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| Olagnon, Michel; Kpogo-nuwoklo, Komlan; Guede, Zakoua. |
| Accurate estimation of long-term sea conditions is a major issue for the design of coastal and offshore structures, for the preparation of marine operations, and for other applications such as marine energy, and coastal erosion. It requires, on the one hand, proper parametric models of the sea state spectra and the statistics of the parameters, and on the other hand, representations of their time evolutions. In some locations such as West Africa, sea conditions are complex with wave spectra showing many well separated peaks corresponding to several swells and wind sea. The present study focuses on swell at a West Africa location. First, a time-consistent triangular model is assessed for the spectral shapes of the swell components. Then statistical analysis... |
| Tipo: Text |
Palavras-chave: Joint probabilities; Metocean time-series; Swell spectral models; Ocean wave climate; Event tracking; Offshore fatigue design. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00156/26695/24761.pdf |
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| Olagnon, Michel; Guede, Zakoua. |
| This paper provides theoretical formulas to calculate conservative estimates of the rainflow fatigue damage from the spectral parameters for spectra composed of the combination of one or several narrow-band low-frequency loads and a higher frequency one, such as are often encountered with moored marine structures. With respect to the semi-empirical formulas that have been proposed by other authors, those presented here are theoretically constructed from the mathematical definition of rainflow and from the statistical properties of Gaussian processes. (C) 2008 Elsevier Ltd. All rights reserved. |
| Tipo: Text |
Palavras-chave: Random loading; Rainflow; Spectral fatigue; Fatigue. |
| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-4197.pdf |
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| Prevosto, Marc; Le Louarne, Jean-franois; Guede, Zakoua. |
| In this study we discuss various methods to assess the statistics of extreme response of a floating structure subjected to random waves. This issue is of great importance in the case of low frequency motion of floating bodies in shallow water. Those methods are based on the evaluation of the level crossing rate, which is easily related to the extreme value statistics for stationary random processes and large levels. Four main methods are considered, namely the Rice formula with either a Gaussian assumption or an approximation of the joint distribution of the response and its first derivative by a projection method; the Breitung's formula; the Hagberg's approaches using either an asymptotic expansion or a Monte-Carlo integration and finally the time domain... |
| Tipo: Text |
Palavras-chave: Low frequency motion; Shallow water; Second order wave loading; Crossing rate; Extreme response. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/acte-6329.pdf |
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| Morvan, Barthelemy; Priour, Daniel; Guede, Zakoua; Bles, G.. |
| The evaluation of the mesh resistance to opening of fishing nets is an important issue in assessing the selectivity of trawls by numerical methods. Sala et al. (2007) proposed a method using a relatively expensive experimental device ensuring the 2D deformation of net sample. De la Prada and Gonzales (2015) proposed a simple uni-axial experimental set-up, which stretches a sample in the transverse direction of the meshes while leaving free its deformation in the normal direction. Both authors (Sala and De la Prada) assumed that the deformation is uniform in the sample. The present study aims at developing a finite element model taking into account the mesh resistance to opening of nets, allowing the simulation of non-uniform deformation. Mechanical... |
| Tipo: Text |
Palavras-chave: Netting; Mesh resistance to opening; Bending stiffness; Experiment; Numerical model. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00347/45813/49043.pdf |
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| Guede, Zakoua; Suldret, B; Lemaire, M. |
| A probabilistic approach of the current thermal fatigue design of nuclear components is set up. It aims at incorporating all kinds of uncertainties that affect the thermal fatigue behaviour. This approach is based on the theory of structural reliability. Two dual approaches of reliability analysis for the thermal fatigue are defined, respectively, in the time domain and in the frequency domain. Beside the probability of failure calculation, the sensitivity of the reliability index to each random variable is estimated. The proposed method is applied to a pipe submitted to thermal loading due to water flow. Both high cycles fatigue (HCF) and low cycles fatigue (LCF) regimes are investigated. The results show that it is possible to perform a complete... |
| Tipo: Text |
Palavras-chave: Spectral methods; Structural reliability; Thermal fatigue; Life time. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2730.pdf |
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| Guede, Zakoua; Olagnon, Michel; Pineau, Hélène. |
| The purpose of this study is to validate the use of the so-called Iterative Component Addition (ICA) formulas for the assessment of fatigue damage of marine structures subjected to complex (multimodal) wave loading conditions, as prevail in West Africa areas where the sea states are usually described as combinations of three wave systems (e.g. main swell, secondary swell and wind sea). In this context, operators specifications require to consider a very large set of fatigue loading cases, which lead to excessive computation times if the conventional procedure is used for fatigue assessment. The use of the ICA formulas is expected to simplify the evaluation of the damage and to allow a drastic reduction of computation time, keeping a slight level of... |
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| Ano: 2009 |
URL: https://archimer.ifremer.fr/doc/00484/59556/62540.pdf |
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