LaVision (United Kingdom)

This paper presents the development and demonstration of simultaneous planar measurements of instantaneous temperature and velocity fields using Planar Laser-Induced Fluorescence (PLIF) in alumina-water nanofluids under transient turbulent natural convection. Specifically, the 2-colour/2-dye LIF technique is employed to measure instantaneous temperature fields in the central region of a cubic convection cell. Two fluorescent dyes (Rhodamine B and Rhodamine 110) are excited at 532 nm by an Nd:YAG laser sheet. The intensity ratio of the emitted fluorescent intensities at two different spectral bands quantified the instantaneous temperature distribution with temperature sensitivity of ∼3 %/°C. Furthermore, wavelet-based Optical Flow Velocimetry (wOFV) is applied to the instantaneous temperature fields to estimate local velocity. This will enable new understanding on the correlation between heat transfer performance, thermal plume dynamics, and flow characteristics of pure water and alumina-water nanofluids under transient conditions of turbulent natural convection (Rayleigh number ∼10 9 ). However, these insights are not included in the present paper, which focuses solely on the development and application of the measurement technique. To the best of our knowledge, this is the first successful application of 2-colour LIF temperature measurements in nanofluids, offering insights into the behaviour of the instantaneous and time-averaged temperature and velocity fields. It is noted that due to the opaqueness of denser nanofluids, we limited the maximum nanoparticle concentration of the nanofluid to 0.0025 vol%. The present methodology can be applied to other nanofluid systems of interest. • Alumina-water nanofluids are studied under conditions of transient turbulent natural convection. • 2-colour/2-dye planar laser-induced fluorescence is employed to measure instantaneous liquid temperature. • Non-invasive instantaneous planar liquid temperature measurements demonstrated in nanofluids for the first time. • Uncertainty of temperature measurement ( ± 1.51 °C) reduced through a developed frame-rejection algorithm. • Wavelet-based optical flow velocimetry is applied to the nanofluid thermography images.

Encoding information in patterns printed with magnetic ink can extend the usability of barcode and QR code technologies to applications that do not require a line of sight between the sensor and the code. Such an implementation garners an interest in security, track-and-trace and recyclable packaging applications. Previous work has demonstrated a device that can read a barcode obscured by a layer of opaque and 1 mm thick material. However, given that the most widespread magnetic toners are soft magnetic, a permanent magnet is needed in the system alongside the sensor to magnetically bias the barcode, which affects the sensor sensitivity. Here we describe a protocol to evaluate the impact of different permanent magnet geometries on the performance of the sensor and validate it with experimental results, enabling an active feedback for integration in the scanner system. As a result, we have reached an improved geometry that increases the reading distance of the device to at least 2 mm. This study is also useful for other applications that require optimization of the interaction between a permanent magnet and a magnetic sensor (e.g. nanoparticle tracking in magnetoresistive biosensors).

Magma intrusions grow to their final geometries by deforming the Earth’s crust internally and by displacing the Earth’s surface. Interpreting the related displacements in terms of intrusion geometry is key to forecasting a volcanic eruption. While scaled laboratory models enable us to study the relationships between surface displacement and intrusion geometry, past approaches entailed limitations regarding imaging of the laboratory model interior or simplicity of the simulated crustal rheology. Here we apply cutting-edge medical wide beam X-ray Computed Tomography (CT) to quantify in 4D the deformation induced in laboratory models by an intrusion of a magma analogue (golden syrup) into a rheologically-complex granular host rock analogue (sand and plaster). We extract the surface deformation and we quantify the strain field of the entire experimental volume in 3D over time by using Digital Volume Correlation (DVC). By varying the strength and height of the host material, and intrusion velocity, we observe how intrusions of contrasting geometries– cryptodomes, cup shapes, cone sheets and dikes – grow, and induce contrasting strain field characteristics and surface deformation in 4D. We observe dominantly mixed-mode (opening and shear) fracture localisation in low-cohesion material overburden versus opening-mode fracture localisation in high-cohesion material overburden. The results demonstrate how the combination of CT and DVC can greatly enhance the utility of optically non-transparent crustal rock analogues in obtaining insights into shallow crustal deformation processes. This unprecedented perspective on the spatio-temporal interaction of intrusion growth coupled with host rock deformation provides a conceptual framework that can be tested by geological field observations at eroded volcanic systems and by the ever increasing spatial and temporal resolution of geodetic data at active volcanoes.

This study focuses on microstructural changes that occur within the mammalian lung when subject to blast and how these changes influence strain distributions within the tissue. Shock tube experiments were performed to generate the blast injured specimens (cadaveric Sprague-Dawley rats). Blast overpressures of 100 kPa and 180 kPa were studied. Synchrotron tomography imaging was used to capture volumetric image data of lungs. Specimens were ventilated using a custom-built system to study multiple inflation pressures during each tomography scan. This data enabled the first digital volume correlation (DVC) measurements in lung tissue to be performed. Quantitative analysis was performed to describe the damaged architecture of the lung. No clear changes in the microstructure of the tissue morphology were observed due to controlled low to moderate level blast exposure. However, significant focal sites of injury were observed using DVC, which allowed detection of bias and concentration in the patterns of strain level. Morphological analysis corroborated the findings, illustrating that the focal damage caused by a blast can give rise to diffuse influence across the tissue. It is important to characterise the non-instantly fatal doses of blast, given the transient nature of blast lung in the clinical setting. This research has highlighted the need for better understanding of focal injury and its zone of influence (alveolar inter-dependency and neighbouring tissue burden as a result of focal injury). Digital volume correlation techniques show great promise as a tool to advance this endeavour, providing a new perspective on lung mechanics post-blast.

Particle image velocimetry methodology results in a spatial averaging of the real velocity field into a set of discrete measured velocities: one for each interrogation cell. In the absence of measurement noise, this filtering process results in a reduction of the measured turbulent kinetic energy and other second-order statistics of the velocity field. The reduction in this energy will naturally be dependent upon the amount of turbulent energy at lengthscales smaller than can be resolved by the interrogation cells that make up the measurement grid. This paper investigates the effects of sub-grid scale filtering on the second-order statistics of velocity. Several experiments are reported for which interrogation cell size to turbulent integral lengthscale ratios were varied. In addition, synthetic turbulent velocity fields with known spatial correlation functions are used to support experimental results and provide calibration for the estimation of the level of sub-grid filtering. It is suggested that to accurately capture most turbulent kinetic energy using PIV the interrogation cell should be at least of order ten times smaller than the integral lengthscale of the flow. A method is then provided to estimate the level of sub-grid filtering should the interrogation cell be larger than this limit up to around the size of the integral lengthscale. With interrogation cells larger than this lengthscale then sub-grid filtering is such that second-order statistics are reduced by over 50% and it should be considered unwise to rely on any second-order statistics from such a scenario, corrected or otherwise.