Jet Noise Excitation of an Integrally Stiffened Panel

Abstract

The free vibrations and random response to jet noise of an integrally stiffened five bay panel have been studied both theoretically and experimentally. A finite element approach was used to represent the panel for both parts of the study, and the predictions were verified by measurements on a model panel integrally machined from solid Aluminum stock. The comparison between predicted and measured vibration modes and frequencies revealed good correlation of frequencies while the correlation of mode shapes was only fair, especially for higher modes. The predicted modes and frequencies were used in a modal analysis of the panel's response to jet noise with a consistent finite element method being introduced to calculate the required cross spectral modal force terms. Quantitative agreement between predicted and measured rms stresses and displacements was realized, whereas only qualitative agreement was obtained for the associated spectra. Nomenclature ai,bi,ci = finite-element dimensions, Fig. 9 c 0 = speed of sound ei,{E] = polynomial coefficients, Eq. (9) = jth mode shape {F(£,-n)} = column vector of polynomial terms, Eq. (7) Hjfa) = complex admittance for jth mode IjkM = modal force cross spectral matrix, Eq. (4) rrij = generalized mass for jth mode Po = root mean square pressure { PO}, { PI }, {Pz} = consistent finite-element load vectors [Q(co)] = cross spectral matrix for generalized coordinates, Eq. (17) R(x,y,r) = noise correlation function, Eq. (2) w = panel and finite-element displacement Wrms = root mean square displacement {W} = column vector of generalized displacements for finite element, Eq. (8) fy = damping ratio for jth mode Downloaded by UNIVERSITY OF CALIFORNIA -DAVIS on February 3, 2015 | http://arc.aiaa.org |

Finite element free vibration analysis of stiffened plates

“…Nair and Rao ( l l ) presented the results of vibration of plates having varying stiffener length based on the finite element method using the same plate element as given in Ref. 5. All the above methods suffer from certain limitations inherent in the formulation.…”

“…Kirk (4) has applied the Ritz method for determining natural frequencies of first symmetric and first antisymmetric modes for an eccentrically stiffened rectangular plate with a central stiffener. Olson et a/ (5,6) applied the finite element method for studying free and forced vibration characteristics of stiffened plates. A high precision triangular element for modelling the plate part in conjunction with refined beam bending and torsional element for the rib stiffeners was used for obtaining the theoretical values which were subsequently verified experimentally by using laser holography.…”