The work presented in this thesis is motivated by a need for an advanced understanding of the governing mechanisms for vibrations in complex structures. In order to obtain a simplified description of the complex structure with the dominant information of the structure enhanced, one removes some unimportant structural information from the description by identifying secondary contributing substructures and couplings, then describing them using simplified models. It is found that the secondary substructures are those substructures being required for their vibrational transmission characteristics only, and the secondary couplings are the weak couplings in the structure. Moreover, it is demonstrated that the transmission characteristics can be sufficiently described by using only the direct wave and the fIrst reflection in the structure, and the secondary coupling can be simplified as an idealised coupling. The procedure for establishing such a simplifIed description for the complex structure is illustrated by a two-element built-up structure. Finally, the efficiency of using such a simplifIed description to analyse the complex structure is demonstrated for two mechanical artefacts, one being a laboratory structure consisting of a cylindrical shell attached to a plate via two beams, and the other a full-scale aircraft - Eurofighter 2000.

The University of Tennessee Space Institute’s (UTSI) active airborne science program often requires extensive modification to its fleet of aircraft in order to meet mission and customer requirements. These modifications can alter the flight characteristics of the aircraft. In order to determine if the aircraft is safe to fly after modification and to find any new flight characteristics resulting from the modifications, the flight test engineer (FTE) must plan and conduct limited flight testing on the aircraft and evaluate the resulting data to ensure safety of flight. The more efficient the data reduction and analysis process the quicker the aircraft can be released to the customer for flight operations. Flight-Data Analysis and RePorting System (F-DARPS) was developed in an attempt to decrease the time spent reducing data by automating the entire data reduction process. F-DARPS searches through a data file, determines when the aircraft is in a trim state, processes the data, and presents a limited number of performance and stability and control (S&C) parameters to the FTE in a meaningful manner. Because F-DARPS is in an early stage of development, the system requirements, architecture, code techniques, and a self case study with future revision recommendations will be discussed in detail.