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May 2001

Volume 105, Issue 5, pp. 2388-L12

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Counteracting moment device for reduction of earthquake-induced excursions of multi-level buildings

Kosuke Nagaya, Toshiyuki Fukushima, and Yasuhiro Kosugi

J. Acoust. Soc. Am. Volume 105, Issue 5, pp. 2695-2703 (1999); (9 pages)

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A vibration-control mechanism for beams and columns was presented in our previous report in which the earthquake force was transformed into a vibration-control force by using a gear train mechanism. In our previous report, however, only the principle of transforming the earthquake force into the control force was presented; the discussion for real structures and the design method were not presented. The present article provides a theoretical analysis of the column which is used in multi-layered buildings. Experimental tests were carried out for a model of multi-layered buildings in the frequency range of a principal earthquake wave. Theoretical results are compared to the experimental data. The optimal design of the control mechanism, which is of importance in the column design, is presented. Numerical calculations are carried out for the optimal design. It is shown that vibrations of the column involving the mechanism are suppressed remarkably. The optimal design method and the analytical results are applicable to the design of the column. © 1999 Acoustical Society of America.
Show PACS
43.40.Cw Vibrations of strings, rods, and beams
43.55.Vj Vibration-isolating supports in building acoustics
43.20.Ks Standing waves, resonance, normal modes

Circumferential waves on an immersed, fluid-filled elastic cylindrical shell

X. L. Bao, P. K. Raju, and H. Überall

J. Acoust. Soc. Am. Volume 105, Issue 5, pp. 2704-2709 (1999); (6 pages) | Cited 5 times

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The existence of various types of circumferential waves, both predominantly shell or fluid borne, and the repulsion of their dispersion curves is discussed here for an infinite, thin elastic, circular-cylindrical shell immersed in a fluid and filled with another fluid. The study is based on an analytic calculation of the partial-wave resonances in the acoustic scattering amplitude of a normally incident plane wave. A large number of cases of repulsion are found in the phase-velocity dispersion curves of the various types of circumferential waves due to the shell–fluid coupling. © 1999 Acoustical Society of America.
Show PACS
43.40.Ey Vibrations of shells
43.40.Fz Acoustic scattering by elastic structures

Applications of the causality condition to one-dimensional acoustic reflection problems

J. Gregory McDaniel

J. Acoust. Soc. Am. Volume 105, Issue 5, pp. 2710-2716 (1999); (7 pages) | Cited 2 times

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The causality condition is examined as a means of determining frequency-domain information about a submerged object from a partial knowledge of its acoustic reflection characteristics. A one-dimensional problem is considered in which an acoustic wave reflects from an object that is described by the impedance it presents to the fluid. Two new applications of the causality condition to the frequency-domain analysis of this problem are investigated and illustrated by numerical examples. In each application, the causality condition is used to find the object’s complex impedance from a knowledge of the reflected wave’s magnitude. The first application is to experimental studies where one desires a knowledge of an object’s complex impedance but practical limitations only allow a measurement of the reflected wave amplitude. Analysis shows that the causality condition may be used to determine the phase of the reflected wave, and hence the object’s impedance, if the reflection coefficient is minimum phase. When this is true, examples suggest that the phase of the reflection coefficient may be accurately determined from the causality condition even in the presence of noise and band-limited data. The second application is to design situations, where one wishes to create an object that reflects sound with a specified frequency-dependent magnitude. The causality condition may aid the designer by providing a knowledge of all causal object impedances that produce the same reflection coefficient magnitude. A numerical example is presented in which a variety of causal object impedances produce the same reflection coefficient magnitude over an infinite frequency range. © 1999 Acoustical Society of America.
Show PACS
43.40.Fz Acoustic scattering by elastic structures
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