We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions...We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions. The phase patterns have a lot of sets composed of two phase vortices with opposite signs or four phase vortices which are positive and negative vortices alternately. Cases are also found where two adjacent phase vortices have the same topological charges. The density of phase vortices becomes larger with the increase of the radius of circumference and the number of pinholes on screen.Then, the relative positions of phase vortices can be adjusted by changing the radius of circumference and the number of pinholes.展开更多
In this paper, the evolution of the pattern transition induced by the vortical electric field (VEF) is investigated. Firstly, a scheme is suggested to generate the VEF by changing the spatial magnetic field. Secondl...In this paper, the evolution of the pattern transition induced by the vortical electric field (VEF) is investigated. Firstly, a scheme is suggested to generate the VEF by changing the spatial magnetic field. Secondly, the VEF is imposed on the whole medium, and the evolutions of the spiral wave and the spatiotemporal chaos are investigated by using the numerical simulation. The result confirms that the drift and the breakup of the spiral wave and the new net-like pattern are observed when different polarized fields are imposed on the whole medium respectively. Finally, the pattern transition induced by the polarized field is discussed theoretically.展开更多
Particle image velocimetry (PIV) experimental results of wake flow structure of a NACA0012 airfoil with small attack angle mounted above water surface are introduced.The experiment was carried out in a small-scale w...Particle image velocimetry (PIV) experimental results of wake flow structure of a NACA0012 airfoil with small attack angle mounted above water surface are introduced.The experiment was carried out in a small-scale wind-wave tunnel.The diameter of wind-wave tunnel test section is 1.7 m (long) × 0.4 m (width) × 0.4 m (height).The flow fields around the airfoil were measured under four diffierent conditions by varying the distance between the airfoil and the water surface.The attack angle of the airfoil was kept 10- during the experiment.For each experimental condition,the time series of particle images was captured to calculate continuous evolution of the velocity fields.The velocity fields were ensemble averaged to get the statistic parameters such as mean velocity and vorticity.Typical instantaneous velocity fields for each case are introduced to show the basic flow structure of wind surface flow separation.The aerodynamic loads acting on the airfoil are analyzed qualitatively according to the mean vorticity distribution in the flow field based on the theory of vorticity aerodynamics.The results indicate that the flow structures and drag/lift force of the airfoil alter remarkably with the changing distance between the airfoil and water surface.展开更多
In this paper,steady solutions of solitary waves in the presence of nonuniform shear currents are obtained by use of the high-level Green-Naghdi(HLGN)model.We focus on large-amplitude solitary waves in strong opposing...In this paper,steady solutions of solitary waves in the presence of nonuniform shear currents are obtained by use of the high-level Green-Naghdi(HLGN)model.We focus on large-amplitude solitary waves in strong opposing shear currents.The linear-type currents,quadratic-type currents and cubic-type currents are considered.In particular,the wave speed,wave profile,velocity field,particle trajectories and vorticity distribution are studied.It is demonstrated that presence of the nonuniform shear current modifies the velocity field and vorticity field of the solitary wave.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11404179)
文摘We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions. The phase patterns have a lot of sets composed of two phase vortices with opposite signs or four phase vortices which are positive and negative vortices alternately. Cases are also found where two adjacent phase vortices have the same topological charges. The density of phase vortices becomes larger with the increase of the radius of circumference and the number of pinholes on screen.Then, the relative positions of phase vortices can be adjusted by changing the radius of circumference and the number of pinholes.
基金supported by the National Natural Science Foundation of China (Grant Nos 10747005,10572056 and30670529)the Fund of Lanzhou University of Technology of China (Grant No Q200706)
文摘In this paper, the evolution of the pattern transition induced by the vortical electric field (VEF) is investigated. Firstly, a scheme is suggested to generate the VEF by changing the spatial magnetic field. Secondly, the VEF is imposed on the whole medium, and the evolutions of the spiral wave and the spatiotemporal chaos are investigated by using the numerical simulation. The result confirms that the drift and the breakup of the spiral wave and the new net-like pattern are observed when different polarized fields are imposed on the whole medium respectively. Finally, the pattern transition induced by the polarized field is discussed theoretically.
基金Project supported by the National Natural Science Foundation of China (Grant No.10572082)and the Shanghai Leading Academic Discipline Project (Grant No.Y0103)
文摘Particle image velocimetry (PIV) experimental results of wake flow structure of a NACA0012 airfoil with small attack angle mounted above water surface are introduced.The experiment was carried out in a small-scale wind-wave tunnel.The diameter of wind-wave tunnel test section is 1.7 m (long) × 0.4 m (width) × 0.4 m (height).The flow fields around the airfoil were measured under four diffierent conditions by varying the distance between the airfoil and the water surface.The attack angle of the airfoil was kept 10- during the experiment.For each experimental condition,the time series of particle images was captured to calculate continuous evolution of the velocity fields.The velocity fields were ensemble averaged to get the statistic parameters such as mean velocity and vorticity.Typical instantaneous velocity fields for each case are introduced to show the basic flow structure of wind surface flow separation.The aerodynamic loads acting on the airfoil are analyzed qualitatively according to the mean vorticity distribution in the flow field based on the theory of vorticity aerodynamics.The results indicate that the flow structures and drag/lift force of the airfoil alter remarkably with the changing distance between the airfoil and water surface.
基金Supported by the National Natural Science Foundation of China(Nos.11772099,11972126,11572093 and 51490671).
文摘In this paper,steady solutions of solitary waves in the presence of nonuniform shear currents are obtained by use of the high-level Green-Naghdi(HLGN)model.We focus on large-amplitude solitary waves in strong opposing shear currents.The linear-type currents,quadratic-type currents and cubic-type currents are considered.In particular,the wave speed,wave profile,velocity field,particle trajectories and vorticity distribution are studied.It is demonstrated that presence of the nonuniform shear current modifies the velocity field and vorticity field of the solitary wave.