| 1. |
- Bogsjö, Klas, et al.
(författare)
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Models for road surface roughness
- 2012
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 0042-3114 .- 1744-5159. ; 50:5, s. 725-747
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Tidskriftsartikel (refereegranskat)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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| 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. |
- Johannesson, Pär, 1969, et al.
(författare)
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Laplace distribution models for road topography and roughness
- 2017
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Ingår i: International Journal of Vehicle Performance. - 1745-3194 .- 1745-3208. ; 3:3, s. 224-258
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Tidskriftsartikel (refereegranskat)abstract
- Gaussian models are frequently used for road elevations. However,these models are often only valid for short sections of the road. Here we presenta comprehensive approach to describe various aspects of road surface/elevationby using extensions of Gaussian models arising from random gamma distributedvariances. These random variances result in the Laplace distribution and thuswe refer to the so defined models as Laplace models. The approach is shownto perform well in modelling road topography, road roughness and multi-valuedresponses of forces and bending moments containing transients. The differentLaplace models are presented together with numerical examples and Matlab codefor simulation.
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| 4. |
- Podgorski, Krzysztof, et al.
(författare)
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Distributions at random events
- 2016
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Ingår i: 2016 2ND INTERNATIONAL CONFERENCE ON EVENT-BASED CONTROL, COMMUNICATION, AND SIGNAL PROCESSING (EBCCSP). - 9781509041961 ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- We discuss the generalized Rice formula approach to deriving long-run distributions of characteristics defined at random events of a stochastic process or field. The approach stems from the same principle originally introduced by Rice for the level crossing intensity in a random signal and we review its extensions to more general contexts.Events are defined on random surfaces through crossing levels of (multivariate) stochastic fields.We also account for the dynamics of spatial-temporal fields using observed velocities. Extensions beyond the Gaussian model are shown and models for sampling from the level crossing distributions are presented.The importance of these generalizations for applications is illustrated through examples.
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| 5. |
- Podgorski, Krzysztof, et al.
(författare)
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Distributions of spatial wave size for random fields
- 2016
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Ingår i: 2nd International Conference on Event-Based Control, Communication, and Signal Processing (EBCCSP), Krakow, POLAND, JUN 13-15, 2016. - 9781509041961
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Konferensbidrag (refereegranskat)abstract
- A method of measuring three-dimensional spatial wave size is proposed and statistical distributions of the size characteristics are derived in explicit integral forms for Gaussian sea surfaces. New definitions of wave characteristics such as the crest-height, the length, the size and the wave front location are provided in fully dimensional context. The joint statistical distributions of these wave characteristics are derived using the Rices formulas for expected numbers of local maximum and distance from a local maximum to a level crossing countour. %The methodology will be also illustrated by some examples from other type of engineering applications. Review of the Rice's method to study crossing distributions is given.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
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| 10. |
- 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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