TITLE:
Variability of Sand Mobility Surrounding Cylinder Object Freely Resting on the Seabed under the Action of Typhoon
AUTHORS:
Chongguang Pang, Liqian Liu
KEYWORDS:
Scour Process, Sediment Grain Size, Bottom Orbital Velocity, Typhoon Events, Variability of Sand Mobility, DRAMBUIE Model
JOURNAL NAME:
International Journal of Geosciences,
Vol.5 No.7,
June
19,
2014
ABSTRACT: In sandy
sediments, scour and fill is the key process contributed to mine burial. The
scour processes surrounding the cylinder mines freely resting on the sandy
seabed under the 12-hr combined action of tidal currents and wind-generated
waves, especially over typhoon events are numerically simulated using the
DRAMBUIE model. The East China Sea is a good case study due to the dominant
impact of summer typhoon events on sediment transport and scour. The numerical
results show that the scour depth generally increases with time under the
combined current and wave stresses exerted on the seabed, while the depth of
the scour pit depends on infill once the currents subside. There is a positive
relationship between the scour depth and the bottom orbital velocity after
experiencing 12-hr wave action including storm waves, while the relation is not
linear. The experimental results also display an elevated trend for scour
depth with the increase of orbital velocity. The numerical results
reveal a surprising phenomenon: the mobility of sand altering with the
increasing bed shear stress larger than the certain
threshold, which is also manifested as the curves of scour depth
with the different grain size might cross each other. For laboratory
experiments, the variability of sand mobility does not
occur, likely because typhoon storm waves cannot be reproduced in the flume. More numerical tests indicate that the intersection will be triggered by the division
of critical Shields parameter. The preliminary analysis suggests that the
phenomenon never documented is likely generated from the error of empirical formulae.