| Summary: | 碩士 === 國立中興大學 === 土木工程學系 === 84 === AbstractThe main objective of this study was to investigate the
variations of the distribution of shear stress along the scour
hole downstream of a weir during the evolution of the scour
hole.The shapes of the scour hole were selected based on the
results of the local scour testswith standard sand. An
electromagnetic current was used to measure the flow field in
theplunge pool. Based on the analysis of the laboratory dada, it
was found that in general the scour holecan be described with
two straight lines and one curve or semi-circle. An
exponentialfunction was used to describe the dimensionless
maximum scour depth. Expressionsfor the unit erosion rate and
area factor were also developed. These function and
expressionwere proved by other investigators.Both the energy and
momentum correction factors, trere were found to increase from
the toe of the weir. Their values remained in the same order of
magnitude along the first straight lineof the scour hole. The
values of both increased for one to three order of magnitude
alongthe curved portion of the hole due to the free overfall jet
impact. The values decreased tobe around 1 along the second
straight line due to the dissipation of energy. The
relationshipof alpha and bata was also satisfied along the
second straight line of the scour hole.The shear stress was
found to decrease in the downstream direction of the scour hole
forboth the results of strain transducter and strain gages.
These results were probably dueto the fact that the energy
dissipated in the downstream direction. For a given distragethe
value of the shear stress decreased with time, and eventually
approached the criticalshear stress of the sand particle.
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