17th SNAME Texas Section Offshore Symposium
This paper discusses the propulsion and stationkeeping aspects in the design and development of the AURORA BOREALIS (AB), a dynamically-positioned Polar Research and (Scientific) Drill Vessel for the European Polar Research Icebreaker Consortium (ERICON). The design of the vessel was contracted with Waertsilae Ship Design Germany (WSDG) under the project management of Alfred Wegener Institute for Polar and Marine Research (AWI).
The AB is a heavy icebreaker of the highest ice class. She is powered to break continuously in more than 2.5 m of multi-year ice and is able to manage ridges up to 15 m. The ship is designed to perform research tasks including scientific drilling year-round in the Arctic and Antarctic without any support vessels.
The key issue in the performance specification of the vessel is the mandatory requirement of performing stationkeeping operations in drifting solid ice of more than 2.0 m thickness during drilling and other research tasks.
This paper presents and discusses some of the design challenges and problems, as well as the test results and design solutions. It includes selected results of the ice tests for stationkeeping in drifting solid ice of up to 2.0-meter thickness, i.e., icebreaking in a practically stationary mode, which were carried out in two ice tanks in Helsinki and Hamburg.
For the various propulsion tasks -- transit at 16 knots, icebreaking, and stationkeeping in ice -- a propulsion system is installed totaling 108,000 kW. The selected propulsion arrangements is described and several alternate propulsion concepts are discussed.
Conclusions: A great amount of propulsive power is required to implement the tasks of stationkeeping and icebreaking applying conventional ice breaking techniques, i.e., providing icebreaking forces through propulsors. As an alternative, the breaking of ice in stationary mode of the vessel by means of induced motions on the vessel was investigated.
Based on the results of the AB design ef ort, we conclude that stationkeeping operation in solid drift ice is feasible.
Currently, several leading oil companies are conducting research regarding exploration in Arctic waters. The presented results are of significant importance for all projects dealing with stationkeeping of of shore vessels in ice. The results are a valuable addition to the database of knowledge regarding Arctic vessels in general and, in particular, stationkeeping in ice.
Experimental Investigation of Sail Aerodynamic Behavior in Dynamic Conditions
The aerodynamic behavior of a 48’ yacht rig 3D scale model was characterized by means of wind tunnel tests. The experimental program, performed in the Politecnico di Milano Twisted Flow Wind Tunnel, allowed the aerodynamicforces to be characterized using forced motion tests and the aeroelastic behavior of the sail plan to be studied. Preliminary results are presented with reference to the typical encounter frequency range and typical pitch amplitudes corresponding to best yacht Velocity Made Good (VMG) condition for different true wind speeds and related sea states. A new representation of the aeroelastic effects is proposed in the form of aerodynamic hysteresis loops, obtained by plotting the sail plan aerodynamic coefficients against instantaneous apparent wind angle, varied using a harmonic law combining wind tunnel constant wind speed with sail plan center of effort velocity induced by yacht pitch motion. A “sail plan reduced velocity” concept is defined, and experimental results show that this reduced velocity play a fundamental role in sail plan aerodynamics. Finally, an estimate of the aerodynamic added mass effects is provided based on the comparison between the measured pitch moment during the “wind off” tests and the experimental test rig pitch moment of inertia.
Addressing challenges in the validation of dynamic stability simulation tools
Significant challenges remain in the validation and formal accreditation of dynamic stability simulation tools, which can have a limiting effect on operations or concept design due to a need for conservatism. These challenges primarily consist of validation metrics and criteria, uncertainty characterization, and defining the scope of conditions (both environmental and operating) that must be examined in order to ensure that the simulation tool is valid for all conditions of interest. In discussing these challenges, this paper proposes solutions to the problem of validation and formal accreditation that can be applied in future efforts.
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