Collaborative Research : Nonlinear Long Wave Amplification in the Shadow Zone of Offshore Islands

最近海啸的实地调查报告显示，在被附近岛屿笼罩的大陆地区，当地居民可能认为这些岛屿可以保护他们免受海啸的侵袭。最近使用被称为“主动学习”的数学程序的数值结果引起了世界媒体（《经济学人》、《明镜周刊》、《科学》、《韩国先驱报》、《Kathimerini》）的大量关注，因为它们表明，在大多数情况下，岛屿放大了海啸背后阴影区的海啸。在这个应用中，主动学习方法需要的计算量比传统数学方法少10万倍左右，而且目前还不清楚这种放大效应是否真实。通过综合的实验室实验，研究这种效应的物理表现。如果物理实验确实证实了数字理想化，这项研究将通过更好地针对高危人群开展教育活动来帮助拯救生命。例如，将确定美国太平洋沿岸被近海岛屿笼罩的海岸线是否比之前认为的更脆弱。主动学习的早期数值结果只适用于非破碎波。虽然许多现有的数字代码试图模拟轻微的长波断裂，正如它们有时所做的那样，但尚不清楚它们在散射长波断裂和相互作用时的表现如何。同样不清楚的是，岛屿之间的地峡是分散了波浪能量，还是进一步集中在岛屿后面的大陆上，或者在什么地理条件下，这两种效应都会发生。通过实验室实验，将确定波浪破裂时这种令人烦恼的现象是否仍然存在。结果将有助于验证主动学习作为一种减少不确定性的数学过程，大大降低了计算成本。此外，将开发大量的实验室数据集，以帮助在尚未研究的条件下相互作用的破波锋面的基准数值计算。计划开展一项外联运动，教育处于危险中的人口，提高应急管理人员对这一不寻常的扩大现象的认识。

Field survey reports from recent tsunamis suggest that local residents in mainland areas shadowed by nearby islands may be under the impression that these islands protect them from tsunamis. Recent numerical results using the mathematical procedure known as "active learning" have generated substantial attention in world media (The Economist, Der Spiegel, Science, Korean Herald, Kathimerini), because they suggest that, in most cases, islands amplify tsunamis in the shadow zones behind them. In this application, the active learning methodology requires about 100,000 times fewer computations than conventional mathematical approaches, and it is unclear if the amplification effect is real. Through comprehensive laboratory experiments, the physical manifestation of this effect will be studied. If indeed the physical experiments confirm the numerical idealizations, this research will help save lives by better targeting educational campaigns to at risk populations. For example, it will be determined if coastlines shadowed by offshore islands along the Pacific Coast of the US are more vulnerable than earlier believed. The early numerical results from active learning are only applicable for non-breaking waves. While many existing numerical codes attempt to model mild long-wave breaking, as they sometimes do, it is unclear how well they perform when scattered long waves break and interact. It is equally unclear if the isthmus between islands scatters the wave energy or focuses further in the mainland behind them, or under what geographical conditions either effect prevails. Through the laboratory experiments, it will be determined if this vexing phenomenon persists when waves break. The results will help validate active learning as a mathematical procedure for uncertainty reduction which greatly reduces computational costs. Also, a substantial laboratory data set will be developed to help benchmark numerical computations for interacting breaking wave fronts, under conditions as yet unstudied. An outreach campaign is planned to educate populations at risk and improve the awareness of emergency managers on this unusual amplification phenomenon.