Page 239 - Practical Design Ships and Floating Structures

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TABLE 1
CHEMICAL AND BIOLOGICAL COMPARTMENTS IN COASTAL ECOSYSTEM MODEL

In the meantime, for environmental impact assessment of the VLFS, numerical simulation by means of
the coastal ecosystem model is thought to be one of the useful tools. Recently, the model can reproduce
general variations in marine environment by a method of real time simulation, in which boundary
conditions change every time (Kitazawa et al. (2001)). And several simulations of the coastal
ecosystem around a VLFS are also conducted and its effects on surrounding marine environment are
discussed (Kyozuka et al. (1997), Kitazawa & Fujino (1999)). However, in these simulations, an
imaginary VLFS is installed in the constant condition of marine environment in summer, and
numerical results are not compared directly with the field data around the VLFS. Therefore, the
purpose of the present paper is to simulate the coastal ecosystem around a Mega-Float model by a
method of real time simulation, and to examine the effects of the floating structure on the surrounding
marine environment by direct comparison of predictions with observations.

2 NUMERICALMODEL

2.1 Coastal Ecosystem Model
Numerical model adopted in the present study is what was used by the authors previously. The model
consists of physical and chemical-biological submodels, the latter of which is divided into pelagic and
benthic submodels. In physical submodel, governing equations are as follows; the equations of fluid
motion, the equation of continuity, the diffusion equations of water temperature and salinity, and the
state equation of water density. And in the chemical-biological submodel, compartments summarized
in Table 1 and interactions among these compartments are taken into account. Time variations of
compartments in pelagic environment (listed in the left side of Table 1) are described by
advection-diffusion equations. These equations in physical and chemical-biological submodel are
solved by a finite difference scheme. Details of physical and chemical-biological submodels refer to
Kitazawa and Fujino (1999), and Kitazawa et al. (2001), respectively. When a Mega-Float model is
assumed to exist, activities of sessile organisms adhering to the floating structure are formulated
according to Kitazawa et al. (2000).

22 Numerical Conditions
Figure 1 shows location of Tokyo Bay in Japan, and modeling of Tokyo Bay and of the sea area
adjacent to the Mega-Float model. The sea area in Tokyo Bay is latticed with square grids in the
horizontal direction, and multilevel model, in which the number of the layers is 10, is adopted in the
vertical direction. To get detailed knowledge on the variation of current speed and water quality around
the Mega-Float model, much finer grids are adopted in the sea area adjacent to the floating structure.
Four kinds of square-grid are used; 1620m (Rank I), 540m (Rank 2), 180m (Rank 3) and 60m (Rank
4). The Mega-Float model (Length 300m, Width: 6Om, Draft 0.5m) is moored in the sea area off