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Wright-Patterson AFB, OH, United States

The Air Force Institute of Technology is a graduate school and provider of professional and continuing education for the United States Armed Forces and is part of the United States Air Force. It is located in Ohio at Wright-Patterson Air Force Base, near Dayton. Wikipedia.


Torvik P.J.,Air Force Institute of Technology
Journal of Sound and Vibration | Year: 2011

As damping determines the maximum vibratory response of a system at resonance, reliable estimates of damping are critical both to the design and qualification of systems to be subjected to a vibratory environment and for the evaluation of the effectiveness of modifications or additions provided to increase damping. The sharpness of the frequency response at resonance is often used for this purpose, quantified by the width of the frequency range (bandwidth) for which the response is above some fraction of the maximum response. Several aspects of the use of bandwidth methods in interpreting test results are considered. It is shown that the use of an excessive rate of change of test frequency in a sine sweep leads to overestimates of system damping. A criterion is offered for the identification of the maximum sweep rate for which an observed frequency response function provides a true indication of system damping, rather than an erroneous value dominated by the sweep rate. Applicability of the criterion is demonstrated through the use of results from actual tests. Excessive sweep rates are shown to inflate estimates of system loss factors above the true values in proportion to the square root of the sweep rate. It is also demonstrated with a specific form for an amplitude-dependent stiffness that the resulting nonlinearity can lead to erroneous observations of bandwidth frequencies, as well as the need for further reductions in the sweep rate. © 2011 Elsevier Ltd. All rights reserved. Source


Freris N.M.,University of Illinois at Urbana - Champaign | Graham S.R.,Air Force Institute of Technology | Kumar P.R.,University of Illinois at Urbana - Champaign
IEEE Transactions on Automatic Control | Year: 2011

We characterize what is feasible concerning clock synchronization in wireline or wireless networks. We consider a network of n nodes, equipped with affine clocks relative to a designated clock that exchange packets subject to link delays. Determining all unknown parameters, i.e., skews and offsets of all the clocks as well as the delays of all the communication links, is impossible. All nodal skews, as well as all round-trip delays between every pair of nodes, can be determined correctly. Also, every transmitting node can predict precisely the time indicated by the receiver's clock at which it receives the packet. However, the vector of unknown link delays and clock offsets can only be determined up to an (n-1)-dimensional subspace, with each degree of freedom corresponding to the offset of one of the (n-1) clocks. Invoking causality, that packets cannot be received before they are transmitted, the uncertainty set can be reduced to a polyhedron. We also investigate structured models for link delays as the sum of a transmitter-dependent delay, a receiver-dependent delay, and a known propagation delay, and identify conditions which permit a unique solution, and conditions under which the number of the residual degrees of freedom is independent of the network size. For receiver-receiver synchronization, where only receipt times are available, but no time-stamping is done by the sender, all nodal skews can still be determined, but delay differences between neighboring communication links with a common sender can only be characterized up to an affine transformation of the (n-1) unknown offsets. Moreover, causality does not help reduce the uncertainty set. © 2006 IEEE. Source


Jackson J.A.,Air Force Institute of Technology
IEEE Transactions on Antennas and Propagation | Year: 2012

We derive an analytic scattering model for 3D bistatic scattering from a dihedral using geometrical optics (GO) and physical optics (PO). We use GO to trace ray reflections, and we evaluate the PO integral(s) for the field scattered by each plate of the dihedral. Multiple cases of reflection geometry are considered to account for effects of the dihedral plate size and antenna aspect angles. The complex-valued (amplitude and phase) scattering response is derived. The resulting parametric scattering model is presented in terms of the vertical and horizontal co-polarization and cross-polarization responses that correspond to the outputs of industry-standard numerical prediction codes. Comparing the derived model to available codes for method of moments (MoM), shooting and bouncing rays (SBR), and parametric models (PM), we demonstrate that the derived solution achieves the same accuracy as SBR, approximates MoM, is more accurate than PM, and does so in fast computation time comparable to a PM. © 2006 IEEE. Source


Hyde M.W.,Air Force Institute of Technology
Optics Communications | Year: 2014

The physical optics solution for the scattering of a partially coherent wave from a circular cylinder is presented. The derivations of the far-zone scattered fields are presented and discussed. Scattering width relations are developed from the physical optics fields that are functions of the coherence of the incident field. The scattering width relations are evaluated asymptotically to show the behavior of the backscattered and forward scattered energy in the incoherent- and coherent-field limits. Results are presented comparing and contrasting the physical optics results to those obtained using a previously published exact series solution approach. A physical discussion of the results is included. © 2014 Published by Elsevier B.V. Source


Hu M.,Mississippi State University | Wu T.,Arizona State University | Weir J.D.,Air Force Institute of Technology
IEEE Transactions on Evolutionary Computation | Year: 2013

Particle swarm optimization (PSO) has attracted much attention and has been applied to many scientific and engineering applications in the last decade. Most recently, an intelligent augmented particle swarm optimization with multiple adaptive methods (PSO-MAM) was proposed and was demonstrated to be effective for diverse functions. However, inherited from PSO, the performance of PSO-MAM heavily depends on the settings of three parameters: the two learning factors and the inertia weight. In this paper, we propose a parameter control mechanism to adaptively change the parameters and thus improve the robustness of PSO-MAM. A new method, adaptive PSO-MAM (APSO-MAM) is developed that is expected to be more robust than PSO-MAM. We comprehensively evaluate the performance of APSO-MAM by comparing it with PSO-MAM and several state-of-the-art PSO algorithms and evolutionary algorithms. The proposed parameter control method is also compared with several existing parameter control methods. The experimental results demonstrate that APSO-MAM outperforms the compared PSO algorithms and evolutionary algorithms, and is more robust than PSO-MAM. © 1997-2012 IEEE. Source

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