The new Coastal and Ocean Basin (COB) located at the Greenbridge Science Park in Ostend, Belgium is under construction since February 2017. The laboratory will provide a versatile facility that will make a wide range of physical modelling studies possible, including the ability to generate waves in combination with currents and wind at a wide range of model scales. The facility is serving the needs in Flanders, Belgium, in the fields of mainly offshore renewable energy and coastal engineering. The COB will allow users to conduct tests for coastal and offshore engineering research and commercial projects. The basin will have state-of-the-art generating and absorbing wavemakers, a current generation system, and a wind generator. It will be possible to generate waves and currents in the same, opposite and oblique directions. The basin is expected to be operational in 2019. This paper presents an overview of the basin’s capabilities, the ongoing work, and selected results from the design of the COB.
To meet the demands of practicing engineers for realistic-scale engineering problems, the authors propose a new and fast wave proxy approach for wave-structure interaction. In this approach, a rigid FDEM version SOLIDITY_R is employed to simulate structure-structure (e.g. armour unit) interaction. Hydraulic forces on units are calculated by the surface integral of fluid pressure at the local element level. Then these forces are integrated and applied to each unit. For the time history of water pressure imposed on the breakwater and armour units, the approach can accept velocity data from any sources, e.g. derived from theory, measured from experiments, even from a CFD wave simulator. For example, a wave generator (IHFOAM/IH2VOF) was used to generate a one-hour 50/100 year return period storm and the storm forcing was applied to armour the units. In this paper, the authors illustrate the workflow of the wave proxy and some preliminary results showing the hydraulic flow and wave action loads coupled to our FDEM solver, SOLIDITY_R, via the wave proxy.
This paper presents an analysis of field measurements obtained at an offshore platform in the Southern North Sea. These measurements are used to examine the accuracy of a wide range of wave height and crest height statistical models. More specifically, the available field data are used to define the model that provides the best description for a broad range of incident wave conditions; the latter corresponding to conditions arising in the shallow end of the intermediate water depth regime. Additionally, the primary sources of the discrepancies are investigated, and guidance is provided for the selection of appropriate models. Taken together, the results presented herein provide insights as to the importance of physical mechanisms such as wave breaking, and have significant implications in the selection of appropriate design parameters.
In the UK £150bn of assets and 4 million people are at risk from coastal flooding, whilst the construction of sea wall defence schemes typically cost £10,000 per linear meter. With reductions in public funding and 3200 km of coastal defences, cost savings are required that do not cause a reduction in flood resistance. Increasingly there is a requirement to design new coastal flood defences with site specific tolerable hazard thresholds, with regard to wave overtopping during storms of varying severity. The traditional and preferred method for establishing these thresholds has always been physical modelling, but it is recognized that these can cost many 10s thousands of Euros. This is not always feasible, and coastal asset managers have long been looking for affordable methods that can be used to assess overtopping in the field. Recent advances in technology mean existing wave height sensors can now measure at the high frequencies (a few 100 Hz) required to obtain overtopping data, making this the ideal time to initiate a step-change in coastal hazard monitoring capabilities. By converting the existing wave measurement technology into an overtopping monitoring system "WireWall", we can measure the excursions of overtopping volumes and velocities in the lee of a structure. These then can be readily integrated to obtain wave-by-wave volumes and overtopping discharges (l/s/m). At Crosby in the north west of England, the 900 m sea wall will reach the end of its design life in the next 5 years. Deployments of WireWall at this site will provide site-specific data and calibrated overtopping that will feed into the design of a new sea wall. Before deployment in the field, an extensive set of tests were carried out in a 2D wave flume. Starting with known wave conditions from a buoy near the Crosby sea wall, and values from a joint probability wave and water level study, a representation of the sea wall has been tested. Extensive testing was performed to calibrate the WireWall rig. Using traditional methods of assessing wave overtopping in the flume, the WireWall measurements could be directly calibrated against the known volumes collected in the overtopping tanks. At the time of writing, analysis of the laboratory and the flume wave overtopping data is ongoing. The paper describes how WireWall works, describes the laboratory measurements, the field deployments and presents and compares the analysis from the two systems. A successful deployment of the calibrated WireWall rig at Crosby was during the winter of 2018/2019, where waves can be seen overtopping the sea wall is shown in Fig. 1.
Infrastructure and the development of logistics are a pre-requisite for economic growth in remote islands. Air and seaports are important hubs in the exchange of cargo and transfer of passengers in any logistic transport network. Once designed and constructed, seaports interfere with the local hydroand morphodynamic system and potentially affect adjacent coastal areas. Small reef islands are particularly sensitive towards sea-level rise and impacts due to coastal structures as implementation may increase their exposure and increase the vulnerability of the local population, if infrastructure development compromise or even imperil the natural equilibrium. This study documents and validates the erosion on the east coast of the Maldivian coral reef island of Fuvahmulah. Two numerical models help to identify the key drivers and interdependent processes of sediment transport on the coral reef and assess the port’s influence in aggravating formerly balanced sediment budgets. Our results highlight the significant susceptibility of reef islands in regard of inherent coastal processes as it calls for thoughtful investigations in the design stage prior to implementation of coastal infrastructures in order to avoid any misdesigning of seaports or even to maladaptation practices in remote islands.
Numerical models have played a big role in gaining new understanding of processes in the swash zone. Until recently, intra-wave sediment transport and morphology has almost exclusively been studied by depth-averaged models and rarely by depth-resolving models. In this paper we highlight some of the important differences between these model types with respect to their application in the swash zone. We compare the depth-resolving OpenFOAM model with the depthaveraged XBeach nonhydrostatic model when applied to a dambreak case. The models reproduce the overall dynamics of the swash event but tend to overpredict the swash depths and velocities. We also find that the depth-resolving model produces large vertical variation in flow velocity. Depth-averaged models cannot reproduce these vertical variabilities. For this reason, the models differ in their treatment of breaking waves. This leads to differences in the uprush, while the backwash flows are more similar. We conclude that depth-resolving models are an important tool to study the swash flows and potentially sediment transport and morphology. Swash zone, numerical modelling, hydrodynamics, CFD, breaking waves, turbulence
Wave overtopping is commonly measured using overtopping tanks. In this paper, an alternative system is developed by using two laser scanners. It measures wave run-up, as well as layer thicknesses and front velocities, both during normally and obliquely incident waves on a dike in the field. The paper considers the first field validation tests with the system, with normal and oblique waves generated by the wave run-up simulator on a grass dike slope. Furthermore, a range of environmental conditions are simulated, to determine the robustness of the system. From the measured distance and reflection, the run-up is determined, which corresponds well to the observed run-up. From the data, the layer thickness and front velocity are determined as well. Layer thicknesses and front velocities are determined reliably with the laser scanners. Also, the (virtual) wave overtopping discharge can be calculated, which corresponds well with the most commonly used overtopping equations.
Mozambique is one of the countries most exposed to coastal and river flooding in Africa. The majority of flood and erosion protection investments are still made in the rehabilitation and construction of grey infrastructure, such as drainage canals, retention basins, protection walls and their appurtenant infrastructures. While there are several reasons to consider for and against grey infrastructure including the degree of urbanization, existing infrastructure, local capacities (construction and operation), etc., nature-based solutions are becoming a preferred option by international financing institutions, national agencies as well as local stakeholders. Especially when looking at small-scale interventions (e.g. afforestation measures), nature-based solutions can be a more cost-effective option and may also be implemented and operated / maintained by local agents, including communities and NGOs (Non-governmental organization). INROS LACKNER SE is involved in several climate change adaptation projects in Mozambique. The primary outcomes of the recent project on nature-based coastal protection in the pilot city of Beira and consultancy work on upscaling nature-based flood protection in the cities of Quelimane and Nacala are described and discussed in the present paper.
In this paper we present a new method for numerically modelling landslide-generated tsunamis in OpenFOAM ® by using a new approach based on the Overset mesh technique. This technique, which is based on the use of two (or more) numerical domains, is new in the coastal engineering field and appears to be extremely powerful to model the interaction between a moving body and one or more fluids. Indeed, the accurate resolution around the moving body (i.e. body-fitted approach), guaranteed by this method, offers a great advantage to study the momentum exchange between the body and the water. Furthermore, in order to overcome a drawback of the Overset mesh implementation we modelled the solid boundaries, along which the landslide body moves, as a porous media with a very low permeability. The new approach has been preliminarily, and successfully, validated through the numerical reproduction of past experiments for landslide-generated tsunamis triggered by a solid and impermeable wedge at a sloping coast.
Accurate generation of wave climates in the context of numerical models (and in particular CFD models) is a challenging problem, as these are increasingly used to provide design support to coastal engineering projects. In this paper we will briefly present a technique that addresses the generation (and active absorption) of non-repeating wave sequences for modelling storm events in a meaningful manner. This technique includes a spectral window preprocessing method that is used to reduce the computational costs associated with wave generation algorithms. These can be particularly cumbersome for generating storm events. It was demonstrated that numerical cost can be reduced by about 40 times by using O(101) frequencies for wave reconstruction, rather than O(104) which current methods would need to accurately reproduce long wave series, without any noticeable difference in terms of the generated wave signal. The technique is already in use within the context of the computational toolkit Proteus (https://github.com/erdc/proteus) and is it is combined with both the CFD and shallow water module of the model. The methodology is also fit with a 2nd order correction for generating nonlinear random wave series. Case studies are also presented that prove i) the capability of the technique to reproduce meaningful sea states in the context of numerical modelling of coastal structures and ii) the improvement of computational cost, when compared to currently available techniques. These case studies comprise modelling of random waves in a numerical wave tank to acquire wave statistics by using both CFD and shallow water models, as well as modelling coastal structures such as a low-crested levees and a caisson breakwater using random sea states.
Flood gates in storm surge barriers or outlet sluices can be prone to violent wave impacts. When an obstruction is present at the sea side above the gate, confinement of the incoming waves can lead to impulsive wave loads, even when the waves are non-breaking. The large loads can increase the stresses in the gate and structure considerably. One of the measures that is often discussed to relieve the pressures of these impacts is to apply small openings in the gates. In this paper the potential effect of these venting holes on the wave impact loads is determined. The decrease in impact pressure impulse is determined for a range of venting hole geometries is determined by numerical 2D and 3D solutions of a schematized wave impact. In this model the pressure impulse P (integral of the local pressure over the small impact duration) is determined directly by the so-called pressure impulse theory. The potential decrease in pressure impulse due to wave impacts is presented. Moreover, some initial CFD modelling is applied, and the applicability of the pressure impulse theory is discussed.
David Lucio, Javier L. Lara and Antonio Tomas are indebted to the Spanish Ministry of Science, Innovation and Universities for the funding provided under the grant BIA2017-87213-R.
Velocities derived from X-band radar were compared to depth averaged ADCP measurements in a complex tidal inlet system at Ameland, the Netherlands. Inclusion of depth assimilation and ensemble averaging in radar calculations led to smaller differences between ADCP and radar. The observed differences were clustered and related to water level elevations, wind velocities, wave periods, wave heights, spatial coherence in radar output and error metrics of the radar fitting procedure. Larger waves and higher wind velocities were observed to benefit radar agreement with ADCP results. Rising water levels benefitted agreement in east west direction. Falling water levels benefitted agreement in north south direction. Confidence intervals of the fitting procedure were observed to coincide with differences between ADCP and radar and potential for filtering based on them was shown. Nevertheless, an unclarified tendency towards northwestern bias, which may be specific to the comparison locations, remains. The radar at Ameland monitors the whole inlet system and provides current velocities everywhere in its range. This study shows that its currents are in good agreement with ADCP depth averaged currents throughout most of the tidal cycle. Furthermore, it stresses radar’s potential for better monitoring of the coast and for cost effective coastal field measurements to obtain large datasets, even in hydrodynamically very complex regions.
