Manipulating Natural Frequencies with Tunable Spring Masses

摘要

Tuned Mass Dampers (TMDs) aid in many applications from civil engineering, to reducing vibrations of automotive systems, to damping out problematic modes in spacecraft and instruments. While TMDs traditionally concentrate on diminishing modal responses thru coupling with a damping element, this paper concentrates on changing existing modes by coupling them to a single degree of freedom (DOF) spring and mass system called a Tunable Spring Mass (TSM). The dynamics of adding a TSM into an existing single DOF system are well established. When placed at the right location and tuned to the correct frequency a TSM will split a mode or effectively move a mode to a lower or higher frequency. The interactions of a TSM with a complex system being subtle, several techniques help in determining the best location, orientation, mass, and frequency of a TSM for a given application. Craig-Bampton reduction reduces computation time to manageable levels. Matlab based optimization functionality finds optimum TSM solutions. Algorithms designed to modify modal frequencies and modal effective masses in partially reduced models can then determine the robustness of a given TSM Solution. TSMs are designed with an adjustable mass system for fine tuning of the frequency. Together these techniques allow for the designing of a TSM solution which can confidently maneuver modes away from problematic frequencies on existing complex spaceflight instruments with only 2% of the system mass.