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Influence of platform configuration on the hydrodynamic performance of semi-submersibles for offshore wind energy
Published in C. Guedes Soares, T.A. Santos, Trends in Maritime Technology and Engineering Volume 2, 2022
M. Hmedi, E. Uzunoglu, C. Guedes Soares
The two platforms are subjected to irregular waves of a significant height Hs=4m, a peak period Tp=8s, and the JONSWAP peak parameter γ=2.87 with a frequency bandwidth between 0.05 and 0.25Hz to estimate their RAOs in the main DOF. Results are presented in Figure 4, and the applied frequency limit for the plots corresponds to the first-order wave frequency excitation range (DNV 2017). The NAUTILUS platform is more excited by the waves and presents multiple peaks in its RAOs plots. Even though these peaks are small, they can affect the life of the floating structure as they are located inside the most occurrent waves frequency range (0.1 to 0.2 Hz). In other words, the peaks correspond to a relatively significant displacement in the main DOFs, which might affect other components such as the moorings and the tower bending moments, intensifying the structural fatigue
Large-scale Flooding in Europe, 1961–2005
Published in Zbigniew W. Kundzewicz, Changes in Flood Risk in Europe, 2019
Christel Prudhomme, Simon Parry, Marie Genevier, Jamie Hannaford, Zbigniew W. Kundzewicz
Fluvial flood events are exceptionally high river discharges associated with water levels sometimes higher than the river bank and leading to inundations. They can be caused by various combinations of extreme conditions such as: intense/persistent precipitation, snowmelt, flow obstruction (e.g. ice jam, landslide), dam failure, and storm surge. In addition, heavy rainfall of short duration, deep snow cover rapidly melting and even moderate rainfall on ice, frozen ground or saturated soil can all contribute to rapid and large runoff. From the records of peak discharge of major runoff events and complementary information, such as rainfall measurements or atmospheric circulation patterns prior to a flood event, it is possible to interpret better some of the main mechanisms leading to the generation of floods.
Diffuse pollution-principles, definitions and regulatory aspects
Published in R. Hranova, Diffuse Pollution of Water Resources, 2005
The methods described above are event orientated. They allow for the determination of peak flow rates from selected storm events, defining specified conditions, which usually are connected with the design of flood protection structures. In addition, they assume constant values for the rainfall losses as evapotranspiration and infiltration. Continuous simulation models attempt to represent the entire hydrologic system, simulating the natural environment. They consider the whole runoff process, including surface runoff storage, infiltration, overland routing and channel flow on a continuous basis, considering the variation of parameters in time and space. The major advantage of models is the possibility to apply large data sets and to simulate and predict different scenarios at conditions closer to the naturally happening events.
Evaluating changes in flood regime in Canadian watersheds using peaks over threshold approach
Published in ISH Journal of Hydraulic Engineering, 2022
Kampanad Bhaktikul, Mohammed Sharif
An efficient alternative to annual maxima approach is the peak over threshold approach. A major advantage of the POT approach is that it provides reliable estimates of flood magnitudes of different return periods, even for hydrometric stations with relatively short record length. Therefore, the present research utilizes peaks over threshold (POT) approach to extract flow and timing measures that can lead to the identification of changes in flood regime. A comparison of the efficiency of the AMS and POT approaches has been presented by Cunnane (1988). The author was able to demonstrate that the sampling variance with POT approach was significantly less than with the POT approach. However, the method was not implemented in an automatic or a semi-automatic manner. Guidelines for operational implementation of the POT approach have been presented by Burn et al. (2016). Two major issues in implementing a POT approach are (i) determining an appropriate threshold, and (ii) ensuring the independence of flooding events above the chosen threshold. The present paper aims to address these issues comprehensively, and describes a generic semi-automatic methodology for implementing a POT approach. The intent is to investigate changes in flood behaviour of several Canadian rivers through an analysis of peaks over threshold data.
The design flood under two approaches: synthetic storm hyetograph and observed storm hyetograph
Published in Journal of Applied Water Engineering and Research, 2020
Catine António Chimene, José Nilson B. Campos
During the application of a flood frequency analysis, hydrologists usually focus on peak flows. However, it is important to also consider the variables of flood volume and duration. Therefore, the bivariate statistical analysis, peak flow and volume have more reliability in sizing reservoir spillways (Mediero et al. 2010). In Europe, the legislation on flood risk assessments for infrastructure with a Tr ranging from 50 to 500 has established that frequency analyses are the method to be used (Botero and Francés 2010). The statistical method has been compared with the rainfall-runoff method in a data rich catchment in southern China. For the simulated discharges, they used two models: the Xinanjiang (XAJ) and Hydrologiska Vattenbalansadelning (HBV). The results showed that both models yielded acceptable results. The maximum error was 11% for a Tr equal to 100 years. The XAJ model oversized, whereas the HBV model undersized the design flood (Zeng et al. 2016). Okoli et al. (2019) used two different methods for the estimation of design floods such as statistical method and hydrological concepts (event-based simulation “EBS” and continuous simulation “CS”).
Seismic hazard analysis of Silchar city located in North East India
Published in Geomatics, Natural Hazards and Risk, 2023
Aman Kumar, Goutam Ghosh, Praveen Kumar Gupta, Virendra Kumar, Prabhu Paramasivam
The seismic hazard of the site commonly characterizes peak acceleration, peak velocity, and response spectrum ordinates. This method is a simple and quick method for Hazard analysis and has been used for many years in designing large dams, power plants, and other critical facilities. This method provides a scenario for evaluating the worst-case ground motions, and this method does not provide any information regarding the occurrence of that controlling earthquake. It does not consider the uncertainty in size, location, and time.