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.

The fish farming industry faces some problems for the future as the escaping of fish and fish lice. One solution to these problems could be to move the farms further offshore. The main focus of the industry is on the cages the fish is held in, but the feed barge is the brain of a fish farm. Before offshore fish farming is an acceptable solution for the future the design criteria for the feed barge has to be sufficient for more exposed areas.Some regulations both for fish farming and the oil industry have been evaluated. The conclusion from the evaluation of the regulations is that the regulation for floating fish farms is the least strict regulation. The purpose of this report is to enlighten the need for new thinking for design criteria for offshore feed barges by doing a hydrodynamic analysis in HydroD by using WADAM and potential theory applied to a panel model. The computer program is a recognized program developed by DNV. The model in this report is a design which is believed to be the best design for exposed areas. The model is analyzed in both hydrostatic and hydrodynamic conditions. The hydrostatic analyses conclude that the barge is stable and valid for operation in Norwegian waters. For the hydrodynamic analysis it as assumed two different locations with different wave data to enlighten the need to design a barge to a specific location. There is also assumed extra restoring as simulation of mooring. The result from the hydrodynamic analyses is used to evaluate the required freeboard for each location and the motions and accelerations of the barge. The results show that the barge in both locations will experience water on deck already for significant wave height of 2 meters, which actually is low even for the regulations today. The rotation and acceleration results are compared against limits for human tolerance and they show that there is a need for evaluating this in the design criteria.The conclusion is that the regulation valid today for fish farming is insufficient for offshore fish farming and that it is possible to look towards the offshore industry for leads on how the regulations should be formed. For the future it would be appropriate to change the design criteria and design of the feed barge if the fish farming is to be moved further offshore.

The ice cap surrounding the Arctic Ocean has been significantly reduced during the last decades. As the ice continues to diminish the economic potential of the NSR is becoming stronger. However there are still challenges and uncertainties connected to navigation in the Arctic. Among these are the lack of marine infrastructure, the uncertainties regarding the regulations and length of the ice free season. The purpose of this master thesis is therefore to develop a transport simulation model to investigate the economic feasibility of a NSR transport system. The route has not been evaluated as a year-round substitute for the traditional route through the Suez Canal, but has been integrated with the southern passage. As a result the Northern Sea Route is only used as an alternative in the navigation season between August and the end of November. In order to investigate the feasibility of the route a case study is developed. Container cargo is evaluated as the most suitable shipping cargo; therefore the case study presents a possible container transport between Rotterdam in the Netherlands and Yokohama in Japan. The shorter distance of the NSR is exploited in two ways, either by slow steaming or increasing the number of transits a year. In addition the transport systems are evaluated for 4 different ice classes, 7 different ice scenarios and a fleet consisting of 6 or 7 vessels. The transport simulation model calculates the speed and fuel consumption in ice with the use of an ice thickness-speed curve (h-v curve). The h-v curve is found by calculating the ice resistance of the vessel for variable ice thicknesses and the corresponding net thrust available to overcome this resistance. Further the model simulates the schedules and calculates the total fuel consumption for the entire fleet. The output of the model is the required freight rate (RFR) for the NSR transport systems and the Suez Canal route.The simulation results indicate that:-The optimal fleet size consist of 7 vessels-The slow steaming schedule is more profitable than the maximum transits schedule-The optimal ice class for the less severe ice scenarios are IC, while IB is better when the ice conditions harshen-All ice classes are more profitable than the SCR if the ice conditions are less severe than ice scenario 5

Measured in volume approximately 80 % of world trade is carried at sea and with just as many different actors the shipping industry acts close to a perfect market. The highly volatile nature of the industry with unexpected market fluctuations is the basis for the major decisions shipping companies are making. Especially the fleet size and mix problem in a strategic setting involving fleet changes during several planning periods as a company growth policy. This decision is therefore highly dependent on correct timing for those who want to succeed and an introduction to the shipping industry is given to state these properties. In this thesis various optimization models solving the fleet size and mix problem are presented where the best suited model structure related to the topic is chosen. This model is of deterministic nature, meaning that all input values are known, and based upon predefined routes. The decision regarding the fleet composition during several planning periods is aiming at determining an optimal fleet for a given market. The validity of the results solely relies on input data, which is highly uncertain into an unknown future. The predictions need to coincide with the real life development in order for the results to maintain its validity.Two different trades are used as cases, solved with the models presented. Some input parameters are changed and the differences are investigated. The main findings imply that only relative small changes of the input parameters resulted in very different decisions. The related loss of making the wrong decision is observed in the region of 100 – 200 million USD during three years. This large loss potential and the uncertainty related to the input parameters leads to a need for a method minimizing these effects. An approach is developed to treat uncertainties minimizing the losses by finding a robust fleet capable of handling a large set of generated future scenarios, called the “Scenario Algorithm”. The approach is divided into three main steps; the scenario generating step where development are based on historical fluctuations, a deterministic solution with the given scenario as basis and finally storing of all the solutions with a statistical analysis of the output. The algorithm is used on the two cases with two different scenario generating approaches, based on an exponential- and a continuous uniform distribution. The fleet size and mix decisions which appeared with the highest frequency were chosen, and gave a consistent estimate based on risk aversion decreasing the potential of making losses.The approaches presented in this thesis is not meant to give a correct answer on how the future will be, but help the decisions makers reduce the uncertainty connected to the strategic decision. The deterministic model give valuable information with a given scenario as input, but the model is only capable of evaluate the scenarios individually. The result found by the scenario algorithm evaluating scenarios collectively is therefore of higher value since it provide a more robust solution.