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Hampton, VA, United States

The National Institute of Aerospace is a non-profit research and graduate education institute headquartered in Hampton, Virginia, near NASA's Langley Research Center. NIA's mission is to conduct leading-edge aerospace and atmospheric research, develop new technologies for the nation and help inspire the next generation of scientists and engineers.NIA was formed in 2002 by a consortium of research universities to ensure a national capability to support NASA's mission by expanding collaboration with academia and leveraging expertise inside and outside NASA. NIA performs research in a broad range of disciplines including space exploration, systems engineering, nanoscale materials science, flight systems, aerodynamics, air traffic management, aviation safety, planetary and space science, and global climate change.NIA is headed by Dr. Douglas O. Stanley, who was named interim to the post of president and executive director in July 2012. He succeeded Dr. Robert Lindberg, who became the first President and Executive Director in October 2003. Wikipedia.

Nishikawa H.,National Institute of Aerospace
Computers and Fluids | Year: 2011

In this paper, we introduce a general principle for constructing robust and accurate viscous discretization, which is applicable to various discretization methods, including finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. The principle is based on a hyperbolic model for the viscous term. It is to discretize the hyperbolic system by an advection scheme, and then derive a viscous discretization from the result. A distinguished feature of the proposed principle is that it automatically introduces a damping term into the resulting viscous scheme, which is essential for effective high-frequency error damping and, in some cases, for consistency also. In this paper, we demonstrate the general principle for the diffusion equation on uniform grids in one dimension and unstructured grids in two dimensions, for node/cell-centered finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. Numerical results are presented to verify the accuracy of the derived diffusion schemes and to illustrate the importance of the damping term for highly-skewed typical viscous grids. © 2011 Elsevier Ltd.

Nishikawa H.,National Institute of Aerospace
Journal of Computational Physics | Year: 2014

In this paper, we present constructions of first-, second-, and third-order schemes for diffusion by the method introduced in Nishikawa (2007) [10]. In this method, numerical schemes for diffusion are constructed by advection schemes via an equivalent hyperbolic system. This paper demonstrates that the method enables straightforward constructions of diffusion schemes for finite-volume methods on unstructured grids. In particular, it is demonstrated that a robust first-order upwind scheme leads to a robust first-order diffusion scheme, and a high-order advection scheme leads to a high-order diffusion scheme. It is shown that first-, second-, and third-order schemes are capable of producing first-, second-, and third-order accurate solution gradients, respectively, on irregular grids. Accuracy, Fourier stability, and the energy stability of the developed schemes are discussed. A new hyperbolic diffusion system having virtually no source terms is also introduced to simplify the construction of the third-order scheme. Numerical results are presented for regular and irregular triangular grids to demonstrate not only the superior accuracy but also the accelerated steady convergence over a traditional method. © 2013 Elsevier Inc.

Rallabhandi S.K.,National Institute of Aerospace
Journal of Aircraft | Year: 2011

This paper presents an approach to predict the sonic boom ground signatures accurately by numerically solving the augmented Burgers equation entirely in the time domain. The method is capable of predicting the shock thicknesses, thus improving the frequency spectrum of the ground signatures. This also improves the loudness calculation when compared with linear theory methods, because the shock rise times are computed and not empirically adjusted or corrected. The method is capable of predicting undertrack and offtrack ground signatures, with or without wind effects, along with consideration for aircraft maneuvers. This method is very efficient and accurate, making it a very useful design tool in the development of supersonic cruise aircraft. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Nishikawa H.,National Institute of Aerospace
Journal of Computational Physics | Year: 2012

In this paper, we propose to write a source term in the divergence form. A conservation law with a source term can then be written as a single divergence form. We demonstrate that it enables to discretize both the conservation law and the source term in the same framework, and thus greatly simplifies the construction of numerical schemes. To illustrate the advantage of the divergence formulation, we apply the new formulation to construct a uniformly third-order accurate edge-based finite-volume scheme for conservation laws with a source term. Third-order accuracy is demonstrated for regular and irregular triangular grids for the linear advection and Burgers' equations with a source term. © 2012 Elsevier Inc.

Lin Y.,National Institute of Aerospace | Connell J.W.,NASA
Nanoscale | Year: 2012

The recent surge in graphene research has stimulated interest in the investigation of various 2-dimensional (2D) nanomaterials. Among these materials, the 2D boron nitride (BN) nanostructures are in a unique position. This is because they are the isoelectric analogs to graphene structures and share very similar structural characteristics and many physical properties except for the large band gap. The main forms of the 2D BN nanostructures include nanosheets (BNNSs), nanoribbons (BNNRs), and nanomeshes (BNNMs). BNNRs are essentially BNNSs with narrow widths in which the edge effects become significant; BNNMs are also variations of BNNSs, which are supported on certain metal substrates where strong interactions and the lattice mismatch between the substrate and the nanosheet result in periodic shallow regions on the nanosheet surface. Recently, the hybrids of 2D BN nanostructures with graphene, in the form of either in-plane hybrids or inter-plane heterolayers, have also drawn much attention. In particular, the BNNS-graphene heterolayer architectures are finding important electronic applications as BNNSs may serve as excellent dielectric substrates or separation layers for graphene electronic devices. In this article, we first discuss the structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures. Then, various top-down and bottom-up preparation methodologies are reviewed in detail. Several sections are dedicated to the preparation of BNNRs, BNNMs, and BNNS-graphene hybrids, respectively. Following some more discussions on the applications of these unique materials, the article is concluded with a summary and perspectives of this exciting new field. © 2012 The Royal Society of Chemistry.

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