October 2024
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5 Reads
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Publications (106)
October 2024
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4 Reads
September 2024
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23 Reads
The Morse-Smale complex is a standard tool in visual data analysis. The classic definition is based on a continuous view of the gradient of a scalar function where its zeros are the critical points. These points are connected via gradient curves and surfaces emanating from saddle points, known as separatrices. In a discrete setting, the Morse-Smale complex is commonly extracted by constructing a combinatorial gradient assuming the steepest descent direction. Previous works have shown that this method results in a geometric embedding of the separatrices that can be fundamentally different from those in the continuous case. To achieve a similar embedding, different approaches for constructing a combinatorial gradient were proposed. In this paper, we show that these approaches generate a different topology, i.e., the connectivity between critical points changes. Additionally, we demonstrate that the steepest descent method can compute topologically and geometrically accurate Morse-Smale complexes when applied to certain types of grids. Based on these observations, we suggest a method to attain both geometric and topological accuracy for the Morse-Smale complex of data sampled on a uniform grid.
August 2024
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21 Reads
April 2024
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13 Reads
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4 Citations
November 2023
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29 Reads
Wall-bounded turbulent flows as those occurring in transportation (e.g. aviation) or industrial applications (e.g turbomachinery), are usually subjected to pressure gradients (PGs). The presence of such PGs affects greatly the development and physics of the turbulent boundary layer (TBL), making it an open research area. An important phenomena associated with the presence of strong adverse PGs (APGs) as appearing in wings, is the separation of the boundary layer, which can lead to stall.
November 2023
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50 Reads
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9 Citations
November 2022
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41 Reads
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1 Citation
September 2022
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25 Reads
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3 Citations
IEEE Transactions on Visualization and Computer Graphics
Creating a static visualization for a time-dependent scalar field is a non-trivial task, yet very insightful as it shows the dynamics in one picture. Existing approaches are based on a linearization of the domain or on feature tracking. Domain linearizations use space-filling curves to place all sample points into a 1D domain, thereby breaking up individual features. Feature tracking methods explicitly respect feature continuity in space and time, but generally neglect the data context in which those features live. We present a feature-based linearization of the spatial domain that keeps features together and preserves their context by involving all data samples. We use augmented merge trees to linearize the domain and show that our linearized function has the same merge tree as the original data. A greedy optimization scheme aligns the trees over time providing temporal continuity. This leads to a static 2D visualization with one temporal dimension, and all spatial dimensions compressed into one. We compare our method against other domain linearizations as well as feature-tracking approaches, and apply it to several real-world data sets.
![Iso-surface of the λ2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varvec{\lambda }_{\mathbf {2}}$$\end{document} criterion [12] to identify near-wall vortical structures for the 3D turbulent flow around a NACA 4412 wing section](https://www.researchgate.net/publication/353073413/figure/fig4/AS:1121043305496588@1644288960886/Iso-surface-of-the-l2documentclass12ptminimal-usepackageamsmath_Q320.jpg)
![Average execution time per process on each time step over the entire simulation for n=1000\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathbf {n=1000}$$\end{document} in log scale. Different numbers of scaling configurations, 256 (green), 512 (purple), 1024 (orange), and 2048 (brown) cores, are used in each test case (color figure online)](https://www.researchgate.net/publication/353073413/figure/fig5/AS:1121043305496589@1644288960936/Average-execution-time-per-process-on-each-time-step-over-the-entire-simulation-for_Q320.jpg)
February 2022
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685 Reads
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10 Citations
The Journal of Supercomputing
In-situ visualization on high-performance computing (HPC) systems allows us to analyze simulation results that would otherwise be impossible , given the size of the simulation data sets and offline post-processing execution time. We develop an in-situ adaptor for Paraview Catalyst and Nek5000, a massively parallel Fortran and C code for computational fluid dynamics (CFD). We perform a strong scalability test up to 2, 048 cores on KTH's Beskow Cray XC40 supercomputer and assess in-situ visualization's impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in-situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ≈ 21% on 2,048 cores (the relative efficiency of Nek5000 without in-situ operations is ≈ 99%). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses the Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in-situ processing time between rank 0 and all other ranks. In our case, better scaling and load-balancing in the parallel image composition would considerably improve the performance of Nek5000 with in-situ capabilities. In general, the result of this study highlights the technical challenges posed by the integration of high-performance simulation codes and data-analysis libraries and 2 Marco Atzori et al. their practical use in complex cases, even when efficient algorithms already exist for a certain application scenario.
Citations (82)
... Among the four AI-creators, Sportify [25] and AiCommentator [1] leverage AI-creators to communicate automatically identified data insights in sports games to humans. Ying et al. [67] and Shi et al. [46] support chart and dataset understanding with AI-creators who communicate insights to humans with animations and narrations. Comparing these cases with the interview study, we can notice that the AI-creator communicates AI-created stories in these tools rather than presenting human-created stories as their proxies. ...
- Citing Conference Paper
April 2024
... Multi-GPU HPC nodes have become omnipresent in largescale supercomputers to support a variety of accelerated scientific workloads, ranging from weather forecast [2], computational fluid dynamics [3], [4], molecular dynamics [5], plasma simulation [6], and quantum computer simulators [7]. Currently, large-scale HPC clusters exhibit computing nodes with multiple GPUs on the same node, interconnected via a high-performance interconnect or through PCIe. ...
- Citing Conference Paper
November 2023
... Specifically, our framework augments any lossy compressor in order to preserve the contour tree in terms of its critical points and the connectivity among those critical points. Preserving the contour tree of the reconstructed data is crucial to support a variety of post hoc scientific visualization tasks, since the contour tree has been used for feature extraction, tracking, comparison, and interactive contour exploration (e.g., [27,64]). ...
- Citing Article
September 2022
IEEE Transactions on Visualization and Computer Graphics
... For current HPC systems, this gap due to the limitations in the data input/output (I/O) can be as large as up to four orders of magnitudes, even for highly parallel systems [14]. To overcome this limitation, workflows for in-situ visualizations have been set up to export compressed pictures of the flow field during runtime, see [15] for an in-situ visualization workflow with Nek5000 [16]. A common technique to visualize turbulence are iso-surfaces of the so-called Q-criterion exported for each time-step, which can later be integrated into a video. ...
- Citing Article
- Full-text available
February 2022
The Journal of Supercomputing
... The topological skeleton consisting of first order critical points and the invariant manifolds of saddles have been visualized for a long time [15]. Many extensions to 3D [12], higher order critical points [34], [36], [50], boundary switch points [10], [35], periodic orbits [51], [52], discrete topology [7], [20], [30], [40], and time-dependent flow [4], [29] have been suggested in the literature. Fig. 1: The different types of first order non-degenerate 2D critical points visualized with line integral convolution (LIC) [5] and arrow glyphs. ...
- Citing Conference Paper
January 2005
... Experimental studies have shown that suction leads to a decrease in skin friction on an aerofoil (Braslow et al. 1951;Hwang 1997), which would improve a plane's fuel efficiency by reducing the drag on its wings. More recent studies (Koepp et al. 2020) have used sophisticated numerical simulations and found similar results. Other applications include cooling a turbine's blades (Zhou et al. 2019) and reducing drag due to wind on high-rise buildings (Zheng & Zhang 2012). ...
- Citing Conference Paper
November 2020
... Such methods exploit transparency, or the selection of relevant lines [Gün20]. While some flow visualization approaches [PWK20] are adapted to visualize the dMRI data, they do not fit the brain tractograms constraints. Streamline methods [LS07] generate representative streamlines, but any approximation or representation that is not medically justified should be avoided in our context. ...
- Citing Article
July 2020
IEEE Transactions on Visualization and Computer Graphics
... A related topological approach, Percolation theory, studies the connectivity of an infinite network in terms of the size and extent of the largest connected component, as vertices or edges are included/excluded from the network [2,8]. A discontinuity in the resulting percolation function provides a threshold that describes an intrinsic porosity property of the material [27]. It has been adapted to finite domains and large material images [14]. ...
- Citing Chapter
June 2019
... A discontinuity in the resulting percolation function provides a threshold that describes an intrinsic porosity property of the material [27]. It has been adapted to finite domains and large material images [14]. ...
- Citing Conference Paper
October 2019
... In Section 2, we detail the three layout-related metrics that we subsequently calculated in our study from the labeled UIs: Balance, Equilibrium and Symmetry. In Section 3, we describe the experimental study with 368 web UI screenshots, 177 human participants and 2 computer visionbased web designs analysis services: VA [6] and AIM [8]. In Section 4, we present the regression models built with the collected experimental data, benchmark their quality and analyze the effects of the factors. ...
- Citing Conference Paper
October 2018
