Now showing 1 - 7 of 7
  • Publication
    Particle Migration and Clogging in Porous Media: A Convergent Flow Microfluidics Study
    The migration and retention of fine particles in porous media are important phenomena in natural processes and engineering applications. Migrating particles experience physicochemical interactions with carrier fluids, pore walls, and other migrating particles. The governing dimensionless ratios capture particle-level forces, flow conditions, and geometric characteristics. This study explores micron-size particle migration and retention in microfluidic chips during convergent radial flow, which is the prevalent flow condition in water extraction and oil production. Pore-scale observations reveal the role of electrostatic interactions on clogging mechanisms: Glass particles experience retardation-accumulation bridging, while quasi-buoyant latex particles involve capture and clogging. Consequently, flow rates exert opposite effects on the clogging behavior of inertial glass particles versus electrostatically affected latex particles. Migrating particles experience a varying fluid velocity field in convergent radial flow, and clogging reflects the evolving local conditions (Nad, Ar, Stk, and Re). In particular, clogged pores alter local flow and promote further clogging nearby. Pore network model simulations suggest that such “dependent clogging” lowers the permeability of the porous medium more effectively than independent clogging at random locations.
      130Scopus© Citations 53
  • Publication
    Inverse Analysis of Deep Excavation Using Differential Evolution Algorithm
    This paper presents the applications of the differential evolution (DE) algorithm in back analysis of soil parameters for deep excavation problems. A computer code, named Python‐based DE, is developed and incorporated into the commercial finite element software ABAQUS, with a parallel computing technique to run an FE analysis for all trail vectors of one generation in DE in multiple cores of a cluster, which dramatically reduces the computational time. A synthetic case and a well‐instrumented real case, that is, the Taipei National Enterprise Center (TNEC) project, are used to demonstrate the capability of the proposed back‐analysis procedure. Results show that multiple soil parameters are well identified by back analysis using a DE optimization algorithm for highly nonlinear problems. For the synthetic excavation case, the back‐analyzed parameters are basically identical to the input parameters that are used to generate synthetic response of wall deflection. For the TNEC case with a total of nine parameters to be back analyzed, the relative errors of wall deflection for the last three stages are 2.2, 1.1, and 1.0%, respectively. Robustness of the back‐estimated parameters is further illustrated by a forward prediction. The wall deflection in the subsequent stages can be satisfactorily predicted using the back‐analyzed soil parameters at early stages.
      203Scopus© Citations 41
  • Publication
    An FDEM study of particle breakage under rotational point loading
    The most commonly adopted method to test the strength of single sand particles is based on platen experiments. This setup tends to align the loading direction towards the particle minimum axis and provide an upper limit for the breakage stress. This paper numerically bypasses such limitation by using a combined finite and discrete element method (FDEM). FDEM was first validated via a mesh size analysis of a spherical particle and calibrated by in-situ experimental compressions of the single quartz sand particle, where the particle shape was obtained by X-ray micro-computed tomography (XCT) and then imported into the numerical model. Systematic point loading tests were recreated to explore the role of the curvature at contacting points on the breakage behaviour. The simulations allow to probe the same non-spherical particles, i.e., realistic quartz sand and ellipsoid particles, with multiple measurements highlighting the importance of the loading direction, which was inaccessible experimentally. Results show that FDEM can capture not only the crack initiation but also fracture patterns, while taking into account realistic shapes. It is found that the distance between two contact points and their combined curvedness reflecting the particle morphology are the two major factors governing fracture patterns and stresses. When loading is roughly parallel to the minimum principal dimension of particles, the obtained breakage stress and the number of fragments approach the upper limits.
      220Scopus© Citations 41
  • Publication
    Particle shape quantification using rotation-invariant spherical harmonic analysis
    (ICE Publishing, 2017-06-01) ; ;
    A three-dimensional (3D) particle surface can be mathematically represented by a spherical harmonic (SH) coefficient matrix through surface parameterisation and SH expansion. However, this matrix depends on not only the particle shape but also the size, position and orientation. This study adopts a rotation-invariant analysis to explore the relationship between SH coefficient matrices and particle shape characteristics. Particle shapes are quantified at different scales (i.e., form, roundness and compactness). These methods are applied to two groups of particles (i.e., Leighton Buzzard sand (LBS) particles and LBS fragments) with distinct shape features. By using rotation invariants, the multi-scale nature of particle shape is illustrated, and two novel shape descriptors are defined. The results in this paper serve as a starting point for the generation of particle shapes with prescribed shape features using spherical harmonic.
      238Scopus© Citations 27
  • Publication
    Investigation of particle breakage under one-dimensional compression of sand using X-ray microtomography
    (Canadian Science Publishing, 2020-05-05) ; ; ;
    Particle breakage alters particle-scale properties of granular soils including particle size, shape, and contact conditions, and changes macroscale properties including soil compressibility, shear strength, and permeability. This study monitors the crushing of natural quartz sands under one-dimensional compression with in situ X-ray tomography, i.e., X-ray scans during loading. We use the assembly-scale and particle-scale images to characterize particle failure patterns, e.g., chipping, major splitting, and comminution. Image processing and analysis enable us to determine the failure patterns around the yield stress, and the influence of initial density and particle morphology on the particle survival probability. We further quantify the degree of particle breakage with fractal dimension, breakage factor, and specific surface. Particle shape and coordination number both show a scale-dependent evolution pattern.
      314Scopus© Citations 54
  • Publication
    A simple method for particle shape generation with spherical harmonics
    (Elsevier, 2018-05-01) ; ;
    The increasing interest in particle shape influence on granular mechanics necessitates a fast and robust particle shape generation method. We describe a new approach based on rotation-invariant spherical harmonic (SH) analysis. The core of this method is to construct morphology features at various length scales and superimpose them together to form the overall morphology. This method uses four rotation-invariant SH factors to construct SH coefficient matrices. We quantify particle shape at form, roundness, and compactness to establish the linkage between SH factors and traditional shape parameters. It is found that SH factors effectively control particle features at different scales. This method has a great potential to facilitate the research on granular mechanics considering particle shape effects.
      251Scopus© Citations 56
  • Publication
    Desiccation crack formation beneath the surface
    (ICE Publishing, 2020-02-01) ;
    Desiccation cracks affect all mechanical and conduction properties. Previous studies have investigated the formation of surface desiccation cracks in fine-grained sediments in relation to their compressibility and suction potential. This study explores the formation of internal desiccation cracks in saturated kaolinite specimens consolidated inside self-reactive oedometer cells to reproduce the initial effective stress in buried sediments. X-ray tomography is used to monitor internal processes during consolidation and drying. Images capture the evolution of a perimetric fracture, transverse contraction, volumetric changes in entrained gas bubbles and the development of internal desiccation cracks. Entrained gas bubbles act as nucleation sites. They shrink during loading and early stages of desiccation. Eventually, the gas-water interface penetrates the soil at the bubble surface, pushes particles away, enlarges local pores and facilitates further growth of the internal desiccation crack. While air entry is grain-displacive in soft, fine-grained sediments, it becomes pore-invasive in stiff, coarse-grained sediments and internal desiccation cracks are not expected in silts or sands.
      281Scopus© Citations 22