相似理论下的桨-轴系统振动特性分析

为更好地了解桨-轴系统的振动特性，以某桨-轴系统为研究对象，基于ANSYS Workbench平台下多个模块建立仿真分析，对缩尺模型下的桨-轴系统计入水压力和离心力的振动进行研究。桨-轴系统振动相似性的研究采用原尺寸模型与缩尺模型，分别求解其固有频率、振型及幅频曲线进行相似性验证。将验证的缩尺模型进行考虑水压力与离心力的振动特性研究。水压力利用Fluent模块对螺旋桨进行敞水计算。将计算结果采用单向流固耦合的方法进行加载。离心力模拟以设置不同的旋转速度实现。谐响应分析采用模态叠加法进行计算。研究表明，缩尺模型在固有频率、振型及幅频曲线上的结果与原模型计算结果基本一致。计入水压力与离心力的桨-轴系统固有频率会有所降低。水压力对桨-轴系统的纵向固有频率影响较大。离心力对桨-轴系统的固有频率影响不明显。     

基于体积力法的半悬挂舵和全悬挂舵回转性对比

针对半悬挂舵和全悬挂舵回转性能差异问题，建立用于模拟螺旋桨推力的体积力模型，评估两种不同形式舵的回转性。对标模KCS船型回转运动进行计算流体动力学（Computational Fluid Dynamics，CFD）模拟，船后螺旋桨作用使用体积力模型替代。开展半悬挂舵回转性CFD模拟，并与试验结果对比验证。设计全悬挂舵并模拟其回转性，与半悬挂舵回转性进行比较。结果显示，半悬挂舵除战术直径与试验结果相差9.48%外，其他回转特性参数与试验结果相差均在3%以内，说明基于体积力法模拟回转性具有较高的可信度。全悬挂舵的回转特性参数均优于半悬挂舵，说明全悬挂舵的回转性能更佳。     

中国首批大型LNG船振动问题及解决方案研究

阐述我国首批大型液化天然气（Liquefied Natural Gas，LNG）船（1.47×105 m3）艉部局部振动问题产生的原因及解决方案。通过在船体机舱线型区域加装涡流发生器等附加装置，改善流经螺旋桨的流场并降低螺旋桨激振力，从而大幅度改善艉部的局部振动。对于新造船的振动问题，选择正确的研究方案是成功解决问题的第一步，但受时间、成本等客观条件的限制，在研究技术方案时可供选择的手段往往不多，采用水下摄像观测、传感器信息采集和计算流体力学（Computational Fluid Dynamics，CFD）模拟分析等技术手段可大幅提高方案制订的效率和准确性。通过剖析LNG船安装、优化涡流发生器解决振动问题的案例，为相关问题及其解决方案的研究提供可借鉴的方法和经验。     

Numerical investigations into the influence of geometric configurations on hydrodynamic characteristics of torpedo anchors

Torpedo anchors are an innovative and cost-effective technology in marine foundation engineering; however, there is a lack of systematic and comprehensive studies on the influence of torpedo anchor geometry on its hydrodynamic characteristics, especially the effect of anchor fin configuration on the hydrodynamic characteristics is rarely reported in the existing literature. Therefore, this study investigates the influence of geometric characteristics of both finless and finned torpedo anchors on their terminal velocity, drag coefficient and installation directional stability in water through CFD numerical analysis in a systematical manner. The considered geometric characteristics include the center of gravity position, shape and angle of anchor tip, shaft and fin aspect ratio, fin number, fin thickness, fin shape, fin position and fin area. Based on the obtained numerical results, some practical design recommendations and impact weighting charts of different anchor geometric factors are provided, which enables a quick qualitative and quantitative assessment of torpedo anchors. In addition, a simple weight-based approach for estimation of terminal velocity and drag coefficient of torpedo anchors considering multiple geometric configuration factors is proposed, which may provide some reference and scientific guidance for experimental and engineering design of torpedo anchors.     

计算流体力学方法在船舶领域的实用性研究

通过CFD（计算流体力学）方法对船舶领域两个典型的工程实例进行了数值计算和流场模拟,模拟的流场与船池试验的流场很吻合。数值计算结果和试验值比较,在特定n范围内相对误差在6．6％以内,满足工程要求。表明数值方法在船舶航速预报方面具有一定的工程实用性,以CFD计算结果为依据光顺流场流线优化船舶阻力性能的可行性也得到工程实例证明。     

外部气流影响下的船舶通风口烟气扩散试验

为预先确定船舶初步设计中的通风口系统在外部气流场作用下的排气效果，找出设计方案在通风口排气方面存在的问题，采用计算流体力学（Computational Fluid Dynamics，CFD）和风道试验的方法进行研究。以外部气流作用下的通风口烟气扩散试验为研究对象，建立含通风口边界条件的风道三维网格模型，求解不同气体流速下的黏性不可压缩定常流动。计算不同外部气流速度下和不同通风口布局下排气中的CO2分布扩散情况，结果表明来流速度增大会加快CO2体积分数沿流向的衰减速率，削弱CO2横向扩散程度。根据试验结果验证计算的准确性，证明应用CFD技术可评估通风口布局的优劣。     

Numerical simulation of piggyback pipelaying under current loadings

For piggyback pipelaying operations, current-induced force and its effect on the piggyback pipe have not been thoroughly studied. In the present study, an improved method in hydrodynamic load calculation and structural modelling is proposed to simulate the pipelaying of a piggyback pipeline. In order to obtain the mean drag and lift force coefficients for the piggyback pipeline subjected to different inflow angles, two-dimensional Computational Fluid Dynamics (CFD) simulations are performed by modelling the piggyback pipeline as two cylinders attached to each other without gap. Then, the acquired force coefficients are used to calculate the hydrodynamic loads through a user-defined function in OrcaFlex based on a cross-flow principle approach. The interaction between the pipeline and the piggyback cable is modelled using two types contact elements which are ring penetrator and non-penetrating contact. The present proposed method is compared with other two widely used engineering methods based on (1) the equivalent diameter and (2) two separate cylinders without accounting for hydrodynamic interaction, in terms of the top tension, and the bending moments at Hang-off Clamps (HOC) and sagbend of the pipeline. The comparison shows that the two widely used engineering methods are not always conservative in force and response predictions. Hence, it is important to consider the hydrodynamic and structural interactions between the piggyback cable and the pipeline. With different current directions, the bending moments at the HOC predicted by the present method vary from 40% lower to 100% higher than those predicted by the two widely used engineering methods.     

基于CFD的船舶水动力计算收敛性分析

为基于计算流体动力学（Computational Fluid Dynamics，CFD）的单体船型水动力性能计算参数提供参考依据，开展相关的收敛性分析。采用CFD数值计算，分析网格尺度、湍流模型和时间步长对于船舶水动力计算的收敛性影响，提出基于CFD的船舶水动力计算优化参数模型，并以水池模型试验验证所提方案的准确性。采用船长2.83%的非结构化网格进行流体计算域网格划分，采用Realizable k-ε湍流模型，计算时间步长取波浪遭遇周期Te的1/200，可更加合理地模拟船舶在规则波中的运动响应，为基于CFD的船舶阻力与耐波性计算提供确定依据。     

LNG船液舱预冷中甲烷双液滴自然对流传热特性分析

针对液化天然气（Liquefied Natural Gas，LNG）船液舱喷雾预冷过程中上下垂直的双液滴在自然对流条件下同种蒸汽中液滴之间影响研究的欠缺，运用计算流体力学（Computational Fluid Dynamics，CFD）方法，基于气液界面能量守恒原理，对不同温差、粒径和相对距离条件下甲烷双液滴自然对流传热特性进行分析。研究结果表明：液滴表面热流密度、传热量和质量蒸发率随温差10～190 K的增大而线性增大；液滴表面热流密度随粒径0.1～2.5 mm的增加先快速减小后缓慢减小，传热量和质量蒸发率随粒径的增加而快速增加；上液滴表面热流密度、传热量和质量蒸发率随相对距离10～70的增加基本不变，下液滴表面热流密度、传热量和质量蒸发率随相对距离10～70的增加而缓慢增加。     

Effects of roughness on hydrodynamic characteristics of a submerged floating tunnel subject to steady currents

The effects of surface roughness as induced by marine fouling on the hydrodynamic forces on a submerged floating tunnel (SFT) are experimentally and numerically investigated in detail at Reynolds numbers Re = 8.125 × 10³–5.25 × 10⁴. A sensitivity analysis to different roughness parameters including roughness height, skewness, coverage ratio, and spatial arrangement is performed. In addition, an optimized parametric cross-section for an SFT is proposed, and the hydrodynamic performance of the parametric shape and circular SFT cross-section shape with roughness elements is compared. The pressure distribution along the SFT, flow separation and wake characteristics are analyzed to provide a systematic insight into the fundamental mechanism relating the roughness parameters and flow around an SFT. In order to better understand the nonlinear relationships among structural geometry, roughness parameters, flow states, and structural response, an artificial intelligence method using Random Forest (RF) for feature importance ranking is applied. The results show that with the parametric shape, the hydrodynamic forces on the fouled SFT can be effectively mitigated. The roughness height and coverage ratio affect the equivalent blockage and hence, change flow separation and recirculation length in the wake. Lower skewness of the roughness elements can increase the critical Re by changing the relative roughness parameter. Horizontal arrangement of the roughness elements on an SFT generally results in the largest hydrodynamic forces, compared to staggered and vertical distributions. Throughout the feature importance ranking, the flow regime is found to be the most important feature of the hydrodynamics of the SFT. In addition, the SFT cross-section shape and roughness coverage ratio play a dominant role.