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  • Resultat 1-10 av 26402
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1.
  • Pieringer, Astrid, 1979-, et al. (författare)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; s. 444-451
  • Konferensbidrag (refereegranskat)abstract
    • Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomain approach for curve squeal are compared. In particular, the capability of the frequency-domain model to predict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stability is investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functions approach and uses a convolution procedure to obtain the system response. To ensure comparability, the same submodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled by adopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving element method is used to model the track. The local friction characteristics in the contact zone is modelled in accordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due to geometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact model including the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in each time step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of the force-displacement relation obtained with NORM around the quasi-static state and full-slip conditions are considered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed to severe curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient and the direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predicted squeal frequencies.
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2.
  • Kyprianidis, Konstantinos, 1984-, et al. (författare)
  • Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine
  • 2014
  • Ingår i: Journal of engineering for gas turbines and power. - 0742-4795. ; 136:1, s. Article number 011203
  • Tidskriftsartikel (refereegranskat)abstract
    • The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
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3.
  • INNOTRACK: Concluding technical report
  • 2010
  • Samlingsverk (redaktörskap) (övrigt vetenskapligt)abstract
    • The track structure, rails, switches and crossings account for more than 50% of maintenance and renewal costs for the rail industry. To improve the competitiveness of rail transportation, the cost-efficiency of these areas needs to be addressed. This the background to INNOTRACK, an integrated research project funded by the European Commission’s 6th research framework pro- gramme. Running from September 2006 to December 2009, INN- OTRACK has developed a multitude of innovative solutions in the areas of track substructure, rails & welds, and switches & crossings. The solutions have been assessed from technical, logistics and life cycle cost point of views. This Concluding Technical Report of INNOTRACK includes an overview of the project. It further details implementable results, and clusters them into ”highlight” areas. In addition, the book acts as a ”key” to the vast amount of information from INNOTRACK: All sections refer to project reports where more information can be found.
4.
  • Högman, Ulf, 1961-, et al. (författare)
  • Requirements on New Technology and the Technology Implementation Process
  • 2010
  • Ingår i: 8th International NordDesign Conference, NordDesign 2010; Goteborg; Sweden; 25 August 2010 through 27 August 2010. ; 2, s. 289-300
  • Konferensbidrag (refereegranskat)abstract
    • In literature, many authors have pointed to the importance of technology and technology development for company competitiveness. In this study we aim to study the technology in more detail and attempt to develop an understanding on the requirements and needs on “technology” from the perspective of product development. The research question which we aim to answer in this study is: “What are the requirements on maturity of technology when this technology is about to enter into the product development process?“ A qualitative research strategy, based on three study cases involving 17 interviewees, has been chosen. All three cases come from one single company, Volvo Aero Corporation (VAC) in Sweden, in the context of the aero engine industry. The study contributes with a broad mapping of requirements and how they relate to different categories of technologies, showing big differences both regarding content and timing. It is concluded that attention should be payed both to how the organization builds new capabilities and to the capabilities of the technology itself. A surprisingly complicated picture on the requirements relating to the implementation of new technologies has emerged in the study. This contributes to the understanding regarding the difficulties of developing new technology and integrating it into an application.
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7.
  • Lundberg, Oskar, 1980- (författare)
  • On the influence of surface roughness on rolling contact forces
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
8.
  • Torstensson, Peter, 1981-, et al. (författare)
  • Hybrid model for prediction of impact noise generated at railway crossings
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; s. 539-545
  • Konferensbidrag (refereegranskat)abstract
    • A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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9.
  • Bergseth, Ellen, 1979- (författare)
  • On tribological design in gear tooth contacts
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The correct tribological design will have a considerable effect on a gear’s service life and efficiency. The purpose of this thesis is to clarify the impact of variation in the gear tooth flank tribological system on the gear contact load capacity – to increase the understanding of how surface topography and lubricant interact.In this thesis the variation in surface topography inherent in the manufacturing method has been shown, by experimental work and computer simulations, to be an important factor for the contact condition in the early life of gears. Surface analysis revealed that the formation and composition of surface boundary layers depends strongly on the chemical composition of the lubricant, but also on pre-existing surface boundary layers. Additionally, surface boundary layers play a major role in frictional behaviour, wear and in allowing the lubricant to react properly with the surfaces.Paper A presents the current ISO 6336 calculation of surface durability. A robust design approach was used to investigate the extent to which the current standard for calculation of surface durability allows for manufacturing variations and the choice of lubricant.Paper B investigates the extent to which a logarithmical profile modification can increase gear contact pressure robustness compared to traditional lead profiles for gears.Paper C compares different gear manufacturing methods and their as-manufactured (fresh unworn) surface topographies, using measured surface topographies as input to a contact simulation program.Paper D examines surface boundary layer formation and the corresponding wear in relation to different anti-wear additives in an environmentally adapted base oil.Papers E and F make use of specimens with surface topographies imitating two gear manufacturing methods (grinding and superfinishing) to be used in a twin-disc and barrel-on-disc machine respectively. The contacts are analysed by friction measurements and simulations combined with methods for surface analysis.
10.
  • Horn, Agnes-Marie, et al. (författare)
  • ISSC committee III.2 - Fatigue and fracture
  • 2012
  • Ingår i: Proceedings of the Eighteenth International Ship and Offshore Structures Congress (ISSC 2012) in Rostock, Germany, September 9-13, 2012. - 978-3-87700-131-8 ; Vol 1, s. 365-434
  • Konferensbidrag (refereegranskat)
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