4,239 research outputs found
Area and Length Minimizing Flows for Shape Segmentation
©1997 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.Presented at the 1997 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, June 17-19, 1997, San Juan, Puerto Rico.DOI: 10.1109/CVPR.1997.609390Several active contour models have been proposed to unify the curve evolution framework with classical energy minimization techniques for segmentation, such as snakes. The essential idea is to evolve a curve (in 20) or a surface (in 30) under constraints from image forces so that it clings to features of interest in an intensity image. Recently the evolution equation has. been derived from first principles as the gradient flow that minimizes a modified length functional, tailored io features such as edges. However, because the flow may be slow to converge in practice, a constant (hyperbolic) term is added to keep the curve/surface moving in the desired direction. In this paper, we provide a justification for this term based on the gradient flow derived from a weighted area functional, with image dependent weighting factor. When combined with the earlier modified length gradient flow we obtain a pde which offers a number of advantages, as illustrated by several examples of shape segmentation on medical images. In many cases the weighted area flow may be used on its own, with significant computational savings
Tools for developing continuous-flow micro-mixer : numerical simulation of transitional flow in micro geometries and a quantitative technique for extracting dynamic information from micro-bubble images
Recent advance in the microfluidics including its fabrication technologies has
led to many novel applications in micro-scale flows. Among them is the
continuous-flow micromixer that utilizes the advantages associated with
turbulent flows for rapid mixing, achieving the detection of fast kinetic
reaction as short as tens of microseconds. However, for developing a high
performance continuous-flow micromixer there are certain fundamental
issues need to be solved. One of them is an universal simulation approach
capable of calculating the flow field across entire passage for entire regime
from very low Reynolds number laminar flow through transition to fully
turbulent flow. Though the direct numerical simulation is potentially possible
solution but its extremely high computing time stops itself from practical
applications. The second major issue is the inevitable occurrence of
cavitation bubbles in this rapid flow apparatus. This phenomenon has
opposite effects: (a) deteriorating performance and damaging the micromixer;
(b) playing a catalyst role in enhancing mixing. A fully understanding of
these micro bubbles will provide a sound theoretical base for guiding the design of micromixer in order to explore the advantage to maximum while
minimizing its disadvantages. Therefore, the objectives of this PhD
programme is to study the tools that will effectively advance our fundamental
understandings on these key issues while in short term fulfil the requires from
the joint experimental PhD programme held in the life science faculty for
designing a prototype experimental device. During this PhD study, an
existing numerical approach suitable for predicting the possibly entire flow
regime including the turbulence transition is proposed for simulating the
microscale flows in the microchannel and micromixer. The simulation results
are validated against the transitional micro-channel experiments and this
numerical method is then further applied for the micromixer simulation. This
provides the researcher a realistic and feasible CFD tool to establish
guidelines for designing high-efficiency and cost-effective micromixers by
utilizing various possible measures which may cause very different flows
simultaneously in micromixer. In order to study microscale cavitation
bubbles and their effects on micromixers, an innovative experimental setup is
purposely designed and constructed that can generate laser-induced
micro-bubbles at desired position and size for testing. Experiments withvarious micro-scale bubbles have been performed successfully by using an
ultra high-speed camera up to 1 million frame rate per second. A novel
technique for tracking the contours of micro-scale cavitation bubble
dynamically has been developed by using active contour method. By using
this technique, for the first time, various geometric and dynamic data of
cavitation bubble have been obtained to quantitatively analyze the global
behaviours of bubbles thoroughly. This powerful tool will greatly benefit the
study of bubble dynamics and similar demands in other fields for fast and
accurate image treatments as well
Pore-scale Study of Bio-mineral and Bio-gas Formations in Porous Media
abstract: The potential of using bio-geo-chemical processes for applications in geotechnical engineering has been widely explored in order to overcome the limitation of traditional ground improvement techniques. Biomineralization via urea hydrolysis, referred to as Microbial or Enzymatic Induced Carbonate Precipitation (MICP/EICP), has been shown to increase soil strength by stimulating precipitation of calcium carbonate minerals, bonding soil particles and filling the pores. Microbial Induced Desaturation and Precipitation (MIDP) via denitrification has also been studied for its potential to stabilize soils through mineral precipitation, but also through production of biogas, which can mitigate earthquake induced liquefaction by desaturation of the soil. Empirical relationships have been established, which relate the amount of products of these biochemical processes to the engineering properties of treated soils. However, these engineering properties may vary significantly depending on the biomineral and biogas formation mechanism and distribution patterns at pore-scale. This research focused on the pore-scale characterization of biomineral and biogas formations in porous media.
The pore-scale characteristics of calcium carbonate precipitation via EICP and biogenic gas formation via MIDP were explored by visual observation in a transparent porous media using a microfluidic chip. For this purpose, an imaging system was designed and image processing algorithms were developed to analyze the experimental images and detect the nucleation and growth of precipitated minerals and formation and migration mechanisms of gas bubbles within the microfluidic chip. Statistical analysis was performed based on the processed images to assess the evolution of biomineral size distribution, the number of precipitated minerals and the porosity reduction in time. The resulting images from the biomineralization study were used in a numerical simulation to investigate the relation between the mineral distribution, porosity-permeability relationships and process efficiency. By comparing biogenic gas production with abiotic gas production experiments, it was found that the gas formation significantly affects the gas distribution and resulting degree of saturation. The experimental results and image analysis provide insight in the kinetics of the precipitation and gas formation processes and their resulting distribution and related engineering properties.Dissertation/ThesisDoctoral Dissertation Civil, Environmental and Sustainable Engineering 201
Quantifying Phase Configuration Inside an Intact Core Based on Wettability Using X-ray Computed Tomography
The ability to evaluate rock and fluid properties on the order of a few microns opens new areas in reservoir engineering and reservoir simulation. Multiple studies have been done on the application of x-ray computed tomography (microCT) for the pore-scale evaluation of fluid interfaces and rock-fluid interaction. A majority of the fluid flow governing interactions occur at the pore scale level and is usually overseen on large reservoir scales. Hence, it is important to carefully investigate such interactions. Multi-fluid-phase distribution and interaction of two immiscible fluids such as oil and water is one of the most important and constantly investigated subjects in the oil and gas industry. Oil-water interaction is a complex phenomenon governed by various flow mechanisms in addition to fluid and rock physical properties. Wettability is one of the major concepts of the fluid flow through the porous media and a physical property of the rock that influences hydrocarbon recovery and the recovery methods. Oil and water phase distribution and residual blob configurations in water-wet and oil-wet Berea sandstone cores were successfully identified using x-ray computed tomography. Residual and remaining oil saturations were calculated from the obtained images. Rock porosity was calculated using indicator kriging segmentation technique and fluid saturations were calculated using watershed segmentation. Residual oil blob geometry in the water-wet core was successfully obtained from the segmented images. Oil saturations and phase configurations were in agreement with the oil saturation estimations obtained through the capillary desaturation analysis
Investigation of Mass Transport Phenomena in Polymer Electrolyte Membrane Water Electrolysers
Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) are considered a promising candidate for large-scale renewable energy storage and green hydrogen production. To improve efficiency and minimize cost for large-scale deployment, operation at high current densities is necessary. However, a consequence of high current density operation is increased mass transport hindrance which degrades performance. Two components are critical to mass transport in PEMWEs, namely the porous transport layer (PTL) and the flow-field plates. Both are expected to transport liquid water, product gases, electrons, and heat with minimal fluidic, thermal and voltage losses. However, the influence of morphology and configuration of both these components and operating conditions on cell performance are not well understood. This research investigates the mass transport phenomena in the PTL and in the flow-field channels in relation to performance in PEMWEs. The influence of flow-field configuration and two-phase flow characteristics in the flow channels on performance was studied by combined high-speed optical imaging and electrochemical characterization at various operating conditions. Results showed a strong correlation of performance with the flow path length and flow regime. Further, a correlative ex-situ X-ray tomography and in-situ electrochemical characterization approach was used to investigate the influence of PTL microstructural parameters such as mean pore diameter, pore size distribution, porosity, tortuosity, and porosity distribution on performance. Results indicated that minimizing contact resistance is most beneficial for improved performance over the range of current density studied. The influence of flow channel depth on performance was investigated by electrochemical impedance spectroscopy and a design of experiment (DoE) approach was employed to investigate the relative importance and interaction effects of mass transport factors on cell performance. Results showed the water feed rate and two-way interaction between the flow-field and PTL are most significant. This study provides enhanced understanding of the mass transport characteristics in PEMWEs for optimized design and improved performance
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