Seiche oscillations in a partially enclosed basin
UDC
532.59 + 551.466Abstract
The study of seiche oscillations in the open entrance basins is an important applied problem. Even relatively small level fluctuations caused by seiches can be accompanied by strong horisontal flows which impede navigation and are dangerous for moored ships. In this work within the framework of the linear shallow water theory the seiche oscillations are studied in a rectangular basin of constant depth. The analytical solution is obtained for the case of the nodal level line location at the entrance to the basin. The structures of the seiche oscillations is compared for closed and partially closed basins. Their similarities and differences are revealed. It is established that the seiche oscillation periods in a basin with an open entrance are always smaller than the periods of the corresponding modes in same dimensions and depth closed basin. It is shown that the transverse seiches have a two-dimensional structure in open entrance basin. Their wave flows velocities depend on the horizontal dimensions and depth of the basin. In a closed basin, the wave flows of transverse seiches are one-dimensional, their magnitude does not depend on the horizontal dimensions of the basin and is inversely proportional to the square root of the basin depth. In the open entrance basin nodal level lines of the longitudinal seiches are shifted from basin entrance as compared to the nodal lines in a closed basin. The lower mode of the seiche in the open entrance basin is the Helmholtz mode. The wave flow for the Helmholtz mode is always directed perpendicularly to the entrance to the basin and its maximum velocity does not depend on the width and length of the basin. It is directly proportional the initial deviation amplitude of the free surface and inversely proportional to the square root of the basin depth. The greatest velocities of the flows take place at the open boundary of the basin.The estimates of seiche periods and wave flow velocities are obtained for the Akhtarskiy frith (the Azov Sea).
Keywords:
seiches, free waves, long waves, wave flows, open entrance basin, partially enclosed basin, Helmholtz mode, analytical solutions, Azov Sea, Akhtarskiy frithAcknowledgement
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