Aspects of Unstructured Grids and Finite-Volume Solvers for the Euler and Navier-Stokes Equations

One of the major achievements in engineering science has been the development of computer algorithms for solving nonlinear differential equations such as the Navier-Stokes equations. In the past, limited computer resources have motivated the development of efficient numerical schemes in computational fluid dynamics (CFD) utilizing structured meshes. The use of structured meshes greatly simplifies the implementation of CFD algorithms on conventional computers. Unstructured grids on the other hand offer an alternative to modeling complex geometries. Unstructured meshes have irregular connectivity and usually contain combinations of triangles, quadrilaterals, tetrahedra, and hexahedra. The generation and use of unstructured grids poses new challenges in CFD. The purpose of this note is to present recent developments in the unstructured grid generation and flow solution technology

Walking Assistant - A Mobile Aid for the Visually-Impaired

The most common navigation aid visually-impaired people employ is a white cane, but, recently, technology has given rise to a varied set of sophisticated navigation aids. While these new aids can provide more assistance to a visually-impaired person than a white cane, they tend to be expensive due to a small market segment, which in turn can reduce their accessibility. In an effort to produce a technologically-advanced yet accessible navigation aid, an Android application is proposed that detects and notifies users about obstacles within their path through the use of a smartphone\u27s camera. While the smartphone is mounted on a harness worn by the user, the Walking Assistant application operates by capturing images as the user walks, finding features of objects within each frame, and determining how the features have moved from image to image. If it is discovered that an object is moving towards the user, the Walking Assistant will activate the smartphone\u27s vibration mode to alert the user to the object\u27s presence. Additionally, the user can control the Walking Assistant through the use of either touch or voice commands. By conducting real-world tests, it was determined that the Walking Assistant can correctly identify obstacles 42.1% of the time, while generating false positive obstacle identifications only 15.0% of the time. The accuracy of the Walking Assistant can be further improved by implementing additional features, such as a fuzzy-decision-based thresholding system or image stabilization

Optical instrumentation for fluid flow in gas turbines

Both a novel shearing interferometer and the first demonstration of particle image velocimetry (PIV) to the stator-rotor gap of a spinning turbine cascade are presented. Each of these techniques are suitable for measuring gas turbine representative flows. The simple interferometric technique has been demonstrated on a compressor representative flow in a 2-D wind tunnel. The interferometer has obvious limitations, as it requires a clear line of sight for the integration of refractive index along an optical path. Despite this, it is a credible alternative to schlieren or shadowgraph in that it provides both qualitative visualisation and a quantitative measurement of refractive index and the variables to which it is dependent without the vibration isolation requirements of beam splitting interferometry. The 2-D PIV measurements have been made in the stator-rotor gap of the MTI high-pressure turbine stage within DERA's Isentropic Light Piston Facility (lLPF). The measurements were made at full engine representative conditions adjacent to a rotor spinning at 8200 rpm. This is a particularly challenging application due to the complex geometry and random and periodic effects generated as the stator wake interacts with the adjacent spinning rotor. The application is further complicated due to the transient nature of the facility. The measurements represent a 2- D, instantaneous, quantitative description of the unsteady flow field and reveal evidence of shocks and wakes. The estimated accuracy after scaling, timing, particle centroid and particle lag errors have been considered is ± 5%. Non-smoothed, non-time averaged measurements are qualitatively compared with a numerical prediction generated using a 2-D unsteady flow solver (prediction supplied by DERA). A very close agreement has been achieved. A novel approach to characterising the third component of velocity from the diffraction rings of a defocusing particle viewed through a single camera has been explored. This 3-D PIV technique has been demonstrated on a nozzle flow but issues concerning the aberrations of the curved test section window of the turbine cascade could not be resolved in time for testing on the facility. Suggestions have been made towards solving this problem. Recommendations are also made towards the eventual goal of revealing a temporally and spatially resolved 3-D velocity distribution of the stator wake impinging on the passing rotor

The Grid Dependence of Well Inflow Performance in Reservoir Simulation

Imperial Users onl

Propagation and reconstruction of re-entry uncertainties using continuity equation and simplicial interpolation

This work proposes a continuum-based approach for the propagation of uncertainties in the initial conditions and parameters for the analysis and prediction of spacecraft re-entries. Using the continuity equation together with the re-entry dynamics, the joint probability distribution of the uncertainties is propagated in time for specific sampled points. At each time instant, the joint probability distribution function is then reconstructed from the scattered data using a gradient-enhanced linear interpolation based on a simplicial representation of the state space. Uncertainties in the initial conditions at re-entry and in the ballistic coefficient for three representative test cases are considered: a three-state and a six-state steep Earth re-entry and a six-state unguided lifting entry at Mars. The paper shows the comparison of the proposed method with Monte Carlo based techniques in terms of quality of the obtained marginal distributions and runtime as a function of the number of samples used

Process monitoring and control using live cell imaging for the manufacturing of cell therapies

Regenerative medicine (RM) represents a promising enabling technology to revolutionize healthcare. This said there are still major gaps between the commercial promise and the reality of the cell therapy sector of regenerative medicine. There is consensus to develop high through-put, automated technologies for the manufacture of RM products. Imaging methods will have the capacity to contribute to this technological gap for cell therapies and are particularly attractive to provide non-destructive monitoring with high spatial and temporal resolution. This work applied an automated, non-invasive phase contrast imaging platform (Cell-IQ) to measure, analyse and ultimately quantify image derived metrics for human embryonic stem cells (hESCs) and haematopoietic stem cells (HSCs) as part of the colony forming unit (CFU) assay. This work has shown through thresholding and machine vision identification technology, imaging has the ability to improve the precision of current evaluation methods for cell culture, providing novel information regarding culture state and show image derived metrics to be predictive of future culture state. Building on this, differentiation through the addition of a growth factor cocktail highlighted how in-process monitoring enables protocol optimisation. After equilibrating the Cell-IQ incubator to a standard incubator, the progress of the CFU assay was monitored and image metrics representative of colony phenotype were analysed. Cell count, distance between cells and cell migration within individual colonies were identified to be informative and provide a degree of colony phenotype separation. Quantitative, novel, image derived metrics were identified that improve reliability through computer automation, cost by removing user verification and time by reducing the assay time from 14 days to 7 days. Non-invasive imaging provides a fantastic opportunity to create bespoke sampling frequencies to achieve desired precision for manufacturing cell therapies, this work has developed and shown improvement and a level of control to current culture process for ESCs and HSCs