Offshore structures are founded on submerged foundations. The excavation of submerged foundations in the sea bed is a difficult task to accomplish when it comes to the decommissioning of these offshore structures. The extraction resistance is a lot higher than the pressure acting on the structure due to hydrostatic pressure, earth pressure and its self-weight. Once the extraction begins, a negative pore water pressure is created until inflowing pore water compensates this negative pore water pressure. This depression is hindering the extraction of the submerged foundation. Additionally, the resistance is dependent on the embedment depth of the structure, the soil properties as well as the extraction velocity, which influences the dimension of the negative pore water pressure. The numerical investigation of this dynamic problem is a limitation for continuum based approaches like the Finite Element Method (FEM) due to the occurring large deformations. These results from the soil bed failing under the movement of the structure and hence starting to flow. Additionally, in order to estimate the created depression, the investigation of the water-soil-interaction is crucial, as the change of the pore water pressure plays a significant role. Therefore, it is necessary to analyze the behavior of the soil particles and the pore water pressure. In order to do this, a coupled Euler-Lagrange approach, namely the combination of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), is used. In these simulations on one hand, the liquid phase, e.g. the water, is considered as a continuum, while on the other hand, for the solid phase, e.g. the soil, a particle representation is chosen. Hence, it is possible to compute the particle-particle — as well as the fluid-particle-interactions. The calculations are carried out with the open source software package CFDEMcoupling®, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. This paper introduces the coupled CFD-DEM approach to simulate the extraction of a submerged plate in the soil bed. In this work, the soil grains are idealized by spherical particles of different diameters. In order to consider effects of dilatancy and contractancy in the soil bed, different relative densities are investigated. Additionally, a variation of the extraction velocity of the plate is carried out to examine the dependence on the creation of negative pore water pressure. For each case, the extraction resistance is calculated. The flow velocity and the pressure distribution in the vicinity of the structure are analyzed.
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ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
June 25–30, 2017
Trondheim, Norway
Conference Sponsors:
- Ocean, Offshore and Arctic Engineering Division
ISBN:
978-0-7918-5777-9
PROCEEDINGS PAPER
Numerical Investigations of the Extraction of Submerged Foundations by Coupled CFD-DEM
Manuela Kanitz,
Manuela Kanitz
Hamburg University of Technology, Hamburg, Germany
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Juergen Grabe,
Juergen Grabe
Hamburg University of Technology, Hamburg, Germany
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Alice Hager,
Alice Hager
DCS Computing GmbH, Linz, Austria
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Christoph Goniva,
Christoph Goniva
DCS Computing GmbH, Linz, Austria
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Christoph Kloss
Christoph Kloss
DCS Computing GmbH, Linz, Austria
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Manuela Kanitz
Hamburg University of Technology, Hamburg, Germany
Juergen Grabe
Hamburg University of Technology, Hamburg, Germany
Alice Hager
DCS Computing GmbH, Linz, Austria
Christoph Goniva
DCS Computing GmbH, Linz, Austria
Christoph Kloss
DCS Computing GmbH, Linz, Austria
Paper No:
OMAE2017-61299, V009T10A017; 10 pages
Published Online:
September 25, 2017
Citation
Kanitz, M, Grabe, J, Hager, A, Goniva, C, & Kloss, C. "Numerical Investigations of the Extraction of Submerged Foundations by Coupled CFD-DEM." Proceedings of the ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. Volume 9: Offshore Geotechnics; Torgeir Moan Honoring Symposium. Trondheim, Norway. June 25–30, 2017. V009T10A017. ASME. https://doi.org/10.1115/OMAE2017-61299
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