Characteristics of velocity field and vortex structure nduced by solitary waves propagating over a submerged barrier

• Main Authors: Chia-Feng Hu, 胡家逢
• Other Authors: 林呈
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/30228708258335019769

碩士 === 國立中興大學 === 土木工程學系所 === 105 === This study presents an experimental investigation of the propagation of solitary waves over a rectangular submerged structure (length to height ratio L/D = 0.2) on a horizontal bottom by utilizing particle trajectory technique and high-speed particle image velocimetry (HSPIV). The velocity vector fields are obtained by HSPIV. The wave-height (H0) to water-depth (h0) ratio of the incident solitary waves are H0/ h0 = 0.10, 0.25, 0.33 and 0.50. Several preliminary tests are carried out such as the validation repeatability of the incident solitary wave free surface elevation or/and profile, testing of the spatial resolution sensitivity for vorticity calculation, and time resolution sensitivity for acceleration calculation. The evolution of two vortices at the leading edge and the trailing edge of the top surface of the barrier are observed and the vortices grow in size respectively. The vortex developing at the trailing edge is found to get entrained into the primary vortex that generated from the leading edge and moved downstream. The evolution of the primary vortex on the top edge of the barrier can be categorized as the series of: (1) generation of the separated shear layer; (2) generation of the vortex structure; (3) movement of the vortex structure; (4) detachment of the vortex structure; and (5) breakdown of the vortex. The relationship between the temporal variation of the flow acceleration and the vorticity of the vortex core is presented in this study. The incidence of the solitary wave supplies energy for the free stream on the top edge of the barrier and the momentum transfer to the vortex core via the separated shear layer and hence the vorticity and the vortex strength of the primary vortex increase. When the solitary wave passes over the barrier, the velocity of the free stream over the top surface of the barrier starts to decelerate and no more energy supply to the vortex core, thus leading to the dissipation of the vortex structure and the occurrence of the turbulent flow.