Effects of Hydrodynamic Forces acting on Cold Water Pipe and Mooring Line on Motions of OTEC Platform

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Other Title
  • 海洋温度発電のためのステーションの運動と係留 : その2.係留鎖の動的影響について
  • 海洋温度差発電のためのステーションの運動と係留-2-係留鎖の動的影響について
  • カイヨウ オンドサ ハツデン ノ タメ ノ ステーション ノ ウンドウ ト ケ

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Abstract

Effects of hydrodynamic forces acting on the cold water pipe and mooring lines on motions of the OTEC platform are investigated experimentally and theoretically. Hydrodynamic forces acting on the cold water pipe and mooring chains oscillating in a water are obtained by using mode methods. The computer time needed for the calculations are very short, so these methods proposed in this paper are of much practical use. Calculated results of the bending moment and shearing force of the cold water pipe at its upper end, the horizontal and vertical components of the dynamic tension of the mooring chain at the mooring point are compared with those of experiments. They are in good agreements. Wave exciting forces and hydrodynamic forces acting on the platform are obtained with the surface integral equation method. The results of calculations are compared with those of forced-surging tests and wave force measurements. The calculated results coinside with experimens. Experiments and theoretical calculations on the motions of the moored OTEC platform show that the viscous drag forces acting on the cold water pipe and mooring chains have a great effect on the pitching motion at its resonant period. They act as the viscous damping forces for the motion of the platform at its resonant period, and reduce its magnification factor. We could not confirm this fact experimentally in the cases of heaving and surging motion, because resonant periods of these motions are very long and beyond the ability of our experimental facilities, but the applicability of the calculation method is well confirmed by the experiments on the pitching motion. The heaving and surging motion at their resonant periods can be estimated with enough accuracy by using the calculation method proposed in this report.

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