Masters Theses

Date of Award

8-2022

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Nicholas Wierschem

Committee Members

Mark D. Denavit, Nicholas E. Wierschem, Timothy J. Truster

Abstract

Transmitted noise and vibration from equipment and machinery is an ongoing and serious priority onboard marine vessels as noise and vibrations interfere with system operations and can compromise the functionality of the vessel. Vibration isolation systems have been widely studied for civil and mechanical applications because of the damage that can occur from extreme vibrations and excessive motion. Conventional vibration isolation systems often include components such as springs and dampers in the isolation layer, but researchers have begun to incorporate other devices including, linear rotational inertial mechanisms (RIMs), often known as inerters, to enhance traditional vibration isolation systems. The inerter is a mechanical device with two terminals in which the equal and opposite force produced is equal to a constant known as inertance multiplied by the relative acceleration between the two terminals. The inertance is a calculated value based on characteristics of the inerter including the geometry of its flywheel. When an inerter is incorporated in an isolation system, the inerter reduces the natural frequency of the system and reduces displacements, but also results in high-frequency transmitted forces, or loads induced back into the system. The high-frequency transmitted forces caused by inerters have encouraged the investigation of nonlinear rotational inertial mechanisms (NRIMs). The objective of this thesis was to investigate the behavior of NRIMs, with an emphasis on gap-type mechanisms, for use in machinery isolation in marine environments. A numerical study was performed to compare a conventional inerter with three different NRIMs. To experimentally investigate linear rotational inertial mechanisms and nonlinear rotational inertial mechanisms, a test apparatus was designed to analyze the effects of incorporating these devices in an isolation layer. A gap-type NRIM, referred to as the bushing-crown gap inerter that would engage and disengage a flywheel based on the primary mass displacement, was designed, fabricated, and tested to determine the effectiveness of the device. The test apparatus was tested without a RIM, with a linear RIM, and with a NRIM to compare responses. The bushing-crown gap inerter significantly reduced high-frequency transmitted forces compared to the RIM. The natural frequency of the isolation mode of the system increased slightly with the gap-type NRIM compared to the no RIM case. Additionally, the amplitude of the peak at the natural frequency was decreased compared to the no RIM case but was still slightly higher than the conventional inerter. The gap-type NRIM flywheel configuration has potential to reduce the natural frequency peak amplitude while avoiding high-frequency transmitted forces that is observed with the inerter when subjected to broadband loading. The results of this research indicate the potential of gap-type NRIMs and encourage further study of them.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS