1,721,082 research outputs found
Parametric design of a resonant point absorber with a fully submerged toroidal shape
No full textThe parametric design of a resonant point absorber, equipped with a fully submerged toroidal shape and connected to a permanent magnet linear generator lying on the seabed, is performed to investigate the effectiveness of the new WEC device in terms of power production and cost of energy. After developing a non-linear time-domain model for the heave, surge and pitch motions of the floating buoy and the vertical motion of the Power Take-Off translator mass, a comparative analysis is performed among a reference WEC device and the new layout. The Annualised Energy Production of the WEC devices is assessed with reference to a candidate deployment site located in the western Mediterranean Sea. The scantling of the tensioned line, connecting the floating buoy to the Power Take-Off unit, is carried out based on both Ultimate and Fatigue Limit State design conditions. Subsequently, the Levelised Cost of Energy is determined and a sensitivity analysis is performed to detect a possible pathway to further reduce the power production costs. Based on current results, the new WEC device seems to be a promising layout to gain the EU target for the marine renewable energy sector that should be reached by 2025
Incidence of Pitting Corrosion Wastage on the Hull Girder Ultimate Strength
No full textThe paper focuses on the assessment of the hull girder ultimate strength, combined with random pitting corrosion wastage, by the incremental-iterative method. After a brief review about the state of art, the local ultimate strength of pitted platings under uniaxial compression is preliminarily outlined and subsequently a closed-form design formula is endorsed in the Rule incremental-iterative method, to account for pitting corrosion wastage in the hull girder ultimate strength check. The ISSC bulk carrier is assumed as reference ship in a benchmark study, devoted to test the effectiveness of the incremental-iterative method, by a comparative analysis with a set of FE simulations, performed by Ansys Mechanical APDL. Four reference cases, with different locations of pitting corrosion wastage, are investigated focusing on nine combinations of pitting and corrosion intensity degrees. Finally, a comparative analysis between the hull girder ultimate strength, combined with pitting corrosion wastage, and the relevant values, complying with the Rule net scantling approach, is performed. Based on current results, the modified incremental-iterative method allows efficiently assessing the hull girder ultimate strength, combined with pitting corrosion wastage, so revealing useful both in the design process of new vessels and in the structural health monitoring of aged ships
Improved design formulas for the ultimate strength of platings with circular openings and manholes under uniaxial compression
No full textThe paper focuses on the ultimate strength of perforated platings with circular openings and manholes, eventually reinforced by ringed or carling stiffeners, in order to develop a comprehensive and rationale format, useful to assess the ultimate capacity of perforated plate panels under uniaxial compression. In this respect, a large number of FE simulations is performed by Ansys Mechanical APDL, in order to provide new design formulas for the ultimate strength of platings with circular openings or manholes and, subsequently, for perforated plate panels reinforced by local stiffeners. The design formulas are developed by properly varying the opening size and the scantlings of ringed or carling stiffeners, in order to provide a comprehensive set of design curves. Hence, the incidence of the opening longitudinal position on the ultimate capacity of perforated platings, without and with local stiffeners, is also investigated. Finally, the proposed equations are applied in a straightforward design example. Based on current results, the new design formulas allow a reliable assessment of the ultimate capacity of platings with circular openings or manholes and the incidence of local stiffeners on the plating ultimate strength, so providing a rationale design format that could be easily embodied in current Rules and guidelines
Comparative study among non-redundant and redundant stationkeeping systems for floating offshore wind turbines on intermediate water depth
No full textThe paper focuses on the design and selection of mooring systems for Floating Offshore Wind Turbines, deployed on intermediate water depths, and provides a comparative analysis among non-redundant and redundant layouts, consisting of 3 and 9 lines, respectively. After developing the non-linear time-domain hydrodynamic model, the Ultimate, Accidental and Fatigue Limit State Design Conditions for mooring systems are briefly discussed. Subsequently, an improved optimization procedure, devoted to detect the minimum weight configuration of the mooring system, constrained to the fulfilment of several restraint criteria, is outlined and applied to a reference case study. The OC4-DeepCwind semisubmersible tri-floater platform, equipped with the 5 MW NREL wind turbine, is assumed to be deployed in the Northern North Sea. The optimization procedure is embodied to preliminarily detect a set of candidate configurations, satisfying the Ultimate and Accidental Limit State design conditions, that are subsequently checked to assess the expected fatigue life. The preliminarily design of anchor foundations is also performed. Finally, a cost analysis is carried out to investigate the impact of the line number on the total installation costs of the stationkeeping system. Some considerations, concerning the impact of line number on the expected cost due to maintenance operations, are also provided
Ultimate strength assessment of simply supported pitted platings: A new stochastic approach based on Monte Carlo simulation
No full textThe ultimate strength assessment of platings affected by random corrosion wastage is a key factor for the reliable design of new ships and the structural health monitoring of aged structures, as pitting corrosion wastage significantly affects the ultimate capacity of platings under compression. In this respect, significant efforts have been undertaken in the last decade to assess the ultimate strength drop-off of pitted platings under compression and several interpolating design formulas, based on a large number of FE simulations, have been developed. Nevertheless, current Rules and guidelines don't provide any explicit strength check criterion for pitted platings. Hence, the main aim of current research is the development of a new framework for the ultimate strength assessment of pitted platings, based on a stochastic approach and the endorsement of Monte Carlo simulation. A new formula, which allows evaluating the statistical properties of the plating ultimate strength in presence of random corrosion wastage, is developed. Subsequently, a benchmark study is carried out, to compare the new formula with the existing ones available in literature and a wide set of FE simulations, carried out by Ansys APDL. Current results are discussed, and the effectiveness of the new formula is verified
Design of a new point absorber with a fully submerged toroidal shape
No full textA new point absorber, equipped with a fully submerged toroidal shape, is designed to increase the power production of the WEC device, by properly matching the heave natural period of the floating buoy with the prevailing sea states at the deployment site. A non-linear time-domain model is developed and applied to assess the Annualised Energy Production and perform the strength check of the tensioned line, connecting the floating buoy to the Power Take-Off unit, lying on the seabed. Two candidate deployment sites, located in the Mediterranean Sea and in the Atlantic Ocean, are chosen for the possible deployment of a wave farm and the toroidal shape main dimensions are selected accordingly. Hence, a comparative analysis between a reference point absorber, consisting of a floating hemispherical buoy, and the new WEC device is performed to investigate the incidence of the proposed layout on the Annualised Energy Production. Finally, both Ultimate and Fatigue Limit State criteria are embodied for the strength check of the connection line. The new layout allows properly tuning the device heave natural period and increasing up to 60% the Annualised Energy Production, as regards the reference configuration, so making the marine energy more competitive on the international market
Towards a unified formulation for the ultimate strength assessment of uncorroded and pitted platings under uniaxial compression
No full textA benchmark study, devoted to systematically investigate the ultimate strength of simply supported platings under uniaxial compression, is performed to develop unified design formulas, accounting for geometrical imperfections, welding residual stresses and pitting corrosion wastage. Particularly, two boundary conditions for the in-plane motion of longitudinal edges, namely free and fully restrained, are considered as they significantly affect the plating behaviour in the post-buckling regime. Several practical design equations for uncorroded platings are derived to account for different levels of initial deflections and residual stresses, based on a wide and systematic series of elasto-plastic large deflection analyses performed by Ansys Mechanical APDL. Subsequently, proposed formulas are extended to platings affected by pitting corrosion wastage, on the basis of a new series of FE analysis, where the pitting intensity and corrosion degrees are systematically varied based on random distribution of the corrosion wastage on the plate panel. Finally, the goodness of proposed formulas is checked against current Rule equations, as well as several experimental collapse tests and FE results available in literature
Dynamic equilibrium and resistance assessment for warped hulls by means of total pressure distribution
No full textA new method for the assessment of the resistance and dynamic trim, by the integration of the pressure distribution and the equilibrium equations, is presented. To evaluate the 3-dimensional hydrostatic and hydrodynamic pressure distribution acting on the bottom of a planing hull the Morabito's empirical method (2010, 2014) is used. The implemented method enables the determination of the three-dimensional total pressure distribution, the evaluation of the lift, the buoyancy force and the centre of pressure, the assessment of the dynamic trim and resistance. The developed method has been applied for a non-monohedral hard chine hull form, with variable deadrise angles along the length, for a range of Cv values (Froude number relative to the beam) ranging from 2.255 to 3.657. To assess the accuracy of the implemented method the obtained numerical results have been compared against experimental data. The model has been tested in the towing tank of the Department oflndustrial Engineering of the University of Naples "Federico II"
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