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681.
Vineet K.Srivastava 《船舶与海洋工程学报》2014,(2)
This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied. The established governing equations for the system have been solved using the central implicit finite-difference method. The obtained difference non-linear coupled equations are solved by Newton's method and satisfactory results were achieved. The solution of this problem has practical importance in the estimation of dynamic loading and motion, and hence it is directly applicable to the enhancement of safety and the effectiveness of the offshore activities. 相似文献
682.
For the purpose of identifying the stern of the SWATH (Small Waterplane Area Twin Hull) availably and perfecting the detection technique of the SWATH ship's performance, this paper presents a novel bidirectional image registration strategy and mosaicing technique based on the scale invariant feature transform (SIFT) algorithm. The proposed method can help us observe the stern with a great visual angle for analyzing the performance of the control fins of the SWATH. SIFT is one of the most effective local features of the scale, rotation and illumination invariant. However, there are a few false match rates in this algorithm. In terms of underwater machine vision, only by acquiring an accurate match rate can we find an underwater robot rapidly and identify the location of the object. Therefore, firstly, the selection of the match ratio principle is put forward in this paper; secondly, some advantages of the bidirectional registration algorithm are concluded by analyzing the characteristics of the unidirectional matching method. Finally, an automatic underwater image splicing method is proposed on the basis of fixed dimension, and then the edge of the image's overlapping section is merged by the principal components analysis algorithm. The experimental results achieve a better registration and smooth mosaicing effect, demonstrating that the proposed method is effective. 相似文献
683.
Vineet K. Srivastava 《船舶与海洋工程学报》2014,13(2):185-192
This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied. The established governing equations for the system have been solved using the central implicit finite-difference method. The obtained difference non-linear coupled equations are solved by Newton's method and satisfactory results were achieved. The solution of this problem has practical importance in the estimation of dynamic loading and motion, and hence it is directly applicable to the enhancement of safety and the effectiveness of the offshore activities. 相似文献
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操纵性能是无人潜器(UUV)航行的重要性能之一,其优劣直接影响到UUV的航行安全和稳定性,UUV操纵性能评判和优化是UUV优化设计的重要组成部分.基于AUTOSUB型无人潜器的设计模型,在充分分析艇体操纵性能的基础上,重点研究UUV水平运动和垂直运动性能,提出了较为完备的UUV操纵性能优化数学模型.采用模糊评判方法构造操纵性系统总目标函数,利用专家咨询法确定了各子系统的权重;通过大量艇体操纵性能数据对各个性能指标进行统计分析,选择模糊数学中对应的隶属度函数进行拟合,确定相应隶属度函数参数;利用禁忌搜索算法对遗传算法的改进而得到的遗传禁忌搜索算法(GA-TS),由并行和分层策略改进遗传算法得到的并行遗传算法(PGA)以及遗传二次载波算法(LGA),将数学模型与这3种算法集成,利用C++语言编写了UUV操纵性能优化软件.通过对总系统优化得到的遗传禁忌搜索算法寻优能力最强,利用该算法研究水平面运动和垂直面运动2个子系统,得到各个性能指标权重对系统目标函数影响程度的排序,同时分别得到-组最佳性能的权重分配. 相似文献
686.
水下爆炸中的气泡脉动载荷会造成舰船的鞭状运动,对其总纵强度产生很大威胁,是战争中造成船体总体毁伤与丧失生命力的主要原因之一。基于势流理论,推导并建立船体梁气泡弯矩的理论与计算方法,同时综合考虑气泡弯矩、船体静水弯矩、波浪弯矩及砰击弯矩等其他影响因素,建立一套完整的气泡作用下船体梁总纵强度估算方法。通过算例,校核典型工况下多种弯矩同时作用时船体梁的总纵强度。计算结果表明,气泡脉动载荷产生的总纵弯矩具有周期性鞭振特性,且数值大于其他弯矩。在评估舰船总纵强度与生命力时,应充分考虑气泡脉动载荷的影响。 相似文献
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689.
The near-field underwater explosion poses a great threaten to marine ships by introducing both local and overall damage on their hull structures. In this paper, a series of near-field underwater explosion experiments were carried out on the mimic steel hull structures to investigate the effects of the standoff distance on their dynamic behavior. Special attention was paid on their deformation process and failure modes. After that, a fluid-solid coupling algorithm was implemented in establishing a finite element (FE) model to simulate dynamic response of the hull structures under a near-field underwater explosion. The numerical results showed a good agreement with the experimental data. A standoff distance threshold was found to result in the maximum structural deformation. The deformation magnitude was monotonically decreased by either increasing or decreasing the standoff distance from the threshold value. 相似文献
690.
The application of floating wind turbines is limited by the high cost that increases with the water depth. Offshore installation and maintenance continue to consume a high percentage of the project budget. To improve the installation efficiency of the floating offshore wind turbine, a novel concept is proposed by the SFI MOVE project. Several wind turbine superstructure components are preassembled onshore and carried to the installation site by a catamaran construction vessel. Each assembly can then be installed using only one lift, and the concept is less sensitive to weather conditions. In this paper, a control algorithm of the proposed hydraulic active heave compensator system is developed using singular perturbation theory to cancel the relative motion between the spar top and gripped preassembly bottom. Closed-loop stability is proven, and the simulation results show that the installation efficiency is improved with an increase in the acceptable weather conditions. 相似文献