基于试验数据优化辨识孤立冰块的流拖曳系数

Optimization and identification on current drag coefficients of isolated ice floe based on experimental data

流拖曳系数是海冰动力学模型中的重要参数,实际海冰运动时受到水流的底面剪切作用和侧面正压力作用,对应的拖曳系数分别为摩拖曳系数和形拖曳系数.利用实验室波流水槽设备,对长方体平底、长方体粗糙底和圆饼形淡水冰试样进行拖曳运动试验,获得26组冰样运动数据.根据这些试验数据,利用动量法原理和优化方法构造了识别摩拖曳系数和形拖曳系数的参数辨识模型,并计算出相应的拖曳系数.在此基础上,引入描述表面粗糙度的两个指标——轮廓支承长度率和轮廓均方根偏差,统计分析了粗糙度指标对拖曳系数的影响.此外还得到摩拖曳系数同冰样长度和吃水深度之比的关系,该关系可用于计算冰山和浮冰的摩拖曳系数.

Current drag coefficients are most important parameters in sea ice dynamics model. Both shear stress on ice bottom and pressure on ice draft section contributed to ice floe movement, and in the numerical simulations ice corresponding coefficients for their contributions are skin drag coefficient and form drag coefficient respectively. By using a wave-current flume, current-ice drag experiments were performed by freshwater ice blocks with different shapes, including cuboids with smooth bottom surface and rough surface and disk with smooth bottom surface, and 26 data sets were obtained. Using these data, the parameter identification model is established to distinguish skin drag coefficient from form drag coefficient by applying momentum method theory and optimization method, and the corresponding drag coefficients are obained. Based on the two roughness index-profile bearing length rate and root-mean-square deviation of the profile, relationships of the coefficients and the index are analyzed. In addition, the relationship between skin drag coefficient and the ratio of ice block length to draft is obtained, which can be used to compute the skin drag coefficients of the iceberg and ice floe.