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Published Articles

The Volume 15, No 1, March 2010

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Aspects of Lamb-Wave Generation and Transmission

Nicolae Constantin, Stefan Sorohan, Mircea Gavan and Viorel Anghel


This paper presents numerical and experimental results concerning Lamb-wave actuation and reception in metallic or layered composite panels and pipes. The numerical simulations were carried out with LS-Dyna, run under ANSYS platform. The main goals of this approach were to find better models for actuating Lamb waves and tracking the wave transmission in order to get efficient in situ structural health monitoring. Prior adequate choice of the signal frequency using the dispersion curves proved to be beneficial for better transmission, in terms of signal detection, and it extended inspection range. The effects of the transducer-inspected item interface and transducer shape on the wave transmission were also evaluated. Signal generation with rectangular transducers, batteries of round piezoceramic transducer (PZT) patches or the use of prisms, which value Snell?s law, were alternatively considered for getting guided waves in the inspected item. The experiments showed the performance of various transducers and devices used on the experimental chain. The Lamb waves were generated by PZT, in various shapes and configurations, aiming to lower the inspection cost. Experiments always aligned with theoretical results so that robust models could be selected for further investigations.

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Review of Coupled Vibration Problems in EMS Maglev Vehicles

Danfeng Zhou, Colin H. Hansen, Jie Li, Wensen Chang


The maglev train is a new type of guideway transportation for both long distance and urban applications in the 21st century. Recent progress in maglev technology indicates a probability of widespread commercial application of maglev systems in the near future. However, some economic and technical issues remain to be solved before the commercial application, and the vehicle-guideway coupled vibration problem is the most urgent technical problem that needs to be solved. In this article, the maglev vehicle-guideway coupled vibration problem, especially for the EMS system, is presented and divided into three main areas: the stationary vehicle-guideway, self-excited vibration; the moving vehicle-bridge coupled vibration; and the vehicle-guideway interaction caused by track irregularity. The available literature relevant to all the three coupled vibration problems is reviewed here, and the methodologies and main conclusions corresponding to each coupled vibration problem are compared and generalized as a reference for future work. The solutions proposed in the literature aiming to solve the coupled vibration problems are also enumerated, and their feasibility is discussed. Finally, work still required to solve the remaining problems is identified, and some suggestions for future research aimed at solving these remaining problems are provided.

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Transverse Plane-Wave Analysis of Short Elliptical End-Chamber and Expansion-Chamber Mufflers

A. Mimani and M. L. Munjal


The flow-reversal end chambers are used quite often in commercial automotive mufflers. The conventional axial plane-wave theory is not able to predict their acoustic performance because of the fact that the length of the end chambers is not enough for the evanescent three-dimensional modes generated at the junctions to decay sufficiently for frequencies below the cut-off frequency. Also, due to the large expansion ratio at the inlet, the first few higher- order modes get cut on even in the low-frequency regime. This necessitates a finite element or boundary element analysis, which is cumbersome and time-consuming. Therefore, an ingenious one-dimensional method has been developed. It models plane-wave propagation in the transverse direction between the incoming pipe and the return pipe, with the lateral-end cavities being modeled as variable-area quarter-wave resonators. Making use of this novel approach, the transfer matrices have been derived for elliptical and circular cross-section mufflers, which enable these elements to be analyzed along with the rest of the muffler elements by means of the transfer matrix- based muffler program. Through a comparison with a full, three-dimensional analysis on commercial software, it is shown that the one-dimensional approach presented in this paper is able to predict the transmission loss quite accurately up to about 1000 Hz for typical automotive mufflers.

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Seismic Response of Adjacent Structures Connected with Semi-Active Variable Friction Dampers

Chiragbhai Chandubhai Patel and Radhey Shyam Jangid


In this paper, the responses of two adjacent structures connected with semi?active variable friction dampers (SAVFD) under various earthquake excitations are investigated. By controlling the clamping force, SAVFD is able to adjust its slip force and remain in slip state during an earthquake of arbitrary intensity. The objective of this study is to evaluate the optimum value of the gain multiplier and its importance in the structural?response reduction of coupled structures. The optimum gain multiplier, defined as the ratio of damper force to critical damper control force, is investigated for the SAVFD connected, adjacent structures subjected to four different types of earthquake ground motions. A numerical study is carried out for two adjacent, multi?degree?of?freedoms (MDOF) structures connected with SAVFD. The investigation is also carried out to determine the effectiveness of dampers in terms of the reduction of structural responses?namely, displacement, acceleration, and shear forces of adjacent, connected structures. In addition, to minimize the cost of the dampers, the study is conducted with only 50 percent of to- tal dampers at optimal locations, rather than placing the dampers at all floor levels. The predictive control with direct?output feedback concept is considered, and the results are compared with uncontrolled and passive?control cases. Results show that by using SAVFD to connect the adjacent structures of different fundamental frequen- cies, earthquake-induced responses of either structure can be effectively reduced. Further, it is observed that two adjacent MDOF structures connected with 50 percent of the total dampers at proper locations reduces earthquake? induced responses as much as when they are connected at all floor levels; thus, the cost of the dampers can be significantly reduced.

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