scispace - formally typeset
Search or ask a question

Showing papers on "Modal testing published in 1970"


DOI
01 Jan 1970
TL;DR: In this article, an experimental verification of a container crane structure modal parameters which are numericaly obtained by using the Finite Element Method is presented, where the crane was forced into a specific vibration mode with limited operational movements using inertial forces of the masses in motion.
Abstract: Experimental verification of a container crane structure modal parameters which are numericaly obtained by using the Finite Element Method is presented. To validate the numericaly calculated natural frequencies and vibration mode shapes, and to define the modal damping values, a full-scale forced vibration experiment was performed. The simplest possible experiment was chosen to obtain these objectives. Some kind of intersection between forced vibration test, with the control of the input (forcing function), and step relaxation test, with the release of the structure from a statically deformed position, was made. Instead of releasing the deformed structure, the crane was forced into the specific vibration mode with limited operational movements, using inertial forces of the masses in motion. Therefore, the input excitation was not directly controlled, but was more or less under control. Ambient vibration testing, due to wind loading and due to forcing with crane motion, was also performed and is briefly presented.

10 citations



ReportDOI
01 Jun 1970
TL;DR: In this paper, the mass, stiffness and damping parameters in Lagrange's equations of motion of an n-degree-of-freedom damped linear elastic structure can be determined directly from impedance-type test data without prior assumption of an intuitive mathematical model.
Abstract: : It is shown that the mass, stiffness and damping parameters in Lagrange's equations of motion of an n-degree-of-freedom damped linear elastic structure can be determined directly from impedance-type test data without prior assumption of an intuitive mathematical model. The damping is assumed to be such that the model vectors are orthogonal with respect to damping. A method is derived for determination of the exact modal eigenvector of the dominant mode at any forcing frequency by iteration on the damped impedance measurements in matrix form. A similar eigenvalue equation yields the vector in the inverse transpose of the modal matrix; this vector called the gamma vector, is identified with the dominant mode. The generalized masses, stiffnesses and damping terms are related to the mass, stiffness and damping matrices of the equations of motion through products of the gamma vectors. Using the gamma vectors, obtained by iteration on test data, the natural frequencies and other modal parameters are determined. Natural frequencies which are not visible in response plots may be determined by this method. Computer experiments were conducted to test the sensitivity of the theory to errors in input data.

2 citations


Journal ArticleDOI
TL;DR: The work of Dyer as mentioned in this paper was extended to derive expressions for the sound pressure cross spectrum and cross correlation within a hard circular duct and with arbitrary boundary conditions, where the internal impedance concept was used to account for the source end boundary condition.
Abstract: The work of Dyer [J. Acoust. Soc. Amer. 30, 833–841 (1958)] was extended to derive expressions for the sound pressure cross spectrum and cross correlation within a hard circular duct and with arbitrary boundary conditions. Results are expressed either in terms of a source plane pressure cross spectrum or in terms of a modal spectral distribution. An internal impedance concept was used to account for the source end boundary condition. Reflected waves are included, the termination being specified by a local impedance. In order to estimate sound power from pressure cross‐correlation measurements in the cross‐mode region, programs were written to compute the exact sound power and the error of the estimate by use of the plane‐wave formula for given measuring positions, given modal spectra, and given modal correlation. Depending on the type of source, optimum measuring positions were determined. Methods to measure modal spectra of a certain source were developed. [Essential support of this work was given by Air Conditioning and Refrigeration Institute.]

1 citations