Institution
Naval Surface Warfare Center
Facility•Washington 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: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.
Papers published on a yearly basis
Papers
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TL;DR: In this paper, a nanostructured WC-12 pct Co coating was synthesized using mechanical milling and high velocity oxygen fuel (HVOF) thermal spraying, and the variation of powder characteristics with milling time and the performance of the coatings were investigated using scanning electron microscopy, X-ray, transmission electron microscope (TEM), thermogravimetric analyzer (TGA), and microhardness measurements.
Abstract: A nanostructured WC-12 pct Co coating was synthesized using mechanical milling and high velocity oxygen fuel (HVOF) thermal spraying. The variation of powder characteristics with milling time and the performance of the coatings were investigated using scanning electron microscope (SEM), X-ray, transmission electron microscope (TEM), thermogravimetric analyzer (TGA), and microhardness measurements. There is no evidence that indicates the presence of an amorphous phase in the sintered WC-12 pct Co powder, and the binder phase in this powder is still crystalline Co. Mechanical milling of up to 20 hours did not lead to the formation of an amorphous phase in the sintered WC-12 pct Co powder. During the initial stages of the milling, the brittle carbide particles were first fractured into fragments and then embedded into the binder phase. This process gradually formed polycrystal nanocomposite powders of the Co binder phase and W carbide particles. The conventional cold welding and fracturing processes primarily occurred among the Co binder powders and polycrystal composite powders. The nanostructured WC-12 pct Co coatings, synthesized in the present study, consist of an amorphous matrix and carbides with an average particle diameter of 35 nm. The coating possesses an average microhardness of 1135 HV and higher resistance to indentation fracture than that of its conventional counterpart.
91 citations
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01 Sep 1996TL;DR: In this article, a detailed analysis of the Wigner and pseudo-Wigner distributions (PWDs) is presented, along with three-dimensional (3D) plots of 3D plots of Wigners.
Abstract: Time series data have been traditionally analyzed in either the time or the frequency domains. For signals with a time-varying frequency content, the combined time-frequency (TF) representations, based on the Cohen class of (generalized) Wigner distributions (WD's) offer a powerful analysis tool. Using them, it is possible to: (1) trace the time-evolution of the resonance features usually present in a standard sonar cross section (SCS), or in a radar cross section (RCS) and (2) extract target information that may be difficult to even notice in an ordinary SCS or RCS. After a brief review of the fundamental properties of the WD, we discuss ways to reduce or suppress the cross term interference that appears in the WD of multicomponent systems. These points are illustrated with a variety of three-dimensional (3-D) plots of Wigner and pseudo-Wigner distributions (PWD). The plots are all obtained from an extensive analysis we have made over the years of the resonance acoustic echoes backscattered by a variety of elastic shells submerged in water, when they are excited by various types of incident pressure waves, including the short pulses generated by explosive charges. We also review studies we have made of the echoes returned by conducting or dielectric targets in the atmosphere, when they are illuminated by broadband radar pings. These short incident pulses are used to analytically model the performance of ultrawide band (UWB) radars, often called impulse radars. A TF domain analysis of these impulse radar returns demonstrates their superior information content.
91 citations
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91 citations
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TL;DR: In this article, a flux-weakening control specifically designed for surface-mounted permanent magnet machines is presented. But the proposed method does not require knowledge of the machine or system parameters and is not suitable for high-speed machines.
Abstract: Permanent-magnet synchronous machines fed from current-regulated converters feature nearly ideal performance at low-to-moderate speeds. However, as rotor speed increases the back emf rises which results in loss of current regulation and decreased torque. In buried-magnet machine drives, flux weakening is often used to extend the speed range. This paper sets forth a flux-weakening control specifically designed for surface-mounted permanent-magnet machines which is simple and does not require knowledge of the machine or system parameters. The proposed method is demonstrated both experimentally and through the use of computer simulation. >
90 citations
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TL;DR: This study designs a three cell, class 2 tensegrity swimmer, uses a graphical design method to construct and test the closed-loop system, and performs perturbed tests of the swimmer to illustrate the robustness of CPG control.
Abstract: Rhythmic motion employed in animal locomotion is ultimately controlled by neuronal circuits known as central pattern generators (CPGs). It appears that these controllers produce efficient, oscillatory command signals by entraining to an efficient or economic gait via sensory feedback. This property is of great interest in the control of autonomous vehicles. The objective of this study is to experimentally validate synthesized CPG control of a tensegrity swimmer. The prestressed cables in a tensegrity structure provide a method of simultaneous actuation and sensing, analogous to the biological motor control mechanism of regulating muscle stiffness through motoneuron activation and sensing the resulting motion by stretch receptors. A three cell, class 2 tensegrity swimmer is designed and built, and open-loop control tests characterize its swimming performance. We then determine gaits for desired entrainment, and use a graphical design method to construct and test the closed-loop system. Lastly, we perform perturbed tests of the swimmer to illustrate the robustness of CPG control.
90 citations
Authors
Showing all 2860 results
Name | H-index | Papers | Citations |
---|---|---|---|
James A. Yorke | 101 | 445 | 44101 |
Edward Ott | 101 | 669 | 44649 |
Sokrates T. Pantelides | 94 | 806 | 37427 |
J. M. D. Coey | 81 | 748 | 36364 |
Celso Grebogi | 76 | 488 | 22450 |
David N. Seidman | 74 | 595 | 23715 |
Mingzhou Ding | 69 | 256 | 17098 |
C. L. Cocke | 51 | 312 | 8185 |
Hairong Qi | 50 | 327 | 9909 |
Kevin J. Hemker | 49 | 231 | 10236 |
William L. Ditto | 43 | 193 | 7991 |
Carey E. Priebe | 43 | 404 | 8499 |
Clifford George | 41 | 235 | 5110 |
Judith L. Flippen-Anderson | 40 | 205 | 6110 |
Mortimer J. Kamlet | 39 | 108 | 12071 |