1,721,071 research outputs found
Ultimate Strength of Platings Under Uniaxial Compression with Edges Elastically Restrained Against Torsion: A New Comprehensive Approach
No full textThe ultimate strength of platings under compression is one of the most important factors to be addressed in the ship design. Current Rules for ship structural design generally provide explicit strength check criteria against buckling for simply supported and clamped platings. Nevertheless, ship platings generally exhibit an intermediate behaviour between the simple support and the clamped conditions, which implies that the torsional stiffness of supporting members should be duly considered. Hence, the main aim of this study is the development of new design formulas for the ultimate strength of platings under uniaxial compression, with short and/or long edges elastically restrained against torsion. In this respect, two benchmark studies are performed. The former is devoted to the development of new equations for the elastic buckling coefficients of platings with edges elastically restrained against torsion, based on the results of the eigenvalue buckling analysis, performed by Ansys Mechanical APDL. The latter investigates the ultimate strength of platings with elastically restrained edges, by systematically varying the plate slenderness ratio and the torsional stiffness of supporting members. Finally, the effectiveness of the new formulation is checked against a wide number of finite element (FE) simulations, to cover the entire design space of ship platings
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
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
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
Incidence of wind spectrum and turbulence intensity on the design of mooring systems for floating offshore wind turbines
No full textThe paper focuses on the incidence of wind spectrum and turbulence intensity on the design of stationkeeping systems for Floating Offshore Wind Turbines. After a brief review about the employed nonlinear time-domain hydrodynamic model, some basics about the Ultimate and Fatigue Limit State design conditions of the mooring system are provided. Subsequently, the two wind spectra, employed in the numerical simulations, are briefly introduced. The former is the NPD wind spectrum, generally applied for the design of mooring systems for typical offshore structures, employed in the oil and gas sector. The latter is the Kaimal wind spectrum, generally employed for the design of offshore wind turbines in conjunction with different turbulence models, depending on the operative scenario. The numerical investigation is performed considering the DeepCwind platform, equipped with the 5 MW NREL wind turbine, as reference support structure, deployed in the North Sea area. Three different water depths, from 200 up to 400 m, are considered. It is verified that both the wind spectrum and turbulence model play a fundamental role not only for the optimum design of the stationkeeping system, but also for the proper selection of the line scope, as well as of the leading usage factors
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
Modified incremental-iterative method for bulk carriers under alternate hold loading conditions
No full textA modified incremental-iterative method for bulk carriers under alternate hold loading condition is outlined, focusing on the assessment of the local stress field, due to double bottom bending by the orthotropic plate theory, and the development of a modified strain field of double bottom structures, after first failure of bottom stiffeners occurs. Particularly, the ISSC bulk carrier is assumed as reference ship and a comparative analysis with the FE results available in literature is performed to investigate the effectiveness of the proposed method. Subsequently, the influence of bottom strengthening and corrosion wastage on hull girder hogging capacity, under pure bending and alternate hold loading conditions, is investigated. Current results, obtained by a dedicated code developed in Matlab, are fully discussed to prove the effectiveness of the proposed method for practical design purposes
Ultimate strength assessment of intact and pitted platings under biaxial compression
No full textThe paper focuses on the ultimate strength assessment of intact and pitted platings under uniaxial and biaxial compression, in order to provide a unified formulation, which can be embodied both in the design phase of new ships and in the assessment procedures of aged structures. In this respect, a large number of FE simulations, performed by Ansys Mechanical APDL, is preliminarily carried out, in order to derive, by best-fit interpolation, new design formulas for intact platings under uniaxial and biaxial compression. Subsequently, a two-step procedure for pitted platings is outlined and checked against a new series of FE results, based on random generation of localized corrosion wastage over the plate panel for several combinations of pitting and corrosion intensity degrees, in order to investigate the effectiveness of the proposed procedure. Finally, current formulas are compared with additional FE results available in literature and with the design equations embodied in the Harmonized Common Structural Rules for Bulk Carriers and Oil Tankers. Based on current results, the new equations for uniaxial and biaxial compression, as well as the two-step procedure for pitting corrosion wastage, reveal to be effective for practical design purposes
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