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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, a smooth flat-plate turbulent boundary layer (TBL) was measured at nominal Reθ values of 0.5 × 105, 1.0 × 105 and 1.5× 105.
Abstract: Smooth flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century. However, there is a relative dearth of measurements at Reynolds numbers typical of full-scale marine and aerospace transportation systems (Reθ = Ueθ/ν > 105, where Ue = free-stream speed, θ = TBL momentum thickness and ν = kinematic viscosity). This paper presents new experimental results for the TBL that forms on a smooth flat plate at nominal Reθ values of 0.5 × 105, 1.0 × 105 and 1.5 × 105. Nominal boundary layer thicknesses (δ) were 80–90mm, and Karman numbers (δ+) were 17000, 32000 and 47000, respectively. The experiments were conducted in the William B. Morgan Large Cavitation Channel on a polished (k+ 2δ. To within experimental uncertainty, the measured mean velocity profiles can be fit using traditional zero-pressure-gradient (ZPG) TBL asymptotics with some modifications for the mild favourable pressure gradient. The fitted profile pairs satisfy the von-Karman momentum integral equation to within 1%. However, the profiles reported here show distinct differences from equivalent ZPG profiles. The near-wall indicator function has more prominent extrema, the log-law constants differ slightly, and the profiles' wake component is less pronounced.

35 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the scattering of plane acoustic waves by spherical objects near a plane hard surface and used the method of images to predict the distorted sonar cross section of a hard spherical object near a hard flat bottom.
Abstract: We consider the scattering of plane acoustic waves by spherical objects near a plane hard surface. The angles of incidence are arbitrary and so are the distances of the objects from the hard boundary. We use the method of images. The final result for the sound field consists of four parts: the incident field and its reflection from the boundary, which are shown combined; the scattered field from the sphere, and that scattered by its image. These last two appear coupled since both sphere and image are repeatedly interacting with each other. The entire solution is referred to the center of the real sphere. This can be accomplished in an exact fashion by means of the addition theorems for spherical wave-functions. These theorems are taken from the atomic physics literature, where they are more frequently used. The required coupling coefficients, b/sub mn/, are obtained from the solution of an infinite linear complex system of transcendental equations with coefficients given by series. The system is suitably truncated to obtain numerical predictions for the form-functions by means of the Gauss-Seidel iteration method. Many calculations are displayed exhibiting the distortion that the proximity of the hard boundary causes on the free-space solution. The form-functions are graphed versus ka, for various values of the normalized separation D/spl equiv/d/a of the sphere from its image. They are also plotted versus the angle of observation, for fixed values of /spl Omega/=La and D. These plots are the exact benchmark curves against which the accuracy of approximate solutions, found by other methods, could be assessed. They could also serve to determine the distances above the bottom, beyond which the bottom effect could be neglected. This is an idealized model to predict the distorted sonar cross section of a hard spherical object near a hard flat bottom.

35 citations

Proceedings ArticleDOI
01 Jul 2012
TL;DR: In this article, the simulation results of a simulation of a bare hull DARPA SUBOFF submarine were used to predict the flow field around the hull and the forces and moments for several steady turns.
Abstract: The application of viscous-flow solvers to calculate the forces on ship hulls in oblique motion has been studied for a long time. However, only a few researchers have published work in which the flow around ships in steady turns was studied in detail. To predict ship manoeuvres, an accurate prediction of the loads due to rotational motion is also required. In a collaborative CFD exercise, the Submarine Hydrodynamics Working Group (SHWG) performed calculations on the bare hull DARPA SUBOFF submarine to investigate the capability of RANS viscous-flow solvers to predict the flow field around the hull and the forces and moments for several steady turns. In the study, different commercial as well as bespoke flow solvers were used, combined with different turbulence models and grid topologies. The work is part of a larger study aiming to improve the knowledge and understanding of underwater vehicle hydrodynamics. In this paper, the results of the exercise will be presented. For several cases, verification studies are done to estimate the uncertainties in the results. Flow fields predicted by the different members of the SHWG are compared and the influence of the turbulence model will be discussed. Additionally, the computed forces and moments as a function of the drift angle during the steady turns will be validated. It will be demonstrated that using sufficiently fine grids and advanced turbulence models without the use of wall functions will lead to accurate prediction of both the flow field and loads on the hull.© 2012 ASME

35 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented two approaches to simulate maneuvers of a model radio-controlled submarine, in the direct simulation approach and in the coupled approach, where the overset computational fluid dynamics (CFD) solver and a potential flow propeller code exchanged velocities at the propeller plane and wake.
Abstract: This article presents two approaches to simulate maneuvers of a model radio-controlled submarine In the direct simulation approach, rudders, stern planes, and propellers are gridded and treated as moving objects using dynamic overset technology The second approach couples the overset computational fluid dynamics (CFD) solver and a potential flow propeller code, with both codes exchanging velocities at the propeller plane and wake, body forces, and propeller forces and moments, whereas rudders and stern planes are still explicitly resolved It is shown that during the maneuvers, the range of advance coefficients does not deviate much from the design point, making a coupled approach a valid choice for standard maneuvering simulations By allowing time steps about an order of magnitude larger than for the direct simulation approach, the coupled approach can run about five times faster The drawback is a loss of resolution in the wake as the direct propeller simulation can resolve blade vortical structures Open water propeller curves were simulated with both the direct propeller approach and the coupled approach, showing that the coupled approach can match the direct approach performance curves for a wide range of advance coefficients Simulations of a horizontal overshoot maneuver at two approach speeds were performed, as well as vertical overshoot and controlled turn maneuvers at high speed Results show that both CFD approaches can reproduce the experimental results for all parameters, with errors typically within 10%

35 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effects of the size of hollow glass microspheres (20 μm vs. 40 μm) and composition on the energy absorption capacity of the silicate glass foams under both the quasistatic and high-strain rate (∼10^(−3) s^( −1)) loading conditions.
Abstract: This study investigates the effects of the size of hollow glass microspheres (20 μm vs. 40 μm) and composition on the energy absorption capacity of the silicate glass foams under both the quasistatic (∼10^(−3) s^(−1)) and high-strain rate (∼10^3 s^(−1)) loading conditions. These measurements revealed that while the size difference of the hollow glass microspheres and the foam composition have negligible effects on the uniaxial quasistatic response, their effects were significant under the dynamic loading conditions. The results suggest that the smaller glass microspheres (20 μm) dominated the dynamic behavior of the glass foams in comparison to the larger glass microspheres (40 μm), leading to a significant increase of the energy absorption capacity of the 20 μm-based glass foams at high-strain rates. Glass foams exhibited energy absorption capacity of about 54 kJ/kg under the dynamic loading that is greater in comparison to that of the typical metallic and syntactic foams.

35 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