Ice Loads

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Bernt J Leira - One of the best experts on this subject based on the ideXlab platform.

  • probabilistic methods for estimation of the extreme value statistics of ship Ice Loads
    Cold Regions Science and Technology, 2018
    Co-Authors: Wei Chai, Bernt J Leira, Arvid Naess
    Abstract:

    Abstract It is well known that when a ship sails in Ice-covered regions, the ship-Ice interaction process is complex and the associated Ice Loads on the hull is a stochastic process. Therefore, statistical models and methods should be applied to describe the Ice load process. The aim of this work is to present a novel method for estimating the extreme Ice Loads which is directly related to the reliability of the vessel. This method, briefly referenced to as the ACER (average conditional exceedance rate) method, can provide a reasonable extreme value prediction of the Ice Loads by efficiently utilizing the available data, which was collected by an Ice load monitoring (ILM) system. The basic idea for the ACER approach lies in the fact that a sequence of nonparametric distribution functions are constructed in order to approximate the extreme value distribution of the collected time history. The main principle of the ACER method is presented in detail. Furthermore, the methods based on the classic extreme value theory are also introduced in order to provide a benchmark study.

  • short term extreme Ice Loads prediction and fatigue damage evaluation for an Icebreaker
    Ships and Offshore Structures, 2018
    Co-Authors: Wei Chai, Bernt J Leira, Arvid Naess
    Abstract:

    ABSTRACTIn this paper, the short-term extreme value statistics of the Ice Loads acting on ship hull and the fatigue damage due to Ice Loads actions are studied. Due to the stochastic nature of the Ice-induced Loads and randomness of the Ice thickness, probabilistic methods and models are applied in order to find some correlations between the Ice-induced Loads statistics and the prevailing Ice conditions. For the extreme value prediction, the average conditional exceedance rate method is applied to approximate the exact extreme value distribution. The short-term fatigue damage is estimated based on the S–N curve approach. Furthermore, probabilistic models, such as the Weibull distribution and the three-parameter exponential distribution are applied to approximate the distribution of the stress ranges due to Ice Loads actions and the performance of the fatigue damage evaluation based on probabilistic distribution functions of the stress ranges is studied.

  • a response comparison of a stiffened panel subjected to rule based and measured Ice Loads
    ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014
    Co-Authors: Boris Erceg, Rocky Taylor, Soren Ehlers, Bernt J Leira
    Abstract:

    Ships operating in Ice-covered waters are exposed to intense Loads from Ice features. Thus, their structures have to be designed to resist these Ice Loads. To achieve compliance with classification societies’ rules, analysis of these Ice Loads is achieved through the introduction of a uniform pressure patch applied to the hull surface. This uniform pressure approach does not account for the high degree of spatial and temporal variations observed in Ice load measurements, which are inherent to the Ice failure process. Thus, this paper will compare the response of a stiffened panel to Ice loading by applying a rule-based uniform pressure patch as well as instantaneous non-uniform pressures based on measured spatial distributions of Loads from field tests in order to investigate the effect of spatially localized Loads due to high pressure zones on local plastic deformation of the hull.Copyright © 2014 by ASME

  • short term extreme statistics of local Ice Loads on ship hulls
    Cold Regions Science and Technology, 2012
    Co-Authors: Abdillah Suyuthi, Bernt J Leira, Kaj Riska
    Abstract:

    Abstract This paper focuses on prediction of short term extreme values of local Ice Loads on ship hulls. The analysis is based on the exact classical method, which utilizes the selected statistical models as its initial distribution. A conventional approach, where the number of events is considered as a fixed value, i.e. equal to the expected number of events for a given duration, is employed. An alternative approach, which accommodates the number of Ice load peak events as a random variable, is also investigated. An asymptotic approach, which is based on the one-minute maxima, is also investigated. When compared with the other two methods, the asymptotic approach tends to give similar level of extreme values.

  • Variation of the Short Term Extreme Ice Loads Along a Ship Hull
    29th International Conference on Ocean Offshore and Arctic Engineering: Volume 4, 2010
    Co-Authors: Abdillah Suyuthi, Bernt J Leira, Kaj Riska
    Abstract:

    This paper focuses on the short term probabilistic analysis of Ice Loads acting on a ship hull. The Ice load data was obtained from full scale measurement onboard the Norwegian coast guard vessel KV Svalbard during the winter of 2007. The available data corresponds to discrete peak amplitude time histories of estimated Ice impact Loads as well as corresponding measurements of Ice thickness in addition to ship speed and course. There were several number of sensors installed along the hull, either on the port side and starboard side of the bow part. The present paper focuses on the variation of the predicted extreme Ice Loads acting on the ship hull for a short time duration. The short term prediction of Ice Loads as an integral part of an Ice Loads Monitoring (ILM) system is very important in relation to the tactical navigation plan. An inexpensive ILM system would requires less number of sensors mounted on the hull. By addressing the variation of the extremes along the hull, it will be possible to make decisions regarding the minimum number of sensors and their location without loosing the accuracy of the predicted extremes. Three different approaches for predicting the short term extremes are considered, i.e. the classical extreme value distribution approach, the time window approach, and the up-crossing rate approach. In general, all the approaches involve the following two steps: (i) establishment of the estimated distribution model, (ii) calculation of the expected largest extreme Ice impact load for an extrapolated duration. Comparison of the results obtained by the three different approaches is made, and some limitations of the various approaches are discussed.Copyright © 2010 by ASME

Kaj Riska - One of the best experts on this subject based on the ideXlab platform.

  • numerical modeling of Ice Loads on an Icebreaking tanker comparing simulations with model tests
    Cold Regions Science and Technology, 2013
    Co-Authors: Li Zhou, Kaj Riska, Torgeir Moan, Biao Su
    Abstract:

    Abstract A numerical model is presented to simulate the dynamic Ice Loads acting on an Icebreaking tanker in level Ice, considering the action of Ice in the vicinity of the waterline caused by breaking of intact Ice and the effect of submersion of broken Ice floes. The numerical simulations are also compared with Ice tank tests. For these tests, Ice rubble accumulation contributes to a high Ice load and thus was taken into consideration in the simulations in addition to the Ice-breaking forces. In the simulations, an Icebreaking tanker fixed by artificial high stiffness mooring lines was towed through an intact Ice sheet. The setup of the numerical simulation was as similar to the Ice tank setup as possible. The Ice Loads were compared between model tests and simulations by varying the Ice drift speed, the relative Ice drift angles and Ice properties. The results show that the simulated Ice Loads are in good agreement with the experimental results in terms of the mean values, standard deviations, and maximum and extreme force distributions, although there are some deviations between the predicted and measured results for certain cases. Some of the possible reasons that may explain the differences have been presented. The numerical model can be applied to predict the Ice Loads on moored or dynamic structures with station-keeping operations in level Ice with a constant drift direction, and it can be extended to variable relative Ice drift directions.

  • short term extreme statistics of local Ice Loads on ship hulls
    Cold Regions Science and Technology, 2012
    Co-Authors: Abdillah Suyuthi, Bernt J Leira, Kaj Riska
    Abstract:

    Abstract This paper focuses on prediction of short term extreme values of local Ice Loads on ship hulls. The analysis is based on the exact classical method, which utilizes the selected statistical models as its initial distribution. A conventional approach, where the number of events is considered as a fixed value, i.e. equal to the expected number of events for a given duration, is employed. An alternative approach, which accommodates the number of Ice load peak events as a random variable, is also investigated. An asymptotic approach, which is based on the one-minute maxima, is also investigated. When compared with the other two methods, the asymptotic approach tends to give similar level of extreme values.

  • numerical simulation of local Ice Loads in uniform and randomly varying Ice conditions
    Cold Regions Science and Technology, 2011
    Co-Authors: Biao Su, Kaj Riska, Torgeir Moan
    Abstract:

    Abstract The Ice loading process has a clear stochastic nature due to variations in the Ice conditions and in the Icebreaking processes of ships. The statistical characteristics of local Ice Loads are typically studied on the basis of field measurements. In this paper, a numerical method was applied to simulate a ship moving forward in either uniform or randomly varying Ice conditions, where the thickness and strength properties of the Ice encountered by the ship were assumed to be constant or randomly generated using the Monte Carlo method. The purpose of this simulation is to show the origin of the statistical variation in Ice loading, which is difficult to identify in field measurements. To validate the numerical results, an Icebreaking tanker, MT Uikku, was then modeled in a simulation program, the Ice loading process was stochastically reproduced and the calculated amplitude values of the Ice-induced frame Loads were compared with the field measurements.

  • Variation of the Short Term Extreme Ice Loads Along a Ship Hull
    29th International Conference on Ocean Offshore and Arctic Engineering: Volume 4, 2010
    Co-Authors: Abdillah Suyuthi, Bernt J Leira, Kaj Riska
    Abstract:

    This paper focuses on the short term probabilistic analysis of Ice Loads acting on a ship hull. The Ice load data was obtained from full scale measurement onboard the Norwegian coast guard vessel KV Svalbard during the winter of 2007. The available data corresponds to discrete peak amplitude time histories of estimated Ice impact Loads as well as corresponding measurements of Ice thickness in addition to ship speed and course. There were several number of sensors installed along the hull, either on the port side and starboard side of the bow part. The present paper focuses on the variation of the predicted extreme Ice Loads acting on the ship hull for a short time duration. The short term prediction of Ice Loads as an integral part of an Ice Loads Monitoring (ILM) system is very important in relation to the tactical navigation plan. An inexpensive ILM system would requires less number of sensors mounted on the hull. By addressing the variation of the extremes along the hull, it will be possible to make decisions regarding the minimum number of sensors and their location without loosing the accuracy of the predicted extremes. Three different approaches for predicting the short term extremes are considered, i.e. the classical extreme value distribution approach, the time window approach, and the up-crossing rate approach. In general, all the approaches involve the following two steps: (i) establishment of the estimated distribution model, (ii) calculation of the expected largest extreme Ice impact load for an extrapolated duration. Comparison of the results obtained by the three different approaches is made, and some limitations of the various approaches are discussed.Copyright © 2010 by ASME

  • the role of discrete failures in local Ice Loads
    Cold Regions Science and Technology, 1998
    Co-Authors: Claude Daley, Jukka Tuhkuri, Kaj Riska
    Abstract:

    Abstract A conceptual model of Ice failure is proposed. The model describes Ice failure as a nested hierarchy of discrete failure events. In this model, each failure event changes the geometry of the problem, and thus, sets one of the important initial conditions of the next failure event. The Ice load, along with other results of the Icestructure interaction, depends on how the sequence of failure events progresses. It is argued that the best method of understanding Ice Loads is to treat Ice failure as a process of discrete failure events. The literature on discrete failure events in Ice is reviewed. The experimental background and specific solutions using discrete failure processes are described. Specific attention is given to those local failure processes that take place at an Ice–structure interface. The mechanics of pulverisation, showing possible alternative discrete mechanisms are presented. Finally, an event tree for local Ice failure is given.

K. R. Croasdale - One of the best experts on this subject based on the ideXlab platform.

  • Limit Force Ice Loads – An Update
    2020
    Co-Authors: K. R. Croasdale
    Abstract:

    Ice feature creating the Ice load. This condition is known as the “Limit Force” Ice load, and it is an important check in looking at Ice interaction scenarios, especially interaction by thick features for which there may not be enough driving force for the full “Limit Stress” condition to apply. Limit Force Ice Loads are an important aspect of probabilistic modeling of Ice Loads because not all interactions have sufficient driving force for the larger Limit Stress Ice load to develop. For relatively small, thick Ice features, the most important driving force is that imposed from the surrounding pack Ice. This component is more significant than the wind and current which also may contribute. Pack Ice driving forces are limited by ridge-building and Ice rubbling in the thinner Ice. Values for pack Ice driving forces to be used in Limit Force calculations come from a range of sources. These include in-situ pressure sensors in floes in the pack Ice; measurements on platforms when Ice rubbling is occurring or when a floe is stopped in front of it; mathematical models and model tests. Recent work has reviewed all available data and created a new relationship for pack Ice driving forces as a function of Ice thickness, and Ice feature width. The results of this work are included in the emerging ISO 19906 code for Arctic Offshore Structures. This paper describes this recent review and the new relationship developed. Examples of use of the Limit Force approach are given.

  • sea Ice Loads due to managed Ice
    Proceedings of the International Conference on Port and Ocean Engineering Under Arctic Conditions, 2009
    Co-Authors: K. R. Croasdale, J R Bruce, Pavel Liferov
    Abstract:

    Managed Ice is the term given to Ice that has been broken ahead of a platform or anchored vessel in order to reduce the Ice Loads or other effects of Ice interaction such as rubble build up. Ice features which would create Loads greater than the mooring Loads of the stationary platform or vessel are broken into small pieces to reduce the Ice Loads. This is usually done with several Icebreakers; one or more breaking Ice in the far field and one or more breaking Ice in the near field. Although there is some experience on how much management is required to reduce mooring Loads, the present methods for managed Ice Loads rely on expert judgment and are empirical. In this paper, simple concepts for managed Ice Loads have been developed and quantified. Ice load concepts and equations are presented based on piece size of the managed Ice, Ice and rubble thickness, and whether there is any Ice pressure in the Ice field. These concepts can be used to specify piece sizes to be achieved and operational tactics in various Ice management scenarios for a given floating platform and mooring system. Comparisons are made with the Kulluk experience and Loads in the Canadian Beaufort Sea in order to help verify the equations and calibrate the inputs.

  • limit force Ice Loads an update
    Proceedings of the International Conference on Port and Ocean Engineering Under Arctic Conditions, 2009
    Co-Authors: K. R. Croasdale
    Abstract:

    Ice feature creating the Ice load. This condition is known as the “Limit Force” Ice load, and it is an important check in looking at Ice interaction scenarios, especially interaction by thick features for which there may not be enough driving force for the full “Limit Stress” condition to apply. Limit Force Ice Loads are an important aspect of probabilistic modeling of Ice Loads because not all interactions have sufficient driving force for the larger Limit Stress Ice load to develop. For relatively small, thick Ice features, the most important driving force is that imposed from the surrounding pack Ice. This component is more significant than the wind and current which also may contribute. Pack Ice driving forces are limited by ridge-building and Ice rubbling in the thinner Ice. Values for pack Ice driving forces to be used in Limit Force calculations come from a range of sources. These include in-situ pressure sensors in floes in the pack Ice; measurements on platforms when Ice rubbling is occurring or when a floe is stopped in front of it; mathematical models and model tests. Recent work has reviewed all available data and created a new relationship for pack Ice driving forces as a function of Ice thickness, and Ice feature width. The results of this work are included in the emerging ISO 19906 code for Arctic Offshore Structures. This paper describes this recent review and the new relationship developed. Examples of use of the Limit Force approach are given.

  • How well can we predict Ice Loads?
    IAHR, 2006
    Co-Authors: Gw Timco, K. R. Croasdale
    Abstract:

    use as a reference to the widespread consensus on Ice load modelling

  • Ice Loads consensus study update
    1996
    Co-Authors: K. R. Croasdale, K.p. Kennedy
    Abstract:

    Current North American design codes have been written with enough flexibility to allow several methods to be used to derive global design Ice Loads. For example, derived Loads will vary according to whether the methodology is based on small-scale laboratory tests or large-scale measurements. This issue is further complicated when Russian design codes, which are generally more explicit but more conservative than their Western counterparts, are brought into the picture. A Joint Industry-Government Project is underway in Canada aimed at better understanding the differences in global design Ice load predictions on arctic offshore structures, with the ultimate goal of reaching an international consensus on the subject. The background behind the project, the methodology employed, and the status as of March 1, 1996 are presented.

Mark Fuglem - One of the best experts on this subject based on the ideXlab platform.

  • methodology to evaluate sea Ice Loads for seasonal operations
    ASME 2015 34th International Conference on Ocean Offshore and Arctic Engineering, 2015
    Co-Authors: Jan Thijssen, Mark Fuglem
    Abstract:

    Offshore structures designed for operation in regions where sea Ice is present will include a sea Ice load component in their environmental loading assessment. Typically Ice Loads of interest are for 10−2, 10−3 or 10−4 annual probability of exceedance (APE) levels, with appropriate factoring to the required safety level.The ISO 19906 standard recommends methods to determine global sea Ice Loads on vertical structures, where crushing is the predominant failure mode. Fitted coefficients are proposed for both Arctic and Sub-Arctic (e.g. Baltic) conditions. With the extreme Ice thickness expected at the site of interest, an annual global sea Ice load can be derived deterministically. Although the simplicity of the proposed relation provides quick design load estimates, it lacks accuracy because the only dependencies are structure width, Ice thickness and provided coefficients; no consideration is given to site-specific sea Ice conditions and the corresponding exposure. Additionally, no term is provided for including Ice management in the design load basis.This paper presents a probabilistic methodology to modify the deterministic ISO 19906 relations for determining global and local first-year sea Ice Loads on vertical structures. The presented methodology is based on the same Ice pressure data as presented in ISO 19906, but accounts better for the influence of Ice exposure, Ice management and site-specific sea Ice data. This is especially beneficial for Ice load analyses of seasonal operations where exposure to sea Ice is limited, and only thinner Ice is encountered. Sea Ice chart data can provide site-specific model inputs such as Ice thickness estimates and partial concentrations, from which corresponding global load exceedance curves are generated. Example scenarios show dependencies of design Loads on season length, structural geometry and sea Ice conditions. Example results are also provided, showing dependency of design Loads on the number of operation days after freeze-up, providing useful information for extending the drilling season of MODUs after freeze-up occurs.Copyright © 2015 by ASME

  • implementation of iso 19906 for probabilistic assessment of global sea Ice Loads on offshore structures encountering first year sea Ice
    OCEANS Conference, 2014
    Co-Authors: Jan Thijssen, Mark Fuglem, Martin Richard, Tony King
    Abstract:

    Ice failure during Ice-structure interactions is a complex process and the development and improvement of Ice load models is challenging, in large part because of difficulties obtaining full-scale data and scaling issues when extrapolating from model test data. The ISO 19906 standard provides guidance for the calculation of design Ice Loads on offshore structures in Arctic and subarctic regions. This paper examines issues in implementing available formulae for probabilistically determining design Ice Loads from first-year Ice on sloping and vertically-faced offshore structures. Methodologies suggested in ISO 19906 are applied to simulate structure interactions with Ice floes and embedded Ice ridges in subarctic regions, such as the Northern Caspian Sea and Baltic Sea where no multi-year Ice is anticipated to contribute to design Loads. In these regions design Ice Loads are determined by first-year Ice, which is less severe than the Ice Loads that result from multi-year Ice features in Arctic regions. When compared multi-year Ice features, lower Ice strength coefficients are appropriate for both first-year level Ice and first-year ridges. Structure interactions with first-year ridges are modeled differently than with multi-year ridges. The keels of first-year ridges are not yet consolidated, so that a different model approach is required for keel failure than for the failure of fully consolidated multi-year ridges. Challenges in defining the required input data for the appropriate ISO 19906 formulae are discussed in this paper. Sensitivity analyses performed using the Sea Ice Loads Software (SILS), a Monte-Carlo type simulator developed by C-CORE for determining first and multi-year sea Ice Loads using probabilistic methods are also presented and discussed. Suggested ISO 19906 models of potential failure modes are implemented in SILS for first-year level Ice and ridge interactions with different structure types. The sensitivity analyses compare design Ice Loads from Ice impacts with different structures and for different Ice loading scenarios, illustrating the influence of different model assumptions on calculated design Loads.

Tianyu Wu - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue Damage Evaluation of Pile-Supported Bridges under Stochastic Ice Loads
    Advances in Civil Engineering, 2020
    Co-Authors: Tianyu Wu, Guangrun Wu
    Abstract:

    The Bohai Sea is the sea area with the worst Ice condition in China, and the Ice Loads significantly threaten the safety of structures in the sea. The intense vibrations of the pile-supported bridge under stochastic Ice Loads will increase the fatigue damage of a bridge structure and reduce the fatigue life of a bridge structure. In the present study, a comprehensive analysis model is presented to study fatigue damage for pile-supported bridges under Ice Loads in Bohai Sea. On the basis of measured statistical data of Ice parameters and stochastic Ice Loads spectrum of Bohai Sea, the time histories of the stochastic Ice Loads of Bohai Sea are simulated. Fatigue damage analysis is carried out in time domain utilizing the finite element method considering soil and bridge structure interaction. The effect of soil conditions and water depth on the cumulative fatigue damage of the pile-supported bridges is studied. Numerical results indicate that in comparison with stiff soil conditions, pile-supported bridges in soft oil conditions can increase the cumulative fatigue damage substantially; pile-supported bridges in deep water also can increase the cumulative fatigue damage obviously. The study presented the first danger position of cumulative damage of the pile cross section under stochastic Ice Loads. The findings of this study can be used to fatigue damage evaluation and bridge construction in the Ice-covered sea area.

  • dynamic analyses of pile supported bridges including soil structure interaction under stochastic Ice Loads
    Soil Dynamics and Earthquake Engineering, 2020
    Co-Authors: Tianyu Wu
    Abstract:

    Abstract The Gulf of Bohai has a huge area of floating Ice in winter each year, and when seawater freezes, significant uncertainties are introduced in the offshore structural design. In this study, a complete bridge analysis model is proposed to investigate the dynamic responses of offshore bridges in the Bohai Sea subjected to stochastic Ice Loads by floating sea Ice. Based on a real stochastic Ice load spectrum, a simulation methodology to generate the stochastic Ice load process is proposed. The soil resistance is modelled utilising the American Petroleum Institute-based cyclic p-y, t-z, and Q-z springs. A dynamic analysis is conducted in the time domain utilising the finite element method and considering stochastic Ice Loads. The influences of undrained soil strength and water depth on the dynamic behaviours of the bridge are systematically investigated. The results show that the dynamic responses of bridges in deep water are much larger than those in shallow water, and the soil–structure interaction (SSI) can substantially affect the structural vibrations. The result from the method can also be used to identify the most critical condition for bridge design under Ice Loads.