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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Conference papers on iCGMGE

The following conference papers have been presented by the research students at 1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), 20-22 November, 2017, Sydney.

[1] Yanyao Bao, Ling Li, Luming Shen, and Yixiang Gan, Smoothed Particle Hydrodynamics Simulations for Hysteretic Behaviours of Capillary Interactions. Proceedings of the 1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), Page 141-147. [PDF]

[2] Nanwangzi Wu and Yixiang Gan, Modelling Thermo-mechanical Behaviour of Geothermal Energy Piles under Cyclic Loading. Proceedings of the 1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), Page 148-153. [PDF]

[3] Guanzhe Cui, Shuoqi Li, Saba Gharehdash, and Yixiang Gan, Pore-scale Simulation of Water Patch Formation in Unsaturated Granular Media. Proceedings of the 1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), Page 154-159. [PDF]

[4] Weipeng Meng, Mingchao Liu, Yixiang Gan, and C.Q. Chen. From cracking to curling in drying colloidal films with varying water content. Proceedings of the 1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), Page 267-268. [PDF]

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IWMEM2017 Workshop, Suzhou, China

The Second International Workshop on Mechanics of Energy Materials (IWMEM2017) has been successfully hosted at The University of Sydney Centre in China, 8-11 November, 2o17. The workshop contained 27 technical presentations, regarding a wide range of research on challenging engineering problems in energy systems (nuclear fusion / fission, batteries, and photovoltaic systems), and 45 participants from Germany, China, India, USA and Australia.

The workshop was organised by The University of Sydney,Tsinghua University and CAS Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO). At the end of the workshop, the plan to host the next IWMEM at IIT Madras, Chennai, India, 2018.

The group photo is taken in front of The University of Sydney Centre in China, Suzhou, China.

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Honour thesis student awarded with poster prize

Mr Xu Wang, an honour thesis student working on numerical modelling of capillary forces between rough interfaces in our group, has been awarded with John Main 2nd Prize for Poster Presentation event on 3 November, 2017.

The Poster Presentation 2017 is the School of Civil Engineering’ major annual event to showcase the research undertaken by students over the past year. It is an ideal opportunity for our academics and students to network and share research experiences with each other. This year’s event was held in the Civil Engineering Drawing Office with around 70 contributions, from traditional lines of research to emerging fields in the broad areas of Civil Engineering. More details via this link.

Congratulations to Xu for his great work.

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Chongpu and Shuoqi submitted their theses

In the past few weeks, Mr Chongpu Zhai has just submitted his PhD thesis titled “Stress-dependent electrical conduction in granular materials” to summarise his PhD work from 2014. Ms Shuoqi (Sharon) Li has also submitted her MPhil thesis titled “The distribution of saturated clusters in wetted granular materials” for the research conducted in the past two years. Both Chongpu and Shuoqi were c0-supervised by Dr Dorian Hanaor from TU Berlin, Germany.

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Paper online (Int J Mech Sci) on contact mechancis

Zhai, C., Hanaor, Gan, Y. (2017) Contact stiffness of multiscale surfaces by truncation analysis. International Journal of Mechanical Sciences. 131–132: 305–316.
[DOI][PDF:048_IJMS_2017]

Abstract: In this paper, we study the contact stiffness of a fractal rough surface compressed by a rigid flat plane. A numerical model based on the analysis of flat punch indentation is proposed for simulated hierarchical surfaces, which are generated using statistical and fractal descriptors collected by surface profilometry. The contact stiffness of surfaces under increasing normal load is determined on the basis of the total truncated area at varying heights. The results are compared with experimental data from nanoindentation on four types of treated rough surfaces, showing good agreement with experimental observations below a certain truncation depth. Furthermore, the limits of the model’s validity are discussed by focusing on surface geometries and deformation of contacting asperities. With this proposed truncation method, we present a parametric analysis to establish a correlation between contact stiffness and surface roughness descriptors. The contact stiffness shows a unified power-law scaling with respect to the applied load over a wide range for simulated surfaces with distinct sets of roughness descriptors. The exponent of the power-law relationship is found to correlate positively to the fractal dimension while its amplitude is inversely correlated to the surface roughness amplitude. This study provides an easily implemented and computationally efficient method to connect mechanical behaviour with multi-scale surface structure, which can be utilized in design and optimization of engineering applications involving rough contacts.

Full paper can be downloaded via Publications page.

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Paper online (Heliyon) on crumple-formed materials

Hanaor, D., Flores Johnson, E.A., Wang, S., Quach, S., Dela-Torre, K.N., Gan, Y., Shen, L. (2017) Mechanical properties in crumple-formed paper derived materials subjected to compression. Heliyon. 3 (2017) e00329.
[DOI][PDF:047_Heliyon_2017]

Abstract: The crumpling of precursor materials to form dense three dimensional geometries offers an attractive route towards the utilisation of minor-value waste materials. Crumple-forming results in a mesostructured system in which mechanical properties of the material are governed by complex cross-scale deformation mechanisms. Here we investigate the physical and mechanical properties of dense compacted structures fabricated by the confined uniaxial compression of a cellulose tissue to yield crumpled mesostructuring. A total of 25 specimens of various densities were tested under compression. Crumple formed specimens exhibited densities in the range 0.8–1.3 g cm−3, and showed high strength to weight characteristics, achieving ultimate compressive strength values of up to 200 MPa under both quasi-static and high strain rate loading conditions and deformation energy that compares well to engineering materials of similar density. The materials fabricated in this work and their mechanical attributes demonstrate the potential of crumple-forming approaches in the fabrication of novel energy-absorbing materials from low-cost precursors such as recycled paper. Stiffness and toughness of the materials exhibit density dependence suggesting this forming technique further allows controllable impact energy dissipation rates in dynamic applications.

Full paper can be downloaded via Publications page.

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Paper online (Fusion Eng. Des.) on ellipsoidal DEM

Moscardinia, M., Gan, Y., Annabattula, R.K., Kamlah M. (2017) A Discrete Element Method to simulate the mechanical behavior of ellipsoidal particles for a fusion breeding blanket. Fusion Engineering and Design. 121: 22-31.
[DOI][PDF:046_FED_2017_M]

Abstract:

The breeder materials proposed for the solid tritium breeding blanket concepts are ceramic lithium-based compounds in the form of pebble beds. Different fabrication processes have been developed to produce pebbles with a high sphericity. However, a small deviation from a perfectly spherical shape exists. In this paper the influence of non-sphericity on the mechanical behaviour of a pebble bed is assessed representing the currently produced pebbles by means of ellipsoidal particles. To this end, the in-house Discrete Element Method code KIT-DEM was further extended. The multi-sphere approach was implemented to generate the ellipsoidal particles while the existing random close packing algorithm was modified to create the assemblies. Uniaxial compression of the assemblies, under periodic boundary conditions, was simulated to investigate the bulk stress-strain behaviour of the bed. Sensitivity studies were carried out with different packing factors of the assembly and several aspect ratios of the particles. In agreement with previous studies carried on assemblies of spherical pebbles, the initial packing factor was found to noticeably affect the mechanical response of the investigated assemblies. Moreover, a remarkable influence of the shape on the mechanical behavior of the simulated assemblies was observed. Therefore it is concluded that for production techniques that result in poor sphericity, DEM simulations with non-spherical particles are necessary to reproduce realistic stress-strain behavior of pebble beds.
Keywords: Discrete element method; Pebble bed thermomechanics; Nuclear fusion; Multi-sphere approach; Ellipsoidal particles

Full paper can be downloaded via Publications page.

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Paper accepted (Powder Tech.) on packing structures

Title: X-ray tomography investigations of mono-sized sphere packing structures in cylindrical containers

Author(s): Joerg Reimann, Jerome Vicente, Emmanuel Brun, Claudio Ferrero, Yixiang Gan, Alexander Rack

Powder Technology, in press. [DOI]

Abstract: The structure of mono-sized sphere packings (diameter d) in cylindrical containers (diameter D and height H) both with and without inner cylinders (diameter Di) has been investigated in detail by means of advanced X-ray computed tomography. The geometrical parameters were varied in a wide range; in all experiments 1d vertical vibration was applied. Five experiments were selected with characteristically differing local packing structures. The influence of container geometry, filling and vibration procedures on the formation of regular packings is discussed and a simple correlation is presented to assess whether structured packings occupy a significant fraction of the total packed volume.

For a packing with moderate densification, the regular structures are restricted to small wall zones and a random packing exists in the largest part of the packing volume. By selecting appropriate vibration parameters, the zones with regular structures can increase considerably and can persist in the total packed volume. The increasing crystallisation causes an increase of the container packing fraction. For cylinders with H/D > > 1 and moderate D/d, regular structures develop preferentially in radial direction from a hexagonal layer at the concave wall. For H/D < 1 and D/d > > 1, hexagonal dense structures grow preferentially above the flat bottom plate and can occupy a great portion of the total volume. The role of granular convection on these crystallisation processes has been addressed. Previous statements that the thickness of wall zones is ≈(4-5)d are not generally valid for mono-sized sphere packings; the development of a comprehensive correlation is the task of a future work.

Structural details of the packings close to concave, plane and convex walls are analysed via void fraction distributions, sphere centre positions, contact angle distributions, coordination numbers, radial distribution function and Voronoi tessellation. The combination of these methods provides a comprehensive understanding of structural details. Only a few characteristic results are presented; special topics will be the subject of forthcoming publications.

Full paper can be downloaded via Publications page.

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IWMEM2017 website online

The website of International Workshop on Mechanics of Energy Materials (IWMEM2017) is now online via http://iwmem.org/. The information will be updated in the near future.

The workshop will be hosted in Suzhou, 8-11 November, 2017. The venue is the newly established University of Sydney Centre in Suzhou, in Suzhou Industrial Park. The previous workshop was held in Sydney, some more details can be found here.

The brochure can be downloaded via:

IWMEM2017_Brochure
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Dr Gan visited universities and institutions in China

In April 2017, Dr Gan visited a few universities and institutions in China. These institutions include CAS Suzhou Institute of Nano-Tech and Nano-Bionics, Sydney Centre in China, Tongji University, Tsinghua University, CAS Institute of Plasma Physics, Southeast University, Zhejiang University, and Ningbo University. He discussed with other co-organisers for hosting the 2nd Workshop on Mechanics of Energy Materials (IWMEM2017) in Suzhou, earlier November 2017. In addition, he gave invited departmental seminars on the topic of “Mechanics of Compacted Granular Materials: From Interface, Morphology to Complex Networks” at Tsinghua University, Southeast University and Ningbo University.

The following briefly summarises the highlights of these visits:

(1) Discussion with Mrs Cathryn Hlavka (left) and her team at Sydney Centre in China regarding the organisation of coming workshop on mechanics of energy materials, to be hosted here in November, 2017 (more details).

(2) On 12 April, group photo with the research group of Professor Jianzhuang Xiao at Tongji University.

(3) On 14 April, dinner with the research group of Professor Changqing Chen at Tsinghua University.

(4)  On 17 April, photo taken in front of EAST (Experimental Advanced Superconducting Tokamak) fusion system at ASIPP with Professor Songlin Liu’s team.

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