| 1. |
- Rychlik, Igor, 1952, et al.
(författare)
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Estimation of return values for significant wave height from satellite data
- 2011
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Ingår i: Extremes. - : Springer Science and Business Media LLC. - 1386-1999 .- 1572-915X. ; 14:2, s. 167-186
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Tidskriftsartikel (refereegranskat)abstract
- Estimation of extreme wave height across the oceans is important for marine safety and design, but is hampered by lack of data. Buoy and platform data are geographically limited, and though satellite observations offer global coverage, they suffer from temporal sparsity and intermittency, making application of standard methods of extreme value estimation problematical. A possible strategy in the face of such difficulty is to use extra model assumptions to compensate for lack of data. In this spirit we report initial exploration of an approach to estimation of extreme wave heights using crossings methods based on a log-Gaussian model. The suggested procedure can utilize either intermittent satellite data or regular time series data such as obtained from a buoy, and it is adapted to seasonal variation in the wave height climate. The paper outlines derivation of the method and illustrates its application to data from the Atlantic and Pacific oceans. A numerical comparison is made with the results of an annual maximum analysis for sites at which both satellite and buoy data are available. The paper concludes with a discussion of the applicability of the new approach, its relationship to other extreme value methods and desirable directions for further development.
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| 2. |
- Hildeman, Anders, 1984, et al.
(författare)
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Joint spatial modeling of significant wave height and wave period using the SPDE approach
- 2022
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Ingår i: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 68
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Tidskriftsartikel (refereegranskat)abstract
- The ocean wave distribution in a specific region of space and time is described by its sea state. Knowledge about the sea states a ship encounters on a journey can be used to assess various parameters of risk and wear associated with this journey. Two important characteristics of the sea state are significant wave height and mean wave period. We propose a joint spatial model of these two quantities on the north Atlantic ocean. The model describes the distribution of the logarithm of the two quantities as a bivariate Gaussian random field, modeled as a solution to a system of coupled fractional stochastic partial differential equations. The bivariate random field is non-stationary and allows for arbitrary, and different, smoothness for the two marginal fields. The parameters of the model are estimated from data using a stepwise maximum likelihood method. The fitted model is used to derive the distribution of accumulated fatigue damage for a ship sailing a transatlantic route. Also, a method for estimating the risk of capsizing due to broaching-to based on the joint distribution of the two sea state characteristics is investigated. The risks are calculated for a transatlantic route between America and Europe using both data and the fitted model. The results show that the model compares well with observed data. It further shows that the bivariate model is needed and cannot simply be approximated by a model of significant wave height alone. © 2022 Elsevier Ltd
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| 3. |
- Bengtsson, Anders, et al.
(författare)
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Uncertainty in fatigue life prediction of structures subject to Gaussian loads
- 2009
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Ingår i: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 24:2, s. 224-235
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we shall concentrate on Gaussian (or close to Gaussian) loads acting on a structure. The goal is to compute a measure of risk for fatigue of a component during a specific time period and the so called "safety index" will be used to combine different types of uncertainties. The presented methodology can be applied in a more general situation of environmental loads which properties may vary with time of the year. The load is assumed to be "locally" stationary such that the mean load is constant (and taken to be zero) but the variance of the load can change slowly with time. Non-stationary hierarchical processes, separable into a stationary Gaussian process and a process describing the load amplitude and period, e.g. processes with Pierson-Moskowitz or JONSWAP spectrum, are treated in detail. The variability of a load, relevant for the fatigue accumulation process, will be described by means of rainflow cycles counted in the load. Moreover, common damage intensity approximations are reviewed and evaluated in a simulation study. © 2008 Elsevier Ltd. All rights reserved.
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| 4. |
- Bengtsson, Anders, et al.
(författare)
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Uncertainty of estimated rainflow damage for random loads
- 2009
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 22:2, s. 261-274
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Tidskriftsartikel (refereegranskat)abstract
- One way to assess the uncertainty in fatigue damage analysis is to use a so-called safety index. In the computation of such an index the coefficient of variation for the accumulated damage is needed. Employing the rainflow cycle count method for fatigue damage leads to, in most cases, complicated calculations. Here we present a new and simplified method to estimate the coefficient of variation for the accumulated damage when only one sample path of the load is available. Non-stationary, slowly changing, Gaussian loads are given special attention. The approach is illustrated by means of stationary Gaussian loads with nine different spectra, a measured non-Gaussian load, a skewed load and the wave load accumulated during one year in a "seasonally changing environment"
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| 5. |
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| 6. |
- Bogsjö, Klas, et al.
(författare)
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Vehicle fatigue damage caused by road irregularities
- 2009
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Ingår i: Fatigue and Fracture of Engineering Materials and Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 32:5, s. 391-402
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Tidskriftsartikel (refereegranskat)abstract
- Road roughness causes fatigue-inducing loads in travelling vehicles. Road sections with a high degree of roughness are of special interest because these have a significant impact on vehicle's fatigue life. This study is focused on the statistical description and analysis of vehicle damage caused by irregularities. Standard statistical analysis tools are not straightforwardly applicable because of the non-stationary property of the irregularities. However, it is found that the road irregularities' influence on vehicles can be accurately described using a 'local' narrow-band approximation of the fatigue damage intensity. © 2009 Blackwell Publishing.
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| 7. |
- Hildeman, Anders, 1984, et al.
(författare)
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Deformed SPDE models with an application to spatial modeling of significant wave height
- 2021
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Ingår i: Spatial Statistics. - : Elsevier BV. - 2211-6753. ; 42
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Tidskriftsartikel (refereegranskat)abstract
- A non-stationary Gaussian random field model is developed based on a combination of the stochastic partial differential equation (SPDE) approach and the classical deformation method. With the deformation method, a stationary field is defined on a domain which is deformed so that the field becomes non-stationary. We show that if the stationary field is a Matérn field defined as a solution to a fractional SPDE, the resulting non-stationary model can be represented as the solution to another fractional SPDE on the deformed domain. By defining the model in this way, the computational advantages of the SPDE approach can be combined with the deformation method's more intuitive parameterization of non-stationarity. In particular it allows for independent control over the non-stationary practical correlation range and the variance, which has not been possible with previously proposed non-stationary SPDE models. The model is tested on spatial data of significant wave height, a characteristic of ocean surface conditions which is important when estimating the wear and risks associated with a planned journey of a ship. The model parameters are estimated to data from the north Atlantic using a maximum likelihood approach. The fitted model is used to compute wave height exceedance probabilities and the distribution of accumulated fatigue damage for ships traveling a popular shipping route. The model results agree well with the data, indicating that the model could be used for route optimization in naval logistics.
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| 8. |
- Johannesson, Pär, 1969, et al.
(författare)
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Modelling roughness of road profiles on parallel tracks using roughness indicators
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The vertical road input is the most important load for durability assessments of vehicles. We focus on stochastic modelling of the parallel road profiles with the aim to find a simple but still accurate model for such bivariate records. A model is proposed that is locally Gaussian with randomly gamma distributed variances leading to a generalized Laplace distribution of the road profile. This Laplace model is paired with the ISO spectrum and is specified by only three parameters. Two of them can be estimated directly from a sequence of roughness indicators, such as IRI or ISO roughness coefficient. The third parameter needed to define the cross spectrum between the left and right road profiles is estimated from the sample correlation. Explicit approximations for the expected fatigue damage for the proposed Laplace-ISO model are developed and its usefulness is validated using measured road profiles.
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