CN104111032A - Fiber bragg grating sensor network based large-scale structure body deformation measurement method - Google Patents

Abstract

The invention provides a fiber bragg grating sensor network based large-scale structure body deformation measurement method which aims to detect the condition of deformation of a large-scale structure body which is stressed by an external force or an internal force and real-timely monitors health conditions of the large-scale structure body. The fiber bragg grating sensor network based large-scale structure body deformation measurement method includes arranging a fiber bragg grating sensor network on a structure body to be detected, using a fiber bragg grating strain sensor to detect strain borne by the structure body, using a fiber bragg grating temperature sensor as temperature compensation of the strain sensor, interpolating detected disperse strain data into polynomials, performing twice integration, and bringing in initial conditions to obtain a deformation curve of the structure body. The fiber bragg grating sensor network based large-scale structure body deformation measurement method is mainly used for monitoring health conditions of the large-scale structure body and is suitable for large-scale networking; compared with traditional resistance strain gages for measuring strain of the structure body, the fiber bragg grating sensor network based large-scale structure body deformation measurement method has the advantages that defects that resistance strain gages are difficult to network and prone to be interfered by electromagnets and many shield cables are heavy are overcome.

Description

A kind of large structure deformation measurement method based on optical fiber grating sensing network

Technical field

The invention belongs to monitoring structural health conditions field, particularly a kind of large structure deformation measurement method based on optical fiber grating sensing network.

Background technology

The development of aircraft, spacecraft, the inexorable trend of maximize, complicated, functionalization becomes modern project structural development gradually, this makes the Service Environment of structure self constantly complicated, the damage type of structure self is constantly various, and the structural damage problem causing due to factors such as shock and vibration, extreme environments also constantly highlights.For heavy construction structure, disguise structural failure mechanism strong, that damage the causes structural failure degree more complicated, that damage causes that the main damage types such as inside configuration crackle, composite inner fracture, Rust of metal structures have its damage existence is difficult to the features such as judgement.These features make structure under arms the reliability in process significantly reduce, as also it not taked to corresponding remedial measures in the case, will form damage accumulation phenomenon in inside configuration, and then impel integral body or partial structurtes generation catastrophic failure, cause huge property loss and casualties.

Therefore study intelligent structural health monitoring technology to guarantee Large Scale Space Vehicle structure can be for a long time, high reliability military service is significant.Structural health prison (Structural Health Monitoring, SHM) be exactly by structure is carried out to Non-Destructive Testing, the global behavior of real-time monitoring structure, the damage position of structure and degree are diagnosed, military service situation, reliability, permanance and load-bearing capacity to structure are carried out intelligent evaluation, for some are in the early warning signal that sets out when severely subnormal appears in structure under special climate, particular job state, for maintenance, maintenance and the management decision of structure provides foundation and guidance.

Fiber grating is the photosensitivity of utilizing fiber optic materials, produces the refractive index changing along fibre core axial cyclic in fibre core.Due to the anti-electromagnetic interference (EMI) of Fiber Bragg Grating FBG, corrosion-resistant, highly sensitive, to electrical isolation, cost is low and be easy to realize the advantages such as multiplexing, make Fiber Bragg Grating FBG once appearance, just at sensory field of optic fibre, play an important role, and be used widely in the monitoring structural health conditions of Aero-Space, bridge, mine, geologic prospecting, railway, natural gas line.

At present to large scale structure monitoring structural health conditions means mainly based on two kinds of sensors, electrical sensor is as resistance strain gage, piezoceramic transducer etc., light kind sensor is as Fiber Bragg Grating FBG, fiber F-P cavity etc., electrical sensor application comparative maturity wherein, but it is only suitable for networking on a small scale, when large-scale network-estabilishing, in order to shield crosstalking between each sensor, shielded cable used becomes the increase of how much multiples, makes the very huge heaviness of system; And along with wavelength-division multiplex technique and space division multiplexing technology reach its maturity, fiber-optic grating sensor becomes a kind of sensor that is applicable to very much large-scale network-estabilishing, and without any need for shielded cable, only with several optical fiber, just can go here and there a upper hundreds of sensor, form extensive sensing network, can to structure, monitor easily.A lot of developed countries mainly concentrate monitorings such as structural strain, temperature, distortion the application of fiber grating in the world at present, and domesticly seldom there is the distortion of pair structure to monitor, the present invention is immediately following the developing steps of international sophisticated technologies, utilize optical fiber grating sensing network to measure structure stress distortion, there is very important practice significance.

Summary of the invention

The object of the invention is to, overcome existing technology limitation, Fiber Bragg Grating FBG is set up to sensor network, a kind of large structure deformation measurement method based on optical fiber grating sensing network is provided, the method effectively monitoring of structures body cause the distortion of structure because of external force or internal force.

The technical solution used in the present invention is: a kind of large structure deformation measurement method based on optical fiber grating sensing network, fiber Bragg grating sensor network is recorded to wavelength data to carry out data and on average obtains the mean wavelength data in the time period to be measured, substitution has been demarcated in advance again the temperature control coefficient of temperature sensor and temperature control coefficient and the ga(u)ge factor of strain transducer, after calculating, temperature compensation obtains the discrete strain value of all strain transducers, discrete strain value is carried out to the polynomial expression that interpolation obtains strain, strain polynomial expression is carried out to twice integration and obtain the polynomial expression that structure is out of shape, according to the state substitution integration starting condition of structure, be the final sag curve that slope of a curve and biasing obtain structure distortion again.

Further, by discrete strain value, carrying out the interpolation method that interpolation obtains in the polynomial expression of strain is cubic spline interpolation.

Further, by the integration method of strain polynomial expression being carried out to twice integration and obtain in the polynomial expression of structure distortion, be the numerical integrating based on cubic spline.

The present invention's advantage is compared with prior art: can utilize the strain of fiber grating networking technology monitoring of structures body multiple spot, thereby extrapolate the deformation of structure, overcome electrical sensor and be difficult to networking, be subject to the shortcomings such as electromagnetic interference (EMI).And the net result of this programme is to ask structure deformation, rather than monitor strain simply, data processing method is the place of the innovation of this programme.By monitor strain, obtain the application of distortion in engineering more rare, do not have corresponding data to disclose this kind of deformation processing method yet, in the data processing method that the present invention takes, strain is taked cubic spline interpolation to obtain the strain polynomial expression place of the present invention's innovation especially, cubic spline curve has been actually segmentation cubic curve and has been spliced, in stitching portion, not only function is continuous, and first order derivative and second derivative are also continuous, so SPL has good slickness, the distribution situation that can reflect more really strain when large structure is stressed, recycling Spline Integral just can obtain the deformation curve of beam, and substitution integration starting condition is the final sag curve that slope of a curve and biasing obtain structure distortion.The introducing of cubic spline curve and Spline Integral, convenient programming, can carry out curve fitting more compactly, and calculated amount is little, and efficiency is high, can realize the Real-time demodulation of distortion.Demodulation method, based on large-scale optical fiber grating sensing system, has utilized the advantages such as optical fiber sensing system volume is little, quality is light, anti-electromagnetic interference (EMI) again, is applicable to being applied to the deformation in line measurement of aircraft, has the incomparable advantage of traditional resistor foil gauge.

Accompanying drawing explanation

Fig. 1 is free beam stress deformation schematic diagram;

Fig. 2 is structure deformation measurement method;

Fig. 3 is that certain structural metal plate grating sensor is arranged schematic diagram; 1 is point of fixity, and 2 is fiber-optic grating sensor, and 3 is force application location;

Fig. 4 is for to apply displacement (side view) schematic diagram to structural slab; 4 is screw, and 5 is aluminium flake pad, and 6 is a fixed support part, and 7 is panel side;

Fig. 5 is structural slab deflection metrology curve when applying maximum displacement;

Fig. 6 is vernier caliper measurement value and measured value contrast.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, to understand better the present invention.Requiring particular attention is that, in the following description, when adopting the detailed description of known function and design perhaps can desalinate main contents of the present invention, these are described in here and will be left in the basket.

The principle that malformation is measured, when unknown force F acts on upper 1 C of free beam AB, the distortion of beam as shown in Figure 1:

Be depicted as free beam and occur bending and deformation, the axis of beam becomes curve from original straight line, and the axis becoming after curved is called curved axis.After the point deformation that on beam axis, coordinate is x, in the displacement of the lines perpendicular to beam axis direction, can be expressed as y (x), be called the amount of deflection of this point.For girder construction, the pass between neutral line radius-of-curvature ρ and moment M is 1/ ρ=M/EI, and wherein E is elastic modulus, and I is the moment of inertia of cross-sectional area to central shaft.

By radius-of-curvature, defined, on curved axis, any point curvature has following approximation relation:

$\frac{d^{2}y}{{\mathrm{dx}}^2}=\frac{1}{\mathrm{\ρ}\left(x\right)}=\frac{M\left(x\right)}{\mathrm{EI}}---\left(1\right)$

Above formula is called curved axis approximate differential equation.From the mechanics of materials, certain strain stress=z/ ρ a bit being produced by bending of beam surface, wherein z is the distance of this point to central shaft, this distance of the girder construction that is rectangle for cross section equals half of cantilever thickness h.So obtain the relation of surface strain and curved axis curve:

$\mathrm{\ϵ}\left(x\right)=\frac{M\left(x\right)}{\mathrm{EI}}\·\frac{h}{2}=\frac{1}{\mathrm{\ρ}\left(x\right)}\·\frac{h}{2}=\frac{d^{2}y}{{\mathrm{dx}}^2}\·\frac{h}{2}---\left(2\right)$

From above formula, on beam surface, the strain value of every bit is all directly proportional to the second derivative of curved axis curve at this point, and this formula is not only for free beam, but is all suitable for for the flexural deformation of any shape.ε (x) is carried out to twice integration and just can obtain curved axis function y=f (x), as shown in the formula:

$f\left(x\right)=\frac{2}{h}{\∫}_0^x\left[{\∫}_0^x\mathrm{\ϵ}\left(x\right)\mathrm{dx}\right]\mathrm{dx}+x{f}^{\′}\left(0\right)+f\left(0\right)---\left(3\right)$

From above formula, know curved axis function f (x), must know that f (x) is in the value of 0 and the value of first order derivative, these two values are called starting condition.As long as know ε (x) and initial value, just can obtain curved axis curve twice to its integration.

The deformation curve that solves beam need to carry out quadratic integral to recording strain, then bring starting condition into, just can record the final distortion of beam, because fiber Bragg grating strain sensor is that dispersed placement is on beam, the strain data recording can be regarded as along the discrete function of x axle, be referred to as ε (x _n), n=1,2 ..., m.Wish is carried out integration to discrete value, first need to use the method for interpolation to obtain the smooth curve ε (x) by all discrete points, ε (x) can regard the approximate analysis expression formula that actual strain distributes as, and then it is carried out to quadratic integral, bring starting condition into and try to achieve beam and the final deformation of side panel.

Here to ε (x _n) carry out cubic spline interpolation, can obtain the analytical expression ε (x) of funtcional relationship between the strain stress of piecewise polynomial representation and x.From mathematics, cubic spline is actually the curve that a section cubic polynomial curve is spliced, and in stitching portion, not only function is continuous, and first order derivative and second derivative be also continuous, so SPL has good slickness.

ε (x) is comprised of 36 cubic polynomials, and concrete form is as follows:

$\mathrm{\&epsiv;}\left(x\right)=\left\{\begin{array}{cc}{a}_{11}{x}^3+a_{12}{x}^2+a_{13}x+a_{14}& (x_1\&le;x<x_2)\\ a_{21}{x}^3+a_{22}{x}^2+a_{23}x+a_{24}& (x_2\&le;x<x_3)\\ a_{31}{x}^3+a_{32}{x}^2+a_{33}x+a_{34}& (x_3\&le;x<x_4)\\ .........& \\ a_{(m-1)1}{x}^3+a_{(m-1)2}{x}^2+a_{(m-1)3}x+a_{(m-1)4}& (x_{(m-1)}\&le;x<x_m)\end{array}\right.---\left(4\right)$

Total m * 4 of ε (x) unknowm coefficient, needs 4m constraint condition just can solve matrix of coefficients.According to definition cubic spline functions ε (x), need to meet following condition: 1, ε (x) will pass through ε (x _n) all m point; 2, at m-2 interior nodes place, functional value, first order derivative and second derivative are all continuous.The definition of cubic spline provides m+ (m-2) * 3 condition, also needs the subsidiary condition at two end points places, is referred to as boundary condition.Here adopt conventional not-a-knot disposal route, assert that three order derivatives of first cubic polynomial and three order derivatives of second cubic polynomial equate, three order derivatives of last cubic polynomial equate with three order derivatives of penultimate cubic polynomial.

From formula (4), if ask curved axis function f (x) by ε (x), also need to know that upper certain any the value of f (x) and first order derivative thereof, as starting condition, know initial condition f'(0) and f (0) just can solve f (x).

Take free beam as example, and beam has two bearings, and the amount of deflection at bearing place beam is 0, so there is f (x ₁)=f (x ₂)=0 (x ₂, x ₂be respectively wherein two journal stirrup coordinates that support), its substitution (4) formula just can be calculated to the sag curve f (x) of beam.

ε (x) is brought into formula (4) and brings the starting condition f'(0 trying to achieve into) and f (0) can obtain following formula:

$f\left(x\right)=\left\{\begin{array}{cc}{c}_{11}{x}^5+c_{12}{x}^4+c_{13}{x}^3+c_{14}{x}^2+c_{15}x+c_{16}& (x_1\&le;x<x_2)\\ c_{21}{x}^5+c_{22}{x}^4+c_{23}{x}^3+c_{24}{x}^2+c_{25}x+c_{26}& (x_2\&le;x<x_3)\\ c_{31}{x}^5+c_{32}{x}^4+c_{33}{x}^3+c_{34}{x}^2+c_{35}x+c_{36}& (x_3\&le;x<x_4)\\ .........& \\ c_{(m-1)1}{x}^5+c_{(m-1)2}{x}^4+c_{(m-1)3}{x}^3+c_{(m-1)4}{x}^2+c_{(m-1)5}x+c_{(m-1)6}& (x_{(m-1)}\&le;x<x_{(m-1)})\end{array}\right.---\left(5\right)$

Formula (5) is segmentation five order polynomials, and f (x) is required curved axis function, has represented on beam the amount of deflection of certain point (vertical range that departs from initial position) in the x-direction.

As shown in Figure 2, a kind of large structure deformation measurement method based on optical fiber grating sensing network, fiber Bragg grating sensor network is recorded to wavelength data (1) to carry out data and on average obtains the mean wavelength data (2) in the time period to be measured, substitution has been demarcated in advance again the temperature control coefficient of temperature sensor and the temperature control coefficient of strain transducer and ga(u)ge factor (3), after calculating, temperature compensation obtains the discrete strain value (4) of all strain transducers, discrete strain value (4) is carried out to the polynomial expression (5) that interpolation obtains strain, strain polynomial expression (5) is carried out to twice integration and obtain the polynomial expression (6) that structure is out of shape, according to the state substitution integration starting condition (7) of structure, be the final sag curve that slope of a curve and biasing obtain structure distortion again.Wherein, by discrete strain value (4), carrying out the interpolation method that interpolation obtains in the polynomial expression (5) of strain is cubic spline interpolation.Wherein, by the integration method of strain polynomial expression (5) being carried out to twice integration and obtain in the polynomial expression (6) of structure distortion, be Spline Integral method.

As shown in Figure 3, on structural slab, there are two point of fixity, along structural slab direction, between two point of fixity, can regard free beam as, in this direction, arrange fiber Bragg grating strain sensor, the side of each strain transducer is posted fiber-optical grating temperature sensor and is done temperature compensation, distance between two point of fixity is 1400mm, the thickness of plate is 5mm, every 100mm, arrange a fiber Bragg grating strain sensor and fiber-optical grating temperature sensor, strain and temperature compensation while being respectively used to detection architecture distortion are used.

Fig. 4 is that schematic diagram is implemented in experiment, this experiment implementation process is: utilize a screw as shown in Figure 4, on-x panel, fix a king bolt, the screw of wherein-x panel withstands on the aluminium sheet of side, pass through rotary screw, make the distortion of its generation+x direction, the step-length of measuring is that screw revolves the advanced distance that turns around and is about 1mm, size with vernier caliper measurement distortion, maximum deformation quantity is that screw rotates the result of six times, concrete size is measured by vernier caliper, do altogether three circulations, concrete steps are:. the distortion that makes side panel start court+x direction from initial position progressively increases so that reaches maximum, step-length of every increase allows it stablize 8 minutes, progressively reduce to get back to again origin-location.

When structure is subject to external force generation deformation, utilizing fiber-optic grating sensor to record wavelength data carries out data and on average obtains the mean wavelength data in the time period to be measured, substitution has been demarcated in advance again the temperature control coefficient of temperature sensor and temperature control coefficient and the ga(u)ge factor of strain transducer, after calculating, temperature compensation obtains the discrete strain value of all strain transducers, discrete strain value is carried out to the polynomial expression that cubic spline interpolation obtains strain, strain polynomial expression is carried out to twice Spline Integral and obtain the polynomial expression that structure is out of shape, again according to the state substitution integration starting condition of structure be slope of a curve and biasing obtain structure distortion final sag curve as shown in Figure 5.

Be deformed into-the 6.6mm of structure maximum in experiment, be deformed into-the 6.3mm that this experiment detects, the trend of distortion is symmetrical, and distortion size is basically identical, but have very little error, one of reason may be during this is measured, not to be free beam model but approximate free beam model.

For the measurement validity of illustrative system in further detail, now the deformation values of middle position on the panel that system records each time and vernier caliper measurement value are made in to (the distortion maximum at place, centre position in a width figure, and vernier caliper records, be also the distortion at place, centre position), as shown in Figure 6, wherein horizontal ordinate is vernier caliper measurement value, ordinate is systematic survey value, from scheming, can find out, systematic survey value has good linearity, slope reaches 0.97, can be corresponding with vernier caliper measurement value well, thereby the validity that also illustrative system is measured, the feasibility of this measuring method.

Although above the illustrative embodiment of the present invention is described; so that the technician of this technology neck understands the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various variations appended claim limit and definite the spirit and scope of the present invention in, these variations are apparent, all utilize innovation and creation that the present invention conceives all at the row of protection.

Claims (3)

1. the large structure deformation measurement method based on optical fiber grating sensing network, it is characterized in that, fiber Bragg grating sensor network is recorded to wavelength data (1) to carry out data and on average obtains the mean wavelength data (2) in the time period to be measured, substitution has been demarcated in advance again the temperature control coefficient of temperature sensor and the temperature control coefficient of strain transducer and ga(u)ge factor (3), after calculating, temperature compensation obtains the discrete strain value (4) of all strain transducers, discrete strain value (4) is carried out to the polynomial expression (5) that interpolation obtains strain, strain polynomial expression (5) is carried out to twice integration and obtain the polynomial expression (6) that structure is out of shape, according to the state substitution integration starting condition (7) of structure, be the final sag curve that slope of a curve and biasing obtain structure distortion again.

2. a kind of large structure deformation measurement method based on optical fiber grating sensing network according to claim 1, it is characterized in that, by discrete strain value (4), carrying out the interpolation method that interpolation obtains in the polynomial expression (5) of strain is cubic spline interpolation.

3. a kind of large structure deformation measurement method based on optical fiber grating sensing network according to claim 1, it is characterized in that, be the numerical integrating based on cubic spline by the integration method of strain polynomial expression (5) being carried out to twice integration and obtain in the polynomial expression (6) of structure distortion.