| 1. |
- Aggestam, Emil, 1992, et al.
(författare)
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Numerical model reduction with error control in computational homogenization of transient heat flow
- 2017
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 326, s. 193-222
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Tidskriftsartikel (refereegranskat)abstract
- Numerical Model Reduction (NMR) is exploited for solving the finite element problem on a Representative Volume Element (RVE) that arises from the computational homogenization of a model problem of transient heat flow. Since the problem is linear, an orthogonal basis is obtained via the classical method of spectral decomposition. A symmetrized version of the space–time variational format is adopted for estimating the error from the model reduction in (i) energy norm and in (ii) given Quantities of Interest. This technique, which was recently developed in the context of the (non-selfadjoint) stationary diffusion–convection problem, is novel in the present context of NMR. By considering the discrete, unreduced, model as exact, we are able to obtain guaranteed bounds on the error while using only the reduced basis and with minor computational effort. The performance of the error estimates is demonstrated via numerical results, where the subscale is modeled in both one and three spatial dimensions.
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| 2. |
- DAWODY, JAZAER, 1959, et al.
(författare)
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An integrated system for energy-efficient exhaust aftertreatment for heavy-duty vehicles
- 2015
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Ingår i: Renewable Energy in the Service of Mankind. - Cham : Springer International Publishing. - 9783319177779 - 9783319177762 ; , s. 133-143
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- © Springer International Publishing Switzerland 2015. This chapter presents a unique system approach applied in a joint academic- industrial research programme, E4 Mistra, to attain the goals of high energy efficiency and low emissions in an exhaust aftertreatment system for heavy-duty vehicles. The high energy efficiency is achieved by heat recuperation, onboard hydrogen production for NOx reduction, and by finding new solutions for making the aftertreatment system active at low exhaust temperatures. To reach low particulate emissions, a mechanical filter using a sintered metal powder is developed and coated with catalytic material to improve the soot oxidation efficiency. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The integrated E4 Mistra system comprises four technological advances: thermoelectric (TE) materials for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using either the onboard diesel or biodiesel, H2 from a high-efficiency fuel reformer, and particulate filtration over a porous metal filter. The TE materials are used in a TE generator (TEG) which converts thermal energy into electricity. The TEG is used to recuperate heat from the exhaust-gas recirculation (EGR) circuit of heavy-duty trucks and is expected to generate ~1 kW electric power from 20 kW heat in the exhaust gas. The TEG is integrated in a plate heat exchanger (HEX) designed particularly for this application. Apart from the knowledge and experiences in TEG and heat exchange technologies, a thorough fluid dynamics and TE analysis are performed in this project to understand the governing processes and optimize the system accordingly. The components of the E4 Mistra system are explained in the chapter in addition to test results, which show the system's capacity for H2 production, NOx conversion, particulate matter filtration and soot oxidation, and finally electric power generation via heat recuperation from the exhaust gas using the developed TEG-HEX system.
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| 3. |
- Ekre, Fredrik, 1992, et al.
(författare)
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On error controlled numerical model reduction in FE2-analysis of transient heat flow
- 2019
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 119:1, s. 38-73
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Tidskriftsartikel (refereegranskat)abstract
- Numerical model reduction is exploited for solving the two-scale problem that arises from the computational homogenization of a model problem of transient heat flow. Since the problem is linear, an orthogonal basis is obtained via the method of spectral decomposition. A key feature is the construction of a symmetrized version of the space-time variational format, by which it is possible to estimate the error from the model reduction in (i) energy norm and in (ii) a given quantity of interest. In previous work by the authors, this strategy has been applied to the solution of an individual representative volume element problem, whereas the error transport to the macroscale problem in the finite element squared (FE2) approach was ignored. In this paper, such transport of error is included in the error estimate. It is remarkable that it is (still) possible to obtain guaranteed bounds on the error, as compared to the fully resolved discrete finite element problem, while using only the reduced basis and with minor extra computational effort. The performance of the error estimates is demonstrated via numerical results, whereby the subscale is modeled in three dimensions, whereas the macroscale problem is either one or two dimensional.
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| 4. |
- Sedigh, Amir, et al.
(författare)
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Perfusion of Porcine Kidneys With Macromolecular Heparin Reduces Early Ischemia Reperfusion Injury
- 2019
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Ingår i: Transplantation. - : LIPPINCOTT WILLIAMS & WILKINS. - 0041-1337 .- 1534-6080. ; 103:2, s. 420-427
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Tidskriftsartikel (refereegranskat)abstract
- Background: Previously, we have been able to demonstrate the possibility of coating the inner surface of the renal arteries in porcine kidneys with a heparin conjugate during hypothermic machine perfusion (HMP). The purpose of this study was to assess the efficacy of this treatment in reducing early ischemia-reperfusion injury.Method: Brain death was induced in male landrace pigs by stepwise volume expansion of an epidural balloon catheter until negative cerebral perfusion pressure (CPP) was obtained. Both kidneys (matched pairs; n = 6 + 6) were preserved for 20 hours byHMP during which 50mg heparin conjugate was added to one of the HMP systems (treated group). A customized ex vivo normothermic oxygenated perfusion (NP) system with added exogenous creatinine was used to evaluate early kidney function. Blood, urine and histological samples were collected during the subsequent 3 hours of NP.Results: Kidney weight was lower at the end of NP (P = 0.017) in the treated group compared with control kidneys. The rate of decline in creatinine level was faster (P = 0.024), total urinary volume was higher (P = 0.031), and the level of urine neutrophil gelatinase-associated lipocalin (NGAL) was lower (P = 0.031) in the treated group. Histologically, less tubular changes were seen (P = 0.046). During NP intrarenal resistance remained lower (P < 0.0001) in the treated group.Conclusions: Perfusion of porcine kidneys with heparin conjugate during HMP reduces preservation injury and improves organ function shortly after reperfusion. No increased risk of bleeding was seen in this setup. This protective strategy may potentially improve the quality of transplanted kidneys in the clinical setting.
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| 5. |
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| 6. |
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| 7. |
- Andersson, David, 1979, et al.
(författare)
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DN Debatt: LRF och Svenskt flyg svarar inte om klimatmålen
- 2015
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Ingår i: Dagens Nyheter. - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Sammantaget ser vi inget i motdebattörernas argument som talar emot att införa styrmedel, till exempel konsumtionsskatter, inom dessa områden där inga stora tekniska lösningar finns i sikte, skriver 14 miljö- och energiforskare i slutrepliken till sin text om flyg- och köttskatt (26/2).
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| 8. |
- Andersson, David, 1979, et al.
(författare)
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Nu krävs kraftfulla åtgärder mot nötkött och flygresor
- 2015
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Ingår i: Dagens Nyheter. - 1101-2447. ; 2015-02-27
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Svenskarnas globala utsläpp från köttkonsumtion och flygresor motsvarar hälften av de totala utsläppen på hemmaplan. I vår rapport till Naturvårdsverket föreslår vi tydliga styrmedel – som nya skatter – för att begränsa konsumtionen på dessa områden, skriver 14 miljö- och energiforskare.
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| 9. |
- Andersson, Robin, 1986, et al.
(författare)
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An efficient approach to the analysis of rail surface irregularities accounting for dynamic train–track interaction and inelastic deformations
- 2015
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:11, s. 1667-1685
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional computational model for assessment of rolling contact fatigue induced by discrete rail surface irregularities, especially in the context of so-called squats, is presented. Dynamic excitation in a wide frequency range is considered in computationally efficient time-domain simulations of high-frequency dynamic vehicle-track interaction accounting for transient non-Hertzian wheel–rail contact. Results from dynamic simulations are mapped onto a finite element model to resolve the cyclic, elastoplastic stress response in the rail. Ratcheting under multiple wheel passages is quantified. In addition, low cycle fatigue impact is quantified using the Jiang–Sehitoglu fatigue parameter. The functionality of the model is demonstrated by numerical examples.
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| 10. |
- Andersson, Robin, 1986, et al.
(författare)
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Evaluation of stress intensity factors under multiaxial and compressive conditions using low order displacement or stress field fitting
- 2018
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944. ; 189, s. 204-220
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for evaluation of stress intensity factors from the asymptotic displacement (or stress) fields at a crack front is proposed. The methodology strives to be of practical use in conjunction with commercial FE-codes, also when approaches such as XFEM are employed. To this end, the matching of the fields is carried out through a minimalistic, low order, ansatz of the displacement and stress fields. As demonstrated, the proposed methodology can deal with multiaxial loading of curved crack fronts in three-dimensional bodies. The methodology shows good accuracy also for compressive loading when crack face friction can be neglected.
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