Naval Postgraduate School

About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Boundary layer. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.

Vision-Based Tracking and Motion Estimation for Moving Targets Using Unmanned Air Vehicles

Abstract: This paper addresses the development of a vision-based target tracking system for a small unmanned air vehicle The algorithm performs autonomous tracking of a moving target, while simultaneously estimating geographic coordinates, speed, and heading of the target Tight real-time integration of unmanned air vehicle's video and telemetry data streams with georeferenced database allows for reliable target identification, increased precision, and shortened time of target motion estimation A low-cost off-the-shelf system is used, with a modified radiocontrolled aircraft airframe, gas engine, and servos Tracking is enabled using a low-cost, miniature pan-tilt gimbal The control algorithm provides rapid target acquisition and tracking capability A target motion estimator was designed and shown in multiple flight tests to provide reasonable targeting accuracy The impact of tracking loss events on the control and estimation algorithms is analyzed in detail

Dynamics of teleconnections and Walker circulations forced by equatorial heating

Abstract: Using a linearized model with constant mean wind on an equatorial β-plane, two types of atmospheric response to steady tropical forcing are studied by an eigenmode analysis. The first type is the less rotationally trapped “barotropic” motions which show some of the characteristics of the teleconnection patterns observed by Bjerknes (1966) and Horel and Wallace (1981). The second type is the more rotationally trapped, warm-core, deep baroclinic motions which resemble the Walker circulations. The analysis reveals several important inadequacies in previous modeling studies and provides a relatively comprehensive explanation of the dynamics of both types of motions. A vertical normal mode consideration shows that the barotropic-type motions are difficult to excite by internal beating. Surface heating, which has been neglected in many previous numerical modeling studies, is found to be important in directly forcing this type of motion. Furthermore, the possible contribution by large equivalent depth i...

Experimental Robustness Study of Positive Position Feedback Control for Active Vibration Suppression

Abstract: : POSITIVE position feedback (PPF) control was introduced by Goh and Caughey in 1985 to control vibrations of large exible space structures. A PPF controller has several distinguished advantagesas compared to then widely used velocity feedbackcontrol laws. It is insensitive to spillover, where contributions from unmodeled modes affect the control of the modes of interest. As a second-order low-pass lter, a PPF controller rolls off quickly at high frequencies and is well suited to controlling the lower modes of a structure with well separated modes. Because of these advantages, PPF controller along with smart materials, in particular PZT (lead zirconatetitanate) type of piezoelectricmaterial, has been applied to many exible systems to achieve active damping. The design of a PPF controller requires the natural frequency of a structure. In practice, the structuralnatural frequencymay not be known exactlyor itmay varywith time.When the frequencyused in thePPF controller is different from that of the structure, the performance of the PPF control will adversely affected. Despite that PPF control is widely researched in literature, robustness study of PPF control when natural frequency is inexactly known is not reported. This motivates the authors to conduct experimental study of robustness of PPF control in active vibration suppression of a smart exible structure.

Development of nanocrystalline structure in Cu during friction stir processing (FSP)

Abstract: The characteristics of microstructures at various locations behind the pin tool extraction site were studied in copper after FSP that had been conducted with continuous quenching to enhance cooling rates. The substructures initially formed around the pin tool consist of very small crystallites having sizes of a few tens of nanometers. It is proposed that the processing conditions result in formation of microband structures around pin tool in the presence of severe strain heterogeneity. The microbands appear as nano-scale elongated crystallites surrounded by high-angle boundaries. The elongated crystallites transform to nearly random oriented and equiaxed grain structures by shape adjustment during the initial stages of cooling from the peak temperature. Nanocrystalline structures ∼174 nm in size were produced in OFHC copper by FSP.