The age of the easy accessible hydrocarbon goes towards the end and new more challenging fields is the future of the oil industry. This is often synonymous with large depths where sea bed mounted platforms are highly uneconomical options. Floating platforms are therefore commonly chosen solutions.In this thesis two types of deep foating platforms are investigated; The spar buoy, a well known, well documented concept and the Octabuoy, a newly developed concept. Both platforms are analysed in two DNV programs, Wasim and Waqum. Wasim is a non linear time domain hydrodynamic program and Waqum is an impulse response function operator with the possibility of adding non linear eects. The spar bouy concept is used as a pilot test in the softwares. A recreation of the experimental results from H.A. Haslum's doctoral thesis from 2000 is attempted. The impact of non linear effects and mooring on both platforms is discussed. The subject of viscous damping is also approached.As has previously been confirmed by many researchers, the spar buoy is susceptible to non linear eects. The triggering of the Mathieu effect is shown in the Wasim analyses. Discussion is also made as to whether the spar might also be susceptible to large excitations due to second order difference frequency interactions between surface waves and body motions. Both these effects happen at low frequencies where radiation damping is low. Viscous damping is therefore of importance. From previous research mooring is found to be important to avoid the Mathieu effect by increasing the damping and moving pitch periods out of the danger zones.After analysing the spar buoy, the Octabuoy's motion characteristics are tested in mild to severe sea states in both softwares. Non linear effects are found to be significant in the vertical rotational degrees of freedom. The heave motion however seems relatively unaffected by non linear effects. Since Wasim models the free surface linearly, what makes the pitch/roll motion affected by non linearities is found to be either non linear hydro statics or non linear Froude-Krylov forces. The Octabuoy is designed to avoid the variation on hydrostatic stiffness. However, the deadrise angle is 10 degrees larger than the ideal angle. Whether this is what leads to non linear pitch/roll motion is not known at this stage.Two softwares are used in the thesis. Wasim has very long CPU time but calculates accurately and detailed information is easily accessed with for instance the Wasim application ForceInspector. Waqum is very quick, with CPU time in the order of minutes. The program requires an experienced user who knows what must be included for a complete analysis. There are uncertainties about the results from Waqum analysis and more verication is needed for the author to feel confident about the software.To conclude, the programs might work well together. Much can be tested quickly in Waqum, and then final configurations can be run more thoroughly in Wasim. It is the experience of the author that at least until the new version of HydroD is finished, running time domain analysis in Wasim should be done through scripting. This gives a larger control over the actual input and might decrease the chance for error.Keywords: Octabuoy, Spar Buoy, Non Linear Effects, Mooring, Wasim, Waqum.

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.

This Master thesis details the development of a mathematical model of ROV SF30k, and its implementation into a DP control system developed by Espen Tolpinrud.The project was performed as a part of the Applied Underwater Robotics atNTNU.A 6DOF model of the ROV was developed. The parameters of the model werefound using both the 3D model of the ROV provided by Sperre AS, and based onthe parameters found previously for ROV Minerva. Both ROVs were developedby Sperre AS and share many similarities. Thrust configuration was developed forthe ROV based on the geometric positions and orientations of its thrusters, whilethrust coefficients were found using propeller data provided by Sperre AS. The DPcontrol system was configured to operate SF 30k by using a configuration file basedon the found parameters.A number of modules were ported from the old DP system, which was tailormadefor ROV Minerva, to the new one. This includes the Kalman Filter, controllersand thrust allocation. An adaptive passive nonlinear observer was developedand implemented.The existing simulator model for ROV Minerva was modified to be able tosimulate ROV SF 30k. This was done by changing the parameters of the processplant model and thrust dynamics.The parameters in the configuration file for the new control system were verifiedduring sea trials onboard R/V Gunnerus on May 29-30th 2012. The thrust allocationparameters were found to be satisfactory during ROV operation, however, themathematical model of the ROV could not be verified due to the small window ofoperation during the sea trials.

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.