Diffusion-controlled dissolution of a binary solid into a ternary liquid with partially-molten zone formation

We build a theoretical model of equilibrium dissolution of a homogeneous, solid mixture of two salts A and B, KCl and NaCl being used as the type example, into an aqueous solution of the two salts, with diffusive transport. We find that there are two sharp dissolution fronts, separating fluid, a partially molten zone containing a single solid and mixed solid. The phase change happens almost entirely at the two sharp fronts. In equilibrium, the leading front exhibits a small amount of precipitation of NaCl, simultaneous with complete dissolution of KCl. There is a unique surface in the space of far-field fluid KCl concentration, far-field fluid NaCl concentration and solid composition, dividing conditions where NaCl is the solid in the partially molten zone, from conditions where KCl is the solid in the partially molten zone. The movement rates of the dissolution fronts decrease as the concentration of either salt in the far-field fluid is increased. The movement rates of the dissolution fronts increase as either far-field temperature is increased, but this effect is smaller than that of concentration. In most circumstances, the dissolution front for a given salt moves more slowly, the more of that salt is present in the original solid, although the mass dissolution rate is not greatly affected by the solid composition

Compositional controls on melting and dissolving a salt into a ternary melt

We explore theoretically the controls on dissolution of salt A, in an undersaturated brine of salts A and B. We show that, as the concentration of B increases, the dissolution rate of A decreases, for brine of given temperature. We also show that there is a sharper decrease in dissolution rate with increasing concentration, for concentrations of B above a critical value, where B limits the equilibrium concentration. We explore the implications of the predictions for dissolution of KCl or NaCl, by a mixed brine of NaCl and KCl, a common reaction that may arise in dissolution of evaporites. We predict that, with mixed-composition brine, KCl crystals dissolve more rapidly than NaCl crystals, unless the (far-field) brine is nearly saturated in KCl. We also predict that the dissolution rate of these salts is largely independent of fluid temperature and is controlled by compositional diffusion

eights: BS 8888:2011 first angle projection drawings from FreeCAD 3D model

eights.py is a Python module intended for use with the open-source three-dimensional (3D) computer-aided design (CAD) package FreeCAD (FreeCAD version 0.15 user manual, n.d.). The module automates the construction of a page of two-dimensional (2D) axonometric drawings in first angle projection, in a style consistent (to the best of the module author’s ability) with the BS 8888:2011 standard (Technical product documentation and specification BS 8888, 2011). The module includes: - a class whose purpose is to provide a method which adds, to an existing FreeCAD document, a drawing sheet object whose formatting is intended to be consistent with the BS 8888:2011 standard, and populates the title block of the sheet, again in a way intended to be consistent with BS 8888:2011; - a class whose purpose is to provide a method which adds the standard BS 8888:2011symbol, indicating that a set of drawings are in first angle projection, to an existing FreeCAD drawing sheet object; and - a class whose purpose is to provide a method which takes any existing FreeCAD 3D shape object, and adds a set of axonometric drawings of that shape, in first angle projection, to an existing FreeCAD drawing sheet object, following the conventions in BS 8888:2011. Also supplied with the module are a detailed documentation file, and three example filesillustrating its application to particular 3D CAD models

Towards use of Dijkstra Algorithm for Optimal Navigation of an Unmanned Surface Vehicle in a Real-Time Marine Environment with Results from Artificial Potential Field

The growing need of ocean surveying and exploration for scientific and industrial application has led to the requirement of routing strategies for ocean vehicles which are optimal in nature. Most of the optimal path planning for marine vehicles had been conducted offline in a self‐made environment. This paper takes into account a practical marine environment, i.e. Portsmouth Harbour, for finding an optimal path in terms of computational time between source and end points on a real time map for an USV. The current study makes use of a grid map generated from original and uses a Dijkstra algorithm to find the shortest path for a single USV. In order to benchmark the study, a path planning study using a well‐known local path planning method artificial path planning (APF) has been conducted in a real time marine environment and effectiveness is measured in terms of path length and computational time

Optimal path planning of unmanned surface vehicles

The publisher has released this paper this under the Creative Commons CC BY-NC-ND licence. This release is used to provide the authority for open access deposit in Pearl, but please note that the licence forbids commercial use and the distribution of derivative works.Present study reviews the current methodologies adopted for optimal path planning of single unmanned surface vehicles and studies associated with swarm of unmanned surface vehicles. This also discusses the challenges and scopes, which can act as objectives, for future research towards path planning of such marine craft

USV Navigation in a Real-Time Map using Intelligent Path Planner

Oral presentation and print abstract only; no proceedings. Abstract appeared in Journal of Applied Mechanical EngineeringUnmanned surface vehicles (USV) are the recent trend in marine robotics due to their diverse application and easy deployment. Navigation of such USV in a real time marine environment is a major challenge and creates a need towards development of intelligent path planners which can increase the system autonomy. Many such intelligent path planning studies have been conducted in the area of mobile robotics but needs a lot more research to be conducted in area of marine robotics. In this study, a well know intelligent path planner A* has been implemented in a real time map using safety distance from obstacle as the criteria towards generating optimal trajectory for a single USV navigation. Different safety distances from obstacles ranging from 10 pixels to 40 pixels have been used to generate optimal trajectory and comparative performance has been analyzed in terms of computational time and path length. In this study, Portsmouth Harbour has been considered as area of study to determine the effectiveness of A* algorithm with different safety distance from obstacle as constraint. Algorithm has been validated on computer-based simulations using C++ and OpenCV libraries

Feasibility study of a constrained Dijkstra approach for optimal path planning of an unmanned surface vehicle in a dynamic maritime environment

Copy deposited in PEARL for open access under terms in penultimate paragraph of Optimal path planning is an important part of mission management hierarchy in a modern unmanned surface vehicle (USV) guidance, navigation and control frame work. USVs operate in a complex dynamic marine environment comprising of moving obstacles and sea surface currents. These characterising variables of configuration space change spatially as well as temporally. The current work investigates a well-known search technique, the Dijkstra algorithm, to resolve the problem of motion planning for a USV moving in a maritime environment. The current study extends the implementation of Dijkstra algorithm in a space cluttered with static and moving obstacles. In addition, downstream and upstream effects of sea surface currents of different intensities on optimal path planning are studied. The performance is verified in simulations with total path length and elapsed computational time considered as parameters to determine the effectiveness of the adopted approach. The results showed that the approach is effective for global path planning of USVs

A constrained A* approach towards optimal path planning for an unmanned surface vehicle in a maritime environment containing dynamic obstacles and ocean currents

Even after embargo period expires, authors' right to distribute as green open access is conditional on the green open access version including a DOI link, and on the green open access version being distributed under the Creative Commons CC-BY-NC-ND licence. In addition, the authors' right to distribute as green open access extends only to the author-generated post-print, not to any version with Elsevier typography.Efficient path planning is a critical issue for the navigation of modern unmanned surface vehicles (USVs) characterized by a complex operating environment having dynamic obstacles with a spatially variable ocean current. The current work explores an A* approach with an USV enclosed by a circular boundary as a safety distance constraint on generation of optimal waypoints to resolve the problem of motion planning for an USV moving in a maritime environment. Unlike existing work on USV navigation using graph based methods, this study extends the implementation of the proposed A* approach in an environment cluttered with static and moving obstacles and different current intensities. The study also examines the effect of headwind and tailwind currents moving in clockwise and anti clockwise direction respectively of different intensities on optimal waypoints in a partially dynamic environment. The performance of the proposed approach is verified in simulations for different environmental conditions. The effectiveness of the proposed approach is measured using two parameters, namely, path length and computational time as considered in other research works. The results show that the proposed approach is effective for global path planning of USVs