Mesoscale Numerical Simulations Research Articles

Mesoscale Modeling of Microcapsule-Based Self-Healing Cementitious Composites under Dynamic Splitting Tension

Microcapsule-based self-healing cementitious composite (MSCC) offers autonomous damage repair, extending the service life of structures. However, most of the existing studies focus on static behavior and healing effectiveness but rarely explore dynamic responses. This study developed the mesoscale modeling approach to investigate MSCC behavior under dynamic split tensile loading. At the mesoscale, MSCC can be treated as a four-phase composite consisting of coarse aggregates, interfacial transition zones, cement mortar, and microcapsules. Alternatively, it can be simplified as a two-phase composite comprising a homogeneous mortar matrix and microcapsules. Four-phase and two-phase mesoscale MSCC models were developed for 2D simulations, while a two-phase 3D model was also developed for comparison. Mesoscale numerical simulations were conducted based on Split-Hopkinson Pressure Bar Brazilian disk-splitting tests, considering various strain rates. Simulation results of different mesoscale models were compared with experimental results. All of the models accurately predicted the tensile strength of MSCC, with the 2D four-phase model providing the best representation of failure modes and crack propagation. Both experimental and numerical data exhibited obvious strain rate effects, indicating that MSCC’s mechanical properties were sensitive to the loading rate. Dynamic increase factors were obtained, quantifying rate sensitivity. The obtained dynamic mechanical properties of MSCC provide insights for designing MSCC components and structures that can better withstand collisions or explosions.

Mesoscopic finite-element prediction method for impact-energy absorption mechanism of multiphase STF/Kevlar composite fabric

Shear-thickening fluids (STFs) effectively enhance the impact-energy absorption of Kevlar fabrics and offer an extensive range of applications for human-safety protection. To precisely depict the impact-energy absorption mechanism and stress transfer behavior of multiphase STF/Kevlar composite fabrics under high strain rates, this study introduces a yarn-interface-friction constitutive model that accounts for the strain rate-thickening effect of STFs. The model is incorporated into a mesoscale numerical simulation to enhance computational accuracy. Theoretical models (impact-pit morphology, yarn-strain, and fabric-strain energy models) are employed to evaluate the off-plane displacement, strain distribution, and impact-energy absorption during impact imprint tests. The established simulation model shows high similarity (0.99) to the impact imprint profile curve and reveals that the strain energy and interfacial friction energy of the composite fabrics contribute primarily to energy dissipation during the impact process. Furthermore, in all specimens, C-STF/Kevlar (CNTs reinforced STF/Kevlar) exhibits reduced off-plane displacement, increased primary-yarn stress, and a higher capacity for impact kinetic-energy absorption. The proposed interface-friction constitutive model can accurately predict the deformation and energy absorption levels of the composite fabrics at various strain rates, thereby offering effective simulation guidance for the preliminary design of composite fabrics.

The influence of initial static shear on the torsional performance of BFRP bars-RC beams with different sizes

To reveal the influence of the initial static shear on the torsional performance of Basalt Fiber Reinforced Polymer Bars-Reinforced Concrete (BFRP bars-RC) beams, in this study, 52 BFRP bars-RC beam models with geometric similarity using a three-dimensional mesoscale numerical simulation method were established. The effects of initial shear static loadings (F0 = 0, 0.25Vu, 0.5Vu, and 0.75Vu) on the failure modes, torsional strength, ductility, and size effect of BFRP bars-RC beams under various equivalent strain rates were quantitatively analyzed. The results show that, regardless of whether the beams have initial damage, their load-bearing capacity and deformation ability increase as loading strain rates increase. For beams with initial damage, the increased degrees in load-bearing capacity relative to their respective initial static shear decreases as the initial static shear level increases but then increases as the subsequent loading strain rate increases. Increasing the beams’ initial damage degree makes the beams’ ductility worse. In addition, the more severe the beams’ initial damage, the more significant the strength size effect. However, increasing the strain rate can weaken the beams’ strength size effect.

Mesoscale formation and energy release characteristics of PTFE/Al reactive jet

AbstractIn order to investigate the mechanical formation, the mechanical‐thermo coupling mesoscale mechanism and the corresponding energy release characteristics of PTFE/Al composite material reactive jet, a mesoscale discretization model of PTFE/Al reactive liner with a mass ratio of 73.5 %/26.5 % is developed on the basis of the random delivery principle. The mesoscale numerical simulation is used to perform PTFE/Al reactive jet formation, obtaining the relative distribution characteristics of material, pressure, and temperature. The overpressure experiments for the energy release of reactive jets are conducted. The results show that there is an increasing tendency in the amount of Al particles from the jet's tip to its tail due to the velocity variance between PTFE and Al. The high temperature zones are found to be concentrated on the tip and axis of the jet, with particle deformation, collision and friction in the reactive jet accounting for the temperature rise. Moreover, the Al particle size has a significantly influence on the particle distribution and the mechanical‐thermo coupling behavior in the reactive jet, and the decrease of particle size is beneficial to the chemical reaction among the components of the reactive jet. To be more specifically, under the conditions of Al particle size of 400 μm, 600 μm and 800 μm, the overpressure peaks of reactive jet in 13 L chamber are 3.32 MPa, 2.86 MPa and 2.61 MPa, respectively. The variation of the overpressure with Al particle size obtained by experiment is consistent with the analysis of the mechanical‐thermo coupling characteristics of mesoscale numerical simulation.

The Influence of Topography on the Diurnal Rainfall Propagation in the Bay of Bengal

Abstract A significant diurnal offshore propagation of rainfall is observed extending from the eastern coast of India to the central Bay of Bengal. This study focuses on understanding the influence of topography over the Indian subcontinent on this rainfall propagation through a series of semi-idealized mesoscale numerical simulations. These simulations with varying topography highlight the crucial role of inertia–gravity waves, driven by diurnal mountain–land–sea thermal contrast between India and the Bay of Bengal, in initiating and promoting the offshore propagation of convective systems in the Bay. These waves’ phase speed of around 14.8 m s−1 aligns well with the speed of diurnal rainfall propagation. Even after eliminating the impact of Indian topography, the offshore propagating signal persists, suggesting a secondary rather than dominant effect of terrain on offshore rainfall propagation. Furthermore, the topography affects the depth of diurnal heating within the land’s boundary layer, which thus influences the amplitude, phase, and speed of the inertia–gravity waves. Specifically, the presence of higher mountains along the coastal area drives faster waves by increasing heating depth, resulting in faster rainfall propagation. Significance Statement This study advances our comprehension of the fundamental driver behind diurnal offshore rainfall propagation and the manner in which coastal terrain influences the rainfall pattern. We demonstrate that the diurnal offshore propagation of rainfall is closely related to inertia–gravity waves generated by thermal contrasts, and we successfully distinguish these waves in our study. Furthermore, our findings indicate that elevated coastal topography contributes to a greater heating depth near the coastline, which plays a crucial role in driving faster gravity waves and, consequently, leading to faster rainfall propagation. These outcomes provide a deeper insight into the mechanism governing offshore rainfall propagation and underscore the impact of real-world topography.

Formation mechanism and development potential of wind energy resources on the Tibetan plateau

It is important to understand whether the wind energy resources on the Tibetan Plateau have power potential suitable for development. To this end, we conducted sodar wind measurement experiments in areas of typical terrain, analyzed radiosonde and surface meteorological observations, and performed mesoscale numerical model simulations to study the characteristics and formation mechanisms, and to assess the technical potential, of the wind energy resources on the Tibetan Plateau. Results showed that the wind energy resources on the Tibetan Plateau are very abundant and of high quality with enormous development potential. The total technical potential of the wind energy resources at 100-m height above ground level is 1.02 billion kW, accounting for 26 % of the total technical potential of China's wind energy resources. The technical potential of the wind energy resources at very rich and rich levels accounts for 63 % of the total. The strengthening effect of the superposition of valley wind circulations and the synoptic-scale background wind field is the fundamental formation mechanism of the abundant wind energy resources on the Tibetan Plateau.

Simulating Brownian motion in thermally fluctuating viscoelastic fluids by using the smoothed profile method

To investigate the Brownian motion of individual particles suspended in viscoelastic fluids, the stochastic smoothed profile method (SPm) for direct numerical simulation is developed by extending deterministic SPm for suspensions in viscoelastic media. To simulate viscoelastic flow driven by thermal fluctuations in the suspending medium, the random stress in the fluid momentum equation as well as the random driving force for the conformation tensor in the Oldroyd-B model are incorporated according to the fluctuating hydrodynamics and fluctuating viscoelasticity formalisms. The thermal equilibrium and dynamical properties calculated by using numerical simulations successfully reproduce the analytic predictions, validating the direct simulation for the coupled fluctuating Navier–Stokes and Oldroyd-B equations and for the coupling between the stochastic viscoelastic medium and individual particles. As an application of the stochastic SPm, we investigate finite system-size effects under periodic boundary conditions (PBCs) on the passive microrheological relationship between the mean-square displacement (MSD) of a Brownian particle and the medium's dynamic modulus. Comparing the modulus that was microrheologically calculated from the MSD with the input modulus reveals that the effect of periodic image cell interaction appears not only in the long-time diffusive regime but also in the short-time region. A frequency-dependent finite system-size correction is implemented by phenomenologically extending the long-time diffusive regime correction, allowing passive microrheology analysis under PBCs. This result can be directly applied to other mesoscale numerical simulations including coarse-grained molecular dynamics and dissipative particle dynamics simulations.

A Comparative Study on Shear Size Effect of Steel-And BFRP-RC Shear Walls Under Cyclic Lateral Loads

ABSTRACT This paper presents a comparative study on the size effect behaviors of shear performances of concrete shear walls reinforced by steel bars and Basalt Fiber Reinforced Polymer (BFRP) bars. All the works are conducted through a two-dimensional meso-scale numerical simulation model representing the concrete shear wall. The horizontal reinforcement ratio and the sectional size are the main parameters concerned by the present study. Both the seismic behaviors under cyclic loading and the size effect behaviors of the shear performances were simulated and investigated. It can be concluded from the simulation results, (1) the use of steel bars or BFRP bars as horizontal reinforcement does not change the shear failure modes of concrete shear walls, (2) the size effect on the nominal shear strength of BFRP reinforced concrete (BFRP-RC) shear wall is more significant compared to that for steel-RC shear wall, (3) the increase of horizontal reinforcement ratio improves the shear capacity of the concrete shear wall, while weakens the size effect on the nominal shear strength, and (4) the size effect law for the nominal shear strength of steel-RC shear wall is applicable to BFRP-RC shear wall. Finally, the importance of considering size effect in the evaluation of shear performance of steel-/BFRP-RC shear wall is manifested by comparing the predictive results of several popular design codes with the simulation results.

Determining appropriate level of detail of 3D aggregate model for accurate and efficient mesoscopic simulation of asphalt concrete

The levels of detail (LODs) of aggregate models significantly impact both the accuracy and efficiency of the mesoscale numerical simulation of asphalt concrete. This study proposed a quantitative evaluation framework to find an appropriate LOD that allows accurate simulation of asphalt concrete with relatively low model complexity. First, the coarse aggregates in asphalt concrete were reconstructed from computed tomography (CT) images, and their LOD was defined as level-0. Each reconstructed aggregate was then simplified using a surface simplification method that obtains aggregate models with four descending LODs (levels-1, 2, 3 and 4), consisting of 200, 100, 50 and 20 triangular facets respectively. The simulation accuracy was evaluated according to several aggregate geometric indexes and mesoscopic finite element (FE) compressive simulation results of asphalt concrete. The results indicate that compared to the level-1 model, the level-2 model can achieve a similar simulation accuracy with a 50% reduction in simulation time.

Formation mechanisms of persistent extreme precipitation events over the eastern periphery of the Tibetan Plateau: Synoptic conditions, moisture transport and the effect of steep terrain

The eastern periphery of the Tibetan Plateau (EPTP) is prone to frequent and severe Persistent Extreme precipitation (PEP) events in summer. Given the complexity of weather systems and the intricate nature of terrain over this region, the generation and development mechanisms of the PEP in the EPTP remain to be determined. In this study, the formation and persistence mechanisms are further explored from the perspective of the general features of large-scale circulations, moisture source diagnosis and the influence of steep topography by using a thermal-dynamical diagnosis method, a mesoscale numerical simulation and a Lagrangian identification of the main moisture sources. The results show that during PEP events, the corresponding atmospheric circulation systems are characterized by an anomalous Rossby wave train at middle levels, an intensified westerly jet, an eastward extension of the South Asian high and a westward extension of the western Pacific subtropical high, all of which are possible to facilitate the development of potential instability and anticyclonic convergence of water vapor transport. The evaporative moisture sources from the Southeastern Asia (SEA), Bay of Bengal (BOB), and Southern China Sea (SCS) are remarkably enhanced during PEP events, with a contribution of 56.44%, which is 28.5% higher than the climatic mean. The further sensitive experiment indicates that the steep terrain could enhance the continuous transport of positive potential vorticity and the downward propagation of upper-level isentropic potential vorticity disturbances, thereby playing an essential role in the triggering and development of PEP events.

Universal scaling of the osmotic pressure for dense, quasi-two-dimensionally confined polymer melts reveals transitions between fractal dimensions.

A scaling law for the osmotic pressure of quasi-two-dimensional polymer melts as a function of concentration is obtained, which shows fractal characteristics. Structural properties such as the chains' contour length and their inner-monomer pair distribution function display fractal scaling properties as well. These predictions are confirmed with mesoscale numerical simulations. The chains are swollen and highly entangled, yet Flory's exponent is always ν = 1/2. The melt can be considered a fluid of "blobs" whose size becomes renormalized in terms of the contour's length while the fractal dimension df increases monotonically between 5/4 and 2, as the monomer concentration is increased. The semidilute scaling of the pressure is recovered when df = 1. Our results agree with recent experiments and with numerical reports on quasi-2d melts. This work provides a new paradigm to study and interpret thermodynamic and structural data in low-dimensional polymer melts, namely as fractal macromolecular objects.

Shear performance and size effect of CFRP strengthened RC beams

In this study, a 3D meso-scale numerical simulation method is established for analyzing the shear failure of carbon fiber reinforced polymer (CFRP) strengthened RC beams without stirrups. The inhomogeneity of concrete, the bond-slip relationship between steel bars and concrete, and the interaction between CFRP and concrete are considered. Based on this method, effects of shear-span ratio and CFRP fiber ratio on the shear performance and nominal shear strength size effect of CFRP strengthened RC beams are investigated. Results indicate that the size effect of CFRP strengthened RC beams is obvious, however, the shear-span ratio has little impact on the size effect of nominal shear strength of RC beams. The CFRP fiber ratio enhances the shear strength of RC beams on the one hand, while weakens the shear size effect of RC beams on the other hand. However, its influence on the shear performance of RC beams remains basically unchanged with varying shear-span ratios, indicating that there is no coupling effect between the shear-span ratio and CFRP fiber ratio. The shear-span ratio significantly influences both the shear bearing capacity of RC beams and the shear contribution of CFRP sheets, with the increase in the shear-span ratio, the shear bearing capacity of RC beams decreases to varying degrees, and the shear contribution of CFRP sheets increases initially and then decreases. Finally, the shear strength size effect law (SEL) of CFRP strengthened RC beams is proposed, which can quantitatively describe the effects of the shear-span ratio and the CFRP fiber ratio.

Mesoscale numerical simulation of the multiple step reaction in hydrogen reduction of iron oxides

This work designed a mesoscale method of multi-step reduction of Fe2O3 with H2 based on Lattice Gas Cellular Automata (LGCA). Particles in the LGCA were marked to distinguish all the reactants, intermediates, products, and inert. A self-organized evolutionary mechanism is designed. The hydrogen reduction of Fe2O3 in the temperature range of 460–550 °C and 650–800 °C was simulated. Results show that the intermediate product Fe3O4 was found in both conditions, and its mass fraction quickly reach a peak at ∼0.8 and gradually decrease thereafter. An “induction period” can be identified in the initial stage of the reaction at 650–800 °C, where the reduction rate is slow due to the hindered formation of FeO. The porosity inside the Fe2O3 particles increases continuously through the reduction process, resulting in significant changes in the flow field around the particles. Consequently, the wake vortex gradually decreases and disappears eventually.

Analysis of droplet behavior and breakup mechanisms on wet solid surfaces

The behavior and dynamics of droplet spreading are pivotal phenomena that exert a profound influence on numerous scientific disciplines, technological advancements, and natural processes. This study was conducted with the aim to investigate factors influencing the shape and geometry of a liquid droplet on a solid surface using the lattice Boltzmann method (LBM). LBM as a mesoscale numerical fluid simulation has gained increasing popularity among the most favorable numerical methods for simulating multi-phase/multi-component fluid flow in complex geometries. Accordingly, parameters dependency, surface tension, two-phase diagram, and wettability were evaluated in the LBM, and stable and calibrated forms were used for the droplet simulations. Also, an equation was obtained to determine the contact angle in the LBM system with a determination coefficient of 0.988. Then, droplet behavior was examined for its dependency on wettability, interfacial tension, and line tension. The results showed droplets breakup in a certain interfacial tension at high adhesive force. These breakups were due to the force balance in the triple line. They were not monotonic and first decreased and then increased the volume of the droplets.

Meso-scale numerical simulation of the mechanical behaviour of brick masonry in earth mortar

The paper discusses the mechanical behaviour of masonry composed of fired solid bricks and earth mortar. Such masonry is a typical construction technique in South and Southeast Asia. As its mechanical behaviour is complex due to high anisotropy attributed to noticeable difference in stiffness and strength between bricks and earth mortar, it is still considered challenging to comprehend the mechanical behaviour of such masonry. Taking into account this background, the present research addresses the formulation of the mechanical behaviour of brick masonry in earth mortar. Numerical analysis was performed to reproduce uniaxial compression and diagonal compression tests, referring to empirical evidences on interface behaviour between bricks and earth mortar. Meso-scale analysis was performed, applying a multi-surface failure criterion composed of cracking, shearing and crushing to unit-joint interfaces. The analysis showed very similar stress-strain relations and failure patterns to the tests. The simulation of the uniaxial compression test presented that the distributions of compressive stress shifted along with the progress of cracks. In the reproduction of the diagonal compression test, vertical stress was irregularly distributed after diagonal stepwise cracks appeared. Two comparative studies were conducted to examine the shear performance of brick masonry in earth mortar. First, sensitivity analysis indicated the noticeable influences of compressive strength, friction angle and facture energy of unit-joint interfaces. Second, macro-scale analysis was conducted, using a homogeneous material model. The observed diagonal crack patterns were similar to the test. The paper contributes to the understanding of the mechanical behaviour of brick masonry in earth mortar.

An extended universal morphological model for concrete mode‐I fracture: Formulations and preliminary verifications

AbstractThe purpose of this study is to develop a systematic meso‐level theoretical modeling approach for analyzing the mode‐I fracture failure behaviors of concrete. Firstly, the crack model is developed in a way to be equivalent to the continuum model at the macro‐level. Secondly, an extended universal morphological model (XUMM) for concrete mode‐I fracture analysis is proposed at the meso‐level. Afterwards, both the mesoscopic fracture characteristics and the macroscopic mechanical parameters of concrete are theoretically deduced based on the proposed XUMM. Comparison with existing meso‐level test results shows that the predictions from the XUMM have good consistency, but offsets are obvious as well. At last, the XUMM is calibrated using the limit state method and preliminarily verified via mesoscale numerical simulations.

Mesoscale numerical simulation of chloride ion penetration in geopolymer concrete under the externally applied electric field

This paper presents a numerical investigation on the penetration of chloride ions in a saturated geopolymer concrete under the action of externally applied electric field. The chloride ion transport model in geopolymer concrete is established, and the interactions between different ionic species such as potassium ions, sodium ions, hydroxide ions, and chloride ions are considered. By solving the modified mass conservation equation and the Poisson equation of individual ionic species, the concentration and electrostatic potential of different ions at any position and at any time are obtained. Results show that under the action of externally applied electric field, the ion electromigration plays a leading role, which is characterized by a rectangular wave in the concentration distribution curve. In addition, the average chloride ion penetration depth obtained from the numerical simulations agrees well with that measured from the experiment in the cited literature. Moreover, the transmission speed of the two positively charged ions (or the two negatively charged ions) are almost the same. While there is a striking difference in the transmission speed between the positively charged ions and the negatively charged ions, indicating that the electrostatic potential gradient is not constant, and is region related.

Mesoscale numerical simulation on the deterioration of cement-based materials under external sulfate attack

This paper is focused on the deterioration of cement-based materials subjected to external sulfate attack (ESA). For this purpose, a mesoscale chemo-mechanical model was developed and numerically implemented in ABAQUS. Firstly, a mesoscale cement-based material was geometrically reconstructed to reflect its heterogeneity, and the mechanical performance of its different constituents was quantitatively characterized; Secondly, some models for sulfate diffusion, reaction and expansion were constructed to describe the evolution of sulfates and its products in cement-based materials, the volume expansion characteristics of its matrix; Finally, the developed model was numerically implemented by ABAQUS and verified by the literature, and it was used to numerically analyze the concentration distributions of sulfates and ettringite in cement mortar specimen, mechanical response of matrix and its cracking characteristics, the results obtained agreed well with theoretical analysis and experimental observations. The developed mesoscale chemo-mechanical model may bring insights to the performance and life predictions of concrete structures in marine engineering.

Hyperscaling of the correlation length, interfacial tension, and specific heat in two-dimensional and quasi-two-dimensional liquids.

The line tension of two immiscible liquids under two-dimensional and quasi-two dimensional conditions is calculated as a function of temperature, using mesoscale numerical simulations, finding that it decays linearly. The liquid-liquid correlation length, defined as the thickness of their interface, is also predicted as the temperature is varied, and it diverges as the temperature becomes close to the critical temperature. These results are compared with recent experiments on lipid membranes and good agreement is obtained. The scaling exponents of the line tension (μ) and the spatial correlation length (ν) with temperature are extracted, finding that they fulfill the hyperscaling relationship, μ=d-1ν, where d is the dimension. The scaling of specific heat with temperature of the binary mixture is obtained as well. This is the first report of the successful test of the hyperscaling relation between μ and ν for d = 2 and for the non-trivial case of quasi-two dimensions. This work can help to understand experiments that test properties of nanomaterials using simple scaling laws, without needing to know specific chemical details of those materials.

3D mesoscale investigation on the compressive fracture of concrete with different aggregate shapes and interface transition zones

The purpose of this work is to investigate the effect of aggregate shape parameters and interface transition zone (ITZ) thickness on the mechanical properties and failure behavior of concrete under uniaxial compression. A 3D mesoscopic model including mortar, shape-alterable aggregate and thickness-controllable ITZ was established in ABAQUS software by programming. Based on the concrete damaged plasticity (CDP) method and the cohesive element approach, the simulation analysis was carried out from the aspects of macroscopic mechanical response, macroscopic failure morphology, mesoscale fracture propagation, and energy dissipation. Results indicate that polyhedral aggregate and spherical aggregate have no significant effect on the macroscopic mechanical properties of concrete. Aggregates with sharp edges and corners may cause concrete to be destroyed into more fragments. The ITZ with 0 thickness and medium thickness can predict the compressive strength of concrete, ITZ model with solid thickness is more suitable for meso-crack research. Thinner solid ITZ fits poorly with the experimental value, and the change of ITZ has little influence on polyhedral aggregates. It is proposed to establish a polyhedral aggregate and medium thickness ITZ model for mesoscale concrete numerical simulation.