Ms Verena Becker is visiting the lab

Ms Verena Becker, a second year PhD student at Karlsruhe Institute of Technology (KIT), Germany, is visiting the lab at The University of Sydney. Verena is working on the numerical modelling lithium-ion battery systems, with special focus on the effective properties and the particle shape. She will stay with us for two months (from May until the end of July) and working on modelling electro-mechanical properties of battery systems.

Group photo in front of The Quadrangle at The University of Sydney, 28/05/2019. 
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Paper accepted (Eng Fracture Mech) on non-spherical particle breakage

Wei, D., Zhao, B., Dias-da-Costa, D., Gan, Y. (2019) An FDEM study of particle breakage under rotational point loading. Engineering Fracture Mechanics. In press. [DOI]

Abstract: 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.

Full paper can be downloaded via Publications page, when available.

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Endeavour Executive Leadership Awards

Dr Gan is among the recipients of the recently announced Endeavour Executive Leadership Awards, supported by Australian Government Department of Education and Training. This award will enable him to work with Professor Dominic Vella at the Mathematical Institute in the University of Oxford, on project related to spontaneous directional transport (SDT) of liquids. This collaboration will aim to develop engineering solutions towards harvesting water from atmospheric humidity for addressing freshwater scarcity across the globe.

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Paper accepted (Phys Rev Fluids) on topological disorder of porous media

Wang, Z., Chauhan, K., Pereira, J.M., Gan, Y. (2019) Disorder characterization of porous media and its effect on fluid displacement. Physical Review Fluids. In press.

Abstract: We investigate the effects of topological disorder and wettability on fluid displacement in porous media. A modified disorder index Iv is proposed to characterize the disorder of porous media. By changing Iv, different displacement patterns (stable displacement and fingering) under the same flow condition and fluid property are obtained. We analytically demonstrate how increase in disorder promotes fingering due to uneven distribution of local capillary pressure. It is shown that the displacement efficiency for different wettability conditions and disorder well correlates with the distribution of local capillary pressure. A power law relation between fluid-fluid interfacial length and saturation of invading fluid is proposed by taking geometry into account, where the parameters in power law relation can be predicted by the capillary index, Ic, unifying the effects of topological disorder and wettability.

Full paper can be downloaded via Publications page.

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Funded Australia-India Fellowship

The Australian Academy of Science has announced the successful recipients of the Australia–India Strategic Research Fund (AISRF) Early- and Mid-Career Researcher (EMCR) 2019 Fellowships. Dr Yixiang Gan was named among 11 recipients from different universities in Australia. He will be working with colleagues from IIT Madras and IIT Bhubaneswar on “Optimising thermal energy storage with phase change materials: with applications to solar energy storage”.

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Paper online (JCIS) on designing porous media for capillary flow

Liu, M., Suo, S., Wu, J., Gan, Y. Hanaor, D.A.H., Chen, C.Q. (2019) Tailoring porous media for controllable capillary flow. Journal of Colloid and Interface Science. 539:379-387.
[DOI][PDF:076_JCIS_2019]

Abstract: Control of capillary flow through porous media has broad practical implications. However, achieving accurate and reliable control of such processes by tuning the pore size or by modification of interface wettability remains challenging. Here we propose that the liquid flow by capillary penetration can be accurately adjusted by tuning the geometry of porous media. On the basis of Darcy’s law, a general framework is proposed to facilitate the control of capillary flow in porous systems by tailoring the geometric shape of porous structures. A numerical simulation approach based on finite element method is also employed to validate the theoretical prediction. A basic capillary component with a tunable velocity gradient is designed according to the proposed framework. By using the basic component, two functional capillary elements, namely, (i) flow accelerator and (ii) flow resistor, are demonstrated. Then, multi-functional fluidic devices with controllable capillary flow are realized by assembling the designed capillary elements. All the theoretical designs are validated by numerical simulations. Finally, it is shown that the proposed concept can be extended to three-dimensional design of porous media.

Full paper can be downloaded via Publications page.

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Paper accepted (AMS) on SPH modelling of contact angle dynamics

Bao, Y., Li, L., Shen, L., Lei, C., Gan, Y. (2019) A modified smoothed particle hydrodynamics approach for modelling dynamic contact angle hysteresis. Acta Mechanica Sinica. In press.

Dynamic wetting plays an important role in the physics of multiphase flow, and has significant influence on many industrial and geotechnical applications. In this work, a modified smoothed particle hydrodynamics (SPH) model is employed to simulate surface tension, contact angle, and dynamic wetting effects at meso-scale. The wetting and dewetting phenomena are simulated in a capillary tube, where the liquid particles are raised or withdrawn by a shifting substrate. The SPH model is modified by introducing a newly-developed viscous force formulation at liquid-solid interface to reproduce the rate-dependent behaviour of moving contact line. Dynamic contact angle simulations with interfacial viscous force are conducted to verify the effectiveness and accuracy of this new formulation. In addition, the influence of interfacial viscous force with different magnitude on contact angle dynamics is examined by empirical power law correlations, and the derived constants suggest the dynamic contact angle changes monotonically with interfacial viscous force. The simulation results are consistent with the experimental observations and theoretical predictions, implying that the interfacial viscous force can be associated with slip length of flow and microscopic surface roughness. This work has demonstrated that the modified SPH model can successfully account for the rate-dependent effects of moving contact line, and can be used for realistic multiphase flow simulation under dynamic conditions.

Full paper can be downloaded via Publications page.

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Paper accepted (IJSS) on effective properties of fluid-filled porous media

Liu, M., Wu, J., Gan, Y. Hanaor, D.A.H., Chen, C.Q. (2019) Multiscale modeling of the effective elastic properties of fluid-filled porous materials. International Journal of Solids and Structures. In press. [DOI]

Fluid-filled porous materials are widely encountered in natural and artificial systems. A comprehensive understanding of the elastic behavior of such materials and its dependence on fluid diffusion is therefore of fundamental importance. In this work, a multiscale framework is developed to model the overall elastic response of fluid-filled porous materials. By utilizing a two-dimensional micromechanical model with porosity at two scales, the effects of fluid diffusion and the geometric arrangement of pores on the evolution of effective properties in fluid-filled porous materials are investigated. Initially, for a single-porosity model the effective elastic properties of the dry and fluid-filled porous materials with ordered pores are obtained theoretically by considering a geometrical factor, which is related to the distribution of pores in the matrix. Model predictions are validated by finite element simulations. By employing a double-porosity model, fluid diffusion from macro- to micro-scale pores driven by a pressure gradient is investigated, and the resulting time-dependent effective elastic properties are obtained for both constant pressure and constant injection rate conditions. It is found that the presence and diffusion of pressurized pore fluid significantly affect the elastic response of porous materials, and this must be considered when modeling such materials. It is expected that the proposed theoretical model will advance the understanding of the fluid-governed elastic response of porous materials with implications towards the analysis of geophysical, biological and artificial fluid-filled porous systems.

Full paper can be downloaded via Publications page.

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PostDoc Opening in Clay Modelling

A postdoctoral research associate in modelling of clay behavior has been advertised in the School of Civil Engineering, Faculty of Engineering at the University of Sydney. The official advertisement by The University of Sydney can be found via https://goo.gl/rxhhA4

About the opportunity

The School of Civil Engineering is seeking a Postdoctoral Research Associate that will help to develop new formulations and computer codes for the modelling of fracturing and healing of clay and will use the codes to simulate the behaviour of clay material under cycles of wetting and drying in geotechnical and geoenvironmental engineering applications.

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Funded Australia-Germany joint research project

Our team will be funded under Australia-Germany Joint Research Cooperation Scheme between Universities Australia and German Academic Exchange Service (DAAD). The project will enable us to work closely with the research team from Karlsruhe Institute of Technology on multi-scale modelling of Li-ion batteries in the coming 2 years (2019-2020). The project title is “A microstructure informed model for effective properties in Li-ion batteries”, including seven exchange trips between two research teams.

Media release by Universities Australia.

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Congratulations to Si Suo for the poster award

Last week, Mr Si Suo won the second prize for Student Research Poster Event 2018 at School of Civil Engineering. Si is a first year PhD student working on multiphase flow in heterogeneous porous media.

Congratulations to Si!

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Mari won the poster prize at SOFT2018 conference

Mrs Marigrazia Moscardini won the poster prize at the 30th Symposium on Fusion Technology (SOFT 2018)  held in Giardini Naxos (Messina, Sicily) for presenting a joint work between Karlsruhe Institute of Technology and The University of Sydney on fusion materials, with the title of “Discrete element code to simulate the heat transfer inside ceramic breeder pebble beds”. Mari was conducting part of the research while visiting our lab at The University of Sydney in 2015 and 2017.

Mari, congratulations and good luck with your PhD defence in 1 month time.

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Paper accepted (Transport in Porous Media) on modelling imbibition

Suo, S., Liu, M., Gan, Y. (2018) Modelling imbibition processes in heterogeneous porous media. Transport in Porous Media. In press.  [DOI]

Imbibition is a commonly encountered multiphase problem in various fields, and exact prediction of imbibition processes is a key issue for better understanding capillary flow in heterogeneous porous media. In this work, a numerical framework for describing imbibition processes in porous media with material heterogeneity is proposed to track the moving wetting front with the help of a partially saturated region at the front vicinity. A new interface treatment, named the interface integral method, is developed here, combined with which the proposed numerical model provides a complete framework for imbibition problems. After validation of the current model with existing experimental results of one-dimensional imbibition, simulations on a series of two-dimensional cases are analysed with the presences of multiple porous phases. The simulations presented here not only demonstrate the suitability of the numerical framework on complex domains but also present its feasibility and potential for further engineering applications involving imbibition in heterogeneous media.

Full paper can be downloaded via Publications page.

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Paper online (Transport in Porous Media) on liquid patches

Li, S., Liu, M., Hanoar, D., Gan, Y. (2018) Dynamics of Viscous Entrapped Saturated Zones in Partially Wetted Porous Media. Transport in Porous Media. In press. [DOI]

As a typical multiphase fluid flow process, drainage in porous media is of fundamental interest both in nature and in industrial applications. During drainage processes in unsaturated soils and porous media in general, saturated regions, or clusters, in which a liquid phase fully occupies the pore space between solid grains, affect the relative permeability and effective stress of the system. Here, we experimentally study drainage processes in unsaturated granular media as a model porous system. The distribution of saturated clusters is analysed by optical imaging under different drainage conditions, with pore-scale information from Voronoi and Delaunay tessellation used to characterise the topology of saturated cluster distributions. By employing statistical analyses, we describe the observed spatial and temporal evolution of multiphase flow and fluid entrapment in granular media. Results indicate that the distributions of both the crystallised cell size and pore size are positively correlated to the spatial and temporal distribution of saturated cluster sizes. The saturated cluster size is found to follow a lognormal distribution, in which the generalised Bond number (Bo) correlates negatively to the scale parameter (μ) and positively to the shape parameter (σ). With further consideration of the total surface energy obtained based on liquid–air interfaces, we were able to include additional grain-scale information in the constitutive modelling of unsaturated soils using both the degree of saturation and generalised Bond number. These findings can be used to connect pore-scale behaviour with overall hydro-mechanical characteristics in granular systems.

Full paper can be downloaded via Publications page.

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Paper online (Colloids and Surfaces A) on contact angle hysteresis

Shi, Z., Zhang, Y., Liu, M., Hanoar, D., Gan, Y. (2018) Dynamic contact angle hysteresis in liquid bridges. Colloids and Surfaces A. 555:365-371.
[DOI][PDF:059_CSA_2018]

This work presents an experimental study of dynamic contact angle hysteresis using liquid bridges under cyclic compression and stretching between two identical plates. Under various loading rates, contact angle hystereses for three different liquids were measured by examination of advancing and receding liquid bridges, and the capillary forces were recorded. It is found that for a given liquid, the hysteretic behaviour of the contact angle is more pronounced at higher loading rates. By unifying the behaviour of the three liquids, power-law correlations were proposed to describe the relationship between the dynamic contact angle and the capillary number for advancing and receding cases. It is found that the exponents of obtained power-law correlations differ from those derived through earlier methods (e.g., capillary rise), due to the different kinematics of the contact line. The various hysteretic loops of capillary force in liquid bridges under varied cyclic loading rates were also observed, which can be captured quantitatively by the prediction of our developed model incorporating the dynamic contact angle hysteresis. These results illustrate the importance of varying contact line geometries during dynamic wetting and dewetting processes, and warrant an improved modelling approach for higher level phenomena involving these processes, e.g., multiphase flow in porous media and liquid transfer between surfaces with moving contact lines.

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Yanyao completed MPhil degree

Congratulations to Mr Yanyao Bao! Yanyao recently completed his MPhil degree with a thesis entitled “Smoothed Particle Hydrodynamics Simulations for Dynamic Capillary Interactions”. The review reports were excellent. Yanyao is currently working towards an application for further PhD study at The University of Sydney.

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Best Student Paper Awards (ACCM3) by Yanyao Bao and Si Suo

In February 2018, Yanyao and Si presented their research on the 3rd Australasian Conference on Computational Mechanics (ACCM3) hosted by Deakin University, and were both selected as “Best Student Paper Awards”.

Congratulations! Well done!

[1] Yanyao Bao, Ling Li, Luming Shen, and Yixiang Gan (2018), A modified smoothed particle hydrodynamics formulation for dynamic contact angles. The 3rd Australasian Conference on Computational Mechanics (ACCM3), Geelong, Australia. Best Student Paper Award.

[2] Si Suo, Mingchao Liu, and Yixiang Gan (2018) An SBFEM-based method for capillary flow in porous media with variable-slope boundaries. The 3rd Australasian Conference on Computational Mechanics (ACCM3), Geelong, Australia. Best Student Paper Award.

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Congrats to Dr. Zhai

Chongpu has successfully passed the thesis examination and recently received the award of the degree of Doctor of Philosophy (Engineering and Information Technologies) at the University of Sydney. His PhD dissertation entitled “Stress-dependent Electrical Conduction in Granular Materials” can be downloaded here via [PDF].

Dr Zhai (photo below) has joined Johns Hopkins University as a Postdoctoral researcher.

We wish you the best of success with your future research endeavours, Chongpu!

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Paper online (Int J Heat and Mass Transfer) on capillary penetration

Liu, M., Wu, J., Gan, Y., Hanaor, D., Chen, C.Q. (2018) Tuning capillary penetration in porous media: combining geometrical and evaporation effects. International Journal of Heat and Mass Transfer. 123:239-250.
[DOI][PDF:051_IJHMT_2018]

Abstract: Capillary penetration of liquids in porous media is of great importance in many applications and the ability to tune such penetration processes is increasingly sought after. In general, liquid penetration can be retarded or restricted by the evaporation of volatile liquid at the surface of the porous media. Moreover, when capillary penetration occurs in a porous layer with non-uniform cross section, the penetration process can be accelerated or impeded by adjusting the section geometry. In this work, on the basis of Darcy’s Law and mass conservation, a theoretical model of capillary penetration combining evaporation effects in two-dimensional homogeneous porous media of varying cross-section is developed and further examined by numerical simulations. The effects of sample geometry and liquid evaporation on capillary penetration are quantitatively analyzed. Results show that the penetration velocity is sensitive to the geometry of the porous layer, and can be tuned by varying the evaporation rate for a given geometry. Under given evaporation conditions, penetration is restricted to a limited region with a predictable boundary. Furthermore, we find that the inhibition of liquid penetration by evaporation can be offset by varying the geometry of the porous layer. The theoretical model is further extended to model the capillary flow in three-dimensional porous media. The interplay of geometry and evaporation during the capillary flow process in 3D conditions is also investigated. The results obtained can be used to facilitate the design of porous structures to achieve tunable capillary penetration for practical applications in various fields.

Full paper can be downloaded via Publications page.

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Paper online (Fusion Eng. Design) on thermal DEM with Smoluchowski effect

Moscardini, M., Gan, Y., Pupeschi, S., Kamlah, M. (2018) Discrete element method for effective thermal conductivity of packed pebbles accounting for the Smoluchowski effect. Fusion Engineering and Design. 127: 192-201. [DOI][PDF:050_FED_2018]

Highlights

• A thermal DEM code is proposed for the evaluation of the effective thermal conductivity of ceramic breeder pebble beds.
• The Smoluchowski effect was implemented to consider the influence of the gas pressure.
• Numerical results perfectly resemble the experimental data reported in literature.

Abstract: In this paper, a Discrete Element Method (DEM) for the evaluation of the effective thermal conductivity of pebble beds in fusion blankets is presented. Pebble beds are multiphase materials in which both the solid and the gas phase filling the voids between particles coexist. The effective thermal conductivity of a pebble bed depends on the thermal properties of the two phases as well as on the system properties (e.g. gas pressure, temperature etc.). In particular, the pressure of the system is a key parameter for the heat transfer in a packed granular assembly since the thermal conductivity of a confined gas decreases with decreasing pressure (known as Smoluchowski effect). In this work, the influence of the gas pressure on the effective thermal conductivity in the Knudsen domain was implemented, to our knowledge, for the first time in a DEM code. The heat transfer mechanisms implemented are: when two particles touch each other the conduction through the contact area between them and, in any case, the conduction through the gas phase in the gap between neighbouring solid particles, may they be touching or not. These mechanisms are expected to dominate the heat transfer in a fusion breeder packed bed. Parametric studies were carried out to investigate the influence of the solid and gas materials, temperature, pressure and compression state. Numerical results were compared with existing experimental literature data and recent experiments carried out at Karlsruhe Institute of Technology (KIT).

Full paper can be downloaded via Publications page.

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