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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Mr Guanzhe Cui joined the group

Mr Guanzhe Cui has just started his Master of Philosophy (MPhil) program in March, 2017, and he will work on numerical simulations of multi-component flow in porous media based on Lattice Boltzmann method (LBM). Guanzhe graduated with Master of Architecture and Civil Engineering from School of Civil Engineering and Mechanics at Kunming University of Science and Technology, China in 2016.

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Paper accepted (Fusion Eng. Des.) on effective thermal conductivity

Title: Influence of gas pressure on the effective thermal conductivity of ceramic breeder pebble beds

Author(s): Weijing Dai, Simone Pupeschi, Dorian Hanaor, Yixiang Gan

Fusion Engineering and Design, in press. [DOI][PDF:045_FED_2017]

Figure: Gas pressure related size dependency of the contact units.

Abstract: Lithium ceramics have been considered as tritium breeder materials in many proposed designs of fusion breeding blankets. Heat generated in breeder pebble beds due to nuclear breeding reaction must be removed by means of actively cooled plates while generated tritiums is recovered by purge gas slowly flowing through beds. Therefore, the effective thermal conductivity of pebble beds that is one of the governing parameters determining heat transport phenomenon needs to be addressed with respect to mechanical status of beds and purge gas pressure. In this study, a numerical framework combining finite element simulation and a semi-empirical correlation of gas gap conduction is proposed to predict the effective thermal conductivity. The purge gas pressure is found to vary the effective thermal conductivity, in particular with the presence of various sized gaps in pebble beds. Random packing of pebble beds is taken into account by an approximated correlation considering the packing factor and coordination number of pebble beds. The model prediction is compared with experimental observation from different sources showing a quantitative agreement with the measurement.

Keywords: effective thermal conductivity; ceramic breeding materials; pebble beds; granular materials; gas pressure

Full paper can be downloaded via Publications page.

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Ms Yongmei Zhang joined the group

Ms Yongmei Zhang has just started her PhD program in March, 2017, and she will work on the mechanics of interfaces. Yongmei graduated with Master of Engineering in Solid Mechanics from the School of Aerospace, Xi’an Jiaotong University, China in 2016.

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PostDoc Opening in Carbon Storage

A postdoctoral research associate in carbon storage has been advertised in the School of Civil Engineering, Faculty of Engineering and IT at the University of Sydney. The official advertisement by The University of Sydney can be found via https://goo.gl/wqsvLl

The Postdoctoral Research Associate will undertake a project funded by the Australian Research Council on CO2 storage, named “Assessing reservoir performance for carbon storage in saline aquifers.” The Chief Investigators include A/Professor Luming Shen, Dr Federico Maggi, Dr Yixiang Gan, Professor Abbas El-Zein, Dr Zhejun Pan.


The project aims at developing and testing a modelling framework to assess the injectivity, storage capacity, and containment of supercritical CO2 injected in deep saline aquifers.The project broadly covers multiphase flow in porous/fractured geological materials, and emphasizes physical, hydraulic, and geomechanical processes at multiple spatial and temporal scales. The project is expected to provide a validated computational framework that can be used by stakeholders to improve analysis and assessment of reservoir performance under various scenarios of CO2 injection operations and boundary environmental conditions. This opening is fundamentally based on the development of advanced computational frameworks but it is part of a greater effort that also involves in-situ data collection and experimental laboratory tests conducted by other participants to this project. The project is led by A/Prof Luming Shen in the School of Civil Engineering at the University of Sydney, and involves the collaboration of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia.

 

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ModVal14, Karlsruhe, Germany

From 2-3 March, 2017, Dr Gan attended the 14th Symposium on Fuel Cell and Battery Modeling and Experimental Validation (ModVal14), Karlsruhe, Germany. In the conference, the recent work in the research group on “Universality of the emergent scaling in finite random binary percolation networks” was presented.

The presentation slides can be viewed and downloaded via:

2017_Gan_ModVal14_s

 

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Paper accepted (PLOS ONE) on RC networks

Title: Universality of the Emergent Scaling in Finite Random Binary Percolation Networks

Author(s): Chongpu Zhai, Dorian Hanaor, Yixiang Gan

PLOS ONE, in press. [DOI:10.1371/journal.pone.0172298]

Figure: (Left) A lattice network containing randomly distributed resistors and capacitors; (Right) Normalised admittance module as a function of frequency.

Full paper can be downloaded via Publications page.

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Visitors from KIT

Mr Simone Pupeschi and Mrs Marigrazia Mascardini are visiting us from Karlsruhe Institute of Technology (KIT), Germany from Jan to April, 2017. They have previously visited us in 2015, with the photo attached from their last visit. 

Simone and Mari are two final-year PhD students at KIT and have been working on thermo-mechanical behaviour of tritium breeder materials under extreme loading conditions (high temperature and neutron irradiation) for nuclear fusion reactors (i.e., ITER and Fusion for Energy projects). 

Photo from a Thai dinner taken on 1/2/2017, from left: Simone, Ratna, Yixiang, Mari and Simon.

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Inaugural Sydney Research Accelerator (SOAR) Fellows launch

Last week, Dr Gan attended the launch event of the Inaugural Sydney Research Accelerator (SOAR) Fellows. The fellows from the University’s new Sydney Research Accelerator (SOAR) program came together last week for a networking morning tea with the Vice-Chancellor, Dr Michael Spence, and Deputy Vice-Chancellor (Research), Professor Duncan Ivison.

In its first year, the program will enable 10 early-career and 10 mid-career researchers to further their research in important areas such as preventing melanoma, preparing for the next global pandemic, building more powerful batteries for electric cars and helping those from disadvantaged backgrounds access education.

Group photo (from left): Deputy Vice-Chancellor (Research) Professor Duncan Ivison with SOAR Fellows Associate Professor Xiaoke Yi, Associate Professor Karl Maton, Dr Yixiang Gan, Associate Professor Chris Ling, Dr Wojciech Chrzanowski, Associate Professor Tara Murphy, Dr Stefanie Schurer, Dr Jane Lê, Associate Professor Paulo Ferreira, Associate Professor Michael Valenzuela, Associate Professor Anne Cust, Associate Professor Susan Park, Associate Professor Anika Gauja.

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A few photos from the event (1/12/2016).

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IWMEM2016 workshop

International Workshop on Mechanics of Energy Materials (IWMEM2016) has been successfully hosted at The University of Sydney, 14-15 November, 2o16.

The workshop contained 22 presentations, regarding a wide range of research on challenging engineering problems in energy systems, and 40 participants from Germany, China, India, USA and Australia. After the presentations, an open discussion session has been carried out for variety of questions faced in the current trends in energy systems, and the plan to host the next IWMEM in Suzhou, China, 2017.

The group photo is taken in front of The University of Sydney Quadrangle.

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Also, there are some photos during our open discussion sessions:

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Mingchao awarded Endeavour Research Fellowship

Our previous visiting PhD student, Mr Mingchao Liu,from Tsinghua University has been awarded with Endeavour Research Fellowship from Australian Government. This prestige fellowship will support him to conduct a six-month research project at The University of Sydney in 2017.

Congratulations to Mingchao.

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More details about Endeavour Scholarships and Fellowships (link):

The Endeavour Scholarships and Fellowships are the Australian Government’s competitive, merit-based scholarships and fellowships providing opportunities for Australians to undertake study, research or professional development overseas and for overseas citizens to do the same in Australia.

The Endeavour Scholarships and Fellowships build Australia’s reputation for excellence in the provision of education and research, support the internationalisation of the Australian higher education and research sectors and offer high-achieving Australians opportunities to increase their knowledge and expertise in their field.

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Dr Gan selected as Sydney Research Accelerator fellow

Dr Gan has been selected as one of the inaugural Sydney Research Accelerator (SOAR) fellows at The University of Sydney. The news has just been announced by the University.

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SOAR stands for Sydney Outstanding Academic Researcher program.

Extracted from the announcement (link):

The first cohort of fellows of the University’s new Sydney Research Accelerator (SOAR) program has been announced.

In its first year, the program will enable 10 early-career and 10 mid-career researchers to further their research in important areas such as preventing melanoma, preparing us for the next global pandemic, building more powerful batteries for electric cars and helping those from disadvantaged backgrounds succeed in education.

As part of their two-year program, fellows are awarded $50,000 per year to support their research, innovation and development plans. They also benefit from a personalised program of research development support and structured mentoring.

Deputy Vice-Chancellor (Research) Professor Duncan Ivison said the program recognises and develops the University’s most talented researchers as part of the University’s 2016-20 unprecedented investment in research.

“Through SOAR, we will support up-and-coming research leaders to build momentum and increase the scale and impact of their research.”

“At the University of Sydney, we want to celebrate and nurture high-performing researchers to realise their full potential and SOAR is just one of the many new programs we are developing to do just that.”

Professor Ivison said the program would allow our best and most promising researchers more opportunity to fast-track their career development and position them as pioneers in new fields. It will help them build leadership skills and aid the development of new partnerships with industry and other leading academics around the world.

Dr Andrew Black, Director of Research Development and Collaboration, said the program received an overwhelming level of interest.

“The volume and calibre of the applicants was extremely high, which highlights the University’s ability to attract leading researchers across a variety of disciplines. With the demand and early success of the program, we hope to increase the number of fellowships offered in 2018.”

Highlighting the University’s commitment to gender equity, 50 percent of the fellowships were awarded to women.

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Saba won 1st Prize in Civil Poster Presentation 2016

Congratulations to Mrs Saba Gharehdash, who won Annie B Wilson 1st Prize in Civil Engineering Poster Presentation 2016 last Friday. The presentation is entitled “Mechanical and Hydraulic Behaviour of Blast Induced Fractured Rock”. She is a PhD candidate supervised by A/Prof Luming Shen and Dr Yixiang Gan.

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Professor Marc Kamlah is visiting the lab

My former PhD advisor, Professor Marc Kamlah from Karlsruhe Institute of Technology (KIT) Germany, is visiting the lab for four weeks. Marc is the group leader and now acting as the head of Institute of Applied Materials – Mechanics of Materials and Biomechanics (IAM-WMB) where over 60 Scientists work experimentally and theoretically in the field of the mechanics of materials and bio-mechanics. More details about IAM-WMB via https://www.iam.kit.edu/wbm/index.php

He will attend later the International Workshop on Mechanics of Energy Materials (IWMEM 2016) at The University of Sydney.

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Chongpu presented at IEEE Holm Conference and won Young Investigator Award

Mr Chongpu Zhai (a PhD candidate) presented our work on “Stress-dependent frequency response of conductive granular materials” at The IEEE Holm Conference on Electrical Contacts (9-12 October, 2016, Florida USA) and won the Young Investigator Award.

Well done and Congratulations, Chongpu.

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The paper was co-authored by Chongpu Zhai, Dorian Hanaor, Gwénaëlle Proust, and Yixiang Gan, at The University of Sydney.

Conference website: http://www.ieee-holm.org/

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Mr Oleg Birkholz is visiting the lab

Mr Oleg Birkholz from Karlsruhe Institute of Technology (KIT), Germany is visiting us at The University of Sydney. Oleg is working on the numerical aspects of modelling lithium-ion battery systems, via the discrete element method and resistor-capacity (RC) network. He will stay with us for two months and working on modelling electro-mechanical properties of granular energy systems.
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Conference presentations (ICTAM and SOFT)

Recently, two previous visitors (Mingchao and Mari) have presented their work at two conferences.

(1) In August, Mr Mingchao Liu (Tsinghua University, China) attended the 24th International Congress of Theoretical and Applied Mechanics (ICTAM2016) in Montreal, Canada, presenting “Surface effect on the adsorption-induced deformation of ordered porous materials”.

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(2) In September, Mrs Marigrazia Moscardini (Karlsruhe Institute of Technology, Germany) attended the 29th Symposium on Fusion Technology (SOFT 2016) in Prague, Czech Republic, presenting “Discrete element modelling of ellipsoidal particles for fusion applications”.

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