Calculation of wing response to gusts and blast waves with vortex lift effect

A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex-lattice method, unsteady suction analogy, and Pade approximate. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves

Implementación de la transformada FFT sobre una FPGA orientada a su aplicación en convertidores electrónicos de potencia

La evolución de los esquemas de control para los convertidores electrónicos de potencia exige capacidades de procesamiento cada vez más altas, con altos consumos de tiempo y de recursos. En cuanto a compatibilidad, uno de los retos más importantes es el relacionado con distorsión armónica y el factor de potencia. En el diseño de sistemas electrónicos para medición y corrección, uno de los algoritmos más importantes es el de la FFT (Fast Fourier Transform). La FFT es un eficiente algoritmo que permite calcular la transformada de Fourier discreta (TFD) y su inversa. Dadas las características de la transformada, es posible analizar una señal vista desde su espectro en frecuencia. Este artículo documenta el diseño de una FFT embebida en una FPGA (Field Programable Gate Array) para el análisis de contenido armónico en señales de corriente de baja potencia

Signal Processing for Synthetic Aperture Sonar Image Enhancement

This thesis contains a description of SAS processing algorithms, offering improvements in Fourier-based reconstruction, motion-compensation, and autofocus. Fourier-based image reconstruction is reviewed and improvements shown as the result of improved system modelling. A number of new algorithms based on the wavenumber algorithm for correcting second order effects are proposed. In addition, a new framework for describing multiple-receiver reconstruction in terms of the bistatic geometry is presented and is a useful aid to understanding. Motion-compensation techniques for allowing Fourier-based reconstruction in widebeam geometries suffering large-motion errors are discussed. A motion-compensation algorithm exploiting multiple receiver geometries is suggested and shown to provide substantial improvement in image quality. New motion compensation techniques for yaw correction using the wavenumber algorithm are discussed. A common framework for describing phase estimation is presented and techniques from a number of fields are reviewed within this framework. In addition a new proof is provided outlining the relationship between eigenvector-based autofocus phase estimation kernels and the phase-closure techniques used astronomical imaging. Micronavigation techniques are reviewed and extensions to the shear average single-receiver micronavigation technique result in a 3 - 4 fold performance improvement when operating on high-contrast images. The stripmap phase gradient autofocus (SPGA) algorithm is developed and extends spotlight SAR PGA to the wide-beam, wide-band stripmap geometries common in SAS imaging. SPGA supersedes traditional PGA-based stripmap autofocus algorithms such as mPGA and PCA - the relationships between SPGA and these algorithms is discussed. SPGA's operation is verified on simulated and field-collected data where it provides significant image improvement. SPGA with phase-curvature based estimation is shown and found to perform poorly compared with phase-gradient techniques. The operation of SPGA on data collected from Sydney Harbour is shown with SPGA able to improve resolution to near the diffraction-limit. Additional analysis of practical stripmap autofocus operation in presence of undersampling and space-invariant blurring is presented with significant comment regarding the difficulties inherent in autofocusing field-collected data. Field-collected data from trials in Sydney Harbour is presented along with associated autofocus results from a number of algorithms

Robust adaptive filtering algorithms for impulsive noise environments

Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences, Bilkent University, 1996.Thesis (Master's) -- Bilkent University, 1996.Includes bibliographical references leaves 61-66.In this thesis, robust adaptive filtering algorithms are introduced for impulsive noise environments which can be modeled as o;-stable distributions and/or c-contarninated Gaussian distributions. The algorithms are devcrloped using the Fractional Lower Order Statistics concept. Robust perf()rrnance is obtained.Aydin, GülM.S

Aeronautical Engineering: A continuing bibliography, supplement 96

This bibliography lists 448 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1978

Battle damage assessment using inverse synthetic aperture radar (ISAR)

An imaging radar, like ISAR, offers a combatant the capability to perform long range surveillance with high quality imagery for positive target identification. Extending this attractive feature to the battle damage assessment problem (BDA) gives the operator instant viewing of the target's behavior when it is hit. As a consequence, immediate and decisive action can be quickly taken (if required). However, the conventional Fourier processing adopted by most ISAR systems does not provide adequate time resolution to capture the target's dynamic responses during the hit. As a result, the radar image becomes distorted. To improve the time resolution, time-frequency transform (TFT) methods of ISAR imaging have been proposed. Unlike traditional Fourier-based processing, TFT's allows variable time resolution of the entire event that falls within the ISAR coherent integration period to be extracted as part of the imaging process. We have shown in this thesis that the use of linear Short Time-Frequency Transforms allows the translational response of the aircraft caused by a blast force to be clearly extracted. The TFT extracted images not only tell us how the aircraft responds to a blast effect but also provides additional information about the cause of image distortion in the traditional ISAR display.http://archive.org/details/battledamagesses109451223Approved for public release; distribution is unlimited

Aeronautical Engineering: A continuing bibliography with indexes, supplement 106

This bibliography lists 388 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1979