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While society benefits from Arctic shipping, it is necessary to recognize that ship operations in Arctic waters pose significant risks to people, the environment, and property. To support the management of those risks, this article presents a comprehensive approach addressing both short-term operational risks, as well as risks related to long-term extreme ice loads. For the management of short-term operational risks, an extended version of the Polar Operational Limit Assessment Risk Indexing System (POLARIS) considering the magnitude of the consequences of potential adverse events is proposed. For the management of risks related to long-term extreme ice loads, guidelines are provided for using existing analytical, numerical, and semi-empirical methods. In addition, to support the design of ice class ship structures, the article proposes a novel approach that can be used in the conceptual design phase for the determination of preliminary scantlings for primary hull structural members.

Welded joints have a large variation of their geometry and is one important reason for the comparable large scatter regarding their fatigue life. This study presents and tests an approach for the probabilistic fatigue assessment of welded joints based on their individual local geometry. This approach is adopted from the IBESS research cluster and combined with previous work regarding the evaluation of geometrical parameters from 3D-surface scans. The fatigue life was calculated based on 26 fatigue test series. In this study the fatigue strength calculated by the IBESS approach tended to be overestimated in some cases that is mainly related to the underestimation of the scatter range of the simulated fatigue tests according to the real results. Geometrical parameters were varied in the IBESS calculations and showed that no significant influence on the calculated fatigue strength was determined for weld toe radii > 2 mm and flank angle > 30°.

Thermal cut edges can be found in most maritime structures, e.g. in window openings or hatch corners on ships. It is very common to treat free plate edges by grinding or sandblasting due to fatigue and coating requirements. The aim of this study is to review the fatigue behavior of typical treatment methods. Within this study several fatigue tests are performed to outline the influence of treatment methods used for different steel grades, plate thicknesses and cutting processes. Especially the influence of the local edge geometry caused by treatment like grinding or milling is not covered by fatigue rules and guidelines like Eurocode or IIW. Also, the influence of yield strength is not considered by these regulations. Only in shipbuilding a fatigue bonus for high strength steels is given. However, these rules are based on older data and an update is requested by ship building industries. For the investigation shipyards and partners from other industries produced a big number of specimens for fatigue tests. Steel grades are from S235 to S460. Surface roughness as well as local treatment geometry are well documented. In addition, hardness as well as residual stress measurements were performed. Finally fatigue tests were done. Overall goal of the study is to present applicable FAT curves to be used for fatigue assessment.

Arctic shipping is growing driven by a demand for natural resources, climate change, and technological development, among other factors. While this provides many benefits for society, it also entails risks for people, the environment, and property. The purpose of this article is to assist ship designers, operators, owners, and other stakeholders in managing those risks by defining a comprehensive approach to scenario-based risk management for Arctic waters. The approach covers both the management of short-term operational risks, as well as of risks related to a ship’s long-term extreme (design) ice loads and structural response. For operational risk management, a further developed version of the established Polar Operational Limitations Assessment Risk Indexing System (POLARIS) method is defined. In contrast to the established method, the further developed version considers the consequences of potential accidental events. For managing risks related to a ship’s long-term extreme ice loads and structural response, guidelines are provided for the application of existing methods of assessing ice loads, including analytical, numerical, and semi-empirical methods. In addition, to support the design of ice class ship structures, a new approach based on closed-form expressions is defined that can be used in the conceptual design phase to determine preliminary scantlings of primary hull structural members (e.g., transverse web frames).

Climate change provides for a stronger wave climate and the open water area in this region will increase. The increase in open water area allows for an increase in higher energy surface waves than previously. In addition, human activities are much more complex in this zone, called Marginal Ice Zone, compared to the open ocean, so that there is an increased research interest in the physical processes of wave-ice interaction and the resulting statements on the influence on maritime technology. This work deals with the development of an efficient simulation environment for the 2D wave-ice interaction on the finite platform LS-DYNA. The numerical model based on the coupled ICFD and implicit structural solvers of LS-DYNA. The motion behavior and the mechanical behavior of the ice floe due to the interaction with different waves are investigated. The stronger wave climate in the Marginal Ice Zone intensifies, making the waves more energetic and increasing the wave steepness. The results of the simulation clearly show that larger wave steepnesses have a large influence on the mechanical stress in the ice floe and the deflection increases. These mechanical stresses lead in the critical cases to a fracture of the ice floe into several smaller ice floes. Consideration of the ratio of ice floe length to wave length showed that the smaller the ratio, the larger the heave and surge movements of the ice floe induced by the waves.

The global demand in energy resources is moving the petroleum industry to the Arctic with its huge resource potential. The lack of infrastructure onshore increases the role of the Arctic marine shi...

Ships operating in ice-covered waters may experience structural damage due to ice-induced loads. This can occur even though the ship structure is designed according to rules considering ice loading...

Understanding ice-structure interaction is critical for an efficient and safe design of offshore structures and ships in ice-covered waters. During the last decades a variety of field experiments, ...

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements., H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements.

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action. Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action. Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

This paper presents a finite element model for the simulation of ice–structure interaction problems, which are dominated by crushing. The failure mode of ice depends significantly on the strain rate. At low strain rates, the ice behaves ductile, whereas at high strain rates it reacts in brittle mode. This paper focuses on the brittle mode, which is the dominating mode for ship–ice interactions. A multitude of numerical approaches for the simulation of ice can be found in the literature. Nevertheless, the literature approaches do not seem suitable for the simulation of continuous ice–structure interaction processes at low and high confinement ratios in brittle mode. Therefore, this paper seeks to simulate the ice–structure interaction with the finite element method (FEM). The objective of the here introduced Mohr-Coulomb Nodal Split (MCNS) model is to represent the essential material behavior of ice in an efficient formulation. To preserve mass and energy as much as possible, the node splitting technique is applied, instead of the frequently used element erosion technique. The intention of the presented model is not to reproduce individual cracks with high accuracy, because this is not possible with a reasonable element size, due to the large number of crack fronts forming during the ice–structure interaction process. To validate the findings of the model, the simulated maximum ice forces and contact pressures are compared with ice extrusion and double pendulum tests. During validation, the MCNS model shows a very good agreement with these experimental values.

The microstructure–properties relations and strengthening mechanisms of additively manufactured 316L stainless steel are comprehensively investigated in this work. The orientation dependency and the strain hardening are studied by tensile testing of as-built specimens fabricated by laser-based powder bed fusion (LPBF) in different directions. The results are compared with those obtained for wrought material. The microstructure of the wrought and the LPBF materials are also comprehensively investigated. Equiaxed grains with random orientation and relatively uniform size (≈30 μm) are observed in the wrought material, where the LPBF samples show columnar grains inside as well as fine equiaxed grains in the bottom of the molten pool. A bimodal grain size distribution, higher values of geometrically necessary dislocations density (≈25–32%), and lower fractions of high-angle grain boundaries (≈24–28%) are observed in LPBF 316L. A significant yield strength and considerable ultimate strength improvement without remarkable elongation decrease are obtained for the LPBF tensile specimens, resulting in a high strength-elongation balance (up to 26 122 MPa%). Two-stage strain hardening is depicted in both wrought and LPBF samples. This is successfully predicted with two-stage Hollomon analysis. However, the LPBF samples illustrate lower strain hardening exponents in comparison with the wrought ones.

The size of the fully developed process zone (FDPZ) is needed for the arrangement of displacement sensors in fracture experiments and choosing element size in numerical models using the cohesive element method (CEM). However, the FDPZ size is generally not known beforehand. Analytical solutions for the exact FDPZ size only exist for highly idealised bodies, e.g. semi-infinite plates. With respect to fracture testing, the CEM is also a potential tool to extrapolate laboratory test results to full-scale while considering the size effect. A numerical CEM-based model is built to compute the FDPZ size for an edge crack in a finite square plate of different lengths spanning several magnitudes. It is validated against existing analytical solutions. After successful validation, the FDPZ size of finite plates is calculated with the same numerical scheme. The (FDPZ) size for finite plates is influenced by the cracked plate size and physical crack length. Maximum cohesive zone sizes are given for rectangular and linear softening. Further, for this setup, the CEM-based numerical model captures the size effect and can be used to extrapolate small-scale test results to full-scale.

Several definitions of equivalent ice thickness for simplification of complex ice cover are found in the literature. However, their systematic analysis is currently absent. Therefore, this paper re...

Experiments and numerical simulations of moving (sliding) loads on steel grillage structures have demonstrated a significant difference in plastic capacity when subject to moving loads vers...

For a reliable prediction of the total resistance in ice in an early ship design stage, it is of great importance to have knowledge on the different influencing aspects. Three of the quite ...

In this paper, the semi-empirical coefficients and exponents of an ice resistance prediction method, i.e. refined Lindqvist formula, are investigated. Thereby, the coefficients and exponents which ...

Finding the optimal fleet composition under uncertainties is crucial for the economic success of a business. This paper presents the Fleet Efficiency Factor, a decision support tool for fleet size and mix problems and fleet composition problems. The method is based on a particle swarm optimisation algorithm combined with a stochastic model to include uncertainties into the decision-making progress. This combination allows selecting the best option out of a pool of available vessels, vehicles and aircrafts. Additionally, the FEF is based on the classical ship merit factor and thus capable of comparing different fleet compositions according to their economic efficiency, by describing the efficiency in a simple factor. A case study for the supply of an offshore platform in the high North is conducted. The approach proved to be flexible and applicable to different strategical and tactical planning problems in maritime transportation.

Additive manufacturing (AM) enables the cost-effective production of complex components, many of which are traditionally manufactured using costly production steps among other processes. One widely applied AM process is Laser-based Powder Bed Fusion of Metals (PBF-LB/M); however, internal pores and rough surfaces are typically inevitable with PBF-LB/M, reducing fatigue and corrosion resistance compared to traditional processes involving turning and milling. Additionally, large defects often occur near to or just at the surfaces. Thus, this study investigates the effect of hybrid additive and subtractive manufacturing on the fatigue strength of AISI 316L. For this purpose, different post treatment routes are compared with wrought material. Additionally, computer tomography is used to determine the necessary machining depth of the surface layer. In this study, heat-treatment and machining are both found to significantly increase fatigue strength. Finally, cyclic mean stresses affect wrought and AM specimens differently.

It is well known that material properties undergo significant changes with temperature. In order to meet extreme environmental requirements for ships and offshore structures operating in Arctic regions, the effect of temperature on material behavior needs to be considered. In recent studies, significantly higher fatigue strength was observed for base materials and welded joints in comparison to room temperature. Fatigue strength increased even for temperatures far below the allowed service temperature based on fracture toughness results; however, sub-zero temperatures fatigue data are scarce and the effects of steel strength and welding type on fatigue strength changes are unknown. Material selection for ships and offshore structures is typically based on empirical Charpy and fracture toughness relations at the design temperature, minus a safety margin. Thus, this study presents material test results including fatigue tests of butt-welded joints, tensile test, and Charpy impact toughness tests at room and sub-zero temperatures of different structural steel types. Additionally, the effect of welding techniques and steel strength are discussed. The results can be used to extend design approaches for ships and offshore structures subject to sub-zero temperatures and to improve material selection for ships and offshore structures operating in Arctic regions.

Most merchant ships operating in the cold regions are not able to break ice themselves, they can only navigate in the broken ice, the so-called brash ice channels. Today’s standard requires a model test in real brash ice conditions to be carried out and realistic additional resistances to be estimated from this. The problem is that they can only be performed at the end of the design process. The possibility of changing the ship design within the development process can only be guaranteed by using a simulation tool, based on the Discrete Element Method. The problem with the development of this numerical simulation is the correctness of the mapping of the physical behaviour of brash ice. The physical models used are often simplified and not sufficient to represent the complex mechanical behaviour of brash ice. Thus, another problem with the use of numerical simulation is the selection of the correct parameters to describe the mechanical behaviour. A concrete definition of the used material parameters does not exist and the experimental tests for the determination of the physical properties are often complex and not standardized. This paper examines the mechanical behaviour of brash ice and the descriptive parameters of each ice rubble. On this basis, the physical behaviour in nature is compared with the model used in numerical simulation. As a result, physical inconsistencies are determined and new solution approaches are proposed, for example in the form of a new contact model, an extension of the friction model or a change of the descriptive particle shape.

Ships and offshore structures operating in Artic regions face specific challenges such as ice loads and seasonal low temperatures. In order to meet these extreme environmental requirements, the effect of temperature on material behaviour needs to be considered. It is well known that static material properties (yield strength, fracture toughness etc.) undergo significant changes with temperature. In recent studies, significantly higher fatigue strength was observed in welded joints in comparison to estimates based on international standards. Fatigue strength increased even for temperatures far below the allowed service temperature based on fracture toughness results; however, studies on fatigue strength of structural steel at sub-zero temperatures are scarce. Moreover, material selection for ships and offshore structures is usually based on empirical Charpy and fracture toughness relations at the design temperature, minus a safety margin. This study aims at introducing an S-N curve database for welded joints that can be used to verify the fatigue design approaches for ships and offshore structures subject to sub-zero temperatures. Therefore, the effect of temperature on the fatigue strength of butt-welded normal and high strength steel structures is analysed experimentally for sub-zero temperatures. For this purpose, fatigue test results of SAW and MAG welded joints for temperatures down to −50 °C are analysed and the potential for changes regarding material selection for ships and offshore structures are discussed.