Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Multivariate analysis of extreme metocean conditions for offshore wind turbines
Highlights New multivariate method to assess extreme metocean conditions based on extreme value data. Method useful for designing offshore wind turbines for the extreme storm. Peak spectral period is important in the design of offshore wind turbines.
Abstract Most offshore wind turbines (OWTs) are designed according to the international standard IEC 61400-3 which requires consideration of several design load cases under 50-year extreme storm conditions during which the wind turbine is not operational (i.e. the rotor is parked and blades are feathered). Each of these load cases depends on combinations of at least three jointly distributed metocean parameters, the mean wind speed, the significant wave height, and the peak spectral period. In practice, these variables are commonly estimated for the 50-year extreme storm using a simple but coarse method, wherein 50-year values of wind speed and wave height are calculated independently and combined with a range of peak spectral period conditioned on the 50-year wave height. The IEC Standard does not provide detailed guidance on how to calculate the appropriate range of peak spectral period. Given the varying correlation of these parameters from site-to-site, this approach is clearly an approximation which is assumed to overestimate structural loads since wind and wave are combined without regard to their correlation. In this paper, we introduce an alternative multivariate method for assessing extreme storm conditions. The method is based on the Nataf model and the Inverse First Order Reliability Method (IFORM) and uses measurements or hindcasts of wind speed, wave height and peak spectral period to estimate an environmental surface which defines combinations of these parameters with a particular recurrence period. The method is illustrated using three sites along the U.S. Atlantic coast near Maine, Delaware and Georgia. Mudline moments are calculated using this new multivariate method for a hypothetical 5MW OWT supported by a monopile and compared with mudline moments calculated using simpler univariate approaches. The results of the comparison highlight the importance of selecting an appropriate range of the peak spectral period when using the simpler univariate approaches.
Multivariate analysis of extreme metocean conditions for offshore wind turbines
Highlights New multivariate method to assess extreme metocean conditions based on extreme value data. Method useful for designing offshore wind turbines for the extreme storm. Peak spectral period is important in the design of offshore wind turbines.
Abstract Most offshore wind turbines (OWTs) are designed according to the international standard IEC 61400-3 which requires consideration of several design load cases under 50-year extreme storm conditions during which the wind turbine is not operational (i.e. the rotor is parked and blades are feathered). Each of these load cases depends on combinations of at least three jointly distributed metocean parameters, the mean wind speed, the significant wave height, and the peak spectral period. In practice, these variables are commonly estimated for the 50-year extreme storm using a simple but coarse method, wherein 50-year values of wind speed and wave height are calculated independently and combined with a range of peak spectral period conditioned on the 50-year wave height. The IEC Standard does not provide detailed guidance on how to calculate the appropriate range of peak spectral period. Given the varying correlation of these parameters from site-to-site, this approach is clearly an approximation which is assumed to overestimate structural loads since wind and wave are combined without regard to their correlation. In this paper, we introduce an alternative multivariate method for assessing extreme storm conditions. The method is based on the Nataf model and the Inverse First Order Reliability Method (IFORM) and uses measurements or hindcasts of wind speed, wave height and peak spectral period to estimate an environmental surface which defines combinations of these parameters with a particular recurrence period. The method is illustrated using three sites along the U.S. Atlantic coast near Maine, Delaware and Georgia. Mudline moments are calculated using this new multivariate method for a hypothetical 5MW OWT supported by a monopile and compared with mudline moments calculated using simpler univariate approaches. The results of the comparison highlight the importance of selecting an appropriate range of the peak spectral period when using the simpler univariate approaches.
Multivariate analysis of extreme metocean conditions for offshore wind turbines
Valamanesh, V. (Autor:in) / Myers, A.T. (Autor:in) / Arwade, S.R. (Autor:in)
Structural Safety ; 55 ; 60-69
18.03.2015
10 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
OWT , offshore wind turbine , <italic>V</italic> , hourly mean wind speed at elevation of 5<hsp></hsp>m above sea surface , <italic>H</italic> <inf>s</inf> , significant wave height , <italic>T</italic> <inf>p</inf> , wave peak spectral period , IFORM , Inverse First Order Reliability Method , NOAA , National Oceanic and Atmospheric Administration (USA) , NREL , National Renewable Energy Laboratory (USA) , R-LOS , R Largest Order Statistics , <italic>R</italic> , annual rate of occurrence , <italic>t</italic> <inf>lag</inf> , time lag between the measurement of maximum <italic>V</italic> and the maximum <italic>H</italic> <inf>s</inf> during an extreme event , CDF , cumulative distribution function , GEV , generalized extreme value , <italic>μ</italic> , location parameter of GEV distribution , <italic>σ</italic> , scale parameter of GEV distribution , <italic>ξ</italic> , shape parameter of GEV distribution , <italic>x</italic> <inf>N</inf> , magnitude of a variable <italic>x</italic> with a recurrence period <italic>N</italic>, e.g. <italic>V</italic> <inf>50</inf> is the 50-year wind speed , <italic>g</italic> , gravitational acceleration , <italic>T</italic> , extreme wave period , <italic>N</italic> , recurrence period , <italic>β</italic> , Radius of the sphere in standard uncorrelated normal space used in IFORM , <italic>Φ</italic> , cumulative distribution function for standard normal distribution , Multivariate Metocean Hazard , Extreme value analysis , Offshore wind turbine
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