• Finite element method application of ERBS triangles 

      Kravetc, Tatiana (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11)
      In this paper we solve an eigenvalue problem on a circular membrane with fixed outer boundary by using a finite element method, where an element is represented as an expo-rational blending triangle. ERBS triangles combine properties of B-spline finite elements and standard polynomial triangular elements. The overlapping of local triangles allows us to provide a flexible handling of the surface while ...
    • Flexibility-Enhancing Charging Station to Support the Integration of Electric Vehicles 

      Ilieva, Iliana; Bremdal, Bernt Arild (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-01)
      This paper discusses the Inspiria charging station facility in Norway, which enables various charging point operators to offer different charging systems for different purposes and needs. The charging station can be considered a specific case of a shared economy, as users share the same infrastructure and much of the same space. By utilizing new technology and the differences in charging needs in ...
    • Flexibility-Enhancing Charging Station to Support the Integration of Electric Vehicles 

      Ilieva, Iliana; Bremdal, Bernt Arild (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-01)
      This paper discusses the Inspiria charging station facility in Norway, which enables various charging point operators to offer different charging systems for different purposes and needs. The charging station can be considered a specific case of a shared economy, as users share the same infrastructure and much of the same space. By utilizing new technology and the differences in charging needs in ...
    • The FlexNett Simulator 

      Bremdal, Bernt Arild; Tangrand, Kristoffer (Journal article; Peer reviewed, 2019)
      This paper documents research conducted in the Norwegian FLEXNETT project.<br>It describes a new tool that was developed to study the future impact of prosumers with PV panels on the grid in Norway and the potential energy flexibility that lies with residential prosumers. Systematic use of energy flexibility can be an important instrument for managing peak loads and voltage problems in weak power ...
    • Fluid-structure Interaction for Water Hammers Effects in Petroleum and Nuclear Plants 

      Messahel, Ramzi; Cohen, B; Souli, M; Moatamedi, Mojtaba (Journal article; Tidsskriftartikkel; Peer reviewed, 2011-12-31)
      Fluid-Structure Interaction (FSI) becomes more and more the focus of computational engineering in Petroleum and Nuclear Industry in the last years. These problems are computer time consuming and require new stable and accurate coupling algorithms to be solved. For the last decades, the new development of coupling algorithms, and the increasing of computer performance have allowed to solve some ...
    • Fremtidens fleksible distribusjonsnett : fleksibel nettdrift, forbrukerfleksibilitet, plusskunder og forretningsmodeller 

      Sæle, Hanne; Bremdal, Bernt Arild; Tøndel, Inger Anne; Istad, Maren Kristine; Foosnæs, Jan Andor; Nordbø, Per Erik; Kirkeby, Henrik; Høverstad, Boye Annfelt; Mathisen, Geir (Research report; Forskningsrapport, 2016-02-15)
      Denne rapporten er utarbeidet i WP1 og WP2 i prosjektet "Fleksibilitet i fremtidens smarte distribusjonsnett - FlexNett" (2015-2017). FlexNett-prosjektet har som målsetting å bidra til økt fleksibilitet i fremtidens smarte distribusjonsnett gjennom å demonstrere og verifisere tekniske og markedsmessige løsninger for fleksibilitet på ulike nivå i nettet til nytte for ulike aktører. <br> Målsettingen ...
    • Generalized Chessboard Structures Whose Effective Conductivities Are Integer Valued 

      Lukkassen, Dag; Meidell, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2012-03-06)
      We consider generalized chessboard structures where the local conductivity takes two values 𝑎 and 𝑏 . All integer combinations of 𝑎 and 𝑏 which make the components of effective conductivity matrix integer valued are found. Moreover, we discuss the problem of estimating the effective conductivity matrix by using the finite-element method.
    • Geometric Construction of Some Lehmer Means 

      Høibakk, Ralph; Lukkassen, Dag; Meidell, Annette; Persson, Lars Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-14)
      The main aim of this paper is to contribute to the recently initiated research concerning geometric constructions of means, where the variables are appearing as line segments. The present study shows that all Lehmer means of two variables for integer power k and for k = m 2 , where m is an integer, can be geometrically constructed, that Lehmer means for power k = 0,1 and 2 can be geometrically ...
    • Hardy-type inequalities in fractional h-discrete calculus 

      Persson, Lars Erik; Oinarov, Ryskul; Shaimardan, Serikbol (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-04)
      The first power weighted version of Hardy’s inequality can be rewritten as [<i>mathematical formula</i>] where the constant <i>C</i> =[<i>p</i> / <i>p</i> - <i><b>a</b></i> - 1]<sup><i>p</i></sup> is sharp. This inequality holds in the reversed direction when<math xmlns="http://www.w3.org/1998/Math/MathML"> <mn>0</mn> <mo>&#x2264;<!-- ≤ --></mo> <mi><i>p</i></mi> <mo>&lt;</mo> <mn>1</mn> ...
    • Hardy-type inequalities over balls in R^N for some bilinear and iterated operators 

      Jain, Pankaj; Kanjilal, Saikat; Persson, Lars Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2019)
      Some new multidimensional Hardy-type inequalites are proved and discussed. The cases with bilinear and iterated operators are considered and some equivalence theorems are proved.
    • Homogenization of a singular random one-dimensional PDE with time-varying coefficients 

      Pardoux, Etienne; Piatnitski, Andrey (Journal article; Tidsskriftartikkel; Peer reviewed, 2012-05-04)
      In this paper we study the homogenization of a nonautonomous parabolic equation with a large random rapidly oscillating potential in the case of one-dimensional spatial variable. We show that if the potential is a statistically homogeneous rapidly oscillating function of both temporal and spatial variables, then, under proper mixing assumptions, the limit equation is deterministic, and convergence ...
    • Homogenization of biased convolution type operators 

      Piatnitski, Andrey; Zhizhina, Elena (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-07)
      This paper deals with homogenization of parabolic problems for integral convolution type operators with a non-symmetric jump kernel in a periodic elliptic medium. It is shown that the homogenization result holds in moving coordinates. We determine the corresponding effective velocity and prove that the limit operator is a second order parabolic operator with constant coefficients. We also consider ...
    • Homogenization of biomechanical models for plant tissues 

      Piatnitski, Andrey; Ptashnyk, Mariya (Journal article; Peer reviewed; Tidsskriftartikkel, 2017)
      In this paper homogenization of a mathematical model for plant tissue biomechanics is presented. The microscopic model constitutes a strongly coupled system of reaction-diffusion-convection equations for chemical processes in plant cells, the equations of poroelasticity for elastic deformations of plant cell walls and middle lamella, and Stokes equations for fluid flow inside the cells. The chemical ...
    • Homogenization of biomechanical models of plant tissues with randomly distributed cells 

      Piatnitski, Andrey; Ptashnyk, Mariya (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-15)
      In this paper homogenization of a mathematical model for biomechanics of a plant tissue with randomly distributed cells is considered. Mechanical properties of a plant tissue are modelled by a strongly coupled system of reaction-diffusion-convection equations for chemical processes in plant cells and cell walls, the equations of poroelasticity for elastic deformations of plant cell walls and middle ...
    • Homogenization of Ferromagnetic Energies on Poisson Random Sets in the Plane 

      Braides, Andrea; Piatnitski, Andrei (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-01-06)
      We prove that by scaling nearest-neighbour ferromagnetic energies de ned on Poisson random sets in the plane we obtain an isotropic perimeter energy with a surface tension characterised by an asymptotic formula. The result relies on proving that cells with `very long' or `very short' edges of the corresponding Voronoi tessellation can be neglected. In this way we may apply Geometry Measure ...
    • Homogenization of Levy-type operators with oscillating coefficients 

      Kassmann, Moritz; Piatnitski, Andrey; Zhizhina, Elena (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-05)
      The paper deals with homogenization of Lévy-type operators with rapidly oscillating coefficients. We consider cases of periodic and random statistically homogeneous micro-structures and show that in the limit we obtain a Lévy-operator. In the periodic case we study both symmetric and non-symmetric kernels whereas in the random case we only investigate symmetric kernels. We also address a nonlinear ...
    • Homogenization of Non-Autonomous Operators of Convolution Type in Periodic Media<sup>∗</sup> 

      Piatnitski, Andrei; Zhizhina, Elena (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-23)
      The paper deals with periodic homogenization problem for a para\-bo\-lic equation whose elliptic part is a convolution type operator with rapidly oscillating coefficients. It is assumed that the coefficients are rapidly oscillating periodic functions both in spatial and temporal variables and that the scaling is diffusive that is the scaling factor of the temporal variable is equal to the square of ...
    • Homogenization of nonisothermal immiscible incompressible two-phase flow in porous media 

      Amaziane, Brahim; Jurak, Murat; Pankratov, Leonid; Piatnitski, Andrey (Journal article; Peer reviewed, 2018-03-15)
      In this paper, we consider nonisothermal two-phase flows through heterogeneous porous media with periodic microstructure. Examples of such models appear in gas migration through engineered and geological barriers for a deep repository for radioactive waste, thermally enhanced oil recovery and geothermal systems. The mathematical model is given by a coupled system of two-phase flow equations, and an ...
    • Homogenization of random Navier–Stokes-type system for electrorheological fluid 

      Piatnitski, Andrey; Zhikov, Vasily (Peer reviewed; Journal article; Tidsskriftsartikkel, 2015-11-19)
      The paper deals with homogenization of Navier–Stokes-type system describing electrorheological fluid with random characteristics. Under non-standard growth conditions we construct the homogenized model and prove the convergence result. The structure of the limit equations is also studied.
    • (Hp− Lp -Type inequalities for subsequences of Nörlund means of Walsh–Fourier series 

      Baramidze, David; Persson, Lars-Erik; Tangrand, Kristoffer Meyer; Tephnadze, George (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-07)