Ekaterina Kim

Laboratory experiments on shared-energy collisions between freshwater ice blocks and a floating steel structure

ABSTRACT Ship collisions with floating ice in which the ship sustains damage are in the shared-energy regime – both the ice and the ship dissipate energy through inelastic deformations. The physics of these events are rarely studied. Experience on the conditions of shared-energy collision tests is limited. The aim of this paper is to present an experimental study on a scenario where the impacted structure undergoes permanent deformations together with ice failure. The paper describes a series of laboratory-scale impact tests of freshwater granular ice blocks against stiffened steel panels, and presents the analysis of the main test results and lessons-learned.

Iceberg Shape Sensitivity in Ship Impact Assessment in View of Existing Material Models

Large natural resources in the Arctic region will in the coming years require significant shipping activity within and through the Arctic region. When operating in Arctic open water, there is a significant risk of high-energy encounters with smaller ice masses like bergy bits and growlers. Consequently, there is a need to assess the structural response to high energy encounters in ice-infested waters. Experimental data of high energy ice impact are scarce, and numerical models could be used as a tool to provide insight into the possible physical processes and to their structural implications. This paper focuses on impact with small icebergs and bergy bits.In order to rely on the numerical results, it is necessary to have a good understanding of the physical parameters describing the iceberg interaction. Icebergs are in general inhomogeneous with properties dependent among other on temperature, grain size, strain rate, shape and imperfections. Ice crushing is a complicated process involving fracture, melting, high confinement and high pressures. This necessitates significant simplifications in the material modeling. For engineering purposes a representative load model is applied rather than a physically correct ice material model.The local shape dependency of iceberg interaction is investigated by existing representative load material models. For blunt objects and moderate deformations the models agree well, and show a similar range of energy vs. hull deformation. For sharper objects the material models disagree quite strongly. The material model from Liu et.al (2011) crush the ice easily, whereas the models from Gagnon (2007) and Gagnon (2011) both penetrate the hull. From a physical perspective, a sharp ice edge should crush initially until sufficient force is mobilized to deform the vessel hull. Which ice features that will crush or penetrate is important to know in order to efficiently design against iceberg impact.Further work is needed to assess the energy dissipation in ice during crushing, especially for sharp features. This will enable the material models to be calibrated towards an energy criterion, and yield more coherent results. At the moment it is difficult to conclude if any of the ice models behave in a physically acceptable manner based on the structural deformation. Consequently, it is premature to conclude in a design situation as to which local ice shapes are important to design against.Copyright

Design and Modelling of Accidental Ship Collisions With Ice Masses at Laboratory-Scale

Knowledge about the level of damage after a collision with an ice mass is necessary for designing ships and offshore structures operating in ice-infested waters. An understanding of the physical processes during such a collision is needed to prevent (or limit) accidents, causing loss of life, the loss of a ship or environmental pollution. This study was motivated by the lack of experimental data on ship collisions with ice masses where both the ship and the structure undergo deformations. Laboratory experiments of accidental collisions with ice masses (ACIM) are essential to verify current methods for integrated analysis of the crushing and deformation of the ice and the steel structure. ACIM tests are sensitive to the structural design, i.e., the design of a structure that is flexible enough in relation to the ice mass. Both the ice and the structure should be able to deform during the collision event. The paper addresses issues related to the planning of ACIM at laboratory scale with special emphasis on the choice of: (i) process of ice manufacturing and ice mechanical properties; (ii) flexibility of impacted structure; (iii) scaling of the experiment. Experimental setup of laboratory-scale ACIM for the Aalto Ice Tank is proposed. Non-linear finite element analysis is used as a tool to predict structural damage and to guide the planning of collision experiments. The predicted damage of the test specimens caused by collision is presented. NOMENCLATURE