항만 입구 수로의 세장형 복합방파제로부터 발생하는 연파의 해석

Abstract

This study analyzed and investigated the characteristics of the stem wave due to a series of long breakwaters at the entrance channel. The target structures are 1800m and 900m long breakwaters located at the front of Samcheok LNG production base of KOGAS, which had been constructed to allow mooring stability at the berth of the LNG vessel for natural gas supply in Gangwon and Yeongnam areas.

Under a certain condition, wherein the incident angle of waves is smaller than a critical angle to the vertical breakwater or sea dike, waves propagating along the front of the structures will be generated in addition to incident waves and reflected waves which is defined as a stem wave, and this causes maneuvering difficulty to the passing vessels and also it may bring erosion of shoreline with additional damages to berthing facilities.

Thus, in this study, we have investigated the response of stem wave at the vertical breakwater near the entrance channel and applied numerical models which are commonly used for the analysis of wave response at the harbor design. The basic equations composing models here adopted both the linear parabolic approximation adding the nonlinear dispersion relationship and nonlinear parabolic approximation adding linear dispersion relationship. In order to analyze the applicability of both models, we compared the numerical results with the existing hydraulic model results.

The difference of the stem wave amplification along the vertical breakwater is not significant and the regular wave model with non-linear dispersion relation shows undulation, whereas the Boussinesq model shows smooth response. In general the stem wave height increases at early stage but becomes stable after about 8 wave length away from the structure tip.

The gap of serial breakwaters and aligned angle cause more complicate stem wave generation and it was found a secondary stem wave form through the breakwater gap. Although the clear development of stem wave pattern did not appear, it was found a secondary stem wave form through the breakwater gap. There might be a possible stem wave development at the lee side of breakwaters through the gap depending on the incident wave direction. This impact should be included in the analysis of waterway tranquility near the breakwaters in the approaching channel.

Those analyzed results are to be applied to ship handling simulation study at the approaching channel, together with the mooring test.