The state of the art in modeling ship stability in waves (original) (raw)
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.
Model Experiments of Ship Capsize in Astern Seas
Journal of the Society of Naval Architects of Japan, 1996
Capsizing experiments were carried out for both models of container ship and purse seiner running in regular and irregular astern seas. Dangerous situations in ship speed and heading angle of ship to waves are experimentally and analytically investigated for the phenomena which are the so-called harmonic and parametric resonance, pure loss of stability, surf-riding and broaching-to. An analytical approach was attempted to investigate profoundly the dynamics of ship motions and capsizing in severe astern seas. The results of the analytical approach by making use of computer program are in a good agreement with experiments.
Numerical Investigation of Motion Response of Two Model Ships in Regular Waves
In this paper, the sea keeping performances of two model ships in regular waves are studied by our in-house solver naoe-FOAM-SJTU based on OpenFOAM code package. Volume of Fluid (VOF) method is used to capture the free interface and Finite Volume Method (FVM) is adopted as the discretization scheme. Different wave conditions are set by the wave generation and damping module in the solver. The heave and pitch are simulated, and green water is found during the ship motion. The function of bulbous bow for that is discussed.
Breaking wave at the bow of a fast displacement ship model
Journal of Marine Science and Technology, 2003
We investigated the flow structures under the bow wave generated by a fast displacement ship model (INSEAN model 2340) in the presence of wave breaking. The data acquired were also used for a detailed database for CFD validation. The mean and r.m.s. point-wise values of the wave height were measured by means of a finger probe. The intensity of the breaking wave was taken as the r.m.s value of the wave height. The mean velocity field under the free surface was measured at 0.15 L PP and 0.2 L PP downstream of the fore perpendicular by means of a 5-hole Pitot probe. Uncertainty assessment of the wave height and velocity field results was performed following the AIAA Standards S-071-1995. Preliminary CFD results from a RANSE code with a breaking model are shown in comparison with the measured data.
Simplified Method of Modelling Behaviour of Ship in Waves with Partially Flooded Compartments
Transactions on Maritime Science, 2021
This paper contains a description of a numerical model for calculating behaviour of ships in waves. There are many models available, but the one described here can be characterised with a set of parameters that have a decisive impact on the final values of roll motion amplitude and frequency. In this paper, it is shown how a fitting of a standard-shape hull characterised by certain readily available parameters affects the final roll and frequency of the motion. In addition, calculations for a flooded tank were made, and a range of results for the maximum dynamic heeling forces from this tank is shown. This calculation can further be verified for a range of hull dimensions and geometries to present a viable method to the industry.
Hydrodynamic Impact on Displacement Ship Hulls. An Assessment of the State of the Art. Bibliography
1995
: This bibliography was formulated during the development of the Ship Structure Committee report: Hydrodynamic Impact Loading on Displacement Ship Hulls, An Assessment of the State of the Art, by Dr. John C. Daidola and Dr. Victor Mishkevich. The report provides a comprehensive assessment of the state of the art of hydrodynamic impact loading on displacement ship hulls. The subject is considered in light of the three distinct phenomena of slamming, wave slap, and frontal impact. Factors leading to hydro-dynamic impact are defined in terms of environmental and vessel characteristics. The theories of impact are reviewed in sub-categories of two and three dimensional analytical hydrodynamic models, hydroelastic models, seakeeping theory, model tests and full scale data. The techniques and procedures identified which lend themselves to analysis and potential design application are identified and described, the characteristics of each summarized, and example calculations relating the tec...
An experimental study of hull girder loads on an intact and damaged naval ship
Ocean Engineering, 2017
This work is focused on experimental investigation of the hull girder loads on an intact and damaged naval ship DTMB 5415 at zero speed. The experimental campaign was carried out in head and beam regular waves at the University of Strathclyde. The effect of the use of moorings in the model experimental setup was investigated in the context of loads assessment, and the moorings are shown to influence the measured hull girder loads at some wave frequency compared to the free drift case. Therefore the tests in beam seas are performed with free drifting model while the moored model setup was adopted for head seas. The results for ship motions are compared with those from a previous campaign giving an insight into repeatability and uncertainty of measurements. The roll decay of the ship in both intact and damaged conditions is analysed and the linear and quadratic extinction coefficients for the model and the ship scale are reported and detailed discussion on intact-versus-damaged ship roll damping behaviour is given. The results for the hull girder loads are presented for intact and damaged ship. An investigation of the nonlinear effects due to wave height variation in the range wave height to wave length from 1/50 to 1/22 on shear force and bending moment was carried out for a range of wave lengths to ship length ratios from 0.8 to 1.4. The results of the extensive campaign are compared against similar experimental studies forming a benchmark for validation of numerical methods. Keywords: 5415 DTMB model, wave loads on intact and damaged ship; nonlinear responses; experimental shear force and bending moments assessment, roll decay, equivalent linear roll extinction coefficient NOMENCLATURE A -wave amplitude, m B OA -beam over all, m B WL -beam at waterline, m C B -block coefficient C M -midship section coefficient C P -prismatic coefficient D -depth, m g -acceleration of gravity, 9.80665 m/s 2 GM -transversal metacentric height, m H -wave height, m HBM -horizontal bending moment, Nm HSF -horizontal shear force, N H/λ W -ratio between wave height and wave length k -wave number, 2π/λ W KG -vertical position of the centre of gravity, from BL, m KM -vertical position of the metacentre, from BL, m k XX -radius of gyration with respect to x axis, m,
Dynamic Stability of Ships in Waves
2000
A method is proposed for evaluating the overall dynamic stability of an intact vessel in a seaway. We use an existing ship motions program to study the motion of a vessel with a certain loading condition, speed and heading, in given wave conditions. A deterministic method is discussed for looking at the stability of a vessel over a wide range
eSAFE - cruise ship survivability in waves
Aalto University eBooks, 2019
Recent developments in damage stability legislation have been drawn from ships with simple internal watertight architecture such as RoPax and cargo ships. However, ships with complex internal architecture, such as cruise ships, have been rather neglected. In a regulatory context, cruise ships are currently grouped with RoPax and other passenger ships and this can be misleading. Moreover, it is well known that cruise ships vary significantly in their behaviour post-flooding incidents in comparison to RoPax ships. This problem has been acknowledged by the Cruise Ship Safety Forum Steering Committee who consequently funded the Joint Industry Project eSAFE to undertake cruise ship-focused research on damage stability. This entails analysis of pertinent simplifications embedded in SOLAS, the development of a methodology to combine consequences from collision and grounding accidents, the establishment of new survival criteria for cruise ships and finally the development of guidelines to use numerical flooding simulation in seaways as an alternative approach to assessing ship damage survivability. The findings of this research are presented in this paper, based on a full set of time-domain numerical simulations along with static calculations for a number of cruise ships. A new s-factor is derived catering specifically for cruise ships that accounts more accurately for survivability in a wave environment. A number of simulations are undertaken on varying size cruise ships with the view to deriving a relationship between the critical significant wave height and the residual stability properties of such vessels. The results provide the requisite evidence for comparison between SOLAS 2009 A-Index and the ensuing damage Survivability Index.
Ship capsize assessment and nonlinear dynamics
Contemporary Ideas on Ship Stability, 2000
Certain aspects of ship stability assessment in beam and in following seas are discussed. It is argued that the use of detailed numerical codes of ship motions cannot solve alone the assessment problem. On the other hand, whilst simplified models can be very useful for acquiring a fundamental understanding of the dynamics of capsize, still a good number of theoretical obstacles need to be overcome. In respect to beam sea capsize, we begin by discussing the structure of the mathematical model and the types of excitation. Then we consider the mechanism of roll damping very near to capsize angles and we point out a very interesting connection that exists with the specification of predictors of capsize based on Melnikov's method. Finally we sketch out a constrained design optimization procedure which can be used in order to identify those ship parameters' values where resistance to capsize is maximized. In respect to the following sea, we show that if capsize is examined in a transient sense, it should be possible to have a unified treatment of pure-loss and parametric instability. We also present predictions of the qualitative effect on the stability transition curves coming from bi-chromatic waves.