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.

Selectivity and efficiency of pyrene attachment to polyethylene films by bombardment with MeV-range protons

Abstract: We demonstrate the attachment of pyrene molecules to chains of polyethylene (PE) films using 1−4.5 MeV-range protons (H+). Despite the enormous energy available for reaction, the attachment is exceedingly selective; MeV-range protons lead to photochemistry as selective as that initiated by eV-range photons (>300 nm). The effects of proton kinetic energy, proton dose, polymer crystallinity, and initial pyrene concentration within the films on the selectivity of the attachment process are analyzed on the basis of UV/vis absorption spectroscopy, steady state and dynamic fluorescence measurements, and differential scanning calorimetry. Attachment selectivity is independent of proton kinetic energy but increases with decreasing proton dose. The efficiency of pyrenyl attachment increases with decreasing polymer crystallinity. In polyethylene of 42 % crystallinity, the efficiency of attachment is only slightly dependent on pyrene dopant concentration (in the range 10-4−10-2 mol/kg) at low doses but increases sig...

Comparison of Incoherent and Coherent Wave Field Measurements Using Dual-Polarized Pulse-Doppler X-Band Radar

Abstract: Radar-based remote sensing for measurement of ocean surface waves presents advantages over conventional point sensors such as wave buoys. As its use becomes more widespread, it is important to understand the sensitivity of the extracted wave parameters to the characteristics of the radar and the scatterers. To examine such issues, experiments were performed offshore of the Scripps Institution of Oceanography pier in July 2010. Radar measurements in low wind speeds were performed with a dual-polarized high-resolution X-band pulse-Doppler radar at low grazing angles along with two independent measurements of the surface waves using conventional sensors, a GPS-based buoy, and an ultrasonic array. Comparison between radar cross section (RCS) and Doppler modulations shows peak values occurring nearly in-phase, in contrast with tilt modulation theory. Spectral comparisons between Doppler-based and RCS-based spectra show that Doppler-based spectra demonstrate greater sensitivity to swell-induced modulations, whereas RCS-based spectra show greater sensitivity to small-scale modulations (or generally have more noise at high frequency), and they equally capture energy at the wind wave peak. Doppler estimates of peak period were consistent with the conventional sensors, whereas the RCS differed in assignment of peak period to wind seas rather than swell in a couple of cases. Higher order period statistics of both RCS and Doppler were consistent with the conventional sensors. Radar-based significant wave heights are lower than buoy-based values and contain nontrivial variability of ∼33%. Comparisons between HH and VV polarization data show that VV data more accurately represent the wave field, particularly as the wind speeds decrease.

Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces.

Abstract: Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate’s boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation.

Novel metal-matrix composites with integrally-bound nanoscale carbon

Abstract: : We characterized the chemical, thermophysical, and mechanical properties of nanomaterials with up to 5 wt% nanocarbon (aka covetics) in aluminum and copper metals. The nanocarbon is detectable by EDS and XPS but not by analytical methods such as LECO and GDMS. Nanocarbon raises the melting point and significantly alters surface tension, and thus porosity, during solidification. Open questions remain about the observation of higher density than would be predicted by the rule of mixtures. In aluminum alloys, we observed an increase in as-rolled strength and hardness with increasing amounts of nanocarbon. In copper, thermal conductivity was anisotropic: up to 50% higher in the extrusion direction and at least 25% lower in the transverse direction,and was different between transient and steady state test conditions. In aluminum, we observed a significant increase in electrical conductivity with nanocarbon, from 47 to 67% IACS. These materials are commercially promising because they are produced by conversion of inexpensive carbon powder to nanocarbon in the melt?paving the way for the production of nanomaterials in pyrometallurgical operations with economies of scale.

Fire-retardant characteristics of water-blown molded flexible polyurethane foam materials

Abstract: Polyurethane flexible foam materials have a wide range of industrial applications. These applications include flexible foams for packaging, polyurethane-based foam materials for seat cushions in buses, railways, the airline industry, prisons, and domestic bedding. There is a substantial need for the development of flexible molded foam materials with low heat release rates and smoke release rates. In this study, an extensive series of flexible, molded polyurethane seat cushion materials based on polymeric MDI and polyether polyols were prepared and further modified with commercially available flame retardant additives. The flame retardant behavior of these foam materials was evaluated using Cone Calorimeter (ASTM-E 1354), vertical Bunsen burner test for cabin and cargo component materials [FAR 25.853 (a), Appendix F, Part I, (a)(1)(i) and (a)(1)(ii)], and oil burner test for seat cushions [FAR 25.853 (c), Appendix F, Part IT]. Several formulations that passed the 12-second vertical Bunsen burner test were identified. These include the formulations modified with Firemaster(R) HP-36, Decabromodiphenyl oxide/antimony oxide/Firemaster(R) HP-36, Fyrol(R) FR-2, and Fyrol(R) FR-2/graphite powder. A formulation modified with Antiblaze(R)-230 and a cross-linking agent passed both 12-second and 60-second vertical Bunsen burner tests. But, all of these materials did not pass the oil burner tests for seat cushions. Using the cone calorimeter, materials with a reduction in peak heat release rate of up to 57% were prepared and with up to a fourfold increase in char residue in the cone. However, most FR formulations showed an increase in carbon monoxide and smoke generation. Lowest peak HRR data were obtained with Firemaster(R) HP-36/Sb2O3 and Dow Silicones(R) 1-9641 at 25 kW/m(2) and with Fyrol(R) FR2/cross-linker at 35 kW/m(2) exposure. It appears that there is no correlation between cone calorimeter results and vertical Bunsen burner test results.