Analysis of Seaquake Effects on the Seismic Performance of Tension-Leg Platforms

1. Home
2. Publications
3. Online Library
4. Analysis of Seaquake Effects on the Seismic Performance of Tension-Leg Platforms

Seaquakes refer to compressional (P) seismic waves that propagate from the seabed to the seawater surface and may exert hydrodynamic pressures on floating structures. In this paper, the seismic response of a pile-supported Tension-Leg-Platform (TLP) for Offshore Wind Turbines (OWTs) installed in a granular liquefiable seabed is investigated. The emphasis is on the importance of incorporating the effect of seaquakes in the platform design, via hydrodynamic forces applied to the floater. The problem is analysed numerically, by means of 3D dynamic effective stress analyses that properly simulate the pile-tendon-floater interaction, the complex response of the liquefiable seabed and the seaquake force. The latter is incorporated in the 3D analyses as an external load, calculated separately, from an un-coupled 2D axisymmetric numerical analysis, verified against analytical solutions for the foundation soil, the sea water and the floater. In the 3D analyses, the pile-tendon-floater system is subjected to the concurrent action of the horizontal and vertical acceleration components, as in real earthquakes. The focus here is on the magnitude of the anticipated seaquake forces. The numerical results for a model TLP wind turbine indicate that seaquake forces may become quite high. The effect of this additional axial force, transferred to the pile foundation through the tendons, is an increase of cyclic shear strains in the foundation soil leading to an acceleration of liquefaction onset. In turn, the above effects can lead to a significant increase in the upward pile displacements and the corresponding reduction of the pretension tendon force, compared to the case where seaquake effects are ignored.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

17 - Design Standards, Certification and Risk Mitigation