It has been shown previously that a simple optimization technique (downhill simplex search) operating on free response data, can be used to accurately identify light damping in a single degree of freedom linear system. This approach has the advantage that it is insensitive to phase errors as only one response measurement is required as input, however it is currently restricted to a linear model of the system under investigation. This paper extends the technique to explicitly account for weak non-linear damping terms as might occur in fluidelastic systems. Response data for a single degree of freedom system with a small cubic damping term are obtained by numerical simulation and are used to demonstrate the enhanced procedure. The technique is shown to be robust in the presence of line noise and the effect of initial parameter estimates is explored.
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