STUDY ON INFLUENCE OF WAVE-CURRENT INTERACTION ON PREDICTION OF ROGUE WAVE TAKING VISCOUS EFFECT INTO ACCOUNT

摘要

Wave-current interaction is a common phenomenon in real sea and has significant influence on sea conditions, thus threatening the safety of offshore structures. Waves countering current is one of the main reasons for occurrence of rogue waves, which imperils offshore structures and is of much importance for research. Based on Computational Fluid Dynamics (CFD), the simulation of viscous flow for wave generation in a Circulating Water Channel (CWC) has been carried out. In the calculation model, the motion of an oscillating flap type wave maker is simulated to generate specified waves by controlling movement of dynamic mesh in numerical model. Smoothing and local refreshing of dynamic meshes have been done to adapt meshes. Then, viscous flow simulation of wave generation among current in numerical tank is accomplished by using Reynolds-Averaged-Navier-Stokes (RANS) equation, renormalization group method based (RNG-based) k-e turbulence model and Volume of Fluid (VOF) method as treatment of free surface. Both waves propagating along and against current have been investigated. To validate the numerical model, a part of calculation results are compared with the experimental results in CWC for regular wave propagating along current. Furthermore, calculations based on linear wave theory and modified nonlinear Schrodinger Equation (mNLS) are also performed. For further investigation of occurrence of rogue wave in deep water, focusing technique is adopted by using transient water wave. Results show that wave height and group velocity of wave sequence would change notably when wave propagates along preexisting large-scale current. Wave height decreases as the velocity of uniform current increases and wave sequence arrives at given position earlier when propagating on faster current. On the other hand, on a counter current, waves are steepened and wave height increases dramatically. Based on the numerical results, several characteristics and principal values such as wave height and asymmetry have been discussed. The effects of viscous flow and wave-current interaction on prediction of rogue waves are analyzed and evaluated. Accordingly, some concluding remarks on improving of numerical model of rogue wave are given.