Long Period Oscillations in Kasumi Fishing Port

Abstract

Kasumi Fishing Port occasionally suffers from long period oscillations caused by northwest monsoons in winter. The authors settled 2 wave gauges and a current meter inside the port and a wave gauge outside. They analysed the data observed during 84-85 winter and simulated numerically to identify prevailing modes of long period oscillations. Long period oscillations are summarized as follows. 1) Cargo handling is influenced by long period oscillations when slgnificant wave heights (H_1/3) of surface waves exceed 5 to 6m outsidethe port, corresponding to a third to a probability year. 2) Outside the port, long waves are regarded as surfbeatswhen long wave heights (H) rapidly augment with the increase of H_1/3 above 2m. Long wave periods (T) of surf beats center on one minute. In Kasumi Bay, prevail free oscillations with T over 10 minutes, when H_1/3 falls below 2m. 3) Inside the port, develop forced oscillations with T of approximately 4 minutes when H_1/3 >2m. They are replaced by free oscillations with T over 10 minutes when H_1/3 <2m. 4) Prevailing periods of currents are 1 minutes, 4 minutes and over 10 minutes. In the port, cargo handling is influenced by long wave height, current Velocity approaching to 1m/s at the entrance and oscillatory displacement beyond 20m in some area behind the entrance.