A semi-submersible platform of V-shaped base with NREL 5 MW wind turbine is designed. Hydrodynamic load, aerodynamic load and mooring system were coupled for calculation and analysis. Hydrodynamic load was based on potential flow theory, aerodynamic load was based on leaf element momentum theory, and mooring system was based on quasi-static method. By coupling program F2A, AQWA software and FAST software are linked to complete the time-domain fully coupled simulation of the platform under the combined action of wind, wave and current, and the dynamic response of the floating wind turbine under different current loads are calculated and analyzed. The results show that velocity and incidence angle of current load have great influence on motion response and mooring force of floating wind turbine.
The effect of different obstacle arrangements on the explosion flame dynamics of inhomogeneous hydrogen-air mixture is investigated by numerical simulation,and the explosion characteristic parameters predicted by the simulation are all in good agreement with the experimental results.The simulation results show that the premixed flame undergoes four stages of evolution in the tube:spherical flame,finger flame,conical flame,and flocculent flame.When the flame passes through the obstacle,the flow field is seriously unstable,resulting in serious distortion of the flame.When the obstacle is ar-ranged on both sides,the flame reaches the pipe outlet first,and the pressure reaches the peak the fastest.The obstacle at the tube top can significantly increase the explosion pressure,and compared with the bottom arrangement,the explosion peak overpressure increases by 23％and 74％when the obstacle is arranged on both sides and at the top of the tube,respectively.This study can provide theoretical guidance for hydrogen safety planning and explosion protection.
The simulation of radiated noise from underwater vehicles and the signal propagation characteristics in un-derwater acoustic channels are two hot topics in the field of underwater acoustics.Simulate the radiated noise power spec-trum of underwater vehicles through empirical formulas and the design of FIR filters.On this basis,combined with the Bell-hop acoustic toolbox,simulate radiated noise signals transmitted through ocean channels.A study was conducted on the ocean channel under the ice water interface using the Burke-Twersky(B-T)ice water model.The results show that the power spectrum amplitude undergoes varying degrees of attenuation based on horizontal propagation distance and sound source depth.Moreover,the presence of boundaries on ice water causes additional reflection and loss of sound lines,resulting in an additional attenuation of the power spectrum at the receiving point of 20～30 dB.
Addressing the ongoing challenge of enhancing propulsion efficiency in rim-driven thrusters (RDTs), a novel energy-saving appendage was designed to mitigate energy dissipation and improve efficiency. Computational fluid dynamics was utilized to examine the disparities in open-water performance between RDTs with and without this appendage. The Reynolds-Averaged Navier–Stokes equations were solved using the Moving Reference Frame approach within the established STAR-CCM+ software. The accuracy of these methodologies was confirmed through a comparison of numerical simulations with experimental data. A meticulous analysis evaluated the alterations in propulsion efficiency of RDTs pre- and post-appendage integration across various advance coefficients. Additionally, a comprehensive assessment of thrust and torque coefficient distributions facilitated a comprehensive understanding of the appendage’s energy-saving potential. Results demonstrated that the new appendage diminishes the diffusive wake behind the rotor disk, fostering a more uniform flow distribution. A notable reduction in the low-pressure zone on the rotor blade’s thrust side was observed, accompanied by an elevation in the high-pressure area. This generated a distinct pressure disparity between the blade’s thrust and suction sides, mitigating the low-pressure region at the blade tip and reducing the likelihood of cavitation. The manuscript further elucidates the rationale behind these alterations, providing detailed insights into flow field dynamics.
Considering the background of ship emission control area, multi-objective ship speed optimization is carried out with fuel cost and charter cost as optimization objectives to reduce ship operating costs and improve ship energy efficiency. A multi-objective optimization method based on the combination of butterfly optimization algorithm and linear weighting is selected to obtain the Pareto optimal solution set. Finally, the ideal point distance method is used as the decision-making approach to determine the best compromise solution from the Pareto optimal solution set. The results show that when optimizing the sailing speed, fuel costs decrease by 1.98%, sailing costs decrease by 17.32%, and overall operating costs for ships can be effectively reduced by 5.62%, greatly improving the economic efficiency of shipowners and shipping companies while meeting environmental requirements.
Ocean towing system is a classic fluid-structure coupling system.However,towing systems are typically dy-namically simulated based on constant drag coefficients determined from experimental data.To improve the method of se-lecting a fixed empirical drag coefficient for simulation,this paper applies the Morrison equation to the nodal position finite element method.The improved nodal position finite element method(NPFEM)is combined with the Reynolds number aver-aged N-S(RANS)method to predict the hydrodynamic forces along the cable within the Reynolds number range.By calcu-lating the obtained hydrodynamic forces,the NPFEM is interpolated for fluid dynamics.The results indicate that the simula-tion results obtained by this method are more consistent with the experimental results,and better simulate the real motion of the towing cable.This FSI method reveals the vibration caused by the cable dynamics and vortex structures determined by the real strong fluid dynamics around the towing system.
为了抑制船舶柴油机的进排气以及空调通风管路内的噪声,亥姆霍兹共振器通常被用作消声器来耗散声波.声学数值模型基于有限元方法,运用COMSOL5.3软件,对平行耦合型亥姆霍兹共振器在频域内建立模型,求解线性化的Navier-Stokes方程.通过仿真分析共振器侧壁穿孔率、孔的数量以及来流马赫数的变化对共振频率、传递损失以及吸声性能的影响.结果表明:穿孔率由25％增至50％时,能够拓宽消声频带和提高吸声性能;在固定穿孔率情况下,侧壁孔数的增加有益于提升共振器的吸声性能,特别是高来流马赫数工况(Ma≥0.07)比较明显.此外随着来流马赫数的增加,由于2个平行耦合的共振腔之间的共振作用,使得模型能产生3个及以上的共振频率.
显控台是舰船电子信息系统的重要组成部分,其功能性能反映了舰船电子信息系统装备技术的发展,本文研究国外舰船基础软硬平台发展,对计算机体系、基础软硬件、计算机工程、显控与人机交互、显示、测试性可靠性和保障性技术等核心关键方面进行分析研究,阐述舰船显控台总体技术发展趋势,展望未来新一代舰船显控台总体技术的研究方向.
针对舰船红外图像获取性难和敏感性问题,提出一种舰船红外目标图像视觉传达增强方法,提升舰船红外目标图象质量.采用改进的中值滤波预处理舰船红外图像,有效去除舰船红外图像中海浪的冲击噪声;通过Renyi熵方法将处理后的舰船红外图像二值化分割为前景域和背景域,以区分舰船目标和背景;通过改进的平台直方图均衡方法剔除舰船目标和背景红外图像冗余的像素点,均衡分配灰度值,实现舰船目标和背景增强;经改进的Canny对增强后舰船目标和背景图像边缘加权融合,得到最终的舰船增强图像.实验结果表明,所提方法可以有效去除舰船图像噪声,提升舰船红外图像的对比度,对图像和图像边缘的信息保有量充分,大幅提高了红外图像的质量和清晰度,加大了舰船红外目标图像视觉传达增强的可行性.
船舶尾浪数值计算可以辅助评估船舶的尾浪性能,优化船舶的船体形状和运行参数,提高航行性能和燃油效率,也可以用于预测船舶尾浪对其他船舶、港口和海岸线的影响,帮助船舶运营者和港口管理者做出合理的决策,确保船舶运行和港口安全.本文介绍一种广义边界元法的流体动力学分析方法,通过建立高速排水型船舶的控制方程,并在有限元仿真软件Fluent中进行了高速排水型船舶的尾浪数值计算和仿真.
船舶在恶劣海况下会受到低频波浪载荷的作用,船体主机基座结构常处于交变应力状态,同时持续性工作的主机会对主机基座产生高频主机振动载荷作用,可能会带来主机基座结构的疲劳破坏.为了探究高低频载荷耦合作用下的疲劳损伤计算,提出一种计及主机振动载荷的高低频载荷联合作用下主机基座疲劳强度计算法.首先,采用线性频域的谱分析法直接计算波浪载荷作用下的主机基座结构热点疲劳损伤;然后采用时域分析计算法和S-N曲线计算出主机振动载荷作用下的热点疲劳损伤.最后,结合双峰谱疲劳计算理论,对高低频载荷耦合作用下的应力响应谱进行计算,提出一种计及主机振动载荷的高低频载荷联合作用下主机基座疲劳强度计算法.结果显示,相比较将2种载荷作用下的疲劳损伤直接叠加计算法,考虑2种载荷耦合的计及主机振动载荷的高低频载荷联合作用下主机基座疲劳强度计算法得到的疲劳损伤结果其损伤度约增加了15％～50％.研究表明,对航行在恶劣海况下的船舶局部主机基座结构进行疲劳评估时,使用所提方法可以提高疲劳损伤计算的准确性.
本文提出一种水下无人航行器集群仿真试验系统的设计方法,在构建UUV平台仿真模型、目标模型、海洋环境模型、关键算法模型等的基础上,开展了UUV集群仿真系统架构、想定及任务规划、仿真运行流程、系统接口、系统部署方式等全系统、全流程的UUV集群仿真试验系统设计.通过本系统方案设计研究,能为UUV集群仿真试验平台的开发提供有效支撑.
为了提高船舶电力系统的安全性和可靠性,本文通过对船舶电力系统的特点和需求进行分析,设计了一种电力系统智能继电保护整体方案,分别从方案开发的软件层面和硬件层面进行详细介绍.硬件层面采用了模块化设计的方法,根据继电器保护的原理搭建了模块的功能和接口,基于TMS320F2808搭建了高性能的信号处理上位机;软件层面基于Microsoft Visual Studio 2008设计了相应的软件架构,包括数据采集模块、数据处理模块和控制模块等.最后,基于虚拟仪器技术进行了电力系统智能继电保护方案的仿真测试.
为了提高舰船的网络安全,降低网络攻击的影响,提出深度学习算法的舰船网络安全状态识别方法.采集舰船网络流量数据,使用随机森林算法计算舰船网络流量数据特征基尼系数,以此为标准比较、排序每一个特征在随机森林中的贡献平均值,得出不同特征的重要程度,将重要程度高的特征输入BiLSTM神经网络之中,利用神经网络的自我学习完成对舰船的网络安全状态的识别,并且增加注意力机制进一步提高学习效率和分类准确率.实验数据表明,在利用随机森林进行特征提取时,特征数量选择为75个时,可兼顾特征充分参与分支、计算效率与识别准确度;网络受到攻击后流量有明显的改变,根据网络流量改变情况,使用该方法能够判断出船网络遭受的攻击方式.
海上分布式作战是利用海上有人无人平台组成的具备部署分散、信息联通、指控智能、火力集中的作战体系,以较低成本消耗/牵制敌作战力量,对敌形成"非对称"优势.美国是分布式作战概念的提出者及引领者,将其视为应对未来可能发生的大国战争的制胜关键,大力支持DARPA积极开展水下无人平台研制、水下无人体系构建及水下有人无人协同指控等项目.本文以促进水下体系构建、形成有人无人联合作战能力为目标,分析国外典型项目、典型作战模式,总结国外水下无人系统及有人无人协同应用发展趋势,探讨分布式作战概念下的水下有人无人作战新模式,可为水下体系发展及装备研制提供借鉴.
换热器是一种把热量从一种介质传递到另一种介质的装置.由于换热表面污垢的存在,换热器的性能随着时间的推移而恶化.为了保持换热器的高效率,有必要定期对换热器的性能进行评估,在线监测的工艺参数能够帮助对换热器换热性能进行预测.本文利用温度和流量等参数计算表征换热器性能相关的指标,并基于共享权重长短时记忆网络(SWLSTM)建立预测模型,利用历史运行数据对其进行训练.通过与验证数据比较,验证了所建立模型预测的高精度和快速性;同时与传统神经网络模型进行比较,可见本模型在预测精度的优越性.通过换热性能参数的预测,能够合理规划停机清洗时间,降低成本.
为了研究燃气轮机在水下非接触爆炸冲击载荷作用下的抗冲击能力,以燃气轮机中的重要部件压气机为抗冲击数值模拟研究对象,利用商用软件Hyper Mesh开展压气机的有限元建模,并对原始模型进行简化.将有限元模型导入Abaqus软件,通过模态计算验证简化模型的合理性,利用正负三角波分别从垂向、横向和纵向作为冲击载荷输入,基于显示求解器对压气机开展抗冲击能力的时域计算和分析,得到压气机部件在冲击环境下的薄弱环节.结果表明,压气机的垂向冲击响应远大于其他2个方向的冲击响应;支架是压气机结构的抗冲击薄弱环节;动叶片在垂向冲击的作用下和机匣之间没有发生碰撞的现象.所得结论可以为压气机抗冲击试验提供思路.
加速度计测量误差决定了惯导系统中位置、姿态、速度等导航信息精度.针对环境温度变化对加速度计测量精度的影响展开讨论,分析了工作温度与测量误差间的关系;提出一种基于相关向量机(Relevance vector machine,RVM)的加速度计温度误差建模及补偿方法,能够实现温补模型参数的准确与快速解算.结果表明,补偿后的加速度计在10℃～50℃的温度范围内测量误差减小了50％以上,提高了其对环境温度变化的适应能力.
为推进国家水上救助打捞能力现代化,基于对水上应急救援作业特点与发展现状的分析和水上应急救援装备技术体系的构建,摸清了我国救捞系统现有装备技术的"家底".围绕充分发挥行业专家优势,建立了综合采用层次分析和模糊综合评判的多层次能力评估模型.综合考虑水上应急救援的影响因素,从陆、海、空、天4个维度建立了水上应急救援装备技术保障能力评估指标体系.实践结果表明,基于对我国水上应急救援装备技术体系构建的综合多层次能力评估模型能有效评估我国水上应急救援装备技术的保障能力,较好地反映装备技术发展实际.
基于计算流体力学和计算结构动力学方法,对气液两相流诱导水平U型管振动进行数值仿真研究.对比分析气液两相流典型流型,重点研究了段塞流工况下流体动态激励特性和管道振动响应特性.结果表明:段塞流是振动最强烈的流型;在气相折算速度不变的情况下,随着液相折算速度的增大,段塞速度和段塞频率增大,段塞长度减小;水平U型管两弯头的振动响应基本对称;段塞频率、流体激励力、管道模态以及振动响应之间相互关联.本研究可为气液两相流流固耦合振动数值仿真提供参考.
