Spatial Distribution of the Wave Around Multiple Floating Bodies

摘要

When multiple cylinders are placed in waves with equal separation distance, the near-trapped mode may occur between cylinders at some critical frequencies. To discuss validity of a linear potential theory and nonlinear effects around near-trapping frequencies, spatially dense measurements are carried out for the free-surface elevation around four truncated circular cylinders placed at regular intervals in a straight line. At each of three wavelengths selected after preliminary measurements, two different waves in amplitude are generated with wave steepness H/lambda set approximately to 1/50 and 1/20. Measured data are Fourier analyzed, separating into first- and second-order quantities. By comparison with computed results, linear-theory results at a neartrapped mode are found to be closer to the results measured at H/lambda approx = 1/20 than to the ones at H/lambda approx = 1/50. At places where the first-order wave amplitude takes local maximum or minimum, the second-order wave amplitude becomes large. This experimental fact, however, can not be explained only with the second-order component computed from quadratic products of the first-order quantities, implying that the contribution of the second-order velocity potential is important in the wave interactions.