In the present study, a Modified-Landl model is introduced to estimate the structural oscilla- tion amplitude of a circular cylinder, which is subjected to a fluid flow, during lock-in. The Modified-Landl model is exactly the same as Landl model with regard to the van der Pol and forth order terms while just the coefficients are modified and corrected in a different way than Landl and with a new approach. Here, the displacement, velocity and acceleration cou- plings are used to solve the Modified-Landl equation for wake oscillators. The response of the coupled equations is assumed to be harmonic. A linear approach is adopted to simplify and derive the solutions algebraically. The results for amplitude during lock-in versus the re- duced velocity and maximum structural oscillation amplitude versus the Skop-Griffin pa- rameter are plotted and compared with those of Facchinetti and de Langre. The present modi- fied model evinces a better compliance with experiment with respect to van der Pol model.

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