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.

Multi-fidelity modelling via recursive co-kriging and Gaussian-Markov random fields.

Abstract: We propose a new framework for design under uncertainty based on stochastic computer simulations and multi-level recursive co-kriging. The proposed methodology simultaneously takes into account multi-fidelity in models, such as direct numerical simulations versus empirical formulae, as well as multi-fidelity in the probability space (e.g. sparse grids versus tensor product multi-element probabilistic collocation). We are able to construct response surfaces of complex dynamical systems by blending multiple information sources via auto-regressive stochastic modelling. A computationally efficient machine learning framework is developed based on multi-level recursive co-kriging with sparse precision matrices of Gaussian–Markov random fields. The effectiveness of the new algorithms is demonstrated in numerical examples involving a prototype problem in risk-averse design, regression of random functions, as well as uncertainty quantification in fluid mechanics involving the evolution of a Burgers equation from a random initial state, and random laminar wakes behind circular cylinders.

Northeasterly Cold Surges and Near-Equatorial Disturbances over the Winter MONEX Area During December 1974. Part II: Planetary-Scale Aspects

Abstract: In Part I of this pre-winter MONEX study a synoptic analysis on the interaction between cold air surges off the East Asian continent and the synoptic-scale disturbances, especially their associated convection, in the equatorial South China Sea during December 1974 was carried out. In this paper we investigate some kinematic characteristics of the planetary-scale circulation changes during the same period in the midlatitudes and tropics in relation to the cold surge and the synoptic-scale disturbances. The main findings suggest a picture of coherent variations of several planetary-scale circulation features which may he described by the following sequence of events: 1) The East Asia local Hadley circulation strengthens as the cooling due to cold air advection over northern China increases prior to a cold surge on the South China coast. This is accompanied by an intensified jet stream maximum centered over Japan, which is apparently a result of the upstream acceleration by the upper level poleward ...

Analyzing the Vulnerability of Critical Infrastructure to Attack and Planning Defenses

Abstract: We describe new bilevel programming models to (1) help make the country's criti- cal infrastructure more resilient to attacks by terrorists, (2) help governments and businesses plan those improvements, and (3) help influence related public policy on investment incentives, regulations, etc. An intelligent attacker (terrorists) and defender (us) are key features of all these models, along with information transparency: These are Stackelberg games, as opposed to two-person, zero-sum games. We illustrate these models with applications to electric power grids, subways, airports, and other critical infrastructure. For instance, one model identifies locations for a given set of electronic sensors that minimize the worst-case time to detection of a chemical, biological, or radiological contaminant introduced into the Washington, D.C. subway system. The paper concludes by reporting insights we have gained through forming "red teams," each of which gathers open-source data on a real-world system, develops an appro- priate attacker-defender or defender-attacker model, and solves the model to identify vulnerabilities in the system or to plan an optimal defense.

Real-Time Dispatch of Petroleum Tank Trucks

Abstract: A highly automated, real-time dispatch system is described which uses embedded optimization routines to replace extensive manual operations and to reduce substantially operating costs for a nation-wide fleet of petroleum tank trucks. The system is currently used in daily operations by the Order Entry and Dispatch segment of the Chevron U.S.A. Marketing System. Refined petroleum products valued at several billion dollars per year are dispatched from more than 80 bulk terminals on a fleet exceeding 300 vehicles in approximately 2600 loads per day. Centralized use of the dispatch system required its design and implementation as a set of transaction modules within a large management information system. This environment presents special challenges for the optimization methods; an heuristic sequential network assignment was developed for certified performance on these dispatch models in lieu of their solution as integer programs. Objectives include minimizing transportation costs approaching $100 million annually while maintaining equitable man and equipment workload distribution, safety standards, and customer service, and satisfying equipment compatibility restrictions.

Principal-components-based display strategy for spectral imagery

Abstract: A new pseudocolor mapping strategy for use with spectral imagery is presented. This strategy is based on a principal components analysis of spectral data, and it capitalizes on the similarities between three-color human vision and high-dimensional hyperspectral datasets. The mapping is closely related to three-dimensional versions of scatter plots that are commonly used in remote sensing to visualize the data cloud. The transformation results in final images where the color assigned to each pixel is solely determined by the position within the data cloud. Materials with similar spectral characteristics are presented in similar hues, and basic classification and clustering decisions can be made by the observer. Final images tend to have large regions of desaturated pixels that make the image more readily interpretable. The data cloud is shown to be conical in nature, and materials with common spectral signatures radiate from the origin of the cone, which is not (in general) at the origin of the spectral data. A supervised method for locating the origin of the cone based on identification of clusters in the data is presented, and the effects of proper origin orientation are illustrated.