Introduction

Abstract

A flexible structure is a linear system of specific properties. What are the special features that distinguish a flexible structure from other systems? For structural or mechanical engineers its special properties include periodic vibrations with dominating few frequencies, resonances, and natural modes of vibrations. The term “flexible structure” is commonly used within the control engineering community to refer to a linear system with oscillatory properties characterized by strong amplification of a harmonic signal for certain frequencies, a system with weakly correlated states, and which complex conjugate poles have small real parts.