Heavy interaction problems in FRS

In a precedent paper / 1 / the procedure for the computation of FRS was discussed; basically three typical cases have been identified: Conventional case, in which the response of the equipment is dominated by the structure - behaviour and no feed back action from the equipment was identified. Intermediate case, in which the modal behaviour of the structure is unchanged, however the retroaction effect of the equipment is such as to modify the amplification ratio from the structure to the equipment. This effect has been studied by means of CYRANO code / 1 / and it has found large applications in the design of such equipment as electronics mounted on racks etc./ 2 /. Heavy interaction case, in which the modal behaviour of the structure is changed due to the retroaction effects of the equipment. Very often such heavy equipments have been modelled in the structural dynamic analysis, however changes, particularly in the stiffness (and hence dynamic characteristics) of the equipment may take place .