The calculation of ice-induced loads on ships is still mainly based on empirical models. In order to gain a better physical understanding of the loading on ice-going vessels, Det Norske Veritas launched an <i>ice load monitoring<i> project involving full scale trials with the coastguard vessel KV Svalbard during the winters 2006, 2007 and 2011. The results from the full scale measurements conducted with KV Svalbard has been topic of several earlier master's thesis at NTNU,The master thesis consists of four parts. The first part is a literature review of the mechanical and physical properties of sea ice.The second part is a review of the rule sets developed by DNV and the IACS regarding vessels operating in ice infested waters. Both design principles and numerical values have been evaluated. The main difference between the designs principles used, is that IACS base their rules on a plastic method of approach, while DNV uses an elastic method. Despite the difference in the design principles, when comparing their numerical values turned out to be quite similar. The DNV rules are in general most conservative for the smaller vessels and the IACS rules the most conservative for large vessels. The third part consists of a finite element study of a part of the bow on KV Svalbard. A systematic load scheme is used, consisting of 102 load cases. For each of the stress factors there where made graphs that showed the stress at the sensor location when moving the patch load. The sensor mounted on the frame were able to measure load that was within the frame loading area and sensor mounted on the stringer could measure stress for all of the load cases in the horizontal directions. One of the explanations for this is that the stringer transfers stress from the load patch area that could be measured by the sensors.The last part consists of a comparison between measurements from the full scale trials and the results from the 102 load cases. This comparison is done through a weighted summation method where 5 different load cases are combined to represent the measured result, and a load factor is calculated for each load case for its contribution of the measured results. The stress component used in this comparison is the shear stress tau xy The load cases were tested against the 11 measurements from the full scale trials. There were in total 11 load cases that gave positive factors for all of the 11 measurements at the same time. A figure was made to show which load cases were likely to contribute in the solution of the load cases. Load cases inside the frame loading area have the largest load factors for the solution of measurements.This load decision scheme is very sensitive to the selection of load cases and boundary conditions. A change of the boundary conditions for the model was tried out for 7 load cases, and with changed boundary conditions, only 5 gave positive load factors.The results of this thesis shows that is possible to find many solution to the measured result by combining many load case, but is it not possible to decide <i>the<i> solution.

The exible pipelines has been widely used by the oil and gas industry the lastdecades and this trend is expected to continue as the operating depths are increasedfurther. For deep water applications the radial and lateral buckling modes can becritical. Many studies has been carried out using nite element models to studythese failure modes.In this thesis a nite element model is created with the aim to recreate resultsobtained in a recently published article by Vaz and Rizzo. The model is built upusing pipe, beam, contact and spring elements to represent the complex behaviourof the cross section. The loading is carried out by rst applying the dry mass, thenthe external pressure and nally end compression.When comparing buckling loads generated in this thesis by the ones in thearticle by Vaz and Rizzo the observation made is that the buckling loads from thisthesis are signicantly higher. When comparing only the inclination of the endshortening versus buckling load curves it was seen that the curves from article hada only slightly larger inclination than the results from the analyses in this thesis.This indicates that there is a small dierence in the stiness used. By modifyingthe stiness it should be possible to get the same inclination of the curve.Analyses were also carried out on how the slip distance aects the bucklingloads. By increasing the slip distance by 50% and 100% it was observed thatthe buckling loads were reduced drastically. In the article by Vaz and Rizzo noinformation is given on the slip distance. By tuning the slip distance and stinessof the springs it should therefore by possible to obtain the exact same results as inthe article. This clearly illustrates the importance of stating all assumptions andinput parameters when describing models used for analysis.

The ITTC78 method was originally designed for conventional single screw ships, but has later been modified to adapt twin screw ships and podded propulsors. Nowadays even more unconvensional propulsors are introduced, and the need for a new powering performance method is increasing. This thesis covers the load varying self propulsion method, and looks into how this corresponds to the standard ITTC78 method. The load varying method uses data from a self propusion test only, and uses a predefined increment value to change the revolutions during each run. In this way there are no need for an open water test or a resistance test, and time can be saved. In addition the vessel is tested as a unit, and not broken down into separate pieces like with the ITTC78 method.

An explosion on a typical offshore installation is a critical, however rare accidental event which may result in damage and loss of property, and in the worse case loss of lives. Top-side sections on an offshore installation which are exposed to an explosion blast should be designed to withstand such an event in a way that further escalation of the damage on personnel or property is avoided. There is however limited information on the modeling and analysis procedures for dealing with such events, and most classification rules on this subject give limited information and guidelines on the practical implementation of such effects for general analysis purposes. This thesis has been an investigation on these matters.The basis of this Master thesis has been on a pipe rack structure from one of Aker Solutions' top-side projects. It has been assumed that this structure is exposed to an accidental hydrocarbon explosion, and the resulting structural response has been investigated. A parameter study has been performed by varying blast load levels and durations. The effects due to the weight of the piping on the structure have also been studied. The main task of this thesis has been to compare simplified, static analysis models against dynamic analysis models as to calculate dynamic amplification factors (DAF), the purpose of this is to better understand the dynamic behavior of the structure due to the blast loading. The intention is that the dynamic amplification factors are to be used further by the engineers at Aker Solutions for dimensioning and designing of similar structures.Results showed that the blast loads as used in the analyses did not cause any structural responses within the material's plastic range. Further on, it was found that the magnitude of dynamic amplification is depending on both the blast duration emph{and} the weight of the pipes on the pipe rack. Typical results indicated that this dynamic amplification was reduced with increased blast duration.

Due to a rising interest in oil exploration in Arctic areas several new platform designs have been introduced to combat the problems with level ice loads. This has led to research into ice strengthening and how this affects the open water behaviour. One of the new designs, called the Total Buoy, has a slanted hull in the waterline intended to deflect level ice down and around the structure, but this hull design introduces a geometrical non-linearity. This non-linearity causes problems in the design of these types of structures, because most hydrodynamic program cannot handle the rapid change of geometry in the waterline. This has inspired several attempts to write a simple numerical model to handle the calculation, and avoid costly model tests in the pre-design.A large part of this thesis presents the theory and methods used in the development of this new numerical model. This is meant to document the thought process in a way which can allow others to continue the development. The numerical model was developed to calculate motion results from regular waves in the three symmetric motions; Surge, Heave and Pitch. In addition to this a very simple ice calculation was included as a starting point for further development.As part of this work on a new numerical model a parallel study of an alternative commercial program was done. This is to test the usability of an (expensive) commercial program in relation to this non-linear problem. The DNV program Wasim was selected for this purpose, and the modelling has also been documented and the input files are included in the electronic appendix.After documenting the basis of the numerical model and Wasim model it was necessary to do a comprehensive comparison study of the models. To help with the comparison Force Technology allowed the use of model tests results which were performed on the Total Buoy concept in 2006. The comparisons showed that while the numerical model was showing some large responses around the heave natural period in both heave and pitch the results were in general close to the model tests. The Wasim model did not show the same correlation in surge and pitch, but the heave results were shown to be close, but the use of the Wasim program is believed to be unwise on this type of problem.Finally, an assessment of the Total Buoy's open water and level ice behaviour was done. This assessment showed that the Total buoy would most likely have problems with large pitch motions. This was shown to be true in both the Norwegian Sea and the Eastern Barents Sea, the Norwegian Sea was found to be a unlikely deployment area due to the lack of level ice. The pitch motion was so large that it would make year round human habitation impossible, and it was advised that the buoy should not be used for this purpose, and only in the eastern Barents Sea. Finally, it was found that the ice theory which was applied for the ice calculation could not give a true assessment of the level ice capabilities of the buoy, and the lack of other alternative solutions made the assessment impossible.

The main contribution of this thesis is an investigation of model predictive control(MPC) for marine diesel electric power plants. Recommendations and new ideasfor further development are emphasized.The motivation of the thesis is to develop a controller for diesel electric power plantsthat can control the plant in a more efficient way. This includes reducing wear andtear, fuel consumption, and emissions. However, the safety aspect is always themost important factor and must be handled with care.The case plant to be studied is a diesel electrical power plant consisting of severaldiesel driven generators (genset). These gensets produce electrical power to servethe electrical demands on a marine vessel. The consumers can be propulsion units,heave compensators, drilling equipment, and hotel loads. These highly dynamicconsumers are large compared with the producers. This gives unwanted fluctuationof frequency. In some vessels this effect is so large that more gensets are requiredfor transients than for peak demands. This can be avoided with better controlstrategies.The controller developed in this thesis adjusts the local controllers on the dieselengines. The objective is to keep the genset at a given load sharing, while keepingthe frequency within rules and regulations. In addition is the plant controlled to astate where a single point failure does not lead to blackout.Blackout is prevented by calculating a failure case in addition to the normal case.The failure case may be a disconnection of the largest genset on the power bussegment. The case is calculated in the controller to make sure that if the caseoccurs the plant is able to handle the failure without a blackout. A normal case,where everything goes as normal, is calculated to optimize the current operation.The controller is verified by simulation done in MATLAB/Simulink. Theimplemented controller performs well during all of the simulated cases. However,the predictions made by the controller are in some cases conservative. This is dueto the choice of the fuel rate constraints. Lastly, suggestions for how to improvethe performance of the controller are included. The most important suggestionsare to include a model of the turbocharger in the control plant model and toinclude more failure cases.

AbstractThe wind power business has in recent times changed its focus from land-based installations to offshore installations. This has presented challenges both technological and financial, mainly related to construction and maintenance. To optimize the availability of the offshore wind turbines it is important to have support vessels and boarding systems that can handle as rough sea conditions as possible, and the relative motions between these vessels and the wind turbines become increasingly important to predict, as the offshore wind business expands.For this purpose, a need has been expressed for a simple tool for quick estimation of such motions. In this thesis, a MATLAB program has been developed for this purpose. It takes various input from the user, such as information on the sea state and the physical situation to be considered, as well as limiting criteria. The program provides the user with information on the local vessel motions and the relative motions between a point on the vessel and a fixed point on the wind turbine, and then compares it to the given criteria. It also gives out various plots to illustrate the motions and the relevant transfer functions.The final version of Relative Motion Calculator, RMC 2.3, features the following options:•Two types of wave spectra•Arbitrary placement of the moving coordinate system•Arbitrary placement of the considered points•Long- or short-crested wave theoryRMC 2.3 has undergone thorough testing to prove its validity, and all test results are reasonable and according to expectation. Although the program is a bit difficult to use, it can be used as intended, for calculating relative motions between a moving point on a vessel and a fixed point. Furthermore, the program might provide a good platform for further development.

In this thesis the response variables (RAOs) of a semi submersible unit are inspected. Both operational and survival condition as well as a shallow draft are inspected. The survival condition is inspected with respect to an element analysis. And both operational- and shallow draft condition are case studies, where the operational condition is inspected for two different damage cases. The unit in question is a four column semi submersible, based on the GG5000 design. This is a relatively new design, and the first vessel to get this design is in its final engineering stage. Construction start is planned to be in August this year (2012). This unit will get the name COSLProspector and will be built in CIMC Yantai Raffles shipyard in China.The unit is symmetrical about the centre line and close to symmetrical about the vertical transverse plane, only pontoon tips are different. Because of this, no significant simplifications have been necessary in order to simplify the calculation due to computational time. Another reason for not doing any simplifications to the geometry is due to the fact that the results are desired to be the most realistic. However, to reduce computational time, only half the unit has been modelled due to symmetry about centre line.To find the appropriate element size for the mesh, an element analysis has been carried out. The results from this analysis resulted in a chosen element size of 2.5m. This element size both gives accurate results, and requires a relatively short computational time. The units’ resonance periods has been investigated, and verified by help of hand calculations and comparison with RAOs done by Global Maritime (2011). However not all the values were identical to each other, but many factors can influence on that result. The GM value was not changed in this thesis, but was in Global Maritime (2011), in addition the additional damping was in this thesis taken as 3% of critical damping, while in Global Maritime (2011), Morrison elements were taken into account. These factors, and perhaps a few shortenings are assumed to be the reason for the small difference in the responses, they are however small differences for most of the periods.Two damage cases have been modelled by flooding two different water ballast tanks. These damages will give an angle of list for the unit. Damage case 1 gives an angle of list of 13.18o with a rotation of heel axis of 7o forward. Damage case 2 gives a list angle of 11.68o with a rotation of the heel axis of 39o forward. An earlier study like this one is done by Henriksen (2011), found in Grenland Groups internal archive. AQWA does not give out the tilt angles in damage cases as this is not the main purpose of this program. Therefore, the list angles for the different cases have been obtained from the report done by Henriksen (2011). However, AQWA will be used to obtain the RAOs for both cases, as well as confirm floating equilibrium in such conditions.It is assumed that the tanks are completely emptied for air, and that seawater is filling the entire volume. A table showing the different tanks flooded and its weight with seawater is shown in table 1.UnitVolume [m3]Sea water weight [MT]BWT ST-2692.51709.82BWT ST-8616.83632.25Table 1: Weight of water for flooded tanksWhen it comes to the RAOs in the damage cases, they are very hard to read. This is mainly due to the fact that the motions in these cases are highly dependent on each other due to coupled motions. Due to an angle of list, the unit is no longer symmetric. As a consequence of this a RAO for a specific degree of freedom can no longer be read like it is only this degree of freedom which is affecting the responses, but one or more of the other degrees of freedom are strongly influencing. This makes some of the peaks appear where not normally expected.It is also noticeable that the highest motions are encountered for damage case 1, which is natural because this case has the highest list angle. The resonance periods are lower in the damage cases compared to the normal operational condition, however not to a degree which is dangerously low. The lowest resonance period is still in heave.From the RAOs in the shallow draft case, it can be noticed that the highest responses in heave are encountered for the shallow condition (14.5m) compared to the survival condition (15.5m) and operational condition (17.5m), however only up to about 18s, where after that it has the smallest response, and the operational condition has the highest.In roll and pitch the trends are fairly similar. The graphs are a little uneven until the first cancellation period, and then the shallow draft gives a higher response until reaching the resonance period. In the resonance region, the operational condition has the highest response for both roll and pitch, same as for the heave.As a conclusion, the optimal approach in a situation where the unit is heavily tilted is to try to ballast the unit to an even keel. But of course risks of doing this are a possibility, such as slamming problems and the fact that the resonance periods will be shorter.

Installation of deep water Xmas trees for subsea oil production is sometimes done by lowering the tree using one wire. Xmas trees are interfacing with other equip- ment on the seafloor and will therefore need to be positioned, and oriented correct. Today aligning the Xmas tree to existing interfacing structures on the seabed dur- ing installation is done by manual control of an ROV. In this thesis it is proposed to automate this process. The benefits of doing this is to gain a faster and more precise control of the position of the tree, as well as being less prone to human errors. This will make the operation faster, safer and less expensive.This thesis is a feasibility study of this new solution for aligning the Xmas tree in the installation process. In order to investigate the feasibility of the solution a mathematical model of an ROV and a Xmas tree that is hanging in a wire has been developed. Interaction forces between these objects are then defined. A model of the environment and sensor output from the ROV is also developed.A controller algorithm has been defined that uses the position of the Xmas tree to calculate the control forces the ROV need to control the motions of the Xmas tree. This controller algorithm is a nonlinear PID-controller where the output is translated from the body-centre of the Xmas tree to the body centre of the ROV in order to use some of the existing control system in the ROV. In addition to the controller an extended kalman filter has been implemented in order to handle the sensor feedback, and a reference model has been made to generate smooth and feasible trajectories as input to the control system.The mathematical model is used to simulate the behavior of the system, when the control system is connected. The simulations shows very promising results.An experimental setup has been made in order to test the control system in real life. The experimental setup consists of a downscaled Xmas tree model, a docking frame, and a small scale ROV. This setup was used to test the control system in the Trondheim fjord using R/V Gunnerus. Due to an error in the programming the testing was not able to fully verify the simulation results. The results obtained during the test did however seem promising when this error is taken into account, and thus proof of concept was established.

This thesis consists of three main parts. The first part of the master thesis looks at the identification of thruster dynamics and low speed ship dynamics. The relevant parameters identified are time constants and time delays in the system. Simple step tests are used for the identification. Different models for identification are suggested, both for uncoupled surge, sway, and yaw dynamics. Other test results, such as agility plots, DP 4 corner tests, and pure DP tests (stationkeeping) are reported. All the results are to be compared to similar tests performed after R/V Gunnerus has a retrofit of the thruster system.The second part discusses another problem, and that is the topic of numerically estimat- ing the body frame position of the GNSS and MRU sensors. For the GNSS position an Luenberger observer design and an adaptive scheme are proposed and analyzed. The es- timation designs are tested using numerical simulations and experimental data from the Gunnerus sea trials. A similar Luenberger observer is proposed for the MRU positions, and experimental data from the sea trials are used to test the observer.The third part discusses a hybrid augmentation of integral action. The motivation is a DP system, where typically the integral action is tuned very low to avoid oscillations due to the integral action. When there is a sudden load change, such as a ice load that hits the vessel, or if a mooring wire snaps, then a hybrid update augmentation could be useful, to speed up the convergence of the integral action. The update law is a linear update law based on the error in the states (the velocity for the DP system). The augmentation can significantly improve performance, especially for very large disturbance changes.