| 1. |
- Romano, Luigi, 1994, et al.
(författare)
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Analytical results in transient brush tyre models: theory for large camber angles and classic solutions with limited friction
- 2022
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Ingår i: Meccanica. - : Springer Science and Business Media LLC. - 1572-9648 .- 0025-6455. ; 57:1, s. 165-191
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Tidskriftsartikel (refereegranskat)abstract
- This paper establishes new analytical results in the mathematical theory of brush tyre models. In the first part, the exact problem which considers large camber angles is analysed from the perspective of linear dynamical systems. Under the assumption of vanishing sliding, the most salient properties of the model are discussed with some insights on concepts as existence and uniqueness of the solution. A comparison against the classic steady-state theory suggests that the latter represents a very good approximation even in case of large camber angles. Furthermore, in respect to the classic theory, the more general situation of limited friction is explored. It is demonstrated that, in transient conditions, exact sliding solutions can be determined for all the one-dimensional problems. For the case of pure lateral slip, the investigation is conducted under the assumption of a strictly concave pressure distribution in the rolling direction.
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| 2. |
- Hjorth, Urban, 1941, et al.
(författare)
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Subsample distribution distance and McMC convergence
- 2005
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Ingår i: Scandinavian Journal of Statistics. - : Wiley. - 0303-6898 .- 1467-9469. ; 32:2, s. 313-326
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Tidskriftsartikel (refereegranskat)abstract
- A new measure based on comparison of empirical distributions for sub sequences or parallel runs and the full sequence of Markov chain Monte Carlo simulations, is proposed as a criterion of stability or convergence. The measure is also put forward as a loss function when the design of a Markov chain is optimized. The comparison is based on a Kullback-Leibler (KL) type distance over value sets defined by the output data. The leading term in a series expansion gives an interpretation in terms of the relative uncertainty of cell frequencies. The validity of this term is studied by simulation in two analytically tractable cases with Markov dependency. The agreement between the leading term and the KL-measure is close, in particular when the simulations are extensive enough for stable results. Comparisons with established criteria turn out favourably in examples studied.
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| 3. |
- Zhu, Li-wei, et al.
(författare)
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Fault Diagnosis On The Highway Surveillance And Control System Based On Petri Net Model
- 2013
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Ingår i: Proceedings of the 16th International Conference Road Safety on Four Continents. - Linköping : Statens väg- och transportforskningsinstitut.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Highway Surveillance and Control System (HSCS) is the critical system to improving the traffic safety and efficiency of highway. In this paper, the fault diagnosis model of HSCS based on Petri Net Model is provided in line with the composition, fault types and features of HSCS, and subsequently the fault diagnostic algorithm is given. In the end of this paper, the fault diagnosis of Microwave Vehicle Detector (MVD) in HSCS is presented to verifying the proposed fault diagnosis model and algorithm.
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| 4. |
- Vadeby, Anna, 1969-
(författare)
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Computer based statistical treatment in models with incidental parameters : inspired by car crash data
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bootstrap and Markov chain Monte Carlo methods have received much attention in recent years. We study computer intensive methods that can be used in complex situations where it is not possible to express the likelihood estimates or the posterior analytically. The work is inspired by a set of car crash data from real traffic.We formulate and develop a model for car crash data that aims to estimate and compare the relative collision safety among different car models. This model works sufficiently well, although complications arise due to a growing vector of incidental parameters. The bootstrap is shown to be a useful tool for studying uncertainties of the estimates of the structural parameters. This model is further extended to include driver characteristics. In a Poisson model with similar, but simpler structure, estimates of the structural parameter in the presence of incidental parameters are studied. The profile likelihood, bootstrap and the delta method are compared for deterministic and random incidental parameters. The same asymptotic properties, up to first order, are seen for deterministic as well as random incidental parameters.The search for suitable methods that work in complex model structures leads us to consider Markov chain Monte Carlo (MCMC) methods. In the area of MCMC, we consider particularly the question of how and when to claim convergence of the MCMC run in situations where it is only possible to analyse the output values of the run and also how to compare different MCMC modellings. In Metropolis-Hastings algorithm, different proposal functions lead to different realisations. We develop a new convergence diagnostic, based on the Kullback-Leibler distance, which is shown to be particularly useful when comparing different runs. Comparisons with established methods turn out favourably for the KL.In both models, a Bayesian analysis is made where the posterior distribution is obtained by MCMC methods. The credible intervals are compared to the corresponding confidence intervals from the bootstrap analysis and are shown to give the same qualitative conclusions.
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| 5. |
- Ait Ali, Abderrahman, 1991-, et al.
(författare)
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A disaggregate bundle method for train timetabling problems
- 2020
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Ingår i: Journal of Rail Transport Planning & Management. - : Elsevier BV. - 2210-9706 .- 2210-9714. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- The train timetabling problem (TTP) consists of finding a feasible timetable for a number of trains which minimises some objective function, e.g., sum of running times or deviations from ideal departure times. One solution approach is to solve the dual problem of the TTP using so-called bundle methods. This paper presents a new bundle method that uses disaggregate data, as opposed to the standard bundle method which in a certain sense relies on aggregate data. We compare the disaggregate and aggregate methods on realistic train timetabling scenarios from the Iron Ore line in Northern Sweden. Numerical results indicate that the proposed disaggregate method reaches better solutions faster than the standard aggregate approach.
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| 6. |
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| 7. |
- Carlsson, Arne, et al.
(författare)
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Metod för beräkning av fördröjningar på vägavsnitt utan omkörningsmöjlighet
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta VTI notat presenterar en beräkningsmetod för beräkning av förväntad kölängd och restidsfördröjning för enfältiga vägavsnitt utan omkörningsmöjligheter. Metoden utvecklades 2001 och presenterades i ett PM. Bakgrunden till modellutvecklingen var att dåvarande Vägverket (nu Trafikverket) planerade att införa så kallade 1+1-vägar, det vill säga, vägar med längre delsträckor utan omkörningsmöjlighet. Den utvecklade beräkningsmetoden har sedermera visat sig värdefull även vid framkomlighetsberäkningar för 2+1-vägar med varierande andel tvåfältsavsnitt och har använts vid framtagning av hastighetsflödessamband till Trafikverkets ”Effektsamband för vägtransportsystemet”. Metoden använder avsnittslängd, trafikflöde samt medelhastighet och standardavvikelse som indata. Metoden är uppdelad på beräkning av effekter på grund av enstaka långsamtgående fordon samt effekter vid ”normal” hastighetsfördelning. Då mätdata saknades vid modellutvecklingen jämfördes metoden med simuleringskörningar med den mikroskopiska trafiksimuleringsmodellen AIMSUN. Resultaten visar på en relativt god korrelation men generellt så ger den analytiska metoden cirka 1,2 procent lägre restidsfördröjning. En stor del av skillnaden mellan modellerna vid måttliga flöden bör kunna härledas till det stokastiska inslaget i simuleringen. Det bör även påpekas att varken den analytiska modellen eller trafiksimuleringsmodellen har kalibrerats och validerats mot verkliga data för denna typ av väg. Skillnaden mellan modellerna innebär således inte att den analytiska modellen självklart är den som avviker från verkligheten.
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| 8. |
- Johansson, Fredrik
(författare)
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Pedestrian traffic simulation platform
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Den häar notatet innehåller dokumentationen till en simuleringsplattform för simulering av fotgängartrafik, så som på stora bytespunkter för kollektivtrafik. Simuleringsplatformen har ett mikroskopiskt perspektiv, dvs den simulerar varje enskild fotgängare separat. Som grund f¨or simuleringen ligger den så kallade “social force model”. Detta dokument beskriver i detalj modellen och implementeringen av den för att möjliggöra en diskussion av metodiken, utsätta den för granskning, samt att underlätta för andra att implementera liknande modeller.
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| 9. |
- Romano, Luigi, 1994, et al.
(författare)
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Development and analysis of the two-regime transient tyre model for combined slip
- 2023
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 61:4, s. 1028-1062
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Tidskriftsartikel (refereegranskat)abstract
- This paper refines the two-regime transient theory developed by Romano et al. [Romano L, Bruzelius F, Jacobson B. Unsteady-state brush theory. Vehicle Syst Dyn. 2020;59:11–29. DOI: 10.1080/00423114.2020.1774625.] to include the effect of combined slip. A nonlinear system is derived that describes the non-steady generation of tyre forces and considers the coupling between the longitudinal and lateral characteristics. The proposed formulation accounts for both the carcass and the bristle dynamics, and represents a generalisation of the single contact point models. A formal analysis is conducted to investigate the effect of the tyre carcass anisotropy on the properties of the system. It is concluded that a fundamental role is played by the ratio between the longitudinal and lateral relaxation lengths. In particular, it is demonstrated that the maximum slip that guarantees (partial) adhesion conditions does not coincide with the stationary value and decreases considerably for highly anisotropic tyres. The dissipative nature of the model is also analysed using elementary tools borrowed from the classic theory for nonlinear systems. A comparison is performed against the single contact point models, showing a good agreement especially towards the full-nonlinear one. Furthermore, compared to the single contact point models, the two-regime appears to be able to better replicate the exact dynamics of the tyre forces predicted by the complete brush theory. Finally, the transient model is partially validated against experimental results.
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| 10. |
- Romano, Luigi, 1994, et al.
(författare)
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Rolling, tilting and spinning spherical wheels: Analytical results using the brush theory
- 2022
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Ingår i: Mechanism and Machine Theory. - : Elsevier BV. - 0094-114X .- 1873-3999. ; Volume 173:0094-114X
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the rolling dynamics of spherical wheels using the theoretical framework provided by the brush models. The analysis is mainly conducted under the assumption of vanishing sliding inside the contact patch. Different types of kinematics are considered: simply rolling wheels, rolling and tilting, and purely spinning. For the first two cases, a complete solution is derived concerning both the steady-state and transient behaviours. Some qualitative trends for the forces and moments generated inside the contact patch are then provided when accounting for limited friction. For the case of a purely spinning spherical wheel, it is shown that steady-state conditions are never possible owing to the assumption of vanishing sliding. Moreover, it is demonstrated that the shear stresses acting inside the contact patch grow unbounded if the additional contribution relating to the deflection of the bristle is not taken into account when calculating the total sliding velocity. In this case, a stationary solution may be eventually recovered as an asymptotic distribution only by assuming limited friction inside the contact patch.
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