A small-scale field experiment is conducted on a U-Oscillating Water Column (U-OWC) incorporated into a model of caisson breakwater at the Natural Ocean Engineering Laboratory (NOEL) laboratory of Reggio Calabria (Italy). The U-OWC or REWEC (REsonant Wave Energy Converter) is a device belonging to the family of Oscillating Water Columns (OWCs), characterized by the introduction of a U-duct. Such a device is innovative, absorbing a high percentage of incoming sea energy and, then, to produce electricity via a Power-Take-Off (PTO). The aim of the present study is the investigation of the wave pressures and forces acting on the U-OWC monolithic coastal defense structure. Moreover, the structural response of the U-OWC structure is also investigated under the occurrence of wave crests, by calculating the hydrodynamic forces realized in the active parts of the U-OWC. It is shown as a global additional force is realized, which contributes to increase the overall stability of the structure. Considering the wave loads acting on the U-OWC caisson, the post-process of the overall dataset recorded during the real field experiment at NOEL laboratory reveals the occurrence of both quasi-static loading (non-breaking), and of impact loading (impulsive) due to wave breaking. Thus, a systematic analysis is pursued in order to identify the loading cases acting on the U-OWC breakwater. When high non-breaking sea waves interact with the breakwater, “Quasi-Standing (QS)” wave pressures and forces occur at modified structure with two peaks of equal intensity. Instead, the impact of extreme breaking waves against the U-OWC structure generates asymmetrical wave pressure records beneath the wave crests, with two peaks with different intensity: the first one greater than the second one. In these cases, “Slightly Breaking (SB)” wave forces and “Impact Loads (IL)” are identified. Wave pressure distributions and forces acting on the U-OWC model are, then, investigated for the three classes of wave loads. Moreover, the probability of occurrence of maximum positive peak forces is determined from the experimental dataset, given a number of parameters. In particular, when QSWs occur, the maxima peak forces are recorded for deeper water depths , and , at given significant wave height . Instead, for SBWs and ILs, the extreme wave loads are realized, when the most severe sea states occur with higher , and for decreasing water depth . and Then, the influence both of the length of the berm and of the width of the U-duct in the front structure is considered. When the dimensions of both structural elements is reduced, the maxima wave forces occur in a fixed recorded sea state. Then, the Quasi-Determinism (QD) nonlinear model at the U-OWC breakwater is introduced for evaluation of Quasi-Standing wave loads, showing a good agreement among analytical and experimental results. Finally, the Goda's model is applied to calculate the wave pressure distributions acting on the external walls of the U-OWC model. The theoretical results given by the Goda's formulae are compared with experimental data, overestimating experimental results for both QSWs and SBWs and, significantly, underestimating IL conditions.

中文翻译：

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U-OWC 防波堤上波浪力的小规模现场实验

在意大利雷焦卡拉布里亚自然海洋工程实验室 (NOEL) 实验室，对纳入沉箱防波堤模型的 U 型振荡水柱 (U-OWC) 进行了小规模现场实验。U-OWC 或 REWEC（共振波能转换器）是属于振荡水柱 (OWC) 系列的设备，其特点是引入了 U 形管道。这种装置具有创新性，可吸收大量传入的海洋能量，然后通过动力输出装置 (PTO) 发电。本研究的目的是研究作用在 U-OWC 整体式海岸防御结构上的波浪压力和力。此外，通过计算 U-OWC 活动部分实现的水动力，还研究了出现波峰时 U-OWC 结构的结构响应。它表现为实现了全局附加力，这有助于提高结构的整体稳定性。考虑到作用在 U-OWC 沉箱上的波浪载荷，NOEL 实验室实际现场实验期间记录的整个数据集的后处理揭示了准静态载荷（非破坏）和冲击载荷（脉冲载荷）的发生。 ）由于波浪破碎。因此，我们进行了系统分析，以确定作用于 U-OWC 防波堤的载荷情况。当高的非破碎海浪与防波堤相互作用时，“准驻（QS）”波浪压力和力出现在修改后的结构上，具有两个强度相等的峰值。相反，极端破浪对 U-OWC 结构的冲击会在波峰下方产生不对称的波压记录，有两个不同强度的峰值：第一个峰值大于第二个峰值。在这些情况下，会识别“轻微破碎 (SB)”波浪力和“冲击载荷 (IL)”。然后，研究三类波浪载荷的波浪压力分布和作用在 U-OWC 模型上的力。此外，在给定许多参数的情况下，最大正峰值力发生的概率是根据实验数据集确定的。特别是，当 QSW 发生时，会记录较深水深和给定有效波高的最大峰值力。相反，对于 SBW 和 IL，当最严重的海况发生在较高的 和较低的水深时，会实现极端波浪载荷。然后，考虑前部结构中护堤长度和U型管宽度的影响。当两个结构元件的尺寸减小时，最大波浪力出现在固定记录的海况中。然后，引入 U-OWC 防波堤的准决定论 (QD) 非线性模型来评估准驻波载荷，结果显示分析结果与实验结果具有良好的一致性。最后，采用Goda模型计算U-OWC模型外壁上的波浪压力分布。将 Goda 公式给出的理论结果与实验数据进行了比较，高估了 QSW 和 SBW 的实验结果，并且显着低估了 IL 条件。