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.

Boron and Polytetrafluoroethylene as a Fuel Composition for Hybrid Rocket Applications

Abstract: A composition consisting of 80% polytetrafluoroethylene and 20% boron (by weight) was considered as a potential high-density solid fuel mixture for mixed hybrid rocket propulsive applications. Constant-pressure strand burner experiments for the given formulation indicated a low-pressure self-deflagration limit of approximately 2.2 MPa (319 psia), and a burning rate correlation rb[cm/s]=0.042(P[MPa])0.531 was determined. Pressurized counterflow burner experiments conducted using pure oxygen revealed formation of surface char, which prevented measurement of solid fuel regression rates below 2 MPa, indicating an additional resistance for heat and mass transfer. Static-fired rocket motor experiments, conducted to determine the pressure and flow dependencies of the system, exhibited characteristic exhaust velocity efficiencies ranging from approximately 86 to 96%. Whereas classical hybrids do not have a strong dependence of fuel regression rate on pressure, a pressure dependence was observed in this system bel...

A Model for Transitions in Oxidation Regimes of ZrB2

Abstract: A mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as the temperature is varied from 600°C to 2500°C is presented. Available thermodynamic data and literature data for vapor pressures, oxygen permeability in boria, and viscosity of boria were used to evaluate the model. Three regimes and the temperatures of transition between them were identified. In the intermediate temperature regime, viz., 1000°C to 1800°C, good correspondence was obtained between theory and experiments for weight gain, recession, and scale thickness as functions of temperature and oxygen partial pressure. In this regime, the rate-limiting step is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base of the oxidation product. At lower temperatures, an external boria scale forms, but it was not found to contribute significantly to oxidation resistance. Comparison with literature data on recession is very good, but weight gain is predicted to be higher than experimentally observed unless flow of viscous boria is included. At higher temperatures, the boria is lost by evaporation, and the oxidation rate is limited by diffusion of molecular oxygen through the capillaries between nearly columnar blocks of the oxide MO2.; this regime is soon followed by a rapid acceleration of recession due to vaporization of the oxide MO2 itself.

On optimal synchronous and asynchronous track fusion

Abstract: In practice, multisensor systems use dissimilar sensors that may have different data rates. Such sensors may also have inherent delays due to multitasking as well as communication delays between the sensor platform and a remote central processing site. Track fusion algorithms are presented that are valid for asynchronous sensors (the sensors have different data rates and different delays) as well as synchronous sensors (all of the sensors take measurements at the same time and the same rate with no delays). The asynchronous track fusion problem is formulated and solved first. Then the synchronous track fusion problem is obtained as a special case of the asynchronous one. Finally, using simulated target tracks, the performance of the asynchronous track fusion (ASTF) algorithm is analyzed and compared to an existing track fusion algorithm. Different sensor data rates and communication delays are used in the simulations. It is found that the ASTF algorithm outperforms its counterpart and is able to handle relatively large communication delays. The results presented set the foundation for deriving optimal track fusion algorithms when taking into account realistic constraints such as sensors with different data rates and different communication and/or processing delays. The results can also be used as a benchmark to evaluate existing suboptimal track fusion algorithms.

Nanosecond and picosecond laser-induced cracking and ignition of single crystals of ammonium perchlorate

Abstract: Nanosecond and picosecond laser irradiations have been used to study the decomposition of ammonium perchlorate (NH4ClO4) crystals, a main component of propellants. Chlorate (NH4ClO3) decomposition product was detected via X-ray photoelectron spectroscopy. The decomposition is initiated amid associated mechanical deformations and microcracking processes occurring on a time scale commensurate with actual frequencies of energetic crystal decompositions pertinent to propellant combustion. Optical, scanning electron and atomic force microscopy methods have been applied to characterization of the laser-damage zones. Individual initiation or residual “hot spot” sites have been detected in the electron and atomic force microscope images, and are related to the cracking behaviour of the perchlorate allotropic phases. Evidence of the 240°C orthorhombic to rock-salt type cubic transformation was obtained in nanosecond laser irradiations through a remnant microstructure of ultrafine cracks whose intersection points marked an array of decomposition sites. A dislocation model description is given for the connected cracking and decomposition site observations.

Fire safety of composites in the US Navy

Abstract: Composite materials for marine applications offer the benefit of weight savings, corrosion resistance, and reduced life-cycle costs. The composite structures used in marine applications tend to be large, complex, and thick. As such, the use of low-temperature non-autoclave cure resins is desirable. The US Navy is presently using fire-retardant (brominated) vinyl-ester resin for some topside composite structures. These composites are produced by the vacuum-assisted resin transfer method. Brominated vinyl-ester resin generates dense heavy smoke with high yields of carbon monoxide. Acid gases such as hydrogen bromide are also produced. Several alternative resins with and without non-halogenated fire retardants have recently been evaluated by the Naval Surface Warfare Center, Carderock Division in small-scale fire test methods. These included cone calorimeter testing at three different fluxes of 25, 50, and 75 kW m−2. The summary of results, including smoke production rate and carbon monoxide yield, is presented for various vinyl-ester resins with and without additives. Brominated epoxy vinyl ester marked #1168 exhibited lower heat release rates but significantly higher smoke generation and CO yield than non-brominated vinyl esters. Of the additives studied, aluminum trihydrate (15 phr, #1196) shows a 20 and 25% decrease in peak heat release rates, 24 and 13% decrease in average heat release rates, and 27 and 24% decrease in average mass loss rates at radiant heat fluxes of 50 and 75 kW m−2, respectively.