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.

When a ship-owner orders a vessel from a shipyard, a contract is written to confirm and guarantee the agreement for both parts. An important requirement of the contract is the vessel's speed at a given engine power, RPM and draught, in "ideal" conditions (i.e. calm, infinitely deep and current free water, with smooth hull and propeller surfaces at with no wind and zero drift and rudder angle). The speed capacity of the recently built ship is measured carrying out a speed trial. It is rarely possible to perform the trial under ideal, contractual conditions, and the speed will normally be reduced by environmental factors. Whenever the test is carried out in conditions deviating from those contractually specified, the speed must be corrected for, to best coincide with the contractual stipulations. These corrections can be of significant magnitude and are of great economic importance. Penalties of considerable size are given to shipyards that fail to deliver in accordance with the contract. There are various standards published providing guidelines regarding the execution of speed trials, the measurements that are to be performed during the trials and corrections for environmental factors that are to be made in retrospect. ISO (2002), Perdon (2002), Bose (2005) and B. Henk (2006) were chosen for evaluation and comparison in this thesis. The recommendations of the standards are occasionally disagreeing.The main resistance contribution is claimed to be wind and wave (Bose (2005) and B. Henk (2006)). B. Henk (2006)) states; "these corrections (small displacement deviations, shallow water, and salinity deviations) are relatively small compared to wind and wave directions". Reinertsen (2011) suspects that the added wave resistances calculated by the Hyundai shipyard are too large. This assumption is based on Haugan (2011)'s (employee of KGJS) mean wave load calculations that generally gave results 30 % lower than those found by Hyundai. An unrealistically large correction factor for wave resistance is most definitely advantageous for the shipyard. This will give a higher calculated contractual speed, and the shipyard is consequently more likely to meet the contractual requirements. The Hyundai shipyard's correction procedures were evaluated based on the relevant standards. The shipyard neglects all resistance components, but the added resistance due to wind and waves (they also correct for large discrepancies between the trim/draught obtained at speed trial and that contractually stipulated. This is however not relevant for tankers, as these generally are capable of achieving design draught at the sea trial). This is consistent with the recommendations of Perdon (2002) and B. Henk (2006). The shipyard does not have the speed trials conducted in head - or following waves, nor head - or following wind. B. Henk (2006) and Perdon (2002) underline the importance of executing the speed trials in head - or following waves. Perdon (2002) argues; "in the case when the waves do not come from the bow or the stern the correction methods are not sufficiently reliable and the effects of steering and drift on the ship's performance may be underestimated". ISO (2002) recommends performing the trials in head and following wind (note that there usually is a correlation between true wind - and wave direction).The Hyundai shipyard assumes that the wave direction with respect to the ship's centerline equals the relative wind angle. This conflicts with the recommendations of the standards. They advise to obtain the wave direction by visual observations or instruments such as buoys or sea wave analysis radars. Furthermore, Hyundai's assumption is highly illogical from a scientific standpoint. In this thesis, the added wave resistance (due to diffraction) was computed by a handful of methods proposed in the literature. The computed values obtained in this report were all substantially larger than those found by Hyundai. This denies Reinertsen (2011)'s suspicion of Hyundai's correction factors for wave resistance being unrealistically high. B. Henk (2006) emphasizes the importance of accounting for the location of the anemometer in the computations of added resistance due to wind. This is not done by the shipyard. B. Henk (2006) proposes a formula for correction of improper placements of the anemometer. In this thesis, the added wind resistance was calculated, including this correction. The added resistance found was 28 % smaller than the value obtained by Hyundai. This is relevant as the wind tends to be a key resistance contribution.Finally, the Energy Efficiency Design Index (EEDI) has been described. The EEDI estimates a ship's CO2 emission per ton-mile of goods transported; put differently, the vessel's impact on the environment in relation to its benefit for society. The EEDI is to be implemented for all new ships, 1st of January 2013. The value of this index will be determined based on results from speed trials.

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.

The main objective of this thesis is to investigate and present the most relevant techniques and topics within the field of robot modeling and control. The studies will then be used to develop a working control system for the 'Raptor' manipulator stationed on the ROV 'SubFighter 30K'. Due to insufficient information, a simplified model is made to resemble the actual manipulator. This model forms the foundation of all subsequent actions, including the model based control design. The dynamic model is developed by the well known method of Euler-Lagrange. Since this is an energy based method, both the kinetic and the potential energy of the system must be calculated. Systematic procedures are given to clarify the process of these calculations. In this thesis, a sliding-mode controller is derived and proposed as a suitable controller for the given manipulator. The control objective is to force the manipulator to track a time dependent, desired path in the joint space. However, since it is inconvenient for the operator to specify joint space trajectories, several inverse kinematics algorithms are suggested. Due to the kinematic structure of the manipulator, no closed-form solutions can be obtained. The focus is thus directed towards numerical Jacobian based methods. A full-scale implementation requires a working interface between the developed control system and the manipulator system. For that reason, the main concepts of digital communication are presented. Although no communication data is logged from the Raptor, this presentation will pose an advantage if the work is continued. When no control forces are applied to the dynamic model, the manipulator model is expected to behave like a multi joint, three dimensional pendulum. The simulations corresponds to this assumptions, thus the model is assumed to be correct and valid. Simulations of the complete system shows that the sliding-mode controller works as intended. Two chosen IK algorithms are then implemented and compared through simulations. The DLS method proves to be superior to the simple inverse Jacobian method. Finally, the control system is implemented in LabVIEW and thus prepared for full-scale testing.

Long-term statistics for wave power describes the waves that will occur over years and their energy. This can be found by putting together short-term statistics for individual waves and statistics from sea states. All the calculations are done both by the use of wave scatter diagrams and analytical expressions. It is generally seen that the two different methods gives similar results.For the long-term statistics the quality of the results is dependent on both the resolution of the calculations, and the size of which the calculations span over. Most of the waves have low values for wave energy, wave height and wave period. It is seen that the wave power varies with the square of the wave height which is expected. The long-term marginal pdf of wave power is very steep and resembles an exponential curve, but it is not an exact match. The CDF of wave energy is also very steep, and here the differences between the two methods become visible.To optimize the motion of a WEC in waves a control system is necessary. The goal of the control system is to change the WEC's parameters so that it increases the motion of the moving parts. The key control variable, the machinery force, can be divided in three categories: resistive loading, reactive loading and non-linear loading. Different concepts that uses reactive loading is approximate complex conjugate control, tracking of approximate optimal velocity and model predictive control. These give the highest power output, but they use some energy in order to control the motion. These methods use prediction because the machinery force is dependent on future values. Resistive loading, i.e. no machinery force, is presented by phase control by latching and clutching. Latching is a method keeping the absorber fixed during parts of the cycle, and clutching is a method which is coupling and decoupling the machinery at intervals. These methods give smaller energy output, but do not use energy in order to control the phase.A good wave energy converter is a device that has low cost of electricity per kilowatt hour. This criterion is dependent on the cost of the device, which is generally not known, and the power absorption that can be estimated. The power absorption has been estimated for four different concepts: a heaving buoy, a heaving two bodies system, a pitching device and a floating OWC. The power absorption varies for different sea states and is generally increasing as the total present wave power increases, but the WEC's have different optimal values that give the best power absorption and best efficiency. The efficiency can for some areas be very large, even larger than 100% mainly because of focusing techniques and limited accuracy on the raw data used in the calculations. However most of the efficiency results are much lower than that. The efficiency of the WEC's is combined with the long-term wave power statistics to obtain long-term power absorption. The differences between the concepts are large, as they have efficiency between 11% and 47%.

Calculations have been made with the commercial CFD-software Ansys Fluent, with dynamic mesh.

Viscous flow around circular cylinders is a classical research topic in fluid dynamics with a vast amount of practical applications in the field of offshore marine technology. In the flow around cylinders of finite length, complex wake behaviours and coherent structures occur even at relatively low Reynolds numbers. An understanding of the nature and dynamics behind such behaviour could form a basis for improved designs and innovative solutions for offshore and subsea constructions.In the present study, flow around long finite cylinders at Re = 100 is investigated numerically using the incompressible Navier-Stokes Equations solver MGLET. To study the isolated flow near the free end, a cylinder with aspect ratio L/D = 50 is chosen. The flow over the free end gives rise to a wake consisting of two vortex shedding cells with different shedding frequencies; one small near the free end and one larger in the central region of the span. It is found that each vortex shed in the end cell bends horizontally and connects with the upstream vortex shed from the opposite side of the cylinder. The horizontal vortex shedding is found to give rise to a pair of trailing vortices in the time averaged flow.When a vortex is shed with a large phase difference between the two cells, the vortex is split and connects with other surrounding vortices. This phenomena is commonly referred to as vortex dislocations and occurs with the beat frequency, i.e. the difference between the two vortex shedding frequencies. It is found that this frequency can be detected in time histories of $u$ in the wake at the spanwise centre.A second configuration, consisting of a wall mounted cylinder with aspect ratio L/D = 25 is simulated in order to study the effect of introducing a no-slip surface. The effect on the end cell is found to be minimal, while the central cell shedding frequency is reduced. Comparisons with published data on a cylinder with aspect ratio L/D = 25 and two free ends shows that both the reduction of aspect ratio and the introduction of the no-slip boundary condition contributes to the reduced shedding frequency.

The number of collisions between ships and icebergs are increasing in correlation with the increase of the number of ships sailing in Arctic areas. Due to the exploitation of gas fields in Arctic areas, the LNG shipping in these areas is expected to increase. The consequences of an iceberg impact can be critical for ship structure, the crew and the cargo, and it is important to be able to predict the result of such a scenario.Different relevant impact scenarios have been discussed, and it has been concluded that the most critical scenario for a spherical type LNG carrier is an impact at the bow shoulder where the distance between the outer hull and the cargo tanks is at its shortest. Based on this study, a bow shoulder impact has been chosen as the scenario investigated in the thesis.To investigate the influence of the surrounding water, an ALE-model representing this was therefore supposed to be modelled in LS-DYNA. After several unsuccessful tests this work was postponed to further work, but a detailed description of the ALE-modelling and the different options tested has been carried out.A detailed FE model of the bow shoulder section of an ice strengthened spherical type LNG carrier has been carried out. The mesh in this section has been modelled sufficiently fine to capture the governing deformation mechanisms and the total number of elements in the model are therefore large. This will lead to increased computation time, but this is acceptable based on the accuracy of the results obtained. In addition to the local bow shoulder model, a FE model of a global 125 000 dwt. LNG tanker has been established. The outer shell and coarse geometry has been provided by Ph.D. candidate Martin Storheim, and the detailed bow shoulder model has been included in this global model. The global model is meshed with large rectangular four-node elements, and transitions to the detailed model have been created. Properties have been added to the global model in terms of getting a model which represents the real ship to the best extent possible.The steel material model used is developed by Hagbart Alsos and includes a RTCL fracture criterion. The ice material model is developed by Zhenhui Liu and is modelled to represent a physical approach to the crushing of the ice. The aluminium material is based on studies performed by Moss Maritime and simple power law calculations.The added mass and weight of the LNG cargo has been included as increased density in the outer hull below the water line and in the tank shells respectively. The aim of the simulations has been to investigate similarities and differences in different collision approaches. Three different approaches have therefore been simulated for two different impact angles. For the local model, two simplified approaches have been simulated:•A prescribed displacement has been applied to the iceberg. This is the most common approach in collision simulations due to lower requirements to computer performance.•An initial velocity has been given to the iceberg. This approach requires more computer resources, but will probably yield less conservative results.Pinned boundary conditions have been applied to the bow shoulder model for all the local analyses. In addition to the local analyses, a full global analysis has been performed for the two different impact angles. In these simulations no boundary conditions have been applied to any of the colliding bodies, and initial velocity is given to the ship structure. The mass of the iceberg is approximately 2500 tons and for the global analyses no velocity of the iceberg has been assumed.The results obtained from these simulations have shown that both of the local simulations tends to over-estimate the indentations. The prescribed displacement analyses yields over-conservative results for long duration simulations, but at large impact angles the results obtained are reasonable for longer simulated time than for small impact angles. The initial velocity method yields more reasonable results, and this approach is therefore better to apply when the damage from a collision scenario is estimated by simplified methods.To investigate the effect of the iceberg size, two simulations including an iceberg of approximately 19 000 tons have been carried out. These simulations have shown that the damage in such collision is significantly larger than for the small iceberg. It has also been seen that there is less difference between the simplified approach and the full analysis for the large iceberg than for the small iceberg approaches. This is remarkable, since the boundary conditions have been assumed to give larger contribution to the result for the large iceberg.Unreasonable large accelerations have been found in collision simulations described in different papers. To investigate this in the simulations performed in this thesis, the accelerations and motions have been observed in different spots which is not directly impacted by the collision. No extreme values of either accelerations or motions have been found, and it is concluded that this is not a problem for the collision scenario simulated in this thesis.