1,720,958 research outputs found
Solitary wave loads on submerged breakwater: Laboratory tests
No full textA solitary wave almost halves its propagation speed passing over a submerged breakwater for coast defense. This is the basic assumption made by Filianoti & Piscopo (2008) for their calculation of horizontal wave loads on the breakwater. They calculated this slowing down, through a BEM model, on assuming that it has the same value both for
a periodic and a solitary wave. Once estimated the speed slowing down, it is straightforward to obtain solitary wave loads thorugh the calculation of the Froude-Krilov force.
Laboratory tests carried out on a small scale model of submerged breakwater interacting with solitary waves, permit us to experimentally reproduce the phenomenon, to check whether the speed slowing down exists, and to measure it
Large eddy simulation within the smoothed particle hydrodynamics: Applications to multiphase flows
No full textIn this paper, the large eddy simulation (LES) model introduced in the smoothed particle hydrodynamics (SPH) by Di Mascio et al. [Phys. Fluids 29, 035102 (2017)] and called d-LES-SPH, is extended to treat multiphase flows. This is achieved by modifying the multiphase d-SPH by Hammani et al. [Comput. Methods Appl. Mech. Eng. 368, 113189 (2020)] by switching the viscous and density diffusion constants to dynamic variables evaluated as turbulence closure terms. The equation for energy conservation is also written for the presented model. The validation is performed for two-dimensional problems, by comparison with other established SPH solvers, with a finite volume method solver based on the turbulence closure corresponding to that adopted for the Lagrangian scheme, and with experimental data. The first test case investigated is a modified Taylor-Green vortex in which the introduction of macro-bubbles of a lighter fluid phase inside the domain is considered. In the second test case, a more violent problem involving wave breaking and splashing dynamics is analyzed. In the final test, the dynamic of a sloshing problem is reproduced. An analysis of turbulence resolution is conducted by considering modeled and resolved turbulent kinetic energies, as well as viscous dissipation and turbulent viscosity dissipation
Design of a ducted wind turbine for offshore floating platforms
No full textWithin the Marine Energy Laboratory project, funded by the Italian Ministry for Education, University and Research, one of the first offshore wind plants on floating hulls, hosting ducted wind turbines, has been considered. The confinement of horizontal-axis wind turbines inside divergent ducts is reconsidered, in light of material innovation and direct drive coupling. Ducted wind turbines can take
advantage of the flow rate increase due to the effect of the divergent shrouds. The conventional blade element momentum theory has been reformulated in order to deal with ducted turbines. Furthermore, computational fluid dynamics simulations have been carried out based on the solution of the steady two-dimensional Reynolds-averaged Navier–Stokes equations for axisymmetric swirling flows. In order to avoid any expensive mesh refinement near the actual rotor blades, the turbine effect on the flow field is taken into account by means of source terms for the momentum equations solved inside the domain swept by the rotor. This technique allowed us to optimize the geometry of the ducted wind turbine in an extremely effective way
UKF-based fault detection and isolation algorithm for IMU sensors of Unmanned Underwater Vehicles
No full textSensor fault detection and isolation (SFDI) is a fundamental topic in unmanned underwater vehicles (UUV) development, since control system reliability strongly depends on the accuracy of attitude estimation. In small UUVs, typical redundant architectures, based on triplex redundancy, can represent a strong limitation in terms of payload and power consumption. This work proposes an FDI algorithm for small UUVs equipped with duplex sensor architecture. Here, attitude estimation relies upon the usage of two 9-DoF inertial measurement units (IMUs) including 3-axis accelerometers, gyroscopes and magnetometers. The proposed SFDI algorithm is based on an unscented Kalman filter (UKF) approach to efficiently detect and isolate faulted IMU sensors. Its effectiveness and robustness were proved through experimental tests involving realistic faults on a real underwater vehicle. A sensitivity analysis was carried out on the relevant algorithm parameters in order to find a trade-off between performance, computational burden and reliability
Numerical prediction of the natural frequency of an Oscillating Water Column operating under resonant conditions
Full text linkAmong the different technologies developed in order to harness wave energy, the Oscillating Water Column devices are the most accredited for an actual diffusion. Recently, Boccotti has patented the REWEC1 (REsonant sea Wave Energy Converter solution 1), a submerged breakwater that performs an active coast protection, embedding an Oscillating Water Column device, which is capable of operating under resonant conditions with that sea state, which gives the highest yearly energy contribution. The REWEC1 dynamic behavior can be approximated by means of a mass-springdamper
system. According to this approximation, a criterion for evaluating the oscillating natural frequency of the REWEC1 has been derived. This criterion has been validated against both experimental results and computational fluid dynamics simulations, performed on a REWEC1 laboratory-scale model. The numerical simulations have shown a good agreement between measurements and predictions
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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