Strong ocean structures

Norway controls one of the world's largest fleets, with 1,800 ships and roughly 60 mobile offshore rigs. More than 90,000 people work in the country's maritime trades. At CeSOS, the Centre for Ships and Ocean Structures, NTNU researchers are providing the technical know-how to build Norway's maritime future.

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How do 1000 tonnes of liquid petroleum behave inside a tank during a storm? What happens when a wrecked ship starts to take on water? Can a vessel be steered automatically while relying on information from its onboard weather service? CeSOS researchers are hard at work on these and other questions that are of critical interest to seafarers -- and their companies -- who need ships and ocean structures that are both safe and environmentally friendly.

From the bottom of the sea to the ice floes of the Arctic

New demands for maritime transportation and resource exploitation are changing the marine industry worldwide in dramatic ways. The shipping industry wants faster ships, the aquaculture industry is booming, the petroleum sector is moving into ever-deeper offshore conditions and vulnerable Arctic areas. All of these developments offer major opportunities, but also represent enormous financial, scientific and technological challenges as well as raising important safety and environmental issues.

CeSOS provides fundamental knowledge about how ship structures, oil installations and other marine structures can be built to withstand waves, ocean currents, ice, and wind. The centre investigates the physics of the battle between the seas and human-engineered structures, with a focus on hydrodynamics, structural mechanics and automatic control.

CeSOS research gives the maritime industry the ability to build structures that are strong, ecologically friendly and cost-effective, which in turn creates jobs both on shore and at sea.

Photo: Paul S. Amundsen

Norway — shipping and oil

As a natural consequence of its extensive coastline, Norway has been a shipping nation for centuries. Today, the country is an international leader in shipbuilding, advanced shipping equipment, and the offshore petroleum technology. With oil and gas as its most important natural resource, it should come as no surprise that Norway has developed expertise that is of benefit across the globe.

The Norwegian University of Science and Technology (NTNU) supplies the shipping and oil industries with highly trained researchers in a number of specialized fields in marine technology, energy and petroleum. These are the researchers who in turn have helped develop companies such as StatoilHydro and Det Norske Veritas.

Researchers crossing oceans

CeSOS prioritizes international research projects with selected researchers and marine technology institutes abroad. In fact, the CeSOS staff is itself highly international, with roughly half from 20 different countries, including China, Indonesia, Italy, Russia, and the USA.

" Two key people at the Centre, Professor Torgeir Moan and Professor Odd M. Faltinsen are both so well known in international maritime circles that we easily attract visiting researchers," said Carl Martin Larsen, professor of structural engineering. "Our cooperation with MIT in Boston is particularly strong, with four visiting professors often travelling across the Atlantic to Trondheim. Many people want to come here because of our unique laboratory facilities.

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A miniature ocean in your backyard

Computer modelling is an important part of designing ships and structures, but being able to actually see how a real structure behaves in difficult ocean conditions provides priceless information. Through a cooperative agreement with MARINTEK, the independent Norwegian Marine Technology Research Institute, CeSOS researchers have access to two large experimental tanks, a 260 metre long towing tank, and a 80x50 metre ocean basin. The tanks are fitted out with equipment that can create waves, currents and wind, all in controlled conditions. Accurate scale model ships and ocean structures give researchers the chance to test new ideas or examine old beliefs to find the best possible designs.

In 2006, a towing tank experiment led CeSOS researchers to one of their most startling findings, one that had ramifications across the maritime community. In short, researchers found that the vibrations in a ship's hull increase with the size of the waves, no matter how hydrodynamic the bow's design. Round or pointed, with or without wave-absorbing devices, these vibrations will cause fatigue and have resulted in cracks in brand new tankers.

"Ideal structures from an engineering perspective require the least possible resources during construction at the same time as they meet all safety requirements," says Torgeir Moan, Director of the Research Centre.

The ocean basin enables researchers to test structures in heavy waves that come from all directions, and the laboratory allows for complex experiments with everything from new types of platforms, aquaculture equipment and ship manoeuvring to floating structures. Industry is the primary funder of the ocean basin research, but CeSOS has access to the results from the measurements, which enables researchers to improve their own calculation models.

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Plunging and sloshing – the physics of liquid fluids

CeSOS researchers primarily develop mathematical models and statistical methods to describe the physics of what happens when structures are exposed to extreme loads.

Imagine a wave breaking against the hull and flowing onto the deck. The water rises in a vertical wall on one side of the deck before washing at high speed across to the other side, perhaps tearing down equipment or damaging important parts of the structure in the process.

If you have ever carried water in an open bucket while you are running, you know that the water pitches and hits the sides before eventually sloshing out. The water moves in a dancing, self-reinforcing rhythm. The same dance occurs aboard huge tankers that sail across the ocean. Many of them carry thousands of tonnes of liquefied natural gas (LNG) that will supply cities with heat and light. But the sloshing can cause major problems, which is why it is a priority research area at CeSOS.

Researchers calculate the probability of events occurring before developing methods to handle these events. One look at the sea tells you that waves are random. If you observe an area long enough, you will discover that the wave height is rather unpredictable. Scientists can use what are called stochastic mathematical models to describe reality as accurately as possible, because stochastic models include a factor for unpredictability. But instead of calculating random waves indefinitely, researchers refine their models by concentrating on finding an extreme wave or one particular wave height suitable for generalization, such as determining when a wave with a certain probability will occur.

"We are looking for computer programs that we can use more generally. If they work, they can also be used for other studies of the phenomena without experiments with models," Moan explains.

Other research looks at the structural engineering properties that gives ships and structures strength. What is the most ideal shape for a pentamaran, a tanker or a cruise ship? And as oil and gas production moves into deeper waters, companies will need to know how ocean currents affect pipelines, risers, and seabed installations. Research on the mechanics of slender marine structures could eventually provide the answers.
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The future at sea – floating airports and flexible fish farms

The future will look different. Huge floating farms will provide fish and seafood, while large floating barges instead of bridges may enable us to cross straights and channels. We will be building floating airports and fast and light multihull vessels,and tidal-and wave-power stations. These topics are being discussed in large fishing and shipping nations such as Japan, Norway, and the USA. CeSOS is working cooperatively with the Megafloat Programme in Japan, and the Mobile Offshore Base Programme in the US.

Fish farms must be able to withstand powerful forces at sea and be capable of being towed from place to place,when farmers need to move the farms to reduce their environmental impact.. The aquaculture industry also needs new vessels, new types of harvesting tools, and a totally new infrastructure for transport and processing. The challenges are numerous – this is a field where we need fundamental qualifications, and brand new ideas.

For this reason, CeSOS arranges creative workshops with innovative researchers such as Robert Skelton from the University of California, San Diego, to generate ideas for new projects. Skelton is working on new types of structures, transferring principles from biology to marine technology in a approach that is called tensigrety. "Traditionally we have thought in terms of large and robust, but why not go in the opposite direction: flexible and adaptable?", asks Professor Skelton. "The wing of an insect, which is lighter than a feather, can stand enormous wind loads compared to its size."

Never again – major accidents at sea can be prevented

A ship or structure out on the ocean is a universe unto itself. Lives depend on safe and reliable structures, well-functioning machinery, fire prevention, navigation and communication equipment, and rescue equipment. But the single most important safety factor is a hull or platform that can withstand sea loads.

Norway intensified its safety research after a catastrophic accident in 1980 killed 123 people. The disaster, the capsize of the floating accomodation platform the Alexander Kielland, was a turning point for the marine industry. Professor Moan was a member of the commission of inquiry that discovered that a minor structural defect – basically a small problem – led to the entire platform capsizing.

"Since then, we have introduced a system of testing for accidental loads before starting the production of ships and platforms. That means that damage to one part of the structure should never lead to a total collapse. Defects occurring more than once per 10 000 years are to be eradicated. We investigate what may happen and map out how to prevent it from happening. In this way, research and cooperation on regulations function as a basis for safety at sea. DNV and other classification societies continuously cooperate with the research environment at CeSOS," Moan says.

Last updated 22 April 2009

FACTS ABOUT CeSOS

CeSOS researchers work to develop fundamental knowledge about how ships and other structures behave in the ocean environment, using analytical, numerical, and experimental studies. This knowledge is vital for the design of safe and environmentally friendly structures used for transport, fish farming and energy production at sea.

Research Centre Director:
Professor Torgeir Moan, NTNU

Web: http://www.cesos.ntnu.no/
Phone: (+ 47) 73 59 55 35
Fax: (+ 47) 73 59 55 28
Email: coe@marin.ntnu.no

Offices and laboratories:
Marine Technology Centre
Otto Nielsens v 10
Trondheim, Norway

Total budget:
NOK 34.3 million/EUR 4.21 million/USD 5.7 million