A study on tilting lift up of a large object from a porous bed
Date Issued
2007
Date
2007
Author(s)
Huang, Hsueh-Mei
DOI
zh-TW
Abstract
Breakout phenomenon is the whole process that an object is tilting lifted up from rest at first, and finally separated from the seabed. In the process, the object has to overcome the huge adhesive force exerted by the fluid flowing into the gap at the time it was formed. The force-time relation of breakout phenomenon was discussed in Mei et al. (1985), through cases of a horizontal gap and a wedged gap. However, the analysis was carried out by a few assumptions, which made the study somewhat incomplete -- the vertical velocity was neglected; the inertia term exhibiting the transient effect under small time scale of breakout was absent -- owing to the adoption of lubrication theory. Moreover, the boundary layer was left out in the seabed because of the employment of Darcy’s law, which was unable to reflect the viscosity perfectly.
The sudden breakout effect under small time scale was mainly characterized by the huge adhesive force exerted by the fluid in the gap, the potential flow theorem was introduced in the present study to deal with the sudden time effect accordingly. The huge force was found successfully, and the possible flow field in the gap and porous seabed was brought up as well. After some time later, the viscosity started to work out, whence the flow pattern under long time scale was different from the one under small time scale. The low Reynold’s number flow theory was accordingly adopted to describe the flow filed in the present study. On the aid of regular perturbation method and the boundary correction method, the irrotational velocity driven by pressure gradient in the seabed as well as the rotational one coming from the shear stress were cleared up. Meanwhile, through the analysis of such flow field, it was inferred that the object at the apex of the gap was likely to move during the lifting process, which might be helpful to the practical engineering.
Subjects
突破效應
掀起大型物體
多孔介質底床
勢流
低雷諾數流
breakout phenomenon
tilting lift up of a large object
porous bed
potential flow
low Reynold number flow
Type
thesis
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