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Item type:Publication, Access status: without files , Scenario-based risk management for arctic waters(American Society of Mechanical Engineers (ASME), 2022-06); ; ; ; 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 semiempirical 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).Publicationtype: Conference Paper25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A comprehensive approach to scenario-based risk management for Arctic waters(Taylor & Francis, 2022-03-22); ; ; ; 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.Publicationtype: Journal ArticleScopus© Citations 11 47 274 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Development of environmental contours for first-year ice ridge statistics(2020-11); ; ; ; Ice ridges represent a major threat to ships and offshore structures in areas with sea ice but no icebergs, since they frequently determine and govern the structural design loads. This work focuses on the development of environmental contours for first-year sea ice ridge statistics, which are able to represent the key parameters that will influence the extreme loads that would be acting on ice-capable vessels sailing in Arctic regions. Based on the inverse first order reliability method (IFORM), the development of environmental contours to be applied for the reliability-based design of ice-capable vessels in Arctic regions is elaborated. The number of relevant parameters and hence the dimension of the space containing the environmental contour will depend on the particular ice-vessel interaction model that is to be applied. Furthermore, the influence from the degree of correlation between the environmental parameters as well as from the number of ship-ice ridge interaction during the voyage on the environmental contour shapes are studied.Publicationtype: Journal Article95 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Time-variant rule-based reliability of corroded structures by Monte Carlo simulationGeneral widespread corrosion is of increasing concern for structural reliability of ageing marine structures, particularly for semi-submersible pontoons. Conditional failure rate, also termed hazard function is sought to describe the increasing maintenance required with age. Literature is reviewed connecting corrosion degradation to hazard rate, either through a time degrading limit state function, or statistical data for time to failure. Here, a rule based failure definition is applied based on corrosion tolerance levels, together with a linear corrosion degradation model to make a time variant limit state function. Monte Carlo simulation is applied based on statistical models for the basic variables including importance sampling, to obtain the time to failure distribution from which the hazard curve is deduced. A more realistic hazard function is also produced, requiring average of 3 simulations to exceed the tolerance in order to fail. It is seen that this approach delays the increase of the hazard curve, at the expense of higher failure rates.Publicationtype: Conference PaperScopus© Citations 5 335 215 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Evaluation of extreme design wave loads for hull girder strength assessmentShips may operate in extreme seas, and partial safety factors are incorporated in the corresponding structural design rules in order to ensure adequate safety levels. However, the impact of so-called freak waves on the global loads is still under intensive investigations as certain vessels may not be able to survive extreme conditions-. This applies especially for unfavorable freeboard conditions. Direct extreme design wave load measurements do not exist or are derived from measurements. Model tests in stochastic irregular seas or deterministic tailored extreme wave conditions are indispensable for a complete understanding. This paper deals with linear hydrodynamic analysis of the vertical bending moment, where a commonly applied assumption for the incoming wave angle is discussed. Model test results for a freak wave event is also conducted in order to analyze the wave—induced vertical bending moment during such an event. For comparison, long-term analyses for an LNG carrier are performed by using hindcast data for the North Sea (i.e. the Statfjord field).Publicationtype: Conference Paper190 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A comparative study of the stochastic averaging method and the path integration method for nonlinear ship roll motion in random beam seas(2018-12); ; ; In this paper, the energy-based stochastic averaging method and the path integration method are applied to study the stochastic response of the nonlinear roll motion in random beam seas. Specifically, the Markov diffusion theory is applied to describe the random roll motion such that the probabilistic properties of the ship roll motion are governed by the Fokker–Planck (FP) equation. The stochastic averaging method focuses on the roll energy envelope process and reduces the difficulty in calculating the stochastic response via a dimensional reduction of the original system. In contrast, the path integration method is based on the Markov property of the original dynamical system and provides approximate solutions to the FP equation by linking the explicitly known local solutions. Although the stochastic averaging technique is well established in the study of the stochastic responses of various dynamical systems, its accuracy for determining the high-level roll response has not yet been a focus of study. This paper aims to provide a comparative study for the performance of the two above-mentioned methods; additionally, the advantages and shortcomings of using each method for studying the nonlinear roll motion in beam seas are demonstrated by practical calculations.Publicationtype: Journal Article169 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical prediction of ship-ice interaction-a project presentation(American Society of Mechanical Engineers (ASME), 2017-06); ; ; ; It is inevitable that commercial shipping and oil and gas resource exploitation activities in the Arctic will increase due to decreasing sea ice extent caused by global climate changes. Significantly more demanding and at the same time less well known environmental conditions create a need for reliable methods to assess icebreaking performance guaranteeing safe performance of the ships operating in this area subjected to various ice conditions. The classic approach of assessing ice-going performance, which combines class rules, experience and model tests, may not be applicable for the Arctic region in full. Furthermore, ship yards experience difficulties due to decreasing time frames and financial restrictions. Therefore this paper seeks to introduce a new development for a realistic and validated direct simulation approach for prediction of the hull load and icebreaking resistance that covers all aspects of the industrial design process and allows a more comprehensive analysis. The breaking model will provide a variable breaking pattern and is able to mimic the influence of the vessel speed and the environment on the ice loading and the predicted breaking length. In order to predict the extreme representative conditions to be simulated, a reverse extreme load prediction methodology is incorporated. An efficient, time dependent dynamic coupling between broken ice fragments, ice features, the 3D flow field and the ship's hull provides resistance values for performance calculations. The computational model will be validated against full-scale data and class rules using deterministic and probabilistic measures. This simulation approach is developed within international research collaboration between Pella Sietas, Rolls Royce Marine, TUHH and NTNU. An overview of the project together with the current status of the ongoing work including first results is presented.Publicationtype: Conference Paper147 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comparative study of the path integration method and the stochastic averaging method for nonlinear roll motion in random beam seasIn this work, the path integration method and the energy-based stochastic averaging method are introduced in order to study the stochastic responses of ship roll motion in random beam seas. Based on the Markov property of the dynamical system, the path integration (PI) method provides approximate solution to the governing Fokker-Planck (FP) equation. On the other hand, the stochastic averaging method leads to a dimension reduction of the original system, but the essential behavior is retained. Then numerical solution or even analytical solution of the low-dimensional FP equation can be obtained. Since the principles of the above two stochastic methods are different, a comparative study is valuable and noticeable. The accuracy and performance of each method are evaluated with the assistance of Monte Carlo simulation (MCS).Publicationtype: Journal ArticleScopus© Citations 4 276 487 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Education of maritime doctoral students as part of international university network(2015-12); ; ; ; Aalto University, together with four other universities, has received significant funding for an international Research Centre of Excellence for Arctic Shipping and Operations from Lloyd's Register Foundation (LRF), a UK registered charity that invests in science, engineering and technology for public benefit, worldwide.. The Centre is headed by the Aalto University (Finland), in partnership with the Hamburg University of Technology (Germany), the University of Helsinki (Finland), the Norwegian University of Science and Technology (Norway) and the Memorial University of Newfoundland (Canada). The Centre will support 15 doctoral dissertations on risk in Arctic operations over a period of five years. The Centre is the first of its kind in the Nordic Countries and the only centre concentrating on Arctic challenges. The funding provided by LRF is a very significant contribution to the activities of the consortium allowing it to continue to develop global expertise in the challenging operational environment owing to the long distances involved, the large fluctuation in ice conditions, and the unpredictable behaviour of ice. The breakthrough innovations are only possible through on-going research and development, in which theoretical modelling, laboratory tests and full-scale observations are in balance, which can be achieved most efficiently by international networking. The mobility of the doctoral students has key importance for the success of the project. This paper will describe the basic principles of organizing the mobility of the doctoral students and analyse the first experiences gathered from this mobility. The network of the students and their thesis topics will be described together with main links between the studied topics so that the overall challenging targets of the research activities can be achieved.Publicationtype: Conference Paper39