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

Electrical distribution system power line characterization

Abstract: An impedance versus frequency characterization of a 60 Hz power distribution system has been performed from 30 Hz to 1 MHz. The impedance characterization involves both empirical and theoretical aspects utilizing transmission line theory. The characterization yielded transmission line attributes that determine the power distribution system's performance for auxiliary functions such as data propagation. Potential applications of the characterization include analyzing the applicability of a residential power distribution system for data communications.

Direct Method for Optimization of a Centrifugal Compressor Vaneless Diffuser

Abstract: A Direct Method for Optimization (DMO) is developed for investigating pressure rise and energy loss in a vaneless diffuser of a generic compressor used in shipboard air-conditioning systems. The scheme uses Reynolds Averaged Navier-Stokes (RANS) results and evaluates gradients of a predetermined objective function. The current Direct Method for Optimization differs from the popular Inverse Design Method in the process of obtaining final configurations and in the final configurations obtained. The Direct Method for Optimization achieves a final shape from maximizing/minimizing a nonlinear function; i.e., the objective function. Both gradient and non-gradient Direct Methods for Optimization are compared with respect to accuracy and efficiency.The coupled DMO/RANS optimization code is benchmarked using a plane turbulent diffuser also investigated by Zhang et al. using an adjoint method. The benchmark indicates that if a global optimum exists, the result should be independent of the methodologies or design parameters used.The DMO/RANS method is applied to redesign a 3-D centrifugal vaneless diffuser used in a modern generic compressor. The objective function is a composite function of the diffuser’s pressure rise and total energy loss. The new optimum diffuser has a minimum width at a location far beyond the conventional diffuser pinch point. The new diffuser also provides an efficient section for pressure recovery, which takes place after the minimum width location. Test data for the new diffuser validates the current approach at the design condition. Furthermore, improved performance is also recorded experimentally at off-design conditions for the optimized diffuser.Copyright © 2000 by ASME

Time-Dependent Model of RF Energy Propagation in Coupled Reverberant Cavities

Abstract: A simple time-dependent model for the analysis of RF energy propagation in coupled reverberant cavities is presented. The cumulative buildup and full exchange of radiated electromagnetic energy between coupled spaces are important issues for electronic systems compatibility in reverberant environments such as below-deck compartments in ships and aircraft cabins and bays. Based on conservation of average energy, the general model formulation is valid for both weak and strong couplings between the cavities caused by window materials, open apertures, closed and open hatches, seams, and cable/pipe penetrations through bulkheads. Application of the model is demonstrated using time-resolved received power measurements conducted in nested reverberation chambers.

Shack-Hartmann wavefront sensor testing of aero-optic phenomena

Abstract: Missile interceptor seeker windows undergo significant heating and stress during supersonic flight. These effects lead to window and flow field distortions that can significantly degrade the image quality on the seeker. We have applied a ShackHartmann wavefront sensor for measuring these effects in ground test. The Shack-Hartmann sensor measured the near-field intensity and phase distribution. Because these distributions are linear, relative (or flow on/flow off) measurements can be made where test instrumentation errors can be subtracted out. The image quality, or point spread function, can be computed from these near field measurements. This allows for measurement of the aero-optic quantities that are a simulation of flight conditions, and an accurate prediction of sensor end-to-end performance. In making point spread function predictions, it is first necessary to establish that the near-field measurements have sufficient accuracy and resolution. To this end a laboratory experiment was constructed that allows direct comparison between measured point spread function and wavefront sensor based predictions. Excellent results were observed with strong, high spatial frequency aberrations. The wavefront sensor was then applied to make measurements in supersonic flow. Tests have been conducted of simulated seeker windows at Mach 7 and 8 conditions, and time-resolved wavefront sensor measurements have been made in some conditions. While early results have significant facility induced vibration in some conditions. Nevertheless, aero-thermal window heating has been observed in low stress conditions.