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.

Effect of intrinsic damping on vibration transmissibility of nickel-titanium shape memory alloy springs

Abstract: A research study was undertaken to measure the transmissibility of nickel-titanium (Ni-Ti) shape memory alloy (SMA) springs and to compare the results to corresponding data on steel and IN-CONEL springs. It was motivated by interest in an effective metal alternative to rubber-based machinery isolation mounts, with possible active control features. Ni-Ti was used due to its well-known properties of shape memory and high intrinsic damping. Acceleration transmissibility was measured on a spring-mass system. Due to the distributed mass in the spring coils, standing waves occurred at high frequencies. However, due to the high intrinsic damping in Ni-Ti, the standing wave resonance peaks were as much as 20 dB lower than corresponding peaks in steel and 1NCONEL springs. Thus, the capability of Ni-Ti springs for high frequency acoustic isolation is significantly better than that of steel or INCONEL. Also, it is judged that the Ni-Ti material could be used in a variety of other isolation mount designs with a high likelihood for further improvement in passive isolation properties. In addition, it may be possible to use the shape memory effect (SME) in active control concepts.

Dynamic mechanical relaxation in some polyurethanes

Abstract: Dynamic mechanical measurements of complex shear modulus versus frequency and temperature were made on a series of polyurethanes of varying soft-segment molecular weight. The time-temperature shifted data (master curves) mapped out the soft-segment glass transition. Shift factor curves were fitted to the Williams-Landel-Ferry (WLF) equation to obtain shift constants. The fractional free volume and coefficient of thermal expansion at the glass transition, determined from the shift constants, decrease as the molecular weight increases. Master curves were fitted to the modified Havriliak-Negami equation and the fitting parameters related to molecular structure. The limiting low-frequency modulus is dependent on the soft-segment molecular weight and percent crystallinity, but the limiting high-frequency modulus is about the same for all these polymers. The average relaxation time decreases with increasing soft-segment molecular weight and is correlated with glass transition temperature.

Derivation of a Signed Cameron Decomposition Asymmetry Parameter and Relationship of Cameron to Huynen Decomposition Parameters

Abstract: An alternate definition of the asymmetry parameter τ, appearing in the Cameron decomposition is presented. The new definition is signed as τs, but in absolute value, it is equivalent to the previous definition. The Cameron decomposition signed asymmetry parameter τs is given in terms of the Huynen decomposition parameters, including but not limited to the Huynen helicity (asymmetry) parameter. It is demonstrated that the Huynen decomposition asymmetry parameter is a poor indicator of scatterer symmetry. The relationship between the Cameron and Huynen decomposition parameters is examined for special cases.

Large-eddy simulations of plasma-based asymmetric control of supersonic round jets

Abstract: Localised arc filament plasma actuators are modelled with a validated technique to examine asymmetric control of a perfectly expanded round free jet to deflect its downstream trajectory. The nominal Mach and Reynolds numbers are 1.3 and 1 million, respectively. No-control, symmetrically controlled, and under-expanded jets are also simulated for comparison purposes. Parametric variation of actuation frequency and duty cycle indicate that asymmetric control can alter the trajectory, and, within the confines of the parameters investigated, the optimal forcing scheme was found to correspond to the jet's column-mode frequency and a duty cycle of approximately 60%. Increasing frequency and duty cycle beyond these values have a detrimental effect on control, which is consistent with experimental findings. Asymmetric actuation resulted in significant mixing enhancement on the actuated side, as evidenced by the increased growth rate of the non-dimensional momentum thickness. The effectiveness of control is reduced for under-expanded jet conditions.

Detection of counterfeit electronic components through ambient mass spectrometry and chemometrics.

Abstract: In the last several years, illicit electronic components have been discovered in the inventories of several distributors and even installed in commercial and military products. Illicit or counterfeit electronic components include a broad category of devices that can range from the correct unit with a more recent date code to lower-specification or non-working systems with altered names, manufacturers and date codes. Current methodologies for identification of counterfeit electronics rely on visual microscopy by expert users and, while effective, are very time-consuming. Here, a plasma-based ambient desorption/ionization source, the flowing atmospheric pressure afterglow (FAPA) is used to generate a mass-spectral fingerprint from the surface of a variety of discrete electronic integrated circuits (ICs). Chemometric methods, specifically principal component analysis (PCA) and the bootstrapped error-adjusted single-sample technique (BEAST), are used successfully to differentiate between genuine and counterfeit ICs. In addition, chemical and physical surface-removal techniques are explored and suggest which surface-altering techniques were utilized by counterfeiters.