3D Numerical modelling of pile scour with free surface profile under waves and current using the level set method in model REEF3D

Wave action stirs up sediments and keeps it in suspension while currents wash it away from the coastal zone. The combined action of the waves and current close to the sediment bed may worsen the situation by creating excessive sediment transport leading to the failure of hydraulic structures. In this study, numerical modeling of local scour under waves and current is carried out using the open source CFD model REEF3D, which solves the Navier-Stokes equation using the finite difference method. The simulated flow field from the Navier-Stokes equations is coupled with sediment transport algorithms in a numerical waves tank. Further, the calculated bedload and suspended load are linked with the Exner formula to calculate bed elevation changes. The free surface and scoured bed surface are captured using the level set method. Two case scenarios, namely scour under waves and scour under current are run until the equilibrium scour condition is achieved. The simulated results are compared with experimental data of Link (2006) and Sumer & Fredsøe (2001). Good comparison between experimental data and simulated results is observed. It is observed that for equal flow velocity in the flume, sediment transport under current only condition is larger than under waves alone

Efficient numerical computation and experimental study of temporally long equilibrium scour development around abutment

YesFor the abutment bed scour to reach its equilibrium state, a long flow time is needed. Hence, the employment of usual strategy of simulating such scouring event using the 3D numerical model is very time consuming and less practical. In order to develop an applicable model to consider temporally long abutment scouring process, this study modifies the common approach of 2D shallow water equations (SWEs) model to account for the sediment transport and turbulence, and provides a realistic approach to simulate the long scouring process to reach the full scour equilibrium. Due to the high demand of the 2D SWEs numerical scheme performance to simulate the abutment bed scouring, a recently proposed surface gradient upwind method (SGUM) was also used to improve the simulation of the numerical source terms. The abutment scour experiments of this study were conducted using the facility of Hydraulics Laboratory at Nanyang Technological University, Singapore to compare with the presented 2D SGUM-SWEs model. Fifteen experiments were conducted over a total period of 3059.7 hours experimental time (over 4.2 months). The comparison shows that the 2D SGUM-SWEs model gives good representation to the experimental results with the practical advantage

Numerical Modelling of Scour Around an Offshore Jacket Structure Using REEF3D

In the present paper, a numerical investigation of the scouring around offshore jacket structure is carried out. The open-source CFD model REEF3D is used for the numerical modelling. The model solves the Reynolds-averaged Navier–Stokes equations with k-ω turbulence closure to calculate the flow hydrodynamics. The simulated flow field is coupled with sediment transport module in the model to calculate the scouring process. The scouring calculations are based on the Exner formula. The free surface and sediment bed topography are captured with the level set method. Results discuss the numerical modelling of an in situ local scour around the jacket foundations at the C-power wind farm Thornton bank. The key finding from the paper is the local scour around the individual jacket foundations and the global scour which takes place in form of a saucer-shaped. Additionally, the hydrodynamics and the temporal evolution of the scouring process under the wave and current action are discussed. The implication of the study is to set up a CFD model for the hydrodynamics and the scour calculations around offshore jacket foundations

Effect of Emerged Coastal Vegetation on Wave Attenuation Using Open Source CFD Tool: REEF3D

Coastal vegetation is a soft solution for protecting the coast from the action of waves by attenuating the wave height and reducing the energy of the waves. Effect of wave height attenuation as a result of the presence of emerged coastal vegetation is studied numerically by resolving the Reynolds-averaged Navier–Stokes (RANS) equations. A three-dimensional numerical wave tank model is simulated using an open source computational fluid dynamics (CFD) software REEF3D, and wave attenuation due to emerged coastal vegetation is determined. An artificial, rigid, emerged vegetation for a length of 2 m is developed in a numerical wave tank of REEF3D. The model is tested for regular waves of height 0.08, 0.12, and 0.16 m and wave periods of 1.8 and 2 s in a water depth of 0.40 and 0.45 m. The wave heights are measured at different locations along the vegetation meadow at 0.5 m intervals. The devolved numerical model is corroborated by comparing the obtained numerical results with the experimental results as reported by John et al. (Experimental investigation of wave attenuation through artificial vegetation meadow, ISH—HYDRO, [1]). The numerically obtained results are concurrent with the experimental results