Wake II model for hydrodynamic forces on marine pipelines including waves and currents

The Wake II model for the determination of the hydrodynamic forces on marine pipelines is extended to include currents and waves. There are two main differences between the Wake II and the traditional model. First, in the Wake II model the velocity is modified to include the pipe's encounter with the wake flow when the velocity reverses. Second, the model uses time dependent drag and lift coefficients. The flow field is assumed to be the linear superposition of regular waves and uniform current and is treated as wave only but in two different phases. The model requires eight empirical parameters that are obtained from comparisons with field data for various Keulegan–Carpenter numbers and current to wave ratios. The effective velocity and the force predictions are compared with field data from Exxon Production Research Company and with the conventional model. The model gives satisfactory results and predicts lift forces that in shape, magnitude and phase relative to the velocity are in very close agreement with measured forces. For the horizontal forces the results are very accurate. A substantial improvement is obtained over the predictions with the conventional model. This work is applicable to the design of submarine pipelines laying on the sea bottom in water depths where waves or waves and currents contribute to the hydrodynamic forces.     

顶管施工对相邻平行地下管线位移影响因素分析

顶管施工引起的管道周围土体移动会对相邻地下管线造成危害。采用三维有限元方法分析了顶管施工引起的相邻平行地下管线的位移,研究了注浆、纠偏、离顶管距离的远近、地下管线埋深、管线与土体弹性模量比及不同管材对地下管线位移的影响。计算结果表明,注浆与纠偏压力越大,地下管线的位移越大;地下管线距离顶管越远,引起的位移越小;地下管线弹性模量越小,产生的位移越大。     

海管碎石保护结构抵抗拖锚危害的模型试验研究

船舶走锚时可能对海底管线造成破坏,实际工程中常用碎石保护结构来对海底管道进行保护。为了研究这种结构的保护效果和保护机理,在大型试验槽中对三种尺寸模型锚进行了模型试验。在试验中测量了锚爪尖端位置和锚爪力在保护结构中的变化,得到锚体从细砂进入保护结构时的运动过程和运动规律,据此研究了碎石保护结构对海底管线的保护效果并分析了保护机理。     

波流联合作用下掺氢输气海管泄漏扩散研究

由于氢气密度低,泄漏后的掺氢天然气在海洋波流作用下的浮升扩散行为有别于纯天然气,其泄漏扩散规律有待明晰。利用计算流体力学方法数值模拟了波流联合作用下掺氢输气海管泄漏扩散的过程,结果表明气体泄漏的过程可分为泄漏初期、向上浮升以及横向迁移3个阶段。当掺氢比φH2 <50%时,氢气泡的运动轨迹受天然气泡的影响显著。气体浮升高度和扩散直径的变化与时间成正相关,且随着掺氢比的增大,泄漏气体到达液面所需的时间延长。天然气泡和氢气泡直径在上升的过程中都逐渐增大,两者的浮升速度随浮升高度的增加先增大后减小,天然气泡的浮升速度衰减更快。氢气泡直径随掺氢量的增加而增大,天然气泡直径随掺氢量的增大而减小,两者的上升速度随着掺氢量的增大都表现出先增大后减小的趋势,且氢气泡的上升速度大于天然气泡的上升速度。波长和海流流速越大,泄漏气体的扩散直径越大。     

基于缓冲区的电力管网重复管线合并算法

针对电力地下管网数据核查过程中因为数据迁移或者数据更新等其他原因导致的电力管线重复问题,提出了一种基于缓冲区的地理拓扑关系判断方法来检测并合并重复管线。在服从电力管线布局原则下,首先,对电力管线进行插值处理;然后,构造出管线缓冲区,其缓冲半径受插值距离调节,在此缓冲范围可以判断出地理点线包含关系;最后,根据不同的地理点线包含关系可以分析出管线间的线-线拓扑关系,从而可以判断出是否存在重复管线从而采取相应的重复管线处理措施。实验结果表明,提出的方法能够高效准确地处理电力管网数据核查中的重复管线问题。     

Analysis on Interface Shear Stress of Thermally Insulated Ocean Pipelines Under Installation

1.IntroductionMost of the crude oil producedfromoffshore China has a highcontent of wax,which makesthe oilagglomerate at hightemperature.Heat preservation measures,therefore,must be adopted to maintainthe temperature higher thanthe oil’s pour point,sotha…     

Buckle propagation in pipelines with non-uniform thickness

Finite element solutions for the steady-state buckle propagation pressure in a pipeline with non-uniform thickness are given. The results are useful in finding buckle propagation pressures in corroded pipelines. It has been found that when corrosion is equal to or less than 10% of the original pipeline thickness, the pipeline collapses in an overall shell buckling mode; otherwise, the pipeline experiences local buckling. The propagation pressure decreases with both the thickness and angular extent of the reduced section, but the rate of decrease with thickness reduction is almost independent of the angular extent of corrosion when it is greater than 90°.     

Seismic response of natural gas and water pipelines in the Ji-Ji earthquake

In order to study the damage patterns of natural gas and water pipelines in the Ji-Ji earthquake, a GIS database and analysis procedures were established. Repair statistics was obtained from major natural gas companies and the Taiwan Water Supply Corporation (TWSC), and entered into the system. Then, repair rates (RR) were calculated. Previously, damage was analyzed without considering the corresponding pipeline material and diameters. In this study, new attempts were made to collect more data including those related to the composition of pipelines to provide a more detailed analysis of the relationship between earthquake forces and the resulting damage. Statistical analysis was also conducted to understand the correlation between RR and seismic parameters such as the peak ground acceleration, peak ground velocity, and spectrum intensity.     

A simplified analysis model for determining the seismic response of buried steel pipes at strike-slip fault crossings

The seismic response analysis of buried pipelines at fault crossings is a complex problem requiring nonlinear 3D soil-structure and large deformation analyses. Such analyses are computationally expensive and the results are hard to evaluate. Therefore, a simple numerical model is needed for engineering and design offices to determine the seismic demand of steel pipes at fault crossings. This paper presents a simplified numerical model for buried steel pipes crossing strike-slip faults and oriented perpendicular to the fault. Two pipes with different diameter to thickness (D/t) ratios and steel grades are used in the study. The proposed model permits plastic hinge formations in the pipe due to incrementally applied fault movements, allows determination of the critical length of the pipeline and measure strains developed on the tension and compression sides in the pipe. The model also considers the effect of bending as well as axial strains due to stretching.     

液化场地地下管线地震反应研究述评

本文简要介绍了地下管线的震害特征和主要影响因素。对国内外在液化场地地下管线方面的研究现状从试验研究和理论分析2个方面进行了论述并探讨了液化场地地下管线反应需进一步研究的一些问题。