Measuring Propeller Blade Width Using Binocular Stereo Vision

Propeller blade width measurement has been extensively studied in the past using direct and indirect methods, and it plays a great role in determining the quality of the finished products. It has surveyed that previous techniques are usually time-consuming and erroneous due to a large number of points to be processed in blade width measurement. This paper proposes a new method of measuring blade width using two images acquired from different viewpoints of the same blade. And a new feature points matching approach for propeller blade image is proposed in stereo vision measurement. Based on these, pixel coordinates of contour points of the blade in two images are extracted and converted to real world coordinates by image algorithm and binocular stereo machine vision theory. Then, from the real world coordinates, the blade width at any position can be determined by simple geometrical method.

基于辨识理论的船舶时域运动快速计算

根据时域运动方程快速计算的需求,采用4种基于辨识理论并适用于时延函数快速计算的方法,建立替代卷积分项的状态空间模型,同时满足时延函数性质与拟合质量;以海洋石油286船为研究对象,分别采用频域和时域辨识方法进行时延函数拟合结果的对比。计算结果表明:当置信度为0.99时,频域回归法和频域迭代法拟合结果与期望值整体趋势一致,在频率为0.92～1.05rad·s-1时达到峰值,然后逐渐衰减,最后趋于0;在频率为0.05～0.50rad·s-1时,频域回归法的拟合结果与期望值偏差约为20%,准确度明显低于频域迭代法;当置信度为0.99时,脉冲响应曲线拟合法和实现理论法拟合结果与时延函数期望值趋势一致,都是由初始峰值逐渐衰减到约3.5s达到最小值,然后逐渐增大,在约15s趋于0;在7～11s时,脉冲响应曲线拟合法拟合精度低于实现理论法;在考虑垂荡对纵摇方向影响时,实现理论法在横荡、垂荡、纵摇方向拟合的状态空间模型阶数分别为4、3、3阶,是4种方法中最小的;在不考虑垂荡对纵摇方向影响时,频域迭代法在横荡、垂荡、纵摇方向拟合的状态空间模型阶数分为3、2、2,是4种方法中最小的;采用脉冲响应曲线拟合法在考虑垂荡对纵摇方向影响去拟合状态空间模型时,拟合纵摇所需的状态空间模型阶数是不考虑时的2倍,而实现理论法阶数相同。