CeSOS Centre for Ships and Ocean Structures

Transcription

1 Annual Report 2005 CeSOS Centre for Ships and Ocean Structures

2 Our vision: To establish a world-leading centre for developing fundamental knowledge about the behaviour of ships and ocean structures in chaotic sea, by integrating theoretical and experimental research in marine hydrodynamics, structural mechanics and automatic control. The centre will contribute to improved international competiviveness of the Norwegian marine industries, as well as to safety and protection of the marine environment.

3 Table of Contents Our vision 2 The third year in brief 4 CeSOS in facts and figures 6 Research plan 7 Research achievements Hydrodynamics highlights 10 Structural mechanics highlights 13 Slender marine structures risers and tethers highlights 18 Automatic control highlights 22 Safety of DP drilling operations on the norwegian continental shelf 23 Harnessing wave energy 28 Aquaculture- our future supply of seafood 29 The strategic research areas at NTNU 30 National cooperation 32 International cooperation 32 Workshops 33 Recruiting and educating researchers 34 A road less travelled 34 Organisation and management 36 Management team 37 Photo gallery Board of Directors 38 Infrastructure and research facilities 42 Statement of accounts 44 Appendices 45

4 The third year in brief Research at CeSOS aims 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, both now and in the future, for the design of safe, cost effective and environmentally friendly structures as well as in the planning and execution of marine operations. The importance of such work cannot be over-emphasised: in tonnage terms 95 percent of all international transport is by sea; and 20 percent of the world s oil and gas is produced from subsea reservoirs via offshore structures and pipelines. In the future, food production in aquacultural plants and exploitation of renewable energy from the oceans is expected to play a growing role. The scientific and engineering research carried out in the Centre takes account of such future needs, and extends current knowledge in relevant disciplines. The emphasis is on hydrodynamics, structural mechanics and automatic control, and in the synergy between them. In each of the past years, our research projects have proved valuable basis for the innovative design of structures, risers and automatic control systems. Safety in ship design and operation Ship-related research is driven particularly by the need for larger or faster vessels of correspondingly novel design. Another important factor is concern for safety and the environment, especially survival in severe sea states and freak waves and in handling wave-induced loads and responses. In 2005, research was undertaken to determine loading due to violent liquid motion (sloshing) in part-filled LNG tanks, and their structural effects in harsh conditions. Such knowledge is vital for the design of future large LNG carriers. Significant progress was made in developing computational fluid methods to deal with nonlinear phenomena such as water entry and exit, sloshing and green water. Particularly noteworthy results have been obtained by an analytical model method to describe sloshing in ship tanks. A Computational Fluid Dynamics (CFD) Code has been developed to deal with green water on deck. Various green water phenomena have been classified according to the relative vertical and horizontal velocity of the wave and wave steepness. The nonlinear, high-frequency wave-loading mechanism which can cause fatigue-crack growth in ships with blunt bows was identified and characterised: this phenomenon

5 has a major economic impact due to concerns about the possible leakage of oil through cracks, or of water into the cargo. An efficient method to determine slamming response of flared bows was also developed. Particular efforts were made to assess variability and uncertainty in extreme wave-induced loads and structural response, which can have a direct effect on the reliability of ships. A study was also initiated into the effect of human factors on heavy-weather avoidance. With regard to vessel operation, a unified timedomain theory for manoeuvring and sea-keeping was developed which allows for the inclusion of systems for feedback control, such as autopilots, dynamic-positioning systems and roll-damping. This unified model was derived using a statespace approach, the standard representation used in feedback control systems. Responding to offshore demands Research into structural design and operations relating to oil and gas production must take into account a combination of deep waters, harsh wave conditions and strong ocean currents, and their effect on safety and the environment. While the methods developed to deal with slamming and green-water effects on ships are also relevant to offshore structures, particular research efforts for the latter were devoted to dynamic positioning, mooring analysis and marine operations. They included a novel approach to controlling thruster capacity of DP systems in severe sea states as well as a procedure for safety analysis of critical situations involving the human element. In the design of risers and pipelines, a major challenge is vortex-induced vibrations (VIV), which can lead to costly failures. Most work (at CeSOS and elsewhere) has hitherto been related to crossflow vibrations, though the importance of the in-line component is also recognised. An initial step to predict in-line oscillations was taken, as described on page 19, and this will be continued together with research on stochastic VIV as found in long structures responding at high mode orders. Other examples of our achievements during 2005 may be found in the Research Highlights section on pages They are documented in various publications and conference presentations, all listed in the Appendices. Aquaculture and renewable energy To meet future demand for structures for food production and renewable energy, CeSOS has initiated research on fishfarms and wave energy converters. The wide variety of concepts envisaged in these areas are stimulating from both their scientific and engineering aspect; efficient methods for time-domain analysis of such structures have been developed, appropriately combining hydrodynamics, structural mechanics as well as automatic control. The latter is crucial for wave energy converters. Cooperation pays dividends Many of the results obtained in CeSOS were obtained through cooperation between our researchers in hydrodynamics, structural mechanics and automatic control, as well as with staff in MARINTEK, SINTEF and international partners. Particular synergy is achieved with MARINTEK through the use of common laboratories. The research into aquacultural structures continued in joint activities with SINTEF Fishery and Aquaculture, especially in conjunction with the Strategic Institute programme Intellistruct. Research into wave energy-conversion devices has also gained momentum, not least thanks to growing worldwide interest in wave energy exploration. Close links were established with other research groups at NTNU, for example through strategic university programmes funded by the Research Council of Norway. Now in its fourth year, CeSOS has become recognised as a truly international centre. About half of the researchers employed during the year were from outside Norway, representing some 20 different countries. Cooperation with our international partners involved a significant number of research staff, while many others paid visits to

6 CeSOS to deliver guest lectures or seminars, and to take part in discussions. CeSOS staff are involved in international research networks, and in organisations such as ISO, ISSC and ITTC which link research and engineering practice. Our staff are involved in international research networks, and in organisations such as ISO, ISSC and ITTC which link research and engineering practice. Our original aim of fostering a dynamic, effective working environment has proved itself, as evidenced by the global interest in working together with CeSOS staff in projects, publications and conferences. Making the results known Dissemination of scientific research occurs through active publishing in leading international journals and books, and at conferences. For example, a comprehensive textbook on the hydrodynamic aspects of high-speed craft, authored by a senior CeSOS researcher, was published by Cambridge University Press. Dissemination also takes place through direct communication with partner companies and others in industry. In particular, three of the key persons in CeSOS have established the company Marine Cybernetics, exploiting the competence gained in their CeSOS activities. The many invitations to deliver keynote addresses and other presentations at conferences are clear evidence of the Centre s international standing. Research training Research training and education is an important feature of our activities. 33 PhD students were affiliated to the Centre in 2005, three PhD candidates graduating. Theoretical aspects of their training include lectures by visiting professors, and PhD courses run by key CeSOS personnel. In addition, we have looked closely at how quality is achieved in research, aiming always to ensure systematic interaction between PhD students and their supervisors. CeSOS 2005 in facts and figures Personnel at the end of key persons 17 Postdoc./researchers (13.9 man-years) 17 PhD (14.2 man-years) Four arrived in PhD associated (13.3 man years) 7 visiting professors (short term) 6 visiting CSSRC, INSEAN and MIT researchers (short term) A total of 49.8 research man-years Revenues Income MNOK 34.3 Costs MNOK 33.7 Publications 2 books and 6 book chapters 9 international Keynote Lectures 27 refereed Journal papers 83 refereed Conference papers International Journals, Conferences and Workshops 19 editorial boards of Journals 13 international Conference organising committees 2 international Workshops organised at CeSOS Some 30 guest lectures have been delivered by international visitors to CeSOS. Torgeir Moan

7 Research plan The research plan for CeSOS is formulated on two levels: in terms of overall aim, subjects, disciplines and their integration, and the combined use of analytical, numerical and experimental approaches. 15 project themes through which this overall aim can be realised. Intention of the initial plan was to be flexible: in addition to these themes, therefore, we have identified further research areas as need has arisen. The initial 15 project themes can be classified as follows: Loads for structural response 1. Strongly nonlinear wave-induced motions and loads on floating structures 2. Green water loading 3. Sloshing in tanks Response due to wave-induced, stochastic loads 4. Stochastic dynamic analysis of extreme load effects 5. Extremes for multiple stochastic load effects 6. Fatigue due to nonlinear effects 7. Wave load effects in damaged floating structures Response including the effect of automatic control 8. Control of wave-induced motion, loads and structural load effects of high-speed catamarans Catamaran Catamaran with motion control by use of hydrofoils Marine operations Station-keeping and manoeuvring 9. Station-keeping and manoeuvring of ships in waves 10. Risk analysis of positioning systems for deep-water FPS

8 Lifting and other operations 11. Control of loads through the wave zone in marine operations 12. Control of extreme response of marine risers Slender structures risers and pipelines 13. Analysis and control of continuously changing systems 14. Vortex-induced vibrations (VIV) of free-span pipelines Hydrodynamic and structural modelling and automatic control 15. Control of large mobile interconnected aquaculture structures for harsh conditions Future research trends The research plan as described above dates from the establishment of CeSOS in As results are achieved and experience gained, and as new maritime and ocean systems develop, we must continuously monitor and revise these aims. An important aspect of engineering science is to envisage possible novel devices or processes, and the need to document serviceability and safety. Risk methodology and reliability-based ship design, for example, are high on the agenda, and could encourage new areas of research. While challenges still remain regarding larger, faster ships, and offshore structures and operations in deeper water, new challenges relate to ships and floating terminals in shallow water. Even more important is the need for oil and gas exploitation and transport in arctic conditions. 25% of the worlds undetected gas reserves are believed to be in the arctic region, where oil and gas exploitation call for drilling operations, production, offloading and transport. This demands new research into icebreaker design, manoeuvring and navigation, and on the performance of a ship and a fleet in ice. Detection and forecasting of ice are important issues in planning and executing operations. Station-keeping and underwater operations, emergency and rescue in ice conditions, safety of the environment, will all need comprehensive research. In the methodologies applied in all our various disciplines, the potential use of computational fluid dynamics is already being explored to a larger extent than initially foreseen, and will be further extended. Above all, perhaps, we recognise that the assessment of risk and reliability, in all aspects of maritime and offshore activity, must increasingly take into account the effect of human factors. Besides the development of ships for transport and offshore structures for oil and gas exploitation, the production of food from the sea by aquacultural facilities and of renewable energy from waves and wind are expected to be of growing importance. Both these areas will be reflected in our research projects. The expansion of activities to include marine arctic operations and CFD will be made by establishing working relationships with leading researchers, including part-time professors, and institutions.

9 Research achievements 2005 The main goal for CeSOS as a research centre is to enable participants to undertake first-rate research, at the same time setting the standards of a demanding, dynamic and daring research environment. Research is organised in three disciplines: hydrodynamics, structural mechanics and automatic control, and the interdisciplinary research based on these. Scientific activities involve generating new knowledge, training PhD and post-doctoral researchers, and disseminating information in its broadest sense. Our scientific activities are documented in: Publications Conference presentations, guest lectures, seminars PhD courses offered Doctoral degrees achieved Wide international networking Dissemination of information at large. A prime measure of the Centre s success is its publications in international Journals and Conferences. In 2005 the Centre contributed 27 referred Journal papers, 9 referred Conference keynote plenary lectures, and 83 other Conference papers. Three PhD students graduated during the year. These aspects of the Centre s work are documented in the Appendices. Some of the results achieved in 2005 are briefly described in the following pages, organised according to the three disciplines even if many of them are multidisciplinary. Selected research achievements in brief Novel developments include: - Analytical method to predict sloshing in tanks. - CFD approaches to deal with water entry and exit, sloshing and green water. - Classification of green water phenomena. - An improved experimentally based numerical model for calculating loads on seismic cables. - Efficient second order frequency domain methods for wave induced response analysis. - An efficient stochastic time-domain approach for slamming response analysis of ships. - Identification and characterisation of a new wave excitation mechanism of fatigue in ships. - A unified time-domain theory for manoeuvring and sea-keeping of ships for feed-back control. - Hydrodynamic coefficients for in-line vortex induced vibrations (VIV). - Improved understanding of the interaction between in-line and cross-flow vortex induced vibrations (VIV) of free spanning pipelines and risers. - Promising results from a novel analysis technique for identification of hydrodynamic coefficients valid for high mode order VIV based on an inverse finite element method. - A novel model for riser interference for use in a system for collision prevention based on active control. - Improved modeling of steel catenary risers relevant for stochastic analysis under extreme conditions. - Methods for efficient stochastic load effect analysis and combination of load effects, both with respect to extreme and fatigue effects, for ships and offshore structures. - A novel approach to control thruster capacity in DP systems in severe sea states. - A model for safety analysis of critical marine operations, involving the human element. - Efficient time-variant reliability approach for structures subjected to strength degradation.

10 Hydrodynamics highlights Our challenge is the hydrodynamic problems facing ships and ocean structures, often exploiting our links with structural mechanics and automatic control. Solving these problems requires patience and the combined use of analysis, numerical methods and experiments. Green water on deck CeSOS work on green water on deck involved developing a Computational Fluid Dynamics (CFD) code. A domain decomposition method is used where the less violent flow at a distance from the ship is described using a boundary element method. This reduces the computational time, a major limiting factor for practical applications. An attempt has been made to classify how the different green water phenomena occur as a function of wave parameters in head sea conditions for stationary ships with blunt bows, based on experimental and theoretical studies of a restrained two-dimensional body. A typical application is to an FPSO vessel. Interaction between the incident waves and the hull plays an important role. One type of green water is the so called dambreaching phenomenon, where a vertical wall of water is generated at the edge of the deck due to the relative vertical motion between the ship and the waves. The subsequent motion of the water resembles the breaching of a dam, water flooding at high speed (15-20 m/s) along the deck. Its impact against deck structures and equipment can cause serious damage. A second scenario is water hitting the deck as a plunging breaker, and a third is the hammer fist effect of water on deck, using an analogy to karate. This is shown in Fig. H.1, where a large mass of water rises above the deck and collapses heavily over a substantial area of the ship. Fig. Fig. H. 2: The effect of green water on deck as a function of the incident wave steepness and Ww/Wb-ratio. Ww is the maximum vertical incoming wave velocity and Wb is the maximum relative fluid velocity at the bow. H. 2 shows how these different phenomena occur as a function of the incident wave steepness and the W w /W b -ratio. Here W w is the maximum vertical velocity of the incident waves and W b is the maximum vertical fluid velocity at the ship s bow. Wave-body interaction plays a similar decisive role in bow stem slamming as in the green-water situation. Sloshing in tanks Fig. H.1: Hammer-fist effect of water on deck. Left: experimental snapshots. Right: hammer-fist strike in karate. Time increases from top to bottom. We have further developed our analytically based modal method to describe sloshing in ship tanks. Violent fluid motion can occur inside a tank with little interior structure, such as in an LNG tank. CeSOS is in the forefront of such research, with seven papers published in the prestigious Journal of Fluid Mechanics and in Physics of Fluids. The method has been experimentally validated for both two-dimensional and three-dimensional flow. 10

11 as perforated walls in the pool. To optimise their performance, we must better understand the physics involved. A similar resonance phenomenon occurs between two adjacent ships in waves, or for a ship alongside a terminal. Conventional engineering tools based on linear panel methods cannot accurately describe the flow, and we aim to generalise our nonlinear multimodal method for sloshing. Dedicated model tests have been carried out to validate the theoretical model. Fig. H. 3: Sloshing experiments: evolution of a flip-through phenomenon. Time increases from left to right and from top to bottom. Work is now under way on the effects of slamming, the fluid impacts that occur in sloshing. Slamming is of primary importance in the design of prismatic LNG tanks, in which pressures greater than 10 bar may occur. Present tank designs are largely based on model tests, and major questions relate to the scaling of such tests to full scale. One challenge, for example, is to account for the fact that LNG is boiling. There are three important slamming scenarios. Impacts may be associated with flip- through, air cushion and hydroelasticity. Flip-through means that the free surface near a tank wall makes a sudden change in direction, resulting in a fluid wedge impacting on the tank roof at high velocity, Fig. H. 3. An air cushion can occur as a consequence of the geometry of the impacting free surface. It leads to impact pressures oscillating with the natural frequency of the air cushion, and requires special consideration when scaling model tests to full scale. Hydroelastic impact studies, from a hydrodynamic point of view, are so far limited to steel structures. Both experimental and theoretical work is being carried out in these areas. Resonant fluid motion in moonpools Work also began on describing resonant pistonlike fluid motion in a moonpool. An important issue is to design efficient damping devices, such Theoretical and numerical work has also begun to enable us to study the interaction between two or more ships at speed in waves, and its effects on steering and manoeuvring. Behaviour of a damaged ship Knowledge gained in describing green water on deck and sloshing in tanks is important in studying the wave-induced behaviour of a damaged ship suffering water ingress/egress. The problem is being attacked along two paths. One approach is to use CFD tools. Special requirements are then needed to properly describe bilge keels, which are important for predicting rolling. The development of suitable overlapping grid systems is an essential part of the computational procedure. The second approach recognises that CFD solvers are still too time-consuming and can only be used for special studies, such as the details of water ingress/egress for two-dimensional fluid motion. In this case the aim is to improve engineering tools by determining more accurately the time for a damaged ship to capsize. The dynamic effect of flood water in a heeling ship must be accounted for, as must the effects of forward speed and attempts to steer the vessel. Such work will provide a better basis for class rule development. High-speed vessels In cooperation with INSEAN, experimental tests have been undertaken on semi-displacement monohull, catamaran and trimaran designs. Extensive measurements were made of the wave elevation in calm water, important in determining the waves (wash) generated by high-speed craft. 11

12 An example of the measured wave elevation for the trimaran is shown in Fig. H. 4. Wave-induced response was also studied, where challenges are to describe accurately the hollow of water created behind the dry transom stern, and the nonlinear features of breaking waves. Our aim is to develop a numerical method that can describe calm-water performance, wave-induced response, dynamic stability and manoeuvring of semi-displacement vessels. Nonlinear effects and coupling between different modes of motion may occur in steering a trimaran in waves, and an understanding of this is vital in designing an automatic control system. Theoretical studies have also been made on planing vessels in calm water. While the wave-induced response of displacement vessels can normally be adequately described by linear theory, this is not true for planing vessels, and theoretical work must take this into account. An important aspect of CeSOS work during the year was publication of a textbook on Hydrodynamics of High-Speed Marine Vehicles (Cambridge University Press). The hydrodynamic aspects of the three main categories of high-speed vessels - submerged hull, or supported by foils or air cushion - were here described in detail, with emphasis on the links with automatic control and structural mechanics. an automatic control system aims to maintain them in a steady vertical and lateral position. A mathematical model of the cables is an essential part of the analysis, and the experimental results of forced transverse oscillations of a towed rigid cylinder were applied to numerical studies of the dynamic hydroelastic response of typical towed cables. The main uncertainty is the hydrodynamic model, but research shows that the experimentally based numerical models of hydrodynamic loads are a clear improvement over numerical methods. Fig. H. 4: Model tests on high-speed trimaran in calm water. Wave elevation measurements at Froude number 0.4, and colour code for the ratio between the wave elevation and the ship length. Towed seismic cables A further research project was related to the towing of flexible seismic cables. In practice, controllable foils are located along each cable, and Fig. H. 5: Complete network streamer system in seismic surveying. 12

13 Floating structures in shallow water There is worldwide interest today in planning for offshore LNG terminals located in relatively shallow waters, in depths ranging typically from 15m to 50m. This presents growing challenges in hydrodynamic modelling, very different from those met in deep water. For ships and large floating structures, particularly when moored, low-frequency effects in irregular waves require attention. Numerical modelling, too, is more challenging. Verification by model testing is essential. For accurate experimental results in such cases, laboratory techniques need to be carefully reviewed, and possibly updated, to avoid their being influenced by laboratory-specific effects. Research in this area was initiated in 2005 through a cooperative study between CeSOS, MARINTEK, ExxonMobil and MIT, planned to continue until The goal Fig. H. 6: Model test on an LNG terminal in shallow water. is to develop improved procedures and tools in the combined use of numerical and experimental studies of large and moored structures in shallow-water waves. Initial studies on improved laboratory generation of shallow-water, irregular waves were made in 2005, a principal topic being the reproduction of nonlinear low-frequency effects in wave groups. Systematic experiments on diffraction caused by large structures were also carried out, to compare with nonlinear numerical modelling. An international seminar on Shallow Water Hydrodynamics wh ich took place at CeSOS in December 2005, is described and illustrated on page 33. Fig. H. 7: Example of bi-chromatic wave measurement in shallow water, showing entire wave and low-frequency component. Structural mechanics highlights The need for rational, transparent design codes and operational procedures for ships and other ocean structures demands explicit criteria, based on the first principles of mechanics, to determine hydrodynamic loads and their effects. A further refinement in design and operations planning is to account rationally for stochastic variability and uncertainties by probabilistic and reliability methods. These are especially important in the design of novel concepts now being incorporated in high-speed vessels, offshore oil and gas installations and large fish farms. Wave load effects in marine structures Among our goals in this discipline is to develop new methods for predicting wave-induced load effects in marine structures, considering the nonlinear and stochastic character of the loads. Also important are the effects of automatic control and of human intervention. CeSOS activities during 2005, therefore, addressed: efficient and accurate methods for determining wave-induced load effects and structural response accounting for the fundamental short- and long-term variability of sea waves, and quantification of the uncertainty involved in wave data. For some loading phenomena, such as slamming and severe sloshing, and nonlinear springing excitation mechanisms, adequate analytical approaches do not exist and design loads must be established by testing reliability analysis in the development of design codes and operations planning, to account in a rational manner for this variability and uncertaint In many projects the mechanics and probabilistic aspects are integrated.in principle, the long-term 13

14 response of ship structures is identified by combining the response in all sea states, wave heading and forward speed according to their probability of occurrence. However, our research has shown that extreme response values can be accurately calculated by considering certain sea states that can be identified by linear response analyses, and particular episodes (comprising a number of waves) in each sea state. In this way nonlinear effects relating to violent, strongly nonlinear load phenomena can be accounted for in the load-effect analysis. Analysis of water impact load effects most important modification has been to divide the calculations into two separate steps. First, the velocity potentials around the section are calculated and stored for unit relative velocities. In a real sea state, these data are used together with the real velocity profiles to obtain the slamming pressure distributions. In Fig. S. 1, predictions are compared with experimental values for a cruise ship. The method is similarly validated for other ship types. Together with a nonlinear hydroelastic ship-analysis program, it can be used for time-domain whipping analysis. Currently, such programs use simpler slamming load models, Fig. S. 1: Slamming pressure on a panel in the flare of a 290m cruise ship in a sea state with significant wave height of 7m. Impact between the water surface and a vessel s hull structure may give rise to large local pressures. Slamming pressures may govern the design of the local structure, but can also result in global hull girder vibrations known as whipping. Even in moderate seas, the whipping vibrations can contribute significantly to fatigue damage, and on passenger vessels they may lead to severe comfort problems. The ability to understand and predict the slamming pressures and the corresponding hull girder responses is therefore of vital importance in ship design, as well as for other ocean structures. Efficient theoretical methods for prediction of these pressures on ships in oblique seas were studied by considering various effects such as pile-up and 3D effects on the relative velocity between the bow and the water surface. The slamming calculation method, first developed a decade ago, was modified for increased efficiency in the analysis of long time series. The since the more refined models have been too time-consuming. Implementing and validating this improved whipping analysis method will be an important activity in A new method of predicting whipping stresses, combining modal superposition and the direct use of rigid body modes, was developed and has been applied to a large high-speed pentamaran, an LNG carrier and a container carrier. Avoiding heavy weather in the North Atlantic For long voyages with no opportunity to seek shelter, a crew s actions depend on rapid onboard monitoring of response, accurate sea-state forecasting and time to carry out any necessary speed reduction, change of heading or rerouting. These issues have been investigated in relation to North Atlantic storm patterns such as that shown in Fig. S. 2. The likelihood of heavy weather avoidance depends upon whether the decision is to be based on measured response of the ship only, 14

15 Fig. S. 2: Development of significant wave height pattern during a North Atlantic storm in March The red curves in the middle figure show the envelopes of bulk carrier routes between Canadian and European ports. or whether reliable two-three day sea-state forecasts are available. CeSOS will be undertaking research on these aspects in cooperation with meteorological institutes. Hydroelastic analysis of large floating structures Significant progress has been made in using floating bridges in benign waters, and in developing the technology for floating airports or other potential very large floating structures (VLFS), especially in connection with the Megafloat programme in Japan and the Mobile Offshore Base programme in the USA. A CeSOS Workshop on VLFS was documented in a special issue of the Journal of Marine Structures in Methods for Second-order forces due to the coupling of the first-order wave potentials in multi-directional waves are also considered in the analysis of VLFS. Efficient algorithms to deal with both large and slender components were developed, considering viscous forces (Fig S.4). Particular challenges are posed by wave and current forces on the net structure of aquaculture plants. Such structures could be relevant in future floating terminals, and in renewableenergy structures. In some of these facilities the interaction between the structure and its mooring system represents a particular challenge, and hydroelasticity and different types of module connectors must also be considered. Response analysis of prismatic LNG tanks Fig. S. 3: Vertical displacement amplitude (with different phase angle) along the longitudinal centreline of a 60 x 300m floating structure subjected to a regular wave. The structure has a transverse connector with different rotational stiffness at the transverse midline. The red curve corresponds to a pin joint connector and the black curve to a rigid connector. The filled circle symbols indicate experimental results for the case with rigid connector. Prismatic LNG tanks consist of an inner membrane and a thick insulation layer supported on the steel framework. The insulation also has a load-carrying function, and must resist fluid pressures due to sloshing response on relatively small areas, and rigid body and whipping- induced pressures on larger areas. CeSOS research has addressed the determination of characteristic extreme values of pressure, based on the stepwise approach shown in Fig. S. 5. The first step in dynamic analysis of single- and multi-module structures are being developed, and Fig. S. 3 shows the results of a hydroelastic analysis of a typical large floating structure. Fig. S. 4 Displacement in the centre of the bow in a 60 by 300 m rectangular VLFS subjected to two oblique wave patterns obtained by a second order frequency domain method. 15

16 Fig. S. 5: Procedure for determining sloshing load effects for design of membrane tank insulation analysis is to identify the critical sea states, using two simplified methods for analysing ship motion and sloshing response. Ship motion results in violent fluid motion in the tanks, causing high pressures on the tank structure. Measurements in model tests recognise the spatial and temporal characteristics of such pressure. Emphasis has been placed on statistical postprocessing of sloshing pressure peaks. Two probability models, Weibull and generalised Pareto, were fitted to measured data samples as well as to samples obtained by hydrodynamic analysis of the measured peaks. In practice, the static stress level of the lower part of a Mark III tank system supported by a flexible steel structure is found to be higher above the stiffeners and lower over the middle part of the plate. The dynamic structural response should be determined based on dynamic time-domain analysis taking account of spatial extent, added mass effect and pressure time history. We have investigated the effects of sloshing impact rise time and load on the maximum dynamic stress level of the lower part of the Mark III system, based on rigid and flexible steel plate supports. For impulse-type sloshing pressures relative to the steel plate, this plate behaves as a rigid support, resulting in vertical responses that exhibit a limited variation over the area. Further work will aim at the development of an accurate yet robust method of determining wave-induced stochastic sloshing response reflecting long-term characteristics of loading, by accounting for variation of such parameters as significant wave height, mean wave period, ship speed and filling ratio. It will consider the various sources of uncertainty in order to establish a rational basis for proposed safety factors. Wave-induced vibration of large ships Research which received some outside attention was that on the effect of wave-induced vibrations on large ships. Such vibrations contribute both to accelerated fatigue damage and to higher extreme loading. None of these effects are included in current design rules for ships. In March 2005 the Norwegian television channel NRK1 presented our research in a popular science programme. Extensive model experiments were carried out to investigate the additional fatigue damage from the vibrations. An 8.7m model, weighing some 5.6t loaded, was tested with three different bow shapes in both ballast and cargo condition. The 16

17 hull was flexible and could vibrate as in a full-size 300m bulk carrier. The research confirmed that both springing and whipping contribute to fatigue damage. Surprisingly, the slender bow without bow and stem flare did not display any effective reduction in vibration damage, indicating that the contribution is not restricted to blunt ships and bow flare. Cooperation between CeSOS and Det Norske Veritas has been initiated to pursue this problem further by model testing and full-scale measurements. So far, evaluation of full-scale measurements shows that the vibration damage is of similar magnitude to that caused by conventional wave loading. Stochastic analysis of wave-induced response CeSOS work on stochastic dynamic response analysis explored frequency as well as time-domain analysis methods. The simulated wave elevation was found to have its non-gaussian properties, such as skewness and kurtosis, agree favourably with not only the empirical fits based on in-situ measurements but also the analytical solutions provided by statistical analyses. Structural components in the surface zone are exposed to strongly nonlinear forces due to the Morison drag forces and water surface-induced inundation effects, as well as to wave nonlinearity. Efficient frequency domain methods have been developed to determine the Morison forces and the corresponding response of platforms, using a third-order Volterra model. Good agreement between frequency-domain results and time-domain simulation data have been obtained by using this procedure for jackup platforms. Through spectral analysis, it was found that the contribution of wave nonlinearity to structural superharmonic response is comparable to that due to inundation effects. However, unlike inundation effects, the wave nonlinearity results in negative skewness of both force and platform response. In contrast to the linear random wave case, the force and response have skewness and kurtosis excess significantly greater, implying that higher extreme values will be expected. Fig. S. 6 shows a flexible model of a modern 294m container ship with a flat overhanging stern and pronounced bow flare. Tests were carried out in the towing tank at the Marine Technology Centre. The experimental data is being analysed to evaluate nonlinear loading mechanisms that can induce fatigue damage, as well as the characteristics of extreme motions and global loads and how well these can be predicted by theoretical methods. Fig. S. 7: Power spectrum of platform deck response. (i) linear random waves without inundation; frequency-domain (ii) linear random waves with inundation; frequency-domain (iii) nonlinear random waves without inundation; frequency-domain (iv) nonlinear random waves without inundation. Stochastic load combination Extreme loading due to different sources of loads is often determined separately. Since assuming that the maximum of the two loads occurs at the same time is conservative, there is a need to combine them more accurately, using stochastic models of the load processes and their combined values. Based on stochastic Poisson square-wave processes for still-water and wave loading, a new 17

18 Fig. S. 8: Model of combined still-water and wave load processes. solution for the combined load effect has been derived for FPSOs. fatigue, corrosion and other degradation. Such formulations have proved useful in making decisions regarding design, inspection, maintenance and repair of marine structures. In steel-plated structures such as ships, cracks are detected by means of close visual inspection when they have already propagated through the thickness. The propagation of long cracks in stiffened panels must be considered, as they may be present in critical details of the deck and/or bottom plating Combination of cyclic load processes with respect to fatigue is needed, for example, when wave- and low-frequency loading in mooring lines are calculated separately. The combined loading would then be a wide band process and the fatigue cycles should be taken into account by rainflow counting. It is often computationally efficient to determine the fatigue damage under such a combined loading by separately considering high- and low- frequency stress histories. Simple, accurate formulations for both Gaussian and non-gaussian load processes have been derived. Numerical simulations show that the estimated combined fatigue damage is very close to the rainflow prediction. This approach applies when the vessel or structure s service life involves 10,000 cycles or more. If one of the load processes varies only slowly, such as the still-water loads on ships, we propose to consider the cycles induced by the wave loading, and account for the varying still-water loading through a mean stress effect. Time-variant reliability In recent years, significant efforts have been devoted to reliability formulations relating to Fig. S. 9: Degradation of resistance due to crack growth with time and load, showing probability density functions of resistance (blue) and load effect (red) at different times. of the vessel. In such situations strength gradually deteriorates, with the probability that the loads exceed the strength. An efficient time-variant reliability formulation was developed for the safety assessment of ageing steel-plated ships and platforms with through-thickness cracks (i.e. long cracks), and compared with a proposed simple time-invariant reliability approach. It was found that the latter, computationally efficient approach is a good approximation to the time variant reliability problem. Time-variant analyses of mooring systems were also addressed. Slender marine structures risers and tethers highlights Slender marine structures such as risers, tethers and pipelines are key components in many deepsea offshore production systems. The response of such structures to waves and currents is often dominated by non-linear effects, with strong feedback from the dynamic response to hydrodynamic loads. All these present design challenges, and much research effort has been put into various aspects of response analysis. 18

19 Three aspects of slender structures were research topics of at CeSOS during the year: Vortex induced vibrations (VIV) Stochastic analysis under extreme conditions Use of active control for response reduction. Vortex-induced vibrations Research activity on VIV was coordinated with related work at MARINTEK, with a long-term goal to improve the prediction of VIV for slender marine structures exposed to ocean currents. Insight from such research projects should contribute to improvements in analysis tools for engineering purposes. But to ensure practical application we must improve our understanding of the basic physics of VIV, experimental techniques and empirical methods for their prediction. Computational fluid dynamics (CFD, or direct numerical simulation - DNS) is considered to be the future alternative to empirical methods. A strategic university programme on CFD methods sponsored by the Norwegian Research Council is currently under way in the Department of Marine Technology. There is good communication between the two research groups, to the benefit of both. The following aspects of VIV were the subject of research at CeSOS during 2005: Fig. S. 10: Example of digital image from PIV data acquisition. The cylinder undergoes forced oscillations and particles are seen in the fluid. Local flow velocities are found by following the motion path of individual particles from succeeding images. Fig. S. 11: Flow direction and velocity at a large number of grid points are found by processing digital images. The picture shows a detail of a larger image with cylinder at the lower right corner. Experiments with a motion-controlled cylinder The purpose has been to find hydrodynamic coefficients for in-line oscillations, and cases with combined cross-flow and in-line motions. The particle image velocimetry (PIV) technique, as well as conventional instrumentation, were used for force and displacement measurement. Figures S.10 and S. 11 show results of experiments using PIV: Fig. S. 10 shows seeding particles in the fluid illuminated by laser light, while Fig. S. 11 is a result of post processing of subsequent images. Here the estimated velocity vectors are shown. (The two images do not represent the same flow situation). Fig. S. 12: Power density spectrum for the hydrodynamic force on a cylinder with forced IL and CF motions. Higher order harmonic components are clearly seen. This work was partly carried out by a PhD candidate, and partly as a post-doctoral project. Experiments with a long flexible beam The aim of this project has been to improve understanding of the interaction between in-line and cross-flow vibrations in long flexible pipes. The first set of experiments was conducted in the 19

20 large towing tank. Fig. S. 13 shows the carriage and the horizontally mounted test cylinder, 10 m long and 20 mm in diameter. The accelerations in two directions were recorded along the pipe. These data will be processed to define a second set of experiments. Here the test cylinder will have forced motions identical to the measured vibrations, and the flow will be studied by use of Particle Imaging Velocimetry (PIV). used in a strip theory approach for response calculations. However, a slender structure will respond as a flexible beam, and there will be a hydrodynamic communication in the fluid that has been disregarded, or taken into account by some simplifying assumptions. One possible way of improving the empirical methods is to find hydrodynamic coefficients from experiments with long flexible beams and system identification techniques. This has been the task for a guest PhD student from the University of Stellenbosch in South Africa. She has applied an inverse finite-element method for system identification, based on data from previous experiments at MARINTEK with a flexible beam. A typical result is presented in Fig. S. 14, in terms of contour lines for lift coefficients as a function of oscillation amplitude and frequency. The results are promising, and will be confirmed by further work. Fig. S. 13: Experiment set-up in the towing tank elongation. An instrumented flexible pipe is suspended horizontally beneath the carriage. Stochastic vortex-induced vibrations VIV at high mode orders (above 10) appear in stochastic form, in contrast to the single- frequency response of lower modes. However, no reliable method exists today for their prediction. A current PhD project sponsored by Shell International addresses this, with the aim of developing methods for predicting stochastic VIV. System identification applied to VIV Empirical methods for VIV analysis have hitherto been based principally on hydrodynamic coefficients identified from tests with short cylinders and harmonic motions. The data have been used in terms of added mass, damping and force coefficients valid for a given frequency and/or oscillation amplitude. These coefficients have then been Fig. S. 14: Plots of contour lines for lift coefficient as function of dimensionless frequency and amplitude. Extended analysis of data from previous experiments In past work on VIV, there has been a tendency to initiate experiments without allocating sufficient resources for subsequent analysis of recorded data. In particular this has been the case for experiments with flexible beams having multi-modal and/or stochastic response. The main reasons 20

21 are that such analyses are time-consuming, and that standard analysis techniques such as modal decomposition may fail to give correct results. There has hence been a need to improve analysis methods, and to carry out further analyses on past experiments. Such a project has been carried with the involvement of MARINTEK, and the results have been published in international journals. Stochastic analysis of slender structures under extreme conditions Motivation for this project, carried out by a Marintek post-doctoral researcher, was to improve methods for estimating lifetime extreme response for slender marine structures, with a minimum use of computer resources. The type of structure studied in this project was the steel catenary riser (SCR), which in many cases is the optimum solution for floating production units. The failure mode of concern is beam buckling due to loss of tension close to the touchdown point, caused by large downward movement at the top of the riser. Modelling aspects and statistics of the response were studied, and Fig. S. 15 shows envelope curves (maximum and minimum values during one wave period) for bending moments for similar risers in varying water depths. The wave-induced response increases with decreasing water depth, while the response close to the touchdown point shows the opposite trend. Active control for response reduction Tensioned risers are the preferred solution for production risers on tension leg platforms. There may be 20 or more risers on a unit with high production from a large number of wells. In this case the requisite spacing between risers may determine the size of the deck, and hence be important in total field costs. Minimum spacing on deepwater TLPs will normally be limited by the risk of collision between adjacent risers, which could lead to dents in the riser pipe and also damage of the coating, with the risk of consequent fatigue and corrosion. Tension in this type of riser is normally maintained close to constant by an individually controlled heave-compensation system. This can result in the following scenario: if one riser is in the wake of another, the upstream riser will experience larger current forces than its downstream neighbour. But if both risers have the same tension, the deflections of the upstream riser will exceed the deflections of the downstream, and the two risers may collide. One means of preventing collision is to replace the constant tension control system by a system based on equal payout, illustrated in Fig. S. 16. The tension systems for the two risers must communicate so as to agree on a common payout, and decide tension accordingly. An ongoing PhD research project sponsored by CeSOS is to design a control system based on this principle. The candidate is spending six months at MIT while undertaking the work. Fig. S. 15: Bending moment envelope curves for regular waves, equivalent catenary risers at 5 different water depths. Fig. S. 16: Illustration of effect from an equal payout control strategy in contrast to an equal tension strategy. 21

22 Automatic control highlights Ships and ocean structures are designed to operate reliably and cost-effectively. This calls for extending the range of operational and environmental conditions and speed regimes under which they carry out their roles with adequate performance and safety. Ships must do this in changing vessel operational conditions (VOCs); the VOC in turn defines control objectives for different marine operations. At CeSOS, research into these aspects of automatic control includes a number of related PhD projects. Marine control systems architecture The guidance, navigation and control systems on board ship have different functions to achieve their control objectives for given speed and environmental conditions. These functions may also offer various sub-modes, depending on the particular operation, environmental conditions and type of ship. This, in turn, calls for the design of various control systems to undertake or improve performance in any combination of conditions. Introduction of hybrid control for marine controlsystem design will make it possible to develop integrated systems (so-called super systems ) for dynamic positioning, manoeuvring and transit operations, for example, subject to faults or other incidents, and changing environmental conditions. The control aspects are handled at three different levels, as described below. Integration must be reflected at the different levels within the control hierarchy: as shown in Figure 1, there is a hierarchical division between real-time control and monitoring, and operational and business enterprise management within the structure of a control system. Hybrid control systems will be concerned primarily with the real-time level, which is further divided into three sub-levels: Actuator controller (low level): Actuators in marine systems are normally thrusters, propellers, rudders, interceptors, fins, flaps, T-foils and mooring systems. Others include pumps, separators, compressors, HVAC equipment, drilling drives, cranes and winches. These are often associated with a local control system which ensures the relevant action takes effect. Depending on whether the actuators are mechanical, hydraulic or electric, the controllers will have different properties. Plant controller (high level): At this level, the control systems focus on a vessel s operational objectives and generate the desired control commands. The low-level controllers receive these control commands, and operate the actuators to implement the control action. In station-keeping operations, for example, the DP system must counteract wave, wind and current loads acting on the vessel. The plant controller calculates the necessary surge and sway forces and yaw moment needed to compensate the disturbances. These force commands become the input to the thrust allocation system which determines the command to each actuator. The command generated by the thrust allocation system may be power, torque or rotational speed, and serves as the input to each local actuator controller. Similar examples include ballast and loading control, the power- or energy-management system, motion damping and fleet formation control. Local optimisation: Depending on the marine operation in which a vessel is involved (such as drilling, weather-vaning, pipe-laying or transit), different optimisation of desired set points is used. At this level, we find the guidance systems. Implementing such a concept will increase operational availability, making it possible to conduct year-round marine operations, such as sub-sea installation and intervention, drilling and pipe laying in harsh environments. This year-round ability will be essential for oil companies and contrac- 22

23 tors to conduct safe and cost-effective exploration and production. In particular, when conducting marine operations in deep water, hybrid control is important as the operations are more timeconsuming, and hence more sensitive to changes in sea states. Such systems can also incorporate fault-tolerant control. Fig. AC. 1. Controller structure Company spin-off Marine Cybernetics AS is a spin-off company founded by staff of CeSOS and NTNU in Trondheim in The company offers independent testing and verification of control systems on ships and offshore installations using unique Hardware-in-the-Loop (HIL) testing technology. Advanced control systems used, for example, in dynamic positioning, navigation, manoeuvring and drilling, are of growing importance for safe and cost-effective marine and offshore operations, as well as in ensuring safe interaction between technology and human operators. It is in these areas that Marine Cybernetics sees its principal markets. Development work is being carried out in cooperation with Det Norske Veritas and NTNU. In April 2002 DNV introduced a new safety regime for certification of control systems, based on this technology. The services and products of Marine Cybernetics and DNV are available worldwide to ship designers, builders and operators, and to vendors, contractors and oil companies. Initial development was funded by DNV and Innovation Norway, and Statoil has been a prime mover through its supplier development programme. Other project partners include Hydro, NTNU and a group of contractors, shipping companies, suppliers, yards and government agencies. Statoil will help develop the technology to improve safety and efficiency in offshore operations, and sees it of value for future remote operation of offshore installations. With the Marine Cybernetics technology, control systems can be thoroughly tested while a ship is being built and during operation. This results in improved safety and reduces the time and cost of sea-trials, and of in-service downtime. In addition, the technology can assist simulator-based training of ship and offshore rig operators, and verification of operational procedures. The HyMarCS- hybrid marine control systems Depending on its type, a ship s voyage could typically include ocean passage, confined-water passage, replenishment at sea and collision avoidance. Specialist designs might add, for example, ROV support and crane operations. All these vessel operational conditions (VOCs) can be defined in terms of the craft s service and speed, and the weather and sea state. The vessel s mode of operation in turn calls for different services which are provided according to the resources available on the vessel, such as power, thrust and manual intervention. Typical services include motion damping using fins, rudders or thrusters, station-keeping by dynamic positioning or thruster-assisted position mooring, manoeuvring control by way-point tracking, speed control and course keeping. Due to the changes in operational conditions encountered during a particular voyage or mission, the design of fault-tolerant guidance, navigation and control systems must be able to adapt. With the current availability of models, theory and 23

24 a wide range of environmental conditions, while maintaining safety and reliability. Scope of the programme includes: Modelling of vessels in changing operational conditions, such as environment and speed System identification and adaptive guidance and control in changing VOCs Dynamic positioning and thruster-assisted position mooring in moderate to extreme seas Propulsion and thruster control in varying seas Fig. AC. 2: Example of Vessel Operation Conditions (VOC) going from station keeping to transit operations subject to changing enviromental conditions technology, this can be achieved by designing controllers using different models characteristic of particular VOCs, and which perform the necessary changes as a mission evolves. This design methodology falls within so-called hybrid system modelling and hybrid control, in which the system to be controlled and/or the control system are described by a mix of two types of components: Continuous - with signals evolving in dense sets. Discrete - with signals evolving in discrete sets. Hybrid control is similar to adaptive control in that it allows changes in the controller. It also allows changes in the parameters and control structure. This is necessary for the design of marine systems operating across different VOCs. Hybrid control design can also cover the design of fault-tolerant control schemes which aim for the graceful degradation of an automated system in case of faults, so that it continues to meet functional requirements. The HyMarCS programme is a research project coordinated by CeSOS and NTNU, with participants from industry and from universities and research centres. It is dedicated to the analysis and design of fault-tolerant and multi-objective guidance, navigation and control systems for marine craft in changing operational conditions. Aim of these designs is to permit operations in Methods for control of switched and hybrid systems Fault-tolerant, nonlinear and supervisory control Reliability and risk analysis, and human aspects, of marine operations. Active control of slender structures A group of PhD students, under the supervision of the key persons from the Department of Marine Technology, are working on a variety of related topics on slender structures and new concepts for aquaculture, including tensegrity structures. The focus is on new control methods for collision avoidance of an array of tensioned risers at a deep-water tension-leg platform. This work is being carried out in cooperation with the Department of Ocean Engineering at Massachusetts Institute of Technology. Another activity is dedicated to work on wavecompliant tensegrity structures, in cooperation with SINTEF Fisheries and Aquaculture, as part of the strategic institute programme IntelliStruct. A patent on the application of tensegrity structures in aquaculture was filed during the year by NTNU, on behalf of CeSOS and SINTEF. The Marine Systems Simulator The Marine Systems Simulator (MSS) is a simulation environment that provides the resources and tools for quickly implementing mathematical models of marine systems, particularly for the analysis of dynamic behaviour and in control- 24

25 system design. The simulator integrates mathematical models of hydrodynamics, structural dynamics, sensor systems and propulsion systems with electrical and mechanical machinery systems. MSS provides examples of different floating structures, with machinery and control systems performing various operations. The platform adopted for the development of MSS is Matlab/Simulink. This allows a modular simulator structure, and the possibility of distributed development and simulation of complex marine systems and operations. Use of rapid control prototyping ensures swift transfer of control-system designs from simulation to experimental work in the Marine Cybernetics laboratory. MSS also makes possible the systematic accumulation and reuse of knowledge, and results in efficient tools for research and education. During 2005, a new module was added: Hydro Add-in. This enables data to be imported from different hydrodynamic programs, such as VE- RES, OCTOPUS and WAMIT, into the MSS, where a dedicated Simulink model reads this data and implements a time-domain simulation environment. For further information see Dynamic positioning and manoeuvring: a unified vessel simulator and control model Simulators for ships, underwater vehicles and semi-submersibles are based on different hydrodynamic models for dynamic positioning (DP) and manoeuvring, usually using one model for each speed regime. The mathematical models depend on sea state, currents and wind loads. Switching between different models during timedomain simulations introduces non-physical effects and unwanted responses, a major problem when simulating marine operations at different speeds. This also propagates to the model-based feedback control system. Hence feedback control systems must be designed for different applications and speed regimes, making them largely impractical since it is difficult and timeconsuming to switch between DP, autopilot and way-point tracking systems. Research at CeSOS has developed a unified model representation for different speed regimes. Fig. AC. 3: Marine Systems Simulator with Hydro Add-in. 25

26 The proposed representation unifies low-speed seakeeping theory with manoeuvring equations up to Froude numbers , enabling conventional strip theory programs such as ShipX (VERES), OCTOPUS and WAMIT to be used to compute the hydrodynamic coefficients and sea loads (diffraction and Froude-Krylov forces). Data from these programs is post-processed in Matlab and imported into Simulink. By using model-reduction techniques and Cummins equation it is possible to represent the fluid memory effects by a set of ordinary differential equations. A vessel model in six degrees of freedom (6 DOF) will typically be represented by such equations. Assuming linear superposition, it is possible to model viscous effects, nonlinear manoeuvring coefficients and higher-order damping terms directly in the time domain. Response from the simulator can be validated against experimental data and model tests to improve performance: the final result is a time-domain vessel simulator that computes position, attitude, velocity and acceleration in 6 DOF for different speeds and sea states. Future work will include validating the numerical methods, and developing a Matlab/Simulink toolbox for post-processing the hydrodynamic data. This process will be automated as much as possible, to formulate a vessel simulator in Matlab for time-domain simulation and testing feedback control systems by starting with the vessel general arrangement and hull geometry. The design methodology and Matlab toolbox will be made available in a textbook by T. Perez and T. I. Fossen to be published in Safety of DP drilling operations on the norwegian continental shelf A typical, dynamically positioned mobile offshore drilling unit (MODU) performing DP drilling is illustrated in Figure 1. In normal operation the vessel is positioned within the central green zone. In a drive-off or drift-off, the vessel loses capability to maintain its position by means of thruster force and may drift beyond the yellow or even the red limit. If the vessel passes the yellow limit, drilling must be stopped and preparation made for disconnection. If it passes the red limit, emergency disconnection must be initiated, to disconnect the riser package and shut in the well. Failure to disconnect may result in damage to the riser, blowout preventer (BOP) or wellhead. This could incur significant vessel downtime and cost, and in the worst case could escalate into a subsea blowout. Dynamically positioned (DP) drilling operation vessel, operational limits and water depth (not to scale). 26

27 Safety modeling Following a study in , a safety-modeling approach using a barrier concept has been developed. Safety of a DP drilling operation was modeled in terms of three main barrier functions: to prevent loss of position to arrest vessel movement, given loss of position to prevent loss of well integrity, should a loss of position become critical. Comprehensive analysis of these barriers has been made and appropriate barrier elements identified. It became evident that powered driveoff can be caused by simultaneous, erroneous position data from two global positioning satellites (DGPSs). Barrier elements have been proposed to prevent DGPSs generating erroneous position data, as well as to prevent erroneous data being used by DP software. Deficiencies of each barrier element, based on operational experience on the Norwegian Continental Shelf, have been considered and recommendations highlight the following aspects: The DP operator is the only barrier element associated with arresting vessel movement. A number of deficiencies that could significantly affect the DP operator s reactions in a timecritical drive-off scenario have been identified. They are associated with four influencing factors: bridge ergonomics, alarm systems, procedures and training. Loss of well integrity means that there is an open hole in the well due to an unsuccessful disconnection, caused by riser breakage combined with BOP blind shear ram not closed, or a damaged BOP or wellhead. Three barrier elements are identified in order to prevent loss of well integrity given a critical loss of position: an Emergency Quick Disconnection system (EQD), Safe Disconnection system (SDS) and Well Shut-in function. Analysis of these barrier elements has identified the relevant sub-barrier elements, the influencing factors and their deficiencies. Based on this barrier analysis, we have made recommendations for improvements in collecting and handling DGPS data, using additional position data, design of bridge and DP-operator workstation, and appropriate alarm systems. We have also made recommendations on DP operational procedures and training of DP operators. Statoil and Hydro have incorporated our recommendations in their specifications of DP drilling systems. Safety of DP operations A joint industry research project Safety of dynamic positioning (DP) operation on mobile offshore drilling units (MODUs) on the Norwegian Continental Shelf was completed in 2005, undertaken by CeSOS and offshore companies in the Norwegian Shipowners Association. The project was sponsored by these two organisations and by the oil companies Statoil and Hydro. Scandpower Risk Management and Smedvig Offshore were also involved in the research work. The research activities and results were reviewed by a reference group which included representatives from drilling operator and rig owner Stena Drilling, Saipem, Fred Olsen Energy, Prosafe Offshore the Petroleum Safety Authority, HSE (UK), NMD and DNV. The system vendor Kongsberg Maritime and the Ship Manoeuvring Simulator Centre in Trondheim were also involved. Industry-oriented research in MARINTEK MARINTEK is an independent research company in the SINTEF group serving the same industry segment as the Department of Marine Technology. MARINTEK carries out research funded by the research council and by industry. The close cooperation between MARINTEK and CeSOS ensures rapid dissemination of results generated by basic research in CeSOS, for use in system design and planning of marine operations. Projects which have benefited in this way include the global wave-induced response of novel ship concepts such as trimarans, pentamarans and LNG vessels, sloshing in LNG tanks and vortex-induced vibrations of risers and pipelines. This contact with the users of research results is valuable for CeSOS in receiving feedback for future research planning. 27

28 The human element in marine operations Human operators play a vital role in the safety of marine operations. There are two sides to the picture: on one human actions are seen as the root cause or triggering cause of unwanted system events; and on the other they are seen as the last resort that saves the system in an emergency situation. In ship operations restrictions may apply to speed and heading depending on the sea state, particularly for high-speed craft. In heavy weather larger vessels, too, may have to take avoiding action. If restrictions are not complied with, a critical situation may develop. Another situation influenced by the human element is navigation in complex waterways. In offshore operations two case studies carried out by CeSOS, relating to FPSO and shuttle tanker tandem offloading, and to DP operations on mobile offshore drilling units, demonstrate the importance of human factors. Similar studies have been made in other fields such as aviation and the process industries. The challenge is how to integrate the human element in the modeling and analysis of safety in marine operations, which can be affected by environmental forces, automatic control, and not least human operators. By applying lessons and principles from other industries to marine operations, and accounting for the unique features of marine systems, the risk may be assessed and design and operational improvements identified. The ultimate goal is to strengthen the human element as one of the safety barriers in the overall man/machine system. CeSOS has developed a generic probabilistic model of an accident during marine operations which highlights and incorporates human actions in emergency situations. The model consists of three stages: detecting a critical condition, deciding on a response and executing the actions. The probabilistic model has been demonstrated in the studies mentioned above. Our findings show that, in order to prevent human failure and recurrence of incidents, an effective approach is to change the situations in which human operators are placed. We must consider, for example, the available indicators in critical situations (alarms) and the time for human operators to diagnose failure and formulate recovery tasks. Adequate operator training is crucial. Three-stage model for assessment of human behaviour in critical situations. Three-stage model for assessment of human behaviour in critical situations. Harnessing wave energy In 1998 the European Commission set a target for the market share of renewable energy to reach 12% by the year What will this imply in practical terms? A small fraction of the solar energy received by our planet is converted to wind energy, and a small fraction of this is converted to wave energy when the winds blow over the oceans. Averaged over the year, solar power per square metre of the earth s surface is typically W, depending on such factors as latitude and the local climate. Per square metre of vertical area in the air, the average flow of wind power equals around half a kilowatt, while the corresponding figure for wave power is typically 2-3 kw. Hence the practical value of wave-power technology. The market will be huge, as the total amount 28

29 of wave power in the world s oceans could, if harnessed, meet today s entire global electricity consumption. The concept is not new: more than a thousand proposals for utilising wave energy have been described in the patent literature. The petroleum crisis in 1973 stimulated individual inventors, universities and research institutions to initiate significant R&D projects on wave power, in particular in the UK, Norway and Sweden. Most of this activity was discontinued during the early 1980s, when the petroleum price declined and public concern about energy and environmental problems faded. However, the Kyoto protocol on carbon dioxide emission into the atmosphere has, in many countries, stimulated renewed interest in waveenergy converters. A growing number of private companies have become involved in developing wave-energy technology, such as shipowner Fred Olsen with a floating-body design which has already been tested at 1/3 scale. CeSOS is active in the next generation of Olsen s WEC design; a full-scale prototype is to be launched in The process of transforming wave energy to useful energy may be subdivided into two or three different conversion steps. The first step is to convert One-third scale version of proposed wave-energy rig, the Buldra converts oscillating motion of the buoys into electric power. Buoys and structure are of composite materials. Photo courtesy Fred Olsen wave energy into energy of an oscillating system, such as a heaving buoy or water oscillating within a structure. Secondly, the oscillatory motion is transmitted to pumps or other suitable energy-conversion machinery. Hydraulic or pneumatic motors, or mechanical means such as racks and pinions, convert this into useful energy through rotating shafts. These in turn spin electrical generators. For some applications, wave energy could be utilised more directly. Examples are in vessel propulsion, desalination of sea water, cooling for refrigeration plants, heating sea water for fish farms and swimming pools, and pumping clean sea water to fish farms and to contaminated lagoons and other sea areas with insufficient water circulation. WECs utilising the heave motion of floating bodies were investigated in the 1970s in Norway and Sweden, and later in Denmark. The design in which CeSOS is involved exploits all of the Centre s multidisciplinary skills - hydrodynamics, structural mechanics and cybernetics. The overall project goal is to produce electric power at lower cost than offshore wind energy. Aquaculture our future supply of seafood Fish products are a vital part of the world s supply of food protein, and aquaculture will play a major role in filling the growing gap between supply and demand for seafood products. Aquaculture is in a phase of rapid expansion worldwide, and is expected to replace natural fish stocks as the main supplier of seafood. New technology will improve the efficiency of production and operation, the safety of handling fish farming gear and the economics of production, and CeSOS is actively involved with relevant research in these areas. Future technical requirements can be summarised under four key criteria: financial viability, environmental sustainability, fish welfare and human health and safety. They must also minimise social conflict with other users of the marine environment and reduce environmental impacts such as escapes, diseases and nutrient pollution. 29

30 To provide better growing conditions for the fish, and in response to environmental concerns and coastal use conflict, farms need to be located in harsher sea areas. The recent high number of escapes from coastal facilities highlights the need for different technologies for these more exposed locations. Globally, farm installations and technologies capable of operating profitably in the open ocean are a target for development in many regions that lack indented coastlines. See CeSOS is expected to be further expanded in the future. Traditional fish farms are unable to withstand the forces of large waves far out at sea; further growth, therefore, calls for new types of large fish farm, which can continue operation in all weather and sea conditions. Net cages today are often arranged in farms of 6-10 units, each with a diameter of 40m; as the size of farms increases and they are used in more exposed locations, handling of mooring systems, nets, surface floaters, and attached ancillary equipment will involve greater loads and forces. Especially critical is the netting, which is susceptible to damage from excessive loading and must at the same time offer adequate volume for the fishes welfare. Mechanisation and automation of farms will continue to increase, and better tools will be required to perform operations safely. Boats and platforms must be designed to integrate equipment in a way that creates a safe working environment: critical equipment includes cranes, winches and other lifting and hauling devices, all of which place farm structures under heavy strain. CeSOS cooperates with SINTEF Fishery and Aquaculture (SFH) in helping develop innovative technology which could enhance the cost benefits of aquaculture. In particular this cooperation involves the IntelliSTRUCT programme, funded by the Research Council of Norway for the period and run by SFH. The programme seeks to combine the disciplines of hydrodynamics, structural mechanics, automatic control and fish ethology, and to design structures that both adapt to sea loads and optimise the well-being of the fish. CeSOS is a partner in the IntelliSTRUCT programme, and during the year key persons in CeSOS supervised two PhD students and a postdoctoral fellow. Cooperation between SFH and Possible future fish farms The strategic research areas at NTNU NTNU aims to serve society by developing and maintaining the technological knowledge and skills needed for sustainable growth. To realise this goal NTNU has given priority to six strategic research areas: Marine and Maritime Technology, Information and Communication Technology (ICT), Energy and the Environment, Materials, Medical Technology and Globalisation. Maritime technology The long Norwegian coastline and sea areas with rich oil and fish resources have given favourable 30

31 New research vessel CeSOS is looking forward to using NTNU`s new research vessel Gunnerus in its research projects. The vessel is 31 m long and has a deck space of 100 m² for extra equipment. It is readily accessible next to Sintef`s Sealab at the harbour in the centre of Trondheim. 25 people can participate in lectures or meetings in a fully equipped conference room. The vessel is well equipped with computer facilities and two laboratories, and the newest navigation technology including advanced instrumentation for dynamic positioning and ROV operations. It is designed to reduce hydro-acoustic noise levels. A diesel electric plant with 3 x 450 kw generator sets, 2 x 500 kw electric propulsion motors and FP propellers, and a bow thruster of 200 kw provide good manoeuvrability. The vessel has been designed for assignments related to marine technology, biology, fisheries, fish farming and oceanographic research carried out by both NTNU and its associates. Rolls Royce university technology centre On 9 May 2005, Rolls-Royce plc, MARINTEK and NTNU opened a University Technology Centre (UTC) on Performance in a Seaway. The centre focuses its research on propulsion in a seaway, with investigations of thrust loss and dynamic forces on propellers and azimuthing thrusters, and involves researchers from NTNU and MARINTEK. Other activities are related to the development of ship simulator software for a ship in a seaway, and of software tools for prediction of DP capability, motions and speed loss. Annual budget is approximately 5 million NOK. Located adjacent to CeSOS, the Centre provides important local support for our research activity on manoeuvring and dynamic positioning. In rough seas a ship s stern and propeller can rise clear of the surface, resulting in instantaneous loss of thrust. Even when it remains below the surface, the propeller can be operating in an air/water mixture, causing severe cavitation. Photo: courtesy Rolls Royce Drawing of the new research vessel This figure shows ventilation by a propeller close to the surface. growth conditions for shipping, fishing, aquaculture and oil and gas production.today these resources form the basis for Norway s most important industries, and jointly account for 60 percent of Norway s total exports. Technological competence at the highest level is crucial in order to maintain the ability to compete in these fields. In this strategic area are two facets of special interest: development of sustainable marine technology, and the creation of values from marine biological resources. There NTNU will generate, manage and disseminate the knowledge required to create sustainability and competitiveness. This demands expertise from many disciplines. A total of around 260 researchers are currently working in the marine and maritime field at NTNU, with about 25 PhD students graduating annually. Marine/maritime research groups in Trondheim undertake an annual total of around 600 man-years in the University s comprehensive laboratories for marine technology and biology. 31

32 Initiator and sponsor Sponsors R & D partners National cooperation CeSOS main partner in Norway is MARINTEK. In 2005 one PhD student and four postdoctors/researchers fully employed by CeSOS came from MARINTEK, and others were engaged in research at the Centre. CeSOS is directly involved in MARINTEK s Strategic Institute Programme Deepline. CeSOS personnel are also involved in challenging research tasks for the industry. In 2005 cooperation with SINTEF Fishery and Aquaculture gained momentum, notably through the Strategic Institute Programme Intellistruct described on page 30. We also benefit from contact with researchers from other Norwegian universities and research institutes in various contexts, including their visits to CeSOS. Contact with researchers from Det Norske Veritas, Norsk Hydro and Statoil continued to take place through workshops and individual contacts specific to relevant research projects. CeSOS is located close to NTNU s Department of Marine Technology. Interaction is important between colleagues working in related areas, and integration between the different groups of PhD students and postdoctors is also encouraged, including a seminar series run by the PhD students. Formalised cooperation between CeSOS and other NTNU units is established through Strategic University Programmes run by others but involving CeSOS key persons. These are detailed in the Appendices. Our staff are also in contact with the Rolls Royce University Technology Centre, which focuses on propulsion technology and is closely linked to CeSOS activity in dynamic positioning and manoeuvring. International cooperation CeSOS employs researchers from a number of overseas countries, and cooperates with researchers from such partners as CSSRC, INSEAN and MIT. A number of MIT professors spent time at CeSOS in 2005, contributing to seminars and supervising our PhD students. Four research staff from INSEAN and two from CSSRC also stayed with us during the year. Mike Triantafyllou Jean-Jacques E. Slotine Dick Yue Kim Vandiver In addition many international visiting professors and other researchers called upon the Centre in Some 30 guest lectures were delivered, and two international workshops attracted about 40 participants. The Centre is involved in the EC networks SAFRELNET and MARSTRUCT, and the Marie Curie Training Sites Rossite and CyberMar. The Specific Target Project SEEWEC, in the 6th EU framework programme, was initiated in Key persons in the Centre serve as editors of three international journals as well as on the editorial boards of 16 other journals, and were involved in organising 13 conferences held in 2005 or planned for Our staff serve on international scientific committees, carry out journal reviews and evaluate research proposals. 32

33 Workshops Workshop on tensegrity structures Engineering science deals with man-made structures, equipment and devices, and their design, fabrication and use. A two-day Course and Think Tank on Tensegrity Structures and a one-day Workshop on Slender Marine Structures were held at CeSOS during June 2005, with 40 delegates from academic and industrial organisations. Presentations were made by, among others, SINTEF, Statoil, Aquasmart, MARINTEK, Norsk Hydro and Det Norske Veritas. The purpose was to stimulate future CeSOS research by looking at new concepts, in particular the potential of s tensegrity in offshore and aquaculture engineering. Tensegrity from tension and integrity implies a structure of two different types working together. Instead of counteracting, they interact with environmental forces. The result is a smart, compatible construction, more resistant to load and stress than traditional structures. Professor Robert E. Skelton of the University of California, San Diego intrigued participants with his ideas for these intelligent structures. Inspired by the artist Kenneth Snelson, he has made tensegrity into a new scientific field based on knowledge of cybernetics and physics. Skelton s tensegrity structures aim to to be flexible and adaptable, rather than over-dimensioned for strength. Skelton looks to nature s diversity of solutions an insect s wing or a spider s web, for example - and uses the same principals in his theories. Engineering structures in offshore and aquacultural applications can be inspired by each other as well as exploiting ideas from the aerospace industry. Adapting both new and traditional technologies makes for the active exchange of knowledge. The Workshop called for interaction between disciplines as well as international cooperation, as a basis for introducing the tensegrity concept into practical application. Workshop on shallow water hydrodynamics In connection with the work initiated on Shallow Water Hydrodynamics, an international Workshop devoted to this research topic took place at CeSOS in December Nine papers were presented, by experts from Norway, the USA and Europe. Topics included nonlinear hydrodynamics, shallow-water coastal and harbour wave spectra, ships in shallow water, modelling of currents and tsunamis, laboratory wave modelling, and numerical modelling of one or more floaters in shallow water. In discussion at the Shallow Water Hydrodynamics workshop - Professors O.M. Faltinsen and C.C. Mei. Professor Robert E. Skelton of the University of California, San Diego, demonstrates practical flexibility of a tensegrity structure. Participants at the CeSOS Shallow Water Hydrodynamics workshop in December

34 Recruiting and educating researchers An important part of the Centre s activities is the recruiting and training of future researchers the doctoral candidates. In 2005 four new PhD students joined CeSOS. Among them were Bjørn Christian Abrahamsen and Eivind Ruth, who both received MSc scholarships in the Shell Campus Ambassador Scheme at NTNU, in competition with MSc students from other faculties. Bjørn Christian is also the first PhD candidate in CeSOS to enter the researcher school scheme, implying that he fulfils his 5 th year MSc programme and starts his PhD studies in an integrated manner. Some of the key CeSOS personnel are also involved in running the international MSc programme in Marine Structures. reporting and an assessment of the thesis by a committee. The main evaluation according to these institutional requirements is after the fact and there is limited opportunity to improve deficiencies. Hence, Centres of Excellence have a particular role as doctoral schools, to provide research quality, research methodology and the research process - including the interaction between PhD candidates and supervisors and other experienced researchers - in a stimulating environment. An important issue is to achieve synergy among the many PhD candidates and other researchers at the Centre. In 2005 focus on quality was highlighted in CeSOS Postdoctor Petter A. Bertelsen spells out the best way to obtain a PhD. Key personnel offer several PhD courses, listed in the Appendices. In 2005 three PhD students supervised by key personnel in the Centre graduated. CeSOS continues to offer opportunities to work in the Centre to excellent MSc students specialising in structural mechanics, hydrodynamics or marine cybernetics. Six students had such summer engagements in students who gained an MSc degree in 2005 were supervised by personnel from the Centre. Quality of PhD studies PhD studies serve two purposes: to educate research personnel for industry and governmental bodies and to generate new knowledge that is disseminated throughout society. The quality of the PhD research education is governed at the institutional level by entrance requirements, submission of research plan, pro gress Bjørn Chr. Abrahamsen(right) and Eivind Ruth both received MSc scholarships in the Shell Campus Ambassador Scheme. by familiarising PhD students through seminars and discussions exemplifying good research, and by interaction with postdoctors. In particular, Estelle Phillips, PhD and author of the successful book How to get a PhD (McGraw-Hill Education, 2005), gave a one-day seminar for supervisors and PhD students. PhD Graduates in 2005 Arne Fredheim Current Forces on Net Structures Roger Skjetne The Manoeuvring Problem Rune Yttervik Ocean Current Variability in Relation to Offshore Engineering 34

35 A road less travelled Dr Roger Skjetne, PhD The background of CeSOS research staff includes wide and often international experience. A home-grown CeSOS success story which doesn t follow the usual path is that of Dr Roger Skjetne (33) who completed his PhD at CeSOS in Now working as a senior engineer for Marine Cybernetics AS in Trondheim, Dr Skjetne gained the 2005 Esso Award for the best NTNU PhD thesis on applied research. A prize-winning engineer? Skjetne must have a strong scholastic background. This he has, but academic focus wasn t immediate: he began his career as a shipyard electrician. A practical start Roger Skjetne grew up in Stord, an island community south of Bergen. Home to the largest offshore yard in the country, Aker, it was perhaps inevitable that a young Skjetne would want to work there. One of his school teachers thought it was a waste that the high-achieving 14 year-old was applying for an electrician s apprenticeship, but young Skjetne had a plan. His aim was always to study engineering, but he was determined also to have practical experience. Skjetne completed his apprenticeship and a topup educational year, then moved to Bergen College. Planning ahead was already paying off. His college summer job, in contrast to those of his class-mates, involved well-paid, relevant work as a skilled electrician. He finished the last six months of his controlengineering degree as an Erasmus student in Manchester, England. He decided to continue with a Master of Science degree in electrical engineering, and now the sunshine of California beckoned. greatly enjoyed his studies. But then an inviting PhD project at CeSOS with Professor Thor I. Fossen meant it was time to head back to Norway. Skjetne retained links to the US by working with both Professors Kokotovic and Fossen at CeSOS during his PhD work. Having Professor Fossen as a supervisor and Prof. Kokotovic as a co-advisor was a great advantage, says Skjetne. He also describes the CeSOS/NTNU tank-testing facilities as being instrumental in his attaining a high standard of work. Though surprised and pleased at winning the Esso award for his PhD thesis, Skjetne never doubted that his career would have a marine focus. They say Norwegians are born with skis on their feet, but for me it was the ocean beneath my feet. Does his electrician s background provide him with an edge in his PhD and current line of work? Maybe I approach problems in a slightly less theoretical way, he ponders. If you don t think about problems too much they tend to solve themselves. CeSOS is proud to contribute to the success of its diverse range of students and staff. And Skjetne? He will no doubt continue on a unique path his very own road less travelled. Text: Jae Spinaze. Further afield The University of California, Santa Barbara (UCSB) offered an attractive Master s programme, and Skjetne was lucky enough to be assigned to work with Professor Petar Kokotovic. With this world leader in nonlinear control theory as a mentor, plus gaining a sound basis in research, Skjetne Dr Roger Skjetne 35

36 Organisation and management CeSOS is formally organised at the faculty level of the Norwegian University of Science and Technology (NTNU). This is partly due to the interfaculty membership of key persons, but primarily to the emphasis that NTNU has placed on the three Centres of Exellence that the Research Council of Norway has recognised at NTNU. CeSOS is located at the Marine Technology Centre, which also houses the Department of Marine Technology (DMT) of the Faculty of Engineering Science and Technology, as well as the SINTEF research institute MARINTEK. This location of CeSOS ensures a unique environment of researchers and access to extensive laboratories, library facilities and other infrastructure. other two disciplines. Realising the strategy of combining use of theoretical and experimental methods is encouraged by the selection of researchers and PhD candidates. One of the 8 key personnel is in charge of each project. Organising and managing such a research group is challenging. In just three years it has developed into a Centre with about 80 researchers of differing educational and cultural backgrounds, half of them from outside Norway. In total, their work represents some 50 man-years annually. The main challenge is to balance the need to reach our goals, while still allowing researchers the freedom for creativity. Research in CeSOS is organised according to the dominant discipline in each project, with stimulating cooperation with personnel from the Photo courtesy of MARINTEK A view of Marine Technology Centre in the foreground and to the right. 36

37 Management team Activities in the Centre are organised in the three project areas defined in Research Highlights In each project area there are key persons, postdoctors and doctoral candidates. Typically, projects involve two or three of the main disciplines represented in the Centre. The project areas are organised according to the leading discipline for each individual project. Projects initiated so far are primarily relevant to the design and operation of future ships and offshore structures. Key persons are Project Managers Prof. Torgeir Moan Director Prof. Odd M. Faltinsen Head, Hydrodynamics Prof. Olav Egeland Head, Automatic Control Man-efforts in CeSOS during first three years of operation. Staff man-years Centre Director Adm. personnel Summary Key persons, research Visiting researchers - Professors Researchers 1.7 Postdoctors ,9 PhD students * Summary Total * Including personnel associated with CeSOS but with other financial support. People At the end of 2005, the Centre involved 8 key persons and 12 fulltime visiting professors, postdoctors or researchers. 17 PhD students were employed by the Centre, while 16 other PhD students who were supervised by key persons had financial support from other sources. Eight other researchers from our partners MA- RINTEK, MIT, INSEAN and CSSRC were involved in research on a part-time basis. In addition 7 visiting professors from different universities and 6 researchers spent on the average 2-3 months at the Centre. All visiting researchers are full time employees of their own organisations, and their research in the mother organisation is not counted in the research man-years of CeSOS. Administrative support An administrative secretary, Sigrid Bakken Wold, deals with personnel contracts and accounting analysis, and handles preliminary enquiries. She Number of researchers and man-years, according to category and nationality. Nationality Key persons Visiting professors1 Visiting researchers Postdocs PhD students SUM Norwegian Other nationalities SUM 8 (3.8) (1.7) 17 (8.8) 33 (27.5) 82 (49.8) 1 including MIT professors. (Man-years in brackets) 37

38 Key Personnel CeSOS Prof. Torgeir Moan Director Prof. Odd M. Faltinsen Head, Hydrodynamics Prof. Olav Egeland Head, Automatic Control Prof. Carl M. Larsen Administration -a dynamic, daring and demanding international research community Prof. Thor I. Fossen Prof. Arvid Næss Prof. Asgeir J. Sørensen Prof. Rong Zhao Sigrid Bakken Wold Executive Officer Post.Docs Dr. Ole Hermundstad Dr. Tristan Perez Dr. MingKang Wu Dr. Elizabeth Passano Dr. Xujun Chen Dr. Oleg Gaidai Dr. Svein Ersdal Dr. Martin Murillo Dr. Yilmaz Türkylimaz Dr. Kjetil Skaugset Dr. Torkel Bjarte-Larson Dr. Shixiao Fu Dr. Jerome Jouffroy Dr. Wenbo Huang Dr. Xiang Yuan Zheng Dr. Fabio Celani Dr. Olav Rognebakke Dr. Petter Andreas Berthelsen PhD Students Andrew Ross Anne Marthine Rustad Ivar-Andre Flakstad Ihle Saverio Messineo Morten Breivik Zhen Gao Eivind Ruth Anders S. Wroldsen David Kristiansen 38 Ingo Drummen Renato Skjeic Reza Taghipour Prashant Kumar Soni Sun Hui Huirong Jia Trygve Kristiansen Bjørn Christan Abrahamsen

39 Visiting Scientists Prof. Alexander Timokha Prof.II Mogens Blanke Prof. Changkong Hu Dr. Anna Ivanova Olsen Dr. Haibo Chen Dr.Marilena Greco Dr. Huang Xiaoping PhD Students Csaba Pakozdi Erlend Kristensen Celeste Bernardo Mateusz Graczyk Xiangjun Kong Xinying Zhu Jie Wu 39 Øyvind Notland Smogeli Kari Unneland Kristoffer Høyem Aronsen Jose Marcal Zhi Shu Gaute Storhaug Tone M. Vestbøstad

40 is also the contact person for visiting professors and students. In 2005 Jorunn Fransvåg, MSc and Ellen Knudsen, BSc were engaged for 8 and 1.5 months, respectively, to provide administrative assistance in textbook projects, contribute to information on the web, and organise international workshops. IT support is provided through the host department, and institutional formalities of PhD students in NTNU are handled by their respective faculties. Safety, health and environment CeSOS aims to create a daring, demanding and dynamic environment for research and development. At the same time, an important issue is safety, health and the working environment (SHE). This provides the framework to ensure physical and mental well-being and safety, especially in laboratory work, and the positive atmosphere of a successful organisation. Board of Directors The Board met twice in 2005, on March 3 and October 10. Statement by the board The Board is very satisfied with the activity at CeSOS. During 2005 more than persons were affiliated with CeSOS, among them 17 postdocs and researchers and 33 PhD-students including those with other financial support. CeSOS has succeeded in recruiting the best PhD students, generally with A level grades. Fifty percent are other nationalities and as many as 13 visiting professor/researchers from highly recognized international universities or research institutions paid short term visits to the Centre, consistent with our goal of international cooperation. Publications from the Centre show a significant increase compared to 2004 and are of high quality given that two of the publications were awarded. We also observe with satisfaction, that the interesting results are being applied in industrial developments, including cooperation with the spin-off company Marine Cybernetics AS. Public information about CeSOS increased in 2005, due to more frequent appearance in newspapers and television. The Centre has succeeded beyond expectations to attract funding in addition to what the Research Council and NTNU contribute. The Board is satisfied with the increased number of PhD students with excellent grades and look forward to an exiting and productive period with an increasing number of high quality publications and PhDs. The Board s endorsement of the annual report Board visiting the MC laboratory. Carl Arne Carlsen, Senior VicePresident, Head of DNV Research, Det Norske Veritas. Torbjørn Digernes, Dean of Faculty of Engineering Science and Technology, Chairman until October , Rector of NTNU as of August 1, Trond Singsås, Director of the organisation and development. Member of the Board until August 31, Ingvald Strømmen, Dean, Faculty of Engineering Science and Technology, NTNU joined the board on September 1, 2005 and serve as chairman from October 10, Arne Sølvberg, Dean of Faculty of Information Technology, Mathematics and Electrical Engineering, NTNU. Oddvar Aam, President, MARINTEK. The main responsibility of the Board of Directors is to ensure that CeSOS achieves its goals within the resources available. As a part of their duties, the Board members have discussed this Annual Report and endorse it. Professors Faltinsen, Fossen and Moan were invited to deliver keynote plenary lectures at prestigious Conferences in Professor Torgeir Moan delivering his Keppel lecture on Nov.30. at the National University of Singapore, before an audience of more than 350 in two auditoria. 40

41 Honors and awards In 2005 two publication awards were received: Professor Torgeir Moan received the Best Paper in SIE Award for 2005 for his paper on Reliability-based management of inspection, maintenance and repair of offshore structures in J. Structure and Infrastructure Engineering. Trong Dong Nguyen was awarded the KKCNN C.K. Choi Award for outstanding young researchers in 2005 for the paper on Hybrid Controller for Dynamic Positioning from Calm to Extreme Seas - Experiments with a Model Ship, which was co-authored with A. J. Sørensen and S. T. Quek and was presented at The 18th KKCNN Symposium on Civil Engineering in December in Kaohsiung,Taiwan. Public information about CeSOS in 2005 has appeared in newspapers, journals as well as on NRK television, in the popular science program Schrødingers Katt. The model test of a large bulk carrier which was carried out to investigate the fatigue damage from the wave loading was presented in one episode. The vibration effect is not included in current design rules of ships. The vibration superposed on the conventional loading of the vessel increases the fatigue damage and the crack growth rate. The research confirms that the vibration effect is of similar importance as the conventional wave loading, and that vibration originates from several sources of wave excitation, which all must be included in reliable design predictions. Gaute Storhaug on the towing tank carriage. The bulk carrier runs into short head waves with encounter frequency half of the resonance frequency (wave length is roughly 1/5 of the ship length) making the 2-node vertical hull vibration easily visible. Books Hydrodynamics of high-speed marine vehicles. In 2005 Professor Odd.M. Faltinsen published a comprehensive treatise of the hydrodynamics of various categories of high speed vessels at Cambridge University Press. This book summarises extensive research on wave environment, resistance, propulsion, sea keeping, sea loads and manoeuvring, based on rational and simplified methods. Links to automatic control and structural mechanics are emphasized. Detailed description on waterjet propulsion and the effect of water depth on wash; slamming; and air cushion-supported vessels, including a detailed discussion of wave-excited resonant oscillation in air cushion and hydrofoil vessels. Professor Faltinsen has produced more than 200 scientific papers and a textbook on Sea loads and offshore structures (1990) which is used at universities worldwide. Dr Tristan Perez has published a book on Ship motion control at Springer Verlag. This book introduces ship motion control by studying the particular problems of control system design for course of autopilots with rudder stabilisation and combined rudder-fin stabilisers. The book proposes a contemporary control system design approach. 41

42 Infrastructure and research facilities CeSOS has a well equipped infrastructure including an up-to-date computer network, extensive library and worldleading laboratories. Three major facilities in particular are relevant for CeSOS: Towing Tank Ocean Basin Marine Cybernetics Laboratory Further test facilities have been specially made by CeSOS, such as the means of studying sloshing in tanks. These are described in detail below. Towing tank The towing tank, 260m in length and 10.5 m wide, permits complex testing in waves up to a height of 0.9 m and a period in the range s. Tank depth varies between 5.6 and 10 m. The dynamometers are compatible with computerised data collection and reduction. Strain-gauge dynamometers can measure towing force and undertake open-water and propulsion tests. Test equipment for fixed and floating structures can measure: Pressure Forces and moments in six degrees of freedom Displacement in six degrees of freedom. Flexibility for special instruments is provided by use of modular force gauges, 5-hole pitot tubes permit three-dimensional wake measurements and marine track-motion capture systems make motion measurements in six degrees of freedom. Other equipment includes strain gauges and inductive propeller nozzle dynamometers. The ocean basin With a surface of 80 x 50 m and water depth variable to a maximum of 10 m, the ocean basin is used in ship manoeuvring, sea-keeping, marine offshore operations, floating and offshore structure tests. The picture shows a model of a 294m long modern container vessel tested by CeSOS in the tank. Drawing of ocean basin 42

43 Both basic and applied ship and offshore problems can be addressed. Wind, waves and currents can be simulated, to provide unique testing conditions for all models of any type of fixed or floating structure. 3-dimensional wave conditions are also possible. Stiffened steel tank 0.8 m x 1.0 m x 0.8 m, with an opening for insertion of a flexible plate. This is positioned at the top of one of the tank ends. The tank has been used to study sloshing induced impacts and the effect of hydroelasticity. Marine cybernetics laboratory MCLab is our experimental laboratory for testing ships, rigs, underwater vehicles and propulsion systems. Since 2002 it has also been a Marie Curie Training Site. Equipment Wave-Maker System Inertial Measurement Technology Towing Carriage Wind and Current generators Seakeeping tests use scale models, which can be telemetered without cables thanks to a wireless ethernet connection and a micro-pc onboard. Plexiglass tank for sloshing experiments, 1.0 x 0.6 x 0.6m internal dimensions. Other tanks operated by MARINTEK have also been applied. Dimensions: 40 m long, 6.45 m wide, 1.5 m deep Length of Ship Models: 1-3 m Typical Scale Ratios: Sloshing tanks Three tanks have been designed and installed to undertake sloshing experiments in CeSOS. Plexiglass tank with internal dimensions of 1.0x0.6x0.6m (see Figure). This tank contains a moveable wall, so that different inner compartment sizes can be studied. A special mesh attached to the inner roof can be let down to dampen out wave motions inside. The tank has mainly been used to study three-dimensional sloshing and high-filling sloshing, using highspeed imaging to capture the sloshing-induced impact flow. Plexiglass tank 1 m x 1 m x 0.1 m. This tank has been used for particle image velocimetry (PIV) and high-speed imaging of high-filling sloshing induced impacts, and also for an isolated study of low-filling impact. Software developments New methods developed at the Centre are implemented in computer codes intended for commercial use or for further research. Partly inhouse NTNU/MARINTEK software is used for commercialization. We also note that the methods developed are implemented by others. For instance, Fluent INC. ( in their advancement of their world-leading commercial CFD software to deal with hydrodynamics of high-speed surface ships for U.S Office of Naval Research adapts the method developed by Colicchio, Greco and Faltinsen in a joint CeSOS-INSEAN effort and presented at the 25th Naval Hydrodynamics Conference in