Ändra sökning
Avgränsa sökresultatet
1 - 39 av 39
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Adaptive computation of aeroacoustic sources for a rudimentary landing gear using lighthill's analogy2011Ingår i: 17th AIAA/CEAS AeroacousticsConference 2011: 32nd AIAA Aeroacoustics Conference, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present our simulation results for the benchmark problem of the ow past a Rudimentary Landing Gear (RLG) using a General Galerkin (G2) nite element method, also referred to as Adaptive DNS/LES. In G2 no explicit subgrid model is used, instead the compuational mesh is adaptively re ned with respect to an a posteriori error es-timate of a quantity of interest in the computation, in this case the drag force on the RLG. Turbulent boundary layers are modeled using a simple wall layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we nd good agreement in sound pressure levels, surface velocities and ow separation. We also compare with detailed surface pressure experimental data where we nd largely good agreement, apart from some local dierences for which we discuss possible explanations.

  • 2.
    de Abreu, Rodrigo Vilela
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Adaptive Computation of Aeroacoustic Sources for Rudimentary Landing Gear2010Ingår i: Benchmark problems for Airframe Noise Computations I, Stockholm 2010, 2010Konferensbidrag (Övrigt vetenskapligt)
  • 3.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    de Abreu, Rodrigo Vilela
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Müller, Kaspar
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Nazarov, Murtazo
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Spühler, Jeannette Hiromi
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Unicorn: Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry2013Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 80, nr SI, s. 310-319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 efficient 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.

  • 4.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Nazarov, Murtazo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Unicorn: a unified continuum mechanics solver; in automated solution pf differential equations by the finite element method2011Ingår i: Automated Solution of Differential Equations by the Finite Element Method, Springer Berlin/Heidelberg, 2011Kapitel i bok, del av antologi (Refereegranskat)
  • 5.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC). Basque Center for Applied Mathematics (BCAM), Bilbao, Spain.
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). Basque Center for Applied Mathematics (BCAM), Bilbao, Spain.
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Spühler, Jeannette Hiromi
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Vilela de Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Larcher, Aurélien
    Norwegian University of Science and Technology, Trondheim, Norway.
    FEniCS-HPC: Coupled Multiphysics in Computational Fluid Dynamics2017Ingår i: High-Performance Scientific Computing: Jülich Aachen Research Alliance (JARA) High-Performance Computing Symposium / [ed] Edoardo Di Napoli, Marc-André Hermanns, Hristo Iliev, Andreas Lintermann, Alexander Peyser, Springer, 2017, s. 58-69Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a framework for coupled multiphysics in computational fluid dynamics, targeting massively parallel systems. Our strategy is based on general problem formulations in the form of partial differential equations and the finite element method, which open for automation, and optimization of a set of fundamental algorithms. We describe these algorithms, including finite element matrix assembly, adaptive mesh refinement and mesh smoothing; and multiphysics coupling methodologies such as unified continuum fluid-structure interaction (FSI), and aeroacoustics by coupled acoustic analogies. The framework is implemented as FEniCS open source software components, optimized for massively parallel computing. Examples of applications are presented, including simulation of aeroacoustic noise generated by an airplane landing gear, simulation of the blood flow in the human heart, and simulation of the human voice organ.

  • 6.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    FEniCS-HPC: Automated predictive high-performance finite element computing with applications in aerodynamics2016Ingår i: Proceedings of the 11th International Conference on Parallel Processing and Applied Mathematics, PPAM 2015, Springer-Verlag New York, 2016, Vol. 9573, s. 356-365Konferensbidrag (Refereegranskat)
    Abstract [en]

    Developing multiphysics nite element methods (FEM) andscalable HPC implementations can be very challenging in terms of soft-ware complexity and performance, even more so with the addition ofgoal-oriented adaptive mesh renement. To manage the complexity we inthis work presentgeneraladaptive stabilized methods withautomatedimplementation in the FEniCS-HPCautomatedopen source softwareframework. This allows taking the weak form of a partial dierentialequation (PDE) as input in near-mathematical notation and automati-cally generating the low-level implementation source code and auxiliaryequations and quantities necessary for the adaptivity. We demonstratenew optimal strong scaling results for the whole adaptive frameworkapplied to turbulent ow on massively parallel architectures down to25000 vertices per core with ca. 5000 cores with the MPI-based PETScbackend and for assembly down to 500 vertices per core with ca. 20000cores with the PGAS-based JANPACK backend. As a demonstration ofthe high impact of the combination of the scalability together with theadaptive methodology allowing prediction of gross quantities in turbulent ow we present an application in aerodynamics of a full DLR-F11 aircraftin connection with the HiLift-PW2 benchmarking workshop with goodmatch to experiments.

  • 7.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). Basque Ctr Appl Math, Spain.
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). Basque Ctr Appl Math, Spain.
    Jansson, Niclas
    RIKEN Advanced Institute for Computational Science, Kobe, Japan.
    De Abreu, Rodrigo Vilela
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Towards a parameter-free method for high Reynolds number turbulent flow simulation based on adaptive finite element approximation2015Ingår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 288, s. 60-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present work towards a parameter-free method for turbulent flow simulation based on adaptive finite element approximation of the Navier-Stokes equations at high Reynolds numbers. In this model, viscous dissipation is assumed to be dominated by turbulent dissipation proportional to the residual of the equations, and skin friction at solid walls is assumed to be negligible compared to inertial effects. The result is a computational model without empirical data, where the only parameter is the local size of the finite element mesh. Under adaptive refinement of the mesh based on a posteriori error estimation, output quantities of interest in the form of functionals of the finite element solution converge to become independent of the mesh resolution, and thus the resulting method has no adjustable parameters. No ad hoc design of the mesh is needed, instead the mesh is optimised based on solution features, in particular no bounder layer mesh is needed. We connect the computational method to the mathematical concept of a dissipative weak solution of the Euler equations, as a model of high Reynolds number turbulent flow, and we highlight a number of benchmark problems for which the method is validated. 

  • 8.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Johnsson, Claes
    Vilela de Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Turbulent flow and fluid-structure interaction; in automated solution of differental equations by the finite element method2011Ingår i: Automated Solution of Differential Equations by the Finite Element Method / [ed] Anders Logg Kent-Andre Mardal, Garth Wells, Springer Berlin/Heidelberg, 2011Kapitel i bok, del av antologi (Refereegranskat)
  • 9.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). Basque Center for Applied Mathematics, Spain .
    Jansson, Niclas
    RIKEN Advanced Institute for Computational Science, Japan .
    Vilela De Abrea, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Time-resolved adaptive FEM simulation of the DLR-F11 aircraft model at high Reynolds number2014Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014, 2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We present a time-resolved, adaptive finite element method for aerodynamics, together with the results from the HiLiftPW-2 workshop, where this method is used to compute the flow past a DLR-F11 aircraft model at realistic Reynolds number. The mesh is automatically constructed by the method as part of the computation, and no explicit turbulence model is needed. The effect of unresolved turbulent boundary layers is modeled by a simple parametrization of the wall shear stress in terms of the skin friction. In the extreme case of very high Reynolds numbers we approximate the small skin friction by zero skin friction, corresponding to a free slip boundary condition, which results in a computational model without any model parameter that needs tuning. Thus, the simulation methodology by- passes the main challenges posed by high Reynolds number CFD: the design of an optimal computational mesh, turbulence (or subgrid) modeling, and the cost of boundary layer res- olution. The results from HiLiftPW-2 presented in this report show good agreement with experimental data for a range of different angles of attack, while using orders of magnitude fewer degrees of freedom than what is needed in state of the art methods such as RANS. 

  • 10.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Vilela de Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Johnson, Claes
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Computability and Adaptivity in CFD2018Ingår i: Encyclopedia of Computational Mechanics / [ed] Erwin Stein and René de Borst and Thomas J. R. Hughes, John Wiley & Sons, 2018, 2Kapitel i bok, del av antologi (Refereegranskat)
  • 11.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Vilela de Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Müller, Kaspar
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Nazarov, Murtazo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Spühler, Jeannette Hiromi
    Unicorn: Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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

  • 12.
    Hoffman, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    A computational study of turbulent flow separation for a circular cylinder using skin friction boundary conditions2011Ingår i: Quality And Reliability Of Large-Eddy Simulations II, Springer Netherlands, 2011, Vol. 16, nr 1, s. 57-68Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a computational study of turbulent flow separation for a circular cylinder at high Reynolds numbers. We use a stabilized finite element method together with skin friction boundary conditions, where we study flow separation with respect to the decrease of a friction parameter. In particular, we consider the case of zero friction corresponding to pure slip boundary conditions, for which we observe an inviscid separation mechanism of large scale streamwise vortices, identified in our earlier work. We compare our computational results to experiments for very high Reynolds numbers. In particular, we connect the pattern of streamwise vorticity in our computations to experimental findings of spanwise 3d cell structures reported in the literature.

  • 13.
    Jansson, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Simulation of 3D unsteady incompressible flow past a NACA 0012 wing section2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 14.
    Jansson, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Simulation of 3d unsteady incompressible flow past a NACA 0012 wing sectionManuskript (preprint) (Övrigt vetenskapligt)
  • 15.
    Jansson, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Krishnasamy, Ezhilmathi
    Leoni, Massimiliano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Time-resolved Adaptive Direct FEM Simulation of High-lift Aircraft Configurations: Chapter in "Numerical Simulation of the Aerodynamics of High-Lift Configurations'", Springer2018Ingår i: Numerical Simulation of the Aerodynamics of High-Lift Configurations / [ed] Omar Darío López Mejia andJaime A. Escobar Gomez, Springer, 2018, s. 67-92Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    We present an adaptive finite element method for time-resolved simulation of aerodynamics without any turbulence-model parameters, which is applied to a benchmark problem from the HiLiftPW-3workshop to compute the flowpast a JAXA Standard Model (JSM) aircraft model at realistic Reynolds numbers. The mesh is automatically constructed by the method as part of an adaptive algorithm based on a posteriori error estimation using adjoint techniques. No explicit turbulence model is used, and the effect of unresolved turbulent boundary layers is modeled by a simple parametrization of the wall shear stress in terms of a skin friction. In the case of very high Reynolds numbers, we approximate the small skin friction by zero skin friction, corresponding to a free-slip boundary condition, which results in a computational model without any model parameter to be tuned, and without the need for costly boundary-layer resolution. We introduce a numerical tripping-noise term to act as a seed for growth of perturbations; the results support that this triggers the correct physical separation at stall and has no significant pre-stall effect. We show that the methodology quantitavely and qualitatively captures the main features of the JSM experiment-aerodynamic forces and the stall mechanism-with a much coarser mesh resolution and lower computational cost than the state-of-the-art methods in the field, with convergence under mesh refinement by the adaptive method. Thus, the simulation methodology appears to be a possible answer to the challenge of reliably predicting turbulent-separated flows for a complete air vehicle.

  • 16.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    High performance adaptive finite element methods for turbulent fluid flow2011Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Understanding the mechanics of turbulent fluid flow is of key importance for industry and society as for example in aerodynamics and aero-acoustics. The massive computational cost for resolving all turbulent scales in a realistic problem makes direct numerical simulation of the underlying Navier-Stokes equations impossible. Recent advances in adaptive finite element methods offer a new powerful tool in Computational Fluid Dynamics (CFD). The computational cost for simulating turbulent flow can be minimized where the mesh is adaptively resolved, based on a posteriori error control. These adaptive methods have been implemented for efficient serial computations, but the extension to an efficient parallel solver is a challenging task.

    This work concerns the development of an adaptive finite element method for modern parallel computer architectures. We present efficient data structures and data decomposition methods for distributed unstructured tetrahedral meshes. Our work also concerns an efficient parallellization of local mesh refinement methods such as recursive longest edge bisection.

    We also address the load balance problem with the development of an a priori predictive dynamic load balancing method. Current results are encouraging with almost linear strong scaling to thousands of cores on several modern architectures.

  • 17.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    High Performance Adaptive Finite Element Methods: With Applications in Aerodynamics2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Den höga beräkningskostnaden för att lösa upp alla turbulenta skalor för ett realistiskt problem gör en direkt numerisk simulering av Navier-Stokes ekvationer omöjlig. De senaste framstegen inom adaptiva finita element metoder ger ett nytt kraftfullt verktyg inom Computational Fluid Dynamics (CFD). Beräkningskostnaden för en simulering av turbulent flöde kan minimeras genom att beräkningsnätet adaptivt förfinas baserat på en a posteriori feluppskattning. Dessa adaptiva metoder har tidigare implementerats för seriella beräkningar, medan en effektiv parallellisering av metoden inte är trivial. I denna avhandling presenterar vi vår utveckling av en adaptiv finita element lösare, anpassad för att effektivt beräkna tidsupplösta approximationer i komplicerade geometrier med a posteriori felkontroll. Effektiva datastrukturer och metoder för ostrukturerade beräkningsnät av tetrahedrar presenteras. Avhandlingen behandlar även effektiv parallellisering av lokala nätförfiningsmetoder, exempelvis recursive longest edge bisection. Även lastbalanseringsproblematiken behandlas, där problemet lösts genom utvecklandet av en prediktiv dynamisk lastbalanseringsmetod, baserad på en viktad dualgraf av beräkningsnätet. Slutligen avhandlas även problematiken med att effektivt utnyttja nytillkomna superdatorarkitekturer, genom utvecklandet av en hybrid parallelliserings modell som kombinerar traditionell meddelande baserad parallellisering med envägskommunikation. Detta har resulterat i en generell samt effektiv implementation med god skalning upp till fler än tolv tusen processorkärnor.

  • 18.
    Jansson, Niclas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, Parallelldatorcentrum, PDC.
    Improving Strong Scalability Limits of Finite Element Based Solvers2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Current finite element codes scale reasonably well as long as each core has sufficient amount of local work that can balance communication costs. However, achieving efficient performance at exascale will require unreasonable large problem sizes, in particular for low-order methods, where the small amount of work per element already is a limiting factor on current post petascale machines. One of the key bottlenecks for these methods is sparse matrix assembly, where communication latency starts to limit performance as the number of cores increases. We present our work on improving strong scalability limits of message passing based general low-order finite element based solvers. Using lightweight one-sided communication, we demonstrate that the scalability of performance critical, latency sensitive kernels can achieve almost an order of magnitude better scalability. We introduce a new hybrid MPI/PGAS implementation of the open source general finite element framework FEniCS, replacing the linear algebra backend with a new library written in UPC. A detailed description of the implementation and the hybrid interface to FEniCS is given, and we present a detailed performance study of the hybrid implementation on Cray XC40 machines.

  • 19.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Optimizing Sparse Matrix Assembly in Finite Element Solvers with One-Sided Communication2013Ingår i: High Performance Computing for Computational Science - VECPAR 2012, Springer Berlin/Heidelberg, 2013, s. 128-139Konferensbidrag (Refereegranskat)
    Abstract [en]

    In parallel finite element solvers, sparse matrix assembly is often a bottleneck. Implemented using message passing, latency from message matching starts to limit performance as the number of cores increases. We here address this issue by using our own stack based representation of the sparse matrix, and a hybrid parallel programming model combining traditional message passing with one-sided communication. This gives an significantly faster insertion rate compared to state of the art implementations on a Cray XE6.

  • 20.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Towards a Parallel Algebraic Multigrid Solver Using Partitioned Global Address Space2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The Algebraic Multigrid (AMG) method has over the years developed into an ecient tool for solving unstructured linear systems. The need to solve large industrial problems discretized on unstructured meshes, has been a key motivation for devising a parallel AMG method. Despite some success, the key part of the AMG algorithm; the coarsening step, is far from trivial to parallelize eciently. We here introduce a novel parallelization of the Ruge-Stüben coarsening algorithm, that retains the good interpolation properties of the original method. Our parallelization is based on the Partitioned Global Address Space (PGAS) abstraction, which allows for a simple, yet efficient implementation. The solver is described in detail and a performance study on a Cray XE6 is presented.

  • 21.
    Jansson, Niclas
    et al.
    RIKEN Advanced Institute for Computational Science, Kobe, Japan.
    Bale, Rahul
    RIKEN Advanced Institute for Computational Science, Kobe, Japan.
    Onishi, Keiji
    RIKEN Advanced Institute for Computational Science, Kobe, Japan.
    Tsubokura, Makoto
    Kobe University and RIKEN Advanced Institute for Computational Science, Kobe Japan.
    CUBE: A scalable framework for large-scale industrial simulations2019Ingår i: The international journal of high performance computing applications, ISSN 1094-3420, E-ISSN 1741-2846, Vol. 33, nr 4, s. 678-698Artikel i tidskrift (Refereegranskat)
  • 22.
    Jansson, Niclas
    et al.
    RIKEN Advanced Institute for Computational Science.
    Bale, Rahul
    RIKEN Advanced Institute for Computational Science.
    Onishi, Keiji
    RIKEN Advanced Institute for Computational Science.
    Tsubokura, Makoto
    Department of Computational Science, Graduate School of System Informatics, Kobe University and RIKEN Advanced Institute for Computational Science.
    Dynamic Load Balancing for Large-Scale Multiphysics Simulations2017Ingår i: High-Performance Scientific Computing: Jülich Aachen Research Alliance (JARA) High-Performance Computing Symposium / [ed] Edoardo Di Napoli, Marc-André Hermanns, Hristo Iliev, Andreas Lintermann, Alexander Peyser, 2017, s. 13-23Konferensbidrag (Refereegranskat)
    Abstract [en]

    In parallel computing load balancing is an essential component of any efficient and scalable simulation code. Static data decomposition methods have proven to work well for symmetric workloads. But, in today’s multiphysics simulations, with asymmetric workloads, this imbalance prevents good scalability on future generation of parallel architectures. We present our work on developing a general dynamic load balancing framework for multiphysics simulations on hierarchical Cartesian meshes. Using a weighted dual graph based workload estimation and constrained multilevel graph partitioning, the required runtime for industrial applications could be reduced by 40%" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">%% of the runtime, running on the K computer.

  • 23.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    A Hybrid MPI/PGAS Finite Element Solver2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We present our work on developing a hybrid parallel programming model for a general finite element solver. The main focus of our work is to demonstrate that legacy codes with high latency, two-sided communication in the form of message passing can be improved using lightweight one-sided communication. We introduce a new hybrid MPI/PGAS implementation of the open source finite element framework FEniCS, replacing the linear algebra backend (PETSc) with a new library written in UPC.  A detailed description of the linear algebra backend implementation and the hybrid interface to FEniCS is given. We also present a detailed analysis of the performance of this hybrid solver on the Cray XE6 Lindgren at PDC/KTH including a comparison with the MPI only implementation, where we find that the hybrid implementation results in improvements of up to 33% in communication intensive parts of the solver.

  • 24.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Computer simulation of incompressible flow past a circular cylinder at a very high Reynolds numbers2011Manuskript (preprint) (Övrigt vetenskapligt)
  • 25.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Improving Parallel Performance of FEniCS Finite Element Computations by Hybrid MPI/PGASManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We present our work on developing a hybrid parallel programming model for a general finite element solver. The main focus of our work is to demonstrate that legacy codes with high latency, two-sided communication in the form of message passing can be improved using lightweight one-sided communication. We introduce a new hybrid MPI/PGAS implementation of the open source general finite element framework FEniCS, replacing the linear algebra backend (PETSc) with a new library written in UPC. A detailed description of the linear algebra backend implementation and the hybrid interface to FEniCS is given. We also present a detailed analysis of the performance of this hybrid solver on the Cray XE6 Lindgren at PDC/KTH including a comparison with the MPI only implementation, where we find that the hybrid implementation results in significant improvements in performance of the solver.

  • 26.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Improving Parallel Performance of FEniCS Finite Element Computations by Hybrid MPI/PGAS2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We present our work on developing a hybrid parallel programming model for a general finite element solver. The main focus of our work is to demonstrate that legacy codes with high latency, two-sided communication in the form of message passing can be improved using lightweight one-sided communication. We introduce a new hybrid MPI/PGAS implementation of the open source general finite element framework FEniCS, replacing the linear algebra backend (PETSc) with a new library written in UPC. A detailed description of the linear algebra backend implementation and the hybrid interface to FEniCS is given. We also present a detailed analysis of the performance of this hybrid solver on the Cray XE6 Lindgren at PDC/KTH including a comparison with the MPI only implementation, where we find that the hybrid implementation results in significant improvements in performance of the solver.

  • 27.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Framework For Massively Parallel Adaptive Finite Element Computational Fluid Dynamics On Tetrahedral Meshes2012Ingår i: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 34, nr 1, s. C24-C42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we describe a general adaptive finite element framework for unstructured tetrahedral meshes without hanging nodes suitable for large scale parallel computations. Our framework is designed to scale linearly to several thousands of processors, using fully distributed and efficient algorithms. The key components of our implementation, local mesh refinement and load balancing algorithms, are described in detail. Finally, we present a theoretical and experimental performance study of our framework, used in a large scale computational fluid dynamics computation, and we compare scaling and complexity of different algorithms on different massively parallel architectures.

  • 28.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Nazarov, Murtazo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Adaptive simulation of turbulent flow past a full car model2011Ingår i: State of the Practice Reports, SC'11, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    The massive computational cost for resolving all turbulent scales makes a direct numerical simulation of the underlying Navier-Stokes equations impossible in most engineering applications. We present recent advances in parallel adaptive finite element methodology that enable us to efficiently compute time resolved approximations for complex geometries with error control. In this paper we present a LES simulation of turbulent flow past a full car model, where we adaptively refine the unstructured mesh to minimize the error in drag prediction. The simulation was partly carried out on the new Cray XE6 at PDC/KTH where the solver shows near optimal strong and weak scaling for the entire adaptive process.

  • 29.
    Jansson, Niclas
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Adaptive finite element computational fluid dynamics for large scale massiverly parallel computing2012Ingår i: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197Artikel i tidskrift (Refereegranskat)
  • 30.
    Jansson, Niclas
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Beräkningsvetenskap och beräkningsteknik (CST).
    Laure, Erwin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Beräkningsvetenskap och beräkningsteknik (CST).
    Towards a Parallel Algebraic Multigrid Solver Using PGAS2018Ingår i: 2018 Workshop on High Performance Computing Asia, New York, NY, USA: Association for Computing Machinery (ACM), 2018, s. 31-38Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Algebraic Multigrid (AMG) method has over the years developed into an efficient tool for solving unstructured linear systems. The need to solve large industrial problems discretized on unstructured meshes, has been a key motivation for devising a parallel AMG method. Despite some success, the key part of the AMG algorithm; the coarsening step, is far from trivial to parallelize efficiently. We here introduce a novel parallelization of the inherently sequential Ruge-Stüben coarsening algorithm, that retains most of the good interpolation properties of the original method. Our parallelization is based on the Partitioned Global Address Space (PGAS) abstraction, which greatly simplifies the parallelization as compared to traditional message passing based implementations. The coarsening algorithm and solver is described in detail and a performance study on a Cray XC40 is presented.

  • 31.
    Onishi, Keiji
    et al.
    RIKEN Advanced Institute for Computational Science.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). RIKEN Advanced Institute for Computational Science.
    Bale, Rahul
    RIKEN Advanced Institute for Computational Science.
    Wang, Wei-Hsiang
    RIKEN Advanced Institute for Computational Science.
    Li, Chung-Gang
    Kobe University and RIKEN Advanced Institute for Computational Science.
    Tsubokura, Makoto
    Kobe University and RIKEN Advanced Institute for Computational Science.
    A Deployment of HPC Algorithm into Pre/Post-Processing for Industrial CFD on K-Computer2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Pre- and post-processing is still a major problem in industrial computational fluid dynamics (CFD). With the rapid development of computers, physical solvers are getting faster, while pre- remains slow because it's mainly a serial process. A methodology using MPI+OpenMP hybrid parallelization has been proposed to eliminate the manual work required during pre-processing for correcting the surface imperfections of CAD data. Compared to the rapidly increasing amount of data in recent years, the speed-up of visualization is insufficient. We address this limitation of post- by adapting the in-situ visualization to parallelize the post-processing using libsim (Visit) library. The performance of pre-/post- processing is investigated in this work, and we show that the pre-processing time has been reduced from several days in the conventional framework to order of minutes. The post-processing time has been reduced seconds order per frame, and approximately 30% increase of computational time was observed in vehicle aerodynamics cases. 

  • 32.
    Spühler, Jeannette H.
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    3D Fluid-Structure Interaction Simulation of Aortic Valves Using a Unified Continuum ALE FEM Model2018Ingår i: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, artikel-id 363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to advances in medical imaging, computational fluid dynamics algorithms and high performance computing, computer simulation is developing into an important tool for understanding the relationship between cardiovascular diseases and intraventricular blood flow. The field of cardiac flow simulation is challenging and highly interdisciplinary. We apply a computational framework for automated solutions of partial differential equations using Finite Element Methods where any mathematical description directly can be translated to code. This allows us to develop a cardiac model where specific properties of the heart such as fluid-structure interaction of the aortic valve can be added in a modular way without extensive efforts. In previous work, we simulated the blood flow in the left ventricle of the heart. In this paper, we extend this model by placing prototypes of both a native and a mechanical aortic valve in the outflow region of the left ventricle. Numerical simulation of the blood flow in the vicinity of the valve offers the possibility to improve the treatment of aortic valve diseases as aortic stenosis (narrowing of the valve opening) or regurgitation (leaking) and to optimize the design of prosthetic heart valves in a controlled and specific way. The fluid-structure interaction and contact problem are formulated in a unified continuum model using the conservation laws for mass and momentum and a phase function. The discretization is based on an Arbitrary Lagrangian-Eulerian space-time finite element method with streamline diffusion stabilization, and it is implemented in the open source software Unicorn which shows near optimal scaling up to thousands of cores. Computational results are presented to demonstrate the capability of our framework.

  • 33.
    Spühler, Jeannette Hiromi
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    3D Fluid-Structure Interaction Simulation of Aortic Valves Using a Unified Continuum ALE-FEM ModelManuskript (preprint) (Övrigt vetenskapligt)
  • 34.
    Spühler, Jeannette Hiromi
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). BCAM - Basque Center for Applied Mathematics, Spain.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). BCAM - Basque Center for Applied Mathematics, Spain.
    A finite element framework for high performance computer simulation of blood flow in the left ventricle of the human heart2015Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 35.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Towards the development of adaptive finite element methods for aeroacousticsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We report the latest results obtained in the development of an adaptive nite ele- ment method for computational aeroacoustics (CAA). The new methodology is based on the General Galerkin (G2) method, which has been successfully used for the computation of incompressible, turbulent ow. Here, we simulate the ow past an in-duct mixer plate and compare the results with available experimental data. The compar- isons include mean velocity pro les and frequency content of the turbulent signal. No direct simulation of sound or sound wave propagation has been performed; instead, simple analogy arguments have been used to extract acoustic results from incompressible simulations by assuming a direct correlation between the computed pressure drop signal and the sound at the far eld. We were able to reproduce the sound signal from experiments with our incompressible simulation and our results compared well with both the level and the broadband frequency peak of the measured sound. We suggest that the methodology presented here is mainly suitable for the prediction of sound in low Mach number pipe flows.

  • 36.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Adaptive computation of aeroacoustic sources for a 4-wheel rudimentary landing gear benchmark problem2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present our simulation results for the benchmark Rudimentary Landing Gear using a General Galerkin (G2) nite element method, also referred to as Adaptive DNS/LES. In G2 no explicit subgrid model is used, instead the computational mesh is adaptively re ned with respect to an a posteriori error estimate of a quantity of interest in the computation, in this case drag force. Turbulent boundary layers are modeled using a simple wall shear stress proportional to the skin friction, which here is assumed to be small and is approximated by zero skin friction, resulting in a slip velocity boundary condition. We compare our results with experimental data and other state of the art computations, where we nd good agreement in sound pressure levels, surface velocities and ow separation. We also compare with detailed surface pressure experimental data where we nd largely good agreement, apart from some local dierences for which we discuss possible explanations.

  • 37.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Adaptive Computation of Aeroacoustic Sources for a Rudimentary Landing Gear2014Ingår i: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 74, nr 6, s. 406-421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present our simulation results for the benchmark problem of the flow past a rudimentary landing gear using a General Galerkin FEM, also referred to as adaptive DNS/LES. In General Galerkin, no explicit subgrid model is used; instead, the computational mesh is adaptively refined with respect to an a posteriori error estimate of a quantity of interest in the computation, in this case, the drag force on the rudimentary landing gear. Turbulent boundary layers are modeled using a simple wall-layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we find good agreement in sound pressure levels, surface velocities, and flow separation. We also compare with detailed surface pressure experimental data where we find largely good agreement, apart from some local differences for which we discuss possible explanations.

  • 38.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Computation of Aeroacoustic Sources for a Gulfstream G550 Nose Landing Gear Model Using Adaptive FEMManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This work is a direct comparison of our unsteady, turbulent flow simulations with measurements performed using a Gulfstream G550 Nose Landing Gear Model. The experimental campaign, which was carried out by researchers from the NASA Langley Research Center, provided a series of detailed, well documented wind-tunnel measurements for comparison and validation of computational fluid dynamics (CFD) and computational aeroacoustics (CAA) methodologies. Several computational efforts were collected and presented at the Benchmark for Airframe Noise Computation workshops, BANC-I and II. For our simulations, we used a General Galerkin finite element method (G2), where no explicit subgrid model is used, and where the computational mesh is adaptively refined with respect to a posteriori error estimates for a quantity of interest. The mesh is fully unstructured and the solutions are time-resolved, which are key ingredients for solving relevant, industrial applications in the field of aeroacoustics. The comparisons presented here are an attempt to quantify the accuracy of our models, methods and assumptions, and the results, although not perfect, are of relevant quantitative quality. We present several results containing both time-averaged and unsteady flow quantities, always side by side with its corresponding experimental values. The main finding is that we are able to simulate such a complex, unsteady flow problem as the flow past a nose landing gear using a parameter-free methodology for high Reynolds numbers (Re), external aerodynamics and aeroacoustics applications.

  • 39.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Computation of aeroacoustic sources for a Gulfstream G550 nose landing gear model using adaptive FEM2016Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 124, s. 136-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work presents a direct comparison of unsteady, turbulent flow simulations with measurements performed using a Gulfstream G550 nose landing gear model. The experimental campaign, which was carried out by researchers from the NASA Langley Research Center, provided a series of detailed, well documented wind-tunnel measurements for comparison and validation of computational fluid dynamics (CFD) and computational aeroacoustics (CAA) methodologies. Several computational efforts were collected and presented at the Benchmark for Airframe Noise Computation workshops, BANC-I and II. For our simulations, we used a General Galerkin finite element method (G2), where no explicit subgrid model is used, and where the computational mesh is adaptively refined with respect to a posteriori estimates of the error in a quantity of interest, here the source term in Lighthill's equation. The mesh is fully unstructured and the solution is time-resolved, which are key ingredients for solving problems of industrial relevance in the field of aeroacoustics. Moreover, we choose to model the boundary layers on the landing gear geometry with a free-slip condition for the velocity, which we previously observed to produce good results for external flows at high Reynolds numbers, and which considerably reduces the amount of cells required in the mesh. The comparisons presented here are an attempt to quantify the accuracy of our models, methods and assumptions; to that end, several results containing both time-averaged and unsteady flow quantities, always side by side with corresponding experimental values, are reported. The main finding is that we are able to simulate a complex, unsteady flow problem using a parameter-free methodology developed for high Reynolds numbers, external aerodynamics and aeroacoustics applications.

1 - 39 av 39
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf