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Numerical modeling of floating vertical axis wind turbines for offshore renewable energy generation
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A novel optimisation process for static structural finite element analysis of offshore wind turbine floating foundations
Full text linkThe study presents a novel optimisation process for structural finite
element analysis for a floating foundation for offshore wind turbines.
The methodology is based on Ansys Pymechanical scripting for a
semisubmersible platform. The structural analysis includes hydrostatic
pressure, static aerodynamic thrust and turbine weight, and mooring
loads. The optimisation is single objective, aiming to reduce mass and
constrained by yield stress and buckling instability. The results show the
capabilities of the methodology to achieve an optimal configuration of
thicknesses and dimension of internal stiffeners
Floating Vertical Axis Wind Turbines for offshore applications among potentialities and challenges: A review
Full text linkAmong the primary uses of Vertical Axis Wind Turbines (VAWTs) are small-scale applications, such as electricity generation in urban areas or isolated contexts, which are not grid-connected. However, a promising field of application for VAWTs to be investigated concerns floating offshore applications, where the more consolidated technologies based on HAWTs face significant challenges due to the harsh environment. The purpose of this study is to review the main floating VAWT concepts developed over the last few years and those currently under development, focusing on the projects and analysing the experimental prototypes and small-scale demonstrators. The main advantages of VAWTs compared to HAWTs are elaborated and presented: among the main ones is the more cost-effective maintenance due to the arrangement of the rotor nacelle assembly at the base of the VAWT, the increased static stability, which allows to reduce the mass of the floating foundation or to support a larger turbine, the reduced aerodynamic losses which allow turbines to be installed closer together and require a small installation area. A particular focus is made on the most urgent needs that demand to be addressed for the development of VAWTs, like the lack of experimental data and the installation of a multi-MW demonstrator to corroborate the technology reliability and challenges, such as the power upscale, the fatigue damage and mooring lines loads. Among the possible floating applications investigated is the energy supply for small isolated islands or offshore installations, like oil and gas platforms or fish farms
Fatigue assessment of a new concept for a floating barge with pendulum for offshore wind turbines in MOST
Full text linkAmong floating foundations for offshore wind turbines, the barge is considered one of the most cost-effective platforms, owing to its ease of manufacturing, transport, and installation. However, the barge platform is susceptible to wave-induced stress due to its extensive waterplane area, potentially leading to fatigue in critical structural components such as the platform, tower, nacelle components and moorings. This paper delves into the prospect of mitigating fatigue damage in the barge concept by introducing a pendulum ballast, which can be installed at the offshore site using polyester ropes. The primary focus of this research is the assessment of the 'barge-pendulum' concept, aimed at reducing load cycles that could lead to fatigue failure, with a specific emphasis on the tower base as a representative indicator of device damage. The analysis is conducted using MOST, a time-domain simulation code developed in Matlab-Simscape environment. The findings show that the barge-pendulum concept has a poorer performance in terms of fatigue life, due to the increased sensitivity to wave forces
Mooring System Design and Analysis for a Floating Offshore Wind Turbine in Pantelleria
Full text linkThe mooring system plays a key role in a floating offshore wind turbine: it connects the floating structure to its anchor on the seabed and it is designed to prevent the platform from drifting under the action of wind, waves and currents. The layout of the mooring system is strictly connected to the installation site: in the first place it depends on the bathymetry and the type of seabed which conditions the type of anchor that can be used; secondly by the wind and waves loads in extreme sea states.
To properly design the mooring system, three different configurations are proposed and discussed, respectively
adapting catenary, taut leg and semi-taut methodologies for a floating offshore wind turbine located near the island of Pantelleria, in Sicily. For each configuration, the Hexafloat foundation, developed by Saipem, is considered. Important design constraints such as how large the nominal sizes are, how long the mooring lines are, how far the anchor points are located, are demonstrated in detail. The material used will range from steel chains and wires to polyester ropes, to grant economically viable solutions
Development of a floating Vertical Axis Wind Turbine for the Mediterranean Sea
Full text linkDifferently from Horizontal Axis Wind Turbines (HAWTs), which are the reference technologies in the wind market for their reliability and maturity, Vertical Axis Wind Turbine (VAWT) applications are related to small-scale contexts, such as providing electricity in isolated areas or urban settings. Consequently, the capacity of VAWTs results significantly lower than the order of megawatts and does not exceed a few tens of kilowatts. A promising field of application for VAWTs is the floating offshore: among the main advantages there are an increased static stability, by placing the rotor-nacelle assembly (RNA) at the base of the VAWT and reduced operational and maintenance (O&M) costs. Moreover, the different wake dynamics allows to reduce the aerodynamic losses, allowing closer turbine installations. However, to be competitive with floating HAWTs, it is necessary to have numerical models for the analysis and simulation of multi-megawatt VAWTs. This paper aims to introduce a time domain model of a floating vertical axis wind turbine, developed within the Matlab-Simscape environment. The model comprises an aerodynamics module, based on Double Multiple Stream Tube theory while hydrodynamics is modelled using WEC-Sim. A case study, involving a Darrieus H-rotor VAWT tested in the Mediterranean Sea and supported by a semisub foundation, the OC4-DeepCwind, is introduced. The results obtained are compared with those from QBlade, a software developed by TU Berlin, demonstrating a good agreement between the two codes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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