This thesis introduces a fragility-based framework in order to perform a custom assessment of the complex Eastern Scheldt storm surge barrier. By applying a conditional approach to loading parameters, the statistical dependency between failure mechanisms and structure elements can be described separately for the strength and loading part of the assessment, allowing for a reduction of the conservatism. This report applies this fragility-based assessment to assess the barrier on the failure mechanisms ‘height’ and ‘failure due to failing closure’.

After the failure of several large breakwaters in late 1970’s and early 1980’s where the role of rocking and breakage of armour became apparent, the importance of understanding this rocking phenomenon is given a great emphasis. Single layer randomly placed armour units are widely used in breakwater designs as they are more economical due to the less volume requirement. But these single layer units have a much more “brittle” behaviour and strength of the units becomes a critical factor. As the stresses developed after the impact is difficult to measure directly in the scale models, currently percentage rocking is used as a design criterion. But a clear relationship between this quantity and breakage has not been identified. Even though the single layer armour unit types are widely used the knowledge on the rocking behaviour of this type of units are limited. Therefore, to get a better insight into the rocking behaviour of single layer armour units a previously proposed technique of instrumented unit with embedded sensor was adopted. This technique was found to be promising in detecting the rocking motion in standalone mode. However, one issue of that technique was relatively lower sampling frequency. Because of that, enough data could not be captured to resolve the rocking motion in time very accurately. Therefore, in this report the measurements with standalone IMU sensor embedded in 3D printed model armour unit has been developed further. Firstly , different techniques were adopted to get the optimum sampling frequency and sampling frequency was increased from 25 Hz to 100 Hz. This report includes further details on the processing method and obtained results after performing the 2D physical model testings. It is the first time that stand alone rocking motions are reported for single layer armour units. By increasing the sampling frequency from25 Hz to 100 Hz, rocking events can now be resolved in time by 5-10 measurements points. Gyroscope data and accelerometer data were combined to separate the linear acceleration from raw accelerometer data. Upward and downward rotational motions were distinguished, and impact velocities were calculated based on both accelerometer and gyroscope. By analyzing the data it was observed that the angle of rotation during the rocking event is small and usually unit returns to its original position after a full rotation.

XblocPlus is a new uniformly placed single layer armour unit, developed by Delta Marine Consultants (BAM Infraconsult). This report focuses on the stability of the first row of armour units, as this row is interlocked less than other rows. When the first row starts to slide, this is a big threat to the stability of the entire armour layer. Furthermore, not much is known what exactly influences the stability of the first row. In this study physical modelling is used to determine the stability the first row of an XblocPlus armour layer and investigate what influences this stability. The results of the tests were analysed with a method called Digital Displacement Analysis. Two simplistic theoretical models were devised. The first model considers the destabilizing forces to consist only of the drag and uplift forces caused by the wave on the armour units of the first row itself, this is called direct hydraulic loading. The second model also considers destabilizing forces transferred by the armour layer to the first row, this is called indirect hydraulic loading. From the model tests, it was found that indirect hydraulic loading plays an important role, as the movement clearly occurred during down-rush. When waves started to plunge, the waves failed to destroy the breakwater. Furthermore, loose armour units placed in front of the first row moved at higher heights than the first row, indicating that the armour layer pushes out the first row. Water depth influences stability, as lower water depth gave a lower stability. It is feasible that this effect is caused by the down rush being closer to the first row. The second model is most appropriate when taking these findings into account. From the tests it was found that a toe berm increases stability as it adds weight to the first row and thus increases friction resistance. A foundation layer also increases stability as friction between the foundation layer and the first row is higher than between the first row and the concrete slab that was used in other tests. Both measures also increase the damage threshold. The damage threshold is the amount of damage that a first row can take before brittle failure occurs. Brittle failure is an increase in damage of 0.2Dn (Dn is the nominal armour unit diameter). When both measures are used together, the foundation layer makes the toe berm more stable and this is why the stability of the first row is also increased. Based on the tests in this study the stability of the first row can be stated as Ns =3.87 (Ns=Hs/(delta*Dn), the stability number is defined as the significant wave height divided by the nominal diameter of the armour units and the relative density of the armour units) as at the end of the tests the damage was only 0.13Dn. The test results were used to determine a working hypothesis for a design formula. More tests are necessary to validate this formula and determine its accuracy. A remarkable finding of this study is that two test series showed contradictory influences of wave steepness. The first test series showed that a lower wave steepness is detrimental for stability of the first row, while the second test series showed the opposite. More research should be conducted to investigate on this curiosity.

This thesis focuses on modelling a gravitational launch of gravity based foundations (GBF's) for offshore wind turbines. This is an extension of the Blyth Offshore Demonstrator project by BAM Infraconsult. To become more competitive in the offshore wind energy market, the construction of self-buoyant GBF's installed using the `float and submerge' technique needs to be optimized. GBF's will need to be constructed on land, which calls for a way to `launch' the GBF's. Another study suggests the use of semi-submersibles or immersion structures, which are very expensive. Due to the GBF's high strength and stability, it might be suitable for a gravitational launch. Although these launching methods have been widely applied on steel ships and jackets, the application for reinforced concrete structures is rare, especially using slipways with an abrupt ending. A conceptual design is needed to test the technical and economic feasibility of this launching technique. For the purpose of making a conceptual design, the launching process must be modelled. The goal of this thesis is to develop models that can be used in a conceptual design phase to easily determine the optimal shape and dimension of the slipway used to gravitationally launch GBF's. This thesis contains three modelling methods: (simple) mathematical models, physical scale model tests and a Computational Fluid Dynamics (CFD) model in ANSYS Fluent. Simple mathematical models were derived to model each phase of the launching process. Translational movements when the GBF is in full contact with the slipway were described using a simple force balance, both for a dry and a partially submerged slipway. For the kinematics as it tips over the slipway edge, equations of motion were derived and solved. The main limitation of this set of equations of motion is that hydrodynamic forces are not included. For the kinematics of the freely floating structure, equations of motions were solved and hydrodynamic components were determined analytically from literature and numerically using ANSYS Aqwa. Physical scale model tests were performed to (1) validate and calibrate the mathematical models, (2) determine the most favourable slipway geometry, and (3) develop more insight into the GBF behaviour during a gravitational launch. The tests were conducted at a 1:100 scale. For calibration of the hydrodynamic components, free decay tests were performed. In the abruptly ending slipway launch tests, slipway inclination (9°, 14° and 21°), freeboard height (positive, zero and negative), and initial GBF velocity (high and low) were taken as variables to investigate their effect on the severity of GBF dynamics. Severity of the dynamics was parameterized by the maximum GBF rotation measured around the horizontal axis during the launch (pitch). A large GBF rotation means large motion amplitudes thus violent movements, which are undesirable. Comparisons to mathematical models show good agreement in most cases after a calibration of the hydrodynamic components. The full launch procedure was not modelled accurately by the mathematical models. An empirical formula was developed relating the slipway variables to maximum GBF rotation, which provided more accurate results for a larger range of variables. A lower freeboard and a steep slipway inclination was always favourable. No such trend was observed for the initial velocity. Most favourable slipway geometry tested had a slipway inclination of 21° and a slipway ending below the water surface (negative freeboard), resulting in a maximum GBF rotation of 29° around the horizontal axis. A CFD modelling strategy was proposed and used to compare to the physical model tests. The CFD model was set-up in 3D using a dynamic mesh and a three degree of freedom solver to compute all acting forces on the moving body. Despite a coarse mesh with insufficient quality, the solution converged and showed numerical stability, also for large motion amplitudes. Depending on the scale, the CFD model showed good agreement to the physical scale model tests. The CFD model has a high potential in terms of the range of initial conditions, flexibility in structure shape and dimension, and amount of output data. The simple mathematical models (force balance, equations of motion and an empirical formula) are sufficiently accurate to analyse key differences between slipway alternatives to make choices in the conceptual design phase, after a calibration using physical scale model tests. Due to a long computational time and time consuming improvements, the CFD model is more suitable in a more detailed design phase, where it could be very valuable. A first estimate of most important launch requirements was made using the mathematical models for abruptly ending slipways and showed technical feasibility. More research should mainly focus on improving the CFD modelling strategy and on making a conceptual design for a specific location to further investigate economic and technical feasibility.