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.

Analysis of scattering from very large three-dimensional rough surfaces using MLFMM and ray-based analyses

Abstract: Several techniques are considered for the analysis of electromagnetic scattering from rough ocean surfaces. A rigorous Multi-level Fast Multipole Method (MLFMM) is employed, as well as a high-frequency ray-based solution. The MLFMM analysis is implemented in scalable form, allowing consideration of scattering from very large surfaces (in excess of 100/spl lambda//spl times/100/spl lambda/, where A represents the electromagnetic wavelength). Plane-wave incidence is assumed, and a key aspect of the MLFMM study involves investigating techniques for rough-surface truncation. The rough surface is modeled as a target placed in the presence of an infinite half-space background; to minimize edge effects, the surface is smoothly tapered into the planar half space. We also consider the technique of employing a resistive taper on the edges of the rough surface. These two truncation techniques are compared in accuracy, memory requirements (RAM), and in computational time (CPU). The MLFMM results are used to validate an approximate ray-based high-frequency model that allows rapid analysis of large surfaces. The computational results are compared to measured forward-scattering data from scaled laboratory measurements, used to simulate scattering from an ocean surface.

Acoustic scattering by a three-dimensional elastic object near a rough surface

Abstract: The ensemble-averaged field scattered by a smooth, bounded, elastic object near a penetrable surface with small-scale random roughness is formulated. The formulation consists of combining a perturbative solution for modeling propagation through the rough surface with a transition (T-) matrix solution for scattering by the object near a planar surface. All media bounding the rough surface are assumed to be fluids. By applying the results to a spherical steel shell buried within a rough sediment bottom, it is demonstrated that the ensemble-averaged “incoherent” intensity backscattered by buried objects illuminated with shallow-grazing-angle acoustic sources can be well enhanced at high frequencies over field predictions based on scattering models where all environmental surfaces are planar. However, this intensity must compete with the incoherent intensity scattered back from the interface itself, which can defeat detection attempts. The averaged “coherent” component of the field maintains the strong evanes...

Analysis of a current-regulated brushless DC drive

Abstract: Current-regulated brushless DC machines are used in a wide variety of applications including robotics, actuators, electric vehicles, and ship propulsion systems. When conducting system analysis of this or any other type of drive, average-value reduced-order models are invaluable since they provide a means of rapidly predicting the electromechanical dynamics and are readily linearized for control system synthesis. In this paper, a highly accurate average-value reduced-order model of a hysteresis current-regulated brushless DC drive is set forth. In so doing it is demonstrated that the drive exhibits five distinct operating modes. The physical cause of each of these modes is explained and a mathematical model for each mode is set forth. The mathematical models are verified both experimentally and through the use of computer simulation. It has been found that the model set fourth herein is on the order of 300 times faster than a detailed computer simulation in calculating electromechanical transients. >

Demonstration of a Novel Man-Portable Magnetic STAR Technology for Real Time Localization of Unexploded Ordnance

Abstract: We report results of field tests of the first prototype of a novel man-portable Magnetic Scalar Triangulation and Ranging (STAR) technology. The new magnetic sensor system technology is being developed with support from the Strategic Environmental Research and Development Program (SERDP) to provide an easily deployable magnetic sensor system for real-time, point-by-point Detection, Localization and Classification (DLC) of magnetic targets such as Unexploded Ordnance (UXO) and buried mines. The STAR technology is based on a multi tensor gradiometer approach that uses magnetic gradient tensor magnitudes, i.e., "gradient- contraction-type" parameters to perform DLC of magnetic targets. The magnetic STAR sensor uses the scalar functions to triangulate a magnetic UXO-type target's position vector and to calculate the target's magnetic signature vector. The vector components of an object's magnetic signature provide a basis for real time classification of its type, i.e. UXO-like or not. In order to provide proof of principle of the STAR concept and demonstrate its advantages for high mobility magnetic sensing applications, we designed, constructed and field-tested a prototype man-portable STAR Gradiometer. The portable gradiometer's hardware and software are completely self- contained and provide a practical and user friendly capability for real time DLC of magnetic targets. Target DLC parameters: e.g., range, bearing, elevation and magnetic signature are correlated with Global Positioning System time and position data and displayed in near real time (total delay < 3 seconds) on a heads-up display that clips onto the operator's safety glasses. Interactive software controls data acquisition, performs signal processing to remove residual motion noise effects and runs the STAR Algorithm to generate and display the target's DLC parameters. Field tests have demonstrated proof-of-principle of the STAR concept and conclusively demonstrated that the technology has unique advantages for DLC by highly mobile sensing platforms. While being carried and operated by a single individual, the portable sensor has demonstrated very robust, motion noise resistant performance even while undergoing rotational motion of more than 40 degrees per second. The field test results very strongly indicate that the man-portable STAR technology can provide a wide variety of highly maneuverable sensing platforms (including Autonomous Underwater Vehicles) with uniquely effective, motion-noise-resistant magnetic sensing modalities for DLC of magnetic targets such as UXO and underwater mines.