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Abstract: Three relationships are presented for indirect determination of the structural dynamic properties of substructures, namely the blocked force, mobility and free velocity. First, it is shown that the blocked force of a vibration source can be obtained from measurements made in situ, i.e. when the source is connected to a receiver structure. This potentially removes the need for special test rigs employing blocked terminations. A corollary of this relationship is that a theoretically exact transfer path analysis can be made on a fully assembled structure, such as a vehicle. Next, a relationship for indirect measurement of substructure mobility is derived. In this case, it is necessary to separate the substructures, but the advantage is that excitation is only required at user defined points on the substructures; excitation at the contact points is not required, so commonly encountered measurement difficulties can be avoided. Finally, it is shown that the free velocity of a vibration source can be obtained indirectly from measurements made in the installed condition; the need for a free suspension, which is impossible in practise for many important vibration sources, is thus avoided. The relationships are validated using semi-analytical simulations of rods and beams, and errors are briefly discussed. [Copyright &y& Elsevier]

• A framework is presented for the propagation of correlated uncertainty in dynamic substructuring. • Concise expressions are derived for the numerical implementation of the proposed framework. • A numerical validation is provided using a continuous beam-like system. • Results show that neglecting inter-FRF correlation leads to large over estimations of uncertainty. Dynamic sub-structuring (DS) is the procedure by which the passive properties (i.e. frequency response functions) of an assembled structure are predicted from those of its constituent sub-structures. In this paper we are concerned with the propagation of correlated uncertainty through such a prediction. In this work a first-order covariance based propagation framework is derived based on the primal and dual formulations of the sub-structuring problem and the complex bivariate description of FRF uncertainty. The proposed framework is valid also in the case of sub-structure decoupling, since the underlying equations are of an identical form. The present paper extends previous work into a more general framework by accounting for the presence of correlated uncertainty. This is important as recent work has demonstrated that the neglect inter-FRF correlation (i.e. the correlated uncertainty associated with impact-based FRF measurements) can lead to large errors in uncertainty estimates. Efficient algorithms are introduced for implementation of the proposed framework. Results are compared against Monte-Carlo simulations and shown to be in good agreement for both correlated, uncorrelated and mixed uncertainty. These results further illustrate that the neglect of inter-FRF correlation, when physically present, can lead to large over-estimations in the uncertainty of coupled structures. This result justifies use of the proposed framework. [ABSTRACT FROM AUTHOR]

In noise and vibration engineering, a structure's passive dynamic properties are often quantified by frequency response functions (FRFs). This paper focuses on acquiring FRFs from experimental tests, considering both, translational (x, y, z) and rotational (e.g. moments around these axes) terms. In practical applications, test structures may not allow FRFs to be measured directly due to the impracticality of applying a controlled excitation in a particular direction (e.g. in-plane), the inability to measure rotational dynamics (e.g. moment excitation), insufficient signal-to-noise ratio (SNR) between excitation and response degrees of freedom, or simply due to restricted access. Methods exist to resolve some of the mentioned issues using indirect experimental techniques, such as the round-trip identity. However, these methods are limited to cases in which the driving-point FRFs are sought-after. The present paper extends previous work into a more generalised formulation of the round-trip identity feasible for reconstructing driving-point and transfer mobilities from in-situ measurements conducted in coupled assemblies. By using the round-trip identity, the excitation of moments and/or inaccessible points is avoided altogether and instead replaced by a number of applied forces remote to the points of interest. Manipulation of this round-trip identity yields a formulation for long distance transfer FRFs, expressed in terms of multiple shorter transfer path elements, which are less prone to insufficient SNR. These practical applications of the generalised round-trip concept are experimentally validated for multi-input multi-output assemblies. [ABSTRACT FROM AUTHOR]