A refined analytical analysis of submerged pipelines in seabed laying

The paper analyzes the elastic deflection of submerged pipelines laid with a stinger by taking into account the overall effects of the ovalization of the cross section. The analysis is performed by means of a singular perturbation technique and the analytical solution obtained is shown to offer different advantages over the finite element method. Two examples demonstrate the effectiveness of the procedure by means of a comparison with results from other less refined analytical solutions and from the commercial finite element code .     

埕北海域海底管线冲刷稳定性研究

根据埕北海域水下三角洲的工程地质条件和水动力条件,分析海底管线在两种铺设方式情况下的冲刷稳定性。第一种为埋置在一定土层深度处的管线：根据整个埕北海域海底长期冲淤变化规律,利用１９９２～１９９６ 年的实测水深资料得出的冲刷速率,推算出管线被冲出泥面所需的时间。第二种为裸露在海底的管线：根据海流对管线周围沉积物产生冲刷效应,冲刷达到一定程度时处于平衡状态,认为此状态下,海流在该点产生的剪切力等于形成可冲蚀海床沉积物的临界牵引力,据此计算出在管线周围冲刷的最大深度     

Reliability of Lifeline Networks with Multiple Sources under Seismic Hazard

Lifelines are networks extending spatiallyover large areas. Transportation systems, pipelines,communication and power transmission systems areexamples of lifelines. The performance of a lifelineafter a major earthquake is particularly vital for acommunity because of the emergency services that areusually required after such events. Performancemeasures are usually expressed in terms of quantitiesthat are assessed based on statistical andprobabilistic methodologies. The major performancemeasure is the probability of reaching from aspecified point to another one successfully after acatastrophic event, such as an earthquake. Evaluationof this performance measure requires a seismic hazardmethodology, capacity determination techniques andnetwork reliability assessment methods. By combiningthese three aspects in one model, it is possible tocalculate the reliability of any lifeline system underseismic danger. The aim of this paper is to present aprobabilistic model for the evaluation of the seismicreliability of lifeline networks having multiplesources. The seismic reliability of a waterdistribution system located in Bursa, Turkey isassessed in order to show the implementation of theproposed model. The numerical calculations are carriedout by the LIFEPACK software, which is developed forthis purpose.     

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.     

航道区碎石层对霍尔锚落锚条件下海底管道防护效果研究

航道中船舶抛锚作业使海底管道可能受意外撞击,造成管道局部损伤甚至失效,进而对油气生产安全和生态环境等造成重大危害。采用碎石层防护是航道区等海域海底管道最常用的防护手段。首先基于大比尺落锚模型试验,观测了霍尔锚下落贯入碎石的3个阶段及其贯入过程中管道的应力应变状态。通过建立光滑粒子流体动力学法（SPH）和有限元法（FEM）耦合的数值模型,针对实际不同吨位通航船舶常用的霍尔锚,研究了其贯入碎石层深度及埋设管道受力和凹陷变形规律。最后分析了不同锚质量、碎石层形状和厚度等因素下埋设管道的响应规律。结果表明：采用暗埋式碎石防护层有利于撞击能量吸收,能更好地防护海底管道受损;且采用3 m以上碎石防护层能有效保护海底管道抵抗各类实际常见霍尔锚的撞击损伤。     

考虑流固耦合时的海底管道悬跨段非线性动力分析

通过对管道的涡激振动试验,提出了考虑流固耦合的非线性涡激升力表达式,并用该式进行了海底管线悬跨段非线性动力响应时程分析。对考虑流固耦合与未考虑流固耦合情况下得到的管道动力响应时程进行对比,算例表明:当管外流场流速与管道顺流向振动速度值较接近时,不考虑流固耦合时的计算结果明显小于考虑流固耦合时的计算结果。分析认为,在管外流场流速与管道顺流向振动速度值较接近的情况下,管道的涡激振动计算宜采用非线性涡激力模型。     

鼓丘和巨型冰川线理的冰川摩擦学:剥蚀和沉积的争论之谜得到解决?

冰流是指冰盖中快速流动(高达10 km/a)的区域。冰流通常长达1000 km,宽200 km,嵌入在冰盖中。沿其流动方向形成了低幅度波纹状基岩床。这些波纹状基岩床由一些高度拉伸的沿着流向呈平行状分布的脊和沟槽(巨型冰川线理)组成。这些巨型冰川线理在空间上继承自体积大、拉伸程度低的鼓丘。由于鼓丘核部的地质条件复杂多变且不存在特征性的岩相,同时很难直接观察到现代冰盖下鼓丘的形成,因而鼓丘的起源在世界上仍然是未解之谜。基于新的高分辨率(0.5 m)LiDAR数据绘制的地形图和对更新世古冰流岩床进行野外地质考察表明,鼓丘和巨型冰川线理是底形连续体(后者由前者演化而来)。它们由基岩或部分岩石和早期较老的沉积物组成,基于此部分学者提出了鼓丘的侵蚀起源说。本文重点介绍了类似鼓丘和巨型冰川线理的椭圆-流线型和带有沟槽的表面,这些表面广泛形成于多种非冰川的地质环境中(无论是在地球上还是在火星上),它们是由于受限剪切作用下颗粒状碎屑对基底面的磨损所产生的。变质核杂岩中的大型滑脱断层和俯冲带巨型逆冲断层的表面显示出槽状表面,其形状和规模能够与巨型冰川线理相类比。多尺度的断层面上都表现出了逐渐消除的类似鼓丘...     

地下管线数据库的建立与管线地形图的自动绘制

利用Excel软件管理地下管线外业记录表,利用程序自动导入全站仪采集的管线点数据形成地下 管线数据文件,导入Access数据库管理软件,实现管线点数据资料的添加、修改、浏览、查找、删除等功能。利用 Visual Basic6．0可以操纵数据库、开发数据库的功能,利用ADO和DataGrid控件,通过对Excel数据库的操纵, 在南方公司的Cass5．0成图软件中实现地下管线地形图的自动绘制。     

Deformation analysis of tunnel excavation below existing pipelines in multi‐layered soils based on displacement controlled coupling numerical method

The effect of tunneling on surrounding environments, especially on existing buried pipelines is a problem that engineers designing and practicing in urban geotechnical environments encounter more frequently than in the past. However, previous studies are usually based on the assumption that the soil is homogeneous. How to reflect soil stratification is the main focus for the problem of tunneling in multi‐layered soils. A displacement controlled coupling numerical method is presented for the displacement analysis of tunnel excavation below existing pipelines in multi‐layered soils. On the basis of the layered soil model, to consider the soil nonhomogeneous characteristic, the finite element method and boundary element method are coupled to simulate the deformation of existing pipelines induced by tunneling. The solutions indicate that good agreements are obtained between the proposed coupling numerical method and the commercial software. The accuracy of the proposed numerical method is better than the two stages method based on the existing closed‐form solutions. Moreover, the results discussed in this paper show that the error obtained by the previous method of weighted average on the basis of homogeneous half space converted from layered soils is not negligible for the obvious difference of elastic parameters among successive layers. Copyright © 2012 John Wiley & Sons, Ltd.     

东方气田海管悬跨段安全评估分析

从工程实际问题出发,利用实际测量资料,通过建立近底床悬跨海管的有限元模型,计算了不同底床形状下海管最大静挠度随海流流速变化的规律,对东方1-1气田某标段海管进行了安全评估．筛选出了危险悬跨段。这一计算结果对海管的防护维护工程实践具有切实的指导意义。