Skip to main content

Environmental design of low crested coastal defence structures (DELOS)

Article Category

Article available in the folowing languages:

Fluid dynamics models for low crested structures

The Sediment Dynamics Research Group (SDRG) at the University of Southampton set about building on the rich history of European scientists in the field of fluid dynamics. Their goal was to properly model the myriad of forces affecting marine breakwaters.

Climate Change and Environment

Over the past several centuries, Europeans from England (William Froude) to France (Augustin Cauchy) to Germany (William Weber) have made important contributions to fluid dynamics theory. The Southampton SDRG endeavoured to determine which fluid dynamic theory is most appropriate for modelling Low Crested Structures (LCS). LCS are manmade breakwaters put in place to preserve shoreline from the threats of erosion and flooding. LCS provide particular challenges for fluid dynamicists. For one, all three material phases must be dealt with simultaneously: gas (the air), liquid (the seawater) and solid (the LCS). Thus, in certain situations the constraint of compressibility holds true, while in others it does not. Also, a wide range of forces comes into play whose importance depends strongly upon dimensional scale. Another peculiarity that must be addressed is the difference in physical properties between seawater and freshwater. Finally, the marine life inhabiting LCS further complicate flow dynamics. Hence, the model, and the theory upon which it is based, must be flexible to adapt to these difference circumstances. In fact, what the Southampton SDRG found is that no one theory is universal and can be successfully applied in all conditions. Various scaling model approaches were tested, from Froude to Cauchy to Weber and also Reynolds. On the whole, Froude theory provided the best overall results. Another important result of the research was the identification of a parameter to assist in the analysis of impulsive events. With respect to LCS, waves crashing over the LCS are the most common impulsive events. The parameter is generated by integrating the change in pressure divided by density at the point of interest. Laboratory experiments revealed discrepancies between the models and the data collected from LCS in the field, indicating once again that models are not a perfect analogy to the real world. For example, certain flow regimes that were laminar in the lab turned out to be turbulent in the field. Despite these limitations, the research represents new, important knowledge gained in this specialised discipline. Dissemination of the report summarising these results is underway and targeting potential users of the information, such as local authorities, engineering firms and environmental consultants.

Discover other articles in the same domain of application