Control-Structure Interaction: Nonlinear coupling of flexible structure and power hydraulic system
G.F. Follet (TU Delft - Civil Engineering & Geosciences)
A. Metrikine – Mentor (TU Delft - Offshore Engineering)
A. Tsetas – Mentor (TU Delft - Dynamics of Structures)
A. Cabboi – Graduation committee member (TU Delft - Mechanics and Physics of Structures)
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Abstract
The growing number and increasing size of Offshore Wind Turbines (OWTs) in Europe have raised significant challenges for monopile foundation design. As turbines become larger and are installed in deeper waters, structural demands and foundation requirements have also increased. Additionally, stricter noise regulations have been established, limiting the use of traditional impact driving techniques and further increasing the complexity of installation methods.
To address these challenges, vibratory methods like Gentle Driving of Piles (GDP) have recently gained traction. However, when powered by hydraulic shakers, they can experience dynamic coupling with the structure, which interferes with both the generation and control of the vibrations needed for effective driving.
To this end, a nonlinear model incorporating the dynamic interactions between the electrical, hydraulic, and structural subsystems has been developed. A parametric study was conducted to determine the minimum pressure required to operate and control the structure when utilizing a PID-based control system.
It was determined that the primary nonlinear dynamic behavior was due to the velocity-pressure coupling and its impact on the nonlinear flow. To address this, a controller was designed that effectively mitigated these effects. Specifically, it was found that the supply pressure could be reduced by up to 25\% while still maintaining effective sinusoidal displacement control. Additionally, the conditions under which synchronization between the shaker-structure could occur were identified, along with ways to avoid this phenomena, as synchronization can lead to system damage and a loss of control authority over the structure.
This study demonstrates the effectiveness of using a PID controller to reduce the coupling between subsystems, thereby enhancing the efficiency of vibratory pile driving methods, promoting their use in monopile installation.