Generation method of wind waves under long-fetch conditions over a broad range of wind speeds

Naohisa Takagaki , Satoru Komori , Koji Iwano , Naoya Suzuki , Hiroshige Kumamaru
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引用次数: 3

Abstract

It is important to develop a wave generation method for extending the fetch in laboratory experiments, because current laboratory studies are limited to fetch shorter than 100 m. Two wave generation methods are proposed for generating wind waves under long-fetch conditions in a wind-wave tank using a programmable irregular-wave generator. The first method is the spectral-model-based wave-generation method (SBWGM), which is appropriate at normal wind speeds for extending the fetch. The SBWGM also can be used at extremely high wind speeds if we know the spectral shape. In SBWGM, a conventional model of the wind-wave spectrum is used for the movement of the programmable irregular-wave generator. The second method is the loop-type wave-generation method (LTWGM), which can be used at wide range of wind speeds and is especially appropriate to be used at extremely high wind speeds, where the spectral shape is unknown. In LTWGM, the waves whose characteristics are most similar to the wind waves measured at the end of the tank are reproduced at the entrance of the tank by the programmable irregular-wave generator to extend the fetch. Water-level fluctuations are measured at both normal and extremely high wind speeds using resistance-type wave gauges. The results show that SBWGM can produces wind waves with a fetch over 500 m, but only at normal wind speeds. However, LTWGM can produce wind waves with long fetches exceeding the length of the wind-wave tank across a broad range of wind speeds, but considerable time is required to produce wind waves at long-fetch conditions, i.e. fetch over 500 m. It is observed that the wind-wave spectrum with a long fetch reproduced by SBWGM is consistent with that of the modelled wind-wave spectrum, although the generated wind waves are different from those in the open ocean because of the finite width of the tank. In addition, the fetch laws with significant wave height and period are confirmed for wind waves under long-fetch conditions. This implies that the ideal wind waves under long-fetch conditions can be reproduced using SBWGM with the programmable irregular-wave generator.

大范围风速下长时间风浪的产生方法
由于目前的实验室研究仅限于短于100米的提取,因此开发一种波的产生方法来延长实验室实验的提取是很重要的。提出了两种利用可编程不规则波发生器在风浪箱中产生长时间风浪的方法。第一种方法是基于频谱模型的波浪产生方法(SBWGM),该方法适用于正常风速,可以扩大提取范围。如果我们知道光谱形状,SBWGM也可以在极高的风速下使用。在SBWGM中,常规的风浪谱模型用于可编程不规则波发生器的运动。第二种方法是环型波浪产生法(LTWGM),这种方法可以在很宽的风速范围内使用,特别适合在极高的风速下使用,在这种情况下,频谱形状是未知的。在LTWGM中,通过可编程的不规则波发生器在水箱入口处再现与水箱末端测量到的风浪特征最相似的波浪,以延长提取时间。在正常风速和极高风速下,使用阻力式波浪计测量水位波动。结果表明,在正常风速下,SBWGM可以产生长度超过500 m的风浪。然而,LTWGM可以在很宽的风速范围内产生超过风浪箱长度的长距离风浪,但在长距离条件下,即超过500米的距离,产生风浪需要相当长的时间。结果表明,虽然由于槽体宽度有限,产生的风浪与公海上的风浪有所不同,但SBWGM模拟的长航段风浪谱与模拟的风浪谱基本一致。此外,还确定了长时间风浪的波高和周期显著的取风规律。这表明,采用可编程不规则波发生器的SBWGM可以再现长时间提取条件下的理想风浪。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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