Spatial Distribution of the Wave Around Multiple Floating Bodies

摘要

When multiple cylinders are placed in waves with equal separationdistance, the near-trapped mode may occur between cylindersat some critical frequencies. To discuss validity of a linearpotential theory and nonlinear effects around near-trapping frequencies,spatially dense measurements are carried out for thefree-surface elevation around four truncated circular cylindersplaced at regular intervals in a straight line. At each of threewavelengths selected after preliminary measurements, two differentwaves in amplitude are generated with wave steepness H/X setapproximately to l/50 and l/20. Measured data are Fourier analyzed,separating into first- and second-order quantities. By comparisonwith computed results, linear-theory results at a neartrappedmode are found to be closer to the results measured atH/X ~1120 than to the ones at H/X -l/SO. At places where thefirst-order wave amplitude takes local maximum or minimum, thesecond-order wave amplitude becomes large. This experimentalfact, however, can not be explained only with the second-ordercomponent computed from quadratic products of the first-orderquantities, implying that the contribution of the second-order velocitypotential is important in the wave interactions.