分类： 交通运输工程 >> 船舶、舰船工程 提交时间： 2024-03-23
摘要： 近年来，船舶智能化的发展对船舶目标的检测与分类精度要求越来越高，准确检测并识别船舶的类型及判断船舶的位置是船舶安全航行重要保障。由于船舶目标光学成像过程中易受到风、流、雨、雾等外部背景环境影响，导致基于深度学习的船舶目标检测算法性能降低；同时，船舶类型多样、形态各异以及几何尺寸大小不一等因素均使得船舶目标的检测和识别存在一定的困难。鉴于此，本文提出一种基于多尺度神经网络的目标检测方法用以提高光学影像中船舶目标的检测精度。该方法采用卷积神经网络（Convolutional Neural Networks）对图像予以特征提取，通过改进的基于CSPDarkNet骨干网络以及多尺度网络以实现船载光学摄像头对水上船舶目标的准确检测，提高模型对小目标和密集目标的检测精度。同时利用标签平滑化来防止模型陷入过拟合，并采用非极大值抑制降低重复检测。实验结果表明本文所提出的方法在Ship-Detection数据集上均值的平均精度(Mean Average Precision, mAP)可达84.80%，与Faster-RCNN、CO-DETR等先前目标检测的研究方法相比，检测效果更好，更具备潜在的应用优势。
分类： 交通运输工程 >> 船舶、舰船工程 提交时间： 2018-03-30
摘要： The hydroelastic behavior of very large floating structures (VLFSs) is investigated based on the proposed multi-modules beam theory (MBT). To carry out the analysis, the VLFS is first divided into multiple sub-modules that are connected through their gravity center by a spatial beam with specific stiffness. The external force exerted on the sub-modules includes the wave hydrodynamic force as well as the beam bending force due to the relative displacements of different sub-modules. The wave hydrodynamic force is computed based on three-dimensional incompressible velocity potential theory, and the boundary element method with the free surface Green function as the integral kernel is adopted to numerically find the solution. The beam bending force is expressed in the form of a stiffness matrix. The coupled motion equation is established according to the continuous conditions of the displacement and force. The motion response defined at the gravity center of the sub-modules is solved by the multi-body hydrodynamic control equations, then both the displacement and the structure bending moment of the VLFS are determined from the stiffness matrix equations. To account for the moving point mass effects, the proposed method is extended to the time domain based on impulse response function (IRF) theory. The accuracy of the proposed method is verified by comparison with existing results. Detailed results through the displacement and bending moment of the VLFS are provided to show the influence of the number of the sub-modules, and the influence of the moving point mass.
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