A new method for structural safety and reliability analysis of offshore wind turbines

With the motivation to overcome the shortcomings of the Rosenblatt Inverse-First-Order Reliability environmental contour method, in this study, the use of bivariate kernel density estimation with smoothed cross-validation bandwidth selection method is proposed for generating more accurate environmental contour lines. The environmental contour lines at a chosen offshore site obtained by using the proposed new method were compared with those obtained by using the Rosenblatt Inverse-First-Order Reliability environmental contour method, and the accuracy and effectiveness of the proposed new method have been fully and clearly substantiated. Next, the 50-year extreme structural dynamic responses of a monopile-supported 5MW offshore wind turbine installed at this chosen offshore site based on the proposed new method and the Rosenblatt Inverse-First-Order Reliability environmental contour approach were calculated. Analyzing the calculating results, it can be found that the 50-year extreme fore-aft shear force value based on the 50-year extreme sea state obtained using the proposed new method is 78.9% larger than the corresponding value obtained based on the Rosenblatt Inverse-First-Order Reliability contour method. The calculation results in this paper were further systematically analyzed and compared, and the necessity and importance of using more realistic environmental contour lines (such as those generated using the proposed new method) have been finally highlighted.

Dynamic recovery actions in multi-objective liner shipping service with buffer times

This paper investigates the dynamic recovery policies for liner shipping service with the consideration of buffer time allocation and uncertainties. We aim to allocate the buffer time at the tactical level and then determine the optimal policy, including speed optimization strategy, port skipping and acceleration rate choice, for recovering from disruptions due to various uncertainties or random adverse events, which cause vessel delays. To achieve this, we attempt to obtain the optimal balance among economic, environmental and service-reliable objectives. A novel mathematical formulation is introduced to solve the robust vessel scheduling problem with short- and long-term decisions. Furthermore, we propose and test two heuristics to solve the proposed model. Experiments on the container liner shipping service show the validity of the model and some managerial insights are gained from them.