Infant mortality is a significant problem in mooring design. The objective of this thesis is to design a generic fault detection system for mooring line failures, which can accurately detect a mooring line failure within a certain time frame. The research is done through Catenary Arm Leg Mooring (CALM) buoy systems, as this thesis is a Proof of Concept. Two types of mooring line failures are considered in the XZ-plane, a top segment failure close to the buoy and a bottom segment failure close to the anchor. Both failures characterize themselves by a constant offset in equilibrium position and a changed mooring stiffness. Using theoretic concepts about mooring configurations and waves, it is shown that the shift in equilibrium position has most potential for detecting a mooring line failure. These analysis are verified by hydrodynamic simulations in OrcaFlex. For the bottom segment failure the breaking stage cannot be predicted, as this stage depends on the mooring design, the external loads, and the location of the failure. The focus must lie on what stage the failure becomes detectable, rather than how long it takes. The fault detection algorithm is using a model-based approach for fault detection as a general framework which can be used for any variation in mooring design. Current flows, tankers mooring at the buoy, and non-linear effects of mooring configurations in waves cause a constant offset in position as well. By including measurements of the current flow velocity and the tanker hawser tension as inputs of the CALM buoy model, the fault detection algorithm can distinguish between the sources of the constant offset. Additionally, the non-linear effects of a mooring configuration in waves are for small wave heights not significant and not included in the modeling of the buoy. The mooring tensions and system parameters are introduced as specific parameters per mooring design. Via an Unknown Input Observer (UIO), the two unknown input loads are estimated: the wave load and the residual force. The residual force is chosen to represent the mooring line failure in the model. When there is no mooring line failure this force should be zero. The two unknown input forces are estimated by decoupling them in the frequency domain. Using a shaping filter the wave forces are restricted by a predefined frequency bandwidth. The non-linear effects of a mooring configuration in waves are determining the thresholds for the fault detection algorithm. Therefore, no wave load can be mistaken for a mooring line failure. The load cases show that for small offsets the fault detection algorithm is capable of accurately detecting the mooring line failures. The two unknown forces are decoupled in a way that the residual force can be used as residual for fault detection. The residual signal in RY-direction can be used for fault detection. Additionally, it is shown that no step in position data is required for the algorithm to detect a failure. The answer on the research question, is yes. It is possible to accurately detect to accurately detect a mooring line failure. Since this thesis is only applied for the three Degrees of Freedom (DoF) in the XZ-plane, a six DoF model needs to be investigated in future research. Furthermore, by including the non-linear effects in the modeling of the CALM buoy, higher wave amplitudes could be considered. Another possible way to deal with these non-linear effects is to use adaptive thresholds.

Experience-based decision making by crew plays a key role in the safe and effective execution of maritime operations. For yachts and naval vessels, common operations can be identified as helicopter operations (take-off and landing), launch and recovery of small craft and (dis)embarkment to and from these small craft. All of these operations are limited by wave-induced ship motions. For these operations, experience-based decision making does however not always guarantee that the operations are carried out in the most safe and effective manner possible. Also, the level of comfort as experienced by a yacht-owner or guests can be directly affected by this type of decision making. With this in mind, Feadship aims to develop a Feadship Comfort System (FCS), which can contribute to the decision making process. One of the elements of this system is ought to be a waveradar. The aim of this thesis is to describe how the waveradar can be included effectively in the FCS, and how it can be used for the above mentioned operations. The waveradar is in basis a common navigation radar that can perform measurements of the surface elevation in the direct surrounding of a vessel. These measurements can be used to predict the ship's motions up to approximately two minutes ahead in time. With this, windows of opportunity can be distinguished when operations can be carried out best. These windows depend on the corresponding limiting criteria that are set on the ship's motions. A major issue is however that sea trials have shown that the roll prediction is inaccurate. Due to this problem, two methods are evaluated in this thesis to improve the accuracy of the roll prediction. These methods are set up such that they are practical in use and can be applied directly to the deterministic wave predictions from the waveradar. The first method is scaling the response based on the roll motion history, whereas the second method is based on scaling the roll damping. The latter is effectively linearising the viscous contribution to the roll damping. As no data from sea-trials is present to compare these methods, a benchmark calculation is carried out based on Cummins approach. In these time-domain calculations, a linear and non-linear roll damping coefficient are taken into account, which are based on a decay test that is available at De Voogt Naval Architects (DVNA). This follows from model tests performed by MARIN. Comparing both methods to this benchmark calculation showed that the method of scaled damping resulted in the best approximation, with a Pearson correlation coefficient of (only) 33 %. Also, in terms of the behaviour of the motion envelope, this method showed the closest approximation of the two methods. It is found that the way in which both methods influence the RAO of the roll motion has a great influence on the results found. More suitable methods that should provide a better approximation are suggested from this, such as a frequency dependent scaling of the roll damping. This is however not discussed further. With the method of scaled damping, the practical application of the waveradar within the FCS is evaluated. For the common operations of yachts and naval vessels, limiting criteria on ship motions are obtained from literature or stated by the author. The majority of these criteria are RMS values, for which a method is suggested to use them real-time. In this method, the most probable maxima are obtained from the RMS criteria, which are then applied as real-time criteria. This showed impractically large results, which showed that this method does not suffice. From this conclusion it follows that the analysis of the practical application of the waveradar is only carried out for the (dis)embarkment of small craft. From this, design considerations for the FCS are obtained, from which the main result is that heading suggestion is one of the most important tasks that the system needs to be capable of. Finally, a performance monitor has been evaluated for yachts at anchor. This performance monitor displays the predicted Comfort Rating (CR) real time, which can be used by the yachts crew to evaluate the current anchor location. This is a specific desire of Feadship and is developed next to the other operations. For this application, heading suggestion is also one of the most important tasks that the FCS needs to be capable of.

Long distance ocean towing is a commonly used transportation method in the oil & gas and renewable energy industries. Barges with cargo, vessels and various offshore structures are towed from and to location. Boskalis participates in this industry through its subsidiaries Smit and Fairmount Marine. From experience with these transports, it was found that the preliminary calculations do not match with the experiences offshore and that the impact of wave drift on these calculations is most promising for further research. To investigate this impact, the problem is split into three parts: wave drift estimation for a stationary vessel, wave drift estimation for a sailing vessel and the analysis of the towing stability.From the literature, eleven methods are identified for the wave drift estimation of a stationary vessel. These are compared for the surge, sway and yaw force components. The different methods are computed using the diffraction program Delfrac, the strip theory solver ShipMo and own implementations in Matlab. With vessel velocities included, ten wave drift estimation methods for the sailing vessel are compared. Specific attention is paid to the wave drift damping, which relates the stationary wave drift to vessel velocities. It is implemented using Aranha's formulations and the panel pressure output of Delfrac. The most applicable methods with respect to the sailing tow resistance are the far field and near field methods in combination with the wave drift damping. With respect to the total tow resistance, the wave drift contribution is found to make up roughly 25% of the total resistance, irrespective of forward velocity. The dynamic behaviour of the tow operation is examined for two barges: one course stable and one course unstable barge. Their towing stability properties are assessed without waves present and for head waves conditions. It is found that the head waves do not affect the stability of the course stable barge assuming the towing tug has sufficient available towing force. For the course unstable barge, the main stabilising effect is identified as the extra resistance due to the head waves and not the direct wave drift moment. The relative contribution of the waves with respect to the wind and current shows that the head waves have a significant stabilising contribution to the towing stability although the specific relative contributions are highly dependent on the environmental conditions. Head waves either reduce the path width of the fishtailing motion or dampen these oscillations into a stable towing position. This was verified by simulations in the time domain. Irregular waves also promote the stability: they stabilise the unstable barge in the entire range of physically relevant wave periods, irrespective of towline length.Overall, the contribution of the wave drift to the tow resistance is significant, especially while sailing. Head waves are beneficial for the towing stability of a course unstable barge, both in regular and irregular sea states. This increased insight reduces the uncertainty in the tow resistance prediction and contributes to the understanding of the towing stability properties of unstable barges.

The shipping industry is currently under pressure to reduce its pollutant emissions and, thus, to alleviate its negative impact on the environment and human health. With this aim, in the last years, the International Maritime Organization issued significant measures to improve the energy efficiency of ships (see the Energy Efficiency Design Index) as well as restrictive regulations to limit the amount of contaminating emissions from seaborne transport. Arguably one of the most impactful measures will be enforced at the commence of 2020 when the world fleet will have to use cleaner fuels or otherwise will need to install expensive exhaust gas cleaning systems (known as scrubbers) to comply with the new regulations. The use of cleaner and more expensive fuels will increase the ship operating costs and this, in turn, will make investments into fuel-saving devices more attractive....@en

With many operations at sea carried out by ships or or other floating vessels, risks are involved because of the waves and resulting motions of the ships. Examples are the landing of helicopters on ships, transferring crew from a ship to a wind turbine, or working on the deck of an anchor handling tug. It is common practice to assess the workability of a certain operation by statistical criteria. The rationale behind such criteria is in general that the probability of some phenomenon (e.g. the vertical motion of a helicopter landing deck) exceeding a certain threshold value has to be less than a chosen acceptable level. Operability analysis usually qualify a given wave condition as workable or not workable based on such statistical criteria, assuming that no information is available about when critical wave induced events occur. In this thesis, the feasibility is investigated to obtain a short term, ’deterministic’, i.e. time-specific prediction of the critical response: making available a short term prediction of approaching waves and vessel response real time, on-board, would give crew the opportunity to anticipate and chose the optimal moment to perform a critical operation. The research is motivated by two possible advantages of such a deterministic prediction: 1. It further enhances safety in conditions that were considered as workable from a statistical point of view. 2. It possibly increases workability by pointing out windows of opportunity in conditions that were considered as unworkable from a statistical point of view. The chosen approach to obtain the mentioned deterministic prediction of waves and induced motion response, is to use the ship’s navigation radar as a remote wave sensor. The spatial domain that can be covered by a navigation radar to observe the sea surface is of course limited: both its minimum and maximum range is limited. Besides it is obvious that the wave observation will only be available in the past, and by no means in the future. Therefor, the first chapter answers the theoretical question where in the spatio-temporal domain waves can be accurately predicted, given a perfect spatio temporal observation of the waves. An indicator is proposed that specifies predictability in space and time based on the spatio-temporal observation and based on a given wave condition. It is confirmed that the group velocity of the waves is governing concerning this question. In the remaining chapters basically 2 different approaches are proposed and investigated to solve a linear wave representation based on input from synthesized radar images of sea waves. Finally the methods are applied to real radar data acquired during a sea trial. Based on the solution of the linear wave field, ship motions were predicted using pre-computed linear motion tranfer functions. Correlation coefficients up to 0.86 were obtained for the heave motion predicted 60 sec in advance. @en

In this thesis I present a novel discretization procedure which combines two relatively new technologies for solving partial di_erential equations (PDE's): IsoGeometric Analysis (IGA) is a new paradigm which provides an exact geometry description and tight integration of Computer Aided Design (CAD) and Finite Element Analysis (FEA) by using the same basis for representation of the unknown _eld variables as is used for describing the geometry in CAD. Mimetic Discretization Methods on the other hand combine concepts from the Finite Element Method (FEM) and the Finite Volume Method (FVM) and provide a uni_ed and straightforward approach to model any physical _eld problem. Mimetic Methods aim at preserving as much as possible the structure of a PDE by 'mimicking' at the discrete level, important properties of the continuous realm, such that symmetries and conserved quantities are preserved. Central in this framework is the relation between physics and geometry. The Mimetic Discretization approach developed in this thesis is based upon B-splines1 for representing the unknown _eld variables. Besides inheriting all advantages from the IsoGeometric Analysis framework, B-splines appear as a natural basis for Mimetic Discretization Methods. They can be seen as higher order Whitney forms and provide vector spaces which are discretely conservative by construction. The resulting discretization approach resembles a Finite Volume Method on a staggered grid for the representation of the conservation laws and a Finite Element Method for the representation of the constitutive equations. In short, the scheme features the following advantages, - exact geometry description and tight integration with CAD; - fundamentally a higher order approach, featuring spectral like convergence. In practice though, IGA is con_ned to low or medium order due to bad conditioning of inner product mass matrices as a function of the polynomial order; - increased continuity resulting in continuous representations of _eld variables and derivatives; - a strong indication exists that these methods automatically meet the inf-sup conditions, leading to naturally stable discretizations of any physical problem; - local conservation of primal variables (strong) and secondary variables (weak); - in contrast to FVM and FEM which describe variables only locally, the Mimetic discretization is induced with a global topology which makes it possible to make useful decompositions of _eld variables.

The equations governing fluid-flow are a set of partial differential equations, as is the case for a host of other continuous field problems. Analytical solutions to these problems are not always available and computers are unable to handle continuous representations of variables. This makes a finite-dimensional projection mandatory for all variables and this may result in a loss of information. At the same time, invoking the inherent association between physical field variables and geometric quantities, as seen in [1, 2, 3], it is known that stable discretisation schemes can be constructed. In this spirit, mimetic discretization strategies are based on minimizing the loss of information in going from a continuous to a discrete setting by making a clear distinction between exact/topological and approximate/constitutive relations in a physical law, and then focussing on an exact representation of the former and a suitable approximation of the latter. For further reading, please see [4, 5, 6, 7].

Slamming of ships is a phenomenon characterized by a high wave load of short duration. Usually the ships structure responds in a vibratory manner on this load; the response can be either a local or a global vibration mode or it can be in both modes together. These short duration loads are caused by large amplitude motions, even to the point that the fore body of the ship emerges from the water and slams upon re-entry, or they are caused by very steep waves that impact against the hull. The global elastic vibratory response of the structure is called whipping. It is characterized by a very low damping, so it takes many oscillations before it is extinguished. This dynamic response of the structure increases as well the maximum load as the number of load cycles relevant for fatigue damage due to seakeeping loads. Local and global responses can result in local high stresses such that it results in plastic deformation. Slamming loads can lead to catastrophic damage as illustrated by the accidents with the ferry Estonia and the container ship Napoli. Slamming loads are known to be a major reason for operators to change course and/or reducing speed, therefore there is a large effect on the economy of a ship. These aspects are the motivation for carrying out this study. @en

Numerical procedures and simulation techniques in science and engineering have progressed significantly during the last decades. The finite element method plays an important role in this development and has gained popularity in many fields including fluid mechanics. A recent finite element solution strategy is isogeometric analysis. Isogeometric analysis replaces the usual finite element basis functions by higher-order splines. This leads to significantly more accurate results and equips the numerical method with several desirable properties. By naively applying the finite element isogeometric method one may obtain solutions that are seriously perturbed and are as such not physically relevant. The reason is often linked to the stability of the method; a finite element method is not a priori stable. The overall objective of this thesis is centered around this point. The aim is to develop numerical techniques that inherit the stability properties of the underlying physical system. In particular we are interested in finite element techniques that can be applied to free-surface flow simulations. Stability issues in free-surface flow computations may already appear in single-fluid flow problems. Other causes of instabilities are steep layers or discontinuities and instabilities arising from the numerical treatment of the interface that separates the fluids. This thesis addresses each of these topics. Several stabilized finite element methods @en

Due to a low restoring force as well as lack of damping, the roll motion of a vessel is usually the motion with the highest amplitude of all degrees of freedom. Therefore, in history many have tried to stabilize rolling ship starting with Watts in 1883. He described the damping of the roll motion by having a group of men running to the "high" side of the vessel. Since then, a great deal have been written about the subject of roll damping for stationary vessels. The principle however has been the same ever since, a shift of mass to counter the roll motion. Water tanks, carts on a curved track and sliding masses, all tend work with this principle. In 1904 Schlick introduced another device to damp roll motions was introduced, the gyroscope. By controlling the precession angle, the roll motion could be damped. Following from an increase in computational power more advanced control strategies could be applied, leading to a renewed interest in the subject as well as different methods to model the vessel for controller design. In the current paper, the performance of a gyroscope is compared with the performance of a moving mass, modeled as a double pendulum, for dynamic performance of a showcase vessel, the Huisdrill P10000. Results of this analytic study are promising, a reduction of more than 80% for both systems was achieved at the natural frequency of the Huisdrill. The decay time after a roll amplitude of 5.7 degree was reduced from about 250 seconds to 60 seconds for the gyroscope controller model and 70 seconds for the double-pendulum controller model. A static heel control system is modeled based on the double- pendulum equations. This proves to be able to compensate for the heeling moment depending on the weight at the crane tip as well as the weight and distance available to compensate. Combing the static an dynamic approach is possible with the note that there should be sufficient space for the mass to deviate after compensating for static heel. In irregular waves the 4-DoF model shows good performance for the showcase of the Huisdrill P10000. The RMS value for the roll-roll motion was decreased by 65% For other degrees of freedom, similar reductions were obtained. From this it can be included that for the given seastate, significant reductions can be achieved using the ballast train. In the time domain, it was shown that great reductions in most probable maximum of reduction of roll amplitude were achieved for time periods close to the natural frequency of the vessel. For no time period, reductions in performance were measured. It was found that the most probable maximum roll angle linearly increased with the wave height, as well as the most probable deviation did. Interpreting the results of this study, it can be stated that both the gyroscopic control system as well as the double-pendulum system are able to introduce great reduction in dynamic roll motions. The main benefit of using the double-pendulum system is its ability to compensate for the heeling moment induced by the swiveling crane as well as compensating for the dynamic motions that a vessel will undergo offshore. It is recommended to do a simulation of a non-linear time-domain model or to perform model tests for verification of the results found in this report. The gap between static and dynamic control should be filled by a master control which is to be designed and run in the time domain.

For the real-time simulation of ship manoeuvring, it is required to estimate the hydrodynamic forces with high accuracy. Current methods to determine the hydrodynamic coefficients prove to be time consuming and labour intensive. In this thesis, a method based on Singular Value Decomposition is proposed to determine the hydrodynamic coefficients from a manoeuvre executed by a vessel. The method applies Singular Value Decomposition (SVD) on the equations of motion in the horizontal plane using estimated propeller and rudder forces. With use of numerical differentiation the velocities and accelerations of the vessel are calculated. The set of coefficients determined by the method is based on low aspect ratio lift theory. By comparing the trial manoeuvres simulated with results from the MMG method, it shows that the manoeuvres agree well with the MMG results. However since the method is only tested on simulated trial manoeuvres there are still some problems to be solved such as influence of measuring errors, determining the set of coefficients to be predicted and the search for the best manoeuvre(s) to predict the coefficients.

Broaching-to is a highly complex, non-linear dynamic instability event that several vessels might face when sailing in the same direction of the waves, for example when returning to port during a storm. This condition is referred to as following sea. Vessels such high-speed craft but also patrol and rescue boats, fishing trawlers or small frigates are the most subjected to the severity of the sea, and therefore also the most vulnerable to the broaching. A broach occurs when the ship is captured by the incoming stern waves (surf-riding), and is turned beam-to-sea by the large wave yawing moment. This yawturning motion is so sudden and the acceleration is so high that even the most skilled mariners are not able to avoid it, losing dangerously the control of the vessel. In extreme cases, a broach can cause the capsize of the vessel. The first apparitions of the term broaching-to date back to the 18th century. Sailors have always been frightened by the potentially devastating consequences of sailingwindward, but this phenomenon has been consistently studied starting from the 1950s only. Several naval architects put in evidence the main characteristics of the physical phenomenon of the broaching-to in following sea, developed useful and accurate techniques meant to predict the behaviour of the vessel sailing in those scenarios. Although the great efforts spent in the research on this subject, there is still some uncertainty about the causes of a broaching-to event, and about the characteristics of the vessel that might lead to an unsafe behaviour in following waves. This thesis aims to investigate these aspects, with the final desirable result of providing guidelines for safer vessels to designers and shipbuilders.@en

The publication of the Energy Efficiency Design Index (EEDI) by the International Maritime Organization (IMO) has recently stimulated the accurate assessment of actual sea performance of ships, which is evaluated as added resistance in waves. However, a satisfactory consensus on the evaluation method has not yet been reached owing to uncertainty in wave added resistance. This uncertainty can be improved by developing analytical methods that recognize nonlinearities. A typical factor contributing to the uncertainty of added resistance is the breaking of the bow wave. In this study, an evaluation method is developed to explain the nonlinearity of added resistance due to the uncertainty of bow-wave breaking. The accuracy of evaluation of added resistance can be improved by considering the speed of the ship, which affects the stability of the bow wave. This study also confirms that the breaking of the bow wave causes a violation of the linear relation between the pressure and the relative wave elevation of the bow wave. In order to express the nonlinearity of added resistance due to the breaking of the bow wave, a transfer function including the speed of the ship is proposed because the speed of the ship affects the stability type of bow-wave breaking. By analyzing the results of the added resistance measured in a fast ship series test, it was confirmed that the added resistance should be evaluated by considering the ship’s speed. In addition, hull pressures and relative wave elevations are measured for the mother ship of the series test, and analysis tools are developed to represent the nonlinearity between these two signals. This analysis confirms that the nonlinear relationship between the hull pressure and the relative wave elevation, which significantly contributes to the added resistance, is greatly influenced by the speed of the ship. This study provides important insight into the violation of the linear relation by using the proposed analysis tools. The results show that the nonlinearity due to the plunging breaking of a bow wave is intuitively detected. The nonlinearity is shown to vary with the ship’s speed. The findings provide a better understanding of the process of plunging breaking of bow waves. Based on the above findings, a correction model is proposed to improve the accuracy of numerical calculation performed using the linear potential theory. The calculation of the fast ship is compared with the experimental results. The results reveal that the accuracy of added resistance estimation can be improved through the physics-based correction. Furthermore, a method for improving the reliability of the added resistance estimation is proposed by identifying the nonlinearity of the plunging breaking of the bow wave on a fast displacement ship.@en