Offshore wind farms have become an increasingly important source of clean andrenewable energy. Most recent offshore wind farms are deployed close to the coastin shallow waters. One of the major factors influencing the initial investment of thistechnology is the design of the substructure and foundation. The physical processesassociated with the non-linear shallow water hydrodynamics are rather complex sincethe wave motion is strongly influenced by the seabed. Breaking waves exert significanthydrodynamic loading on offshore wind turbine substructures and these impulsive loadsof short duration can cause permanent structural damage.Wave impact force characteristics greatly depend on the evolution of free surfaceprofiles and wave height, changes in velocities, and geometric properties associated withthe breaking process. Understanding hydrodynamic loads from breaking waves has manydesign-related implications for structures employed in shallow and intermediate waters.Although extensive experimental, theoretical and numerical research has been carriedout on modelling the breaking wave forces, the breaking mechanism and their waveimpact characteristics are not yet fully understood due to many parameters involved inthe complex physical processes. The main aim of the present research was to investigatewave breaking in shallow waters and breaking wave forces on slender cylinders.The open source CFD model REEF3D has been used for modelling wave breakingand computing wave breaking forces on slender cylinders in shallow waters. Themodel is based on the Reynolds-Averaged Navier-Stokes (RANS) equations togetherwith the level set method for the free surface and the k − ω model for the turbulence.Numerical experiments on wave breaking on sloping sea beds and submerged structuresare performed in a three-dimensional wave tank and breaking wave forces on slendercylinders are evaluated. Moreover, the numerical model is thoroughly validated againstthe experimental measurements for each case individually. First, the characteristicsand geometric properties of wave breaking over slopes and submerged structures fordifferent environmental parameters are examined. Comparison of the hydrodynamiccharacteristics and geometric properties of spilling and plunging breakers are also presented and discussed. Breaking wave forces on slender cylinders are evaluated forsolitary and periodic waves. For both cases, the influence of the relative cylinder locationwith respect to the breaking point on the breaking wave forces is investigated for differentincident wave characteristics.The numerical results for different cases are consistent with previous studies. Astrong dependence of water depth, offshore wave steepness, and seabed slope on thebreaking characteristics is observed for different slopes and submerged structures.Further, the evaluation of geometric properties of waves at breaking for different seabedconditions and wave characteristics suggests that the application of the wave steepnessand asymmetry factors are appropriate for describing the breaker type and the waveprofile at breaking. Analysis of breaking wave forces indicates that the relative cylinderlocation with respect to the breaking point has a large influence on the breaking waveforce. It is seen from the results that the characteristics and geometric properties atbreaking can be related to the wave impact forces from breaking waves. Moreover,the prominent flow features associated with breaking waves and their interaction withslender cylinders are reasonably well represented in the numerical simulation.
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