1,720,986 research outputs found
Level 1 vulnerability criterion for the dead ship condition: A practical methodology for embedding operational limitations
Full text linkThe framework of second generation intact stability criteria (MSC.1/Circ.1627) allows introducing so-called “operational limitations”, by specifying alternative environmental conditions based on the expected operation of the ship. Relevant calculation parameters of the criteria are correspondingly modified, according to standardized procedures specified by the Explanatory Notes. This is a significant novelty, and information is available for implementing operational limitations for most of the failure modes and levels of assessment. However, this is not the case for the level 1 vulnerability criterion for the dead ship condition. Therefore, the paper investigates the development of a rational simple procedure to contribute filling this gap. The devised approach provides a tool for determining a modified reference wind speed based on the environmental conditions representative of the considered operational limitations. Specifically, the modified wind speed is defined as the wind speed with a specified probability of exceedance. The reference probability of exceedance is determined considering the standard conditions and assumptions in the framework of MSC.1/Circ.1627. The modified reference wind speed can then be used to re-define all the calculation parameters of the criterion, according to the relevant theoretical background. Two example applications of the devised approach are also provided
Effect of environmental data uncertainty in the framework of second generation intact stability criteria
Full text linkThe framework of second generation intact stability criteria in MSC.1/Circ.1627 includes a number of novelties for intact stability assessment. One of such novelties is the inherent possibility of designing a vessel for a specific operational area, by embedding area-specific environmental conditions. This is practically achieved through modification of the relevant calculation parameters in the criteria, on the basis of available MetOcean data. However, MetOcean data for a given area are generally available from multiple sources, and different sources provide information on environmental conditions on the basis of different approaches. This leads to a source-related variability that eventually reflects in the results of stability assessment, to an extent that is yet to be fully explored. The present study aims at providing quantitative indications in this respect. The Mediterranean Sea is considered as operational area, five different sources of MetOcean data are used, and level 1 and level 2-check 1 vulnerability criteria for parametric rolling are applied to two sample ships. The variability in the obtained safe zones of loading conditions is presented and discussed, also with reference to the effect of bilge keels. Some difficulties in the practical implementation of the procedure for embedding operational limitations are also highlighted and discussed
Ship evacuation simulation using a game engine: Modelling, testing and validation
Full text linkThe topic of evacuation analysis plays an important role in the maritime field, because of its natural link to safety and also because of relevant SOLAS requirements. In this context, this paper focuses on the description, testing and validation of an agent-based mathematical model. As primary goal, the model has been developed targeting a use in evacuation simulations using immersive virtual reality, also with the possibility of real-time human participation. At the same time, the model is suitable also for standard evacuation simulations. The model has been developed starting from existing social force models and introducing a series of improvements, modifications, new modelling, and adaptations. The model is described in detail, providing and discussing all adopted parameters. The choice of a game engine as development environment is also discussed, highlighting benefits and limitations. Results from IMO test cases, validations using experimental data, and comparisons with FDS+Evac are presented. A more realistic test case, relevant to the maritime field, with a two-cabin-deck geometry is also presented, together with corresponding simulation results. Particular attention is paid to the post-processing and reporting of the results from Monte Carlo simulations, in order to properly reflect, quantify and emphasize the underlying aleatory uncertainty
Assessment of infection probability indices for airborne diseases in confined spaces: combination of CFD and analytical modelling
Full text linkThe paper presents a framework for probabilistic assessment of likelihood of infection from airborne diseases in confined spaces which are continuously occupied for relatively long periods (e.g., school classrooms). The proposed approach is based on a combination of computational fluid dynamics (CFD) pre-calculations and analytical post-processing, to define relevant indices of infection probability. The practical applicability of the method is demonstrated through a case study, where different ventilation scenarios are considered for a school classroom. Corresponding infection probability indices are determined globally for the group of occupants. Furthermore, since the method does not rely on the well-mixing assumption, local probability indices are determined for each occupied location. The obtained results confirm the intuition that an increase of ventilation and/or air filtration reduces the overall likelihood of infection, though the observed positive effect is not uniform within the space. The presented methodology can also be considered as complementary to simpler approaches
Quantifying error in deterministic predictions based on phase-resolved linear wave models
No full text
Theoretical, numerical and experimental study on the problem of ergodicity and 'practical ergodicity' with an application to parametric roll in longitudinal long crested irregular sea
No full textThis paper addresses the problem of ergodicity of stochastic processes starting from a theoretical point of view, with the aim of obtaining a deeper understanding for practical applications. The problem is tackled bearing in mind the concept of 'practical ergodicity', that is, the possibility of obtaining reliable information about ensemble averages by using temporal averages. Some general analytical tools are given to address the problem of accuracy of temporal averages and an example of their use in a possible design of experiments is given. A series of Monte Carlo numerical simulations are performed by means of an analytical non-linear 1.5-DOF model of parametrically excited roll motion. The outcomes of such simulations are analysed to show the effect of ship speed and sea spectrum shape. The effect of wave grouping phenomenon is discussed with particular attention to the Doppler effect. Qualitative indications given by the numerical simulations are then compared with experimental tests showing a good agreement. Practical ergodicity of generated sea in towing tank is also briefly addressed. (C) 2005 Elsevier Ltd. All rights reserved
Nonlinear and stochastic aspects of parametric rolling modeling
No full textThis paper addresses, starting from an extensive series of tests in longitudinal regular waves (already done) and irregular waves (in progress), the problems connected with the threshold formulation for parametric rolling and its amplitude modeling above threshold. Both head and following waves have been considered, also in view of the greater attention to head sea conditions called for during International Maritime Organisation Subcommittee on Stability and Load Lines, and on Fishing Vessels Safety (IMO/ SLF) discussion on the revision of the Intact Stability Code. Particular attention is given in the regular wave case to the nonlinear damping, nonlinear restoring, and nonlinear parametric excitation terms. The mathematical models so developed are "compared" with experimental results by means of an ad hoc parameter estimation technique. It is, on the other hand, well known that several different thresholds can be proposed in the case of irregular waves and that the nonlinear modeling of roll motion variance above threshold is at present not properly addressed. Here, too, a series of experiments will be conducted in the presence of narrow band irregular waves having the bandwidth as parameter. A mathematical description of the nonlinear parametric rolling can be obtained with the use of approximate analytical techniques
A contribution on the problem of practical ergodicity of parametric roll in longitudinal long crested irregular sea
No full textOn the nonlinear modeling of parametric rolling in regular and irregular waves
No full textThis paper summarizes the results and the problems still open regarding the development of a 1.5DOF nonlinear mathematical model of the parametric rolling in longitudinal waves with particular regard to the head sea condition. A first part is devoted to the case of regular waves, while the second concerns parametric rolling generated by irregular waves obtained by means of white noise filtered through a linear filter with adjustable bandwidth and by using a Bretschneider spectrum. The availability of an extensive series of test results on scale models conducted at University of Trieste and at INSEAN, allows a thorough discussion of the problems connected with the threshold formulation for parametric rolling and its amplitude modelling above threshold
- …
