Fundamentals of overtopping from individual violent water wave impacts

水波冲击海岸建筑物，如海堤、堤防和防波堤，可导致水漫过建筑物。这可能会给建筑保护的区域带来困难，并可能损坏结构。以前大多数关于溢流的研究都考察了给定海况下的总水流，而考虑个别海浪事件的研究要少得多。后者专注于收集有关溢流事件的数据，而不是将其与入射波的行为直接联系起来，这是拟议工作的重点。许多类型的扰动和破坏与单个溢流事件的关系比与较长时期的总流量更密切。我们最近对波浪撞击墙壁进行了大量的实验和数值模拟工作，表明了相对罕见的非常剧烈的撞击可能具有的重要性，并为波浪漫顶的定量模拟提供了基础，无论是猛烈的波浪还是更普通的波浪。更多地了解这些罕见事件对海岸工程研究人员和从业者来说都是很有价值的。本次调查将再次利用交互式物理和数值模型研究的优势，作为获得对复杂波浪现象的新见解的一种手段。因此，建议将重点放在具有特殊科学意义的情况上，而不是进行广泛的参数检验。例如，我们注意到，在陡峭的海滩/缓坡结构上，很少有人研究破碎和不破碎的波浪之间的过渡，预计会发现陡坡上坍塌和涌动的破浪在波浪和溢流方面存在显著差异。还将研究结构几何形状的影响，如不同的坡度和屋脊宽度。即将到来的海浪要么越过平面倾斜的河床，要么与建筑物底部的土丘相遇，这可能会触发俯冲或溢出的破碎机。将进行水高、流量和压力的实验测量。流动将通过修改现有程序进行数值模拟，其中一个程序包括可压缩性，当空气被水困住或夹带时，可压缩性可能是重要的。通过纳入这些影响，可以改进从实验室测量结果到原型规模的比例。我们预计流过建筑物的水流在很大程度上取决于它的表面粗糙度，而许多防护结构是由非常粗糙的单元组成的。研究将考虑简单的粗糙度元素；例如，从表面突出的圆柱体。单个粗糙度元素周围和上方的流动将与它们的整体效果相关。在最猛烈的波浪冲击情况下，我们预计粗糙度也可以通过其对流动的扰动作用来减小最大压力。理论工作将包括分析研究以及利用现有的数值程序。分析研究是这项提议的一个“蓝天”因素，因为它相当具有挑战性。它将建立在斯瓦什模型的基础上，因为之前很少有关于超越性的结果。然而，分析结果对于理解不同的水流流态是非常有价值的。总而言之，本研究各方面的结果将被用来开发改进的溢流事件模型，预计将对防波堤和海堤等海岸建筑物的设计者有用。

Water wave impact on coastal structures such as sea walls, dikes and breakwaters, can lead to water overtopping the structure. This can cause difficulties in the area the structure was built to protect, and possibly damage the structure. Most previous studies of overtopping have examined the total flow of water for a given sea state, and many fewer studies consider individual wave events. These latter have focussed on collecting data on the overtopping event rather than relating it directly to the behaviour of the incident wave, which is the focus of the proposed work. Many types of disturbance and damage are more closely related to individual overtopping events than to the total flow over a longer period. Our recent substantial experimental and numerical modelling work on wave impact on walls, shows the likely importance of relatively rare very violent impacts, and provides a basis for quantitative modelling of wave overtopping, of both violent and more ordinary waves. Greater understanding of these infrequent events will be valuable for both coastal engineering researchers and practitioners alike.The present investigation will again capitalise on the advantages of interactive physical and numerical model studies as a means of gaining new insights into complex wave phenomena. Thus, it is proposed to concentrate in detail on situations of particular scientific interest rather than engage in extensive parametric testing. We note, for example, that there has been little study of the transition between breaking and non-breaking waves on steep beaches / gently sloping structures and expect to find significant differences in swash and overtopping between collapsing and surging breakers on a steep slope. Effects of the structure's geometry, such as different slopes and crest width, will also be examined. The approaching waves will either come over a plane sloping bed or meet a mound at the base of the structure that can trigger plunging or spilling breakers. Experimental measurements of water height, flow rate and pressure will be made. The flow will be numerically modelled by modifying existing programs, one of which includes the compressibility that can be important when air is trapped or entrained by the water. Scaling of results from laboratory measurements to prototype scale can be improved by including such effects. We expect the flow over a structure to depend significantly on its surface roughness, and many protective structures are made of units which are very rough. The study will consider simple roughness elements; for example circular cylinders projecting from the surface. Flow around and over a single roughness element will be related to their overall effect. In the case of the most violent wave impacts we expect that the roughness may also diminish the maximum pressure, by its disturbing effect on the flow.Theoretical work will include analytical study as well as making use of existing numerical programs. Analytical study is a 'blue skies' element of this proposal in that it is rather challenging. It will build on models of swash, since there are very few previous results for overtopping. However, analytical results can be of great value in comprehending different flow regimes.Overall, results from all aspects of this study are to be used to develop improved models of overtopping events that are expected to be useful for designers of coastal structures such as breakwaters and seawalls.