scholarly journals An Experimental Characterization of the Impedance and Spectral Content of Multistable Structural Responses During Dynamic Bifurcations

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Benjamin A. Goodpaster ◽  
Ryan L. Harne

The ability to predict multistable structural dynamics challenges the development of future high-performance air vehicles that will be subjected to extreme multiphysics loads. To aid in the establishment of methodologies that characterize the response states of harmonically excited multistable structures, a catalog of empirical and practical evidence is necessary. Recent research has suggested that evolving aspects of mechanical impedance metrics may be correlated with measurable quantities, although their relation to bifurcations of the dynamic response remains incompletely understood. Motivated to begin establishing such knowledge base, this research seeks to construct a library of experimental evidence from which to draw generalized insights on the impedance- and spectral-changing trends of multistable structures undergoing severe nonlinear response due to harmonic loading. A connection between vanishing real and imaginary components of impedance and dynamic bifurcations is uncovered. In the process, a technique to forecast dynamic bifurcations is articulated, which utilizes mechanical impedance measurements in real-time to monitor the susceptibility of postbuckled structural components to undergo dynamic bifurcations. An examination of higher-order harmonics of the dynamic responses further illuminates the nearness to bifurcations and may help classify the precise response regime. Thus, by correlating the real-time impedance and spectral response with analytical predictions, a future tool may be established for condition monitoring and diagnosis.

2015 ◽  
Vol 24 (6) ◽  
pp. 1703-1711 ◽  
Author(s):  
Rosana Alves Dias ◽  
Filipe Serra Alves ◽  
Margaret Costa ◽  
Helder Fonseca ◽  
Jorge Cabral ◽  
...  

1986 ◽  
Vol 58 (13) ◽  
pp. 2831-2839 ◽  
Author(s):  
D. Bruce. Skoropinski ◽  
James B. Callis ◽  
J. D. Sheldon. Danielson ◽  
Gary D. Christian

Author(s):  
Osama M. Arafa ◽  
Said A. Wahsh ◽  
Mohamed Badr ◽  
Amir Yassin

Meta-heuristic optimization techniques are important tools to define the optimal solutions for many problems. In this paper, a new advanced artificial intelligence (AI) based direct torque control (DTC) speed drives are optimally designed and implemented in real time to achieve a high performance permanent-magnet synchronous-motor (PMSM) drive. Grey wolf (GW) algorithms are used with the standard PID-based DTC (PIDDTC) and with the DTC with fuzzy logic (FDTC) based speed controllers. DSPACE DS1202 is utilized in the real-time implementation. MATLAB SIMULINK is used to simulate the steady-state (S.S.) and dynamic responses. The overall system is tested at different operating conditions for both simulation and practical work and all results are presented. A comparison between experimental and simulation results is performed and also a comparison between different applied intelligent techniques is introduced.


2014 ◽  
Vol 941-944 ◽  
pp. 261-265
Author(s):  
Fabrizia Ghezzo ◽  
Xi Geng Miao ◽  
Chun Lin Ji ◽  
Ruo Peng Liu

In recent years, polyurea has been successfully applied as a coating material for increasing the survivability of structures and components subjected to critical impact loading conditions. It was also shown that if a polyurea coating is reinforced with ceramic particles or short glass fibers, an enhanced benefit on the overall impact resistance due to the increased dissipation properties of the material can be observed. Notwithstanding the use of polyureas as coating materials for structures protection, other applications where control and damping of vibrations is of concern would benefit from the high dissipation characteristics of the reinforced elastomer. Nevertheless, there are well known drawbacks in the use of the reinforced elastomers which can be identified in their pronounced nonlinear behavior under cyclic loads and the softening of their mechanical properties. In order to investigate such a phenomenon, in this manuscript we present an experimental investigation conducted on the effects of different volume fractions of the same filler on the response of a polyurea elastomer at varying amplitudes of the applied strain. The characterization of the materials was conducted by using a dynamic mechanical analyzer (DMA). From our preliminary results we observed that in the case of polyurea reinforced with short glass fibers, the nonlinear response of the polymer at varying strain amplitudes becomes evident for fillers volume contents of 10%. Furthermore, the nonlinearity of the response of the material due to the Payne effect seems to be associated with the complex fibers-matrix interaction rather than the disruption of the agglomeration of the fillers under load.


1979 ◽  
Vol 44 ◽  
pp. 41-47
Author(s):  
Donald A. Landman

This paper describes some recent results of our quiescent prominence spectrometry program at the Mees Solar Observatory on Haleakala. The observations were made with the 25 cm coronagraph/coudé spectrograph system using a silicon vidicon detector. This detector consists of 500 contiguous channels covering approximately 6 or 80 Å, depending on the grating used. The instrument is interfaced to the Observatory’s PDP 11/45 computer system, and has the important advantages of wide spectral response, linearity and signal-averaging with real-time display. Its principal drawback is the relatively small target size. For the present work, the aperture was about 3″ × 5″. Absolute intensity calibrations were made by measuring quiet regions near sun center.


1984 ◽  
Vol 51 (01) ◽  
pp. 016-021 ◽  
Author(s):  
S Birken ◽  
G Agosto ◽  
B Lahiri ◽  
R Canfield

SummaryIn order to investigate the early release of NH2-terminal plasmic fragments from the Bβ chain of fibrinogen, substantial quantities of Bβ 1-42 and Bβ 1-21 are required as immunogens, as radioimmunoassay standards and for infusion into human volunteers to determine the half-lives of these peptides. Towards this end methods that employ selective proteolytic cleavage of these fragments from fibrinogen have been developed. Both the N-DSK fragment, produced by CNBr cleavage of fibrinogen, and Bβ 1-118 were employed as substrates for plasmin with the finding of higher yields from N-DSK. Bβ 1-42 and Bβ 1-21 were purified by gel filtration and ion-exchange chromatography on SP-Sephadex using volatile buffers. When the purified preparation of Bβ 1-42 was chromatographed on reverse-phase high performance liquid chromatography, two peaks of identical amino acid composition were separated, presumably due either to pyroglutamate or to amide differences.


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