1,721,642 research outputs found
Reliability analysis of the primary strength of an oil tanker
No full textA procedure is presented to perform a second order reliability-based structural analysis of the mid ship
section of a vessel. The procedure accounts for the combination of the vertical and horizontal components of
the wave induced bending moment as well as of the still water bending moment, in order to determine the
actual angle gamma formed with the vertical plane by the total resultant bending moment.
The ultimate strength of the midship section is considered as a function of the same angle.
The proposed analysis is applied to a double hull tanker on a particular route (Persic Gulf - North Europe
and ballast return trip) and directional scatter diagrams are used for the description of the sea states
encountered during the voyage.
The results are compared to those obtained on the same test case with a simpler model, which takes into
account only the vertical components of loads and strength. The comparison shows that the introduction in
the load model of the horizontal component of the bending moment does not reduce the structural reliability
of the considered oil tanker ship. Such result is to be related to the shape of the curve of hull girder ultimate
strength as a function of gamma, which shows a local minimum for pure vertical bending moment: in the examined
case, the most dangerous condition is obtained in such situation
Second Level Reliability Analysis of a Double Hull Oil Tanker
No full textA second-level reliability analysis is carried out on a realistic case study, represented by a 150,000 DWT double-hull tanker on service on a North Europe – Persian Gulf route. The object of the investigation is the longitudinal strength of the hull girder subject to bending loads. The scope of the analysis is to evaluate different stochastic models for the load variables and various combination criteria for the static and dynamic load components. A reference period of one year is adopted in the analysis and, as regards the loading conditions, use is made of detailed records collected from the owner during the first year of activity of the ship. The collapse equation describes the failure mode due to pure vertical bending moment, considering the ultimate capacity of the hull girder in its “as-built” conditions. A FORM procedure is adopted to calculate the reliability index and failure point co-ordinates. The present work is intended as a first step for the set up of a second-level reliability procedure to be adopted in the calibration of partial safety factors formats for the verification of the longitudinal strength of ships. Values of the reliability index are obtained for an existing, typical and well designed oil tanker on a common route: such values can be used for future comparisons between different design solutions or practices
DFT study of the interaction free energy of π-π complexes of fullerenes with buckybowls and viologen dimers
No full textWe present a theoretical investigation, by means of DFT protocols, of the complexation thermodynamics of (i) complexes of C70 and C 60 fullerenes with bowl-shaped hexabenzocoronene derivatives and (ii) complexes of C60 with viologen dimers. The recent functionals of the M06 family, accounting for π-π interactions to a good level of approximation, have been used to calculate the interaction free energies. For the former complexes, the good agreement between the calculated results and the experimental data confirms the reliability of the protocol used. On these grounds, we then checked the stability of a series of complexes of C 60 with some viologen dimers, 1BPnBP1 (n = 6-9), where two N-methylated bipyridinium units are linked by an alkyl chain of variable length, acting as molecular tweezers. Both forms of the viologen cores, that is the cation (each core doubly charged) and the reduced neutral form, were considered. For a suitable chain length a free energy gain upon complexation is predicted for the neutral form while the complexation of C60 by the cationic form is disfavoured mainly for entropic reasons. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique
Exploring the maturity of Discrete-event simulation in logistics: is this a new research domain?
No full textThis paper explores the research area of discrete event simulation in logistics, with the final goal to infer whether this area has achieved the maturity of a new, stand-alone, research domain. Scientometric techniques, such as co-author analysis and topic analysis (keyword and co-occurrence mapping), supported by adequate software packages, as well as some statistical elaborations, were used to explore the evolution of research in time, so as to delineate the trend of this scientific field and to evaluate its current maturity. A representative sample of nearly 900 papers, retrieved from the Scopus database and expressively related to discrete event simulation and logistics, was used for the analysis. Results show that from the point of view of the contents covered, the research field appears to be sufficiently mature. Indeed, a sound quota of established topics was found among the themes treated; at the same time, a continuous introduction of unique new topics was observed, especially in recent times, thus denoting an expansion of the research field towards adjacent or interrelated areas. From the point of view of the collaborations among authors, instead, at present their number is still limited. Nonetheless, prospects are goods, as most of the relationships were established in the recent years; thus, they could be expected to increase in the future. Taken together, the outcomes of this study suggest that the topic of discrete event simulation in logistics is progressively acquiring scientific maturity and is expected to reach the status of autonomous research field in the future
An Agent-Based and Context-Oriented approach to Symbol Recognition in Diagrammatic Drawings
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