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arXiv 1802.03586physics.flu-dyn
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重力水波破碎强度的预测

Predicting the breaking strength of gravity water waves

M. Derakhti, M. L. Banner, J. T. Kirby

摘要:

我们重温经典的,但尚未解决的问题,预测打破2-D和3-D重力水波的强度,量化的波能量耗散每个破碎事件。根据Duncan(1983)的观点,单位破碎波峰长度的波浪能量耗散率可能与波速的五阶矩和无因次破碎强度参数$b$有关。我们使用具有LES分辨率和流体表面体积重建的有限体积Navier-Stokes求解器(Derakhti和Kirby 2014 a,2016)来模拟波包演化,破裂开始和破裂后演化,这些波包的代表性情况是由于色散聚焦和调制不稳定性而破裂的波包。本研究使用这些结果来研究Barthelemy等人(2018)最近提出的断裂强度参数$b$和断裂起始参数$B$之间的关系。后者由通过局部能量密度和局部波峰速度归一化的局部能通量形成,在波浪表面上简化为流体速度与波峰速度的比率。在波峰之后,当$B$在波峰处超过一般阈值时(Barthelemy等人,2018年,破局在即。我们发现一个强大的破断强度参数$b$和破断起始参数,$dB/dt$在波峰的变化率之间的关系,因为它通过通用的破断起始阈值($B\sim 0.85$),按比例缩放的本地周期的破波过渡。这一结果显着细化以前的努力来表达$b$在一个波包陡度参数,这是很难定义的鲁棒性和不提供一个通用的准确预测的能量消耗的破碎。

英文摘要:

We revisit the classical but as yet unresolved problem of predicting the strength of breaking 2-D and 3-D gravity water waves, as quantified by the amount of wave energy dissipated per breaking event. Following Duncan (1983), the wave energy dissipation rate per unit length of breaking crest may be related to the fifth moment of the wave speed and the non-dimensional breaking strength parameter $b$. We use a finite-volume Navier-Stokes solver with LES resolution and volume-of-fluid surface reconstruction (Derakhti and Kirby 2014a, 2016) to simulate wave packet evolution, breaking onset and post-breaking evolution for representative cases of wave packets with breaking due to dispersive focusing and to modulational instability. The present study uses these results to investigate the relationship between the breaking strength parameter $b$ and the breaking onset parameter $B$ proposed recently by Barthelemy et al. (2018). The latter, formed from the local energy flux normalized by the local energy density and the local crest speed, simplifies, on the wave surface, to the ratio of fluid speed to crest speed. Following a wave crest, when $B$ exceeds a generic threshold value at the wave crest (Barthelemy et al., 2018), breaking is imminent. We find a robust relationship between the breaking strength parameter $b$ and the rate of change of breaking onset parameter, $dB/dt$ at the wave crest, as it transitions through the generic breaking onset threshold ($B\sim 0.85$), scaled by the local period of the breaking wave. This result significantly refines previous efforts to express $b$ in terms of a wave packet steepness parameter, which is both difficult to define robustly and which does not provide a generically accurate forecast of the energy dissipated by breaking.

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