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首页> 外文期刊>Journal of Physical Oceanography >The Formation Of Parasitic Capillary Ripples On Gravity-capillary Waves And The Underlying Vortical Structures
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The Formation Of Parasitic Capillary Ripples On Gravity-capillary Waves And The Underlying Vortical Structures

机译：重力-毛细管波上的寄生毛细管波纹的形成及其下伏的涡旋结构

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The evolution of moderately short, steep two-dimensional gravity-capillary waves, from the onset of the parasitic capillary ripples to a fully developed quasi-steady stage, is studied numerically using a spectrally accurate model. The study focuses on understanding the precise mechanism of capillary generation, and on characterizing surface roughness and the underlying vortical structure associated with parasitic capillary waves. It is found that initiation of the first capillary ripple is triggered by the fore-aft asymmetry of the otherwise symmetric carrier wave, which then forms a localized pressure disturbance on the forward face near the crest, and subsequently develops an oscillatory train of capillary waves. Systematic numerical experiments reveal that there exists a minimum crest curvature of the carrier gravity-capillary wave for the formation of parasitic capillary ripples, and such a threshold curvature (≈0.25 cm~(-1)) is almost independent of the carrier wavelength. The characteristics of the parasitic capillary wave train and the induced underlying vortical structures exhibit a strong dependence on the carrier wavelength. For a steep gravity-capillary wave with a shorter wavelength (e.g., 5 cm), the parasitic capillary wave train is distributed over the entire carrier wave surface at the stage when capillary ripples are fully developed. Immediately underneath the capillary wave train, weak vortices are observed to confine within a thin layer beneath the ripple crests whereas strong vortical layers with opposite orientation of vorticity are shed from the ripple troughs. These strong vortical layers are then converted upstream and accumulate within the carrier wave crest, forming a strong "capillary roller" as postulated by Longuet-Higgins. In contrast, as the wavelength of the gravity-capillary wave increases (e.g., 10 cm), parasitic capillary ripples appear as being trapped in the forward slope of the carrier wave. The strength of the vortical layer shed underneath the parasitic capillaries weakens, and its thickness and extent reduces. The vortices accumulating within the crest of the carrier wave, therefore, are not as pronounced as those observed in the shorter gravity-capillary waves.
机译：使用频谱精确模型，对从寄生毛细血管波纹的发作到完全发展的准稳态阶段的中等短而陡峭的二维重力毛细管波的演化进行了研究。这项研究的重点是了解毛细血管产生的精确机理，并表征表面粗糙度和与寄生毛细波相关的潜在涡旋结构。已经发现，第一毛细管波纹的产生是由另外对称的载波的前后不对称触发的，然后在波峰附近的前表面上形成局部压力扰动，并随后产生振荡的毛细管波列。系统的数值实验表明，在寄生毛细血管波纹的形成过程中，存在载流子重力毛细管波的最小波峰曲率，这种阈值曲率（≈0.25cm〜（-1））几乎与载波波长无关。寄生毛细管波列的特性和所引起的下面的涡旋结构表现出对载波波长的强烈依赖性。对于具有较短波长（例如5cm）的陡峭重力毛细管波，在毛细管波纹充分发展的阶段，寄生毛细管波列分布在整个载波表面上。在毛细管波列的正下方，观察到弱涡旋限制在波纹波峰下方的薄层内，而具有相反涡旋方向的强涡旋层则从波纹波谷中脱落。然后，这些强涡旋层向上游转换并在载波波峰中积累，形成了Longuet-Higgins所假定的强“毛细管辊”。相反，随着重力-毛细管波的波长增加（例如10cm），寄生毛细管波纹被捕获在载波的前向斜率中而出现。脱落在寄生毛细管下方的涡旋层强度减弱，厚度和范围减小。因此，在载波波峰中累积的涡旋不如在较短的重力毛细管中观察到的涡旋明显。

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