Transient responses of a VLFS during landing and take-off of an airplane

The transient elastic deformation of a pontoon-type very large floating structure (VLFS) caused by the landing and take-off of an airplane is computed by the time-domain mode-expansion method. The memory effects in hydrodynamic forces are taken into account, and great care is paid to numerical accuracy in evaluating all the coefficients appearing in the simultaneous differential equations for the elastic motion of a VLFS. The time-histories of the imparted force and the position and velocity of an airplane during landing and take-off are modeled with data from a Boeing 747-400 jumbo jet. Simulation results are shown of 3-D structural waves on a VLFS and the associated unsteady drag force on an airplane, which is of engineering importance, particularly during take-off. The results for landing show that the airplane moves faster than the structural waves generated in the early stage, and the waves overtake the airplane as its speed decreases to zero. The results for take-off are essentially the same as those for landing, except that the structural waves develop slowly in the early stage, and no obstacle exists on the runway after the take-off of airplane. The additional drag force on an airplane due to the elastic responses of the runway considered in this work was found to be small in magnitude.     

载人潜器阻力性能的数值计算和模型试验及船型优化

采用多块结构化网格对某载人潜器模型周围计算区域进行网格离散,采用Realizable k-ε湍流模型对潜器周围绕流场进行数值模拟.在船模拖曳水池中进行载人潜器模型不同艏向角和垂直上升及下潜航行时的阻力试验.将阻力的数值计算结果与试验值进行对比,两者的偏差在可接受范围内.考虑载人潜器主体的舯纵剖面的二维外形,用多岛遗传算法对其粘性流场的阻力数值计算结果进行船型的一体化优化,得到二维阻力最小的优化外形.将舯纵剖面外形的优化结果应用到三维载人潜器主体,比较优化前后的主体阻力.数值计算结果表明,载人潜器主体外形优化前后阻力的优化收效在30%以上.     

柔性立管阻力特性试验数据处理技术

本文提出3种数据处理方法分析均匀来流中柔性立管的初始阻力特性。首先通过分析柔性立管在均匀来流中的变形及振动情况,分离出立管流向的初始变形对应的弯曲应变。根据复杂梁的弯曲变形理论,建立起弯曲应变与平均阻力之间的微分方程。随后,针对试验中获取的立管轴向力及立管表面弯曲应变,提出计算平均阻力的数据处理方法,并进行算例验证与分析。最终使用提出的数据处理方法分析试验数据,得到立管表面各截面处的阻力分布。     

弹性变形对大口径炮弹气动特性影响的靶道试验

为了研究气动弹性对大口径炮弹气动特性和飞行稳定性的影响,利用室内弹道靶道,进行了大口径柔性和刚性炮弹模型的靶道自由飞行试验,利用试验数据判读处理出模型飞行过程中的飞行速度、攻角、进动角、空间质心坐标x,y,z和柔性弹模型的弹性变形量,拟合处理出其主要气动力和力矩系数,对比分析了大口径柔性和刚性炮弹模型的动特性和飞行稳定性。研究结果表明,柔性弹模型的阻力系数明显大于刚性弹模型的阻力系数,柔性弹模型变形后升阻比降低,滚转力矩显著增大;根据拍摄的闪光阴影照片和数据处理得到的章动曲线可看出,柔性弹的弹性变形对弹丸稳定性有较大影响,导致弹丸飞行不稳定。     

Response prediction of long flexible risers subject to forced harmonic vibration

Several research efforts have been directed toward the development of models for response prediction of flexible risers. The main difficulties arise from the fact that the dynamic response of flexible risers involves highly nonlinear behavior and a self-regulated process. This article presents a quasi-steady approach for response prediction of oscillating flexible risers. Amplitude-dependent lift coefficients are considered, as is an increased mean drag coefficient model during synchronization events. Experimental validation of the proposed model was carried out using a 20-m riser model excited by forced harmonic vibration at its top end. Large variations in the hydrodynamic force coefficients, a low mass ratio value, and synchronization events are the main features of the model presented in this article. Experimental validation was provided for the asymmetric, transverse, diagonal, and third vortex regimes.     

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。     

斜面升船机原体水力学试验研究

在小型纵向斜面升船机中,坝顶用链条传动机构转移船厢的布置是可行的,试验中观测了牵引力、系缆力和水体波动,给出了计算这些数值的公式。     

近底管线绕流及涡激振动的二维有限元数值模拟

应用有限元方法通过求解原始变量的二维不可压粘性流体的N-S方程和管线振动方程,数值模拟了近底管线的绕流及漩涡脱落引起的管线振动,采用ALE方法解决因管线振动引起的动网格问题和流固耦合问题。数值模拟了雷诺数90相似文献   

机场跑道延伸设计技术

通过总结境外某机场跑道延伸总体设计的思路,提出根据环境条件因地制宜合理确定跑道延伸方案,分析在满 足规范规定和使用要求的前提下,跑道长度、纵坡、调头坪、跑道端安全区和升降带等关键尺度的优化和确定,为同类工 程设计降低工程造价,提高土地利用率提供了有益的尝试和借鉴。     

Ship hull form optimization by evolutionary algorithm in order to diminish the drag

This study presents a numerical method for optimizing hull form in calm water with respect to total drag which contains a viscous drag and a wave drag. The ITTC 1957 model-ship correlation line was used to predict frictional drag and the corrected linearized thin-ship theory was employed to estimate the wave drag. The evolution strategy (ES) which is a member of the evolutionary algorithms (EAs) family obtains an optimum hull form by considering some design constraints. Standard Wigley hull is considered as an initial hull in optimization procedures for two test cases and new hull forms were achieved at Froude numbers 0.24, 0.316 and 0.408. In one case the ES technique was ran for the initial hull form, where the main dimensions were fixed and the only variables were the hull offsets. In the other case in addition to hull offsets, the main dimensions were considered as variables that are optimized simultaneously. The numerical results of optimization procedure demonstrate that the optimized hull forms yield a reduction in total drag.     

潜伏式高速船型变航态自航数值模拟

针对一种具有半潜-水面航态变换功能的新型潜伏式高速船型,基于非稳态RANS方程组与VOF模型求解粘性流场,结合动态流域边界与滑移网格技术,对目标船在垂直面内三自由度运动及其喷水推进器叶轮随船定轴高速旋转的耦合运动进行数值模拟。结果表明：在相同主机平均转速条件下,所预报自航点体积傅氏数与自航模型试验结果的相对误差在7%以内;从半潜到水面的航态变换过程中,船体有显著的纵倾与升沉,船体主要克服压差阻力,船体兴波由相互叠加的首波、肩波、尾波逐渐发展为首尾分明的两个波系,在喷水推进器射流区内捕捉到生成和发展的高强度涡系。     

高速航行体的自然超空泡流阻力特性研究

利用Fluent6.2对水下带圆盘空化器高速航行体的自然超空泡流动进行了数值模拟,计算分析了超空泡高速航行体的阻力特性,研究了空化器直径、航行体长细比对航行体超空泡减阻效果的影响,分析了高速航行体的超空泡减阻率。结果表明,超空泡形态下随着航行体速度衰减,航行体压差阻力系数缓慢减小,粘性阻力系数迅速增大,航行体的总阻力系数增加;航行体阻力系数与头部空化器直径的平方成反比;增加航行体的长细比,可以获得更小的阻力系数;高速航行体的超空泡减阻率可达95%以上。最后将仿真计算结果与水靶道试验进行了对比,二者基本相符。     

二维凹槽内加机翼减阻效果的数值分析

对平板、二维凹槽和二维凹槽内加机翼三种模型进行对比分析，数值探讨二维凹槽内加机翼的减阻效果。数值摸拟采用商业软件fluent，结果表明在二维凹槽内加入机翼后的阻力比平板的阻力有14．8％的减阻效果。     

拖曳嵌入式板锚在中国的研究近况(英文)

Experimental and theoretical studies of drag embedment plate anchors recently carried out in Tianjin University are summarized in this research paper, which involve a series of important topics relevant to the study of drag anchors. The techniques for measuring the trajectory and movement direction of drag anchors in soils, the techniques for measuring the moving embedment point and reverse catenary shape of the embedded drag line, the penetration mechanism and kinematic behavior of drag anchors, the ultimate embedment depth of drag anchors, the movement direction of the anchor with an arbitrary fluke section, the reverse catenary properties of the embedded drag line, the interactional properties between drag anchor and installation line, the kinematic model of drag anchors in seabed soils, and the analytical method for predicting the anchor trajectory in soils will all be examined. The present work remarkably reduces the uncertainties in design and analysis of drag embedment plate anchors, and is beneficial to improving the application of this new type of drag anchor in offshore engineering.     

Effect of surface roughness and initial gap on the vortex-induced vibrations of a freely vibrating cylinder in the vicinity of a plane wall

We studied the effects of the surface roughness and initial gap on the responses of vortex-induced vibration (VIV) of a circular cylinder near a stationary plane wall, employing numerical methods. The VIV response amplitudes, lock-in regions, hydrodynamic forces, VIV trajectories and flow fields for three different surface roughnesses and two different initial gaps were systematically compared. The results reveal that the reduced velocity range can be divided into three regions based on the VIV amplitude as pre-lock-in, lock-in, and post-lock-in regions. The width of the lock-in region is not sensitive to the variation of the roughness. The mean drag coefficient has a decreasing tendency with the increased roughness. For a small initial gap, the clockwise wall boundary layer vortices has coalesced with the clockwise vortices shed from the upper side of the cylinder, which further suppresses the shedding of the counter-clock wise vortices from the lower side of the cylinder. The vortex shedding flow pattern displays a weak 2S mode. However, for a large initial gap, there is no coalescing action operating in the wake region and hence most of the vortex shedding flow patterns show an asymmetric 2S mode.     

Bending behavior modeling of unbonded flexible pipes considering tangential compliance of interlayer contact interfaces and shear deformations

Rigorous analytical formulations are given to describe the gross slip initiation and progression in tensile armor layers of unbonded flexible pipes. Then two mechanisms are thought to contribute to the decrease of layer stiffness before gross slip begins. The first one considers the micro-slip occurred at the interlayer contact interfaces. The relative displacement between an armor wire and the underlying layer is determined according to the theory of contact mechanics. Shear deformations of the supporting plastic layer are taken into account in the other mechanism where plane sections no longer remain plane. The results of bending moment-curvature relationship from the presented models are compared with the available test data and good correlations are found. The shear model is seen to describe the slip transition better than other models do.     

实尺度喷水推进船拖泵工况数值模拟与分析

对于四泵推进的喷水推进船,在巡航工况时中间加速泵通常处于锁轴状态,其拖曳阻力的大小对喷水推进器的选型以及船泵机的最优匹配有着重要影响。然而,拖泵阻力很难通过船模试验的方法获得。为此,该研究在验证均匀和非均匀条件喷水推进器数值模型的准确性基础上,采用数值试验的方法对18节航速下某双泵推进喷水推进船的实尺度"船体+两台喷水推进器"系统带自由液面的流场进行了数值模拟,计算此时喷泵拖曳阻力及其所占船体阻力的百分比。以此喷泵拖曳阻力作为参考,对尺寸与上述喷水推进泵相近的某四泵推进喷水推进船的喷泵进行了选型和设计,并对该船在18节航速下加速泵拖曳阻力的大小进行了计算,进一步验证选型时拖曳阻力取值的合理性。为消除尺度效应的影响采用实尺度模型对"船体+四台喷水推进器"系统带自由液面的非定常流场进行计算,并探索了大尺度条件下船泵系统考虑自由液面和重力影响的非定常计算方法。     

Improvement of Propeller Hydrodynamic Drag and Efficiency on USCG Cutters Operating in Trailshaft Mode

Large US Coast Guard cutters spend much of their underway time with only one of two propellers operating. The offline propeller is "trailed," often creating a significant amount of hydrodynamic drag. Operators from the fleet do not appear to have any specific guidance on how best to reduce this drag. Using the propeller analysis tools PSF-3 and PSF-10, propeller thrust coefficient values versus advance coefficient values were created for the propellers of the USCG 270' cutters. These values—and the associated drag—vary significantly in magnitude based on the trailed propeller pitch. Based upon sea trial measurements, expected magnitudes of this drag versus pitch setting were predicted. Minimum drag pitch settings were identified for an operational 270' cutter at 8 knots. RPM and pitch settings for maximum hydrodynamic efficiency for the online shaft are sometimes developed during ship acquisition. In the current work, a methodology for conducting such a study is discussed to demonstrate to ship operators the relative ease with which they could perform this analysis on board, if effective power and propeller thrust coefficient values are available. Consideration of prime mover specific fuel consumption rates together with propeller hydrodynamic efficiencies is discussed.     

稳定流作用下海底悬跨管线涡激振动研究

讨论了目前用于海底悬跨管线涡激振动预报的主要数值模型,针对海底管线悬跨段涡激振动问题编制了有限元分析程序,程序采用梁单元模拟管跨结构,动力响应计算方法采用VIVANA模型,模型控制方程采用Newton-Raphson迭代算法求解。采用Larsen,Koushan等人(2002)和Larsen,Baarholm等人(2004)给出的两组不同的用于确定升力曲线的参数曲线进行计算,将计算结果与Tsahalis(1984,1987)的模型实验结果进行了比较。结果表明本文的涡激振动模型能够预报间隙比e/D=∞时海底悬跨管线的涡激振动响应;采用Larsen,Koushan等人(2002)参数曲线得到的计算结果与间隙比e/D=∞时的实验结果符合较好,Larsen,Koushan等人(2002)参数曲线较Larsen,Baarholm等人(2004)参数曲线更适合于海底悬跨管线的涡激振动预报。     

基于MOGA的潜器快速性和操纵性综合优化研究

基于Pareto解的多目标优化方法NSGA-II应用至潜器的快速性与操纵性综合优化设计之中。通过回转体潜器阻力性能的数值计算结果建立了阻力的近似计算模型,并与系列模型试验结果进行了比较;通过估算潜器的水动力系数,根据水平面线性运动方程得出水平面操纵运动稳定性和机动性的衡准指标。优化后,得到了阻力与回转直径的Pareto最优解的散点图,设计者可针对不同需求的潜器,从中进行选择,保证了Pareto最优解对应的每一艇型设计方案在满足操纵性要求下阻力最小,或在该阻力值的条件下操纵性最优。