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: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Tracking unstable periodic orbits in nonstationary high-dimensional chaotic systems:Method and experiment

Abstract: We consider the adaptive control of chaos in nonstationary high-dimensional dynamical systems. In particular, we propose and experimentally implement a technique to stabilize and track unstable periodic orbits based on the use of time series. In our technique, the position of the periodic orbit and other parameters in the controller are continually updated from recent measurements of the system state and perturbation histories, while the environment, simulated by one or several of the system's parameters, drifts independent of the control algorithm. We demonstrate the effectiveness of the technique computationally for the H\'enon map, a chemical reaction model, and a coupled driven Duffing oscillator, and experimentally for a magnetoelastic ribbon system.

Inverse acoustic scattering from an elastic sphere

Abstract: A technique is presented to determine the material properties of elastic spheres using the resonance features present in their backscattering cross sections. The method is based on an asymptotic solution of the elastodynamic equations governing the sphere’s response in the high‐frequency (x≡k1a≫1) regime. Our study shows that the modal resonances that an elastic sphere communicates to its echo fall into two distinct families. The set of broader resonances is the dilatational family. The narrower set is the shear family. They are both present in all the modes (n>0) contained within the sonar cross section except for the n=0 mode that contains only broad resonances. Both sets of resonances are separated by spacings that asymptotically (x≫1) tend to uniform values that we have respectively called Δ and Δ’. The dilatational and shear wave speeds in the elastic sphere are shown to be respectively proportional to these spacings, so that the two wave speeds can be immediately determined from them. The sphere’s d...

Acoustic optic hybrid (AOH) sensor

Abstract: The ability of laser vibrometers to receive and process acoustic echoes from the water surface above a submerged target is established and evaluated. Sonar echoes from a submerged target are collected from the water surface by a laser vibrometer. Feasibility of this approach to sensing underwater sound is demonstrated. If the acoustic excitation at an otherwise undisturbed water surface is 195 to 168 dB re: 1 μPa, signal-to-noise ratio (SNR), at the vibrometer output, is shown to range from about 46 to 6 dB. Capillary waves and gravity waves at the water surface are expected and shown to have some destructive effect on the process of echo retrieval. A series of experiments to quantify the surface wave effects is described. The wave experiment results are reported. A successful attempt to acquire echoes from a submerged target over a grid of points for further processing into a three-dimensional image is made and described. The data acquisition and beamforming techniques constitute a three-dimensional, aco...

Development of a digital array radar (DAR)

Abstract: Twenty-first century littoral and open-sea missions present USA Navy (USN) shipboard-radar systems with the challenge of detecting small targets in severe clutter and against multiple sources of interference. In fiscal year 2000 (FY00), the Office of Naval Research (ONR) sponsored a program to develop an active array radar that includes a digital beamforming (DBF) architecture. The DBF radar system has the potential for improved time-energy management, improved signal-to-clutter (S/C) ratios, improved reliability and reduced life-cycle costs. This paper summarizes the latest developments of the program during FY00.