Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Motion Simulation and Monitoring of an HVDC Platform’s Topside
during Transportation and DP Float-over Installation
Hao Sun1,2, Liancai Cai1, Mingyuan Sun1, Meng Yuan1,4, Hanwen Yao1, Andy Wang3
1. Marine Technology Division, COSCO Shipping Specialized Carriers Co. Ltd.
Guangzhou, Guangdong, China
2. College of Shipbuilding Engineering, Harbin Engineering UniversityHarbin, Heilongjiang, China
3. Marine & Offshore Operations, DNV Singapore Pte. Ltd.
Singapore
4. Corresponding Author

ABSTRACTINTRODUCTION

A mega topside of an HVDC platform located in the North Sea wastransported by a DP-2 heavy transport vessel, M/V Xiang He Kou fromDubai, UAE to the German offshore installation site. After the voyage,
the topside was successfully installed by dynamic positioning (DP) floatover installation method.

An HVDC platform is installed off the coast of Borkum in the Germansector 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 forexport. 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.

This paper presents a comprehensive description of the engineering
analysis, motion monitoring of the topside during transportation andinstallation. 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 fromsimulations during sailing in real-time, which are found well within thedesign limits. It is found that the concerned parameters are below thelimits with sufficient safety margin and thus are well engineering
covered.

Before sailing, the motion and acceleration response of the vessel CoG,and the topside CoG under the design environmental conditions areanalyzed. The voyage operational limiting weather conditions are also
defined according to the guidelines for marine transportations (GL NobleDenton, 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 andthe 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.

KEY WORDS: DP float-over; voyage monitoring; engineering design.
NOMENCLATURE
COG = Center of Gravity
COSCO = COSCO Shipping Specialized Carries
DP = Dynamic Positioning
DSF = Deck Support FrameDSU = Deck Separation UnitsHTV = Heavy Transport Vessel
HVDC = High Voltage Direct Current
LMU = Leg Mating Unit
MPE = Most Probable Extreme

After the sailing, the topside was installed by DP float-over method byusing the same transport vessel. This “one-stop” T&I method can offer
the client to transport the topside tens of thousands of nautical miles
away from the installation site, and directly install the topside without
the assistance of AHTs or mooring system. Consequently, this will
reduce the cost of the installation engineering package, also saving theoffshore preparation work like pre-lay the mooring anchor and offshore
mooring connections.

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