Academic literature on the topic 'Extreme event frequencies'
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Journal articles on the topic "Extreme event frequencies"
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Diffenbaugh, Noah S. "Verification of extreme event attribution: Using out-of-sample observations to assess changes in probabilities of unprecedented events." Science Advances 6, no. 12 (March 2020): eaay2368. http://dx.doi.org/10.1126/sciadv.aay2368.
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Independent verification of anthropogenic influence on specific extreme climate events remains elusive. This study presents a framework for such verification. This framework reveals that previously published results based on a 1961–2005 attribution period frequently underestimate the influence of global warming on the probability of unprecedented extremes during the 2006–2017 period. This underestimation is particularly pronounced for hot and wet events, with greater uncertainty for dry events. The underestimation is reflected in discrepancies between probabilities predicted during the attribution period and frequencies observed during the out-of-sample verification period. These discrepancies are most explained by increases in climate forcing between the attribution and verification periods, suggesting that 21st-century global warming has substantially increased the probability of unprecedented hot and wet events. Hence, the use of temporally lagged periods for attribution—and, more broadly, for extreme event probability quantification—can cause underestimation of historical impacts, and current and future risks.
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Al-Saqaf, Walid, and Peter Berglez. "How Do Social Media Users Link Different Types of Extreme Events to Climate Change? A Study of Twitter During 2008–2017." Journal of Extreme Events 06, no. 02 (June 2019): 1950002. http://dx.doi.org/10.1142/s2345737619500027.
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This study examines how three types of extreme events (heat waves, droughts, floods) are mentioned together with climate change on social media. English-language Twitter use during 2008–2017 is analyzed, based on 1,127,996 tweets (including retweets). Frequencies and spikes of activity are compared and theoretically interpreted as reflecting complex relations between the extreme event factor (the occurrence of an extreme event); the media ecology factor (climate-change oriented statements/actions in the overall media landscape) and the digital action factor (activities on Twitter). Flooding was found to be by far the most tweeted of the three in connection to climate change, followed by droughts and heat waves. It also led when comparing spikes of activity. The dominance of floods is highly prevalent from 2014 onwards, triggered by flooding events (extreme event factor), the climate science controversy in US politics (media ecology factor) and the viral power of celebrities’ tweets (digital action factor).
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Teixeira, Mateus da Silva, and Prakki Satyamurty. "Trends in the Frequency of Intense Precipitation Events in Southern and Southeastern Brazil during 1960–2004." Journal of Climate 24, no. 7 (April 1, 2011): 1913–21. http://dx.doi.org/10.1175/2011jcli3511.1.
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Abstract A new approach to define heavy and extreme rainfall events based on cluster analysis and area-average rainfall series is presented. The annual frequency of the heavy and extreme rainfall events is obtained for the southeastern and southern Brazil regions. In the 1960–2004 period, 510 (98) and 466 (77) heavy (extreme) rainfall events are identified in the two regions. Monthly distributions of the events closely follow the monthly climatological rainfall in the two regions. In both regions, annual heavy and extreme rainfall event frequencies present increasing trends in the 45-yr period. However, only in southern Brazil is the trend statistically significant. Although longer time series are necessary to ensure the existence of long-term trends, the positive trends are somewhat alarming since they indicate that climate changes, in terms of rainfall regimes, are possibly under way in Brazil.
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Zhang, Xiaodan, Guoyu Ren, Yuda Yang, He Bing, Zhixin Hao, and Panfeng Zhang. "Extreme historical droughts and floods in the Hanjiang River Basin, China, since 1426." Climate of the Past 18, no. 8 (August 3, 2022): 1775–96. http://dx.doi.org/10.5194/cp-18-1775-2022.
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Abstract. The major droughts and floods in the Hanjiang River Basin, central China, have a significant impact on flood prevention and control in the middle reaches of the Yangtze River and water resources management in the areas of the South–North Water Diversion Middle Line Project. However, there is a lack of understanding of the multi-decadal to centennial-scale patterns of extreme droughts and floods in the area. Applying the yearly drought and flood records from historical documents and precipitation data in the period of instrumental measurements, this study constructs a time series of extreme droughts and floods in the Hanjiang River Basin from 1426–2017 and analyzes the temporal and spatial characteristics of the extreme drought and flood event variations. The results show that there were a total of 45 extreme droughts and 52 extreme floods in the basin over the past 592 years. Extreme droughts and floods were highly variable on a multi-decadal to centennial scale, and the frequencies were higher in the first and last 100 years or so of the study period and lower in between. Spatially, the frequencies of extreme droughts and floods were generally higher in the middle and lower reaches than in the upper reaches. It was also found that there is a good correlation of drought and flood frequencies between the upper Hanjiang River Basin and North China. These results are informative for the study of mechanisms and predictability of multi-decadal to centennial-scale variability of extreme hydroclimatic events in the river basin.
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Cimò, Giuseppe, T. Beckert, T. P. Krichbaum, L. Fuhrmann, A. Kraus, A. Witzel, and J. A. Zensus. "A Very Rapid Extreme Scattering Event in the IDV Source 0954+658." Publications of the Astronomical Society of Australia 19, no. 1 (2002): 10–13. http://dx.doi.org/10.1071/as01097.
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AbstractExtreme scattering events (ESEs) are dramatic variations of the flux density at gigahertz frequencies caused by ray path distortions within an isolated inhomogeneity (‘plasma lens’) in the interstellar medium. These events are characterised by a deep flux density minimum in the light curve with, in some cases, surrounding maxima. The variability time scales range from weeks to months. These phenomena show a strong frequency dependence, in which the variability amplitudes increase with wavelength. During an intraday variability (IDV) monitoring project (March 2000), a feature resembling an ESE-like event appeared in the variable light curve of 0954+658, however with a time scale of less than two days. We will discuss this effect and its implications for a better description of the interstellar medium.
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Crimmins, Michael A. "Interannual to decadal changes in extreme fire weather event frequencies across the southwestern United States." International Journal of Climatology 31, no. 11 (June 15, 2010): 1573–83. http://dx.doi.org/10.1002/joc.2184.
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J. Mykletun, Reidar, and Maira Rumba. "Athletes’ experiences, enjoyment, satisfaction, and memories from the Extreme Sport Week in Voss, Norway." Sport, Business and Management: An International Journal 4, no. 4 (October 7, 2014): 317–35. http://dx.doi.org/10.1108/sbm-12-2013-0046.
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Purpose – The purpose of this paper is to demonstrate how experiences, sport careers and biographic variables predict: enjoyment, satisfaction and memories from the unique and spectacular Extreme Sport Week (Ekstremsportveko), Voss, Norway, as reported by the extreme sport athletes. Design/methodology/approach – An electronic questionnaire was distributed to all participants during 2011, and collected responses from 292 athletes (27 per cent response rate). Data were analysed by frequencies, mean values, correlations and multiple regression. Findings – Extreme sport athletes were typically amateurs with serious leisure careers. Social ties between participants and volunteers were found. They had positive experiences at the event, and the realms of education, aesthetics and entertainment were the strongest predictors of enjoyment, satisfaction and memories. Level of excitement augmented the explained variance, especially when predicting memories. Most participants intended to re-visit future Extreme Sport Weeks. Research limitations/implications – The moderate response rate warrants generalisations from the study. As the study is cross-sectional, cause-effect relationships cannot be established. Practical implications – For event organisers, the study shows the athletes’ appreciations with its managerial implications. Social implications – The Voss area is highly appreciated for its natural beauty and extreme sport resources, and re-visits are likely to occur, hence contributing to its growth as extreme sport venue and to sport tourism. Originality/value – This study is the first to explore the experiences of athletes who participated in the unique and spectacular event Extreme Sport Week. For researchers and practitioners, it is an example of how to measure experiences and their outcomes of (extreme sport) events.
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Schindler, N., J. Tränckner, and P. Krebs. "Extreme value statistics for river quality simulations." Water Science and Technology 61, no. 2 (January 1, 2010): 397–406. http://dx.doi.org/10.2166/wst.2010.820.
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Various methods have been proposed to assess intermittent pollution loads and impacts on rivers in urban areas. Although the variables to describe the impact are mainly the same, the standards show significant differences in the assessment of permitted concentration level, duration and return period. The probability of an event is derived using either frequencies of occurrence or predefined extreme value distributions. Both methods have drawbacks. To bypass these, an a posteriori estimation of the statistical distribution of data based on the peak-over-threshold method is proposed. The method is exemplarily demonstrated using a semi-virtual case study.
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Yazdanpanah, Hojjatollah, Josef Eitzinger, and Marina Baldi. "Analysis of the extreme heat events in Iran." International Journal of Climate Change Strategies and Management 9, no. 4 (August 21, 2017): 418–32. http://dx.doi.org/10.1108/ijccsm-04-2016-0046.
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Purpose The purpose of this paper is to assess the spatial and temporal variations of extreme hot days (H*) and heat wave frequencies across Iran. Design/methodology/approach The authors used daily maximum temperature (Tmax) data of 27 synoptic stations in Iran. These data were standardized using the mean and the standard deviation of each day of the year. An extreme hot day was defined when the Z score of daily maximum temperature of that day was equal or more than a given threshold fixed at 1.7, while a heat wave event was considered to occur when the Z score exceeds the threshold for at least three continuous days. According to these criteria, the annual frequency of extreme hot days and the number of heat waves were determined for all stations. Findings The trend analysis of H* shows a positive trend during the past two decades in Iran, with the maximum number of H* (110 cases) observed in 2010. A significant trend of the number of heat waves per year was also detected during 1991-2013 in all the stations. Overall, results indicate that Iran has experienced heat waves in recent years more often than its long-term average. There will be more frequent and intense hot days and heat waves across Iran until 2050, due to estimated increase of mean air temperature between 0.5-1.1 and 0.8-1.6 degree centigrade for Rcp2.6 and Rcp8.8 scenarios, respectively. Originality/value The trend analysis of hot days and heat wave frequencies is a particularly original aspect of this paper. It is very important for policy- and decision-makers especially in agriculture and health sectors of Iran to make some adaptation strategies for future frequent and intense hot days over Iran.
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Hamdeno, Manal, Hazem Nagy, Omneya Ibrahim, and Bayoumy Mohamed. "Responses of Satellite Chlorophyll-a to the Extreme Sea Surface Temperatures over the Arabian and Omani Gulf." Remote Sensing 14, no. 18 (September 17, 2022): 4653. http://dx.doi.org/10.3390/rs14184653.
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Extreme events such as Marine Heat Waves (MHWs) and Low Chlorophyll-a (LChl-a) in the ocean have devastating impacts on the marine environment, particularly when they occur simultaneously (i.e., the compound of MHWs and LChl-a events). In this study, we investigate the spatiotemporal variability of MHWs and LChl-a events in the Arabian and Omani Gulf. For this purpose, we used satellite-based high-resolution observations of SST (0.05° × 0.05°; from 1982 to 2020) and chlorophyll-a concentration data (0.04° × 0.04°; from 1998 to 2020). Hourly air temperature, wind, and heat flux components from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) were used to explain the link between these extreme events and atmospheric forcings. Moreover, our results revealed that the annual frequency of MHW and LChl-a is related to the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). The results revealed an average SST warming trend of about 0.44 ± 0.06 °C/decade and 0.32 ± 0.04 °C/decade for the Arabian Gulf (AG) and the Gulf of Oman (OG), respectively. This warming rate was accompanied by MHW frequency and duration trends of 0.97 events/decade and 2.3 days/decade, respectively, for the entire study region from 1982 to 2020. The highest annual MHW frequencies were recorded in 2010 (6 events) and 2020 (5 events) associated with LChl-a frequency values of 4 and 2, respectively. La Niña events in 1999, 2010, 2011, and 2020 were associated with higher frequencies of MHW and LChl-a. The positive phase of IOD coincides with high MHW frequency in 2018 and 2019. The longest compound MHW and LChl-a event with a duration of 42 days was recorded in 2020 at OG. This extreme compound event was associated with wind stress reduction. Our results provide initial insights into the spatiotemporal variability of the compound MHW and LChl-a events that occurred in the AG and OG.
Dissertations / Theses on the topic "Extreme event frequencies"
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Colonna, François. "Les conséquences du changement climatique sur les ressources en eau et le peuplement piscicole des cours d’eau de Corse." Thesis, Corte, 2021. http://www.theses.fr/2021CORT0012.
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Le changement climatique est un phénomène global pour lequel de nombreuses études ont été menées sur de nombreux compartiments. A l’échelle européenne comme à l’échelle méditerranéenne ainsi qu’à l’échelle locale de la Corse, les mêmes conséquences sont observées et toutes les tendances confirment les conclusions du Groupement d’experts Intergouvernemental sur l’Evolution du Climat. Nous subissons une augmentation générale des températures ainsi qu’une amplification des fréquences et de l’intensité des évènements météorologiques extrêmes. Ces changements appliquent de fortes contraintes au milieu naturel. Les cours d’eau de Corse et les organismes qui y sont associés y sont également soumis.Face à ce constat, les travaux de recherche développés dans le cadre de cette thèse tentent d’apporter des connaissances supplémentaires sur les conséquences du changement climatique sur les cours d’eau de Corse et les poissons qui peuplent ces hydrosystèmes.Une nouvelle synthèse climatique comparant la période 1960-1984 à la période 1985-2020 est proposée et montre dans quelle proportion le réchauffement climatique impacte la région corse et quelles sont les zones les plus touchées par ses conséquences. L’intensification des périodes de sècheresse est abordée. Une attention particulière est accordée aux espèces de poissons d’eau douce pour lesquelles nous avons proposé une comparaison de la vitesse de croissance dans un contexte de changement climatique.Enfin, dans des travaux de recherche appliquée, nous proposons un outil d’aide à la décision à destination des gestionnaires des cours d’eau de Corse afin de leur permettre d’être alerter par un écart aux modèles proposés. Ces modèles servent de valeurs de référence mis au point à partir de résultats de recensements piscicoles pratiqués partout en Corse depuis la fin des années 80Climate change is a global phenomenon for which numerous studies have been carried out on many compartments. On a European scale as well as on a Mediterranean scale and on the local scale of Corsica, the same consequences are observed and all the trends confirm the conclusions of the Intergovernmental Panel on Climate Change. We are experiencing a general increase in temperatures as well as an increase in the frequency and intensity of extreme weather events. These changes apply strong constraints to the natural environment. Corsica's waterways and their associated organisms are also subject to them.Faced with this observation, the research work developed within the framework of this thesis attempts to provide additional knowledge on the consequences of climate change on Corsican rivers and the fish that populate these hydrosystems.A new climatic synthesis comparing the period 1960-1984 with the period 1985-2020 is proposed and shows in what proportion global warming is impacting the Corsican region and which areas are most affected by its consequences. The intensification of drought periods is discussedParticular attention is paid to freshwater fish species for which we have proposed a comparison of growth rates in the context of climate change.Finally, in applied research work, we propose a decision-support tool for managers of Corsican rivers to enable them to be alerted by a deviation from the proposed models. These models serve as reference values developed from the results of fish surveys carried out throughout Corsica since the late 80’s
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Tetzlaff, G. "Extreme Weather: Mitigation Enhancement by Better Forecasts or by Better Knowledge on Event Frequencies?" 2005. https://ul.qucosa.de/id/qucosa%3A15925.
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The quality of forecasts can be measured with a wide variety of indices and formulae. All these approaches rely basically on the relation between the numbers of correct forecasts, wrong forecasts, false alarms and rejected cases. In the case of extreme events damage is the major topic. All extreme events by definition are more or less rare events. In many applications the events frequency of an extreme event is selected to be one event per 100 hundred years. Depending on the application other such event frequencies are in use. The mitigation of damage mainly uses rules for the design structures such as buildings. In principle their proper application would allow damage to occur only if a meteorological event oversteps a certain predefined threshold value. In practice the threshold proves to represent more something like
a soft shoulder and damage is already observed to be caused by events somewhat smaller than the damage threshold value for the extreme weather case. No matter what its exact definition each threshold value is connected to an event frequency. This event frequency is hard to obtain in particular in the vicinity of the threshold of the extreme event case, because it has to be derived from data scarce by definition, however long the observation time series are. Therefore, these threshold values are subject to a certain inaccuracy. In addition, the low frequencies show some variability with time. Recently, climate changes support the idea that also the occurrence frequency of extreme values will change, increase, in the future. Calculating the forecast quality using the basic data leads to two formulations of the forecast quality, both based on the same principles. The fraction formulation correctly is free from any absolute damage height, it is sufficient to find one reference value. When going to the cumulative formulation the role of the effect of the frequency of occurrence can clearified. The two equations allow to compare the effects of long term changes and inaccuracies of the frequency of occurrence of extreme events with the effects of the improvements of the weather prediction.
Books on the topic "Extreme event frequencies"
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United States. National Aeronautics and Space Administration., ed. Remote sensing of surficial process responses to extreme meteorological events: Final report. [Washington, DC: National Aeronautics and Space Administration, 1997.
Find full textBook chapters on the topic "Extreme event frequencies"
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Harr, Patrick A., Antoni Jordi, and Luke Madaus. "Analysis of the Future Change in Frequency of Tropical Cyclone-Related Impacts Due to Compound Extreme Events." In Hurricane Risk in a Changing Climate, 87–120. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-08568-0_5.
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AbstractTropical cyclone-related hazards are often comprised of compound, connected events that individually amplify the total impacts. Often, hazard risk assessments focus on one factor rather than the compound nature of multiple forcing mechanisms. It is possible that extreme event analysis in a univariate context may underestimate the probabilities and impacts of extreme events. In this study, a framework addresses multivariate analysis of risk due to compound hazards related to tropical cyclone characteristics. Combinations of observations and simulations are used to identify possible frequencies of annual chance extreme events forced via connected individual events. The framework emphasizes the statistical dependence of multiple physical variables that contribute to extreme compound events when individual events are not extreme.To make the analysis clear, specific locations are analyzed using both univariate and a joint analysis. The joint analysis is conducted using copula functions to remove the restriction that marginal distributions need come from the same family of probability functions. The primary results suggest that univariate and joint return periods for key tropical cyclone-related hazards could shorten in the future and univariate frequency analysis may underestimate the magnitude of the extreme events because the univariate analyses do not account for the dependence structure between the paired environmental factors.
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Priya, Prachi, Prashant Kumar, and Rajni. "Wave Spectral Analysis of Visakhapatnam Port Under the Resonance Conditions." In Advances in Transdisciplinary Engineering. IOS Press, 2023. http://dx.doi.org/10.3233/atde221335.
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The Visakhapatnam port, India is a major natural port, situated in between the Kolkata and Chennai on the East Coast and in terms of latitude and longitude its location is 17.6856∘ N, 83.2160∘ E has experienced an extreme wave oscillations 2.0 to 6.0 m in the midst of its severe weather events. In this paper numerical studies are performed to analyze the frequency distribution over the oceanic surface of standing waves in Visakhapatnam port at four respective synthetic record stations in presence of partially reflecting harbor. The convergence study is conducted to obtain the numerical accuracy of the scheme and simulation results are validated with the available studies experimentally from Ippen and Goda (1963) and Lee (1971) also with the analytical approximations. Further, the spectral density is determined corresponding to the wave period for the incident waves striking with several directions towards the Visakhapatnam port at four different record stations. The computation of the resonant frequencies is conducted in the Visakhapatnam port to examine the safe locations for the moored ship. Abstract goes here.
Conference papers on the topic "Extreme event frequencies"
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Ewans, Kevin, and Bas Buchner. "Wavelet Analysis of an Extreme Wave in a Model Basin." In ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/omae2008-57499.
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Analyses of laboratory wave records including extreme crests, based on the continuous wavelet transform, are reported. The analyses have provided further insight into the spectral characteristics of these extreme events. During the period of the extreme wave crest, spectral levels over all frequencies are substantially elevated by comparison with average spectrum for the complete wave record. This was also observed in a similar analysis of the famous New Year wave event that occurred at the Draupner platform. The analyses also indicate that nonlinear effects are active during the crest event, second-order effects being particular strong and indicating phase-locking of high frequency waves to freely-propagating waves with frequencies close to the spectral peak. These nonlinear effects appear to be strong only in the vicinity of the extreme.
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Guinard, L., S. Parey, L. Grammosenis, and H. Cordier. "Protection of Nuclear Power Plants Against Natural Hazards: Consideration for EDF’s Nuclear Facilities of Decamillennial Events (WENRA RL T4.2)." In 2020 International Conference on Nuclear Engineering collocated with the ASME 2020 Power Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icone2020-16187.
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Abstract Following the Fukushima Daiichi accident, the Western European Nuclear Regulators Association (WENRA) updated in 2014 the safety reference levels (SRL) for existing reactors, introducing a new chapter specific to natural hazards. In 2015, in preparation for the 4th periodic safety review of its 900 MW units, EDF aimed at meeting these new reference levels. While many of them were already satisfied for a long time by EDF (for example: Identification of natural hazards, Site specific natural hazard screening and assessment, Protection against design basis events), several of them were new objectives: - T4.2: The exceedance frequencies of design basis events shall be low enough to ensure a high degree of protection with respect to natural hazards. A common target value of frequency, not higher than 10−4 per annum, shall be used for each design basis event. Where it is not possible to calculate these probabilities with an acceptable degree of certainty, an event shall be chosen and justified to reach an equivalent level of safety. - T6.1: Events that are more severe than the design basis events shall be identified as part of DEC analysis. This article focuses on the first objective that is WENRA RL T4.2. Estimating a 10−4 Return Level for natural hazards is generally based on the application of the statistical Extreme Value Theory (EVT). In case of lack of reliable data or intermittent phenomenon, it is difficult to estimate such a level. With regard to the intensity of natural hazard to be used to define the protections, EDF has developed an approach distinguishing 3 types of hazards: - Those for which 10−4 level is definable, as earthquake, external flooding and tornado. For these hazards, the facilities are already protected against this level of hazard. - Those for which the 10−4 level is evaluated indirectly, such as cold temperatures, warm temperatures, and high winds. For those, EDF defined a “WENRA hazard”, which complements the Design Basis Hazard, and verified the capacity of the facilities to cope with it. This hazard is determined on the basis of a value with a “reasonably quantifiable” frequency of occurrence (typically a 100-year return period), to which EDF then adds a margin to target a level of risk that can reach a 10−4 level. The method of quantification of this margin crosses different approaches (mainly the gap between the observed records and statistical extrapolation) - Those for which the 10−4 level is considered not relevant, such as lightning or snow. For lightning, the robustness is ensured on the one hand by taking into account for the Design Basis lightning the highest level of the standard AFNOR NF EN 62305-1 and on the other hand by the protection of the hardened safety core equipments against an extreme lightning level. For snow, protection is based on the normative context with margins for some sites. The robustness of the structures and the organizational arrangements make it possible to cope with snow levels higher than those used for the design basis. In conclusion, the capacity of the EDF 900 MW NPPs to cope with high level of natural hazard (equivalent to decamillennial events) is being verified through the 4th periodic safety reviews, in compliance with WENRA reference level T4.2.
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Notohardjono, Budy, Shawn Canfield, Suraush Khambati, and Richard Ecker. "Analysis of Mainframe Computer Structures Using Implicit and Explicit Finite Element Analysis." In ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84831.
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Abstract This paper discusses the finite element analysis (FEA) methods used to analyze the performance of a mainframe computer’s structural frame under a standard seismic loading such as that defined by Telcordia NEBS Zone 4. Specialists in the earthquake robustness area need to consider the basic mainframe structural information such as the total mass and the center of gravity in order to properly size and install tiedowns to prevent tiedown failure which can lead to hazardous tip-over events. To ensure successful operation through a seismic event, the total deflection of the top of the mainframe is a good indicator of ensuring the mainframe computer’s continuous operation. As the mainframe computer’s total weight and the center of gravity varies depending on the specific customer configuration, this paper will examine the two extreme end cases: the lowest mass configuration with the highest location of the center of gravity and the highest mass configuration with the highest center of mass location. From a structural perspective, the higher the initial resonance frequencies, the more rigid the structure and the smaller the upper frame deflection will be. Thus, given a mainframe structure, the finite element analysis results will provide information on the weakest direction resonance frequency, which is in the narrow, side-to-side direction, along with the mainframe rack tiedown loads and maximum top frame deflection. Given a mainframe structure’s finite element model and standard time domain seismic acceleration input at the base of the frame structure, the explicit finite element method will provide the performance of the structure namely the first resonance frequency, the maximum stresses at the rack structure, load at the tie down locations and the maximum top frame deflection. The explicit finite element analysis model can take into account the non-linear contact regions around weld areas and between adjacent sheet metal frame components as well as material non-linearities. The result of the FEA analysis of the several mainframe configurations will be compared to the results from actual seismic earthquake mainframe tests.
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Leong, Darrell, Ying Min Low, and Youngkook Kim. "Long-Term Extreme Response Prediction of Mooring Lines Using Subset Simulation." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77064.
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Rigorous methods of probabilistic evaluations on long-term extremes are integral components in reliability research of offshore structures against overload events. Assessment across all conceivable sea states requires accounting for variabilities of long-term environmental loads and short-term stochastics, traditionally captured through extensive sampling or numerical expectation integration. The amount of environmental load variables render numerical integrations across high dimensions computationally prohibitive, while industry requirements of high return periods demand large Monte Carlo samples of timedomain dynamic analyses. Subset simulation offers a promising alternative to classic methods of statistical analysis, dividing ultra-low probability problems into subsets of intermediate probabilities. The methodology is uniquely advantageous for the assessment of heavy-tail overload events, which are unpredictably severe and occur at exceedingly rare frequencies. Subset simulation is experimented on a mooring case study situated in the hurricane-prone Gulf of Mexico, with the structure exposed to a joint-probabilistic description of wave, wind and current loads. The devised methodology is found to successfully evaluate hurricane-stimulated extreme events at ultra-low probabilities, beyond the feasible reach of Monte Carlo simulation at reasonable lead times.
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Chakrabarti, Partha. "Nonlinear Time Domain Seismic Analysis for a Coupled Mooring Jacket-Yoke-FSO System." In ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79180.
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A mooring facility for a Floating Storage and Offloading (FSO) system, due to site conditions such as shallow water, often uses a fixed mooring tower for mooring of the FSO. When a fixed mooring tower in the form of a jacket structure is used, the turntable is mounted on the top of the jacket so that the FSO can weathervane due to actions of wind, wave and current forces. Product swivels are also located on this structure for uninterrupted flow of the product to the FSO when it rotates. The connection of the FSO to the turntable is through a rigid yoke. The yoke consists of two yoke arms meeting at a point hinged at the turntable, one large diameter cylinder for providing the stabilizing ballast load and two pendants supporting the ballast. The jacket has to be designed for the mooring loads in addition to the wind, wave and current loads on itself. The rigid yoke system is designed so that the varying draft conditions of the FSO as well as its motions can be suitably handled and absorbed. Complications may arise when the jacket is located in a seismically active site. When a site is prone to very strong ground motions, seismic response of the jacket in conjunction with the moored FSO has to be studied. The additional requirement is that any vibration of the jacket is suitably absorbed by the yoke system or a suitable isolation device is designed between the link or the yoke structure and the FSO. The weight of the suspended mass is a key design variable which affects this behavior. A structural dynamic model of the coupled jacket-yoke-frame-FSO system is analyzed using nonlinear time domain analysis technique. The calibrated El Centro ground accelerations are used for this analysis as a representative seismic excitation. A comparison of the results for jacket alone and the coupled system enables us to determine the effect of the yoke-frame-FSO on the dynamic response. The requirement, if any, of vibration isolation device for the nonlinear link (yoke) structure is decided from the dynamic analysis results. The dynamic analysis of the coupled system is complex. The complexities in the model arise due to: • The nonlinearity of the soil-pile system; • Nonlinearity of the yoke mechanism; • The fact that the FSO is a floating structure and it is free from the base excitation; • The FSO involves a large mass and is essentially free floating in water. The dynamic analyses are performed in several stages in view of the above complexities. Initially, the mode shapes and frequencies of the jacket alone are evaluated. Then the jacket is analyzed using the response spectrum approach with the design seismic spectrum. Subsequently time domain analysis of the jacket alone is performed using the calibrated El Centro seismic time history. Finally, the coupled system is analyzed for the time history of ground motion. Since the seismic event represents the design Strength Level Earthquake (SLE) condition, which is a rare event, only the FSO is coupled to the jacket, the offtake tanker is not assumed to be present during this extreme event. The nonlinear time domain analysis includes the nonlinear link (yoke) which is a mechanism by virtue of the hinges present. Therefore, the analysis requires geometric nonlinearity of the link to be considered to simulate the large displacements and the large rotations of the link, in addition to the nonlinearities of the pile-soil system. From the results of the analyses conclusions are drawn about effectiveness of vibration isolation by comparing the results of the jacket-yoke-FSO system to those of the jacket alone.
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Rudland, David L. "Predicting Pipe Rupture Frequencies Using xLPR." In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21080.
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Abstract Over the last several years, the U.S. Nuclear Regulatory Commission (NRC), in cooperation with the Electric Power Research Institute (EPRI), conducted a multi-year project that focused on the development of a viable method and approach to address the effects of primary water stress corrosion cracking (PWSCC) in primary piping systems approved for leak-before-break (LBB). This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations. Version 2.0 of this code has been completed and is currently awaiting public release. Since the focus of xLPR Version 2.0 is investigating the impacts of active piping degradation on the leak-before-break behavior of reactor coolant piping, questions have been raised to whether xLPR can be used to confirm pipe rupture frequencies developed in other efforts, such as NUREG-1829, “Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process.” This paper discusses an initial study focused on whether xLPR can be used to estimate pipe rupture frequencies. A series of analyses were conducted, based on inputs developed by the xLPR program team, focused on the reactor pressure vessel outlet nozzle geometry of a typical pressurized water reactor. Additional analyses were conducted using the same radius-to-thickness ratio but decreasing the pipe diameter. Due to computer memory restrictions, it was difficult calculating low probability events when considering PWSCC initiation, typical residual stresses, leak detection and in-service inspection. Therefore, to bound the problem, an aggressive weld residual stress was assumed with multiple pre-existing defects. By modifying the size and number of these initial defects, results were generated that indicated the conditional probability of rupture was related to the percentage of the inner circumference cracked and the pipe diameter. Using the PWSCC initiation model from xLPR Version 2, the yearly rupture frequency with leak detection and in-service inspection was calculated. The results indicate that the rupture frequencies in NUREG-1829 appear conservative relative to the results from this study. Due to the limited scope of this study, the assumptions used in these analyses were limited or conservative; therefore, additional analyses are needed for a more robust comparison. However, the results suggest that conducting xLPR analyses with pre-existing defects may be useful in bounding LBB applicability with active degradation.
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Dankert, Heiko, Jochen Horstmann, and Wolfgang Rosenthal. "Detection of Extreme Waves in SAR Images and Radar-Image Sequences." In ASME 2002 21st International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2002. http://dx.doi.org/10.1115/omae2002-28160.
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Extreme waves are often enclosed by other waves which are also higher than the average. These wave groups have to be taken into account for instance for the design of offshore platforms, breakwaters or ships, because successive high waves can cause more damage on those structures than the same waves separated by smaller waves. Further they can excite the resonance frequencies of moored structures like platforms due to non-linear effects or cause capsize. They are therefore of interest for engineers and scientists (e.g. Goda 1983). A method is presented to localize wave groups spatial and spatio-temporal utilizing synthetic aperture radar (SAR) images and nautical radar-image sequences. The approach to detect wave groups is based on the detection of the wave envelope. It is assumed that the sea surface elevation can be treated as a Gaussian process. The method is applied to SAR images acquired by the European satellite ERS-1 and to radar-image sequences recorded by tower-based nautical radars. In contrast to 1D sensors like buoys the SAR records an image and gives therefore a 2D description of the sea surface by measuring the radar backscatter from the sea surface. The measurements taken by a nautical radar provide the possibility to record time series of images and therefore to get a 3D description of the sea surface. Radar-image sequences are acquired by recording the spatial and temporal evolution of the sea surface backscatter, which is modulated through the surface wave field. Nautical radar-image sequences allow to detect wave groups within a time span that makes it possible to start safety programs before the group reaches a platform. The existing data sets are exploited with respect to the recognition of extreme wave events.
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Wu, Zhongyou, and Yaoyu Li. "Real-Time Optimization of Wind Farm Energy Capture With Delay Compensated Nested-Loop Extremum Seeking Control." In ASME 2017 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/dscc2017-5262.
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Real-time optimization of wind farm energy capture for below rated wind speed is critical for reducing the levelized cost of energy (LCOE). Performance of model based control and optimization techniques can be significantly limited by the difficulty in obtaining accurate turbine and farm models in field operation, as well as the prohibitive cost for accurate wind measurements. The Nested-Loop Extremum Seeking Control (NLESC), recently proposed as a model free method has demonstrated its great potential in wind farm energy capture optimization. However, a major limitation of previous work is the slow convergence, for which a primary cause is the low dither frequencies used by upwind turbines, primarily due to wake propagation delay through the turbine array. In this study, NLESC is enhanced with the predictor based delay compensation proposed by Oliveira and Krstic [1], which allows the use of higher dither frequencies for upwind turbines. The convergence speed can thus be improved, increasing the energy capture consequently. Simulation study is performed for a cascaded three-turbine array using the SimWindFarm platform. Simulation results show the improved energy capture of the wind turbine array under smooth and turbulent wind conditions, even up to 10% turbulence intensity. The impact of the proposed optimization methods on the fatigue loads of wind turbine structures is also evaluated.
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Beeson, Lisa A., and George A. Schott. "Low Frequency Noise Considerations for Combustion Turbine Projects." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-140.
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Combustion turbine projects have become a popular choice for providing a clean and efficient source of electricity. However, since combustion turbines generally produce low frequency sound energy, special siting considerations should be evaluated to minimize the potential for impacts on sensitive receptors, such as residences, churches, hospitals, and schools. For successful siting of combustion turbine projects near sensitive receptors, it is necessary to incorporate noise control features into plant designs to reduce not only audible noise but also noise at frequencies which are even lower than the human ear can perceive. These extremely low frequencies can rattle walls and windows, causing pressure pulsations which may be perceived by some people, or vibration of small objects inside houses and other structures. Even “quiet” plants which include extensive noise control features may still result in perceptible low frequency noise due to the relative difficulty of attenuating low frequency sound energy. Noise attenuation options are discussed, including active, passive, and reactive technologies, along with the impacts associated with each type of design. Guidelines for siting combustion turbine power generation facilities near sensitive receptors are presented, to enable development of projects which not only meet applicable noise requirements, but also reduce the potential for community complaints.
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Hanno, Reckmann, Heinisch Dennis, Herbig Christian, Hohl Andreas, Peters Volker, and Krueger Sven. "New Generation Rotary Steerable Bottom Hole Assembly for Extreme Drilling Dynamics Conditions." In ADIPEC. SPE, 2022. http://dx.doi.org/10.2118/211788-ms.
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Abstract The industry trend to drill wells faster and with greater precision in hard, dense, difficult to drill formations results in challenging drilling dynamics conditions. In particular, high-frequency torsional oscillations (HFTO) occur in such drilling situations. This kind of vibration creates loads that can quickly lead to fatigue or electronics damage, which translates into non-productive time (NPT) and cost. There have been different approaches proposed to mitigate vibrations or design tools that withstand these vibrations. This paper presents a new generation rotary steerable bottom hole assembly (BHA) system specifically designed for extreme drilling dynamics conditions. Field tests and field applications demonstrate the new level of performance. The cutting process in hard and dense formations triggers the occurrence of HFTO. In the design process, emphasis is on fatigue performance to optimize tools and their components, particularly with respect to torsional resonances in the HFTO frequency range of 100 Hz to 500 Hz. General reduction of vibration loads uses integration of mechanical isolation and damping principles with a rugged design. Different design options are first modeled, simulated, and optimized. Tests validate the best design against vibration requirements to prove robustness for maximum durability. New features of the tools like downhole frequency analysis and load measurements support the pre-well BHA optimization and the real-time drilling optimization. New procedures for tool management and BHA planning use dynamics field data consequently captured and systematically evaluated with big data analytics methods. The modeled HFTO frequencies and amplitudes agree very well with field measurements. Modeling and field tests show that the implementation of mechanical isolation concepts can protect portions of the BHA from harmful HFTO vibrations. The introduction of mechanical damping elements can reduce the occurrence of HFTO up to complete suppression, while maintaining high performance drilling parameters. Compared to previous tool generations, the new system specifically considers HFTO during design and is thus better able to withstand this kind of vibration. The design of new thread connections increases their (load) capacity over standard thread connections. The implementation of multi-chip module (MCM) electronics with the tools significantly extends the electronic lifetime and durability. A simulation system particularly developed to optimize BHA configurations in the pre-job planning phase with respect to HFTO, analyzes various configurations to select the best fit-for-purposes BHAs. Case studies demonstrate increased reliability, utilization, and footage (more than a mile-a-day drilling), making a significant difference in the rotary steerable (RSS) market. New mechanical isolation, damping, and MCM concepts, complemented by novel real-time downhole measurement capabilities, enable an effective, holistic approach to overcome critical drilling situations and react on HFTO events. This all new, relentlessly iterated design demonstrates superior reliability and drilling performance, maximizing customer value.
Reports on the topic "Extreme event frequencies"
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Weber, A. H. Tornado, Maximum Wind Gust, and Extreme Rainfall Event Recurrence Frequencies at the Savannah River Site. Office of Scientific and Technical Information (OSTI), December 1998. http://dx.doi.org/10.2172/4876.
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