Institute for design and analysis of ship structure

History shows that ferry and RoPax collisions with tankers can be
devastating for human life. This paper follows up such a scenario
to contribute to rational increase of safety of marine structures.
Through the coupling of multi-objective structural optimization
and crashworthiness analysis, a conventional tanker structure is
optimized for higher collision tolerance, accounting for the change in hull mass, so that the increase in safety is efficient. Two new concepts, proposed here, are deemed necessary for the successful execution of this task: a ‘two-stage’ optimization approach, reducing the number of needed collision simulations, and a rapid collision simulation approach that utilizes coarse FE mesh and reduces calculation time. Combining the obtained results with the state-of-the-art knowledge, a new insight about crashworthy design of tanker structures is also realized.

This paper investigates the influence of weld rotation stiffness on the global bifurcation buckling strength of laser-welded web-core sandwich plates. The study is carried out using two methods, the first is the equivalent single-layer theory approach solved analytically for simply supported plates and numerically for clamped plates. First-order shear deformation theory is used. The second method is the three-dimensional model of a sandwich plate solved with finite element method. Both approaches consider the weld through its rotation stiffness. The weld rotation stiffness affects the transverse shear stiffness. Plates are loaded in the web plate direction. Four different cross-sections are considered. Weld stiffness is taken from experimental results presented in literature. The results show a maximum of 24% decrease in buckling strength. The strength was affected more in plates with high reduction of transverse shear stiffness and high bending stiffness. Furthermore, clamped plates were influenced more than simply supported. The intersection between buckling modes shifted towards higher aspect ratios, in the maximum case by 24%. The results show the importance of considering the deforming weld in buckling analysis.

The corrosive marine environment is a threat to the ultimate strength of steel sandwich structures. Therefore, ultimate strength experiments were carried out in three-point bending for beams with different corrosion exposure times, i.e. one and two years. Standard laser-welded web-core sandwich beams are studied and different corrosion protection systems considered. The beams experienced general corrosion. The thickness reduction in unprotected plates and laser welds is around the typical 0.1 mm/year. This led to an ultimate strength reduction of 10% and 17% for beams with exposure times of one and two years, respectively. The experimental ultimate strength is in agreement with finite element simulations. The ultimate strength was maintained for the beams protected with coating or closed-cell polyurethane (PU) foam.

This paper introduces a model to estimate the consequences and related risk resulting from a collision between a LNG tanker and
a tug during harbour entrance manoeuvres. The analysis is carried out for Zeebrugge harbour, where very dense traffic, including
LNG tankers, is observed. The conditional probability that the collision seriously damages the LNG tanker during the mooring
operations is estimated by means of a Bayesian Belief Network (BBN). Furthermore, the events that lead to a collision are identified
as well as the prior probabilities of each event are evaluated in the course of numerical simulations, observations and a literature
survey. The consequences of the collision are related to the costs of LNG tanker repair and the risk, expressed in monetary terms,
is determined on the annual basis.

Maritime accidents involving ships carrying passengers may pose a high risk with respect to human casualties. For effective risk mitigation, an insight into the process of risk escalation is needed. This requires a proactive approach when it comes to risk modelling for maritime transportation systems. Most of the existing models are based on historical data on maritime accidents, and thus they can be considered reactive instead of proactive.

This paper introduces a systematic, transferable and proactive framework estimating the risk for maritime transportation systems, meeting the requirements stemming from the adopted formal definition of risk. The framework focuses on ship-ship collisions in the open sea, with a RoRo/Passenger ship (RoPax) being considered as the struck ship. First, it covers an identification of the events that follow a collision between two ships in the open sea, and, second, it evaluates the probabilities of these events, concluding by determining the severity of a collision. The risk framework is developed with the use of Bayesian Belief Networks and utilizes a set of analytical methods for the estimation of the risk model parameters.

Finally, a case study is presented, in which the risk framework developed here is applied to a maritime transportation system operating in the Gulf of Finland (GoF). The results obtained are compared to the historical data and available models, in which a RoPax was involved in a collision, and good agreement with the available records is found.

Shipping activity and offshore operations in Arctic areas are increasing as a result of more effective transportation routes and oil/gas exploration. Vessels navigating in ice covered areas are exposed to additional loads from different ice conditions. In this paper the dynamic loads on propellers are investigated to better understand the impact on propeller, power transmission elements and engine. An ice-propeller interaction model is implemented with a full propulsion machinery to simulate the systems response to ice loads. The ice load models are developed based on the DNV and IACS rules for ice-propellers. Modelling and simulation of interactive multi body systems is a rather complex task, involving hydrodynamics, mechanics, electronics and control systems. This paper describes an approach to link the different models to simulate the overall system response and the interactions between the sub-systems. Therein, the rule-based ice loads are implemented in two ways for comparison: a) a coupled and b) an uncoupled treatment of the ice load and system response. The simulation results show that the dynamic peak loads are 10-20% lower than the maximum peaks predicted by the uncoupled simulation, i.e. conventional rule-based. Simulations also show that the peak loads are damped through the transmission elements, and therefore reducing the load on critical machinery components.

In this paper, an attempt is made to define a new, proactive model for estimation the ship- ship collision consequences, assuming a RoPax as a struck ship.
Therefore two major issues are addressed by this paper, one is an identification of the events that follow a collision between two ships at open sea and another is an estimation of the prior probabilities of the events. The latter are obtained in the course of the numerical simulations, observations and literature survey. Then the model is developed by means of Bayesian Belief Network.
Furthermore the sensitivity analysis of the proposed BBN is performed and results are compared withthe available models, thus an initial verification of the results is provided.
Finally the probability of ship loss and human loss given a collision is estimated and the obtained results are discussed.

A vessel navigating in ice-covered waters experiences an additional ice-related load that acts on the propulsion machinery. Thus, the influence of this load on the propulsion machinery must be known, because it affects the safety and efficiency of the design and operation of the ice-going vessel. The ice-related load, in full-scale trials and model-scale tests, is typically measured at the shaft line between the propeller and diesel engine. Hence, the measured load includes a dynamic response of all elements in the mechanical transmission line. Therefore, this paper describes an approach to link the measured ice-related response of the shaft with the ice-propeller load. Therein, the rule-based DNV ice-propeller load is implemented in a bond graph model of the propulsion machinery system, which is used to obtain the dynamic response of all elements of the machinery system from the propeller to a diesel engine. The obtained shaft response is collected, filtered with different sampling frequency and converted to the ice-propeller load using a developed reverse model of the propulsion machinery. Furthermore, two different models of the shaft line: a rigid and a first order flexible are developed and verified. As a result, the converted ice-propeller load is compared with the rule-based DNV ice-propeller load and the influence of the sampling frequency and shaft models on the converted ice-propeller load is presented.

In this paper, an attempt is made to define a new, proactive model for estimation the ship- ship collision consequences, assuming a RoPax as a struck ship. Therefore two major issues are addressed by this paper, one is an identification of the events that fol- low a collision between two ships at open sea and another is an estimation of the prior probabilities of the events. The latter are obtained in the course of the numerical simulations, observations and literature survey. Then the model is developed by means of Bayesian Belief Network. Furthermore the sensitivity analysis of the proposed BBN is performed and results are compared with the available models, thus an initial verification of the results is provided. Finally the probability of ship loss and human loss given a collision is estimated and the obtained results are discussed.