Application Of PIV On Flow Field Measurement Under Floe Ice In Laboratory Modeling

Sea ice movement is an important element in the global water cycle.It also plays a vital role in both the global climate change and the maritime economic activities in the cold water region.Drag coefficient is the key parameter in the sea ice dynamic model.Its accuracy decides the precision of the dynamic model.In the past,vortex motion method,cross-section method and activity level method were used to gain the empiric values of sea ice drag coefficient in some regions;hence the fixed value in some certain territorial waters shows great discreteness.So it is necessary to establish the relation between the drag coefficient and the geometric shape such as the floating ice thickness and the surface roughness,and it will greatly raise the accuracy and adaptability of the drag coefficient,and further improve the precision of the sea ice dynamic model.The main task of this thesis is to study the variations of flow field under floe ice with the change of ice thickness and surface roughness.This thesis firstly presents an introduction of the theory of the Particle Image Velocimetry(PIV) technology and set up a theoretical foundation for its application in the tests of flow field under floe ice.Then the equipments of the PIV system,tank used in the test and floe models are mentioned,velocity of flow in the ice free flow field is calibrated,and applications of PIV technology in measuring floe field under floe ice with different shadings and sizes are carried out.Studies on the flow field under floe ice can be divided into three parts:the first part is to analyze the disturbance range of flow field under floe ice by different shadings,sizes of the floe ice and current velocity.The results reveal that the disturbance range of flow field shows linear increase with the shading angle and the draft,while has no obvious relationship with the change of current velocity.In the second part,through calculations of the roughness length under different conditions,a conclusion about the linear relationship between the roughness length and the angle of floe ice shading is drawn out.The third part is to study the wake flow behind floe ice a logarithmic distribution of the current velocity in the wake flow is found.Vortexes always exist close to the floe ice,and the farther the floe ice is,the bigger influence of flow-making speed to the wake flow.