In order to monitor elliptical fatigue crack growth in ferromagnetic steel using magnetic methods, analternative to the self magnetic flux leakage method must be derived as elliptical cracks can grow to significant sizes before they reach through the thickness of the plate material. An approach is sought by translating subtle changes in magnetisation back to the Villari effect, a phenomenon which depicts how applied stress induces changes in magnetisation in ferromagnetic objects. Since the magnitude of these changes in magnetisation is small, other nonlinear effects of similar order such as magnetic relaxation and hysteresis are identified, measured and quantified preliminarily.

The magnetic behaviour in this project is assumed to be quasi-static, and derivations of the expressions for the magnetic field around simple geometric shapes are provided in order to understand magnetic behaviour and verify the outcome of the numerical simulations. It is shown that the numerical simulations
produce identical magnetostatic induction fields as the analytically derived expressions when using a sufficiently refined mesh.

An attempt is made to measure long-term magnetic relaxation by subjecting a solid prolate spheroid to a continuous uniform background field for periods of an hour while trying to measure differences in the induction field at a fixed distance. Short-term relaxation, the time it takes for an object to reach a certain
magnetisation when the background field is abruptly changed, is also investigated. It is concluded that both effects could not be successfully measured using the current setup. In order to draw proper conclusions, further research into this topic should be conducted using more accurate equipment for extended periods of time.

Upon investigation it is discovered that it can not be assumed that the steel specimens exhibit a uniform permanent magnetisation. A self-developed method is introduced through which non-uniform magnetisation in three directions can be calculated by means of inversion using a set of magnetic induction field measurements in a plane below the specimen when the background field is zero. These measurements are translated to magnetisation using a set of higher order square Gaussian distribution functions that are spaced in a grid over the domain of the test specimen in order to vary the magnetisation locally.

Literature that shows comparable results regarding description of non-uniform permanent magnetisation using an array of induction field measurements has not been found. The concept of hysteresis is introduced and a method is presented through which the parameters of the Jiles-Atherton hysteresis model can be determined using parameter fitting in combination with a forward numerical model created in COMSOL. Closure of minor loops require modifications to the original JA equations which are implemented in the forward model. The numerical model is encapsulated within the Shuffled Leaping Frog parameter optimisation algorithm in order to compute the correct hysteresis
parameters. It is found that it is possible to successfully determine the parameters of multiple specimens using weak magnetic fields, and therefore minor loops, which is unparalleled in literature.

Eventually, the Villari effect is introduced and an attempt is made to measure and model the effect usingan extension of the Jiles-Atherton model proposed by Naus. Experiments have shown that using this methodology the magnetostriction parameters can be succesfully obtained. A recommendation is
provided into how these results can be implemented in crack-propagation models in future research.

Dykstra Naval Architects are regularly designing large classic sailing yachts or motor-sailors, of which the draft is an important design restriction.The sailing performance is increased by adding lift-generating appendages,without increasing the draft. An example is a retractable centre board, havinga big influence on the sailing properties. Predicting the performance of the centre board contribution in a hull-keel-centre board configuration is the subject of this research. When predicting the performance of large sailing yachts, Dykstra wants to keep the ability to superpose an appendage to the data of a hull-keel configuration obtained from towing tank experiments or CFD simulations. This means that a method must be developed to estimate the contribution of the centre board, in terms of side force, resistance and centre of effort. Both towing tank experiments and CFD simulations are conducted for this research. The Maltese Falcon is used as the 'case ship'. A towing tank model of the Maltese Falcon was already made and tested at the TU delft in 2002. This model is again subjected to towing tank experiments, with a new keel and two new centre boards, resulting in 9 different hull-keel-centre board configurations. The main focus was on the towing tank experiments, executed in the Delft Hydromechanics Laboratory. CFD simulations were done to validate the results of the towing tank experiments and to gain visual insight in the flow around the vessel. The lift-carry-over on the keel and hull above the centre board can clearly be seen, as well as the influence of the centre board on the circulation in the flow around the underwater body of the yacht. After post-processing all experimental data, the results of the towing tank experiments are used to develop formulations to predict the performance contribution of the centre board. The measured lift of the centre board contribution was roughly a factor 2 higher than the centre would generate according to Wicker & Fehlner theory. Additionally, it was found that the lift-carry-over does not only have a positive effect on the generated side force, but also on the resistance. Furthermore, it was found that heeling the Maltese Falcon model by 15 degrees, yields the same magnitude oflift-carry-over as for the upright conditions. This resulted in the conclusion that heeling the yacht has no influence on the lift-carry-over from centre board to keel-hull. The new prediction methods, derived from the towing tank experiment data, are validated on YACHT1 and Adela. These are existing yachts with hull-keel-centre board configurations, but both very different. This enabled an interesting examination on the influence of certain aspects of the configuration on the performance of the centre board contribution. All in all, it was found that the predicted centre board contribution corresponded really well to the measured data of YACHT1 and Adela. This provides enough trust to implement the new centre board performance prediction methods in the Dykstra performance prediction tool. Every new design cycle of a yacht with hull-keel-centre board configuration will serve as a validation of the derived performance prediction methods.

Damen Dredging Equipment is a yard dedicated to the dredging industry. The yard specializes in the design, manufacture and supply of a wide variety of dredging tools. One of the tools Damen offers is the Trailing Suction Hopper Dredger(TSHD).

The performance of such a TSHD is described by its production: the amount of sediment loaded in the hopper per unit time. The overflow loss, the material lost overboard, can easily reach up to 30%, which causes a significant decrease of the production. In addition, the turbidity plume caused by these overflow losses can have a negative environmental impact. This turbidity plume reduces light penetration, clogs filter feeders, and disperses contaminants which can be attached to the sediment. Damen is interested in estimating and reducing these overflow losses. Different models to estimate the amount of material lost overboard exist. All these models have their pros and cons. The analytical model of Miedema & Vlasblom(1996) gives a quick and good estimate of the overflow losses, but gives no insight in the flow inside the hopper. The 2DV model of Van Rhee(2002) is able to accurately simulate the flow inside the hopper, but has a large computation time. The 2DV model of this thesis gives a good estimate of the overflow losses, gives insight in the flow inside the hopper, and has an acceptable computation time.

The new 2DV model was developed in OpenFOAM. At the start of this thesis, it was possible to model mixture flow in OpenFOAM, but a sand bed could not be modelled yet. Several features had to be added to OpenFOAM to overcome this problem. The sand bed was regarded as a solid body inside the computational domain. To simulate the influence of this solid body on the mixture flow, boundary conditions were added at the bed interface. Sedimentation was modelled by adding a moving mesh. The closed flume experiments of Van Rhee(2002) have been used to validate that sedimentation is simulated accurately. By comparing hopper simulations with the hopper experiments of Van Rhee(2002), it was shown that the flow in the hopper was also simulated accurately. The computed overflow losses are, however, on the low side. The current version of OpenFOAM can calculate with only one particle fraction. In reality, the smaller fractions of the Particle Size Distribution are pushed upwards, causing the overflow losses to be higher. The 2DV-model gave a deeper insight to the phenomena in the hopper. It was possible to derive several equations which describe the flow in the hopper. With these new formulas, a simple phenomenological model was developed, which was named the 'Layer Model'.

The main focus of this research is determining when dredging of reservoirs is feasible. First the main issues associated with the sedimentation of reservoirs are investigated. Most important are the loss of reservoir volume, sediment shortages downstream of the dam and possible blockage of water intakes.
The sedimentation issues occur mostly in sediment laden rivers. Reservoirs close to the origin of the river, for instance in mountainous terrain usually do not suffer from severe sedimentation issues.

A survey is held under authorities responsible for different reservoirs. Results indicate that not all reservoirs suffer sedimentation issues, but part of the worldwide dams and reservoirs does.

The most important conclusion is that sedimentation at this moment will only be dealt with if it is clearly affecting the function of a reservoir or if the function of a reservoir is threatened in the near future. The matter has to be urgent enough that owners are willing to spend funds on mitigating sedimentation issues. If added value can be gained through removing sediment this improves the business case of dredging. In the survey this is verified by the respondents.

Methods of dealing with reservoir sediment are discussed. Different dredging methods for the dredging of reservoirs are presented and investigated. The main advantages of dredging are found to be precise removal of sediment, avoiding large sediment flushes and no excessive loss of water.
Using a 1-dimensional Sobek model, it is shown that part of the sediment entering the reservoir can be used for downstream river restoration.

Different factors that influence the feasibility of dredging are identified. The function of the reservoir is important. For the functions of irrigation, storage of hydro power, water supply and flood control the available volume is for example important. Sediment control is therefore important.

By modelling different shapes for reservoirs using Delft3D, it is found that the type of reservoir only partly determines the location of sediment in the reservoir. Other factors influencing the deposit location are sediment concentration and the type of sediment. The maximum reservoir depth is found to be linked to the dam height.

To determine if the dredging of reservoirs is feasible it has to be clear that the reservoir function or intake is threatened by sediment. Based on the function of the reservoir a business case can be made comparing costs and benefits. Benefits of extra reservoir volume are estimated. Possible added values are taken into account, such as the possible sale of dredged material. A dredging model is created to estimate the costs of reservoir dredging.

This model takes different parameters such as sediment composition, dredging depth, reservoir type and transport distance into account. Using this model for different scenarios it is shown that dredging prices can start as low as 1.01 euro.
If the sediment is made up of soft and loose material this reduces the price of dredging. Furthermore the transport distance of the dredged material to shore has a large influence on the dredging costs. The transport distance for the dredged material must be kept small and the volume of material dredged must be over 25,000 $m^3$ to find a stable price. For all reservoirs these parameters are different, leading to a reservoir specific dredging price estimate.

Low dredging prices are possible under favourable conditions. At these prices, dredging can compete with other sediment management techniques.
On top of that, the added benefits of dredging have to be taken into account: downstream river restoration, the possible sale of dredged sediment and increased downstream soil fertility. These benefits increase the feasibility of dredging a reservoir further. The dredging of certain reservoirs is seemingly beneficial. Reference reservoir dredging projects have to be performed to confirm that this

Further research into the deposition of sediment in different types of reservoirs is recommended. Also more investigations into the downstream return of sediment are recommended.

The sliding force was a contributing factor to the displacement of caissons from the Kamaishi composite breakwater during the Great East Japan tsunami 2011 (Arikawa et al., 2012). The pressure reduction on the landward wall of the caisson due to non-aeration of the overflowing jet gives rise to an additional horizontal force which increases the sliding force. The estimation of this additional horizontal force and the proper understanding of the physical processes which cause it are imperative in establishing stability of a caisson breakwater during tsunami overtopping.
Tsunami is associated with accelerating flows with massive heads that results in detached overflow nappes. In this research, a simplified tsunami was modelled in the laboratory as a steady breakwater overflow and the respective pressure drop behind the overflow nappe is derived. The nappe trajectories are derived theoretically based on general projectile motion for both the aerated and non-aerated scenarios. This ballistic model is validated using measurements of the physical model. For the aerated nappe, the theoretical results and measurements are in agreement. For the non-aerated nappe, the ballistic model provides comparatively high deviations from the measured nappe. A sensitivity analysis of pressure reduction indicates the deviations can be attributed to the derived pressure drops.
In addition, the governing physical processes related to caisson breakwater overflowing are investigated. The flow conditions below the overflow nappe are hydrostatic, which is implied by a time-averaged stationary water level below the nappe. The dynamic pressure arising from the stagnation pressure at the jet impingement on the flume bed is estimated and is compared with the pressure drop behind the nappe. The results suggest the above-mentioned dynamic pressure is negligible with respect to the pressure drop. Thus, it is concluded that the governing mechanism responsible for the pressure reduction is the air entrainment process during jet impingement. The air entrainment rate from the cavity behind the nappe is compared against the impinging velocity of the overflow jet. The results suggest that air entrainment rate increases with increasing jet impingement velocity, establishing the fact that higher inertia forces leads to rapid air entrainment.
The ratio of additional horizontal force due to non-aeration to the total horizontal force is found to be between 0.15 and 0.25. However, some eccentricities are evident with extreme tail water depths and flow rates. Scaled-up forces are obtained using Froude scaling criteria. Reynolds numbers suggest that the flow is fully turbulent at both the lab and field scales, while Weber numbers show that surface tension effects might be more pronounced in the lab than in the field.
As surface tension effects may affect the direct scaling up of model tests to field scale, the utility of numerical model simulations is apparent. In OpenFOAM, the k-epsilon turbulence model with the InterFoam solver is used for this purpose. Prior to investigating the validity of OpenFOAM to simulate the caisson overflowing scenario, the model is validated for open channel flow. The results indicate that OpenFOAM correctly simulates the open channel flow with respect to the logarithmic profile and the free-surface slope. Furthermore, simulation of the flow atop the caisson very closely matches that of the physical laboratory model test. The model results for nappe behaviour follows existing trends found in literature. The simulated overflow nappe is a clinging nappe rather than a detached one due to the inability of the 2D model to allow air into the void behind the nappe.
The significance of the present study has various aspects. The ballistic model enables the derivation of the nappe’s trajectories during steady overflow of a caisson breakwater. As a result, an explicit relationship between kinematics (ballistics) and dynamics (forces) can be developed. The estimation of the additional horizontal force due to non-aeration effects pave the way to improve design guidelines for the stability of caisson breakwaters during tsunami overtopping.