Bubbles breaking the wall: Two-dimensional stress and stability analysis

Suspensions can be deformed through rearrangement of grains during the motion of a gas-liquid interface. Regions of jammed beads at the interface, can lead to intermittent behavior in the dynamics. We study the stability of layers of saturated jammed beads around stuck air bubbles, and the deformation mechanism leading to air channel formations in these layers. We describe a two-dimensional extension of a previous model of the eective stress in the jammed packing. We discuss how the tangential stress component alters the yield stress, in particular how arching eects may impact the yield threshold. We further develop a linear stability analysis, to study undulations which develop under certain experimental conditions at the air-liquid interface. The linear analysis gives estimates for the most unstable wavelengths for the initial growth of the perturbations. The estimates correspond well with peak to peak length measurements of the experimentally observed undulations

Structural Analysis in Virtual Reality for Education with BMLY

Virtual reality (VR) is an engaging and immersive medium for interacting with a digital environment. The educational benefits of implementing virtual reality into learning modules has recently been explored. This work presents a process for creating a virtual reality learning module on beam bending and a preliminary study on its effectiveness. In this work, virtual reality and structural analysis are combined to create an interactive virtual experiment on a steel beam. A VR user can select the location of a gravity load along the member and increase its magnitude while following the deformation and stresses in real time. The VR environment is implemented using the open source three.js library. The results of a survey to assess student interaction and evaluation of the developed learning module is presented.The authors would like to acknowledge the support of The University of Sydney for the time in the Immersive Learning Laboratory which facilitated this work

Monitoring steel fibre orientation in self-compacting cementitious composite slabs during pouring with dynamic X-ray radiography

This paper presents a new technique based on dynamic X-ray radiography that can be used to assess fibre orientation during pouring of steel fibre reinforced cementitious composites. Synthetic examples were used to assess the suitability and robustness of the technique, which was shown to provide reliable measurements of fibre orientation even when the signal-to-noise ratio is relatively high. A study was then carried out on the effect of formwork aspect ratio, time/duration of pouring, and rebar placement on the fibre orientation while pouring self-compacting cementitious composite slabs. Results demonstrated the ability of the technique in monitoring the movements of fibres while pouring, and the strong effect of the flow in inducing preferential fibre alignment within the slabs. Fibre orientation was found to vary progressively over time and could take about half of the duration of pouring to fully stabilise.University of Sydney - Sydney Research Accelerator (SOAR) programm

Single-projection reconstruction technique for positioning monodisperse spheres in 3D with a divergent x-ray beam

International audienceThe measurement of the position of single-sized spheres in 3D from a single, divergent, radiographic projection is addressed in the present study with the development of a novel method. Generally speaking, the location of the shadow cast by a single sphere on a detector defines a source-detector ray; the position of the particle along this ray is identified by the strong prior knowledge of its radius and the size of the shadow. For a dense assembly of equal-sized particles whose projections overlap, a novel Fourier transform based technique is introduced to give a first 3D determination of the particle centres. The uncertainty of this measurement is calculated from synthetic data with a known noise distribution. A further refinement of this measurement is performed based on the minimisation of the projection residual. The combined approach is validated both on synthetic data, and on real radiographs of a glass bead packing. The effect of noise on the measurement uncertainty is evaluated. The technique is made available to the community in the open source python package radioSphere

Dispersion in Fractures With Ramified Dissolution Patterns

The injection of a reactive fluid into an open fracture may modify the fracture surface locally and create a ramified structure around the injection point. This structure will have a significant impact on the dispersion of the injected fluid due to increased permeability, which will introduce large velocity fluctuations into the fluid. Here, we have injected a fluorescent tracer fluid into a transparent artificial fracture with such a ramified structure. The transparency of the model makes it possible to follow the detailed dispersion of the tracer concentration. The experiments have been compared to two dimensional (2D) computer simulations which include both convective motion and molecular diffusion. A comparison was also performed between the dispersion from an initially ramified dissolution structure and the dispersion from an initially circular region. A significant difference was seen both at small and large length scales. At large length scales, the persistence of the anisotropy of the concentration distribution far from the ramified structure is discussed with reference to some theoretical considerations and comparison with simulations

The behaviour of free-flowing granular intruders

Particle shape affects both the quasi-static and dynamic behaviour of granular media. There has been significant research devoted to the flowability of systems of irregularly shaped particles, as well as the flow of grains around fixed intruders, however the behaviour of free flowing intruders within granular flows remains comparatively unexplored. Here, the effect of the shape of these intruder particles is studied, looking at the kinematic behaviour of the intruders and in particular their tendency of orientation. Experiments are carried out within the Stadium Shear Device, which is a novel apparatus able to continuously apply simple shear conditions to two-dimensional grain analogues. It is found that the intruder shows different behaviour to that of the bulk flow, and that this behaviour is strongly shape dependent. These insights could lead to the development of admixtures that alter the flowability of granular materials

The behaviour of free-flowing granular intruders

Particle shape affects both the quasi-static and dynamic behaviour of granular media. There has been significant research devoted to the flowability of systems of irregularly shaped particles, as well as the flow of grains around fixed intruders, however the behaviour of free flowing intruders within granular flows remains comparatively unexplored. Here, the effect of the shape of these intruder particles is studied, looking at the kinematic behaviour of the intruders and in particular their tendency of orientation. Experiments are carried out within the Stadium Shear Device, which is a novel apparatus able to continuously apply simple shear conditions to two-dimensional grain analogues. It is found that the intruder shows different behaviour to that of the bulk flow, and that this behaviour is strongly shape dependent. These insights could lead to the development of admixtures that alter the flowability of granular materials