Force frequency shifting for structural excitation

This paper develops concepts and equations for the characterisation of a fr equency shifting force shaker which can be employed to excite low frequency structures into resonance. Force which is developed at a high frequency ca n be employed for excitation at a very low frequency. Frequency shifting is accomplished by moving a shaker to and fro in a reciprocating manner paral lel to the structure which it is exciting while the shaker force acts perpe ndicular to the structure. Simple equations which relate the generalised fo rce ratio to a length ratio are developed along with the positions on a str ucture where a frequency shifting shaker should be placed. This information allows the engineer some simple choices for the design and operation of a frequency shifting shaker. Also, this investigation develops criteria for w hich the frequency shifting shaker outperforms an ordinary shaker operating at the natural frequency of a structure. (C) 1999 Academic Press.