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.

Initial evaluation of the new real-time tracking gradiometer designed for small unmanned underwater vehicles

Abstract: The shallow water localization of buried mines places increased emphasis on sensor and sensor platform size and maneuverability. The Office of Naval Research (ONR) has funded a number of projects to develop efficient buried minehunting capabilities. In particular, they are supporting the development of two Unmanned Underwater Vehicles (UUVs) designed specifically for shallow water minehunting. In addition, the ONR has funded the development of two magnetic sensors for use on these UUV's. This paper documents the recent progress that has been made in operating one of these sensors, the uuv-Real-time Tracking Gradiometer (uuv-RTG) underwater and in motion. The new uuv-RTG, with a 165 mm baseline, consists of four, 3-axis fluxgate magnetometers, each located within a 3-axis Helmholtz coil. The coils on the fourth magnetometer are not connected to allow its use as a reference sensor that provides magnetic feedback to the other three sensors. The feedback developed by the reference sensor is used to null the signals caused by motion, allowing the three primary sensors to operate at low noise levels in large magnetic fields. These three magnetometers are then used to develop six gradients, five of which are independent. With the appropriate software algorithms, this system is able to provide useful range and bearing to ferromagnetic targets, as well as their magnetic moment. Initial evaluation of RTG technology underwater was accomplished by installing a field prototype RTG (RTG-fp) with a 305 mm baseline, onboard a towed, low mag sled designed by Florida Atlantic University (FAU) for their Buried Object Scanning Sonar (BOSS II). The RTG-fp operating in unison with the BOSS II system on the BOSS sled, provided limited but useful data regarding its performance and ability to be fused with a sonar, such as the BOSS II. Prior to their planned integration in late 2005, the new generation uuv-RTG and the BOSS III are currently undergoing performance testing on individual AUVs called Bluefin 12s. Operating a magnetic sensor onboard a small AUVs such as the 324 mm diameter Bluefin 12 is especially difficult. This is due, not only to the close proximity of the magnetometers to multiple magnetic interference sources that are integral to the vehicle, but also to magnetic interference generated by other sensors that are present and share the same payload section. An extensive noise mitigation package consisting of three, 3-axis magnetometers and 2 current sensors were installed on the Bluefin 12 to mitigate this problem. The uuv-RTG is currently being magnetically characterized. Once the characterization is completed, it will be integrated with BOSS III on a winged version of the Bluefin 12. Here it will be evaluated both independently and in fusion with the BOSS III.

Well-defined intended uses: an explicit requirement for accreditation of modeling and simulation applications

Abstract: A modeling and simulation (M&S) application is built for a specific purpose and its acceptability assessment is carried out with respect to that purpose The accreditation decision for an M&S application is also made with respect to that purpose The purpose is commonly expressed in terms of intended uses The quality of expressing the intended uses significantly affects the quality of the acceptability assessment as well as the quality of making the accreditation decision The purpose of this paper is to provide guidance in proper definition of the intended uses It uses an M&S application for simulating the US National Missile Defense (NMD) system design as an example to illustrate the definition of the intended uses

Thermally Stable Ni-rich Austenite Formed Utilizing Multistep Intercritical Heat Treatment in a Low-Carbon 10 Wt Pct Ni Martensitic Steel

Abstract: Austenite reversion and its thermal stability attained during the transformation is key to enhanced toughness and blast resistance in transformation-induced-plasticity martensitic steels. We demonstrate that the thermal stability of Ni-stabilized austenite and kinetics of the transformation can be controlled by forming Ni-rich regions in proximity of pre-existing (retained) austenite. Atom probe tomography (APT) in conjunction with thermodynamic and kinetic modeling elucidates the role of Ni-rich regions in enhancing growth kinetics of thermally stable austenite, formed utilizing a multistep intercritical (Quench-Lamellarization-Tempering (QLT)-type) heat treatment for a low-carbon 10 wt pct Ni steel. Direct evidence of austenite formation is provided by dilatometry, and the volume fraction is quantified by synchrotron X-ray diffraction. The results indicate the growth of nm-thick austenite layers during the second intercritical tempering treatment (T-step) at 863 K (590 °C), with austenite retained from first intercritical treatment (L-step) at 923 K (650 °C) acting as a nucleation template. For the first time, the thermal stability of austenite is quantified with respect to its compositional evolution during the multistep intercritical treatment of these steels. Austenite compositions measured by APT are used in combination with the thermodynamic and kinetic approach formulated by Ghosh and Olson to assess thermal stability and predict the martensite-start temperature. This approach is particularly useful as empirical relations cannot be extrapolated for the highly Ni-enriched austenite investigated in the present study.

Simulation of DD-963 ship airwake by Navier-Stokes method

Abstract: The ship airwake is defined as an arbitrary volume of air, namely an air burble, surrounding the ship. This note describes simulating the airwake of a DD-963 ship configuration by using a multizone, thin-layer Navier-Stokes method.