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  • 301.
    Basir, Hadi Mahdavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Javaherian, Abdolrahim
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran;Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Shomali, Zaher Hossein
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran 1136511155, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Explorat Directorate, Dept Geophys, Tehran 1994814695, Iran.
    Acoustic wave propagation simulation by reduced order modelling2018Inngår i: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 49, nr 3, s. 386-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wave propagation simulation, as an essential part of many algorithms in seismic exploration, is associated with high computational cost. Reduced order modelling(ROM) is a known technique in many different applications that can reduce the computational cost of simulation by employing an approximation of the model parameters. ROM can be carried out using different algorithms. The method proposed in this work is based on using the most important mode shapes of the model, which can be computed by an efficient numerical method. The numerical accuracy and computational performance of the proposed method were investigated over a simple synthetic velocity model and a portion of the SEG/EAGE velocity model. Different boundary conditions were discussed, and among them the random boundary condition had higher performance for applications like reverse time migration (RTM). The capability of the proposed method for RTM was evaluated and confirmed by the synthetic velocity model of SEG/EAGE. The results showed that the proposed ROM method, compared with the conventional finite element method (FEM), can decrease the computational cost of wave propagation modelling for applications with many simulations like the reverse time migration. Depending on the number of simulations, the proposed method can increase the computational efficiency by several orders of magnitudes.

  • 302.
    Bastian, Peter
    et al.
    University of Heidelberg.
    Berninger, Heiko
    Dedner, Andreas
    University of Warwick.
    Engwer, Christian
    University of Münster.
    Henning, Patrick
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    Kornhuber, Ralf
    FU Berlin.
    Kröner, Dietmar
    University of Freiburg.
    Ohlberger, Mario
    University of Münster.
    Sander, Oliver
    TU Dresden.
    Schiffler, Gerd
    Shokina, Nina
    Smetana, Kathrin
    University of Münster.
    Adaptive Modelling of Coupled Hydrological Processes with Application in Water Management2012Inngår i: Progress in Industrial Mathematics at ECMI 2010 / [ed] Michael Günther and Andreas Bartel and Markus Brunk and Sebastian Schöps and Michael Striebel, Springer Berlin/Heidelberg, 2012, s. 561-567Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents recent results of a network project aiming at the modelling and simulation of coupled surface and subsurface flows. In particular, a discontinuous Galerkin method for the shallow water equations has been developed which includes a special treatment of wetting and drying. A robust solver for saturated–unsaturated groundwater flow in homogeneous soil is at hand, which, by domain decomposition techniques, can be reused as a subdomain solver for flow in heterogeneous soil. Coupling of surface and subsurface processes is implemented based on a heterogeneous nonlinear Dirichlet–Neumann method, using the dune-grid-glue module in the numerics software DUNE.

  • 303.
    Bauer, Pavol
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Parallelism and efficiency in discrete-event simulation2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Discrete-event models depict systems where a discrete state is repeatedly altered by instantaneous changes in time, the events of the model. Such models have gained popularity in fields such as Computational Systems Biology or Computational Epidemiology due to the high modeling flexibility and the possibility to easily combine stochastic and deterministic dynamics. However, the system size of modern discrete-event models is growing and/or they need to be simulated at long time periods. Thus, efficient simulation algorithms are required, as well as the possibility to harness the compute potential of modern multicore computers. Due to the sequential design of simulators, parallelization of discrete event simulations is not trivial. This thesis discusses event-based modeling and sensitivity analysis and also examines ways to increase the efficiency of discrete-event simulations and to scale models involving deterministic and stochastic spatial dynamics on a large number of processor cores.

  • 304.
    Bauer, Pavol
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Parallelism in Event-Based Computations with Applications in Biology2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Event-based models find frequent usage in fields such as computational physics and biology as they may contain both continuous and discrete state variables and may incorporate both deterministic and stochastic state transitions. If the state transitions are stochastic, computer-generated random numbers are used to obtain the model solution. This type of event-based computations is also known as Monte-Carlo simulation.

    In this thesis, I study different approaches to execute event-based computations on parallel computers. This ultimately allows users to retrieve their simulation results in a fraction of the original computation time. As system sizes grow continuously or models have to be simulated at longer time scales, this is a necessary approach for current computational tasks.

    More specifically, I propose several ways to asynchronously simulate such models on parallel shared-memory computers, for example using parallel discrete-event simulation or task-based computing. The particular event-based models studied herein find applications in systems biology, computational epidemiology and computational neuroscience.

    In the presented studies, the proposed methods allow for high efficiency of the parallel simulation, typically scaling well with the number of used computer cores. As the scaling typically depends on individual model properties, the studies also investigate which quantities have the greatest impact on the simulation performance.

    Finally, the presented studies include other insights into event-based computations, such as methods how to estimate parameter sensitivity in stochastic models and how to simulate models that include both deterministic and stochastic state transitions.

  • 305.
    Bauer, Pavol
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Engblom, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Sensitivity estimation and inverse problems in spatial stochastic models of chemical kinetics2015Inngår i: Numerical Mathematics and Advanced Applications: ENUMATH 2013, Springer, 2015, s. 519-527Konferansepaper (Fagfellevurdert)
  • 306.
    Bauer, Pavol
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Engblom, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Mikulovic, Sanja
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för neurovetenskap, Genetisk utvecklingsbiologi.
    Senek, Aleksandar
    Multiscale modelling via split-step methods in neural firing2018Inngår i: Mathematical and Computer Modelling of Dynamical Systems, ISSN 1387-3954, E-ISSN 1744-5051, Vol. 24, s. 426-445Artikkel i tidsskrift (Fagfellevurdert)
  • 307.
    Bauer, Pavol
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Engblom, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Tillämpad beräkningsvetenskap.
    Widgren, Stefan
    Fast event-based epidemiological simulations on national scales2016Inngår i: The international journal of high performance computing applications, ISSN 1094-3420, E-ISSN 1741-2846, Vol. 30, s. 438-453Artikkel i tidsskrift (Fagfellevurdert)
  • 308. Bayer, Christian
    et al.
    Hoel, Håkon
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    von Schwerin, Erik
    Tempone, Raul
    On nonasymptotic optimal stopping criteria in monte carlo simulations2014Inngår i: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 36, nr 2, s. A869-A885Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider the setting of estimating the mean of a random variable by a sequential stopping rule Monte Carlo (MC) method. The performance of a typical second moment based sequential stopping rule MC method is shown to be unreliable in such settings both by numerical examples and through analysis. By analysis and approximations, we construct a higher moment based stopping rule which is shown in numerical examples to perform more reliably and only slightly less efficiently than the second moment based stopping rule.

  • 309.
    Bayisa, Fekadu
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Zhou, Zhiyong
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Cronie, Ottmar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Yu, Jun
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Adaptive algorithm for sparse signal recovery2018Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Spike and slab priors play a key role in inducing sparsity for sparse signal recovery. The use of such priorsresults in hard non-convex and mixed integer programming problems. Most of the existing algorithms to solve the optimization problems involve either simplifying assumptions, relaxations or high computational expenses. We propose a new adaptive alternating direction method of multipliers (AADMM) algorithm to directly solve the presented optimization problem. The algorithm is based on the one-to-onemapping property of the support and non-zero element of the signal. At each step of the algorithm, we update the support by either adding an index to it or removing an index from it and use the alternatingdirection method of multipliers to recover the signal corresponding to the updated support. Experiments on synthetic data and real-world images show that the proposed AADMM algorithm provides superior performance and is computationally cheaper, compared to the recently developed iterative convex refinement (ICR) algorithm.

  • 310.
    Bazarganzadeh, Mahmoudreza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik.
    Free Boundary Problems of Obstacle Type, a Numerical and Theoretical Study2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis consists of five papers and it mainly addresses the theory and schemes to approximate the quadrature domains, QDs. The first deals with the uniqueness and some qualitative properties of the two QDs. The concept of two phase QDs, is more complicated than its one counterpart and consequently introduces significant and interesting open.

    We present two numerical schemes to approach the one phase QDs in the paper. The first method is based on the properties of the free boundary the level set techniques. We use shape optimization analysis to construct second method. We illustrate the efficiency of the schemes on a variety of experiments.

    In the third paper we design two finite difference methods for the approximation of the multi phase QDs. We prove that the second method enjoys monotonicity, consistency and stability and consequently it is a convergent scheme by Barles-Souganidis theorem. We also present various numerical simulations in the case of Dirac measures.

    We introduce the QDs in a sub domain of and Rn study the existence and uniqueness along with a numerical scheme based on the level set method in the fourth paper.

    In the last paper we study the tangential touch for a semi-linear problem. We prove that there is just one phase free boundary points on the flat part of the fixed boundary and it is also shown that the free boundary is a uniform C1-graph up to that part.

  • 311.
    Bazarganzadeh, Mahmoudreza
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik.
    Bozorgnia, Farid
    Numerical Approximation of One Phase Quadrature Domains2013Inngår i: Numerical Methods for Partial Differential Equations, ISSN 0749-159X, E-ISSN 1098-2426, Vol. 29, nr 5, s. 1709-1728Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    In this work, we present two numerical schemes for a free boundary problem called one phase quadrature domain. In the first method by applying the proprieties of given free boundary problem, we derive a method that leads to a fast iterative solver. The iteration procedure is adapted in order to work in the case when topology changes. The second method is based on shape reconstruction to establish an efficient Shape-Quasi-Newton-Method. Various numerical experiments confirm the efficiency of the derived numerical methods.

  • 312.
    Beckius, Peter
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling.
    Hübel, Alexander
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling.
    Vädrets påverkan på försäljningen inom svensk dagligvaruhandel: En studie om vädrets påverkan på ICA:s försäljning2010Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [ar]

    ICA is the largest general dealer in the Swedish market as well as the largest supplier to the independent ICA-dealers. The principal and one of the biggest stakeholders of this thesis is the department Supply Chain Development who is responsible for the development of ICA’s Supply Chain.

    The purpose of this study is to examine how ICA’s sales are affected by weather and to make recommendations on how ICA should proceed with its work regarding this issue. By leveraging their forecasts by including weather, ICA hopes that their logistical metrics amount of spoilage, service levels and number of inventory days will improve. This thesis describes how ICA is working with weather currently, and furthermore it discusses the existing literature within this area. Extensive statistical surveys have been conducted in order to identify the products that are affected by weather, and to examine how they are affected by different weather variables. Finally, the thesis gives recommendations to ICA on how they can improve their forecasting by taking this study’s results into account.

    Presently ICA has no consistent approach when it comes to considering weather’s impact on sales. Each individual product planner uses his own experience and gut feeling and there is no central guidance or other quantitative information there to help them.

    This thesis is organised around two major statistical studies. First, a correlation study examines the correlation between sales and deviation from mean temperature. The weather parameter was selected following recommendations from earlier studies and from SMHI - the national weather institute in Sweden. The study was conducted on ICA’s entire assortment and identified which items that were affected by weather. These turned out to be about a hundred in number and were affected mainly during the summer; however a few items were also affected in the winter. Most of the affected items were rather logical regarding weather’s effects on sales and have also been pointed out by planners as products that are likely to be affected by weather. Following that, several regression analyses were conducted on the selected weather affected assortment.

    The regression analyses were conducted with various combinations of one or more weather parameters as explanatory variables. Surprisingly, in most cases the deviation from mean temperature alone was the parameter that best explained the variance in sales figures. The result or output of this thesis is a value for the expected change in sales for a selected assortment, given a change in deviation from mean temperature.

    The recommendations given at the end of this thesis explains how ICA in a simple and cost effective way could implement the study's results in their daily work. The proposal is to divide the work by what should be done centrally by the forecasting department, and by what should be done individually by each planner. The forecasting department should regularly collect weather forecasts over different time periods, calculate the deviation from mean temperature and distribute it to the supply planner. After that, it is up to the supply planners on how to best take advantage of this information by taking into account other unique factors affecting each category, such as campaigns, holidays and daily indexes that in many cases have more effect on sales than the weather.

  • 313.
    Beckman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Fornberg, Bengt
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Tengvald, Arne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    A method for acceleration of the convergence of infinite series1969Inngår i: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 9, s. 78-80Artikkel i tidsskrift (Annet vitenskapelig)
  • 314.
    Beermann, Marie
    et al.
    Linnéuniversitetet, Fakultetsnämnden för hälsa, socialt arbete och beteendevetenskap, Institutionen för pedagogik, psykologi och idrottsvetenskap, PPI.
    Eriksson, Kerstin
    Linnéuniversitetet, Fakultetsnämnden för hälsa, socialt arbete och beteendevetenskap, Institutionen för pedagogik, psykologi och idrottsvetenskap, PPI.
    Vardagsmatematik: Pedagogers gruppsamtal om vardagsmatematiken i de tidigare skolåren2011Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Syftet med vår studie var att synliggöra hur pedagoger som undervisar i grundskolans tidiga år samtalar om undervisningen av matematikens användning i vardagen utifrån den socio­kulturella teorin. Gruppsamtalen utgick från rubrikerna konkretisering, individ­uali­se­ring, mate­matik och språk samt matematiksvårigheter kopplade till vardagsmatematiken. Vi använ­de oss av fokusgrupper som undersökningsinstrument. I studien ingick 13 peda­goger som alla undervisade i matematik på skolans lågstadium. Deltagarna i studien var verk­samma på fyra olika skolor i två olika kommuner.

    Undersökningens resultat bearbetades utifrån en hermeneutisk innehållsanalys. I resultatet synliggörs en omfattande och medveten undervisning kring vardagsmatematiken hos de med­­verkande pedagogerna. Det som upplevs som hinder eller skapande av möjligheter är resurstilldelningen både materiellt och personellt. Gruppstorlek och gruppsammansättning upp­levs också som avgörande för en undervisning som lever upp till pedagogernas ambi­tioner. Konkretiseringen ges en stor betydelse för att fånga och förklara den abstrakta mate­matiken. Individualiseringen ses av pedagogerna som nödvändig för att få med sig alla elev­erna i matematikundervisningens gemenskap och för att alla elever ska nå målen. Den sam­talande matematiken beskrivs som ovärderlig för elevernas tänkande och därmed för­ståelse och lärandet. Det framgår att för elever med matematiska svårigheter är det konkreta materi­alet, tid tillsammans med pedagog och ett varierat undervisningssätt faktorer som skapar för­utsättningar för lärande. 

  • 315. Beilina, Larisa
    et al.
    Samuelsson, Klas
    Åhlander, Krister
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    A hybrid method for the wave equation2001Rapport (Annet vitenskapelig)
  • 316. Beilina, Larisa
    et al.
    Samuelsson, Klas
    Åhlander, Krister
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Efficiency of a hybrid method for the wave equation2001Inngår i: Finite Element Methods: Three-dimensional problems, Tokyo: Gakkotosho , 2001, s. 9-21Konferansepaper (Fagfellevurdert)
  • 317.
    Belkotain, Mehdi
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    X-Value Adjustments for Interest Rate Derivatives2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this report, we present the X-Value Adjustments and we introduce a simulation approach to compute these adjustments. We present the steps for the calculation of the Credit Value Adjustment (CVA) on interest rate derivatives as a practical example.

    An important part of the report will focus on the different methods to compute the expected future exposure. In this context, we consider two methods based on Monte Carlo simulations in order to compute the expected exposure. We study also the G2++ interest rate model used for the simulations and we detail the calibration process and apply it on market data.

  • 318.
    Belov, I.
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik.
    Alavizadeh, Z.
    Lindgren, M.
    Application of engineering optimization to evaluate heating-based humidity management in electronics enclosures2011Inngår i: Electronic Environment Konferens & Mässa 2011, Stockholm Älvsjö,5-6 April 2011, Invited speech, 2011, s. 161-162Konferansepaper (Annet vitenskapelig)
  • 319.
    Belov, Ilja
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Anti-Moisture Methodology for Electronics Enclosures in Harsh Storage Environments2008Konferansepaper (Annet vitenskapelig)
  • 320.
    Belov, Ilja
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Evaluation of Anti-Moisture Measures in Electronics Enclosure: Application of CFD Modelling2009Konferansepaper (Annet vitenskapelig)
  • 321.
    Belov, Ilja
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Humidity Management in Electronics Enclosure under Severe Climatic Conditions2008Konferansepaper (Annet vitenskapelig)
  • 322.
    Belov, Ilja
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Optimization of PCB Heater Heating Profile for Power-efficient Humidity Management in Electronics Enclosures: OPTIMUS Worldwide User Meeting 2010, Antwerp, Belgium, November 22-23, 20102010Annet (Annet vitenskapelig)
  • 323.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Bespalov, Michail
    Klochkova, Ludmila
    Kuleshov, Alexander
    Suzan, Dmitriy
    Tishkin, Vladimir
    Транспортная модель распространения газообразных примесей в атмосфере города = Transport model of gas impurities spread processes in urban area2000Inngår i: Математическое моделирование: (Mathematical Modelling), ISSN 0234-0879, Vol. 12, nr 11, s. 38-46Artikkel i tidsskrift (Fagfellevurdert)
  • 324.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Bespalov, Michail
    Klochkova, Ludmila
    Pavlova, Natalya
    Suzan, Dmitriy
    Tishkin, Vladimir
    Сравнение моделей распространения загрязнений в атмосфере = Comparative Analysis of models of pollutions spreading in atmosphere1999Inngår i: Математическое моделирование: (Mathematical Modelling), ISSN 0234-0879, Vol. 11, nr 8, s. 52-64Artikkel i tidsskrift (Fagfellevurdert)
  • 325.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Lindgren, Mats
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Bergner, Fredrik
    Bornoff, Robin
    CFD aided reflow oven profiling for PCB preheating in a soldering process2007Inngår i: Proceedings of the 8th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Micro-Electronics and Micro-Systems: EuroSimE 2007, Piscataway, NJ.: IEEE , 2007, s. 535-542Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A CFD-aided reflow oven profile prediction algorithm has been developed and applied to modelling of preheating of a PCB with non-uniform distribution of component thermal mass in a forced air convection solder reflow oven. The iterative algorithm combines an analytic approach with CFD modelling. It requires an experimentally validated CFD model of the solder reflow oven and a CFD model of the PCB as main inputs. Results of computational experiments have been presented to reveal good agreement between predicted PCB profiles and corresponding CFD calculations. Application guidelines contained in the description of the algorithm will assist potential users both during the virtual prototyping phase of a PCB including designing for assembly and in the phase of reflow oven profiling.

  • 326.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Lindgren, Mats
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Bergner, Fredrik
    Bornoff, Robin
    CFD aided reflow oven profiling for PCB preheating in a soldering process: Part 1(2)2007Inngår i: Electronic Environment, nr 3, s. 25-28Artikkel i tidsskrift (Annet vitenskapelig)
  • 327.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Lindgren, Mats
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Bergner, Fredrik
    Bornoff, Robin
    CFD aided reflow oven profiling for PCB preheating in a soldering process: Part 2(2)2007Inngår i: Electronic Environment, nr 4, s. 25-27Artikkel i tidsskrift (Annet vitenskapelig)
  • 328.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Lindgren, Mats
    Ryden, Jan
    Alavizadeh, Zahra
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    CFD Assisted Design Evaluation and Experimental Verification of a Logic-Controlled Local PCB Heater for Humidity Management in Electronics Enclosure2010Inngår i: IEEE EuroSimE 2010, 26-28 April, Bordeaux, France, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Humidity management of commercial-of-the-shelf electronic components in non-controlled climatic environments can be realized e.g. by introducing a local printed circuit board heater. By choosing appropriate size and location of the heater plate in the vicinity of the critical electronic packages, and utilizing logic control function, it is possible to improve the quality of local humidity management and reduce power consumption of the heater, which is important especially in case of battery driven portable or vehicle mounted devices. A computational fluid dynamics assisted methodology has been developed to determine the best feasible design of the heater, followed by experimental verification of the constructed logic controlled heater. The experiment has been performed in a harsh climatic environment including temperature variation from +33°C to +40°C, and relative humidity variation from 54% to 80%. Analysis of the experimental %RH and temperature curves as well as power profile of the heater has confirmed the feasibility of the chosen approach to maintain greater than 9°C difference between the electronics package surface temperature and the local dew point temperature, by applying discrete power pulses with the amplitude less than 6 W.

  • 329.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Rydén, Jan
    Lindblom, Joakim
    Zhang, Yafan
    Hansson, T
    Bergner, Fredrik
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Application of CFD Modelling for Energy Efficient Humidity Mangement of an Electronics Enclosure in Storage under Severe Climatic Conditions2008Inngår i: International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems, 2008: EuroSimE 2008., IEEE , 2008, s. 430-437Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A CFD modelling methodology including experimental validation has been developed and applied for investigation of anti-moisture measures in a non- hermetic electronics enclosure containing a number of printed circuit boards, and placed in a severe storage environment. In the climatic test the temperature and the relative humidity have been varried from +33degC to +71degC and from 14% to 80%, respectively. Enclosure heater solutions have been parametrically studied by simulation. A heating strategy involving various power levels has been determined, which is just sufficient to maintain the internal relative humidity below 60%, thereby reducing the risk for dew formation on the electronics assembly.

  • 330.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Wingbrant, Helena
    Spetz, Anita-Lloyd
    Sundgren, Hans
    Thuner, Bo
    Svenningstorp, Henrick
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Thermal and flow analysis of SiC-based gas sensors for automotive applications2004Inngår i: Proceedings of the 5th International Conference on Thermal and Mechanical Simulation and Experiments in Microelectronics and Microsystems, 2004: EuroSimE 2004., IEEE , 2004, s. 475-482Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Different block and tube mounting alternatives for SiC-based gas sensors were studied by means of temperature measurements and simulation of heat transfer and gas flow for steady state conditions. The most preferable tube mounting design was determined. Simulation-based guidelines were developed for designing tube-mounted gas sensors in the exhaust pipes of diesel and petrol engines, taking into account thermal constraints and flow conditions.

  • 331.
    Belov, Ilja
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    Wingbrant, Helena
    Spetz, Anita-Lloyd
    Sundgren, Hans
    Thuner, Bo
    Svenningstorp, Henrik
    Leisner, Peter
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning - Ytteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsområde Robusta inbyggda system.
    CFD analysis of packaging and mounting solutions for SiC-based gas sensors in automotive applications2006Inngår i: Sensor Letters, ISSN 1546-198X, Vol. 4, nr 1, s. 29-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simulation-based guidelines were developed for designing tube-mounted gas sensors in the exhaust pipes of diesel and petrol engines, taking into account thermal constraints and gas flow conditions. Different block and tube mounting alternatives for SiC-based gas sensors were studied by means of temperature measurements and simulation of steady state heat transfer and gas flow. Design variables included the number of fins in the heat sink mounted on the inlet tube, the inlet construction, the mounting tube orientation, and the micro-heater substrate placement inside the mounting tube. The most preferable tube mounting design was determined with respect to the thermal performance of the sensor structure and with respect to the gas flow parameters, which are important for the sensor's selectivity, sensitivity and response time.

  • 332.
    Belova, Anna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Rigorous enclosures of rotation numbers by interval methods.2016Inngår i: Journal of Computational Dynamics, ISSN 2158-2491, Vol. 3, nr 1, s. 81-91Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We apply set-valued numerical methods to compute an accurate enclosure of the rotation number. The described algorithm is supplemented with a method of proving the existence of periodic points, which is used to check the rationality of the rotation number. A few numerical experiments are presented to show that the implementation of interval methods produces a good enclosure of the rotation number of a circle map.

  • 333.
    Belova, Anna
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Gorbovickis, Igors
    Critical points of the multiplier map for the quadratic family.Manuskript (preprint) (Annet vitenskapelig)
  • 334. Benedusi, Pietro
    et al.
    Garoni, Carlo
    Krause, Rolf
    Li, Xiaozhou
    Serra-Capizzano, Stefano
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Discontinuous Galerkin discretization of the heat equation in any dimension: The spectral symbol2018Rapport (Annet vitenskapelig)
  • 335. Benedusi, Pietro
    et al.
    Garoni, Carlo
    Krause, Rolf
    Li, Xiaozhou
    Serra-Capizzano, Stefano
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Space–time FE–DG discretization of the anisotropic diffusion equation in any dimension: The spectral symbol2018Inngår i: SIAM Journal on Matrix Analysis and Applications, ISSN 0895-4798, E-ISSN 1095-7162, Vol. 39, s. 1383-1420Artikkel i tidsskrift (Fagfellevurdert)
  • 336.
    Bengtsson, Ivar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Fichter, Michael
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Modelling and optimizing transaction fees in a proof-of-stake cryptocurrency2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    This paper is an attempt to analyze the role of transaction fees in a proof-of-stake cryptocurrency currently in development. The authors have employed a microeconomic, static equilibrium approach to model a market in which the cryptocurrency is exchanged for a physical good. Furthermore, the relationship between transaction capacity and the size of the network has been investigated. It has been shown that the total amount of validator capital and the number of validators can be controlled by setting a fixed fee on transactions as well as a minimum capital requirement on individual validators. The total surplus in the economy has then been optimized by setting a fee and the authors have discussed how a minimal capital requirement could be used to also optimize transaction capacity.

  • 337.
    Bengtsson, Martin
    Linköpings universitet, Matematiska institutionen.
    Analytical Expressions for the Hawking Mass in slowly rotating Kerr and Kerr-Newman Space-times2007Independent thesis Advanced level (degree of Magister), 20 poäng / 30 hpOppgave
    Abstract [en]

    Penrose's inequality which relates the total mass of a space-time containing a black hole with the area of the event horizon, is a yet unproven condition that is required for the cosmic censorship hypothesis. It is believed that the inequality could be proved by using properties of the Hawking mass. This thesis gives analytical expressions for the Hawking mass in slowly rotating Kerr and Kerr-Newman space-times. It is also shown that the expressions are monotonically increasing, a result that does not contradict Penrose's inequality.

  • 338.
    Berezovsky, Vladimir
    et al.
    Pomorskii State University, Arkhangelsk.
    Men'shikov, Leonid
    Russian Research Centre, Kurchatov Institute, Moscow.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Latham, Chris
    Effect of dipole-dipole interactions between atoms in an active medium2008Inngår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, nr 3, s. 458-462Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On the basis of the results of numerical modeling, it is shown that dipole-dipole interactions among atoms in the active medium strongly influences the character of the associated superradiation. The main effect is to make the nuclear subsystem behave chaotically. Its strength increases with the atom density and leads to the suppression of distant collective correlations and superradiation. Near correlations between the atoms are established, causing a confinement effect: a shielding of radiation in the active medium.

  • 339.
    Berezovsky, V.V.
    et al.
    Lomonosov Pomor State University, Arkhangelsk.
    Men'shikov, L.I.
    Russian Research Centre, Kurchatov Institute, Moscow.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Latham, Chris
    Effect of the dipole-dipole interaction of particles in an active medium on the character of superradiation2008Inngår i: Plasma physics reports (Print), ISSN 1063-780X, E-ISSN 1562-6938, Vol. 34, nr 7, s. 555-561Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The motion of a system of interacting nonlinear charged oscillators is investigated numerically. Because of nonlinearity, the total collective electric field gives rise to a phasing effect-correlations in the phases of the oscillators. The consequence is superradiation-the enhanced spontaneous short-term emission of the energy stored in the oscillators. It is shown that the oscillations of the oscillators become stochastic because of the dipole-dipole interaction between them and their nearest neighbors. As a result, as the density of the oscillators increases, distant collective correlations are suppressed, superradiation ceases to be generated, and radiation is shielded in the medium. The phenomena considered in the present paper can play an important role in cyclotron emission from a plasma and thus should be taken into account in emission calculations. The process whereby the energy of the transverse electron motion in electron cooling devices decreases is analyzed as an example. This process occurs as a result of the development of cyclotron maser instability and has the nature of superradiation. The onset of correlations between individual electrons moving in their Larmor circles is the initial, linear stage of instability developing in the plasma. Superradiation is the final, nonlinear instability stage.

  • 340.
    Berg, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Stable and High-Order Finite Difference Methods for Multiphysics Flow Problems2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Partial differential equations (PDEs) are used to model various phenomena in nature and society, ranging from the motion of fluids and electromagnetic waves to the stock market and traffic jams. There are many methods for numerically approximating solutions to PDEs. Some of the most commonly used ones are the finite volume method, the finite element method, and the finite difference method. All methods have their strengths and weaknesses, and it is the problem at hand that determines which method that is suitable. In this thesis, we focus on the finite difference method which is conceptually easy to understand, has high-order accuracy, and can be efficiently implemented in computer software.

    We use the finite difference method on summation-by-parts (SBP) form, together with a weak implementation of the boundary conditions called the simultaneous approximation term (SAT). Together, SBP and SAT provide a technique for overcoming most of the drawbacks of the finite difference method. The SBP-SAT technique can be used to derive energy stable schemes for any linearly well-posed initial boundary value problem. The stability is not restricted by the order of accuracy, as long as the numerical scheme can be written in SBP form. The weak boundary conditions can be extended to interfaces which are used either in domain decomposition for geometric flexibility, or for coupling of different physics models.

    The contributions in this thesis are twofold. The first part, papers I-IV, develops stable boundary and interface procedures for computational fluid dynamics problems, in particular for problems related to the Navier-Stokes equations and conjugate heat transfer. The second part, papers V-VI, utilizes duality to construct numerical schemes which are not only energy stable, but also dual consistent. Dual consistency alone ensures superconvergence of linear integral functionals from the solutions of SBP-SAT discretizations. By simultaneously considering well-posedness of the primal and dual problems, new advanced boundary conditions can be derived. The new duality based boundary conditions are imposed by SATs, which by construction of the continuous boundary conditions ensure energy stability, dual consistency, and functional superconvergence of the SBP-SAT schemes.

  • 341.
    Berg, Jens
    Uppsala universitet, Avdelningen för beräkningsvetenskap.
    Stable and High-Order Finite Difference Methods for Multiphysics Flow Problems2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Partial differential equations (PDEs) are used to model various phenomena in nature and society, ranging from the motion of fluids and electromagnetic waves to the stock market and traffic jams. There are many methods for numerically approximating solutions to PDEs. Some of the most commonly used ones are the finite volume method, the finite element method, and the finite difference method. All methods have their strengths and weaknesses, and it is the problem at hand that determines which method that is suitable. In this thesis, we focus on the finite difference method which is conceptually easy to understand, has high-order accuracy, and can be efficiently implemented in computer software.

    We use the finite difference method on summation-by-parts (SBP) form, together with a weak implementation of the boundary conditions called the simultaneous approximation term (SAT). Together, SBP and SAT provide a technique for overcoming most of the drawbacks of the finite difference method. The SBP-SAT technique can be used to derive energy stable schemes for any linearly well-posed initial boundary value problem. The stability is not restricted by the order of accuracy, as long as the numerical scheme can be written in SBP form. The weak boundary conditions can be extended to interfaces which are used either in domain decomposition for geometric flexibility, or for coupling of different physics models.

    The contributions in this thesis are twofold. The first part, papers I-IV, develops stable boundary and interface procedures for computational fluid dynamics problems, in particular for problems related to the Navier-Stokes equations and conjugate heat transfer. The second part, papers V-VI, utilizes duality to construct numerical schemes which are not only energy stable, but also dual consistent. Dual consistency alone ensures superconvergence of linear integral functionals from the solutions of SBP-SAT discretizations. By simultaneously considering well-posedness of the primal and dual problems, new advanced boundary conditions can be derived. The new duality based boundary conditions are imposed by SATs, which by construction of the continuous boundary conditions ensure energy stability, dual consistency, and functional superconvergence of the SBP-SAT schemes.

  • 342.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    A stable and dual consistent boundary treatment using finite differences on summation-by-parts form2012Inngår i: Proc. ECCOMAS Congress 2012, Austria: Tech. Univ. Wien , 2012, s. 7557-7570Konferansepaper (Fagfellevurdert)
  • 343.
    Berg, Jens
    et al.
    Uppsala University, Department of Information Technology.
    Nordström, Jan
    Linköpings universitet, Matematiska institutionen, Beräkningsmatematik. Linköpings universitet, Tekniska högskolan.
    A stable and dual consistent boundary treatment using finite differences on summation-by-parts form2012Inngår i: European Congress on Computational Methods in Applied Sciences and Engineering, Vienna University of Technology , 2012Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper is concerned with computing very high order accurate linear functionals from a numerical solution of a time-dependent partial differential equation (PDE). Based on finite differences on summation-by-parts form, together with a weak implementation of the boundary conditions, we show how to construct suitable boundary conditions for the PDE such that the continuous problem is well-posed and the discrete problem is stable and spatially dual consistent. These two features result in a superconvergent functional, in the sense that the order of accuracy of the functional is provably higher than that of the solution.

  • 344.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    A stable and dual consistent boundary treatment using finite differences on summation-by-parts form2012Rapport (Annet vitenskapelig)
  • 345.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    Duality based boundary conditions and dual consistent finite difference discretizations of the Navier–Stokes and Euler equations2013Rapport (Annet vitenskapelig)
  • 346.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    Duality based boundary conditions and dual consistent finite difference discretizations of the Navier–Stokes and Euler equations2014Inngår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 259, s. 135-153Artikkel i tidsskrift (Fagfellevurdert)
  • 347.
    Berg, Jens
    et al.
    Uppsala University, Sweden.
    Nordström, Jan
    Linköpings universitet, Matematiska institutionen, Beräkningsmatematik. Linköpings universitet, Tekniska högskolan.
    Duality based boundary conditions and dual consistent finite difference discretizations of the Navier–Stokes and Euler equations2014Inngår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 259, s. 135-153Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we derive new farfield boundary conditions for the time-dependent Navier–Stokes and Euler equations in two space dimensions. The new boundary conditions are derived by simultaneously considering well-posedess of both the primal and dual problems. We moreover require that the boundary conditions for the primal and dual Navier–Stokes equations converge to well-posed boundary conditions for the primal and dual Euler equations.

    We perform computations with a high-order finite difference scheme on summation-by-parts form with the new boundary conditions imposed weakly by the simultaneous approximation term. We prove that the scheme is both energy stable and dual consistent and show numerically that both linear and non-linear integral functionals become superconvergent.

  • 348.
    Berg, Jens
    et al.
    Uppsala University, Department of Information Technology.
    Nordström, Jan
    Linköpings universitet, Matematiska institutionen, Beräkningsmatematik. Linköpings universitet, Tekniska högskolan.
    Duality based boundary treatment for the Euler and Navier-Stokes equations2013Inngår i: AIAA Aerospace Sciences - Fluid Sciences Event, 2013, s. 1-19Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In this paper we construct well-posed boundary conditions for the compressible Euler and Navier-Stokes equations in two space dimensions. When also considering the dual equations, we show how to construct the boundary conditions so that both the primal and dual problems are well-posed. By considering the primal and dual problems simultaneously, we construct energy stable and dual consistent finite difference schemes on summation-by-  parts form with weak imposition of the boundary conditions.

    According to linear theory, the stable and dual consistent discretization can be used to compute linear integral functionals from the solution at a superconvergent rate. Here we evaluate numerically the superconvergence property for the non-linear Euler and Navier{ Stokes equations with linear and non-linear integral functionals.

  • 349.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    Duality based boundary treatment for the Euler and Navier-Stokes equations2013Inngår i: Proc. 21st AIAA CFD Conference, AIAA , 2013Konferansepaper (Fagfellevurdert)
  • 350.
    Berg, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Nordström, Jan
    On the impact of boundary conditions on dual consistent finite difference discretizations2012Rapport (Annet vitenskapelig)
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