The combined action of waves and currents can lead to the generation of freespans that have significant influence on both pipeline on-bottom stability and structural integrity. Several studies have been carried out since the 80’s to analyse the onset of the scour process and the related phenomena in the presence of either waves or currents, while only a few studies regard the combination of waves and currents. Moreover, the main empirical expressions coming from such studies cannot adequately represent the physics of the phenomena and lead to non-conservative results. For that purpose, a reanalysis of existing datasets on the onset of scour due to waves and/or currents has been carried out to obtain a coherent method for the evaluation of the critical embedment associated to such mixed flow conditions. In addition, an analytical study has been used to quantify the parameter when waves are combined with currents, for a more correct application of such empirical formulas. These results will be integrated into a probabilistic model for the long-time evolution of freespans for the evaluation of the structural stability of pipelines in the marine environment, although the present approach can be exploited for a broader range of offshore applications that deal with the combined action of waves and currents.

中文翻译：

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关于管道冲刷的开始：协调波浪和水流的强迫

波浪和水流的共同作用会导致自由跨度的产生，这对管道底部稳定性和结构完整性产生重大影响。自20世纪80年代以来，已经开展了几项研究来分析在波浪或水流存在的情况下冲刷过程的开始和相关现象，而只有少数研究涉及波浪和水流的组合。此外，来自这些研究的主要经验表达式不能充分代表现象的物理原理并导致非保守的结果。为此，对波浪和/或水流引起的冲刷发生的现有数据集进行了重新分析，以获得用于评估与此类混合流条件相关的临界嵌入的一致方法。此外，还通过分析研究对波浪与水流结合时的参数进行了量化，以便更正确地应用此类经验公式。这些结果将被整合到自由跨度长期演化的概率模型中，以评估海洋环境中管道的结构稳定性，尽管本方法可以用于更广泛的海上应用，处理组合波浪和水流的作用。