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Item type:Publication, Access status: without files , Numerical and experimental analysis of the extraction mechanism of an anchor plate embedded in saturated sand(2019-07); ; ; Floating offshore structures can be founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads and its resistance has to be known. At the end of the lifetime cycle, the anchor plates have to be removed from the seabed. The extraction resistance of the anchors is thereby a lot higher than the sum of its self-weight and hydrostatic and earth pressure. When the anchor plate is moved, the volume underneath increases. This leads to a suction until inflowing pore water fills the newly created volume. In order to investigate this effect, an experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with the particle image velocimetry method (PIV). In the conducted experiments different extraction velocities are considered to investigate its effect on the extraction resistance. Numerical investigations with unresolved coupled CFD-DEM are carried out and validated against the experimental results.Publicationtype: Journal Article217 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical investigations of the extraction of submerged foundations by coupled CFD-DEM(American Society of Mechanical Engineers (ASME), 2017-06); ; ; ; 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.Publicationtype: Conference Paper91