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Ice Management in Arctic Offshore Operations and Field Developments
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Civil and Transport Engineering.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject ice management has been studied with the main objective to deduce a methodology that incorporates the effect of ice management on the structural reliability of offshore installations. This was done by first studying Arctic projects in the past and summarizes the learning’s. All available reports were unanimous and highlighted ice management as a key for the successes in the projects. Based on the reported experiences, an unambiguous definition of ice management was made:

“Ice management is the sum of all activities where the objective is to reduce or avoid actions from any kind of ice features”

Despite the number of similarities between sea ice management and iceberg management, it was decided to study each of the fields individually. The motivation for doing so was that iceberg management in general focus on reducing the frequency of impacts between icebergs and installations while sea ice management generally focus on reducing the sizes in the ice floe distributions and thereby reduces the severity of the ice actions. One methodology for including iceberg management and one for including sea ice management in the offshore installation design process has been proposed.

In order to develop the models for ice management efficiency a number of studies of the various elements were conducted. Individual papers regarding subsurface ice intelligence, iceberg drift modelling, iceberg deterioration, iceberg deflection in ice and ice load variability has been published and are included in this thesis. Each of these papers is of importance for the proposed models for ice management efficiency.

The possibility to disconnect an installation and escape the site has been considered both in the methodologies for iceberg management and sea ice management. When considering the number and magnitude of uncertainties both with respect to load calculations from icebergs and sea ice, it is concluded that disconnection capabilities should be considered in all Arctic projects. It was shown that icebreakers not necessarily are sufficient to reduce extreme or abnormal loads on a structure. However, there may still be a number of reasons for why icebreakers also should be considered in Arctic projects.

The methodologies presented in this work provide adequate tools for evaluating the effect of various icebreaker fleets and iceberg management systems. However, the approaches rely on a number of tools and formulations with inherent weaknesses and advantages. The weaknesses are discussed and recommendations for further work in order to improve the models have been proposed.

Place, publisher, year, edition, pages
NTNU, 2010.
Series
Doctoral theses at NTNU, ISSN 1503-8181 ; 2010:210
Identifiers
URN: urn:nbn:no:ntnu:diva-12214ISBN: 978-82-471-2402-4 (printed ver.)ISBN: 978-82-471-2403-1 (electronic ver.)OAI: oai:DiVA.org:ntnu-12214DiVA: diva2:403006
Available from: 2011-03-10 Created: 2011-03-10 Last updated: 2011-04-13Bibliographically approved
List of papers
1. Review of Experiences within Ice and Iceberg Management
Open this publication in new window or tab >>Review of Experiences within Ice and Iceberg Management
2008 (English)In: Journal of navigation (Print), ISSN 0373-4633, E-ISSN 1469-7785, Vol. 61, no 4, 557-572 p.Article, review/survey (Refereed) Published
Abstract [en]

A review of existing knowledge regarding how to manage ice during offshore work in cold waters has been carried out. The objective has been to contribute to increased safety and efficiency in future projects by learning from world-wide experiences. It was found that offshore drilling has been carried out in a wide range of ice conditions and at water depths spanning from five metres to more than a thousand metres. Icebergs in open waters have been handled safely over several years and the possibility of detecting icebergs is considered good. With respect to icebergs frozen in sea ice, both detection and deflection is considered difficult and the technology for doing so is not proven. Good ice management systems are considered to represent the main factors for operating successfully in the covered waters. Future work should focus on how to include the effect of ice management statistically in a design process.

Keyword
Ice management, Ice detection, Risk evaluation, Operability
Identifiers
urn:nbn:no:ntnu:diva-12201 (URN)10.1017/S0373463308004839 (DOI)000260660800001 ()
Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
2. Specifications for a Subsurface Ice Intelligence System
Open this publication in new window or tab >>Specifications for a Subsurface Ice Intelligence System
2009 (English)In: Proceedings of the ASME 28th International Conference on Ocean, Offshore and Arctic Engineering / [ed] Ertekin, R. Cengiz, Riggs, H. Ronald, ASME Press , 2009Conference paper (Refereed)
Place, publisher, year, edition, pages
ASME Press, 2009
Identifiers
urn:nbn:no:ntnu:diva-12202 (URN)
Conference
OMAE2009
Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
3. Iceberg drift modelling and validation of applied metocean hindcast data
Open this publication in new window or tab >>Iceberg drift modelling and validation of applied metocean hindcast data
2009 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, Vol. 57, no 2-3, 67-90 p.Article in journal (Refereed) Published
Abstract [en]

An iceberg drift model covering the Barents and Kara Seas has been developed. The skills of the model relies both on the ability to describe physical actions from the environment on the icebergs and the accuracy of the applied metocean variables (wind, waves and currents). Experiences from the East Coast of Canada show that iceberg modelling may work reasonably well and indicate that iceberg drift models are able to fulfil both of the above mentioned requirements. By applying similar models in other regions, it may be assumed that wind, waves and currents affect the iceberg in a similar way as at the East Coast of Canada. However, the reliability of available metocean data sources will vary significantly from region to region. Due to this, a study with the objective to evaluate the quality of the underlying metocean models has been performed. A significant amount of recorded wind, wave and current data from various regions in the Barents Sea have been applied in comparisons with hindcast data from selected atmospheric and oceanographic models. Results show that the quality of wind and wave data applied by the iceberg drift model is very good. Regarding current velocity, there is a poor match between data from the applied oceanographic model and measurements. A method for improving the current magnitude has been introduced. The relative importance of winds, waves and currents on iceberg drift has also been investigated. In general, currents are most important for iceberg drift. However, in open waters, the wave drift may become the most important forcing. The presented iceberg drift model is considered to provide good results in situations with strong winds (and waves) and low currents while situations with low winds will give less reliable results. It is concluded that the quality of incorporated metocean data in any iceberg drift model need to be documented in order to fully understand possible limitations in iceberg drift simulations. Further work should focus on improvements in oceanographic modelling in order to establish a more reliable oceanographic hindcast for the Barents Sea. (C) 2009 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
Iceberg drift, Hindcast validation, Barents Sea
Identifiers
urn:nbn:no:ntnu:diva-12200 (URN)10.1016/j.coldregions.2009.02.009 (DOI)000267153300002 ()
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
4. Wave Drift Force on Icebergs - Tank Model Tests
Open this publication in new window or tab >>Wave Drift Force on Icebergs - Tank Model Tests
2009 (English)In: Proceedings - International Conference on Port and Ocean Engineering under Arctic Conditions, 2009Conference paper (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12203 (URN)
Conference
POAC09
Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
5. Iceberg Deterioration in the Barents Sea
Open this publication in new window or tab >>Iceberg Deterioration in the Barents Sea
2009 (English)In: Proceedings - International Conference on Port and Ocean Engineering under Arctic Conditions, 2009Conference paper (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12204 (URN)
Conference
POAC09
Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-04-13Bibliographically approved
6. Model tests of iceberg towing
Open this publication in new window or tab >>Model tests of iceberg towing
2010 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, Vol. 61, no 1, 13-28 p.Article in journal (Refereed) Published
Abstract [en]

Icebergs may cause a threat to offshore installations, vessels and operations in a number of Arctic regions. In order to increase the understanding of what happens when an iceberg tow is started in ice covered waters; physical tank model tests have been carried out in various concentrations of sea ice. The objectives with these tests have been to evaluate the practical arrangements for iceberg towing and to collect data regarding tow loads and iceberg behaviour during the tow. The tank model tests were carried out in scale 1:40 in the ice tank at Hamburg Ship Model Basin (HSVA), Germany. Two different iceberg models were used and each towed in four different ice concentrations. From all tests, tow line forces, iceberg displacements and rotations were recorded. It was concluded that towing in 50% ice concentrations and higher were not realistic due to high resistance. During the tows in high concentrations, ice was breaking in flexural mode, crushing, rafting and ridging continuously in front of the iceberg models. With respect to the tow line, the line was fully extended and lifted up from the water/ice. In real operations this may increase the risk for tow line rupture and subsequent "snapping". In 50% ice concentration, total loads in the tow line will most of the time be lower than maximum bollard pull for powerful diesel electric icebreakers indicating that towing up to this concentration may be feasible. However, tow lines will have to resist even the highest peak loads during a tow and it is unclear whether sufficiently strong tow lines can be produced. With respect to tows in 20% concentration and open water, loads are significantly lower indicating that towing in low ice concentrations should be feasible. Measured loads seem to be reasonable well described by a log-normal distribution. The concentrations of surrounding sea ice are found to be most important for the load magnitude while variations in speed, acceleration, course and iceberg shape seem to be less important. A log-normal distribution, in which the parameters are functions of the sea ice concentration, has been fitted to recorded data. Combined with information regarding expected tow length, this distribution may be applied in order to provide crude estimate on extreme loads during an iceberg tow. By performing additional model tows in different ice conditions and with larger variations in iceberg size, this model may be further developed to be applicable in a wide range of scenarios. (C) 2009 Elsevier By. All rights reserved.

Keyword
Iceberg towing, Tank model tests, Tow line tension
Identifiers
urn:nbn:no:ntnu:diva-12199 (URN)10.1016/j.coldregions.2009.12.002 (DOI)000275586500003 ()
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
7. Iceberg management and impact on design of offshore structures
Open this publication in new window or tab >>Iceberg management and impact on design of offshore structures
2010 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, Vol. 63, no 1-2, 15-28 p.Article in journal (Refereed) Published
Abstract [en]

A methodology is presented for the systematic evaluation of the need for an iceberg management system and the efficiency of various components such as detection, deflection and disconnection. The approach involves the numerical modelling of iceberg drift and probabilistic analysis. Experiences from the Canadian iceberg detection studies and iceberg deflection operations have been incorporated into the approach. The methodology describes the concept: an offshore installation and an iceberg management system, as a traditional industrial system, i.e. a system which is designed so that it works well under normal conditions. Under some circumstances, an event occurs which stops the operation of the system. In order to prevent such a stop, different types of safety functions may be considered in order to increase the redundancy in the system and thereby increase the operability. In the present work, the iceberg management means are treated as such safety functions. For a selected site in the Barents Sea, it was found that the maximum impact load corresponding to a 10000 year event was 85 MJ for a concept without any iceberg management capabilities. An alternative system with iceberg detection, iceberg deflection and disconnection capabilities including emergency disconnect indicated a corresponding abnormal load of about 1.8 MJ. (C) 2010 Elsevier B.V. All rights reserved.

Keyword
Iceberg drift modelling, Iceberg management, Offshore installation design
Identifiers
urn:nbn:no:ntnu:diva-12198 (URN)10.1016/j.coldregions.2010.04.008 (DOI)000280023600002 ()
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-10Bibliographically approved
8. Sea-ice management and its impact on the design of offshore structures
Open this publication in new window or tab >>Sea-ice management and its impact on the design of offshore structures
2011 (English)Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2011
Identifiers
urn:nbn:no:ntnu:diva-12212 (URN)10.1016/j.coldregions.2010.10.009 (DOI)
Available from: 2011-03-10 Created: 2011-03-10 Last updated: 2011-03-10Bibliographically approved
9. Characterisation of peak loads on a moored production vessel in ice
Open this publication in new window or tab >>Characterisation of peak loads on a moored production vessel in ice
2010 (English)In: 20th IAHR International Symposium on Ice / [ed] Leppäranta, Matti, 2010Conference paper (Refereed)
Identifiers
urn:nbn:no:ntnu:diva-12215 (URN)
Conference
20th IAHR
Available from: 2011-03-10 Created: 2011-03-10 Last updated: 2011-04-13Bibliographically approved

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