1 

Evaluation of the IH2VOF model for modelling of hydraulic properties near breakwater toes
The IH2VOF model can be used to simulate wavestructure interaction. This additional thesis aims to evaluate the performance of the IH2VOF model for determining the local hydraulic properties (flow velocities and water pressures) near the toe structure of a rubble mound breakwater.
Firstly, the model is introduced and the appropriate computational domain and mesh size are determined, along with the other input variables for the model.
The results of the IH2VOF model are compared to actual measurements of a breakwater experiment that was performed in a wave flume.

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2 

Numerical analysis of the Forchheimer coefficients and the maximum pressures for a dike with impermeable core and permeable Elastocoast layer
Breakwaters are important objects to protect coastal and harbour areas. To minimize the probability of failure of breakwaters, a lot of research has been conducted concerning the stability of breakwaters. After Hudson and Iribarren, an influential research is conducted by van der Meer.
The stability of the dike revetment is investigated by van der Meer. van der Meer formula takes the Iribarren number, number of waves and damage level into account. It also contains a factor P which describes the “notional permeability” of the breakwater. This factor is based on the fact that a more permeable structure dissipates more energy and hence requires less heavy armouring. Its value depends on the different layer designs of the breakwater. This is not the real permeability of the dike. The notional permeability (P) was empirically determined by van der Meer [1988] for three different standard situations, to be exact the P=0,1, P=0,5 and P= 0,6. It is difficult to find the exact value of this parameter.
One of the main failures of the dike is if the revetment fails. This has major implications for society and economy, hence it is important that the dike (revetment) is constructed well according to the hydraulic parameters.
Before an embankment construction can be numerically calculate, the Forchheimer coefficients are important to determine this. Without these coefficients a dike cannot be accurately calculated in the numerical model. The intention of this research is to use the IH2VOF model and to determine the pressures by the transition zone from the core to the dike revetment for a dike with impermeable core and permeable layer.
In the Großer Wellen Kanal in Germany are tests done for a dike with impermeable core and permeable Elastocoast layer with a porosity of 0,388 and a stoned diameter of 34mm. The maximum pressure which is measured in the GWK is 5,6 kPa.
This test is simulated in the IH2VOF model with non impact regular waves with Hm = 0,18m, Tm = 5,93 sec and a water depth of 3,40 m. For these study 190 combinations of Forchheimer coefficients are run with the VOF model. The Forchheimer coefficient α is varied between 200 and 2000 and the coefficient β is varied between 1,0 and 1,9. Finally, twelve possible combinations of the coefficients gave an error less than one percent and two of these combinations gave the smallest error of 0,3 percent. This combinations are α = 200 and β = 1,7 and α = 1700 and β = 1,7.
By the impact regular wave test with Hm = 0,98m and Tm = 2,99 with the same Forchheimer coefficient as above, the model gave an error of approximately 45%.
There is also considered by a constant Forchheimer coefficient of α = 1700 and β = 1,7 to change the stone diameter and the porosity to look at the impact of the maximum pressure. The porosity is varied between 0,25 and 0,55 and the stone diameter is varied between 8,5 mm to 136 mm. The results of the tests are close to each other. Only the tests with a porosity of 0,25 and stone diameter of 8,5 mm are not near to the real value of 10,77 kPa.
The porosity and the stone diameter have an impact on the maximum pressure. However, after a certain value, the impact is noticeable. Hence it is possible to choose by a porosity of 0,388 a stone diameter between 0,017 m and 0,136 m and by a
stone diameter of 0,034 m a porosity between 0,35 and 0,45. These values have not a big impact on the maximum pressure.
The dike is also tested with Irregular waves with number of waves of 400 and the wave height Hm = 0,8 m. Different tests are run with the model for different Iribarren numbers which is varied between 1,0 to 5,0. It is visible that the Iribarren number and the maximum pressure are related to each other for both plunging and surging waves.
In contrast to what has been mentioned above, the maximum pressure and the filter velocity for surging waves has not a regularity whereas by plunging waves is a regularity with the filter velocity and maximum pressure.

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3 

Damage on rock slopes under wave attack
The aim of this study is the particularisation of the accuracy margins for the determination of the damage level in the experimental plan proposed by Remon Kik at his thesis for the study of Notional Permeability of breakwaters “The experimental research of the permeability factor P”.
The evaluation of the proposed technique took place by means of comparisons between different test cases in order to specify the existence of similarities in the statistical behaviour of original tests and their repetitions. Therefore, statistical tests are used to examine the behaviour of the individual tests not only individually, but also in combination with the rest of the test components.
For the selected statistical and computational approaches the optimum measurement space step had to be specified. Therefore, a comparison took place between measurements every 5cm and every 10cm. The length of the confidence intervals was used to quantify the difference in accuracy and the two fundamental non parametric tests of MannWhitney U/ Wilcoxon W and KolmogorovSmirnov (theoretical explanation Appendix B) were applied in order to qualitatively investigate the magnitude of the behavioral change of the distribution due to the addition of the inbetween measurements (profile measurements every 5cm). The analysis showed that although the smaller measuring step increased the accuracy at about 10 30% the differences in absolute damage values were trivial.
Furtherupon, differences among tests that occur in the plunging and in the surging area were examined and tendencies were recorded. The outcome showed that an imperceptible difference occurs. The deviation was steadily bigger for the case of tests located in the plunging area (28% in contrast to 21.5% of the surging area), but this difference is considered to be trivial.
Finally, the accent was paid in the limitations of the available means and equipment. The observed higher damage values at the sides were investigated. The 13 cross sections of the structure were divided into two groups of side and middle cross sections and comparisons between them were accomplished. Then the influence of the boundary measurements was quantified in order to interpret any existing tendencies of higher damage values and local irregularities that may affect the output of the computations. In fact, the data analysis showed that the variation of damage values at the side cross sections was for all the cases larger than the middle ones. In half of the cases the difference was significant while for the other half, difference occurred, but with a lower magnitude.

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4 

Modellering van de stroomsnelheden bij de teen van een golfbreker
Het doel van dit bachelor eindproject is een antwoord vinden op de vraag of het mogelijk is door middel van het IH2VOF model resultaten gevonden in een stroomgoot te simuleren. Dit moet worden uitgezocht omdat door gebruik te maken van dit model de teen van een golfbreker beter, veiliger en eenvoudiger ontworpen kan worden.
Het onderzoek bestaat uit twee delen:
 Bekend raken met, en kalibreren van het model.
 Uitvoeren van de vergelijking met de resultaten uit de stroomgoot.
Ten eerste het bekend raken met het model en het vinden van de juiste instellingen voor de modellering. Het IH2VOF model is een numeriek model dat in staat is stroomsnelheden, drukken en vloeistof niveaus te berekenen in een virtuele 2D stroomgoot. In deze stroomgoot kan een object, in dit geval een golfbreker, geplaatst worden.
Het kalibreren van het model is lastig. Dit omdat de exacte werking niet geheel bekend is vanwege de ingewikkelde numerieke structuur en het feit dat de code niet in te zien is. Als gevolg hiervan is als startpunt gekozen voor de door de literatuur bij het model gegeven uitgangspunten. Vervolgens is gekeken of het model bij deze uitgangspunten convergent is. Dit bleek erg lastig en veel tijd te kosten. Daarna is gekeken of de rekentijd van het model verkort kan worden door middel van het aanpassen van het rekenrooster (de mesh) of het verkorten van de stroomgoot. Wat betreft de mesh bleek dit slechts in de yrichting mogelijk, echter werd zo geen rekentijd bespaard. Wat betreft de lengte van de goot is het zo dat in het laboratorium een flinke lengte nodig is om de golven goed in te kunnen stellen. In het model blijkt een dergelijke lengte echter niet perse nodig. Het is waarschijnlijk belangrijk dat er meer dan 2x de golflengte aangehouden wordt als minimale lengte van de goot in het model, ongeacht de lengte van de oorspronkelijke goot. Dit is echter niet onomstotelijk bewezen. Een verkorting van de goot heeft wel rekentijdverkorting tot gevolg.
Ten tweede volgt de vergelijking van de door NammuniKrohn [2009] gevonden waarden voor de stroomsnelheden bij de teen van een golfbreker in een stroomgoot, met de door het model gesimuleerde waarde. Als gevolg van de tijdsplanning van dit bachelor project is er helaas weinig tijd over gebleven voor deze vergelijking. Echter een korte simpele vergelijking van een aantal punten uit het rapport van NammuniKrohn [2009] liet zien dat het model wel degelijk goede waarde simuleert.
Concluderend kan gesteld worden dat met de instellingen die in dit verslag beschreven staan het model waarschijnlijk wel in staat is de werkelijkheid te benaderen. Hiervoor moet echter wel eerst nog beter naar de convergentie en het gedrag van de golfserie gekeken worden.

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5 

Stone stability in breakwater toes based on local hydraulic conditions
This study investigates the stability of rocks in breakwater toes. Previous studies have coupled the toe stability directly to the wave height, which is not physically accurate. In this study the local hydraulic conditions at the point of incipient motion are considered.
First the forces acting on a single stone are identified. Thereafter the moment of force about the rotation point of the stone is computed. When this moment becomes positive, the stone is expected to move. This is called the 'moment criterion'.
To verify the moment criterion, a wave flume experiment was designed. In this experiment all the outfacing stones were glued together, so that no movement could occur. Seven cavities were left open on the toe, in which seven 'target stones' were place. Pressure sensors were place underneath these stones and a velocity sensor and a wave gauge above the toe. Using this arrangement the local hydraulic properties at the point of incipient motion were determined. It was found that the pressure difference over a stone is the most important local hydraulic parameter to determine the point of incipient motion.
The forces and moments on the stones are computed using the measured local hydraulic conditions, thereafter the performance of the moment criterion is determined.
It was found that the moment criterion does have predictive capabilities, but it cannot pinpoint the point of incipient motion. The moment criterion can be improved by including turbulent forces and incorporating a damage parameter to increase the applicability of the criterion.

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6 

Damping of wind waves in the IJmuiden breakwaters
The breakwaters of IJmuiden are of a unique design; a riprap core is covered with a thick impermeable asphalt slab. During construction and after completion, slope instability caused extensive damage. Placement of a concrete cube armour layer prevented further damage to the asphalt, but proved to be unstable and required a significant amount of maintenance. Rijkswaterstaat (RWS), which is responsible for the maintenance, contracted a number of companies to investigate the strength and loading of the breakwaters. Lifting of the asphalt slab as a result of overpressure in the breakwater core was found to be the decisive failure mechanism. To determine the amount of overpressure, measurements were performed in both breakwater heads. A bigger favourable damping of wind waves was measured in the southern breakwater.
Based on these measurements and other research outcomes RWS decided to change the maintenance strategy; armour units above the NPA – 2 m line will not be maintained in the future. The new strategy is based on the reasoning that the damping of wind waves reduces lifting forces and makes the weight of the armour layer redundant to prevent lifting. The mechanism(s) causing the larger damping in the southern breakwater are however unknown, this makes it hard to predict the amount of damping and therefore the magnitude of the loading of the asphalt during storm conditions.
Aim of this thesis is to get insight in the stability of the asphalt slab during design storm conditions, and the necessity of an armour layer. Therefore the damping mechanism and the amount of damping during storm conditions need to be determined. Numerical modelling is performed to describe wave transmission through the breakwater and to evaluate the influence of different damping mechanisms.
Most important mechanism causing additional damping is siltation of the toe structure of the southern breakwater. Along the Dutch coast the net longshore sediment transport is directed northwards. Therefore sediment passes the southern breakwater, part of the sand might settle in the toe and core of the breakwater. A sand layer with a height of 3.3 m reduces the flow of water enough to cause the measured damping. The stability of the sand during storm conditions is checked using open filter sediment transport formula. Erosion of the sand layer is expected, however the erosion is expected to be in the order of centimetres which is insignificant.
The damping mechanism causing the measured damping in the southern breakwater is determined; hence loading of the asphalt slab during design storm conditions can be determined. The thickness and quality of the asphalt slab is uncertain and might vary significantly over the length of the breakwaters. In order to get insight in the quality of the asphalt two cores were drilled in 2004. One showed high quality cohesive asphalt, the other showed low quality with low cohesion.
Lifting of the asphalt cannot be ruled out. The dead weight of the designed asphalt slab in combination with a partial armour layer is not sufficient to resist the upward pressures during a design storm. The additional resistance needed against lifting can be provided by the weight of a complete armour layer or bending strength of the asphalt slab. The bending strength of the asphalt slab depends on the quantity and quality of the asphalt present. In order for the asphalt slab to have sufficient bending strength a top layer of high quality cohesive asphalt is required.
Concluding, without additional information concerning the asphalt quality and thickness lifting of the asphalt slab and thereby failure of the breakwaters cannot be ruled out in case the armour layer erodes above a level of NAP 2 m.

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7 

Analysis of the notional permeability of rubble mound breakwaters by means of a VOF model
When designing a rubble mound breakwater, one would like to predict the stability of the armour layer of the breakwater. For this purpose several armour layer stability formula are developed. The most reliable is considered to be the stability formula of Van der Meer (1988). With this method, the armour layer stability is predicted based on several parameters. One of these parameters is the socalled notional permeability, P.
The definition of the word notional is important to keep in mind; existing as or based on a suggestion, estimate, or theory; not existing in reality. Or, in other words, the notional permeability is not a physical description of the real permeability of a breakwater. Furthermore, there are no methods to calculate the notional permeability. This makes it difficult to estimate a safe and reliable Pvalue for an arbitrary structure.
The definition of the notional permeability suggests that a single Pvalue can be attributed to a structure. However, previous research has suggested that the notional permeability is not only dependent on structural parameters, but also on hydraulic parameters. This makes the assumption of a single Pvalue for a particular structure under arbitrary hydraulic conditions invalid. The Pvalue should therefore vary under varying hydraulic conditions.
This thesis aims for a better understanding of the physical processes the notional permeability. Some of the original physical model tests of Van der Meer (1988) are selected for analysis to achieve this goal. As a tool the numerical model IH2VOF is used. This 2D vertical model is able to simulate flow interaction with porous media. And makes it possible to measure pressures and flow velocities at any point within a breakwater. In this way physical processes can be described as functions of pressures and flow velocities.
The model is able to simulate porous flows by Volume Averaging the Reynolds Averaged Navier Stokes equations. This Volume Averaging introduces a porosity into the equations. Furthermore, the extended Forchheimer equation is needed to close the equations. This additionally introduces the laminar and turbulent Forchheimer coefficients and added mass coefficients to the equations. These four variables describe the porous media and are required as input to the model.
Based on a literature study a hypothesis is made about the variables on which the notional permeability is dependent. The Buckingham PI theorem is applied to these variables, resulting in four dimensionless PI terms. Eventually it is concluded that the PI terms are best measured 0.5 times the significant wave height below the initial water level, inside the armour layer and in a normal direction to the front slope of the structure. With this approach, all four PI terms show a positive correlation with P.

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8 

Stability of a Crown Wall on a Breakwater: A refinement of existing design formulae
This thesis investigates the stability of a crown wall situated above SWL (Still Water Level) on top of a rubble mound breakwater. Crown walls are concrete super structures implemented commonly to provide a flat surface for pipelines and to make the breakwater accessible for vehicles.
The vertical distance between SWL and the bottom of the crown wall is referred to as the freeboard in this thesis. Current design formulae do not take the freeboard into account when calculating the uplift force on the crown wall. Furthermore design formulae assume that the maximum of the horizontal and vertical force occur at the same time. Previous research noticed that these two maxima might not occur simultaneously. The time difference between both maxima is referred to as phase lag.
The first goal of this research is to gain insight in the influence of the freeboard on the uplift force and the uplift pressure distribution. The second goal is to quantify the phase lag. A dataset is needed to achieve both study goals. Two approaches are investigated to obtain a dataset. The first is a numerical model, the second is a physical scale model. The research question is: to determine in what way a numerical model or a physical scale model can be used in order to gather a reliable dataset to realise the project goals.
The selected numerical model is the IH2VOFmodel. Currently the VOFmodel is only validated when the crown wall is (partly) situated below SWL. An experimental dataset was acquired to validate the model. Because the dataset did not provide the exact water depth, it cannot be used to validate the model.
For this research physical scale model tests are conducted, in which wave pressures were measured. The recorded pressure data contain a significant amount of noise. Therefore the data are unsuitable to obtain the actual wave force and the exact pressure distribution on the crown wall. It is concluded that the data are only suitable to partially reach the project goals.
Current design formulae assume that the uplift pressure reaches the rear end of the crown wall. However, the measured pressure data indicate that the uplift pressure does not reach the rear end. A correlation is found between the relative freeboard and the location at which the uplift pressure becomes 0. A conceptual model is proposed which explains what part of the crown wall experiences an uplift pressure.
Furthermore the pressure data are analysed to gain insight in the phase lag. The phase lag appears to be dependent on the relative freeboard and seems to increase with a higher relative freeboard. This finding is explained by a conceptual model which assesses the vertical distance the water travels through the breakwater.
This study shows that current design formulae appear to overestimate the uplift force on a crown wall for situations with a freeboard. It also indicates the presence of a phase lag. Furthermore it points out that there are uncertainties about the uplift force on a crown wall. Hence, it is recommended to perform scale model tests whenever a crown wall is designed to gain insight in its stability. Based on investigated articles the VOFmodel seems to be a promising tool to perform a stability analysis. However a phase lag was not present in the results of the VOF simulations. Furthermore, options to reduce computation time should be investigated.

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9 

Static and dynamic loads on the first row of interlocking, single layer armour units
Interlocking, single layer concrete armour units are placed in a specific grid depending on the type of armour unit. Within this grid, armour units are placed in horizontal rows. The number of horizontal rows of single layer armour units on a breakwater is limited to 20. This limit is proposed in order to prevent major settlements, which might affect the interlocking of the armour units. The limit on the number of rows is based on experience from prototypes and is not yet confirmed in a systematic study. Then number of rows also might have an effect on the load on the first (bottom) row of armour units, which affects the structural integrity of the armour units. The load on the first row of armour units is however unknown. The research presented in this thesis is a study on the load on the first (bottom) row of concrete armour units placed on a breakwater.
Both the static load and the dynamic load were examined. The static load is defined as the load on the bottom row of armour units resulting from the higher positioned rows of armour units during conditions without waves. The dynamic load is defined as the load on the bottom row of armour units during conditions with wave attack minus the static load. These loads were studied by physical model tests.
The static load was studied in an experiment in which the down slope force on the bottom rows of armour units (Xbloc units of 366 grams) was continuously measured during the placement of 20 rows of armour units on a slope of 37 degrees (slope of 3:4) in a series of 15 tests. The dynamic load was studied in a physical model test in a wave flume. The first row of armour units was placed on a movable frame which was connected to a load cell. The dynamic load was measured during tests with regular waves of 20% to 100% of the maximum wave height corresponding to the used armour unit (Xbloc units of 61.7 gram which were positioned on a typical breakwater slope of 3:4) and a wave period corresponding to an Iribarren number of 3, 4 and 5 for all of the described wave heights.
This static load experiment resulted in a relationship of the measured static load on the first row of armour units with the number of rows applied on the slope of the model. From this relationship appeared that the static load approaches a maximum value after 10 rows. An analytical model was developed and validated against the measured results. This model gives an interpretation of the cause of the maximum value.
The measurements of the dynamic load showed two clear phenomena. The dynamic load appeared to be a harmonic load with the same period as the waves imposed on the model. The dynamic load is the result of the flow of water along the armour layer. The maximum dynamic load on the first row of armour units occurred simultaneous with the maximum downwash which is in line with expectations. A relation between the downwash velocity and the amplitude of the dynamic load was found.
The second observed phenomenon is the increase of the wave averaged load on the first row of armour units during the test. During the tests the harmonic load oscillated around an equilibrium line which showed a positive trend. The measured load after testing was significant higher than the measured load at the beginning of the tests. A relation was found between the wave characteristics and the increase of the load on the first row of armour units.

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10 

Numerical and experimental research of wave interaction with a porous breakwater
The design formula for rubble mound breakwaters by Van der Meer has an unclear Notional Permeability term. This term causes a lot of confusion for designers. In the past many people have tried to derive a better formulation for that term by experimental and analytical research. The goal of this study was to obtain a better formulation along a numerical way. This study explores the numerical possibilities and tries to define which direction has to be taken in future research.
As a first step, a very simplified case is taken with a vertical homogeneous breakwater which interact with monochromatic waves. In total six different blocks were made of epoxy and elastocoast. Only 4 out of the 6 blocks were tested. Also the porosity (n), laminar friction (α) and turbulent friction constant (β) of the blocks were determined experimentally. This way the experimental results could be compared with computations.
These experiments have been done in the large flume of the Environmental Fluid Mechanics Laboratory of the TU Delft. Two types of data were collected: pore pressures and water levels in front and behind the block. The water levels seemed to be the most reliable data. The main deficit of the setup was the wave absorber at the end of the flume. The wave absorber is not able to sufficiently absorb long waves. So the dataset had to be corrected for that effect. The created dataset was in line with results from earlier experiments.
Results were compared with an analytical solution and the numerical SWASH model. Comparisons with the analytical solution showed a reasonable fit without any calibration. The SWASH model showed in first instance large deviations using the same dataset. By calibrating the turbulent flow resistance β, it was possible to generate a decent fit. However, the used β constants are 610 times higher than the measured β constants. This is physically unrealistic high. Therefore the most likely explanation is an error in the transition between the water and the porous medium. During the experiment discontinuities can occur on this transition while SWASH uses an continuity requirement.
Numerical tests were performed on some multilayered combinations of the different blocks in order to derive a "Vertical P" value in a similar way as Van der Meer determined his P=0.4 structure. The results showed, nevertheless, quite some different patterns as the computations done by Van der Meer. However, taking into account all the problems with calibrating the SWASH model the results for the notional permeability seemed very promising. This numerical method shows the possibility of numerically calculating a notional permeability and should be investigated further in the future.

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11 

Stability of open filter structures
Granular filters are used for protection against scour and erosion. For a proper functioning it is necessary that interfaces between the filter structure, the subsoil and the water flowing above the filter structure are stable. Stability means that there is no transport of subsoil material through the filter to the water above the filter, and that no filter material is removed by currents above the filter.
Three types of granular filters can be distinguished; 1) Geometrically closed filter structures, 2) Stable geometrically open filter structures, 3) Unstable geometrically open filter structures. This research is focusing on stable geometrically open filter structures.
Recently, a desk study has been carried out by Deltares resulting in a new theoretical formula for single layered geometrically open filter structures (CUR, 2010). Hoffmans improved the theoretical formula that had been founded by Deltares (Hoffmans G. , 2012)
The goal of this research was to verify the formula found by Hoffmans [2012] for structures loaded by currents (flow parallel to the filter construction). As part of the verification of the design formula ten flume experiments were performed in the Environmental Fluid Mechanic Laboratory at Delft University of Technology.
After the execution of the model tests an extensive analysis was made based on the performed model tests and model tests performed in the past (Bakker [1960], Haverhoek [1968], Wouters [1982], Konter et al. [1990], Van Huijstee and Verheij [1991] and Van Velzen [2012]).
The analysis showed that the formula is valid for single layered geometrically open filter structures loaded by currents. Two adjustments to the design formula are proposed:
1. The relative layer thickness fits better when related to the nominal diameter of the filter material;
2. The alpha value proposed by Hoffmans [2012] is too high (new alpha values are 30% to 60% lower).
The original formula as proposed by Hoffmans [2012] gives unrealistic values for situations with wide graded filter material. Model tests showed that the relative layer thickness is better represented when related to the nominal diameter of the filter material.
The design formula can be used for design purposes. The design of a single layered geometrically open filter structure can be schematized in two steps;
1. Firstly, determination of the material that should be used for the toplayer;
2. Secondly, determination of the layerthickness of the filter/toplayer taking into account filter and base material characteristics.

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12 

Managing knowledge: Towards a framework for selecting and implementing a knowledge management strategy for projectbased organizations in the construction industry
A Knowledge Management Strategy can help to maintain or improve a knowledge management process. There are two knowledge management strategies; personalization and codification. A personalization strategy focuses on the flow of tacit knowledge through personal contacts while in a codification strategy In codification strategies, explicit knowledge is transferred to information which can be stored in database and can be analyzed independently of the current carriers of the knowledge. Knowledge Management Strategy Conditions can help to determine which knowledge management strategy is best suited for an organization. These (ten) conditions are: Innovation, Networks, Motivation, Attitude, Organization, Community, Sharing, Frequency of repeating tasks, Willingness to follow processes and protocols and the costefficiency of a database.

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13 

Ecologybased bed protection of offshore wind turbines
The offshore wind industry is a growing market in Europe due to the sustainable energy targets of European Union. In the coming years the Dutch government will invest in offshore wind farms at the North Sea. For a contractor like Boskalis the inclusion of favorable ecological conditions in designs is a unique selling point and can help to win tenders to build offshore wind farms and acquire projects. This was the starting point of this thesis.
The thesis is split up in two parts. The first part is an extensive literature study and searches for opportunities and influencing parameters to provide favorable ecological conditions for marine life. The second part of the thesis will explore one opportunity in detail, which can be included in bed protection design of offshore wind farms.
The research question is formulated as follows:
"How can technical aspects of bed protection designs of offshore wind turbines be altered to provide favorable ecological conditions for marine life?"
Part I: Literature review and parameter study
In the first part of the thesis interviews with ecologists are conducted to gain knowledge about ecological systems, and to explore the social acceptability besides the motivation to win tenders. The ecologists don’t support installations of offshore wind farms, because it is not natural and anthropogenic interferences are in principal not good. However, in the past a significant part of the North Sea floor consisted of hard substrate, but due to trawling activities by humans this hard substrate is removed. Nowadays the North Sea floor consists of sand. By placing stones for the bed protection of offshore wind farms, hard substrate will be added which was present in the past. So, the hard substrate balance will more or less be restored. Furthermore, offshore wind turbines will be built, so then it is better to build them properly and in consultation with the environment.
In the extensive literature study a technical analysis and an ecological analysis are conducted. During this literature study the context and scope of this research are defined. The scope is set to the bed protection of one offshore wind turbine. The technical analysis resulted in the structure, failure mechanisms, and design calculations of the bed protection. The ecological analysis focuses on the two key species, and biodiversity in general. The key species are the European lobsters and the European cod. The outcome of the literature study is a list of controllable parameters for functional requirements. This is a list with potential parameters in combining favorable ecological conditions and technical requirements. From this list the poresize distribution is chosen to investigate in further detail. The poresize distribution includes the cavity sizes and openings in which species can find shelter. The parameter study and selection of the parameter poresize distribution is the outcome of the first part of this thesis.
Part II: Model and interpretation
The second part of the thesis focuses on the poresize distribution and the pore openings, derived from a stonesize distribution. Furthermore, it focuses on the ecological interpretation of the derived distributions.
First of all models are designed and evaluated to crack this problem. The chosen models are an analytical model of spheres and an experimental model. The analytical model of spheres is based on geometry and is derived to give indications and to validate the results of experimental model.
The analytical model provides results to describe the pore size and the pore openings of uniform spheres. The poresize distribution of multisized spheres could not be derived. However, the poreopening distribution of multisized spheres is derived. The results of this distribution are approximated with a curve fit of a normal distribution.
The experimental model is executed with a medical CT scanner and imaging software. First, a test scan is made to identify the possibilities and limits of this method. Secondly, a validation scan is made of glass balls to explore the errors and the accuracy of the medical CT scanner and the imaging software. The results of the validation scan are compared with the analytical results. Both models showed the same result.
Therefore, an experimental program is designed and 8 scans are performed on stones (quarry material). The sieve curve of the stones is in advance specified and manufactured. The formula that describes the poresize distribution, after analyzing the scans with the imaging program and postprocessing of the data, is derived. Also a formula that describes the number of pores is found.
The pore openings are also investigated during the same experiment. However, the constrictionsize distribution is not derived using the experimental model. Most of the constrictions are connected using this model. Therefore, a few constrictions are manually investigated and the results could not falsify the analytical results.
The derived formulas for the poresize distribution and the pore opening distribution are applied on a brief case study of a bed protection of an offshore wind turbine. In this calculation example, the pore sizes are compared with the preferred pore sizes for the lobster. Targeted pore sizes can be created by applying another grading width, other stone sizes, or changing the porosity. In this way the bed protection could be adapted to the preferences of the lobster.
The research question is answered within the scope of this research: the poresize distribution is one of the technical aspects found, which can be included and altered in bed protection designs to provide favorable ecological conditions for marine life. The poresize distribution has until now not been included in bed protection designs, while, in fact, it is always installed. This distribution can be derived, and future bed protections can be designed based on favorable cavity sizes for species, as well as technical stability. This holds for the constrictionsize distribution.
The main recommendation for the industry is: The poresize distribution can be included in future designs to estimate the impact of the structure on the species. Moreover, designs of civil rock works can be based on the preferred pore sizes for native species. This fits perfectly in the philosophy of Building with Nature.
The four main recommendation for further research are:
* Testing this principle with an ecological pilot.
* Scanning and analyzing more samples to make the formula statistical more reliable.
* Further development of the experimental model. Extra properties of the pores, such as the shape, can be derived and included in the model.
* Adding more species by describing the limiting conditions of these species in a matrix.

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14 

Temperature Regulated Concrete Bridges
Concrete bridges are subjected to large lateral deformations, which if restrained will also lead to large (axial) stresses in the structure. If unrestrained these deformations caused by temperature variation and shrinkage, can become problematic for bridges of sufficient continuous length. If deformation is restrained to some degree, then the structure will also be subjected to large stresses proportionally to how much the structure resits deformation. Both deformation and stresses can cause problems if it becomes too large. If the relative weak to tensile stresses concrete is subjected to tensile stresses exceeding concrete tensile strength, than in case of axial stress, large thorough cracks will develop in the bridge deck. To prevent this are expensive and maintenance heavy expansion joints often used to allow free deformation and prevent the development of stresses. In this study an alternate approach was proposed to reduce temperature load. Temperature of the bridge deck can be regulated by embedding hydronic heat exchangers into the concrete. This results in large reduction of temperature and with it temperature related deformation and stresses. Total axial stresses could be reduced enough that in most or all cases no thorough cracks will develop, reducing or removing the need of expansion joints. Furthermore longer bridges are possible as the limiting factor, thermal deformation, can significantly be reduced. The Thermal Energy Reservoir needed to store and extract the thermal energy from the bridge, is smaller in size per square bridge in comparison to similar projects (deicers). Regulating bridge temperature can due to the relative low thermal energy cost and ease to reduce temperature load be an efficient method to increase the application of continuous bridges and reducing the need of dilatation.

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15 

Stability of open granular filters under wave loading
A filter can be applied to protect a bed against scour. Normally, these filters are geometrically closed, to prevent winnowing of the base material through the filter. However, geometrically closed filters are expensive and difficult to realize in the field.
Geometrically open filters can serve as an alternative. Within an open filter, the pores of the filter material are large enough for the base material to move trough. The philosophy behind this concept is to reduce the hydraulic loading within the filter, in order to avoid initiation of the base material.
This research focusses on open filters. A design formula for open filters was established by Hoffmans (2012). This formula is recently validated for uniform flow (Van de Sande, 2012) and for flow with additional turbulence by a sill and a pier (Joustra, 2013). The applicability for wave loading  although suggested by Hoffmans is not yet confirmed. No validations study was carried out in which Hoffmans formula was validated for wave loading. In this research, the use of Hoffmans formula for horizontal filters under wave loading was evaluated.
Laboratory experiments are carried out in a wave flume. For several configurations, the critical wave height was determined for a wave period of 2.0s, 2.5s and 3.0s. The critical wave height is defined as the height for which incipient motion of the base material occurs. The filter material was stable during all tests. The depth above the filter was held constant for the tests.
Together with an older dataset from Halter (1999), the results were analyzed. With the introduction of several assumptions, insight was gained in the damping of the hydraulic load inside the filter. The analysis showed that the Hoffmans formula cannot be applied in the same way as for uniform flow, since no constant value for the load damp coefficient alpha is found under wave loading. Two hypotheses which were stated for the applicability of Hoffmans formula under wave loading by Hoffmans & Verheij (2013). For the experimentally obtained results, these hypothesis did not give accurate results.
It is speculated that the hydraulic gradient should be included in Hoffmans formula. In the original formula as proposed by Hoffmans (2012), this term was neglected.

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16 

Stability of widegraded rubble mounds
The reshaping of temporary rubble mounds like the core of breakwaters or reclamation bunds is often a concern for contractorsi n the construction stages of marine structures. The formulas found in literature for the prediction of such behavior are few, and they do not provide clear insight on the influence of relevant parameters, in particular the small dimensions and wide stonesize gradation of the material involved, usually consisting of quarry run or resulting from dredging. The previous research in the field of dynamic stability focused on berm breakwaters and gravel beaches. These two typologies of structures define the range to which the rubble mounds considered in this study generally belong. An overview on the design tools provided by the technical literature shows that, whenever the grading was included as a governing parameter, some influence was recognized in the characteristics of the structure (e.g. the permeability) and in the dynamism of the different fractions of stone sizes. However, very wide ranges of the parameter grading were never investigated and a specific analysis in this direction constitutes the main significance of this study. The Delft University of Technology provided the laboratory facilities to carry out physical model tests on a wide graded rubble mound structure representative of the core of a breakwater. The parameter D85/D15, describing the stonesize gradation of the construction material, was varied between the values 2.71 and 17.7, and two different seaward slopes of the model structure were also tested. The reshaped crossshore profiles measured during the tests showed how if the grading increases the stability of the structure is reduced. This is not always in accordance with the findings of previous researchers, showing how the extrapolation of existing empirical formulas to structures with high values of the ratio D85/D15 do not give reliable results. Instead, the formulas given by van de Meer (1992) to estimate the whole reshaped profile of a dynamic slope predict with good agreement the shape of the measured profiles, although the physical model shows a larger horizontal extension of the displacements. This difference is governed by the grading, being more noticeable as this parameter increases. This result leads to the definition of new formulas, some of them being modifications of the ones given by van der Meer, to describe the geometry of a reshaped profile. The formulas, all including the parameter grading, are derived through curve fitting of the measured data. Also a formula for the direct estimation of the crest recession is given. As a final step, a simple numerical model is proposed in which the new formulas are implemented, constituting a quick way to assess the shape of a slope after a wave attack.
As a suggestion for further utilization of the results of physical modeling, a brief comparison is also carried out between the output of the tests and the prediction of the numerical model XBeach (developed mainly at UNESCOIHE).
In conclusion, this research points out how the formulas provided by the technical literature are not reliable in representing the effects of a very wide stonesize gradation in the stability of a rubble mound structure. Physical model tests proved to be a suited way to investigate these effects, as the nature of the phenomena who play a role in the stability does not allow a simple analytical representation. The tests carried out within the present study lead to the implementation of a numerical model of practical use for engineers and contractors: further investigations through laboratory tests are recommended to validate and extend the findings of this study. Another proposed direction for further research is the comparison between the results of physical model tests and the output of numerical models.

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17 

Effectiveness of a multipurpose artificial underwater structure as a coral reef canopy: hydrodynamic and ecological connectivity
The following research focuses on artificial underwater structures (a.k.a. artificial reefs) in a coral reef environment to mitigate the natural and anthropogenic pressures which reef systems are increasingly facing worldwide. The research question is stated as: “Establishing a method to determine if a multipurpose artificial underwater structure (MAUS) can perform the functions of a natural canopy cover on a coral reef flat”. To investigate this research question both ecological and hydrodynamic parameters are considered. The MAUS selected for this investigation is composed of a canopy of 1000’s of interlocking synthetic hooks known as ground consolidators (GCs). This investigation employs both a physical and numerical model.
The relevant parameters required to assess the research question can be found by obtaining the flow characteristics inside the canopy and wave induced hydrodynamic dampening across the canopy. Wave driven velocities recorded in a 1:5 scale GC canopy model are used to assess the success of larval recruitment. In addition to ecological considerations in the canopy, the bulkwave height reduction is computed. This component allows for GC canopy design and schematization in a numerical model application. A link between the bulk waveheight reduction and internal wave driven velocities within the canopy is desirable to understand the connectivity of hydrodynamics and larval recruitment.
The evidence collected in this study gives an indication of the GC arrangement which can provide a suitable climate for the establishment, and longterm vitality of a benthic community within its pore structure. This study is unique in that it incorporates various fields of research to bridge the gaps needed to present a more complete and comprehensive design guideline for GCs, and other MAUS concepts. Additional outcomes from this study include a more thorough oversight and understanding of the required changes and considerations needed to improve current interpretation of porous canopy media.

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18 

Physical model tests of the notional permeability on breakwaters
Breakwaters are important objects to protect coastal and harbour areas. To minimalize the probability of failure of breakwaters, a lot of research has been conducted concerning the stability of breakwaters. After Iribarren and Hudson, an influential research is conducted by Van der Meer. The literature research of this report will provide more background information concerning their researches on the stability of breakwaters.
Van der Meer tested three sorts of breakwater constructions. The first breakwater structure contained a homogeneous construction (P=0.6) The second and third structure consisted of respectively a construction with impermeable core (P=0.1) and a structure with a filter layer and a permeable core (P=0.5). These variants of breakwaters were constructed with different slopes angles to require as much information possible concerning the stability of breakwaters.
Van der Meer discovered two formulas for the stability of breakwaters. The first formula is used for plunging waves while the second formula is used for surging waves.Within these formulas, important factors as damage, wave height and notional permeability are included. The most important parameter of the formulas of Van der Meer is the notional permeability factor P.
Van der Meer conducted his research on three different constructions and has designed a fourth construction based on the stability curves. This fourth construction has a value of permeability of 0.4. This value is estimated based on curve fitting.
Following the research done by Van der Meer, Kik has subsequently researched the notional permeability of three breakwater constructions. Firstly, Kik repeated the test with a construction of impermeable core (model 1/P=0.08) and the test with the construction of filter layer and permeable core (model 2/ P=0.05) of Van der Meer. Lastly, Kik did a third test existing of a variant of the design of the fourth construction of Van der Meer (model 3 / P=0.35). Concluding from his research, Kik stated that the ‘Root mean square equation’ is a reliable method to determine the notional permeability P.
During this research the influence of the thickness of the filter layer on the notional permeability P is studied. This research will also try to answer the question whether other relevant aspects might influence the notional permeability as well. The elaboration of this research is performed in a practical way in a wave flume in the water laboratory of the faculty of civil engineering of the TU Delft. Scale models of the breakwaters were constructed to test the notional permeability of the breakwaters.
In the water laboratory three models were tested. Firstly, model 3 of Kik is repeated as model 3A, with a calculated value of notional permeability P 0.38. The construction of model 3A is build with a top layer, filter layer 1, filter layer 2 and a impermeable core.
Second, another variant of model 3 of Kik is designed and tested (model 4). However, the measured damage figures were too low and therefore they could not be used to calculate a value for the notional permeability P. The construction of model four is build with a top layer, filter layer 1, filter layer 2 which is thicker as model 3A and an impermeable core.
Finally, model 5 is tested with a calculated value of notional permeability of P 0.45. This model is designed from the fourth construction of Van der Meer. The construction of model 5 is build with a top layer, filter layer 1 and a permeable core with the same material of filter layer 2 of model 3A and model 4.
The results of this research show that the influences of the notional permeability P exists of the ratio of the armour layer thickness and the thickness of the second filter layer. If the layer thicknesses are equal the value for notional permeability P is 0.38, which follows from model 3A. If the second layer has an infinite thickness (permeable core), the value for notional permeability P is 0.45, which follows from model 5.
The value of the notional permeability P of model 5 corresponds to the design calculations of the computer model HADEER. Van der Meer discovered using this computer model that the ratio of dn50a/ dn50f = 5 has a value on the notional permeability P of 0.43 –0.44. During this research, while using two different methods, a value of the notional permeability P of 0.45 was calculated.

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19 

The Effect of Multiple Storms on the Stability of NearBed Structures
Pipeline covers on the seabed are called nearbed structures which are generally made of rip rap. The crest height of a nearbed structure is such that waves do not break over it. Nearbed structures are used to protect pipelines against fishing equipment, ship anchors, dropped objects and preventing destabilizing of the pipeline. There are two ways of designing a nearbed structure. The first is to design a stable construction given the design conditions present in the lifetime of the structure. The second approach is to allow some damage during the lifetime of the structure, and is the approach which this research focuses on.
Presently the Rock Manual advises to use a formula from Wallast and Van Gent [2002] to describe the damage development during a storm. In this formula the damage development in time is forced to a dependency found by Van der Meer [1988]. It is unknown if this time dependency based on the number of waves is valid for damage development with nearbed structures. Besides this, the way to include cumulative damage for several subsequent storm conditions is presently calculated as a first approximation with a method from Van der Meer [1999] designed for breakwaters. It is not verified that this method can also be applied for nearbed structures.
The goal of this research is to determine the actual relation between damage and time, and to investigate the cumulative damage development for nearbed structures in multiple storm events. To answer the research questions which have been made from these goals, an investigation is performed which makes use of physical scale model testing. Tests are performed in the Environmental Fluid Mechanic Laboratory at Delft University of Technology.
After the execution of the model tests, an extensive analysis is performed based on the results of the scale model tests and results of previous research from Lomónaco [1994], Wallast and Van Gent [2002], Saers [2005], Van den Bos [2006] and Tørum et al. [2008].
The analysis concluded that there is not 'one' parameter as assumed so far to describe the relation between damage to nearbed structures and the number of waves. This parameter is thought to be depended on wave height, water depth, stone size and actual damage that occurs after a certain time. Besides this, the damage development did not reach an equilibrium in time with a large number of waves, which was assumed to be the case in other research. The average value for the exponent which describes the relation between the number of waves and damage is used in this thesis. With this relation and more data a new and improved damage prediction formula is investigated. The new prediction found in this thesis calculates the damage to a higher degree of accuracy with less variation present. It includes more parameters than the current prediction formula from Wallast and Van Gent. The extra parameters in this formula are the relative width, structure slope and KeuleganCarpenter number.
The method to include cumulative damage for multiple storm events from Van der Meer was proven to be usable by using the formulas found in this research. An important conclusion from these tests is that damage development stops or reduces to a large degree when a low wave condition passes the nearbed structure when a high condition is already imposed to the nearbed structure.

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20 

Scour below the toe of breakwaters: Investigation of scour formation through a geometrically open filter configuration located at the toe of a rubble mound breakwater lying upon sand
Scour formation at the toe of a rubble mound breakwater can lead to abrupt failure. Nowadays, counteraction of scour via geometrically closed filter rules, geotextiles or combinations is the common practice. Alternatively, in specific cases the use of geometrically open filters can save significant amount of time and decrease constructional costs. As a primary step towards this direction, the prediction of scour formation through a geometrically open filter can provide important information.
Nevertheless, at this moment the knowledge upon this issue is insufficient and limited. A variety of recommendations occurs in literature, separately for toe design/scour protection and for the application of open filter criteria; however none of the studies treats these subjects combined. Therefore the objective of the present thesis is to get insight into scour formation and development through a breakwater toe lying upon sand and designed as a geometrically open filter. Thereby the research aims in drawing the link between scour characteristics with wave loading and filter configuration properties.
In order to accomplish the research objective 2D physical model tests were conducted in the 25m long, 1m deep and 0.6m wide wave flume of DMC, installed in the company’s laboratory. In total, 23 tests were executed with irregular waves (Jonswap spectrum) and by varying wave loading and filter configuration properties. In particular, 5 different filter/base layer combinations were examined and 3 different wave conditions were used to investigate the effects of relative grain diameter, relative filter thickness, grading of filter layer, base layer stability Number and storm duration.
Quantification of damage magnitude was accomplished via laser profile measurements of filter and base layer prior and after the execution of each test. Furthermore, wave particle velocity climate was determined via the use of an Electromagnetic Flow Meter (EMS) placed at the center of the toe. Finally, temporal evolution scour was captured through the side glass and was examined by digitizing and analyzing snapshots from predefined time steps.
Test results and observations have revealed the highly spatial character of scour formation. Nevertheless, tests with identical boundary conditions showed a surprising convergence in averaged maximum scour depth magnitude. In addition, in the majority of tests an Scurve erosion/deposition pattern was shaped while erosion started immediately at the downstream side of the box threatening breakwater stability.
Equilibrium maximum scour depth was reached for less than half the data set; thus erosion process was still in progress. Based on this, two approaches were developed to investigate temporal evolution of scour. Furthermore, dimensional analysis and literature review have revealed the most important parameters that have significant effect in scour formation; their combination has led to the formation of a prediction tool. However, combination of the results from tests with different base materials would not be possible without the introduction of the base material stability Number (critical Shields’ Number).
The derived tool is an empirical expression with limited physical background and range of validity. Additionally, it overestimates maximum scour depth due to a serious model effect; the different buoyancy between filter and base layer that was causing initial damage and damage exaggeration. Nevertheless, it is capable of delineating the relative contribution of each parameter in scour depth formation.
For an overall view of scour formation, further research will be needed to provide a more accurate quantification of the interrelation between parameters that play a role in scour formation and development, and to implement the effect of missing parameters. Consequently the use of the derived expression as a scour prediction tool in real life is not yet recommended.

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