| 1. |
- Pettersson, Pär, 1985, et al.
(författare)
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Influence of hill-length on energy consumption for hybridized heavy transports in long-haul transports
- 2016
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Ingår i: 7th Commercial Vehicle Workshop Graz, 20160513, Graz.
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Konferensbidrag (refereegranskat)abstract
- Goods transports are big producers of CO2, i.e. consumers of energy. The conventional transport vehicles such as tractor-semitrailers can be replaced by long combination vehicles (LCVs). By doing so, fuel consumption will be reduced drastically, with up to 30%, mainly thanks to the reduced aerodynamic resistance per pay load mass and/or volume. Further reduction of CO2 improvements can be made by hybridization, if the road topography demands variable propulsion power due to up- and downhills. This gain is emphasized for heavier vehicles. So, hybridized LCVs are of special interest.When developing vehicles, or selecting vehicle for a certain transport, one needs to assume an operating cycle. To describe the operating cycle correctly is very important for this purpose. Traditionally, the magnitude of road grades is the only topography measure used to characterise the road. In this paper it is studied how an additional measure, hill length, influences these heavy hybridized LCVs. Together one can see these two measures as amplitude and wavelength.It is shown how energy saving varies for different types of roads (combinations of grade magnitude and hill-length) and different energy buffer sizes. Road topography is statistically generated for a good coverage of road types, but also examples of real roads are marked within these synthetic roads. The result can be combined with estimates of hybridization costs and conclusions can be drawn when it is beneficial to hybridize and with how large buffer. The main takeaways from the paper are that the potential energy savings for heavy LVCs due to hybridization are significant and that the hill-length is an important characteristic measure to include in operating cycle definitions.
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| 2. |
- Johannesson, Pär, 1969, et al.
(författare)
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A Robustness Approach to Reliability
- 2013
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Ingår i: Quality and Reliability Engineering International. - : Wiley. - 1099-1638 .- 0748-8017. ; 29:1, s. 17-32
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Forskningsöversikt (refereegranskat)abstract
- Reliability of products is here regarded with respect to failure avoidance rather than probability of failure. To avoid failures,we emphasize variation and suggest some powerful tools for handling failures due to variation. Thus, instead of technicalcalculation of probabilities from data that usually are too weak for correct results, we emphasize the statistical thinking thatputs the designers focus on the critical product functions.Making the design insensitive to unavoidable variation is called robust design and is handled by (i) identification andclassification of variation, (ii) design of experiments to find robust solutions, and (iii) statistically based estimations of propersafety margins.Extensions of the classical failure mode and effect analysis (FMEA) are presented. The first extension consists of identifyingfailure modes caused by variation in the traditional bottom–up FMEA analysis. The second variation mode and effect analysis(VMEA) is a top–down analysis, taking the product characteristics as a starting point and analyzing how sensitive thesecharacteristics are to variation.In cases when there is sufficient detailed information of potential failure causes, the VMEA can be applied in its mostadvanced mode, the probabilistic VMEA. Variation is then measured as statistical standard deviations, and sensitivities aremeasured as partial derivatives. This method gives the opportunity to dimension tolerances and safety margins to avoidfailures caused by both unavoidable variation and lack of knowledge regarding failure processes.
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| 3. |
- Johannesson, Pär, 1969, et al.
(författare)
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AR(1) time series with autoregressive gamma variance for road topography modeling
- 2016
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Ingår i: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 43, s. 106-116
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Tidskriftsartikel (refereegranskat)abstract
- A non-Gaussian time series with a generalized Laplace marginal distribution is used to model road topography. The model encompasses variability exhibited by a Gaussian AR(1) process with randomly varying variance that follows a particular autoregressive model that features the gamma distribution as its marginal. A simple estimation method to fit the correlation coefficient of each of two autoregressive components is proposed. The one for the Gaussian AR(1) component is obtained by fitting the frequency of zero crossing, while the autocorrelation coefficient for the gamma autoregressive process is fitted from the autocorrelation of the squared values of the model. The shape parameter of the gamma distribution is fitted using the explicitly given moments of a generalized Laplace distribution. Another general method of model fitting based on the correlation function of the signal is also presented and compared with the zero-crossing method. It is demonstrated that the model has the ability to accurately represent hilliness features of road topography providing a significant improvement over a purely Gaussian model.
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| 4. |
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| 5. |
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| 6. |
- 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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| 7. |
- Johannesson, Pär, 1969, et al.
(författare)
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Laplace models for describing road profiles
- 2014
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Ingår i: Proceedings of the 3rd International Commercial Vehicle Technology Symposium (CVT 2014) In Berns, K., Schneider, C., Dressler, K., Jörg, B., Kalmar, R., and Zolynski, G. (Eds.),, Shaker Verlag. - 9783844025736 ; , s. 99-108
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Konferensbidrag (refereegranskat)abstract
- Gaussian models are 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. Here we will study road profiles, which is the longitudinal road elevation along a road track. The profile for 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. 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. Laplace models for both a single track and for two parallel tracks will be treated. Further, an approximation of 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.
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| 8. |
- Johannesson, Pär, 1969, et al.
(författare)
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Laplace models for describing road profiles
- 2014
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Ingår i: Proceedings of the 3rd International Commercial Vehicle Technology Symposium (CVT 2014) In Berns, K., Schneider, C., Dressler, K., Jörg, B., Kalmar, R., and Zolynski, G. (Eds.),, Shaker Verlag. - 9783844025736 ; , s. 99-108
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Konferensbidrag (refereegranskat)abstract
- Gaussian models are frequently used for modelling environmentalloads, e.g. sea elevation, wind loads and road profiles. However, the Gaussianmodel is often only valid for short sections of the load. Here we will study roadprofiles, which is the longitudinal road elevation along a road track. The profilefor 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 sectionswith high irregularity. The variability between sections is higher than what can beexplained by the stationary Gaussian model. This phenomenon can be capturedby a Laplace process, which can be seen as a Gaussian process with randomlyvarying variance. Laplace models for both a single track and for two paralleltracks will be treated. Further, an approximation of the expected damage can becomputed from the parameters of the Laplace process. We will give examples ofmodelling road profiles using Laplace models. Especially, it will be demonstratedhow to reconstruct a road profile based on sparse road roughness measurements,such as a sequence of IRI (International Roughness Index) for 100 metre roadsections.
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| 9. |
- Johannesson, Pär, 1969, et al.
(författare)
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Mechanical reliability analysis of flexible power cables for marine energy
- 2022
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 10:6, s. 1-
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Tidskriftsartikel (refereegranskat)abstract
- Marine power cables connected to moving devices at sea may experience millions of load cycles per year, and thus they need to be flexible due to the movements of the cable and designed for mechanical loads. In this study, the focus is on the mechanical life of flexible low- and medium voltage power cables connecting devices to hubs. The reliability design method Variational Mode and Effect Analysis (VMEA) is applied, based on identifying and quantifying different types of uncertainty sources, including scatter, model and statistical uncertainties. It implements a load–strength approach that combines numerical simulations to assess the loads on the cable and experimental tests to assess the strength of the cable. The VMEA method is demonstrated for an evaluation of bending fatigue, and is found to be a useful tool to evaluate uncertainties in fatigue life for WEC (Wave Energy Converter) system cables during the design phase. The results give a firm foundation for the evaluation of safety against fatigue and are also helpful for identifying weak spots in the reliability assessment, thereby motivating actions in the improvement process. Uncertainties in terms of scatter, statistical uncertainty and model uncertainty are evaluated with respect to theWaveEL 3.0, a WEC designed by the companyWaves4Power, and deployed in Runde, Norway. A major contribution to the overall uncertainty is found to originate from the fatigue life model, both in terms of scatter and model uncertainty.
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