Resolved CFD-DEM coupling simulation for wave erosion protection using cemented granular materials

Abstract

Coastal cities have been experiencing rapid development of their coastal fronts in recent years. However, extreme weather conditions, such as tropical cyclones and storm surges, have caused severe damage to offshore structures in the surrounding area. Although large boulders are commonly used to protect coastal embankments from hydraulic and wave erosion, current design guidelines are mainly based on empirical methods derived from limited small-scale experimental data. Extensive seawall collapse in recent typhoon events indicates the current design may not be adequate. With the depletion of quarry stones, it is also urgent to develop more economical, efficient granular systems for coastal protection. Cemented granular material can be used to cement granular rocks and enhance structure stability, and this is becoming a promising method for wave erosion protection resistance to wave erosion. This thesis will study the hydraulic and wave interaction with granular materials and erosion protection with cemented granular materials using numerical methods. Numerical models for the fluid-particle coupling system and cemented granular material are developed. Fundamental objectives include: · Develop an advanced numerical method to study dynamic interaction between two-phase fluids and irregularly shaped particles. A resolved CFD-DEM coupling model is developed to calculate the fluid-particle interaction. The fluid is modeled by the Computational Fluid Dynamics (CFD), and the particle motion is simulated by the Discrete Element Method (DEM). A series of validation cases are executed to demonstrate that the developed coupling model is efficient and reliable for analyzing the interaction between two-phase fluids (such as waves) and irregularly shaped particles. · Develop a mesoscale DEM bond model for cemented granular materials (CGMs). A discrete element method with clumped particles is used to simulate irregularly shaped particles. The Voronoi tessellation is used to analyze the void structure, which forms the basis for determining the cement distribution and geometry properties of the cement bond between the clumped particles. Numerical simulations are compared with experimental uniaxial compression tests, with the cement ratio ranging from 5 to 50%. The numerical results are consistent with the experimental ones, indicating that this numerical model can simulate the behaviors of cemented granular materials with a wide range of cement ratios. · Use the developed numerical schemes to simulate wave erosion and protection with cemented granular materials. These numerical simulations include the non-Darcian seepage in porous media, the dambreak wave impact on a granular rockfill, the overtopping flow on a granular dam with an impermeable core, and the periodic wave erosion on a granular armor layer. These numerical cases show different erosion patterns and are compared with laboratory experiments. The protective effects of using the cemented granular materials are simulated and analyzed. The numerical studies provide a deeper understanding of the wave erosion and protection mechanisms by using cemented granular materials In summary, this study developed numerical methods for simulating the interaction between multi-phase fluid and hybrid granular-cemented materials. Frequently encountered wave erosion problems are studied using the numerical method. This study aims at providing a scientific understanding of hydraulic wave erosion and the protection mechanism of using cemented granular materials through state-of-the-art numerical modeling.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Gang WANG (Supervisor) & Duruo HUANG (Supervisor)