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• Transient and steady heat conduction using an adaptive finite element cad-based approach

  R. Lohner, J. McAnally

  International Journal for Numerical Methods for Heat and Fluid Flow (1994). Vol. 4 (4), pp. 311-327

  
  

  Abstract

  A new heat transfer simulation capability is described. Non-traditional features of this capability include: a seamless link to CAD-CAM for rapid problem specification/description, integrated automatic grid generator tools for rapid mesh generation, nonlinear and/or varying material properties, source-terms and boundary conditions, a one-element type approach for simplicity and efficiency, automatic self-adaptive mesh refinement and coarsening with accurate error estimation, heavy reliance on iterative solvers, and on-line display on workstations for immediate visualization and user feedback. These innovations are documented on several examples that demonstrate the usefulness of the developed capability.

  Abstract
  A new heat transfer simulation capability is described. Non-traditional features of this capability include: a seamless link to CAD-CAM for rapid problem specification/description, [...]

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• A Comparison Study of Two Finite-Element Schemes for Computation of Shock Waves

  H. Luo, J. Baum, R. Lohner

  (1995). Shock Waves @ Marseille I. Springer, Berlin, Heidelberg

  
  

  Abstract

  This paper describes an extensive comparison study of two high-order-accuracy finite-element schemes: one of upwind type, the other of flux-corrected transport type, for the simulation of shock wave propagation on unstructured meshes. The performance of these two schemes for the solution of the Euler equations on unstructured meshes is compared on the basis of solution accuracy and computational efficiency for some well-known test cases. Advantages and disadvantages of the two schemes are discussed.

  Abstract
  This paper describes an extensive comparison study of two high-order-accuracy finite-element schemes: one of upwind type, the other of flux-corrected transport type, for the [...]

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• Mesh adaptation in fluid mechanics

  R. Lohner

  Engineering Fracture Mechanics (1995). Vol. 50 (5-6), pp. 819-847

  
  

  Abstract

  The development, application and impact of mesh adaptation procedures in the field of computational fluid mechanics (CFD) are reviewed. The discussion is restricted to unstructured (i.e. unordered) grids, such as those commonly encountered in finite element applications.

  Abstract
  The development, application and impact of mesh adaptation procedures in the field of computational fluid mechanics (CFD) are reviewed. The discussion is restricted to unstructured [...]

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• Finite element simulation of a turbulent MHD system: comparison to a pseudo-spectral simulation

  R. Frainchtein, S. Zalesak, R. Lohner, D. Spicer

  Computer Physics Communications (1995). Vol. 86 (1-2), pp. 25-39

  
  

  Abstract

  A finite element MHD algorithm is used to simulate a two-dimensional, viscous and resistive turbulent model, namely the Orszag-Tang vortex. The results are compared to a pseudo-spectral simulation of the same system reported by Dahlburg and Picone (Phys. Fluids B 1 (1989) 2153). The agreement of results from both methods supports the contention that the finite element method can appropriately simulate systems exhibiting turbulence, thus enabling the use of realistic geometries and boundary conditions, as well as adaptive refinement on simulations of turbulent systems. A short discussion on the behavior of ▿·B is presented. An inverse correlation between spatial resolution and the magnitude of ▿·B was found. The relevance of our findings to Adaptive Mesh Refinement is briefly discussed.

  Abstract
  A finite element MHD algorithm is used to simulate a two-dimensional, viscous and resistive turbulent model, namely the Orszag-Tang vortex. The results are compared [...]

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• Robust, Vectorized Search Algorithms for Interpolation on Unstructured Grids

  R. Lohner

  Journal of Computational Physics (1995). Vol. 118 (2), pp. 380-387

  
  

  Abstract

      Several search algorithms for the interpolation of data associated with unstructured grids are reviewed and compared. Particular emphasis is placed on the pitfalls these algorithms may experience for grids commonly encountered and on ways to improve their performance. It is shown how the most CPU-intensive portions of the search process may be vectorized. A technique for the proper interpolation of volumetric regions separated by thin surfaces is included. Timings for several problems show that speedups in excess of 1:5 can be obtained if due care is used when designing interpolation algorithms.  

  Abstract
      Several search algorithms for the interpolation of data associated with unstructured grids are reviewed and compared. Particular emphasis is [...]

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• Simulation of complex incompressible flows using a finite element solver on MIMD machines

  R. Ramamurti, R. Lohner

  (1995). Parallel Computational Fluid Dynamics 1993, New Trends and Advances, pp. 443-450

  
  

  Abstract

  An incompressible flow solver based on unstructured grids is implemented on parallel distributed-memory computer architecture. An important phase in the flow solver is the solution of the elliptic equations for the velocities and pressures. This elliptic solver is parallelized and incorporated into both the explicit and implicit versions of the incompressible flow solver. Performance and scalability studies are carried out on both Intel iPSC 860 and the Intel Delta prototype and show that the code is scalable. A parallelizable load balancing algorithm is developed to be used in conjunction with the incompressible flow solver. Steady and unsteady flows over a tri-element airfoil and NACA0012airfoil are computed using the parallel incompressible flow solver. The parallel flow solver is extended to 3D for simulation of flow past a fully appended submarine. The chapter concludes that the future developments will be focused on the incorporation of adaptive regridding in 2D and the parallel implementation of 3-D incompressible flow solver.

  Abstract
  An incompressible flow solver based on unstructured grids is implemented on parallel distributed-memory computer architecture. An important phase in the flow solver [...]

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• Computation of the unsteady flow past a tuna with caudal fin oscillation

  R. Ramamurti, R. Lohner, W. Sandberg

  Transactions on Engineering Science (1996). Vol. 9, pp. 169-178

  
  

  Abstract

  Only recently has a capability for computing three-dimensional, unsteady incompressible flow over a changing geometry become available. In that work, the flow field generated during a torpedo launch from a submarine was computed. This paper describes the extension of that work to carry out a direct computation, making no geometric simplifications, of the unsteady flow past a tuna, including the oscillatory caudal fin motion. In particular, described is the computation of the time variation of the pressure distribution over the entire body and the integration over all surfaces to obtain the unsteady thrust.  

  Abstract
  Only recently has a capability for computing three-dimensional, unsteady incompressible flow over a changing geometry become available. In that work, the flow field generated [...]

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• Large-Scale Blast Simulations

  J. Baum, H. Luo, R. Lohner

  (1996). Computation of Three-Dimensional Complex Flows. Notes on Numerical Fluid Mechanics (NNFM), vol 49. Vieweg+Teubner Verlag

  
  

  Abstract

        This paper describes the application of FEFL096, a three-dimensional, adaptive, finite element, edge-based, ALE shock capturing methodology on unstructured tetrahedral grids, to large-scale simulations of blast wave interaction with structures. The first simulation applied the CFD methodology to the numerical simulation of blast wave diffraction within the B-2 level of the World Trade Center garage. This simulation modeled blast wave diffraction about hundreds of rigidly-modeled structures, spread over a large area. The second simulation applied a new loose-coupling algorithm that combined FEFL096 and DYNA3D, a state-of-the-art Computational Structural Dynamics (CSD) methodology, to the simulation of shock interaction with a structurally-responding truck.  

  Abstract
        This paper describes the application of FEFL096, a three-dimensional, adaptive, finite element, edge-based, ALE shock capturing methodology [...]

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• A parallel implicit incompressible flow solver using unstructured meshes

  R. Ramamurti, R. Lohner

  Computers and Fluids (1996). Vol. 25 (2), pp. 119-132

  
  

  Abstract

      An incompressible flow solver based on unstructured grids is implemented on a parallel distributed memory computer architecture. An important phase in the flow solver is the solution of the elliptic equations for the velocities and pressure. This elliptic solver is parallelized and incorporated into both the explicit and implicit versions of the incompressible flow solver. Performance and scalability studies are carried out on both Intel iPSC 860 and the Intel Delta prototype, and these studies show that the code is scalable. A parallelizable load balancing algorithm is developed to be used in conjunction with the incompressible flow solver. Steady and unsteady flows over a tri-element airfoil and NACA0012 airfoil are computed using the parallel incompressible flow solver.

  Abstract
      An incompressible flow solver based on unstructured grids is implemented on a parallel distributed memory computer architecture. An important [...]

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• Dusty shock flow with unstructured adaptive finite elements and parcels

  S. Siver, E. Loth, J. Baum, R. Lohner

  AIAA Journal (1996). Vol. 34 (5), pp. 1078-1080

  
  

  Abstract

  Our objective is to formulate and develop an Eulerian-Lagrangian (E-L) method with an adaptive grid FEM-FCT flow solver that is computationally efficient. This method is used to predict a particle laden shock wave attenuation as a test case and to compare performance characteristics (computation speed, memory, and accuracy) with an E-E implentation that also includes adaptive unstructured grids  

  Abstract
  Our objective is to formulate and develop an Eulerian-Lagrangian (E-L) method with an adaptive grid FEM-FCT flow solver that is computationally efficient. This method is used [...]

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