| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 92 === In this experimental study, a rectangular submerged obstacle was added on the test seabed for measuring behaviors of a fluidized sandy bed surface. It is particularly aimed at studying time series of motions of a fluidized bed surface and the results of scours of foundation soil in the front and lee sides of a submerged obstacle.
The instrumentation consists of a infrared optical altimetry for measuring the time series of a near fluidized-bed surface motions 5 cm in front of the obstacle and scour depth distributions around the obstacle. Six Pore pressure transducers were installed inside the foundation bed soils to display typical seabed responses. A 3D acoustic Doppler velocimetry was adopted to measure velocity fields in front of the obstacle at 1 cm above the bed. Six wave gauges were adopted to collect wave transformations on both sides of the obstacle. Four optical sediment-concentration probes at 1 cm above the bed were used for studying sediment transport. Two types of waves, i.e. monochromatic waves and regular wave groups, were generated in present laboratory flume tests.
The results illustrate that no surface motions were found from an unfluidized bed. However, relatively significant motions with the same frequency of over-loading waves started to occur after a bed had been fluidized. The amplifications of bed-surface oscillation grew larger as thickness of fluidized soil layers increased. Meanwhile during a fluidized response, wave heights over the fluidized bed relative to those entering the soil basin were clearly found to decrease by about ?% to ?%, especially getting closer to the obstacle. Similarly, the suspended sediment concentrations increased more significantly in the front than in the lee of the obstacle after the occurrence of foundation fluidization.
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