Due to high expectancy of hydrocarbon resources in the Beaufort Sea itis seen as an important area for energy in the future. As the focus nowis shifting towards the deeper parts of the sea, there is a need for floatingproduction platforms that are able to operate year-round in the harsh con-ditions of the Beaufort Sea. In this Master’s thesis the design of such aplatform is performed, with respect to global ice loads acting on the plat-form and the capacity of the stationkeeping system. This is used to analysethe operability of the platform.To be able to develop a floating production platform it is crucial to haveinformation on ice conditions in the Beaufort Sea. Literature has been usedto determine ice conditions in the seasonal transitional zone, where it isexpected that the platform will operate. Factors such as level ice, first-year and multi-year ridge dimensions, floe size and ice island mass havebeen defined. These define some of the most common ice conditions in theBeaufort Sea, and as such represent ice conditions a platform can expect tomeet.Functional specifications have been used to determine the most appropriateplatform type. Several platform types were considered based on factorssuch as production and storage, ice loads, and ice interaction with risersand mooring lines. A circular FPSO was selected due to its insensitivity toice drift direction. To reduce ice loading, the platform was designed as adownward sloping cone.Ice loads on the platform have been calculated using several methods com-monly applied in literature. Results show that managed ice yields lowestloads, followed by level ice. Higher loads are seen for ridges, both first-yearand multi-year, and large ice floes.A water depth of 500 m was assumed for the location of the platform. Since this can be considered as a moderate water depth, a conventional mooring system was selected for stationkeeping. The system has 24 mooring lines connected to a buoy, which again connects to the turret on the platform. Internal mooring was seen as necessary to protect mooring lines from ice. Restoring coefficients have been determined using the inelastic catenary equations. Maximum allowable horizontal displacement is defined as 5 % of the water depth. This is used to determine the maximum allowablehorizontal load on the platform to be 53.38 MN.Lastly, the operability of the platform was judged by comparing various iceloads to the maximum allowable load given by the mooring system. Icemanagement is clearly needed when operating in any ice other than levelice. The requirements of the ice management system has been defined, anda general analysis of the primary and secondary objectives of the ice man-agement system has been performed. It is proposed to use one icebreakerthroughout the year, since the platform may encounter multi-year ice floesduring the summer. As the ice season starts an additional ice breaker isintroduced. In severe ice conditions it may be necessary with a third icebreaker. It is concluded that if proper ice management is ensured, the plat-form should be able to operate year-round.

Non-linear analysis of wind load subjected flare tower in Abaqus

Computational Fluid Dynamics (CFD) have been applied for numerical simulations of the flow around simplified shapes of a Remotely Operated Vehicle (ROV). The simulations have been carried out at Re = 850 000, which coincides with a free stream velocity of one knot in seawater conditions. Detached Eddy Simulation (DES) have been used with the k-w SST turbulence model in the near-wall (unsteady RANS) regions. The CFD code FLUENT from ANSYS Inc. have been used.The first case to be investigated, was a fully submerged rectangular stationary cube with both sharp and rounded edges. The sharp edged case showed good agreement with published reference values. The results for the refined mesh gave Cd = 0.8192, Clrms = 0.0473 and St = 0.1132. The Strouhal number was identical for both meshes, while small discrepancies were seen on the mean drag and the root mean square lift coefficient. For the round edged case, the mean drag coefficient was shown to be about 25% of the sharp edged case (Cd = 0.2257). The lift was more difficult to model correct and large discrepancies were seen both on the Strouhal number and the root mean square lift coefficient. It was concluded that longer time series were needed in addition to further mesh refinement in order to get more stable mean quantities of the lift history. Some effort were also made on trying the realizable k-e turbulence model in the near-wall regions for the round edged case, but without noticeably effect on the results. For both the sharp edged case and the round edged case it was concluded that although the drag was successfully modeled, a further mesh refinement was needed in order to ensure converged results.For the case of the simplified model of the ROV, three meshes were used for the grid convergence study. Small discrepancies were seen, between 2% and 6.2%. The pitch moment through the Center of Gravity (COG) was also measured and a negative mean value of Cm = -0.2563 was obtained. This means that the reported instability for the ROV was also seen in the simplified model. Through a more detailed study of the pressure and velocity distributions, the main problem regions were identified to be above the forward top and below the aft bottom. Here high-velocity regions generate low-pressure regions, which coincides with a negative pitch moment. One proposed solution was the removal of the plate in the aft which span the width of the ROV. The effect of this solution was however found to be questionable. This is due to the components which are placed in front of the plate, and these may actually cause the same effect. For this reason, these components should be relocated.It was concluded that there should be performed numerical simulations without the plate and the components in front included. The effect of these components could then be studied and a decision on whether to remove the plate could be made. Also, numerical simulations where different locations for the components in front of the plate are tried should be an interesting case to run with respect to the stability analysis.

The World’s energy demand is rapidly increasing and a good viable renewable energy source is wind power. The land-based knowledge and experience the onshore wind turbine industry possess is used to develop offshore wind turbines. With this knowledge together with the experience and knowledge of the marine industry we can design and produce a floating wind turbine. The main advantages of an offshore wind turbine are that the wind is stronger and less turbulent at sea, visual and noise annoyances can be avoided and there are large available areas at sea. In this thesis coupled time domain analyses of a floating spar-type wind turbine are performed with the intension to study parameters affecting fatigue damage at base of the tower. The software applied is SIMO/Riflex with the extension TDHmill, which gives the wind thrust force and gyro moment on the wind turbine as point loads in the tower top. Short term environment conditions are chosen from a joint distribution of simultaneous wind and waves which is based on measurements from a site in the North Sea in the period 1973 – 1999. In total 141 different environmental conditions are chosen for the sensitivity study. Mean value, standard deviation, skewness and kurtosis are calculated for axial stresses at the base of the tower. Fatigue damage is calculated from the Palmgren-Miner sum with a nominal stress SN-curve from the DNV fatigue standard. The axial stress-cycle distribution used in the Palmgren-Miner sum is found by rainflow counting. Time domain simulations are carried out for the different sea states and fatigue damage is calculated for each case. The statistical properties and fatigue damage are averaged over seven samples with different random seed number to ensure acceptable statistical uncertainty. Accumulated standard deviation shows that 5 samples of each load case are sufficient to ensure acceptable statistical uncertainty. Sensitivity study of different simulation length shows that 30 minute simulations give close to equal fatigue damage and standard deviation as 2.5 hour simulations. Sensitivity of fatigue to wave height and peak period is carried out to study the effect of varying parameters. This study suggests that the highest waves dominate the fatigue damage for the smallest peak periods. For some small wave heights the damage will be constant for a given peak period range. From this sensitivity study it is shown that if the deviation of fatigue damage between the different load cases is small, then the dominating load case of the accumulated long term fatigue damage will be dominated by the marginal probability of each load case.

Present regulations for offshore structures on the Norwegian continental shelf havea requirement for Accidental Limit State redundancy and Fatigue Limit State redundancyin a damaged state. However, the requirement is far more defined forthe Accidental Limit State than for the Fatigue Limit State. An increased understandingof factors governing fatigue redundancy would create a basis to form acomprehensive definition.In literature, the term redundancy is defined in several ways. The different methodscan be divided into two major categories, namely deterministic and probabilisticapproaches. In general, redundancy may be defined as the absence of memberswhose failure would lead to global collapse. Within both the deterministic and theprobabilistic framework, several redundancy factors are usually defined, and thereare resemblance between some of them. In probabilistic methods, the reliabilitymethod is commonly applied through the First Order Reliability Method.Fatigue damage is a primarily concern regarding the integrity for offshore structures.A near constant subjection to cyclic loadings from wind, current and wavesinitiates a cumulative damage process which leads to a certain fatigue life for themembers in the structure. The lifetime may be calculated using either a fracturemechanics approach or a SN-curve approach. There exists several approaches tocalculate the stress levels to be used in the fatigue analyses, and the choice ofmethod is mainly based on whether or not the structure under consideration isdynamically behaving or may be regarded as quasi-static. Also, there may be nonlinearitiesthat needs to be accounted for and naturally this will affect the choiceof analysis method. However, large uncertainties are associated with fatigue calculationsregardless of analysis approach. Thus, a probabilistic framework is highlyrelevant in order to estimate the risk of failure due to fatigue.A study on how impaired integrity affects the fatigue life has been performed fortwo jackets; one highly redundant four-legged jacket and one less redundant threeleggedjacket. The main goal has been to investigate the fatigue redundancy of thestructures, in order to link up the risk of accelerated fatigue due to damage withthe risk of failure due to extreme environmental actions, which may eventually leadto structural collapse. A stochastic fatigue analysis approach was chosen, and theanalyses was in agreement with the standards governing the Norwegian continentalshelf at the time of this thesis. Pushover analyses has been performed on the jacketsto give an insight in their redundancy, and a calculation of changes in the naturalperiods under impaired integrity has also been done.The four-legged jacket was proven to be highly redundant, and had small changesin the natural period under impaired integrity. The three-legged jacket on the otherhand, had some damage cases with a rather large increase. Also, the redundancyfactor R4 was significantly lower for the three-legged jacket, thus confirming it tobe less redundant than the four-legged jacket. A large change in the natural periodwill alter the dynamic response, thus the fatigue life is vastly connected to changesin global stiffness.Trying to explain the changes in fatigue life for the two jackets under impairedintegrity without using a deterministic approach, i.e. calculate the fatigue life forthe specific damage case, was proven to be very difficult. There seems to be noeasy way to isolate the severity of the fatigue life reduction since large changesare occurring throughout almost the entire structure for several damage cases, aswell as large spread in the values them self. However, there was also found sometrends in the results. One of them, was that the closer a member is to the damagedelement, the larger is the expected reduction in fatigue life. Another trend, is thata large fatigue accelerator factor is expected in almost every damage case, thus onemay expect large changes for most of the damage scenarios.Another vastly occurring phenomenon were the location of the damaged memberswho gave the lowest fatigue life in the structures. For the four-legged jacket, thisinvolved damage in the caisson supports. The three-legged jacket, however, hadthe lowest fatigue lives occurring for damage cases in the top frame where there isa lack of deterministic redundancy.There seems to be no fatigue redundancy for the jackets, as there are large fatigueaccelerator factors occurring. There is also the very low calculated fatigue life inthe most extreme cases. However, there has been found a slight correlation betweena large reduction in fatigue life and a large initial fatigue life. What should also betaken into account though, is both the risk related to the fatigue lives found, andthe accuracy of the values due to the linearised analysis.

for advanced riser analysis. Deep water oil recovery have forced a change in thesystems used to tension risers, the traditional wire-pulley systems are replacedwith direct acting hydraulic-pneumatic systems. In order to design these systemsto obtain the desired operability, analysis tools including the heave compensationsystem is necessary. As a result a pipe in pipe RIFLEX model have been developed.In this masters thesis the pipe in pipe model will be used to investigate drive-offand weak link fracture. Both subjects investigated exposes the riser to large forces,and will push the model to its limits. Another part of the thesis is focused aroundbatch execution of analyses with the use of MATLAB.The focus of the drive-off study lies mainly in investigating the dynamic behaviourof a deep water riser (3000[m] water depth) compared to a shallow water riser(300[m] water depth). Results are presented for upstream and downstream driveoff scenarios. The maximum offset is 100[m] obtained during a 50[s] period. Driveoffscenarios include cases where the vessel remains at the 100[m] offset, and caseswhere the vessel returns to its original position.Drive-off simulations revealed large differences in dynamic behaviour of the deepwater versus the shallow water system. When observing the lower riser anglefor shallow water simulations, the angle were closely related to the vessel offsetposition. Deep water simulations showed a delay of almost one minute before thelower angle responded with a rotation in the vessels movement direction. Duringthe first minute an initial effect that caused the riser to rotate away from the vesselposition was observed. Current had a limiting effect on the lower angle whendriving upstream, and increased the angle for downstream drive-off. By includinga return motion the riser angle increased more rapidly to large values. Variation inreturn motion had little effect on the maximum amplitude. The results show thatit might be difficult to take advantage of the dynamic delay in the riser response.Bear in mind that offsets of only 100[m] was investigated, the picture might changefor simulations including larger vessel offset.Weak link fracture is of concern since it will release large amounts of stored energythat is potentially harmful for personnel and equipment. Establishing analysismethods for weak link fracture can help to better understand the dynamics ofthe problem. In the present work a suitable analysis model was selected and aparametric study on the effect of drag on response was performed.A weak link fracture was simulated with 460 tonnes over pull. Weak link fracturesis a highly complex problem since the high pressure content of the riser is releasedinto the water, causing a rocket effect. The presented results are only accountingfor potential energy stored as strain in the riser and heave compensation system.A parametric study of the tangential drag versus the maximum vertical amplitudeof the riser is presented. The results are meant to be used as a starting point inan investigation of measures to limit the weak link fracture response.The weak link simulations showed that large accelerations are involved during theweak link fracture, and therefore added mass and mass can be of importance tothe response. Due to the rapid movement after fracture, it was found that specialcare needs to be taken when selecting the time incrementation for the simulations.

MARINTEK's ship motion simulation program SIMAN (ShipX manoeuvring module) is used to develop a ship motion model for NTNU's research vessel R/V Gunnerus. SIMAN uses a 3-DOF linear mathematical model to describe the vessel's motions. In order to verify the SIMAN model of R/V Gunnerus, full-scale trials of R/V Gunnerus were performed in deep water in Trondheimsfjorden. Turning circles, zig-zag- and stopping tests were carried out and analysed. Data was recorded using Seapath and the DP-system installed on R/V Gunnerus. Seapath registered data at 200 Hz, while the DP-system registered data at 1 Hz. Data registration at 1 Hz turned out to be too seldom, especially for the zig-zag manoeuvres.Full-scale trials are simulated in SIMAN. Measured full-scale results are compared with simulated results, and differences between measured and simulated results are identified. It was expected that differences would occur as SIMAN is developed for conventional vessels and offshore vessels, while R/V Gunnerus is an unconventional vessel (L=28.9 m, B=9.6m). The deviations may be due to inaccurate field test results or errors in the modelling in SIMAN. SIMAN underestimated tactical diameter, transfer and advance in the turning circle manoeuvres. The difference increased with increasing rudder angle (and consequently drift angle), which may indicate errors in modelling of the non-linear damping forces. The damping forces are then modified using Oltmann's polynomial for the cross-flow drag coefficient for a tanker. This improved the results, all with the exception of transfer and advance at rudder angles of 20 degrees. It is also shown that the results are sensitive to rudder angle, so incorrect full-scale measurement will affect the results. The difference between measured and simulated zig-zag trials are significant. However, only a few seconds or degrees difference between the simulated and the measured zig-zag results cause a large percentage difference. Possible reasons for the differences are inadequate data registration of the full-scale trials, or errors in modelling in SIMAN. Overestimated results in SIMAN may indicate an unstable model. Increasing the models stability index by reducing Nv had a negligible effect on the simulated results. Decreasing rudder angle in the simulations improved the results. Track reach in the stopping manoeuvres are overestimated by SIMAN. This may be due to modelling issues as R/V Gunnerus is much smaller and responds faster than the vessels that SIMAN is developed for.In the literature there exists several empirical methods to calculate the hydrodynamic coefficients used in manoeuvring equations. The hydrodynamic coefficients of R/V Gunnerus were calculated using approaches given by Wagner Smitt, Norrbin, Inoue, Clarke, Lee and Kijima, as well as using strip theory for a flat plate. Using these coefficients did not improve the simulated results.In order to create a complete motion model for R/V Gunnerus further investigation is necessary. It is recommended that PMM tests are performed to determine the hydrodynamic coefficients. It can also be useful to investigate the non-linear damping forces. In addition, new full-scale zig-zag tests should be performed in a way that 10/10 and 20/20 tests are obtained. Performing several reruns could be used to determine the precision errors of the full-scale trials. In the literature there is a need for vessels to be used for validation of simulation tools. R/V Gunnerus can be used as a case vessel to investigate how the simulation tools predict the manoeuvring performance of an unconventional vessel. The 26th ITTC stated that there is a particular need for mathematical models for low speed manoeuvring, and vessels also used for validation of CFD-methods. R/V Gunnerus can be used as a case vessel for this research. It is then necessary to carry out tests intended for these purposes.

In the past, testing of lifeboat design has been carried out solely by experimental means. However, due to the large number of factors which influence the loads on the lifeboat structure and its occupants, optimization studies by experimental means have become both time-consuming and expensive. In addition, many effects cannot be studied at laboratory scale due to the inability to match all similarity requirements.Recent advances in computational fuid dynamics (CFD) have made it possible toanalyze the lifeboats performance under realistic conditions. By not being dependenton a physical model, investigation of a larger range of hull shapes at a variety of launch conditions can be done more easily and cost-ecient.This thesis explores the possibility of using the CD-adapco's CFD-software STARCCM+(STAR) to predict the performance of free-fall lifeboats during the impact phase.The thesis focuses on verification and validation of the software by studying water impact of different two and three-dimensional rigid and elastic wedges.For the two-dimensional case, 2-D rigid wedges with constant vertical velocity andvarying deadrise angles (4 to 81 degrees) are studied with respect to various slammingparameters presented by Zhao and Faltinsen (1992). In the study, good agreementis found between the solution predicted in STAR and the presented numerical andanalytical solutions. It is found that the slamming pressures are strongly dependent onthe deadrise angle; from 300 Pa for the 81 deg. wedge, to 275 000 Pa for the 4 deg. wedge. It is seen that as the deadrise angle is decreased, better resolution in grid size and time step is required to capture the peak pressures.The three-dimensional case includes both rigid and elastic wedges. For the rigid case, a3-D wedge is modeled so to represent an experimental study conducted by Yettou et al.(2006). It is found that STAR predicts a lower impact velocity than what is found inthe experimental study. Following, the pressures predicted are too low. The differenceis however moderate, and STAR is able to predict the displacement and velocity-timehistories of the wedge in a satisfactory manner. It is noted that the reason for thediscrepancy lies in the prediction of motion through air - and not in the simulation ofimpact and motion in water. It is also noted that refinements in grid size and time stepare not of great importance if only displacements and velocities are to be studied.For the elastic wedge case, four different elastic wedges are studied to exploreSTAR's possibilities and limitations related to fuid-structure interaction (FSI). Noverification or validation with existing theory or experimental data is performed. Aqualitative assessment of the results is however carried out and it is found that STARpredicts displacements, velocities, accelerations, pressures, deflections and stresses in a satisfactory manner.

Traditionally ships have been optimized for minimizing the fuel consumption in calm water. For slow, large ships like tankers and bulk carriers this has resulted in very blunt bows with high added resistance due to waves. The objective of this thesis has been to investigate if the optimal bow shape, when realistic wave conditions are taken into account, should be more slender than the current blunt bows. The added resistance is also highly dependent on the actual wave conditions the vessel experiences. Thus a question has been if the optimal bow changes with the operational area, or route, of the vessel.Five designs have been investigated representing a range of waterlines from blunt to sharp. They are based on the MOERI Tanker KVLCC2. KVLCC2A is the original design of the MOERI Tanker with no flare. KVLCC2B has the same water line curve as KVLCC2A, but with straight sides and small bilge radius in the bow. KVLCC2C has a more slender bow by moving volume from the shoulders to above the bulb. KVLCC2D is a blunter design than KVLCC2A and KVLCC2E has been elongated by 8 m compared to KVLCC2C to get a more slender bow.Four routes have been chosen to represent trades and ocean areas. The routes are; Arabian Gulf (AG) to the Gulf of Mexico (GM), AG to Japan, Brazil to China and Norway to the East Coast of US.Calm water resistance has been calculated and verified against experimental data. The wave resistance was calculated numerically using Shipflow. These calculations were not satisfying and should be taken a closer look at. Modification of the results had to be done. The results show that KVLCC2A, KVLCC2C and KVLCC2E have very similar calm water resistance. They have slightly lower values than KVLCC2D. KVLCC2B has the greatest calm water resistance. The added resistance was calculated by ShipX. The sharper bow designs have significantly lower resistance in the diffraction regime, as intended. KVLCC2E has slightly a slightly lower added resistance coefficient in the short wave regime than KVLCC2C.The speed-loss calculations were performed by combining wave statistics for the routes, calm water resistance, added resistance and engine and propulsion characteristics in ShipX. The result is an attainable speed at a given power input, 27 000 kW.The results show that KVLCC2C and KVLCC2E have the lowest speed-loss. The attainable speed is highest for KVLCC2C and it can thus be concluded that a sharper design is more optimal when realistic wave conditions are taken into account. The relative speed loss on different routes between KVLCC2C and KVLCC2A shows that the speed loss of KVLCC2C is 14.2% lower for the AG to GM, 13.8%, 16.2 % and14.9 % for respectively AG to Chiba, Mongstad to East coast of US and Brazil to China. Thus, a small difference can be seen, but not enough to change the best design in this case. A review of innovative bow shapes dealing with added resistance was performed and an evaluation based on working principles and applicability to a large, slow vessel was discussed. The designs reviewed were X-bow (Ulstein Design), a new bow from STX OSV and Beak-bow, Ax-bow and LEADGE-bow designed in Japan especially for larger ships. The two first bows are designed primarily with offshore service vessels in mind and focus more on the long waves. The LEADGE-bow, which is based more or less on the same principles as KVLCC2C, shows that a simple sharpening of the bow is an easy and effective measure. This seems like the most promising bow for large, slow ships of those evaluated.

The importance of offshore renewable energy from wind is expected to increase in the future. Most offshore wind turbines are currently installed in shallow water up to 50 meter water depth on bottom mounted substructures. To harvest more wind energy at deeper waters, offshore floating support structures are needed. Semi-submersible floating wind turbine is one of the proposed floating concepts. Under simultaneous wind and wave loads, fatigue might be an important design consideration. Study of fatigue for such structures is thought to contribute to a better understanding of offshore wind turbines.A local part of a semi-submersible wind turbine was studied. The column-brace connection, or joint, connected a wind turbine tower to a triangular semi-submersible floater. Design, stress concentration factors and fatigue damage of the part were the main topics. To calculate stress concentration factors and fatigue damage, dynamic response analyses and finite element modelling were performed. Only the fatigue limit state was considered.Three different column-brace connection designs were analysed. For the initial design, the stress concentration factors generally were way too large - especially for out-of-plane action. For the third design a horizontal bulkhead at the brace centreline was added. This modification decreased the stress concentrations by a maximum of over 90% for out-of-plane action. The modification was only carried out for brace 1.A long-term fatigue approximation with distribution of mean wind speed in the northern North Sea was considered, while the expected significant wave height and spectral peak period for a given mean wind speed were used, to reduce the simulation effort. The critical fatigue damage was observed for brace 2, with a life time of less than a year. For brace 1 the lowest life time was several hundred years, meaning a conservative design. By reducing and optimizing the brace thickness, one could reduce such conservatism. The critical hot-spot-stresses were found at the crown toe and heel for both brace 1 and brace 2. All fatigue calculations included a design fatigue factor of 3.The modification of brace 1 with horizontal bulkheads as additional stiffening reduced the stress concentrations significantly, and increased the fatigue life considerably. Brace 2 still needs to be modified to decrease the stress concentrations, and thus increase the fatigue life.