以NHWAVE模擬N型波之溯升

Abstract

溯升即海浪抵達陸地後可達之最大高程，是海嘯和波浪在海岸工程中的重要指標之一。海嘯由多個波浪疊加而成，當真實海嘯接近沿岸時，海水面經常被觀察到會先出現退縮的現象。早期，孤立波常作為海嘯替代模型，卻無法表現海水的退縮現象。因此許多學者陸續提出不同的替代波型，其中之一則為 N 型波。然而，以波浪數值模擬軟體模擬 N 型波的溯升，至今並無人制定其方法與流程。本篇文章則透過兩種波浪數值模擬軟體，分別模擬造波及溯升，完成一套有效率的 N 型波溯升模擬方法。完成驗證後並在後續模擬中發現，破碎 N 型波會比相對應之破碎孤立波的溯升值低，原因為損失能量與紊流耗散能量大於孤立波，擁有更強烈的破碎現象，越強烈的破碎現象會對沿岸造成越嚴重的破壞。因此，使用孤立波作為替代波型，可能會低估真實海嘯對沿岸的侵蝕與破壞。

Wave runup, the maximum elevation water can reach on land, is an important parameter in coastal engineering for both tsunamis and water waves. A tsunami is formed by the superposition of multiple waves. When a real tsunami approaches the coast, sea level is often observed to recede first before rising. In the past, solitary waves were often used as a substitute model for tsunamis, but they could not capture the phenomenon of sea water receding. Therefore, many scholars have proposed different alternative waveforms of tsunamis, one of which is the N-wave. However, no one has yet established a method and procedure for simulating the runup of N-waves using numerical wave simulation software. This article presents an efficient N-wave runup simulation method, which uses two simulation software: one for wave generation and the other for wave propagation and runup simulation. After validation and subsequent simulations, it was found that the broken N-wave has a lower runup value compared to the corresponding broken solitary wave. This is because the energy loss and turbulent dissipation in the broken wave are greater than in the solitary wave, resulting in a more intense breaking phenomenon. The stronger the breaking phenomenon, the more severe the coastal damage. Therefore, using solitary waves as a substitute wave type may underestimate the erosion and destruction caused by real tsunamis on the coast.