| 1. |
- Baxevani, Anastassia, 1969, et al.
(author)
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Dynamically evolving Gaussian spatial fields
- 2011
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In: Extremes. - : Springer Science and Business Media LLC. - 1386-1999 .- 1572-915X. ; 14:2, s. 223-251
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
- Bogsjö, Klas, et al.
(author)
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Models for road surface roughness
- 2012
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In: Vehicle System Dynamics. - : Informa UK Limited. - 0042-3114 .- 1744-5159. ; 50:5, s. 725-747
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Journal article (peer-reviewed)abstract
- This study focuses on the statistical description and analysis of road surface irregularities that are essential for heavy-vehicle fatigue assessment. Three new road profile models are proposed: a homogenous Laplace moving average process, a non-homogenous Laplace process and a hybrid model that combines Gaussian and Laplace modelling. These are compared with the classical homogenous Gaussian process as well as with the non-homogenous Gaussian model that represents the road surface as a homogenous Gaussian process with Motor Industry Research Association spectrum enhanced by randomly placed and shaped irregularities. The five models are fitted to eight measured road surfaces and their accuracy and efficiency are discussed.
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| 4. |
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COMMITTEE I.1 ENVIRONMENT
- 2012
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In: 18th International Ship and Offshore Structures Congress (ISSC 2012)}.
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Conference paper (peer-reviewed)
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| 5. |
- Galtier, Thomas, 1982, et al.
(author)
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Approximation of crossing intensities for non linear responses subjected to non Gaussian loadings
- 2010
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In: Proceedings of the ASME 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010) in Shanghai, China, June 6-11, 2010. - 9780791849101 ; 2, s. 109-121
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Conference paper (peer-reviewed)abstract
- Crossing intensity constitute an important response characteristic for randomly vibrating structures, especially if one is interested in estimating the risk against failures. This paper focusses on developing approximations by which estimates of the crossing intensities for response of marine structures can be obtained in a computationally efficient manner, when the loads are modeled as a special class of non-Gaussian processes, namely as LMA processes. Ocean waves exhibit considerable non-Gaussianity as marked by their skewed marginal distributions and heavy tails. Here, a new class of processes the Laplace driven Moving Average (LMA) processes are used to model the ocean waves. LMA processes are non-Gaussian, strictly stationary, can model in principle any spectrum and have the additional flexibility to model the skewness and the kurtosis of the marginal distribution. The structure behavior assumed is limited to quadratic systems characterized by second order kernels, which is common for marine structures. Thus, an estimation of the crossing intensities of the response involves studying the crossing characteristics of a LMA process passing through a second order filter. A new computationally efficient hybrid method, which uses the saddle point approximations along with limited Monte Carlo simulations, is developed to compute crossing intensity of the response. The proposed method is illustrated through numerical examples.
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| 6. |
- Galtier, Thomas, 1982, et al.
(author)
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Crossings of Second-order Response Processes Subjected to LMA Loadings
- 2010
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In: Journal of Probability and Statistics. - : Hindawi Limited. - 1687-952X .- 1687-9538. ; 2010
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Journal article (peer-reviewed)abstract
- The focus of this paper is on the estimation of the crossing intensities of responses for second-order dynamical systems, subjected to stationary, non-Gaussian external loadings. A new model for random loadings—the Laplace driven moving average (LMA)—is used. The model is non-Gaussian, strictly stationary, can model any spectrum, and has additional flexibility to model the skewness and kurtosis of the marginal distribution. The system response can be expressed as a second-order combination of the LMA processes. A numerical technique for estimating the level crossing intensities for such processes is developed. The proposed method is a hybrid method which combines the saddle-point approximation with limited Monte Carlo simulations. The performance and the accuracy of the proposed method are illustrated through a set of numerical examples.
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| 7. |
- Jith, J., et al.
(author)
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Crossing Statistics of Quadratic Transformations of LMA Processes
- 2013
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In: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 33, s. 9-17
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Journal article (peer-reviewed)abstract
- Random loads that exhibit significant non-Gaussianity in terms of asymmetric distributions with high kurtosis can be modeled as Laplace Moving Average (LMA) processes. Examples of such loads are the wave loadings in ships, wind loads on wind turbines, loads arising due to surface roughness in vehicular systems, etc. The focus of this paper is on estimating the crossing statistics of second-order response of structures subjected to LMA loads. Following the Kac–Siegert representation, a second order approximation of the Volterra expansion of the system enables representing the response as a quadratic combination of vector LMA processes. The mean crossing rate of the response is then computed using a hybrid approach. The proposed method is illustrated through two numerical examples.
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| 8. |
- Jith, J., et al.
(author)
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Local maxima in quadratic LMA processes
- 2012
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In: Proceedings of 11th ASCE Conference. 11th ASCE Joint Specialty Conference on Probabilistic Mechanics & Structural Reliability (EMI/PMC 2012), June 17-20 2012 Notre Dame, Indiana.
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Conference paper (peer-reviewed)
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| 9. |
- Johannesson, Pär, et al.
(author)
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Laplace processes for describing road profiles.
- 2013
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In: Procedia Engineering. - : Elsevier BV. - 1877-7058 .- 1877-7058. ; 66, s. 464-473
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Conference paper (peer-reviewed)abstract
- The Gaussian model is frequently used for modelling environmental loads, e.g. sea elevation, wind loads and road profiles. However, the Gaussian model is often only valid for short sections of the load. For example, for roads profiles, short sections of roads, say 100 m, is well modelled by a Gaussian process, whereas longer sections of roads, say 10 km, typically contain shorter sections with high irregularity, and the variability between sections is higher than what can be explained by the stationary Gaussian model. This phenomenon can be captured by a Laplace process, which can be seen as a Gaussian process with randomly varying variance. Thus, the Gaussian process is a special case of the Laplace process. Further, the expected damage can be computed from the parameters of the Laplace process. We will give examples of modelling road profiles using Laplace models. Especially, it will be demonstrated how to reconstruct a road profile based on sparse road roughness measurements, such as a sequence of IRI (International Roughness Index) for 100 metre road sections. Further, IRI data from the Finnish road network will be evaluated.
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| 10. |
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