Research on Application of Numerical Simulation of Sea Water to Ocean Engineering

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In order to validate numerical simulation program of sea water movement, oceanophysical measurement of temperature and salinity of sea water around an existing large floating structure (which is called Mega-Float structure : 300m in length, 60m in breadth, 2m in depth and 0.5m in draft) moored off Oppama in Tokyo Bay was started in August 1996 and is still now underway.The main results of this oceanophysical measurement and numerical experiment are as follows(1) Mega-Float structure does not produce any remarkable oceanophysical effect on the surrounding sea water. The variation of water temperature and salinity in the close vicinity of Mega-Float structure are mainly subject to the tidal current caused in the mooring site of Mega-Float structure.(2) In summer of 1996 and 1997, anomalous sudden fall of sea water temperature and rise of salinity were observed several times along the west coast of Tokyo Bay, i.e.off Oppama and off Negishi. These phenomena occurred in a common situation that typhoons stayd for a while in the western part of Japan or passed though it, and consequently, relative strong blow of southwesterly wind lasted for a few days in Tokyo Bay. On the occasion of the typhoon NO.12 in the middle of August 1996, salinity increase was about 3.5psu and temperature drop was about 6ﾟC.As a result of numerical simulation, it was found that these unusual temperature drop and salinity increase were induced by the so-called coastal up-welling caused by continuous blow of southwester in Tokyo Bay.Besides, numerical simulation can provide us with a very useful tool of predicting the sea water movement in a small sea area such as Mega-Float structure with accuracy enough for practical use.