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"vortex"
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Whirlpools
Whirlpools, swirling vortexes in the ocean sometimes capable of capsizing entire ships, have long been featured in legend as the work of sea monsters or as gateways to other worlds. We now know that they are normal oceanic currents, usually caused by tides. This attractive volume concisely examines the natural and human-made conditions that create whirlpools, eddies, and more, providing a window into the field of oceanography for an elementary audience.
Book
On the stability of a pair of vortex rings
The growth of perturbations subject to the Crow instability along two vortex rings of equal and opposite circulation undergoing a head-on collision is examined. Unlike the planar case for semi-infinite line vortices, the zero-order geometry of the flow (i.e. the ring radius, core thickness and separation distance) and by extension the growth rates of perturbations vary in time. The governing equations are therefore temporally integrated to characterize the perturbation spectrum. The analysis, which considers the effects of ring curvature and the distribution of vorticity within the vortex cores, explains several key flow features observed in experiments. First, the zero-order motion of the rings is accurately reproduced. Next, the predicted emergent wavenumber, which sets the number of secondary vortex structures emerging after the cores come into contact, agrees with experiments, including the observed increase in the number of secondary structures with increasing Reynolds number. Finally, the analysis predicts an abrupt transition at a critical Reynolds number to a regime dominated by a higher-frequency, faster-growing instability mode that may be consistent with the experimentally observed rapid generation of a turbulent puff following the collision of rings at high Reynolds numbers.
Journal Article
Polar vortex : climate change and its effects
\"The events surrounding the 2014 polar vortex did not look the same to everyone involved. Readers can step back in time and into the shoes of a college student, a New Yorker, and a coal miner as readers act out scenes and compare and contrast various perspectives. Written with simplified, considerate text to help struggling readers, books in this series are made to build confidence as readers engage and read aloud. Includes a table of contents, glossary, index, author biography, sidebars, and timeline\"-- Provided by publisher.
Book
Siege in the Southern Stratosphere: Hunga Tonga‐Hunga Ha'apai Water Vapor Excluded From the 2022 Antarctic Polar Vortex
We use Aura Microwave Limb Sounder (MLS) trace gas measurements to investigate whether water vapor (H2O) injected into the stratosphere by the Hunga Tonga‐Hunga Ha'apai (HTHH) eruption affected the 2022 Antarctic stratospheric vortex. Other MLS‐measured long‐lived species are used to distinguish high HTHH H2O from that descending in the vortex from the upper‐stratospheric H2O peak. HTHH H2O reached high southern latitudes in June–July but was effectively excluded from the vortex by the strong transport barrier at its edge. MLS H2O, nitric acid, chlorine species, and ozone within the 2022 Antarctic polar vortex were near average; the vortex was large, strong, and long‐lived, but not exceptionally so. There is thus no clear evidence of HTHH influence on the 2022 Antarctic vortex or its composition. Substantial impacts on the stratospheric polar vortices are expected in succeeding years since the H2O injected by HTHH has spread globally. Plain Language Summary The 2022 Hunga Tonga‐Hunga Ha'apai eruption injected vast amounts of water vapor into the stratosphere. Concern arose that this excess water vapor could affect the 2022 Antarctic stratospheric polar vortex and ozone hole: Water vapor plays a crucial role in forming polar stratospheric clouds, which provide surfaces upon which chemical reactions that destroy ozone take place. Enhanced water vapor also affects temperatures, which in turn affect the powerful winds defining the polar vortex boundary. Antarctic polar vortex development began in April–May; by June the intense vortex‐edge winds presented a formidable obstacle to transport. Satellite trace‐gas measurements show that when water vapor from the Hunga Tonga eruption reached the vortex edge in June, it faced an impenetrable barrier and “besieged” the vortex, building up exceptionally strong water vapor gradients across the vortex edge. Water vapor, ozone, and chemicals involved in ozone destruction remained near historical average levels within the vortex through spring 2022. Because excess water vapor spread throughout the south polar regions after vortex breakup, much larger effects on the Antarctic vortex and chemical processing within it are expected in 2023 and beyond, when high water vapor will be entrained into the vortex as it develops. Key Points Microwave Limb Sounder (MLS) trace gas data show that the Hunga Tonga‐Hunga Ha'apai H2O plume was effectively excluded from the 2022 Antarctic polar vortex Antarctic lower stratospheric vortex strength, size, and longevity were among the largest on record, but within the range of previous years Antarctic chemical ozone loss in 2022 was unexceptional, with MLS ozone and related trace gases observed to be near average
Journal Article
Work/Travail/Arbeid
What would it mean for choreography to perform as an exhibition? That is the question at the origin of Work/Travail/Arbeid, a newly commissioned project by Anne Teresa De Keersmaeker. In response, the legendary Belgian dancer-choreographer takes her stage piece Vortex Temporum, choreographed to the eponymous music of composer Gérard Grisey, and reimagines it for the radically different temporal, spatial, and perceptual conditions of an art space. Rather than simply bringing a dance performance into a different space, De Keersmaeker reimagines and recasts the choreography as a nine-week-long exhibition. The result is a project that transforms the very material and conditions that have long been essential to dance, in particular the rigorous structure and choreographic language for which De Keersmaeker is known, into an entirely new exhibition form. It also reveals, in a way that perhaps no other dance piece by the choreographer could, the complex conceptual, technical, and physical labor-in sum, the work-that is the backbone of her entire oeuvre. This multi-volume boxed catalogue is conceived in parts so that it may accompany the exhibition while it is on and fully document it over its duration. A first set of volumes introduces Work/Travail/Arbeid and traces the preparations for it as well as its connection to Vortex Temporum. Following the exhibition, a second set of volumes documents and reflects on its unfolding. The catalogue includes a re-edition of De Keersmaeker's original Vortex Temporum program book, photographic documentation by Babette Mangolte and Anne Van Aerschot, drawings by De Keersmaeker, and newly commissioned essays by Douglas Crimp, Bojana Cvejicþ, Brian Dillon, Elena Filipovic, and Catherine Wood. Exhibition: Wiels, Brussels, Belgium (20.03-17.05.2015) / Centre Pompidou, Paris, France, (02.2016) / Tate, London, UK (Summer 2016).
Book
Twin vortex computer in fluid flow
Fluids exist universally in nature and technology. Among the many types of fluid flows is the well-known vortex shedding, which takes place when a fluid flows past a bluff body. Diverse types of vortices can be found in this flow as the Reynolds number increases. In this study, we reveal that these vortices can be employed for conducting certain types of computation. The results from computational fluid dynamics simulations showed that optimal computational performance is achieved near the critical Reynolds number, where the flow exhibits a twin vortex before the onset of the Kármán vortex shedding associated with the Hopf bifurcation. It is revealed that as the Reynolds number increases toward the bifurcation point, the input sensitivity of the twin vortex motion also increases, suggesting the modality of information processing within the system. Our finding paves a novel path to understand the relationship between fluid dynamics and its computational capability.
Journal Article
Stratospheric polar vortex dynamics according to the vortex delineation method
The stratospheric polar vortices play a significant role in stratospheric ozone distribution, air mass movement and temperature changes in the polar and subpolar stratosphere. To characterize the main parameters of the stratospheric polar vortices, in particular, vortex area, wind speed along the vortex edge, average temperature and ozone mass mixing ratio inside the vortex, vortex delineation is necessary. In this work, we use a new method of vortex delineation based on geopotential values determined from the maximum temperature gradient and maximum wind speed, thus, characterizing the polar vortex edges. Using the vortex delineation method based on the ERA5 reanalysis data for 1979–2020, we show a comparative characteristic of the Arctic and Antarctic polar vortices in the lower and middle stratosphere. The average polar vortex area in winter from 1979 to 2020 at the 50 and 10 hPa pressure levels equals 28.6 and 35.3·10
6
km
2
in the Arctic, and 41.6 and 54.8·10
6
km
2
in the Antarctic. The average wind speed along the vortex edge in winter at the 50 and 10 hPa pressure levels equals 35.5 and 55.5 m/s in the Arctic, and 52.7 and 79.2 m/s in the Antarctic. The average temperature inside the polar vortex in winter at the 50 and 10 hPa pressure levels equals respectively –69.0 and –61.7°C in the Arctic, and –81.9 and –74.2°C in the Antarctic.
Research highlights
Mean values of the area of the Arctic and Antarctic polar vortices are estimated.
Mean wind speed along the edges of the Arctic and Antarctic vortices are estimated.
Mean temperatures inside the Arctic and Antarctic polar vortices are estimated.
Journal Article
Recent advances on optical vortex generation
This article reviews recent progress leading to the generation of optical vortex beams. After introducing the basics of optical vortex beams and their promising applications, we summarized different approaches for optical vortex generation by discrete components and laser cavities. We place particular emphasis on the recent development of vortex generation by the planar phase plates, which are able to engineer a spiral phasefront via dynamic or geometric phase in nanoscale, and highlight the independent operation of these two different phases which leads to a multifunctional optical vortex beam generation and independent spin-orbit interaction. We also introduced the recent progress on vortex lasing, including vortex beam generation from the output of bulk lasers by modification of conventional laser cavities with phase elements and from integrated on-chip microlasers. Similar approaches are also applied to generate fractional vortex beams carrying fractional topological charge. The advanced technology and approaches on design and nanofabrications enable multiple vortex beams generation from a single device via multiplexing, multicasting, and vortex array, open up opportunities for applications on data processing, information encoding/decoding, communication and parallel data processing, and micromanipulations.
Journal Article
Helicity dynamics in reconnection events of topologically complex vortex flows
In this paper, we address the question of whether total helicity is conserved through viscous reconnection events in topologically complex vortex flows. To answer this question, we performed direct numerical simulations (DNS) focused on two complex vortex flow problems: (1) a trefoil knot and (2) a two-ring link, both simulated for various vortex core radii. The DNS framework relies on a block-structured adaptive mesh refinement (AMR) technique. A third simulation of a colliding pair of unlinked vortex rings, which exhibit no total helicity change, is also performed to serve as a reference case. The results show that a well-defined total helicity jump occurs during the unknotting/unlinking events of cases (1) and (2), which arises from the annihilation of the local helicity density content in the reconnection regions. Changes in total helicity become steeper as thinner core radii are considered for both cases (1) and (2). Finally, an analytical derivation based on the reconnection of two infinitesimal anti-parallel vortex filaments is provided that quantitatively links helicity annihilation and viscous circulation transfer processes, which unveils the fundamental hydrodynamic mechanisms responsible for production/destruction of total helicity during reconnection events.
Journal Article
Deep learning of vortex-induced vibrations
Vortex-induced vibrations of bluff bodies occur when the vortex shedding frequency is close to the natural frequency of the structure. Of interest is the prediction of the lift and drag forces on the structure given some limited and scattered information on the velocity field. This is an inverse problem that is not straightforward to solve using standard computational fluid dynamics methods, especially since no information is provided for the pressure. An even greater challenge is to infer the lift and drag forces given some dye or smoke visualizations of the flow field. Here we employ deep neural networks that are extended to encode the incompressible Navier–Stokes equations coupled with the structure’s dynamic motion equation. In the first case, given scattered data in space–time on the velocity field and the structure’s motion, we use four coupled deep neural networks to infer very accurately the structural parameters, the entire time-dependent pressure field (with no prior training data), and reconstruct the velocity vector field and the structure’s dynamic motion. In the second case, given scattered data in space–time on a concentration field only, we use five coupled deep neural networks to infer very accurately the vector velocity field and all other quantities of interest as before. This new paradigm of inference in fluid mechanics for coupled multi-physics problems enables velocity and pressure quantification from flow snapshots in small subdomains and can be exploited for flow control applications and also for system identification.
Journal Article