A method for evaluating the scattering properties of surface defects of an aircraft

Abstract

The application provides a kind of surface defect aircraft scattering characteristic evaluation method, it is related to aircraft electromagnetic scattering characteristic evaluation field, including: using binocular vision equipment to collect surface defect image, constructs surface defect three-dimensional model point cloud data.According to the actual three-dimensional model parameter of aircraft, establishes the aircraft scattering characteristic analysis model in electromagnetic simulation finite element software.Based on the point cloud data of surface defect, generate the aircraft model with surface defect.According to the electromagnetic scattering characteristic actual measurement method of aircraft, set simulation parameter simulation forms scattering characteristic data at surface defect.Combines the electromagnetic scattering characteristic actual measurement data of aircraft when not appearing defect with the scattering characteristic simulation data at surface defect, obtains the electromagnetic scattering characteristic data of surface defect of aircraft.The application adopts the mode of simulation and actual measurement to evaluate the scattering characteristic of aircraft, alleviates the problems such as complex detection process, heavy workload caused by traditional pure reliance on actual measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aircraft scattering characteristic evaluation, in particular to an aircraft scattering characteristic evaluation method for surface defects. BACKGROUND

[0002] During the service of the aircraft, defects will inevitably appear on the surface of the aircraft. When defects appear on the surface of the aircraft, it is crucial to quickly evaluate the scattering characteristics of the aircraft. At present, the industry mainly uses related equipment to detect the scattering characteristics of the aircraft. However, the actual measurement of the scattering characteristics of the aircraft is time-consuming and complicated to operate, and requires the use of professional equipment. Simple equipment cannot measure the scattering characteristics of the aircraft (such as vertical reflectivity detection equipment, coating thickness gauge, etc.). Due to the complexity of the aircraft structure, the scattering characteristics of the aircraft are very sensitive to the gaps, defects, and coating wear on the surface of the aircraft, and it is difficult to accurately establish a model of the aircraft in simulation software. Therefore, it is difficult to evaluate the scattering characteristics of the aircraft by using simulation methods alone.

[0003] At present, professional equipment is often used to evaluate the scattering characteristics of the first-line aircraft. Based on the principle of SAR radar, the omnidirectional scattering characteristics of the aircraft are measured to form a two-dimensional image of the radar scattering of the aircraft. Then, the center scattering extraction and RCS (Radar Cross Section) inversion methods are used to calculate the RCS parameters of the aircraft. In this process, the related equipment requires a large amount of time to test the scattering characteristics of the aircraft (more than 6 hours for a single aircraft test), and the operation of the equipment is complex (requiring understanding of SAR radar usage, automatic unmanned vehicle usage, and low scattering support frame usage, etc.), which affects the efficiency of the scattering characteristic measurement of the first-line aircraft. SUMMARY

[0004] In order to solve the problems of complex actual measurement process, large workload, low simulation model accuracy, and unreliable simulation data of the scattering characteristics of the aircraft, the present application proposes a rapid evaluation method for the electromagnetic scattering characteristics of the aircraft with surface defects. This method is a fusion of actual measurement and simulation data for the evaluation of the scattering characteristics of the aircraft. The periodic detection data of the scattering characteristics of the aircraft are used as the reference data. After the appearance of surface defects, the simulation analysis of the aircraft model with defects is performed to obtain the scattering characteristic data of the surface defects. Combined with the actual measurement data, the scattering characteristic data of the aircraft with defects is calculated. The present application only needs to capture the image information of the defect part and upload it to the simulation software for the scattering characteristics of the aircraft. Then, the scattering characteristic information of the aircraft after the appearance of surface defects can be analyzed. The present application is convenient to use, has a small workload, and is efficient, and is more suitable for daily evaluation of the scattering characteristics of the aircraft.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] An aircraft scattering characteristic evaluation method for surface defects, comprising the following steps:

[0007] Step 1, a binocular vision device is used to collect surface defect image, and a surface defect three-dimensional model point cloud data is constructed;

[0008] Step 2, according to the actual three-dimensional model parameters of the aircraft, an aircraft scattering characteristic simulation model is established, and based on the surface defect three-dimensional model point cloud data, an aircraft simulation model with surface defects is generated, and the surface defect situation of the aircraft is truly reflected;

[0009] Step 3, according to the electromagnetic scattering characteristic measurement method of the aircraft, the simulation parameters are set, the scattering characteristic data of the surface defect position is simulated, and the scattering characteristic simulation information of the surface defect is obtained;

[0010] Step 4, the electromagnetic scattering characteristic measurement data of the aircraft without defects is fused with the scattering characteristic simulation information of the surface defect, and the final scattering characteristic data of the surface defect of the aircraft is calculated.

[0011] Beneficial effects:

[0012] The method based on simulation and periodic measurement data fusion provided by the application can simply and efficiently evaluate the scattering characteristics of the aircraft after the surface defects. The operator only needs to take pictures and locate the damage position, input to the simulation system, simulate the scattering characteristics of the surface defect of the aircraft, and combine the periodic measurement data of the scattering characteristics of the whole aircraft. The RCS parameter of the aircraft after the surface defect can be evaluated in about 1 hour. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a flow chart of the surface defect aircraft scattering characteristic evaluation method of the application;

[0014] Figure 2 It is a model schematic diagram of F117 in the simulation software;

[0015] Figure 3 It is a schematic diagram of the RCS inversion result of F117. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0017] As Figure 1 shown, the application provides a surface defect aircraft scattering characteristic evaluation method, which fuses the measurement data and the simulation data, quickly evaluates the scattering characteristics of the aircraft with defects, and includes the following steps:

[0018] Step 1, collect defect image: adopt binocular vision equipment to collect surface defect image, and construct surface defect three-dimensional model point cloud data.

[0019] Step 2, generate finite element defect model: generate an airplane simulation model with surface defects in finite element software. According to the actual three-dimensional model parameters of the airplane, an airplane scattering characteristic analysis model is established in the electromagnetic simulation finite element software. Based on the surface defect three-dimensional model point cloud data of the first step, an airplane simulation model with surface defects is generated.

[0020] Step 3, simulate surface defect scattering characteristics: according to the simulation parameters of the actual measurement method of the airplane scattering characteristics, including radar frequency band, radar position, electromagnetic wave polarization setting and other parameters, the scattering characteristic data of the surface defect is simulated.

[0021] Step 4, calculate the airplane scattering characteristic data of the surface defect: the scattering characteristic data of the surface defect is obtained by fusing the scattering characteristic simulation data of the surface defect with the scattering characteristic measurement data of the airplane without defects.

[0022] Specifically, the step 1 comprises:

[0023] Step 1-1, measure the position of the surface defect:

[0024] The binocular vision equipment is used to take close-range multi-angle images of the surface defect far-field image to determine the position information of the defect on the surface of the airplane. When the defect image is not obvious, a marker pen can be used to mark the defect contour to improve the accuracy of image extraction position information, so as to obtain the defect far-field image.

[0025] Step 1-2, take the surface defect image:

[0026] A reference object similar in size to the defect is placed at the defect site, and the binocular vision equipment is used to take images of the defect site from different angles.

[0027] Step 1-3, generate surface defect three-dimensional model point cloud data:

[0028] The body coordinate system is established, and based on the defect far-field image taken in step 1-1, the computer vision and model matching technology is used to determine the coordinates and orientation information of the defect in the body coordinate system.

[0029] Based on the surface defect image taken in step 1-2, the computer vision technology is used to calculate the three-dimensional contour point cloud data of the defect structure, and combined with the coordinates and orientation information of the defect in the body coordinate system, the numerical value of the three-dimensional contour point cloud data of the defect structure in the body coordinate system is obtained, i.e. the surface defect three-dimensional model point cloud data.

[0030] Specifically, the step 2 comprises:

[0031] Step 2-1, build an aircraft scattering characteristic simulation model:

[0032] In the electromagnetic finite element simulation software, the same body coordinate system as in step 1 is established, and according to the parameters of the three-dimensional model of the aircraft, the simulation model of the aircraft scattering characteristic is formed.

[0033] Step 2-2, generate an aircraft simulation model with surface defects:

[0034] Using the numerical values of the defect structure three-dimensional contour point cloud data in the body coordinate system generated in step 1-3, the aircraft simulation model with surface defects is generated based on the aircraft scattering characteristic simulation model established in step 2-1.

[0035] Specifically, the step 3 comprises:

[0036] Step 3-1, simulation parameter setting:

[0037] According to the aircraft scattering characteristic measurement method, the simulation parameters are set, including the electromagnetic wave frequency band, the polarization mode, the relative position of the radar and the aircraft, the radar moving track, the speed, the azimuth and other parameters.

[0038] Step 3-2, surface defect scattering characteristic simulation:

[0039] After the parameter setting is completed, the aircraft scattering characteristic simulation with surface defects is carried out, and the surface defect scattering characteristic data is obtained. That is, the radar two-dimensional imaging data of the aircraft with defects is simulated, and the pixel information (electromagnetic scattering amplitude and phase) at the defect is proposed.

[0040] Specifically, the step 4 comprises:

[0041] The radar two-dimensional imaging data of the aircraft is extracted using the last periodic detection data of the aircraft scattering characteristic before the defect occurs as the reference. The final fusion data is to integrate a small amount of simulated radar two-dimensional imaging data of the aircraft with defects (simulation data) into the measured data, and the measured data is taken as the reference data.

[0042] The simulation data and the measured data are fused, and the aircraft scattering characteristic of the surface defect is calculated, and the specific calculation steps are as follows:

[0043] The radar transmits a linear frequency modulation signal is:

[0044] ;

[0045] Where T is the signal pulse width, f c is the signal carrier frequency, K is the frequency modulation slope, rect( ) is the rectangular window function, j is the imaginary unit, is the distance fast time.

[0046] The radar receives the echo signal scattered by the target scattering source Is expressed as:

[0047] ;

[0048] Wherein, Indicates the azimuth angle of the SAR radar and the aircraft, c indicates the speed of light, and t is a time variable.

[0049] After the radar transmits a signal, after Time, the radar receives the echo signal of the target. Wherein, Indicates the backscattering coefficient of the (x, y) point target, Is the distance between the (x, y) point and the radar, Indicates the phase change of the radar signal caused by the target scattering process.

[0050] The distance Doppler algorithm is used to realize radar imaging. After distance processing and azimuth processing, the final imaging output Is as follows:

[0051] ;

[0052] Wherein, Is the synthetic aperture time, Indicates the shortest slant range of the target to the radar, B is the radar bandwidth, v is the radar moving speed, and λ is the radar wavelength, Is the fast time in the distance direction, and t is the slow time in the azimuth direction. When the beam center passes through the target point , Is the minimum distance between the radar and the target.

[0053] Due to the influence of radar distance resolution, direction resolution and discrete sampling, the two-dimensional imaging graph is discrete, composed of many rectangular grids, and each grid represents a pixel block, each pixel block contains the amplitude and phase information of the target backscattering, and the position and size of the pixel block depend on the radar parameters and the radar motion trajectory, and are irrelevant to the target. Therefore, the final imaging output Can be expressed as the following formula:

[0054] ;

[0055] Wherein, concat represents a picture splicing function, Indicates the scattering amplitude information of the i-th pixel block, Indicates the scattering phase information of the i-th pixel block, and exp( ) indicates an exponential function.

[0056] The present application obtains the radar two-dimensional imaging data of the damaged aircraft through simulation

[0057]

[0058] wherein, represents the scattering amplitude information of the i-th pixel block obtained by simulation, represents the scattering phase information of the i-th pixel block obtained by simulation.

[0059] The pre-damage aircraft radar two-dimensional imaging data obtained by actual measurement As follows:

[0060]

[0061] wherein, represents the scattering amplitude information of the i-th pixel block obtained by simulation, represents the scattering phase information of the i-th pixel block obtained by simulation.

[0062] According to the position information of the damage, the pixel position corresponding to the damage position is taken out, it is assumed that the damage corresponds to the p-th pixel block, the scattering amplitude information of the p-th pixel block obtained by simulation is used to replace the scattering amplitude information of the p-th pixel block obtained by actual measurement, so as to realize the fusion of simulation and actual measurement data, and the scattering amplitude information and phase information of the p-th pixel block after fusion are as follows:

[0063]

[0064] wherein, represents the scattering amplitude information of the p-th pixel block after fusion of simulation and actual measurement data, represents the scattering amplitude information of the p-th pixel block obtained by simulation.

[0065]

[0066] wherein, represents the phase information of the p-th pixel block after fusion of simulation and actual measurement data, represents the scattering phase information of the p-th pixel block obtained by actual measurement. Thus, the scattering amplitude information of the i-th pixel block after fusion of simulation and actual measurement data in the two-dimensional imaging graph , and the phase information of the i-th pixel block after fusion of simulation and actual measurement data are obtained. It should be noted that only the scattering amplitude information and phase information of the p-th pixel block corresponding to the damage position in the two-dimensional imaging graph are replaced, and other information is not changed.

[0067] According to the above fusion of simulation and actual measurement data, the radar two-dimensional imaging information after fusion is obtained As follows: ​​​​​

[0068] .

[0069] According to the scattering center model theory, the scattering characteristics of the target can be represented by the scattering characteristics of several scattering sources on the target, and the radar two-dimensional imaging diagram reflects the scattering characteristics of each region of the target, so the RCS information of the aircraft can be directly calculated from the radar two-dimensional imaging data.

[0070] The spatial position distribution, scattering intensity and phase information of each pixel are extracted from the radar two-dimensional imaging diagram, and the scattering characteristics of the aircraft can be obtained by complex superposition of the data of each pixel. The total RCS of the aircraft is calculated according to the following formula:

[0071] ;

[0072] Wherein, is the total RCS of the aircraft, M is the number of pixel blocks, represents the scattering amplitude information of the i-th pixel block, represents the scattering phase information of the i-th pixel block.

[0073] Embodiment:

[0074] The method proposed in the present application is proved to be able to efficiently analyze the RCS parameters of the aircraft after surface defects in a simulated manner. Based on the network disclosed F117 aircraft parameters, a three-dimensional model thereof is established in a simulation software, as shown in Figure 2 .

[0075] The simulation parameters are set according to the SAR radar near-field test parameters, and the radar two-dimensional imaging data of the aircraft is simulated. The two-dimensional imaging data simulated before the defects appear on the surface of the aircraft is taken as the two-dimensional imaging data periodically measured for the aircraft according to the present application. Through the two-dimensional imaging data simulated after the defects appear on the surface of the aircraft, the RCS information of the aircraft is finally inverted by using the method of fusion of simulation and measurement data proposed in the present application, and the result is shown in Figure 3 .

[0076] Using the method proposed in the present application, the analysis time of the RCS of an aircraft with surface defects is only about one hour, while the traditional measurement method takes at least six hours.

[0077] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of evaluating the scattering properties of surface defects of an aircraft, characterized in that, Includes the following steps: Step 1: Use a binocular vision device to acquire surface defect images and construct point cloud data of a 3D model of the surface defects; Step 2: Based on the actual 3D model parameters of the aircraft, establish a simulation model of the aircraft scattering characteristics, and based on the point cloud data of the 3D model of surface defects, generate an aircraft simulation model with surface defects to truly reflect the surface defect situation of the aircraft. Step 3: Set simulation parameters according to the actual measurement method of aircraft electromagnetic scattering characteristics, simulate and generate scattering characteristic data at the surface defects, and obtain simulation information of scattering characteristics of surface defects; Step 4: Combine the measured electromagnetic scattering characteristics of the aircraft when no defects are found with the simulated scattering characteristics of the surface defects to calculate the final aircraft scattering characteristics data of the surface defects. This includes: using the most recent periodic aircraft scattering characteristics detection data as a benchmark, extracting the radar two-dimensional image, extracting the position of the pixel block corresponding to the damage location based on the damage location information, and replacing the measured scattering amplitude information of the pixel block with the simulated scattering amplitude information of the pixel block, thereby achieving data fusion and calculating the final aircraft scattering characteristics data of the surface defects.

2. The method of evaluating the scattering properties of surface defects of an aircraft according to claim 1, characterized in that, Step 1 includes determining the coordinates and orientation information of the surface defect in the body coordinate system, as well as the numerical value of the three-dimensional contour point cloud data of the defect structure in the body coordinate system. This numerical value is the three-dimensional model point cloud data of the surface defect.

3. The method of evaluating the scattering characteristics of surface defects of an aircraft according to claim 1, characterized in that, In step 2, the established body coordinate system is the same as the body coordinate system used when acquiring surface defect images.

4. The method of evaluating the scattering characteristics of surface defects of an aircraft according to claim 1, characterized in that, In step 3, the simulation parameters include electromagnetic wave frequency band, polarization mode, relative position of radar and aircraft, radar movement trajectory, speed, and azimuth.

5. The method for evaluating the aircraft scattering characteristics of surface defects according to claim 1, characterized in that, The data of the radar two-dimensional imaging graph is divided into a plurality of rectangular grids, and each rectangular grid represents a pixel block. Each pixel block contains scattering amplitude information and scattering phase information. The final imaging output of the radar two-dimensional imaging graph is obtained by combining the scattering amplitude information and the scattering phase information of each pixel block. is represented as: ； where concat denotes a picture concatenation function, denotes the scattering amplitude information of the i-th pixel block, denotes the scattering phase information of the i-th pixel block, exp( ) denotes an exponential function, and i denotes the i-th pixel block.

6. The method for evaluating the aircraft scattering characteristics of surface defects according to claim 5, characterized in that, Data of two-dimensional imaging of radar after aircraft damage is obtained through simulation : ； wherein, is the distance direction fast time, t is the time variable, represents the scattering amplitude information of the i-th pixel block obtained by simulation, represents the scattering phase information of the i-th pixel block obtained by simulation; exp( ) represents an exponential function, and concat represents a picture splicing function; Data of the two-dimensional imaging graph of the airplane radar before the damage is obtained by measurement is: ； wherein, denotes the scattering amplitude information of the i-th pixel block resulting from the test, denotes the scattering phase information of the i-th pixel block resulting from the test, Based on the damage location information, the position of the pixel corresponding to the damage location is extracted. Assuming the damage corresponds to the p-th pixel block, the scattering amplitude information of the p-th pixel block obtained from simulation is used to replace the scattering amplitude information of the p-th pixel block obtained from actual measurement, thereby achieving data fusion. The scattering amplitude information and scattering phase information of the p-th pixel block after fusion are as follows: ； ； wherein, represents the scattering amplitude information of the pth pixel block after the simulation and the measured data are fused; represents the scattering amplitude information of the pth pixel block obtained by simulation; represents the scattering phase information of the pth pixel block after the simulation and the measured data are fused; represents the scattering phase information of the pth pixel block obtained by measurement, and p represents the pth pixel block corresponding to the assumed damage.

7. The method for evaluating the aircraft scattering characteristics of surface defects according to claim 6, characterized in that, Data fusion is performed to obtain data of the fused radar two-dimensional imaging image : ； in, This refers to the scattering amplitude information of the i-th pixel block after fusing simulation and measured data. This represents the phase information of the i-th pixel block after the fusion of simulation and measured data.

8. The method for evaluating the aircraft scattering characteristics of surface defects according to claim 1, characterized in that, Before acquiring surface defect images using binocular vision equipment in step 1, the aircraft surface is inspected to determine the presence of defective areas.

9. The method for evaluating the aircraft scattering characteristics of surface defects according to claim 8, characterized in that, The merged data is then validated.

Images