Variance Evaluation and Optimization of Modal Parameters and an Application to an Outboard Motor

The objectives of the present paper are to propose a variance evaluation method for modal parameters identified by the least, squares method with an experimental transfer-function, and to show that the evaluated variance can be used to optimize the accuracy of the parameters by selection of proper excitation type, weighting function and so on.

The variance of the modal parameters was evaluated by a first order approximation and the discrete values of the experimental transfer functions as were modeled as stochastic variables.

Also, the variance of the transfer function was evaluated using the coherence function based on a theory of statistical error. Application of this method to a simple beam made of acrylic resin showed that the variances can be used to optimize the accuracy of the modal parameters. Furthermore, results for the cowling of an outboard motor show that the proposed method is applicable to actual structures.