Search

In this study, the PORO-FSSI-FOAM model is applied to investigate the wave-induced oscillatory soil response during the caisson installation, where the Reynolds averaged Navier-stokes equation is used to simulate the flow motions, and the poro-elastic equation is used to govern the soil dynamic response around the caisson. Unlike previous studies, the caisson installation process is considered when investigating the wave-induced oscillatory soil response in this paper. Firstly, the accuracy of the PORO-FSSI-FOAM model in simulating the wave-seabed interaction is validated. Then, the effects of the submerged depth, the geometrical dimensions and the installation sequence of the caisson on the wave-induced oscillatory pore pressure response are examined, and the momentary soil liquefaction during the caisson installation is explored. Finally, a simple formula that describes the relationship between the maximum soil liquefaction depth and the caisson submerged depth is proposed. Numerical results indicate that the caisson dimensions can greatly influence the wave-induced pore pressure response, and the relationship between the oscillatory pore pressure response and the caisson submerged depth is inconsistent at different locations surrounding the structure. Moreover, the installation sequence can significantly affect the momentary soil liquefaction and the simple formula proposed in this study can provide reference for engineers to assess the seabed stability during the caisson installation. • A three-dimensional numerical model for wave-seabed-caisson interaction was established based on OpenFOAM. • The wave-induced oscillatory pore pressure response during the caisson installation was studied. • The momentary soil liquefaction during the caisson installation was investigated. • A simple method that describes the variation of the maximum soil liquefaction with the submerged depth for different caisson dimensions was proposed. [ABSTRACT FROM AUTHOR]

Duan, L.; Jeng, D.-S.; Wang, S., and Zhu, B., 2019. Numerical investigation of the wave/current–induced responses of transient soil around a square mono-pile foundation. Journal of Coastal Research, 35(3), 625–636. Coconut Creek (Florida), ISSN 0749-0208. A mono-pile foundation is a commonly used supporting base for marine infrastructure in shallow water, such as offshore wind turbine foundations and cross-sea bridges and platforms. Sea floor instability around a pile foundation has attracted much attention among offshore geotechnical engineers. In this paper, a three-dimensional numerical model for wave–seabed–structure interactions is proposed using open field operation and manipulation (OpenFOAM). Unlike previous studies, currents are included in the proposed model and applied to a square cross-section mono-pile foundation. In the model, the flow motion is described by the Reynolds-averaged Navier–Stokes (RANS) equation and k–ϵ turbulence model, and the water free surface is tracked using the volume of fluid (VOF) method. Meanwhile, the soil response is determined by the Biot's poro-elastic equation (u–p approximation), in which the accelerations of the soil displacements are included. After the model is validated with the previous laboratory experiments, it is further used to investigate the transient soil response around the square mono-pile foundation. Numerical results demonstrate that the cross-section shape has significant influence on the distribution of wave/current–induced transient pore pressure but little influence on the maximum soil liquefaction depth. On the other hand, both the current velocity and the seabed permeability can greatly affect the maximum soil liquefaction depth and slightly affect the distribution of pore pressure. Furthermore, the cross-section dimension significantly affects both the maximum soil liquefaction depth and the distribution of the pore pressure around a mono-pile foundation. [ABSTRACT FROM AUTHOR]

To obtain a better understanding of the oscillatory soil liquefaction around an offshore pipeline, a three-dimensional integrated model for the wave–seabed–pipeline interaction (WSPI) is proposed by combining the Reynolds-Averaged Navier–Stokes equations for flow simulations and the dynamic Biot’s equation (“ u - p ” approximation) for the poro-elastic seabed model. Compared with previous investigations, the wave–current interaction is included in the present WSPI system. At a given time step, the wave pressure extracted from the flow model is applied on the seabed surface to determine the corresponding oscillatory seabed response around an offshore pipeline. The integrated numerical model is first validated using previous laboratory experiments. Then, a parametric study is conducted to examine the effects of flow obliquity and pipeline burial depth on the soil response around an offshore pipeline. Numerical results indicate that the soil under the pipeline is more susceptible to liquefaction at a reduced flow obliquity and pipeline burial depth. Moreover, the liquefaction depth in the case where the wave travels along the current can increase by 10%–30% compared to that in the case where the wave travels against the current, when the magnitude of the current velocity is 1 m/s. [ABSTRACT FROM AUTHOR]

This paper proposes a two-dimensional (2D) coupled model for wave and current-seabed-pipeline interactions to examine oscillatory non-cohesive soil liquefaction around a partially buried pipeline in a trench. Unlike previous studies, two new features are included in this model: (1) wave-current interactions around the pipeline; and (2) fully coupled processes for the wave and current-seabed-pipeline system. In this study, the Reynolds Averaged Navier-Stokes (RANS) equations are applied to simulate the flow field around the pipeline, and Biot's poro-elastic theory for porous media is imposed to govern the soil response due to the wave-current loading. After being validated using data available in the literature, the 2D model is used to investigate the effects of the current velocity, the soil properties, and the wave characteristics on oscillatory non-cohesive soil liquefaction. Using the model, a function for the critical backfill thickness and the wave steepness under various flow and soil conditions is proposed to facilitate engineering practice. [ABSTRACT FROM AUTHOR]

• A novel 3D numerical model for residual seabed response has been developed by redefining the source term of the governing equation. • The wave-current interactions are considered while studying residual soil response near a single pile. • Both the oscillatory pore pressure and the residual pore pressure are considered while determining soil liquefaction potential. The evaluation of seafloor stability is of vital importance for engineers involved in the protection of marine foundations. Hence, it has attracted considerable attention in the field of offshore geotechnical engineering. In this investigation, a novel three-dimensional (3D) numerical model of fluid–seabed-structure interactions (FSSI) is proposed within the framework of OpenFOAM to explore the residual soil dynamic response around a single pile. Different from previous studies, three new features are added in the present model. (i) The wave–current interactions are taken into consideration, (ii) the source term of pore pressure generations is redefined, and (iii) both the oscillatory pore pressure and residual pore pressure are considered while judging the soil liquefaction potential. After verified by previous laboratory experiments available in literature, the novel model is applied to investigate the residual soil response around the single pile induced by natural loadings. The numerical results confirm that the novel 3D model can provide sufficiently accurate predictions of fluid–seabed-structure interactions. Moreover, wave/current characteristics, soil properties, and pile diameter can significantly affect the fluid-induced residual pore pressures along the vicinity of the single pile. [ABSTRACT FROM AUTHOR]