Development of GPS Measurement System and Characteristics Analysis for Long Period Gravity Wave That Induces Long Period Oscillation of Water Surface in Harbour

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When a harbor is designed, a general gravity wave (period about 0.1-10 second degree) causes various problems, but concerning about it some countermeasures are considered by marine engineering and results of research of civil engineering, and a considerable part is already solved. However a ship anchored or moored in a harbor is pitched and rolled by a long period gravity wave (for period dozens of seconds, several minutes), it's countermeasure cannot be still enough, and now some problems on a mooring line strength and cargo handling work are still remained. Such a long period wave (for the amplitude is less than dozens of cm, a period, about dozens of seconds, several minutes) that is propagated from the open sea and coastal waters area includes the following problems.(1) A strong detachment and early flow are caused in harbor mouth neighborhood by long water particle exercise orbit of a long period surge, and they cause a harbor burying by drifting sand of bottom of the sea.(2) By a … More strong detachment and early flow near harbor mouth, it causes a serious and security problem on a ship navigating a narrow area near harbor mouth.(3) Wave energy of a long period gravity wave has a small propagation and reflection decrement, and after incidence to a harbor a greater part of the wave energy is kept and it may grow in the case of resonance with the harbor inherent frequency.Then a dangerous pitching and rolling movements for a mooring or anchoring ship in the harbor are caused by it. These serious problems for harbor design and the anchorage in a harbor caused by such a long period wave is beginning to examine. There development of a study for a long period wave is expected immediately, because the cause and characteristics of a long period wave are not made clear yet.In particular it is appear that a study to make clear the causes and the characteristics of a long period gravity wave on the basis of an observation fact is important. However it is difficult that the measurement is done by conventional wave observation technology, because a period of the long period gravity wave is too long and amplitude of it is too small compared with a normal gravity wave.Therefore in this research arrayed wave observation buoys system whose 3 dimensional movements are measured precisely by the Carrier-Phase Differential GPS is proposed. In this proposed system, a wind wave direction which is observed in before Cloverleaf-Buoy and a 3 dimensional wave information of a long period wave are measured precisely. And an evaluation of effectiveness was carried out by the experiment on land and some computer simulations. As using this proposed system, it made clear the cause and characteristics of a long period gravity wave and solve some problems about a ship's mooring and anchoring or harbor design.In near future, we will be able to clear the characteristics of the long period gravity wave and some problems about safety of port and mooring ship according to the long period gravity wave with the use of our proposed GPS Measurement System. Less