A mega topside of an HVDC platform located in the North Sea was transported by a DP-2 heavy transport vessel, M/V Xiang He Kou from Dubai, UAE to the German offshore installation site. After the voyage, the topside was successfully installed by dynamic positioning (DP) float-over installation method.
This paper presents a comprehensive description of the engineering analysis, motion monitoring of the topside during transportation and installation. The vessel's motion analysis model is tuned and verified by the model tests, which ensure the accuracy of motion response analysis results. A motion monitoring system has been installed onboard to record the actual motion response at the topside COG throughout the voyage. The monitored results are compared to the design limits obtained from simulations during sailing in real-time, which are found well within the design limits. It is found that the concerned parameters are below the limits with sufficient safety margin and thus are well engineering covered.
An HVDC platform is installed off the coast of Borkum in the German sector of the North Sea. The topside of the platform is the world's largest high voltage direct current (HVDC) station that converts the alternating current produced by the offshore wind turbines to direct current for export. The topside was transported by the DP-2 heavy transport vessel, M/V Xiang He Kou, from Dubai, UAE to the German offshore installation site. After the transport voyage, the topside was successfully installed by dynamic positioning (DP) float-over integration method.
Before sailing, the motion and acceleration response of the vessel CoG, and the topside CoG under the design environmental conditions are analyzed. The voyage operational limiting weather conditions are also defined according to the guidelines for marine transportations (GL Noble Denton, 2016). By following the operational limit and operational criteria, the captain can decide to maintain the planned route, or change the heading to avoid the severe weather, based on the daily weather report and forecast along the planned route.
During the whole transport, the motion and acceleration of the vessel and the topside CoG were real-time monitored and interpreted by the onboard installed Octopus-onboard server during the sailing. The real-time motion statistics and motion prediction based on the weather forecast will be supportive to the captain to lead a safe voyage.
