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Item type:Publication, Access status: with files , Experimental and numerical investigation of particle-fluid systems in geotechnical engineering(2021); The macroscopic behaviour of saturated soil is complex and driven by the interaction of pore water and soil grains at particle-scale level. This PhD-thesis is concerned with the numerical and experimental investigation of particle-scale physics in saturated soil. Unresolved coupled CFD-DEM is used for the numerical simulations. Four different geotechnical problems are investigated, where fluid-particle interaction forces have a significant influence. The numerical and experimental results are compared to identify the limits and benefits of unresolved CFD-DEM in geotechnical engineering.Publicationtype: Doctoral Thesis424 746 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The influence of the void fraction on the particle migration: a coupled computational fluid dynamics–discrete element method study about drag force correlationsGranular soils subjected to flow through their soil skeleton can show a behaviour in which fine particles migrate through the pore space between coarser particles. This process is called internal instability or suffusion. This contribution deals with the numerical analysis of the migration of fine particles in a soil column subjected to fluid flow with unresolved coupled computational fluid dynamics–discrete element method (CFD–DEM) with special regards to the used drag force correlation. The contribution investigates the influence of the Schiller–Naumann model and its extension with a voidage term on the migration behaviour of fine particles. The voidage term is further varied with a parameter, which controls the impact of the change of the void fraction on the drag force. It could be observed that the Schiller–Naumann model does not yield in a suffusive behaviour while the extended models show significant particle migration. Thereby, increasing the impact of the void fraction on the drag force results in stronger particle migration. These results reveal the need for good validation techniques. They indicate how the drag force correlation can be adapted to depict the correct particle migration behaviour.Publicationtype: Journal ArticleScopus© Citations 19 176 1020 - Some of the metrics are blocked by yourconsent settings
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 , Influence of Suction Dredging on the Failure Mechanism of Sandy Submarine Slopes: Revisited With a Coupled Numerical ApproachThe installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEMR coupling, which combines the discrete element code LIGGGHTSR with CFD solvers based on OpenFOAMR . Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displa-cement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.Publicationtype: Conference Paper283 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Multiscale investigation of suffusion with coupled CFD-DEM(2019); Publicationtype: Conference Paper92 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental study of the influence of the pore water pressure evolution and the shear band formation on the extraction resistance of submerged anchor platesFloating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive 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 a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.Publicationtype: Conference Paper151 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Multiscale investigations on the failure mechanism of submarine sand slopes with coupled CFD-DEMIn terms of the construction of gravity offshore foundation systems, the short- and longterm stability of submarine sand slopes is of crucial importance. The heavy structures cannot be placed directly on the sea ground. The weak topsoil has to be excavated to place the structure on more stable ground, which results in a pit. A steep but stable inclination of its slopes would thereby meet both economic and ecologic interests as the disturbed area is reduced. Different hydrodynamic disturbances as tidal streaming or waves are hereby influencing the stability of the submarine slopes. The changes in pore water pressure due to the hydrodynamic disturbances and the interaction of the soil grains with the surrounding pore water significantly influences the stability of the slope and its failure mechanism. To take into account these effects, the numerical simulations are carried out with a multiscale approach, namely a coupling of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). In this method, the soil particles are modelled on a microscale level, tracking velocity and position in a lagrangian way. The fluid phase is modelled at a macroscale level using CFD. The numerical modelling aims on investigating the effect of tidal streaming on submarine sand slopes with different packing densities to take into account the influence of dilatancy and contractancy. © 2018 Taylor & Francis Group, London, UK.Publicationtype: Conference Paper142 - 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