| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系 === 88 === When the large floods coming , bridge which become partially or totally submerged are subject to pressure-flow scour. Under this flow condition , a good deal of floatage such as Eichornia Crassipes often float under the water near bridge deck . Its movement and effect on pressurized flow pattern will be discussed.
The experiments were conducted to study the flow field , discharge , and water level at the bridge deck under the pressurized flow condition which Eichornia Crassipes float under the water . The experimental data were all recorded , it were compared with Chang’s data(1999). The velocity data were also compared with the log-law velocity distribution to predict the fore influence region(FIR) and behind influence region(BIR).
With the discharge changed , Eichornia Crassipes float under the water near bridge deck can be divided into three patterns . The experimental data were substituted into energy equation and continuity equation to caculate energy loss and energy loss coefficient. Compared with the energy loss of three patterns , the first pattern which Eichornia Crassipes float under water before bridge deck had the most energy loss.
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