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A coupled vibrating system (for example turbine-generator set), consisting of a main system (for example shaft system) and a sub-system (for example blade system) which are connected at bonding points (for example the centre boss of a blade), is equivalently reduced to a model suitable for analysis. According to this modelling technique, the eigenvalue analysis of the uncoupled flexible sub-system is done first under the assumption of the fixed bonding point. Then, an equivalent mass-spring system is produced for each eigenmode of the uncoupled subsystem. In this way, the main system plus the additional equivalent mass-spring model of the sub-system is combined into a global system model.This modelling technique is applied to the shaft-blade coupled vibration problems in an actual turbine-generator set and its effectiveness is provided with experimental test results.