Efficient calculation of slamming pressures on ships in irregular seas

Hermundstad, Ole Andreas; Moan, Torgeir

doi:10.1007/s00773-006-0238-1

Cited by 8 publications

(6 citation statements)

References 7 publications

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“…Later it was demonstrated by Sames et al [31] that the choice of the tilt angle of the strips in the bow had a large effect on the resulting impact force. The approach is still used today in an improved method whereby the bow wave system at different drafts is incorporated in the estimation of the wetted surface, as demonstrated in a series of publications by Hermundstad & Moan [32,33] and Tuitman [15].…”

Section: Boundary-element Methodsmentioning

confidence: 99%

Slamming of ships: where are we now?

Kapsenberg

2011

Phil. Trans. R. Soc. A.

112

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Literature published on the problem of ship slamming in waves is reviewed from the point of view of someone working at a ship research institute. Such an institute is confronted with rather practical questions regarding the acceptability of certain design parameters such as the acceptable amount of bow flare angle for use at sea. The importance of these questions is illustrated by noting that actual slamming or the presumed danger of slamming is the main reason for ship operators to reduce speed or to change heading. The review shows that such questions cannot yet be answered. The problem of the local effect of the impact is very complicated owing to the importance of air inclusions, bubbles in the water, compressibility of water and cavitation effects. Only a computational method properly including all these effects will give an accurate answer; also model tests will not be capable of doing this, if only because the methods to extrapolate the results of models to full scale are not yet developed. The problem of the global response of the ship to a wave impact is closer to being solved. A two-stage approach is proposed, consisting of a computational fluid dynamics method for individual impacts and an approximate method to be included in long-term simulations. However, to arrive at a realistic longterm distribution, one has to account for the seamanship of the captain; avoiding the worst conditions or adapting the ship speed and course has a large effect on the actual extremes. Research on this topic has hardly begun.

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Section: Boundary-element Methodsmentioning

confidence: 99%

Slamming of ships: where are we now?

Kapsenberg

2011

Phil. Trans. R. Soc. A.

112

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“…The normal component (relative to the free surface) of the fluid velocity is the most decisive variable, when addressing the question of slamming loads on a marine structure. In many stochastic approaches it is the only considered random variable, the slamming loads being assumed to be weakly dependent on the other kinematic variables (see for example [16,17,18,19,20,21]). Helmers et al (2012) [25] implemented a more comprehensive stochastic approach, where the conditional joint distribution of four kinematic variables (vertical velocity, vertical acceleration, wave slope, and seakeeping heel angle) was used to estimate the probability distribution of impact loads on a wedge-shaped body, exposed to unidirectional waves, with no forward speed.…”

Section: Considered Kinematic Variablesmentioning

confidence: 99%

“…In the context of slamming on ships, following the pioneering work of Ochi [13,14] and Ochi and Motter [15,16], different authors investigated the stochastic properties of slamming-induced loads and structural stresses, including the effect of forward speed in the analysis. In most studies, however, the vertical component of the relative fluid velocity is considered as the only kinematic variable relevant to the estimate of slamming loads (see for example [16,17,18,19,20,21]). This assumption greatly simplifies the problem by reducing the conditional distribution of kinematic variables (used as an input for the impact model), given up-crossing, to a univariate distribution, which is of Rayleigh type in the framework of linear wave theory.…”

Section: Introductionmentioning

confidence: 99%

“…Knowing the response amplitude operators of the floating platform, along with the position of the material point on this platform, the transfer function of ζ s can be readily expressed. The variable ζ s may also account for the diffraction waves as well as the waves generated by the steady (forward) and unsteady motions of the vessel, if the related transfer functions are known -see for example Moan (2005, 2007) [41,19] who include the effect of the waves generated by the forward motion of the ship in their analysis.…”

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confidence: 99%

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Effect of forward speed on the level-crossing distribution of kinematic variables in multidirectional ocean waves

2021

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The influence of forward speed on stochastic free-surface crossing, in a Gaussian wave field, is investigated. The case of a material point moving with a constant forward speed is considered; the wave field is assumed stationary in time, and homogeneous in space. The focus is on up-crossing events, which are defined as the material point crossing the free surface, into the water domain. The effect of the Doppler shift (induced by the forward speed) on the up-crossing frequency, and the related conditional joint distribution of wave kinematic variables is analytically investigated. Some general trends are illustrated through different examples, where three kinds of wave direction distribution are considered: unidirectional, short-crested anisotropic, and isotropic. The way the developed approach may be used in the context of slamming on marine structures is briefly discussed.

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“…For this reason, there is a pressing need in the indus try to combine simplified slamming and whipping modules into classical seakeeping programs (e.g., Refs. [2] and [3]). …”

Section: Introductionmentioning

confidence: 96%

A Meshless Boundary Element Method for Simulating Slamming in Context of Generalized Wagner

Helmers

Skeie

2015

Journal of Offshore Mechanics and Arctic Engineering

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A boundary element method (BEM) designed for solving the symmetric generalized Wag ner formulation is presented. The flow field is parameterized with analytical functions and can describe the kinematics at any free surface or body location using a small set of parameters obtained from a collocation scheme. The method is fast and robust for all deadrise angles, even for flat plate impacts where classical BEMs usually fail. The method is easy to implement and is easy to apply. Given a smooth body contour the only additional input is the requested accuracy. There is no mesh involved. When solving the temporal problem, we exploit the analytical distribution of free surface velocities and apply an integral equation formalism consistent with the Wagner formulation. The output of the spatial and temporal scheme is a set of functions and parameters suitable for fast computation o f the complete kinematics for any impact trajectory given the position of the keel and the body velocity. The method is developed to be combined with seakeeping programs for statistical impact and whipping assessment.

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Efficient calculation of slamming pressures on ships in irregular seas

Cited by 8 publications

References 7 publications

Slamming of ships: where are we now?

Slamming of ships: where are we now?

Effect of forward speed on the level-crossing distribution of kinematic variables in multidirectional ocean waves

A Meshless Boundary Element Method for Simulating Slamming in Context of Generalized Wagner

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