John C. O'Callahan

Reallocation of system mass and stiffness for achieving target specifications

The development of a system model involves the assemblage of many important components from a dynamic standpoint. The performance of the system is dependent on the dynamic characteristics of each of the components. In an attempt to improve the overall system characteristics, targets are typically specified at the system level. The determination of the component characteristics to achieve these targets are the purpose of this work. Using these targets, an inverse optimisation process can be utilised to determine the adjustment of the mass and stiffness of the system. However, the inverse process will smear the mass and stiffness over all the system degrees of freedom unless all the system equations are utilised in the inverse process or unless some constraints are applied to the set of equations. This smearing tends to confuse the proper mass and stiffness that are needed to achieve the design targets to meet the desired component dynamic characteristics. This work utilises analytical model improvement techniques along with localisation of model change procedures to determine the component target characteristics. As part of the procedure, the existing topology of the finite element model can be modified to restrict or allow additional elemental connectivities in the optimisation process.

Reallocation of system mass and stiffness for achieving target specifications using a superelement/substructuring methodology

Optimisation of models using desired targets is typically performed at the system level and result from the individual component dynamic characteristics. Optimisation can be performed when the component and system topology is defined. Previous work utilised Analytical Model Improvement techniques along with Localisation of Model Change procedures to determine the component target characteristics. However, the use of superelements or reduced component representations presents complications since no topology exists for these representations. The efforts in this work are directed towards the implementation of the technique using superelements as the component description. The topology of the superelement is mapped with an arbitrary array of simplistic elements to determine the distribution of mass and stiffness necessary to achieve the performance goals specified without allowing smearing to adjacent component interconnection regions.