鲸豚表皮微尺度柔性变形的减阻原理研究

鲸豚类海洋高速动物具有突出的低阻高效游动能力,一直是仿生学的重要研究对象.为了探索柔性表皮减阻的可行性,在参考国外关于活体齿鲸类海洋动物表皮观测结果的基础上,本文采用RANS方法和动网格技术建立了仿生表皮微尺度柔性变形的数值模拟方法.文中对不同柔性变形的仿生表皮,以及刚性波面、刚性平板开展了对比数值计算,详细对比了流场和阻力成分,并重点分析了减阻原理.研究表明,随行波柔性表皮在波速高到一定程度时可实现明显减阻.     

基于PIV测量的柔性壁减阻试验

为了解不同性能的柔性壁对湍流边界层的减阻效果,利用粒子图像测速技术( PIV)对刚性壁面与4种材料的柔性壁面的湍流边界层流向速度分量进行测量.从边界层速度分布求得壁面切应力的分布,并由此得到柔性壁与刚性平板的平均摩擦阻力系数.实验结果表明,柔性壁面的边界层速度分布在对数律上有所平移,具有特定性能的柔性壁具有一定的减阻作用.     

随机粗糙与沟槽面复合结构减阻特性研究

采用旋转锥板式剪切力的测试系统,测试了不同试样对甘油和水混合液的减阻性能.制备得到的优化复合结构在剪切率为200s-1～2000s-1时,可实现减阻约从130%～19%,且减阻率随剪切率的增加呈递增趋势;在剪切率2000s-1时,最大减阻可达18.9%分析表明,粗糙结构、沟槽结构及沟槽的排列方式共同作用,实现了试样减阻效果大幅度提高和减阻范围的扩展.     

基于转盘测阻法的天然乳胶涂层减阻特性研究

利用转盘测阻法对天然乳胶涂层的减阻特性进行探究,确定雷诺数和柔性系数对涂层减阻效果的影响。利用喷涂法将天然乳胶和氨水混合溶液喷涂于转盘上,制成一种柔性涂层,并通过密度测定、硬度测定、力学性能测试和动态热力学分析等试验方法对涂层的物理性能与基本力学性能进行测定。试验结果显示,天然乳胶涂层密度为950 kg/m³,与水的密度接近,并且该涂层具有弹性模量低、撕裂强度大,断裂伸长率大的优点。采用转盘测阻法对涂层阻力进行测试,结果显示,当涂层厚度为0.2 mm、转速为100 r/min时达到最大减阻率15%,因此可断定天然乳胶涂层具有良好的物理机械性能,其减阻效果与水流状态及自身柔性存在一定关系,在特定情况下可实现良好的减阻效果。     

船舶气层减阻和空腔减阻技术的研究进展

对国内外空气润滑减阻技术的研究进展情况进行分析,包括气层和空腔减阻的试验研究、数值计算、实船项目和节能效果分析等;对空气润滑减阻的分类、不同通气方式的比较、影响气层和空腔减阻效果的因素和相应物理现象产生的原因等进行阐述,同时,对国内外实船项目和研究成果以及平板试验和船模试验研究进行介绍.针对我国气层和空腔减阻技术的研究现状,提出相应的前景展望.     

沟槽面减阻效果影响因素及减阻机理的分析

采用雷诺平均N-S方程和RNG k-ε湍流模型计算V型沟槽面的湍流边界层流动和粘性阻力,研究了沟槽尖峰形状和雷诺数对减阻效果的影响规律,初步分析了沟槽面减阻机理.指出:沟槽尖峰处的圆角半径越小其减阻效果越好,沟槽斜面中下部的壁面应力随着圆角半径的减小而降低,但尖峰处的局部壁面应力会随之增大;来流速度对沟槽减阻率的影响很大,对于一种尺度的V型沟槽,存在着一个具有较好减阻效果的来流速度范围,而沟槽面在沿来流方向上的布置位置对减阻效果的影响非常小;沟槽尺度对减阻效果很剧烈;沟槽尖峰处生成的二次涡是产生减阻效果的根本原因,二次涡的强弱与沟槽减阻率的大小紧密相关.     

管道局部减阻装置减阻性能数值研究

针对一突缩管道,在管径变化处加入环状机翼,利用机翼对管道连接处压力分布产生的有利干扰来减阻。采用数值模拟的方法,对该局部减阻装置的阻力性能进行研究,结果表明该减阻装置能达到10%～15%的减阻效果,并且管路流速越大减阻效果越明显,对于船舶管系的设计和优化具有一定的指导意义。     

气泡减阻技术研究进展

总结气泡减阻技术研究的发展历程,介绍微气泡减阻和大气泡减阻技术研究进展,介绍气泡减阻技术的实船应用情况,指出存在的问题和重点技术研究方向.     

船舶减阻技术方法综述

快速性是船舶航行的重要性能之一，新型减阻技术不断被提出推动了船舶快速性的发展。从船舶阻力原理出发，对国内外船舶减阻技术展开分析，指出当前主流研究方向为空气减阻、仿生超疏水减阻、附体减阻以及断级减阻技术；针对这4种减阻技术探究影响减阻效果的主要因素，总结当前减阻技术中存在的问题；并介绍船体加热-超声协同减阻和网状射流等新型减阻技术，对未来减阻技术的发展进行展望，为船舶减阻技术的进一步研究提供借鉴。     

减阻,减摇的响应围裙研究

本文根据围裙柔性动力学的理论分析,并应用系统分析和反馈原理,把气垫船的柔性围裙简化为一个二自由度的气弹和水弹的动力反馈系统,提出了气弹增益、水弹增益、响应度和隔振因子等物理概念。通过船模水池试验和分析,深入地讨论了响应围裙减阻和减摇的原理以及围裙气垫系统参数设计对全垫升气垫船性能的影响.     

随行波仿生减阻材料几何形状的模拟数值计算

为配合研制船用喷涂聚脲仿生减阻材料,用CFD模拟数值计算所设计的材料表面的涡街随行波几何形状,确定出能稳定留驻旋涡的仿海豚皮肤表面微型凹凸起伏的具体尺寸.     

Effect of a drag-reducing polymer solution ejection on tip vortex cavitation

Experiments regarding the modification of the foil geometry and/or active or passive mass injection in the vortex core have been performed to investigate the possibility of inhibiting tip vortex cavitation. The ejection at very low flow rates of drag-reducing polymer solutions at the tip of hydrofoils and propeller blades has demonstrated effectiveness as a tip vortex cavitation inhibitor. This paper reports the results obtained with an elliptical hydrofoil, of 8cm maximum chord and 12cm haif-span, operating at Reynolds numbers, of =10⁶, much larger than those previously reported in the literature. Lift coefficients and critical cavitation numbers were determined for a variety of flow and polymer solution ejection conditions. Tangential and axial components of the mean velocity as well as velocity fluctuations along the vortex path were also measured. At 12.5 m/s free stream velocity and a variety of angles of attack, the ejection of a 500 ppm aqueous solution of a drag-reducing polymer at a flow rate of about 5 cm³/s leads to a decrease of up to 30% in the cavitation number. This occurs without modification of the lift coefficient and, hence, of the midspan bound circulation of the foil. Moreover, water injection does not cause any appreciable change in the cavitation numbers. The tangential velocity profiles along the vortex path during polymer ejection indicate that the potential region remains the same, while the viscous core dimension increases, and the maximum tangential velocity decreases substantially as compared to the no ejection or water ejection experiments. Thus, the pressure coefficients at the vortex axis are smaller than for the no ejection or water ejection cases and cause the reduction of the critical cavitation numbers. It is speculated that this inhibition effect is due only to swelling of the polymer solution when exiting the ejection orifice.List of symbols a core radius (distance to the vortex axis for maximum tangential velocity) - C ₁ lift coefficient - c _max maximum chord - Cp pressure coefficient at the vortex axis - Cp _min minimum pressure coefficient at the vortex axis - d _e diameter of the ejection port - m ejection flow rate - P reference pressure - P _v vapor pressure - V free stream velocity - V _a axial velocity - V _t tangential velocity - v _r radial component of the velocity resulting from jet swelling - x downstream distance from the tip of the foil - y, r distance to the vortex axis - angle of attack - r difference between the swollen jet and the ejection port radii - boundary layer thickness - tip vortex intensity - _d ( _de ) desinent cavitation number (with ejection) - _i ( _ie ) inception cavitation number (with ejection) - _ii normal stresses - viscosity - v kinematic viscosity - p specific mass     

Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel

Determination of the flow structure near the wall is essential for a clear insight into the phenomenon of skin friction reduction by microbubbles in a turbulent boundary layer. An important parameter, is the bubble concentration or void fraction in the wall region in drag-reducing conditions. The purpose of this paper is to show drag-reducing effects due to microbubbles in a water channel and, more importantly, to show the dependence of the drag-reduction values on the near-wall void fraction. A two-dimensional channel with an aspect ratio of 10 was specially built for this purpose with provisions for air injection through porous plates. Skin friction was directly measured by a miniature floating element transducer with a 5-mm circular sensing disk mounted flush on the top wall 67 channel-heights downstream of the injector. The wall friction in the presence of air bubbles was found to be reduced under the same bulk velocity when compared with the value without air. Detailed void fraction profiles across the channel were obtained by a sampling probe and a fiber-optic probe. Better collapse of the drag reduction data, independent of different profile shapes, was found when plotted against the near-wall void fraction than against a cross-sectional mean void fraction. While this dependence reconfirms that the phenomena are essentially inner-region dependent, the lack of influence of the bubble distribution patterns away from the wall implies lack of outer region influence.     

柔性腕的力学性能仿真分析

RCC是针对轴孔装配作业中插轴人孔作业和类似的插拔作业而设计的一种适从装置。主要对非线性有限元方法在RCC柔性腕的力学性能仿真中的应用进行了探讨和研究，进而为新型高性能柔性腕的设计提供理论依据和基础。     

Probability distributions of wave run-up on a TLP model

Wave run-up on multi-column compliant and rigid platforms both on the weather-side and beneath the platform deck is a complex wave–structure interaction problem. Predictions based upon higher order hydrodynamic design codes have been improved our understanding of this phenomena but have not appreciably reduced the reliance on model tests and statistical analyses. In this study a three parameter distribution model is developed based upon the inclusion of linear, second-order, and mean contributions to the wave run-up utilizing the method of L-moments. Explicit expressions are derived relating the L-moments and the input from experimental data. The sample L-moments are developed from a linear combination of ordered sequence of the data and consequently the high order L-moments, i.e. L-skewness and L-kurtosis, are less biased than the corresponding ordinary moments. The L-moment definitions of the variance, skewness and kurtosis are numerically compared with values obtained using the more standard definitions for these parameters. Rigid hull measurements are compared with the compliant hull configuration for a mini-TLP model. The sea-states investigated include the relatively benign sea conditions off of West Africa and the more extreme sea environments of Gulf of Mexico.     

顺应式垂直通路立管的动力响应优化研究

海洋立管的动力响应优化要考虑复杂的环境载荷,如波浪、流以及浮体运动,有时还需考虑立管与海床的耦合作用,这个过程需要执行大量耗时较大的有限元分析,从而使动力优化的工作进展困难。针对此问题,本文将近似模型技术运用到FPSO的顺应式垂直通路立管（CVAR）的动力响应优化问题。优化以壁厚、管径等几何参数作为变量,优化目标是使总重量最小及等效应力在许用应力水平之下。研究给出了3种近似模型方法的比较分析,使得优化结果更具有可靠性。结果表明,3种近似模型方法的优化效果和效率彼此都非常接近,并且都能在CVAR的优化效果和减小耗时方面有出色表现。     

基于Femap的风帆基座局部强度分析

以上海海事大学教学实习船"育明"轮为对象,研究船舶加装风帆装置的船体结构强度问题,通过局部加强风帆基座和船体连接部分来保证风帆安装部位的结构稳定性。利用Solidworks和Femap软件建立了风帆基座和船体的有限元模型,计算得到该模型在10级风载荷下受风角度从0°~60°的应力和应变。最终结果表明,在10级风载荷下,该船风帆基座和局部加强后的船体的强度符合要求。     

电子海图显示与信息系统开发库的设计与实现

电子海图显示与信息系统(Electronic chart display information system,ECDIS)开发库是各种海上信息系统的重要开发平台.满足国际标准的ECDIS开发库分成6大子功能系统,介绍每个子系统的具体作用.从最具特色的两个关键技术着手,说明了S57电子海图数据的解洋方法和步骤,提出了S52数字表示的符号库实现技术和提高物标符号化速度的查找表数据结构.     

适应共同结构规范的30．8万t VLCC船型开发

708研究所以“经济、安全、环保”（ESE）为宗旨，开发了适应双壳油船共同结构规范（CSR）的30．8万t VLCC船型。文中介绍了CSR对结构设计的关键要求以及对总体设计的部分要求，并着重对VLCC总强度储备、中剖面设计和粗网格有限元分析等关键技术进行了分析，以期初步阐明CSR对VLCC结构设计的影响。