<p>A two-fluid model is used to derive a set of boundary conditions. The conditions are produced numerically, and try to imitate the behavior of output injection by using a linearized version of the model. In order to ensure that the model is hyperbolic, virtual mass terms are included in the momentum equations. An observer is presented, using OLGA, a fluid simulator, as its model. The boundary conditions derived are employed in the observer, and its convergence properties are shown to improve. A set of adaption laws for estimating parameters in a two-phase leak model is derived. Estimation of the leakage mass fraction is sacrifced in order to increase performance and stability. A model, also based on OLGA, is used to simulate a leak, and the observer prove to give good estimates of leak parameters as long as estimates of leakage mass fraction is available. Mass flow fraction seem to be a sufficient estimate. A wide range of scenarios are simulated, inspecting the weaknesses of the observer.</p>

<p>This report presents two optimization problems, where three cost-functions are suggested for each. The goal for the first optimization problem is to find a time variant look-ahead distance which improves the performance of the vessel in terms of the cross-track error, relative to constant look-ahead distances. The second optimization problem is an extension of the first, where a time variant surge velocity reference is also calculated. This results in smaller cross-track errors, at the cost of increased calculation time. It is assumed that the path and the desired surge velocity on the path is supplied by some external source. Existing kappa-exponential control laws are used to track the references resulting from the calculated optimal look-ahead distance and surge velocity reference. The predictions needed to solve the optimization problem are made from a model where the control laws are inserted into the dynamics to simplify the model. The optimization problems are solved for two different approaches. The first approach uses an LTV model for predictions and a QP-solver to solve the optimization problem. The second approach forms predictions of the states by numerical integration of the system dynamics and uses an optimization problem solver for general non-linear functions to solve the optimization problem. The latter approach generally results in longer calculation times but better accuracy, while the first approach yields convexity of the optimization problem. A passive observer is used to estimate the current such that it can be included in the predictions. Four of the six suggested cost-functions lead to significantly improved performance of the vessel in terms of the cross-track error. This is true both in the case of no disturbances and in the presence of a constant irrotational current. That is, the position of the vessel converges faster to the path, the vessel stays closer to the path and has less over-shoot in the cross-track error, for the optimal inputs than for constant inputs. The cost-functions includes weights for tuning where the tuning process is easy for some of the cost-functions. One of the cost-functions where only the optimal look-ahead distance is calculated, results in calculation times shorter than the time between samples, after a few time steps. This is a promising result since the application of MPC to fast-dynamic systems such as marine vessels is desired, but often problematic due to too long calculation times for solving the optimization problem. It takes more time to solve the optimization problem when the optimal surge velocity reference is found in addition to the optimal look-ahead distance.</p>

<p>Considerable progress has been achieved in recent years with respect to autonomous vehicles. A good example is the DARPA Grand Challenge, a competition for autonomous ground vehicles. None of the competing vehicles managed to complete the challenge in 2004, but returning in 2005, a total of five vehicles were successful. Effective collision avoidance is a requirement for autonomous navigation, and even though much progress has been done, it still remains an open problem. The focus of this thesis is on the development of a collision avoidance system for unmanned surface vehicles (USVs), which is compliant with the International Regulations for Avoiding Collisions at Sea (COLREGS). The system is based on a modified version of the Dynamic Window algorithm, taking both acceleration and lateral speeds into account for reactive collision avoidance. Path planning is provided by the Rapidly-Exploring Random Tree (RRT) algorithm, extended to use the A* algorithm as a guide, which significantly increases its efficiency. Extensive simulations have been performed in order to determine the value of the modifications done to the original algorithms, as well as the performance of the total control system. Full-scale experiments have also been carried out in an attempt to verify the results from the simulations. The collision avoidance system performed very well during the simulations, finding near-optimal paths through the environment and evading other vessels in a COLREGS-compliant fashion. In the full-scale experiments, important sensor data was erroneous, resulting in reduced avoidance margins. However, the collision avoidance system still kept the controlled vessel safe, showing significant robustness.</p>

<p>The desired properties of a multi-loop PID tuning procedure is to find some parameters that makes the plant robust, meet some desired performance requirements and guarantee failure tolerance. A detailed literature survey of the different multi-loop PID tuning procedures are presented. Properties of the Independent design methods, Detuning methods, Sequential closing methods, Iterative or trial and error methods, Optimization methods and Relay feedback approaches are described in detail and discussed. Most of the tuning procedures result in a too conservative design without integrity. It is shown how the integrity property may be achieved with a multi-loop Hinf optimal tuning method. How to deffine and solve such a Hinf optimal problem is presented. The desired properties of the multi-loop PID tuning procedure is obtained with this method. The method aim for its object to solve a Hinf optimization problem with Linear Matrix Inequality (LMI) constraints. The optimization problem is non-convex, so a Successive Semidefnite Programming (SSP) algorithm is used to find local solutions to the problem. Several initial points must be examen to aim for a global solution. The SSP algorithm is implemented in MATLAB, and applied at a distillation column example. The implemented algorithm does not converge to a solution. Hence no simulation results that back up the theoretical work is presented.</p>

<p>Most of the systems considering wave synchronization in the literature are concerned with moon pool operations. The objective of this thesis is to transition the existing knowledge from some of that work into marine cranes working over the side of the vessel. This aim is mainly motivated by the fact that cranes working over the side of the vessel are more versatile. They can be used for more comprehensive and differently shaped objects. In addition, vessels with cranes mounted this way are more flexible since the moon pool configuration consumes a considerable amount of deck space. The main contribution of this thesis is a consideration of the transition from cranes lifting through a moon pool to cranes lifting over the side of the vessel. This includes consideration of the roll and pitch motion of the vessel, as well as simulating the complete system with wave synchronization control. The system is also simulated without any motion compensation for comparison. The degrees of freedom (DOFs) available for motion compensation control in different crane configurations are discussed, and some comments are made on how the actuators may cooperate in order to achieve better motion compensation. It is found that nothing obstructs the use of control algorithms originally developed for moon pool cranes for cranes working over the side of a vessel. The behaviour of the systems is roughly equal in the two cases, and the physical aspects are the same regarding wave elevation, still water level, and wire behaviour. There is however, one aspect to consider when designing overboard cranes, and that is the response time needed for following the wave elevation with the payload. When the payload is lifted over the side of the vessel, the roll and pitch motions affect the movement of the crane tip. In the worst case scenario, a wave can have a velocity directed upward, while the crane tip has a velocity directed downward. If this is the case, a faster motion compensation system is needed than for the moon pool applications.</p>

<p>This paper describes development of an optimal 3D path planner with collision avoidance for a 9 DOF robot manipulator. The application of the robot manipulator will be on an unmanned oil platform where it will be used for inspection. Most of the time the robot manipulator will follow a pre-programmed collision-free path specified by an operator. Situations where it is desirable to move the end effector from the current position to a new position without specifying the path in advance might occur. To make this possible a 3D path planner with collision avoidance is needed. The path planner presented in this paper is based on the well known Probabilistic Roadmap method (PRM). One of the main challenges using the PRM is to make a roadmap covering the entire collision free Configuration space, Cfree, and connect it into one connected component. It is shown by empirical testing that using a combination of the Bridge Sampling technique and a simple Random sampling technique gives best Coverage of the Cfree space and highest Connectivity in the roadmap for the given environment. An algorithm that increases the Connectivity and sometimes provide Maximal Connection is also described. A backup procedure that can be executed on-line if a query fails is also presented. The backup procedure is slow, but it increases the chances of succeeding a query if the goal is in a difficult area. It is also investigated if the coverage and connectivity can be further improved by using the potential field planner when connecting the waypoints. Empirical testing showed that the improvements of Coverage and Connectivity were limited and the sampling and query time increased. The query time for a roadmap containing 400 nodes and one containing 1000 nodes was compared. It turned out that a large roadmap did not necessarily affect the query time negative because it made it easier to connect the start and goal nodes. Three existing path smoothing algorithms and a new algorithm, called Deterministic Shortcut, were implemented and tested. Empirical testing showed that the Deterministic Shortcut algorithm outperformed the others when it came to path smoothing versus time.</p>

<p>This thesis discusses the theoretical aspects of the unscented Kalman filter (UKF) and nonlinear model predictive control (NMPC) and try to evaluate their practical value in a dynamic positioning (DP) system. A nonlinear horizontal vessel model is used as the basis for performing state, disturbance, and parameter estimation, and attempts at controling the vessel using NMPC are made. It is shown that the extended Kalman filter (EKF), which is much used in various navigation applications including DP, is outperformed both theoretically and practically in simulations by the UKF. Much of which is due to the UKF's improved approximation of the estimated system's true stochastic properties. An attempt to estimate the current from the hydrodynamical damping forces have been applied and shown to be working when the vessel is not subjected to other slowly-varying drift forces. It is implemented a dual estimation approach to try to estimate hydrodynamic damping, which is a very real problem for actual vessels and DP systems. A theoretical evaluation of NMPC is performed and it is concluded that NMPC schemes could fulfill a need in vessel control and DP. Its combination of model based control, optimization approach to achieving performance and predictive properties are indeed useful also for DP. It is found that NMPC could be a step towards a unified control approach combining low and high speed reference tracking, station-keeping and several other control operations which today are handled by separate control approaches. NMPC provides the control designer with an exceptional amount of freedom when quantifying the performance, that it is impossible not to find some use for NMPC.</p>

<p>Wave Power is a technology that was founded in the 70's, but which still not has reached full industrial recognition as a energy source. In this thesis there is a literature study on different concepts of Wave Energy Converters(WEC) which has been build in full scale, and there is a great variety in the concepts. There is a theory chapter where ocean waves theory, mass-spring-damper dynamics, hydrodynamics and maximum power capture are presented. The modeling work was done on a axisymmetric point absorber WEC, which can be said to have the greatest potential for energy absorption because it is small relative to the wavelength of the incident waves. To be able to simulate on the model, a control strategy must be included, and I have included PID control and Model Predictive Control as strategies to be able to capture maximum power with Phase Latching. I believe that Model Predictive Control will be the best choice for control system, although it is not as robust as PID control, but because of its predictive behavior. At last there is a chapter where further work and some concluding remarks are given.</p>

<p>Cargo transfer between two vessels at sea requires the ramp connection between the vessels to be as stable as possible. The complex nature of the system makes employing control methods difficult. This thesis explores two ideas for improving performance of the interconnected system. First idea examines the possibility of actuating the smaller of the vessels with fins, so as to reduce the relative movement between the two points where the ramp is connected to the ships. The second idea using the larger ship to shield the smaller one from incoming waves. It is assumed that the total disturbance is minimized at a certain angle to the waves, and an Extremum-Seeking based controller is used to find this angle. To allow ship models to change dynamically as cargo offloads, the technique of extremum seeking is extended in this thesis to allow a certain type of model uncertainties.</p>

<p>New offshore oil recourses that are developed are more difficult to drill and increase the requirements to the technology in the offshore industry. A relatively new technology is Managed Pressure Drilling where a choke topside is used to control the bottom hole pressure. The bottom hole pressure measurement is unreliable, which motivates the need for an observer. Different methods for estimation will be presented and compared in this thesis. Proofs of convergence are outlined for the Stamnes observer, derived for the Grip observer and some stepping stones for further work are presented for the Optimal Polynomial Filter. Each observer is simulated with a simple step in the mud pump to verify the estimation laws. The results show that all observes estimated the bottom hole pressure correctly for this simple case. A more realistic case, a pipe connection, is also simulated for each observer. The case includes zero flow from the mud pump, which reveals that all observers miss the estimation convergence in this case, but that the estimate converges when there is flow from the mud pump. One of the states that affects the bottom hole pressure is the pressure loss due to friction in drill string and annulus. Earlier work modeled these losses as quadratic with respect to the flow through the bit, which are simplifications. To improve the estimate of the bottom hole pressure, new and better friction models are needed. Measurement data from Gullfaks C are analyzed to get new knowledge of friction loss in the drilling string and annulus. For the drill string the quadratic friction model is found to be good enough, catching the main behavior. On the other hand, the friction loss in the annulus is a more complicated function of flow. The annulus friction is approximated with sets of basis functions and the weighted sum of these functions gives an approximation to the friction curve. Each weight is estimated to get the friction loss estimate. The use of the weighted sum of four 1st-order b-spline functions give a good approximation to the real friction curve, and the weight for each basis function is estimated. This is tested in simulations both with a simple case and the pipe connection case. The simulations show that the annulus friction loss and the bit pressure are estimated correctly.</p>