Active Nonlinear Motion Confinement in Flexible Structures
A. F. Vakakis,* X. Ma
National Science Foundation, CMS 94-57750 NYI

An analytical/numerical study of nonlinear confinement of transient motions in a flexible truss structure is carried out. We investigate nonlinear motion confinement caused by clearance or geometric nonlinearities. We then develop passive or active techniques to enhance the motion confinement phenomenon.

Dynamics of Bolted Joints
A. F. Vakakis,* L. A. Bergman* (Aero. & Astro Engr.), X. Ma
Sandia National Laboratories

In this project we develop techniques for experimental modeling of mechanical joints. Data acquisition is performed through laser vibrometry and post processing 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

We 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, which 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
U.S. Office of Naval Research, N00014-00-1-0187

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

Mesoscopic Thermo-Mechanical (MTM) Water Purifier- An Energy-Efficient Company Approach to Cool, Filtered Drinking Water
A. F. Vakakis,* J. G. Georgiadis,* M. A. Shannon,* M. L. Philpott,* J. Fullilove
Defense Advanced Research Projects Agency, DABT63-98-C-0053

We study ice formation and breaking in a vibrating thin membrane. We use a laser vibrometer to study the vibration problems of the membrane in order to analyze the energetics of the process and to establish the feasibility of steady-state ice production.

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.

Sound Generation Mechanisms of Expansion Devices
N. R. Miller,* S. McLevige
NSF I/UCRC Air Conditioning and Refrigeration Center

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.

System Identification and Diagnosis of Defects in Rotating Machinery and Computational Study of Transient Heat Conduction in Laminated Thermal Coatings
A. F. Vakakis*
National Science Foundation, CMS 94-57750 NYI; Electric Power Research Institute; University of Illinois

System identification and diagnostic methodologies for detecting defective bearings in rotating machinery are developed. This is of direct relevance to the utility industry, where vibrational-related failure in rotating machinery is a leading cause of forced outages in power plants. Modal analysis techniques and nonlinear system identification methodologies (higher-dimensional frequency response functions and Volterra series) are considered. A second problem studied is the computational investigation of transient heat conduction in laminated thermal barriers used for thermal protection of gas turbine components. A double integral transform methodology is used, and numerical inversions are performed by efficient computational algorithms.