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.

Detecting impact damage in experimental composite structures: an information-theoretic approach

Abstract: This work describes a procedure for detecting the presence of damage-induced nonlinearities in composite structures using only the structure's vibrational response. Damage is assumed to change the coupling between different locations on the structure from linear to nonlinear. Utilizing concepts from the field of information theory, we are able to deduce the form of the underlying structural model (linear/nonlinear), and hence detect the presence of the damage. Because information theoretics are model independent they may be used to capture both linear and nonlinear dynamical relationships. We describe two such metrics, the time delayed mutual information and time delayed transfer entropy, and show how they may be computed from time series data. We make use of surrogate data techniques in order to place the question of damage in a hypothesis testing framework. Specifically, we construct surrogate data sets from the original that preserve only the linear relationships among the data. We then compute the mutual information and the transfer entropy on both the original and surrogate data and quantify the discrepancy in the results as a measure of nonlinearity in the structure. Thus, we do not require the explicit measurement of a baseline data set. The approach is demonstrated to be effective in diagnosing the presence of impact damage in a thick composite sandwich plate. We also show how the approach can be used to detect impact damage in a composite UAV wing subject to ambient gust loading.

Development of a tip-leakage flow - Part 1: The flow over a range of Reynolds numbers

Abstract: An extensive experimental investigation was carried out to examine the tip-leakage flow on ducted propulsors The flow field around three-bladed, ducted rotors operating in uniform inflow was measured in detail with three-dimensional laser Doppler velocimetry and planar particle imaging velocimetry Two geometrically similar, ducted rotors were tested over a Reynolds number range from 07 × 10 6 to 92 × 10 6 in order to determine how the tip-leakage flow varied with Reynolds number An identification procedure was used to discern and quantify regions of concentrated vorticity in instantaneous flow fields Multiple vortices were identified in the wake of the blade tip, with the largest vortex being associated with the tip-leakage flow, and the secondary vortices being associated with the trailing edge vortex and other blade-wake vortices The evolution of identified vortex quantities with downstream distance is examined It was found that the strength and core size of the vortices are weakly dependent on Reynolds number, but there are indications that they are affected by variations in the inflowing wall boundary layer on the duct The core size of the tip-leakage vortex does not vary strongly with varying boundary layer thickness on the blades Instead, its dimension is on the order of the tip clearance There is significant flow variability for all Reynolds numbers and rotor configurations Scaled velocity fluctuations near the axis of the primary vortex increase significantly with downstream distance, suggesting the presence of spatially uncorrelated fine scale secondary vortices and the possible existence of three-dimensional vortex-vortex interactions

Quality-Assisted Multi-Objective Multidisciplinary Genetic Algorithms

Abstract: A new method is presented to solve multi-objective multidisciplinary optimization (M-MDO) problems. This M-MDO method is applicable to multi-objective optimization problems that can be decomposed hierarchically into multi-objective subproblems and whose objective functions are either separable or additively separable. In the decomposition, the subproblems may have both common and unique objectives. The method uses a multiobjective genetic algorithm (MOGA) to optimize the multi-objective subproblems; hence, it is referred to as a multi-objective multidisciplinary genetic algorithm (M-MGA). It is shown that for any Pareto point of the original (single-level) problem, M-MGA generates at least one point that is noninferior with respect to that Pareto point. Also a comparison is shown between the computational complexity of M-MGA and a single-level MOGA in terms of number of functions calls. The M-MGA is demonstrated by two engineering examples: the design of a speed reducer and the design of a payload for an undersea autonomous vehicle. In both examples, the generated solutions are similar to solutions generated by solving the examples as single-level problems. M-MGA produces relatively the same solutions from one M-MGA run to another.

Interacting multiple bias model algorithm with application to tracking maneuvering targets

Abstract: The interacting multiple bias model (IMBM) algorithm is presented as an approach to state estimation for systems with Markovian switching coefficients that can be isolated to a system bias. The IMBM algorithm utilizes the interacting multiple model (IMM) algorithm and recent developments in two-stage state estimation. The IMBM algorithm is well suited for tracking maneuvering targets, where the target acceleration is modeled as a system bias. This algorithm is called the interacting multiple acceleration model (IMAM) algorithm. Simulation results for comparing the performances of the IMM and IMAM algorithms are given, together with a computational count for the two algorithms which indicate that the IMAM algorithm requires approximately 43% of the computations of the IMM algorithm when a constant velocity and two constant accelerations models are used. >

Mechanical behavior and properties of mechanically alloyed aluminum alloys

Abstract: The fracture and deformation behaviors of several product forms produced from mechanically alloyed (MA) aluminum alloys 9052 and 905XL were studied. The main operative strengthening mechanism is strengthening due to the submicron grain size. Ductility and toughness were found to be controlled by the morphology of the prior particle boundaries. We propose that the work-hardening behavior of these MA alloys is similar to the behavior exhibited by a deformed fcc alloy that (a) contains rigid barriers to dislocation motion, (b) deforms by wavy slip, and (c) forms a cell substructure upon deformation.