Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Experimental confirmation of the scaling theory for noise-induced crises.

Abstract: We investigate experimentally the scaling of the average time \ensuremath{\tau} between intermittent, noise-induced bursts for a chaotic mechanical system near a crisis. The system studied is a periodically driven (frequency f) magnetoelastic ribbon. Theory predicts that for deterministic crises where \ensuremath{\tau} scales as \ensuremath{\tau}\ensuremath{\sim}\ensuremath{\Vert}f-${\mathit{f}}_{\mathit{c}}$${\mathrm{\ensuremath{\Vert}}}^{\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$ (f${\mathit{f}}_{\mathit{c}}$, f=${\mathit{f}}_{\mathit{c}}$ at crisis), the characteristic time between noise-induced bursts (f\ensuremath{\ge}${\mathit{f}}_{\mathit{c}}$) should scale as \ensuremath{\tau}\ensuremath{\sim}${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$g(\ensuremath{\Vert}f-${\mathit{f}}_{\mathit{c}}$\ensuremath{\Vert}/\ensuremath{\sigma}), where \ensuremath{\sigma} is the noise strength and \ensuremath{\gamma} is the same in both cases. We determine \ensuremath{\gamma} for the low-noise (``deterministic'') system, then add noise and observe that the scaling for \ensuremath{\tau} is as predicted.

Nonlinear missile autopilot design using time-scale separation

Abstract: Time-Scale separation helps improve the robustness of feedback linearized autopilots by simplifying the feedback linearization maps, and by permitting the design of low-order controllers. This paper presents the development of three distinct timescale separation schemes for the design of feedback linearized missile autopilots. A six degrees-of-freedom missile model is used in this work. The performance of these autopilots are compared with the design that does not use time-scale separation. Simulation results illustrating controller tracking performance and robustness are presented.

Fractional Fourier transforms, wavelet transforms, and adaptive neural networks

Abstract: A new optical architecture is developed, based on fractional Fourier transforms, that compromises between shift-invariant (frequency) and position-dependent filtering. The analogy of this architecture to wavelet transforms and adaptive neural networks is also presented. The ambiguity and Wigner distribution functions are obtainable from special cases of the filter. The filter design corresponds to the training of the neural networks, and an adaptive learning algorithm is developed based on gradient-descent error minimization and error back propagation. The extension to multilayer architecture is straightforward.

Combustion of alane and aluminum with water for hydrogen and thermal energy generation

Abstract: The combustion of alane and aluminum with water in its frozen state has been studied experimentally and theoretically. Both nano and micron-sized particles are considered over a broad range of pressure. The linear burning rate and chemical efficiency are obtained using a constant-pressure strand burner and constant-volume cell, respectively. The effect of replacing nano-Al particles by micron-sized Al and alane particles are examined systematically with the additive mass fraction up to 25%. The equivalence ratio is fixed at 0.943. The pressure dependence of the burning rate follows the power law, r b = aP n , with n ranging from 0.41 to 0.51 for all the materials considered. The burning rate decreases with increasing alane concentration, whereas it remains approximately constant with cases containing only Al particles. The chemical efficiency ranged from 32% to 83%, depending on the mixture composition and pressure. Thermo-chemical analyses are conducted to provide insight into underlying causes of the decreased burning rate of the alanized compositions. A theoretical model is also developed to explore the detailed flame structure and burning properties. Reasonably good agreement is achieved with experimental observations.