Evolution of Arctic Marine Structural Forms

(OTC Paper 7461)

Presented at the 26th Annual Offshore Technology Conference (OTC)

Houston, TX, USA,  2-5 May 1994

Author: Frank G. Bercha

Over the last quarter century, the evolution of structural forms for offshore structures in the North American Arctic has been closely tied to developments in our understanding of ice structure interactions. The architecture of offshore structures is one of pure function: to support an operation and to survive. Once the socio-economic and environmental issues are resolved, islands, bottom founded structures, floating structures, and active devices, the principal categories, derive their form almost exclusively from the designer’s understanding of the ice, environmental, and operational forces to which they are expected to be subjected. The evolution of their forms reflects development of ice mechanical knowledge. Islands were initially designed as simple gravel mounds with a flat top, and have evolved to incorporate slope protection, freezing, ice barriers, and for deeper water caisson containment walls. The gravity based structure has taken a multitude of forms on the drawing board, resulting in several different realizations including the Concrete Island Drilling System (CIDS) and the Single Steel Drilling Caisson (SSDC). Monopods, monocones, the Hibernia star structure, and various storage and platform combinations are designed to passively resist the full spectrum of ice forces to which they are likely to be subjected. Active structures, which in some way actively destroy or avoid ice features capable of causing damage to them, have led to fantastic and sometimes bizarre designs. Floating structures, a more conventional variation of active structures, include ice vaning ships, the round Kulluk and various forms of stationary icebreakers. The paper follows the evolution of the forms in each of the principal classes within the context of associated ice mechanical developments. Possible evolutionary directions for the future are considered, including use of new materials and technologies such as space alloys, composite construction, and underwater habitats. The designs, prototypes, and structures presented in the paper are based on those developed in the industry.

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Icecrete - An Ice-Based Construction Material

Presented at the CSME Mechanical Engineering Forum, Ice Mechanics Symposium

Toronto, Canada, 1990

Authors: Frank G. Bercha, President, and T.G. Brown, Associate, Bercha Group / P. Hofseth, Project Engineer, and P. Olsen, President, ICECRETE Contracting & Engineering, A.S., Oslo, Norway

The paper describes the historical development of a particular form of reinforced ice, its properties, and potential uses. The possibility of using ice reinforced with some form of fibrous material has been considered since the Second World War. While most attempts have been fraught with difficulties regarding the composite materials construction, a Norwegian development, called ICECRETE, has partly solved these problems. The composite material exhibits mechanical properties which are considerably better than those of pure ice, particularly the tensile mechanical properties.

The potential uses of the material are discussed and include offshore exploration and production structures, at shore structures, and onshore structures. The general methods of construction and the operational cooling necessary to maintain the structure’s integrity during summer months in high Arctic latitudes are discussed. Finally, certain conclusions regarding the properties and utilization of ICECRETE are discussed.

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Optimal High Latitude Radar Surveillance

Presented at the 1st CircumpolarRemote Sensing Conference

Yellowknife, NWT, Canada, May 1990

Author: Frank G. Bercha and Jim W. Steen / Bercha Group

Northern shipping and offshore operations have created a demand for tactical ice surveillance best carried out using side-looking airborne radars. The need to provide timely ice or iceberg information was most tragically and emphatically illustrated with the Titanic disaster. Since then, northern shipping lanes have begun to be routinely patrolled by observation aircraft. With the availability of side-looking radar, an instrument capable of imaging sea, ice, or iceberg features regardless of atmospheric, visibility, or illumination conditions, the use of such radars has been favoured for ice surveillance. The side-looking radar is a device which emits a systematic spatial and temporal pattern of microwave pulses which travel to the target area through cloud cover or darkness and are reflected from the target and recorded in real time to produce a radar image such as that illustrated in Figure 1 of the paper. In supporting operational arenas, the recorded data are generally processed both digitally and analogously, and the digital data is often electronically transmitted directly from the aircraft to remote ground stations. The configurations for appropriate radar systems, data processing capabilities, platforms, and methods of transmitting information to user stations at ground or sea level, however, must be selected through a systematic optimization process based on a systems approach.

From a practical point of view, the commercial radar industrial sector is largely centred in Canada. In the mid l970s, the Atmospheric Environment Services Branch of the Canadian Government experimented with side-looking airborne radars and in the late 1970s obtained a Motorola APS 94D to be deployed on ice patrols on a routine basis. In 1979, the Bercha Group, in response to requirements by oil companies exploring in Arctic waters, purchased an APS 94D system mounted in a Gulf Stream G159 aircraft, thus being the first Canadian commercial company to own and operate an airborne radar. This organization continues today to own and operate an airborne radar system in support of high latitude radar surveys as well as providing services using CCRS’ dual band advanced synthetic aperture radars. Subsequently, in the early 1980s, another Canadian company called Intera Technologies acquired a synthetic aperture radar which was initially deployed for ice patrols and subsequently for a combination of radar resource mapping assignments. More recently, this company was instrumental in the development of an advanced synthetic aperture radar to be mounted in a Challenger aircraft on contract to the Atmospheric Environment Services for a dedicated Arctic ice patrol service. In the mid to late 1980s, further real aperture radars were developed by Canadian Astronautics Limited and deployed on contract in Atmospheric Environment Services aircraft. From this arsenal of radars, and the associated communication, recording, and other peripheral equipment, it is often necessary to optimize a given patrol configuration using the principles of system design and optimization outlined in this paper.

Accordingly, following this brief introduction, Section B describes the optimization concepts applied to surveillance, Section C discusses the principal subsystems of an ice surveillance system, while Section D describes a specific ice surveillance system which has been subjected to optimal design. The final section gives some conclusions and recommendations.
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Monte Carlo Simulation of Arctic Offshore Drilling Operations

Presented at the Arctic Offshore Technology Conference and Exposition

Anchorage, Alaska, 3-5 September 1985

Authors: Frank G. Bercha and Thomas G. Brown, Bercha Group

Accurate prediction of the distribution and cumulative value of downtime cost-intensive operations such as offshore drilling in arctic waters is often the key to determining the economic feasibility of such operations. Downtime, or inability to operate, can be a result of ice and iceberg action, weather action, or some other operational problems. Although the total risk may be determined conventional risk analytic techniques such as fault trees and decision trees, a good understanding of its distribution, particularly for complex-environment operation interactions such as exist in ice-infested waters in the U.S. and Canadian arctic, off the west coast of Alaska, and off the east coast of Canada, can best be understood through the utilization of simulation techniques. In the present paper, following a brief description of the basics of Monte Carlo simulation, two case studies carried out by the authors are reported. The first involves simulation of the interaction of a wharf-moored drilling platform in the south Beaufort Sea with ice cover and the associated ice management program interaction with the environmental conditions; the second describes the simulation of the interaction of floating drilling operations with all environmental and operational elements, including a detailed simulation of the drilling of specific wells. Each case study is documented through a description of the simulation process, simulated structure, and presentation of representative results. Conclusions and recommendations pertaining to the general applicability of Monte Carlo simulation techniques to the evaluation of feasibility of drilling operations are subsequently presented.

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The Reliability of Ice-Structure Interaction Load Predictions

Presented at IAHR Ice Symposium

Hamburg, West Germany, August 1984

Authors: Frank G. Bercha, President, Bercha Group / R.H. Nagel, Engineering Associate, Amoco Production Company, USA /
T.G. Brown, Senior Engineer, Bercha Group

The paper describes a method for evaluating the reliability of ice-structure interaction load predictions for different interaction modes, structure types, and ice kinematic and mechanical property cases. Specifically, following the derivation of reliability measures which take into consideration the variability of input kinematic and mechanical properties, accuracy of methodology, and reliability of inherent ice-structure interaction assumptions, several reliability case studies are described. These include various combinations of conical, cylindrical, and multi-pod structures interacting with first and multi-year ice sheets, ridges, and their combinations. The work described is based on applications of statistical methods to ice property evaluation as well as techniques of risk and reliability analysis applied to the ice-structure interaction equations and the assumptions upon which they are based. It is believed that a broad reliability evaluation of the type described in this paper has heretofore not been developed and applied, and thus the work described constitutes a novel and useful contribution to the field of Arctic marine and inland ice engineering.

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The State of Art of Statistical Approaches to Ice Mechanics

Invited Paper, IAHR Ice Symposium

Hamburg, West Germany, August 1984

Author: Frank G. Bercha / Bercha Group,

Not available at this time.

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Evaluation of Pile-Up Formation and Structure Interaction Forces

(OTC Paper 4462)

Presented at the 15th Annual Offshore Technology Conference (OTC)

Houston, Texas, USA, 2-5 May 1983

Authors: M.J. Hommel and F.G. Bercha, Bercha Group

Ice pile-ups or rubble fields may form due to the interaction of Arctic offshore structures with sheet and ridge ice formations. Interaction parameters favoring the formation of pile-ups include sufficient driving force to fragment ice formations, adequate generalized flexibility to permit the necessary movements, and sufficiently large structural breadth to preclude clearing of ice fragments. The creation of pile-ups around offshore structures can have a significant influence on associated ice-structure interaction forces. This influence can be one of force magnification or reduction, depending on certain ice pile-up and interaction characteristics.

The ability to predict ice pile-up loading and load transfer characteristics will facilitate design of Arctic artificial islands, platforms, jetties, and other large structures with the potential to generate pile-ups under appropriate ice-structure interaction conditions.

In this paper, following a general review of the basic concepts published by the authors and others in the area of rubble pile formation and force transmittal, extensions of the theory are presented and results are compared with previously published work. The extensions include the incorporation of heretofore unpublished probability density functions to represent slope angles of individual ice pieces idealized through the use of multi-modal failure theory.

A significant dependence of interaction load on the properties of the probability density function is found. In addition, the effect of pile-ups on ice-structure interaction loads is evaluated utilizing techniques based on the theories of granular and cohesive media to evaluate ice pile-up load capacities and load transfer characteristics. Numerical results are generated and compared with relevant related theories.
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The Development and Application of Multimodal Failure Theory

Invited Paper, the IUTAM Symposium on the Physics and Mechanics of Ice

Copenhagen, Denmark, 6-10 August 1979

Author: F.G. Bercha

Multimodal ice failure behavior is important for accurate characterization of numerous ice mechanics phenomena. Ridge formation, pile-ups, and the associated macroscale ice cover properties as well as interactions of ice formations with structures under conditions potentially admitting more than one failure mode require multimodal characterization. In this paper, theoretical approaches with associated results for quantification of multimodal behavior are presented. Simplified approaches applicable directly by designers are outlined and corroborated with a more rigorous probabilistic approach.

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Arctic Offshore Deepwater Ice Structure Interactions

(OTC Paper 3632)

Presented at 11th Annual Offshore Technology Conference (OTC)

Houston, Texas, USA, 30 April to 03 May 1979

Authors: F.G. Bercha, Bercha Group and D.G. Stenning, Dome Petroleum Ltd.

A comprehensive theoretical analysis of deep-water Arctic ice-structure interactions was partially described in this paper. Following identification of a severity hierarchy of ice formations and associated strengths for the 200 ft. water depth range in the South Beaufort Sea, quasi-static and dynamic interactions of these formations with a steel monocone production platform structure were analyzed. The ice formations identified included sheets, ridges, and ice islands. Quasi-static analysis of sheet ridge composites impinging against the structure included development of certain new failure and clearing mechanisms. Dynamic analysis of island-structure collisions was approached utilizing energy balance principles. Probabilistic design theory was applied to the determination of result statistical bounds consistent with severity ratings of input variables. Numerical results for representative quasi-static and dynamic cases were presented and discussed. Certain non-governing interactive modes, including pile-up and in-plane ridge flexure, were also discussed briefly. Conclusions and recommendations for further work were presented.

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On the Scale Effect in Ice Mechanics

Presented at the 6th Canadian Congress of Applied Mechanics

Vancouver, BC, Canada, 29 May to 03 June 1977

Author: Frank G. Bercha

The prediction of forces generated in ice-structure interactions requires deterministic or probabilistic knowledge of the effective unit mechanical properties of ice. Although small sample unit properties of ice have been relatively well documented (Assur, A., 1972; Bercha, F.G., 1975; Croasdale, K.R., 1974) the solutions of important practical problems of large-scale ice-structure interactions are still seriously hampered by the lack of an adequate means of relating small and full-scale ice unit properties. This problem of relating effective full-scale mechanical properties to small sample or index properties is termed scale effect. It has not been adequately solved to date.
In this paper, following a review of previous approaches to the scale effect problem, a definition of the problem is given, and a comprehensive approach to it, illustrated by recent work done by time author, is suggested.

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1975c

(75-03)

Sprung Structures - Present and Future

Bulletin of the International Association for Shell and Spatial Structures, No. 65

Madrid, Spain

Authors: Frank G. Bercha and Phillip D. Sprung

The Sprung structure is a structurally supported membrane space enclosure system, consisting of a series of aluminum arches joined with a composite fabric. It is currently mass manufactured in clear spans ranging from 20 to 120 feet, of any required length but larger spans or special forms of the structure may be produced upon special order. Following a description of the current form of the structures, details and results of investigations of the strength and fulfillment of National Building Code Standards are presented. Subsequently, current research and development programs and future vistas for the structural system are considered.  

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New Solid Mechanics Applications in the Arctic

Presented at the 2nd Symposium on Applications of Solid Mechanics, Sponsored by CSME, CSCE, ASME

McMaster University, Hamilton, Ontario, Canada, 17-18 June 1974

Authors Frank G. Bercha

Numerous new solid mechanics problems arise from current industrial interest and activity in the Arctic. In this paper, a review of the major mechanics problems related to each of five main arctic facility application categories is made. These five categories are: offshore structures, northern enclosures, submarine facilities, ice structures, and transportation facilities. Generally, the treatment corresponding to each category consists of a review of specific facility types, identification of the problems, reference to relevant work completed or in progress, and indication of additional work necessary to solve the problems. It is concluded that the most pressing and significant solid mechanics problems identifiable at this time relate to ice, permafrost, and arctic structural mechanics. However, because of the embryonic level of development of arctic technology today, investigators are certain to encounter novel and unexpected problems which can be solved only with innovative approaches.

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