1 

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.

[PDF]
[Abstract]

2 

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.

[PDF]
[Abstract]

3 

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.

[PDF]
[Abstract]

4 

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.

[PDF]
[Abstract]

5 

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.

[PDF]
[Abstract]

6 

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.

[PDF]
[Abstract]

7 

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.

[PDF]
[Abstract]

8 

Wave overtopping at rubble mound breakwaters with a nonreshaping berm
This thesis focuses on wave overtopping at rubble mound breakwaters with a nonreshaping berm. The research was aimed at gaining insight into the influence of a permeable berm on the overtopping behaviour. Moreover it was desired to validate existing prediction methods for the spatial distribution of overtopping for breakwaters with a nonreshaping berm.
Wave overtopping was investigated by means of a physical model. The breakwater scale model was divided into 8 collection bins. Overtopped volumes were collected and pumped into floating tanks further down the flume. After the experiment the mass of the floating tanks was measured and the mean overtopping discharge could be determined for 8 horizontal positions on the breakwater. The measured total overtopping discharges cannot be predicted accurately by existing prediction methods. On the basis of experimental data a new prediction method was proposed that achieves an excellent fit for total overtopping. The crest freeboard definition was adjusted to account for the permeability of the crest. The reduction factor accounting for slope roughness was made dependent on the Iribarren number. For Iribarren numbers higher than 6, this method calculates no reduction of overtopping due to slope roughness. The effect of a permeable berm on total overtopping was found to be remarkably different from the effect of an impermeable berm. Permeable berms below Still Water Level (SWL) lead to less reduction of overtopping than impermeable berms below SWL. Berms above SWL lead to wave breaking on the slope in front of the berm. Contrarily to impermeable berms above SWL, a permeable berm above SWL leads to significant reduction of overtopping.
The measured spatial distribution of overtopping is associated with a lot of seemingly random behaviour. Large differences were found with the experimental data of Lioutas (2010). It is suspected that the used experiment setup gives rise to significant model effects for the spatial distribution of overtopping. An experiment setup was recommended that is expected to more accurately model the behaviour of the prototype situation. Data on the spatial distribution of overtopping could not accurately be predicted by existing prediction methods. In some cases existing prediction methods provided an upper limit for overtopping (Juul Jensen, 1984) but none led to a good fit with the experimental data. A new reduction factor was found that reduces the amount of scatter and provides a conservative prediction of the experimental data.

[PDF]
[Abstract]

9 

The influence of core permeability on the stability of interlocking, single layer armour units
The permeability of a breakwater is of great importance for the stability of the armour layer. The influence of the structural permeability on the stability of rock armour units was already researched by Van der Meer using the 'notional' permeabiltiy. However, for single layer interlocking armour units the influence core permeability is rather unfamiliar. The goal of this research is to extend the knowledge on the failure mechanism of the armour layer for different structural permeability. To achieve this goal, model tests are conducted in the permeameter of the Technical University of Delft and in the wave flume of Delta Marine Consultants, Utrecht. The tests show that the stability of the armour layer decreases with increasing and decreasing core permeability.

[PDF]
[Abstract]

10 

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.

[PDF]
[Abstract]

11 

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.

[PDF]
[Abstract]

12 

The influence of the under layer on the stability of single layer armour units
This thesis tests the influence of the under layer profile on the stability of the armour layer of concrete interlocking armour units. The analysis is aimed to offer insight into the influence of different under layer profiles on the stability of the armour layer. Furthermore the thesis includes a test of the design guideline of the under layer for Xbloc armour units, which is developed by Delta Marine Consultants (DMC). DMC prescribes that the maximum vertical difference between the constructed and designed profile, i.e. the tolerance, may not exceed 0.5 times the nominal diameter D_n50 of the under layer rocks. This requirement holds in both the positive and negative perpendicular direction.
Physical model tests have been carried out at the wave flume of DMC in Utrecht, The Netherlands. Different vertical deviations have been tested in combination with variable length scales of the deviations. Furthermore convex and concave shaped profiles are also tested to assess the influence of the direction of the deviation. The under layer profiles are measured with a laser device. A spherical foot staff is simulated numerically in order to represent prototype values of the tolerances. The difference between the laser and simulated sphere is comparable to that of the conventional staff and the sphere and therefore in line with the theoretical difference between a sphere and conventional staff. Tolerance levels are tested in the range between 1.0 and 3.5 D_n50. The tests show larger damage numbers with increased tolerance. This can be explained by introducing a transition from a steep slope to a milder slope, i.e. the step. Around the step the quality of interlocking is low and consequently this area is very vulnerable to damage. Furthermore deviated profiles have locally milder slopes which result in less interlocking as well.
No clear influence of the length scales of the deviations is observed. Based on three tests with a convex profile it can be concluded that convex shaped profiles are more stable than concave shaped profiles. This can be explained by the absence of the step. Because convex profiles show a different behaviour, they are excluded from the trend line which describes the trend between tolerances and damage. An additional scenario with a narrower grading and larger D_n50 of under layer material is tested. The results show smaller settlement and larger damage of the armour layer, which are a logical consequence of the increased natural roughness.
It can be concluded that both an increased additional and natural roughness result in more damage of the armour layer. It is therefore recommended not to increase the tolerance requirement for Xbloc armour layers. On the other hand, the experiments show that the lower bound of the tolerance in model situation is close to the prescribed tolerances. It is therefore concluded that sufficient efforts should be made to secure the quality of placement of the under layer. In order to determine the quality of placement of the under layer, a well carried out measurement campaign is recommended.

[PDF]
[Abstract]

13 

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.

[PDF]
[Abstract]

14 

Project procurement in the Oil and Gas industry: Towards improving the project supply process for a market entrant in Oil and Gas contracting

[PDF]

15 

Incorporation of the effects of accelerating flow in the design of granular bed protections
For the design of granular bed protections often a stability parameter is used. The stability parameter represents the forces that are acting on the stones and is used to predict the response of the bed to these forces. Existing parameters are often derived for a limited range of application. When the parameter is used outside this range, the bed response is not predicted sufficiently accurate. Some of the existing stability parameters are derived to incorporate the effects of turbulence properly. Other researches investigated the influence of the acceleration on the stone stability and derived a parameter from that. But none of the existing stability parameters incorporate both effects together. In this thesis the complex interaction between velocities, turbulence and acceleration is incorporated into one stability parameter.
The stability parameter is designed such that it incorporates the effect of turbulence correctly, incorporates the effect of advective acceleration and that can be applied to nonuniform flows. A relation between the proposed stability parameter and the dimensionless entrainment rate is derived. This is done for a wide range of flows and geometries to make the stability parameter as general as possible.
There are three unknown constants in the stability parameter. One for the value of the turbulence relative to the velocity, one for value of the acceleration force relative to the quasisteady forces, and one for the method of determining the acceleration force. These constants are determined with a correlation analysis. The constants that result in the highest correlation between the stability parameter and the dimensionless entrainment rate are chosen. The proposed stability parameter leads to a considerable higher correlation with the bed response than the existing parameters for the data sets used in this report. A power law is used to formulate a relation between the proposed stability parameter and the dimensionless entrainment rate.
The new stability assessment method can be used in the design of granular bed protections and for the recognition of the areas of bed protection that require larger stones. The input for the stability parameter can be obtained from numerical flow models.

[PDF]
[Abstract]

16 

The notional permeability of breakwaters: experimental research on the permeability factor P
The stability formula developed by Van der Meer is used for the design of different kind of rock slopes. In the formula is among a number of other parameters also the permeability of the structure represented. A more permeable structure has the ability to dissipate more water and therefore more energy, this results into a lower required weight of the armour layer.
This coefficient, described as the Notional Permeability P, has been determined for three different types of structures. A homogeneous structure, a structure with a permeable core and an impermeable structure. In practice structures are being build who deviate from these standard situations. Therefore there is a demand for values of P about structures other than the known standard situations. In this thesis P values are found by means of physical scale model tests.
First of all two reference structures were tested. The permeable and the impermeable structure with known values of P= 0.5 and respectively P=0.1. The values found in this study are almost equal to the values above.
The new structure has an impermeable core covered with a thick filter layer. On top of that an under layer is placed and finally there is a double armour layer.

[PDF]
[Abstract]
