Effect of Internal Flow on Vortex-Induced Vibration of Submarine Free Spanning Pipelines

At present, most researches on the vortex-induced vibration of submarine free spanning pipelines ignore the effect of internal flowing fluid; furthermore, there are no research reports considering the coupling effect of internal and external fluid with the free span. In this paper, combining Iwan's wake oscillator model with the differential equation derived for the dynamic response of submarine free spanning pipelines with inclusion of internal flow, the pipe-fluid coupling equations are developed to investigate the effect of internal flow on the vortex-induced vibration of the free spans. The finite element approximation is implemented to derive the matrix equations of equilibrium. The Newmark method combined with simple iteration is used to solve the system of equations. The results indicate that the internal fluid flow may cause the shift of resonance band to the lower frequency and a slight decrease in the peak value; the effect will be more pronounced with the increase of the span length and can be weakened in the presence of the axial tension.

Experimental Study on Free Spanning Submarine Pipeline Under Dynamic Excitation

Seismic load has a significant effect on the response of a free spanning submarine pipeline when the pipeline is constructed in a seismically active region. The model experiment is performed on an underwater shaking table to simulate the response of submarine pipelines under dynamic input. In consideration of the effects of the terrestrial and submarine pipeline, water depth, support condition, distance from seabed, empty and full pipeline, and span on dynamic response, 120 groups of experiments are conducted. Affecting factors are analyzed and conclusions are drawn for reference. For the control of dynamic response, the span of a submarine pipeline is by far more important than the other factors. Meanwhile, the rosponse difference between a submarine pipeline under sine excitation and that under random excitation exists in experiments.

Analysis of Dynamic Characteristics of Submarine Free Spanning Pipelines by Complex Damping Method

Considering the effect of the internal flowing fluid and the external marine environmental condition, the differential equation for the vortex induced vibration (VIV) of the free spanning pipeline is derived and is discretized by the Hermit interpolation function. The free vibration equation with the damping term is solved by the complex damping method for the natural frequency, and then the effect of fluid damping on the natural frequency of the free spanning pipeline is analyzed. The results show that fluid damping has a significant influence on the damped natural frequency of the free spanning pipeline in the lock in state, while it has little influence when the pipeline is out of the lock in state. In the meantime, the change of the free span length has the same effect on the damped natural frequency and the undamped natural frequency.

Study on Model Tests and Hydrodynamic Force Models for Free Spanning Submarine Pipelines Subjected to Earthquakes

A test rig is built to model the dynamic response of submarine pipelines with an underwater shaking table in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, China. Model tests are carried out to consider the effects of exciting wave directions and types. Based on the experimental results, two hydrodynamic force models derived from Morisen equation and Wake model are presented respectively. By use of hydrodynamic force models suitable for free spanning submarine pipelines under earthquakes, diseretized equations of motion are obtained and finite element models are established to analyze dynamic response of free spanning submarine pipeline subjected to multi-support seismic excitations. The comparison of numerical results with experimental results shows that the improved Morison and Wake hydrodynamic force models could satisfactorily predict dynamic response on the free spanning submarine pipelines subjected to earthquakes.

Condition Identification Based on Vibration Measurements for Free Spanning Submarine Pipelines

Free spanning pipelines are suspended between two points on an uneven seaffoor. The variations of structural conditions, such as the changes in soil property, flow velocity, axial force and span length etc., directly affect working performance of the whole submarine pipeline system. But until now few researches have focused on condition identification for free span （CIFS）. A method to identify the operational conditions of free spanning submarine pipelines based on vibration measurements is proposed in this paper. Firstly, the ill-posedness of CIFS is analyzed in detail. Secondly, the framework for CIFS based on the nonlinear kernel discriminant analysis （KDA） is established. Thirdly, the internal structural characteristics of natural frequencies, normalized frequencies and frequency change ratios are studied. And then the condition feature vector for CIFS is extracted by use of the vibration measurements. Finally, the validity of the proposed approach is evaluated by a case study. The results demonstrate that the proposed approach can effectively identify each condition of free span when condition variation occurs even if under measurement noise. It is concluded that the proposed method is a promising tool for CIFS in real applications.

Experimental investigation of vortex-induced vibrations of long free spans near seabed

There are many experimental studies dedicated to determining the effect of the proximity of a plane boundary on the vortex-induced vibration (VIV) of submarine pipeline spans, but they all only concerned the first mode VIV motion of the pipe. In this paper, a pipe model, 16 mm in diameter, 2.6 m in length and with a mass ratio (mass/displaced mass) of 4.30, was tested in a current tank. The reduced velocity was in the range of 0-16.7 and gap ratios at the pipe ends were 4.0, 6.0 and 8.0. The response of the model was measured using optical fiber strain gauges. Results of response amplitude and frequency were presented and the transition from the first dominant mode to the second one was shown. In the tests, it was found that the response amplitude experienced a continuous transition between the two modes, but the dramatic increase in the response frequency appeared with the shift in dominant mode from the first mode to the second one as the flow velocity increased. As the gap ratio decreased, the shift in the dominant mode took place at a higher reduced velocity.

无爪图的支撑k-端点树的存在性

树T中度为1的点称为叶子,叶子数目不超过k的树称为k-端点树.图中存在一个哈密尔顿路,说明图中存在恰好含有两个叶子的支撑树.自然就有了关于哈密尔顿路问题的一个推广:考虑图中至多有k个叶子的支撑树即支撑k-端点树的存在性问题.通过控制集参数,确定了连通无爪图中存在支撑k-端点树条件.

无溶剂体系中Span修饰的猪胰脂酶催化茶油与亚油酸酯交换

在无溶剂体系中以Span20、Span80和Span85修饰的猪胰脂酶（Span20-PPL、Span80-PLL和Span85-PPL）催化茶油与亚油酸进行酯交换，以酯交换量为考察指标，研究Span20、Span80和Span85与猪胰脂酶（PPL）的相互作用对其催化油脂酯交换反应的影响．结果表明：30℃下，相同时间内Span20-PPL、Span80-PPL扣Span85-PPL催化酯交换的交换量与PPL催化酯交换的交换量稍小，24h的酯交换量都在4％～7．5％；50℃下，Span20-PPL、Span80-PPL和Span85-PPL催化酯交换的交换量比PPL催化酯交换的酯交换量高，24h的酯交换量分别为19．9％、22．4％、21．2％和15．6％；70℃下，Span20-PPL、Span80-PPL和Span85-PPL催化酯交换的交换量比PPL催化酯交换的交换量低。24h的酯交换量分剐为23．7％、26．8％、22．3％和31．5％．Span20、Span80和Span85与PPL的相互作用对其催化油脂酯交换结合量的影响与表面活性剂的类型和反应温度有关．

K_（1，r）－Free图的生成树及其算法

证明了任一连通的Ｋ（１，ｒ）－Ｆｒｅｅ图都有最大度小于等于ｒ的生成树，并建立了算法。

无柱大跨地铁车站结构选型优化及敏感性分析

针对无柱大跨地铁车站结构受力情况,以影响地下车站结构受力的不同顶底板结构模型及跨度、覆土、侧压力系数等影响因素为研究对象,采用Midas GTS数值模拟计算软件建立模型,计算分析出无柱大跨地铁车站较优的结构类型。研究结果表明,无柱结构设置拱形顶底板对改善结构受力有显著效果,跨度、覆土、侧压力系数等影响因素对无柱结构受力的敏感性影响不同。

K_（1，r）－free图的次限制树多项式算法

设Ｇ＝（Ｖ，Ｅ）为一连通图，ｄ＞０整数．Ｇ中存在生成树Ｔ，使得Δ（Ｔ）小于ｄ吗？这一问题已被证明是ＮＰ－完全的，故不太可能有多项式解法．本文证明了当Ｇ是Ｋ１，ｒ－ｆｒｅ时，则有Ｏ（ｎ２）的算法求出Ｇ的生成树Ｔ，使Δ（Ｔ）≤ｒ。

任意不等跨等截面连续梁自由振动分析

以等截面任意不等跨连续梁为对象,基于Euler-Bernoulli梁理论,利用分段梁模型和分离变量法,在考虑连续梁边界以及梁段位移连续性条件的基础上,提出了任意多跨不等跨连续梁固有频率和振动模态分析新方法。利用该方法可高效得到任意不等跨连续梁的固有频率和振动模态,该方法将为多跨连续梁车-桥耦合等受迫振动响应研究提供新的思路和便利。

基于调研数据的部分斜拉桥设计关键参数研究

针对部分斜拉桥设计关键参数缺少足够规范指导的问题,通过对国内外的部分斜拉桥进行设计主要参数调研统计,并与现有相关规范、科研成果进行对比研究,讨论了部分斜拉桥各型结构体系适用性、拉索布置形式,总结给出拉索倾角和间距、边主跨比、塔跨比、索梁刚度比和无索区长度等重要设计参数取值范围。结果表明,拉索倾角一般为11°~35°,主梁上拉索间距一般采用3.5 m~8 m,塔上的拉索间距一般采用0.5 m~1.2 m;3跨布置时,边主跨比一般集中在0.41~0.70,塔跨比宜采用1/3~1/13,索梁刚度比宜小于30;主跨跨中无索区长度与跨径之比宜取0.06~0.21。

大跨空间钢结构数字化建模关键技术与应用

自由曲面大跨度空间网格结构建筑外形复杂,对结构建模提出了新的挑战。针对空间网格结构建模的痛点和难点,本文提出了空间网格结构六种建模关键技术和方法:等分弦长法、直线插值法、曲线连线法、网格映射法、函数投影法和智能找形法,并据此开发了空间网格结构建模成套程序,该程序具有专业性强、集成度高、适用范围广、使用方便和算法智能等优点,大大提高了自由曲面空间网格结构的建模效率,具有较高的推广应用价值。

第十届中国花卉博览会世纪馆结构设计

世纪馆是第十届中国花卉博览会的标志性建筑,形如一只蝴蝶,东西向长度约280m,南北向长度约115m,壳体厚度250mm,整个壳体支撑在剪力墙和长细摇摆柱之上,是目前国内较大的自由曲面混凝土薄壳结构。详细介绍了世纪馆的设计重点、难点:1)对于自由曲面的找形,采用了基于薄膜原理的数值逆吊找形方法;2)通过施加间接预应力,为壳体的自由边界提供约束;3)在世纪馆中间通道处设置钢-混凝土组合张弦桁架,从而减小基底水平反力;4)考虑地基基础协同变形的一体化分析方法,可以对桩基进行更合理的布置,进而评估基础变形对上部壳体的影响;5)对于预应力薄壳结构,需有合理的施工顺序,以减少施工过程对结构产生的影响;6)对于自由曲面壳体的建造,施工模板定位采用BIM建模,钢筋布置采用正交和径向布置相结合。分析表明,世纪馆结构是安全、经济、合理的。

悬跨海底电缆涡激振动特性及疲劳损伤分析

悬跨海底电缆作为细长柔性结构,在静力平衡状态下具有一定的垂度,在水流作用下的涡激振动特性与海底管线和海洋立管等结构也有很大的不同,其振动模态受垂跨比影响很大。通过物理模型试验开展了不同垂跨比下悬跨海缆的涡激振动和疲劳损伤特性研究。试验模型按照水弹性相似准则设计,试验中测量了不同流速下海缆模型产生涡激振动时的应变历时数据,采用模态分析法获得了模型涡激振动时的振动模态和振幅。分析了不同流速下海缆模型的振动模态、应变和疲劳损伤的变化和分布特征。试验结果表明:垂跨比显著影响了海缆的涡激振动模态和应变幅值大小。在本试验流速范围内,对一定长度的悬跨海缆模型,当垂跨比较大时,随着流速的增大,模型涡激振动的主响应振动依次出现反对称1阶和对称1阶模态;当垂跨比较小时,模型涡激振动的主响应模态依次出现反对称1阶和对称2阶模态。当涡激振动主响应模态为反对称1阶时,疲劳损伤最大值达到0.1~0.7。

自由悬跨分析在海底管道维修中的应用研究

在册镇管道全线几何检测中,发现KP25.3 km及KP19.7 km处出现较为严重的变形缺陷,变形量分别达到22%及12%,工程中采用结构管卡修复法进行缺陷维修。由于管卡安装时会导致管道产生悬跨,因此,为保证作业安全,需计算施工期管道允许的最大悬跨长度。结合工程实际,采用疲劳筛选准则分析计算了海底管道维修期的最大允许悬跨长度,并基于ABAQUS有限元模拟软件,对海底管道维修期的最大允许悬跨长度进行校核。结果表明,当12%、22%变形点处悬跨长度分别为18.4、21.3 m时,其最大Von-Mises等效应力校核结果均在管道许用应力范围内。

地下连续墙对无柱大跨地铁车站地震反应影响

无柱大跨地铁车站抗震设计是否考虑地下连续墙的影响尚未有统一定论。基于ABAQUS有限元数值分析软件,建立了土-结构静动力耦合有限元模型,分析了水平竖向双向地震作用下,地下连续墙对无柱大跨地铁车站结构动力反应的影响。数值分析表明:地下连续墙会增大无柱大跨地铁车站体系的水平抗侧刚度,考虑地下连续墙时车站侧墙的总体水平相对变形降低;但地下连续墙的存在会放大无柱大跨地铁车站上覆土体的竖向惯性效应,同时也会使得无柱大跨地铁车站内力重分布。考虑地下连续墙时车站底板端部是抗震薄弱环节,抗震设计中应对其进行适当加强。

多波束贴近探测在海管悬空病害治理中的应用

在复杂的海洋生态环境下,随着海底管道服役年限的增加,海底管道的裸露、悬空病害现象显著,严重威胁着海洋石油生产安全。为了准确评价海管悬空病害发育程度,指导治理工程施工作业。采用水下机器人(ROV)搭载多波束测深仪,开展近距离探测的方法。确定了海底管道准确的悬空段位置、悬空高度及悬空长度,引导了悬空抛石治理作业,评价了治理效果。结果表明:ROV搭载多波束测深仪能近距离贴近管道,完成精细化探测,避免海面波浪、潮涌对多波束探测的影响,较为准确地评价病害程度并指导治理施工。

地震时海底悬跨管道动力特性试验研究

铺设在地震活跃区域的海底管道可能在地震荷载作用下发生破坏。利用水下振动台研究了海底悬跨管线在地震作用下的动力反应。试验中考虑了地震波输入方向、管道端部支撑情况、悬跨高度、悬跨长度和管内是否有水等因素。完成了这些因素组合的 12 0组试验 ,得到海底悬跨管道动力响应特性。试验结果表明水中管道与陆地悬空管道的动力反应存在明显差别 ;悬跨长度是控制管道反应的关键 ,水平地震输入对管道反应起控制作用 。