基于首达波与次达波到达时差的深海浅层移动声源定位

为克服海洋环境不确定性、信号接收及处理偶然误差对定位精度的影响,基于单水听器多途声到达时差,利用扩展卡尔曼滤波(EKF)算法对深海浅层移动声源进行定位研究。结合Butterworth带通滤波算法及Bellhop射线模型识别水声试验数据中的多途到达波,对比分析各到达波间的相对能量大小,并确定信噪比较大的首达波与次达波为研究对象;以单频信号作为匹配序列,计算时域相关性大小,得到首达波与次达波的声到达时差;以首达波与次达波的声到达时差为观测值,构建EKF声源定位模型,得到移动声源的深度、水平距离及速度等信息。研究结果表明:在深海水声信道中,当声源和水听器都位于浅表水层时,直达波与海面反射波重合,首达波与第1次海底反射波能量相对较大;滤波结果与实测数据吻合较好,验证了EKF算法可较好地实现对水下移动目标定位。

Effect of Ship Bow Overhang on Water Shipping for Ship Advancing in Regular Head Waves

This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves. To perform this investigation, a series of free-running tests was conducted in regular waves using an experimental model of a multipurpose cargo ship to quantify the amount of shipping water. The tests were performed on five bow overhang variants with several combinations of wavelength and ship speed conditions. It was observed that the quantity of shipping water was affected by some parameters such as wavelength, ship speed, and bow shape in terms of an overhang extension. The results show the significant influence of an overhang extension, which is associated with the bow flare shape, on the occurrence of water shipping. These results involve the combined incoming regular waves and model speed.