The analysis of damage degree of oil and gas pipeline with type II plain dent

Dent is a common type of defect in oil and gas pipelines and the assessment on dented pipelines is carried out with major international standards and specifications based on dent depth as the evaluation criteria. However, such evaluation criteria based on depth does not account for the impact of various parameters (e.g. parameters of dent, parameters of pipeline and the internal pressure of pipeline) on the evaluation result, as a result, many dented pipelines lose their efficacy, even though they meet the depth-based standards. The influence of parameters changes on the damage degree of II-type dented pipelines is investigated on the basis of Oyane's ductile fracture criterion and by the method adopting finite element numerical calculations. Finally, the non-linear regression analysis is conducted and based on the outputs, a specific expression of dent depth and pipeline damage degree is also acquired within a certain scope of application.     

Plastic damage analysis of oil and gas pipelines with unconstrained and constrained dents

Indentation resulting from mechanical damage is one of the main causes of pipeline rupture failure. The primary objective of this case study is to analyze the plastic damage of the pipelines with unconstrained and constrained dents using the existing plastic damage model, namely, the ductile failure damage indicator (DFDI) model. As part of this study, an attempt is made to clarify the influence of the constraint on the behavior of the pipeline. The investigation indicates that the plastic damage of the pipeline interior walls outweighs that of the pipeline exterior walls and cracks start frequently from the pipe interior walls. The position of the maximal circumferential plastic damage deviates from the deepest position of the dent when the critical displacement loading arriving due to the circumferential deformation of the pipeline. The total plastic damage of the unconstrained dented pipeline only depends on the initial displacement loading because the working pressure has very little influence on its behavior under the unconstrained condition. However, the total plastic damage of the constrained dented pipeline depends on the initial displacement loading and the working pressure because the working pressure has a significant effect on its behavior under the constrained condition. Under the same condition, the constrained dented pipeline is easier to crack compared to the unconstrained dented pipeline. In this paper, the model, results and the findings are summarized and discussed.     

基于插值算法和时间序列的容积表拟合方法

在实际测量罐容积表数值的基础上,使用三次样条曲线插值和指数时间序列分析的方法,样条插值生成的数值用以补全在容积表实测采样点区间内的数值,时间序列分析方法用以推算出在罐底和罐顶未测得区间的数值。在实际计量测试中,三次均匀B样条曲线插值方法模拟与实际真值最大偏差小于0.3%,时间序列分析方法测的数据提供参考价值,依次两位向前推得数据,实际偏差小于1%。     

Failure pressure of medium and high strength pipelines with scratched dent defects

It is very important in engineering design and integrity assessment of pipeline to accurately predict its failure pressure, especially for the pipeline with mechanical damages. This paper numerically investigates the failure pressure of medium and high strength pipelines with scratched dent which is on the outer surface of the pipe. Pipe materials of two different grades are chosen in the analysis which represent medium and high strength steel, respectively. Failure pressure of an intact pipeline with fixed ends is derived analytically. On the basis of the maximum plastic strain failure criterion put forward by previous scholars, failure pressure of finite element models containing dent and scratch defects is determined. Parametric studies are carried out to obtain the influencing rule of the dimensions of dent and scratch. The effects of scratch length and depth on failure pressure with various dent depths are obtained. Finally, a formula is fitted for predicting the failure pressure of pipelines with scratched dents on the basis of finite element results. Compared to burst test data from literature, the proposed formula is proved to be reasonable.     

Forced convective heat and mass transfer of a water droplet (effects of vapour concentration)

Abstract

Numerically controlled flame cutting machines used in shipyards are generally equipped only with line‐segment and circle‐arc moving capabilities. This paper attacks the problem of how to approximate a given curve of arbitrary shape by a sequence of line‐segments and circle‐arcs. The given curve is represented by the cubic spline interpolation curve formed by a set of net points on the curve. An efficient method based on the nature of cubic spline is then provided to approximate the interpolation curve by a sequence of linesegments and circle‐arcs. This method has been practically employed by the China Shipbuilding Co. in production line. In order to save storage and expedite the approximation, an effective method is also provided for selecting a near minimal set of net points whose cubic spline interpolation curve can adequately represent the actual given curve. Although the techniques are developed for shipbuilding purpose, they can find applications in other fields.     

Cubic spline boundary elements

The boundary integral method is formulated and applied using cubic spline interpolation along the boundary for both the geometry and the primary variables. The cubic spline interpolation has continuous first and second derivatives between elements, thus allowing the accurate calculation of derivative dependent functions (on the boundary) such as velocity in potential flow. The spline functions also smooth the geometry and can represent curved sections with fewer nodes. The results of numerical experiments indicate that the accuracy of the boundary integral equation method is improved for a given number of elements by using cubic spline interpolation. It is, however, necessary to use numerical quadrature. The quadrature slows calculation and/or degrades the accuracy. The numerical experiments indicate that most problems run faster for a given accuracy using linear interpolation. There seems to be a class of problems, however, which requires higher order interpolation and/or continuous derivatives for which the cubic spline interpolation works much better than linear interpolation.     

建筑能耗分析用逐时干球温度的插值方法

逐时干球温度对建筑能耗动态模拟是必不可少的。利用气象台站报表中的日四次温度值获得逐时值就需要进行插值。本文应用MATLAB语言对常用的四种插值方法做了比较，结果表明，三次样条插值是最佳插值方法。     

基于容量比较法的卧式罐容量表计算方法研究

在卧式罐容量计量容量比较法原理的基础上,讨论了由有限的卧式罐离散(V-H)点计算出全高度量程范围内任意点的容积值的4种计算方法。并以30m³卧式罐为对象进行了试验研究。试验结果表明:Lagrange插值方法、分段线性插值方法、三次多项式拟合方法和三次样条插值方法在中间液位区间的计算结果较为一致;三次样条插值方法计算结果与试验值偏差最小,最大偏差值23.0L,而且稳定性较好;Lagrange插值方法、分段线性插值方法和三次多项式拟合方法在低液位高度或高液位高度的偏差比中间液位区间的计算偏差大;但是在低液位高度和高液位高度区间,由于多节点时边沿振荡原因,Lagrange插值方法的计算偏差大于三次样条插值方法。     

一类加权有理三次样条的区域控制

将插值曲线约束于给定的区域之内是曲线形状控制中的重要问题.本文利用分母为二次的有理三次插值样条和仅基于函数值的有理三次插值样条构造了一类加权有理三次插值样条函数,这类新的插值样条中含有权系数,因而增加了处理问题的灵活性,给约束控制带来了方便.给出了将该种插值曲线约束于给定的折线、二次曲线之上、之下或之间的充分条件及将其约束于给定折线之上、之下或之间的充分必要条件.证明了满足约束条件的加权有理样条的存在性.     

基于T-history曲线计算材料相变潜热方法的改进

目的改进以T-history曲线为基础计算相变材料潜热的方法。方法对相变材料降温过程用温度记录仪测得的数据,分别以高次多项式和三次样条插值法拟合,而后分别计算去离子水和水合盐的相变潜热。对于无过冷度相变材料,以拟合后降温曲线一阶导数最高点、一阶导数突变点和拐点分别作为相变起始位置计算相变潜热。结果三次样条插值法拟合后求得相变潜热值与理论值偏差小于10%,对于无过冷度的相变材料,一阶导数最高点作为相变起始点时,相变潜热计算值与理论值偏差最大为8.01%,最小为1.55%。结论采用三次样条插值拟合法计算PCM的相变潜热,最稳定且接近理论值,以一阶导数最高点为相变起始点计算无过冷度的相变材料的相变潜热结果更精确。     

Treatment of slip locking for displacement‐based finite element analysis of composite beam–columns

In the conventional displacement‐based finite element analysis of composite beam–columns that consist of two Euler–Bernoulli beams juxtaposed with a deformable shear connection, the coupling of the transverse and longitudinal displacement fields may cause oscillations in slip field and reduction in optimal convergence rate, known as slip locking. This locking phenomenon is typical of multi‐field problems of this type, and is known to produce erroneous results for the displacement‐based finite element analysis of composite beam–columns based on cubic transverse and linear longitudinal interpolation fields. This paper introduces strategies including the assumed strain method, discrete strain gap method, and kinematic interpolatory technique to alleviate the oscillations in slip and curvature, and improve the convergence performance of the displacement‐based finite element analysis of composite beam–columns. A systematic solution of the differential equations of equilibrium is also provided, and a superconvergent element is developed in this paper. Numerical results presented illustrate the accuracy of the proposed modifications. The solutions based on the superconvergent element provide benchmark results for the performance of these proposed formulations. Copyright © 2010 John Wiley & Sons, Ltd.     

一种加权有理三次插值函数的凸性分析

利用带导数的和仅基于函数值的分母为二次的有理三次插值样条构造了一类加权有理三次插值函数.在给定的插值数据条件下,通过调整插值函数中的参数和权系数,给出了插值曲线的保凸方法和该方法得以实现的充分必要条件,推广和改进了一些相关结论.这种条件是对参数和权系数的简单的线性的不等式约束,容易在计算机辅助几何设计中得到实际应用.     

Shear flexible field‐consistent curved spline beam element for vibration analysis

In this paper, an efficient curved cubic B‐spline beam element is developed based on the field consistency principle, for vibration analysis. The formulation is general in the sense that it includes anisotropy, transverse shear deformation, in‐plane and rotary inertia effects. The element is based on laminated refined beam theory, which satisfies the interface transverse shear stress and displacement continuity, and has a vanishing shear stress on the top and bottom surfaces of the beam. The lack of consistency in the shear and membrane strain field interpolations in their constrained physical limits causes poor convergence and unacceptable results due to locking. Hence, numerical experimentation is conducted to check these deficiencies with a series of assumed shear/membrane strain functions, redistributed in a field‐consistent manner. The performance of the element is assessed by studying the free vibration behaviour of a variety of problems ranging from a straight beam to a circular ring. Copyright © 1999 John Wiley & Sons, Ltd.     

Errors in cubic spline interpolation

Summary This paper deals with the problem of finding error bounds for cubic spline interpolation of functions of the classC ⁴[a, b], andC ⁵[a, b], by examining a relationship between cubic spline interpolation and piecewise cubic Hermitian interpolation.The method also gives an indication of what happens, in the case of almost uniform meshes, especially if the approximated function is in the classC ⁵[a, b].Comparison is made with recent work carried out by K. E. Atkinson [3], in dealing with natural cubic spline interpolation.     

基于静力凝聚的高精度变截面梁单元及其几何非线性分析研究

基于Euler-Bernoulli梁单元基本假定,通过静力凝聚获得截面特性沿单元轴向连续变化的变截面梁单元高精度刚度矩阵,并提出一种基于随动坐标法求解变截面梁杆结构大位移、大转动、小应变问题的新思路。首先依据插值理论和非线性有限元理论推导出三节点变截面梁单元的切线刚度矩阵,然后使用静力凝聚方法消除中间节点自由度,从而得到一种新型非线性两节点变截面梁单元。结合随动坐标法,在变形后位形上建立随动坐标系,得到变截面梁单元的大位移全量平衡方程。实例计算表明,该新型变截面梁单元具有较高的计算精度,可应用于变截面梁杆系统大位移几何非线性分析。     

单层和双层足尺度海底管道抗冲击性能分析

海底管道在服役过程中除了受到常规荷载作用外,还会受到各种意外的冲击载荷作用而失效.为了研究承受横向冲击载荷作用下海底管道的动态特性,对三个单层和一个双层的足尺度管道进行了落锤冲击试验,获得了横向冲击作用下管道的破坏形态、冲击力时程曲线、位移时程曲线及应变时程曲线.建立了分析冲击荷载作用下海底管道失效过程的有限元模型,并...     

Singular‐ended spline interpolation for two‐dimensional boundary element analysis

A method of interpolation of the boundary variables that uses spline functions associated with singular elements is presented. This method can be used in boundary element method analysis of 2‐D problems that have points where the boundary variables present singular behaviour. Singular‐ended splines based on cubic splines and Overhauser splines are developed. The former provides C²‐continuity and the latter C¹‐continuity across element edges. The potentialities of the methodology are demonstrated analysing the dynamic response of a 2‐D rigid footing interacting with a half‐space. It is shown that, for a given number of elements at the soil–foundation interface, the singular‐ended spline interpolation increases substantially the displacement convergence rate and delivers smoother traction distributions. Copyright © 2000 John Wiley & Sons, Ltd.     

基于三次样条插值的精细积分法

结合指数矩阵的精细算法,提出了一类基于三次样条插值的精细积分方法。针对结构动力学方程一般解中的积分项,考虑在一个时间步长内激励为线性和正余弦两种变化形式,通过对积分项中的指数矩阵进行三次样条插值函数模拟,得到一组新的被积函数,最后通过多次分部积分,构造了一类新的高精度计算格式。在三次样条插值函数构造过程中引入了指数矩阵的精细算法,有效避免了中间过程中有效数字的丢失,同时还有效解决了HPD-F算法中涉及的矩阵求逆问题,大大增加了算法的数值稳定性。数值算例显示了该方法的有效性。     

A new shear flexible cubic spline plate element for vibration analysis

Here, a new cubic B‐spline plate element is developed using field consistency principle, for vibration analysis. The formulation includes anisotropy, transverse shear deformation, in‐plane and rotary inertia effects. The element is based on a laminated refined plate theory, which satisfies the interface transverse shear stress and displacement continuity, and has a vanishing shear stress on the top and bottom surfaces of the plates. The lack of consistency in the shear strain field interpolations in its constrained physical limits produces poor convergence and results in unacceptable solutions due to locking phenomenon. Hence, numerical experimentation for the evaluation of natural frequencies of plates is carried out to check this deficiency with a series of assumed shear strain functions, redistributed in a field consistent manner. Copyright © 2002 John Wiley & Sons, Ltd.