Grain Days 2021
The Australian Association for Granular Media (ANAGRAM) is delighted to host Grain Days 2021. This will be a two day online event, bringing together researchers in the broad field of granular materials. The event will be held on 29 – 30 November 2021.
Please register for Grain Days here. If you are not already a member of ANAGRAM, please note that it is a requirement of attendance to join this association.
Doctoral School – 29 November
Research Forum & AGM – 30 November
Doctoral School (29/11/21, first day)
The first day of the event will be a doctoral school on experimental methods and imaging, delivered across three lectures. The first lecture, presented by Dr Benjy Marks from the University of Sydney, will provide an introduction to imaging – covering the basics of the entire process from setting up and executing experiments till data analysis. The lecture will teach how to process images and videos, with various techniques and examples used to provide a basic overview of the topic and an introduction to more advanced techniques, such as tomography.
The second lecture, presented by Dr Wenbin Fei and A/Prof Guillermo Narsilio from the University of Melbourne, will cover image processing methods for reconstructing X-ray computed tomography image stacks to obtain microstructural characteristics such as particle size and shape.
The microstructure of a granular material dictates many phenomena, including heat transfer through granular materials, which will be covered in the third lecture by Dr Peter Robinson from the University of Newcastle. Fundamentals of heat measurement in granular materials, and how this may be utilised to determine heat transfer properties for use in modelling will be taught and applied in the context specific context of self-heating of biomaterials.
Research Forum (30/11/21, second day)
The research forum is intended to be an opportunity for ANAGRAM members, especially PhD students and young researchers, to showcase their work to the broader granular mechanics community. The day will commence with a round of short teaser presentations, followed by a virtual poster session where the presenters will have an opportunity to interact with the audience in a virtual environment. Here, the audience will be able to walk around a virtual room, from one speaker to another, to ask more detailed questions on their previously presented teasers.
Annual General Meeting (AGM) (30/11/21, second day)
The next AGM will be on the 30th of November for all ANAGRAM members. If you would like to join the committee, please apply. Nominations must be made in writing, signed by two members of the association and accompanied by the written consent of the candidate (which may be endorsed on the form of the nomination), and must be delivered to the secretary of the association at least 7 days before the date fixed for the holding of the annual general meeting at which the election is to take place.
Lecture 1: Imaging of granular materials — Benjy Marks
Granular materials exhibit important structural features at many length scales. At the smallest scales, we can observe the frictional contact of asperities between individual grains. Zooming out we can describe the packing and arrangement of assemblies of particles. At larger scales still we can observe the runout of landslides and the evolution of sand dunes along a beach. The imaging of these systems is characterised by two important phenomena; opacity and heterogeneity. Almost all granular media are optically opaque. Even when the individual grains themselves are transparent, assemblies of particles rapidly become opaque due to refraction of light as it passes between the grains and the interstitial spaces. For this reason, we typically only ever see the outer layers of a granular medium. It is the heterogeneity of the material, and the interstitial spaces, that creates this opacity. The imaging of granular materials, therefore, is an uphill battle at almost all length scales.
In this Lecture we will cover the basics of imaging; from lighting to acquisition and finally data analysis. You will learn how to process both images and videos. We will see examples of reflection and transmission imaging, and put into a basic context more advanced techniques, such as tomography. Finally, we will go into detail on two techniques for measuring displacements of granular media from images. We will introduce both Particle Tracking Velocimetry and Particle Image Velocimetry (also referred to as Digital Image Correlation depending on your background) and provide a brief introduction to their use cases, pitfalls, and freely available software.
Lecture 2: X-ray computed tomography image processing of granular materials — Wenbin Fei and Guillermo Narsilio
In granular materials, force transmission, fluid flow and heat transfer through them are dominated by their microstructure. The development of accurate models to predict these transport processes has been hindered due to the limited ability to capture the microstructural information in traditional physical testing. X-ray computed tomography (XCT) is a powerful emerging technique that can access the microstructure of granular material non-destructively. During an XCT scanning, X-ray lights penetrate a rotating sample and reach a detector that records the attenuation of X-ray energy in a series of 2D X-ray plates. These data are then inversed to generate three-dimensional cross-sectional images of the sample. By applying image processing methods on the (2D and 3D) XCT images, a digital sample can be reconstructed for microstructure characterisation and transport phenomena simulations.
The Lecture will cover the image processing methods to reconstruct a digital sample based on the already inverted 2D XCT image stacks, with the goals to distinguish the different phases and identify individual particles from the sample to calculate microstructural characteristics such as particle size and shape. You will learn the basics of image filters and data analysis on XCT images. The XCT images of Ottawa sand 20-30 will be provided, and we will show the image processing procedures on them using open-source software: ImageJ (Fiji). More advanced examples generated using an XCT image approach under an Artificial Intelligence (AI) framework will be introduced as well.
Lecture 3: Heat transfer in granular materials — Peter Robinson
Heat transfer of granular materials is at the core of several industrial processes. The coking of coal, sintering of iron ore, self-heating of biomass; all are due to the way thermal energy behaves within the material. Granular materials behave differently to other solids and liquids, owing to differences in microstructure within particles and the distribution of particle sizing, and as such conventional methods to determine heat transfer properties need modification. This Lecture discusses the fundamentals of heat measurement in granular materials, and how this may be utilised to determine heat transfer properties for use in modelling. Parameters such as thermal conductivity and diffusivity will be discussed, as well as convective and radiant heat transfer coefficients, and the more complex process of self-heating within materials and the potential for spontaneous combustion.
The move away from fossil fuels has seen global economies strive to develop new renewable technologies. An emerging replacement in Australia and the UK is the use of biofuels for power generation. Taken from agricultural waste or plantations, this material is typically chipped or pelletised, prior to being fed into the power plant. As this material presents the risk of self-heating (similar to a compost pile), new challenges need to be considered to ensure the material is stored and handled safely. Using the information from the Lecture, worked examples will be completed based on actual experimental results, to determine the rate of heat generation and transfer within a biomaterial. From this, predictions can be made as to the safety of storing this material, minimising the risk of spontaneous combustion.