Jidong Zhao

The Hong Kong University of Science and Technology | UST · Department of Civil and Environmental Engineering

Granular matter is ubiquitous in nature and is present in diverse forms in important engineering, industrial and natural processes. Particle-based computational modelling has become indispensable to understand and predict the complex behaviour of granular matter in these processes. The success of modern computational models requires realistic and e...

It remains a challenge for discrete element method to simulate large-scale systems with arbitrarily shaped particles. This paper presents a novel approach called Ray Tracing Discrete Element Method (RTDEM) to offer ultra-high efficiency in simulating particles with arbitrary shapes. In RTDEM, we use a triangular mesh to represent the surface of a p...

It is challenging to model granular particles with arbitrary shapes and related complications to fluid-particle interactions for granular flows which are widely encountered in nature and engineering. This paper presents an improved framework of the immersed boundary method (IBM)-based fully resolved computational fluid dynamics (CFD) and discrete e...

Key to quality control for laser powder bed fusion (L-PBF) is the reduction of porosity in built parts. However, understanding the mechanisms of a complete cycle of keyhole pore evolutions, including the processes of the keyhole pore generation, collapse, and splitting, and the role of metal-vapor condensation, remains a great challenge. In this st...

Constitutive relation remains one of the most important, yet fundamental challenges in the study of granular materials. Instead of using closed-form phenomenological models or numerical multiscale modelling, machine learning has emerged as an alternative paradigm to revolutionise the constitutive modelling of granular materials. However, deep neura...

The coupled thermo-hydro-mechanical (THM) response of liquid-infiltrated porous media underpins the safe operation and maintenance of key engineering infrastructure. Challenges remain in modeling and understanding the complicated multiphysics processes of porous media subjected to THM loads and undergoing large deformation. In this study, we develo...

This paper presents a numerical study on suspensions of monodisperse non-Brownian grains in a Couette flow. Fully resolved coupled smoothed particle hydrodynamics and discrete element method (SPH-DEM) is employed to model the motion of arbitrarily shaped grains in a viscous fluid. The numerical method is benchmarked against its capability in accura...

Coral sand is the main geomaterial on tropical reefs and its constituent particles are featured with complex shapes and abundant intraparticle voids. This work presents a discrete element method (DEM)-based numerical modeling of coral sand in consideration of both the irregular shape and intraparticle voids of particles. To develop the DEM model fo...

DEM) ，亦称非光滑接触动力学(NSCD)法，模拟了堆石料单颗粒的一维压缩破碎过程。 采用多面体颗粒近似真实堆石料颗粒的不规则棱角状形状，并通过 Voronoi 空间划分将母颗粒离散成若干多面体子颗 粒，子颗粒间通过接触面上的内聚力模型(CZM)胶结发生相互作用，胶结断裂则可反映颗粒的破碎过程，可避免传 统 DEM 中常用的碎片替代法和胶结小球法的缺点。首先使用巴西劈裂试验获得 CZM 参数，其后开展了不同粒径颗粒 的一维压缩试验，结果表明颗粒破碎强度服从 Weibull 分布，且破碎强度大小和变异性均随着颗粒尺寸的增大而减小。 还进一步模拟了不同形状颗粒的压缩试验，发现颗粒形状与加载方向均对颗粒破碎强度有显著影响。长轴方向加载破 碎强度通常最低，且在相同等效粒径下，球状、椭球状、扁平状颗...

We propose a multiscale, multiphysics approach by coupling two-phase material point method (MPM) with discrete element method (DEM) (MPM-DEM) to simulate the hydro-mechanical coupling responses of saturated granular media from small strain en route to large deformation under either quasi-static or dynamic loading conditions. The multiscale scheme i...

Plain Language Summary Flexible barriers are increasingly used worldwide to mitigate debris flows, debris/rock/snow avalanches, and rockfalls. Although many methods exist to estimate critical design factors of flexible barriers, a systematic examination of their applicability and underlying relations remains elusive. The status quo has been largely...

A major challenge for material point method (MPM) is to model multi-body and multi- material interactions. Prevailing contact schemes developed for MPM suffer from numerical instabilities, especially for the coexistence of multiple material boundary conditions. This study proposes a generalized contact scheme based on a hybrid scheme of MPM and dis...

Quantitative understanding of the load deflection mechanisms of a flexible barrier in intercepting debris flows is critical for barrier design, but remains practically challenging due to difficulties involved in capturing multi-phase, multi-way interactions. This study employs a physics-based coupled computational fluid dynamics and discrete elemen...

This paper presents a hierarchical multiscale modeling paradigm to simulate the freeze-thaw behavior in granular media. The multiscale strategy features a hierarchical conjugate of a continuum-based mixture theory with a micromechanics-based homogenization technique. It enables the capturing of a typical freeze-thaw process in an engineering settin...

Neighbor searching is an essential and computationally heavy step in particle-based numerical methods such as discrete element method (DEM), molecular dynamics (MD), peri-dynamics (PD) and smooth particle hydrodynamics (SPH). This paper presents a novel approach to accelerate particle-based simulations by leveraging ray tracing (RT) cores in additi...

Laser powder bed fusion represents the future for metal additive manufacturing. Advance of this emerging technology is bottlenecked by the unavailability of high-fidelity prediction tools for cost-effective optimization on printing design. Simulations of selective laser melting of metals must tackle a complex granular solids and multiphase fluids s...

This paper presents a signed distance field (SDF) approach for unified discrete element method (DEM) modeling of granular media using arbitrarily shaped particles. The SDF approach employs a generic SDF-based interface defined by an SDF function and a surface projection function to rigorously model particle shapes and their ensuing complications on...

A generic strain energy-based parameter calibration method is proposed to calibrate the elastic parameters of lattice or bonded-particle modelling of solid materials. Unlike surrogate models or general optimisation-based calibration methods, this approach does not require running any physical simulations to obtain tentative solutions and thus ensur...

The multi-scale characteristics of particle morphology, including the overall form, local roundness and surface roughness, affect the critical state behavior of sands and should be considered in modern critical state-based continuum constitutive modeling. Despite extensive experimental and numerical studies, no consensus has been reached as to how...

The shear strength of granular materials has been found to increase nonlinearly with particle asphericity before reaching a steady value independent of particle asphericity. Although the origin of shear strength has been extensively studied, the underlying mechanism of its nonlinear dependency on particle shape remains unclear. In this study, we pr...

Flexible, slit, and rigid barriers are common countermeasures to mitigate natural geophysical mass flows, but presently, quantitative comparisons of their performance are lacking, due to the challenges involved in accurately representing the multi-body and multi-phase interactions. This study presents a numerical appraisal on this issue using a phy...

Grain crushing underpins key mechanical behaviors of granular materials. A variety of factors, including grading, particle shapes, and loading conditions, have been recognized to affect the crushability of grains and the overall behavior of a granular material. Among them, the role of intermediate principal stress in a general stress condition on t...

Heat generation and transfer in a granular material can be intricately coupled with their mechanical responses, playing a key role in causing excessive large deformation, flow and failure of the material. The coupling may manifest in various forms, including thermal induced stress, mechanically induced heat and thermally induced melting in granular...

This study presents a scalable three‐dimensional (3D) multiscale framework for continuum‐discrete modeling of granular materials. The proposed framework features rigorous coupling of a continuum‐based Material Point Method (MPM) and a discrete approach Discrete Element Method (DEM) to enable cross‐scale modeling of boundary value problems pertainin...

This paper presents a peridynamics-based computational approach for modeling fractures in bolted glass plates that features an explicit consideration of randomly distributed micro-flaws. The glass fabrication procedures are assumed to produce a stochastic distribution of a single population of Pareto-distributed surface flaws and mono-sized edge fl...

Understanding the origin of stress drop of fault gouges may offer deeper insights into many geophysical processes such as earthquakes. Microslips of sheared granular gouges were found to be precursors of large slip events, but the documented relation between microslips and macroscopic stress drops remains largely qualitative. This study aims to qua...

Natural granular materials such as sands often possess complex microstructural features including cleavage and minerals interfaces. Those features bring apparent mechanical anisotropy to particles and are known to have pronounced influence on particle crushing characteristics. This paper presents a multiscale simulation of continuous crushing of gr...

Pullout of plate anchors from granular sands is investigated using a novel computational multi-scale approach. We employ the material point method (MPM) to solve a large deformation boundary value problem and adopt the discrete element method (DEM) to derive the history-dependent material responses required for each material point of the MPM domain...

Fabric anisotropy underpins the mechanical response of granular soils pertaining to a wide range of practical geotechnical applications. This paper presents a multiscale computational study on a strip footing resting on an anisotropic soil foundation. The focus of the study is placed on examining the cross-scale links of key grain-scale mechanisms...

This work revisits the Gilbert–Johnson–Keerthi (GJK) and the radial direction-based shape erosion method for the contact resolution of non-spherical particles in discrete element method (DEM). Tests on single contact indicate that the shape erosion would frequently lead to an overestimation on contact overlap, but has a minor effect on contact norm...

Gap‐graded granular soils are common natural soils composed of cohesionless granular matrix and rock aggregates. Since they are widely used as construction materials worldwide, their deformation behavior is crucial for the design of civil infrastructures. There have been rare constitutive models reported for gap‐graded granular soils in the literat...

This paper presents a novel computational-geometry-based approach to generating random packing of complex-shaped 3D particles with quantitatively controlled sizes and shapes for discrete modeling of granular materials. The proposed method consists of the following five essential steps: (1) partitioning of the packing domain into a prescribed number...

Flexible barriers have been increasingly used worldwide for mitigating natural hazards involving various geophysical flows. The analysis and design of flexible barriers need to distinguish two major impact mechanisms, runup and pileup , which remain poorly understood due to complicated interactions between the impacting flow and the deformable barr...

Footing foundations are sometimes built on sloping grounds of natural sand which is highly anisotropic. The anisotropic mechanical behaviour of sand can significantly influence the bearing capacity of a foundation and the failure mechanism of its supporting slope. Neglecting sand anisotropy may lead to overestimated bearing capacity and under-desig...

The shearing behaviour of reproduced flat LBS grains artificially bonded with ordinary Portland cement (OPC) and plaster of Paris (PP) was examined using micromechanical experiments. Monotonic shearing tests showed a distinct variation in the load–displacement relationship at low, medium and high normal loads, and a nonlinear shear strength envelop...

This paper presents a peridynamics-based computational approach for modeling blasting induced rock fractures. A new non-ordinary state-based peridynamics approach is proposed in conjunction with a Johnson-Holmquist (JH2) constitutive model to consider the pressure dependency, strain rate effect, and viscoplasticity of rocks under blasting loads. Th...

We present a semi-coupled resolved Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to simulate a class of granular media problems that involve thermal-induced phase changes and particle-fluid interactions. We employ an immersed boundary (IB) method to model the viscous fluids surrounding solid particles in conjunction with a fi...

Computational modeling in geotechnical engineering frequently needs sophisticated constitutive models to describe prismatic behavior of geomaterials subjected to complex loading conditions, and meanwhile faces challenges to tackle large deformation in many geotechnical problems. The study presents a multiscale approach to address both challenges ba...

In this paper, a new formulation of material point method (MPM) to model coupled soil deformation and pore fluid flow problems is presented within the framework of the theory of porous media. The saturated porous medium is assumed to be consisting of incompressible pore fluid and deformable soil skeleton made up of incompress-ible solid grains. The...

When a gravity-driven solid-fluid mixture, such as those in geophysical flows, hits a wall-like rigid obstacle, a metastable jammed zone called hydrodynamic dead zone (HDZ) may emerge. The unjammed-jammed transition of HDZ, controlled by the intricate interactions among the obstacle, the fluid and the solid of the flow, remains an open issue to be...

The at-rest coefficient of lateral pressure, K 0 , is a critical macroscopic parameter for evaluating stress transmission in granular media for engineering practice. This paper revisits the microscopic origin of K 0 and its corresponding underlying physics based on micromechanics-based theories and numerical simulations, with a focus placed on the...

Both the solid and fluid phases in a debris flow vitally influence the impact dynamics against a rigid barrier. However, previous numerical and analytical models commonly adopt an equivalent fluid approach, which does not explicitly consider solid-fluid interaction at impacting a barrier. This study investigates the role of solid-fluid interaction...

The flow direction is generally different from the gravity direction in geotechnical structures or slopes, the effect of which during suffusion remains unclear. This paper presents a coupled computational fluid dynamics and discrete element method approach to simulate the particle–fluid interaction relevant to this problem. The CFD-DEM approach is...

Voids play an important role in both transport properties and mechanical deformation of a granular material. It remains challenging to quantify void spatial distributions, especially in realistic granular packing with irregular grain shapes. This paper presents a three-dimensional (3D) framework for Voronoi analysis of realistic grain packing, base...

This paper presents a computational study on the interactive evolution of particle shape and particle breakage for granular material under confined compression. A novel multiscale approach combining peridynamics and non-smooth contact dynamics is employed. Breakage of more than 12,700 particles with different size, shape, and loading condition are...

PySetVoronoi is a Python interface for Set Voronoi Tessellation of poly-superellipsoids and general point clouds from irregular particles, where the kenerl is written in C++. With PySetVoronoi, we can take Set Voronoi tessellation for non-spherical particles (even realistic grains) easily in Python. PySetVoronoi supports parallel computation with O...

Anchors are popular and economic solutions for onshore and offshore engineering to provide adequate resistance for structures. In anchor design, it is critical to evaluate the bearing capacity of soil in supporting an anchor and understand the underlying load-carrying and failure mechanisms. Herein we employ a newly developed multiscale modeling to...

Flexible ring net barriers have become increasingly popular in practical mitigation of debris flow worldwide. Systematic assessments of their response and performance subjected to the impact of realistic debris flows remain challenging. This study presents a novel computational approach based on coupled CFD-DEM to model the impact of debris flow on...

Plain Language Summary Granular materials are ubiquitous in nature and important to a wide range of industrial processes. When driven at slow rates, granular materials deform via intermittent dynamics which alternates slow elastic loading with rapid slips. Such serrated behaviors have attracted attentions from researchers in material science, proce...

This paper presents a novel open-source discrete element code, SudoDEM, for efficient modeling of both 2D and 3D non-spherical particles under a GPL v3 or later license. Built upon a popular open-source code YADE, our code inherits the core of a classic DEM framework empowered by OpenMP acceleration, and further offers unique features of a rich lib...

We employ a hierarchical multiscale modeling approach to investigate the transitions of localized deformation patterns in high-porosity sandstone subjected to sustained shear to understand their underlying physics. The multiscale approach is based on hierarchical coupling between finite element method (FEM) with discrete element method (DEM) to off...

This paper presents a novel, scalable parallel computing framework for large-scale and multi-scale simulations of granular media. Key to the new framework is an innovative thread-block-wise representative volume element (RVE) parallelism, inspired by the resemblance between a typical multiscale computational hierarchy and the hierarchical thread st...

Suffusion involves fine particles migration within the matrix of coarse fraction under seepage flow, which usually occurs in the gap-graded material of dams and levees. Key factors controlling the soil erodibility include confining pressure (p′) and fines content (Fc), of which the coupling effect on suffusion still remains contradictory, as conclu...

Slit dam is an open-check barrier structure widely used in mountainous regions to resist the destructive impacts of granular flows. To examine the dynamics of granular flow impact on slit dams, a numerical study by discrete element method (DEM) is presented in this article. The study considers dry granular materials flowing down a flume channel and...