Vector Field Topology of Time-Dependent Flows in a Steady Reference Frame

Rojo, Irene Baeza; Günther, Tobias

doi:10.1109/tvcg.2019.2934375

Cited by 34 publications

(48 citation statements)

References 49 publications

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“…Due to the relativity between observer and the observed feature, this formally guarantees that translating and rotating flow structures can be faithfully extracted (Günther & Theisel, ). Analyzing a vector field from the perspective of a local observer that moves with the vortices will enable the application of sophisticated steady‐state vortex separation and extraction techniques (Rojo & Günther, ). Initial experience with these advanced analysis methods applied to the current Guadalupe vortex street is encouraging and will be presented in a future paper.…”

Section: Discussionmentioning

confidence: 99%

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

et al. 2020

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Vortex streets formed in the stratocumulus‐capped wake of mountainous islands are the atmospheric analogues of the classic Kármán vortex street observed in laboratory flows past bluff bodies. The quantitative analysis of these mesoscale unsteady atmospheric flows has been hampered by the lack of satellite wind retrievals of sufficiently high spatial and temporal resolution. Taking advantage of the cutting‐edge Advanced Baseline Imager, we derived kilometer‐scale cloud‐motion winds at 5‐min frequency for a vortex street in the lee of Guadalupe Island imaged by Geostationary Operational Environmental Satellite‐16. Combined with Moderate Resolution Imaging Spectroradiometer data, the geostationary imagery also provided accurate stereo cloud‐top heights. The time series of geostationary winds, supplemented with snapshots of ocean surface winds from the Advanced Scatterometer, allowed us to capture the wake oscillations and measure vortex shedding dynamics. The retrievals revealed a markedly asymmetric vortex decay, with cyclonic eddies having larger peak vorticities than anticyclonic eddies at the same downstream location. Drawing on the vast knowledge accumulated about laboratory bluff body flows, we argue that the asymmetric island wake arises from the combined effects of Earth's rotation and Guadalupe's nonaxisymmetric shape resembling an inclined flat plate at low angle of attack. However, numerical simulations will need to establish whether or not the selective destabilization of the shallow atmospheric anticyclonic eddies is caused by the same mechanisms that destabilize the deep columnar anticyclones of laboratory flows, such as three‐dimensional vertical perturbations due to centrifugal or elliptical instabilities.

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Section: Discussionmentioning

confidence: 99%

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

et al. 2020

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“…In the following, we first discuss time‐dependent vector field topology at simple analytical examples, to build intuition about related issues, and compare the efficiency and accuracy of our DHT refinement method to the local refinement approach by Machado et al [MSE13]. Finally, we evaluate the different approaches to obtain initial candidate lines (Section 4.1) at two numerical flow simulation datasets, and compare the approaches by Rojo and Günther [RG20] as well as Machado et al [MBES16] to our DHT refinement approach on these datasets. As ground truth, we compare against ridges in the FTLE fields in all our examples.…”

Section: Resultsmentioning

confidence: 99%

“…Extracting critical points in the Galilean‐invariant frame of reference defined by the feature flow field [MBES16], and in an optimal frame of reference [RG20] both result in missing line segments due to numerical noise in the area behind the cylinder. Therefore, we obtain initial robust segments by filtering, where det ∇ u > −10, i.e., τ h = 10, and integrate from their ends along the respective observer motions (Figures 12o and 12p), as long as integration stays in a hyperbolic region.…”

Section: Resultsmentioning

confidence: 99%

“…Refinement (bifurcation lines [MSE13] magenta, and ours green) of initial candidate lines (initial segments yellow, extended by feature flow blue) of critical points in the Galilean‐invariant frame of reference defined by the feature flow field, at t=5 s (a) and t=7.5 s (c), and of critical points in the optimal frame of reference [RG20], at t=5 s (b) and t=7.5 s (d). Streak topology and VFT in the steady frame of reference [RG20] at t=5 s (e)(f) and t=7.5 s (g)(h). (I) Shown enlarged in Figure 8.…”

Section: Resultsmentioning

confidence: 99%

“…Much of its unsteady topology is generated by a slow moving DHT near the center of the domain, for which an initial candidate can be obtained by tracking critical points in the lab frame. As in the previous section, initial candidates obtained from the optimal frame of reference [RG20] yield the most accurate results (see Section 2 in the supplemental material). The streak manifolds in the space‐time domain are shown in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Extraction of Distinguished Hyperbolic Trajectories for 2D Time‐Dependent Vector Field Topology

Hofmann

Sadlo

2020

Computer Graphics Forum

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This paper does two main contributions to 2D time‐dependent vector field topology. First, we present a technique for robust, accurate, and efficient extraction of distinguished hyperbolic trajectories (DHT), the generative structures of 2D time‐dependent vector field topology. It is based on refinement of initial candidate curves. In contrast to previous approaches, it is robust because the refinement converges for reasonably close initial candidates, it is accurate due to its adaptive scheme, and it is efficient due to its high convergence speed. Second, we provide a detailed evaluation and discussion of previous approaches for the extraction of DHTs and time‐dependent vector field topology in general. We demonstrate the utility of our approach using analytical flows, as well as data from computational fluid dynamics.

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Evolution of an atmospheric Kármán vortex street from high-resolution satellite winds: Guadalupe Island case study

Horváth

Bresky

Daniels

et al. 2019

Preprint

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Vortex streets formed in the stratocumulus-capped wake of mountainous islands are the atmospheric analogues of the classic Kármán vortex street observed in laboratory flows past bluff bodies. The quantitative analysis of these mesoscale unsteady atmospheric flows has been hampered by the lack of satellite wind retrievals of sufficiently high spatial and temporal resolution. Taking advantage of the cutting-edge Advanced Baseline Imager, we derived kilometer-scale cloud-motion winds at 5-min frequency for a vortex street in the lee of Guadalupe Island imaged by Geostationary Operational Environmental Satellite-16. Combined with Moderate Resolution Imaging Spectroradiometer data, the geostationary imagery also provided accurate stereo cloud-top heights. The time series of geostationary winds, supplemented with snapshots of ocean surface winds from the Advanced Scatterometer, allowed us to capture the wake oscillations and measure vortex shedding dynamics. The retrievals revealed a markedly asymmetric vortex decay, with cyclonic eddies having larger peak vorticities than anticyclonic eddies at the same downstream location. Drawing on the vast knowledge accumulated about laboratory bluff body flows, we argue that the asymmetric island wake arises from the combined effects of Earth's rotation and Guadalupe's nonaxisymmetric shape resembling an inclined flat plate at low angle of attack. However, numerical simulations will need to establish whether or not the selective destabilization of the shallow atmospheric anticyclonic eddies is caused by the same mechanisms that destabilize the deep columnar anticyclones of laboratory flows, such as three-dimensional vertical perturbations due to centrifugal or elliptical instabilities.

show abstract

Vector Field Topology of Time-Dependent Flows in a Steady Reference Frame

Cited by 34 publications

References 49 publications

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

Extraction of Distinguished Hyperbolic Trajectories for 2D Time‐Dependent Vector Field Topology

Evolution of an atmospheric Kármán vortex street from high-resolution satellite winds: Guadalupe Island case study

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