Structural performance of non-ice class ships in sliding collision with ice

Omidali, Mahdi (2021) Structural performance of non-ice class ships in sliding collision with ice. Masters thesis, Memorial University of Newfoundland.

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Abstract

Stiffened structures have a high load-bearing capacity beyond the elastic region that can be used in structural design. Collision and grounding scenarios are among the accidental limit states that threaten the structural integrity of marine structures. Collision with ice is one of the scenarios that can occur in Canadian Arctic waters. It is a high priority to understand the structural performance of ships in probable collision cases. As for ice-class ships, the load-carrying capacity is apparent on some level for designers and navigators. For non-ice class ships, however, the reserve strength after yield is not evident in collision with ice. It is crucial for both structural reasons and damage stability of the vessel. International Maritime Organization (IMO) defines damage length requirements for various types of ships in various conventions and codes. It is necessary to study the damage extent in collision scenarios to realize whether amendments are necessary for vessels that might navigate in polar water. In this research, the structural performance of various merchant ships and offshore support vessels has been investigated under collision with ice. Finite element simulation with complex fracture models was implemented in this study. The simulations indicated that the collision with bergy bits causes severe damage to the structure on non-ice class ships. Parameters such as ice shape in the high-pressure zone, ice geometry (mass distribution), and impact angle dramatically affect the results. It was concluded that for the merchant vessels investigated, the damage stability requirements specified in MARPOL are conservative (except for tankers whose length does not exceed 150m), and there is no need to include any additional damage case scenario. For offshore supply vessels, results indicate that the damage cases are not as conservative as they should be, and amendments to the current IMO regulations are necessary. In addition, it is shown that the empirical formulas available in the literature can estimate the steady-state fracture phase in the sliding collision. This finding could be used to construct the probability distribution function for damage extent in collision with ice.

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