Seismic Behavior of Caisson Foundations for Offshore Wind Turbines under the Force of Waves and Sea Currents: Damascus University Study

The global demand on alternative energy is on the increase to mitigate the greenhouse effect- which happens as a result of relying on traditional means of producing energy thereby leading to global warming. For decades, seismic field investigations have shown that many marine structures have been damaged or destroyed due to liquefaction- which highlights the need to obtain values of excess pore water pressure in soil as it indicates the occurrence of liquefaction, and that applies to loose sandy soil in particular.

In this context, a research has been conducted at the Higher Institute for Research and Seismic Studies, Damascus University, under the title:“Numerical Modeling of Seismic Behavior of Caisson Foundation for Offshore Wind Turbines, taking into account wave and marine currents forces”. The research dealt with the behavior of sandy soil from the Mediterranean seabed, which is susceptible to liquefaction in the presence of the caisson foundation supporting the marine wind turbine under loads of waves, sea currents, winds, and earthquakes. A relatively new method of numerical modeling was used, based on the finite element analysis program ABAQUS; the specifications of this soil were extracted by conducting a set of laboratory experiments.

The research highlights the importance of taking wave loads and sea currents into consideration when analyzing these structures, despite their slight impact on increases in pore water pressure values compared to the case of applying earthquake and wind loads only.

The research was done via (Coupled acoustic-structural medium analysis)- the first time to be used in modeling the joint interaction between soil and water, after calibrating this method with experimental and numerical results on the FLAC3D program of one previous study. In addition, there was a numerical modeling of the foundations of offshore wind turbines (caisson type) via Abaqus using the Coupled acoustic-structural medium analysis.

The numerical modeling results showed the success of the proposed model using the Coupled acoustic structural medium analysis in modeling sandy soil and water for the case studied within the Abaqus program. This allowed the values of the pore water pressure to be obtained under dynamic load without the need to use traditional methods.

According to the results of this research, adding the forces of waves and sea currents has a limited effect on changes in pore water pressure compared to the changes resulting from the combination of seismic and wind loads alone.