Showing papers on "Modal testing published in 1969"
TL;DR: In this article, the theoretical mode shapes of vibration of pre-twisted rectangular cross-section beams for various width to depth ratios and pretwist angle in the range 0-90° are examined.
Abstract: An important aspect of the theoretical study of the vibrational characteristics of turbine and compressor blading is the prediction of the modal curves from which the stresses along the length of the blading can be determined.The accurate prediction of the modal curves allowing for such factors as pre-twist, camber, size of cross-section, centrifugal tensile effects, aerodynamic effects, etc., is still not possible. However, a better understanding of the effects of some of these parameters can be obtained by a study of the modal curves of relatively simple idealized models. In this work the theoretical mode shapes of vibration of pre-twisted rectangular cross-section beams for various width to depth ratios and pre-twist angle in the range 0-90° are examined.The theoretical results are obtained by the transformation method given by Carnegie, Dawson and Thomas (1)† and the accuracy of these results is verified by comparison with results obtained by Dawson (2) using the Ritz method. The theoretical results a...
41 citations
TL;DR: In this article, the acoustic radiation into a fluid-filled infinite half-space from a randomly excited, thin rectangular plate inserted in an infinite baffle is discussed, and the modal coupling coefficients are evaluated approximately at both low and high (but below acoustic critical) frequencies.
Abstract: The acoustic radiation into a fluid‐filled infinite half‐space from a randomly excited, thin rectangular plate inserted in an infinite baffle is discussed. The analysis is based on the in vacuo modes of the plate. The modal coupling coefficients are evaluated approximately at both low and high (but below acoustic critical) frequencies. An approximate solution of the resulting infinite set of linear simultaneous equations for the plate modal velocity amplitudes is obtained in terms of modal admittances of the plate‐fluid system. These admittances describe the important modal coupling due to both fluid inertia and radiation damping effects. The effective amount of coupling, and hence the effective radiation damping acting on a mode, depends on the relative magnitudes of the structural damping—i.e., on the widths of the modal resonance peaks and on the frequency spacing of the resonances. Expressions are obtained for the spectral density of the radiated acoustic power for the particular case of excitation by a turbulent boundary layer. [Work supported by the Office of Naval Research.]
22 citations
TL;DR: In this article, the second mode response of the Millikan library building was analyzed and it was found that the damping was about 3.7% of critical value for higher modes of vibration.
Abstract: The paper is devoted to the dynamics of building structures excited by-sinusoidal excitation. The analysis indicates that the complicated response curves found for higher modes of some structures are a result of the interference of lower modes of vibration. A procedure is developed which enables the resonant frequency, mode shape and modal damping of the second mode to be recovered from steady-state response data when interference is present from the fundamental mode. This is a condition that has occurred in tests, and the procedure is applied to the second mode response of the Millikan Library Building to illustrate the method. The damping in the second mode is found to be about 3.7% of critical. The analysis also is generalized to apply to the response of higher modes of vibration with interference from any number of lower modes.
8 citations
TL;DR: Modal control theory is applied to the design of feedback loops for linear time-invariant discrete-time systems as discussed by the authors, and it is also used to demonstrate the explicit relationship which exists between the controllability of a mode of a discrete time system and the possibility of assigning an arbitrary value to the eigenvalue of that mode.
Abstract: Modal control theory is applied to the design of feedback loops for linear time-invariant discrete-time systems. Modal theory is also used to demonstrate the explicit relationship which exists between the controllability of a mode of a discrete-time system and the possibility of assigning an arbitrary value to the eigenvalue of that mode.
2 citations