An image can be decomposed into the structural component and the geometric texturalcomponent.Based on this idea,an efficient two-layered compressing algorithm is proposed,which uses2nd generation bandelets and wavelet...An image can be decomposed into the structural component and the geometric texturalcomponent.Based on this idea,an efficient two-layered compressing algorithm is proposed,which uses2nd generation bandelets and wavelets.First,an original image is decomposed into the structuralcomponent and the textural component,and then these two components are compressed using waveletsand 2nd generation bandelets respectively.Numerical tests show that the proposed method worksbetter than the bandelets and JPEG2000 in some specific SAR scene.展开更多
A challenge in the study of turbulent boundary layers(TBLs) is to understand the non-equilibrium relaxation process after separation and reattachment due to shock-wave/boundary-layer interaction. The classical boundar...A challenge in the study of turbulent boundary layers(TBLs) is to understand the non-equilibrium relaxation process after separation and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.展开更多
文摘An image can be decomposed into the structural component and the geometric texturalcomponent.Based on this idea,an efficient two-layered compressing algorithm is proposed,which uses2nd generation bandelets and wavelets.First,an original image is decomposed into the structuralcomponent and the textural component,and then these two components are compressed using waveletsand 2nd generation bandelets respectively.Numerical tests show that the proposed method worksbetter than the bandelets and JPEG2000 in some specific SAR scene.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11452002, 11372008, and 11521091)the Aeronautical Science Foundation of China (Grant No. 2014ZA71001)
文摘A challenge in the study of turbulent boundary layers(TBLs) is to understand the non-equilibrium relaxation process after separation and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.
