Übergang einer Granulatströmung in die Auslaufzone
Final Report Abstract
We have generated several novel and innovative ideas and pioneering methods, in model development, experiments and hybrid simulation. We proposed fully two-dimensional, novel Coulomb-viscoplastic sliding model to describe the observed phenomena in granular flows, namely the yield strength and a dynamically evolving non-zero slip velocity. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic law. This model is further enhanced by allowing pressure dependent yield stress. We implemented, for the first time, the Coulomb-type internal friction with a Coulomb sliding law at the base in OpenFOAM. The novel aspect in our experiments is the shearing of the velocity field through the flow depth in rapid granular flows. We experimentally analyzed the influence of obstacles on the dynamics of granular chute flow and the deposition behavior. High-speed cameras are used to capture the detailed flow processes. The data were postprocessed with the software developed by ourselves to determine the particle velocities and three-dimensionally evolving geometry and the transitions into the depositions. A small difference in the internal friction can lead to fundamental changes in the flow-obstacle interactions and depositions. This is a significant advance in our understanding. It helps in design and construction attempts of effective catching dams and improved prediction of overtopping of dams. We have modeled and simulated the velocity shearing along and in the flow depth direction for rapid granular flows. This is a novel work. The numerical treatment of the Coulomb-viscoplastic sliding model requires the set-up of a novel pressure equation. This is dynamically and automatically defined by our new approach. Flows subject to slip or no-slip at the bottom are studied numerically with the marker-and-cell method. For a Coulombviscoplastic law observable shearing mainly takes place close to the sliding surface in agreement with observations. For the flows impinging the wall, the pressure-dependent yield stress leads to the observed phenomena which could not be simulated by Bingham material. The coupling of full and depth-averaged models leads to a dramatic reduction of computational complexity and time. For this, we have properly addressed great challenges arising in coupling by setting appropriate boundary conditions at the interfaces between the full and depthaveraged domains, and by adapting the different numerical methods for two domains. We proposed an innovative technique to combine these two models and developed a new coupled hybrid full 2D and reduced 1D computational tool with smooth interface transition. For real 3D avalanches simulations over mountain slopes, we developed new pre- and post-processors in the OpenFOAM with Volume of Fluid. These are the first-ever, real three-dimensional simulations of granular avalanches with applications to proper hazard mapping and improved risk management. The developed physical-mathematical model and the performance of the proposed simulation tools have been validated with various laboratory and field data. The full 2D non depthaveraged Coulomb-viscoplastic model coupled with the 1D depth-averaged model is used to simulate shock waves appearing in rapid flows down inclined channels hitting a wall and the subsequent granular deposit. The theoretical predictions compare well with the experimental data. There exist good comparisons between our numerical solutions (with enhanced OpenFOAM and Coulomb-type friction) and laboratory data. The new real three-dimensional model and simulation software reproduces the large scale avalanche in natural slopes.
Publications
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(2008): Shock waves in rapid flows of dense granular materials: Theoretical predictions and experimental results. Physical Review E, Vol. 78(4)
Pudasaini, S. P. and Kroener, C.
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(2009): Energy Consideration in Accelerating Rapid Shear Granular Flows. Nonlinear Processes in Geophysics, Vol. 16, 399-407
Pudasaini, S.P. and Domnik, B.
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(2011): Some Exact Solutions for Debris and Avalanche Flows. Physics of Fluids, Vol. 23(4)
Pudasaini, S.P.
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(2012): A general two-phase debris flow model. J. Geophys. Res., Vol. 117, F03010
Pudasaini, S.P.
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(2012): A Real Two-Phase Submarine Debris Flow and Tsunami. Proceedings of the American Institute of Physics, Vol. 1479, 197-200
Pudasaini, S.P. and Miller, S.A.
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(2012): Buoyancy Induced Mobility in Two-phase Debris Flow. Proceedings of the American Institute of Physics, Vol. 1479, 149-152
Pudasaini, S.P. and Miller, S. A.
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(2012): Full two-dimensional rapid chute flows of simple viscoplastic granular materials with a pressure-dependent dynamic slip-velocity and their numerical simulations. Journal of Non-Newtonian Fluid Mechanics, Vol. 173-174, 72-86
Domnik, B. and Pudasaini, S.P.
