In support of the foundation installations for Sandbank offshore wind farm by Bilfinger, TWD provided the detailed designs for a monopile gripper tool, hydro sound demper (HSD) deployment frame and upending hinge. In addition we designed various seafastening structures for the monopiles and transition pieces. All items were designed, fabricated, and ready for operation within 9 months.
The gripper design provides a simple and cost effective solution for monopile installation. In addition to meeting all operational requirements, an orientation system has been integrated to achieve correct positioning and rotation of the pile. The entire gripper can be operated by a single person and provides access for inspections and measurements.
To fit all four foundations on deck, the monopile and transition piece seafastening was carefully designed to optimize deck space and spread the transit loads effectively. A stacked cradle featuring a hydraulic hing system enables two piles to be stacked on top of each other, whilst maintaining easy access to the bottom pile. The monopile cradles can accommodate monopiles of varying diameters and utilize a friction interface to void the need for additional fastening. The transition piece seafastening is characterized by a quick and user friendly clamping mechanism with easy access.
During the design phase, Bilfinger was still developing a noise mitigation system. Concurrently, we worked on the design of a HSD deployment frame, which had to be fitted in the very tight area around the gripper. The final design stands out by its elaborate folding mechanism and automated levelling system.
Serving as and oversized swing, the upending hinge was designed to support the 900 t monopiles as the crane can lifted one end of the pile, taking it quickly and safely from horizontal to vertical position. Due to the lean design, the hinge not only operated efficiently, but was easy to manufacture and required minimal vessel modifications.
Complementing the design efforts, our fabrication engineers streamlined the procurement and construction processes. The procurement of critical long lead times was initiated during the design phase, speeding up the project. During construction we applied our in depth knowledge of our own designs to support the fabrication process, minimizing delays and optimizing functionality.
To determine the dynamic loads on the crane and pile gripping frame, a dynamic analysis of the monopile and J-tube cage lowering operation was necessary.
TWD was requested to perform the dynamic analysis of the lowering operation for a range of monopiles and a single J-tube cage. The findings, including recommendations on limitations of environmental parameters such as significant wave heights, wave peak periods, current and wind speed, to ensure a safe installation operation were communicated to the client.
Based on close to a thousand simulations performed using the dynamic analysis software OrcaFlex, TWD determined the workability of the monopile lowering and monopile piling operation for a range of monopile diameters and lengths based on Dynamic Amplification Factor on the crane and dynamic forces on the Pile Gripper Tool.
Additionally, TWD performed simulations for the J-tube cage to determine the behavior of the J-tube cage in the splash zone. Based on the simulation results, TWD made recommendations relating to the following aspects of the operation: