Energy-Injecting Virtual Mass Resonant Column System

Abstract

An innovative resonant column control system is introduced. The system is based on the concepts of energy injection and virtual mass. A unique feature of the system is that it allows the user to specify the resonant frequency and vibrating amplitude for a specimen of unknown mechanical properties. In the system a steady state vibration is maintained by injecting a dissipative energy that automatically compensates for the damping loss, and a prespecified resonant frequency is reached by adding a virtual mass such that the inertia term in the equation of motion matches the stiffness of the specimen for that frequency. This arrangement results in a continuous and automatic measurement of modulus and damping properties under clearly defined test conditions. As a result of automatic operation, the number of vibrating cycles is minimized and so is the disturbance to the soil specimen. In this paper, the principle, the system configuration, the control algorithm, and the calibration and data interpretation procedures are presented. Verification and preliminary test results are reported.