on the definition and concept introduced in this paper, the theoretical expareion of surface slope bispectrum for two-dimensional waves is derived. Furthermore,the skewness of surface elevation distribution and that...on the definition and concept introduced in this paper, the theoretical expareion of surface slope bispectrum for two-dimensional waves is derived. Furthermore,the skewness of surface elevation distribution and that of surface slope distribution are respectively employed to define the up-down and front-back asymmetry of a wavee hape so that the relations between bispectrum and skewness are proposed. Through these relations, the updownand front-back asymmetry of the wave shape can be quantitatively determined by means of the bispectral analyses of observed wave data.展开更多
In this paper a nonlinear diffraction theory due to Stoke's 2nd-order wave for computing the wave force on the large body is presented. The radiation condition as r-∞ for 2nd-order scattered potential has been st...In this paper a nonlinear diffraction theory due to Stoke's 2nd-order wave for computing the wave force on the large body is presented. The radiation condition as r-∞ for 2nd-order scattered potential has been studied in connection with asymptotic solutions. A numerical procedure has been developed for the purpose of calculating the nonlinear wave force on the large body with arbitrary shape.展开更多
It's known that auto-correlation technique is effective in extracting periodical signals from random noises.In the case of fault monitoring of rolling element bearing,we can't acquire the fault information dir...It's known that auto-correlation technique is effective in extracting periodical signals from random noises.In the case of fault monitoring of rolling element bearing,we can't acquire the fault information directly from the original signal because of the difference of signal phases.And the signal is shown as the wide band random signal in auto-correlation function.In this paper,the signal is pre-processed and the results are proved effective.Moreover,by taking the auto-correlation function we can obtain the determined and comparable samples.This is very important for establishing the data base of running condition and for detecting the faults.展开更多
For internal flow with supersonic inflow boundary conditions,a complicated oblique shock reflection may occur.Different from the planar shock reflection problem,where the shape of the incident shock can be a straight ...For internal flow with supersonic inflow boundary conditions,a complicated oblique shock reflection may occur.Different from the planar shock reflection problem,where the shape of the incident shock can be a straight line,the shape of the incident shock wave in the inward-facing axisymmetric shock reflection in steady flow is an unknown curve.In this paper,a simple theoretical approach is proposed to determine the shape of this incident shock wave.The present theory is based on the steady Euler equations.When the assumption that the streamlines are straight lines at locations just behind the incident shock is adopted,an ordinary differential equation can be derived,and the shape of the incident shock wave is given by the solution of this ordinary differential equation.The predicted curves of the incident shock wave at several inlet conditions agree very well with the results of the numerical simulations.展开更多
An interesting discretization method for Helmholtz equations was introduced in B.Despres[1].This method is based on the ultra weak variational formulation(UWVF)and the wave shape functions,which are exact solutions of...An interesting discretization method for Helmholtz equations was introduced in B.Despres[1].This method is based on the ultra weak variational formulation(UWVF)and the wave shape functions,which are exact solutions of the governing Helmholtz equation.In this paper we are concerned with fast solver for the system generated by the method in[1].We propose a new preconditioner for such system,which can be viewed as a combination between a coarse solver and the block diagonal preconditioner introduced in[13].In our numerical experiments,this preconditioner is applied to solve both two-dimensional and three-dimensional Helmholtz equations,and the numerical results illustrate that the new preconditioner is much more efficient than the original block diagonal preconditioner.展开更多
Two-dimensional scalar equation for the displacement of steady cross-plane shear (SH) waves in homogeneous and transversely isotropic media like unidirectional fibrous com-posites is given. Then, thrbugh a simple coor...Two-dimensional scalar equation for the displacement of steady cross-plane shear (SH) waves in homogeneous and transversely isotropic media like unidirectional fibrous com-posites is given. Then, thrbugh a simple coordinate system transform, the scalar equation is standardized into a Helmholtz equation. Corresponding integral equations are derived for the scattering problems and boundary element method (BEM) is used to calculate the scattered fields of arbitrarily shaped obstacles with both soft and rigid boudary conditions numerically.A discussion is given on the numerical results which is mainly focused on the influence of the a-nisotropy of the media to the directivity of the scattered fields by circular cylindrical voids.展开更多
文摘on the definition and concept introduced in this paper, the theoretical expareion of surface slope bispectrum for two-dimensional waves is derived. Furthermore,the skewness of surface elevation distribution and that of surface slope distribution are respectively employed to define the up-down and front-back asymmetry of a wavee hape so that the relations between bispectrum and skewness are proposed. Through these relations, the updownand front-back asymmetry of the wave shape can be quantitatively determined by means of the bispectral analyses of observed wave data.
文摘In this paper a nonlinear diffraction theory due to Stoke's 2nd-order wave for computing the wave force on the large body is presented. The radiation condition as r-∞ for 2nd-order scattered potential has been studied in connection with asymptotic solutions. A numerical procedure has been developed for the purpose of calculating the nonlinear wave force on the large body with arbitrary shape.
文摘It's known that auto-correlation technique is effective in extracting periodical signals from random noises.In the case of fault monitoring of rolling element bearing,we can't acquire the fault information directly from the original signal because of the difference of signal phases.And the signal is shown as the wide band random signal in auto-correlation function.In this paper,the signal is pre-processed and the results are proved effective.Moreover,by taking the auto-correlation function we can obtain the determined and comparable samples.This is very important for establishing the data base of running condition and for detecting the faults.
基金2016YFA0401200 of national key research and development program of China and the national numerical wind tunnel project.
文摘For internal flow with supersonic inflow boundary conditions,a complicated oblique shock reflection may occur.Different from the planar shock reflection problem,where the shape of the incident shock can be a straight line,the shape of the incident shock wave in the inward-facing axisymmetric shock reflection in steady flow is an unknown curve.In this paper,a simple theoretical approach is proposed to determine the shape of this incident shock wave.The present theory is based on the steady Euler equations.When the assumption that the streamlines are straight lines at locations just behind the incident shock is adopted,an ordinary differential equation can be derived,and the shape of the incident shock wave is given by the solution of this ordinary differential equation.The predicted curves of the incident shock wave at several inlet conditions agree very well with the results of the numerical simulations.
基金The second author was supported by the Major Research Plan of Natural Science Foundation of China G91130015the Key Project of Natural Science Foundation of China G11031006National Basic Research Program of China G2011309702.
文摘An interesting discretization method for Helmholtz equations was introduced in B.Despres[1].This method is based on the ultra weak variational formulation(UWVF)and the wave shape functions,which are exact solutions of the governing Helmholtz equation.In this paper we are concerned with fast solver for the system generated by the method in[1].We propose a new preconditioner for such system,which can be viewed as a combination between a coarse solver and the block diagonal preconditioner introduced in[13].In our numerical experiments,this preconditioner is applied to solve both two-dimensional and three-dimensional Helmholtz equations,and the numerical results illustrate that the new preconditioner is much more efficient than the original block diagonal preconditioner.
文摘Two-dimensional scalar equation for the displacement of steady cross-plane shear (SH) waves in homogeneous and transversely isotropic media like unidirectional fibrous com-posites is given. Then, thrbugh a simple coordinate system transform, the scalar equation is standardized into a Helmholtz equation. Corresponding integral equations are derived for the scattering problems and boundary element method (BEM) is used to calculate the scattered fields of arbitrarily shaped obstacles with both soft and rigid boudary conditions numerically.A discussion is given on the numerical results which is mainly focused on the influence of the a-nisotropy of the media to the directivity of the scattered fields by circular cylindrical voids.
