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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS002 Oral Presentation 1742
Experiments and an improvement of model on the inundated flow with
floating bodies
Prof. Hideo Matsutomi
Department of Civil and Environmental Engineering Akita University IASPEI
Takeshi Yamaguchi, Midori Fujii
Inundated flow with floating bodies such as debris, driftwood, cars, bikes and so on was witnessed and
videotaped in Banda Aceh at the time of the 2004 Indian Ocean Tsunami, and attracted a great deal of
public attention, as did the collision force of such floating bodies. In light of the circumstances, a model
to estimate such a flow was presented by the authors in 2005. However, it was confirmed that the
model could only be applied to the flow with fluid like oil or the flow with a small amount of solid
floating bodies in which their effect as a resistance body to the flow was small (Matsutomi et al. 2006).
This study aims to improve the model for estimating the moving velocity of floating bodies, i.e., current
velocity of inundated flow with floating bodies in a steady state. The improved model adopts the notion
of the conventional bore theory regarding the floating bodies as a hypothetical fluid with the same
density as those in the downstream region of the bore, and takes account of the effect of resistance
due to the floating bodies piling up at the surge front of inundated flow. Physical experiments are
carried out to grasp the behavior of floating bodies at the surge front of inundated flow and to model
the inundated flow more exactly. The experimental flume is 0.3m wide, 0.5m high and 11.0m long with
a horizontal bed. Inundated flows are generated by rapidly pulling up a gate, installed 5.0m from the
upstream end of the flume. Two ultrasonic wave gauges are installed at the distance of 3.5m and 5.5m
from the gate respectively to measure the time series of surface elevation of the inundated flow. The
state of the inundated flow is videotaped from the upper and the left sides of the flume to grasp the
behavior of floating bodies, and to estimate the moving velocity u2 and the void ratio e of floating
bodies. The experimental conditions are that the initial water depth h1 in the upstream region of the
gate is three cases of 0.20, 0.25 and 0.30m, the initial void ratio is three cases of 0.4, 0.6 and 0.8, the
dimensions of each floating body is three cases of 1.8x1.8x1.8cm (cube), 1.8x1.8x5.4cm and
1.8x1.8x10.8cm, and hemlock fir is adopted as the floating bodies. Through examinations and
comparisons of the experimental results and the solutions of the model, it is concluded that the
improved model is useful to estimate the inundated flow with floating bodies.
Keywords: tsunami, inundated flow, floating bodies