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In previous studies of ship–ice interactions, most studies focused on ship–level ice interactions, overlooking potential rafted ice conditions in extreme ice conditions. The purpose of this study is to develop a numerical model for predicting ship resistance in rafted ice regions. Numerical modeling of rafted ice was carried out using preset grid cells. By comparing the model test results, the accuracy and reliability of the numerical model are verified. On this basis, we undertook the analysis of the impacts of different ice thicknesses, ship speeds, bending strengths, and crushing strengths on the ice resistance of ships under level and rafted ice conditions. The results show that the ice resistance of ships is significantly higher than that of rafted ice under the condition of level ice; however, level ice and rafted ice have different effects on ship ice resistance. Compared with level ice, the ice resistance of ships navigating in rafted ice is more concentrated. The findings of the present research can serve as a technical reference for studies focused on predicting ship resistance in rafted ice regions. [ABSTRACT FROM AUTHOR]

Autonomous ships represent an emerging paradigm within the maritime sector, poised to bring multiple advantages. Although numerous prototypes have been developed, the deployment of large autonomous ships has predominantly remained confined to domestic waters or specialized military applications. The extensive adoption of autonomous ships is hampered by several challenges, primarily centered around safety. However, the direct assessment of autonomous technologies on large-scale vessels can be very costly. Small-scale autonomy testing may provide a cheaper option. This study reviews the current small autonomous ship models used by maritime researchers and industry practitioners. It aims to evaluate how these autonomous models currently augment and can augment safety assurances on larger autonomous ships. The review identifies relevant very small Unmanned Surface Vessels (USVs), the main research groups behind them and their applications. Then, the current use of USVs for safety and safety assurance is analyzed. Finally, the paper suggests innovative strategies and research directions for using USVs for the safety assurance of larger autonomous ships. [ABSTRACT FROM AUTHOR]

The structural damage of ships in navigational accidents is influenced by the hydrodynamic properties of surrounding water. Fluid structure interactions (FSI) in way of grounding contact can be idealized by combining commercial FEA tools and specialized hydrodynamic solvers. Despite the efficacy of these simulations, the source codes idealizing FSI are not openly available, computationally expensive and subject to limitations in terms of physical assumptions. This paper presents a unified FSI model for the assessment of ship crashworthiness following ship hard grounding. The method uses spring elements for the idealization of hydrostatic restoring forces in 3 DoF (heave, pitch, roll) and distributes the added masses in 6 DoF on the nodal points in way of contact. Comparison of results against the method of Kim et al. (2021) for the case of a barge and a Ro–Ro passenger ship demonstrate excellent idealization of ship dynamics. It is concluded that the method could be useful for rapid assessment of ship grounding scenarios and associated regulatory developments. [ABSTRACT FROM AUTHOR]

Featured Application: A risk assessment framework that supports Arctic voyage planning and real-time operational decision-making through assignment of operational criteria based on the likelihood of ice-induced damage and the potential consequences. The International Code for Ships Operating in Polar Waters (Polar Code) was adopted by the International Maritime Organization (IMO) and entered into force on 1 January 2017. It provides a comprehensive treatment of topics relevant to ships operating in Polar regions. From a design perspective, in scenarios where ice exposure and the consequences of ice-induced damage are the same, it is rational to require the same ice class and structural performance for such vessels. Design requirements for different ice class vessels are provided in the Polar Code. The Polar Operational Limit Assessment Risk Indexing System (POLARIS) methodology provided in the Polar Code offers valuable guidance regarding operational limits for ice class vessels in different ice conditions. POLARIS has been shown to well reflect structural risk, and serves as a valuable decision support tool for operations and route planning. At the same time, the current POLARIS methodology does not directly account for the potential consequences resulting from a vessel incurring ice-induced damage. While two vessels of the same ice class operating in the same ice conditions would have similar structural risk profiles, the overall risk profile of each vessel will depend on the magnitude of consequences, should an incident or accident occur. In this paper, a new framework is presented that augments the current POLARIS methodology to model consequences. It has been developed on the premise that vessels of a given class with higher potential life-safety, environmental, or socio-economic consequences should be operated more conservatively. The framework supports voyage planning and real-time operational decision making through assignment of operational criteria based on the likelihood of ice-induced damage and the potential consequences. The objective of this framework is to enhance the safety of passengers and crews and the protection of the Arctic environment and its stakeholders. The challenges associated with establishing risk perspectives and evaluating consequences for Arctic ship operations are discussed. This methodology proposes a pragmatic pathway to link ongoing scientific research with risk-based methods to help inform recommended practices and decision support tools. Example scenarios are considered to illustrate the flexibility of the methodology in accounting for varied risk profiles for different vessel types, as well as incorporating input from local communities and risk and environmental impact assessments. [ABSTRACT FROM AUTHOR]

With the climate change, polar sea ice is diminishing. This, on one hand, enables the possibility for e.g., Arctic shipping and relevant resource exploitation activities, but on the other hand brings additional risks induced by these activities. Increasing research focuses have been observed on the relevant topics in the complex and harsh polar environment and its fragile ecosystem. However, from risk management perspective, there is still a lack of holistic analysis and understanding towards safe shipping in the ice-covered waters and its available models applicable for managing risks in the system. Therefore, this paper aims to establish a framework and analysis for better understanding of this gap. The paper targets a comprehensive and long-term project specifically focusing on holistic safe shipping in ice-covered waters as the analysis basis. It firstly creates a holistic framework for the shipping system in ice-covered waters and then implements review and analysis of project publications on their overall features. Quantitative prediction models are selected for a structured applicability analysis. Furthermore, an extensive review outside the project following the elements established for the holistic shipping system is conducted so that this paper provides an overview of models for the shipping system in ice-covered waters, addressing the status of the current toolbox. Moreover, it helps to identify the next scientific steps on risk management of shipping in ice-covered waters. • A holistic framework for the shipping system in ice-covered waters is established. • A deep review and structured applicability analysis for a long-term polar project are implemented. • An extensive review outside the project is carried out following the framework. • It forms a toolbox specifically for the ice-covered waters risk management. • It enables to show the potential gaps on the models for relevant topics in the system. [ABSTRACT FROM AUTHOR]

Abstract: Ice bound shipping is considerably more dangerous than shipping under more favourable water conditions. During winter the Baltic Sea can be covered with ice over an average of about 45% of its surface. The ice mostly reaches its maximum extent in late February or early March. The Bay of Bothnia located in the northern basin of the Gulf of Bothnia is prone to extreme frozen ice conditions. During winter the typical ice thickness in the northernmost areas of the Bay of Bothnia is about 70cm for land-fast sea ice. In this paper the ice crushing pressure on a ship''s hull is analysed statistically. A series of tests took place over four days in the Aalto ice tank and involved two different ship models. The peak pressures caused by ice were calculated from four sensor sheets located at different positions on the hull. In the statistical part, the sum of the forces acting on a section of a ship''s hull was modelled as a Poisson random process. Analysis of the cumulative distribution function (CDF) was modelled for the total force. The full scale comparisons of pressure-area values and line loads as a function of the load width were analysed by comparing the model scale data with full scale measurements onboard MS Arcturus and IB Sisu. Finally a short comparison is also conducted with the load level obtained from damage statistics gathered in the Baltic Sea. [Copyright &y& Elsevier]

Ships navigating in ice inevitably encounter different ice conditions. Dynamic ice typically presents severe conditions when it is moving perpendicular towards the parallel midship section, which can lead to ships getting stuck in ice. This can cause delays for ships or even damage to the ship hull. However, there currently is no model to assess ship operability in this dynamic ice. This paper aims to develop a method to assess operability of ships in dynamic ice conditions, which can be used for ship routing to avoid ship stuck. The method is especially useful for emergency response planning purposes, e.g. for marine pollution preparedness and response planning, where an understanding of the operability of response vessels in dynamic ice conditions currently is lacking. First, a transit model is introduced for both independent navigation and escort operations, considering the additional ice resistance by dynamic ice. Then, a ship operability index is proposed based on the modelling of ship's performance. Case studies of independent navigation and escort operations in realistic dynamic ice conditions are investigated to compare with the simulated results. Reasonable agreement is obtained, indicating that the proposed method can be used for ship operability assessment in dynamic ice. • A transit model for both independent navigation and escort operation in dynamic ice is developed. • A ship operability index is proposed based on the modelling of ship's performance. • Case studies show reasonable agreement between the simulated model results and empirical observations. • Model behaviors are tested in a series of sensitivity analyses. • The method is useful for ship routing and emergency response planning to avoid ship stuck in dynamic ice. [ABSTRACT FROM AUTHOR]

For safe and efficient exploitation of ice-covered waters, knowledge about ship performance in ice is crucial. The literature describes numerical and semi-empirical models that characterize ship speed in ice. These however often fail to account for the joint effect of the ice conditions on ship's speed. Moreover, they omit the effect of ice compression. The latter, when combined with the presence of ridges, can significantly limit the capabilities of an ice-strengthened ship, and potentially bring her to a halt, even if the actual ice conditions are within the design range for the given ship. This paper introduces two probabilistic, data-driven models that predict a ship's speed and the situations where a ship is likely to get stuck in ice based on the joint effect of ice features such as the thickness and concentration of level ice, ice ridges, rafted ice, moreover ice compression is considered. To develop the models, two full-scale datasets were utilized. First, the dataset about the performance of a selected ship in ice is acquired from the automatic identification system. Second, the dataset containing numerical description of the ice field is obtained from a numerical ice model HELMI, developed in the Finnish Meteorological Institute. The collected datasets describe a single and unassisted trip of an ice-strengthened bulk carrier between two Finnish ports in the presence of challenging ice conditions, which varied in time and space. The relations between ship performance and the ice conditions were established using Bayesian networks and selected learning algorithms. The obtained results show good prediction power of the models. This means, on average 80% for predicting the ship's speed within specified bins, and above 90% for predicting cases where a ship may get stuck in ice. [ABSTRACT FROM AUTHOR]

The dynamic response of ships following grounding and collision accidents may be influenced by structural topology as well as operational and environmental conditions. Traditionally, the consequences of such events may be assessed by crude empirical methods or laborious experiments. Computational methods offer a useful alternative in terms of accurately capturing crushing mechanisms also accounting the influence of surrounding water. This paper presents a benchmark study that compares the structural dynamic response by explicit nonlinear FEA approaches and the semi-numerical super-element method. Simulations for typical accident scenarios involving passenger ships confirm that implementing the influence of hydrodynamic restoring forces in way of contact may be useful for either collision or grounding. Yet, for grounding scenarios, the damaged area resulting from analytical simulations appears to be sensitive to the failure strain values adopted to model the rupture of the ship bottom floors. • Explicit nonlinear FSI methods utilising FEA and super element methods are benchmarked for various scenarios. • Structural topology, operational scenarios and environmental conditions influence accidental wave loads uncertainties. • Hydrodynamic restoring forces affect both collision or grounding loads. • In grounding breach sizes are sensitive to failure strain values. • Comparisons demonstrate that the super element method may be used for regulatory development. [ABSTRACT FROM AUTHOR]

During escort and convoy operations, an icebreaker opens a channel while the escorted or convoyed ships follow the path along the channel. If the assisted ship is wider than the channel which the icebreaker creates, the created channel cannot fit the assisted ship. Thus, the assisted ship has to break some ice by itself. This is herein referred to as navigation in 'narrow ice channel'. The performance of ships in narrow ice channel is investigated here. For this aim, model-scale test of a ship going through ice channels with different widths and ice thicknesses is firstly conducted. After that, numerical simulation of the model test scenarios is implemented with an in-house simulation program dedicated for ship operation in ice. The simulation correctly captured the main features of ship resistance change as a function of channel width, which indicates its validity as a simulation tool. Subsequentially, numerical simulations are implemented with several other ships in order to gain general insights into performance of ships in narrow ice channel. Focus is given to the influence of channel width on ships' encountered resistance and attainable speed in ice. The general findings through these simulations are useful for decision making tools. • Performance of ships going through narrow ice channels is investigated. • Model scale tests are carried out with different thicknesses in channels of various width. • Numerical simulations are carried out with multiple ships in channels of various width. • General conclusions on ship performance in narrow ice channel are formulated based on simulation results. [ABSTRACT FROM AUTHOR]

Ship performance in level ice involves problems such as attainable speed and maneuverability under different ice thickness. As the alternative to analytical methods, numerical simulation models have been proposed in recent years to improve the accuracy and to analyze more complex operations. However, current numerical models use quite diverse approaches to model the icebreaking components, and focus on rather different aspects, while the choices need more justification. The primary aim of this paper is to propose a framework for the development of effective and efficient numerical models to simulate ship performance in level ice, based on state-of-the-art knowledge of ship-ice interaction. This covers a discussion of modelling purposes and a hierarchical decomposition of the problem, followed by a strategy and two methods which could be applied to improve accuracy and credibility, as well as methodology of validation. Following the proposed framework, a numerical model is proposed as a prototype model, which simulates ship performance in level ice, and can be developed further in future. The numerical simulation results are compared with full-scale measurement results of a ship on the Baltic Sea, indicating reasonable estimation of ship turning. This implies the validity of the model as a prototype of the proposed framework. [ABSTRACT FROM AUTHOR]

The Finnish-Swedish winter navigation system plays an essential role in logistics to the ports surrounded by frozen sea in winter. Coordination of icebreakers is crucial to guarantee sufficient transit speed of merchant ships and minimize the waiting time. Simulation of the winter navigation system provides the opportunity to optimize the system performance and help the planning of future icebreaker fleets. For simulation, estimation of ship performance, such as the actual speed in ice, is essential. Calculation methods to estimate ship performance in such contexts are typically required to be of simple form without the need for heavy computation. Existing ship performance models embedded in route optimization algorithms and winter navigation simulations in the literature are often oversimplified. This paper proposes a systematic ship performance modelling approach which accounts for a wide range of parameters, such as ice condition and parameters, power variation and icebreaker assistance. The approach is validated against real ship voyages. The proposed approach is implemented into a simulation model which simulates the operation of merchant ships and icebreakers on the Baltic Sea. Analyses are conducted on the system level in terms of the waiting time of merchant ships needed for icebreakers as well as the energy consumption. • The coordination of icebreaker operations is crucial to guarantee sufficient traffic flow of merchant ships. • This provides the opportunity to optimize the system performance and help the planning of future icebreaker fleets. • For such simulations, estimation of ship performance, such as the actual speed in ice, is essential. • A ship performance modelling approach accounting for ice condition, power variation and icebreaker assistance is proposed. • The approach is implemented in a winter navigation simulation model to simulate operation of merchant ships and icebreakers. [ABSTRACT FROM AUTHOR]

Analyzing the reliability of autonomous ships has recently attracted attention mainly due to epistemic uncertainty (lack of knowledge) integrated with automatic operations in the maritime sector. The advent of new random failures with unrecognized failure patterns in autonomous ship operations requires a comprehensive reliability assessment specifically aiming at estimating the time in which the ship can be trusted to be left unattended. While the reliability concept is touched upon well through the literature, the operational trustworthiness needs more elaboration to be established for system safety, especially within the maritime sector. Accordingly, in this paper, a probabilistic approach has been established to estimate the trusted operational time of the ship machinery system through different autonomy degrees. The uncertainty associated with ship operation has been quantified using Markov Chain Monte-Carlo simulation from likelihood function in Bayesian inference. To verify the developed framework, a practical example of a machinery plant used in typical short sea merchant ships is taken into account. This study can be exploited by asset managers to estimate the time in which the ship can be left unattended. Keywords: reliability estimation, Bayesian inference, autonomous ship, uncertainty. • Proposing an event perception model for ship system through different Autonomy Degrees. • Establishing a Bayesian inference to formulate the reliability function of a ship system. • Predicting the cumulative number of events for different autonomy degrees over the voyage time. [ABSTRACT FROM AUTHOR]

Analysis of the dynamic response of ships in accident scenarios requires a realistic idealisation of environmental and operational conditions by multi-physics models. This paper presents a procedure that simulates the influence of strongly coupled FSI effects on the dynamic response of ships involved in typical collision and grounding events. Our method couples an explicit 6-DoF structural dynamic finite element scheme with a hydrodynamic method accounting for (a) 6-DoF potential flow hydrodynamic actions; (b) the influence of evasive ship speed in the way of contact and (c) the effects of hydrodynamic resistance based on a RANS CFD model. Multi-physics simulations for typical accident scenarios involving passenger ships confirm that suitable FSI modelling may be critical for either collision or grounding events primarily because of the influence of hydrodynamic restoring forces. • We present an FSI model for assessing ship crashworthiness. • Our model simulates ship evasiveness, seakeeping and hydrodynamic resistance. • An explicit FEA scheme is used to couple structural dynamics and hydrodynamics. • FSI simulations confirm the influence of hydrodynamic restoring forces on dynamic response. [ABSTRACT FROM AUTHOR]