This paper investigates the dynamic response of a fully nonlinear model of a DeepCWind floating offshore wind turbine (FOWT) after one of its three-catenary mooring systems is broken. The drift area of the platform, pitch motion of the wind turbine, and tension on the two ends of the mooring line are the main dynamic response foci; in addition, a single mathematical formula is provided in this study to predict the maximum drift in surge direction. After the platform reaches the new equilibrium position maintained by the remaining two mooring lines, the tower pitch exceeds 20 degrees. The tension change is closely related to the drift motion, necessitating an increase in the minimum breaking load (MBL) of the mooring line components. The mathematical forecast of the maximum surge shows good agreement with the numerical results, even with different water depths

The objective of this paper was to present the modeling and optimization of mooring lines for floating offshore wind turbines (FOWT) located in various water depths from 50 m to 100 m in Taiwan western offshore areas. A semi-submersible floating wind turbine system is considered based on Offshore Code Comparison Collaborative Continuation (OC4) DeepCwind platform with the National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine. The mooring lines proposed consist of a catenary mooring with studless chains. Three nominal sizes of the mooring chain links are taken into account with diameters of 95 mm, 115 mm and 135 mm. According to this configuration, a total of five mooring designs for different water depths (i.e., 50 m, 60 m, 70 m, 80 m, 100 m) are analyzed according to the rules and regulations of the two certification institutions, Det Norske Veritas (DNV) and American Petroleum Institute (API). Considering ultimate limit state (ULS), fatigue limit state (FLS) and maximum operating sea state (MOSS) based on a typhoon with a 50-year return period and current with a 10-year return period, 25-year design life, as well as 1-year return period, respectively, long-term predictions of breaking strength, fatigue and stability are performed. The software OrcaFlex version 10.3 d is used to simulate and design the mooring lines. The obtained results show that the shallow mooring design of 50 m water depth case presents the heaviest chains among the other water depths, increasing their mooring costs. On the other hand, the 100 m water design has much longer mooring lines, making this parameter the cost driving one. Thus, the minimum mooring cost range is from 60 m to 80 m water depth.

A solar photovoltaic system consists of tilted panels and is prone to extreme wind loads during hurricanes or typhoons. To ensure the proper functioning of the system, it is important to determine its aerodynamic characteristics. Offshore photovoltaic (PV) systems have been developed in recent years. Wind loads are associated with wind, wave climates, and tidal regimes. In this study, the orientation of a single panel is adjusted to different angles of tilt (10°–80°) and angles of incidence for wind (0°–180°) that are pertinent to offshore PV panels. The critical wind loads on a tilted panel are observed at lower angles of incidence for the wind, when the angle of tilt for the panel is greater than 30°.

In this paper, a piezoelectric wave-energy converter (PWEC), consisting of a buoy, a frequency up-conversion mechanism, and a piezoelectric power-generator component, is developed. The frequency up-conversion mechanism consists of a gear train and geared-linkage mechanism, which converted lower frequencies of wave motion into higher frequencies of mechanical motion. The slider had a six-period displacement compared to the wave motion and was used to excite the piezoelectric power-generation component. Therefore, the operating frequency of the piezoelectric power-generation component was six times the frequency of the wave motion. The developed, flexible piezoelectric composite films of the generator component were used to generate electrical voltage. The piezoelectric film was composed of a copper/nickel foil as the substrate, lead–zirconium–titanium (PZT) material as the piezoelectric layer, and silver material as an upper-electrode layer. The sol-gel process was used to fabricate the PZT layer. The developed PWEC was tested in the wave flume at the Tainan Hydraulics Laboratory, Taiwan (THL). The maximum height and the minimum period were set to 100 mm and 1 s, respectively. The maximum voltage of the measured value was 2.8 V. The root-mean-square (RMS) voltage was 824 mV, which was measured through connection to an external 495 kΩ resistive load. The average electric power was 1.37 μW.