A numerical study of a tide with four harmonic constituents at the open boundary

• Published in: Journal of the Oceanographical Society of Japan 1990-08, Vol.46 (4), p.143-155
• Main Authors: Kikukawa, Hiroyuki, Ichikawa, Hiroshi
• Format: Article
• Language: English
• Subjects: Marine
• ISSN: 0029-8131; 1573-868X
• DOI: 10.1007/BF02125575

The tidal current in Kagoshima Bay is simulated by the two-dimensional subdomain finite-element method. At the open boundary, the sea level is forced to be oscillatory with a linear combination of the four harmonic constituents (M2, S2, K1, O1) of the tide. A calculation having only M2 sea level at the open boundary is also performed and the harmonic constants of M2 are compared with those calculated by the four components. In the calculated velocity vector, a large difference between the two maxima or the two minima in one day appears when the vector is directed to the open sea. On the other hand, when it is directed into the bay, the two extreme velocities are almost equal. In tide-killer residual flow, the flow pattern is almost independent of the tidal age; however, the absolute value of the current velocity depends on the tidal age. The pattern is nearly the same as that calculated by giving only M2 sea level at the open boundary. In relation to the nonlinear interaction, the kinetic energy ratio KER is defined by the ratio of kinetic energy of the induced harmonic components to that of harmonic constituents given at the open boundary. KER is large where the tidal current is disturbed by obstacles, e.g. along the west coast at the mouth of the bay and in the southern sea of Mt. Sakurajima. The distribution of KER seems to be independent of the number of harmonic constituents (one or four) given at the open boundary. The difference of kinetic energy of the M2 tidal constituent between the two calculations, i.e. with the open boundary conditions of four components (M2, S2, K1, O1) and of a single component (M2), is found to be large where the current velocity is large.