A critical analysis and validation of the accuracy of wave overtopping prediction formulae for OWECs

The development of wave energy devices is growing in recent years. One type of device is the overtopping wave energy converter (OWEC), for which the knowledge of the wave overtopping rates is a basic and crucial aspect in their design. In particular, the most interesting range to study is for OWECs with steep slopes to vertical walls, and with very small freeboards and zero freeboards where the overtopping rate is maximized, and which can be generalized as steep low-crested structures. Recently, wave overtopping prediction formulae have been published for this type of structures, although their accuracy has not been fully assessed, as the overtopping data available in this range is scarce. We performed a critical analysis of the overtopping prediction formulae for steep low-crested structures and the validation of the accuracy of these formulae, based on new overtopping data for steep low-crested structures obtained at Ghent University. This paper summarizes the existing knowledge about average wave overtopping, describes the physical model tests performed, analyses the results and compares them to existing prediction formulae. The new dataset extends the wave overtopping data towards vertical walls and zero freeboard structures. In general, the new dataset validated the more recent overtopping formulae focused on steep slopes with small freeboards, although the formulae are underpredicting the average overtopping rates for very small and zero relative crest freeboards

Probabilistic Design for North Sea Dikes

Weltweit haben sich in den letzten fünf Jahrzehnten vermehrt Naturkatastrophen ereignet. An den meisten Küsten sind erhöhte Sturmflutwasserstände mit ansteigender Tendenz zu verzeichnen, während andererseits weiterhin die Besiedlung und die wirtschaftliche Nutzung des Küstenraumes anwachsen. Probabilistische Methoden bieten vor diesem Hintergrund die Möglichkeit, zur Quantifizierung der Sicherheit von Küstenschutzmaßnahmen beizutragen. Hauptziel der vorliegenden Arbeit war es, ein probabilistisches Bemessungskonzept auf der Grundlage bestehender, zu ergänzender und neu zu entwickelnder Grenzzustandsgleichungen für die maßgebenden Versagensmechanismen und deren Wechselwirkungen vorzuschlagen, das Konzept an Beispieldeichen zu implementieren und die Ergebnisse mit denen herkömmlicher deterministischer Verfahren zu vergleichen. Die Arbeit hat zeigt, dass sich die wichtigsten Versagensmechanismen auf die Erosionsprozesse auf der Außenböschung von Seedeichen beziehen. Außerdem weisen vor allem die Unsicherheiten des Bemessungswasserstandes einen entscheidenden Einfluss auf die Versagenswahrscheinlichkeiten der Grenzzustandsgleichungen und auf die Gesamt- Versagenswahrscheinlichkeit auf. Die Unsicherheiten der Modelle sind dagegen i.d.R. von geringerer Relevanz. Die Ergebnisse der Arbeit sollen die Machbarkeit von probabilistischen Bemessungsverfahren für Küstenschutzwerke veranschaulichen. Die vorgestellte Vorgehensweise liefert die Grundlage für den wesentlichsten Baustein zur Durchführung von Risikoanalysen für durch Hochwasser bedrohte Küstenregionen.Within the last five decades natural disasters have occurred worldwide with increasing tendency. Mean sea level rise has been observed along many coastlines giving a challenge to the coastal engineering profession due to increasing population at the seaside and the parallel increase of economic use of coastal areas. With this background probabilistic methods provide a unique possibility to contribute to the quantification of the safety reserves of coastal defence structures. The main objectives of this thesis are (i) to set up a probabilistic design concept on the basis of existing, improved and new limit state equations for the governing failure modes (here: for sea dikes) as well as their interrelations; (ii) to apply this probabilistic concept to selected case studies; and (iii) to compare the results with results using traditional deterministic design procedures. It has been shown that the most important failure modes are the erosion processes at the seaward slope of dikes. Furthermore, the uncertainty related to the design water level is the most important parameter regarding the failure probabilities of the individual failure modes and the overall failure probability of the sea dike. On the other hand it has to be mentioned that for the cases investigated here the uncertainties of the limit state equations are less relevant. The overall results illustrate the feasibility of probabilistic design procedures for coastal defence systems. The results provide the basis for the most essential element within the task of performing risk analyses for flood prone coastal areas

Reliability Analysis and Breach Modelling of Coastal and Estuarine

Flood Defenc