An Experimental Study on the Flow Characteristics of Wave Bottom Boundary Layer

• Main Authors: Jeng, Chung-Nan, 鄭中南
• Other Authors: Lin Chun
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/15828441799963419753

碩士 === 國立中興大學 === 土木工程學系 === 84 === The purpose of the present study is to introduce a method that can be used tomeasure the velocity field as well as to analyze the phase variation of bottomshear stress. The precise measurements of horizontal velocity field in and nearthe laminar boundary layer, induced by wave propagating over uniform water depth,were first performed by a fiber-optic laser Doppler velocimeter. The phasevariation of bottom shear stress was then evaluated by linear differentiation ofvelocity between some measuring point, 0.08∼0.20mm away from bottom, and theorigin. It is found that the variation tendencies of velocity profile at variousphases are not only well reconstructed by the modified phase average method andFourier (harmonic) analysis, but also very consistent with the calculated resultsof linear wave theory. Moreover, the measured variations in the nondimensionizedmaximum velocity and phase lag are quite in agreement with those of previousstudies. After comparing the relationship between calculated friction factorand Reynolds number of the present investigation with those analyzed by pastwork, a criterion of nondimensional height of z/δ for measuring velocity andfeasibly determining bottom shear stress, with a maximum error of about 4%, isproposed in this study. Finally, the boundary layer and bottom shear stress ofthe standing wave are also investigated in this study.