Research Papers: Polar and Arctic Engineering

A Moored Arctic Floater in First-Year Sea Ice Ridges

[+] Author and Article Information
Oddgeir Dalane

Department of Civil and Transport Engineering,
Marine Civil Engineering,
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway
e-mail: oddd@statoil.com

Vegard Aksnes

The Norwegian Marine Technology
Research Institute (MARINTEK),
Trondheim 7052, Norway
e-mail: vegard.aksnes@marintek.sintef.no

Sveinung Løset

Sustainable Arctic Marine
and Coastal Technology (SAMCoT),
Centre for Research-Based Innovation (CRI),
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway
e-mail: sveinung.loset@ntnu.no

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received March 23, 2014; final manuscript received October 13, 2014; published online November 12, 2014. Assoc. Editor: Arne Gürtner.

J. Offshore Mech. Arct. Eng 137(1), 011501 (Feb 01, 2015) (8 pages) Paper No: OMAE-14-1035; doi: 10.1115/1.4028814 History: Received March 23, 2014; Revised October 13, 2014; Online November 12, 2014

First-year sea ice ridges are a major concern for structures operating in the Arctic offshore and will in many cases give the design mooring load. In this paper, the response of a moored conical floater, somewhat similar to the well-known Kulluk, is studied in first-year ridges. The study is based on model tests performed at Hamburg Ship Model Basin (HSVA) in several ridges with different properties. Mooring forces and floater response, resulting from interaction with different ridges, were compared with respect to ridge properties, ridge behavior, and simulated ice management. Clearance of accumulated rubble upstream the structure was the dominating physical process in the ridge–structure interaction. Accumulation of rubble caused large mooring forces. The amount of accumulated rubble depended on the ridge cross-sectional area, thus the mooring forces increased with ridge cross-sectional area. Large mooring forces were also experienced after the ridge was passed by the structure due to difficulties with clearing of accumulated rubble.

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Fig. 1

Illustration of the Sevan FPU-Ice. Dimensions are given in Table 1 and Fig. 3.

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Fig. 2

Cross-sectional sketch of a typical first-year ridge. Sail, consolidated layer, and keel are indicated, as well as keel depth and sail height. The shaded area defines the ridge cross-sectional area.

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Fig. 3

Model setup and full-scale dimensions of the floater

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Fig. 4

Pictures of the ridges from test series 3000. Left: rafted ice close to tank walls. Right: managed level ice behind the ridge.

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Fig. 5

Schematic view of the test setup for test series 3000, seen from above

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Fig. 6

The motion of rubble from a ridge keel is indicated. Consolidated layer and sail have been removed from the sketch.

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Fig. 7

Plot of maximum horizontal mooring force against cross-sectional area of the corresponding ridge

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Fig. 8

Surge and pitch motion together with longitudinal mooring force in test series 4000. Normalized for comparison purpose.

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Fig. 9

Plot of ridge 4000-1 and longitudinal mooring force against position of the fore perpendicular of the structure

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Fig. 10

Sequence of pictures showing the situations giving the three force peaks in ridge 4000-1, indicated in Fig. 9. The pictures are taken from bow 45 deg, above, and below water.

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Fig. 11

Comparison between the measured and calculated horizontal force according to ISO19906 recommendations




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