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Research for the Opening width and End process on the artificial reefs

人工鱼礁开口宽度及端部工艺研究

基本信息

批准号：
15560449
负责人：
MINAMI Masato
金额：
$ 0.96万
依托单位：
Hachinohe National Collage of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15560449/
关键词：
Artificial Reefs Opening Local Scour Topographical Change Return Flow End process

项目摘要

From views of environment and seascape, artificial reefs are replacing detached breakwaters as coastal protection structures. The purpose of this study is to know the influence of narrowing the reef gap on the bottom current velocity. We conducted numerical analysis by using the fully nonlinear Boussinesq equations derived by Wei etal (1995) and taking account of the energy dissipation due to wave breaking. This method was applied to the actual field in Japan Sea. Three ratios of opening width, W to the top deck length of the artificial reef, Lr; Lr/W=3, 4, and 5 are examined. The return flow velocity at the opening was 1.9 and 1.8 times of that evaluated from the mass transport for Lr/W= 3 and 5, respectively. Increase of return flow velocity is quantitatively shown for narrowing the gap. Moreover, the circulation pattern inside the reefs is changed by the width of the gap. And since the responses of the bottom shear stress, which is the major force to transport the sea bottom sediment, to the bottom water particle velocity are different for steady currents and for oscillatory currents the decomposition of currents into two modes is necessary. The bottom shear stress was evaluated by the decomposed velocities together with the friction factor. The topographical change was computed by the sediment flux and budget equations. The simulated results were verified through the comparison with the experimental ones in the hydraulic laboratory. This method was also applied to the actual field facing Japan Sea and quantitatively reproduced the measured local scour at the offshore region of the reef opening. This application shows that one-storm waves with the duration of 24 hours can produce significant scour of the maximum depth, 3m.

从环境和海景的角度来看，人工鱼礁正在取代独立式防波堤作为海岸防护结构。本研究的目的是了解礁口变窄对底流流速的影响。采用埃塔尔（1995）推导的完全非线性Boussinesq方程，考虑波浪破碎的能量耗散，进行了数值分析。并将该方法应用于日本海的实际现场。三个比率的开口宽度，W的人工鱼礁，Lr的顶部甲板长度，Lr/W=3，4和5进行了检查。在开口处的回流速度分别是Lr/W= 3和5时从质量传递评估的回流速度的1.9和1.8倍。定量地显示了回流速度的增加对于缩小差距的作用。此外，礁内的环流模式也会因差距的宽度而改变。由于海底剪切力是海底泥沙输移的主要动力，对于定常流和振荡流，剪切力对底层水质点速度的响应是不同的，因此有必要将流场分解为两个模态。由分解后的流速和摩阻系数计算出底切应力。地形变化由泥沙通量和收支方程计算。通过与水力学实验室试验结果的对比，验证了模拟结果的正确性。该方法也被应用到面向日本海的实际现场，并定量地再现了在礁口近海区域的实测局部冲刷。该应用表明，持续时间为24小时的一次风暴波可以产生最大深度为3 m的显著冲刷。