NUMERICAL SIMULATION OF FLUID-STRUCTURE INTERACTIONS

A Japanese drum may consist of a hollow wood barrel with diaphragms at both ends. The diaphragms are assumed as a pairs of identical stretched membranes with bending stiffness included. These diaphragms are dynamically coupled through the interior air cavity and the wood body. A numerical model for this coupled fluid-structure system is developed using the finite-element method. Axisymmetrical shell and acoustic elements are developed for the structure and fluid, respectively. MATLAB is used as the pre- and post- processors. The first two non-rigid body modes of the drum are: (1) the two diaphragms vibrate in phase, the push-pull mode, and (2) the two diaphragms vibrate out-of-phase, the push-push (or pull-pull) mode. Without air loading, these two modal frequencies only differ slightly, which means the effect by the wood body is small. With air loading, the push-pull mode frequency becomes lower than that of the unloaded case, while the push-push mode shifts toward higher frequency. The reasons for these are explained via the computed modal structures. In common practice, the two membranes are slightly (intentionally) miss-tuned. Simulation on the effect of this miss-tuning is also discussed