arXiv subjects

Nicolas Jacques

Publications and source records attributed to Nicolas Jacques.

4 recordsLinked to original sources

arXiv2023

On the risk of fatigue failure of structural elements exposed to bottom wave slamming -- Impulse response regime

This study aims to investigate whether fatigue damage induced by bottom wave slamming can be a failure mode important to consider when sizing a marine structural element. The body exposed to wave impacts is assumed to have a shape and structural arrangement such that the duration of wave-impact loads is short relative to the structure's vibratory response time. In this dynamical regime, fatigue is found to be a potentially important failure mechanism: accounting for the risk of failure due to fatigue damage may result in design constraints that are significantly more conservative than those based on the risk of ultimate strength exceedance. The role of fatigue damage depends on the elevation of the body. It is predominant for low elevations, for which slamming events are frequent. Since this study aims to provide general insight, the specific details of the body, such as its shape and structural arrangement, are not specified. Instead, a general framework is used for the analysis. The way forward to address a specific case study, possibly including the effects of forward and seakeeping motions, is briefly explained.

physics.flu-dyn↗

arXiv2021

Stochastic prediction of wave impact kinematics and loads for ship appendages

A stochastic approach is implemented to address the problem of a marine structure exposed to water wave impacts. The focus is on (i) the average frequency of wave impacts, and (ii) the related probability distribution of impact kinematic variables. The wave field is assumed to be Gaussian. The seakeeping motions of the considered body are taken into account in the analysis. The coupling of the stochastic model with a water entry model is demonstrated through the case study of a foil exposed to wave impacts.

physics.flu-dyn↗

arXiv2021

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

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.

physics.ao-ph↗

arXiv2019

A two-dimensional analytical model of vertical water entry for asymmetric bodies with flow separation

The vertical water entry of asymmetric two-dimensional bodies with flow separation is considered. As long as there is no flow separation, linearised Wagner's theory combined with the Modified Logvinovich Model has been shown to provide computationally fast and reliable estimates of slamming loads during water entry. Tassin et al. (2014) introduced the Fictitious Body Continuation (FBC) concept as a way to extend the use of Wagner's model to separated flow configurations, but they only considered symmetric bodies. In the present study, we investigate the ability of the FBC concept to provide accurate estimates of slamming loads for asymmetric bodies. In this case, flow separation may not occur simultaneously on both sides of the body. During an intermediate phase, slamming loads are governed by a competition between the local drop in pressure due to partial flow separation and the ongoing expansion of the wetted area. As a first benchmark for the model, we consider the water entry of an inclined flat plate and compare the FBC estimates with the results of a nonlinear model. Then, we consider the case of a foil and compare the FBC results with Computational Fluid Dynamics predictions. In both cases, we find that the FBC model is able to provide reliable estimates of the slamming loads.

physics.flu-dyn↗