Abstract : Numerical instabilities due to fluid inertia appear when solving the free motion of a solid submerged within a heavy fluid such as water. In the present thesis, a numerical scheme is proposed to overcome this problem. Three-dimensional simulations using Computational Fluid Dynamics and Euler-Newton equations use too much computing resources for a reasonable investigation of the general case. It was therefore decided to design and build a two-dimensional hydrodynamic tunnel in order to validate the numerical tool. First, a static two-dimensional tank has been built to verify the feasibility of such an apparatus. It reveals the chaotic aspect of the trajectories of light objects when viscous forces are highly unsteady. It is observed in the hydrodynamic tunnel that an income flow stabilizes the translations. The evolution of the angle is still controlled by the wake. In the case of a parallelepipedic object, presenting sharp corners, boundary layer separations occur and induce instabilities. The prediction of the angle is then difficult. This method is then used to simulate biomimetic propulsion using a porpoising foil. The hydrodynamic solver is a potential flow code. To understand the influence of each parameter on the performances, all degrees of freedom are fixed. Our results for the thrust loading coefficient are in conformity with the Theodorsen theory over the whole range of parameters. The parametric study confirms that the Strouhal number is playing the same role for the oscillating wing, the advance parameter is playing for the propeller. The two propulsion devices are found to be comparable and a general guidance for comparison between the two propulsion systems is developed.When a change of pace is required, the variable pitch propeller is more efficient than a variation of the pitch amplitude during the foil motion. Results in free motion demonstrate the robustness of the method.