2. HYDRODYNAMIC MODEL 



2.1 A Review 



There exist various time and length scales in the hydrodynamic processes 

 of large bodies of water, ranging from the small scale of the surface waves 

 (1 sec < T < 20 sec, 1 cm < L < 500 m), the mesoscale corresponds to the 

 internal and inertial waves (N"^ < T < f "^ , 100 m < L < 100 Km), to the large 

 scale associated with the long waves (tides, storm surges, and seiches). In 

 addition, turbulent processes that affect the mean circulation and the 

 dispersion of contaminants have to be addressed. Due to the lack of detailed 

 understanding and the limitation of computer resources, existing numerical 

 models of large scale processes do not resolve the small scale and the 

 mesoscale range, but resort to parameterizing the processes in these ranges. 



In addition to the difference in the resolved spatial and time scales, 

 models can differ substantially in numerical features and hence have quite 

 different numerical efficiencies and accuracies. Anticipating long-term 

 simulations for a variety of flow situations, an ideal numerical model should 

 be comprehensive (containing the proper physics) and generalized (requiring 

 minimal tuning, and adaptable to various applications) in terms of its dynamic 

 features, while accurate (containing little numerical damping) and economic 

 (computationally efficient) in terms of its numerical features. To allow 

 relative ease in distinguishing one model from another, it is convenient to 

 classify models in terms of their dynamic features as listed in Table 2.1: 

 spatial dimension, time variation, air-sea interface, scale of interest, 

 turbulence parameterization, and forcing. Table 2.2 lists numerical method, 

 equations solved, time-differencing scheme, spatial-differencing scheme, grid 

 structure, and host computer as the primary numerical features that 

 distinguish models from one another. 



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