"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:7b697465-7e26-48c4-b53f-efbd835f1997","http://resolver.tudelft.nl/uuid:7b697465-7e26-48c4-b53f-efbd835f1997","Hydrodynamic loading on the shaft of a gravity based offshore wind turbine","Smaling, H.W.","Jonkman, S.N. (mentor); Molenaar, W.F. (mentor); Labeur, R.J. (mentor); Segeren, M.L.A. (mentor); Ten Oever, E. (mentor)","2014","Gravity based support structure By a joint venture of BAM and Van Oord an innovative type of Gravity Based Structure (GBS) for an offshore wind turbine was developed. The GBS consist of a concrete caisson and a steel shaft. The applicable water depth range is between 35 and 60m. Hydrodynamic loading on the shaft In order to optimize the support structure, the hydrodynamic loading on the steel shaft is investigated. Previous studies with a CFD package showed an increase of the load on the shaft with a factor 2 compared to the Morison equation. The hypothesis is that the presence of the caisson is responsible for this increase. Therefore the (numerical) CFD model FinLab is used to investigate the influence of the caisson on the wave forces on the steel shaft. The influence of the caisson is investigated within FinLab for the extreme wave (ULS) and for two relative moderate waves (FLS). The presence of the caisson leads to an increase of the maximal horizontal force on the shaft of about 20%. The bending moment cycle (important for fatigue) does not change significantly. It is concluded that the caisson is not responsible for the increase of a factor 2. However, while investigating the influence of the caisson, for the shaft a comparison with the Morison equation is made. It is found that FinLab gives much higher forces for the ULS wave (a 75% higher maximal horizontal force on the shaft) than the Morison equation. By also interpreting the results of the FLS waves there seems to be a relation with the degree of non-linearity of the wave. Different possible causes for the difference are discussed. Those causes give a possible explanation why the Morison equation would be less accurate for a highly non-linear wave. It is however recommended to calibrate the outcomes of FinLab with experimental data. Influence of the hydrodynamic loading analysis on the design The influence of the higher wave forces obtained with FinLab on the design of the shaft is investigated by means of a case study. By performing a FLS and ULS analysis the required dimensions of the shaft can be determined. The FLS analysis is based on a simplified method to be used for pre-design only. With respect to fatigue (FLS), the higher loads found by FinLab for highly non-linear waves do not result in a higher fatigue load. This has to do with the small probability of occurrence of highly non-linear waves. With respect to the extreme event (ULS) the strong increase in bending moment due to waves found by FinLab (+120%) results in a 26% higher total bending moment (wind+waves). Conclusions The most important conclusions of this research are that 1) The caisson does not significantly influence the ULS and FLS analysis 2) The Morison equation gives lower wave forces than an analysis with FinLab. For further design these conclusions have the implication that the caisson does not have to be part of the structural schematisation when the wave loads are determined. For the FLS waves most likely the Morison equation can be used, which has large benefits for the calculation time. For the ULS wave another method than the Morison equation is suggested.","hydrodynamic; offshore wind turbine; FinLab; gravity base structure; GBS","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","Hydraulic Engineering","",""
"uuid:4bf469bf-4284-4610-8c81-a2641a7a8df4","http://resolver.tudelft.nl/uuid:4bf469bf-4284-4610-8c81-a2641a7a8df4","The influence of the wave height distribution on the stability of single layer concrete armour units","Zwanenburg, S.A.A.","Uijttewaal, W.S.J. (mentor); Van Vledder, G.P. (mentor); Verhagen, H.J. (mentor); Ten Oever, E. (mentor)","2012","The dimensions of single layer concrete armour units (interlocking armour units) are calculated with a similar stability relation as the stability relation for quarry stone. In these design formulas an 'average/significant' wave load is used (Hs). Since quarry stone gains its stability only from gravity, this type of armour unit is constructed in a double layer and therefore some damage development is allowed. Interlocking armour units are constructed in a single layer and the design should be based on zero damage. This research investigates whether this different approach to damage leads to a different characteristic design wave load which will increase the accuracy of the design method for interlocking armour units. It is focussed on the influence of the wave height distribution on the stability of single layer concrete armour units in general and Xbloc in particular. For Xbloc, zero damage is defined as a criterion for rocking of the armour units: during design conditions ""not more than 2% of the units are allowed to move during more than 2% of the waves"". To find a stability relation based on this criterion, the stability of Xbloc is investigated according to rocking of armour units contrary to the conventionally approach to stability based on the number of displaced units from the armour layer. To find the relation between waves and rocking, physical model tests are performed. In these tests a model breakwater is loaded by wave series with different wave height distributions, wave steepness and groupiness. It resulted that every wave has a certain probability of causing rocking of an armour unit. This probability of rocking is mainly dependent on the height of individual waves and to a lesser extent on the groupiness of the wave series. The steepness of the waves appeared to have a negligible small influence. When the found rocking probability relation is combined with the criterion for rocking, it appears that H2% is mathematically a better fitting parameter for a stability relation according to rocking. A new stability relation for Xbloc is derived based on H2%. Additionally, it is found that very extreme wave heights can dislodge an armour unit in such a way that this armour unit does not interlock anymore. Because it is undesirable that armour units do not interlock anymore, dislodgement of armour units should be accounted for in the stability calculations. Therefore, also a stability relation based on dislodgement of units is provided.","breakwater; Xbloc; armour unit; rocking; wave height distribution; wave load","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","","",""
"uuid:1f995447-3078-4d99-801f-60b19d1116f2","http://resolver.tudelft.nl/uuid:1f995447-3078-4d99-801f-60b19d1116f2","Stability of single layer armour units on low-crested structures","Van der Linde, J.P.","Uijttewaal, W.S.J. (mentor); Vrijling, J.K. (mentor); Verhagen, H.J. (mentor); Ten Oever, E. (mentor)","2009","Two dimensional physical model tests are executed with Xbloc armour units on low crested structures to answer the objective. On the basis of findings in the literature study it can be expected that the stability of the Xbloc elements on low-crested breakwaters is a function of crest freeboard and crest width. The crest freeboard (Rc/Dn) varied from -0.8 to 0.8 in steps of 0.4 and the tested crest widths (Wc) are 3 and 9 armour units wide. Additionally all tests series are executed with a wave steepness of 2 and 4%. All test series are executed once except the reference test series (Rc/Dn = 0, Wc = 3) which are repeated four times to acquire insight into the reliability of the test results. The number of rocking and displaced armour units is registered for the total breakwater, seaside slope and crest (also termed breakwaters sections). Settlements at both the sea- and leeward slope leads to openings in the armour layer at the transition from the seaside slope to the crest. As a consequence the interlocking properties of the upper part of the seaside slope and crest decreases and the area of the Xbloc crest elements normal to the wave induced flow increases. Moreover due to settlement the distance between two succeeding rows at the upper part of the slope increases whereas for the lower part of the slope it decreases. This together with the already decreased interlocking properties of the upper rows at the slopes and crest rocking results at both the upper part of the seaside slope and the outer seaward rows of the crest.","Xbloc; armour unit; breakwater","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","","",""
"uuid:c329464e-0911-4b30-9a87-94470f298f9c","http://resolver.tudelft.nl/uuid:c329464e-0911-4b30-9a87-94470f298f9c","Generating electricity from waves at a breakwater in a moderate wave climate","Schoolderman, J.E.","Molenaar, W.F. (mentor); Zijlema, M. (mentor); Reedijk, B. (mentor); ten Oever, E. (mentor); Vrijling, J.K. (mentor)","2009","The purpose of this thesis was to develop a preliminary concept design of a wave energy converter. The type of device designed was limited by several starting points which stipulated, among other criteria, a robust structure which can be constructed within a breakwater and can generate electricity from a fairly mild (in the order of Hs=0.5-1.5m) and regularly occurring wave climate. Integration with a caisson breakwater was selected to ensure survivability. Three concepts using the theories of wave overtopping, wave run-up, and wave pressure were evaluated. A multi-criteria analysis was performed on the three concepts. Concepts were scored based on power output, functionality in wide range of conditions, ease of construction, and theory reliability. Theory reliability was scored based on the three aforementioned criteria. The concept analysis concluded the most promising device to further investigate was the concept based on the theory of wave pressure. This device excelled in (theoretical) output having the highest peak power and wider power curves. In the concept, wave pressure is exerted on an underwater opening. This opening leads water into a pipe with a gradual constriction. This constriction increases the pressure allowing the water to be brought to an optimal level above MWL. Through a turbine the water is returned to MWL. A model was built with three different opening ratios and three separate basins open to the wave flume at the bottom. A series of tests were performed of varying wave climates and crest freeboards. During the tests the head difference was measured between the internal basins and the water elevation at the rear of the model. The holes in the bottom of the basins allowed for constant flow of water out of the basins and a calculation of flow rate based on the hydraulic head was required. This allowed for the calculation of the theoretical power generated during the tests. Additionally, the input wave power was known so the device efficiency could be calculated for each test allowing for the identification of the optimal geometry and the generation of a full-scale efficiency curve. The device was evaluated at two design locations in Panama and Japan. The wave climate, tidal influence, system headloss, and sea level rise were calculated in order to discover the power generation at each location. Revenue associated with the generation of electricity was calculated to give an indication of the device’s cost effectiveness. It was found that sea level rise has a negligible impact on efficiency if sea level rise is appropriately accounted for. The impact is in the order of 1.5% over 50 years if the rise is assumed to be 80cm over 100 years. Including sea level rise, the device has been calculated to generate an average of 16,413 and 5,766 kWh/m/yr at Panama and Japan, respectively. The report concludes that the proposed design can be constructed using existing techniques for caisson construction. However, the design must be further optimised and tested in order to become a fully feasible wave energy converter.","wave; energy; converter; caisson; breakwater; pressure; wave energy converter; wave pressure; renewable energy","en","master thesis","","","","","","","","2009-09-27","Civil Engineering and Geosciences","Hydraulic Engineering","","","",""
"uuid:04a06a0a-c790-4fac-9b8e-d3508b3e7762","http://resolver.tudelft.nl/uuid:04a06a0a-c790-4fac-9b8e-d3508b3e7762","Toe structures of rubble mound breakwater: Stability in depth limited conditions","Ebbens, R.E.","Stive, M.J.F. (mentor); Uijttewaal, W.S.J. (mentor); Verhagen, H.J. (mentor); Ten Oever, E. (mentor); Reedijk, J.S. (mentor)","2009","This thesis is about the stability of toe material for rubble mound breakwaters in depth limited conditions. The present equation, Van der Meer 1998, gives results for depth limited conditions but is not validated. The empirical equation is based on physical model tests done by Gerding 1993. The Van der Meer equation implies deep water and breaking waves on the structure slope. For shallow water conditions this assumption is not valid. Waves start breaking at the fore shore slope and toe which results in a different hydrodynamical wave load at the toe. Toe material is exposed to waves and starts behaving as armour rock. The uncertainties, introduced by shallow water situation are investigated in this research. The objective for this thesis is finding a more reliable design equation in this situation. Fore shore slope and wave steepness are considered of influence. The research is done by performing scale model tests in a two dimensional wave flume. The observations from the experiments and the analysis of the performed dataset gave following conclusions: Fore shore slope is strongly influencing toe stability. This is not only valid in shallow water but also in deep water. In shallow water, wave steepness influences toe stability as well. This is not proven for deep water. Very shallow water shows different hydrodynamic behaviour. Wave breaking occurs at the fore shore. The toe structure is attacked by breaking or already broken waves. Although a reduced wave height reaches the toe, damage is larger because the toe is exposed to turbulent wave attack. A new design equation for very shallow water is suggested in which fore shore slope and wave steepness are included. This is an empirical relation, using dimensionless relations like the Hudson stability number and a new damage number in percentages.","toe stability; rubble mound breakwater; depht limited; shallow water; fore shore","en","master thesis","TU Delft, Civil Engineering and Geosciences, Hydraulic Engineering","","","","","","","","Civil Engineering and Geosciences","","","","",""
"uuid:af3b3abb-34f2-409d-9f38-3c6f184c7e05","http://resolver.tudelft.nl/uuid:af3b3abb-34f2-409d-9f38-3c6f184c7e05","Feasibility Study on Tidal Power Barrages: Including general plant design and site selection","van Harn, J.","Stive, M.J.F. (mentor); van Duivendak, J. (mentor); Verhagen, H.J. (mentor); van Overloop, P.J. (mentor); ten Oever, E. (mentor)","2007","","","en","master thesis","TU Delft; Faculty of Civil Engineering and Geosciences, section Hydraulic Engineering","","","","","","","","Civil Engineering and Geosciences","","","","",""