Elandt Ryan B, Shakeri Mostafa, Alam Mohammad-Reza
Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Feb;89(2):023012. doi: 10.1103/PhysRevE.89.023012. Epub 2014 Feb 19.
Here we show that a nonlinear resonance between oceanic surface waves caused by small seabed features (the so-called Bragg resonance) can be utilized to create the equivalent of lenses and curved mirrors for surface gravity waves. Such gravity wave lenses, which are merely small changes to the seafloor topography and therefore are surface noninvasive, can focus or defocus the energy of incident waves toward or away from any desired focal point. We further show that for a broadband incident wave spectrum (i.e., a wave group composed of a multitude of different-frequency waves), a polychromatic topography (occupying no more than the area required for a monochromatic lens) can achieve a broadband lensing effect. Gravity wave lenses can be utilized to create localized high-energy wave zones (e.g., for wave energy harvesting or creating artificial surf zones) as well as to disperse waves in order to create protected areas (e.g., harbors or areas near important offshore facilities). In reverse, lensing of oceanic waves may be caused by natural seabed features and may explain the frequent appearance of very high amplitude waves in certain bodies of water.
我们在此表明，由小的海床特征引起的海洋表面波之间的非线性共振（即所谓的布拉格共振）可用于为表面重力波创建相当于透镜和曲面镜的装置。这种重力波透镜只是对海底地形的微小改变，因此是表面非侵入性的，它可以将入射波的能量聚焦或散焦到朝向或远离任何所需焦点的方向。我们进一步表明，对于宽带入射波谱（即由许多不同频率的波组成的波群），多色地形（占据不超过单色透镜所需的面积）可以实现宽带透镜效应。重力波透镜可用于创建局部高能波区（例如用于波浪能收集或创建人工冲浪区），以及分散波浪以创建保护区（例如港口或重要近海设施附近的区域）。相反，海浪的透镜效应可能由天然海床特征引起，并且可能解释了某些水体中经常出现非常高振幅波浪的现象。
