration sensor is connected with a cable force acquisition industrial personal computer through a signal conditioner.
3. The large cable-stayed bridge cable force on-line monitoring system according to claim 1, characterized in that the cable force acquisition industrial personal computer and the data integration industrial personal computer are connected with a central switch of a remote monitoring center through a field switch.
4. The system as claimed in claim 1, wherein the acceleration sensor is a CA-YD-188 piezoelectric acceleration sensor.
5. The system according to claim 1, wherein a data server program is loaded in the WEB server.
6. The large-scale cable-stayed bridge cable force on-line monitoring system according to any one of claims 1 to 5, which is used for carrying out on-line monitoring on cable force of a cable-stayed bridge, and is characterized by comprising the following specific implementation steps:
the first step is as follows: build an on-line monitoring system
The method comprises the following steps of building an acceleration sensor, a field acquisition station and a remote monitoring center, wherein the acceleration sensor is installed on a cable of a cable-stayed bridge, an acceleration vibration signal is connected to a signal conditioner of the field acquisition station through a cable and then is transmitted to a cable force acquisition industrial personal computer, a cable force acquisition program is loaded on the cable force acquisition industrial personal computer, the program acquires acceleration signals and sends the acceleration signals to a bridge acquisition client program loaded by a data integration industrial personal computer in batches, and the bridge acquisition client program processes the acceleration signals and calculates cable force in real time;
the second step is that: developing software platform
(1) The software platform consists of a cable force acquisition program, a bridge acquisition client, a data server program and a WEB display platform;
(2) this on-line monitoring system design has two collection ends: a cable force acquisition program and a bridge acquisition client program;
the third step: design data processing flow
(I) Acquiring data, namely acquiring vibration signals of a stay cable at a high speed in real time by a cable force acquisition program through an API (application program interface), wherein the acquired data is a packaged two-dimensional matrix structure, the structure comprises a channel number, a voltage value and acquisition time, the cable force acquisition program traverses the matrix, establishes a mapping relation between the channel number and the number of an acceleration sensor, and then transmits the data to a bridge acquisition client program through a TCP (transmission control protocol), and the bridge acquisition client program receives the data and then processes the data;
(II) data caching, namely performing data caching control in a bridge acquisition client program;
(III) performing spectrum analysis, namely detecting the data volume in the cache space, starting to perform multi-thread spectrum analysis after the cache space is filled up, timing by a timer, triggering callback every time T, finishing one spectrum analysis by a thread at the moment and outputting a cable value;
the fourth step: fundamental frequency extraction
According to the relation between the cable force and the natural vibration frequency of each order, the peak values on the power spectrum of the inhaul cable are theoretically equidistant,the value of the distance is the fundamental frequency of the inhaul cable, according to the principle, a self-vibration frequency searching algorithm based on frequency spectrum grouping is designed, and then the fundamental frequency f is obtained according to the searched self-vibration frequency 1 ；
The fifth step: result visualization
And extracting the fundamental frequency of all the inhaul cables, calculating the full-bridge cable force according to the extracted fundamental frequency, and performing visual display monitoring by a WEB display platform.
7. The system of claim 6, wherein in the second step, the cable force collection program, the bridge collection client program, and the data server program are implemented by the WPF technology of NET Framework platform, and the WEB display platform is implemented by the Java EE technology.
8. The system for on-line monitoring of cable force of large cable-stayed bridge according to claim 6, characterized in that in the third step, the data cache space is implemented by using a thread-safe ConcurrentQueue object.
9. The system for on-line monitoring of cable force of large cable-stayed bridge according to claim 6, wherein in the fourth step, the fundamental frequency extraction is as follows:
1) data acquisition, supposing that M groups of inhaul cable vibration time domain signals are provided, wherein each group of signals comprises N sampling points (N is 2) n ) Expressed by matrix a:
2) performing frequency spectrum transformation, namely performing FFT transformation on the vibration time domain signals of each group of inhaul cables to obtain M groups containing 2 n The discrete spectrum sequence of data points is only a half of discrete spectrum sequence B, i.e. the spectrum has symmetry
3) And (4) performing window shifting grouping, namely grouping each group of frequency spectrums of the discrete frequency spectrum sequence B again, wherein the number of points of each group is p, and the value of p is required to be an integer power of 2, so that each group of frequency spectrums can obtain 2 n-1 A/p sets of sub-vectors, wherein the number of elements of the last sub-vector may be less than p, i.e.
4) Extracting peak values, and solving the maximum value of each group of subvectors in the step 3), wherein the maximum values of all groups form a new vector C'
Wherein, c 11 ＝max(b 11 b 12 b 13 …b 1p }，c 12 ＝max{b 1(p+1) b 1(p+2) b 1(p+3) …b 1(2p) }, and so on;
5) eliminating direct current, because the first column in C' is the direct current and near direct current components in the frequency spectrum sequence, eliminating to obtain a peak value vector C
6) Identifying the main amplitude, and taking the global maximum value of the peak vector C matrix in the step 5), namely the amplitude of the main vibration frequency:
E＝max(max(C)) (6)
7) extracting effective amplitude, screening vectors of the peak value vector C, and only keeping values larger than m × E, wherein m is a constant between [0 and 1], so as to obtain a new vector G:
8) extracting the natural frequency, and obtaining the frequency corresponding to each element value in the new vector G to obtain a natural frequency vector F, namely the natural frequency of each order:
F＝{f 1 f 2 f 3 …f k } (8)
9) assuming that k elements exist in the natural frequency vector F and k > is 2, subtracting the previous natural frequency from the extracted 2 nd natural frequency to obtain a frequency difference vector D
D＝diff(F)＝{d 1 d 2 d 3 …d k-1 }，d i ＝f j -f j-1 ，j＝2，3，4，..k (9)
10) Extracting fundamental frequency, and solving the mode of the frequency difference vector D in the step 9) to obtain the fundamental frequency f 1
f 1 ＝mode(D) (10)。
10. The system for on-line monitoring of cable force of large cable-stayed bridge according to claim 6, characterized in that in the fourth step, the cable force T is calculated as follows:
deducing according to a string vibration theory, solving a free vibration equation of the stay cable to obtain a cable force:
wherein T is cable force, K is 4Wl 2 G is a proportionality coefficient, W is the gravity of the unit cable length, l is the cable length, g is the acceleration of gravity, f n For the nth order natural frequency of the cable, it is obvious that the key to find the cable force is to find the fundamental frequency f 1 According to a formula, each peak value on the power spectrum of the stay cable is equal to the distance theoretically, and the value of the distance is the fundamental frequency f of the stay cable 1 The higher order frequencies are integer multiples of the fundamental frequency, so:
T＝K(f 1 ) 2 。
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