1,720,968 research outputs found
Optimal heuristic design of a high efficient SWATH-type vessel
No full textThe paper illustrates the shape optimization of the immersed part of the hulls of a SWATH (Small Waterplane Area Twin Hull) vessel, a particular type of catamaran that has already been used as passenger ship and fast ferry. The optimization tool aims to find the best combination of parameters, such as the shape of the immersed hulls, their distance, and draft that induces the lowest hydrodynamic resistance. This application refers to the same design vessel that has fixed displacement and cruise speed defined for specific mission requirements. Size limits are also imposed by operability requirements.The optimization makes use of a genetic evolutionary algorithm, a stochastic global search method based on the Darwinian concept of natural selection. The optimization environment has been created in Matlab and is based on a parametric geometry definition module, able to define a series of hull forms through the CST technique (Class Function/Shape Function Transformation). For the evaluation of the hydrodynamic resistance, CFD simulations are implemented in STAR-CCM+.The main reasons that motivate this research are the integration of computer-assisted parametric definition of vessels hull shapes with the CFD techniques for the prediction of hydrodynamic performances, and to assemble an optimization tool able to facilitate the design procedure through the creation of complete performance databases of customized hulls.As the amount of the total resistance reduction with an improved hull shape is impressive, the usefulness of applying automated CFD optimization techniques in the design is remarkable and should persuade the reader to consider this alternative in the design stages of a boat
FOWT Modeling and Validation in Extreme Conditions
No full textAs the global energy sector transitions towards sustainable sources, floating offshore wind turbines (FOWTs) have emerged as a promising solution for harnessing wind power in deep-water locations. Achieving accurate, reliable, and efficient numerical models for the de- sign and analysis of FOWTs is paramount. This study investigates how the simplifying approximated assumption of uncertain key parameters af- fects floater motions and mooring line tensions under irregular sea states. The turbine considered is the 5 MW reference model defined by the U.S. National Renewable Energy Laboratory (NREL), supported by the OC4 DeepCwind semisubmersible substructure. The deployed mooring sys- tem was priorly optimized for the chosen site off the coast of Lampe- dusa, Italy. In this paper, a novel two-stage optimization procedure is introduced to calibrate the simplified global linear and quadratic damp- ing parameters, which have been deployed in a hydrodynamic load model developed in OrcaFlex® commercial software to simulate the load effects. The 100-year return period Ultimate Limit State (ULS) event, derived from the environmental conditions of the ERA5 database, is considered for model validation. The numerical predictions show good qualitative agreement with experimental data in capturing resonant frequencies and mooring line tension responses. Nonetheless, further refinement, such as introducing Morison element-based local hydrodynamic damping or leveraging high-fidelity computational Fluid Dynamics (CFD) simula- tions, would improve amplitude predictions
Experimental validation of Orcaflex-based numerical models for the PEWEC device
Full text linkTo design a Wave Energy Converter mooring system that ensures maintainability, resistance, and low costs, without affecting productivity, it is necessary to foster reliable numerical models. In the present paper, the validation of Orcaflex & COPY; simulations against the experiment results of the Pendulum Wave Energy Converter (PEWEC) 1:25 scale model, conducted at the University of Naples Federico II, is presented. The experiments consist of free-decay and static pull-out tests to assess the inertial properties of the model and mooring system; tests in operative and extreme regular and irregular waves to fully characterize the mooring system and the device dynamics. The same wave records measured in the towing tank have been used in numerical simulations. PEWEC motion results from numerical simulations and experiments are given in terms of Response Amplitude Operators (RAOs) for regular waves, as statistical values in tabular form, and in Taylor's diagrams for irregular waves. The most probable fairleads tensions for the load dimensioning have been obtained from the Generalized Extreme Value (GEV) distribution of experimental and numerical data. The obtained differences show that the numerical model accurately predicts the experimental data and correctly estimates the dimensioning load of the mooring lines
Understanding wave energy converters dynamics: High-fidelity modeling and validation of a moored floating body
Full text linkIn ocean engineering, one of the most challenging phenomena to replicate is the interaction between waves and a moored floating body. Accurately evaluating such systems is essential for minimizing uncertainties, mitigating risks, and advancing technologies like wave energy converters. For this purpose, this study aims to develop a high-fidelity numerical model capable of reducing reliance on costly experimental campaigns during the device design phases. The model integrates a fluid dynamics module based on the Navier- Stokes equations, implemented in Star CCm+, with a mooring model utilizing a mass-spring-damper system, specifically MoorDyn. The primary objective is to introduce this coupled approach and demonstrate its efficacy through validation against experimental data from two distinct wave energy converters: ISWEC and PeWEC. The validation process encompasses comprehensive comparisons between simulated and observed kinematic behavior, mooring tensions, and crucially, pressure loads. Results indicate that the model is able to faithfully predict the complex phenomena involving a moored floating body, affirming the accuracy and reliability of the proposed coupling methodology. The coupling developed is available online link, where a simplified case study is present to show how to compile the library and add it in the numerical model
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
EFFECT OF A LOW-NITROGEN DIET SUPPLEMENTED WITH ESSENTIAL AMINO-ACIDS AND KETOACIDS (ARTIFICIAL DIET AD), AND OF HEMODIALYSIS (HD) ON LIPID-METABOLISM IN UREMIA
No full textExperimental investigation of a novel modular multi-purpose floating structure concept
No full textModular multi-purpose floating structures (MMFS) provide a possible solution to the growing need for space resulting not only from the rapidly growing global population but also from the emerging blue economy and specifically offshore renewables sector. The desired space is generated in a more sustainable way than traditional land reclamation methods, by interconnecting together modular floating platforms, making this technology adaptable and suited to a broad range of possible offshore activities. This study experimentally investigates the hydrodynamic response of a novel concept of modular multi-purpose floating structure, composed by floating modules connected with semi-rigid connectors and moored at the seabed using a taut mooring system solution. The 1:50 model consists of three hexagonal floating platforms, linked together by a semi-rigid connector system that emulate the mechanical behaviour of the full-scale system. The model has been tested under representative sea state conditions at the wave basin of the Laboratory of Hydraulic Engineering (LIDR) of Università degli Studi di Bologna. This paper describes the experimental setup and preliminary results of the dynamic behaviour of the MMFS system, with particular focus on platforms kinematics, mooring and connectors loads
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
Capturing wave energy converter's extreme response: Experimental validation of DualSPHysics and STAR CCM+
No full textValidating numerical models against their physical realizations is an integral aspect, very essential for their development and a reliable assessment of their accuracy. This study focuses on comparing two different approaches: the open-source DualSPHysics, and the commercial software STAR CCM+, which have emerged as high-fidelity tools in evaluating wave energy converters’ (WEC) performance. Notably, they belong to opposite ends of the modelling spectrum, with the former relying on a Lagrangian approach, and the latter employing a Eulerian one. As ground through, our validation is performed using an experimental investigation of the Pendulum Wave Energy Converter (PeWEC), focusing on its kinematic and mooring forces. In addition to rigours validations, this comparative analysis provides an overview of the advantages and short-comings of each employed numerical model, discussing pre-processing time, computational performance, and overall code platform flexibility for end-users. The aim of this comprehensive assessment is to under-line and compare performance and accuracy of these models when employed to capture the extreme response of resonant devices, such as WECs
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