NUMERICAL MODELLING OF COASTAL DEFENCES USING THE SMOOTHED PARTICLE HYDRODYNAMIC METHOD A.J.C. CRESPO (1) , C. ALTOMARE (2) , B.D. ROGERS (3) , J.M. DOMINGUEZ (1) & X. GIRONELLA (2) (1) EPHYSLAB, Universidad de Vigo, Facultade de Ciencias de Ourense, Campus As Lagoas s/n 32004, Ourense, Spain. alexbexe@uvigo.es, jmdominguez@uvigo.es (2) Universitat Politecnica de Catalunya, C/ Jordi Girona 1-3, Campus Nord, Edifici D1, Barcelona, 08034, Spain. corrado.altomare@upc.edu, xavi.gironella@upc.edu (3) School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester, UK, M13 9PL, U.K. benedict.rogers@manchester.ac.uk Abstract The present paper reports the results of the application of the Smoothed Particle Hydrodynamics (SPH) method to model the wave run-up over an armour breakwater. The units that form the outer layer of the structure have been modelled in 3D to validate the response under wave attacks. The open-source GPU DualSPHysics code has been used because of its capability to simulate millions of particles required for an accurate modelling. The run-up heights have been computed and compared with empirical solutions. The results are in agreement with the ones obtained using literature formulae. 1. Introduction The response of coastal defences such as rubble mound breakwaters under wave attacks depends on several factors, both geometrical and structural. How the armour seaward layer is built is one of those factors. The pattern of the armour units, their shape, dimension, orientation and inter-locking can define the structural straightness and influence the interaction with the incoming waves, that consists of phenomena such as wave run-up and wave overtopping, significative for a proper structural design. The equivalent roughness of the armour layer is one of the key parameters that determine the run-up and overtopping rates over sea defences (U.S. Army, 2002; CIRIA, 2007). This parameter expresses the dissipation of the wave energy due to the armour units, depending on the geometrical layout and block features. In the design of a coastal defence aiming to prevent risks to people, vehicles, ships and structures, it is necessary to assess correctly the slope roughness to calculate the expected overtopping rate or run-up height. This analysis can be done by means of either physical or numerical models (examples in Shankar and Jayaratne, 2003; Bruce et al., 2009; Geeraerts et al., 2009). Modelling rubble mound breakwaters using numerical schemes is a very challenging task due to the complex geometries and violent hydrodynamics. The present work describes the added-value of using the numerical Lagrangian method named Smoothed Particle Hydrodynamics to predict accurately the surface roughness of an armoured breakwater and simulate properly the waves running up the structure. The main breakwater of the Zeebrugge harbour, in Belgium, has been chosen as geometrical reference case for this study (Figure 1).