Category Archives: Papers

River computations: artificial backwater from the momentum advection scheme

F.W. Platzek, G.S. Stelling, J.A. Jankowski, R. Patzwahl and J.D. Pietrzak

Abstract: 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. Continue reading →

An efficient semi-implicit subgrid method for free-surface flows on hierarchical grids

F.W. Platzek, G.S. Stelling, J.A. Jankowski, R. Patzwahl and J.D. Pietrzak

Abstract: 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. Continue reading →

Accurate vertical profiles of turbulent flow in z-layer models

F.W. Platzek, G.S. Stelling, J.A. Jankowski and J.D. Pietrzak

Abstract. 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. Continue reading →

Assessment of a parallel implementation of a two-dimensional scheme for free surface flows using a GPU

J.A. Jankowski

Abstract: The rapid changes in the present computer architectures throw questions concerning the future of the hardware-oriented programming based on the usage of heterogeneous parallel computing resources, consisting of nodes of interconnected, but separate CPUs and GPUs. However, it is believed that the sustainability of the programming efforts nowadays is to be searched in the fact that the principle source of the performance of the present GPUs as well as the emerging APUs is the hardware acceleration of vector operations. Therefore, this contribution delivers an assessment of a hardware-accelerated parallel implementation of a principal algorithm for a vertically integrated finite difference scheme for free surface flows including non-linear treatment of wetting and drying. Continue reading →

Parallel implementation of a non-hydrostatic model for free surface flows with semi-Lagrangian advection treatment

Jacek A. Jankowski

Abstract. The parallel implementation of an unstructured-grid, three-dimensional, semi-implicit finite difference and finite volume model for the free surface Navier-Stokes equations (UnTRIM) is presented and discussed. The new developments are aimed to make the code available for high performance computing in order to address larger, complex problems in environmental free surface flows. Continue reading →