1,721,297 research outputs found
A reduced order model for the simulation of mooring cable dynamics
No full textIn this paper the feasibility of a reduced order model (ROM) for thehydroelastic analysis of mooring lines is analysed. The local response of a piece of cableis studied through high delity uid structure interaction (FSI) simulations. The high delity model is built by coupling a computational structural dynamics (CSD) solver witha computational uid dynamics (CFD) solver using the approach of software components.The ROM is designed in such a way that it can be added to any beam element from astandard CSD solver. From the outside only the beam degrees of freedoms (DOFs) canbe seen, the ROM DOFs are all internal.The local response of the cable is analysed andthe feasibility of the ROM is discusse
The role of the nonlinear wave kinematics on the global responses of an OWT in parked and operating conditions
No full textCoupled dynamic simulations of offshore wind turbines using linear, weakly and fully nonlinear wave models: the limitations of the second-order wave theory
No full textThe present work investigates the dynamic response of a fixed–bottom offshore wind turbine subjected to the combined wind-waves action employing different nonlinear wave kinematic models. Linear, 2nd-order and fully nonlinear models are imple- mented in the hydrodynamic module of a global hydro-aero-servo-elastic solver. All the wave models are based on the potential flow assumption. A first study of the structural response is performed in regular waves with increasing steepness considering the turbine both in parked condition and in power production. A more realistic simulation is then carried out with irregular waves and turbulent wind. Hydrodynamic loads associated to the three wave models are coupled with aerodynamic loads acting on the rotor of a 5-MW wind turbine. Hydro-aero-elastic calculations are performed using the NREL software FAST. The paper shows that from wave steep- ness ka = 0.1 on the 2nd-order model becomes inaccurate. It underestimates the structural loads as well as the resonant oscillations of the tower caused by the higher-order components
A comparative study about the effects of linear, weakly and fully nonlinear wave models on the dynamic response of offshore wind turbines
No full textThe present work aims at comparing the dynamic response of a fixed–bottom offshore wind turbine subjected to the combined wind–waves action employing different nonlinear irregular wave kinematic models. To this purpose, linear, second–order and fully nonlinear models are implemented in the hydrodynamic module of a global hydro-aero-elastic solver. All the wave models are based on the potential flow assumption. The fully nonlinear wave kinematics is reproduced both on the full simulation time and, in order to save com- putational time, only on some space-time subdomains within a domain decomposition strategy. This approach permits achieving a much higher accuracy in the assessment of the hydrodynamic loads keeping the global computational effort similar to the one required by linear or weakly nonlinear models. The paper represents a preliminary investigation aimed at establishing to what extend the second–order wave model can efficiently capture the system response even when the system is exposed to moderate sea states. Moreover, a comparison between the four wave models seems to reveal that some resonant oscillations of the tower are triggered by nonlinear components higher than the 2nd–order. Hydrodynamic loads associated to the four wave models are coupled with aerodynamic loads acting on the rotor of a 5-MW wind turbine. Hydro-aero-elastic calculations are performed using the NREL open-source software FAST
Coupled dynamic simulations of offshore wind turbines: influence of wave modeling on the fatigue load assessment
No full textNonlinear waves influence to a large extent the coupled hydro-aero-elastic response of offshore wind turbines. Higher-order contributions in the hydrodynamic forcing are responsible for resonant springing-like vibrations of the tower causing an increase of stress cycles and amplitudes. The present study investigates the effects of these amplifications in terms of fatigue load. Equivalent fatigue loads are estimated by means of both time and frequency domain methods. A comparison between linear, second-order and fully nonlinear wave models is proposed and it is shown that the weakly nonlinear model, widely used in the state-of-the-art simulations, may significantly underestimate the actual fatigue load. Hydrodynamic loads associated with the different wave models are coupled with aerodynamic loads acting on the rotor of a 5-MW wind turbine (fixed-bottom)
A reduced order model for the simulation of mooring cable dynamics
Full text linkIn this paper the feasibility of a reduced order model (ROM) for the
hydroelastic analysis of mooring lines is analysed. The local response of a piece of cable is
studied through high fidelity fluid structure interaction (FSI) simulations. The high
fidelity model is built by coupling a computational structural dynamics (CSD) solver with a
computational fluid dynamics (CFD) solver using the approach of software components. The ROM is
designed in such a way that it can be added to any beam element from a standard CSD
solver. From the outside only the beam degrees of freedoms (DOFs) can be seen, the ROM DOFs are
all internal.The local response of the cable is analysed and
the feasibility of the ROM is discusse
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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