海洋波集波レンズの基礎的研究(第二報) : 水槽実験

概要

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We carried out experiments of wave focusing by two kinds of Fresnel lenses, which are 20m long and consist of a horizontally submerged flat plate and an array of submerged circular cylinders, in a wave tank of 30mx50mx2.4m. The results show that the circular cylinder type produces higher wave power magnification at a focal point than the flat plate type in both regular and irregular waves, but that the magnification is affected by the lens' shape and nonlinearity of a free surface. The three dimensional singularity distribution method demonstrates that a Fresnel lens significantly reduces the predicted wave height magnification by slender ship theory and that a convex lens hardly does that even when its slenderness is relatively large. It is shown by experiments in a narrow wave tank that the breaking limit of waves passing over a submerged plate and an array of submerged circular cylinders is given by the ratio of the wave height of incident waves to the submerged depth and independent of wave frequencies and the number of cylinders. Nonlinear effects of a free surface of one dimensional concentration of transient waves agree with those of two dimensional wave focusing very well. Furthermore, an approximated nonlinear wave theory estimates the nonlinear effects with increase of wave slope around a focal point.
社団法人日本船舶海洋工学会の論文