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  • 1.
    Andersen, Emelie
    et al.
    Halmstad University, School of Business, Engineering and Science.
    Nilsson, Bertil
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Sahlén, Göran
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Survival possibilities of the dragonfly Aeshna viridis (Insecta, Odonata) in southern Sweden predicted from dispersal possibilities2016In: Journal of Insect Conservation, ISSN 1366-638X, E-ISSN 1572-9753, Vol. 20, no 2, p. 179-188Article in journal (Refereed)
    Abstract [en]

    We use public records from 1980 to 2014 to analyse survival of the EU Annex IV species Aeshna viridis in Sweden, a dragonfly strongly associated with the plant Stratiotes aloides. We clustered localities with S. aloides based on assumed dispersal abilities of A. viridis, using a dispersing radius of 2–100 km, calculating the proportion of sites with S. aloides that A. viridis is able to reach. If mean dispersal capability is high (40 km or above) 92.6 % or more of the localities are connected. For a good disperser, the probability of long-time survival is good. We further analysed the species richness of other Odonata and aquatic plants at 98 localities from the dataset. A. viridis co-occurred with more Odonata in the presence of S. aloides and running water but not in lakes. S. aloides sites had a higher number of other aquatic plants. Area had no impact on the occurrence of the species. For the present situation we surveyed 32 localities with known occurrence of the species. Only half of the sites for S. aloides contained any specimens while A. viridis occurred in the same number of sites. The species co-occurred in only 8 of 32 sites. In four sites A. viridis larvae appeared among Menyanthes trifoliata, Phragmites australis, Potamogeton natans and Sphagnum spp., indicating that at high latitudes A. viridis breeds among other species. Indirect monitoring based only on S. aloides would underestimate the number of populations of the dragonfly. © 2016 Springer International Publishing Switzerland

  • 2.
    Gåård, Anders
    et al.
    Karlstads Universitet, Karlstad, Sverige.
    Löfgren, Hans
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Nilsson, Bertil
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Hallbäck, Nils
    Karlstads Universitet, Karlstad, Sverige.
    Införandet av Computer Based Mathematics (CBM) i ingenjörsutbildningar2017Conference paper (Other (popular science, discussion, etc.))
    Abstract [sv]

    CBM är ett koncept som innebär användning av datorn och matematikprogramvaror som huvudverktyg i under-visningen. Istället för att som i traditionell undervisning kombinera handräkning med datorlabbar ligger tyngdpunkten i en CBM-kurs på datoriserade beräkningsverktyg. Härav för-flyttas fokus mot konceptförtåelse, modellering och tolkning av resultat. Vid Högskolan i Halmstad och Karlstads Universitet finns idag flera kurser baserat på CBM. Kvantitativt har införandet lett till ökad studentgenomströmning samtidigt som innehållet i kurser har ökat. Kvalitativa markörer, såsom studentens egen uppfattning om konceptuell förståelse och nyfikenhet inom ämnet, har baserat på kursvärderingar också ökat. 

  • 3.
    Nilsson, Bertil
    Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden.
    Adaptive Finite Element Methods for the Reynolds Thin Film Model with Cavitation2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main purpose of this thesis is to use modern goal-oriented adaptive finite element techniques in order to improve the numerical simulation of tribology. Two novel adaptive finite element methods for the Reynolds thin film model including cavitation are presented and their different strategies are compared. The algorithms are inspired by an analogy with the obstacle problem and the cavitation problem that we consider is written as a variational inequality considering in the formulation the fact that the lubricant can not stand negative stresses induced by sub-atmospheric pressure. A posteriori, error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied. The cavitation problem and calculations is introduced and put into historical and modern perspective. Modern thoughts and techniques around the oil-pocket idea in sheet metal forming are presented. The influence of oil pockets on the contact regime is assessed, and in particular the likely effect of oil-pocket-induced cavitation in order to produce lift, is discussed. The ultimate goal with the numerical simulation is to be able to optimize the surface structure so as to take advantage of cavitation effects in the lubricant.

  • 4.
    Nilsson, Bertil
    Chalmers, Matematiska vetenskaper.
    Finite element procedures for virtual tribology2009Doctoral thesis, monograph (Other academic)
  • 5.
    Nilsson, Bertil
    et al.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Hansbo, Peter
    Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden.
    A goal oriented adaptive finite element method for hydrodynamic lubricationManuscript (preprint) (Other academic)
    Abstract [en]

    We present a goal-oriented adaptive finite element method for a cavitation model based on Reynolds' equation. A posteriori error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied.

  • 6.
    Nilsson, Bertil
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Hansbo, Peter
    Chalmers, Matematiska vetenskaper.
    A Stokes model with cavitation for the numerical simulation of hydrodynamic lubrication2011In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 67, no 12, p. 2015-2025Article in journal (Refereed)
    Abstract [en]

    We present a cavitation model based on the Stokes equation and formulate adaptive finite element methods for its numerical solution. A posteriori error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied, in particular with comparison to the simplified Reynolds model of lubrication.

  • 7.
    Nilsson, Bertil
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Hansbo, Peter
    Department of Applied Mechanics, Chalmers University of Technology, Goteborg S-412 96, Sweden.
    Adaptive finite element methods for hydrodynamic lubrication with cavitation2007In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 72, no 13, p. 1584-1604Article in journal (Refereed)
    Abstract [en]

    We present an adaptive finite element method for a cavitation model based on Reynolds' equation. A posteriori error estimates and adaptive algorithms are discussed, and numerical examples illustrating the theory are supplied.

  • 8.
    Nilsson, Bertil
    et al.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Hansbo, Peter
    Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden.
    Adaptive finite element solution of a cavitation problem in hydrodynamic lubricationManuscript (preprint) (Other academic)
    Abstract [en]

    We present an adaptive finite element method for a cavitation model based on Reynolds' equation. A posteriori error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied.

  • 9.
    Nilsson, Bertil
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Hansbo, Peter
    Chalmers, Matematiska vetenskaper.
    Weak coupling of a Reynolds model and a Stokes model for hydrodynamic lubrication2011In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 66, no 6, p. 730-741Article in journal (Refereed)
    Abstract [en]

    The Reynolds model is a reduced Stokes model, valid for narrow lubrication regions. In order to be able to handle locally non-narrow regions such as pits or grooves, often displaying rapid geometrical variations, there is a need to be able to transit to the more accurate Stokes model. A fundamental problem is how to couple the two models in a numerical simulation, preferably allowing for different meshes in the different domains. In this paper, we present a weak coupling method for Reynolds and Stokes models for lubrication computations, including the possibility of cavitation in the different regions. The paper concludes with a numerical example.

  • 10.
    Rosén, Bengt-Göran
    et al.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Nilsson, Bertil
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Thomas, Tom R.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Wiklund, Daniel
    Chalmers University of Technology, Gothenburg, Sweden.
    Xiao, Li
    Chalmers University of Technology, Gothenburg, Sweden.
    Oil pockets and surface topography: Mechanisms of friction reduction2004Conference paper (Other academic)
    Abstract [en]

    Oil pockets reduce friction in two ways: by providing lift themselves by a cavitation mechanism, and also by acting as a reservoir of lubricant which will leak out around their boundaries to minimise direct metallic contact in the surrounding region. The relative importance of these mechanisms is estimated in particular tribological environments. The general cavitation conditions for oil pockets are defined and the cavitation models of Etsion and Kato are compared. Both these models require knowledge of the size and distribution of oil pockets, and an attempt is made to relate these to measurable surface topography parameters. Mechanisms for leakage of lubricant from oil pockets are also discussed. Advantages and disadvantages of the Wihiborg-Crafoord index are presented. The effect of oil pockets on the contact regime in gears is assessed, and in particular the likely effect of oil-pocket-induced cavitation on gear noise, and its relation to existing work on gear roughness, is discussed. Problems of oil pocket measurement on reaÌ surfaces are outlined and the advantages of 3D measurement are identified.

  • 11.
    Wiklund, Daniel
    et al.
    Institutionen för material- och tillverkningsteknik, Tillverkningsteknik, Chalmers tekniska högskola.
    Nilsson, Larsgunnar
    Nilsson, Bertil
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Andersson, Alf
    Rosén, Bengt Göran
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Gunnarsson, Lars
    On the Implementation and Evaluation of a Roughness Based Friction Model in FE Simulations of Sheet Metal Forming2006In: Proceedings of The 12th Nordic Symposium on Tribology, Lyngby: DTU Mechanical Engineering , 2006Conference paper (Refereed)
1 - 11 of 11
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