| 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. |
- Brännlund, Ulf, et al.
(författare)
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Railway Timetabling Using Lagrangian Relaxation
- 1998
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Ingår i: Transportation Science. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0041-1655 .- 1526-5447. ; 32:4, s. 358-369
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel optimization approach for the timetabling problem of a railway company, i.e., scheduling of a set of trains to obtain a profit maximizing timetable, while not violating track capacity constraints. The scheduling decisions are based on estimates of the value of running different types of service at specified times. We model the problem as a very large integer programming problem. The model is flexible in that if allows for general cost functions. We have used a Lagrangian relaxation solution approach, in which the track capacity constraints are relaxed and assigned prices, so that the problem separates into one dynamic program for each physical train. The number of dual variables is very large. However, it turns out that only a small fraction of these are nonzero, wh ich one may take advantage of in the dual updating schemes. The approach has been, tested on a realistic example suggested by the Swedish National Railway Administration. This example contains 18 passenger trains and 8 freight trains to be scheduled during a day on a stretch of single track, consisting of 17 stations. The computation times are rather modest and the obtained timetables are within a few percent of optimality.
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| 3. |
- Haraldsson, Mattias
(författare)
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Diskreta valmodeller för analys av urbana transport- och distributionssystem
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Det arbete som presenteras här, syftar till att pröva ekonometriska analysmetoder för det tvärsnittsdata som samlas in i projektet. Metoderna appliceras på ett datamaterial som tidigare samlats in, och som i flera viktiga avseenden har en struktur som liknar det material som ska analyseras framledes. I notatet utförs analyser av detta material i syfte att testa logitmodellens lämplighet för det fortsatta forskningsarbetet. Utöver att testa logitmodellens värde bidrar arbetet också till en fördjupad analys av det befintliga materialet. Dessutom prövas en teknik för att ersätta saknade data.
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| 4. |
- Li, Xin, 1985, et al.
(författare)
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Prediction of Vertical Dynamic Vehicle–Track Interaction and Sleeper–Ballast Contact Pressure in a Railway Crossing
- 2020
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Ingår i: Lecture Notes in Mechanical Engineering. - Cham : Springer International Publishing. - 2195-4356 .- 2195-4364. - 9783030380762 ; , s. 397-403
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Konferensbidrag (refereegranskat)abstract
- The vertical dynamic vehicle–track interaction in a railway crossing is simulated in the time domain based on a moving Green’s function approach in combination with an implementation of Kalker’s variational method to solve the non-Hertzian, and potentially multiple, wheel–rail contact. The method is demonstrated by calculating the wheel–rail impact load and the sleeper–ballast contact pressure for a hollow-worn wheel profile passing over a nominal crossing geometry.
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| 5. |
- Vadeby, Anna
(författare)
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Modelling and inference of relative collision safety in cars
- 1998
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We propose a new mathematical model for relative collision safety in cars. Our present research is restricted to head-on crashes between two cars and we try to determine how much of the injury risk in a crash that depends on car model. The relative risks include the driver populations of the different car models. When two cars crash they are exposed to the same force, but the damage severity is different depending on various factors such as car mass, change of speed and design of the car. To explore the relative risks between different car models, we build a model where we let car mass, change of speed and design of the car explain the injury outcome in the crashes. The mathematical model we use is a birth process where we let the states correspond to the injury classes. A data base containing police reported traffic accidents and hospital information is used to explore the relationships in our model.A bootstrap analysis is made to produce a picture of the uncertainty of the estimates. The uncertainty from the bootstrap analysis is compared to the asymptotic estimate of the uncertainty given by the inverse of an information sub-matrix.
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