Nodal/modal control and power intensification methods and apparatus for

Abstract

Controllability and performance of resonating, compliant, simply excited, self-attenuating driving and driven sets of structures coupled to pneumatic vibrators is usefully enhanced by means of altering mode shapes by forcibly creating nodes and partial nodal lines and by means of intensifying power transmitted to test items by forcibly increasing acceleration transmissibility. These devices, when included in a vibration system, enable different test items to be vibration tested at selectable repeatable levels under controlled conditions of multi-frequency, multi-degree-of-freedom acceleration history, to achieve a frequency spectrum and acceleration-level control of a broadband quasi-random vibration output. Specific design of the size, mass, and resonant behavior of the driving and driven structure sets with appropriate transmissibility characteristics of the elastomeric interface results in controlled multi-modal, uniform RMS acceleration, multi-degree-of-freedom, frequency-bounded vibration testing. In a first embodiment, points or regions on vibration device structures forcibly are constrained to form nodes by localized immobilization of the driving structure and/or localized stiffening of the elastomer coupling between driving and driven structure and, thereby, to decrease relative displacement between driving and driven structures at these points. Further increase or decrease of modal density and change of test RMS acceleration levels are achieved by altering the transmissibility of power through the elastomer coupling by mechanically compacting or extending the elastomer by preloading.