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.

Modeling of surface energy partitioning, surface temperature, and soil wetness in the Tibetan prairie using the Simple Biosphere Model 2 (SiB2)

Abstract: [1] This paper examines the performance of a stand-alone version of the Simple Biosphere Model 2 (SiB2) to investigate the accuracy of the modeled surface energy components, surface effective radiative temperature, and soil wetness in a Tibetan short grass prairie from 15 July to 14 September 1998. During this monsoon period the mean canopy height and the leaf area index were 0.05 m and 0.5, respectively. The study site represented the prevailing conditions of the high Tibetan plateau with an average elevation of 4500 m. The model was initialized using in situ measurements and was driven by half-hourly atmospheric observations. The modeled values for the two months period were compared with micrometeorological field measurements made through the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME)-Tibet project. Results show that (1) when underestimating net radiation by 11%, the model overestimated sensible, latent, and soil heat fluxes by 8, 3, and 13% respectively; (2) the model generated warmer (colder) ground surface in daytime (nighttime); and (3) soil wetness was estimated reasonably.

An introduction to rapid system prototyping

Abstract: The implementation and maintenance of industrial applications have continuously become more and more difficult. In this context, one problem is the evaluation of complex systems. The IEEE defines prototyping as a development approach promoting the implementation of a pilot version of the intended product. This approach is a potential solution to the early evaluation of a system. It can also be used to avoid the shift between the description/specification of a system and its implementation. This brief introduction to the special section on rapid system prototyping illustrates a current picture of prototyping.

Wake-Vortex Eddy-Dissipation Model Predictions Compared with Observations

Abstract: We describe the latest version of a wake-vortex eddy-dissipation model devised by T. Sarpkaya and to compare its predictions with lidar observations obtained at Memphis and Dallas/Fort Worth airports. The model simulates the evolution of aircraft-generated trailing vortices in an atmospheric environment defined by vertical profiles of potential temperature, eddy-dissipation rate, and crosswind. Visual and quantitative comparisons of the time histories of altitude, circulation, and lateral position of predicted and measured vortices are presented

Coordination of Large Pulsed Loads on Future Electric Ships

Abstract: Part of the technical versatility of future all-electric ships is the potential ability to share large amounts of power among a variety of high-power loads. To help evaluate this potential and to provide information to help guide technology selection, a physics-based model of a power train for an electric ship has been developed and implemented on three modeling platforms. Using this model, three different investigations have been carried out to explore aspects of the behavior of a rotating machine power source for a shipboard rail launcher. These were: 1) influence of rapid charging of the rotating machine system on the ship power system; 2) use of the stored energy in the rotating machines to improve ship power quality; and 3) use of the stored energy in the rotating machines to power a pulsed free-electron laser. Each study highlighted different integration opportunities and challenges. The first showed that, because the charging of the rail launchers was through 5-MW motors, there could be a voltage sag for a few cycles, but this could easily be managed so that the sag could be reduced to an inconsequential level. The second study showed that, with appropriate power electronics, the stored energy in the rail launcher power supply can be used to correct power quality problems introduced by other ship systems. Finally, the stored energy in the launcher power supply can be used to fire a free electron laser for ship defense. This feature opens the possibility of routine operation of the entire ship at highest efficiency, i.e., with the smallest number of gas turbines operating near full power, while providing stored energy needed for ship defense

Optimal Nonlinear Feedback Guidance for Reentry Vehicles

Abstract: It is well-known that onboard, real-time, optimal trajectory generation for reusable launch vehicles can substantially increase safety while reducing cost. Arguably, this is one of the most challenging problems in optimal control theory. In recent years, pseudospectral (PS) methods have shown considerable promise in solving such problems. In this paper, we investigate the utility of a PS guidance algorithm for solving this problem. Based on the X33, a generic vehicle model is constructed for analysis. It is shown that the PS guidance algorithm is capable of compensating for large uncertainties and disturbances that include greater than Category 5-level hurricane-force wind gusts (Hurricane Katrina was Cat 4). A single algorithm is used to guide the vehicle from its entry condition to a final approach corridor of about 2000 ft away from the landing site. Despite that much research is still necessary, results so far suggest that PS guidance methods can enhance safety considerably. Computational times for unoptimized codes range from about a second to 10 seconds under a MATLAB environment running on legacy computer hardware. This suggests that realtime trajectory reshaping, and even abort guidance, are well within the reach of modern methods and existing computational capabilities.