215 research outputs found
A framework for the generation of high-order curvilinear hybrid meshes for CFD simulations
We present a pipeline of state-of-the-art techniques for the generation of high-order meshes that contain highly stretched elements in viscous boundary layers, and are suitable for flow simulations at high Reynolds numbers. The pipeline uses CADfix to generate a medial object based decomposition of the domain, which wraps the wall boundaries with prismatic partitions. The use of medial object allows the prism height to be larger than is generally possible with advancing layer techniques. CADfix subsequently generates a hybrid straight-sided (or linear) mesh. A high-order mesh is then generated a posteriori using NekMesh, a high-order mesh generator within the Nektar++ framework. During the high-order mesh generation process, the CAD definition of the domain is interrogated; we describe the process for integrating the CADfix API as an alternative backend geometry engine for NekMesh, and discuss some of the implementation issues encountered. Finally, we illustrate the methodology using three geometries of increasing complexity: a wing tip, a simplified landing gear and an aircraft in cruise configuration
A semi-structured approach to curvilinear mesh generation around streamlined bodies
We present an approach for robust high-order mesh generation specially
tailored to streamlined bodies. The method is based on a semi-sructured
approach which combines the high quality of structured meshes in the near-field
with the flexibility of unstructured meshes in the far-field. We utilise medial
axis technology to robustly partition the near-field into blocks which can be
meshed coarsely with a linear swept mesher. A high-order mesh of the near-field
is then generated and split using an isoparametric approach which allows us to
obtain highly stretched elements aligned with the flow field. Special treatment
of the partition is performed on the wing root juntion and the trailing edge
--- into the wake --- to obtain an H-type mesh configuration with anisotropic
hexahedra ideal for the strong shear of high Reynolds number simulations. We
then proceed to discretise the far-field using traditional robust tetrahedral
meshing tools. This workflow is made possible by two sets of tools: CADfix,
focused on CAD system, the block partitioning of the near-field and the
generation of a linear mesh; and NekMesh, focused on the curving of the
high-order mesh and the generation of highly-stretched boundary layer elements.
We demonstrate this approach on a NACA0012 wing attached to a wall and show
that a gap between the wake partition and the wall can be inserted to remove
the dependency of the partitioning procedure on the local geometry.Comment: Preprint accepted to the 2019 AIAA Aerospace Sciences Meetin
Estimating the concentrations of pigments and binders in lead-based paints using FT-Raman spectroscopy and principal component analysis
Crack patterns over uneven substrates
Cracks in thin layers are influenced by what lies beneath them. From buried craters to crocodile skin, crack patterns are found over an enormous range of length scales. Regardless of absolute size, their substrates can dramatically influence how cracks form, guiding them in some cases, or shielding regions from them in others. Here we investigate how a substrate’s shape affects the appearance of cracks above it, by preparing mud cracks over sinusoidally varying surfaces. We find that as the thickness of the cracking layer increases, the observed crack patterns change from wavy to ladder-like to isotropic. Two order parameters are introduced to measure the relative alignment of these crack networks, and, along with Fourier methods, are used to characterise the transitions between crack pattern types. Finally, we explain these results with a model, based on the Griffith criteria of fracture, that identifies the conditions for which straight or wavy cracks will be seen, and predicts how well-ordered the cracks will be. Our metrics and results can be applied to any situation where connected networks of cracks are expected, or found
A chemometric study of ageing in lead-based paints
Raw data to accompany the results and discussion in the manuscript "A chemometric study of ageing in lead-based paints"
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