ICASE COUPLING BETWEEN PLATE VIBRATION AND ACOUSTIC RADIATION
A detailed numerical investigation of the coupling between the vibration of a flexible plate and the acoustic radiation is performed. The nonlinear Euler equations are used to describe the acoustic fluid while the nonlinear plate equation is used to describe the plate vibration. Linear, nonlinear, and quasi-periodic or chaotic vibrations and the resultant acoustic radiation are analyzed. We find that for the linear plate response, acoustic coupling is negligible. However, for the nonlinear and chaotic responses, acoustic coupling has a significant effect on the vibration level as the loading increases. The radiated pressure from a plate undergoing nonlinear or chaotic vibrations is found to propagate nonlinearly into the far-field. However, the nonlinearity due to wave propagation is much weaker than that due to the plate vibrations. As the acoustic wave propagates into the far-field, the relative difference in level between the fundamental and its harmonics and subharmonics decreases with distance. 1Research was supported by NASA Langley Research Center under NAS1-19317. 2Research was supported by the National Aeronautics and Space Administration under NASA Contract Nos. NASl-18605 and NASl-19480 while the third author was in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 236810001.
The Effects of Nonlinear Damping on the Large Deflection Response of Structures Subjected to Random Excitation
THE EFFECTS OF NONLINEAR DAMPING ON THE LARGE DEFLECTION RESPONSE OF STRUCTURES SUBJECTED TO RANDOM EXCITATION Chunchu Bhavani Prasad Old Dominion University, 1987 Director: Dr. Chuh Mei Effects of both nonlinear damping and large deflection stiffness are included in the theoretical analysis in an attem pt to explain the experimental phenomena of aircraft panels excited a t high sound pressure levels; th a t is the broadening of the strain response peak and the increase in modal frequency. Beams and sym­ metrically lam inated plates subjected to acoustic excitation are considered in the analyses. The excitations are ergodic and Gaussian with zero mean. A polyno­ mial containing both linear and nonlinear damping terms is considered as a damping model. Galerkin’s method is used to derive modal equations. Direct equivalent linearization is used to solve nonlinear differential equations which contain both nonlinear stiffness and nonlinear damping terms to determine mean square max­ imum deflection, mean square maximum strain and spectral density function of maximum strain for the structures. For beams, simply supported amd clamped, three modes are considered in the analysis. Isotropic m aterial is considered for beams. It is shown that the choice of linear damping is im portant for multiple modes analysis and has more influence on root mean square (RMS) strains than on RMS deflections. Nonlinear damping has maximum influence on the first mode and has considerable influence on deflection and strain and modal frequency. For laminated plates, simply supported and clamped, only single mode analysis is carried out. Immovable and movable inplane edge conditions are considered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Graphite/Epoxy is the material used. It is shown th a t small values of nonlinear damping coefficient have significant influence on panel RMS deflection and strains and modal frequency. It is identified tha t nonlinear structural damping causes the broadening behav­ ior of the stra in response peaks at high sound pressure levels. Nonlinear analysis (laxge deflection with nonlinear damping) would yield more accurate and realistic j * , • i ^ . ._-_r i ___ In_ — a J 1 J4. • ^ 2 , ^ 4 ^ i _ • prCuiCvions on pcinc* rauuOin response. n.nu 8 >iso 11 is snowxi m at u'y one inclusion of nonlinear damping, the linearized frequencies and RMS deflections and strains will be more realistic. This analytical investigation will help to broaden the basic understanding of the role of nonlinear damping on random response of structures and lead to better sonic fatigue design criteria. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Did the metamorphosis from Export Processing Zones to Special Economic Zones improve the efficiency of trade enclaves in India?
In this paper, the efficiency of seven conventional Special Economic Zones in India is analyzed, by adopting a stochastic production frontier technique, for the period between 1986–1987 and 2007–2008.Results indicate that although the efficiency scores of these enclaves have improved over the years, specifically with the introduction of the SEZ policy (2000–2001), it is far below the threshold level as identified in the literature. Besides, one can also observe a discrepancy emerging between better export earning zones and efficient zones. On the determinants side, policy intervention and large geographical area, accompanied by clustering of units, are found to have impacted the efficiency scores of these enclaves positively.