Stochastic analysis of TLP’s tendons Jane V. V. Fernandes 1 • Luis V. S. Sagrilo 2 • Paulo Mauricio Videiro 1 • Denis A. Liang 1 Received: 12 December 2015 / Accepted: 1 September 2016 / Published online: 6 October 2016 Ó Sociedade Brasileira de Engenharia Naval 2016 Abstract This paper deals with the analysis of 100-year extreme von Mises stresses in the tendons of a TLP designed to operate in 1200 m water depth. A simplified joint probabilistic model for the environmental parameters considering the wind velocity correlated to the significant wave height and a fixed current profile is used. The fol- lowing methodologies are compared: regular deterministic design wave, irregular design wave (considering both extreme sea state and sea states located on the extreme environmental contour) and long-term extreme response approach. The interpolation procedure employed to reduce the computational burden and complexity of the long-term integration is also described. Keywords TLP’s tendons  Long-term extreme response  Environmental contour 1 Introduction Among several alternatives to oil exploitation in deep water, the tension-leg platform (TLP) concept shows up as a practicable structural option and is already being used in various locations worldwide. There are a lot of methods available in literature for the design of an offshore structure with a dynamic behavior, such as a TLP, under the environmental conditions it is subjected to at the sea. It is recognized that the most com- plete methodology to properly evaluate the response of such structures under the stochastic loading coming from the environmental actions is the long-term response method- ology [7, 13, 15]. This methodology estimates the extreme long-term response of the structure by integrating the short- term responses over all sea states expected in the long run for the location where it is installed. Although it is recom- mended in some modern design standards [5], due to its higher degree of complexity, this is not a design method- ology frequently used in the design practice. In the everyday design practice, designers try to use other less complex methods for extreme response estimation of such structures. The simpler design methodology for extreme load effects estimation consists of a deterministic dynamic analysis using an extreme regular wave. This methodology is called herein ‘‘design wave approach.’’ Increasing complexity, there is a method called ‘‘design storm approach.’’ It is based on stochastic dynamic analyses (or irregular wave analysis) using some extreme sea state parameters and the associated wind and current parameters. The extreme sea state may be only, for example, the 100-year sea state or a set of 100-year sea states defined according to the methodology of the extreme environmental contours [17]. In contrast to the long-term response analysis, which focuses on the extreme response, the rationale behind these other methodologies is that in some way the extreme response is associated with the extreme environmental condition. This rationale sometimes cannot be true for a compliant offshore structure. In practical terms, there is not a simple way of inferring the degree of conservatism (or non-conservatism) implied in the design approaches based on extreme environmental conditions. This paper presents a contribution on this topic & Luis V. S. Sagrilo sagrilo@coc.ufrj.br Jane V. V. Fernandes janevolotao@petrobras.com.br 1 PETROBRAS S.A., Rio de Janeiro, RJ, Brazil 2 COPPE/Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil 123 Mar Syst Ocean Technol (2016) 11:68–75 DOI 10.1007/s40868-016-0018-7