Transactions of Nanjing University of Aeronautics & Astronautics
Volume 31,Issue 3,2014 Table of Contents
2014, 31(3):219-240.
Abstract:
The emerging new concepts and technologies based on microwave photonics have led to an ever increasing interest in developing innovative radar systems with a net gain in functionality, bandwidth/resolution, size, mass, complexity and cost when compared with the traditional implementations. This paper describes the techniques developed in the last few years in microwave photonics that might revolutionize the way to design multifunction radar systems, with an emphasis on the recent advances in optoelectronic oscillators (OEOs), arbitrary waveform generation, photonic mixing, phase coding, filtering, beamforming, analog to-digital conversion, and stable radio frequency signal transfer. Challenges in implementation of these components and subsystems for meeting the technique requirements of the multifunction radar applications are discussed.
The emerging new concepts and technologies based on microwave photonics have led to an ever increasing interest in developing innovative radar systems with a net gain in functionality, bandwidth/resolution, size, mass, complexity and cost when compared with the traditional implementations. This paper describes the techniques developed in the last few years in microwave photonics that might revolutionize the way to design multifunction radar systems, with an emphasis on the recent advances in optoelectronic oscillators (OEOs), arbitrary waveform generation, photonic mixing, phase coding, filtering, beamforming, analog to-digital conversion, and stable radio frequency signal transfer. Challenges in implementation of these components and subsystems for meeting the technique requirements of the multifunction radar applications are discussed.
2014, 31(3):241-247.
Abstract:
Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homogeneous materials, including semiconductor, superconductor, ferrite and ferroelectrics by using Mie scattering theory. The simulated results demonstrate that the cloaks with these homogeneous materials can drastically reduce the total scattering cross sections of the cloaked system by using the finite element method. These cloaking frequencies can be controlled by external field through tuning the permittivity or permeability of these materials by the applied field, such as temperature, magnetic field and electric field. These may provide some potential ways to design tunable cloaking with considerable flexibility.
Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homogeneous materials, including semiconductor, superconductor, ferrite and ferroelectrics by using Mie scattering theory. The simulated results demonstrate that the cloaks with these homogeneous materials can drastically reduce the total scattering cross sections of the cloaked system by using the finite element method. These cloaking frequencies can be controlled by external field through tuning the permittivity or permeability of these materials by the applied field, such as temperature, magnetic field and electric field. These may provide some potential ways to design tunable cloaking with considerable flexibility.
2014, 31(3):248-254.
Abstract:
The surface plasmon resonance (SPR) of gold （Au） nanorod can be tuned in a large visible-near infrared (Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod, assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end (E-E) and side-by-side (S-S) assembled Au nanorods dimers are studied through finite difference time-domain (FDTD) simulation. With decreasing the gap spacing, the longitudinal SPR (SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR (SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover, a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region, blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field, the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.
The surface plasmon resonance (SPR) of gold （Au） nanorod can be tuned in a large visible-near infrared (Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod, assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end (E-E) and side-by-side (S-S) assembled Au nanorods dimers are studied through finite difference time-domain (FDTD) simulation. With decreasing the gap spacing, the longitudinal SPR (SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR (SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover, a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region, blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field, the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.
2014, 31(3):255-259.
Abstract:
A hybrid method combining simplified sub-entire domain basis function method of moment with finite element method (SSED-MoM/FEM) is accelerated for electromagnetic (EM) scattering analysis of large-scale periodic structures. The unknowns are reduced sharply with non-uniform mesh in FEM. The computational complexity of the hybrid method is dramatically declined by applying conjugate gradient-fast Fourier transform (CG-FFT) to the integral equations of both electric field and magnetic field. The efficiency is further improved by using OpenMP technique. Numerical results demonstrate that the SSED-MoM/FEM method can be accelerated for more than three thousand times with large-scale periodic structures.
A hybrid method combining simplified sub-entire domain basis function method of moment with finite element method (SSED-MoM/FEM) is accelerated for electromagnetic (EM) scattering analysis of large-scale periodic structures. The unknowns are reduced sharply with non-uniform mesh in FEM. The computational complexity of the hybrid method is dramatically declined by applying conjugate gradient-fast Fourier transform (CG-FFT) to the integral equations of both electric field and magnetic field. The efficiency is further improved by using OpenMP technique. Numerical results demonstrate that the SSED-MoM/FEM method can be accelerated for more than three thousand times with large-scale periodic structures.
2014, 31(3):260-268.
Abstract:
An efficient wavelet-based finite-difference time-domain (FDTD) method is implemented for analyzing nanoscale optical devices, especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells, i.e. used memory, while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer. The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions. To demonstrate the efficiency of the parallelized FDTD model, a mirrored cavity is analyzed. The analysis shows that the proposed model reduces computation time and memory cost, and the parallel computation result matches the theoretical model.
An efficient wavelet-based finite-difference time-domain (FDTD) method is implemented for analyzing nanoscale optical devices, especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells, i.e. used memory, while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer. The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions. To demonstrate the efficiency of the parallelized FDTD model, a mirrored cavity is analyzed. The analysis shows that the proposed model reduces computation time and memory cost, and the parallel computation result matches the theoretical model.
2014, 31(3):269-273.
Abstract:
A conformal multi-resolution time-domain (CMRTD) method is presented for modeling curved objects. The effective dielectric constant and area weighting are used to derive the update equations of CMRTD. The backward scattering bistatic radar cross sections (RCS) of the dielectric cylinder and ellipsoid are used to validate the proposed method. The results show that the proposed conformal method is more accurate to deal with the complex curved objects in electromagnetic simulations.
A conformal multi-resolution time-domain (CMRTD) method is presented for modeling curved objects. The effective dielectric constant and area weighting are used to derive the update equations of CMRTD. The backward scattering bistatic radar cross sections (RCS) of the dielectric cylinder and ellipsoid are used to validate the proposed method. The results show that the proposed conformal method is more accurate to deal with the complex curved objects in electromagnetic simulations.
2014, 31(3):274-280.
Abstract:
Electromagnetic scattering from inhomogeneous three-dimensional (3D) bi-anisotropic scatterers is formulated in terms of the volume integral equation (VIE) method. Based on the volume equivalence principle, the VIE is represented in terms of a pair of coupled bi-anisotropic polarized volume electric and magnetic flux densities. The VIE is solved using the method of moments (MoM) combined with tetrahedral mesh. Then the fast dipole method (FDM) based on the equivalent dipole method (EDM) is extended to analyze the scattering of bi-anisotropic media by solving the VIE. Finally, some numerical results are given to demonstrate the accuracy of the developed method for the scattering analysis of the bi-anisotropic media.
Electromagnetic scattering from inhomogeneous three-dimensional (3D) bi-anisotropic scatterers is formulated in terms of the volume integral equation (VIE) method. Based on the volume equivalence principle, the VIE is represented in terms of a pair of coupled bi-anisotropic polarized volume electric and magnetic flux densities. The VIE is solved using the method of moments (MoM) combined with tetrahedral mesh. Then the fast dipole method (FDM) based on the equivalent dipole method (EDM) is extended to analyze the scattering of bi-anisotropic media by solving the VIE. Finally, some numerical results are given to demonstrate the accuracy of the developed method for the scattering analysis of the bi-anisotropic media.
2014, 31(3):281-286.
Abstract:
A simple analytical method is presented to analyze the transmission of electromagnetic plane waves through multilayer stacked composite two-dimensional (2D) structures at microwave frequencies. Unlike the traditional structure, high impedance surface with graphene sheet is proposed. The structure includes graphene and thin metal patches and meshes. Simple analytical formulas are introduced for the surface impedance of graphene and for the grid impedance of electrically dense arrays of metal square patches or strips. The result of transmission properties is based on the dynamic tunable model of the high impedance surface, which considers the surface conductivity of graphene layer. The transmission coefficient obtained by using the equivalent circuit method is validated against full-wave numerical simulations. The considered equivalent circuit method can be useful in the design of graphene tunable planar devices.
A simple analytical method is presented to analyze the transmission of electromagnetic plane waves through multilayer stacked composite two-dimensional (2D) structures at microwave frequencies. Unlike the traditional structure, high impedance surface with graphene sheet is proposed. The structure includes graphene and thin metal patches and meshes. Simple analytical formulas are introduced for the surface impedance of graphene and for the grid impedance of electrically dense arrays of metal square patches or strips. The result of transmission properties is based on the dynamic tunable model of the high impedance surface, which considers the surface conductivity of graphene layer. The transmission coefficient obtained by using the equivalent circuit method is validated against full-wave numerical simulations. The considered equivalent circuit method can be useful in the design of graphene tunable planar devices.
2014, 31(3):287-292.
Abstract:
Inspired by the unique structure of insect compound eyes, a multi-channel image acquisition system is designed to photograph a cylindrical panorama of its surroundings with one shot. The hardware structure consists of an embedded ARM system and one array of 16 micro-image sensors. The system achieves the synchronization of captured photos in 10 ms, as well as 10 f/s video capture. The software architecture includes the TCP/IP protocol, video capture procedures in “Poll/Read” or “video streaming” modes, thread pool monitoring in multi-threading mutex, synchronization control with the“event” “mutex signal” and “critical region” functions, and a synthetic image algorithm characterized by its portability, modularity, and remote transmission. The panoramic imaging system is expected to be a vision sensor for mobile robotics.
Inspired by the unique structure of insect compound eyes, a multi-channel image acquisition system is designed to photograph a cylindrical panorama of its surroundings with one shot. The hardware structure consists of an embedded ARM system and one array of 16 micro-image sensors. The system achieves the synchronization of captured photos in 10 ms, as well as 10 f/s video capture. The software architecture includes the TCP/IP protocol, video capture procedures in “Poll/Read” or “video streaming” modes, thread pool monitoring in multi-threading mutex, synchronization control with the“event” “mutex signal” and “critical region” functions, and a synthetic image algorithm characterized by its portability, modularity, and remote transmission. The panoramic imaging system is expected to be a vision sensor for mobile robotics.
10 Nodal Discontinuous Galerkin Method for Aeroacoustics and Comparison with Finite Difference Schemes
2014, 31(3):293-302.
Abstract:
A nodal discontinuous Galerkin formulation based on Lagrange polynomials basis is used to simulate the acoustic wave propagation. Its dispersion and dissipation properties for the advection equation are investigated by utilizing an eigenvalue analysis. Two test problems of wave propagation with initial disturbance consisting of a Gaussian profile or rectangular pulse are performed. And the performance of the schemes in short, intermediate, and long waves is evaluated. Moreover, numerical results between the nodal discontinuous Galerkin method and finite difference type schemes are compared, which indicate that the numerical solution obtained using nodal discontinuous Galerkin method with a pure central flux has obviously high frequency oscillations for initial disturbance consisting of a rectangular pulse, which is the same as those obtained using finite difference type schemes without artificial selective damping. When an upwind flux is adopted, spurious waves are eliminated effectively except for the location of discontinuities. When a limiter is used, the spurious short waves are almost completely removed. Therefore, the quality of the computed solution has improved.
A nodal discontinuous Galerkin formulation based on Lagrange polynomials basis is used to simulate the acoustic wave propagation. Its dispersion and dissipation properties for the advection equation are investigated by utilizing an eigenvalue analysis. Two test problems of wave propagation with initial disturbance consisting of a Gaussian profile or rectangular pulse are performed. And the performance of the schemes in short, intermediate, and long waves is evaluated. Moreover, numerical results between the nodal discontinuous Galerkin method and finite difference type schemes are compared, which indicate that the numerical solution obtained using nodal discontinuous Galerkin method with a pure central flux has obviously high frequency oscillations for initial disturbance consisting of a rectangular pulse, which is the same as those obtained using finite difference type schemes without artificial selective damping. When an upwind flux is adopted, spurious waves are eliminated effectively except for the location of discontinuities. When a limiter is used, the spurious short waves are almost completely removed. Therefore, the quality of the computed solution has improved.
2014, 31(3):303-307.
Abstract:
Aiming at the large cost of calculating variable bandwidth kernel particle filter and the high complexity of its algorithm, a self-adjusting kernel function particle filter is presented. Kernel density estimation is facilitated to iterate and obtain new particle set. And the standard deviation of particle is introduced in the kernel bandwidth. According to the characteristics of particle distribution, the bandwidth is dynamically adjusted, and the particle distribution can thus be more close to the posterior probability density model of the system. Meanwhile, the kernel density is used to estimate the weight of updating particle and the system state. The simulation results show the feasibility and effectiveness of the proposed algorithm.
Aiming at the large cost of calculating variable bandwidth kernel particle filter and the high complexity of its algorithm, a self-adjusting kernel function particle filter is presented. Kernel density estimation is facilitated to iterate and obtain new particle set. And the standard deviation of particle is introduced in the kernel bandwidth. According to the characteristics of particle distribution, the bandwidth is dynamically adjusted, and the particle distribution can thus be more close to the posterior probability density model of the system. Meanwhile, the kernel density is used to estimate the weight of updating particle and the system state. The simulation results show the feasibility and effectiveness of the proposed algorithm.
2014, 31(3):308-313.
Abstract:
An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple spark camera to understand the flame instability of the deformation process. Methane and oxygen are mixed stoichiometrically to be used in the experiment. Based on Navier-Strokes equations, two-dimensional axisymmetric elementary reactions are numerically simulated. And the simulation results are solved by optical calculation. Shaded pictures by simulation fit well with experimental photos. Focusing reflecton shock waves can affect the flame, which accelerates the deformation of flame and renders violent burning in high-energy flammable gases behind waves. Therefore anticlockwise whirlpool appears. It clusters around the external surface of flame and has a tendency to develop toward the right. Finally, the whirlpool focuses on the right side of the flame, which involves the fresh unfired gases into the whirlpool circle, and consequently the head of mushroom cloud is formed. Meanwhile, when shock wave passes through the flame, the intensity of the shock waves on the axis is strengthened.
An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple spark camera to understand the flame instability of the deformation process. Methane and oxygen are mixed stoichiometrically to be used in the experiment. Based on Navier-Strokes equations, two-dimensional axisymmetric elementary reactions are numerically simulated. And the simulation results are solved by optical calculation. Shaded pictures by simulation fit well with experimental photos. Focusing reflecton shock waves can affect the flame, which accelerates the deformation of flame and renders violent burning in high-energy flammable gases behind waves. Therefore anticlockwise whirlpool appears. It clusters around the external surface of flame and has a tendency to develop toward the right. Finally, the whirlpool focuses on the right side of the flame, which involves the fresh unfired gases into the whirlpool circle, and consequently the head of mushroom cloud is formed. Meanwhile, when shock wave passes through the flame, the intensity of the shock waves on the axis is strengthened.
2014, 31(3):314-324.
Abstract:
Part variation characterization is essential to analyze the variation propagation in flexible assemblies. Aiming at two governing types of surface variation, warping and waviness, a comprehensive approach of geometric covariance modeling based on hybrid polynomial approximation and spectrum analysis is proposed, which can formulate the level and the correlation of surface variations accurately. Firstly, the form error data of compliant part is acquired by CMM. Thereafter, a Fourier-Legendre polynomial decomposition is conducted and the error data are approximated by a Legendre polynomial series. The weighting coefficient of each component is decided by least square method for extracting the warping from the surface variation. Consequently, a geometrical covariance expression for warping deformation is established. Secondly, a Fourier-sinusoidal decomposition is utilized to approximate the waviness from the residual error data. The spectrum is analyzed is to identify the frequency and the amplitude of error data. Thus, a geometrical covariance expression for the waviness is deduced. Thirdly, a comprehensive geometric covariance model for surface variation is developed by the combination the Legendre polynomials with the sinusoidal polynomials. Finally, a group of Lshape sheet metals is measured along a specific contour, and the covariance of the profile errors is modeled by the proposed method. Thereafter, the result is compared with the covariance from two other methods and the real data. The result shows that the proposed covariance model can match the real surface error effectively and represents a tighter approximation error compared with the referred methods.
Part variation characterization is essential to analyze the variation propagation in flexible assemblies. Aiming at two governing types of surface variation, warping and waviness, a comprehensive approach of geometric covariance modeling based on hybrid polynomial approximation and spectrum analysis is proposed, which can formulate the level and the correlation of surface variations accurately. Firstly, the form error data of compliant part is acquired by CMM. Thereafter, a Fourier-Legendre polynomial decomposition is conducted and the error data are approximated by a Legendre polynomial series. The weighting coefficient of each component is decided by least square method for extracting the warping from the surface variation. Consequently, a geometrical covariance expression for warping deformation is established. Secondly, a Fourier-sinusoidal decomposition is utilized to approximate the waviness from the residual error data. The spectrum is analyzed is to identify the frequency and the amplitude of error data. Thus, a geometrical covariance expression for the waviness is deduced. Thirdly, a comprehensive geometric covariance model for surface variation is developed by the combination the Legendre polynomials with the sinusoidal polynomials. Finally, a group of Lshape sheet metals is measured along a specific contour, and the covariance of the profile errors is modeled by the proposed method. Thereafter, the result is compared with the covariance from two other methods and the real data. The result shows that the proposed covariance model can match the real surface error effectively and represents a tighter approximation error compared with the referred methods.
2014, 31(3):325-330.
Abstract:
A control system for correction mechanisms through the whole trajectory is proposed based on the principle of one-dimensional trajectory correction projectile. Digital signal processing (DSP) is utilized as the core controller and gobal positioning system (GPS) is used to measure trajectory parameters to meet the requirements of calculating ballistics and system functions. Firstly, the hardware, mainly including communication module, ballistic calculation module, boosting & detonating module and data storage module, is designed. Secondly, the supporting software is developed based on the communication protocols of GPS and the workflow of control system. Finally, the feasibility and the reliability of the control system are verified through dynamic tests in a car and live firing experiments. The system lays a foundation for the research on trajectory correction projectile for the whole trajectory.
A control system for correction mechanisms through the whole trajectory is proposed based on the principle of one-dimensional trajectory correction projectile. Digital signal processing (DSP) is utilized as the core controller and gobal positioning system (GPS) is used to measure trajectory parameters to meet the requirements of calculating ballistics and system functions. Firstly, the hardware, mainly including communication module, ballistic calculation module, boosting & detonating module and data storage module, is designed. Secondly, the supporting software is developed based on the communication protocols of GPS and the workflow of control system. Finally, the feasibility and the reliability of the control system are verified through dynamic tests in a car and live firing experiments. The system lays a foundation for the research on trajectory correction projectile for the whole trajectory.
2014, 31(3):331-337.
Abstract:
It is difficult to achieve accurate acquisition of weak global positioning system(GPS) signals with traditional methods. A weak signal acquisition strategy based on block processing and differentially coherent (BPDC) is put forward after analyzing the advantages and disadvantages of coherent and non-coherent integration algorithms. Code phase parallel search of the pre-coherent integration is conducted by using fast Fourier transform(FFT), and the results are then differential coherent processed and block processed. BPDC method reduces computation cost compared with coherent and non-coherent(CNC) algorithm.The performance of the two algorithms is also compared based on simulated signals. The result shows that the noise suppression effect of BPDC algorithms is superior to that of traditional CNC algorithm, and the superiority of BPDC is more apparent with the reduction of carrier to noise ratio (CNR).In the case that the pre-coherent integration length is 4 ms and CNR is reduced to 28 dB-Hz, CNC algorithm cannot yet acquire signal correctly while BPDC has well acquisition performance. Therefore, for weak GPS signal acquisition, BPDC algorithm can acquire the signal with lower CNR and has better acquisition property.
It is difficult to achieve accurate acquisition of weak global positioning system(GPS) signals with traditional methods. A weak signal acquisition strategy based on block processing and differentially coherent (BPDC) is put forward after analyzing the advantages and disadvantages of coherent and non-coherent integration algorithms. Code phase parallel search of the pre-coherent integration is conducted by using fast Fourier transform(FFT), and the results are then differential coherent processed and block processed. BPDC method reduces computation cost compared with coherent and non-coherent(CNC) algorithm.The performance of the two algorithms is also compared based on simulated signals. The result shows that the noise suppression effect of BPDC algorithms is superior to that of traditional CNC algorithm, and the superiority of BPDC is more apparent with the reduction of carrier to noise ratio (CNR).In the case that the pre-coherent integration length is 4 ms and CNR is reduced to 28 dB-Hz, CNC algorithm cannot yet acquire signal correctly while BPDC has well acquisition performance. Therefore, for weak GPS signal acquisition, BPDC algorithm can acquire the signal with lower CNR and has better acquisition property.
16 Experiment on Adiabatic Film Cooling Effectiveness in Front Zone of Effusion Cooling Configuration
2014, 31(3):338-344.
Abstract:
Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio, multi-hole arrangement mode, hole-to-hole pitch and jet orientation angle on the adiabatic film cooling effectiveness are concentrated on. The results show that the film layer displays an obvious “developing” feature in the front zone of effusion cooling scheme, for either the staggered or inline multi-hole arrangement. The varying gradient of the laterally-averaged adiabatic cooling effectiveness along the streamwise direction is greater for the staggered arrangement than that for the inline arrangement. The holes array arranged in staggered mode with small hole-to-hole pitches is in favor of obtaining developed film coverage layer rapidly.
Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio, multi-hole arrangement mode, hole-to-hole pitch and jet orientation angle on the adiabatic film cooling effectiveness are concentrated on. The results show that the film layer displays an obvious “developing” feature in the front zone of effusion cooling scheme, for either the staggered or inline multi-hole arrangement. The varying gradient of the laterally-averaged adiabatic cooling effectiveness along the streamwise direction is greater for the staggered arrangement than that for the inline arrangement. The holes array arranged in staggered mode with small hole-to-hole pitches is in favor of obtaining developed film coverage layer rapidly.
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