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  • 2005-2009  (5)
  • 1940-1944
  • 2008  (5)
  • ddc:004  (3)
  • ddc:620  (2)
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  • 2005-2009  (5)
  • 1940-1944
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  • 1
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    A priori Tabulation of Turbulent Flame Speeds via a Combination of a Stochastic Mixing Model and Flamelet Generated Manifolds (2008)
    Details
    Publication Date: 2016-06-09
    Description: In this paper we propose a technique for a priori turbulent flame speed tabulation (TFST) for a given parameter space in standard combustion-regime diagrams. It can be used as a subgrid-scale (SGS) model in Large Eddy Simulation (LES). In a first step, stationary laminar flamelets are computed and stored over the progress variable following the ideas of flamelet generated manifolds (FGM). In a second step, the incompressible one-dimensional Navier-Stokes equations supplemented by the equation for the progress variable are solved on a grid that resolves all turbulent scales. Additionally, turbulent transport is implemented via the linear eddy model (LEM). The turbulent flame structures are solved until a statistically stationary mean value of the turbulent flame speed has been reached. The results are stored in a table that could be used by large scale premixed combustion models, e.g. front tracking schemes. Results are compared to an algebraic model and to direct numerical simulations (DNS).
    Keywords: ddc:620
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 2
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    Linear-Eddy Modeling of Autoignition under Thermal Stratification (2008)
    Details
    Publication Date: 2016-06-09
    Description: The influence of thermal stratification on autoignition at constant volume and high pressure is investigated under turbulent conditions using the one-dimensional Linear-Eddy Model (LEM) and detailed hydrogen/air chemistry. Results are presented for the influence of initial temperature inhomogeneities on the heat release rate and the relative importance of diffusion and chemical reactions. The predicted heat release rates are compared with heat release rates of Chen et al. and Hawkes et al. obtained by two-dimensional Direct Numerical Simulations (DNS). Using the definition of Chen et al. for the displacement speed of the H2 mass fraction tracked at the location of maximum heat release, and a comparison of budget terms, different combustion modes including ignition front propagation and deflagration waves are identified and the results are compared to the DNS data. The LEM approach shows qualitatively and quantitatively reasonable agreement with the DNS data over the whole range of investigated temperature fluctuations. The results presented in this work suggest that LEM is a potential candidate as a sub-model for CFD calculations of HCCI engines.
    Keywords: ddc:620
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 3
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    Performance of Quantum Chromodynamics (QCD) Simulations on the SGI Altix (2008)
    Details
    Publication Date: 2016-06-30
    Description: We study performance and scaling of the Berlin Quantum Chromodynamics Program (BQCD) on the SGI Altix 4700 at Leibniz Supercomputing Centre (LRZ). We employ different communication methods (MPI, MPI with two OpenMP threads per process, as well as the shmem library) and run the MPI version on the two types of nodes of that machine. For comparison with other machines we made performance measurements on an IBM p690 cluster and a Cray XT4.
    Keywords: ddc:004
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 4
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    Adaptives Remeshing von nicht-mannigfaltigen Dreiecksnetzen (2008)
    Details
    Publication Date: 2022-07-19
    Description: In dieser Arbeit wird eine Serie von Remeshing-Verfahren um die Berücksichtigung von nicht-mannigfaltigen Dreiecksvernetzungen und Merkmalskantenzügen erweitert. Die betrachteten Verfahren arbeiten im Wesentlichen lokal. Daher können die im Rahmen dieser Arbeit entwickelten Erweiterungen, die nicht-mannigfaltige Kantenzüge und Merkmalskantenzüge betreffen, separat beschrieben werden. Dabei wird ein Ansatz verfolgt, beide Arten von besonderen Kantenzügen aufgrund ihrer Gemeinsamkeiten einheitlich zu behandeln. Dieser besteht zum einen darin, eine Korrespondenz zwischen Kantenzügen auf der Eingabe- und der Ausgabefläche zu erhalten, indem die Remeshing-Operationen auf den Kantenzügen in entsprechend eingeschränkter Weise verwendet werden. Zum anderen wird beschrieben, wie die Abtastdichte der Kantenzüge dynamisch an die Abtastdichte der Umgebung angepasst werden kann, um für weitgehende Isotropie in der Nähe von Merkmalskantenzügen zu sorgen.
    Description: A unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines is presented. The method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature lines as well as the input mesh.
    Keywords: ddc:004
    Language: German
    Type: masterthesis , doc-type:masterThesis
    Format: application/pdf
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    OPUS
  • 5
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    Dual Streamline Seeding - Method and Implementation (2008)
    Details
    Publication Date: 2022-07-19
    Description: This work introduces a novel streamline seeding technique based on dual streamlines that are orthogonal to the vector field, instead of tangential. The greedy algorithm presented here produces a net of orthogonal streamlines that is iteratively refined resulting in good domain coverage and a high degree of continuity and uniformity. The algorithm is easy to implement and efficient, and it naturally extends to curved surfaces.
    Description: In dieser Arbeit wird eine neue Strategie zur Platzierung von Stromlinien vorgestellt. Hierzu werden zusätzliche duale Stromlinien verwendet, die --im Gegensatz zur üblichen Definition-- orthogonal zum Vektorfeld verlaufen. Der vorgestellte Greedy-Algorithmus berechnet ein Netz aus orthogonalen Stromlinien, welches iterativ verfeinert wird, was zu einer guten Abdeckung der Domäne und einer gleichmäßigen Verteilung der Stromlinien führt. Es handelt sich um einen einfach zu implementierenden und effizienten Algorithmus, der direkt auf gekrümmten Oberflächen anwendbar ist.
    Keywords: ddc:004
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
    Library Location Call Number Volume/Issue/Year Availability
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