Development of a Probabilistic Ice Load Model Based on Empirical Descriptions of High Pressure Zone Attributes

During an ice-structure interaction, the localization of contact into high pressure zones (hpzs) has important implications for the manner in which loads are transmitted to the structure. In a companion paper, new methods for extracting empirical descriptions of the attributes of individual hpzs from tactile sensor field data for thin first-year sea ice have been presented. In the present paper these new empirical hpz relationships have been incorporated into a probabilistic ice load model, which has been used to simulate ice loads during level ice interactions with a rigid structure. Additional aspects of the ice failure process, such as relationships between individual hpzs and the spatial-temporal distribution of hpzs during an interaction have also been explored. Preliminary results from the empirical hpz ice load model have been compared with existing empirical models and are discussed in the context of both local and global loads acting on offshore structures.

Promoting Safety and Managing Risks in Arctic Marine Transportation: A Best Practices Approach and the Polar Code

Currently there are no mandatory, internationally accepted rules written specifically to govern ship operations in Arctic waters. The Arctic is recognized by the IMO Guidelines for Ships Operating in Polar Waters as a significant area for international shipping that requires special attention to crew training and operational procedures. A legally binding Polar Code which should identify and unify the commonalities of what it takes, and what is currently enforced by flag states, to safely operate in all Arctic nation waters, is viewed by many as a sensible way forward. This paper presents a synopsis of the results of a funded research project that aimed to identify best practices currently in place by Arctic ship operators. It also aimed to identify possible new ways in which shipping operations in the Arctic could maximize benefits and reduce risks to all stakeholders. A review of the scientific literature clearly highlighted the chasms of knowledge regarding the impacts of marine related activity in Arctic waters. With respect to a methodological approach, a website search was conducted to look for shipping companies informing that they were involved in Arctic operations. The website search of Arctic shipping companies helped with the creation of a questionnaire aimed at identifying “best practices” currently in place with Arctic shipping operators. The questionnaire was administered electronically. Subsequently, a number of companies, identified from the website search and representing a pan-Arctic sample of operators, were contacted by email to inquire if they were interested in taking part in the online questionnaire.

Backbone for Escape, Evacuation and Rescue From Arctic Facilities: A Systematic Approach

In turn of the global warming and driven by the constant need for resources an increasing number of commercial and scientific activities conquer the Arctic in order to benefit from almost untouched resources like oil and gas but also from the overwhelming nature. These activities are accompanied by a steadily increasing number of vessels transporting goods but also operating personnel, scientists or tourists. Especially the number of tourists visiting the Arctic can reach far more than 1000 per vessel, resulting in growing headaches for the responsible safety and security authorities in the Arctic surrounding countries. Up to now no suitable Escape, Evacuation and Rescue (EER) concept is in place to cope with these challenges when it comes to hazardous situations. In this context IMPaC ([1]) developed a new and appropriate EER concept for the Arctic, exceeding the currently dominant small and isolated settlements along the coastlines in Denmark (Greenland), Norway, Russia, Canada and the US. One question seems to be central: Is there any requirement and benefit beyond the currently used small rescue station? Yes, we strongly believe that there is a growing demand for suitable infrastructure coming from various industries. Beyond rescue objectives there is a demand for people working and living in this area all year long, for a few days, weeks or months using these settlements for their specific needs. This led us to the idea of the provision of a common-use infrastructure for multiple industries. The commonly used infrastructure maximizes the use of the remote and very expensive infrastructure and minimizes the impact on the environment in this part of the world. Potential users of this infrastructure would be: • Oil & Gas Industry, driven by the increased world energy demand • Marine Transport & Tourism Industry, driven by declined arctic ice and new sea routes via the Arctic sea • Fishery Industry • Scientific community Any EER concept for the Arctic has to cope with several specific environmental and spatial challenges as addressed by the EU joint research project ACCESS ([2]), where IMPaC participates. The paper introduces the new EER concept and focuses especially on its beneficial, efficient and safe operability in the Arctic recording an increasing number of commercial and scientific activities.

Mechanics of Dynamic Ice Failure Against Vertical Structures

Ice interaction with vertical faces of structures can result in regular vibrations given certain conditions such as temperature and speed of interaction. The mechanism that can provide this regular behaviour is studied. Fracture in general does not offer a solution in compressive failure. An approach based on viscoelastic theory, with softening resulting from microstructural change, is given. The pivotal observation was a layer of microstructurally modified ice adjacent to the structure or indentor, together with high local pressures transmitted into the layer. The microstructural changes include microfracturing and recrystallization. A series of triaxial tests was performed to determine the inputs into the viscoelastic theory. The theory recognizes changes in the microstructure of the ice by means of a state variable, which is a function of prior stress history, and therefore of location within the ice mass. The theory and the calibration thereof are reviewed, and the results of triaxial tests examined. One feature of these tests is the occurrence of “runaway” strains and associated localization of damage. This appears to be sensitive to confining pressure, and is considered to be a key factor in the rapid load drops observed in ice-structure interaction. Temperature effects are also studied. Directions for future research are identified.

Study of the Volumetric Behaviour of Ice Rubble Based on Bi-Axial Compression Data

Rubble ice in unconsolidated part of ice ridges or rubble fields for some engineering applications can be considered as a granular material. The common practice is to assume that the ice rubble obeys Mohr-Coulomb failure criterion which requires cohesion and internal friction angle as material parameters (see e.g. [1]). In order to obtain friction angle of ice rubble in small scale a bi-axial compression apparatus was proposed by Timco et al. [2]. Later, analyzing test results obtained from this apparatus Timco and Cornett [3] made a rather surprising conclusion that the ice rubble angle of friction is not a constant but has different values for different ratios of strains applied to the sample. This paper gives an overview of biaxial compression data available in the literature. It also shows that if volumetric behavior is included (which is not the case for Mohr-Coulomb criterion) then tests performed on the same types of ice rubble gives the same constant describing shearing resistance independent of applied boundary conditions.

Study on the Ship Ice Resistance Estimation Using Empirical Formulas

The ice resistance estimation technique for icebreaking ships has been studied intensively over recent years to meet the need of arctic vessel design. Before testing in the ice model basin, the estimation of ship ice resistance with high reliability is very important to decide the delivered power necessary for level ice operation. The main idea of this study came from several empirical formulas by B.P. Ionov[1], E. Enkvist[2] and J.A. Shimanskii[3], in which ice resistance components such as icebreaking, buoyancy and clearing resistances were represented by the integral equations along the DLWL (Design Load Water Line). However, this study proposes modified methods considering the DLWL shape as well as the hull shape under the DLWL. In the proposed methodology, the DLWL shape for icebreaking resistance and the hull shape under the DLWL for buoyancy and clearing resistances are included in the calculation. Especially when calculating clearing resistance, the flow pattern of ice particles under the DLWL of ship is assumed to be in accordance with the ice flow observed from ice model testing. This paper also deals with application examples for a ship design and its ice model test results at the Aker arctic ice model basin. From the comparison of results from the model test and the estimation, the reliability of this estimation technique is discussed.

Theoretical Investigation on Ice Resistance Prediction Methods for Ships in Level Ice

The assessment of the ship performance in ice covered waters has become more and more important in view of the increased interest in Arctic field logistics and transportation. The performance of ice-going or ice breaking ships is usually defined by their ability to proceed in uniform level ice, where good performance means low ice resistance, high propulsion efficiency and continuous ice breaking. In order to assess the ice breaking performance in an early design stage, model tests may be executed or several theoretical methods may be applied to predict the ice resistance may be applied. Due to the physical nature of model tests, all processes, i.e. forces contributing to ice resistance are considered. Thus, the execution of model tests is still the most reliable method to determine the ice resistance. But with regard to the high costs of model tests there is continued demand to gain knowledge on the reliability of theoretical prediction methods. The applicability of the method of choice depends on the underlying assumptions of the method itself and thus the method’s capability to predict and consider physical phenomena of interest. In this paper model tests are used to evaluate the influence of hull shape parameters and ice conditions on the breaking process, i.e. the ice resistance and the ship performance. Based on the knowledge gained a systematic comparison of existing, representative ice resistance prediction methods is carried out. The methods considered are state-of-the-art techniques which the original publications introduced with sufficient information to allow for their use in this comparison. It focuses on the suitability of the existing methods as engineering tools for the prediction of different components, as well as the total ice resistance itself. The incorporation of the ice resistance contributions in the different prediction methods is presented and differences are identified. On this basis an assessment of the assumptions and simplifications of these different numerical methods is outlined.

Analysis of the Fatigue Life of Offshore Wind Turbine Generators Under Combined Ice- and Aerodynamic Loading

A modelled wind turbine generator subjected to combined ice- and aerodynamic loading is analyzed with the focus on its fatigue lifetime. A comparison is made between the prediction of a combined analysis, taking both ice- and wind loads into account simultaneously, and a superposition analysis, computing the response of the structure as a result of ice and wind loading separately. The accumulated fatigue damage is computed considering different descriptions of the ice load. Prescribed ice load curves from current design standards, as well as phenomenological models for the prediction of dynamic ice-structure interaction are employed. Results show that the superposition method underpredicts the accumulated fatigue damage in the range of frequency lock-in, but only when phenomenological models, which are more advanced than those recommended by the design standards, are used to model the ice load. Furthermore the predicted fatigue damage computed using the design standards for the description of the ice load is found to be much larger than that resulting from the application of the phenomenological models. It is concluded that the combined analysis is desired when phenomenological models are applied. Furthermore, improvement of the predictive capabilities of such models might ultimately lead to a reduction of the predicted fatigue damage accumulation of the combined ice- and aerodynamic load case, as compared to the current prescribed methods in standards.