Journal of Korean Society of Coastal and Ocean Engineers (한국해안·해양공학회논문집)

Korean Society of Coastal and Ocean Engineers (한국해안·해양공학회)
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Mean Overtopping Discharges and Transmitted Wave Heights for Evaluation of Crest Freeboards of Breakwaters

방파제의 마루높이 산정을 위한 평균 월파량과 전달파고

  • Lee, Cheol-Eung (Department of Architectural, Civil, and Environmental Engineering, Kangwon National University)
  • 이철응 (강원대학교 건축.토목.환경공학부)
  • Received : 2021.03.16
  • Accepted : 2021.04.15
  • Published : 2021.04.30
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Abstract

A method that can take into account the transmitted wave heights and the allowable overtopping discharges together has been presented in order to determine the crest freeboards of breakwaters. Thus, the relationships of the incident waves, mean overtopping discharges and the transmitted wave heights have been quantitatively analyzed by various empirical equations which have separately been used according to the types of breakwaters up to recently. The present results have been satisfactorily calibrated through the comparison with the previous results of EurOtop (2018) for the same condition. The relationships of dimensionless mean overtopping discharges and wave transmission coefficients for any incident waves have also been presented and compared them with the types of breakwaters. In addition, the allowable overtopping discharges can be evaluated from the combinations of the transmitted wave heights and the mean overtopping discharges with respect to the various periods and heights of incident waves. Finally, the method for determining the relative crest freeboards of breakwaters with the allowable overtopping discharges has been applied to both the rubble-mound breakwaters and the composite breakwaters. It has been found that the relative crest freeboards of breakwaters tend to be decreased sharply as the allowable overtopping discharges are increasing. In particular, the relative crest freeboards of composite breakwaters should be larger than those of the rubble-mound breakwaters under the condition of the same overtopping discharges in the small ranges, whereas the opposite trends can be shown for the allowable overtopping discharges in the large range over some amounts of level. This may be due to the effects of that the relatively larger transmitted wave heights can be induced by the direct impacts of the overtopping discharges to the harbors inside the composite breakwaters, while, in the rubble-mound breakwaters, the overtopping discharges are mildly transferred along the inside slopes of breakwaters. However, these effects seem to be neglected when the overtopping discharges become very large, the penetration effects may even be considered in the rubble-mound breakwaters instead.

전달파고와 허용 월파량을 함께 고려하여 방파제의 마루높이를 결정할 수 있는 방법을 제시하였다. 방파제를 형식별로 구분하여 현재 가장 일반적으로 사용되는 경험식들을 활용하여 입사파고와 평균 월파량 그리고 전달파의 관계를 정량적으로 해석하였다. 기존의 연구 결과와 비교하여 만족스럽게 검증되었으며, 임의의 입사파랑에 대하여도 적용할 수 있는 무차원 평균 월파량과 전달계수의 관계도 방파제 형식별로 제시, 비교하였다. 또한 주기 및 파고 변화에 따른 평균 월파량과 전달파고의 관계를 수립하여 허용 월파량을 산정할 수 있었다. 마지막으로 허용 월파량에 따른 상대 마루높이 결정방법을 경사제와 무공 케이슨식 혼성제에 적용하였다. 경사제와 혼성제 모두에서 허용 월파량이 커지면 상대 마루높이는 급격하게 작아지는 경향을 보였다. 특히 상대적으로 작은 범위에서는 허용 월파량이 동일해도 혼성제의 마루높이가 경사제의 마루높이보다 커야 하지만, 일정 수준 이상의 큰 허용 월파량에 대해서는 그 반대의 경향을 보였다. 혼성제의 경우는 월파량이 작아도 항내로 직접 낙하하여 상대적으로 큰 항내 전달파고를 유발하지만, 월파량이 일정 수준을 넘어서면 방파제의 형식에 따른 영향이 작아지면서 제체를 통한 투과파의 영향이 경사제에 고려되기 때문이다.

Keywords

Acknowledgement

본 연구는 해양수산과학기술진흥원의 지원(과제번호 20180323)으로 수행되었으며 지원에 감사드립니다.

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