Hybrid Model Approaches to Predict Multiscale and Multiphysics Coastal Hydrodynamic and Sediment Transport Processes

Coastal ocean processes are complicated and they happen as various phenomena that span a vast range of spatial and temporal scales. For instance, general circulations of oceans occur at global scales (Wunsch & Ferrari, 2004). Tropical waves that eventually impact coastal waters propagate with wavelengths of one thousand kilometers and periods of one month (Legeckis et al., 1983). Langmuir cells, which are pairs of vortices hanging below water surfaces, have spatial sizes ranging from one to hundreds of meters (Weller et al., 1985). Scour near coastal structures is under influence of large-scale current processes but occurs in a relatively small size (Sumer & Whitehouse, 2001). Flows around enormous numbers of swimming microorganisms can occur at scales of micrometers (Pedley, 1992). Here, the scales are either observation scales such as characteristic length and time or process scales such as those in wavelet analysis (Chui, 1992; Kumar and Foufoula-Georgiou, 1997). Since a few decades ago, various geophysical fluid dynamics (GFD) models have been developed for individual coastal ocean phenomena at specific scales. The Princeton Ocean Model (POM), Finite-Volume Coastal Ocean Model (FVCOM), and HYbrid Coordinate Ocean Model (HYCOM) were developed to predict current velocity, sea level, salinity, and temperature at regional scales (Blumberg and Mellor, 1987; Chen et al., 2003; Halliwell, 2004). The WAVEWATCH and SWAN (Simulating Waves Nearshore) models were designed to simulate surface wave propagation at global to coastal scales (Tolman, 1991; Booij et al., 1999). Models have also been proposed to predict sediment transport and seabed morphology for near-coastal regions (e.g., Tonnon et al., 2007; Papanicolaou et al., 2008). In recent years, computational fluid dynamics (CFD), which can accurately model small-scale and detailed flow structures, has been applied to coastal engineering flows (e.g., Young et al., 2001). In view of the multiscale and multiphysics nature of coastal ocean processes, there is a great challenge to simulate them accurately and, until now, the efforts using numerical simulation have been successful merely for individual phenomena and scales. The challenge comes from model restrictions, numerical techniques, and computer capabilities. For