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Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-000499752

The concept of a visualization pipeline is central to many applications providing scientific visualization. In practical usage scenarios, when the pipelines fuse multiple datasets and combine various visualization methods they can easily evolve into complex visualization networks directing data flow. Creating and managing complex visualization networks, especially when data itself is time-dependent and requires time-dependent adjustment of multiple visualization parameters, is a tedious manual task with potential for improvement. Here we discuss the benefits of using Berkeley Database (BDB) snapshots to make it easier to create and manage visualization networks for timedependent data. The idea is to represent visualization network states as BDB snapshots accessed via the widely used Hierarchical Data Format (HDF5), and exploit the snapshot indexing system to flexibly navigate through the high-dimensional space of visualization parameters. This enables us to support useful visualization system features, such as dynamic interpolation of visualization parameters between time points and flexible adjustments of camera parameters per time point. The former allows fast continuous navigation of the parameter space to increase animation frame rate and the latter supports multi-viewpoint renderings when generating Virtual Reality panorama movies. The paper describes how the snapshot approach and the new features can be conveniently integrated into modern visualization systems, such as the Visualization Shell (Vish), and presents an evaluation study indicating that the performance penalty of this convenience compared to maintaining visualization networks in HDF5 files is negligible.

When combined with community specific conventions and application-specific semantics, the Hierarchical Data Format (HDF) provides a robust and reliable foundation that many scientific communities rely on for interoperability and high-performance storage of metadata and data. This foundation addresses many technical obstacles related to sustainable data and software, critical steps towards sustainable science. Building on successes across the communities that are using, or could use, HDF5 successfully, requires significant community engagement and development efforts that are outside of the scope of traditional software development projects in research and non-profit organizations like The HDF Group. Identifying individuals and organizations that are already doing the right things and bringing them together to share best practices for funding and executing these activities is an important step towards our shared goal of sustainable science.

We present a method to compute and visualize the curvature and torsion scalar fields derived from a vector field defined on a multi-block curvilinear grid. In order to compute the curvature and torsion fields, we define a uniform Cartesian grid of points in the volume occupied by the curvilinear grid and interpolate from the curvilinear grid to the Cartesian grid to get the vector field at the Cartesian grid points. We can then use finite difference formulas to numerically compute the derivatives needed in the curvature and torsion formulas. Once the curvature and torsion have been computed at the Cartesian grid points, we employ a multi scale color coding technique to visualize these scalar fields in orthoslices of the Cartesian grid. This multi scale technique allows one to observe the entire range of values of the scalar field, including small, medium and large values. In contrast, if uniform color coding is used to visualize curvature and torsion fields, it sometimes shows most of the values in a single predominant color, which makes it impossible to distinguish between the small, medium and large values. As an example of this multi-scale technique, we displayed the curvature and torsion fields in a computational fluid dynamics (CFD) simulation of an industrial stirred tank and used these images to identify regions of low, medium and high fluid mixing in the tank.

Context. High-resolution numerical methods have been developed for nonlinear, discontinuous problems as they appear in simulations of astrophysical objects. One of the strategies applied is the concept of artificial viscosity. Aims. Grid-based numerical simulations ideally utilize problem-oriented grids in order to minimize the necessary number of cells at a given (desired) spatial resolution. We want to propose a modified tensor of artificial viscosity which is employable for generally comoving, curvilinear grids. Methods. We study a differential geometrically consistent artificial viscosity analytically and visualize a comparison of our result to previous implementations by applying it to a simple self-similar velocity field. We give a general introduction to artificial viscosity first and motivate its application in numerical analysis. Then we present how a tensor of artificial viscosity has to be designed when going beyond common static Eulerian or Lagrangian comoving rectangular grids. Results. We find that in comoving, curvilinear coordinates the isotropic (pressure) part of the tensor of artificial viscosity has to be modified metrically in order for it to fulfill all its desired properties., Submitted to Computer Physics Communications

We describe a method to render a height field given on a triangular mesh in a manner that is similar to wellknown cartographic map views. This approach utilizes hypsometric tints and creates topographic contour lines procedurally as part of the rendering process. We discuss essential graphical enhancement techniques such as line smoothing, gradient compensation, contour line visibility fading, nonlinear elevation mapping, and shininess variation. The method is exemplified upon various numerical data sets from application sciences, demonstrating its ability to visually allow quantitative and qualitative precise assessment of the data values.

Visualization Methods for Numerical Astrophysics

We describe a novel approach to treat data from a complex numerical simulation in a unified environment using a generic data model for scientific visualization. The model is constructed out of building blocks in a hierarchical scheme of seven levels, out of which only three are exposed to the end-user. This generic scheme allows for a wide variety of input formats, and results in powerful capabilities to connect data. We review the theory of this data model, implementation aspects in our visualization environment, and its application to computational fluid dynamic simulation of flow in an impeller-stirred tank. The computational data are given as a velocity vector field and a scalar pressure field on a mesh consisting of 2088 blocks in curvilinear coordinates.

Physical Review Letters