Finite element methods for integrated aerodynamic heating analysis

This report gives a description of the work which has been undertaken during the second year of a three year research program. The objectives of the program are to produce finite element based procedures for the solution of the large scale practical problems which are of interest to the Aerothermal Loads Branch (ALB) at NASA Langley Research Establishment. The problems of interest range from Euler simulations of full three dimensional vehicle configurations to local analyses of three dimensional viscous laminar flow. Adaptive meshes produced for both steady state and transient problems are to be considered. An important feature of the work is the provision of specialized techniques which can be used at ALB for the development of an integrated fluid/thermal/structural modeling capability

Computing parametrized solutions for plasmonic nanogap structures

The interaction of electromagnetic waves with metallic nanostructures generates resonant oscillations of the conduction-band electrons at the metal surface. These resonances can lead to large enhancements of the incident field and to the confinement of light to small regions, typically several orders of magnitude smaller than the incident wavelength. The accurate prediction of these resonances entails several challenges. Small geometric variations in the plasmonic structure may lead to large variations in the electromagnetic field responses. Furthermore, the material parameters that characterize the optical behavior of metals at the nanoscale need to be determined experimentally and are consequently subject to measurement errors. It then becomes essential that any predictive tool for the simulation and design of plasmonic structures accounts for fabrication tolerances and measurement uncertainties. In this paper, we develop a reduced order modeling framework that is capable of real-time accurate electromagnetic responses of plasmonic nanogap structures for a wide range of geometry and material parameters. The main ingredients of the proposed method are: (i) the hybridizable discontinuous Galerkin method to numerically solve the equations governing electromagnetic wave propagation in dielectric and metallic media, (ii) a reference domain formulation of the time-harmonic Maxwell's equations to account for geometry variations; and (iii) proper orthogonal decomposition and empirical interpolation techniques to construct an efficient reduced model. To demonstrate effectiveness of the models developed, we analyze geometry sensitivities and explore optimal designs of a 3D periodic annular nanogap structure.Comment: 28 pages, 9 figures, 4 tables, 2 appendice

Non-modal analysis of spectral element methods: Towards accurate and robust large-eddy simulations

We introduce a \textit{non-modal} analysis technique that characterizes the diffusion properties of spectral element methods for linear convection-diffusion systems. While strictly speaking only valid for linear problems, the analysis is devised so that it can give critical insights on two questions: (i) Why do spectral element methods suffer from stability issues in under-resolved computations of nonlinear problems? And, (ii) why do they successfully predict under-resolved turbulent flows even without a subgrid-scale model? The answer to these two questions can in turn provide crucial guidelines to construct more robust and accurate schemes for complex under-resolved flows, commonly found in industrial applications. For illustration purposes, this analysis technique is applied to the hybridized discontinuous Galerkin methods as representatives of spectral element methods. The effect of the polynomial order, the upwinding parameter and the P\'eclet number on the so-called \textit{short-term diffusion} of the scheme are investigated. From a purely non-modal analysis point of view, polynomial orders between $2$ and $4$ with standard upwinding are well suited for under-resolved turbulence simulations. For lower polynomial orders, diffusion is introduced in scales that are much larger than the grid resolution. For higher polynomial orders, as well as for strong under/over-upwinding, robustness issues can be expected. The non-modal analysis results are then tested against under-resolved turbulence simulations of the Burgers, Euler and Navier-Stokes equations. While devised in the linear setting, our non-modal analysis succeeds to predict the behavior of the scheme in the nonlinear problems considered

A frontal approach for internal node generation in Delaunay triangulations

The past decade has known an increasing interest in the solution of the Euler equations on unstructured grids due to the simplicity with which an unstructured grid can be tailored around very complex geometries and be adapted to the solution. It is desirable that the mesh can be generated with minimum input from the user, ideally, just specifying the boundary geometry and, perhaps, a function to prescribe some desired mesh size. The internal nodes should then be found automatically by the grid generation code. The approach we propose here combines the Delaunay triangulation with ideas from the advancing front method of Peraire et al. and LÖhner et al . Both methods are briefly reviewed in Section 1. Our method uses a background grid to interpolate local mesh size parameters that is taken from the triangulation of the given boundary nodes. Geometric criteria are used to find a set of nodes in a frontal manner. This set is subsequently introduced into the existing mesh, thus providing an update Delaunay triangulation. The procedure is repeated until no more improvement of the grid can be achieved by inserting new nodes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50209/1/1650170305_ftp.pd

La traducción de divulgación científica mediante el uso de recursos de traducción especializada. Estudio empírico con traducción asistida por ordenador (OmegaT) para el par lingüístico inglés-español

Este trabajo tiene como objetivo investigar el uso de las herramientas de traducción asistida por ordenador (TAO) en la traducción de un texto de divulgación científica. El objetivo es averiguar si la memoria de traducción y la base de datos terminológica obtenidas a partir de la traducción de 2 artículos de alto nivel de especialización tienen alguna utilidad en la traducción de un artículo de divulgación que versa sobre el mismo tema. Además, se discutirá sobre las características del lenguaje de los diferentes niveles de especialización (un nivel de especialización alto de los artículos científicos frente a un nivel de especialización intermedio-bajo del artículo de divulgación). Se realiza la traducción mediante OmegaT del primer artículo científico completo y de un fragmento del segundo. A partir de ellos, se obtiene una memoria de traducción y una base de datos terminológica que se utilizan posteriormente en la traducción del artículo de divulgación. Se observa un uso parcial de la base de datos terminológica y muy poca utilización de la memoria de traducción. Los resultados muestran una utilidad limitada de las herramientas TAO obtenidas de la traducción de artículos científicos en la traducción de textos de divulgación. Se especula que dichos resultados tienen relación con el diferente nivel de especialización de los textos.This final master's project aims to investigate the use of computer-assisted translation tools (CAT) in the translation of a popular science text. The objective is to find out if the translation memory and the terminology database obtained from the translation of 2 articles of high level of specialization have any utility in the translation of a popular science text that deals with the same subject. In addition, the language characteristics of the different levels of specialization will be discussed (high level of specialization of scientific articles vs. intermediate-low level of specialization of the popular science text). The translation of the first complete scientific article and a fragment of the second are done with OmegaT. A translation memory and a terminology database are obtained during the translation process, and they were used later in the translation of the popular science text. There was a partial use of the terminology database and very little use of translation memory segments. The results show limited utility of CAT tools obtained from the translation of scientific articles in the translation of popular science texts. It is speculated that these results are related to the different level of specialization of the texts.Aquest treball té com a objectiu investigar l'ús de les eines de traducció assistida per ordinador (TAO) en la traducció d'un text de divulgació científica. L'objectiu és esbrinar si la memòria de traducció i la base de dades terminològica obtingudes a partir de la traducció de 2 articles d'alt nivell d'especialització tenen alguna utilitat en la traducció d'un article de divulgació que versa sobre el mateix tema. A més, es discutirà sobre les característiques del llenguatge dels diferents nivells d'especialització (un nivell d'especialització alt dels articles científics enfront d'un nivell d'especialització intermedi-sota de l'article de divulgació). Es realitza la traducció mitjançant OmegaT del primer article científic complet i d'un fragment del segon. A partir d'ells, s'obté una memòria de traducció i una base de dades terminològica que s'utilitzen posteriorment en la traducció de l'article de divulgació. S'observa un ús parcial de la base de dades terminològica i molt poca utilització de la memòria de traducció. Els resultats mostren una utilitat limitada de les eines TAO obtingudes de la traducció d'articles científics en la traducció de textos de divulgació. S'especula que aquests resultats tenen relació amb el diferent nivell d'especialització dels textos

Implicit large-eddy simulation of compressible flows using the Interior Embedded Discontinuous Galerkin method

We present a high-order implicit large-eddy simulation (ILES) approach for simulating transitional turbulent flows. The approach consists of an Interior Embedded Discontinuous Galerkin (IEDG) method for the discretization of the compressible Navier-Stokes equations and a parallel preconditioned Newton-GMRES solver for the resulting nonlinear system of equations. The IEDG method arises from the marriage of the Embedded Discontinuous Galerkin (EDG) method and the Hybridizable Discontinuous Galerkin (HDG) method. As such, the IEDG method inherits the advantages of both the EDG method and the HDG method to make itself well-suited for turbulence simulations. We propose a minimal residual Newton algorithm for solving the nonlinear system arising from the IEDG discretization of the Navier-Stokes equations. The preconditioned GMRES algorithm is based on a restricted additive Schwarz (RAS) preconditioner in conjunction with a block incomplete LU factorization at the subdomain level. The proposed approach is applied to the ILES of transitional turbulent flows over a NACA 65-(18)10 compressor cascade at Reynolds number 250,000 in both design and off-design conditions. The high-order ILES results show good agreement with a subgrid-scale LES model discretized with a second-order finite volume code while using significantly less degrees of freedom. This work shows that high-order accuracy is key for predicting transitional turbulent flows without a SGS model.Comment: 54th AIAA Aerospace Sciences Meeting, AIAA SciTech, 201