Founded in 2002 as one of the Norwegian Research Council’s ‘Centres of Excellence’, the Centre for Ships and Ocean Structures, CeSOS, in Trondheim undertakes fundamental research into the design of ships and offshore structures. Sponsored by DNV and other Norwegian organisations, it has already made some notable contributions towards maritime safety and environmental protection.
The Centre is organised as a faculty of the Norwegian University of Science and Technology (NTNU). Its offices and laboratories are located at NTNU’s Marine Technology Centre, as are its extensive testing facilities – including a 260m towing tank, 80 x 50m ocean basin and marine cybernetics laboratory.
Director of CeSOS is professor Torgeir Moan. “The Centre’s goal”, he explains, “is fundamental research to take account of the increasing size, speed and complexity of ships, and the trend to deepwater exploration and production of oil and gas. Realisation of the Centre’s research projects, and feedback from them, is assisted through our sponsoring companies: DNV, Norsk Hydro, Statoil and the Norwegian Shipowners’ Association. They help ensure that proposed new research work has practical application and meets the needs of the market.”
DNV-sponsored work on wave loading
One example is a project being undertaken by DNV engineer Gaute Storhaug, currently a post-doctoral researcher at CeSOS studying the phenomenon of bulk-carrier hull cracking due to the effect of waves on their blunt bows. The problem can also affect tankers and large container carriers – whenever a ship hull’s resonant frequency matches wave frequency – and is of concern to both shipbuilders and operators. Storhaug is modelling the effect of wave loading on a variety of hull bow forms, using the Centre’s test tank and computer facilities, while DNV is carrying out full-scale instrumented tests on a large bulk carrier and a 4,000TEU container ship.
The CeSOS organisational structure comprises three departments, Hydrodynamics, Structural Mechanics and Cybernetics or Automatic Control. Dr Carl Arne Carlsen, head of DNV Research and a member of the CeSOS Board of Directors, explains the practical applications of such research: “In DNV, we carry out extensive R&D as a basis for generating new services for our clients. In doing this, we build upon fundamental research – we highly value the work of CeSOS, which aligns well with our own needs in hydrodynamics, structures and cybernetics.”
Professor Odd Faltinsen, head of the hydrodynamics research programme at CeSOS, worked with DNV for seven years and was closely involved in the Moss Rosenberg design of LNG tankers.
Liquid sloshing in ships’ tanks continues to be a significant factor in tanker and LNG carrier design, especially as modern tank interiors are relatively “clean” (without internal baffles or structural members). Impacts can thus be severe. CeSOS research here links theoretical work on tank shape and proportions with model testing in the laboratory and test tanks.
A similar approach – mathematical modelling supplemented by tank testing – also applies in research into slamming, the effect of wave impact on vessel hulls. “This can be a problem with the aft hull on passenger ships”, Faltinsen explains, “and beneath the decks of multi-hull vessels.”
Main objective of CeSOS activities in structural mechanics is to develop new means to predict wave-induced load effects on ships and marine structures. A recent project has been to study bow-flare slamming pressures and response in a 20kt, 120m car carrier. A new mathematical model to determine slamming velocity and pressure is now being investigated.
In the area of offshore structures, the Centre’s research currently focuses on slender marine structures in Norwegian waters, such as pipelines and platform risers. All three research disciplines are involved, since the marine environment in the northern North Sea is unique and calls for new technology to cope with deep water, an uneven seabed and unpredictable waves and currents. Particular attention is being given to vortex-induced vibrations (VIV), both in free-spanning pipelines and in risers linking platforms to the seabed.
Cybernetics and software
Ship manoeuvring and station-keeping is a prime application for the cybernetics and automatic- control projects under way at the Centre. In offshore work, a notable application of the department’s research programme is in manipulating loads between a platform and its supply vessel. Traditional heave-compensation devices are being refined to achieve greater positioning accuracy, and to minimise damage to craft or equipment.
A research project being developed by a separate CeSOS group is a unified theoretical model integrating all aspects of ship manoeuvring and dynamic positioning. The goal is to reduce or eliminate software errors. The team plans to make software available to DNV and other classification societies, introducing a class notation HIL – “hardware in the loop” – so that a ship surveyor can take a laptop simulator on board and test a ship’s automatic control systems. The software can also be used for type approval, and factory assessment testing at a vendor’s plant.
A global resource
Research facilities available to CeSOS are among the world’s best. Laboratories and extensive computer networks supplement three test tanks and a large cavitation tunnel, with a wide range of test and measuring equipment, instrumentation and model-making facilities.
DNV’s Carl Arne Carlsen sums up the important relationship between the work of CeSOS and DNV’s expertise in its practical application. “CeSOS helps bridge the analytical approach, numerical simulation and laboratory testing. It is a global resource, and applying all these aspects of its work is vital in helping enhance ship and offshore safety.”