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Ships --- Stability of ships. --- Seakeeping.

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The seakeeping of a floating body, whether in motion or simply standing still, is recently becoming a crucial part in the design and the engineering process from large offshore platforms to racing sailing yachts. Moreover, even if the importance of the experimental tests is still undoubtedly relevant, nowadays several numerical methods allow to predict, with more or less accuracy, the boat behavior in regular and irregular wave field.
The present work aims to analyze which geometrical, inertial and non-linear aspects must be taken into account in the hydrodynamic design of a sailing yacht concerning its heave, pitch and roll degrees of freedom. The analysis is performed by means of a fast Boundary Element Method (HydroStar from B.V.) and a complex Reynolds Averaged Navier-Stokes CFD code, (Star-CCM+ from CD-Adapco). After a first familiarization with the numerical tools, the comparison will be presented for two cruise-racer VISMARA sailing yachts, trying to identify the main differences in terms of Response Amplitude Operators.
The qualitative study is concentrated on the effect of: - Forward speed and wave heading; - Inertia properties: lifting keel; - Aft shape: soft chines vs. rounded; - Heeling conditions; - Laminar vs. turbulent model: influence in R.A.N.S. simulations; - Linear, quadratic and viscous damping: roll motion;
The calculation performed in the non-viscous frequency domain seemed to be overestimating the amplitude of the yacht Heave motion in the range of the resonance frequencies while the Pitch motions agreed with the viscous time domain RANSE simulations. The dynamic sink and trim configuration experienced by the boat while moving forward seemed to increase the resonance peak in the non-viscous calculation while just modifying the mean value in the viscous case.
In all the tests simulated, a soft chine aft in the topsides volume, actively works as damper and it globally reduces the displacements of the yacht particularly for the Roll angles. While resulted not relevant in the Heave and Pitch motions, the inertia effects due to the lifting keel are bonded to the damping forces so that the Roll motion present a nonlinear trend when acting on bulb vertical position.

CFD, seakeeping, potential method, RANSE, sailing, keel, bulb --- Ingénierie, informatique & technologie > Ingénierie civile

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Diffraction analysis is important in the preparation of offshore operations to assess the vessel
behaviour which impacts the workability and the integrity of the components to be installed (wind
turbine, topside or foundation). The student will familiarize himself with diffraction analysis starting
from creating the mesh, then producing the RAO’s and eventually calculating motions and
accelerations in different sea states. Description of the sea state as a spectrum beyond the
commonly used JONSWAP will be an important part of the understanding of the calculated response.
The diffraction analysis will be carried out in two software packages.
 The calculated motions will be compared with measured motions. Besides the comparison itself the
student is expected to grasp the different aspects of collecting the full scale measurements and the
potential use in engineering models and in real-time on board of the vessel. This is Big Data in
practice, whereby method and framework are as important as the obtained results

Diffraction Softwares, Seakeeping, Wave Structure Interaction, Motion Analysis --- Ingénierie, informatique & technologie > Ingénierie mécanique

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It is of major importance for design purposes that long-term effects coming from the sea are accurately predicted by classification societies, which must not be exceeded during the lifetime operation of a given vessel. It is encountered that Inland-Navigation Bureau Veritas rules (NR247) do not assess the seakeeping behaviour and do not predict sea loads adequately. To deal with this, a development of empirical-formulas was carried to account for inland-vessel responses when operated in stretches of water within the range of navigation of 0.6 m ≤ Hs ≤ 2 m, based on linear potential-flow theory, boundary element method and the 3D linear panel method theory. A frequency-domain linear analysis for an impossed constant speed of 10 knots is taken into account. Using the Belgian Coastal Scatter Diagram, it was found the hydrodynamic long-term response for a return period of 17 years, composed of motions, accelerations, relative elevation, shear forces and bending moments; encountered in a set of 46 inland vessels. Then, by mean of a regression process, a set of empirical equations was proposed accounting for these effects. They were validated against an additional set of 13 direct-calculation results, showing good agreement. Finally, to take into account discrepancies originated from lineartheory assumptions, proposed empirical models are corrected by taking into account nonlinear hydrodynamic effects.

Inland Navigation, Seakeeping, Bending Moment, Potential Flow, Rule-formulas, Linear Analysis, RAO, Long-term value, Statistics, Regression --- Ingénierie, informatique & technologie > Ingénierie civile

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This book presents the papers accepted into the Special Issue “Stability and Seakeeping of Marine Vessels” and includes nine contributions to this Special Issue published in 2020. The overall aim of the collection is to improve knowledge about the most relevant and recent topics in ship stability and seakeeping. Specifically, the articles cover a wide range of topics and reflect the recent scientific efforts in the 2nd generation intact stability criteria evaluation and modelling of the ship dynamics assessment in intact or damaged conditions. These topics were investigated mainly through direct assessments performed both via numerical methods and tools, and experimental approaches. The book is addressed to individuals from universities, research organizations, industry, government agencies and certifying authorities, as well as designers, operators and owners who contribute to improved knowledge about “stability and seakeeping”.

Technology: general issues --- URANS --- VOF --- overset mesh --- side damage --- bottom damage --- flooding process --- motion response --- nonlinear steady flow --- desingularized Rankine panel method --- forward speed --- radiation and diffraction --- adaptive weather routing --- Seakeeping Performance Index --- route optimization --- Dijkstra algorithm --- Cummins equations --- vertical motions assessment --- time domain simulations --- experimental seakeeping --- hard chine displacement hull form --- second generation intact stability criteria --- operational guidance --- operational limitations --- vulnerability levels --- direct stability assessment --- Ro-Ro ferry --- coastal patrol ship (CPS) --- full-scale seakeeping trials --- ship design --- barge platform --- zero-pressurized air cushion --- hydrodynamic performance --- boundary element method --- container ship --- added resistance in waves --- sea states --- potential flow theory --- variation of ship characteristics --- strip theory --- BEM --- RANS --- regular wave --- seakeeping --- URANS --- VOF --- overset mesh --- side damage --- bottom damage --- flooding process --- motion response --- nonlinear steady flow --- desingularized Rankine panel method --- forward speed --- radiation and diffraction --- adaptive weather routing --- Seakeeping Performance Index --- route optimization --- Dijkstra algorithm --- Cummins equations --- vertical motions assessment --- time domain simulations --- experimental seakeeping --- hard chine displacement hull form --- second generation intact stability criteria --- operational guidance --- operational limitations --- vulnerability levels --- direct stability assessment --- Ro-Ro ferry --- coastal patrol ship (CPS) --- full-scale seakeeping trials --- ship design --- barge platform --- zero-pressurized air cushion --- hydrodynamic performance --- boundary element method --- container ship --- added resistance in waves --- sea states --- potential flow theory --- variation of ship characteristics --- strip theory --- BEM --- RANS --- regular wave --- seakeeping