Twenty years after the introduction of Xbloc, DMC, which is a member of Royal BAM Group, introduced a uniformly placed and interlocking concrete armour unit named XblocPlus, which is suitable for straight to mildly curved breakwater sections, whereas Xbloc is currently applied on roundheads. Therefore, this study investigates modifications to the design or placement configuration of XblocPlus to enable its application on roundheads. Two concepts were tested on a H/V=4/3 roundhead slope for hydraulic stability in DMC’s wave flume. The first configuration consisted of regular XblocPlus combined with XP-Curve, a variant adjusted for narrowing radii, and XP-Base, a legged XblocPlus originally devised for bottom row applications. Tests with normative 0.02 wave steepness yielded a stability number (Hs/ΔDn) ranging from 2.72 to 3.09 due to uplift-related damage. The second configuration, featuring solely XP-Base and XP-Curve, resulted in a hydraulic stability number of 1.96 due to significantly less interlocking. No improvements were observed with respect to hydraulic stability compared to previous research. However, these designs notably reduced rotation-induced failure and enhanced applicability by enabling transition to the trunk and increasing maximum construction height. Additionally, this thesis investigated the validity of testing a three-dimensional structure in a 2D configuration, a method employed to maintain consistency with previous research. Wave heights in front of the structure were measured using parallel gauge sets, allowing the determination of the average disparity. This disparity was found to be within the acceptable margins for the principal test configuration. However, further research is needed to assess test conservativeness. In conclusion, this thesis provides recommendations aimed at improving the applicability and stability of XblocPlus on breakwater roundheads.

Large-scale measures within the river programmes such as Room for the River, Natura2000 and Water Framework Directive have increased the biodiversity in Dutch rivers and have achieved a more natural landscape. However, recent river programmes have shown conflicts between safety against flooding and riverine nature rehabilitation with maintaining navigational water depths. Therefore, an integrated approach is called out upon to improve the river management within these programmes. Conventional groynes are typically used to improve functions within the river programmes, whose primary function is to maintain navigational water depth. Groynes are transverse structures in which large turbulent structures are observed around the groynes. Consequently, significant bed shear stresses are developed, leading to significant local scour. Investigations for improving alternative groyne configurations are often studied for optimizing the groyne structure. The flexible groyne is considered an optimization of the conventional groyne structure. The flexible groyne consists of steep slopes and has a permeable characteristic. Although a fair amount of research has already been carried out on various groyne configurations, detailed flow characteristics around and through permeable, sloped groynes are limited. Hence, this research aims to numerically quantify the effects of permeability and head steepness of groynes. A literature study is executed to investigate the critical processes required for capturing within the numerical model to answer the research question. From the literature study, it appears that the most important processes are the non-hydrostatic effects, adapting large turbulent structures and implementing the porous zone using a non-linear function. Multiple software packages have been analyzed. Fluent is chosen, which is analyzed to capture the required processes adequately.
A new numerical model has been set up for investigating the research question by simulating flow around groynes. The model is validated against three experimental studies for various characteristics. The important mean flow characteristics have been validated within an acceptable range. Still, it appears that the numerical model tends to underestimate the mean streamwise flow velocities, overestimate the Reynolds shear stresses and shift the peak values of the Reynolds shear stresses downstream. Four configurations are identified for the simulations of varying head steepness and porosity. It appears that the increase of the porosity reduces the large turbulent structures and bed shear stresses close to the groyne and shifts the peak values of the Reynolds shear stresses, and bed shear stresses further downstream. The porosity reduces the maximum Reynolds shear stresses and bed shear stresses compared with the Reynolds shear stresses, and bed shear stresses for an impermeable groyne. These reductions are because of the momentum exchange between the free flow region and the flow through the porous structure, which reduces the mean flow velocity in the free flow region. For decreasing steepness, the large turbulent structures and bed shear stresses are observed close to the groyne due to increasing deflection. The flow appears to follow the geometry of the sloped groyne more smoothly. This research is seen as a first approach for modelling a porous, sloped groyne. Further improving and analyzing numerical modelling for porous, head sloped groynes are advised to increase the model's accuracy. Furthermore, more simulations for varying the head steepness and porosity is suggested to improve the relations between the increase of porosity and head steepness for the flow characteristics. In addition, including sediment transport models within the model is expected to increase the understanding of the hydrodynamics and morphology around these specific groynes.

XblocPlus is a single layer armour unit that is recently developed by BAM Infraconsult. It is the successor of the Xbloc. An important advantage of the XblocPlus is the relatively high construction speed compared to the Xbloc. The increased construction speed is caused by the possibility to place XblocPlus in a uniform pattern and the relatively large surface area that can be covered with a small number of blocks. A disadvantage of XblocPlus is the limited block stability at the top armour rows of a low crested structure. The limited stability is caused by the reduced interlocking capacity of the blocks on the top armour row. In previously performed studies, a back support is placed behind the blocks to stabilise the top armour row on the front slope. The back support of a concrete element significantly improves the stability of these armour blocks. However, at normative wave conditions, the stability of the top armour row on the front slope is still insufficient to meet the target stability (Ns,c = 3.0). The stability of the top row on the rear slope is not investigated in other studies. Consequently, no conclusions can be drawn about the stability of the crest blocks on the rear slope. In this study, physical model tests in a wave flume were performed to assess the effect of crest modifications on the stability of the top armour rows on the front and rear slope. The main objective of this study is to design a stable breakwater crest that has the best hydraulic performance with respect to the economically most feasible breakwater dimensions. After an exploratory study into the meaning of the main objective, it can be concluded that a relative crest width of 1 is desirable. The relative crest width is determined as the ratio between the crest width (B) and the significant wave height Hs. The principle of previous studies is used to set a reference situation. This crest configuration contains a concrete element between the top armour rows that functions as a support. This is a rather wide structure with a relative crest width equal to 2.7. After testing the reference situation, the top row on the front slope turned out to be normative for the crest stability. The found stability at failure coincides with the stability found in previous studies. The blocks on the top row of the rear slope remained stable. Also after reduction of the crest width to a relative crest width of 1.9, the crest blocks on the rear slope remained stable while the crest blocks on the front slope failed. It can be concluded that the blocks on the top row of the front slope are normative for the crest stability. The weight of these blocks is too limited to meet the target stability. By application of modified XblocPlus blocks is attempted to obtain stable blocks on both top rows. The adjusted blocks are much bulkier and consequently heavier than the original XblocPlus blocks. The blocks shape is modified in such a way that the crest blocks on the front and rear slope can be placed back to back without the support of a crest element. As a result, the relative crest width is reduced to 1.1. Several variants of modified crest blocks are tested to acquire information about the stabilising effect of the applied modifications. Modified blocks with an increased permeability, an increased interlocking capacity and a relatively large resistance against rotational instability were tested. Overall, the bulky block shape, the block's permeability, and the interlocking generated by the almost vertical back of a block, appear to be very important for the crest stability. The acquired information of this first test series is used as a foundation for further optimisation of the permeable block. An attempt to optimise the modified block is done by reducing the volume at places that have the least impact on the block stability. Application of measures that streamline the block shape in flow direction and further increase the block’s permeability were applied in this optimisation phase. Finally, a block with a 44% larger volume than the original XblocPlus block is obtained that meets the target stability of Ns = 3.0.

In the Meuse seven weirs are located in the Dutch reaches, controlling the water level to enable inland navigation through the river. The weirs are being scheduled for replacement, where weir Grave is the first one in 2028. They are reaching their end-of-life time. One of the main issues that became of more importance in the recent years is ship collision. In the past 20 years two major ship collisions happened on two different existing weirs in the Meuse, one at Grave and one at Linne. The place of impact at the weirs was significantly damaged after those collisions. As a consequence, the water level dropped and inland navigation was not possible for one month. In this study an inflatable weir is proposed as replacement of the existing steel weirs in the Meuse. A conceptual inflatable weir design is made for location Grave, for replacement of the existing weir. The design is based on existing literature, such as the inflatable storm surge barrier Ramspol. The design for Grave is considered to be scalable to the overflow (Poirée) parts of the Meuse weirs. One of the aspects that has not yet been considered for those inflatable weirs is ship collision. The theory and formulas found for the existing collision analysis are not fully applicable to the inflatable weir, mainly due to large elastic deformation of the inflatable weir. In literature a standard expression has been found to quantify the ship force on the colliding structure. This expression forms the basis of the analytical model. The inflatable weir in the analytical model is schematized by a two-dimensional plate sheet. An effort was made to validate the strain found in the analytical model by a numerical model in Ansys. However numerical instabilities were found that lead in considerable modification of the desired model and so the results indicated no representative outcomes.
To see what happens during the ship collision a physical scale model was made, with scale 1:25 for accurate representation of the physical phenomena.
Sixteen experiments were done with four different draughts and four different velocities of the ship. For the experiment with the scaled maximum draught (0.14m) and velocity (1.1m/s). The full video experiments are uploaded to the 4TU-datacentrum (https://data.4tu.nl/portal). The two aspects uplift of the ship and gliding over the weir observed in the experiments are not yet included in the analytical model, therefore the analytical model is extended. The extended analytical model showed a 25% deviation with the uplift of the ship and a 15% deviation with the displacement of the weir from the experiments. With the extended model it was calculated that the limit strain is not exceeded and that the strain is maximum 5% on top of the static strain of 1.9%. Concluding, the first steps have been taken into research of ship collision on inflatable weirs. Further investigation on the ship with V-bow, the propeller of the ship and a more extensive numerical model is recommended for ship collision on inflatable weirs.

The Xbloc^Plus is a new type of single layer armour unit for breakwaters. The key difference between earlier single layer armour units is that the unit is not only placed in a regular grid, but also with a regular orientation. The main benefit of this is that it can directly be seen whether the unit is placed correctly. Additionally, the placement always takes place with the same repetitive movement, as is preferred by crane drivers. The benefits to the placement procedure would however be reduced when the requirements for the under layer become very tight. Since the time that is saved during placement of the armour units, then would be lost during the profiling of the under layer. This has led this study to focus on the influence of irregularities in the under layer on the stability of the Xbloc^Plus and the allowed tolerances for the placement of the under layer.
In the process of obtaining a stable armour unit, multiple researches have been conducted. The final shape has been further optimised by adding a hole in the middle of the unit and increasing the interlocking capacity. Better interlocking increased the connection between the units and thereby improved the resistance. The hole increased the porosity and thereby reduced the overpressure underneath the armour layer. Which is a result of a difference in water level inside and outside of the breakwater. The increase in stability due to the enlargement of porosity, validated earlier findings that the acting failure mechanism is extraction due to the overpressure.
The stability was expected to be mainly effected by the amount of interlocking. Subsequently, the amount of interlocking is determined by the relative angle between the armour units. For this research physical model tests have been performed to check that hypothesis. Multiple tests have been conducted with different radii of convex and concave shapes in both long shore and cross shore direction. The goal was to find the critical relative angles of each combination of shape and direction. The convex shape in cross shore direction was the only irregularity that caused failure and proved to be critical. The relation between the relative angle and the stability number resulted to be linear, instead of the expected drop of stability at a certain critical value. The relation showed signicant spreading, for which tests with small deviations from the design profile seem to form the upper bound and large deviations the lower bound. Thereby indicating that the level of stability is not only determined by the relative angle but also by the deviation from the design profile.
In succession of the tests with specific shapes and directions, more realistic tests have been performed with micro irregularities and S-proles. The convex shape in cross shore direction proved to be critical for these congurations as well. Furthermore it was found that for large S-proles, sudden failure could occur without previous indication of loss of interlocking. Further analysis of the divergent failure behaviour of large S-profiles indicated that the arched shape of the profile enabled the lifting of the armour layer. A mechanism similar to the buckling of beams. The pressure inside the breakwater, the drag of the down-rush and the weight of the upper part of the slope, cause the initial distortion of the profile to be enlarged.
The differences between the measurements of the profile before and after the tests, showed that the same movements occur for smaller S-proles and the tested convex shapes in cross shore direction. The movement could even be seen in tests that have not failed. Which implies that the arching mechanism that causes sudden failure for large S-proles, also induces the loss of interlocking for other convex shapes. A simplied model of the forces on the convex sections in the profile indicates that the enforcing of the arching mechanism mainly depends on the length and steepness of the downward part of the convex section and the  atness of the upward part of the convex section. These findings correspond with the test results and explain why the stability performance is the highest for the short length scale micro irregularities and lowest for the large scale S-proles with large deviations from the design profile.
Evaluation of the effect of irregularities is performed with the tolerances of the regular Xbloc, which are also intended to be used on the Xbloc^Plus. To prevent differences in stability due to the size of the under layer, the tolerances are expressed in the unit size (D_n) instead of the under layer grain size (D_n50). The resulting tolerances are maximum 0.25 D_n for the deviation from the design profile and maximum 0.1 D_n deviation between subsequent measurements along the profile. The profile is measured every 10m of the breakwater and subsequent measurements along the profile have a distance of 0.3 D_n. The requirements are a little more liberal than the tolerances of the regular Xbloc since the tolerances of the largest under layer grain size are taken as a starting point. The test results indicate that the tolerances are sufficiently safe, with potential for more liberal requirements.

The world’s oceans contain a vast wave energy potential. Many promising technologies of wave energy conversion have been developed, such as the Oscillating Water Column. BAM Infraconsult B.V. has developed the Ocean Falls concept of an oscillating water column that has the addition of a tube and a back wall which is able to move in order to change resonant characteristics of the structure to match incoming wave frequencies.

A numerical model has been made to capture the dynamic behaviour of the oscillating water column represented as a "rigid piston", where the system is modelled as a linear mass-spring-damper. The internal water surface is assumed to be horizontal and flat, both valid approximations for small chamber widths with respect to the wavelength of the incoming wave. The hydrodynamic coefficients, as well as the excitation force on the piston have been obtained using the ANSYS AQWA software. Thermodynamics in the chamber have been included by assuming a linear, adiabatic and reversible air flow. Furthermore, pressure oscillations in the chamber due to the oscillation of water are assumed small compared to the atmospheric pressure. The equation of motion of the piston is coupled to the pressure oscillations inside the air chamber, which includes linear turbine damping and air compressibility. The response of the system has been studied in the frequency domain for regular and irregular waves.

Model experiments have been performed to compare the linear model to experiment results for regular waves. The turbine damping has been modelled by adding a lid on the air chamber containing an opening where air can flow through. The area of the opening is related to the level of damping induced on the water surface inside the chamber. Two back wall positions and three different damping cases have been studied.

Air compression has been negated from the linear model while comparing to experiments due to scaling complications and the relatively small effect of air compression. For the case with no turbine damping the model experiments indicate a longer resonant period compared to the linear model. This difference, to a smaller extent, is also visible in the damping cases. The measured flow in the damping cases is slightly larger than the linear model. Pressure measurements compare well with the linear model. Efficiency is defined to be the power in the waves divided by the power available to a power take-off system, such as a turbine. For the low damping case the efficiency measured and efficiency computed in the linear model compare well and both give a peak efficiency of around 60\%, contrary to the high damping cases where the model under-predicts the measured efficiency, indicating a higher damping input into the model possibly due to the linearisation of the damping. For high damping the experiments also give an efficiency of around 60\% while the numerical model predicts this to be circa 50\%.