Study On Numerical Method For Acoustic Characteristics Of Double Periodical Stiffened Panels

Structures consist of stiffened plates and shells often find wide application in bridge engineering, aircraft and ship industries owing to their high strength and stiffness, light-weight and low-cost properties. Among various kinds of stiffened structures, periodic stiffened plate is one of the most common used constructions. For the past decades, the study of vibration responses, acoustic radiations and sound transmission from periodic stiffened plates has always been one of the research topics in these fields. Stiffened plates are often subjected to dynamic forces such as air blast loadings or fluid pressures, for which effective analysis method is required to study their dynamic performances under these conditions. So far, many approaches have been proposed such as Rayleigh-Ritz energy method, finite element method, transfer matrix method, modal decomposition method and space harmonic method, etc.In this thesis, both single and double panels stiffened by periodic structures in two directions are investigated employing the finite element method and boundary element method, and acoustic characteristics of three kinds of double dual-dimensional stiffened panels are especially analyzed. The analysis process in this paper includes the following steps: (a) theories of relevant FEM and BEM are researched and major functions and analysis steps of business software ANSYS about FEM and SYSNOISE software about acoustic BEM are simply introduced. (b) Several finite elements such as bending plate element, Mindlin plate element and Timoshenko beam element, which are mainly used to analyze thin plate, thick plate and non-slender beam respectively, are introduced. And some important elements of ANSYS software such as beam elements, shell elements and fluid elements are moderately discussed and introduced. Subsequently, the FEM modes of dual-dimensional stiffened panels consisted of plates and stiffeners are established in ANSYS software. (c) The main acoustic analysis processes and some existing problems are stated, when using ANSYS software combined with SYSNOISE software. To solve these problems and exchange required data between two software, APDL language programs are designed.At last, sound radiation and transmission models of periodic stiffened panels are derived and established, and the acoustic characteristics of the periodic structure are simulated by ANSYS and SYSNOISE software. A number of vibration diagrams, sound pressure and transmission curves are given in this thesis, and the effects of structural parameters on acoustic characters of the periodic stiffened panels are analyzed. Through numerical results, it can be found that if structural parameters are properly adjusted, such as plate's thickness and mass density, stiffener's spacing and cross section, the distance between two panels, the acoustic properties can be improved in specific frequency ranges. It can also be noted that different periodic geometrical structures have significant effects on the vibration response and acoustic radiation on the panels.