Coastal Engineering Journal

During the summer of 2005, we carried out an intensive field survey of current velocity, salinity, temperature, and water density in Inohana Lake, Japan, which is a semi-enclosed and highly stratified estuary. Field and meteorological data were used to investigate the characteristics of currents, and to estimate water-volume and salt fluxes as a measure of water and material exchanges. We undertook a test using a simple box model based on the average salinity and river discharge, and obtained the exchanges of waters between Inohana and Hamana Lakes and within Inohana Lake, respectively. In terms of water exchanges between the two lakes and within Inohana Lake, wind effects were dominant over tide. In terms of water exchange rate between the two lakes, the water-volume flux was about five times as great as freshwater inflow. The water-volume flux between two lakes estimated from the box model showed good agreement with the observed ones by the ADCP. In the box model, the contribution of advection was larger than that of diffusion for the vertical water exchange. The vertical salt flux was estimated using two methods: the direct estimation from field data and a turbulent diffusion model. The turbulent diffusion model showed good agreement with the direct estimation by removing fluctuations with frequency less than 0.2 Hz from the velocity and salinity data.

In a beach morphological process, such as a formation of a sand bar and a beach cusp, sediment sorting plays an important role. To describe a mechanism of sediment sorting directly, the movable bed simulator, which is a granular material model based on the distinct element method is used. In this paper, a hydraulic experiment using an oscillatory water tunnel is conducted to track motion of sediment particles under vertical sorting in sheetflow regime. The three-dimensional movable bed simulator is driven to track detailed motion of individual sediment particles numerically. Performance of the movable bed simulator as a tool of computational dynamics is shown by comparing simulated physical properties, such as series of instantaneous images, velocity profile and number-density distribution of sediment particles, with the result of the experiment.

A simulation of wind-wave activity in the North Atlantic Basin, between June to August of 2002, has been performed using the SWAN model. The results of the simulations were compared with data obtained from the National Data Buoy Center and the results from NOAA's WAVEWATCH III (WW3) wave model. This study tested the applicability of the SWAN model at oceanic scales. The SWAN model was developed for coastal areas, but in version (40.11), spherical coordinates have been included in the code for oceanic applications. It was found that, in general, WW3 produces a somewhat better fit to the observations than SWAN. The same conclusion holds even when global scale WW3 results were used as boundary conditions in the SWAN simulations. Since the same wind forcing was used, we could conclude that this difference in significant wave height, Hs, could be due to the way wind energy is transferred to wave energy and its dissipation due to whitecapping in the models. The wind input parameterization in WW3 [Tolman and Chalikov, 1996] shows a better response to relatively fast changes in wind speed than the parameterization of Komen et al. [1984] used in SWAN. Although comparison between buoy observations and model output tends to favor WW3 over SWAN in deep water, we argue that the ease of use of SWAN, together with the simplification offered by just having to learn to use one model, makes the SWAN model a good option for simulations all the way from deep water up to the near shore.

A dispersion-corrected finite element model is developed to simulate the propagation of distant tsunamis over a slowly varying topography. A linear Boussinesq wave equation is solved to consider the dispersion effect of tsunami waves by employing a linear triangular mesh and an explicit time integration scheme. The numerical dispersion associated with the explicit scheme is minimized by adjusting both the mesh size and the dispersion-correction parameter. In order to test the present model, numerical simulations for the propagation of an initial Gaussian hump over various constant depths are conducted, and the numerical results are compared with analytical solutions of the linear Boussinesq equations. The present model is also tested for the propagation of tsunamis over a submerged circular shoal and the numerical results are compared with the numerical solutions obtained using another Boussinesq model. The present model is shown to be efficient and considerably accurate.

The ship motions moored along quay wall depend on external forces such as waves and wind, ship's hull form, mooring system such as fender and mooring line, and structural type of quay wall. In this paper, the effect of the structure types of quay wall is investigated based on model test and numerical simulation which uses Green function; G = log R. In the numerical simulation, the accuracy of theory in low frequency region is also discussed.