To address the problem of subdividing inflexible rectangular grid models and their poor definition of velocity interfaces,we propose a complex structure triangular net for a minimum traveltime ray tracing global algor...To address the problem of subdividing inflexible rectangular grid models and their poor definition of velocity interfaces,we propose a complex structure triangular net for a minimum traveltime ray tracing global algorithm.Our procedure is:(1) Subdivide a triangle grid based on the Delaunay triangular subdivision criterion and the relationships of the points,lines,and the surfaces in the subdividing area.(2) Define the topology relationships and related concepts of triangular unit ray tracing.(3) The source point and wave arrival points at any time compose the propagating plane wave and the minimum traveltime and secondary source positions are calculated during the plane wave propagation.We adopt the hyperbolic approximation global algorithm for secondary source retrieving.(4) By minimum traveltime ray tracing,collect the path from receiver to source points with the neighborhood point's traveltime and the direction of the secondary source.Numerical simulation examples are given to test the algorithm.The results show that the triangular net ray tracing method demonstrates model subdivision flexibility,precise velocity discontinuity interfaces,and accurate computations.展开更多
In order to suppress the airwave noise in marine controlled-source electromagnetic (CSEM) data, we propose a 3D deconvolution (3DD) interferometry method with a synthetic aperture source and obtain the relative an...In order to suppress the airwave noise in marine controlled-source electromagnetic (CSEM) data, we propose a 3D deconvolution (3DD) interferometry method with a synthetic aperture source and obtain the relative anomaly coefficient (RAC) of the EM field reflection responses to show the degree for suppressing the airwave. We analyze the potential of the proposed method for suppressing the airwave, and compare the proposed method with traditional methods in their effectiveness. A method to select synthetic source length is derived and the effect of the water depth on RAC is examined via numerical simulations. The results suggest that 3DD interferometry method with a synthetic source can effectively suppress the airwave and enhance the potential of marine CSEM to hydrocarbon exploration.展开更多
The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear suscep...The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility is observed to be 1.0 × 10-10 esu at 800nm. The relaxation time of the optical nonlinearity in the films is as short as 60fs. The optical nonlinearity is enhanced due to the quantum confinement of electrons in Si nanocrystals embedded in the SiO2 films. The enhanced optical nonlinearity does not originate from Al dopant because there are no Al clusters in the films.展开更多
Two novel poly[(3-alkylthiophene-2,5-diyl)-(benzylidenequinomethane-2,5-diyl)s] derivatives, poly[ (3-butylthiophene-2,5-diyl)-( p-N,N-dimethylamino) benzylidenequinomethane-2,5-diyl) ] ( PBTDMABQ) and poly [( 3-octyl...Two novel poly[(3-alkylthiophene-2,5-diyl)-(benzylidenequinomethane-2,5-diyl)s] derivatives, poly[ (3-butylthiophene-2,5-diyl)-( p-N,N-dimethylamino) benzylidenequinomethane-2,5-diyl) ] ( PBTDMABQ) and poly [( 3-octylthiophene2,5-diyl) -(p-N, N-dimethylamino ) benzylidenequinomethane-2, 5-diyl)] (POTDMABQ), were synthesized.The band gaps of the two polymers are calculated as 1. 75 eV for PBTDMABQ and 1. 69 eV for POTDMABQ,respectively. The homogenous films of the two polymers were prepared and their third-ordernonlinear optical properties were studied by the backward degenerate four-wave mixing at 532 nm. Byusing the relative measurement technique, the third-order nonlinear optical susceptibilities ofPBTDMABQ and POTDMABQ are calculated as 5. 62 X 10^(-9) and 1. 22 X 10^(-8) ESU, respectively. It isfound that substituted alky groups have strong effects on the band gap and nonlinear opticalproperties of the two polymers. The relatively big third-order nonlinear optical susceptibilitiesand small band gap of POTDMABQ resulted mainly from the longer alkyl with strong electron-donatingability can enhance the delocation degree of conjugated π electronics.展开更多
On the eve of the occurrence of geological hazards,part of the rock and soil body begins to burst,rub,and fracture,generating infrasound signals propagating outward.3D advanced positioning of the landslide has remaine...On the eve of the occurrence of geological hazards,part of the rock and soil body begins to burst,rub,and fracture,generating infrasound signals propagating outward.3D advanced positioning of the landslide has remained unsolved,which is important for disaster prevention.Through the Fourier transform and Hankel transform of the wave equation in cylindrical coordinates,this work established a three-dimensional axisymmetric sound field model based on normal waves,and designed a 4-element helix triangular pyramid array with vertical and horizontal sampling capabilities.Based on this,the three-dimensional matching localization algorithm of infrasound for geological hazards is proposed.Applying the algorithm to the infrasound signal localization of rock and soil layers,it was found that the helix triangular pyramid array can achieve accurate estimation of depth and distance with a smaller number of array elements than the traditional array,and may overcome the azimuth symmetry ambiguity.This study shows the application prospects of this method for predicting geohazards position several hours in advance.展开更多
In this paper it is reported for the first time that the third harmonic generated in EH32 mode of a gas-filled waveguide by fs pulses has higher generation efficiency. The new finding contrasts with the experiment in...In this paper it is reported for the first time that the third harmonic generated in EH32 mode of a gas-filled waveguide by fs pulses has higher generation efficiency. The new finding contrasts with the experiment in It. G. Durfee Ⅲ, S. Backus, M.M. Murnane, and H.C. Kapteyn, Opt. Left. 22 (1997) 1565]. Some possible factors, which produce the contradiction, are discussed briefly.展开更多
A tetrad mechanism for exciting long waves, for example edge waves, is described based on nonlinear resonant wave-wave interactions. In this mechanism, resonant interactions pass energy to an edge wave, from the three...A tetrad mechanism for exciting long waves, for example edge waves, is described based on nonlinear resonant wave-wave interactions. In this mechanism, resonant interactions pass energy to an edge wave, from the three participating gravity waves. The estimated action flux into the edge wave can be orders of magni- tude greater than the transfer fluxes derived from other competing mechanisms, such as triad interactions. More- over, the numerical results show that the actual transfer rates into the edge wave from the three participating gravity waves are two- to three- orders of magnitude greater than bottom friction.展开更多
Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additi...Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additional heating in transformer parts. It leads to higher losses, early fatigue of insulation, premature failure and reduction of the useful life of the transformer. To prevent these problems, the rated capacity of transformer which supplies harmonic loads must be reduced. In this work, a typical 50 kVA three-phase distribution transformer with real practical parameters is taken under non-linear loads generated due to domestic loads. The core losses is evaluated using the three dimensional model of the transformer developed in FEM (finite element method) program based on valid model of transformer under high harmonic conditions. And finally a relation associated with core losses and amplitude of high harmonic order are reviewed & analyzed and then a comparison is being carried out on the results obtained by different excitation current in transformer windings.展开更多
This paper presents a universal third-order Stokes solution with uniform current. This solution is derived on the basis of potential theory by expanding the free surface and potential function in Fourier series and de...This paper presents a universal third-order Stokes solution with uniform current. This solution is derived on the basis of potential theory by expanding the free surface and potential function in Fourier series and determining the Fourier coefficients by solving a set of nonlinear algebraic equations through the Taylor expansion and perturbation method. The universal solution is expressed upon the still water depth with the still water level as datum and retains a global perturbation parameter. The wave set-up term generated by the self-interaction of oscillatory waves is explicitly included in the free surface function. With the use of different definitions for the wave celerity, different water levels as the datum, different non-dimensional variables as the perturbation parameter, and different treatments for the total head, the universal solution can be reduced to the existing various Stokes solutions, thus explaining the reasons and the physical significance of different non-periodic terms in them, such as the positive or negative constant term in the free surface expression and the time-or space-proportional term in the potential function.展开更多
Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave...Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is resonance-enhanced. This program offers a new type of high-power terahertz radiation source.展开更多
This paper concerns a system of nonlinear wave equations describing the vibra- tions of a 3-dimensional network of elastic strings. The authors derive the equations and appropriate nodal conditions, determine equilibr...This paper concerns a system of nonlinear wave equations describing the vibra- tions of a 3-dimensional network of elastic strings. The authors derive the equations and appropriate nodal conditions, determine equilibrium solutions, and, by using the methods of quasilinear hyperbolic systems, prove that for tree networks the natural initial, boundary value problem has classical solutions existing in neighborhoods of the "stretched" equilibrium solutions. Then the local controllability of such networks near such equilib- rium configurations in a certain specified time interval is proved. Finally, it is proved that, given two different equilibrium states satisfying certain conditions, it is possible to control the network from states in a small enough neighborhood of one equilibrium to any state in a suitable neighborhood of the second equilibrium over a sufficiently large time interval.展开更多
The investigation of the interplay between geometry and nonlinearity may open the road to the control of extreme waves. We study three-dimensional localization and dispersive shocks in a bent cigar shaped potential by...The investigation of the interplay between geometry and nonlinearity may open the road to the control of extreme waves. We study three-dimensional localization and dispersive shocks in a bent cigar shaped potential by the nonlinear Schro¨ dinger equation. At high bending and high nonlinearity, topological trapping is frustrated by the generation of curved wave-breaking. Four-dimensional parallel simulations confirm the theoretical model. This work may contribute to novel devices based on geometrically constrained highly nonlinear dynamics and tests and analogs of fundamental physical theories in curved space.展开更多
A triad mode resonance, or three-wave resonance, is typical of dynamical systems with quadratic nonlinearities. Suspended cables are found to be rich in triad mode resonant dynamics. In this paper, modulation equation...A triad mode resonance, or three-wave resonance, is typical of dynamical systems with quadratic nonlinearities. Suspended cables are found to be rich in triad mode resonant dynamics. In this paper, modulation equations for cable's triad resonance are formulated by the multiple scale method. Dynamic conservative quantities, i.e., mode energy and Manley-Rowe relations, are then constructed. Equilibrium/dynamic solutions of the modulation equations are obtained, and full investigations into their stability and bifurcation characteristics are presented. Various bifurcation behaviors are detected in cable's triad resonant responses, such as saddle-node, Hopf, pitchfork and period-doubling bifurcations. Nonlinear behaviors, like jump and saturation phenomena, are also found in cable's responses. Based upon the bifurcation analysis, two interesting properties associated with activation of cable's triad resonance are also proposed, i.e., energy barrier and directional dependence. The first gives the critical amplitude of high-frequency mode to activate cable's triad resonance, and the second characterizes the degree of difficulty for activating cable's triad resonance in two opposite directions, i.e., with positive or negative internal detuning parameter.展开更多
基金the National Natural Science Foundation of China(Grant Nos.50974081,50774051, 51034003)the Foundation for the Author of National Excellent Doctoral Dissertation of PR China(Grant No.200958)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University(Grant No.IRT0843)the Open Research Fund Program of the State Key Laboratory of Coal Resources and Safe Mining(China University of Mining and Technology, Beijing)(No.2007-07)
文摘To address the problem of subdividing inflexible rectangular grid models and their poor definition of velocity interfaces,we propose a complex structure triangular net for a minimum traveltime ray tracing global algorithm.Our procedure is:(1) Subdivide a triangle grid based on the Delaunay triangular subdivision criterion and the relationships of the points,lines,and the surfaces in the subdividing area.(2) Define the topology relationships and related concepts of triangular unit ray tracing.(3) The source point and wave arrival points at any time compose the propagating plane wave and the minimum traveltime and secondary source positions are calculated during the plane wave propagation.We adopt the hyperbolic approximation global algorithm for secondary source retrieving.(4) By minimum traveltime ray tracing,collect the path from receiver to source points with the neighborhood point's traveltime and the direction of the secondary source.Numerical simulation examples are given to test the algorithm.The results show that the triangular net ray tracing method demonstrates model subdivision flexibility,precise velocity discontinuity interfaces,and accurate computations.
基金supported by the national project"Deep Exploration Technology and Experimentation"(SinoProbe-09-02)
文摘In order to suppress the airwave noise in marine controlled-source electromagnetic (CSEM) data, we propose a 3D deconvolution (3DD) interferometry method with a synthetic aperture source and obtain the relative anomaly coefficient (RAC) of the EM field reflection responses to show the degree for suppressing the airwave. We analyze the potential of the proposed method for suppressing the airwave, and compare the proposed method with traditional methods in their effectiveness. A method to select synthetic source length is derived and the effect of the water depth on RAC is examined via numerical simulations. The results suggest that 3DD interferometry method with a synthetic source can effectively suppress the airwave and enhance the potential of marine CSEM to hydrocarbon exploration.
文摘The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility is observed to be 1.0 × 10-10 esu at 800nm. The relaxation time of the optical nonlinearity in the films is as short as 60fs. The optical nonlinearity is enhanced due to the quantum confinement of electrons in Si nanocrystals embedded in the SiO2 films. The enhanced optical nonlinearity does not originate from Al dopant because there are no Al clusters in the films.
基金National Natural Science Foundation of China (60277002)
文摘Two novel poly[(3-alkylthiophene-2,5-diyl)-(benzylidenequinomethane-2,5-diyl)s] derivatives, poly[ (3-butylthiophene-2,5-diyl)-( p-N,N-dimethylamino) benzylidenequinomethane-2,5-diyl) ] ( PBTDMABQ) and poly [( 3-octylthiophene2,5-diyl) -(p-N, N-dimethylamino ) benzylidenequinomethane-2, 5-diyl)] (POTDMABQ), were synthesized.The band gaps of the two polymers are calculated as 1. 75 eV for PBTDMABQ and 1. 69 eV for POTDMABQ,respectively. The homogenous films of the two polymers were prepared and their third-ordernonlinear optical properties were studied by the backward degenerate four-wave mixing at 532 nm. Byusing the relative measurement technique, the third-order nonlinear optical susceptibilities ofPBTDMABQ and POTDMABQ are calculated as 5. 62 X 10^(-9) and 1. 22 X 10^(-8) ESU, respectively. It isfound that substituted alky groups have strong effects on the band gap and nonlinear opticalproperties of the two polymers. The relatively big third-order nonlinear optical susceptibilitiesand small band gap of POTDMABQ resulted mainly from the longer alkyl with strong electron-donatingability can enhance the delocation degree of conjugated π electronics.
基金Project(41877219)supported by the National Natural Science Foundation of ChinaProject(cstc2019jcyj-msxmX0585)supported by Natural Science Foundation of Chongqing,ChinaProject(KJ-2018016)supported by Science and Technology Project of Planning and Natural Resources Bureau of Chongqing Government,China。
文摘On the eve of the occurrence of geological hazards,part of the rock and soil body begins to burst,rub,and fracture,generating infrasound signals propagating outward.3D advanced positioning of the landslide has remained unsolved,which is important for disaster prevention.Through the Fourier transform and Hankel transform of the wave equation in cylindrical coordinates,this work established a three-dimensional axisymmetric sound field model based on normal waves,and designed a 4-element helix triangular pyramid array with vertical and horizontal sampling capabilities.Based on this,the three-dimensional matching localization algorithm of infrasound for geological hazards is proposed.Applying the algorithm to the infrasound signal localization of rock and soil layers,it was found that the helix triangular pyramid array can achieve accurate estimation of depth and distance with a smaller number of array elements than the traditional array,and may overcome the azimuth symmetry ambiguity.This study shows the application prospects of this method for predicting geohazards position several hours in advance.
基金The project supported by National Natural Science Foundation of China under Grant No. 90103025 and the Research Fund for the Doctoral Program of Higher .Education of China under Grant No. 20020027006
文摘In this paper it is reported for the first time that the third harmonic generated in EH32 mode of a gas-filled waveguide by fs pulses has higher generation efficiency. The new finding contrasts with the experiment in It. G. Durfee Ⅲ, S. Backus, M.M. Murnane, and H.C. Kapteyn, Opt. Left. 22 (1997) 1565]. Some possible factors, which produce the contradiction, are discussed briefly.
文摘A tetrad mechanism for exciting long waves, for example edge waves, is described based on nonlinear resonant wave-wave interactions. In this mechanism, resonant interactions pass energy to an edge wave, from the three participating gravity waves. The estimated action flux into the edge wave can be orders of magni- tude greater than the transfer fluxes derived from other competing mechanisms, such as triad interactions. More- over, the numerical results show that the actual transfer rates into the edge wave from the three participating gravity waves are two- to three- orders of magnitude greater than bottom friction.
文摘Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additional heating in transformer parts. It leads to higher losses, early fatigue of insulation, premature failure and reduction of the useful life of the transformer. To prevent these problems, the rated capacity of transformer which supplies harmonic loads must be reduced. In this work, a typical 50 kVA three-phase distribution transformer with real practical parameters is taken under non-linear loads generated due to domestic loads. The core losses is evaluated using the three dimensional model of the transformer developed in FEM (finite element method) program based on valid model of transformer under high harmonic conditions. And finally a relation associated with core losses and amplitude of high harmonic order are reviewed & analyzed and then a comparison is being carried out on the results obtained by different excitation current in transformer windings.
基金supported by Fundamental Research Funds for the Central Universities (Grant No. 2010B02614)Natural Science Foundation of Hohai University (Grant No. 2009423511)+1 种基金National Natural Science Foundation of China (Grant No. 4176008)Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘This paper presents a universal third-order Stokes solution with uniform current. This solution is derived on the basis of potential theory by expanding the free surface and potential function in Fourier series and determining the Fourier coefficients by solving a set of nonlinear algebraic equations through the Taylor expansion and perturbation method. The universal solution is expressed upon the still water depth with the still water level as datum and retains a global perturbation parameter. The wave set-up term generated by the self-interaction of oscillatory waves is explicitly included in the free surface function. With the use of different definitions for the wave celerity, different water levels as the datum, different non-dimensional variables as the perturbation parameter, and different treatments for the total head, the universal solution can be reduced to the existing various Stokes solutions, thus explaining the reasons and the physical significance of different non-periodic terms in them, such as the positive or negative constant term in the free surface expression and the time-or space-proportional term in the potential function.
基金supported by the National Natural Science Foundation of China (No.60801017)the Tianjin Municipal Primary Application and Frontier Technology Research Plan (No.11JCYBJC01100)the Key Technology Research and Development Program of Tianjin (No.09ZCKFSF00200)
文摘Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is resonance-enhanced. This program offers a new type of high-power terahertz radiation source.
基金supported by the DFG SPP1253:Optimization with PDE-Constaintsthe DFG-CE315 Cluster of Excellence:Engineering of Advanced Materials
文摘This paper concerns a system of nonlinear wave equations describing the vibra- tions of a 3-dimensional network of elastic strings. The authors derive the equations and appropriate nodal conditions, determine equilibrium solutions, and, by using the methods of quasilinear hyperbolic systems, prove that for tree networks the natural initial, boundary value problem has classical solutions existing in neighborhoods of the "stretched" equilibrium solutions. Then the local controllability of such networks near such equilib- rium configurations in a certain specified time interval is proved. Finally, it is proved that, given two different equilibrium states satisfying certain conditions, it is possible to control the network from states in a small enough neighborhood of one equilibrium to any state in a suitable neighborhood of the second equilibrium over a sufficiently large time interval.
基金the support of a grant from the John Templeton Foundation(58277)support by the European Research Council Grant ERC-POC-2014 Vanguard(664782)
文摘The investigation of the interplay between geometry and nonlinearity may open the road to the control of extreme waves. We study three-dimensional localization and dispersive shocks in a bent cigar shaped potential by the nonlinear Schro¨ dinger equation. At high bending and high nonlinearity, topological trapping is frustrated by the generation of curved wave-breaking. Four-dimensional parallel simulations confirm the theoretical model. This work may contribute to novel devices based on geometrically constrained highly nonlinear dynamics and tests and analogs of fundamental physical theories in curved space.
基金Supporting Program for Young Investigators,Hunan UniversityNational Science Foundation of China(Grant Nos.11502076 and 11572117)
文摘A triad mode resonance, or three-wave resonance, is typical of dynamical systems with quadratic nonlinearities. Suspended cables are found to be rich in triad mode resonant dynamics. In this paper, modulation equations for cable's triad resonance are formulated by the multiple scale method. Dynamic conservative quantities, i.e., mode energy and Manley-Rowe relations, are then constructed. Equilibrium/dynamic solutions of the modulation equations are obtained, and full investigations into their stability and bifurcation characteristics are presented. Various bifurcation behaviors are detected in cable's triad resonant responses, such as saddle-node, Hopf, pitchfork and period-doubling bifurcations. Nonlinear behaviors, like jump and saturation phenomena, are also found in cable's responses. Based upon the bifurcation analysis, two interesting properties associated with activation of cable's triad resonance are also proposed, i.e., energy barrier and directional dependence. The first gives the critical amplitude of high-frequency mode to activate cable's triad resonance, and the second characterizes the degree of difficulty for activating cable's triad resonance in two opposite directions, i.e., with positive or negative internal detuning parameter.