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

Evaluation of hydrodynamic drag on experimental fouling-release surfaces, using rotating disks.

Abstract: Fouling by biofilms significantly increases frictional drag on ships' hulls. A device, the friction disk machine, designed to measure torque on rotating disks, was used to examine differences among experimental fouling-release coatings in the drag penalty due to accumulated biofilms. Penalties were measured as the percentage change in the frictional resistance coefficient Cf. Drag penalties due to microfouling ranged from 9% to 29%, comparable to previously reported values. An antifouling control coating showed a smaller drag penalty than the fouling-release coatings. There were also significant differences among the fouling-release coatings in drag due to biofilm formation. These results indicate that the friction disk machine may serve as a valuable tool for investigating the effects of experimental coatings, both antifouling and fouling-release, on microfouling and associated drag penalties.

Structure of Pt/Ru Catalysts Using X-ray Absorption Near Edge Structure Studies

Abstract: Pt/Ru catalysts with two very different structures were examined with X-ray absorption near edge structure (XANES). One sample was an industrial methanol fuel cell Pt/Ru alloy catalyst black, and the second was a carbon-supported Pt/Ru catalyst. In both cases the as-prepared Pt/Ru catalysts were found, with XANES, to be predominately in the form of Pt and Ru oxides. When these catalysts were placed in an electrochemical cell and held in the potential region where methanol oxidation occurs, XANES data indicate that the metal oxides were reduced to the metallic form. These results also demonstrate that conclusions about the electrocatalytic activity of Pt/Ru materials for methanol oxidation drawn from the characterization of as-prepared samples have little relevance.

Atomic structure of amorphous Al100-2xCoxCex (x=8, 9, and 10) and Al80Fe10Ce10 alloys: An XAFS study.

Abstract: The local atomic structure of Co, Fe, and Ce in aluminum-rich amorphous alloys of ${\mathrm{Al}}_{100\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$ (x=8, 9, and 10) and Ce in ${\mathrm{Al}}_{80}$${\mathrm{Fe}}_{10}$${\mathrm{Ce}}_{10}$ has been investigated by x-ray-absorption fine structure (XAFS) spectroscopy. The materials, 1- and 3-\ensuremath{\mu}m-thick films, were prepared by vapor quenching using the dc magnetron sputtering method. We show that the composition of the glass-forming region of these magnetron-sputtered alloys strictly follows the theoretical limit calculated on the basis of the atomic size criterion. From analyses of the XAFS data at the K edges of Co and Fe and the ${\mathit{L}}_{3}$ edge of Ce, the following conclusions with regard to local structure are made. The first coordination sphere of Co in ${\mathrm{Al}}_{100\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$ (x=8, 9, and 10) consists of 5.8 to 6.4 Al atoms at a distance of 2.44 \AA{}. The local coordination sphere for Fe in ${\mathrm{Al}}_{80}$${\mathrm{Fe}}_{10}$${\mathrm{Ce}}_{10}$ consists of 6.4 Al atoms at a distance of 2.47 \AA{}. Ce in both systems appears to be coordinated with roughly 5 and 9 Al atoms at distances of 2.95 and 3.15 \AA{}, respectively. These results are discussed in light of the dense random packing (DRP) of hard spheres model. Both Co-Al and Fe-Al bond lengths are anomalously short (9 and 8 % contraction, respectively) with also anomalously low coordination numbers (45% reduction) from values based on the DRP model using the metallic state radii.These anomalous changes indicate a strong interaction between Co or Fe atoms and the Al atoms which perhaps may be a result of a covalently bonded environment. The Ce-Al distance in both the Al-Co-Ce and Al-Fe-Ce systems, on the other hand, is smaller by only 0.17 \AA{} (a contraction of only 5%) and the coordination number is reduced by only 13% from expected values based on the DRP model. The contraction in the distance and reduction in the coordination number for Ce are much smaller than those values of the Co or Fe and, hence, the local bonding for Ce is likely to be metallic in character.

Dynamics of a two-frequency parametrically driven duffing oscillator

Abstract: We investigate the transition from two-frequency quasiperiodicity to chaotic behavior in a model for a quasiperiodically driven magnetoelastic ribbon. The model system is a two-frequency parametrically driven Duffing oscillator. As a driving parameter is increased, the route to chaos takes place in four distinct stages. The first stage is a torus-doubling bifurcation. The second stage is a transition from the doubled torus to a strange nonchaotic attractor. The third stage is a transition from the strange nonchaotic attractor to a geometrically similar chaotic attractor. The final stage is a hard transition to a much larger chaotic attractor. This latter transition arises as the result of acrisis, the characterization of which is one of our primary concerns. Numerical evidence is given to indicate that the crisis arises from the collision of the chaotic attractor with the stable manifold of a saddle torus. Intermittent bursting behavior is present after the crisis with the mean time between bursts scaling as a power law in the distance from the critical control parameter; τ ∼ (A-Ac)-α. The critical exponent is computed numerically, yielding the value α=1.03±0.01. Theoretical justification is given for the computed critical exponent. Finally, a Melnikov analysis is performed, yielding an expression for transverse crossings of the stable and unstable manifolds of the crisis-initiating saddle torus.

Development Process for Custom Three-Dimensional Printing (3DP) Material Systems

Abstract: The development of a new material system for three-dimensional printing (3DP) can be difficult without experience in the field, since the flexibility of the 3DP process implies a large number of material and processing parameters. This paper presents a detailed explanation of the steps involved in developing specific implementations of 3DP, along with tools and insight for each step. This material system development procedure should provide a clear understanding of the 3DP process steps and development decisions to help the user take advantage of the considerable flexibility of 3DP and expedite a new system development. The paper concludes with a demonstration of how the guidance provided is applied in the development of fully dense ceramic dental copings; a research problem uniquely suited to the flexibility of 3DP.