Ice ridges and icebergs generally pose a major threat to both ships and offshore facilities that operate in Polar regions. In many cases these features will govern the structural design loads associated with the Ultimate Limit State (ULS) and the Accidental Limit State (ALS). In general, a large number of load cases must be considered in order to ascertain an adequate structural resistance. Alternatively, conservatively high values of the relevant design parameters can be applied, which implies cost penalties. Accordingly, it is natural to consider methods that can serve to reduce the number of relevant load cases. Based on relevant information about the statistical properties of the parameters that characterize ice ridges and icebergs, the most likely combinations of these parameters for design purposes are highly relevant. On this background, the so-called environmental contour method is applied. Probabilistic models of the key parameters that govern the ship and ice interaction process are introduced. Subsequently, the procedure referred to as inverse reliability methods (IFORM) is applied for identification of the environmental contour. Different forms (i.e., dimensions) of environmental contours are generated to reflect the characteristics of the interaction process. Furthermore, the effect of an increasing correlation between the basic parameters is studied. In addition, the increase of the design parameter values for increasing encounter frequencies is illustrated.

Decision support systems in offshore vessels utilize wave parameters in combination with physics-based vessel models to predict the vessel behavior prior to the initiation and execution of a marine operation. These predictions are, usually, accompanied by significant uncertainties inherent in the estimation of wave statistical parameters, idealized parametric spectra, and system variables. Consequently, the predictions may deviate considerably from the real behavior of the vessel. Therefore, this study uses numerical wave spectra corresponding to a site in the North Sea in conjunction with a hydrodynamic model adapted to measurements to make more accurate intermediate-term response predictions. Considering a weather-restricted marine operation, the intermediate-term predictions involve simulating the responses for any time window within the upcoming 72 hours. The vessel model’s uncertainty is minimized by calibrating the influential parameters utilizing the full-scale response measurements within an optimization framework. The subsequent Roll predictions based on calibrated parameters exhibit better alignment with the measured Roll motions. The application of recursive optimization showed a significant reduction in prediction errors in an actual marine operation.

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Ice ridges and icebergs generally pose a major threat to both ships and offshore facilities that operate in Polar regions. In many cases these features will govern the structural design loads. It is not practical or feasible to design a ship to withstand any possible ice impact load without damage, so following the principles of risk-based design, the tolerable consequences of an impact should be determined also considering the associated probability of occurrence. The following limit state design criteria are usually applied in structural design: (i) Serviceability Limit States (ii) Ultimate Limit States (ULS) (iii)Fatigue Limit States (FLS) (iv)Abnormal/Accidental Limit States (ALS). The ALS corresponds to impact events with a very low probability to occur, and its intention is to ensure that a ship hull structure does not suffer from a complete loss of integrity. It is natural to consider methods that can serve to reduce the number of relevant load cases to be analysed, and to identify the most likely combinations of the relevant design parameters. Accordingly, the so-called environmental contour method becomes of significant interest. Utilization of this approach is illustrated in connection with the ULS and ALS in the present paper.