The Study On The Characteristics Of Flow Field In The Process Of Wave Impact

In coastal and offshore engineering,the wave impact in the splash zone has great influence on the safety of the open structures.In the process of wave slamming,the impact pressure with short duration and high peaks occurs when the water contacts the subface of the structure,which causes the destabilization of superstructure and the fatigue failure of joints. Along with the expansion of the ocean exploitation in the 21th century,the forecast of wave slamming loads in the design of coastal and offshore engineering is increasely valued and has become an important subject.It is significant to deeply research the characteristics in the process of the wave impact.This paper presents the experimental investigation and numerical simulation of the slamming on the horizontal plate suspended over the water surface in the splash zone.In the model experiment,the advanced instantaneous measuring technique,Particle Image Velocimetry(PIV),is applied to acquire the instantaneous velocity field of wave slamming. From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of the wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous pressure peaks and the according velocities of water particles is studied by probability analysis.In the numerical simulation,firstly,a numerical irregular wave flume with active absorption of re-reflected waves is simulated using VOF method.An active absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume.The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures.As for the end of the numerical flume,the numerical sponge layer achieves the damping elimination to the irregular wave.On the conditions of total reflection and partial reflection,the numerical results using the non-reflecting numerical wave flume are compared with that of the ordinary numerical wave flume to verify the performance of the non-reflecting numerical wave flume and the stability of the incident waves along the numerical wave flume.Secondly,the characteristics of pressure and flow field in the irregular wave impacting is investigated by use of the unreflected numerical model.The distributions of characteristic pressures and corresponding vertical velocities of fluid are presented.The influence of relative wave height,relative structure width and relative clearance on wave impact pressure and vertical velocity of fluid is discussed.The relation between irregular peak impact pressures and corresponding peak vertical velocities of fluid is analyzed.Finally,the synchro coupling between the neighbouring flow field of the structure and the external area is achieved by introducing the nested grid refinement(NGR) technique based on VOF method.The boundary conditions of velocity,pressure and wave surface in a 2D SOLA-VOF code is described.Detailed numerical simulation of flow field in the process of wave impact on the marine structures is implemented.The precision of the computed flow fields with nested grid and uniform grid are compared with the experimental flow fields.The computational efficiency of nested grid and uniform grid is discussed.