CN108152799B - Method for rapidly calculating radar scattering cross section of hypersonic aircraft - Google Patents
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Abstract
The invention provides a method for quickly calculating a radar scattering cross section of an ultrahigh-sound-velocity aircraft, which comprises the following steps of: s1, extracting physical field parameters based on plasma flow field data distribution based on the distribution characteristics of the plasmas around the aircraft in the motion state, wherein the physical field parameters comprise plasma electron density and collision frequency; s2, carrying out grid division on the calculation area, and acquiring a corresponding spectral function distribution model under a corresponding motion state based on the discretized plasma flow field data distribution information; s3, solving corresponding radar scattering cross sections based on physical field parameters of plasma flow field data distribution; and S4, setting different incidence angles, and acquiring radar scattering cross sections with different azimuth angles according to the defined grid information. The advantages are that: a simple and quick equivalent electromagnetic wave radar scattering cross section solving method is provided.
Description
Technical Field
The invention relates to the technical field of radar scattering cross section solving, in particular to a method for quickly calculating a radar scattering cross section of an ultrahigh-sound-speed aircraft.
Background
When the hypersonic stealth aircraft in the reentry or near space flies in the atmosphere, plasma detours and trails are formed, and electromagnetic scattering characteristics of the aircraft are seriously influenced, so that the hypersonic stealth aircraft in the near space is obviously different from a conventional aircraft in the atmosphere and an orbital aircraft outside the atmosphere in the electromagnetic scattering characteristics, and a new challenge is brought to the detection and tracking of the aircraft (A.H. Richard. the application of light gas for high-accuracy airborne interference research [ R ]. AIAA 92-98.). When the ultrahigh-speed aircraft flies in the near space, the surrounding air is rapidly compressed, the aircraft and the air are strongly rubbed, the surface is heated to generate infrared radiation and visible radiation, a plasma sheath is formed on the surface of the projectile body, and an ionization trail is formed at the downstream of the aircraft, so that the electromagnetic characteristics of the aircraft are greatly changed (Lejialing, Gaobao, the Jun. Zhan et al. manned Physics [ M ], Beijing: national defense industry Press, 2005. Zhang Shicheng, pneumatic Physics [ M ]. Beijing: national defense industry Press, 20(3), 2013). Previous studies have shown that electromagnetic scattering from objects in the atmospheric space, or hypersonic stealth aircraft, is primarily due to turbulent plasma fields in the wake (G.F. Pippert. on the structure of wave breakdown from field radial sources [ R ]. AIAA Paper 630-.
Generally, the super-high speed aircraft head is in a laminar state around the flow ionization flow field. While the wake flow field is partly laminar and partly turbulent. Laminar electromagnetic scattering is generally specular and has a small proportion of its backscattering. Turbulence is divided into excessive turbulence, which is surface diffuse scattering, and sub-dense turbulence, which is bulk scattering, with respect to the wavelength of the irradiated electromagnetic wave, and the intensity of electromagnetic scattering of sub-dense turbulence is generally much greater than that of excessive turbulence. Therefore, the radar characteristic of the subdense turbulent trail is one of the main research contents for defending radar target recognition, and the analysis of the subdense turbulent trail has important practical significance.
In the aspect of simulating the characteristics of Radar Cross Sections (RCS) of ultra-high-speed aircrafts and streaming, analysis methods can be roughly divided into three categories. The method comprises an accurate analytical method, a high-frequency approximation method and a numerical simulation method (in the form of hucho, Liujiaqi, Liujunyuan and the like. RCS characteristic research of the near space hypersonic aerocraft, astronavigation report 2014, 35(6), 713 and 717). The three methods have advantages and disadvantages, and the accurate analysis method is the most accurate, but can only solve limited shapes. The approximate solution has high operation speed, can solve the problem of large size, but has limited calculation precision, and also has problems for the treatment of complex shapes (Suhan Sheng, Zhang Ying, Liuxiu Xiujin, etc., prediction method for the interaction between the plasma sheath of the aircraft and the electromagnetic wave, Beijing near space vehicle system engineering research institute, patent numbers CN106611083A, 2017.5); numerical simulation methods such as a time domain finite difference method and the like, a rapid multi-machine algorithm, a finite element algorithm and the like, high calculation precision, and capability of conveniently calculating the RCS of an aircraft with complicated appearance and medium, and have the defect that the problem of large electric size is difficult to solve (such as mountain, Dingzhi, Yandanghong and the like, a simulation method for analyzing the electromagnetic scattering characteristics of conformal sub-grids of the aircraft, Nanjing university of science and engineering, patent numbers: CN105653747A and 2014.6). In addition, a radar scattering cross section of a plasma surrounding target is obtained through a testing method (Xishu, Zhao Liang, Qin Yong Qiang, Li Xiaoping, a radar reflection characteristic measuring device and a method of a plasma coating material, the university of electronic technology of Western' an, patent numbers: CN102809577A, 2012.12).
Generally, the research on the RCS characteristic similarity rule of the hypodense turbulence wake of the hypersonic flight vehicle is a very difficult problem, the research on the RCS characteristic similarity rule has not been specially carried out in China, and no existing theory can be used for reference in foreign published documents.
Disclosure of Invention
The invention aims to provide a method for quickly calculating a radar scattering cross section of a hypersonic aircraft, which is a simple and quick equivalent electromagnetic wave radar scattering cross section solving method for solving the radar scattering cross section by extracting plasma flow field data of a surrounding plasma distribution characteristic of the hypersonic aircraft in a motion state to obtain a spectral function characteristic distribution model.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method for quickly calculating a radar scattering cross section of an ultra-high sound speed aircraft is characterized by comprising the following steps:
s1, extracting physical field parameters based on plasma flow field data distribution based on the distribution characteristics of the plasmas around the aircraft in the motion state, wherein the physical field parameters comprise plasma electron density and collision frequency;
s2, carrying out grid division on the calculation area, and acquiring a corresponding spectral function distribution model under a corresponding motion state based on the discretized plasma flow field data distribution information;
s3, solving corresponding radar scattering cross sections based on physical field parameters of plasma flow field data distribution;
and S4, setting different incidence angles, and acquiring radar scattering cross sections with different azimuth angles according to the defined grid information.
The method for quickly calculating the radar scattering cross section of the hypersonic aircraft includes, in step S2:
s21, inputting a geometric model structure of the aircraft, establishing a corresponding model, inputting physical field parameters around the hypersonic aircraft in a motion state, and acquiring the plasma distribution around the aircraft based on the discretization number grid distribution in different motion states, wherein data on each grid corresponds to the plasma tie physical parameters of a corresponding area;
s22, for the electromagnetic scattering characteristics of the sub-dense turbulent wake, adopting a first-order Born approximation method to correct the distortion approximation and transport theory in the form, considering the refraction effect of the plasma under the incident condition of electromagnetic waves, and solving the electromagnetic scattering characteristics of the plasma target;
s23, regarding the electromagnetic scattering property of the dense turbulence wake of the aircraft, bringing the electromagnetic scattering property distribution of the plasma target solved in the step S22 into a Shkarofsky turbulence spectrum function expression, and solving an isotropic spectrum function distribution expression of the aircraft at a certain height and in a flight state;
s24, discretizing a plasma geometric area around the aircraft, dividing the plasma geometric area into a plurality of circular areas along the motion direction according to the characteristics of the calculation area about an axial symmetry structure along the motion direction, and according to the characteristics that the density of the plasma geometric area at the head is high, and the plasma density distribution is non-uniform and small along the tail direction, so as to ensure that each circular area approximately corresponds to one plasma geometric area with uniform physical properties; and for each circular ring area, solving isotropic spectrum function distribution corresponding to each circular ring on the plasma-enclosed aircraft by adopting a method of averaging the discretized electromagnetic scattering distribution data obtained in the step S23.
The method for rapidly calculating the radar scattering cross section of the hypersonic aircraft includes, in step S3:
according to the solved discretization Sharofsky spectral function distribution, a first-order Born approximation method is used for correcting distortion approximation of a form and a Born approximation sub-dense turbulence wake radar scattering cross section solving formula corresponding to a transport theory, discretization radar scattering cross section distribution in the moving direction of the aircraft is obtained, volume division is carried out on the radar scattering cross section distribution, and the size of the total radar scattering cross section in the flying direction is obtained. In the method for quickly calculating the radar scattering cross section of the hypersonic aircraft, in step S24, the geometric area of the plasma around the discretized aircraft is subjected to mesh division based on the geometric area features of the plasma density distribution, so that the attribute distribution of the discretized plasma area is specifically: meshing the plasma region, wherein the geometric region of the model is from the top region to the tail region along the z direction, is in axial symmetry distribution in the y direction and the z direction, the maximum value is the diameter of the tail, and the meshing with sufficient precision is performed on the whole space solving region by adopting a regular hexahedron meshing method; in the above method for rapidly calculating a radar scattering cross section of a hypersonic aircraft, in step S23, the solved discretized electromagnetic scattering distribution is introduced into a Shkarofsky turbulence function expression, and an isotropic spectrum function distribution expression of the aircraft at a certain altitude and in a flight state is solved, and the specific process includes:
for the radar scattering cross section calculation of the plasma model, a method of carrying out grid division on the whole calculation region model is adopted, and the average plasma density corresponding to the incidence direction is calculated and obtained in the corresponding incidence direction;
carrying out discrete Fourier transform on the plasma average electron density of the corresponding grid to obtain a frequency spectrum corresponding to the corresponding electron density:
where the vector x contains n non-uniform sample points, i is the imaginary unit, and ω is e-2πi/nIs one of the whole spaceA plurality of complex roots, j and k respectively represent points from 0 to n-1;
and substituting the frequency spectrum distribution of the electron density into a Sharofsky turbulence spectrum function expression so as to solve the spectrum function expression of the isotropic turbulence.
And then combining a solution formula of the radar scattering cross section of the Bonn approximate sub-dense turbulent trail to obtain a corresponding radar scattering cross section.
The method for rapidly calculating the radar scattering cross section of the hypersonic aircraft includes, in step S24:
firstly, extracting data of a plasma parameter attribute file, and respectively solving average physical parameters on each grid of the divided grids;
for any beam of electromagnetic waves, solving a path passed by the beam of electromagnetic waves under the condition of linear propagation, and counting a regular hexahedron grid passed by the path, so as to obtain path information passed by the electromagnetic waves with corresponding frequencies under the condition of linear transmission;
discretizing and recording the grids, and recording corresponding coordinate information by using the central point of each grid; for the grids through which the electromagnetic wave propagates, acquiring the point of the center of the corresponding grid closest to the path as a reference point; based on these partitioned meshes, the experienced mesh center point may be approximated to be on a straight line;
and solving the radar scattering cross section by using a Sharofsky spectral function formula, thereby obtaining the radar scattering cross section of the electromagnetic wave with the corresponding continuous frequency.
Compared with the prior art, the invention has the following advantages:
1. aiming at the problems that plasma parameters are difficult to obtain under the action of electromagnetic waves and a hypersonic plasma sheath, effective electromagnetic waves and a plasma action physical mechanism explanation are lacked, and the like, the method can solve the scattering problem of the electromagnetic waves propagating in the dynamic plasma sheath, so that an equivalent medium mathematical modeling method based on plasma physical parameter distribution or a complex calculation method based on Monte Carlo can be avoided, and the purposes of reducing the calculation amount and improving the calculation rate are achieved;
2. according to theoretical derivation, the radar scattering cross section is solved by adopting an approximate formula calculation method, so that the traditional method of massive numerical calculation is replaced. The method has certain universality, and although an accurate result cannot be given for a complex geometric structure model, the method has practical application value in the aspect of practical operation;
3. the method is a full-scale based fast calculation method. Due to the problem of calculated amount, most of the current researches are to estimate the radar scattering cross section of a small-size target based on theory and then to deduce the radar scattering cross section of a large-size target by adopting a scaling method;
4. and solving the radar scattering cross section by adopting a method of carrying out full-size grid division on the calculation region and a spectral characteristic method based on plasma density.
Drawings
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a schematic diagram of a geometric model and dimensions of the distribution of the upper half-space region of the wake of an aircraft and the meshing employed in an embodiment of the present invention;
FIG. 3 is a diagram illustrating meshing of plasma regions and selection of a coordinate point of a center of a mesh experienced by an incident electromagnetic wave in accordance with an embodiment of the present invention;
FIG. 4 is a diagram of a method for calculating an angle in coordinates corresponding to any grid in a computation region space and an average physical property of each region according to an embodiment of the present invention;
FIG. 5 is a flow chart of a plasma wake radar cross section solution in an embodiment of the present invention;
fig. 6 shows the solved spectrum function variation curve and the one-dimensional distance image of the sub-dense turbulent trail RCS under the conditions of 10Ma speed, 65km height and χ being 45 ° in the embodiment of the invention.
Detailed Description
The present invention will now be further described by way of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings.
For hypersonic stealth aircraft, a plasma sheath is formed that wraps around the aircraft target during flight. In general, the distribution of the plasma is quite complex. The physical property distribution is closely related to the height, motion state and surrounding environment of the aircraft. The traditional calculation method generally cannot accurately acquire the plasma property distribution, so that the radar scattering cross section cannot be accurately acquired by adopting a numerical calculation method. In the method, an approximation method is adopted, and the ultrahigh-sound-speed aircraft radar scattering cross section calculation method with plasma surrounding is good in adaptability and high in calculation efficiency.
As shown in fig. 1 and 2, the present invention provides a method for rapidly calculating a radar cross section of a hypersonic aircraft, which comprises:
s1, extracting physical field parameters based on plasma flow field data distribution based on the distribution characteristics of the plasmas around the aircraft in the motion state, wherein the physical field parameters comprise plasma electron density and collision frequency;
in this embodiment, the specific implementation process of step S1 is: according to the aerodynamic shape, the flight state and the height of the aircraft, the FD-FASTRAN software is used for performing dynamic simulation to obtain the plasma density and collision frequency distribution information around the corresponding aircraft, so that the physical field information, the surrounding environment information and the plasma property of the electromagnetic waves in the space material are defined.
S2, carrying out grid division on the calculation area, preferably adopting regular hexahedron grid division, and acquiring a corresponding spectral function distribution model of the aircraft in a corresponding state based on the discretized plasma flow field data distribution information; the method comprises the following steps of (1) carrying out grid division on an obtained plasma region so as to discretize the physical property distribution of the plasma, and preparing for numerical solution of the next step, wherein a plasma existence interval is defined in the step so as to define an electromagnetic wave and plasma action interval;
specifically, data extraction is performed on the plasma parameter attribute file. And for any beam of electromagnetic waves, solving a path passed by the beam of electromagnetic waves under the condition of linear propagation, and counting regular hexahedron mesh information passed by the path. Thereby acquiring the path information which is experienced by the electromagnetic wave of the corresponding frequency under the condition of transmitting along the straight line.
The grids are divided in the manner shown in fig. 2, and the solution of the average physical parameters, such as the average electron density and the collision frequency, on each grid is performed separately.
S3, solving corresponding radar scattering cross sections based on physical field parameters of plasma flow field data distribution;
and S4, setting different incidence angles, and acquiring radar scattering cross sections with different azimuth angles according to the defined grid information.
In this embodiment, the step S2 specifically includes:
s21, inputting a geometric model structure of the aircraft, establishing a corresponding model, inputting physical field parameters around the aircraft in a motion state, and acquiring plasma distribution around the aircraft based on discretized number grid distribution in different motion states, wherein data on each grid corresponds to plasma tie physical parameters of a corresponding area;
s22, for the electromagnetic scattering characteristics of the sub-dense turbulent wake, adopting a first-order Born (Bonn) approximation method to correct the distortion approximation and transport theory in the form, considering the refraction effect of the plasma under the incident condition of electromagnetic waves, and solving the electromagnetic scattering characteristics of the plasma target;
s23, regarding the electromagnetic scattering property of the dense turbulence wake of the aircraft, substituting the electromagnetic scattering property distribution of the plasma target solved in the step S22 into a Shkarofsky turbulence spectrum function expression, and solving an isotropic spectrum function distribution expression of the aircraft at a certain height and in a flight state;
s24, discretizing a plasma geometric area around the aircraft, dividing the plasma geometric area into a plurality of circular areas along the motion direction according to the characteristics of the calculation area about an axial symmetry structure along the motion direction, and according to the characteristics that the density of the plasma geometric area at the head is high, and the plasma density distribution is non-uniform and small along the tail direction, so as to ensure that each circular area approximately corresponds to one plasma geometric area with uniform physical properties; for each circular ring area, the method of averaging the discretized electromagnetic scattering distribution data obtained in step S23 is adopted to solve the isotropic spectral function distribution corresponding to each circular ring on the plasma-enclosed aircraft, so as to track the plasma attribute information in the direction of the propagation path of the corresponding incident electromagnetic wave.
In this embodiment, the step S3 specifically includes:
according to the solved discretization Sharofsky spectral function distribution, a first-order Born approximation method is used for correcting distortion approximation of a form and a Born approximation sub-dense turbulence wake radar scattering cross section solving formula corresponding to a transport theory, discretization radar scattering cross section distribution in the moving direction of the aircraft is obtained, volume division is carried out on the radar scattering cross section distribution, and the size of the total radar scattering cross section in the flying direction is obtained.
In step S24, the discretization of the geometric area of the plasma around the aircraft is performed by meshing based on the geometric area features of the plasma density distribution, so that the process of discretizing the attribute distribution of the plasma area specifically includes:
meshing the plasma region, wherein the geometric region of the model is from the top region to the tail region along the z direction, is in axial symmetry distribution in the y direction and the z direction, the maximum value is the diameter of the tail, and the meshing with sufficient precision is performed on the whole space solving region by adopting a regular hexahedron meshing method;
and performing discrete Fourier transform according to the plasma electron density information corresponding to the grids so as to complete statistics of plasma electron density, collision frequency, plasma electron density root mean square and the like on each section and other physical parameters. In this way, the physical parameter properties of each thin cylinder can be obtained. And further can be applied to calculation of a radar scattering cross section formula of Born approximation. Therefore, based on the above analysis, for different electromagnetic wave incidence directions, different plasma thin circular cross sections are provided, which correspond to different one-dimensional distance image radar scattering cross sections. As shown in fig. 4, a ring division manner based on the incident electromagnetic wave at the azimuth angle is given, so that the average plasma physical property statistics and the radar scattering cross section solution are performed according to the physical field information corresponding to the discretization grid based on the divided rings;
correspondingly, according to the corresponding regular hexahedron grids on the path traveled by each beam of electromagnetic wave, the center points of the regular hexahedron grids are obtained, the yz plane where the center points are located and the section of the plasma region are located, as shown in fig. 4, the length of each section on the x axis is the length of the regular hexahedron grids, so that the physical parameter information of each corresponding grid is subjected to file reading to obtain information such as electron density, collision frequency, coordinates in the x, y and z directions respectively, a plane perpendicular to the direction of the incident electromagnetic wave is selected, the section intersected with the plasma region is obtained, then average physical parameters on each section are obtained, and plasma electron root-mean-square density statistics are carried out, wherein the physical parameters are obtained from data statistics of each grid on the section. Here, the cross section parallel to the normal direction of the incident electromagnetic wave is a thin cylinder having a thickness of the length of the mesh.
As shown in fig. 5 and 6, a flow chart for solving the radar scattering cross section of the plasma wake is given, and a calculation result of a specific model is given. The model shows an upper half-space model with a geometric region from [ -0.23,1.81 ] in the z-direction]The distribution along the x and y directions is symmetrical about the z axis, and the area is [ -0.83,0.83 [ -0.83 ]]. For an incident electromagnetic wave, the incident angle θ and
theta and theta are all based on the center point of the plasma in the xy plane as the reference point
All the electromagnetic waves are changed from 0 degree to 360 degrees, so that the electromagnetic wave incident information in all directions can be obtained for the incidence of the electromagnetic waves with any random angle, the solution of the scattered electromagnetic waves can be carried out under the condition of the incidence of the electromagnetic waves, and the corresponding frequency spectrum and the radar scattering cross section can be obtained. As shown in FIG. 6The calculation result shows the spectral function change curve and the RCS one-dimensional range profile of the sub-dense turbulence trail of the aircraft target under the condition of 10Ma flight speed and 65km altitude flight in the model.
For electromagnetic waves incident at any angle, the sum of
And (4) showing.
In this embodiment, the process of calculating the radar scattering cross section of the hypersonic plasma based on the shanofsky function and the spectral transformation in step S23 specifically includes:
based on the plasma density, a discrete Fourier transform method is adopted to obtain a spectral function of the plasma:
where the vector x contains n non-uniform sample points, i is the imaginary unit, and ω is e-2πi/nFor one of the complex roots in the whole space, j and k respectively represent points which are calculated from 0 to n-1;
for the radar scattering cross section calculation of the plasma model, a method of carrying out grid division on the whole calculation region model is adopted, and the average plasma density corresponding to the incidence direction is calculated and obtained in the corresponding incidence direction;
and carrying out discrete Fourier transform on the plasma average electron density of the corresponding grid to obtain a corresponding frequency spectrum, and further applying a solution formula of the Bonn approximation sub-dense turbulent wake radar scattering cross section distributed by a Sharofsky spectral function to obtain a corresponding radar scattering interface.
In this embodiment, the step S24 specifically includes:
firstly, extracting data of a plasma parameter attribute file, and respectively solving average physical parameters on each grid of the divided grids;
for any beam of electromagnetic waves, solving a path passed by the beam of electromagnetic waves under the condition of linear propagation, and counting a regular hexahedron grid passed by the path, so as to obtain path information passed by the electromagnetic waves with corresponding frequencies under the condition of linear transmission;
discretizing and recording the grids, and recording corresponding coordinate information by using the central point of each grid; for the grids through which the electromagnetic wave propagates, acquiring the point of the center of the corresponding grid closest to the path as a reference point; based on these divided meshes, it should be noted that the divided meshes should be small enough so that the experienced mesh center points can be approximated as being on a straight line;
and solving the radar scattering cross section by using a Sharofsky spectral function formula, thereby obtaining the radar scattering cross section of the electromagnetic wave with the corresponding continuous frequency.
In summary, compared with the traditional radar cross section calculation method, the full-wave simulation numerical calculation method based on the physical attributes corresponding to the divided grids is not needed, so that a large amount of calculation resources and time are saved. The method comprises the steps of performing grid division on a region of interest, obtaining the spectral function distribution of a target by adopting a discretized Sharofsky spectral function distribution formula, performing average physical attribute statistics in the electromagnetic wave incidence direction, and solving by using a Born approximate sub-dense turbulence wake radar scattering cross section formula. Therefore, the method is particularly suitable for the radar scattering interface fast solving of the electrically large-size plasma target.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (5)
1. A method for rapidly calculating a radar scattering cross section of a hypersonic aircraft is characterized by comprising the following steps:
s1, extracting physical field parameters based on plasma flow field data distribution based on the distribution characteristics of the plasmas around the aircraft in the motion state, wherein the physical field parameters comprise plasma electron density and collision frequency;
s2, grid division is carried out on the calculation region, and a corresponding spectrum function distribution model in a corresponding motion state is obtained based on the sub-dense turbulence wake electromagnetic scattering property of the aircraft and the Sharofsky function according to the discretization plasma flow field data distribution information;
s3, solving corresponding radar scattering cross sections based on physical field parameters of plasma flow field data distribution;
s4, setting different incidence angles, and acquiring radar scattering cross sections with different azimuth angles according to the defined grid information;
the step S2 specifically includes:
s21, inputting a geometric model structure of the aircraft, establishing a corresponding model, inputting physical field parameters of the hypersonic aircraft in the motion state, and acquiring the plasma distribution of the aircraft in different motion states based on the discretization number grid distribution, wherein the data on each grid corresponds to the plasma average physical parameters of a corresponding area;
s22, for the electromagnetic scattering characteristics of the sub-dense turbulent wake, adopting a first-order Born approximation method to correct the distortion approximation and transport theory in the form, considering the refraction effect of the plasma under the incident condition of electromagnetic waves, and solving the electromagnetic scattering characteristics of the plasma target;
s23, regarding the electromagnetic scattering property of the sub-dense turbulent wake of the aircraft, bringing the electromagnetic scattering property distribution of the plasma target solved in the step S22 into a Shkarofsky turbulent flow spectrum function expression, and solving an isotropic spectrum function distribution expression of the aircraft at a certain height and in a flight state;
s24, discretizing a plasma geometric area around the aircraft, dividing the plasma geometric area into a plurality of circular areas along the motion direction according to the characteristics of the calculation area about an axial symmetry structure along the motion direction, and according to the characteristics that the density of the plasma geometric area at the head is high, and the plasma density distribution is non-uniform and small along the tail direction, so as to ensure that each circular area approximately corresponds to one plasma geometric area with uniform physical properties; and for each circular ring area, solving isotropic spectrum function distribution corresponding to each circular ring on the plasma-enclosed aircraft by adopting a method of averaging the discretized electromagnetic scattering distribution data obtained in the step S23.
2. The method for rapidly calculating the radar cross section of the hypersonic aircraft according to claim 1, wherein the step S3 specifically comprises:
according to the solved discretized Shkarofesky spectrum function distribution, a first-order Born approximation method is used for correcting the distortion approximation of the form and a Born approximation sub-dense turbulence wake radar scattering cross section solving formula corresponding to the transport theory, the discretized radar scattering cross section distribution in the aircraft motion direction is obtained, the volume division is carried out on the radar scattering cross section distribution, and the total radar scattering cross section size in the flight direction is obtained.
3. The method for rapidly calculating the radar scattering cross section of the hypersonic aircraft as claimed in claim 1, wherein the discretization of the geometric area of the plasma surrounding the aircraft in step S24 is performed by meshing based on the geometric area characteristics of the plasma density distribution, so as to discretize the property distribution of the plasma area, specifically:
and meshing the plasma region, wherein the geometric region of the model is from the top region to the tail region along the z direction, is in axial symmetry distribution in the y direction and the z direction, the maximum value is the diameter of the tail, and the meshing with sufficient precision is performed on the whole space solving region by adopting a regular hexahedron meshing method.
4. The method for rapidly calculating the radar scattering cross section of the hypersonic aircraft as claimed in claim 3, wherein the electromagnetic scattering property distribution of the plasma target to be solved is introduced into the Shkarofsky turbulence spectral function expression, and the isotropic spectral function distribution expression of the hypersonic aircraft at a certain altitude and in a flight state is solved, and the specific process comprises the following steps:
for the radar scattering cross section calculation of the plasma model, a method of carrying out grid division on the whole calculation region model is adopted, and the average plasma density corresponding to the incident direction is calculated and obtained in the corresponding incident direction;
carrying out discrete Fourier transform on the plasma average electron density of the corresponding grid to obtain a frequency spectrum corresponding to the corresponding electron density:
where the vector x contains n non-uniform sample points, i is the imaginary unit, and ω is e-2πi/nFor one of the complex roots in the whole space, j and k respectively represent points which are calculated from 0 to n-1;
substituting the frequency spectrum distribution of the electron density into the Shkarofsky turbulence spectrum function expression so as to solve the spectrum function expression of the isotropic turbulence;
and then combining a solution formula of the radar scattering cross section of the Bonn approximate sub-dense turbulent trail to obtain a corresponding radar scattering cross section.
5. The method for rapidly calculating the radar cross section of the hypersonic aircraft according to claim 4, wherein the step S24 specifically comprises:
firstly, extracting data of a plasma parameter attribute file, and respectively solving average physical parameters on each grid of the divided grids;
for any beam of electromagnetic waves, solving a path passed by the beam of electromagnetic waves under the condition of linear propagation, and counting a regular hexahedron grid passed by the path, so as to obtain path information passed by the electromagnetic waves with corresponding frequencies under the condition of linear transmission;
discretizing and recording the grids, and recording corresponding coordinate information by using the central point of each grid; for the grids through which the electromagnetic wave propagates, acquiring the point of the center of the corresponding grid closest to the path as a reference point; based on these partitioned meshes, the experienced mesh center point may be approximated to be on a straight line;
and solving the radar scattering cross section by using a Shkarofsky spectral function formula so as to obtain the radar scattering cross section of the electromagnetic wave with the corresponding continuous frequency.
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| CN109100724B (en) * | 2018-08-09 | 2022-05-10 | 南京信息工程大学 | Method for rapidly acquiring three-dimensional vector data of radar reflectivity data vertical section |
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