| 1. |
- Hoffman, Johan, et al.
(författare)
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Unicorn : Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a framework for adaptive finite element computation of turbulent flow and fluid-structure interaction, with focus on general algorithms that allow for complex geometry and deforming domains. We give basic models and finite element discretization methods, adaptive algorithms and strategies for e cient parallel implementation. To illustrate the capabilities of the computational framework, we show a number of application examples from aerodynamics, aero-acoustics, biomedicine and geophysics. The computational tools are free to download open source as Unicorn, and as a high performance branch of the finite element problem solving environment DOLFIN, both part of the FEniCS project
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| 2. |
- Jansson, Johan, 1978-, et al.
(författare)
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Simulation of 3D unsteady incompressible flow past a NACA 0012 wing section
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present computational simulations of three-dimensional unsteady high Reynolds number incompressible flow past a NACA 0012 wing profile, for a range of angles of attack, from low lift through stall. A stabilized finite element method is used, referred to as General Galerkin (G2), with adaptive mesh refinement with respect to the error in target output, such as aerodynamic forces. Computational predictions of aerodynamic forces are validated against experimental data.
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| 3. |
- Spühler, Jeannette Hiromi, 1981-, et al.
(författare)
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A finite element framework for high performance computer simulation of blood flow in the left ventricle of the human heart
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Progress in medical imaging, computational fluid dynamics and high performance computing (HPC) enables computer simulations to emerge as a significant tool to enhance our understanding of the relationship between cardiac diseases and hemodynamics. The field of cardiac modelling is diverse, covering different aspects on microscopic and macroscopic level. In our research, we develop a cardiac model which is embedded in a computational environment where specific properties of the heart such as fluid-structure interaction of the aortic valve can be modeled, or numerical and computational algorithms as parallel computing or adaptivity can be added in a modular way without extensive efforts. In this paper, we present a patient-specific Arbitrary Lagrangian-Eulerian (ALE) finite element framework for simulating the blood flow in the left ventricle of a human heart using HPC, which forms the core of our cardiac model. The mathematical model is described together with the discretization method, mesh smoothing algorithms, and the parallel implementation in Unicorn which is part of the open source software framework FEniCS-HPC. The parallel performance is demonstrated, a convergence study is conducted and intraventricular flow patterns are visualized. The results capture essential features observed with other computational models and imaging techniques, and thus indicate that our framework possesses the potential to provide relevant clinical information for diagnosis and medical treatment. Several studies have been conducted to simulate the three dimensional blood flow in the left ventricle of the human heart with prescribed wall movement. Our contribution to the field of cardiac research lies in establishing an open source framework modular both in modelling and numerical algorithms.
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| 4. |
- Jansson, Johan, 1978-, et al.
(författare)
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Adaptive error control in finite element methods using the error representation as error indicator
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present a new a posteriori adaptive finite elementmethod (FEM) directly using the error representation as a local errorindicator, and representing the primal and dual solutions in the samefinite element space (here piecewise continuous linear functions onthe same mesh). Since this approach gives a global a posteriori errorestimate that is zero (due to the Galerkin orthogonality), the errorrepresentation has historically been thought to contain no informationabout the error. However, we show the opposite, that locally, theorthogonal error representation behaves very similar to thenon-orthogonal error representation using a quadratic approximation ofthe dual. We present evidence of this both in the form of an a prioriestimate for the local error indicator and a detailed computationalinvestigation showing that the two methods exhibit very similarbehavior and performance, and thus confirming the theoreticalprediction. We also present a stabilized version of the method fornon-elliptic partial differential equations (PDE) where the errorrepresentation is no longer orthogonal, and where both the local errorindicator and global error estimate behave similar to the errorrepresentation using a quadratic approximation of the dual.
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| 5. |
- Jansson, Johan, 1978-, et al.
(författare)
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Automated adaptive error control in finite element methods using the error representation as error indicator
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present a new adaptive finite element method directly using the a posteriori error representation as a local error indicator, and representing the primal and dual solutions in the same finite element space (here piecewise continuous linear functions on the same mesh). Since this approach gives a global a posteriori error estimate that is zero (due to Galerkin orthogonality), the error representation has traditionally been thought to contain no information about the error. However, we show the opposite, that locally, the orthogonal error representation behaves very similar to the non-orthogonal error representation using a higher order approximation of the dual, which is a standard approach to overcome the problem of a zero error estimate. We present evidence of this both in the form of an a priori estimate for the local error indicator for an elliptic model problem and a detailed computational investigation showing that the two methods exhibit very similar behavior and performance, and thus confirming the theoretical prediction. We also present computational results using a stabilized version of the method for non-elliptic partial differential equations where the error representation is no longer orthogonal, and where both the local error indicator and global error estimate behave similar to the error representation using a higher order approximation of the dual. The benefits of this adaptive method are generality and simplicity in formulation, sharpness, and efficiency since high order approximation of the dual and computation of additional constructs such as jump terms over interior facets or local problems are avoided.
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| 6. |
- Jansson, Johan, 1978-, et al.
(författare)
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Automated error control in finite element methods withapplications in fluid flow
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present a new adaptive finite element method for thesolution of linear and non-linear partial differential equationsdirectly using the a posteriori error representation as a local errorindicator, with the primal and dual solutions approximated in the samefinite element space, here piecewise continuous linear functions onthe same mesh. Since this approach gives a global a posteriori errorrepresentation that is zero due to Galerkin orthogonality, the errorrepresentation has traditionally been thought to contain noinformation about the error. However, for elliptic andconvection-diffusion model problems we show the opposite, that locallythe orthogonal error representation behaves very similar to thenon-orthogonal error representation using a higher order approximationof the dual. We have previously proved an a priori estimate of thelocal error indicator for elliptic problems, and in this paper weextend the proof to convection-reaction problems. We also present aversion of the method for non-elliptic and non-linear problems using astabilized finite element method where the a posteriori errorrepresentation is no longer orthogonal. We apply this method to thestationary incompressible Navier-Stokes equation and perform detailednumerical experiments which show that the a posteriori error estimateis within a factor 2 of the error based on a reference value on a finemesh, except in a few data points on very coarse meshes for anon-smooth test case where it is within a factor 3.
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| 7. |
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| 8. |
- Sjöström, Johan, 1978-, et al.
(författare)
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En ny modell för gräsbrandsfara i Sverige
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Risken för antändning och snabb spridning av vegetationsbränder i skogsmark och i gräsmarkerskiljer sig markant. Gräsbränder sprider sig i dött fjolårsgräs, tidigt på våren, innan årets färskagräs hunnit växa till och dessa bränder kan spridas snabbt efter bara några timmars torrt väder.Risken klingar snabbt av med inväxten av färskt gräs för att i stort sett upphöra till sommaren.Skogsbränder har inte samma säsongsberoende av bränslet utan styrs mer av vädret. Därför skerde typiskt under sommaren och kräver oftast flera dagars torrt väder. Dessa skillnader gör attolika riskbedömningssystem måste användas för dessa två karakteristiska typer avvegetationsbränder.Här presenteras en ny modell för gräsbrandsfara som använder potentiell spridningshastighet iobetat, oklippt gräs som indikator på risk. Algoritmen tar väderhistoriken (snötäcke, relativluftfuktighet, vindhastighet, temperatur och solinstrålning) samt progressionen av årsgräsetsinväxt i beaktning. Modellen bygger på en modell för beräkning av fuktkvot i gräs utvecklad iNordamerika samt en modell för hur fuktkvoten och vindhastigheten inverkar påspridningshastigheten. Effekten av årsgräsets inväxt under svenska förhållanden beräknasgenom 25 års insats- och väder-data i tio regioner och en anpassning till tidigare utfördatestbränningar från snösmältning till gräsbrandssäsongens slut. Modellen kan uppdateras varjetimme, i linje med det uppdaterade brandrisksystemet i Sverige.Förslag till hur indelning i risknivåer ska utformas med avseende på riskindikatorn presenterasoch modellen sätts i bruk till våren 2021.
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| 9. |
- Anderson, Johan, 1973-, et al.
(författare)
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Fire Safety of Façades
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Façade fires do not occur often (in comparison to other major structure fires) but in recent years there have been a number of spectacular façade fires in high rise building such as the recent fire in Grenfell Tower, London.Under-ventilated compartment fires may cause flames to spill out of window openings impinging the façade, thus devastating façade fires may start on one floor leap-frogging to adjacent floors. It is therefore necessary to limit or delay fire spread to higher floors. Requirements built on large scale fire testing may decrease the risk of these types of fires provided that the building is constructed according to the specifications provided by the manufacturer. Different countries have different regulations and tests for façades. New materials and façade systems are continuously introduced which might call for an update of these tests and regulations.This report summarizes experimental and modelling efforts in characterizing the fire safety of façades using the Swedish SP Fire 105 and the British BS 8414 methods. Recent experimental results and modelling is presented exploring the variations in the fire exposure, fire load and the fuel used. The fire source and the heat exposure to the façade are characterized by additional temperatures measured by plate thermometers while some other aspects are only treated in the numerical study such as a change in fuel. It is found that the results from the BS 8414 are largely affected by wind and climate since the experimental test was performed outdoors, moreover fire spread on wooden façades is also briefly discussed.In order to obtain a deeper understanding of the test methods and the results CFD (Computational Fluid Dynamics) Modelling in FDS was used. The models were based on measured input parameters including uncertainties and an assessment of the impact of said uncertainties. The models could often reproduce the experimentally found temperatures qualitatively and quantitatively. A detailed discussion on the regulations and the tests that lead to the SP Fire 105 test method is also presented. Summaries of the façade testing methods and conditions in other European countries are presented in the appendices.Finally possible ways forward in updating the façade testing and regulations are discussed.
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| 10. |
- Andersson, Hanna, et al.
(författare)
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Natur på skolgården för lärande, hälsa och hållbarhet
- 2024. - 2024
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Rapport (populärvet., debatt m.m.)abstract
- Gröna och artrika utemiljöer främjar barns och ungas välbefinnande och kunskap, bådegenom hälsofördelar kopplade till biologisk mångfald och genom att skapa förutsättningarför lek och lärande om natur och miljöfrågor. Skolgården skulle kunna bidra till allt detta,men är idag i hög grad en outnyttjad plats för biologisk mångfald och klimatanpassningav städer. I denna policy brief presenteras huvudsakliga motiv och möjliga åtgärder för attutveckla gröna miljöer och biologisk mångfald på skolgårdar och förskolegårdar.
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