Physical model testing I for investigating the effects of managed ice-field characteristics on a dynamic positioning vessel

Abstract

This paper presents details of an extensive physical model testing program for evaluating the performance of a dynamic positioning (DP) controlled vessel in different realistic managed ice environments. It describes the model vessel, the preparation of the ice-field, the procedure of the model tests, the methodologies of data analysis, and highlights of the measurements. A simplified generic drillship model at 1:40 scale was tested in multiple managed ice configurations. A total of 372 test runs were carried out in 17 ice sheets to evaluate the thruster forces and motion responses of the vessel in various ice conditions. The physical and mechanical characteristics of the ice-field were modelled by controlling ice concentration, thickness, floe size, flexural strength, and the ice drift speed and direction. The ice concentration ranged from a light condition (7/10th) to a heavy condition (9/10th+) with multiple ice floe sizes ranging between 25 m to 100 m. Also, multiple ice thicknesses ranging between 0.60 m to 2.0 m and multiple ice drift speeds (0.2 knots, 0.5 knots, and 1.2 knots) with various moderate to extreme ice drift angles were investigated. The thruster forces on the model vessel along the surge and sway directions and the yawing moment were measured. Besides, the vessel model's 6-DOF motions and accelerations were recorded. Multiple cameras were used to capture the global and local ice-structure interactions placed in different above-water locations. All reported values presented in the paper are in full-scale unless otherwise specified.The time series of thruster forces and yawing moments are presented along with the vessel's positioning capabilities in various managed ice conditions. Results and discussions on the effects of various managed ice-field parameters on the time-averaged thruster forces and moment are offered. Generally, the analysis reveals that each of the ice parameters under investigation had a moderate to strong effect on global thruster force in the surge direction. The measurements and the videos showed complex and highly stochastic ice-vessel-basin wall interactions and different ice failure modes. Overall, the DP system used in the testing demonstrated the vessel's capabilities in maintaining the station for the majority of test head-on test cases and the oblique ice tests not exceeding 10°. The program generated a large dataset and video recordings to evaluate and improve understanding of the dynamic ice-vessel interactions and provided sufficient information for developing novel ice force models for real-time applications.