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海底输油管线是海洋油气田开发的生命线工程,在复杂的海洋环境中易发生破坏.为使管线实现自埋防护,提出用柔性材料代替刚性导流板安装在管线顶部,不仅可以增加阻水面积,加大冲刷深度和范围,而且可以减缓刚性导流板对管线上部水流的扰动强度和尾流涡旋的扰动强度,减小管线的振动.利用力学关系由变形方程推导出海底管线与海底间距离为零以及不为零情况下柔性导流板变形的二次曲面方程和自由端最大挠度.在单向流条件下将不同材料不同长度的柔性导流板安装在管线中轴上方开展试验研究,测量柔性导流板在水流作用下的变形曲面.对比分析利用公式计算柔性导流板的自由端最大挠度和曲面变形数据与试验结果,发现两者吻合较好. 相似文献
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海底管道阻流板(Spoiler)自沉埋技术是一种新型管道自埋技术,为深入了解其作用机制及其效果,本文通过分析安装有阻流板的杭州湾海底管道历年检测资料,结合管道附近海域海床、潮流动力特性,深入探讨了阻流板装置在实际工程中的运行效果,分析了其作用机制及其适用条件。研究发现安装阻流板装置的杭州湾海底管道在往复潮流作用下逐渐埋入海床,其埋入段长度由2005年的50%增加到2013年的80%以上,而且平均埋入深度超过2.6 m,自埋效果较好;而在管道路由与海流平行段或管道敷设于抗冲刷强海床上时,阻流板作用不能有效发挥,管道仍然呈现裸露状态。 相似文献
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Estimating the impact forces exerted by a submarine debris flow on a pipeline is a challenge, and there is room for considerably more work to advance the state of the art. To this end, an experimental program was performed to investigate the impact on two pipeline installation scenarios: 1) suspended pipeline and 2) laid-on-seafloor pipeline. The results and observations from the experimental investigation are discussed. The definition of Reynolds number was modified for non-Newtonian fluids and an ad hoc method was developed to estimate the drag force exerted by an impact perpendicular to the pipe axis. The method may be used in prototype situations to estimate the drag force from submarine debris flow impact on pipelines. The experimental program was complemented by Computational Fluid Dynamics (CFD) analyses, the details of which are discussed in the accompanying paper. 相似文献
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In this study an Euler-Euler two-phase model was developed to investigate the tunnel erosion beneath a submarine pipeline exposed to unidirectional flow. Both of the fluid and sediment phases were described via the Navier-Stokes equations, i.e. the model was implemented using time-averaged continuity and momentum equations for the fluid and sediment phases and a modified k−ε turbulence closure for the fluid phase. The fluid and sediment phases were coupled by considering the drag and lift interaction forces. The model was employed to simulate the tunnel erosion around the pipeline laid on an erodible bed. Comparison between the numerical result and experimental measurement confirms that the numerical model successfully predicts the bed profile and velocity field during the tunnel erosion. It is evident that the sediments are transported as the sheet-flow mode in the tunnel erosion stage. Also the transport rate under the pipe increases rapidly at the early stage and then reduces gradually at the end of the tunnel erosion beneath pipelines. 相似文献
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从管道尾流区泥沙颗粒的受力平衡着手,探讨了管道冲刷的临界压力差。在此基础上,提出了一种防止或减少管道冲刷的新方法,即在管道下方安装柔性阻流器。通过物理模型试验,研究了单向恒定流及规则波作用下,柔性阻流器对管道两侧床面压力、冲刷深度的影响。试验结果表明:柔性阻流器的安装能明显减小管道两侧床面的压力差。在单向恒定流作用下,管道的冲刷深度随阻流器长度的增加而减小;当阻流器达到临界长度时,冲刷消失。规则波时,因阻流器的扰动作用,冲刷深度有所增加;但随阻流器长度的增加,其扰动作用减小,对床面的防护作用增加,因而冲刷深度减小。 相似文献
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针对管线绕流剪切层区的水流特征,利用射流分析的类似方法,通过简化控制方程,从理论上探讨了剪切层区的时均速度分布规律。物理试验中采用ADV测速仪对回流区流场进行了测量,对各流区流速和紊动强度变化趋势进行了讨论,并将试验结果与理论推导进行对比,二者基本吻合,为进一步研究海底管线防护措施提供了理论依据。 相似文献
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The instantaneous turbulent velocity field created by the breaking of spilling regular waves on a plane slope was measured in a plane running parallel to the slope using particle image velocimetry. The measurement plane was located at a height of about 1 mm above the bed. The measurement area encompassed the region where the large eddies generated at incipient wave breaking impinged on the bottom inside the surf zone. A total of 30 trials were conducted under identical experimental conditions. In each trial, six consecutive wave cycles were recorded. The measured velocity fields were separated into a mean flow and a turbulence component by ensemble averaging. The instantaneous turbulent velocity fields were analyzed to determine the occurrence frequency, location, geometry and evolution of the large eddies, and their contributions to instantaneous shear stresses, turbulent kinetic energy and turbulence energy fluxes. The motion of single glass spheres along the bed was also investigated. The two-phase flow measurements showed that the velocity and displacement of large solid particles on a smooth bed were significantly affected by the magnitude and direction of turbulence velocities. Overall, this study has examined the kinematic and dynamic properties of large eddies impinging on the bed and the interaction of these large-scale turbulent flow structures with the mean flow. The study has also highlighted the important role of large eddies in sediment transport. 相似文献
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《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(7):1173-1188
Large-scale dense bottom currents are geostrophic to leading order, with the main flow direction along the continental slope. Bottom friction makes the water descend to greater depths, but only at a small angle to the horizontal. Here the effect of a submarine ridge that intersects the slope is considered. It is shown that the presence of a submarine ridge greatly enhances the downward transport. By leaning against the ridge it is possible for the dense water to flow downhill, perpendicular to the depth contours, even though the first-order dynamics are geostrophic. The requirement for downward flow next to the ridge is that the frictional transport that it induces is sufficiently large to counteract geostrophic advection along the isobaths and out of the ridge region. The dynamics are similar to those of downward flow in submarine canyons, but ridges appear to be more effective in channeling the dense water downhill, in particular for narrow ridges/canyons with small seaward slope of the ridge/canyon axis. The downward flow is analyzed using a simplified analytical model and the results are compared to data from the Filchner Overflow, which agree qualitatively with the model. 相似文献
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Modelling of flow around a near-bed pipeline with a spoiler 总被引:1,自引:0,他引:1
Flow around a pipeline with and without a spoiler near a smooth wall is simulated by solving the Navier–Stokes equations. Finite-difference formulation with a second-order upwind scheme in a curvilinear coordinate system is employed. The influences of the spoiler on hydrodynamic forces, pressure distribution, vortex shedding frequency, velocity profile under the pipe, as well as shear stress on the wall are investigated. The attachment of a spoiler significantly increases drag, root-mean-square (RMS) lift, flow through the gap between the pipe and the wall and shear stress on the seabed around the pipe. The spoiler also generates a non-zero mean downward force on the pipeline, which may enhance the self-burial of the pipeline. 相似文献
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The wave pressure and uplift force due to random waves on a submarine pipeline (resting on bed, partially buried and fully buried) in clayey soil are measured. The influence of various parameters viz., wave period, wave height, water depth, burial depth and consistency index of the soil on wave pressures around and uplift force on the submarine pipeline was investigated. The wave pressures were measured at three locations around the submarine pipeline (each at 120° to the adjacent one). It is found that the wave pressure and uplift force spectrum at high consistency index of the soil is smaller compared to that of low consistency index. Just burying the pipeline (e/D=1.0) in clayey soil reduces the uplift force to less than 60% of the force experienced by a pipeline resting on the seabed (e/D=0.0) for Ic=0.33. 相似文献
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Because of the complex geological conditions of the seabed, submarine pipelines buried beneath the ocean floor become suspended over the seabed under the long-term scour of waves eroding the surrounding sediment. Further, most oil fields were built in offshore areas while the country was developing. This gives the waves seen in shallow water obvious nonlinear features, and the abnormal characteristics of these waves must be considered when calculating their hydrodynamic forces. Particularly under such conditions, these suspended spans of submarine pipelines are prone to damage caused by the action of the external environment load. Such damages and eventual failures may result not only in great property losses but also pollution of the marine environment. The span length of these areas is a key predictive factor in pipeline damages. Therefore, determining the allowable span length for these submarine pipelines will allow future projects to avoid or prevent damage from excessive suspended span lengths. Expressions of the hydrodynamic loads placed on suspended spans of pipeline were developed in this work based on the first-order approximate cnoidal wave theory and Morison equation. The formula for the allowable free span length was derived for the common forms of free spanning submarine pipeline based on the point where maximum bending stresses remain less than the material’s allowable stress. Finally, the allowable free span length of real-world pipelines was calculated for a subsea pipeline project in Bohai Bay. This research shows that, with consideration for the complicated marine environment, existing suspended spans are within allowable length limitations. However, continuing to limit the length of these submarine pipeline spans in the Nanpu oil field will require ongoing attention. 相似文献
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以东方1-1平台海底管线路由区为例,多次对该路由区多波束测深、旁扫声纳、浅地层剖面、土质、海流及海底过程的原位监测调查数据和收集的波浪、海流等相关资料进行分析,得出,在水动力条件的作用下,海底会产生沉积物的侵蚀、搬运和沉积等过程,这些过程对海底地貌有重要的改造作用,会对管线稳定性具有重大影响。提出管线铺设需预先了解水下环境的动力条件的规律,识别沿拟定管线路由区可能存在的海床运动和波流冲刷的地质灾害,找到地貌形态对海底管线稳定性影响的原因。进而提出根据不同情况的解决对策,有效地减少地貌形态对海底管线稳定性影响。 相似文献
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海底冲淤变化预测的聚类指数增长模型研究 总被引:1,自引:0,他引:1
提出了一种新的聚类指数增长模型,并用该模型预测了江苏洋口港海区西太阳沙附近海底的冲淤变化。首先采用聚类分析法对空间连续的水深冲淤变化数据序列进行分类,然后针对各类具有不同的冲淤变化趋势的区域分别建立指数增长预测模型。经比较分析预测结果,发现在分类数较大及预测时间不太长的情况下,能够取得满意的预测结果;但随预测时间的增加,要不断的修正参数值,才能得到切合实际的预测结果,所以该模型还具有一定的时间局限性,还有待于改进。该模型的建立不但可以为江苏省东部沿海海港建设提供科学的决策依据,也可以成为近岸海底冲淤变化预测的发展方向之一,有较高的理论意义和广远的应用前景。 相似文献
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南海北部白云深水区东北部小型峡谷内的块体搬运 总被引:2,自引:1,他引:1
The process of mass movements and their consequent turbidity currents in large submarine canyons has been widely reported, however, little attention was paid to that in small canyons. In this paper, we document mass movements in small submarine canyons in the northeast of Baiyun deepwater area, north of the South China Sea(SCS), and their strong effects on the evolution of the canyons based on geophysical data. Submarine canyons in the study area arrange closely below the shelf break zone which was at the depth of –500 m. Within submarine canyons, seabed surface was covered with amounts of failure scars resulted from past small-sized landslides. A complex process of mass transportation in the canyons is indicated by three directions of mass movements.Recent mass movement deposits in the canyons exhibit translucent reflections or parallel reflections which represent the brittle deformation and the plastic deformation, respectively. The area of most landslides in the canyons is less than 3 km2. The trigger mechanisms for mass movements in the study area are gravitational overloading, slope angle and weak properties of soil. Geophysical data indicate that the genesis of submarine canyons is the erosion of mass movements and consequent turbidity currents. The significant effects of mass movements on canyon are incision and sediment transportation at the erosion phases and fillings supply at the fill phases. This research will be helpful for the geological risk assessments and understanding the sediment transportation in the northern margin of the SCS. 相似文献
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Submarine debris flow impact on suspended (free-span) pipelines: Normal and longitudinal drag forces
Arash Zakeri 《Ocean Engineering》2009,36(6-7):489-499
Computational fluid dynamics (CFD) analysis was employed to numerically simulate impact of clay-rich submarine debris flows on a suspended (free-span) pipeline at various angles of attack. The resultant horizontal drag force can be decomposed into two components: normal and parallel to the pipe axis. A method is presented for estimating the normal and longitudinal drag forces on a suspended pipeline and is applicable to a wide of impact situations. The work presented here complements the results of an earlier investigation into the drag forces on suspended and laid-on-seafloor pipelines. The previous investigation consisted of both physical laboratory experiments and CFD numerical analyses, for an impact situation normal to the pipe axis. The impact Reynolds numbers presented in this paper range between about 2 and 320. This range is considered appropriate for practical design purposes. 相似文献