Abstract: Considerable research and effort over the last few decades has taken place in the field of system identification problem for different reasons. One of the most interesting applications involves the monitoring of structural integrity through the identification of damage [1]. The basic idea remains that measured modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties, such as reductions in stiffness resulting from the onset of cracks, loosening of a connection or more in general due to the aging of material, will cause detectable changes in these modal properties.

Among the methods developed for solving the damage identification problem, the use of the conjugate gradient method with the adjoint equation, also named Variational Approach, has recently been presented as a satisfactory choice to face this inverse problem, when small structures are considered [2]. Considering slightly bigger structures, the variational approach can be trapped at local minima [3], i.e., it does not work. Stochastic approaches, such as Genetic Algorithms (GA) represent a powerful choice for solving non trivial problems. By conducting the search in a global domain, the GA approach reduces the chance of converging to local optima, however this approach is very CPU time-consuming.

Therefore, the structural damage assessment problem will be solved through the use of a hybrid method where the stochastic approach, a Parallel Genetic Algorithm (PGA), is firstly employed, reducing the CPU time required and providing an appropriate initial guess for the deterministic approach, the Variational Method. Concerning the PGA, it is codified considering the island model, and the parallel code is generated using calls to the message passing communication library MPI (Message Passing Interface). Moreover, the damage estimation has been evaluated using noiseless and noisy synthetic experimental data, and the reported results are concerned with simple mechanical structures.

References

[1] S.W. Doebling, C.R. Farrar, M.B. Prime and D.W. Shevitz (1996): Damage identification and health monitoring of structural and mechanical systems from changes in their vibration characteristics: a literature review, Los Alamos National Laboratory, report LA-13070-MS, USA.

[2] C.H. Huang (2002): An inverse vibration problem for simultaneously estimating the time-dependent stiffness coefficients, Proceedings of the 4th International Conference on Inverse Problems in Engineering (ICIPE), Angra dos Reis(RJ), Brazil, 26-31 May, 2002.

[3] Chiwiacowsky LD, Campos Velho HF, Gasbarri P. (2003): The damage identification problem: a hybrid approach, 2nd Thematic Congress on Dynamics and Control (DINCON-2003}, Sao Jose dos Campos, Brazil, 2003.