Per Hogström

Survivability analysis of a struck ship with damage opening - influence from model and material properties uncertainties

The conditions for damage stability and survivability of a ship struck in a collision in arbitrary sea-state are, from a structural point of view, determined by the size and shape of the damage opening in its side-shell. In the current investigation, explicit finite element analyses (FEA) are presented of a ship-to-ship collision scenario in which the damage opening of a struck ship is calculated for a selection of damage degradation models and realistic material properties, here referred to as model and material properties uncertainties. The model uncertainty is considered as a possible (user-related) insecurity in the selection of the most appropriate damage criterion for the analysis; the shear failure and the forming limit diagram (FLD) criteria were compared in the current investigation. The uncertainty in material properties is accounted for in the constitutive material model description and the material parameters used in the two damage criteria. The size and shape of the damage openings predicted by the FEA are used in damage stability analyses in which the struck ship is subjected to wave motions in an arbitrary sea-state and flooding into the damage opening. The survivability of the struck ship is estimated for all of the damage opening cases. One of the main conclusions is that the high degree of accuracy that a researcher on structure analysis strives for has to be considered together with the natural variation of the sea-state that defines the characteristics in the following damage stability analysis. Consequently, by adoption of a holistic approach in which structural integrity and damage stability research are combined using a systematic parameter (sensitivity) and collision-scenario-based analysis, simplified models and criteria can be developed more efficiently and with higher precision. It will also be clearer which variables are the most important to focus on when analysing the survivability or risk for capsizing.

What can we learn from uncertainty analysis with respect to survivability or time to capsize of a ship struck in collision

Collisions between ships contribute to ship losses even in modern time, and the International Maritime Organization (IMO) strives towards a more risk-based view on addressing the damage stability of ships. The current paper makes use of a methodology for computing the consequences of ship collisions. This methodology is comprised of structural analysis of a collision scenario followed by dynamic damage stability simulations of the struck ship. The emphasis of this investigation is on uncertainties related to structural computations of the collision event. Explicit finite element analyses are presented for a case study of a collision scenario. For comparison, the model of the bow of the striking ship is considered as either rigid or deformable in separate analyses. The consequences from the model representation of the bow, uncertainties in material properties and failure model (three different ones are presented) in terms of shape and size of the damage opening are studied. This variation also has an impact on the time to capsize of the struck vessel, which is studied in the subsequent damage stability computations for different sea states. One conclusion is that the methodology that has been used is important for future efforts in the research on safety at sea. The study presented demonstrates the importance of incorporating uncertainties in the analysis chain and studying the effect of these on the final results: the time to capsize.

Analysis of a struck ship with damage opening - influence from model and material properties uncertainties

The conditions for damage stability and survivability of a ship struck by collision in arbitrary sea-state are, from a structural point of view, determined by the size and shape of the damage opening in its side shell. In the current investigation, explicit finite element analyses (FEA) are presented of a ship-to-ship collision scenario where the damage opening of a struck ship is calculated for a selection of damage degradation models and realistic material properties; here referred to as model and material properties uncertainties. The model uncertainty is considered as a possible (user-related) insecurity in the selection of the most appropriate damage degradation model for the analysis: the shear failure and the forming limit diagram (FLD) criteria. The uncertainty in material properties is accounted for in the constitutive material model description and the material parameters used in the two criteria. The size and shape of the damage openings predicted by the FEA are used in damage stability analyses in which the struck ship is subjected to wave motions in arbitrary sea-state and flooding into the damage opening.

Designing for safe operations: promoting a human-centred approach to complex vessel design

ABSTRACT The benefits of a human-centred approach to design have been widely recognised throughout industry, in the research community and by regulatory bodies. In the maritime domain, it is also beginning to make an impact. This article explores how a human-centred approach may successfully be achieved within the context of ship design using a case study from a project to create conceptual designs for two offshore wind turbine installation vessels. Using vessel designs as a mediating tool between designers, users and human factors specialists, basic task analysis and link analysis methods were used to incorporate operational knowledge into the design process. After applying this to the integration of a dynamic positioning system on one of the vessels, the designers concluded that a human-centred approach had improved not only ship safety, but also safety, efficiency and cost-effectiveness in operations.

Comparison and assessment of the crashworthiness of three innovative side-shell structures: the X-core, Y-core and corrugation panel structures

Collisions between ships contribute to ship losses even in modern time. In numerous research projects, new innovative side-shell structures have been proposed and assessed in contrast to conventional side-shell structure designs with respect to their crashworthiness properties. The current paper presents an in-depth comparison and assessment (by means of experiments and nonlinear finite element simulations) of three innovative side-shell structures referred to as the X-core, the Y-core and the intrusion-tolerant corrugated panel structures; all of them have been presented separately in the literature before. The objective is to compare the three concepts against a typical reference double-hull side-shell structure and challenge their structural designs with respect to energy absorption, penetration depth at fracture of the inner barrier during a bulb-impact loading condition, weight and manufacturing cost. It is concluded from the investigation that there is not one candidate who is superior to the others. Hence, the structures have to be further developed or trade-offs have to be made depending on the indented functionality of the structure and risk for collision related to e.g. distribution of likely collision angels.