Armour layer scour protections around offshore wind turbine foundations are commonly designed to provide a static protection in storm conditions, which means no or limited movement of rock is allowed (Den Boon et al., 2004, De Vos et al., 2011). This approach often results in large stone sizes and high scour protection costs. Therefore, a dynamic approach can be an interesting alternative. Such a dynamic design can be achieved by decreasing the armour stone size allowing movement of the stones and increasing the armour layer thickness to prevent filter layer exposure. A physical test program was conducted to investigate the feasibility and behaviour of such a dynamically stable scour protection. In this model, a monopile foundation exposed to typical North Sea combinations of unidirectional currents and waves was reproduced in a wave flume. The program included a number of test series each with different water depths. In each test series, the armour layer stone size and the armour layer thickness were varied, in order to obtain a reshaping scour protection, without filter material exposure. Damage and failure were assessed both visually and using a 3D-laser profiler. Because previous works on damage numbers of rock armour layer scour protections mainly focus on static design, a new damage number was introduced and compared to the visual observation. This allowed the definition of a ‘dynamic area’ between static design and failure. Scour pit development in time and equilibrium profiling were also analyzed. The results of the tests showed that the concept of a dynamically stable scour protection is feasible.
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The coastal town Ada in Ghana is threaded by a severe coastal erosion. A protection scheme has to be designed to protect the town. Since the area is ecologically important, e.a. due to the presence of turtles, both during the design process and during the construction phase actions to diminish possible negative effects have to be considered. The design is supported by measuring campaigns and numerical modeling of the currents, waves and morphology.
The XBeach model has been applied for different field sites, each having its specific problems. Cases were ranging from typical 1D beach erosion tests during storm conditions (to compare with Durosta results) which were extended to full 2D models to include the effects of curved coasts. For these kind of applications the XBeach model proved to be at least as good as Durosta for the 1D cases, but also giving the opportunity to include the 2D effects. Other examples are situated on high energy coasts (with long swell waves). Applications there are for example the design of a new coastal protection scheme, but also the study of sedimentation patterns in a shallow harbour surrounded by breakwaters and beaches. XBeach proved to be a powerful tool to get insight into these complex situations.
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