No abstract

This paper proposes a model considering the wave‐current interactions in dynamic analyses of floating offshore wind turbines (FOWTs) and investigates the interaction effects on the FOWT responses. Waves when traveling on current are affected by the current, leading to frequency shift and shape modification. To include such interactions in FOWT analysis, which has not been considered by the researchers till date, a nonlinear hydrodynamic model for multicable mooring systems is presented that is able to consider the cable geometric nonlinearity, seabed contact, and the current effect. The mooring model is then coupled with a spar‐type FOWT model that handles the structural dynamics of turbine blades and tower, aerodynamics of the wind‐blade interaction, and wave‐current effects on the spar. The analytical wave‐current interaction model based on Airy theory considering the current effect is used in the computation of flow velocity and acceleration. Numerical studies are then carried out based on the NREL offshore 5‐MW baseline wind turbine supported on top of the OC3‐Hywind spar buoy. Two cases, (1) when the currents are favorable and (2) when the currents are adverse, are examined. Differences of up to 15% have been observed by comparing the cable fairlead tension obtained excluding and including the wave‐current interactions. In particular, when irregular waves interact with adverse current, a simple superposition treatment of the wave and the current effects seems to underestimate the spar motion and the cable fairlead tension. This indicates that the wave‐current interaction is an important aspect and is needed to be considered in FOWT analysis.

received the B. Sc. (Eng.) degree from Chang Sha University of Electric Power, Changsha, China, in 2002. Currently, she is a Ph.D. candidate at Zhejiang University, China. Her major research interests are distributed generation and electricity market.

Although the probability of vehicle collision with bridge piers is relatively low, it may cause the pier to fracture and even the entire bridge to collapse, resulting in casualties and huge economic losses. Therefore, bridge piers should be properly designed against vehicle collision. This paper aims to make a state-of-the-art review of the research on vehicle collision with bridge piers, to summarize the achievements and current limitations in this field, and to give some suggestions for future research. It is organized within a framework of performance-based design, which is divided into four types of problems, that is, hazard analysis, structural analysis, damage analysis, and loss analysis. Studies show that reinforced concrete (RC) piers under vehicle impact generally exhibit three damage modes, that is, local damage, shear damage, and flexural damage. When a large truck hits a pier, the engine and container (cargo) may contribute to a two-stage impact characteristic, which has a great influence on the response and damage of the pier. The vehicular impact (force) models and nonlinear response models of RC members under impact loads have been developed respectively, which can be combined to quickly analyze the nonlinear response of RC piers under vehicle impact. Deformation-based methods should be developed to quantify the damage level of RC piers under different damage modes. Current codes still mainly adopt the equivalent static force design method, but some provisions regarding probabilistic (reliability) analysis have appeared. More attention should be paid to the statistical analysis of roadside crashes and vehicle-related parameters in order to obtain a more realistic probabilistic analysis model, and further establish a performance-based design method for RC piers subjected to vehicle collision.