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Mechanical and Industrial Engineering

Dynamic Systems
^ Novel Passive Vibration Control Methods for Aerostructures
L. A. Bergman* (Aero. & Astro. Engr.), A. F. Vakakis*
Air Force Office of Scientific Research

This project will study energy pumping in flexible systems of one-way, irreversible transfer of energy from a continuous system to a passive "sink" where the energy localizes and dissipates. Researchers apply this concept to the passive isolation of aerostructures from unwanted disturbances.

^ Sound Generation Mechanisms of Expansion Devices
N. R. Miller,* S. McLevige
22 Company Consortium: Air Conditioning and Refrigeration Center, National Science Foundation

This project builds on a previous project that investigated the sound generated by the expansion of refrigerant through expansion devices. That project successfully identified, applied, and extended an existing flow control noise valve model to this application. This project will investigate the mechanisms of expansion noise in order to obtain a better understanding of known methods of expansion noise attenuation and to be able to propose alternative or more effective solutions. The project will also investigate the "popping" noise reported to occur in capillary tubes under certain operating conditions.

^ High Frequency Vibration Measurements in Head Disk Interfaces
A. A. Polycarpou,* K. Lee
University of Illinois

Typical head disk interfaces in magnetic storage and MEMS experience significant vibration frequencies ranging from DC up to several MHz. A Laser Doppler Vibrometer with a dynamic bandwidth of DC-20 MHz and subangstrom resolution is used to measure transient and steady state vibrations of head disk interfaces. Advanced signal processing methods are used to extract significant features from these measurements. These measurements will be used to develop vibration diagnostics tools for detecting head disk contacts under high speed sliding conditions.

^ Microcontact Stiffness Studies
A. A. Polycarpou,* X. Shi
University of Illinois

Contact stiffness is the stiffness between contacting surfaces, usually due to the asperities that are more compliant than the bulk. The contact stiffness plays a key role in dynamic friction modeling. Even though it can readily be calculated, measurement is often difficult. In macroapplications, it has been shown that there is a good agreement between theoretical predictions and measurements of contact stiffness using the resonance method. A microstiffness tester that is capable of measuring contact stiffness in miniature systems will be developed and measurements will be performed in typical MEMS and head disk interfaces.

^ Dynamics of Bolted Joints
A. F. Vakakis,* L. A. Bergman* (Aero. & Astro Engr.), C. T. Hartwigsen
Sandia National Laboratories

In this project researchers develop techniques for experimental modeling of mechanical joints. Data acquisition is performed through laser vibrometry and postprocessing relies on nonparametric system identification. Hysteresis loops are measured that enable the estimation of the stiffness and damping characteristics of the joints.

^ Experimental Studies of Nonlinear Localization in Repetitive Structures
A. F. Vakakis*
National Science Foundation, CMS 94-57750 NYI

Researchers experimentally investigate transient and steady-state localized modes in periodic flexible systems with stiffness nonlinearities. The goal is to show that for sufficiently small coupling between substructures, these systems possess passive nonlinear motion confinement properties that can be used in new vibration and shock isolation designs.

^ Linear and Nonlinear Passive Vibration Control of Mechanical Systems
A. F. Vakakis,* L. A. Bergman* (Aero. & Astro Engr.), J. G. Georgiadis,* X. Jiang, J. Hoke, X. Ma
Office of Naval Research, N00014-00-1-0187

Researchers develop linear and nonlinear vibration isolation designs for Office of Naval Research related applications. In particular, this research team develops a nonlinear vibration and shock isolator to protect sensitive machines from vibrations transmitted through ship hulls. In addition, researchers examine passive vibration control designs for trusses on board ships and investigate passive approaches for ice delamination on airplane wings.

^ Nonlinear Localization for Seismic Isolation
A. F. Vakakis,* L. A. Bergman* (Aero. & Astro. Engr.)
National Science Foundation, CMS 00-00060

Researchers propose a nonlinear base isolation design for isolating shocks from structures. The design is based on nonlinear localization whereby energy is transferred away from a mode of the structure to be isolated and directed into a secondary subsystem. Experimental verification of the method is planned.

^ Nonlinear Normal Mode Approaches to Study Solitary Waves in Nonlinear Chains of Particles
A. F. Vakakis*
University of Illinois

A new approach for studying traveling or stationary waves with spatially localized envelopes in nonlinear periodic particle chains is studied. The technique used is an extension of previously used nonlinear normal mode (NNM) methodologies for analyzing NNMs of discrete and (bounded, one-dimensional) continuous nonlinear oscillators. In the context of these methods, stationary wave solutions in the chains are regarded as localized NNMs of unbounded, continuous, one-dimensional systems. Propagating, weakly modulated waves are then computed by imposing Lorentz coordinate transformations to the stationary wave solutions.


Summary of Engineering Research