| Summary: | 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.
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