This paper analyzes the eddy currents and the electro-magnetic forces on the lower hybrid wave (LHW) launching antenna on the superconducting Tohamak HT-7 by using a finite element circult method. A new iterative algo...This paper analyzes the eddy currents and the electro-magnetic forces on the lower hybrid wave (LHW) launching antenna on the superconducting Tohamak HT-7 by using a finite element circult method. A new iterative algorithm is developed to analyze the coupled magnetic fields Which are very difficult to be calculated. The method and results obtained are helpful to study the eddy currents and electro-magnetic forces on metal plates which are placed in a rather complicated electro-magnetic environment.展开更多
A driver-pickup probe possesses better sensitivity and flexibility due to individual optimization of a coil.It is fre-quently observed in an eddy current(EC)array probe.In this work,a tilted non-coaxial driver-pickup ...A driver-pickup probe possesses better sensitivity and flexibility due to individual optimization of a coil.It is fre-quently observed in an eddy current(EC)array probe.In this work,a tilted non-coaxial driver-pickup probe above a multilayered conducting plate is analytically modeled with spatial transformation for eddy current nondestructive evalua-tion.Basically,the core of the formulation is to obtain the projection of magnetic vector potential(MVP)from the driver coil onto the vector along the tilted pickup coil,which is divided into two key steps.The first step is to make a projection of MVP along the pickup coil onto a horizontal plane,and the second one is to build the relationship between the pr,ojected MVP and the MVP along the driver coil.Afterwards,an analytical model for the case of a layered plate is established with the reflection and transmission theory of electromagnetic fields.The calculated values from the resulting model indicate good agreement with those from the finite element model(FEM)and experiments,which validates the developed analytical model.展开更多
To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy curre...To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.展开更多
The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing. In this paper, we propose a figure-8-shaped coil being compos...The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing. In this paper, we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils, which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils. Pulsed current is usually the excitation source in the functional magnetic stimulation, so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation, the Laplace transform and the Fourier transform are used in our derivation. Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows： 1） the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil; 2） the greater the scale factor of ellipse is, the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is; 3） the maximum magnitude of eddy current density increases with the increase of spread angle. When spread angle is 180°, there are two additional reverse concentrative areas on both sides of x axis.展开更多
Influence of eddy current on transient characteristics of common rail injector solenoid valve was studied in this paper. Experimental investigations of drive current and power source volt- age of both drive current as...Influence of eddy current on transient characteristics of common rail injector solenoid valve was studied in this paper. Experimental investigations of drive current and power source volt- age of both drive current ascending and descending process were conducted on a common rail injec- tor solenoid valve. A new discretizing calculation method of solenoid valve flux linkage was put for- ward for the first time based on the experimental results and drive circuit principle, and flux linkage of both drive current ascending and descending process were evaluated. New inductance calculation methods for drive current ascending and descending process respectively were also presented. Influ- ence of parasitic inductance was evaluated. Results indicate that the air gap, under which the transi- ent flux linkage of the solenoid valve is the biggest, varies with drive current due to eddy current. Flux linkage of drive current descending process is bigger than that of drive current ascending process under the same drive current and the same air gap width. Eddy current can reduce the delay between the time that drive current begins to descend and the time that armature begins to move downward. Inductance of drive current descending process is bigger than that of drive current as- cending process over larger scope of drive current, but the difference becomes smaller with the in- creasing of air gap width. The differences of both flux linkage and inductance between drive current ascending and descending process are caused by the eddy current in core and armature materials.展开更多
This paper focuses on a numerical simulation of the arc plasma behavior in the arc splitting process, considering the eddy currents in the electrodes and the splitter plate. Based on three-dimensional （3D） magneto-h...This paper focuses on a numerical simulation of the arc plasma behavior in the arc splitting process, considering the eddy currents in the electrodes and the splitter plate. Based on three-dimensional （3D） magneto-hydrodynamic （MHD） theory, a thin layer of nonlinear electrical resistance elements is used in the model to represent the voltage drop of plasma sheath and the formation of new arc root in order to include the arc splitting process in the simulation. In the arcing process, eddy currents in metal parts are generated by a time-varying magnetic field. The arc model is calculated with the time-varying magnetic field term, so that the eddy current effects can be considered. The effect of nonlinear permeability of a ferromagnetic material is also involved in the calculation. Using the simulation results for the temperature, velocity and current density distribution, the arc splitting process is analyzed in detail. The calculated results are compared with the simulation neglecting eddy currents.展开更多
This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced...This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced. In this method, the nonlinear model parameters of the numeral eddy current sensor are optimized by genetic neural network （GNN） according to measurement data. So the method remains both the global searching ability of genetic algorithm and the good local searching ability of neural network. The nonlinear model has the advantages of strong robustness, on-line modelling and high precision. The maximum nonlinearity error can be reduced to 0.037% by using GNN. However, the maximum nonlinearity error is 0.075% using the least square method.展开更多
The eddy current pulsed thermography(ECPT)technique is a research focus in the non-destructive testing(NDT)area for defect inspection.Defect feature extraction for defect information analysis in ECPT is limited by ima...The eddy current pulsed thermography(ECPT)technique is a research focus in the non-destructive testing(NDT)area for defect inspection.Defect feature extraction for defect information analysis in ECPT is limited by image contrast,heat diffusion,background interference,etc.In this paper,a defect feature extraction approach in ECPT has been proposed to improve the quality of defect features,which is based on image partition,local sparse component evaluation,and feature fusion.This method can extract complete defect features by enhancing the defect area and removing background interference,such as noises and heating coil.Two typical steel specimens are utilized to testify the validity of the proposed approach.Compared with other three common feature extraction algorithms in ECPT,the proposed method can reserve more complete defect features and suppress more background interference.展开更多
Crack monitoring at the bolt hole edge is one of the important focuses of aircraft structural health monitoring.In this study,a novel eddy current sensing film based on a parallelogram coil array is developed to quant...Crack monitoring at the bolt hole edge is one of the important focuses of aircraft structural health monitoring.In this study,a novel eddy current sensing film based on a parallelogram coil array is developed to quantitatively monitor the crack characteristics near the bolt hole with fewer layers and coils,compared with the existing methods.The parallelogram coil array configuration is designed and optimized to improve the quantitative monitoring ability of the crack.A 3×3 parallelogram coil array is used to quantify the crack parameters of aluminum bolted joints.Finite element simulation and experiments show that the proposed parallelogram coil array could not only accurately and quantitatively identify the crack angle at the edge of the bolt hole,but also track the crack length along the radial direction of the bolt hole and the depth along the axial direction.展开更多
A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especia...A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a 3D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.展开更多
This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems...This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems, the proposed system employs a fixed position excitation coil while enabling the detection point to move within the detection region. This configuration effectively mitigates the interference caused by the lift-off effect, which is commonly observed in systems with moving excitation coils. Correspondingly, the relationship between the defect characteristics (orientation and position) and the surface vertical magnetic field distribution (amplitude and phase) is studied in detail by theoretical analysis and numerical simulations. Experiments conducted on woven CFRP plates demonstrate that the designed PI-ECMO system is capable of effectively detecting both surface and internal cracks, as well as impact defects. The excitation current is significantly reduced compared with traditional eddy current magneto-optical (ECMO) systems.展开更多
Due to the electrical anisotropy of carbon fiber reinforced polymer(CFRP),this paper presents a method to inverse the anisotropic conductivity of unidirectional CFRP laminate using eddy current testing(ECT). The relat...Due to the electrical anisotropy of carbon fiber reinforced polymer(CFRP),this paper presents a method to inverse the anisotropic conductivity of unidirectional CFRP laminate using eddy current testing(ECT). The relationship between the conductivity and probe signal of ECT is studied by means of numerical simulation. Finally,the accuracy of inversion result is improved by optimizing the initial conductivity by use of experimental data.展开更多
The paper is mainly concerned with the penalty incurred in finite element analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node qua...The paper is mainly concerned with the penalty incurred in finite element analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node quadrilateral isoparametric elements is formulated for the present problem. Unlike the conventional vector potential scheme in use for electromagnetic field problem, the present work features a direct computational approach to eddy current loss. Simplicity and remarkable enhancement in computational accuracy can be obtained with the proposed method.展开更多
To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic array...To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic arrays,four stators and displacement sensors.The dynamics model of this stage was a complex nonlinear,strong coupling system which made the control strategy to be a focus research.The nonlinear controller of the system was proposed based on the theory of differential geometry.Both simulation and experimental results show that either the decoupling control of the movement can be realized in horizontal and vertical directions,and the control performance was improved by the damper,verifying the validity and efficiency of this method.展开更多
The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the...The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.展开更多
The insulation aging of cross-linked polyethylene(XLPE)cables is the main reason for the reduction in cable life.There is currently a lack of rapid and effective methods for detecting cable insulation defects in power...The insulation aging of cross-linked polyethylene(XLPE)cables is the main reason for the reduction in cable life.There is currently a lack of rapid and effective methods for detecting cable insulation defects in power-related sectors.To this end,this paper presents a method for identifying insulation defects in XLPE cables based on deep learning algorithms.First,the principle of the harmonic method for detecting cable insulation defects is introduced.Second,the ANSYS software is used to simulate the cable insulation layer containing bubbles,protrusions,and water tree defects,and the effects of each type of defect on the magnetic field strength and eddy loss current of the cable insulation layer are analyzed.Then,a total of 10 characteristic quantities of the total harmonic content and 2nd to 10th harmonic currents are constructed to establish a database of cable insulation defects.Finally,the deep learning algorithm,long short-term memory(LSTM),is used to accurately identify the types of insulation defects in cables.The results indicate that the LSTM algorithm can effectively diagnose and identify insulation defects in cables with an accuracy of 95.83%.展开更多
According to the B-H curve and structural dimensions of the snubber by the Fink- Baker Method, the inductive voltage and the eddy current of any core tape with the thickness of the saturated regions are derived when t...According to the B-H curve and structural dimensions of the snubber by the Fink- Baker Method, the inductive voltage and the eddy current of any core tape with the thickness of the saturated regions are derived when the accelerator breakdown occurs. Using the Ampere＇s law, in each core tape, the eddy current of the core lamination is equal to the arc current, and the relation of the thickness of the saturated regions for different laminations can be deduced. The total equivalent resistance of the snubber can be obtained. The transient eddy current model based on the stray capacitance and the equivalent resistance is analyzed, and the solving process is given in detail. The exponential time constant and the arc current are obtained. Then, the maximum width of the lamination and the minimum thickness of the core tape are determined. The experimental time constant of the eddy current obtained, with or without the bias current, is approximately the same as that by the analytical method, which proves the accuracy of the adopted assumptions and the analysis method.展开更多
The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well...The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.展开更多
A preliminary analysis of plasma current quenching is presented in this paper based on the disruption database.It demonstrates that 26.8%of discharges have been disrupted in the last 2012 campaign,in addition,the plas...A preliminary analysis of plasma current quenching is presented in this paper based on the disruption database.It demonstrates that 26.8%of discharges have been disrupted in the last 2012 campaign,in addition,the plasma disruptive rate grows with the increase of plasma current.The best-fit linear and instantaneous plasma current quench rate is extracted from the recent EAST disruptions,showing that an 80%-30%interval of the maximum plasma current is well fit for the EAST device.The lowest area-normalized current quench time is 3.33 ms/m;with the estimated plasma electron temperature being 7.3 eV;9.5 eV.In the disruption case the maximum eddy current goes up to 400 kA,and a fraction of currents are respectively driven on the upper and lower outer plate with nearly 100 MPa-200 MPa stress in the leg.展开更多
Analysis of the electromagneto-mechanical coupling effect contributes greatly to the high accuracy estimation of the EM load of many EM devices, such as a tokamak structure during plasma disruption. This paper present...Analysis of the electromagneto-mechanical coupling effect contributes greatly to the high accuracy estimation of the EM load of many EM devices, such as a tokamak structure during plasma disruption. This paper presents a method for the numerical analysis of the electromagnetomechanical coupling effect on the basis of Maxwell＇s equations in the Lagrangian description and staggered load transfer scheme, which can treat the coupled behaviors of magnetic damping and magnetic stiffness effects at the same time. Codes were developed based on the ANSYS development platform and were applied to solve two typical numerical examples： the TEAM Problem 16 and dynamic behavior analysis of a shallow arch under electromagnetic force. The good consistency of numerical results and experimental data demonstrates the validity and accuracy of the proposed method and the related numerical codes.展开更多
文摘This paper analyzes the eddy currents and the electro-magnetic forces on the lower hybrid wave (LHW) launching antenna on the superconducting Tohamak HT-7 by using a finite element circult method. A new iterative algorithm is developed to analyze the coupled magnetic fields Which are very difficult to be calculated. The method and results obtained are helpful to study the eddy currents and electro-magnetic forces on metal plates which are placed in a rather complicated electro-magnetic environment.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61701500,51677187,and 51465024)
文摘A driver-pickup probe possesses better sensitivity and flexibility due to individual optimization of a coil.It is fre-quently observed in an eddy current(EC)array probe.In this work,a tilted non-coaxial driver-pickup probe above a multilayered conducting plate is analytically modeled with spatial transformation for eddy current nondestructive evalua-tion.Basically,the core of the formulation is to obtain the projection of magnetic vector potential(MVP)from the driver coil onto the vector along the tilted pickup coil,which is divided into two key steps.The first step is to make a projection of MVP along the pickup coil onto a horizontal plane,and the second one is to build the relationship between the pr,ojected MVP and the MVP along the driver coil.Afterwards,an analytical model for the case of a layered plate is established with the reflection and transmission theory of electromagnetic fields.The calculated values from the resulting model indicate good agreement with those from the finite element model(FEM)and experiments,which validates the developed analytical model.
基金supported by the National Defense Basic Technology Research Program of China(Grant No.Z132013T001)
文摘To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50807001)
文摘The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing. In this paper, we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils, which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils. Pulsed current is usually the excitation source in the functional magnetic stimulation, so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation, the Laplace transform and the Fourier transform are used in our derivation. Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows： 1） the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil; 2） the greater the scale factor of ellipse is, the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is; 3） the maximum magnitude of eddy current density increases with the increase of spread angle. When spread angle is 180°, there are two additional reverse concentrative areas on both sides of x axis.
基金Supported by the National Natural Science Foundation of China(51076014)the Research Fund for the Doctoral Program of Higher Education(20101101110011)
文摘Influence of eddy current on transient characteristics of common rail injector solenoid valve was studied in this paper. Experimental investigations of drive current and power source volt- age of both drive current ascending and descending process were conducted on a common rail injec- tor solenoid valve. A new discretizing calculation method of solenoid valve flux linkage was put for- ward for the first time based on the experimental results and drive circuit principle, and flux linkage of both drive current ascending and descending process were evaluated. New inductance calculation methods for drive current ascending and descending process respectively were also presented. Influ- ence of parasitic inductance was evaluated. Results indicate that the air gap, under which the transi- ent flux linkage of the solenoid valve is the biggest, varies with drive current due to eddy current. Flux linkage of drive current descending process is bigger than that of drive current ascending process under the same drive current and the same air gap width. Eddy current can reduce the delay between the time that drive current begins to descend and the time that armature begins to move downward. Inductance of drive current descending process is bigger than that of drive current as- cending process over larger scope of drive current, but the difference becomes smaller with the in- creasing of air gap width. The differences of both flux linkage and inductance between drive current ascending and descending process are caused by the eddy current in core and armature materials.
基金supported by National Natural Science Foundation of China (Nos.51177124,51007072)the Doctoral Foundation of Ministry of Education of China (Nos.20110201130006,20110201120069)China Postdoctoral Science Foundation (No.2012M512002)
文摘This paper focuses on a numerical simulation of the arc plasma behavior in the arc splitting process, considering the eddy currents in the electrodes and the splitter plate. Based on three-dimensional （3D） magneto-hydrodynamic （MHD） theory, a thin layer of nonlinear electrical resistance elements is used in the model to represent the voltage drop of plasma sheath and the formation of new arc root in order to include the arc splitting process in the simulation. In the arcing process, eddy currents in metal parts are generated by a time-varying magnetic field. The arc model is calculated with the time-varying magnetic field term, so that the eddy current effects can be considered. The effect of nonlinear permeability of a ferromagnetic material is also involved in the calculation. Using the simulation results for the temperature, velocity and current density distribution, the arc splitting process is analyzed in detail. The calculated results are compared with the simulation neglecting eddy currents.
基金Project supported by the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,Chinathe Foundation of Huaiyin Teachers College Professor,China(Grant Nos07KJD510027 and 06HSJS020)
文摘This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced. In this method, the nonlinear model parameters of the numeral eddy current sensor are optimized by genetic neural network （GNN） according to measurement data. So the method remains both the global searching ability of genetic algorithm and the good local searching ability of neural network. The nonlinear model has the advantages of strong robustness, on-line modelling and high precision. The maximum nonlinearity error can be reduced to 0.037% by using GNN. However, the maximum nonlinearity error is 0.075% using the least square method.
基金the National Natural Science Foundation of China under Grants No.51607024 and No.61671109.
文摘The eddy current pulsed thermography(ECPT)technique is a research focus in the non-destructive testing(NDT)area for defect inspection.Defect feature extraction for defect information analysis in ECPT is limited by image contrast,heat diffusion,background interference,etc.In this paper,a defect feature extraction approach in ECPT has been proposed to improve the quality of defect features,which is based on image partition,local sparse component evaluation,and feature fusion.This method can extract complete defect features by enhancing the defect area and removing background interference,such as noises and heating coil.Two typical steel specimens are utilized to testify the validity of the proposed approach.Compared with other three common feature extraction algorithms in ECPT,the proposed method can reserve more complete defect features and suppress more background interference.
基金supported by the Natural Science Foundation of China(No.11902280)Aeronautical Science Fund(No.20200033068001)+1 种基金Innovation Fosundation for Young Scholar of Xiamen(No.3502Z20206042)the Fundamental Research Funds for the Central Universities(No.20720210049)。
文摘Crack monitoring at the bolt hole edge is one of the important focuses of aircraft structural health monitoring.In this study,a novel eddy current sensing film based on a parallelogram coil array is developed to quantitatively monitor the crack characteristics near the bolt hole with fewer layers and coils,compared with the existing methods.The parallelogram coil array configuration is designed and optimized to improve the quantitative monitoring ability of the crack.A 3×3 parallelogram coil array is used to quantify the crack parameters of aluminum bolted joints.Finite element simulation and experiments show that the proposed parallelogram coil array could not only accurately and quantitatively identify the crack angle at the edge of the bolt hole,but also track the crack length along the radial direction of the bolt hole and the depth along the axial direction.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51137004,61427806 and 51577184the Equipment Development Project of Chinese Academy of Sciences under Grant No YZ201507
文摘A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a 3D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.
基金the National Natural Science Foundation of China under Grants No.U2030205,No.62003075,No.61903065,and No.62003074Sichuan Science and Technology Planning Project under Grant No.2022JDJQ0040.
文摘This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems, the proposed system employs a fixed position excitation coil while enabling the detection point to move within the detection region. This configuration effectively mitigates the interference caused by the lift-off effect, which is commonly observed in systems with moving excitation coils. Correspondingly, the relationship between the defect characteristics (orientation and position) and the surface vertical magnetic field distribution (amplitude and phase) is studied in detail by theoretical analysis and numerical simulations. Experiments conducted on woven CFRP plates demonstrate that the designed PI-ECMO system is capable of effectively detecting both surface and internal cracks, as well as impact defects. The excitation current is significantly reduced compared with traditional eddy current magneto-optical (ECMO) systems.
基金supported by the research fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Nanjing University of Aeronautics and astronautics)(No. MCMS-I-0518K01&MCMSI-0519G02)Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the Natural Science Funding (No. 51875277)
文摘Due to the electrical anisotropy of carbon fiber reinforced polymer(CFRP),this paper presents a method to inverse the anisotropic conductivity of unidirectional CFRP laminate using eddy current testing(ECT). The relationship between the conductivity and probe signal of ECT is studied by means of numerical simulation. Finally,the accuracy of inversion result is improved by optimizing the initial conductivity by use of experimental data.
文摘The paper is mainly concerned with the penalty incurred in finite element analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node quadrilateral isoparametric elements is formulated for the present problem. Unlike the conventional vector potential scheme in use for electromagnetic field problem, the present work features a direct computational approach to eddy current loss. Simplicity and remarkable enhancement in computational accuracy can be obtained with the proposed method.
基金Supported by the National Natural Science Foundation of China (60674052)
文摘To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic arrays,four stators and displacement sensors.The dynamics model of this stage was a complex nonlinear,strong coupling system which made the control strategy to be a focus research.The nonlinear controller of the system was proposed based on the theory of differential geometry.Both simulation and experimental results show that either the decoupling control of the movement can be realized in horizontal and vertical directions,and the control performance was improved by the damper,verifying the validity and efficiency of this method.
基金the National Natural Science Foun-dation of China(Grant Nos.91963201 and 12174163)the 111 Project(Grant No.B20063).
文摘The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.
基金supported by the technology project of the State Grid Shanxi Electric Power Company.The name of the project is“Research and Application of Cable electrification diagnosis Technology based on Harmonic method”(5205C02000GL).
文摘The insulation aging of cross-linked polyethylene(XLPE)cables is the main reason for the reduction in cable life.There is currently a lack of rapid and effective methods for detecting cable insulation defects in power-related sectors.To this end,this paper presents a method for identifying insulation defects in XLPE cables based on deep learning algorithms.First,the principle of the harmonic method for detecting cable insulation defects is introduced.Second,the ANSYS software is used to simulate the cable insulation layer containing bubbles,protrusions,and water tree defects,and the effects of each type of defect on the magnetic field strength and eddy loss current of the cable insulation layer are analyzed.Then,a total of 10 characteristic quantities of the total harmonic content and 2nd to 10th harmonic currents are constructed to establish a database of cable insulation defects.Finally,the deep learning algorithm,long short-term memory(LSTM),is used to accurately identify the types of insulation defects in cables.The results indicate that the LSTM algorithm can effectively diagnose and identify insulation defects in cables with an accuracy of 95.83%.
基金supported by Research Fund for the Doctoral Program of Higher Education of China (No.20060248012)Shanghai-Canada Research Council cooperation (06SN07113)Auxiliary Heating Project of EAST upgrade, National Program on Key Basic Research Project (973 Program) of China (No.2010GB108003)
文摘According to the B-H curve and structural dimensions of the snubber by the Fink- Baker Method, the inductive voltage and the eddy current of any core tape with the thickness of the saturated regions are derived when the accelerator breakdown occurs. Using the Ampere＇s law, in each core tape, the eddy current of the core lamination is equal to the arc current, and the relation of the thickness of the saturated regions for different laminations can be deduced. The total equivalent resistance of the snubber can be obtained. The transient eddy current model based on the stray capacitance and the equivalent resistance is analyzed, and the solving process is given in detail. The exponential time constant and the arc current are obtained. Then, the maximum width of the lamination and the minimum thickness of the core tape are determined. The experimental time constant of the eddy current obtained, with or without the bias current, is approximately the same as that by the analytical method, which proves the accuracy of the adopted assumptions and the analysis method.
基金supported by the National Natural Science Foundation of China (No.50974103, No.61003196)the Specialized Research Plan of Shaanxi Province Education Department (No.2010JK787)
文摘The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Grant Nos.2014GB103000 and 2013GB102000)the National Natural Science Foundation of China(Grant No.11205199 and 11205192)
文摘A preliminary analysis of plasma current quenching is presented in this paper based on the disruption database.It demonstrates that 26.8%of discharges have been disrupted in the last 2012 campaign,in addition,the plasma disruptive rate grows with the increase of plasma current.The best-fit linear and instantaneous plasma current quench rate is extracted from the recent EAST disruptions,showing that an 80%-30%interval of the maximum plasma current is well fit for the EAST device.The lowest area-normalized current quench time is 3.33 ms/m;with the estimated plasma electron temperature being 7.3 eV;9.5 eV.In the disruption case the maximum eddy current goes up to 400 kA,and a fraction of currents are respectively driven on the upper and lower outer plate with nearly 100 MPa-200 MPa stress in the leg.
基金supported by National Magnetic Confinement Fusion Program of China(No.2013GB113005)the National Natural Science Foundation of China(Nos.51277139,11321062)the National 973 Program of China(No.2011CB610303)
文摘Analysis of the electromagneto-mechanical coupling effect contributes greatly to the high accuracy estimation of the EM load of many EM devices, such as a tokamak structure during plasma disruption. This paper presents a method for the numerical analysis of the electromagnetomechanical coupling effect on the basis of Maxwell＇s equations in the Lagrangian description and staggered load transfer scheme, which can treat the coupled behaviors of magnetic damping and magnetic stiffness effects at the same time. Codes were developed based on the ANSYS development platform and were applied to solve two typical numerical examples： the TEAM Problem 16 and dynamic behavior analysis of a shallow arch under electromagnetic force. The good consistency of numerical results and experimental data demonstrates the validity and accuracy of the proposed method and the related numerical codes.
