The vibration activity of a structure-borne source can be expressed as a free velocity, the velocity at the contact points when freely suspended, or the blocked force, the contact forces when attached to a receiving structure of low mobility. An advantage of the blocked force approach is that the machine can vibrate under normal load conditions. A disadvantage is that force transducers must be inserted between the machine and the receiving structure and this can significantly alter the normal mounting conditions. A calibrated reception plate method is proposed which preserves the advantage of the blocked force approach and eliminates the above disadvantage. A large resiliently supported 20mm aluminium plate was numerically modelled in terms of point and transfer mobility. The agreement with measured point mobility was improved by model updating. The transfer mobility matrix then was assembled for four contacts and four remote response positions on the plate. With an attached machine operating normally, the plate velocities, at the four remote positions, were recorded. Inversion of the transfer mobility matrix yields the contact forces. The indirectly obtained contact forces approximate the blocked forces since the reception plate mobility is much lower than that of the source (i.e. machine) mobility.
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