Acoustical influence of stiffeners on acoustic radiation of plates

This paper deals with acoustic effects of ribs on sound radiation. This question has been raised by the difficulties encountered in boundary element modelling for structural details like ribs. The final objective is to improve modelling and design of ribs in an acoustic radiation sense. In the present paper the acoustic influence of ribs is divided into three physical effects : the “vibrating” effect, the “source” effect and the “obstacle” effect. These effects are studied for stiffened plates. The vibrating effect is rapidly presented, as it has been already studied, especially in the 80th (J. Phys. III 2(C1) (1992) 487; Sound and Structural Vibration, Academic Press, New York, 1985, pp. 72-89; J. Sound Vib. 138(2) (1990) 173; J. Acoust. Soc. Am. 34(6) (1962) 809; J. Sound Vib. 123(2) (1988) 293; J. Sound Vib. 123(2) (1988) 309; J. Sound Vib. 179(3) (1981) 439; Ph.D. Thesis of the Science University of Toulouse, 1989; J. Sound Vib. 198(2) (1996)). Attention is then focused on the two other effects. A preliminary experimental investigation is presented on square stiffened plates, and shows that source and obstacle effects of ribs can be important. A numerical investigation is carried on, using a boundary element method. Source and obstacle effects are then studied separately. For each effect, phenomena observed on plates are explained with analytical models and some evaluating criteria are proposed.