CN106932135B - Flexible inhaul cable force testing method for identifying vibration frequency based on weighted narrow-band peak searching method - Google Patents
Flexible inhaul cable force testing method for identifying vibration frequency based on weighted narrow-band peak searching method Download PDFInfo
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- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/04—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring tension in flexible members, e.g. ropes, cables, wires, threads, belts or bands
- G01L5/042—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring tension in flexible members, e.g. ropes, cables, wires, threads, belts or bands by measuring vibrational characteristics of the flexible member
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Abstract
The invention providesA flexible cable searching force testing method for recognizing vibration frequency based on a weighted narrow-band peak searching method comprises the following steps: measuring vibration data of the flexible inhaul cable, and carrying out frequency domain transformation on the vibration data of the flexible inhaul cable to obtain a vibration frequency spectrum of the flexible inhaul cable; method for obtaining each order frequency f of flexible inhaul cable by narrow-band peak searching method i And amplitude a thereof i Calculating the difference value delta f of two continuous-order frequencies of the flexible inhaul cable i And calculating the product w of the two consecutive orders of frequency amplitude i By the product w i As frequency difference Δ f i The weight value of (1) is calculated according to the difference value delta f of two continuous-order frequencies of the flexible inhaul cable i And w i Product calculation of vibration fundamental frequency f of flexible inhaul cable 1 (ii) a Calculating the cable force of the flexible cable by adopting a formula: t is 4mL 2 f 1 2 . The weighted narrow-band peak searching method takes the weighted average value of the difference values between continuous orders of frequency as the base frequency, can quickly obtain the searching force of the flexible inhaul cable by modern tools of a computer and the like or manual calculation, and has the advantages of simple operation, simple calculation method and accurate result.
Description
Technical Field
The invention belongs to the field of structural engineering monitoring, and particularly relates to a flexible cable force testing method for recognizing vibration frequency based on a weighted narrow-band peak searching method.
Background
With the rapid increase of the number of bridges and the increasingly complex and severe operating environment of bridges in China, the safety problem of bridge engineering is increasingly prominent. According to incomplete statistics, more than 50 bridge collapse accidents occur in China during the 1999-2016 years, and huge life and property losses and severe social influences are caused. The safety of bridge structures is receiving increasing public attention from governments and society.
The construction monitoring is a means for ensuring that design ideas are perfectly reflected in the construction or use stage of large structures such as bridges, and along with the great breakthrough of the span and the structural form of the large structures such as bridges, the stress conditions of the structures under various working conditions are difficult to accurately obtain by conventional calculation or measurement means, the monitoring is required to be introduced as an auxiliary control means, and the construction monitoring plays a role in guiding and adjusting the construction sequence in the construction of the large structures such as bridges. Construction monitoring mainly has two aspects: the construction monitoring can ensure the safety of large structures such as bridges and the like in the construction process, and the construction monitoring result also provides data for the construction control, and the construction control is to carry out effective control in the whole construction process, so that the linear shape and the internal force of the formed structure can meet the design requirements. The construction monitoring mainly comprises deflection observation, temperature effect observation, stress observation (strain is measured through a strain gauge), bridge main parameter observation, prestress observation (for a prestress structure), cable force observation (comprising a cable-stayed bridge cable, a suspension bridge, a suspender arch bridge suspender tensioning force, a steel pipe arch hoisting and cable buckling force value) and the like.
Structural Health Monitoring (SHM) is an important field of development of civil engineering discipline. The structural health monitoring is to monitor the mechanical property of a structure and the environment where the structure is located, monitor the whole or local behavior of the structure in real time or discontinuously, diagnose the damage displacement and degree of the structure, intelligently evaluate the service condition, reliability, durability and bearing capacity of the structure, trigger an early warning signal for the structure under an emergency or when the structure is seriously abnormal in use condition, and provide basis and guidance for the maintenance, maintenance and management decision of the structure. The structure health monitoring technology is a comprehensive technology which is multi-field and across subjects, and relates to multiple research directions of civil engineering, dynamics, materials science, sensing technology, testing technology, signal analysis technology, computer technology, network communication technology, pattern recognition technology and the like.
The stay cable, the suspender and the like are structural members which can efficiently bear tensile force, and are widely applied to large-scale cable bearing bridges such as cable-stayed bridges, suspension bridges, arch bridges and the like. As a main bearing component, the service performance of the stay cable is directly related to the overall safety of the bridge, and plays a vital role in the safe service operation of the bridge. In the use process of the bridge, the stay cable is often damaged due to corrosion, vibration and the like, and as an important component of a tension structure, the damage of the stay cable can bring disastrous results to the bridge.
The cable force is an important index for evaluating whether the stress state of the cable body structure is good or not, and is particularly suitable for cable-stayed bridges, suspension bridges and some large cable membrane structures which take the stay cable as a main stress body. The damaged guy cable has cable force change (relaxation) to influence the force distribution in the structure and the structure line type, and the serious corrosion of the guy cable even can cause the fracture to further cause the collapse of the structure.
Disclosure of Invention
The technical problem is as follows: in order to overcome the defects of the prior art, the invention provides a flexible cable force testing method for identifying vibration frequency based on a weighted narrow-band peak searching method.
The technical scheme is as follows: the invention provides a flexible cable force testing method for identifying vibration frequency based on a weighted narrow-band peak searching method, which comprises the following steps:
step 3, marking as f according to the vibration frequency of each order of the known flexible inhaul cable i * Wherein i represents the order of the vibration frequency, i is a continuous natural number, i is 1,2,3 … …, the frequency spectrum is divided into narrow bands, and the narrow band neighborhood (f) of each order of vibration frequency is determined i * (1-ε),f i * (1+ε))；
Wherein, Δ f i ＝f i+1 -f i ，
w i ＝a i+1 *a i ；
Wherein the content of the first and second substances,
and 7, calculating the cable force of the flexible cable by adopting a formula (I):
T＝4mL 2 f 1 2 (I)；
wherein:
t-flexible cable force;
m represents the mass of the flexible inhaul cable in unit length, namely the linear density of the flexible inhaul cable;
l-the nominal length of the cord member.
The formula (I) is obtained according to the following method:
the measurement of the cable force comprises a vibration method, an oil pressure method, a stress method and the like, and the vibration method is developed in the engineering monitoring field due to the factors of simple operation, low cost and the like. The vibration method is used for testing the cable force of the cable, firstly, vibration data of the cable are obtained, then, frequency spectrum analysis is carried out, and the cable force is theoretically calculated by utilizing a fundamental frequency (a first-order frequency), but in actual engineering, the fundamental frequency (influenced by various noises) of the cable cannot be necessarily and effectively obtained.
The invention utilizes the frequency doubling characteristic of the flexible inhaul cable to identify the multi-order frequency of the inhaul cable, calculates a plurality of difference values of continuous frequencies of each order to be equivalent to the fundamental frequency of the inhaul cable, and calculates the inhaul cable force according to the geometrical physical characteristic of the inhaul cable.
The basic principle of measuring the cable force by the vibration method is to measure the natural vibration frequency of the cable and then calculate and analyze according to the string vibration theory to determine the cable force of the cable. The vibration method adopts environment random excitation to measure the first several orders of natural vibration frequency of the inhaul cable, and then the solution is analyzed according to the string vibration theory to obtain the internal force of the inhaul cable.
When the boundary condition of the two ends of the cable member can be simplified to hinge, the calculation formula of the cable force is as follows:
T＝4m(f i 2 /i 2 )·L 2 -EIπ 2 (i 2 /L 2 ) (1)
wherein:
t-axial force (cable force) to which the cable member is subjected;
m-mass per unit length of the cord member (linear density);
EI-bending stiffness of the cable member;
f i -the nth order vibration frequency (in Hz) of the cable member;
i-vibration order;
l-the nominal length of the cord member.
When the member satisfies the definition of a flexible cable-like member, that is, the slenderness ratio is sufficiently large, the second term of the formula (1) is negligible, and the formula (1) can be simplified as follows:
T＝4m(f i 2 /i 2 )·L 2 (2)
if the nominal length L of the cable member is known, the unit mass m along the length direction is measured, and the first order vibration frequency of the cable member is measured, the cable force can be calculated according to the formula (2); in practical applications, it is often not easy to determine the order of a certain order of frequency, so the cable force is generally calculated according to the fundamental frequency or the frequency difference of the cable, and equation (2) can be expressed as:
T＝4mL 2 f 1 2 (3)
the weighted narrow-band peak searching method of the invention is characterized in that a plurality of frequency peak values are identified in the neighborhood of each identified order of frequency, a frequency difference is calculated according to the difference value between continuous orders of frequency and a weight, the base frequency is replaced by the frequency difference according to the frequency doubling characteristic, and then the inhaul cable force is calculated by using the formula (3).
In step 2, the frequency domain transformation method is fourier transformation.
In step 3, the position of the narrow band needs to be determined according to the known vibration frequency of each order of the flexible cable, and the known vibration frequency of each order of the flexible cable may be a theoretical calculation result (for example, obtained by calculation by using a finite element model method) or historical vibration frequency data of the flexible cable; due to the simplification of the finite element model, the loss of the flexible rope, and the like, the vibration frequency of each order of the known flexible inhaul cable may be different from the current actual vibration frequency.
In the step 3, the value of epsilon ranges from 3% to 5%, and can be determined according to actual conditions or experience.
Has the advantages that: the weighted narrow-band peak searching method takes the weighted average value of the difference values between continuous multi-order frequencies as the base frequency, can quickly obtain the searching force of the flexible inhaul cable by using modern tools of a computer or manual calculation, and has the advantages of simple operation, simple calculation method and accurate result.
In particular, the present invention has the following outstanding advantages over the prior art:
(1) the calculation method is simple, convenient to operate and understand, and the result is accurate;
(2) the method is convenient for realizing computer programs and is convenient for quick and automatic batch processing of the computer;
(3) the method can search the multi-order vibration frequency of the flexible inhaul cable, and can obtain the current actual vibration frequency according to the priori knowledge;
(4) the method can effectively describe the cable force change condition.
Drawings
FIG. 1 is a curve of acceleration time course of a certain cable of a certain bridge within 15 minutes;
FIG. 2 is a graph of the vibration spectrum of a flexible rope;
FIG. 3 is a diagram of the present method and anchor rope meter simultaneously identifying the change in cable force at a certain day;
FIG. 4 is a graph of the error conditions of the method and anchor line gauge: the error characteristics of the method are described by taking the anchor cable as a standard, and the error characteristics comprise absolute error and relative error.
Detailed Description
The method of the present invention for weighting narrow-band peak search to measure flexible cable search is further described below.
Example 1
The method for measuring the flexible cable searching force by weighting narrow-band peak searching comprises the following steps:
wherein, x (N) is a discrete acceleration time interval data sequence, N is a serial number of an acceleration data point, N is a data amount of the acceleration time interval data sequence, that is, the number of sampling points, in this example, the sampling frequency is 20Hz, the sampling duration is 15 minutes, the number of sampling points is N15 × 60 × 18000, j is an imaginary number, x (k) is a transformed frequency domain data sequence, and k is a serial number of a frequency domain data point;
step 3, marking as f according to the vibration frequency of each order of the known flexible inhaul cable i * Where i is 1,2,3 … …, where i represents the order of the frequency, narrow band division is performed on the spectrum, and a narrow band neighborhood (f) of each order of frequency is determined i * (1-ε),f i * (1+ ε)), ε may be determined empirically, taking 5% in this example;
in this example, the vibration frequency of each order of the known flexible inhaul cable is obtained by analyzing historical vibration data, f i * See table 1;
Wherein, Δ f i ＝f i+1 -f i ，
w i ＝a i+1 *a i ；
In this example, the weight w is obtained according to the analysis of the historical data i Sum frequency difference Δ f i See table 1.
TABLE 1
| Order of the scale | f i * (Hz) | f i (Hz) | Δf i (Hz) | a i | |
| 1 | 0.3501 | 0.3500 | 0.3511 | 3.0102 | 26.4458 |
| 2 | 0.7003 | 0.7011 | 0.3500 | 8.7854 | 63.6168 |
| 3 | 1.0501 | 1.0511 | 0.3477 | 7.2412 | 35.4464 |
| 4 | 1.3921 | 1.3988 | 0.3468 | 4.8951 | 29.1665 |
| 5 | 1.7491 | 1.7456 | 0.3477 | 5.9583 | 31.8894 |
| 6 | 2.0916 | 2.0933 | 0.3589 | 5.3521 | 50.1235 |
| 7 | 2.4562 | 2.4522 | 0.3411 | 9.3652 | 76.9286 |
| 8 | 2.7953 | 2.7933 | 0.3545 | 8.2143 | 105.5883 |
| 9 | 3.1453 | 3.1478 | 0.3511 | 12.8542 | 117.3126 |
| 10 | 3.4981 | 3.4989 | 0.3525 | 9.1264 | 76.3460 |
| 11 | 3.8565 | 3.8514 | 0.3489 | 8.3654 | 70.4308 |
| 12 | 4.2016 | 4.2003 | 0.3486 | 8.4193 | 69.1671 |
| 13 | 4.5429 | 4.5489 | 0.3544 | 8.2153 | 64.5484 |
| 14 | 4.9032 | 4.9033 | 0.3511 | 7.8571 | 53.1541 |
| 15 | 5.2598 | 5.2544 | 0.3478 | 6.7651 | 45.3153 |
| 16 | 5.6109 | 5.6022 | 0.3500 | 6.6984 | 51.5388 |
| 17 | 5.9511 | 5.9522 | 0.3389 | 7.6942 | 46.0667 |
| 18 | 6.2899 | 6.2911 | —— | 5.9872 | —— |
| …… | …… | …… | …… | …… |
Wherein the content of the first and second substances,
and 7, calculating the cable force of the flexible cable by adopting a formula (I):
T＝4mL 2 f 1 2 4606.1043kn (i); wherein:
m＝72.125kg/m；
L＝361.123m。
the accuracy and reliability of the method of the invention pass the verification of a real bridge test:
the method firstly measures a vibration time domain curve of a certain cable of a certain bridge (see figure 1), then obtains a vibration frequency spectrum of the cable (see figure 2) according to the vibration time domain curve, and calculates weighted average frequency difference to replace fundamental frequency by utilizing the vibration frequency and amplitude of each order identified by the method.
The method of the invention and the anchor cable meter are used for simultaneously measuring the cable force change condition of a certain cable of a certain bridge within one day (see figure 3), and the cable force change trends measured by the two methods are consistent as can be seen from figure 3; FIG. 4 shows the error of the two methods, based on the cable force measured by the anchor cable meter, the absolute error of the cable force measured by the method of the present invention is within 20kN, and the relative error is within 0.4%.
Claims (2)
1. A flexible cable searching force testing method for recognizing vibration frequency based on a weighted narrow-band peak searching method is characterized in that: the method comprises the following steps:
step 1, measuring vibration data of a flexible inhaul cable, namely time domain vibration data of the flexible inhaul cable;
step 2, performing frequency domain transformation on the time domain vibration data of the flexible inhaul cable to obtain a vibration frequency spectrum of the flexible inhaul cable;
step 3, marking as f according to the known vibration frequency of each order of the flexible inhaul cable i * Wherein i represents the order of the vibration frequency, i takes the value as a continuous natural number, the frequency spectrum is divided into narrow bands, and the narrow band neighborhood (f) of each order of vibration frequency is determined i * (1-ε)，f i * (1+ε))；
The vibration frequency of each order of the known flexible inhaul cable is obtained by analyzing according to historical vibration data, and the value of epsilon is 3-5%;
step 4, in narrow band neighborhood (f) i * (1-ε)，f i * (1+ epsilon)) to obtain the peak value a i Peak value a i Corresponding vibration frequency f i The actual ith order vibration frequency of the flexible inhaul cable is obtained;
step 5, calculating the difference value delta f of two continuous-order vibration frequencies of the flexible inhaul cable i And its weight w i ，
Wherein, Δ f i ＝f i+1 -f i ，
w i ＝a i+1 *a i ；
Step 6, calculating the vibration fundamental frequency f of the flexible inhaul cable 1 ，
Wherein the content of the first and second substances,
and 7, calculating the cable force of the flexible cable by adopting a formula (I):
T＝4mL 2 f 1 2 (I)；
wherein:
t-flexible cable force;
m-the mass of the flexible inhaul cable in unit length, namely the linear density of the flexible inhaul cable;
nominal length of the L-cable member.
2. The flexible cable force testing method based on vibration frequency identification by the weighted narrow-band peak searching method according to claim 1, characterized in that: in step 2, the frequency domain transform method is fourier transform.
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