Coastal Engineering Journal

To design a model for the settling of Suspended Organic Matter (SOM), the decomposition rate of organic matter, and variations in the particle size and the density of SOM were studied in the course of decomposition. The decomposition rate of SOM is estimated using the analyzed results of SOM properties (i.e. particle density, particle size, IL, and resolvability). The Multi-G Model, which formulates the decomposition of organic matter derived from phytoplankton, was chosen to calculate the decomposition rate of SOM. The parameters of each fraction in the Multi-G Model were estimated on the basis of the correlation between the deposition age and the decomposition rate of SOM. In addition, it has become possible to determine the mean decomposition rate of organic matter using the C/N ratio. Temporal variations of the particle size and the particle density of SOM during decomposition were estimated from the C/N ratio, and approximate expressions for the variations were proposed. Based on these results, it is possible to calculate the settling velocity of SOM in considering the variation of its properties due to decomposition

Small-scale physical and numerical experiments were conducted to investigate the local concentration of waves (monochromatic and group) due to abrupt change of nearshore bathymetry in alongshore direction. Wave run-up motions along the shoreline were measured using an image analysis technique to compare localized concentration of wave energy, when waves propagate over a bathymetry composing rhythmic patterns of mild/steep slope bottom configurations. Measured alongshore variation of maximum wave run-up heights showed significant peak near the boundary, which has sudden alongshore change of depth, both under monochromatic and group wave trains. This phenomenon is found to be due to the interaction of waves with nearshore currents, which is further enhanced by excitation of long-wave components by breaking of group waves. Furthermore, this paper discusses results of preliminary experiments carried out to test the effectiveness of several shore protection structure layouts in mitigating such wave concentrations. Numerical simulations were performed using a model based on Boussinesq-type equations; coupled with a transport equation to model energy dissipation due to wave breaking.

This paper concerns the storm surge calculation based on the algorithm of ensemble empirical mode decomposition (EEMD). An accurate storm surge result is key information for coastal disaster warning and prevention. Separation of storm surge magnitude from sea level data has typically been done by specifying tidal input from main tidal harmonics. Obtaining accurate storm surge magnitude with harmonic analysis (HA) requires at least one month. This study discusses possible storm surge separation from short-term sea level time series using EEMD. The current work reveals that EEMD is predominant for short-term sea level data analysis shorter than thirty-five days. Due to different residues obtained from EEMD, this work proposes a method to determine most ideal residue for representing the storm surge.

For wave propagation problems in infinite-domains, truncation of the far-field by an artificial boundary is essential to define a bounded domain of interest; resultant difficulties are the radiation condition and generation of incident waves. Instead of the radiation condition, an absorbing boundary condition (ABC) is implemented in an inhomogeneous exterior domain, based on the perfectly matched layer (PML) technique. Complex coordinate stretching, a key PML concept, analytically continues a governing equation in the domain of interest into a PML equation as an anisotropic absorbing boundary in the exterior domain; a system of equivalent equations governs waves in the whole computational domain, and thus the PML is reflectionless at the artificial boundary, an interface between the PML and the domain of interest. For generation of incident waves, wave-maker modeling is proposed based on an idea of plain topography and wave-ray tracing. A source function along the interface is a curvilinear integral in a weak form for the governing equation. Finite element examples for wave propagation in one-dimension verify ability and efficiency of techniques with PML ABCs; besides, those for wave scattering by a circular cylinder on a slope show effectiveness of the wave-maker modeling.