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URN etd-0213112-134747
Author Yu-feng Gao
Author's Email Address playingjy@yahoo.com.tw
Statistics This thesis had been viewed 5344 times. Download 417 times.
Department Marine Biotechnology and Resources
Year 2011
Semester 1
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Characteristics of bed shear stress in the coastal waters
Date of Defense 2012-01-19
Page Count 69
Keyword
  • inertial dissipation method
  • bed shear stress
  • wave height
  • acoustic backscatter intensity
  • turbidity
  • Abstract A 3-axis acoustic Doppler Velocimeter (ADV) with high sampling rate was used to measure the bed shear stress and turbulence under wave-current interaction conditions in this study. Experimental sites include laboratory tank, Love River in Kaohsiung and Howan coastal waters in Pingtung. Bed shear stress is estimated primarily by the inertial dissipation method, also by the turbulent kinetic energy method and eddy correlation method. Results of the laboratory experiments indicate that the bed shear stress increases as both the flow speed and wave height increase, and the flow speed is a more important factor.
    Field experiments can be divided into several types. The first type is under slow flows and calm waves. Love River is a typical condition of this type with turbid waters and a low flow speed. During the experimental period the ADV correlations reach 90% or more. Because the river flow is quite small, no significant bed shear stress is produced and u* is mostly less than 1 cm/s. As a result the deposition effect is much larger than erosion, thus a very thick layer of mud is formed on the riverbed. The observations in Howan in April 2010 also reveal the condition of slow flows and small waves, and the bed shear stress is also quite small. Due to the factors of clean coastal waters and weak turbulence in this season, the quality of ADV signals is poor. The second type is under large flows and small waves, as shown from the observations of Howan in April 2011, during which the maximum speed reached 25 cm/s and wave heights less than 20 cm. In this experiment the shear stress is large, the u* are mostly greater than 0.8 cm/s and the value of the drag coefficient is 0.0021; the ADV signals have good quality and the inertial sub-range is well defined. The third type is under weak flows and large waves. The observations of Howan in July 2011 show significant rainfall and maximum wave heights of 90 cm. In this case the u* are mostly centered around 1 cm/s. The acoustic backscatter intensity is positively correlated with the turbidity and wave height. Sizable bed shear stress induced by the orbital velocity of waves contributes a significant part to the total bed shear stress.
    Advisory Committee
  • James T. Liu - chair
  • Zhi-Cheng Huang - co-chair
  • C.C. Huang - co-chair
  • Ruo-Shan Tseng - advisor
  • Files
  • etd-0213112-134747.pdf
  • indicate access worldwide
    Date of Submission 2012-02-13

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