Many methods are proposed to deal with the type synthesis of parallel kinematic mechanisms（PKMs）, but most of them are less intuitive to some extent. Thus, to propose a concise and intuitive type synthesis method fo...Many methods are proposed to deal with the type synthesis of parallel kinematic mechanisms（PKMs）, but most of them are less intuitive to some extent. Thus, to propose a concise and intuitive type synthesis method for engineering application is a very challenging issue, which should be further studied in the field. Grassmann line geometry, which can investigate the dimensions of spatial line-clusters in a concise way, is taken as the mathematic foundation. Atlas method is introduced to visually describe the degrees of freedom（DOFs） and constraints of a mechanism, and the dual rule is brought in to realize the mutual conversion of the freedom-space and constraint-space. Consequently, a systematic method based on Grassmann line geometry and Atlas method is generated and the entire type synthesis process is presented. Three type 4-DOF PKMs, i.e., 1T3R, 2T2R and 3T1R（T： translational DOF; R： rotational DOF）, are classified according to the different combinations of the translational DOFs and rotational DOFs. The type synthesis of 4-DOF PKMs is carried out and the possible configurations are thoroughly investigated. Some new PKMs with useful functions are generated during this procedure. The type synthesis method based on Grassmann line geometry and Atlas method is intuitive and concise, and can reduce the complexity of the PKMs＇ type synthesis. Moreover, this method can provide theoretical guidance for other PKMs＇ type synthesis and engineering application. A novel type synthesis method is proposed, which solves the existing methods＇ problems in terms of complicated, not intuitive and unsuitable for practical application.展开更多
This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two node...This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two nodes is briefly presented on the basis of the total Lagrangian formulation. The static and dynamic equilibrium equations of mooring lines are established. An incremental-iterative method is used to determine the initial static equilibrium state of cable systems under the action of self weights, buoyancy and current. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method, and examine the effect of various parameters.展开更多
In this paper, a new class of three term memory gradient method with non-monotone line search technique for unconstrained optimization is presented. Global convergence properties of the new methods are discussed. Comb...In this paper, a new class of three term memory gradient method with non-monotone line search technique for unconstrained optimization is presented. Global convergence properties of the new methods are discussed. Combining the quasi-Newton method with the new method, the former is modified to have global convergence property. Numerical results show that the new algorithm is efficient.展开更多
Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on phy...Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimiza-tion procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncer-tainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters.展开更多
In this study, the method of lines (MOLs) with higher order central difference approximation method coupled with the classical fourth order Runge-Kutta (RK(4,4)) method is used in solving shallow water equations (SWEs...In this study, the method of lines (MOLs) with higher order central difference approximation method coupled with the classical fourth order Runge-Kutta (RK(4,4)) method is used in solving shallow water equations (SWEs) in Cartesian coordinates to foresee water levels associated with a storm accurately along the coast of Bangladesh. In doing so, the partial derivatives of the SWEs with respect to the space variables were discretized with 5-point central difference, as a test case, to obtain a system of ordinary differential equations with time as an independent variable for every spatial grid point, which with initial conditions were solved by the RK(4,4) method. The complex land-sea interface and bottom topographic details were incorporated closely using nested schemes. The coastal and island boundaries were rectangularized through proper stair step representation, and the storing positions of the scalar and momentum variables were specified according to the rules of structured C-grid. A stable tidal regime was made over the model domain considering the effect of the major tidal constituent, M2 along the southern open boundary of the outermost parent scheme. The Meghna River fresh water discharge was taken into account for the inner most child scheme. To take into account the dynamic interaction of tide and surge, the generated tidal regime was introduced as the initial state of the sea, and the surge was then made to come over it through computer simulation. Numerical experiments were performed with the cyclone April 1991 to simulate water levels due to tide, surge, and their interaction at different stations along the coast of Bangladesh. Our computed results were found to compare reasonable well with the limited observed data obtained from Bangladesh Inland Water Transport Authority (BIWTA) and were found to be better in comparison with the results obtained through the regular finite difference method and the 3-point central difference MOLs coupled with the RK(4,4) method with regard to the root mean square error values.展开更多
In this paper a meshless method of lines is proposed for the numerical solution of time-dependent nonlinear coupled partial differential equations. Contrary to mesh oriented methods of lines using the finite-differenc...In this paper a meshless method of lines is proposed for the numerical solution of time-dependent nonlinear coupled partial differential equations. Contrary to mesh oriented methods of lines using the finite-difference and finite element methods to approximate spatial derivatives, this new technique does not require a mesh in the problem domain, and a set of scattered nodes provided by initial data is required for the solution of the problem using some radial basis functions. Accuracy of the method is assessed in terms of the error norms L2, L∞ and the three invariants C1, C2, C3. Numerical experiments are performed to demonstrate the accuracy and easy implementation of this method for the three classes of time-dependent nonlinear coupled partial differential equations.展开更多
The finite element method (FEM) and the boundary element method (BEM) are often adopted. However, they are not convenient to spatially vary thermal properties of functionally graded material (FGM). Therefore, the meth...The finite element method (FEM) and the boundary element method (BEM) are often adopted. However, they are not convenient to spatially vary thermal properties of functionally graded material (FGM). Therefore, the method of lines (MOL) is introduced to solve the temperature field of FGM. The basic idea of the method is to semi-discretize the governing equation into a system of ordinary differential equations (ODEs) defined on discrete lines by means of the finite difference method. The temperature field of FGM can be obtained by solving the ODEs. The functions of thermal properties are directly embodied in these equations and these properties are not discretized in the domain. Thus, difficulty of FEM and BEM is overcome by the method. As a numerical example, the temperature field of a plane problem is analyzed for FGMs through varying thermal conductivity coefficient by the MOL.展开更多
The method of lines is applied to the boundary-value problem for third order partial differential equation. Explicit expression and order of convergence for the approximate solution are obtained.
The three-dimensional finite element method of lines is presented, and the basic processing description of 3D FEMOL in cracking questions is given in detail. Applications to 3D bodies with cracks indicate that good ac...The three-dimensional finite element method of lines is presented, and the basic processing description of 3D FEMOL in cracking questions is given in detail. Applications to 3D bodies with cracks indicate that good accuracy can be obtained with relatively coarse girds. In particular, application to the tension specimen shows very good agreement with the evaluation of stress intensity factors, which is better than the results of other methods. This implies a considerable potential for using this method in the 3D analysis of finite geometry solids and suggests a possible extension of this technique to nonlinear material behavior.展开更多
We investigated exact traveling soliton solutions for the nonlinear electrical transmission line. By applying a concise and straightforward method, the variable-coefficient discrete（G /G）-expansion method, we solve ...We investigated exact traveling soliton solutions for the nonlinear electrical transmission line. By applying a concise and straightforward method, the variable-coefficient discrete（G /G）-expansion method, we solve the nonlinear differential–difference equations associated with the network. We obtain some exact traveling wave solutions which include hyperbolic function solution, trigonometric function solution, rational solutions with arbitrary function, bright as well as dark solutions.展开更多
The Finite Element Method of Lines （FEMOL） is a semi-analytic approach and takes a position between FEM and analytic methods. First, FEMOL in Fracture Mechanics is presented in detail. Then, the method is applied to...The Finite Element Method of Lines （FEMOL） is a semi-analytic approach and takes a position between FEM and analytic methods. First, FEMOL in Fracture Mechanics is presented in detail. Then, the method is applied to a set of examples such as edge-crack plate, the central-crack plate, the plate with cracks emanating from a hole under tensile or under combination loads of tensile and bending. Their dimensionless stress distribution, the stress intensify factor （SIF） and crack opening displacement （COD） are obtained, and comparison with known solutions by other methods are reported. It is found that a good accuracy is achieved by FEMOL. The method is successfully modified to remarkably increase the accuracy and reduce convergence difficulties. So it is a very useful and new tool in studying fracture mechanics problems.展开更多
Nonlinear conjugate gradient methods have played an important role in solving large scale unconstrained optimi-zation problems,it is characterized by the simplicity of their iteration and their low memory requirements...Nonlinear conjugate gradient methods have played an important role in solving large scale unconstrained optimi-zation problems,it is characterized by the simplicity of their iteration and their low memory requirements.It is well-known that the direction generated by a conjugate gradient method may be not a descent direction.In this paper,a new class of nonlinear conjugate gradient method is presented,its search direction is a descent direction for the objective function.If the objective function is differentiable and its gradient is Lipschitz continuous,the line sbarch satisfies strong Wolfe condition,the global convergence result is established.展开更多
We present a time domain hybrid method to realize the fast coupling analysis of transmission lines excited by space electromagnetic fields, in which parallel finite-difference time-domain (FDTD) method, interpolation ...We present a time domain hybrid method to realize the fast coupling analysis of transmission lines excited by space electromagnetic fields, in which parallel finite-difference time-domain (FDTD) method, interpolation scheme, and Agrawal model-based transmission line (TL) equations are organically integrated together. Specifically, the Agrawal model is employed to establish the TL equations to describe the coupling effects of space electromagnetic fields on transmission lines. Then, the excitation fields functioning as distribution sources in TL equations are calculated by the parallel FDTD method through using the message passing interface (MPI) library scheme and interpolation scheme. Finally, the TL equations are discretized by the central difference scheme of FDTD and assigned to multiple processors to obtain the transient responses on the terminal loads of these lines. The significant feature of the presented method is embodied in its parallel and synchronous calculations of the space electromagnetic fields and transient responses on the lines. Numerical simulations of ambient wave acting on multi-conductor transmission lines (MTLs), which are located on the PEC ground and in the shielded cavity respectively, are implemented to verify the accuracy and efficiency of the presented method.展开更多
The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(F...The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes.Over a ten-second period,the phases shift by 18°while the amplitudes fluctuate by 6 mK.Thus,we developed the fast Fourier transform(FFT)filter method to eliminate these standing waves for every individual spectrum.The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate.Compared to other methods such as sine fitting and running median,the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%.Additionally,the FFT filter method avoids the flux loss issue encountered with some other methods.The FFT is also efficient in detecting harmonic radio frequency interference(RFI).In the FAST data,we identified three distinct types of harmonic RFI,each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1,0.5,and 0.37 MHz,respectively.The FFT filter,proven as the most effective method,is integrated into the H I data calibration and imaging pipeline for FAST(HiFAST,https://hifast.readthedocs.io).展开更多
Transient simulation are more economical and adaptable means of studying lightning overvoltage for overhead distribution line system compared to experiments.A hybrid multi-transmission-line(MTL)-partial element equiva...Transient simulation are more economical and adaptable means of studying lightning overvoltage for overhead distribution line system compared to experiments.A hybrid multi-transmission-line(MTL)-partial element equivalent circuit(PEEC)method proposed for lightning-induced electromagnetic pulse(LEMP)simulation is verified using the rocket-triggered experimental results under a more complex line configuration for the first time.This method can improve computational efficiency while ensuring calculation accuracy.The agreement between experimental and simulation results further validates the adaptability and accuracy of the proposed method,which is adopted to calculate the LEMP on the extended double-circuit parallel unequal length line.The effects of various factors,such as the strike-point location,the amplitude and waveform of the lightning current,the line shape and length on the amplitude of overvoltage and pole flashover along the line are discussed.For double-circuit distribution lines,when lightning strikes the ground in front of centre of circuit I,the three-phase voltage waveforms are similar,all of which are negative or bipolar oscillation waves.The closer the lightning strike point is to the line,the greater the amplitude of the lightning current,and the voltage waveform develops towards a bipolar waveform,but the main peak remains negative.As the amplitude of lightning current increases,the maximum lightning-induced voltage amplitude along the line increases.The LEMP caused by the subsequent return-stroke current is always greater than that caused by the first returnstroke current.When the grounding resistance increases,the maximum voltage peak amplitude along the line remains unchanged.展开更多
One of the evolving hand biometric features considered so far is finger knuckle printing,because of its ability towards unique identification of individuals.Despite many attempts have been made in this area of researc...One of the evolving hand biometric features considered so far is finger knuckle printing,because of its ability towards unique identification of individuals.Despite many attempts have been made in this area of research,the accuracy of the recognition model remains a major issue.To overcome this problem,a novel biometric-based method,named fingerknuckle-print(FKP),has been developed for individual verification.The proposed system carries key steps such as preprocessing,segmentation,feature extraction and classification.Initially input FKP image is fed into the preprocessing stage where colour images are converted to gray scale image for augmenting the system performance.Afterwards,segmentation process is carried out with the help of CROI(Circular Region of Interest)and Morphological operation.Then,feature extraction stage is carried out using Gabor-Derivative line approach for extracting intrinsic features.Finally,DCNN(Deep Convolutional Neural Network)is trained for the processed knuckle images to recognize imposter and genuine individuals.Extensive experiments on standard FKP database demonstrates that the proposed method attains considerable improvement compared with state-of-the-art methods.The overall accuracy attained for the proposed methodology is 95.6%which is achieved better than the existing techniques.展开更多
As the environmental problems become increasingly serious,distributed electrical propulsion systems with higher aerodynamic efficiency and lower pollution emission have received extensive attention in recent years.The...As the environmental problems become increasingly serious,distributed electrical propulsion systems with higher aerodynamic efficiency and lower pollution emission have received extensive attention in recent years.The distributed electrical propulsion usually employs the new aero-propulsion integrated configuration.A simulation strategy for internal and external flow coupling based on the combination of lifting line theory and body force method is proposed.The lifting line theory and body force method as source term are embedded into the Navier-Stokes formulation.The lift and drag characteristics of the aero-propulsion coupling configuration are simulated.The results indicate that the coupling configuration has the most obvious lift augmentation at 12°angle of attack,which can provide an 11.11%increase in lift for the airfoil.At 0°angle of attack,the pressure difference on the lip parts provides the thrust component,which results in a lower drag coefficient.Additionally,the failure impact of a ducted fan at the middle or edge on aerodynamics is investigated.For the two failure conditions,the lift of the coupling configuration is decreased significantly by 27.85%and 26.14%respectively,and the lip thrust is decreased by 70.74%and 56.48%respectively.展开更多
基金supported by National Natural Science Foundation of China(Grant No.51135008)National Basic Research Program of China(973 Program,Grant No.2013CB035400)China Postdoctoral Science Foundation(Grant Nos.2012M520256,2013T60107)
文摘Many methods are proposed to deal with the type synthesis of parallel kinematic mechanisms（PKMs）, but most of them are less intuitive to some extent. Thus, to propose a concise and intuitive type synthesis method for engineering application is a very challenging issue, which should be further studied in the field. Grassmann line geometry, which can investigate the dimensions of spatial line-clusters in a concise way, is taken as the mathematic foundation. Atlas method is introduced to visually describe the degrees of freedom（DOFs） and constraints of a mechanism, and the dual rule is brought in to realize the mutual conversion of the freedom-space and constraint-space. Consequently, a systematic method based on Grassmann line geometry and Atlas method is generated and the entire type synthesis process is presented. Three type 4-DOF PKMs, i.e., 1T3R, 2T2R and 3T1R（T： translational DOF; R： rotational DOF）, are classified according to the different combinations of the translational DOFs and rotational DOFs. The type synthesis of 4-DOF PKMs is carried out and the possible configurations are thoroughly investigated. Some new PKMs with useful functions are generated during this procedure. The type synthesis method based on Grassmann line geometry and Atlas method is intuitive and concise, and can reduce the complexity of the PKMs＇ type synthesis. Moreover, this method can provide theoretical guidance for other PKMs＇ type synthesis and engineering application. A novel type synthesis method is proposed, which solves the existing methods＇ problems in terms of complicated, not intuitive and unsuitable for practical application.
基金supported by the National Natural Science Foundation of China (Grant No.11072052)the National High Technology Research and Development Program of China (863 Program,Grant No.2006AA09A109-3)
文摘This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two nodes is briefly presented on the basis of the total Lagrangian formulation. The static and dynamic equilibrium equations of mooring lines are established. An incremental-iterative method is used to determine the initial static equilibrium state of cable systems under the action of self weights, buoyancy and current. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method, and examine the effect of various parameters.
文摘In this paper, a new class of three term memory gradient method with non-monotone line search technique for unconstrained optimization is presented. Global convergence properties of the new methods are discussed. Combining the quasi-Newton method with the new method, the former is modified to have global convergence property. Numerical results show that the new algorithm is efficient.
基金support of the János Bolyai Research Fellowship of the Hungarian Academy of Sciences. T.U. is grateful for partial funding of this work by an EPSRC Leadership Fellowship [EP/I005420/1, EP/K039237/1, EP/K034650/1, EP/L018616/1 and EP/K034332/1] for the study of irradiation damage in zirconium alloys
文摘Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimiza-tion procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncer-tainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters.
文摘In this study, the method of lines (MOLs) with higher order central difference approximation method coupled with the classical fourth order Runge-Kutta (RK(4,4)) method is used in solving shallow water equations (SWEs) in Cartesian coordinates to foresee water levels associated with a storm accurately along the coast of Bangladesh. In doing so, the partial derivatives of the SWEs with respect to the space variables were discretized with 5-point central difference, as a test case, to obtain a system of ordinary differential equations with time as an independent variable for every spatial grid point, which with initial conditions were solved by the RK(4,4) method. The complex land-sea interface and bottom topographic details were incorporated closely using nested schemes. The coastal and island boundaries were rectangularized through proper stair step representation, and the storing positions of the scalar and momentum variables were specified according to the rules of structured C-grid. A stable tidal regime was made over the model domain considering the effect of the major tidal constituent, M2 along the southern open boundary of the outermost parent scheme. The Meghna River fresh water discharge was taken into account for the inner most child scheme. To take into account the dynamic interaction of tide and surge, the generated tidal regime was introduced as the initial state of the sea, and the surge was then made to come over it through computer simulation. Numerical experiments were performed with the cyclone April 1991 to simulate water levels due to tide, surge, and their interaction at different stations along the coast of Bangladesh. Our computed results were found to compare reasonable well with the limited observed data obtained from Bangladesh Inland Water Transport Authority (BIWTA) and were found to be better in comparison with the results obtained through the regular finite difference method and the 3-point central difference MOLs coupled with the RK(4,4) method with regard to the root mean square error values.
文摘In this paper a meshless method of lines is proposed for the numerical solution of time-dependent nonlinear coupled partial differential equations. Contrary to mesh oriented methods of lines using the finite-difference and finite element methods to approximate spatial derivatives, this new technique does not require a mesh in the problem domain, and a set of scattered nodes provided by initial data is required for the solution of the problem using some radial basis functions. Accuracy of the method is assessed in terms of the error norms L2, L∞ and the three invariants C1, C2, C3. Numerical experiments are performed to demonstrate the accuracy and easy implementation of this method for the three classes of time-dependent nonlinear coupled partial differential equations.
文摘The finite element method (FEM) and the boundary element method (BEM) are often adopted. However, they are not convenient to spatially vary thermal properties of functionally graded material (FGM). Therefore, the method of lines (MOL) is introduced to solve the temperature field of FGM. The basic idea of the method is to semi-discretize the governing equation into a system of ordinary differential equations (ODEs) defined on discrete lines by means of the finite difference method. The temperature field of FGM can be obtained by solving the ODEs. The functions of thermal properties are directly embodied in these equations and these properties are not discretized in the domain. Thus, difficulty of FEM and BEM is overcome by the method. As a numerical example, the temperature field of a plane problem is analyzed for FGMs through varying thermal conductivity coefficient by the MOL.
文摘The method of lines is applied to the boundary-value problem for third order partial differential equation. Explicit expression and order of convergence for the approximate solution are obtained.
文摘The three-dimensional finite element method of lines is presented, and the basic processing description of 3D FEMOL in cracking questions is given in detail. Applications to 3D bodies with cracks indicate that good accuracy can be obtained with relatively coarse girds. In particular, application to the tension specimen shows very good agreement with the evaluation of stress intensity factors, which is better than the results of other methods. This implies a considerable potential for using this method in the 3D analysis of finite geometry solids and suggests a possible extension of this technique to nonlinear material behavior.
基金supported by the Scientific Commission/ENS/University of Maroua 2013AM is grateful to the Abdus Salam International Center for Theoretical Physics(ICTP),Trieste,Italy through the Associate Program for financial support
文摘We investigated exact traveling soliton solutions for the nonlinear electrical transmission line. By applying a concise and straightforward method, the variable-coefficient discrete（G /G）-expansion method, we solve the nonlinear differential–difference equations associated with the network. We obtain some exact traveling wave solutions which include hyperbolic function solution, trigonometric function solution, rational solutions with arbitrary function, bright as well as dark solutions.
文摘The Finite Element Method of Lines （FEMOL） is a semi-analytic approach and takes a position between FEM and analytic methods. First, FEMOL in Fracture Mechanics is presented in detail. Then, the method is applied to a set of examples such as edge-crack plate, the central-crack plate, the plate with cracks emanating from a hole under tensile or under combination loads of tensile and bending. Their dimensionless stress distribution, the stress intensify factor （SIF） and crack opening displacement （COD） are obtained, and comparison with known solutions by other methods are reported. It is found that a good accuracy is achieved by FEMOL. The method is successfully modified to remarkably increase the accuracy and reduce convergence difficulties. So it is a very useful and new tool in studying fracture mechanics problems.
文摘Nonlinear conjugate gradient methods have played an important role in solving large scale unconstrained optimi-zation problems,it is characterized by the simplicity of their iteration and their low memory requirements.It is well-known that the direction generated by a conjugate gradient method may be not a descent direction.In this paper,a new class of nonlinear conjugate gradient method is presented,its search direction is a descent direction for the objective function.If the objective function is differentiable and its gradient is Lipschitz continuous,the line sbarch satisfies strong Wolfe condition,the global convergence result is established.
基金Project supported by the National Natural Science Foundation of China(Grant No.61701057)the Chongqing Research Program of Basic Research and Frontier Technology,China(Grant No.cstc2017jcyjAX0345).
文摘We present a time domain hybrid method to realize the fast coupling analysis of transmission lines excited by space electromagnetic fields, in which parallel finite-difference time-domain (FDTD) method, interpolation scheme, and Agrawal model-based transmission line (TL) equations are organically integrated together. Specifically, the Agrawal model is employed to establish the TL equations to describe the coupling effects of space electromagnetic fields on transmission lines. Then, the excitation fields functioning as distribution sources in TL equations are calculated by the parallel FDTD method through using the message passing interface (MPI) library scheme and interpolation scheme. Finally, the TL equations are discretized by the central difference scheme of FDTD and assigned to multiple processors to obtain the transient responses on the terminal loads of these lines. The significant feature of the presented method is embodied in its parallel and synchronous calculations of the space electromagnetic fields and transient responses on the lines. Numerical simulations of ambient wave acting on multi-conductor transmission lines (MTLs), which are located on the PEC ground and in the shielded cavity respectively, are implemented to verify the accuracy and efficiency of the presented method.
基金supported by the China National Key Program for Science and Technology Research and Development of China (2022YFA1602901,2023YFA1608204)the National SKA Program of China (No.2022SKA0110201)+5 种基金the National Natural Science Foundation of China (NSFC,grant Nos.11873051,11988101,12033008,12041305,12125302,12173016,and 12203065)the CAS Project for Young Scientists in Basic Research grant (No.YSBR-062)the K.C.Wong Education Foundationthe science research grants from the China Manned Space Projectsupport from the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the China Postdoctoral Science Foundation grant No.2024M763213
文摘The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes.Over a ten-second period,the phases shift by 18°while the amplitudes fluctuate by 6 mK.Thus,we developed the fast Fourier transform(FFT)filter method to eliminate these standing waves for every individual spectrum.The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate.Compared to other methods such as sine fitting and running median,the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%.Additionally,the FFT filter method avoids the flux loss issue encountered with some other methods.The FFT is also efficient in detecting harmonic radio frequency interference(RFI).In the FAST data,we identified three distinct types of harmonic RFI,each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1,0.5,and 0.37 MHz,respectively.The FFT filter,proven as the most effective method,is integrated into the H I data calibration and imaging pipeline for FAST(HiFAST,https://hifast.readthedocs.io).
基金supported by National Natural Science Foundation of China(No.52507193).
文摘Transient simulation are more economical and adaptable means of studying lightning overvoltage for overhead distribution line system compared to experiments.A hybrid multi-transmission-line(MTL)-partial element equivalent circuit(PEEC)method proposed for lightning-induced electromagnetic pulse(LEMP)simulation is verified using the rocket-triggered experimental results under a more complex line configuration for the first time.This method can improve computational efficiency while ensuring calculation accuracy.The agreement between experimental and simulation results further validates the adaptability and accuracy of the proposed method,which is adopted to calculate the LEMP on the extended double-circuit parallel unequal length line.The effects of various factors,such as the strike-point location,the amplitude and waveform of the lightning current,the line shape and length on the amplitude of overvoltage and pole flashover along the line are discussed.For double-circuit distribution lines,when lightning strikes the ground in front of centre of circuit I,the three-phase voltage waveforms are similar,all of which are negative or bipolar oscillation waves.The closer the lightning strike point is to the line,the greater the amplitude of the lightning current,and the voltage waveform develops towards a bipolar waveform,but the main peak remains negative.As the amplitude of lightning current increases,the maximum lightning-induced voltage amplitude along the line increases.The LEMP caused by the subsequent return-stroke current is always greater than that caused by the first returnstroke current.When the grounding resistance increases,the maximum voltage peak amplitude along the line remains unchanged.
基金RUSA PHASE 2.0, University of Alagappa, Karaikudi has supported this research projectThe UGC-NFSC fellowship has helped support this research
文摘One of the evolving hand biometric features considered so far is finger knuckle printing,because of its ability towards unique identification of individuals.Despite many attempts have been made in this area of research,the accuracy of the recognition model remains a major issue.To overcome this problem,a novel biometric-based method,named fingerknuckle-print(FKP),has been developed for individual verification.The proposed system carries key steps such as preprocessing,segmentation,feature extraction and classification.Initially input FKP image is fed into the preprocessing stage where colour images are converted to gray scale image for augmenting the system performance.Afterwards,segmentation process is carried out with the help of CROI(Circular Region of Interest)and Morphological operation.Then,feature extraction stage is carried out using Gabor-Derivative line approach for extracting intrinsic features.Finally,DCNN(Deep Convolutional Neural Network)is trained for the processed knuckle images to recognize imposter and genuine individuals.Extensive experiments on standard FKP database demonstrates that the proposed method attains considerable improvement compared with state-of-the-art methods.The overall accuracy attained for the proposed methodology is 95.6%which is achieved better than the existing techniques.
基金the funding support from the Taihang Laboratory,China(No.D2024-1-0201).
文摘As the environmental problems become increasingly serious,distributed electrical propulsion systems with higher aerodynamic efficiency and lower pollution emission have received extensive attention in recent years.The distributed electrical propulsion usually employs the new aero-propulsion integrated configuration.A simulation strategy for internal and external flow coupling based on the combination of lifting line theory and body force method is proposed.The lifting line theory and body force method as source term are embedded into the Navier-Stokes formulation.The lift and drag characteristics of the aero-propulsion coupling configuration are simulated.The results indicate that the coupling configuration has the most obvious lift augmentation at 12°angle of attack,which can provide an 11.11%increase in lift for the airfoil.At 0°angle of attack,the pressure difference on the lip parts provides the thrust component,which results in a lower drag coefficient.Additionally,the failure impact of a ducted fan at the middle or edge on aerodynamics is investigated.For the two failure conditions,the lift of the coupling configuration is decreased significantly by 27.85%and 26.14%respectively,and the lip thrust is decreased by 70.74%and 56.48%respectively.
