J Coast Disaster Prev > Volume 7(4); 2020 > Article
Journal of Coastal Disaster Prevention 2020;7(4):181-193.
DOI: https://doi.org/10.20481/kscdp.2020.7.181    Published online October 30, 2020.
Numerical Analysis of the Changes in Sea Wave Conditions by the Presence of LCB [Low Crested Breaker]: Centered on Rip Current Formed at the Open Inlet between LCB
Yong Jun Cho
저천단방파제 거치로 인한 해양 수환경 변화 수치해석
조용준
 
Abstract
In this study, we numerically analyzed the sea wave conditions change induced by the presence of LCB[Low Crested Breaker] with an emphasis on the rip current formed at the open inlet between LCB. The current formed at the open inlet between LCB went through a lot of changes, and these changes can be summarized as the phase lag behind LCB, intensified offshore directed flow and weakened shoreward flow, increased duration period of offshore directed flow. The growth rate of offshore directed flow reaches its maximum in RUN 1D where the highest transmitted ratio of incoming wave energy is anticipated due to the low crest height of LCB. The growth rate is around 35%, and the maximum growth rate is observed to occur near the sea bottom. Numerical results show that offshore directed flow persists for nearly 75% of unit wave period in RUN 1D where Cnoidal waves of the shortest period is used as incoming waves. Shoreward flow most visibly weakened in RUN 1D where transmitted ratio is relatively high, and from these facts we can induce that the rip current formed at the open inlet between LCB is strongly correlated with a transmitted ratio of incoming wave energy. It is also shown that the period of incoming waves bears a great impact on the rip current formed at open inlet, and an intensified offshore directed flow and weakened shoreward flow are most visible in RUN 2D where LCB is exposed to relatively longer Cnoidal waves. The triggers of these tendencies are traced back to the facts that as waves are getting longer, the water volume above mean water level increases and as a result, the transmitted mass per unit wave period is getting increased, leading the lager wave set-up at down wave side of LCB and intensified rip current.
Key Words: LCB[Low Crested Breaker]; rip current at the open inlet; counter measures against beach erosion; optimization of LCB; IHFOAM; RANS[Reynolds Averaged Navier-Stokes equation]
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