Tensile strength of sea ice using splitting tests based on the digital image correlation method

The splitting test is a competitive alternative method to study the tensile strength of sea ice owing to its suitability for sampling.However,the approach was questioned to the neglect of local plastic deformation during the tests.In this study,splitting tests were performed on sea ice,with 32 samples subjected to the regular procedure and 8 samples subjected to the digital image correlation method.The salinity,density,and temperature were measured to determine the total porosity.With the advantage of the digital image correlation method,the full-field deformation of the ice samples could be determined.In the loading direction,the samples mainly deformed at the ice-platen contact area.In the direction vertical to the loading,deformation appears along the central line where the splitting crack occurs.Based on the distribution of the sample deformation,a modified solution was derived to calculate the tensile strength with the maximum load.Based on the modified solution,the tensile strength was further calculated together with the splitting test results.The results show that the tensile strength has a negative correlation with the total porosity,which agrees with previous studies based on uniaxial tension tests.

基于实船测量的船舶结构冰激振动特性研究

冰区航行的船舶结构在冰载荷作用下产生明显的振动现象,明确冰激振动特性对冰级船舶的结构设计与冰区航行安全评估具有重要意义。为研究船舶的冰激振动特性,在我国第8次北极科学考察中对“雪龙”号科考船的结构振动开展了系统的实船测量。由于冰船作用区域主要位于船体艏部,该研究采用三向加速度传感器对艏尖舱区域的振动响应进行了测量。为研究海冰类型对结构振动的影响,通过视频摄像机对航线冰情进行了观测,并对比分析了开阔水域、碎冰区、平整冰区、冰脊区中船体的振动响应特性。采用ISO 6954—2000规范对“雪龙”号科考船进行冰激振动评价,并对实船振动频率和幅值进行统计学分析。结果表明,冰激振动的幅值介于有害振动和无害振动之间,其中沿船长方向的振动幅值最小,而沿船宽方向的振动幅值最大,船体的振动幅值服从广义极值分布。此外,海冰的附加质量影响了船体冰激振动频率,冰激振动的幅值均随航速和冰厚的增加而增大。

基于动力效应的船体远场冰载荷测量与识别

[目的]提出一种基于动力效应的冰载荷反演识别方法。[方法]针对船−冰相互作用过程和结构响应特性之间的卷积关系,使用格林函数建立描述冰载荷的卷积积分方程。针对“天恩”号极地运输船的北极航行,安装应变传感器测量船艏区域的冰激响应。对于求解矩阵的病态性与测量中的随机噪声,引入正则化方法解决识别计算中的不适定问题,并获取动冰载荷时程的数值近似稳定解。依托“天恩”号极地运输船的北极航行实测数据,通过船体在海冰作用下的应变响应对冰载荷进行反演识别。[结果]结果表明,格林函数能够有效识别远场冰载荷的时间历程。[结论]载荷识别的有效性受应变信号强度的影响较为明显。此外,在不同海冰破坏模式下,浮冰尺寸和船−冰接触面积是影响冰载荷特征的关键因素。

基于实船试验的河冰载荷特性研究

冰载荷是船舶在冰区航行的主要威胁。为确定内河破冰船在破冰作业中的河冰载荷特性,论文开展了船体结构冰载荷的实船测量。在轻型破冰船上安装了分布式应变测试系统,采用双片式剪应变测试方法对船首部位的结构变形进行测试。通过有限元法建立了船首部位的数值模型,采用影响系数矩阵法对船首监测区域内6个子区域的冰压力进行了识别。试验结果显示,结构冰载荷主要为单峰三角形形式。对破冰过程中的冰载荷峰值和周期的均值、最大值进行了提取与统计分析,统计结果表明河冰载荷的峰值服从Weibull分布。此外,将河冰的冰载荷特征与海冰进行对比,不同厚度的河冰载荷作用形式和周期与海冰具有较高的相似性。由于河冰的强度高于海冰,河冰的载荷峰值略高于相同厚度的海冰。