An experimental investigation of ship manoeuvrability in pack ice

Brown, Robert C. (2002) An experimental investigation of ship manoeuvrability in pack ice. Masters thesis, Memorial University of Newfoundland.

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Abstract

A 1:40 scale model of the R-Class icebreaking hullform and a 1:80 scale model of the MV. Arctic bulk carrier were tested in the Faculty of Engineering and Applied Science towing tank at Memorial University of Newfoundland. The models were tested first in open water and then in modelled pack ice covered water at approximately 8.3 tenths concentration. The pack ice model consisted of various sizes of hexagonally shaped paraffin wax with a mean thickness of about 13mm. -- Two main types of tests were conducted for both models in each water surface condition - constant velocity and constant acceleration. The former involved towing at constant velocities of 0.5 and l.Om/s to determine sway velocity damping coefficients while the latter was a new technique proposed for determining acceleration manoeuvring coefficients and for quickly determining the sway velocity damping coefficients compared with conventional constant velocity test methods. The accelerations used for testing were 0.02 and 0.04 m/s2. -- The test series consisted of simple straight-line towing for each model with constant heading angles 0°, 2°, 4°, 6°, 8° and 10° and rudder angles 10° port and starboard, 5° port and starboard and rudder amidships. A total of 480 tests were conducted in all. -- It was shown that crosstalk in a three-component dynamometer could be mathematically removed by developing a 3x3 calibration matrix whose off-diagonal terms represented the crosstalk coefficients. Removing crosstalk measurements provided a more accurate measurement of the actual load applied to the individual load cells. -- The manoeuvring coefficients for sway velocity damping and rudder were calculated using results from the constant velocity segment of the test series. Only coefficients for the sway and yaw equations were calculated for this study. The coefficient values foundsemi-empirical methods given in the literature. The coefficients compared closely. As well, the sign of the coefficients for sway force were correct according to the literature and the sign of yaw moment implied that both models were bow-dominant. -- Comparison of the constant velocity pack ice test results with those in open water showed in general that the loads were higher, regression fits were more nonlinear, the spread in the data points increased with increasing sway velocity, the bow remained dominant for both models and differences forces for varied rudder angles were less distinct. Sway velocity damping coefficients were calculated in pack ice using the same methods as for open water. -- It was shown that by employing a constant tow carriage acceleration, manoeuvring coefficients for sway acceleration could be determined for open water, but that using the same methodology for pack ice resulted in poor regression fits to the data. -- Finally, it has been shown that through the use of constant tow carriage acceleration, the sway velocity damping coefficients can be calculated in a fraction of the time required by using conventional constant velocity testing methods. during the open water portion of the test series were compared with those found from

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