Non-Obstructive Particle Damping (NOPD) Treatment Optimization for Composite Honeycomb Panels

Abstract

Non-Obstructive Particle Damping (NOPD) technology is a passive vibration damping approach. Herein spherical or irregular shaped metallic or non-metallic particles, of heavy or light consistency and even liquid particles, are placed inside cavities of or attached to structures by an appropriate means at strategic locations, to absorb vibration energy. Optimum NOPD treatment of a structure requires careful analysis and design of cavity location, size, and shape as well as characterization of the proper particles and their fill levels for maximum damping effectiveness for a given set of vibration modes of concern. Recent research in this field has shown the complexity of response prediction of an ensemble of granular particles placed in a cavity. One critical problem is that, particle damping design tools for application on vibrating structures are not yet well developed. A study funded by NASA was carried out to develop an approach to design an optimum damping treatment of Honeycomb Structures using particles. The optimization procedure consisted of defining a global objective function to determine the optimal values of the design variables through quadratic linear programming. The optimization process was carried out by targeting the highest dynamic displacements of several vibration modes of the structure and the added weight of the particles, and then finding an optimal treatment configuration that will minimize them. An optimal design was thus derived and laboratory tests were conducted to evaluate its performance under different vibration environments. Three honeycomb composite panels, with Nomex core and aluminum face sheets, empty (untreated), uniformly treated with NOPD, and optimally treated with NOPD, according to the analytically predicted optimal design configuration, were tested in the laboratory. It is shown that the panel with optimal treatment provides the lowest response amplitude. Described below are results of FEM analyses and modal vibration tests of honeycomb panels under zero, 50% uniform treatment and an optimal NOPD treatment design configuration. Nomenclature x& & = Acceleration