Interest in water wave power generation, a promising source of renewable energy, is increasing. Numerous types of wave energy converters (WECs) have been designed to transform wave energy into electricity. In this study, we focus on heaving point absorbers (HPAs) of the Wavestar type, which consist of multiple floats connected to a bottom-fixed ocean structure by structural arms and hinges. Each float moves up and down due to wave forces and produces electricity using the hydraulic power take-off (PTO) system connected directly to the float. A numerical procedure using the three-dimensional augmented formulation was developed to calculate the rotational motion of the float. The frequency-dependent coefficients were calculated using the hydrodynamic solver WAMIT. The nonlinear Froude–Krylov and hydrostatic forces were considered. For the environmental conditions, the wave data of four nearshore areas in Korea, obtained from the Korea Meteorological Administration (KMA), were used. Under the given environmental conditions, Buan was found to be the most suitable area among the locations selected for installing a Wavestar-type WEC without considering installation and maintenance costs.
This study is a structural analysis of slewing bearings for wind turbines. The ball of a bearing delivers load while making contact with raceways of the inner and outer rings. To facilitate stress analysis of the slewing bearing, which has more balls than other types of bearing, the balls were converted into spring elements. Considering the shape of contact between balls and raceways, one, two, and three spring elements were introduced. Global finite element analysis of the bearing, with balls as spring elements, showed that the bearing experienced different degrees of deformation depending on the number of springs. Using the bearing deformation obtained from the global analysis, cut boundary constraint was applied for local contact analysis of balls and raceways. The contact stress between balls and raceways showed that more uniform stress could be achieved by increasing the number of springs.
A fast, reliable and optimized numerical procedure of the hydrodynamic response analysis of a slender-body structure is presented. With this method, the dynamic response and reliability of a six-leg jack-up-type wind turbine installation vessel under various environmental conditions is analyzed. The modi¯ed Morison equation is used to calculate the wave and wind-driven current excitation forces on the slender-body members. The Det Norske Veritas (DNV) rule-based formula is used to calculate the wind loads acting on the superstructure of the jack-up leg. From the modal analysis, the natural period and standardized displacement of the structure are determined. The Newmark-beta time-integration method is used to solve the equation of motion generating the time-varying dynamic responses of the structure. A parametric study is carried out for various current velocities and wind speeds. In addition, a reliability analysis is conducted to predict the e®ects of uncertainty of the wave period and wave height on the safety of structural design, using the reliability index to indicate the reliability of the dynamic response on the critical structural members.
Energy consumption is increasing rapidly with population growth and technological development. In particular, the excessive development and use of fossil energy cause a global pollution problem, and excessive greenhouse gas emissions, including carbon dioxide, leads to global warming and various environmental problems. Therefore, it is essential to develop technologies for renewable energy, which is a sustainable and eco-friendly energy source (Muliawan et al., 2013;Ullah et al., 2020).Among renewable energy sources, offshore wind energy, wave energy, and current energy, which are representative offshore energy sources, require future-oriented and continuous technology development. In particular, many technologies have been developed for offshore wind energy because it has benefits in terms of wind homogeneity and speed as well as the installation location compared to onshore wind energy (land-based wind energy). Large-scale commercial power generation is also possible because it is free of the restrictions of many wind turbine installation spaces and noise (Bae and Kim, 2013). As offshore wind turbine technology has grown into a major energy source worldwide, including in Europe, many studies have been conducted to increase the economic feasibility of offshore wind turbine platforms (Global Wind Energy Council Global, 2019).A combined wind-wave energy platform in which wave energy converters (WECs) are attached to floating wind turbines has been reported as one way to increase the economic feasibility of floating offshore wind turbine (FOWT) in many studies. The combined energy platform is based on the typical characteristics of ocean environments: relatively high waves accompany high wind speeds. Moreover, using two energy sources makes it possible to reduce the energy extraction variability of a single offshore wind turbine and increase the economic effects (Kim et al., 2015). As a combined wind-wave energy platform type, there is a combined platform model that combines the OC4 model (Robertson et al., 2014), a semi-submersible wind turbine structure disclosed by the National Renewable Energy Lab (NREL) in the United States, with Wavestar-type WECs (Hansen et al., 2013). Si et al. (2021
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.