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 & Nonlinear system. 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.

Toward an improved understanding of thruster dynamics for underwater vehicles

Abstract: This paper proposes a novel approach to modeling the four quadrant dynamic response of thrusters as used for the motion control of ROV and AUV underwater vehicles. The significance is that these vehicles are small in size and respond quickly to commands. Precision in motion control will require further understanding of thruster performance than is currently available. The model includes a four quadrant mapping of the propeller blades lift and drag forces and is coupled with motor and fluid system dynamics. A series of experiments is described for both long and short period triangular, as well as square wave inputs. The model is compared favorably with experimental data for a variety of differing conditions and predicts that force overshoots are observed under conditions of rapid command changes. Use of the model will improve the control of dynamic thrust on these vehicles.

A numerical model of seasonal primary production within the Chukchi/Beaufort Seas

Abstract: A coupled three-dimensional circulation and ecological model provided numerical analysis of daily carbon/nitrogen cycling by the planktonic and benthic components of western Arctic shelf/basin ecosystems during 2002, when extensive field data were obtained by American and Canadian ice-breakers. Seasonal model budgets of April–May, July–August, and September–October 2002 allowed both interpolation and extrapolation of these validation data, suggesting that the most productive shelf regime of the Chukchi/Beaufort Seas was that of summer. Yet, during this period of July–August, a combination of light-limitation and nutrient-limitation limited shelf-wide mean simulated net photosynthesis to only � 709 mg C m � 2 day � 1 for shelf waters of o220 m depth. This modeled seasonal carbon fixation then accounted for � 45% of the annual shelf primary production of 97.4 g C m � 2 yr � 1 Identification of the relative importance of natural control factors of light and nutrients by the coupled model provided insight into possible consequences of future global climatic changes at these high latitudes. The model’s seasonal penetration of relatively saline, nutrient-rich Anadyr Water of Pacific origin into the eastern Chukchi Sea replicated the time series of observed salinity fields. A similar fidelity of the simulated nitrate, silicate and dissolved inorganic carbon fields with the observed ones yielded an assessment of nutrient uptake and photosynthesis during a natural fertilization experiment. The simulated chlorophyll, dissolved organic carbon (DOC), and NH4 stocks also mimicked these shipboard observations. We found that the spring 2002 stocks of new nutrients were stripped by the end of summer, with little fall nutrient resupply by physical and biotic factors, when incident light waned. However, because of extensive ice cover and nutrient-poor upper waters within the Canadian Basin, the slope regions remained

Equilibrium transport in double-diffusive convection

Abstract: A theoretical model for the equilibrium double-diffusive transport is presented which emphasizes the role of secondary instabilities of salt fingers in saturation of their linear growth. Theory assumes that the fully developed equilibrium state is characterized by the comparable growth rates of primary and secondary instabilities. This assumption makes it possible to formulate an efficient algorithm for computing diffusivities of heat and salt as a function of the background property gradients and molecular parameters. The model predicts that the double-diffusive transport of heat and salt rapidly intensifies with decreasing density ratio. Fluxes are less sensitive to molecular characteristics, mildly increasing with Prandtl number and decreasing with diffusivity ratio . Theory is successfully tested by a series of direct numerical simulations which span a wide range of and .

Knowledge-based knowledge management in the reengineering domain

Abstract: A fundamental problem with knowledge management is the information technology (IT) employed to enable knowledge work appears to target data and information, as opposed to knowledge itself. In contrast, knowledge-based systems (KBS) maintain an explicit and direct focus on knowledge. The research described in this article is focused on innovating knowledge management through KBS technology. We refer to this KBS-enabled transformation of knowledge work as knowledge-based knowledge management. Drawing from the recent literature, we identify a number of key activities associated with knowledge management to establish a set of requirements for knowledge management support. We match these requirements with textbook capabilities of intelligent systems and use this analysis to evaluate KOPeR, a KBS employed to automate and support knowledge management in the reengineering domain. We find KOPeR possesses the capabilities required for knowledge management support. And its field application, as part of a major reengineering engagement, reveals four important knowledge effects enabled by this KBS. From this study, we also find KOPeR to be effective in its automation and support of key knowledge management activities. And through its successful use and knowledge effects in this study, we conclude that KBS can be developed and employed for effective knowledge management support.

On the turbulent Prandtl number in the stable atmospheric boundary layer

Abstract: This study focuses on the behaviour of the turbulent Prandtl number, Prt, in the stable atmospheric boundary layer (SBL) based on measurements made during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA). It is found that Prt increases with increasing stability if Prt is plotted vs. gradient Richardson number, Ri; but at the same time, Prt decreases with increasing stability if Prt is plotted vs. flux Richardson number, Rf, or vs. ζ = z/L. This paradoxical behaviour of the turbulent Prandtl number in the SBL derives from the fact that plots of Prt vs. Ri (as well as vs. Rf and ζ) for individual 1-h observations and conventional bin-averaged values of the individual quantities have built-in correlation (or self-correlation) because of the shared variables. For independent estimates of how Prt behaves in very stable stratification, Prt is plotted against the bulk Richardson number; such plots have no built-in correlation. These plots based on the SHEBA data show that, on the average, Prt decreases with increasing stability and Prt < 1 in the very stable case. For specific heights and stabilities, though, the turbulent Prandtl number has more complicated behaviour in the SBL.