This paper presents the recent efforts made by the authors in developing CFD-DEM approach to model non-spherical and multiary-sized marine sands. It mainly covers several important aspects: fluid-particle interaction forces, CFD-DEM coupling methodologies (Arbitrary resolved and un-resolved) including locally averaged procedure method (as un-resolved) and non-DLM/FD method (as fully resolved). In the arbitrary resolved approach, with the help of Gaussian-based weighting function, the CFD-DEM model is further able to overcome the difficulties in particle size discrepancy. Meanwhile, using a new fluid-particle drag force model considering the effects of particle shape and flow regimes, the CFD-DEM model is more powerful to simulate the fluid seepage flow behaviour within natural sand such as calcareous sand of irregular-shaped particles. The applications of the developed CFD-DEM to the simulation of hydraulic behaviour of different marine sands in fluids is presented. The main findings are discussed and summarized in this paper. Finally, the requirements of future development are highlighted.
The hydraulic properties of marine soils in seabed, such as falling velocity, critical shear stress, permeability, transport rates in seawater, have been attracting increasing attentions of the researchers and engineers from the offshore geotechnical engineering field (Zhang et al., 2015; Ma et al., 2018). These properties are essentially considered in design and safety assessment for the anchoring system and foundation of marine structures, e.g., boats, offshore oil & gas platforms, wind turbines. DEM (discrete element method) coupled CFD (computational fluid dynamics) approach has been recognized as a promising method to meet the challenges. The Discrete Element Method (DEM) is an effective tool to simulate the behavior of granular soil particles (Cheng et al., 2017), and can be coupled with Computational Fluid Dynamics (CFD) to model the interaction between the particles and the surrounding fluid. Such coupled CFD-DEM codes have been developed and widely used to study the multiphase flow in chemical engineering. However, their application to fluid flow in soils has been seldom and only very few studies have been reported (El Shamy and Denissen, 2010; Zhao and Shan, 2013; Cheng et al., 2018). With the aid of this CFD-DEM coupling model, the particle-scale investigation to the water flow and fine particle migration can be achieved. Marine sand particles encountered in the nature and engineering are usually not spherical in shape and not uniform in size. Particle shape and size grading play a key role in determining the interaction between fluid and soil particles, which poses a number of challenges in modelling and simulation of hydraulic behaviour of marine soils.
