1,721,088 research outputs found
Towards efficient control synthesis for nonlinear wave energy conversion systems: impedance-matching meets the spectral-domain
Full text linkExisting studies within the literature that focus on designing parametric energy-maximizing controllers for Wave Energy Converter (WEC) systems predominantly rely on the impedance-matching (IM) principle, originally developed for linear time-invariant systems. Alternatively, iterative optimization routines are commonly employed for nonlinear WECs. However, these approaches often face a trade-off between effectiveness in maximizing energy extraction and computational efficiency. To address this limitation, this study proposes a computationally efficient controller tuning method for analogous synthesis in the case of nonlinear WECs. The proposed approach combines a statistical linearization technique known as spectral-domain modeling with the IM principle, to synthesize a Proportional–Integrative (PI) controller for a nonlinear WEC. Furthermore, a comparison is performed with two other synthesis methods: one based on a standard (i.e. linear) frequency-domain representation of the WEC that incorporates the IM principle, and the other employing a gradient-free optimization routine applied to the nonlinear time-domain model of the WEC for PI parameter tuning through exhaustive numerical search. A discussion on the effectiveness of each tuning method in maximizing energy absorption is provided, including an appraisal of their associated computational time requirements. Numerical analyses demonstrate that the proposed method, which integrates spectral-domain modeling and IM, can achieve (almost) optimal PI controller design for a nonlinear WEC. Furthermore, this study addresses the inaccuracies inherent in the frequency-domain approach and significantly reduces the computational time compared to the exhaustive search procedure. The findings of this research represent a significant advancement towards the development of simple, effective, and efficient IM-based techniques for synthesis of controllers in nonlinear WEC system
Improving Computational Efficiency in WEC Design: Spectral-Domain Modelling in Techno-Economic Optimization
Full text linkWave energy converter (WEC) optimization often underlines incremental and iterative approaches that result in suboptimal solutions, since all the elements that concur with a techno-economical evaluation are optimized separately due to computation constraints. A design process should rely on precise WEC models to ensure high result accuracy while minimizing the computational demand. These conflicting objectives can be addressed with non-linear time-domain models, known to be numerically accurate, and frequency-domain models due to their high computational efficiency. This work pursues the development of an all-encompassing optimization tool for a gyroscopic-type WEC called ISWEC that applies a new modelling technique named spectral-domain technique as a substitution to the complex time-domain model previously employed. In particular, the spectral-domain technique provides accurate and fast performance predictions of the ISWEC system and offers the possibility to model a hydraulic power take-off, not representable in the frequency domain. The article illustrates techno-economic trends associated with an early-stage design of the ISWEC in high-energy sea-sites, where the low-speed and high-torque profiles call for the use of hydraulic transmissions as opposed to the old electro-mechanical transmissions. The design tool proposed could facilitate the development of WEC technologies via efficient and accurate power assessment and via the possibility of carrying out advanced techno-economic optimisation that goes beyond linear models
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
Spectral-domain modelling of a non-linear wave energy converter: Analytical derivation and computational experiments
No full textHarvesting energy from waves is gaining popularity in the last decades, due to growing
technological maturity and reduction of manufacturing costs of Wave Energy Converter (WEC)
devices. However, the optimal design of WECs represents a challenge to its large-scale commercialisation. Behind this multi-objective optimisation, a significant number of simulations
are necessary to identify the optimal configuration of the device that minimise certain technoeconomic parameter. Frequency-domain models are suggested in an early stage since they
provide a simple and fast simulation tool. On the other hand, non linear time-domain numerical
models are more suitable during an advanced design phase where it is essential to assess
performance and acting loads with greater reliability. The aim of this work is the development of
a spectral-domain model of a WEC device that combines the computational speed of frequencydomain models with the accuracy of non-linear models to improve the design in early stage.
Three different models of the ISWEC, a WEC developed by the MOREnergy Lab of Politecnico di
Torino (Italy), are derived and compared: a fully non-linear time-domain model, a frequencydomain model, and a spectral-domain model. The spectral-domain modelling of the ISWEC
system represents an important novelty for the technological development of the system and
an example framework for similar technologies. Moreover, in the energy harvesting field, no
previous work addressed the analytical representation of a realistic electro-mechanical converter
with both torque and power saturation, and the representation of a gyro-pendulum system in
spectral-domain remains untreated. The numerical experiments demonstrate that the spectraldomain model shows an improved accuracy compared with the frequency-domain model, with
a reduction of percentage error of the computed gross power in the order of two times. Despite
a not perfect accuracy of the spectral-domain model against the time-domain one, the spectraldomain framework is considered as a valid solution due to its computational efficiency, that is
demonstrated to be, at least, three order of magnitude higher than the time-domain on
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
Made in Italy in beer production: from historical family business to inphant microbrewers
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