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: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Distributed Subgradient-Based Coordination of Multiple Renewable Generators in a Microgrid

Abstract: For a microgrid with high renewable energy penetration to work autonomously, it must maintain its own supply-demand balance of active power. Maximum peak power tracking algorithms, which emphasize high renewable energy utilization, may cause a supply-demand imbalance when the available renewable generation is more than demanded, especially for autonomous microgrids. Currently, droop control is one of the most popular decentralized methods for sharing active and reactive loads among the distributed generators. However, conventional droop control methods suffer from slow and oscillating dynamic response and steady state deviations. To overcome these problems, this paper proposes a distributed subgradient-based solution to coordinate the operations of different types of distributed renewable generators in a microgrid. By controlling the utilization levels of renewable generators, the supply-demand balance can be well maintained and the system dynamic performance can be significantly improved. Simulation results demonstrate the effectiveness of the proposed control solution.

The Sandia Fracture Challenge: blind round robin predictions of ductile tearing

Abstract: Existing and emerging methods in computational mechanics are rarely validated against problems with an unknown outcome. For this reason, Sandia National Laboratories, in partnership with US National Science Foundation and Naval Surface Warfare Center Carderock Division, launched a computational challenge in mid-summer, 2012. Researchers and engineers were invited to predict crack initiation and propagation in a simple but novel geometry fabricated from a common off-the-shelf commercial engineering alloy. The goal of this international Sandia Fracture Challenge was to benchmark the capabilities for the prediction of deformation and damage evolution associated with ductile tearing in structural metals, including physics models, computational methods, and numerical implementations currently available in the computational fracture community. Thirteen teams participated, reporting blind predictions for the outcome of the Challenge. The simulations and experiments were performed independently and kept confidential. The methods for fracture prediction taken by the thirteen teams ranged from very simple engineering calculations to complicated multiscale simulations. The wide variation in modeling results showed a striking lack of consistency across research groups in addressing problems of ductile fracture. While some methods were more successful than others, it is clear that the problem of ductile fracture prediction continues to be challenging. Specific areas of deficiency have been identified through this effort. Also, the effort has underscored the need for additional blind prediction-based assessments.

Physically based comparison of hot-carrier-induced and ionizing-radiation-induced degradation in BJTs

Abstract: A physically based comparison between hot-carrier and ionizing radiation stress in BJTs is presented. Although both types of stress lead to qualitatively similar changes in the current gain of the device, the physical mechanisms responsible for the degradation are quite different. In the case of hot-carrier stress the damage is localized near the emitter-base junction, which causes the excess base current to have an ideality factor of two. For ionizing radiation stress, the damage occurs along all oxide-silicon interfaces, which causes the excess base current to have an ideality factor between one and two for low total doses of ionizing radiation, but an ideality factor of two for large total doses. The different physical mechanisms that apply for each type of stress imply that improvement in resistance to one type of stress does not necessarily imply improvement in resistance to the other type of stress. Based on the physical model, implications for correlating and comparing hot-carrier-induced and ionizing-radiation-induced damage are discussed. >

Analysis of X-ray Absorption Spectra of Some Nickel Oxycompounds Using Theoretical Standards

Abstract: X-ray absorption spectra have been measured for NiO, β-Ni(OH)2, α-Ni(OH)2, LiNiO2, and KNiIO6 samples, which contain nickel with valency in the range 2−4. Information on the local structure and nature of bonding of nickel compounds has been derived using theoretical standards generated with the FEFF code. The Ni K-edge energy was found to shift to higher values by about 1.5 eV per unit change in valency of nickel. The energy of the preedge peak (generally attributed to the transition from the 1s core states to the 3d unoccupied states) shifts to higher values by about 0.6 eV per unit change in valency of nickel. A many body amplitude reduction factor ( ) of 0.77 ± 0.03 for Ni K-edge absorption can be used to scale theoretical spectra to fit the experimental ones in order to accurately determine the coordination numbers for compounds with complex structures. Our results show that chemical effects are very small and can be ignored for reliable structural analysis. Results of local structure for the first, s...