  We propose a multi-objective global pattern search algorithm for the task of
locating and quantifying damage in flexible mechanical structures. This is
achieved by identifying eigenfrequencies and eigenmodes from measurements and
matching them against the results of a finite element simulation model, which
leads to a nonsmooth nonlinear bi-objective parameter estimation problem. A
derivative-free optimization algorithm is required since the problem is
nonsmooth and also because complex mechanical simulation models are often
solved using commercial black-box software. Moreover, the entire set of
non-dominated solutions is of interest to practitioners. Most solution
approaches published to date are based on meta-heuristics such as genetic
algorithms. The proposed multi-objective pattern-search algorithm provides a
mathematically well-founded alternative. It features a novel sorting procedure
that reduces the complexity in our context. Test runs on two experimental
structures with multiple damage scenarios are used to validate the approach.
The results demonstrate that the proposed algorithm yields accurate damage
locations and requires moderate computational resources. From the engineer's
perspective it represents a promising tool for structural health monitoring.
