Jacek A . Jankowski | Bundesanstalt für Wasserbau (original) (raw)

Papers by Jacek A . Jankowski

Vorgeschlagene Zitierweise/Suggested citation: Platzek, Frank; Stelling, Guus; Jankowski, Jacek; ... more Vorgeschlagene Zitierweise/Suggested citation: Platzek, Frank; Stelling, Guus; Jankowski, Jacek; Patzwahl, Regina (2012): On the representation of bottom shear stress in z-layer models. In: Hinkelmann, R. (Hg.): Proceedings of 10th International Conference on Hydroinformatics : HIC 2012 ; understanding changing climate and environment and finding solutions ; Hamburg, Germany, July 14 18, 2012. Hamburg: TuTech Innovation.

International Journal for Numerical Methods in Fluids, 2015

We present a new modelling strategy for improving the efficiency of computationally intensive flo... more We present a new modelling strategy for improving the efficiency of computationally intensive flow problems in environmental free-surface flows. The approach combines a recently developed semi-implicit subgrid method with a hierarchical grid solution strategy. The method allows the incorporation of high-resolution data on subgrid scale to obtain a more accurate and efficient hydrodynamic model. The subgrid method improves the efficiency of the hierarchical grid method by providing better solutions on coarse grids. The method is applicable to both steady and unsteady flows, but we particularly focus on river flows with steady boundary conditions. There, the combined hierarchical grid-subgrid method reduces the computational effort to obtain a steady state with factors up to 43. For unsteady models, the method can be used for efficiently generating accurate initial conditions on high-resolution grids. Additionally, the method provides automatic insight in grid convergence. We demonstrate the efficiency and applicability of the method using a schematic test for the vortex shedding around a circular cylinder and a real-world river case study.

Journal of Hydraulic Research, 2018

The established method for determining dike heights and dimensioning river training structures is... more The established method for determining dike heights and dimensioning river training structures is to assess the resulting backwater by numerical modelling. The common consensus is that bottom friction determines the backwater and that momentum advection only has a local effect. We demonstrate that the numerical/artificial backwater contribution from the momentum advection approximation can be of the same order of magnitude as the bottom friction contribution, depending on the advection scheme. This is realized using a one-dimensional analysis and verified using a set of one-and two-dimensional test problems including a wavy bed case, flow over emerged and submerged groynes and finally an actual river. We compare first-and second-order accurate advection schemes and compute their artificial contribution to the backwater, for a range of practicallyfeasible grid resolutions. The tests demonstrate that the conservation/constancy properties of the scheme determine the size of this contribution, rather than the order of the scheme.

This contribution concerns the verification and performance assessment of a hardwareaccelerated p... more This contribution concerns the verification and performance assessment of a hardwareaccelerated parallel implementation of an algorithm for the semi-implicit finite difference method for solving the vertically integrated shallow water equations including a non-linear treatment of wetting and drying and conservative advection schemes. Instead of adapting an existing serial, OpenMP-, or MPI-parallelised code with all necessary compromises to be met, the selected approach is to write the code from scratch exposing the fine-grained parallelism of the scheme and execute the whole computational kernel of the code on a state-of-the-art streaming processor, i.e. a GPU. The reached speedups compared to a single CPU core are in the order of 20 or 30 for the double or single precision, respectively, which confirms the attractivity of the presently available advanced programming technologies for detailed, high-resolution river modelling applying commodity hardware.

We present a restructured version of GPUSPH [4], [8], [11], a CUDA-based implementation of SPH. T... more We present a restructured version of GPUSPH [4], [8], [11], a CUDA-based implementation of SPH. The new version is extended to allow execution on multiple GPUs on one or more host nodes, making it possible to concurrently exploit hundreds of devices across a network, allowing the simulation on larger domains and at higher resolutions. Partitioning of the computational domain is not limited anymore to parallel planes and can follow arbitrary, user-defined shapes at the resolution of individual cells, where the cell is defined by the auxiliary grid used for fast neighbor search. This allows optimal partitioning even in the case of complex domains, such as rivers with Uturns. The version we present also includes many additional features that have been developed on GPUSPH. Particularly important are: the uniform precision work by Hérault et al. [13], which is essential for numerical robustness in the case of very large ratios between the domain size and particle resolution; a compact neighbor list, which allows larger subdomains to be loaded on each device; the semi-analytical boundary conditions by Ferrand et al. [9], [12], and support for floating objects [14]. All of these features are seamlessly supported in single-GPU, multi-GPU and multi-node modes.

Karlsruhe, Oct 1, 2016

Section of the lock with Semi-Analytical boundaries in the second test. .. . 28 Section of the lo... more Section of the lock with Semi-Analytical boundaries in the second test. .. . 28 Section of the lock with dynamic boundaries and piston (third test). .. .. . 28 Section of the XVases (communicating vessels) test case with horizontal jet.. 30 Section of the XInjection test case with vertical and horizontal gravity. .. .. 31 Bundesanstalt für Wasserbau Evaluation and adaption of the SPH method BAW-No. B3953.05.04.70002-October 2016

Kompetenz für die Wasserstraßen — Heute und in Zukunft. Forschungs- und Entwicklungsprojekte der BAW, 2017

Es wird eine neue Modellierstrategie zur Effizienzsteigerung rechenintensiver Simulationen von Fl... more Es wird eine neue Modellierstrategie zur Effizienzsteigerung rechenintensiver Simulationen von Flüssen vorgestellt. Der Ansatz kombiniert einen semi-impliziten Subgrid-Ansatz zur Berücksichtigung von hochaufgelösten Geländeinformationen auf gröberen Netzen mit einer auf Hierarchischen-Netzen basierenden Strategie. Diese Kombination führt zu einer Genauigkeitsund Effizienzsteigerung hydro-numerischer Flussmodelle sowohl im stationären als auch instationären Fall. Die hier präsentierte Arbeit beschränkt sich auf den stationären Fall und zeigt, dass der "Hierarchische-Gitter-Subgrid"-Ansatz zu einer bis zu 43-fachen Verringerung der Rechenzeiten führen kann. Zusätzlich gewährt die Methode einen direkten und automatisierten Einblick in das Gitterkonvergenzverhalten. Es werden die Effizienz und Anwendbarkeit des Ansatzes sowohl an einem schematischen Beispiel als auch an einem realen Flussmodell aufgezeigt. Diesem Beitrag liegt folgende Veröffentlichung zugrunde: Platzek et al. (2015): An efficient semi-implicit subgrid method for free-surface flows on hierarchical grids. Int.

The theoretical background of a new finite-element non-hydrostatic model for simulation of free s... more The theoretical background of a new finite-element non-hydrostatic model for simulation of free surface flows based on the fractional step method and pressure decomposition is presented. One of the verification cases concerning the solitary wave propagation is provided. Further developments concerning more sophisticated turbulence modelling for practical applications as flows around structures or scour formation are discussed and illustrated with preliminary, but very promising results.

This contribution deals with further developments of UnTRIM, an unstructured-grid, three-dimensio... more This contribution deals with further developments of UnTRIM, an unstructured-grid, three-dimensional, semi-implicit finite difference-finite volume model for the shallow water equations [5]. Attractive numerical properties of the method like its robustness due to the unlimited stability and successes in practical applications spawned efforts aimed at making the available code fit for the high performance computing in order to address larger, complex problems in hydraulic engineering. The paper concentrates on the parallel implementation of the program, based on the domain decomposition method and message passing, which has been achieved without negatively affecting any of the properties of the serial code. A special attention is paid to a new, autonomous parallel streamline tracking algorithm, which allows using semi-Lagrangian methods in decomposed meshes without compromising the scalability of the code. The new developments have been carefully verified not only with the numerous simple, abstract test cases illustrating the application domain of the code, but also with advanced, high resolution models presently applied for research and engineering projects, where the hydrodynamics can be coupled with wave, transport and morphodynamical models. The presented achievements pair robust and efficient numerical methods with the state-of-the art high performance computing know-how in order to deliver a solid base for computationally intensive hydraulic engineering applications.

The paper discusses the advantages and disadvantages of numerical modelling of rivers with a grid... more The paper discusses the advantages and disadvantages of numerical modelling of rivers with a grid of very high resolution using the new MPI version of UnTRIM as the computational engine. The main aim of the investigation is to assess the economy of this approach taking especially into account the effort required for the mesh generation and its modification, which is usually laborious in the case of coarser meshes requiring exact reproduction of structure lines defining the flow. In the first step the results of a low-resolution Telemac-2D grid are compared to the results obtained for the same river stretch topography with a high-resolution UnTRIM model. In the second step the results of two-and three-dimensional modelling applying a high-resolution mesh based on a high quality digital terrain model are studied. It is concluded that under the assumption of appropriate computational resources readily available, the high-resolution modelling reduces significantly the effort required for the initial model setup and for adjustments due to changes in the model topography. The calibration, parametrisation and validation of the models is simplified without affecting the accuracy, freeing the engineer to concentrate on the project aims and not bypass the weak points of the methodology.

Proceedings of OCEANS'94, 1994

The paper critically reviews the presently available experimental data from various tests and exp... more The paper critically reviews the presently available experimental data from various tests and experiments connected with the deep-sea mining issue with regard to their feasibility in supporting and validating the developed numerical models. Numerical modelling is applied mainly to predetermining the plume development a n d seaaoor blanketing caused by v arious sediment discharges. The paper describes processes included in these models and discusses the experimental acquisition of needed model parameters. The existing models and their validation are shortly reviewed and parameters essential to operate and validate them are pointed out. Recommendations for further studies are given in order to improve the quality of model forecasts.

Water Resources Research, 2014

Three-dimensional hydrodynamic z-layer models, which are used for simulating the flow in rivers, ... more Three-dimensional hydrodynamic z-layer models, which are used for simulating the flow in rivers, estuaries, and oceans, suffer from an inaccurate and often discontinuous bottom shear stress representation, due to the staircase bottom. We analyze the governing equations and clearly show the cause of the inaccuracies. Based on the analysis, we present a new method that significantly reduces the errors and the grid dependency of the results. The method consists of a near-bed layer-remapping and a modified nearbed discretization of the k 2 e turbulence model. We demonstrate the applicability of the approach for uniform channel flow, using a schematized two-dimensional vertical model and for the flow over a bottom sill using the Delft3D modeling system. Conversely, the z-layer discretization allows simple horizontal discretizations for pressure, advection, and diffusion and it efficiently handles shallow areas. However, the bottom and free-surface boundaries are represented as ''staircases,'' see Figure 1. Even using a partial-cell or shaved-cell approach [see e.g.,

Journal of Geophysical Research, 1996

Deep Sea Research Part II: Topical Studies in Oceanography, 2001

The evaluation of marine environmental impacts resulting from the exploitation of marine resource... more The evaluation of marine environmental impacts resulting from the exploitation of marine resources requires the numerical description, parametrization, and modelling of such processes in order to be able to transfer, compare, and forecast the effects of anthropogenic activities in the deep sea. One of the controversial effects is the formation and behaviour of sediment clouds as a consequence of anthropogenic activities on the seafloor. Since there is a need for reliable data, two subprojects of the ''Interdisciplinary Deep-sea Environmental Protection Group (TUSCH)''-project ''Impacts from Technical Activities on the Deep-Sea Ecosystem of the South East Pacific Offshore Peru (ATESEPP)'' were devoted to the assembly of such data. Based on the German technical approach for deep-sea mining, the possible environmental impacts by a miner were estimated, the impacts on the seafloor were simulated and investigated by tests with large volume undisturbed sediment samples on board the research vessel and in the laboratory, and the results were evaluated and extrapolated. This report gives a comprehensive presentation of the physical problems, the technical approach, and the results of these investigations.

International Journal for Numerical Methods in Fluids, 2009

... Correspondence to: Jacek A. Jankowski, Bundesanstalt für Wasserbau, Postfach 21 02 53, Karlsr... more ... Correspondence to: Jacek A. Jankowski, Bundesanstalt für Wasserbau, Postfach 21 02 53, Karlsruhe 76152, Germany. E-mail: jacek.jankowski@baw.de Copyright q 2008 John Wiley & Sons, Ltd. Page 2. 1158 JA JANKOWSKI ...