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.

Empirical Evaluation of Auction-Based Coordination of AUVs in a Realistic Simulated Mine Countermeasure Task

Abstract: In this work, we evaluate performance of our distributed cooperation framework, DEMiR-CF, for Naval Mine Countermeasure missions on the US NAVY’s ALWSE-MC simulator against different contingencies that may arise run time. Our cooperation framework integrates a distributed task allocation scheme, coordination mechanisms and precaution routines for multirobot team execution. Its performance has been demonstrated in Multi-robot Multi-target exploration and Object Construction domains. Marine applications provide additional challenges such as noisy communication, position uncertainty and the likelihood of robot failures. There is a high probability that the initial assignments are subject to change during run time, in these kinds of environments. Our framework ensures robust execution and efficient completion of missions against several different types of failures. Preliminary results for MCM missions are promising in the sense of mission completion, and AUV paths are close to optimal in the presence of uncertainties.

Tip-Vortex Induced Cavitation on a Ducted Propulsor

Abstract: An extensive experimental investigation was carried out to examine tip-vortex induced cavitation on a ducted propulsor. The flowfield about a 3-bladed, ducted rotor operating in uniform inflow was measured in detail with three-dimensional LDV; cavitation inception was measured; and a correlated hydrophone/high-speed video system was used to identify and characterize the early, sub-visual cavitation events. Two geometrically-similar, ducted rotors were tested over a Reynolds number range from 1.4×106 to 9×106 in order to determine how the tip-vortex cavitation scales with Reynolds number. Analysis of the data shows that exponent for scaling tip-vortex cavitation with Reynolds number is smaller than for open rotors. It is shown that the parameters which are commonly accepted to control tip-vortex cavitation, vortex circulation and vortex core size, do not directly control cavitation inception on this ducted rotor. Rather it appears that cavitation is initiated by the stretching and deformation of secondary vortical structures resulting from the merger of the leakage and tip vortices.Copyright © 2003 by ASME

Development of a Tip-Leakage Flow Part 2: Comparison Between the Ducted and Un-ducted Rotor

Abstract: The vortical flow in the tip region of a three-bladed rotor was examined using particle imaging velocimetry (PIV). The vortex forming at the tip of the un-ducted propeller was compared to the tip-leakage vortex of the ducted rotor. The planar flow fields were used to identify regions of concentrated vorticity and determine instantaneous vortex properties, revealing the presence of a primary tip-leakage vortex surrounded by a number of secondary vortices. Comparison between the ducted and un-ducted rotor indicated that the presence of the duct reduced the relative strength of the primary tip vortex, making its strength a smaller fraction of the overall shed circulation near the tip. The weaker tip-leakage vortex then became closer in strength to the other secondary vortices in the tip-flow region. However, for the rotor tip geometry considered here, the radius of the primary vortex core did not vary substantially between the ducted and un-ducted cases. The variability of the flow was larger for the ducted case, in terms of the primary vortex position, its identified circulation, core size, and inferred core pressure. This variability was also observed in the scaled velocity fluctuations near the core of the vortex.