Naval Undersea Warfare Center

Newport, RI, United States

Naval Undersea Warfare Center

Newport, RI, United States

The Naval Undersea Warfare Center is the United States Navy's full-spectrum research, development, test and evaluation, engineering and fleet support center for submarines, autonomous underwater systems, and offensive and defensive weapons systems associated with undersea warfare. One of the corporate laboratories of the Naval Sea Systems Command, NUWC is headquartered in Newport, Rhode Island, and has two major subordinate activities — Division Newport and Division Keyport . NUWC also controls the Fox Island Facility and Gould Island.NUWC employs more than 4,400 civilian and military personnel, with budgets of over US$1 billion. Wikipedia.


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Truscott T.T.,Brigham Young University | Epps B.P.,Dartmouth College | Belden J.,Naval Undersea Warfare Center
Annual Review of Fluid Mechanics | Year: 2014

The free-surface impact of solid objects has been investigated for well over a century. This canonical problem is influenced by many physical parameters, including projectile geometry, material properties, fluid properties, and impact parameters. Through advances in high-speed imaging and visualization techniques, discoveries about the underlying physics have improved our understanding of these phenomena. Improvements to analytical and numerical models have led to critical insights into cavity formation, the depth and time of pinch-off, forces, and trajectories for myriad different impact parameters. This topic spans a wide range of regimes, from low-speed entry phenomena dominated by surface tension to high-speed ballistics, for which cavitation is important. This review surveys experimental, theoretical, and numerical studies over this broad range, utilizing canonical images where possible to enhance intuition and insight into the rich phenomena. Copyright © 2014 by Annual Reviews. All rights reserved.


Incze M.L.,Naval Undersea Warfare Center
Ocean Dynamics | Year: 2011

Lightweight Autonomous Underwater Vehicles (AUVs) were developed for Naval Special Warfare (NSW) Group 4 search and survey missions from a commercial AUV baseline (Iver 2) through integration of commercial off-the-shelf (COTS) hardware components, and through software development for enhanced on-board Command and Control functions. The development period was 1 year under a project sponsored by the Office of Naval Research TechSolutions Program Office. Hardware integration was completed by the commercial AUV vendor, OceanServer Technology, Inc., and software development was conducted by the Naval Undersea Warfare Center, Naval Oceanographic Office, and U MASS Dartmouth, with support from hardware and software application providers (YSI, Inc., Imagenex Technology Corp., and CARIS). At the conclusion of the integration and development period, an at-sea performance evaluation was scheduled for the Lightweight NSW AUVs with NSWG-4 personnel. The venue for this evaluation was the NATO exercise Recognized Environmental Picture 10A (REP 10A), hosted by Marinha Portuguesa, and coordinated by the Faculdade de Engenharia-Universidade do Porto. REP 10A offered an opportunity to evaluate the performance of the new AUVs and to explore the Concept of Operations (CONOPS) for employing them in military survey operations in shallow coastal waters. Shore- and ship-launched scenarios with launch/recovery by a single operator in a one-to-many coordinated survey, on-scene data product generation and visualization, data push to Reach Back Cells for product integration and enhancement, and survey optimization to streamline survey effort and timelines were included in the CONOPS review. Opportunities to explore employment of hybrid AUV fleets in Combined Force scenarios were also utilized. The Naval Undersea Warfare Center, Marinha Portuguesa, the Faculdade de Engenharia-Universidade do Porto, and OceanServer Technology, Inc., were the primary participants bringing in-water resources to REP 10A. Technical support and products were provided by the Naval Research Laboratory-Stennis Space Center, Naval Oceanographic Office, NATO Undersea Research Centre, University of Massachusetts-Dartmouth, and YSI, Inc. REP 10A proved to be a very effective exercise in meeting each of the critical goals. Results of the performance evaluation guided final development and Independent Verification and Validation (IV&V) for the Lightweight NSW AUV, leading to on-time, successful Factory Acceptance Testing and delivery of the three contracted vehicles to NSWG-4 in September, 2010. © 2011 Springer-Verlag (outside the USA).


Donovan G.T.,Naval Undersea Warfare Center
IEEE Journal of Oceanic Engineering | Year: 2012

This paper presents comprehensive testing and analysis of a particle filter (PF) framework for real-time terrain navigation on an autonomous underwater vehicle (AUV). The goal is to obtain georeferenced localization for an AUV navigation system using reference bathymetry maps and bathymetric measurements in lieu of Global Positioning System (GPS) updates or acoustic localization methods such as long baseline (LBL). The algorithms are tested using navigation and sensor data collected during a long-distance run of the midsize autonomous reconfigurable vehicle (MARV) AUV, during which the Inertial Navigation System (INS) accumulated significant horizontal position error (>100 m). Run data sets over areas of both high and low bathymetric relief are used to compare performance with different altitude sensors, including multibeam and single-beam sonar, and four-beam Doppler velocity logger (DVL) sonar. A comparison of established techniques for dealing with tide levels is also presented. The technique of adding a third dimension to the PF state vector to compensate for changing water levels allowed the estimator to work consistently in areas of low bathymetric relief, where relative terrain profiling methods broke down and even slight errors in tide prediction models otherwise caused significant position errors. The effects of decreased vertical resolution and accuracy of the reference map is also investigated. To address problems of insufficient sample size, a novel PF resampling technique is presented in which jittering noise added to duplicate samples is scaled based on the particle cloud volume. This technique allows the PF to consistently recover a position fix over a search area of several kilometers without needing to significantly increase the number of particles used. © 2012 IEEE.


Jordan S.A.,Naval Undersea Warfare Center
Physics of Fluids | Year: 2015

Notable deviations of the asymmetric turbulent boundary layer (TBL) statistics from their axisymmetric counterpart along long thin circular cylinders are vitally important to the naval and oceanographic jurisdictions. Although the available experimental evidence backs their concern, the realm of parametric variability (both geometric and kinematic) is extremely limited to draw solid conclusions. We know that only small misalignments which quantify less than one degree of incidence between the freestream and the straight cylinder axis can substantially alter the boundary layer thicknesses, mean axial velocity, and Reynolds stresses. But the statistical database is plainly inadequate to justify modifying the design tools that were founded solely for axisymmetric flow conditions. Herein, we begin rectifying this drawback by numerical means. The investigation centers on low turbulent Reynolds numbers (500 ≤ Rea ≤ 2500) and small angles-of-incidence (0° < α < 9°) to validate and complement the lions-share of the present database (Rea = aUo/ν, where a, Uo, and ν are the cylinder radius, freestream velocity, and kinematic viscosity, respectively). In particular, we numerically resolved the statistical responses of the TBL, mean axial velocity, Reynolds stresses, and skin friction under angles-of-incidence up to the earliest signs of Strouhal-type shedding. Clearly, the first prominent response was the thinning and thickening of the TBL along the respective windward and leeward sides to only a minor misalignment. Tilting the straight cylinder to slightly higher yaw angles transformed the TBL to a transitional boundary layer along the windward side for all simulated Reynolds numbers. For yaw angles α > 2°, all turbulent statistics of the asymmetric boundary layer were measurably dissimilar to those of the axisymmetric state. © 2015 U.S. Government.


Jordan S.A.,Naval Undersea Warfare Center
Journal of Fluids and Structures | Year: 2011

Understanding the salient physics within the turbulent boundary layer of towed thin cylinders is paramount to the Navy sonar array communities. However, the required long array length to achieve wide acoustic aperture creates unique and consistent flow characteristics that suggest simplified tangential forcing expressions suitable for design purposes. One well-known fact is that the majority of the array surface experiences very thick turbulent boundary layers (TBL) and large Reynolds numbers. The resultant statistics are most commonly dependent on the inner and outer length scales. Herein, we resolve the near-wall TBL structure under those flow conditions by large-eddy simulation. The turbulent mean-flow statistics showed near-wall consistency using only inner scaling. But both inner and outer variables were found necessary to properly scale the turbulent fluctuations. An expression for the tangential wall-friction coefficient (C t) indicates two distinct flow regimes as characterized by the near-wall turbulent flow structure. The respective parameters appear independent of the outer length scale. Thickening (or thinning) the cylinder near their common threshold (defined by a radius-based Reynolds number) transitioned the turbulent character between the two regimes. © 2010.


Jordan S.A.,Naval Undersea Warfare Center
Physics of Fluids | Year: 2011

The experimental evidence leads us to believe that long slender circular cylinders have similar axisymmetric turbulent statistics along most of their axial length. The respective boundary layer reaches a maximum thickness (δ) with no further downstream net growth. Despite their small radius (a), these long cylinders still own high radius-based Reynolds numbers (Rea) as well as transverse curvatures (δ/a). The influence of these flow conditions (and others) on the turbulent statistics is still chiefly unknown. The present effort begins an investigation that targets axial similarity (or homogeneity) of the long thin cylinder statistics. The database is a collection of previous experimental measurements and observations as well as the present computational results by the large-eddy simulation methodology. Interestingly, this investigation shows that reaching axial homogeneity is reliant essentially on Rea with lesser influence by the transverse curvature. But the Rea value depends on the turbulent statistic of interest. Likewise, this same result was found for spotting the radial location of the respective statistical peak. Axial homogeneity starts near the cylinder wall then migrates outward radially with increasing Rea until full saturation through the turbulent intermediate layer. © 2011 American Institute of Physics.


Jordan S.A.,Naval Undersea Warfare Center
Physics of Fluids | Year: 2013

Only a few engineering design models are presently available that adequately depict the axisymmetric skin friction (Cf) maturity along long thin turbulent cylinders. This deficit rests essentially on the experimental and numerical difficulties of measuring (or computing) the spatial evolution of the thin cylinder turbulence. Consequently, the present axisymmetric Cf models have questionable accuracy. Herein, we attempt to formulate a more robust Cf model that owns acceptable error. The formulation is founded on triple integration of the governing equation system that represents a thin cylinder turbulent boundary layer (TBL) at statistical steady-state in appropriate dimensionless units. The final model requires only the radius-based Reynolds number (Rea) and transverse curvature (δ/a) as input parameters. We tuned the accompanying coefficients empirically via an expanded statistical database (over 60 data points) that house new Cf values from large-eddy simulations (LES). The LES computations employed a turbulence inflow generation procedure that permits spatial resolution of the TBL at low-high Reynolds numbers and transverse curvatures. Compared to the new skin friction database, the Cf model revealed averaged predictive errors under 5% with a 3.5% standard deviation. Apart from owning higher values than the flat plate TBL, the most distinguishing characteristic of the axisymmetric skin friction is its rising levels when the boundary layer thickness exceeds the cylinder radius. All Cf levels diminish with increasing Reynolds number. These unique features differentiate the axisymmetric TBL along thin cylinders as a separate canonical flow when compared to the turbulent wall shear-layers of channels, pipes, and planar-type geometries. © 2013 U.S. Government.


Baggenstoss P.M.,Naval Undersea Warfare Center
Journal of the Acoustical Society of America | Year: 2011

In this paper an algorithm is described for the localization of individual sperm whales in situations where several near-by animals are simultaneously vocalizing. The algorithm operates on time-difference of arrival (TDOA) measurements observed at sensor pairs and assumes no prior knowledge of the TDOA-whale associations. In other words, it solves the problem of associating TDOAs to whales. The algorithm is able to resolve association disputes where a given TDOA measurement may fit to more than one position estimate and can handle spurious TDOAs. The algorithm also provides estimates of Cramer-Rao lower bound for the position estimates. The algorithm was tested with real data using TDOA estimates obtained by cross-correlating click-trains. The click-trains were generated by a separate algorithm that operated independently on each sensor to produce click-trains corresponding to a given whale and to reject click-trains from reflected propagation paths. © 2011 Acoustical Society of America.


Baggenstoss P.M.,Naval Undersea Warfare Center
Journal of the Acoustical Society of America | Year: 2011

In this paper an algorithm is described for grouping sperm whale clicks received at a single hydrophone into click-trains associated with a given whale and propagation path. To accomplish this, features are extracted from pairs of clicks in order to derive a statistical measure of click similarity. Then, the algorithm maximizes a global measure of similarity between the associated clicks. In addition to grouping clicks according to click-trains, it classifies click-trains into a propagation path (direct, surface, bottom reverberation). The propagation path is identified using a combination of (1) a statistical classifier operating on features extracted from individual clicks and (2) the cross-correlation of click-trains to identify the relative time delays. The algorithm is demonstrated on at-sea recorded data, showing the elimination of time-delay ambiguities associated with the reverberation paths observed at sensor pairs. © 2011 Acoustical Society of America.


Jordan S.A.,Naval Undersea Warfare Center
Physics of Fluids | Year: 2014

Useful empirical and semi-empirical models of the turbulent boundary layer (TBL) and skin friction evolution along planar geometries are not applicable for axisymmetric thin cylinder flows. Their dissimilarity is readily detectable once the TBL thickness exceeds the cylinder radius (a). Although several recent empirically based axisymmetric models recognize this fact, their acceptable fidelity is either restrictive or deficient for general applicability. Herein, we correct this deficit by building a simple model for the specific canonical class of axisymmetric turbulent flows along long thin cylinders with a zero streamwise pressure gradient. Streamwise growth of the TBL thickness (δ/a), integral scales [displacement (δ */a) and momentum thicknesses (δ/a)] and skin friction coefficient (Cf) can be estimated along the cylinder length via the respective axial mean velocity profile in wall units. This profile is given by Spalding's formula with algebraic expressions for the two input parameters (κ, κ β) that cover all turbulent Reynolds numbers. The necessary database for empirically tuning Spalding's parameters entails both experimental measurements and new numerical computations. Our present-day understanding of the axisymmetric TBL is replicated by the simple model where δ/a, δ */a, and θ/a grow slower than the planar-type flow with Cf comparatively elevating once δ/a > O(1). These differences manifest themselves in the radial impact imposed by the thin cylinder transverse curvature. Interestingly, the axial-based Reynolds numbers Rea ≈ 7500 and a+ ≈ 350 at δ/a ≈ 21 mark earliest signs of a homogeneous streamwise state (constant Cf) near the cylinder wall. Owning a simple model of axisymmetric turbulent flows along thin cylinders eliminates expensive and timely experiments and/or computations. Its practicality targets both the Naval and oceanographic communities.

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