| 1. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Dynamically Evolving Gaussian Spatial Fields
- 2008
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We discuss general non-stationary spatio-temporal surfaces that involve dynamics governed by velocity fields. The approach formalizes and expands previously used models in analysis of satellite data of significant wave heights. We start with homogeneous spatial fields and by applying an extension of the standard moving average construction we arrive to stationary in time models. The obtained surface although changing in time can be considered dynamically inactive since its velocities when sampled across the field have distributions centered at zero. We introduce a dynamical evolution to such a field by composing it with a dynamical flow governed by a given velocity field. This leads to non-stationary models that are extensions of the previous discretized auto-regressions accounting for a local velocity of traveling surface. For such a surface we demonstrate that its dynamics is a combination of dynamics introduced by the flow and the dynamics resulting from the covariance structure of the underlying stochastic field. We extend this approach to fields that are only locally stationary and have their parameters varying over a larger spatio-temporal horizon.
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| 2. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Dynamically evolving Gaussian spatial fields
- 2011
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Ingår i: Extremes. - : Springer Science and Business Media LLC. - 1386-1999 .- 1572-915X. ; 14:2, s. 223-251
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Tidskriftsartikel (refereegranskat)abstract
- We discuss general non-stationary spatio-temporal surfaces that involve dynamics governed by velocity fields. The approach formalizes and expands previously used models in analysis of satellite data of significant wave heights. We start with homogeneous spatial fields. By applying an extension of the standard moving average construction we obtain models which are stationary in time. The resulting surface changes with time but is dynamically inactive since its velocities, when sampled across the field, have distributions centered at zero. We introduce a dynamical evolution to such a field by composing it with a dynamical flow governed by a given velocity field. This leads to non-stationary models. The models are extensions of the earlier discretized autoregressive models which account for a local velocity of traveling surface. We demonstrate that for such a surface its dynamics is a combination of dynamics introduced by the flow and the dynamics resulting from the covariance structure of the underlying stochastic field. We extend this approach to fields that are only locally stationary and have their parameters varying over a larger spatio-temporal horizon.
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| 3. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Fatigue life prediction for a vessel sailing the North Atlantic route
- 2007
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Ingår i: Probabilistic Engineering Mechanics. - : Elsevier BV. ; 22:2, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- A method for calculating the wave load induced fatigue damage accumulated by a vessel sailing along the North Atlantic route (NAr) is presented. This method is based on the Palmgren-Miner additive rule and the rainflow cycle (RFC) count. For simplicity, the load the vessel experiences is assumed to be proportional to the encountered significant wave height process, $H_s$. The asymptotically normal character of the nominal damage is proved and used to derive the probability distribution of the fatigue life prediction. The proposed method improves the already existing ones by making use of the information contained in the variance of the fatigue damage accumulated during the voyages. The method is illustrated through numerical examples.
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| 5. |
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| 6. |
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| 7. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Spatial models for the variability of the significant wave height on the world oceans
- 2008
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 18:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Significant wave height ($H_s$) is a measure of the variability of the ocean surface. Benefits from knowing the spatial and temporal characteristics of this field are multiple: it is useful to dimension offshore structures, to foresee the fatigue of the ship's hull depending on its route and season, to compute probabilities of risks associated with marine operations. In this paper, we describe a method for modeling the $H_s$ in space. The method is based on the Gaussian hypothesis for the logarithms of $H_s$ and consists of estimating the mean and the covariance structure of $\log(H_s)$ using the information provided by the total variation. We then use the estimated parameters of every area in the world to construct maps of the median and the correlation structure. These maps are used to compute the probability the $H_s$ exceeds a pre-defined level, and the distribution of the length of a storm. The data used are that of the TOPEX-Poseidon satellite.
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| 8. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Spatio-temporal modelling of significant wave height
- 2007
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Ingår i: Environmetrics. ; 19, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we construct a homogeneous spatio-temporal model to describe the variability of significant wave height over small regions of the sea and over short periods of time. Then, the model is extended to a non-homogeneous one that is valid for larger areas of the sea and for time periods up to ten hours. To validate the proposed model, we reconstruct the significant wave height surface under different scenarios and then compare it to satellite measurements and the C-ERA-40 field.
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| 9. |
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| 10. |
- Baxevani, Anastassia, 1969, et al.
(författare)
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Spatio-temporal statistical modelling of significant wave height
- 2009
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Ingår i: Environmetrics. - : Wiley. - 1180-4009 .- 1099-095X. ; 20:1, s. 14-31
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Tidskriftsartikel (refereegranskat)abstract
- In this paper. we construct a homogeneous spatio-temporal model to describe the variability of significant wave height over small regions of the sea and over short periods of time. Then. the model is extended to a non-homogeneous one that is valid over larger areas of the sea and for time periods of up to 10 h. To validate the proposed model. we reconstruct the significant wave height surface under different scenarios and then compare it to satellite measurements and the C-ERA-40 field. Copyright (C) 2008 John Wiley & Sons, Ltd.
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