The state of the art in modeling ship stability in waves (original) (raw)
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A Mathematical Model to Describe ShipMotions Leadingto Capsize in Severe Astern Waves
Journal of the Society of Naval Architects of Japan, 1998
A reasonable method used in prediction of ship motions leading to capsize in severe waves is developed on the basis of strip method. In this method the variation of metacentric height in waves is taken into account. Several simulations were conducted to predict the stability against capsizing of a container carrier 15000GT in severe waves due to parametric rolling. Finally the stable and unstable areas of the ship running in severe astern seas are computed
2014
The safety of ships at sea is a key aspect of shipping. Tragic passenger vessel accidents during the years motivates that large effort is spent on understanding the mechanisms of survivability of damaged ships. In the past few decades the development and use of numerical tools have resulted in a steady increase of the understanding and ability to assess these complex mechanisms. This thesis describes the mathematical model and numerical implementation of a tool for assessment of the behavior of damaged or intact ships in a seaway. It includes three validation studies, where the simulation results are compared to physical scale model tests. It also includes four applied studies. vii : Natural frequency of roll All vectors are expressed by bold font. All quantities are expressed in SI units unless otherwise stated. Trapezoidal integration is used unless otherwise stated. viii ix Contents 1 Introduction ______________________________________________________________________________ 1.1 Background/Motivation of work _____________________________________________________________ 1.2 Objectives _________________________________________________________________________________________ 1.3 Literature survey ________________________________________________________________________________ 1.4 Focus and limitations ___________________________________________________________________________ 1.5 Scientific contribution __________________________________________________________________________ 1.6 Outline and summary of the thesis ___________________________________________________________ 2 Theory _____________________________________________________________________________________ 2.1 Potential flow _____________________________________________________________________________________ 2.2 Potential flow-linear approach ____________________________________________________________ 2.3 Hydrodynamic forces in the frequency domain-linear strip theory ________________ 2.4 Hydrodynamic forces in the time domain _________________________________________________ 3 Method ___________________________________________________________________________________ 3.1 Coordinate systems and kinematics ________________________________________________________ 3.2 Geometry of the ship ___________________________________________________________________________ 3.3 Waves _____________________________________________________________________________________________ 3.4 Equations of motion ____________________________________________________________________________ 3.5 Forces and moments ___________________________________________________________________________ 3.5.1 Radiation forces _________________________________________________________________________________ 25 3.5.2 Wave diffraction forces _________________________________________________________________________ 26 3.5.3 Froude-Krylov forces ___________________________________________________________________________ 28 3.5.4 Viscous damping forces ________________________________________________________________________ 31 3.6 Damage simulation ____________________________________________________________________________ 3.6.1 Compartments ___________________________________________________________________________________ 31 3.6.2 Damage openings and flooding process _____________________________________________________ 31 3.6.3 Progressive flooding ____________________________________________________________________________ 33 3.6.4 Excitation forces from floodwater ____________________________________________________________ 34 3.6.5 Inertia forces from floodwater ________________________________________________________________ 34 3.6.6 Pressure gradient over damage opening ____________________________________________________ 35 3.7 Solution method and time stepping _________________________________________________________ 4 Validation studies ______________________________________________________________________ 4.1 Ro-Pax capsize in waves _______________________________________________________________________ 4.2 Progressive flooding ___________________________________________________________________________ 4.3 Parametric roll __________________________________________________________________________________ x 5 Applied studies _________________________________________________________________________ 61 5.1 Ro-Pax capsize in waves _______________________________________________________________________ 61 5.2 Parametric roll __________________________________________________________________________________ 66 5.3 Collision survivability in waves ______________________________________________________________ 73 5.4 Accident investigation _________________________________________________________________________ 91
Journal of Applied Mathematics, 2012
This paper describes the development of alternative time domain numerical simulation methods for predicting large amplitude motions of ships and floating structures in response to incoming waves in the frame of potential theory. The developed alternative set of time domain methods simulate the hydrodynamic forces acting on ships advancing in waves with constant speed. For motions' simulation, the diffraction forces and radiation forces are calculated up to the mean wetted surface, while the Froude-Krylov forces and hydrostatic restoring forces are calculated up to the undisturbed incident wave surface in case of large incident wave amplitude. This enables the study of the above waterline hull form effect. Characteristic case studies on simulating the hydrodynamic forces and motions of standard type of ships have been conducted for validation purpose. Good agreement with other numerical codes and experimental data has been observed. Furthermore, the added resistance of ships in waves can be calculated by the presented methods. This capability supports the increased demand of this type of tools for the proper selection of engine/propulsion systems accounting for ship's performance in realistic sea conditions, or when optimizing ship's sailing route for minimum fuel consumption and toxic gas emissions.
Ship capsizing analysis using advanced hydrodynamic modelling
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2000
A ship's stability is fundamental to the safety of its crew, its cargo, and the environment. Several ocean-going vessels are lost due to instability each year, particularly in high seas. To prevent such losses, a better understanding of ship stability is necessary. In this paper we analyse the stability of ships using advanced mathematical models and methods. All the rigid-body motions of a ship, as well as memory e¬ects in the ®uid, are accounted for. The analysis shows that a ship's dynamics depend strongly on the nonlinearities of the ship{®uid system. In our analysis of a particular ship, we notice a sequence of bifurcations when wave heights increase, and we believe that this is an explanation for capsizing. Critical wave heights for capsize were identi ed. In quartering seas, the required wave height was much lower compared with following seas. A path-following method to determine the stability limits in a systematic manner is being developed.
Numerical modeling of breaking waves generated by a ship?s hull
Journal of Marine Science and Technology, 2004
functions, the traditional boundary-fitted grid is not suitable and other approaches have been devised to overcome the problem. We note the marker-and-cell method, initially proposed by Harlow and Welch, 3 and with further developments by Chen et al., 4,5 the volumeof-fluid method by Hirt and Nichols 6 (see also the review by Scardovelli and Zaleski, 7 and the level-set method, 8,9 which has recently been used for the simulation of a three-dimensional viscous flow featuring the plunging of the bow breaker with subsequent air-entrapment and the formation of a second jet. 10 Despite their limitations, when they are applicable surface-fitting approaches deliver excellent results, as is evident from the workshop held in Gothenburg, 11 and many researchers worldwide use this type of algorithm.
Numerical Prediction of Impact-Related Wave Loads on Ships
Journal of Offshore Mechanics and Arctic Engineering, 2007
We present a numerical procedure to predict impact-related wave-induced (slamming) loads on ships. The procedure was applied to predict slamming loads on two ships that feature a flared bow with a pronounced bulb, hull shapes typical of modern offshore supply vessels. The procedure used a chain of seakeeping codes. First, a linear Green function panel code computed ship responses in unit amplitude regular waves. Ship speed, wave frequency, and wave heading were systematically varied to cover all possible combinations likely to cause slamming. Regular design waves were selected on the basis of maximum magnitudes of relative normal velocity between ship critical areas and wave, averaged over the critical areas. Second, a nonlinear strip theory seakeeping code determined ship motions under design wave conditions, thereby accounting for the nonlinear pressure distribution up to the wave contour and the frequency dependence of the radiation forces (memory effect). Third, these nonlinearly computed ship motions constituted part of the input for a Reynolds-averaged Navier-Stokes equations code that was used to obtain slamming loads. Favorable comparison with available model test data validated the procedure and demonstrated its capability to predict slamming loads suitable for design of ship structures.
Numerical Study of Damaged Ship Motion in Waves
Contemporary Ideas on Ship Stability, 2019
An integrated numerical method, which couples a seakeeping solver and a Navier-Stokes (NS) solver with the volume of fluid (VOF) model, has been developed to study the behavior of a damage ship in waves. The dynamics of water flooding and sloshing in the compartments were calculated by the NS solver, while the hydrodynamic forces induced by the sea wave on the external hull surface were calculated using the seakeeping solver. To validate its performance, the solver was applied to the flooding problem of a damaged Ro-Ro ferry in regular beam seas. The computed results are satisfactory in comparison with the experimental data.
Ocean Engineering , 2020
Results are presented of a benchmark and uncertainty assessment study organised by the MARSTRUCT Virtual Institute on global linear wave loads on damaged ship. The study has two aims: to acquire valuable information regarding damage modelling in seakeeping analysis of damaged ships and to contribute to a rational approach for definition of the model uncertainty of linear seakeeping tools. Eight institutes participated in the benchmark, with six codes, representative of important linear seakeeping theories in use nowadays. The benchmark ship is the DTMB 5415 hull, with well documented and accessible data to perform seakeeping analysis and experimental results for motion and global wave loads. The uncertainty analysis is performed using the Frequency Independent Model Error as the uncertainty measure. The analysis is performed for vertical motions, vertical and horizontal global wave load components, and for torsional moments. Uncertainty measures of individual motion and load predictions are presented and compared. In addition, a comparative analysis of linear seakeeping theories is performed and the accuracy of the simplified methods used for the prediction of seakeeping of a damaged ship is assessed. Finally, recommendations are provided for efforts to improve modelling uncertainties in transfer functions of wave loads on damaged ships.