Effect of geometric and material discontinuities on the reeling of pipelines     

《Applied Ocean Research》2017

The winding and unwinding of a pipeline onto a large diameter reel as practiced in the reeling installation method, induces bending strains of 1–3% followed by straightening, and reverse bending. The operator must ensure that such plastic deformations are sustained free of local buckling or rupture in the line. Such failures are for example precipitated by pipeline discontinuities in wall thickness and yield stress as they act as stress risers, lead to localized deformations severe enough to result in local buckling. The effect of such discontinuities is studied using a large-scale nonlinear finite element model that simulates the reeling/unreeling of a pipeline. Nonlinear kinematic hardening is used to capture the elasto-plastic behavior of the material imposed by the bending/reverse bending history. Discontinuities in wall thickness and yield stress are shown to result in sharp local changes in curvature that extend over 3–4 pipe diameters accompanied by severe local straining and ovalization. The extent of the disturbance is governed by the bending strain imposed by the ratio of pipe to reel diameter. It can be reduced by an increase in the applied tension but at the expense of additional ovalization of the pipeline. It can also be reduced by increasing the pipe wall thickness but with the consequent increase in costs. A parametric study of the effect of such discontinuities demonstrates that for some combinations of process parameters, the disturbance can lead to local buckling either during winding or unwinding. It is concluded that a modeling framework such as the one presented should be used to generate a design protocol for reel-installed pipelines.  相似文献   

风浪流中半潜式风机系统动力响应特性研究     

毛莹  范菊  张新曙  尤云祥 《海洋工程》2017,35(1):60-70

以三浮筒(Tri-floater)型半潜式风机系统为对象,采用时域方法,考虑垂荡板的黏性阻尼效应,研究系泊缆直径、长度、预张力和布置方式等参数对其在风浪流中动力响应特性的影响规律,提出了一种系泊参数优化方法。在此基础上,根据东海和南海三个不同水深区域百年一遇海洋环境条件,通过调整Tri-floater型浮式基础的吃水和垂荡板等参数,有效地提高了其运动响应周期,减小了其运动响应幅值。同时,根据风机浮式基础运动幅值的设计规范要求,针对三个不同水深区域特点,设计了Tri-floater型浮式基础的系泊系统。计算结果表明,改进后的Tri-floater型半潜式风机系统能满足百年一遇极端环境下的作业要求,适合于东海和南海海洋环境下海上风能资源的开发。  相似文献   

FSRU码头系泊模型实验与数值模拟研究   总被引：1，自引：0，他引：1  

周宏康  李欣  杨建民  罗勇 《海洋工程》2017,35(1):12-20

FSRU在恶劣环境条件下的作业和安全停靠性能与系泊缆张力、靠垫挤压应力、船体6自由度运动等参数有关。针对FSRU码头处海洋环境条件,进行FSRU不同装载状况的模型实验,获得FSRU的6自由度运动及其系泊载荷的动力特性。基于三维辐射和绕射理论,使用Sesam软件进行频域计算,以此为基础在相应海洋环境条件下进行时域耦合分析,获得FSRU 6自由度运动、系泊载荷、靠垫应力等参数的响应时历。结果表明:30%装载、横浪条件下FSRU的运动响应最大,系泊缆张力未达到破断值,靠垫压力超过其压缩60%时的载荷;模型实验对FSRU运动响应和系泊缆张力的预测结果可信,靠垫受力情况需要数值仿真进行辅助研究。  相似文献   

Third-Order Stokes Wave Solutions of the Free Surface Capillary-Gravity Wave and the Interfacial Internal Wave     

MENG Rui-jun  CUI Ji-feng  CHEN Xiao-gang  ZHANG Bao-le  ZHANG Hong-bo 《海洋工程》2017,(6):781-787

Based on the Stokes wave theory, the capillary-gravity wave and the interfacial internal wave in two-layer constant depth''s fluid system are investigated. The fluids are assumed to be incompressible, inviscid and irrotational. The third-order Stokes wave solutions are given by using a perturbation method. The results indicate that the third-order solutions depend on the surface tension, the density and the depth of each layer. As expected, the first-order solutions are the linear theoretical results (the small amplitude wave theoretical results). The second-order and the third-order solutions describe the nonlinear modification and the nonlinear interactions. The nonlinear impact appears not only in the n (n≥2) times'' high frequency components, but also in the low frequency components. It is also noted that the wave velocity depends on the wave number, depth, wave amplitude and surface tension.  相似文献   

Motion and Dynamic Responses of A Semisubmersible in Freak Waves     

LI Xin  DENG Yan-fei  LI Lei  TIAN Xin-liang  LI Jun 《海洋工程》2017,(6):754-763

The present research aims at clarifying the effects of freak wave on the motion and dynamic responses of a semisubmersible. To reveal the effects of mooring stiffness, two mooring systems were employed in the model tests and time-domain simulations. The 6-DOF motion responses and mooring tensions have been measured and the 3-DOF motions of fairleads were calculated as well. From the time series, trajectories and statistics information, the interactions between the freak wave and the semisubmersible have been demonstrated and the effects of mooring stiffness have been identified. The shortage of numerical simulations based on 3D potential flow theory is presented. Results show that the freak wave is likely to cause large horizontal motions for soft mooring system and to result in extremely large mooring tensions for tight mooring system. Therefore, the freak wave is a real threat for the marine structure, which needs to be carefully considered at design stage.  相似文献   

Sensitivity of interfacial hydraulics to the microtopographic roughness of water‐lain gravels          下载免费PDF全文

Stephen P. Rice  Thomas Buffin‐Bélanger  Ian Reid 《地球表面变化过程与地形》2014,39(2):184-199

Flow within the interfacial layer of gravel‐bed rivers is poorly understood, but this zone is important because the hydraulics here transport sediment, generate flow structures and interact with benthic organisms. We hypothesized that different gravel‐bed microtopographies generate measurable differences in hydraulic characteristics within the interfacial layer. This was tested using a high density of spatially and vertically distributed, velocity time series measured in the interfacial layers above three surfaces of contrasting microtopography. These surfaces had natural water‐worked textures, captured in the field using a casting procedure. Analysis was repeated for three discharges, with Reynolds numbers between 165000 and 287000, to evaluate whether discharge affected the impact of microtopography on interfacial flows. Relative submergence varied over a small range (3.5 to 8.1) characteristic of upland gravel‐bed rivers. Between‐surface differences in the median and variance of several time‐averaged and turbulent flow parameters were tested using non‐parametric statistics. Across all discharges, microtopographic differences did not affect spatially averaged (median) values of streamwise velocity, but were associated with significant differences in its spatial variance, and did affect spatially averaged (median) turbulent kinetic energy. Sweep and ejection events dominated the interfacial region above all surfaces at all flows, but there was a microtopographic effect, with Q2 and Q4 events less dominant and structures less persistent above the surface with the widest relief distribution, especially at the highest Reynolds number flow. Results are broadly consistent with earlier work, although this analysis is unique because of the focus on interfacial hydraulics, spatially averaged ‘patch scale’ metrics and a statistical approach to data analysis. An important implication is that observable differences in microtopography do not necessarily produce differences in interfacial hydraulics. An important observation is that appropriate roughness parameterizations for gravel‐bed rivers remain elusive, partly because the relative contributions to flow resistance of different aspects of bed microtopography are poorly constrained. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献   

潮湿环境中稻草的防腐效果及极限拉伸性能     

石茜  柴寿喜  李敏  魏丽 《吉林大学学报(地球科学版)》2011,41(1):200-206

滨海盐渍土存在盐胀、溶陷和吸湿软化等问题,需对其进行处理。设想使用高分子材料SH胶防腐处理稻草,以防腐后的稻草加筋滨海盐渍土。为评价浸胶稻草的防腐效果及其力学性能,测试了天然和浸泡SH胶稻草的吸水率,及天然、浸水、浸胶及浸胶后再浸海水稻草的极限拉力和极限延伸率。结果表明：（1）浸胶稻草与天然稻草相比,吸水率最多可降低50%,证实防腐效果较好;（2）浸胶后,稻草的极限延伸率和极限拉力最大提高了26%和23%;（3）同是浸泡在海水中,浸胶后稻草较天然稻草,其极限延伸率和极限拉力的最大增长率为12%和11%;（4）浸胶稻草的SEM照片观察及能谱分析表明,SH胶包裹了纤维并进入到稻草的孔隙中,增强了纤维间的联结,提高了稻草的极限抗拉性能。SH胶防腐后的稻草作为加筋材料是可行的。  相似文献   

非饱和土粒间吸力研究的若干思考和进展          下载免费PDF全文

张鹏程  汤连生  邓钟尉  姜力群 《水文地质工程地质》2012,39(2):30-36

非饱和土粒间吸力是建立非饱和土有效应力原理和抗剪强度理论的基础前提,从各力的本质、概念、大小等不同角度出发,对目前非饱和土研究中常见的几种吸力进行了详细地对比和分析。基质吸力表示土壤吸水的趋势,强调的是土颗粒与水之间的相互作用,并非土颗粒间的相互作用,与有效应力概念的本质不符,是Bishop和Fredlund强度理论中分别存在着物理意义不明确参数x和φb的根本原因;广义吸力虽然考虑了结构吸力的作用,但仍将基质吸力作为有效应力的一部分,使原本“实用、简化”的目标更加复杂化;附加内压力将基质吸力以及表面张力的作用进行叠加,存在力作用大小上的重复,同时未考虑结构吸力的作用;张力吸力将表面张力沿两土颗粒连线方向的分量——张力吸力和基质吸力进行叠加,一是仍将基质吸力作为有效应力的一部分,二是同样未考虑结构吸力的作用;粒间吸力（湿吸力和结构吸力）考虑了因土体结构性引起的结构吸力作用,同时也考虑了气液界面上收缩膜的效应——湿吸力的作用,基于粒间吸力的非饱和土有效应力及强度理论不仅符合有效应力定义的本质,而且合理地解释了非饱和土中诸如收缩膜张力的方向性、土中应力概念的平均性、土体物理本质的唯一性、随含水率变化的连续性以及对不同类型土的适应性等众多现象。因此,从粒间吸力的角度出发来研究非饱和土的有效应力原理是正确、可行的。  相似文献   

强震作用下多层土质边坡破坏规律与变形特征     

张坤  胡新丽  李长冬 《煤田地质与勘探》2011,39(1):52-56

通过对汶川地震受灾区北川县陈家坝地区的地质灾害调查,根据现场松散土质边坡破坏情况,由工程地质类比法选择了计算模型和地震波,采用岩土弹塑性理论和FLAC3D软件分析了多层土质边坡在动荷载作用下边坡单元的剪切拉伸破坏和剪切应变动力响应规律。研究表明,在水平和竖直地震波联合作用下,地震边坡单元首先在坡体内产生剪切破坏。随着震动时间的增加,剪切破坏单元向坡脚和坡肩处延伸,而在坡肩处主要产生拉破坏,一旦剪切破坏面和拉破坏面贯通,将导致边坡失稳。强震过后边坡坡脚鼓出,坡肩下凹,整个坡体呈弧形破坏。   相似文献   

强化空气扰动技术中表面活性剂的选择     

赵勇胜  郑苇  秦传玉  王冰  连子尧  罗景阳 《吉林大学学报(地球科学版)》2010,40(5):1157-1162

为了提高空气扰动技术（air sparging,AS）的效果,做了一系列的实验,研究了表面活性剂强化空气扰动技术（surfactant-enhanced air sparging, SEAS）中表面活性剂的选择方法。结果表明：在气流运行方式以鼓泡为主要机制时,表面活性剂的加入强化了气泡的起泡性和稳泡性,使空气饱和度增加;在气流运行方式以微孔道为主要机制时,表面活性剂的加入因减小了表面张力而减小了空气驱替水所需的毛细压力,使空气饱和度增加。比较Tween-80、TritonX-100、SDS和SDBS在介质上的吸附损失,确定出在中砂中TritonX-100为优,在砾石中SDBS为优。  相似文献