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.

Investigation Of A Laser-controlled, Copper-doped GaAs Closing And Opening Switch For Pulsed Power Applications

Abstract: This paper describes the recent power scaling of the Bulk Optically Controlled Semiconductor Switch (BOSS). The processes of persistent photoconductivity followed by photo-quenching have been demonstrated in copper-compensated, silicon-doped, semi-insulating GaAs (GaAs:Cu:Si). These processes allow a switch to be developed which can be closed by the application of one laser pulse and opened by the application of a second laser pulse of longer wavelength. The high-power switching results indicate that the BOSS device will operate at multi-megawatt power levels. The results of our power scaling effort have suggested improvements to the basic BOSS design that will allow us to achieve reliable operation at high power levels.

Depletion of Lubricity Improvers from Hydrotreated Renewable and Ultralow-Sulfur Petroleum Diesels by Marine Microbiota

Abstract: Relative to the high-sulfur diesel in use for decades, the U.S. Navy is facing exposure to new fuels that may behave differently in the marine environment. This laboratory work investigated the effects of biofouling and seawater exposure to high-sulfur diesel, ultralow-sulfur diesel, Fischer–Tropsch synthetic diesel, fatty acid methyl ester (FAME) biodiesel, and hydrotreated renewable diesel fuels. Bulk chemical changes were not detectable under the laboratory test conditions, but changes in fuel lubricity, controlled by traces of polar compounds in fuel, were detectable in several fuels by both physical and chemical testing. A marine microbial assemblage rapidly metabolized the lubricity improver (as 14C-linoleic acid) as it partitioned to seawater from hydrotreated renewable and ultralow-sulfur diesel fuels. Equipment dependent upon fuel lubricity, such as fuel pumps and fuel injectors, may be at risk when new fuels enter use in the near future, given that certain U.S. Navy ship classes store fuel wet, ...

Acoustic scattering by an air-bubble near the sea surfaceacoustic scattering by an air-bubble near the sea surface

Abstract: Sound scattering by and air bubble in a boundless fluid is an old classical problem (19). If the air bubble is near and strongly interacting with the (flat) surface of a liquid half-space, then the scattering cross section (SCS) of the bubble differs substantially from its value far-away from the interface. We present the exact solution for this scattering problem which is valid for any incidence direction of the (plane) sound waves, and for any bubble depth, obtained by the general method of images. The bubble is no longer assumed to be a point simple, harmonic, radially pulsating oscillator, but is described as a continuous, spatially extended body, having an infinity of modes and resonances. The interaction with the boundary, or the image is not treated by means of the simple Lloy's mirror formula for point source ( or scatterers), but by a general extended continuum approach, This benchmark solution makes use of the addition theorems for the spherical wavefunctions. The resulting SCS contains contributions from the bubble, its image, the invident wave, and the reflected wave from the boundary. It is expressed in terms of coupling coefficients, bmn, products of Wigner-3j simbols. The formulations in illustrated with many computed plots for bubbles at various depths, and the results compare favorably with earlier experimental observations. The approach also serves to describe scattering by fish near the sea surface, in an exact fashion. Acoustic scattering by near-surface bubbles also has many other applications such as in the improvement of the performance of sensor that must operate through hubby media, and in the understanding of its connection with approaches to model oceanic fluxes.

Broadbeam multi-aspect synthetic aperture sonar

Abstract: Broadband multi-aspect processing promises to improve the image quality and target detection/classification capabilities of imaging systems since the different aspects or 'looks' can provide additional clues about the shape and dimension of targets. To obtain high cross-range resolutions, these different 'looks' can be obtained by steering the main beam of a synthesized aperture. Synthetic aperture beam steering can be performed on data that was collected in stripmap mode. Accurate beam steering requires correct data handling by the reconstruction algorithm since the target area is in the near-field of the aperture. The limits of steering are determined primarily by the beamwidth of the system in question. The low-frequency synthetic aperture sonar system in use at the Coastal Systems Station in Panama City, Florida is well suited to this type of beam steering because of its broad beams (100/spl deg/ for the receiver and 50/spl deg/ for the transmitter) and its spatially oversampled design. Results obtained from simulated point targets as well as real data are presented.

Superconducting Magnetic Gradiometers for Mobile Applications with an Emphasis on Ordnance Detection

Abstract: Passive magnetic sensors provide one means to conduct mobile area surveys and search operations, useful for a number of applications, including sea mine countermeasures and the detection of unexploded ordnance and packaged biological, chemical and radioactive waste for environmental cleanup. To date, the generally accepted method for such detection involves the generation of two-or three-dimensional magnetic anomaly field maps, using primarily total-field magnetometers. Sensor configurations measuring spatial gradients of magnetic field offer a new opportunity for better localization and classification. Sensors incorporating Superconducting Quantum Interference Devices (SQUIDS) provide the greatest sensitivity available with current technology for magnetic anomaly detection. During the late 1970’s and early 1980’s, the Naval Surface Warfare Center Coastal Systems Station (CSS) developed the Superconducting Gradiometer/Magnetometer Sensor (SGMS) specifically for mobile operations outside the laboratory environment. This sensor technology utilized niobium superconducting components cooled by liquid helium. The SGMS has demonstrated nagged, reliable performance even onboard airborne and undersea towed platforms. In this article, a general perspective for the use of passive magnetic sensors for mobile operations will be established. The SGMS design will be described in some detail. General design principles underlying its mobile application, fundamental sensor and environmental noise issues, and approaches to compensate for them, will be presented. The magnetic sensor detection and classification concept developed for sea mine countermeasures and results from that demonstration will be discussed. Recent developments and future opportunities, especially encompassing the use of high temperature (high-Tc) superconducting components cooled by liquid nitrogen, will be addressed.