When working with large FE models, a bottom-up modeling, testing and assembly approach should be considered.
The updating methods are based on the use of sensitivity coefficients that iteratively update selected physical element properties (like for example material properties, and joint stiffness) so that correlation between simulated responses and target values improves.
Other examples are a launcher tested with different levels of fuel, or differently shaped test specimens made of a composite material that needs to be identified.
From measured harmonic operational shapes, and an updated finite element model, a system of equations can be solved to obtain the excitation forces.
Sensitivity analysis and model updating require that the user selects reference responses and parameters.
Sensitivity coefficients are computed internally by FEMtools using a differential or finite difference method.