A Study Of Local Dynamic Effects On The Vibro-Acoustic Transmission Mechanisms Of Frame-panel Built-up Structures

The main components of the car body can be divided into rib-like and panel-like structures,which can be regarded as different types of beam-plate built-up structures,as well as other auto parts.In order to investigate the insight of the vibro-acoustics of car bodies,a frame-panel model is set up by in line with the major structure-borne sound transmission mechanisms of Body in White.The thesis focuses on the study of local dynamic effects on the vibro-acoustic characteristics of the frame-plate model by comprehensively combined analytical-,numerical-and experimental-modelling techniques.In the first part,a set of classical conventional vibro-acoustic theory of elastic structures is summarized,which follows a study of the local mass effects on the vibration and sound radiation characteristics of thin rectangular plate models.Through the theoretical and numerical results,it is found that both the vibration and radiation characteristics of the lower ordered plate modes tended to be more affected by the local mass value than by its location on the plate.Meanwhile,the vibro-acoustic characteristics of a coupled plate-cavity system(with five rigid walls)are investigated according to the structural-acoustic coupling theory.And good agreement is found between the numerical and experimental results.It is proved that the smaller size of the cavity shows the stronger coupling effect between the plate and the cavity.In the second part,a frame-panel built-up structure is introduced,of which,the stiff frame is connected with the flexible thin plate via different types of joints.The major local parameters within the frame,plate and coupling interfaces are analyzed,respectively,by using FEM(finite element method),semi-analytical method and experimental methods.As a result,the key sensitive parameters in the dynamic characteristics of the built-up structures are identified.It is found that the plate stiffness and the top border of the frame tend to play the most important roles on the dynamic properties of the frame-panel as a whole,especially for the lower ordered structural modes.In the last two parts,the structure-borne sound transmission from the frame,being a source structure,to the plate,being a receiver and major sound radiator as well,is investigated.The local parameters on affecting the vibrational power input to the frame and that transmitted to the plate are particularly addressed.The results have shown that the power flow characteristics of frame-panel built-up structures mainly depended on the frame parts,while natural frequencies and amplitudes of the vibrational powers are slightly effected by the stiffened-plates.Meanwhile,the stiffness of the stiffened-plates is in proportion to its coupling effects.Detailed experimental results are provided to support the validity of the finite element modelling.