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Institution

Naval Surface Warfare Center

FacilityWashington D.C., District of Columbia, United States
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: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors extended the previous vibration based damage detection method by using Operating Deflection Shape (ODS) derived from experimental Frequency Response Function (FRF) data to detect the locations and extent of damage in steel beams, composite beams and plate-like structures.
Abstract: The present study extends the previous vibration based damage detection method (Yoon et al. in J. Nondestruct. Eval., 2008) by using Operating Deflection Shape (ODS) derived from experimental Frequency Response Function (FRF) data to detect the locations and extent of damage in steel beams, composite beams and plate-like structures. The present method requires to use FRF data obtained only from the damaged structure based on an assumption that the undamaged structure is homogeneous and smooth. The procedure uses the Global Fitting Method (GFM) that fits a smooth and analytic ODS to the measured ODS. Both the analytic and measured ODS are differentiated twice to yield the Curvature Operating Shapes (COS). The Structural Irregularity Index (SII) at each grid point on the structures is the difference between the analytic and measured COS. The procedure is repeated for each frequency in the FRF. Then, SII are averaged over the selected frequencies to obtain the frequency-averaged SII, which are statistically treated to locate damage. The present method is originally developed for one-dimensional (1D) beam models but can be extended further to any two-dimensional (2D) plate-like models by adding the results in the horizontal and/or vertical directions. The present method using experimental FRF successfully identified the locations and extents of the notches in steel beams, delaminations in the composite beams and plates, and dry spots in a composite hull structure. The present method is compared with different damage detection methods and showed improved performance in terms of detecting damage and computation cost. The present method also showed improved performances when ODS rather than mode shapes (MS) data are used.

53 citations

Journal ArticleDOI
01 Nov 2013-Carbon
TL;DR: In this article, Ar+ ions were used to create a larger density of surface defects, which were then characterized by X-ray photoelectron spectroscopy and near-edge x-ray absorption fine structure analysis.

52 citations

Proceedings ArticleDOI
Alex Askari1, R.A. Stark1, Joseph Curran1, Donald Rule1, Kevin Lin1 
13 May 2015
TL;DR: In this article, the effects of seawater conductivity on underwater resonant wireless power transfer, compared to the basic system concepts exhibited in air, are investigated. And the results indicate that the losses due to seawater become noticeable for frequencies around 20 kHz, and can be large for frequencies above 50 kHz.
Abstract: The feasibility of transferring power over a wide range of distances and orientation offsets has been proven in air for various commercial applications, notably in the electric vehicle industry, by using two loosely-coupled RLC circuits that are tuned to resonate at the same frequency. Key system concepts for resonant wireless power transfer, such as frequency splitting, maximum operating distance, and behavior of the system as it becomes over and under coupled, are well understood theoretically, and demonstrated experimentally. Although prior work on WPT in air is quite extensive and mature, very little research has been conducted on underwater WPT. In particular, no studies have been published describing how basic system concepts vary within a conducting medium such as seawater. In this paper, we report the results of experiments addressing the effects of seawater conductivity on underwater resonant wireless power transfer, compared to the basic system concepts exhibited in air. Results indicate that the losses due to seawater become noticeable for frequencies around 20 kHz, and can be large for frequencies above 50 kHz.

52 citations

Journal ArticleDOI
TL;DR: In situ X-ray absorption spectroscopy study of phases shows that the Ni K edge continuously shifts to higher energies with a decrease in Li content in a manner consistent with oxidation of Ni(III) to Ni(IV) as discussed by the authors.
Abstract: In situ X‐ray absorption spectroscopy study of phases shows that the Ni K edge continuously shifts to higher energies with a decrease in Li content in a manner consistent with oxidation of Ni(III) to Ni(IV) The Ni K‐edge energy for is consistent with that observed for chemically prepared quadrivalent Ni in . Variations in the coordination numbers, bond lengths, and disorders as a function of state of charge (i.e., the value of x) are consistent with the following facts: (i) a Jahn‐Teller distortion for Ni(III), (ii) an undistorted environment for Ni(IV), and (iii) an electrochemical oxidation of Ni(III) to Ni(IV). © 2000 The Electrochemical Society. All rights reserved.

52 citations

Journal ArticleDOI
TL;DR: In this paper, the conditional probability density function (pdf) is developed for each monopulse measurement of a Rayleigh target by conditioning the pdf of the complex monopulse ratio on the measured amplitude of the sum signal.
Abstract: The conditional probability density function (pdf) is developed for each monopulse measurement of a Rayleigh target by conditioning the pdf of the complex monopulse ratio on the measured amplitude of the sum signal. The conditional pdf is used to develop the conditional Cramer-Rao Lower Bound (CRLB) for any unbiased estimator of the direction-of-arrival (DOA). Conditional maximum likelihood (CML) and conditional method of moments (CMM) estimators of the DOA are developed along with estimates of the variances associated with the monopulse ratio and DOA estimate. Using simulation results, the performances of the CML and CMM estimators of the DOA are compared with the performance of standard monopulse ratio and the performances of the variance estimators are also studied.

52 citations


Authors

Showing all 2860 results

NameH-indexPapersCitations
James A. Yorke10144544101
Edward Ott10166944649
Sokrates T. Pantelides9480637427
J. M. D. Coey8174836364
Celso Grebogi7648822450
David N. Seidman7459523715
Mingzhou Ding6925617098
C. L. Cocke513128185
Hairong Qi503279909
Kevin J. Hemker4923110236
William L. Ditto431937991
Carey E. Priebe434048499
Clifford George412355110
Judith L. Flippen-Anderson402056110
Mortimer J. Kamlet3910812071
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20233
20227
202172
202071
201982
201884