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Fully nonlinear wave interaction with a fixed breakwater is investigated in a numerical wave tank (NWT). The potential theory and high-order boundary element method are used to solve the boundary value problem. Time domain simulation by a mixed Eulerian-Lagrangian (MEL) formulation and high-order boundary integral method based on non uniform rational B-spline (NURBS) formulation is employed to solve the equations. At each time step, Laplace equation is solved in Eulerian frame and fully non-linear free-surface conditions are updated in Lagrangian manner through material node approach and fourth order Runge-Kutta time integration scheme. Incident wave is fed by specifying the normal flux of appropriate wave potential on the fixed inflow boundary. To ensure the open water condition and to reduce the reflected wave energy into the computational domain, two damping zones are provided on both ends of the numerical wave tank. The convergence and stability of the presented numerical procedure are examined and compared with the analytical solutions. Wave reflection and transmission of nonlinear waves with different steepness are investigated. Also, the calculation of wave load on the breakwater is evaluated by first and second order time derivatives of the potential.

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Interference effect between catamaran demi-hulls has been considered as an adverse fluid-solid interaction; the narrower separation distance between the two hulls, the greater drag force acts upon the catamaran. However, this study is aimed at introducing a novel phenomenon contrasting outcome in semi-planing and planing regimes. As speed and accordingly the Froude number increase the catamaran transits across different modes, free surface profile becomes complicated and so does the interference effect as well as the prediction of catamaran dynamic response. The situation will be even more complex if demi-hull separation narrows where nonlinearity in interference effect is more pronounced. So, free-running tests in six degrees of freedom as well as obtaining fluid flow characteristics using computational fluid dynamics were conducted for a high-speed catamaran vehicle with asymmetric non-prismatic demi-hulls to tackle the problem. The results of catamaran dynamic response reveal that not only is drag reduced substantially up to 15%, but also trim angle diminishes by 30% as hulls separation distance decreases in semi-planing and planing modes. In other words, with increasing speed, and decreasing trim angle by 2.3 o , the current method achieved the goal of consequently reducing the risk of porpoising instability, without the increase of delivered power.