Experimental Study on the Characteristics of Bottom Boundary Layer Flow Induced by a Solitary Wave

• Main Authors: Yan-Lin Huang, 黃彥霖
• Other Authors: 林呈
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/02991162205084979885

碩士 === 中興大學 === 土木工程學系所 === 95 === The object of this paper is to study experimentally the bottom boundary layer flow under a solitary wave propagating over either a horizontal or a sloping bottom. The wave height, H, is 1.1 cm and the water depth, h, is 7 cm. The slope of sloping bottom is 1/10. The particle image velocimetry (PIV), and laser Doppler velocimetry (LDV) were used to obtain quantitatively velocity distribution of the boundary layer flow. Particle trajectory photography was also used for flow visualization to observe flow fields near the bottom boundary. The PIV was based on phantom camera and Ar+ laser system. Image processing techniques are utilized in the study to improve time and space resolution of PIV system. The effects of glare at the bed are reduced by using High pass filter (Edge Laplacian 5 5 method). The boundary layer flow near a plane boundary with uniform incoming flow was tested first using this system. The result obtained is much better than the traditional PIV. Furthermore, this technique was used to measure the boundary layer under a solitary wave near either a horizontal or a sloping bottom. The velocity distribution near the horizontal bottom was compared with that obtained by FLDV. The PIV system and image processing technique are proved to be successfully applied for the measurement of boundary layer flow. Finaly, the boundary characteristics under a solitary wave were investigated. It is find that: (1)The similarity profile of the velocity distribution of boundary layer flow was obtained near horizontal bottom. (2) The maximum value of positive and negative horizontal velocity increases gradually with the decrease of the water depth in the shoaling process. (3) The space resolution of PIV data is tiny enough to estimate the bed shear stress by calculating velocity gradient of the horizontal velocity near the bed.