Multiscale modelling of physical processes along water-soil interface

The research proposal is focused on erosion- , transport- and sedimentation processes at water-soil interface, especially at channel beds and embankment slopes due to hydrodynamic effects of flow and waves as well as the effect of under-water construction work. It is of fundamental interest to know the maximum stable slope angle both on short and long term. This is of interest for embankment slopes and ground construction work on-shore as well as off-shore. Based on experimental, theoretical and numerical investigation a method for prediction of maximum short and long term stable slope angle will be developed. To date these predictions are made on empirical basis (1:3 to 1:10), which can lead to either unstable slopes or excessive use of area and resources. The numerical modelling of above processes will be based on multiple scales and the numerical method of coupled CFD-DEM simulations will be used. A consortium of research groups from Germany and Austria under the frame of the D-A-CH lead agency program will be formed. The research partner in Germany will be the Institut für Geotechnik und Baubetrieb (B-5) at the Technischen Universität Hamburg-Harburg (TUHH), represented by Prof. Dr.-Ing. Jürgen Grabe. During preliminary cooperation between the research groups the open source Software CFDEMcoupling, developed by DCS, was successfully applied and further work packages were defined. The research proposal will be submitted to the DFG, as the initiative of the work was started by TUHH and the TUHH will require higher financial resources to accomplish the desired tasks.

Goal of the DACH cooperation project (FWF project number I 2257) between Prof. Grabe (Institute of Geotechnical Engineering and Construction Management at the Technical University of Hamburg) and Dr. Christoph Goniva (DCS Computing GmbH) was the investigation of the effects different disturbances have on the short- and long-term stability of underwater slopes. The considered scenarios comprise both nature-induced and artificially created disturbances, namely the destabilization of underwater soil by suffusion, tidal flow, waves, grad dredging or suction dredging. For the investigations we used a combination of experiments, which were conducted from the cooperation partners at TUHH, and numerical simulations. The latter were carried out with CFDEMcoupling, a coupling between the Open Source Computational Fluid Dynamics (CFD) software OpenFOAM and the Discrete Element Method (DEM) code LIGGGHTS. The soil was modelled as a packing of particles for being able to depict effects on the smallest scales. In a first step the models for the materials used in the experiments (Hamburger Sand and glass spheres) had to be calibrated. For this a well-established combination of experiments and simulations was used. In the next step we determined the dominating forces and implemented a lubrication force model for the particle side. Some additional tests showed that the dilatancy can be depicted. For being able to depict all above mentioned cases a new solver which accounts for multiple phases on the fluid side has been developed. Due to the large number of particles coarsegraining was used. This is a method where clusters of particles are summarized to single objects and the force calculation is adapted accordingly. Case setups of all discussed cases were developed and provided to our partners. Particularly for the execution of the computationally intensive detailed investigations of grab and suction dredging the software was transferred to the parallel computer Cray XC30 at Norddeutscher Verbund für Hoch- und Höchstleistungsrechnen (HLRN). The investigations showed that the experiments could be depicted by the numerical simulations very well, particularly when it comes to the final state of the forming slopes. It is thus possible to make reasonable predictions given that the boundary conditions are well known. Only the duration and the slope formation process until the final state was reached could not be depicted in detail. Both cooperating parties presented the results and outcomes of the research project at international conferences and to specialists from both the field of geotechnics and numerical simulation.