CN104614342A - Three-dimensional reconstruction measurement method of air refractive index under high-temperature airflow disturbance - Google Patents

Abstract

The invention relates to a three-dimensional reconstruction measurement method of an air refractive index under high-temperature airflow disturbance, and belongs to the technical field of pneumatic optical measurement and three-dimensional reconstruction. The method comprises the following steps that a three-dimensional reconstruction measurement system of the air refractive index under airflow disturbance is established firstly; at least two CCD cameras and speckle background plates the number of which is the same with that of the CCD cameras are adopted; the CCD cameras are used for photographing the speckle background plates by penetrating through a measured air field from different angles in the same plane, so that a speckle image is obtained; because an air convection disturbance refractive index is changed non-uniformly, the speckle image photographed by the cameras is distorted; deflection angles of light penetrating through the measured air field from the different angles are obtained by adopting a digital image correlation method; the three-dimensional distribution of the refractive index of the measured air field is obtained by calculation by adopting a three-dimensional reconstruction algorithm, and therefore, the real-time measurement of the airflow disturbance is realized. According to the method, the three-dimensional real-time measurement of the air refractive index under the high-temperature airflow disturbance is realized; the device is simple, flexible, and simple and convenient to operate; and the three-dimensional reconstruction measurement method is applied to measuring the airflow disturbance conditions in real time under severe air convection disturbance conditions in engineering.

Description

Air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance

Technical field

The present invention relates to a kind of acquisition under high temperature gas flow disturbance by digital image correlation technique and reconstruct disturbance air field refractive index distributed in three dimensions method through air field deflection of light, belong to Pneumatic optical and measure and three-dimensional reconstruction field.

Background technology

Optical means, owing to having the advantage of noncontact, measurement of full field, is widely used in deformation measurement.But under high temperature air environment, utilize optical means to carry out deformation measurement and face many difficulties, the difficult problem wherein faced is flow perturbation severe jamming optical imagery.General more than 200 DEG C, air turbulence will be out of shape by severe jamming optical method for measuring, and along with temperature rising, air turbulence severe degree is aggravated.Especially high-precision deformation under high temperature is measured, the interference of air turbulence must be removed.One method vacuumizes, but in large scale structure deformation measurement, particularly practical implementation, vacuumize and be difficult to accomplish.Another kind method is exactly the disturbance rule providing air under high temperature in real time, optical method for measuring is out of shape, need to obtain real-time air refraction distributed in three dimensions, calculate the distortion that in deformation measurement, air turbulence causes optical imagery thus, measure in deformation process this amount of distortion removing air turbulence and cause, thus under realizing high temperature, remove the object of air turbulence.

From the problem of backprojection image reconstruction three-dimensional spatial distribution physical quantity, mathematician Radon provides its theoretical foundation Central slice theorem in theory, namely the one-dimensional Fourier transform of measured body image parallel projection under a certain visual angle is equal to a center slice of this two-dimensional image Fourier transform, obtain image different angles projection result around 180 degree, measured object space distribution information can be obtained through inverse Fourier transform.For the disturbance of high temperature downstream, finding a kind of simple and reliable method to the projection information after obtaining light therethrough disturbance air field to rebuild the refractive index distributed in three dimensions of air field, is the key realizing obtaining in deformation measurement under high temperature air turbulence situation.

People are measured in real time for air turbulence and adopts schlieren method and laser interference method in the early time, but schlieren method qualitatively can only provide the roughly situation of air turbulence, laser interference subtraction unit is complicated, poor anti jamming capability, all cannot meet in engineer applied and accurately measure air refraction under high temperature gas flow disturbance.Digital Image Correlation Method is that a kind of non-contact optical of widespread use now measures deformation method, and because device is simple, simple operation, antijamming capability be strong, and the method is applicable to engineering field application.

Summary of the invention

The object of the invention is to propose air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance, the method can overcome prior art deficiency, is applicable to Practical Project in-site measurement, realizes the three-dimensional measurement of full field in real time of air refraction under high temperature gas flow disturbance.

Technical scheme of the present invention is as follows:

Air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance, it is characterized in that, described method comprises the steps:

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is set up, this system comprises: m CCD camera and m speckle background board, CCD camera is identical with speckle background board quantity, CCD camera and speckle background board are arranged in same plane centered by tested air field circumferentially, this circle diameter is D, and equidistantly arrange, each CCD camera through tested air field just to a speckle background board, m be more than or equal to 2 positive integer;

2) before tested air field is heated, take corresponding speckle background board by a described m CCD camera through tested air field, the speckle image that shooting obtains is as reference image simultaneously;

3) tested air field is heated to more than 200 DEG C, in heating process, a certain moment takes corresponding speckle background board by a described m CCD camera through by the tested air field of heating simultaneously, take the speckle image that obtains and step 2) middle reference picture contrasts, CCD camera and speckle background board place plane are set to Oxy plane, z-axis direction, perpendicular to Oxy plane, calculates speckle image on each speckle background board caused due to air turbulence and to distort displacement field v along the z-axis direction by Digital Image Correlation Method;

4) m the CCD camera 180 °/m in interval angle in same plane, calculates m corresponding angle speckle image z-axis direction displacement field through tested air field shooting speckle background board, remembers v respectively ₁, v ₂..., v _m, by obtaining the speckle image displacement field v of 0 to 180 degree unspecified angle θ by spline interpolation _θ, θ ∈ (0, π);

5) by step 4) obtain the speckle image displacement field v that 0 to 180 spend unspecified angle θ _θ, by following formula:

$\frac{\∂n}{\∂z}=\frac{\∂n(x,y,z)}{\∂z}=\underset{0}{\overset{\mathrm{\π}}{\∫}}\underset{-\∞}{\overset{\∞}{\∫}}{S}_{\mathrm{\θ}}\left(\mathrm{\ω}\right)\left|\mathrm{\ω}\right|e^{j2\mathrm{\π\ω}(x\cos \mathrm{\θ}+y\sin \mathrm{\θ})}\mathrm{d\ωd\θ}$

Calculate tested air field air refraction n partial derivative along the z-axis direction three-dimensional spatial distribution, wherein j is imaginary unit s _θ(ω) be speckle image displacement field v _θfourier transform value, t=xcos θ+ysin θ, x, y, z is respectively the volume coordinate along x-axis, y-axis, z-axis that speckle image is put;

6) establish tested air field edge air to be in constant temperature, its air refraction is n _o, with above-mentioned air refraction partial derivative along the z-axis direction by following formula:

$n=n(x,y,z)=n_o+\underset{0}{\overset{z}{\∫}}\frac{\∂n(x,y,z)}{\∂z}\mathrm{dz}$

The distributed in three dimensions of air refraction n is inscribed, wherein when calculating this measurement for tested air field air refraction z-axis Directional partial derivative along the integration of z-axis, not repeating step 3 in the same time) ~ 6) inscribe air refraction distributed in three dimensions under high temperature gas flow disturbance when can obtain corresponding.

Described CCD camera number is preferably 2 ~ 10, and is positioned at circumference the same side.Described speckle background board is the flat board that surface spraying is manufactured with random speckle.

The present invention compared with prior art, has the following advantages and high-lighting effect: utilize Digital Image Correlation Method to obtain light from different perspectives through the deflection angle of tested air field, calculate tested air field refractive index distributed in three dimensions by three-dimensional reconstruction algorithm.The method can realize the whole audience of air refraction under high temperature gas flow disturbance, real-time, online, non-intervention measurement, and antijamming capability is strong, and device is simple, and simple operation, measures under being applicable to engineering site complex environment.

Accompanying drawing explanation

Fig. 1 is air refraction three-dimensionalreconstruction measuring system structural representation under high temperature gas flow disturbance of the present invention.

Fig. 2 is a kind of available background speckle.

Fig. 3 is light therethrough tested air field deviation principle schematic.

Fig. 4 is three-dimensionalreconstruction tested air field refractive index principle schematic.

In figure: 1a-first CCD camera; 1b-second CCD camera; 1c-the 3rd CCD camera; 1d-the 4th CCD camera; 2a ?the first speckle background board; 2b ?the second speckle background board; 2c ?the 3rd speckle background board; 2d ?the 4th speckle background board; The tested air field of 3-.

Embodiment

Further illustrate the specific embodiment of the present invention below in conjunction with accompanying drawing, but should not limit the scope of the invention with this.

The present invention proposes air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance, its concrete steps:

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is first set up, this system comprises: m CCD camera and m speckle background board, CCD camera is identical with speckle background board quantity, CCD camera and speckle background board are arranged in same plane centered by tested air field 3 circumferentially, and equidistantly arrange, this circle diameter is set to D, each CCD camera through tested air field just to a speckle background board, m be more than or equal to 2 positive integer, be preferably 2 ~ 10; As embodiment, the present invention adopts 4 CCD camera and 4 speckle background boards to be example, CCD camera and speckle background board be arranged in same plane, centered by tested air field 3 circumferentially, and equidistantly arrange, each CCD camera is through tested air field just to a speckle background board, and speckle background board is the flat board (as shown in Figure 1) that surface spraying is manufactured with random speckle.

2) before tested air field 3 is by heating, 4 CCD camera take corresponding speckle background board through tested air field 3 simultaneously, and the speckle image that shooting obtains is as reference image.

3) tested more than 3 to 200 DEG C, air field is heated, in heating process, a certain moment takes corresponding speckle background board by 4 CCD camera through tested air field 3 after heating simultaneously, take the reference picture obtained in the speckle image and previous step obtained to contrast, CCD camera and speckle background board place plane are set to Oxy plane, z-axis direction, perpendicular to Oxy plane, calculates speckle image on each speckle background board caused due to air turbulence and to distort displacement field v along the z-axis direction by Digital Image Correlation Method.

4) 4 CCD camera degree angles in 45 °, interval in same plane are taken speckle background board through tested air field 3 and are calculated corresponding 4 angle z direction displacement speckle displacement fields, remember v respectively ₁, v ₂, v ₃, v ₄, by obtaining the speckle displacement field v of 0 to 180 degree unspecified angle θ by spline interpolation _θ, θ ∈ (0, π), inscribes the distributed in three dimensions of tested air field refractive index n during by calculating this measurement, not repeating step 3 in the same time) ~ 4) inscribe air refraction distributed in three dimensions under high temperature gas flow disturbance when can obtain corresponding.

Principle of work of the present invention is as follows:

As shown in Figure 3, the tested air field of light therethrough, due to air refraction non-uniform Distribution, light generation deviation, refraction angle is φ, and by geometric relationship, deflection angle Oyz in place component is φ _z, itself and speckle image along the z-axis direction displacement field v have following relation:

${\mathrm{\φ}}_z=\frac{2v}{D}---\left(I\right)$

Wherein D/2 is the spacing of air field to be measured to speckle background board.By optical analysis deflection of light with closing between air refraction be:

${\mathrm{\φ}}_z=\underset{-B/2}{\overset{B/2}{\∫}}\frac{\∂n}{\∂z}\mathrm{dy}---\left(\mathrm{II}\right)$

Wherein n is air refraction, for refractive index n partial derivative in the z-direction, then simultaneous (I) and (II) formula:

$\underset{-B/2}{\overset{B/2}{\∫}}\frac{\∂n}{\∂z}\mathrm{dy}=\frac{2v}{D}---\left(\mathrm{III}\right)$

B is tested air field areas diameter, as shown in Figure 4, and the speckle displacement field v that light is clapped from a direction through tested air field _θ(t, z) is equivalent to air refraction partial derivative projection under this view directions, by Central slice theorem, the one-dimensional Fourier transform of this parallel projection is equal in (III) formula by long-pending air refraction partial derivative a center slice of two-dimensional Fourier transform.At acquisition θ after all angles projection in 0 to 180 degree, can be obtained by long-pending air refraction partial derivative by inverse Fourier transform distributed in three dimensions:

$\frac{\∂n}{\∂z}=\frac{\∂n(x,y,z)}{\∂z}=\underset{0}{\overset{\mathrm{\π}}{\∫}}\underset{-\∞}{\overset{\∞}{\∫}}{S}_{\mathrm{\θ}}\left(\mathrm{\ω}\right)\left|\mathrm{\ω}\right|e^{j2\mathrm{\π\ω}(x\cos \mathrm{\θ}+y\sin \mathrm{\θ})}\mathrm{d\ωd\θ}---\left(\mathrm{IV}\right)$

Wherein j is imaginary unit s _θ(ω) be speckle image displacement field v _θfourier transform value, t=xcos θ+ysin θ, x, y, z is respectively the volume coordinate along x-axis, y-axis, z-axis that speckle image is put.In an embodiment, we choose 4 measurement of angle speckle image displacements along the z-axis direction by 4 CCD camera at equal intervals at θ within the scope of 0 to 180 degree, are designated as 0 degree of v ₁, 45 degree of v ₂, 90 degree of v ₃, 135 degree of v ₄, by symmetry, at the speckle image displacement v along the z-axis direction of 180 degree of angle shots ₅obtained by following formula:

v ₅＝v ₁(Ⅴ)

Pass through v ₁, v ₂, v ₃, v ₄, v ₅the speckle displacement field v of 0 to 180 degree unspecified angles is obtained by spline interpolation _θ, namely obtain air refraction partial derivative speckle displacement field v along θ angle from 0 to 180 degree direction projections _θthe one-dimensional Fourier transform of (t, z) (IV) formula of bringing into obtains air refraction partial derivative distributed in three dimensions.If tested air field edge air is in constant temperature, this place's refractive index is n _o, by above-mentioned air refraction partial derivative the air refraction distributed in three dimensions of corresponding measurement moment tested air field along z-axis integration thus under obtaining high temperature gas flow disturbance:

$n=n(x,y,z)=n_o+\underset{0}{\overset{z}{\∫}}\frac{\∂n(x,y,z)}{\∂z}\mathrm{dz}---\left(\mathrm{VI}\right)$

In formula for tested air field air refraction partial derivative along the integration of z-axis.

Claims (3)

1. an air refraction three-dimensionalreconstruction measuring method under high temperature gas flow disturbance, it is characterized in that, described method comprises the steps:

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is set up, this system comprises: m CCD camera and m speckle background board, CCD camera is identical with speckle background board quantity, CCD camera and speckle background board are arranged in same plane centered by tested air field (3) circumferentially, and equidistantly arrange, this circle diameter is D, each CCD camera through tested air field just to a speckle background board, m be more than or equal to 2 positive integer;

2) before tested air field (3) is by heating, take corresponding speckle background board by a described m CCD camera through tested air field (3), the speckle image that shooting obtains is as reference image simultaneously;

3) tested air field (3) is heated to more than 200 DEG C, in heating process, a certain moment takes corresponding speckle background board by a described m CCD camera through by the tested air field (3) of heating simultaneously, take the speckle image that obtains and step 2) middle reference picture contrasts, CCD camera and speckle background board place plane are set to Oxy plane, z-axis direction, perpendicular to Oxy plane, calculates speckle image on each speckle background board caused due to air turbulence and to distort displacement field v along the z-axis direction by Digital Image Correlation Method;

4) m the CCD camera 180 °/m in interval angle in same plane, calculates m corresponding angle speckle image z-axis direction displacement field through tested air field (3) shooting speckle background board, is designated as v respectively ₁, v ₂..., v _m, by obtaining the speckle image displacement field v of 0 to 180 degree unspecified angle θ by spline interpolation _θ, θ ∈ (0, π);

5) by step 4) obtain the speckle image displacement field v that 0 to 180 spend unspecified angle θ _θ, by following formula:

$\frac{\∂n}{\∂z}=\frac{\∂n(x,y,z)}{\∂z}=\underset{0}{\overset{\mathrm{\π}}{\∫}}\underset{-\∞}{\overset{\∞}{\∫}}{S}_{\mathrm{\θ}}\left(\mathrm{\ω}\right)\left|\mathrm{\ω}\right|e^{j2\mathrm{\π\ω}(x\cos \mathrm{\θ}+y\sin \mathrm{\θ})}\mathrm{d\ωd\θ}$

Calculate tested air field (3) air refraction n partial derivative along the z-axis direction three-dimensional spatial distribution, wherein j is imaginary unit s _θ(ω) be speckle image displacement field v _θfourier transform value, t=xcos θ+ysin θ, x, y, z is respectively the volume coordinate along x-axis, y-axis, z-axis that speckle image is put;

6) establish tested air field edge air to be in constant temperature, its air refraction is n _o, with above-mentioned air refraction partial derivative along the z-axis direction by following formula:

$n=n(x,y,z)=n_o+\underset{0}{\overset{z}{\∫}}\frac{\∂n(x,y,z)}{\∂z}\mathrm{dz}$

The distributed in three dimensions of air refraction n is inscribed, wherein when calculating this measurement for tested air field air refraction z-axis Directional partial derivative along the integration of z-axis, not repeating step 3 in the same time) ~ 6) inscribe air refraction distributed in three dimensions under high temperature gas flow disturbance when can obtain corresponding.

2., according to air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance according to claim 1, it is characterized in that: in step 1) described in CCD camera number be 2 ~ 10, and be positioned at circumference the same side.

3., according to air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance described in claim 1 or 2, it is characterized in that: in step 1) described in speckle background board be the flat board that surface spraying is manufactured with random speckle.