CN108168691B - A kind of drag-line second-order natural frequency of vibration measurement method of combination sine excitation device and video instrument - Google Patents
A kind of drag-line second-order natural frequency of vibration measurement method of combination sine excitation device and video instrument Download PDFInfo
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- CN108168691B CN108168691B CN201711390650.1A CN201711390650A CN108168691B CN 108168691 B CN108168691 B CN 108168691B CN 201711390650 A CN201711390650 A CN 201711390650A CN 108168691 B CN108168691 B CN 108168691B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H17/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves, not provided for in the preceding groups
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H13/00—Measuring resonant frequency
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Abstract
A kind of drag-line second-order natural frequency of vibration measurement method of combination sine excitation device and video instrument of the present invention, belongs to technical field of civil engineering；The inventive method estimates the second order frequency range of rope first, and vibration excitor is installed at rope a quarter length, and vibration excitor is allowed to estimate scanning frequency excitation within the scope of second order frequency, utilizes the vibration displacement at video instrument observation rope half length a and at a quarter length b.Using displacement ratio at two as the key index for determining that resonance occurs, if a certain excited frequency of vibration excitor to be displaced, ratio changes over time very little and Displacement Ratio is close to 0, can determine that excited frequency at this time is the second order frequency of rope.By proposing a kind of completely new drag-line second order frequency measurement method, the measurement accuracy of drag-line second order frequency is improved.
Description
Technical field
The present invention relates to a kind of measurement methods of cable system bridge cable natural frequency of vibration, belong to technical field of civil engineering.
Background technique
Cable system bridge mainly carries out the transmitting and distribution of power by drag-line, and drag-line is the main stress structure of cable system bridge
Part.The second-order natural frequency of vibration (hereinafter referred to as second order frequency) of drag-line is that cable system bridge construction control and assessment bridge are normal
The important indicator of use state even more identifies the important parameter of Cable power.
The accuracy of drag-line second order frequency measurement is influenced by many factors, such as test method, tool, observation instrument
Deng.Measurement means common at present are mainly to use the environmental excitation free vibration test of acceleration transducer and artificial excitation total
Vibration test.
There is problem in above-mentioned measurement means: when using environmental excitation, for shorter grommet border in practical engineering applications
Excitation is difficult to excite the second order vibration of drag-line, therefore is unable to measure drag-line second order frequency；When carrying out artificial excitation using vibration excitor, lead to
It crosses naked-eye observation and is difficult that whether accurate judgement rope has occurred resonance, contained more noise by the signal that acceleration transducer measures
Also it is difficult to determine resonance.So existing measurement means are unable to satisfy technical need for shorter rope.
Summary of the invention
The purpose of the present invention is to solve above-mentioned technical problems, and then provide a kind of combination sine excitation device and video instrument
Drag-line second-order natural frequency of vibration measurement method.
Technical solution of the present invention:
A kind of drag-line second-order natural frequency of vibration measurement method of combination sine excitation device and video instrument the following steps are included:
Step a: it according to drawing and field observation situation, is estimated using theoretical formula by the second-order natural frequency of vibration f of measuring rope2
Range [fD, fU],
F in formulaDFor by the second-order natural frequency of vibration f of measuring rope2Lower range bound, fUFor by the second-order natural frequency of vibration f of measuring rope2
Upper range limit, L are that rope is long (m), and EI is rope section bending stiffness (Nm2), m is unit linear mass (kg/m), T1It estimates
Rope tensility (N) lower limit value, T2For rope tensility (N) upper limit value estimated.
Step b: vibration excitor is installed at the rope a quarter length for needing to measure, and in fixed bottom boundary restocking setting video instrument
Observe the vibration displacement at rope half length a and at a quarter length b.
Step c: the excited frequency θ of vibration excitor is fixed on [f by starting vibration excitorD, fU] a certain value in range, and allow rope
Vibration, which is stablized, enters steady-state process, observes displacement d at a simultaneously at this timeaWith displacement d at bb, note
For Displacement Ratio.
Step d: under the premise of excited frequency θ is constant, if Displacement Ratio λ changes over time very little and Displacement Ratio λ is close to
0, then illustrate that this excited frequency θ is the second order frequency f of the rope2, if not, change excited frequency θ repeated measures.
Further, the vibration excitor in step b is sinusoidal vibration excitor.
The invention has the following advantages: the method for the present invention estimates the second order frequency range of rope first, Suo Si/
Vibration excitor is installed at one length, allows vibration excitor estimating scanning frequency excitation within the scope of second order frequency, video instrument is utilized to observe Suo Erfen
One of vibration displacement at length a and at a quarter length b.Refer to displacement ratio at two as the key for determining resonance generation
Mark, if a certain excited frequency of vibration excitor makes, displacement ratio changes over time very little and Displacement Ratio is close to 0, can determine that at this time
Excited frequency is the second order frequency of rope.By proposing a kind of completely new drag-line second order frequency measurement method, drag-line second order frequency is improved
The measurement accuracy of rate.
Detailed description of the invention
Fig. 1 is the drag-line second-order natural frequency of vibration measurement method schematic diagram based on sine excitation device and video instrument；
Fig. 2 be excited frequency be 35.0Hz when, video instrument observe rope half length at be displaced daWith rope a quarter
D is displaced at lengthbFigure；
Fig. 3 be excited frequency be 45.0Hz when, video instrument observe rope half length at be displaced daWith rope a quarter
D is displaced at lengthbFigure；
Fig. 4 be excited frequency be 40.0Hz when, video instrument observe rope half length at be displaced daWith rope a quarter
D is displaced at lengthbFigure；
Fig. 5 be excited frequency be 42.5Hz when, video instrument observe rope half length at be displaced daWith rope a quarter
D is displaced at lengthbFigure；
Fig. 6 be excited frequency be 42.8Hz when, video instrument observe rope half length at be displaced daWith rope a quarter
D is displaced at lengthbFigure；
Fig. 7 be excited frequency be 35.0Hz, 45.0Hz and 40.0Hz when video instrument record observed result calculate Displacement Ratio
Change over time situation map；
Fig. 8 be excited frequency be 42.5Hz and 42.8Hz when video instrument record observed result calculate Displacement Ratio become at any time
Change situation map；
1- is by measuring rope in figure, 2- rope anchored end, 3- sine excitation device, 4- video instrument, a displacement at 5- rope half length
Measuring point, b displacement measuring points at 6- rope a quarter length；
When line style 7 represents excited frequency as 45.0Hz in Fig. 7, video instrument, which is observed, is displaced d at rope half lengthaAnd rope
D is displaced at a quarter lengthbObserved result calculates Displacement Ratio λ, changes over time waveform diagram；Line style 8 represent excited frequency as
When 40.0Hz, video instrument, which is observed, is displaced d at rope half lengthaWith displacement d at rope a quarter lengthbObserved result calculates
Displacement Ratio λ, changes over time waveform diagram；When line style 9 represents excited frequency as 35.0Hz, video instrument observes rope half length
Place's displacement daWith displacement d at rope a quarter lengthbObserved result calculates Displacement Ratio λ, changes over time waveform diagram；
When line style 10 represents excited frequency as 42.5Hz in Fig. 8, video instrument, which is observed, is displaced d at rope half lengthaWith
D is displaced at rope a quarter lengthbObserved result calculates Displacement Ratio λ, changes over time waveform diagram；Line style 11 represents excited frequency
When for 42.8Hz, video instrument, which is observed, is displaced d at rope half lengthaWith displacement d at rope a quarter lengthbObserved result meter
Displacement Ratio λ is calculated, waveform diagram is changed over time；
Specific embodiment
The specific embodiment of the invention is described in further detail below；
A kind of drag-line fundamental natural frequency measurement method of the combination sine excitation device and video instrument of the present embodiment, including with
Lower step:
Step a: according to drawing and field observation situation, using theoretical formula and comparison experienced mode estimate it is tested
The second-order natural frequency of vibration (hereinafter referred to as second order frequency) f of rope2Possible range [fD, fU].Wherein fDFor second order frequency f2Possible model
Enclose lower bound, fUFor second order frequency f2The possible range upper bound.Wherein range [fD, fU], it can be calculated by following formula.
L is that rope is long (m) in formula, and EI is rope section bending stiffness (Nm2), m is unit linear mass (kg/m), T1It is pre-
Rope tensility (N) lower limit value estimated, T2For rope tensility (N) upper limit value estimated.
In the present embodiment, 498 100Nm of the long L=10m of rope, rope section bending stiffness EI=834, rope tensility T estimation
Value range is 1800~2200kN, linear mass m=432.51kg/m.According to Classical Beam Theory of Vibration, and compare it
His measured result, the second order frequency of the rope should be in the section [28.3Hz, 45.0Hz].
Step b: vibration excitor is installed at the rope a quarter length for needing to measure, and in fixed bottom boundary restocking setting video instrument
Observe the vibration displacement at rope half length a and at a quarter length b.
Sine excitation device, amplitude of exciting force 1.0kN, in distance are installed at rope a quarter length in the present embodiment
Video instrument is set up at rope about 5m, as shown in Figure 1.
Step c: the excited frequency θ of sine excitation device is fixed on [f by starting sine excitation deviceD, fU] a certain in range
Value, and Suo Zhen dynamic stability is allowed to enter steady-state process, observe displacement d at a simultaneously at this timeaWith displacement d at bb, note
For Displacement Ratio.
In the present embodiment, excited frequency θ is chosen respectively in section [28.3Hz, 45.0Hz]1=35.0Hz, θ2=
45.0Hz、θ3=40.0Hz, θ4=42.5Hz, θ5=42.8Hz is motivated to implement, and waits Suo Zhendong steady after starting vibration excitor
It is fixed, observe displacement d at a simultaneously using video instrumentaWith displacement d at bb, a length of 0.5s when observing in this example, displacement sample frequency is
100Hz, displacement observation precision are 0.001mm, daAnd dbObserved result is as shown in Fig. 2-Fig. 6.
Excited frequency θ respectively1=35.0Hz, θ2=45.0Hz, θ3=40.0Hz, θ4=42.5Hz, θ5When=42.8Hz according to
According to the d of recordaAnd dbObserved result calculates Displacement Ratio λ, as a result as shown in Figure 7, Figure 8.
Step d: under the premise of excited frequency θ is constant, if Displacement Ratio λ changes over time very little and Displacement Ratio λ is close to
0, then illustrate that this excited frequency θ is the second order frequency f of the rope2.If not, change excited frequency θ repeated measures.
As seen from Figure 7, in the present embodiment, excited frequency θ1=35.0Hz, θ2=45.0Hz, θ3It is displaced when=40.0Hz
It is changed over time than λ all larger；And excited frequency θ in Fig. 84=42.5Hz, θ5Displacement Ratio λ is changed over time when=42.8Hz
It is smaller；Wherein θ5=42.8Hz Displacement Ratio λ variation is minimum, and Displacement Ratio λ is close to 0, therefore visual 42.8Hz is the second order of the rope
Frequency measurement.
This embodiment is just an exemplary description of this patent, does not limit its protection scope, those skilled in the art
Member can also be changed its part, as long as it does not exceed the essence of this patent, within the protection scope of the present patent.
Claims (2)
1. the drag-line second-order natural frequency of vibration measurement method of a kind of combination sine excitation device and video instrument, it is characterised in that: including
Following steps:
Step a: it according to drawing and field observation situation, is estimated using theoretical formula by the second-order natural frequency of vibration f of measuring rope2Range
[fD, fU],
F in formulaDFor by the second-order natural frequency of vibration f of measuring rope2Lower range bound, fUFor by the second-order natural frequency of vibration f of measuring rope2In range
Boundary, L are that rope is long, unit m；EI is rope section bending stiffness, unit Nm2；M is unit linear mass, unit kg/m；
T1For the rope tensility lower limit value estimated, unit N；T2For the rope tensility upper limit value estimated, unit N；
Step b: vibration excitor is installed at the rope a quarter length for needing to measure, and is observed in fixed bottom boundary restocking setting video instrument
Vibration displacement at rope half length a and at a quarter length b；
Step c: the excited frequency θ of vibration excitor is fixed on [f by starting vibration excitorD, fU] a certain value in range, and allow Suo Zhendong
Stablize and enter steady-state process, observes displacement d at a simultaneously at this timeaWith displacement d at bb, it is denoted as Displacement Ratio:
Step d: under the premise of excited frequency θ is constant, if Displacement Ratio λ changes over time very little and Displacement Ratio λ is close to 0,
Illustrate that this excited frequency θ is the second order frequency f of the rope2, if not, change excited frequency θ repeated measures.
2. the drag-line second-order natural frequency of vibration measurement side of a kind of combination sine excitation device according to claim 1 and video instrument
Method utilizes displacement d at video instrument observation a after starting vibration excitor it is characterized by: in step caWith displacement d at bb, wherein when observing
A length of 0.5s, displacement sample frequency are 100Hz, and displacement observation precision is 0.001mm.
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| CN101201282A (en) * | 2007-12-20 | 2008-06-18 | 宁波大学 | Fundamental frequency identification method for detecting cord force of cable-stayed bridge |
| CN101368860B (en) * | 2008-09-12 | 2010-09-01 | 江苏工业学院 | Method for correcting FFT data in stayed-cable force of stayed-cable bridge detected by frequency method |
| CN101762347B (en) * | 2009-12-31 | 2011-07-20 | 北京市建筑工程研究院 | Method for measuring rope force of multi-span steel stay rope by using half-wave method |
| CN101762346B (en) * | 2009-12-31 | 2011-07-13 | 北京市建筑工程研究院 | Method for measuring rope force of multi-span steel stay rope by using multi-frequency method |
| CN101893497B (en) * | 2010-06-13 | 2012-01-11 | 东南大学 | Out-of-plane frequency method for testing cable force of planar cable rod system |
| LT5962B (en) * | 2011-10-13 | 2013-09-25 | Vilniaus Gedimino technikos universitetas | Method and equipment of steel rope quality diagnostics |
| CN102829898B (en) * | 2012-08-08 | 2014-08-20 | 广西交通科学研究院 | Internal force detecting method for hanger rod with shock absorber |
| CN104658383B (en) * | 2015-02-25 | 2018-04-27 | 天津大学 | Suspension cable Parametric excitation demonstrating experiment device and its application method |
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