When ice meets steel

By Ivan Muzychka

Perhaps it's fitting that Memorial University is currently involved in researching the engineering problems associated with operating ships and offshore structures in iceberg strewn waters. After all, it was off Newfoundland's coast that the most dramatic display of an iceberg's power took place: the 1912 sinking of the massive ocean liner Titanic.

The antagonist of the Titanic's dramatic end was the iceberg that ripped open the hull and sent the ship to the bottom of the Atlantic together with more than 1,500 passengers.

ICEBERGS AND OIL DON'T MIX

Today, as a result of radar and air patrols, the threat of icebergs to ships has been greatly reduced. However, the modern world's dependence on oil has pushed petroleum exploration activities into harsher environments - into places like the Canadian north, and in areas off the coast of Newfoundland and Labrador. These areas are rich in petroleum deposits but are also routinely exposed to icebergs ranging in size from small "growlers" and "bergy bits" to floating ice blocks the size of several large office buildings.

Drilling and producing oil in such areas is risky business. Dr. Ian Jordaan, holder of the Natural Sciences and Engineering Research Council (NSERC)/Mobil industrial research professorship at Memorial, has spent almost 15 years researching icebergs and their effect on ships and offshore structures. The structural engineer and Titanic buff points out that there are only two possibilities for any structure facing an oncoming iceberg: get out of the way, or withstand the force.

While he offers the observation somewhat jocularly, the truth is that it's simple and accurate. And it is these two possibilities that are at the heart of a comprehensive research project - led by Dr. Jordaan - which is aimed at understanding the problem of ice/structure interaction.

MAJOR UNDERTAKING

Funded by a $776,000 grant from the Canada-Newfoundland Offshore Development Fund Agreement, the three-year project is marshalling several disciplines and approaches. Dr. Jordaan's team at Memorial's Ocean Engineering Research Centre (OERC) is examining ice/structure interaction from a systems point of view. The project is being conducted with the collaboration of other researchers from the Faculty of Engineering and Applied Science, the Centre for Cold Ocean Resources Engineering (C-CORE), and the Institute of Marine Dynamics. The team's work will weave technical and practical considerations, and blend the business constraints of petroleum exploration into the problem of how to minimize the risk of damage caused by icebergs. To do this, the team is studying the composition of ice, having a fresh look at structure design, creating mathematical models of iceberg impacts, and analysing the actual risks and probabilities of encountering icebergs in the ocean.

Dr. Jordaan noted that while the force unleashed by a floating piece of ice is tremendous, engineers are able to build structures which can withstand certain loads. The large Gravity Based Structure (GBS) currently being built in Bull Arm is an example of such an ice resistant structure.

ALTERNATIVES TO GBS

However, Dr. Jordaan and his team of researchers are putting together data which could be used for alternate designs. These alternatives, if successful, could save oil companies millions in construction and operating costs. "First, design criteria are becoming more competitive all the time," Dr. Jordaan said. "With any new technology one has to compensate for the fact that maybe one doesn't know as much as one might - all the details of ice mechanics or the design of systems. As one learns more, one can actually refine the design...Perhaps designing a structure with less reinforcement might allow one to save money without compromising safety."

ICE AND ITS BEHAVIOR

A fundamental plank of the project is researching ice mechanics, or understanding ice as a material. How does ice behave when it smashes into a bow of a ship or an offshore structure? One answer that has emerged is that after impact the ice changes; it fractures, recrystallizes, and develops micro-cracks, which lessens its impact.

"The distribution of ice forces is one of the issues we are looking at, because we find that ice force can be very peaked locally [at the point of impact], yet the global force is less than once thought," Dr. Jordaan said. "We are trying to understand why this should be." Barry Stone, a research engineer with Dr. Jordaan's team, specializes in laboratory mechanics and testing. He is working with a postdoctoral fellow, Dr. Irene Meglis, a geophysicist with a background in the structural failure of rock and ice. Mr. Stone has been working on ice mechanics for a number of years, and is looking carefully at the physical structure of ice. A special cold room laboratory is used for experiments where he subjects laboratory-grown ice samples to shear stress, essentially simulating what happens during ice/structure interaction.

"We started out trying to measure the intrinsic properties of ice as a material," Mr. Stone explained. "But in doing that we found that the material changes [under loads]. We saw the recrystallization and the change in material...We asked how does the material change and recrystallize? And we looked at micro-crack formation. We found that the material properties of ice change during the impact."

A crucial part of the project is understanding how the kinetic energy of the impact is absorbed.

"The energy of the impact has to be consumed," Dr. Jordaan noted. "A large amount of energy gets consumed during these impacts, and we are examining how this happens"

RUSSIAN EXPERTISE

For that reason, the expertise of Dr. Dmitri Matskevitch - a Russian scientist trained in St. Petersburg - has been brought into play. In an irony of the new world political scene, the Russian scientist's work at Memorial was funded by NATO. He has been working with the OERC team since January 1995 and will be in Newfoundland until later this year. After his postdoctoral fellowship concludes he will return to Russia where his skills and training on this project will be put to use as Russia begins to develop its own oilfields in the far north.

Most of Dr. Matskevitch's work has been aimed at understanding ice mechanics through the use of mathematical models of the movements of an iceberg on impact. "I have to estimate how the ice behaves," he said. "I have to factor several aspects of the iceberg's motion - its rotational movement on impact for example - into a mathematical model of impact."

Not surprisingly, the corresponding mathematical model is complex, and must factor in motions that could in fact reduce the actual impact to a structure.

"Because of the extent of the impact, the iceberg can turn around," he said, "and I believe that a great amount of kinetic energy is transferred by this rotational motion."

ICE DESIGNS

Knowing about the properties of ice, and about the kinds of forces it can exert, is only part of a basic equation. Applying this information to the structure itself is a connection that is being made by Trevor Butler, a graduate of Memorial's engineering program who is currently pursuing his master's degree. He is working out the pressures and subsequent design considerations in light of the ways plating (the skin of a ship or offshore structure), and the frame, react to iceberg collisions.

"I have been working on what is called maximum bow force problems, a related project for the Canadian Coast Guard," Mr. Butler said. "My thesis will look at how to design vessels and the sorts of loads they can expect."

"What I want to do [in my thesis] falls in line with this project. We have done a lot of simulations of how plating reacts to impacts, from ice. Now I would like to look at how the structure reacts," he said. "The behavior of plates and frames together as a system is different from just the plating, or the structure itself."

Dr. Jordaan notes that the educational component of the project has been important from the beginning. "This is one area where we can be specialists, where we can market our expertise in other parts of the world," he said. "I think this is a very important aspect...a lot of people will come out of this with enhanced knowledge of this area."

REDUCING THE RISK OFFSHORE

Another valuable aspect of the research project is to incorporate the science of risk analysis and probability into the larger challenge of operating offshore structures in ice strewn waters. Dr. Jordaan and his team aren't just looking at the physical and structural problems, but are trying to establish the risks involved. How often can an offshore rig in a given area expect to encounter an iceberg?

How many of these icebergs will pose a serious threat? This part of the project will go a long way to developing strategies aimed at simply avoiding icebergs altogether. Mark Fuglem, a research engineer with the project, has a mathematics and physics background, and has worked in the petroleum industry in the past. He is currently focusing his energies on the statistical and probability analysis component of the OERC project. He is working with Karen Muggeridge, a research engineer who also assisted in the Canada Coast Guard project. She is specializing in design optimization and risk analysis.

"My work involves determining how many icebergs the structure encounters, how many will go past the structure, and how many will be detected and avoided," Mr. Fuglem said. "This information is important for the effective management of these risks. You might have a support vessel to look for icebergs, or an aircraft. If we know the total number of icebergs in that area, and know how quickly they are moving, we can actually figure out how much of that area will be covered [by the iceberg's path], and then factor in the position of the offshore structure, you can determine the probability of an impact."

The project will wind up in 1997, and will go a long way toward making offshore exploration and production activities more cost effective. More importantly, it will make them safer.