A study of one-dimensional mechanical vibrating systems with piecewise constant properties and its applications as an optical viscosimeter
Date Issued
2009
Date
2009
Author(s)
Stachiv, Ivo
Abstract
This thesis deals with an analysis and application of the vibrating one-dimensional mechanical systems with piecewise constant properties. It is a well known fact that the fist step in a vibration analysis of any mechanical system is to find spectrum of their natural frequencies. It can be done either numerically or analytically. For simple vibrating systems like beam, string or cantilever with constant mechanical properties the analytical determination of the normal modes is known and is preferable one. However many real applications involve not a constant but a piecewise constant and, factually discontinuous properties. For composed systems the numerical determination of the normal modes is usually performed. We have found here that the normal modes for one–dimensional mechanical problems with piecewise constant properties can be obtained by solving an appropriate transcendental equation. This equation of course contains all information about given mechanical system (elastic moduli, density, cross-sectional area of material, thickness of each layer with constant mechanical properties, etc.). In this thesis transcendental equation is derived for case of one-dimensional systems with N - piecewise constant properties. The physical interpretation of normal modes for this kind of mechanical systems by introducing the “effective” propagation velocity has been put forward. An optical method utilizing a forward light scattering pattern has been carried out to test the validity of the theory for N = 2. Theoretical predictions of the first mode frequency and experimental data agree precisely. Moreover the extension of the analysis and experiments for a case of the partially submerged fiber in fluid with taking into account of a viscous damping has been performed. From obtained results a simple way for viscosity extraction from either the maximum vibrational amplitude or the power bandwidth variation has been suggested and tested experimentally. Besides an explicit formula for the achievable accuracy of the viscosity sensing is derived here as well.
Subjects
normal modes
optical viscosimeter
vibration
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-D92543015-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):c69f75bc9741a6217acc1a6071eeb152