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.

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.

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.

In this thesis, the effects on regular waves when propagating from deep to shallow water have been investigated, assuming linear wave theory. The effects of shoaling, refraction, reflection and diffraction have been studied. The process and types of breaking waves has also been reviewed.Linear wave theory, second and higher order Stokes theory, Stream function theory, Solitary wave theory and Cnoidal theory have been reviewed. The relative validity of the different wave theories was also assessed.The effects on the wave spectrum as a sea state travels from deep to shallow water, described by the energy balance equation, has also been addressed. The effects addressed were wind, nonlinear wave-wave interactions, white-capping, bottom friction and surf-breaking. Two computer models for numerically solving the energy balance equation was mentioned, being SWAN and STWAVE where SWAN was chosen for use in the analyses.The NORA10 hindcast was believed not to properly take the change in water depth into account at the Dogger Bank Zone. At a point north of the location of interest, the water depth was of such a magnitude (81m) that the NORA10 hindcast was believed to yield credible data for the significant wave height and spectral peak period. A long term estimate of the 50 year significant wave height was performed from the NORA10 data at the point north of the Dogger Bank Zone, by the environmental contour method. This resulted in an estimated 50 year significant wave height of 11.74m and spectral peak period of 15.68s.The SWAN model was used on a test case from Svangstu (2011) to get familiar with the program, and investigate how the different physical effects influence the solution. With the knowledge acquired from the test case, the Dogger Bank case was analyzed in SWAN, to obtain the 50 year sea state parameters at the location of interest. The 50 year sea state north of the Dogger Bank Zone, the Dogger Bank bathymetry, as well as a constant wind of 23.3 m/s was used as input. The 50 year sea state at the location of interest was found to be characterized by a significant wave height of 7.34m and a spectral peak period of 15.56s. SWAN was found to result in a significant wave height of some 15-27% lower than what was found in NORA10.By performing a short term analysis on the 50-year sea state at the location of interest, the 50-year design wave height was found to be 12.5m, assuming the individual wave heights to be modeled by the Gluhovski distribution. The 90% confidence interval of the design wave period was found to be 9.6s <T< 16.3s. This was estimated from studying the ratio between the period of the three largest waves in a time series, and the spectral peak period of the sea state in 95 time series from Svangstu (2011) By evaluating only the limiting values of the period range, the longest and shortest design wave was found to be 80% and 97.4% of the breaking wave height respectively, assuming linear theory.The wind turbine structure geometry was simplified to be modeled by a cylinder with a diameter of 6m. By computing the kinematics from the Stream Function theory, the maximum base shear and overturning moment using Morison’s equation was found to be 3.67MN and 65.93MN respectively. The effects of the rate of change of added mass momentum was also assessed.From a simplified and conservative approach, the impact loads from a breaking wave was estimated. This resulted in a base shear and overturning moment of such a magnitude that en extensive analysis is recommended on this topic in the future.

The conventional way of transporting personnel from shore to offshore platforms is done by helicopter. For large distances of transportation this results in high costs due to the limitations in the maximum number of persons each helicopter can transport per trip and due to the high prices on helicopter fuel. In this thesis is an alternative solution to this conventional transportation proposed by the utilization of a logistical HUB. The concept is based ferries doing the transportation of personnel from shore to the HUB and helicopters doing the remaining, relatively short, transfer from the HUB to the respective platforms. The HUB evaluated is based on the characteristic Sevan 650 design, having a cylindrical shape with diameter D=78m in the waterline.The models that have been analyzed in this thesis were modeled in GeniE, the hydrodynamic analyses were done in Wadam and the post processing was performed using Postresp.Models of a platform with a single tunnel cut out with varying tunnel length L have been evaluated, and the motions of these models as well as the surface elevation inside the tunnel were studied in detail. It was recorded a two peaked response in heave for the models with tunnel lengths ranging from 30m<L<40m. This unexpected behavior was found to be due to diverging values for the added mass in heave for increasing tunnel lengths for models with intact tunnel bottoms. This was adjusted for by removing the bottom of the tunnel to add damping to the system, resulting in the usual one peaked response in heave being retrieved. The reason the two peaked response in heave occurred was concluded to be due to Wadam neglecting viscous effects including the viscous damping. This leads to the system having little or no damping and the added mass to diverge towards negative infinity giving unphysical motion representations.Since critical situations for the platform-ferry interaction will occur during loading and unloading of personnel from the ferry to the platform and during entry of a ferry into a tunnel, the wave pattern inside and on the immediate outside of this tunnel have been studied and evaluated. A total of 4 different designs for the layout of the tunnels have been proposed and evaluated to find the design that results in the least surface elevation inside the tunnel and at the tunnel entrance. A window of acceptance for the incoming wave headings were established with the intention of minimizing the surface elevation. The designs were also evaluated regarding their ability to resist large motion for a variety of incoming wave periods. It was concluded that a three tunnel solution with the tunnels being shifted 120 degrees relative each other would result in the smallest platform motions for wave periods smaller than 18s. A design consisting of 4 tunnels, where three of the tunnels are shifted 30 degrees relative each other and the last tunnel being located opposite of these three would result in the smallest surface elevations. An operability study was done for all 4 designs proposed based on the elevations inside and at the tunnel entrance. It was found that the 4 tunnel design described above would result in the largest operability for the platform. It was also found that this 4 tunnel solution would be unstable in roll due to an unsatisfactory low transverse metacentric height. This low metacentric height could be adjusted for by installing a vertical wall in the waterline in the transverse direction of the tunnels orientation.

This thesis considers a foil propulsion system on a supply vessel. In analysing the potential of a foil propulsion system, it is imperative to establish a rigid mathematical model. In that respect, modelling of the dynamic system is emphasised, and a comprehensive study is presented on the matter. The equations of motion for an oscillating foil and a vessel are derived, separately. The two systems are then combined, to form the coupled vessel-foil structure. For the vessel, a time-domain model based on Cummins' equation is proposed. Cummins' equation has proven efficient in assessing a unified seakeeping and manoeuvring problem (Fossen [2011]). In line, the vessel-foil system will be exposed to both vessel oscillatory motion due to waves and forward speed effects, i.e seakeeping and manoeuvring. Moreover, the efficiency of the foil is directly dependent on the two.Additionally, aspects of foil control is looked into. In theory, active control could maximise thrust while preventing stall, which would be ideal. The validity of simulations with active control, however, is highly dependent on the accuracy of the emph{basic} vessel-foil model. Consequently, effort has been focused on presenting a rigid mathematical foundation.

A stepped cylinder could be a desired design for an offshore buoy or SPAR platform. The geometry of a stepped cylinder consists of a small diameter cylinder (d) placed on top of a large diameter cylinder (D). This master thesis has investigated numerically the flow around a stepped cylinder with different diameter ratios (d/D) for a Reynolds number, ReD = 150. The commercial software Fluent v13.0 by Ansys was used for the numerical investigation.The aim of the study has been exploring the nearby wake flow as well as the region where the two cylinders are joined. The hydrodynamic forces and vortex shedding frequency have been analysed and compared for the four different diameter ratios: d/D = 0.3, 0.5, 0.8 and 0.9The major part of the published papers on the topic is based on experimental studies. Only two papers are based on numerical studies, having considered d/D = 0.5 exclusively. Earlier studies have focused mainly on vortex shedding in the wake flow, omitting the forces acting on the stepped cylinder.The stepped cylinder has been modelled using the software GAMBIT. A convergence study investigating the domain size and element density was conducted to ensure a grid independent solution. Special attention was directed at the step region to fully resolve the complex flow in this region. The numerical model was verified to be in good agreement with previous experimental- and numerical studies.For the stepped cylinders significant spanwise velocity was detected in the step region. For d/D = 0.3 and 0.5, upflow was detected over the leading edge of the step whereas downwash characterised the trailing edge of the step. Similarities to the flow around a finite length cylinder could be drawn for d/D = 0.3 and 0.5, whereas d/D = 0.8 and 0.9 resembled that of a straight cylinder.The step was found to affect the wake flow ≈ 10D into D independent of diameter ratio. The wake flow behind the small diameter cylinder was less affected by the step than the large for d/D < 0.5. In the step region two distinct streamwise vortices were detected. A pair of edge vortices as well as a junction vortex were readily detected for d/D = 0.3 and 0.5. The junction vortex was not detected for d/D = 0.8 and 0.9 due to the small step change in diameter.The drag force on D was found to increase as d/D increased. Similarly, the amplitude of the lift force was also found to increase as d/D increased. The mean drag-coefficient varied along the span with peaks in the local drag-coefficient observed in close vicinity of the step.Regular spanwise vortex shedding was detected away from the step at a frequency similar to that of a straight cylinder. In the step region, located mainly on D, a cell of lower vortex shedding frequency was detected for d/D = 0.3 and 0.5. As d/D increased this cell seemed to disappear. Suppression of regular vortex shedding close to the step for d/D = 0.3 was observed for ReD = 150, 300 and 600. For ReD > 150 the large spanwise vortex structures were still discernible, but the presence of small-scale streamwise vortices complicated the flow.