CN106649197A - Calculation method of internal scattering characteristic of complicated cavity - Google Patents
Calculation method of internal scattering characteristic of complicated cavity Download PDFInfo
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Abstract
The invention discloses a calculation method of an internal scattering characteristic of a complicated cavity. The calculation method comprises the following steps: S1, constructing a virtual aperture plane of the cavity according to the appearance of the cavity; S2, carrying out radiation integration on an excitation source to obtain an electromagnetic field distribution of the virtual aperture plane; S3, carrying out electromagnetic calculation on the overall cavity by taking the electromagnetic field distribution on the virtual aperture plane as the excitation source, and constructing and adopting a linear equation set to calculate internal scattering of the cavity; S4, calculating the linear equation set by adopting a Krylov subspace iteration method; and S5, obtaining stable cavity inner wall current, obtaining an aperture field, and calculating a far field scattering characteristic by taking the aperture field as the excitation source. According to the calculation method disclosed by the invention, the aperture field excitation replaces a low-scattering carrier, on one hand, the unknown quantity of calculation is reduced, and the design of the low-scattering carrier is also eliminated.
Description
Technical field
The present invention relates to radar target signature emulation technology, more particularly to a kind of calculating of complicated cavity scattering-in characteristic
Method.
Background technology
It is the important base of Stealth design and Target Signature Analysis technology to the analysis of EM scattering of cavities characteristic
Plinth, there is important realistic meaning, always Computational electromagnetics a focus.There is strong nearly resonance phenomena in cavity, by
The matrix that electromagnetic field integral equation is obtained often has larger conditional number, and in iterative, convergence rate is very slow, Er Qie electricity
Large cavity belongs to TV university problem.Low frequency numerical method because subdivision density is big, unknown quantity is more, by calculator memory and when calculating
Between restriction be difficult to solve the scattering properties of full-size(d) cavitys with these methods.Ray method based on geometric optics solves chamber
Body has the advantages that to realize that simple, solving speed is fast, but solving precision is not high, be difficult to solution processes complex-shaped cavity.
Institutes Of Technology Of Nanjing is in patent " based on moment method and the target with open cavity Analysis of Electromagnetic Scattering method of parabolic equation "
(publication number：CN104778151A in), cavity portion in target is individually solved with Fast Multiple Method, with field integral
Equation solution goes out the electric current of housing surface, and obtains the electric field of various discrete point needed for the upper parabolical equation of cavity hatch face
Value, post processing is carried out to the electric field on last tangent plane and solves RCS；In patent, " cavity contains for Institutes Of Technology Of Nanjing
Dielectric object electromagnetic scattering hybrid analysis " (publication number：CN104915324A in), honorable integral equation and mesh free are thrown
Thing line equation combines, it is to avoid parabola can not calculate the defect of Scattering of Cavities；Northwestern Polytechnical University is in a kind of patent " aviation
Engine jet pipe EM scattering of cavities test device and method of testing " (publication number：CN105021899A in), electromagnetic scattering test
Device carries out the electromagnetic scattering test of jet pipe cavity, outside wall surface using pointed cone type absorbing material is coated in device body outside wall surface
Pointed cone absorbing material can absorb most radar wave, the electromagnetic wave of jet pipe model outside wall surface is effectively shielded in electromagnetism test
Reflection.
Specially treated is done in emulation to the cavity in target with open cavity by above-mentioned patent, Institutes Of Technology Of Nanjing, solves what is come
RCS is the population effect of target with open cavity；Northwestern Polytechnical University uses pointed cone type absorbing material bag in method of testing
Jet pipe cavity is covered, the reflection of electromagnetic wave of jet pipe model outside wall surface is shielded, test can exactly reflect that the electromagnetism of jet pipe cavity dissipates
Penetrate characteristic.Both do not have the methods for solving inside cavity scattering properties from emulation angle explanation, if by the method for the latter's test
It is applied directly in emulation, calculating unknown quantity can be sharply increased, it is impossible to carries out the calculating of electrically large sizes cavity properties conscientiously.
The content of the invention
It is an object of the invention to provide a kind of computational methods of complicated cavity scattering-in characteristic, by bore field excitation generation
On the one hand the unknown quantity of calculating is reduced for low scattering carrier, while also eliminating the design of low scattering carrier.
In order to realize object above, the present invention is achieved by the following technical solutions：
A kind of computational methods of complicated cavity scattering-in characteristic, are characterized in, the computational methods are comprised the steps of：
S1, according to cavity profile the virtual port diametric plane of cavity is built；
S2, to driving source radiation integration is carried out, and draws the magnetic distribution of the virtual port diametric plane；
S3, electromagnetism calculating is carried out using the magnetic distribution on virtual port diametric plane as driving source to overall cavity, and is constructed
Using system of linear equations, inside cavity scattering is solved；
S4, using Krylov subspace solution by iterative method system of linear equations；
S5, obtains stable cavity inner wall electric current, and obtains aperture field, is solved as driving source using described aperture field remote
Field scattering properties.
Virtual port diametric plane forms a closed shape with cavity in described step S1.
The step for including described virtual port diametric plane discretization before described step S2.
Radiation integration is carried out to driving source using formula (1) (2) in described step S2,
In formula, Εi(ra) and Hi(ra) virtual port diametric plane r is represented respectivelyaThe electric field at place and magnetic field, R represents source point to site
Unit footpath arrow, J and M represents respectively current source and magnetic current source distribution, and k represents the wave number of free space, Z0Represent free space
Wave impedance.
Described step S3 is specifically included：
Step S3.1, electromagnetic field meter is carried out using the magnetic distribution on virtual port diametric plane as driving source to overall cavity
Calculate；
Step S3.2, discretization cavity and according to the electromagnetic field on described virtual port diametric plane solves the electricity of cavity inner wall
Magnetic field, and then system of linear equations is constructed, solve inside cavity scattering.
Described step S4 is specially：Segment processing is made to whole cavity, it is every using Krylov subspace solution by iterative method
The system of linear equations of section cavity.
Aperture field is solved using formula (1) (2) in described step 5, and the solution Far Field Scattering characteristic is cavity
Scattering-in characteristic.
The present invention compared with prior art, with advantages below：
1st, low scattering carrier is replaced on the one hand to reduce the unknown quantity of calculating by bore field excitation, while also eliminating low
The design of scattering carrier.
2nd, by using Huygen's principle twice, and on the premise of reasonable approximately bore in-field, using Krylov
Subspace iteration method Efficient Solution large linear systems, obtain inside cavity scattering properties.
Description of the drawings
Fig. 1 is structural representation of the present invention to cavity sections process；
Fig. 2 is the structural representation of cavity of the present invention and its virtual port diametric plane；
Fig. 3 is WBR housing surface current distributing figure；
Fig. 4 is that bore irradiates Cobra housing surface current distributing figures；
Fig. 5 is to the structural representation after virtual port diametric plane discretization；
Fig. 6 is a kind of flow chart of the computational methods of complicated cavity scattering-in characteristic of the invention.
Specific embodiment
Below in conjunction with accompanying drawing, by describing a preferably specific embodiment in detail, the present invention is further elaborated.
As shown in fig. 6, a kind of computational methods of complicated cavity scattering-in characteristic, the computational methods are comprised the steps of：
S1, according to cavity profile the virtual port diametric plane of cavity is built, and typically requires that virtual port diametric plane is relatively regular, smooth,
Be conducive to solving magnetic distribution thereon；
S2, to driving source radiation integration is carried out, and draws the magnetic distribution of the virtual port diametric plane；
S3, electromagnetism calculating is carried out using the magnetic distribution on virtual port diametric plane as driving source to overall cavity, and is constructed
Using system of linear equations, inside cavity scattering is solved；
S4, using Krylov subspace solution by iterative method system of linear equations；
S5, obtains stable cavity inner wall electric current, and obtains aperture field, is solved as driving source using described aperture field remote
Field scattering properties.
Virtual port diametric plane forms a closed shape with cavity in described step S1 (referring to Fig. 2).
Include (such as Fig. 5) the step for described virtual port diametric plane discretization before above-mentioned step S2.
Radiation integration is carried out to driving source using formula (1) (2) in above-mentioned step S2,
In formula, Εi(ra) and Hi(ra) virtual port diametric plane r is represented respectivelyaThe electric field at place and magnetic field, R represents source point to site
Unit footpath arrow, J and M represents respectively current source and magnetic current source distribution, and k represents the wave number of free space, Z0Represent free space
Wave impedance；Before magnetic distribution on virtual port diametric plane is solved, need to carry out discretization to formula (1) (2), typically
Using RWG basic functions by the discrete expansion of target surface equivalent electromagnetic current.
Housing surface CURRENT DISTRIBUTION when Fig. 3 and Fig. 4 are respectively WBR, bore irradiation.As can be seen that WBR
When, high more than 10dB when the cavity bottom electric current for shining directly into is encouraged than bore.
Above-mentioned step S3 is specifically included：
Step S3.1, electromagnetic field meter is carried out using the magnetic distribution on virtual port diametric plane as driving source to overall cavity
Calculate；
Step S3.2, discretization cavity and according to the electromagnetic field on described virtual port diametric plane solves the electricity of cavity inner wall
Magnetic field, and then system of linear equations is constructed, solve inside cavity scattering.
Above-mentioned step S4 is specially：(referring to Fig. 1) makees segment processing to whole cavity, using Krylov subspace iteration
Method solves the system of linear equations of every section of cavity, and segmentation is solved on the premise of Matrix condition number is improved, and reduces the outer iteration later stage
Krylov subspace, substantially reduces required iterations.
Krylov subspace method is the one kind in projecting method, and it has been widely used in each of computational science
Field.There is the status being even more important in the iterative of large-scale linear system.The solution throughway of classical iterative methods is different from,
Krylov subspace method finds the approximate solution of linear system in Krylov subspace, and another is proposed strange and newly
The method for solving linear system.
There is strong nearly resonance phenomena in cavity, the matrix obtained by electromagnetic field integral equation often has larger condition
Number, in iterative, convergence rate is very slow.Classical iterative methods for the solution of Scattering of Cavities problem be often difficult to convergence, even
Tend to spread out, Krylov subspace iterative method (general conjugate residual error, GCR) can overcome Large Scale Sparse Linear equation to restrain
And the slow problem of convergence rate.
Segmentation is solved on the premise of Matrix condition number is improved, and more fully can be asked using general conjugate residual error iteration
The advantage of solution.The Krylov subspace in outer iteration later stage is reduced, required iterations is substantially reduced.For electrically large sizes complexity chamber
Portion's electromagnetic scattering in vivo is solved and can obtain reliable and stable numerical solution.
Aperture field is solved using formula (1) (2) in described step 5, and the solution Far Field Scattering characteristic is cavity
Scattering-in characteristic.
In sum, a kind of computational methods of complicated cavity scattering-in characteristic of the invention, are replaced by bore field excitation
On the one hand low scattering carrier reduces the unknown quantity of calculating, while also eliminating the design of low scattering carrier.
Although present disclosure has been made to be discussed in detail by above preferred embodiment, but it should be appreciated that above-mentioned
Description is not considered as limitation of the present invention.After those skilled in the art have read the above, for the present invention's
Various modifications and substitutions all will be apparent.Therefore, protection scope of the present invention should be limited to the appended claims.
Claims (7)
1. a kind of computational methods of complicated cavity scattering-in characteristic, it is characterised in that the computational methods are comprised the steps of：
S1, according to cavity profile the virtual port diametric plane of cavity is built；
S2, to driving source radiation integration is carried out, and draws the magnetic distribution of the virtual port diametric plane；
S3, using the magnetic distribution on virtual port diametric plane as driving source electromagnetism calculating is carried out to overall cavity, and constructs employing
System of linear equations, solves inside cavity scattering；
S4, using Krylov subspace solution by iterative method system of linear equations；
S5, obtains stable cavity inner wall electric current, and obtains aperture field, solves far field as driving source using described aperture field and dissipates
Penetrate characteristic.
2. computational methods of complicated cavity scattering-in characteristic as claimed in claim 1, it is characterised in that described step S1
Middle virtual port diametric plane forms a closed shape with cavity.
3. computational methods of complicated cavity scattering-in characteristic as claimed in claim 1, it is characterised in that described step S2
The step for including described virtual port diametric plane discretization before.
4. computational methods of complicated cavity scattering-in characteristic as claimed in claim 1, it is characterised in that described step S2
Middle employing formula (1) (2) carries out radiation integration to driving source,
In formula, Εi(ra) and Hi(ra) virtual port diametric plane r is represented respectivelyaThe electric field at place and magnetic field, R represents source point to the list of site
Position footpath arrow, J and M represents respectively current source and magnetic current source distribution, and k represents the wave number of free space, Z0Represent the ripple of free space
Impedance.
5. computational methods of complicated cavity scattering-in characteristic as claimed in claim 4, it is characterised in that described step S3
Specifically include：
Step S3.1, Electromagnetic Calculation is carried out using the magnetic distribution on virtual port diametric plane as driving source to overall cavity；
Step S3.2, discretization cavity and according to the electromagnetic field on described virtual port diametric plane solves the electromagnetic field of cavity inner wall,
And then construction system of linear equations, solve inside cavity scattering.
6. computational methods of complicated cavity scattering-in characteristic as claimed in claim 1, it is characterised in that described step S4
Specially：Segment processing is made to whole cavity, using the system of linear equations of every section of cavity of Krylov subspace solution by iterative method.
7. computational methods of complicated cavity scattering-in characteristic as claimed in claim 4, it is characterised in that described step 5
Middle employing formula (1) (2) solves aperture field, and the solution Far Field Scattering characteristic is inside cavity scattering properties.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109813969A (en) * | 2017-11-21 | 2019-05-28 | 深圳市通用测试系统有限公司 | A kind of diagnostic method of array antenna, equipment, system and computer readable storage medium |
| CN110866361A (en) * | 2019-11-26 | 2020-03-06 | 中国舰船研究设计中心 | Waveguide port excitation method for electromagnetic finite element solution |
| CN112731325A (en) * | 2020-12-23 | 2021-04-30 | 北京航空航天大学 | Target scattering measurement method for air inlet channel cavity |
| CN113779804A (en) * | 2021-09-16 | 2021-12-10 | 招商局重庆交通科研设计院有限公司 | Height design method for mounting cavity of immersed tube fireproof plate |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104077482A (en) * | 2014-06-27 | 2014-10-01 | 上海无线电设备研究所 | Quick calculation method of super-low-altitude target and land-sea rough surface composite scattering |
| CN104778151A (en) * | 2014-01-09 | 2015-07-15 | 南京理工大学 | Electromagnetic scattering analysis method of target with cavity on the basis of moment method and parabolic equation |
-
2016
- 2016-10-13 CN CN201610895166.3A patent/CN106649197A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104778151A (en) * | 2014-01-09 | 2015-07-15 | 南京理工大学 | Electromagnetic scattering analysis method of target with cavity on the basis of moment method and parabolic equation |
| CN104077482A (en) * | 2014-06-27 | 2014-10-01 | 上海无线电设备研究所 | Quick calculation method of super-low-altitude target and land-sea rough surface composite scattering |
Non-Patent Citations (5)
| Title |
|---|
| NATHAN R.GRADY ET AL: "UV Raman Scattering Measurements of Supersonic Reacting Flow over a Piloted, Ramped Cavity", 《50TH AIAA AEROSPACE SCIENCES MEETING INCLUDING THE NEW HORIZONS FORUM AND AEROSPACE EXPOSITION》 * |
| 刘胜军: "复杂目标电磁散射的有限元/边界积分法分析", 《万方学位论文库》 * |
| 孟敏: "电大尺寸口径面含腔目标电磁散射算法研究", 《万方学位论文库》 * |
| 张文: "复杂目标电磁散射的有限元/边界积分法", 《万方学位论文库》 * |
| 杨明林等: "电大不均匀腔体的并行高阶合元极分析", 《电波科学学报》 * |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109813969A (en) * | 2017-11-21 | 2019-05-28 | 深圳市通用测试系统有限公司 | A kind of diagnostic method of array antenna, equipment, system and computer readable storage medium |
| CN109813969B (en) * | 2017-11-21 | 2021-08-03 | 深圳市通用测试系统有限公司 | Array antenna diagnosis method, equipment and system |
| CN110866361A (en) * | 2019-11-26 | 2020-03-06 | 中国舰船研究设计中心 | Waveguide port excitation method for electromagnetic finite element solution |
| CN110866361B (en) * | 2019-11-26 | 2023-05-05 | 中国舰船研究设计中心 | Waveguide port excitation method for electromagnetic finite element solution |
| CN112731325A (en) * | 2020-12-23 | 2021-04-30 | 北京航空航天大学 | Target scattering measurement method for air inlet channel cavity |
| CN112731325B (en) * | 2020-12-23 | 2023-12-01 | 北京航空航天大学 | Method for measuring scattering of air inlet channel type cavity target |
| CN113779804A (en) * | 2021-09-16 | 2021-12-10 | 招商局重庆交通科研设计院有限公司 | Height design method for mounting cavity of immersed tube fireproof plate |
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