93,596 research outputs found
A high-precision liDAR-based method for surveying and classifying coastal notches
Formation of notches is an important process in the erosion of seaside cliffs. Monitoring of coastal notch erosion rate and processes has become a prime research focus for many coastal geomorphologists. Observation of notch erosion rate considers a number of characteristics, including cliff collapse risk, distinction of historical sea levels, and recognition of ongoing erosional mechanisms. This study presents new approaches for surveying and classifying marine notches based on a high-precision light detection and ranging (LiDAR)-based experiment performed on a small region of a coastal cliff in southern Portugal. A terrestrial LiDAR scanner was used to measure geometrical parameters and surface roughness of selected notches, enabling their classification according to shape and origin. The implemented methodology proved to be a highly effective tool for providing an unbiased analysis of marine morphodynamic processes acting on the seaside cliffs. In the analyzed population of voids carved into Miocene calcarenites in a coastal cliff section, two types of notch morphology were distinguished, namely U-shaped and V-shaped. The method presented here provides valuable data for landscape evaluation, sea-level changes, and any other types of analyses that rely on the accurate interpretation of cliff morphological features.National Science Centre [UMO-2015/17/D/ST10/02191
Transient analysis of third-grade viscoelastic nanofluid flow external to a heated cylinder with buoyancy effects
Nanotechnology is rapidly embracing numerous areas of manufacturing and process
engineering. New types of nanomaterials are being exploited to improve, for example, coating
integrity, anti-corrosion characteristics and other features of fabricated components. Motivated
by these developments, in the current study a mathematical model is developed for unsteady
free-convective laminar flow of third-grade viscoelastic fluid (doped with nano-particles) from
a semi-infinite vertical isothermal cylinder, as a model of thermal coating flow of a pipe
geometry. Non-Newtonian behavior is simulated with the thermodynamically robust third
grade Reiner-Rivlin model which accurately represents polymer fluids. Nanoscale effects are
analyzed with the Buongiorno two-component nanofluid model. The governing equations
comprise a set of highly coupled, nonlinear, multi-degree partial differential equations
featuring viscoelastic and nanofluid parameters. An implicit Crank-Nicolson numerical scheme
is implemented to solve the emerging nonlinear problem with appropriate initial and boundary
conditions. Detailed graphical plots for velocity, temperature and nano-particle volume fraction
are presented for a range of different parameters (i.e., third-grade fluid parameter, Brownian
motion parameter, thermophoretic parameter, buoyancy ratio parameter, Lewis number).
Additionally, distributions of the heat transfer coefficient, skin friction and Sherwood number
at the cylinder surface are visualized. Furthermore, streamlines, isotherms and nano-particle
volume fraction contour plots are included for variation of the third-grade parameter. Contour
plots for the third-grade nanofluid flow are found to deviate significantly from those
corresponding to Newtonian nanofluids. Validation of the numerical solutions with earlier
studies is also included.
KEYWORDS: Third-grade viscoelastic nanofluid, Thermal convection, Cylinder, Thermophoresis,
Brownian motion, Implicit numerical method, Contour plots, Industrial coating
Towards multiple 3D bone surface identification and reconstruction using few 2D X-ray images for intraoperative applications
This article discusses a possible method to use a small number, e.g. 5, of conventional 2D X-ray images to reconstruct multiple 3D bone surfaces intraoperatively. Each bone’s edge contours in X-ray images are automatically identified. Sparse 3D landmark points of each bone are automatically reconstructed by pairing the 2D X-ray images. The reconstructed landmark point distribution on a surface is approximately optimal covering main characteristics of the surface. A statistical shape model, dense point distribution model (DPDM), is then used to fit the reconstructed optimal landmarks vertices to reconstruct a full surface of each bone separately. The reconstructed surfaces can then be visualised and manipulated by surgeons or used by surgical robotic systems
Automated pebble mosaic stylization of images
Digital mosaics have usually used regular tiles, simulating the historical
"tessellated" mosaics. In this paper, we present a method for synthesizing
pebble mosaics, a historical mosaic style in which the tiles are rounded
pebbles. We address both the tiling problem, where pebbles are distributed over
the image plane so as to approximate the input image content, and the problem
of geometry, creating a smooth rounded shape for each pebble. We adapt SLIC,
simple linear iterative clustering, to obtain elongated tiles conforming to
image content, and smooth the resulting irregular shapes into shapes resembling
pebble cross-sections. Then, we create an interior and exterior contour for
each pebble and solve a Laplace equation over the region between them to obtain
height-field geometry. The resulting pebble set approximates the input image
while presenting full geometry that can be rendered and textured for a highly
detailed representation of a pebble mosaic
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A Method to Generate Exact Contour Files for Solid Freeform Fabrication
Existing methods to create contour files generate a polygonal approximation of
the contours instead of an exact representation. This paper presents a method to generate
exact contours from Constructive Solid Geometry (CSG) representations. The method
preserves the accuracy of the contour files provided the primitives used to generate the
CSG tree are polygonal or quadric objects. Due to the inclusion of quadric objects into
the primitive set an additional effort to solve for the intersection points between two
quadric curves is required. The paper also presents a method to convert piecewise
quadratic contours to toggle point files for raster scanning solid freeform fabrication
processes.Mechanical Engineerin
Using Anisotropic Micro-Scale Topography to Manipulate the Wettability of Aluminum and Reduce the Retention of Water
A method is described for fabricating controlled micro-scale, topographical features on aluminum surfaces
for the purpose of exploiting those features to affect the surface wettability. Using a photolithographic approach, a
photoresist-masked surface is subjected to a plasma etch in a mixture of gaseous BCl3 and Cl2. Parallel grooves,
microns to tens of microns in width, depth and spacing are studied, because this geometry is scaleable for mass
production by roll-to-roll micro-embossing, and because the anisotropic nature of these features provides a
directional change in wettability that can reduce the retention of water on the surface. Aluminum was studied
because it is naturally hydrophilic and widely used in wet-surface heat exchanger applications, because of its low
cost and excellent mechanical and thermal properties.
Water droplets placed on a micro-grooved aluminum surface using a micro-syringe exhibit significantly
increased apparent contact angles, and for water condensed onto an inclined, micro-grooved surface, the droplet
volume at incipient sliding is reduced by more than 50% compared to droplets on a surface without micro-grooves.
No chemical surface treatment is necessary to achieve this water repellency; it is accomplished solely through the
anisotropic surface topography. The droplet geometry shows an elongated base contour relative to a surface without
micro-grooves, and discontinuities in the three-phase contact line are also introduced by the grooves. A mechanistic
model is presented for predicting the critical droplet size on micro-grooved surfaces. This model extends earlier
work by accounting for the droplet geometry and contact-line changes caused by the micro-grooves. The model is
validated through comparisons of predicted to measured critical droplet sizes, and it is then used to provide guidance
for the development of surfaces with enhanced water drainage behavior.
In a broad range of air-cooling applications, water retention on the air-side surface of metallic heat
exchangers is problematic, because it can reduce the air-side heat transfer coefficient, increase core pressure drop,
and provide a site for biological activity. In refrigeration systems, the accumulation of frost on metallic fins requires
periodic defrosting and reduces energy efficiency. When water is retained on these surfaces following the defrost
cycle, ice is more readily formed in the subsequent cooling period, and such ice can lead to shorter operation times
before the next defrost is required. Thus the management and control of water droplets on heat-transfer and airhandling
surfaces is vital to energy efficiency, functionality, and maintenance in air-cooling systems. The microstructured
surfaces introduced in this work are proposed for use in air-cooling and dehumidifying applications, but
they may have other applications where the management of liquids on a surface is important.Air Conditioning and Refrigeration Project 166Air Conditioning and Refrigeration Project 20
Transition Contour Synthesis with Dynamic Patch Transitions
In this article, we present a novel approach for modulating the shape of transitions between terrain materials to produce detailed and varied contours where blend resolution is limited. Whereas texture splatting and blend mapping add detail to transitions at the texel level, our approach addresses the broader shape of the transition by introducing intermittency and irregularity. Our results have proven that enriched detail of the blend contour can be achieved with a performance competitive to existing approaches without additional texture, geometry resources, or asset preprocessing. We achieve this by compositing blend masks on-the-fly with the subdivision of texture space into differently sized patches to produce irregular contours from minimal artistic input. Our approach is of particular importance for applications where GPU resources or artistic input is limited or impractical
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