V ector fields are a common concept for the representation of many different kinds of flow phenomena in science and engineering. Methods based on vector field topology are known for their convenience for visualizing and analyzing steady flows, but a counterpart for unsteady flows is still missing. However, a lot of good and relevant work aiming at such a solution is available. We give an overview of previous research leading towards topologybased and topology-inspired visualization of unsteady flow, pointing out the different approaches and methodologies involved as well as their relation to each other, taking classical (i.e., steady) vector field topology as our starting point. Particularly, we focus on Lagrangian methods, space-time domain approaches, local methods, and stochastic and multi-field approaches. Furthermore, we illustrate our review with practical examples for the different approaches.
R ecent work has shown the great potential of interactive flow analysis by the analysis of path lines. The choice of suitable attributes, describing the path lines, is, however, still an open question. This paper addresses this question performing a statistical analysis of the path line attribute space. In this way we are able to balance the usage of computing power and storage with the necessity to not loose relevant information. We demonstrate how a carefully chosen attribute set can improve the benefits of state-ofthe art interactive flow analysis. The results obtained are compared to previously published work.
Room air flow and air exchange are important aspects for the design of energy-efficient buildings. As a result, simulations are increasingly used prior to construction to achieve an energy-efficient design. We present a visual analysis of air flow generated at building entrances, which uses a combination of revolving doors and air curtains. The resulting flow pattern is challenging because of two interacting flow patterns: On the one hand, the revolving door acts as a pump, on the other hand, the air curtain creates a layer of uniformly moving warm air between the interior of the building and the revolving door. Lagrangian coherent structures (LCS), which by definition are flow barriers, are the method of choice for visualizing the separation and recirculation behavior of warm and cold air flow. The extraction of LCS is based on the finite-time Lyapunov exponent (FTLE) and makes use of a ridge definition which is consistent with the concept of weak LCS. Both FTLE computation and ridge extraction are done in a robust and efficient way by making use of the fast Fourier transform for computing scale-space derivatives.
High fish densities negatively impact catch welfare and the survival of unwanted catches released from purse seines. To avoid overcrowding fish before being released, regulations have been implemented in the Northeast Atlantic mackerel and herring fisheries that limit the proportion of the seine that can be retrieved before catches are released. However, it is yet unknown how seine volume, and thus fish density, relates to proportion of seine retrieved. In this study, we have estimated the in-water volume of purse seines used in the Norwegian mackerel and herring fisheries as a function of proportion seine hauled and seine size. Purse seine geometry was monitored with multibeam sonar at sea and a log-linear mixed effects model was applied to the estimated seine volumes. The results indicate a 33-fold decrease in contained volume from 10 to 80% seine hauled and a threefold difference in volume between the largest and smallest measured seines. Fish densities in the seine were predicted to vary greatly depending on seine and catch size and under some conditions exceed safe crowding levels before the catch release limit is reached. This study questions the rationale of having the same catch release limit for all seine and catch sizes.
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