Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Final Activity Report Summary - WAB-ART (Modelling of Wave Breaking at Artificial Coastal Reefs)

The objectives of the project were to provide advanced training and create new knowledge in the field of modelling of wave breaking at artificial coastal reefs, i.e. at reef breakwaters, via the implementation of an extensive scientific research, numerical simulations and physical model tests.

The influence of main reef properties, such as geometry, permeability and type of revetment, was evaluated based on analysis of previous test data, as well as on implementation of additional model tests carried out at the 'Wellenkanal Schneiderberg' (WKS) wave flume at Franzius-Institut for waterways, Hydraulic and coastal engineering (FIWK), at the Leibniz University of Hannover. Measurements on the wave profile, velocity field and water level variations were carried out. Special efforts were put to analyse velocity distribution and turbulence intensity. Some general criteria for occurrence and type of breaking were also developed, based on physical model tests.

A basic free water surface Reynolds averaged Navier-Stokes equations (RANSE) model was established for the purpose of simulating interaction of waves with reef breakwaters. The Volume of fluid (VOF) technique was used to track the discontinuous free surface. A commercial Computational fluid dynamics (CFD) code was used for the calculations. Simulations were transient. The standard model was chosen as a turbulence model. Work on this model included some original approach in defining boundary conditions, especially in generating various types of waves in the 'numerical flume', and related solving techniques.

A series of simulations was carried out with various types of waves, such as a solitary wave, regular waves, group and irregular waves, with varying incident wave parameters. Numerous approaches were checked when attempting to simulate different cases of breaking, such as spilling and plunging. Reef breakwaters with several geometries and permeabilities were considered and implemented in the numerical model. Numerical results were compared to physical model test data in order to calibrate and verify the numerical model.

Furthermore, special attention was paid to develop tools and methodology for the generation of extreme solitary waves in the laboratory wave flume. A unique method based on spreading of a collapsing water column was successfully used. In addition, extreme waves were also simulated in the virtual CFD numerical flume, as described above. The CFD model could be successfully applied to study and evaluate flooding risk due to the run-up of such extreme waves at coastal beaches, with a typical example being the tsunami waves approaching coasts. The effect of artificial reefs on reducing wave energy could be significant; therefore reefs could be successfully applied to reduce damages due to severe action of extreme waves.

Finally, basic guidelines for the hydraulic design of artificial submerged reefs were drafted, based on integrated modelling, numerical analysis and verification with the physical model test data.

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