Research and Development of a Hybrid Ocean Model for analysis of flows and diffusions around artificial structures in the coastal seas

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Outbreaks of red tide caused by the eutrophication are frequently reported around the coastal seas of Japan in recent years. They lead the water degradation of the sea and the coastal ecosystem is strongly damaged by the oxygen deficient water.Purpose of the development of a new ocean model is that we are interested in not only the analysis of the ocean environment but also the control of the ocean environment by manmade structures and apparatus. This requires a new model applicable in two different scales, small scale around such structures and large scale in the ocean. We have developed a hybrid model which consists of two different methods, a full three-dimensional (3-D) analysis using fine meshes in small fluid domain and a hydrostatic analysis in wider ocean. Experts for both methods in the group could work cooperatively and effectively.In this study, we have developed a hybrid model as following sub-problems :(1) Mesh generation method in coastal seas of Japan(2) A hydrostatic model used for the wider seas(3) A full 3D model used for the narrow water sea(4) Parallel or nested calculations in both domains(5) Visualization of the resultsAs an application example, the effects of the "Density current generator" on the density stratification were demonstrated in Gokasho Bay. We are also preparing a research paper on an upwelling structure on the sea-bottom. We conducted ocean measurements in Ariake Sea for the validation of our numerical model, and the part of the results on the physical environments in Ariake Sea was reported at some academic societies.