In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the transmission of airborne noise into a stiffened cylindrical shell. The stiffeners are longitudinal stringers and are modeled as discrete structural elements. The numerical cases examined were typical of a narrow-bodied jet transport fuselage. The stringers appeared to raise the cylinder transmission loss in the masscontrolled region, although they produced dips at the stringer resonances. The ring-frequency dip in transmission loss, which is characteristic of monocoque shells, was found to still be present. There appeared to be a small increase in transmission loss as the number of stringers was increased. The effect of high damping was also investigated. I. Introduction T HE work reported herein is an extension of an earlier study1 of the sound transmission through a monocoque shell structure. In the context of airborne-nois e transmission through an aircraft fuselage, the specific problem studied was that of an incident oblique plane wave impinging upon a flexible cylindrical shell. The work in Ref. 1 was an extension of earlier work of Smith 2 and treated the "fuselage" as a monocoque shell. An attempt was made3 to improve the model by including the effects of ring frames and stringers by means of a "smeared-stiffener" theory formulated by Rosen and Singer.4 However, the effort met with only limited success, although Rosen and Singer demonstrated in Ref. 4 that good results were obtained in shell vibration studies. Apparently, the smeared-stiffener approach, while valid at low frequencies, breaks down at the higher frequencies of interest in sound transmission work. To correct this, the present work replaces the smeared-stiffener theory by one which treats the stringers as discrete elements, in the manner of Rinehart and Wang,5'6 and studies the effects of the longitudinal stiffeners on the transmission of airborne noise.
[1]
Leslie Robert Koval,et al.
Effect of Stiffening on Sound Transmission into a Cylindrical Shell in Flight
,
1977
.
[2]
J. L. Sewall,et al.
An analysis of free vibration of orthogonally stiffened cylindrical shells with stiffeners treated as discrete elements.
,
1967
.
[3]
S. Rinehart,et al.
Vibration of simply supported cylindrical shells with longitudinal stiffeners
,
1972
.
[4]
S. A. Rinehart,et al.
FREE VIBRATIONS OF LONGITUDINALLY STIFFENED CYLINDRICAL SHELLS
,
1974
.
[5]
N. Mclachlan.
Bessel functions for engineers
,
1934
.
[6]
Leslie Robert Koval,et al.
On sound transmission into a thin cylindrical shell under “flight conditions”
,
1976
.
[7]
P. W. Smith,et al.
Sound Transmission Through Thin Cylindrical Shells
,
1955
.
[8]
J. Singer,et al.
Vibrations of axially loaded stiffened cylindrical shells
,
1974
.
[9]
L. R. Koval.
On sound transmission into a heavily-damped cylinder. [aircraft noise in fuselage]
,
1978
.