Estimating Design Loads with Environmental Contour Approach Using Copulas for an Offshore Jacket Platform
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Estimating Design Loads with Environmental Contour Approach Using Copulas for an Offshore Jacket Platform ZHAO Yuliang1), LIU Dahui2), and DONG Sheng1), * 1) College of Engineering, Ocean University of China, Qingdao 266100, China 2) CIMC Offshore Engineering Institute Co., Ltd., Yantai 264670, China (Received December 22, 2019; revised March 23, 2020; accepted April 12, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract Jacket-type offshore platforms are widely used for oil, gas field, and energy development in shallow water. The design of a jacket structure is highly dependent on target environmental variables. This study focuses on a strategy to estimate design loads for offshore jacket structures based on an environmental contour approach. In addition to the popular conditional distribution model, various classes of bivariate copulas are adopted to construct joint distributions of environmental variables. Analytical formulations of environmental contours based on various models are presented and discussed in this study. The design loads are examined by dynamic response analysis of jacket platform. Results suggest that the conditional model is not recommended for use in estimating design loads in sampling locations due to poor fitting results. Independent copula produces conservative design loads and the extreme response obtained using the conditional model are smaller than those determined by copulas. The suitability of a model for contour construction varies with the origin of wave data. This study provides a reference for the design load estimation of jacket structures and offers an alternative procedure to determine the design criteria for offshore structures. Key words method
design loads; jacket platform; joint probability distribution; conditional model; copula theory; environmental contour
1 Introduction Jacket-type platform, a common structural system used in shallow water, plays a crucial role in offshore oil and gas development. In recent years, this type of structure has been widely employed as a supporting structure for offshore wind turbines (Wei et al., 2016). Alessi et al. (2019) investigated the possibility of converting actual structures for gas extraction into offshore platforms for wind turbine towers. Compared with land-based steel jacket structures, water-based jacket structures face more complex environmental conditions, such as wind, waves, currents, ice, and earthquakes. Vahdati et al. (2020) conducted an experimental study to investigate combined solutions to reduce scouring around complex foundations. Moreover, due to the strong hydrodynamic interaction effects faced by water-based jacket platforms during their service lifetime, dynamic response analysis for such platforms is essential in the design stage (Tian et al., 2019). Mourão et al. (2020) performed a combined fatigue damage evaluation using local damage parameters for an offshore jacket-type structure. Meng et al. (2020) conducted reliability-based optimization for offshore structu
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