1,720,954 research outputs found
Efficient algorithms for non-linear four-wave interactions
No full textThis paper addresses the on-going activities in the development of efficient methods for computing the non-linear four-wave interactions in operational discrete third-generation wind-wave models. It is generally assumed that these interactions play an important role in the evolution of wind generated surface gravity waves. Therefore, present day wave models contain parameterizations of these interactions. Despite the fact that a closed mathematical formulation is available for the description of these interactions, a full solution is not applicable in operational modelling as it requires excessive computational requirements. To overcome this limitation, various approximate methods have been developed that retain most of the basic properties of the full solution. However, the present operational parameterisations of these interactions have various weaknesses that degrade model performance and which generally lead to too broad spectra. Efficient and more accurate algorithms are therefore needed to improve model performance. As with each approximate method, a gain in computational speed goes together with a loss in accuracy in evaluating the basic integral, but this may not translate in less accurate wave model results. Therefore the definition of efficiency in the context of approximate methods for computing the four-wave interactions is addressed. Two main lines of development are identified in the development of efficient algorithms: extended Discrete Interaction Approximations, and reduced quasi-exact solution techniques.Hydraulic EngineeringCivil Engineering and Geoscience
Computation of the nonlinear energy transfer in a narrow gravity wave spectrum with a method derived by Dungey and Hui
No full textIn this report the method of Dungey and Hui is summarized and extended to include the effect of skewness of the directional distribution. Additional information is given about the derivation and computation of the single integrations mentioned above. The method of Dungey and Hui is applied to a number of theoretical spectra. The results of these computations are compared with the results of exact computations by Sell and Hasselmann (1972) and Hasselmann and Hasselmann (1981). Finally, some comments are made about computational aspects of the method of Dungey and Hui.Hydraulic EngineeringCivil Engineering and Geoscience
Het gebruik van SWAN en SWASH voor het ontwerp van kustconstructies
No full textDoel: Mogelijkheden laten zien van het gebruik van de numerieke golfmodellen SWAN en SWASH voor het ontwerp van kustconstructies. Beschrijving golfparameters en processen voor correcte keuze en toepassing van deze modellenHydraulic EngineeringCivil Engineering and Geoscience
Preliminary investigation into the occurance of wave groups in seas and swell / Toetsing van het model van Kimura voor de beschrijving van golfgroepen
No full textHet doel van deze studie is het onderzoeken van het model van Kimura (1980) voor de beschrijving van golfgroepen. Zoals in deel 1 van dit verslag werd aanbevolen, bestaat dit onderzoek uit de volgende onderdelen 1. Toetsen van het model van Kimura aan metingen. Beoordeling van groeplengteverdelingen met een statistische toets. 2. Vergelijking van methoden om de correlatiecoefficient tussen opeenvolgende golfhoogten te berekenen. 3. Nagaan wat de invloed is van correlaties tussen niet opeenvolgende golfhoogten op de groeplengteverdeling.VloeistofmechanicaHydraulic EngineeringCivil Engineering and Geoscience
Onderzoek onzekerheid extreme golfbelastingen: Effect stromingen op golven Stappenplan toepassing SWAN model
No full textTen behoeve van het ontwerp van zeewerende constructies van nieuwe landaanwinningswerken van de Maasvlakte 2 is onderzoek verricht naar onzekerheden in de bepaling van golfrandvoorwaarden onder ontwerpcondities. In dit deelrapport is gekeken naar het effect van stromingen op de golfcondities voor de zeewerende constructies. Hierbij is gebruik gemaakt van bestaande resultaten van stromingsberekeningen onder gemiddelde springtij situaties. Vervolgens zijn een aantal golfberekeningen uitgevoerd met het SWAN model om het effect van stromingen op de golfcondities te bepalen. Tevens is een stappenplan opgesteld voor het uitvoeren van SWAN berekeningen voor ontwerpcondities
Analysis SWAN hindcasts Wadden Sea, Oosterschelde and Slotermeer
No full textResults of hindcast studies with the SWAN wave model in the Amelander Zeegat, the Oosterschelde estuary and the Slotermeer were analyzed to detect the cause of under-prediction of low-frequency wave energy in the coastal zone, the causes of prediction errors in the presence of currents and the underprediction of wave heights In depth-limited conditions. The results of this study show that the under-prediction of low-frequency energy is most likelycaused by propagation effects, although the whitecapping formulation and bottom friction may also play a role. Wave heights are overpredicted in opposing current and th is is made worse by application of the adapted whitecapping formulation of WL (2007). The under-prediction of the wave heights in depth-limited situations is clearly worse for steep waves. It was also found that shallow water source terms affect the total source term balance. The under-prediction was the least by applying the surf breaking term with the breaking parameter gamma=O.8.SB
Impact of access channel geometry on wave penetration in harbours
No full textAccess channels (entrance channels) to ports are a relevant part of port facilities, and they have a strong influence on the port operations as well. However, little information is available about their analysis and design regarding the wave interaction with access channels. This study is focused on the interaction of waves with entrance channels regarding wave propagation. This report has three parts: i) a qualitatively assessment of diffraction effects carried out with SWAN; ii) a comparison between SWAN (phase averaged wave model) and SWASH (phase resolving model) results, regarding refraction and diffraction effects; and ii) a systematic analysis of the results in SWAN on several wave conditions and a few access channel geometries (slopes). SWASH is used to test SWAN capabilities in an environment where significant refraction and diffraction is expected. The results of the comparison are analyzed and recommendations for future comparison are presented. The systematic analysis of conditions provides information about performance of SWAN and its ability to correctly represent physical phenomena particularly regarding refraction and diffraction. Additionally, recommendations for wave propagation analysis for entrance channels are presented. Finally, based on the results, engineering recommendations and considerations are presented regarding operations of ports and the design of related structures such as breakwaters.CoMEM - Coastal and Marine Engineering and ManagementHydraulic EngineeringCivil Engineering and Geoscience
Spectral partitioning and swells in the black sea
No full textThe swell climate of the Black Sea has been determined using a long-term 31-year wave hindcast with the thirdgeneration spectral wave model SWAN in combination with spectral partitioning. This technique enables decomposing wave spectra into individual wave systems representing wind seas or swells and computing integral wave parameters of each partition. Results are presented of the partition technique and of spatial and seasonal characteristics of wind sea and swell systems. In addition, the average amount of swell energy and the occurrence probability of dangerous crossing sea states are determined.Environmental Fluid Mechanic
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