Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Jacob Michelsen (1) F P Michael Hansen (1) Hans Erik Sederberg-Olsen (1) Michael Macdonald Arnskov (1)
(1) FORCE Technology, Kgs. Lyngby, Denmark
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Presenter's biographyBiographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited
Mr. Jacob Michelsen M.Sc. has been working in the maritime industry for almost 20 years and holds a Ph.D. in Naval Architecture. He is currently a senior specialist at FORCE Technology in the Division for Maritime Industry, and focuses on training simulator software and onboard systems.
Simulation of dp vessels having jack-up capability
Jack-up vessels during leg deployment are characterized by undergoing considerable changes in their motional behavior, stability and often also the effectiveness and limitations of their maneuvering devices, thus impacting the performance of the DP system. As the legs are lowered, making contact with or being raised from the seabed, the environmental forces will therefore change as legs are being subjected to wind and/or waves and currents.
Most DP systems will respond to these gradual changes and compensate by applying less or more thrust. Applying too much thrust involves a risk of overstressing the legs if applied after the legs have made contact with the seabed, while applying too little thrust might raise the risk for collisions if the vessel is in close proximity of installations. The usual approach in such situations is to pause the positioning, thereby allowing the DP system to acquire the new forces under steady conditions before continuing.
Main body of abstract
To support such simulator based training, a simulation model has been extended with both Jack-up functionality including control and monitoring, plus interfaces enabling DP systems to be integrated into the control loop and operator training to be conducted. Furthermore a generic DP system with an “open” architecture has been implemented, allowing for different control strategy plug-ins to be developed, tested and tuned in a simulated environment. Failures and errors on both the necessary sensor inputs and on the propulsion units can be fully controlled, as well as all relevant environmental conditions. Wind-tunnel and towing tank experiments ensure a high degree of realism in the performance characteristics of the applied underlying vessel model, including wind loads, leg loads, hydrodynamic behavior, thruster-thruster and hull-interactions etc.
This extended mathematical models opens up for fast-time simulations to be carried out, whereby lowering or raising of the legs while maneuvering the vessel into a position or maintaining a position on DP, can form risk- and capability/performance analysis in all kind of weather conditions. In this paper case studies are presented, comparing performance and obtained position error for several combinations of configuration and environmental setup.
In terms of training perspectives, special focus has been given to the simulation of critical phase transitions for wind turbine installation vessels like:
• Shift from transit mode to DP mode
• DP during leg lowering and leg raising for Jack-Up vessels
• DP performance during leg touch-down and soft pinning for Jack-Up vessels
The modular architecture of the developed system provides a unique and robust design tool which allows:
• Testing of various control strategies (e.g. from simple PID controllers to sophisticated Kalman filter based optimal control algorithms)
• Interfacing to commercial DP systems (a number of communication protocols can be supported)