The company Deepwater Energy BV, Netherlands developed a unique water turbine called as the Oryon Watermill (OWM). It was the aim of the company to obtain an efficient numerical model for the turbine. A numerical model, which serves as a good starting point, has already been developed by Maniyara [1]. This model suffered from certain limitations and to tackle these it was realized that a smaller and simpler problem needs to be solved. The current thesis deals with developing a numerical model for this smaller problem. In this problem, an airfoil is hinged at its leading edge and rotating under the influence of a periodic water flow. Further, the rotation of the airfoil is restricted by a stopper. This restriction leads to a collision between the airfoil and the stopper due to which the motion of the airfoil is changed suddenly. This is a Fluid-Structure Interaction (FSI) problem. To model the structural part i.e. the airfoil motion, a non-smooth dynamical analysis is needed. Then, the entire FSI problem is solved in a faster and efficient way using the harmonic balance method. For this purpose, the non-smooth dynamics of the airfoil have to be solved using the harmonic balance method. In the thesis, a novel approach is developed to solve the non-smooth dynamics problem using the harmonic balance method. Initially, this new approach is implemented and verified in MATLAB on a 1D level. Later, a MATLAB-OpenFOAM coupled solver is developed to compute the solution to the airfoil problem using this newly developed approach.