Fracture response of pipelines subject to large plastic deformation under bending

Demand for long-distance offshore pipelines is steadily increasing. High internal pressure combined with bending/tension, accompanied by large plastic strains, along with the potential flaws in girth welds make the structural integrity of pipelines a formidable challenge. The existing procedures for the fracture assessment of pipelines are based on simplified analytical methods, and these are derived for a load-based approach. Hence, application to surface cracked pipes under large deformation is doubtful. The aim of this paper is to understand and identify various parameters that influence the fracture response of cracks in pipelines under more realistic loading conditions. The evolution of CTOD of a pipeline segment with an external circumferential surface crack is investigated under pure bend loading as well as bending with internal pressure. Detailed 3D elastic–plastic finite element simulations are performed. The effects of crack depth, crack length, radius-to-thickness ratio and material hardening on fracture response are examined. The results show that at moderate levels of CTOD, the allowable moment capacity of the pipe decreases significantly with increase in internal pressure. Further, the variation of CTOD with strain can be well approximated by a simple linear relationship.     

Practical values of various parameters for PV system design

In order to reasonably design a PV system, it is important to use appropriate parameter values. Few papers, however, describe design parameters that are defined systematically. The authors have been entrusted by the New Energy and Industrial Technology Development Organization (NEDO) with research and development of PV system evaluation since 1990 in order to establish optimum design and operation methods of various kinds of PV systems which are expected to be put into commercial use in the future.In this research, which is based on the data obtained from test facilities which were constructed at Hamamatsu site, various design parameters were calculated and reported as primary values provisionally estimated. This paper presents practical values of various parameters for PV system design as a table, revised with design parameter values studied later on. In particular, cell temperature factor was studied in view of regional differences and module mounting.The authors will confirm reasonable design of PV system by using such various design parameter values.     

Recommendations on X80 steel for the design of hydrogen gas transmission pipelines

By limiting the pipes thickness necessary to sustain high pressure, high-strength steels could prove economically relevant for transmitting large gas quantities in pipelines on long distance. Up to now, the existing hydrogen pipelines have used lower-strength steels to avoid any hydrogen embrittlement. The CATHY-GDF project, funded by the French National Agency for Research, explored the ability of an industrial X80 grade for the transmission of pressurized hydrogen gas in large diameter pipelines. This project has developed experimental facilities to test the material under hydrogen gas pressure. Indeed, tensile, toughness, crack propagation and disc rupture tests have been performed. From these results, the effect of hydrogen pressure on the size of some critical defects has been analyzed allowing proposing some recommendations on the design of X80 pipe for hydrogen transport. Cost of Hydrogen transport could be several times higher than natural gas one for a given energy amount. Moreover, building hydrogen pipeline using high grade steels could induce a 10 to 40% cost benefit instead of using low grade steels, despite their lower hydrogen susceptibility.     

柴油机曲轴可靠性辩析

从设计、制造和使用方面对影响曲轴可靠性诸因素做简要分析。根据升降法弯曲疲劳试验结果,用具体失效率下的极限承载能力估算值和安全系数,对曲轴的可靠性进行评价。讨论了评价指标,并提出参考值;同时,根据强度和应力项的分析,指出提高曲轴可靠性的方向。     

Design of steel storage tanks with spherical bottoms

A new approach to the design of a vertical cylindrical storage vessel with a spherical bottom, based on bending theory instead of membrane analysis of shells, is proposed. The design of cylindrical shells employs the analysis of a cylindrical shell subjected to a wind load. Axial membrane stresses along the height caused by wind loading are evaluated from the prepared charts for various R/h ratios. These stress values are multiplied by a multiplication factor to obtain the meaningful bending stresses. The design of the spherical bottom involves the analysis of a shallow spherical shell on a Pasternak foundation. The distribution of membrane and bending stresses in the spherical bottom is plotted against the radial distance. To facilitate the work of the designer charts have been provided for rapid determination of various terms involved in the calculation of net stresses in the bottom.     

Numerical investigations into influence of scanning path curvature on deformation behavior during curvilinear laser bending of magnesium sheets

In laser bending process, metal sheets are deformed by using thermal stresses induced due to controlled laser heating. Straight line heating is used to manufacture simple shapes while curvilinear irradiation is used to generate 3D complex shapes. Scanning path curvature is an important parameter that controls the deformation profile of a worksheet. This article presents systematic investigations into influence of scanning path curvature on the thermal stresses based deformation behavior, temperature distribution and warping of the magnesium M1A sheets. Initially, a three-dimensional nonlinear thermomechanical finite element model of curvilinear laser bending process has been developed. Mathematical correlations have been derived to model the curvilinear irradiations. The developed model has been validated by using experimental studies. Then, numerical investigations have been performed on temperature distribution, stress–strain distribution and distortions occur in the laser bent magnesium alloy sheets. Results indicated that sheet bends away from the scanning path. One of the key findings is that low to medium levels of arc height reduce the edge effect during laser bending, while higher values of arc height produce warping at the free edge. It is envisaged that presented results will be useful to manufacture 3D complex shapes and to align complex geometry sheets.     

流化床扬析速率常数的三相传质模型

本文基于上气泡集合理论建立的流化床三相传质模型,模拟细粉在流化床中的浓度分布,并以此对流化床设计,运行中的重要参数－细粉扬析速率常数Ｋ进行了计算与讨论,计算值与试验结果有良好的一致性。     

电控柴油机在线故障诊断系统实用简单计算方法研究

本文使用简单实用C＋＋算法及基本数学理论进行快速、实用电控柴油机在线故障诊断的研究。首先,进行了特有的故障码设计,按照故障码的原理,对故障进行了分类。接着,充分运用故障码编制形成的框架,对基本故障的诊断算法进行了编制。然后,对多参数故障及复杂故障进行了算法设计。最后,为提高故障库的扩展功能,设计了“未知故障”处理功能。另外,进行了软件可靠性的研究。通过模拟实验结果表明：系统设计合理,工作可靠,达到了预期的目标,证明故障论断实用简单算法的可行性。     

Steady state process simulations of a novel containerized power to ammonia concept

A simple novel small-scale time flexible containerized power to ammonia concept, employing conventional technology only, which is going to be realized in 2023 in Italy, is being investigated.The design focuses on investment cost minimization and time-flexibility, presenting a middle way between large-scale conventional ammonia plants and more sophisticated small-scale power to ammonia designs.Reducing the investment cost of the cycle components shall be achieved by a simple cycle design and by operating at lower pressures and temperatures.Time-flexibility, desired for the concept to act as chemical energy storage for the fluctuating renewables, is achieved by the novel cycle design, mainly by electrical start-up heaters.Process simulation results regarding the optimum sizing of the reactor, reactor temperature profile, and inlet ratio for hydrogen to nitrogen are presented.Due to the simple design, the resulting energetic degree of efficiency is, as expected, lower than the values in the literature.     

Transferability of decompression wave speed measured by a small-diameter shock tube to full size pipelines and implications for determining required fracture propagation resistance

The control of propagating ductile (or tearing) fracture is a fundamental requirement in the fracture control design of pipelines. The Battelle two-curve method developed in the early 1970s still forms the basis of the analytical framework used throughout the industry. GASDECOM is typically used for calculating decompression speed, and idealizes the decompression process as isentropic and one-dimensional, taking no account of frictional effects. While this approximation appears not to have been a major issue for large-diameter pipes and for moderate pressures (up to 12 MPa), there have been several recent full-scale burst tests at higher pressures and smaller diameters for which the measured decompression velocity has deviated progressively from the predicted values, in general towards lower velocities. The present research was focused on determining whether pipe diameter was a major factor that could limit the applicability of frictionless models such as GASDECOM. Since potential diameter effects are primarily related to wall friction, which in turn is related to the ratio of surface roughness-to-diameter, an experimental approach was developed based on keeping the diameter constant, at a sufficiently small value to allow for an economical experimental arrangement, and varying the internal roughness. A series of tests covering a range of nominal initial pressures from 10 to 21 MPa, and involving a very lean gas and three progressively richer compositions, were conducted using two specialized high-pressure shock tubes (42 m long, I.D. = 38.1 mm). The first is honed to an extremely smooth surface finish, in order to minimize frictional effects and better simulate the behaviour of larger-diameter pipelines, while the second has a higher internal surface roughness. The results show that decompression wave speeds in the rough tube are consistently slower than those in the smooth tube under the same conditions of mixture composition and initial pressure &; temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation indicates that the primary reason for the slower decompression wave speed in the rough tube is the higher spatial gradient of pressure pertaining to the decompression wave dynamics, particularly at lower pressure ratios and higher gas velocities. The magnitude of the effect of the slower decompression speed on arrest toughness was then evaluated by a comparison involving several hypothetical pipeline designs, and was found to be potentially significant for pipe sizes DN 450 and smaller.     

基于均匀设计的汽油机喷油脉宽标定方法研究

应用课题组开发的ECU及上位机软件对MR479Q汽油机进行基本喷油脉宽的标定。利用均匀设计多项式回归理论建立喷油脉宽预测模型,制取了喷油脉宽MAP图,并通过试验检验。研究结果表明,与全面试验相比,试验点从170个减少至30个,预测基本喷油脉宽平均误差为112.6μs。该模型能够准确预测发动机不同工况下的喷油脉宽,具有一定的工程应用价值。     

Effects of nonlinear hygrothermomechanical loading on bending of FGM rectangular plates resting on two-parameter elastic foundation using four-unknown plate theory

In the present study, a simple four-unknown exponential shear deformation theory is developed for the bending of functionally graded material (FGM) rectangular plates resting on two-parameter elastic foundation and subjected to nonlinear hygrothermomechanical loading. The elastic properties, coefficient of thermal expansion, and coefficient of moisture expansion of the plate are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of volume fractions of material constituents. Unlike first-order and other higher-order plate theories, the present theory has four independent unknowns. The in-plane displacement field of the present theory uses exponential functions in terms of thickness co-ordinate for calculating out-of-plane shearing strains. The transverse displacement includes bending and shear components. The principle of virtual displacement is employed to derive the governing equations and associated boundary conditions. A Navier solution technique is employed to obtained an analytical solutions. The elastic foundation is modelled as two-parameter Winkler–Pasternak foundation. The numerical results obtained are compared with previously published results wherever possible to prove the efficacy and accuracy of the present theory. The effects of stiffness and gradient index of the foundation on the hygrothermomechanical responses of the plates are discussed.     

Transport properties of non-spherical nanoparticles studied by Brownian dynamics: theory and numerical simulations

We have succeeded in extending the Brownian dynamics analyses to systems consisting of non-spherical nanoparticles interconnected by conservative forces or holonomic constraints. The formal theory takes fully into account both nanoparticle size and surface topography. Our theory also incorporates stretching, bending and torsional stiffness between nearest neighbor subunits, excluded volume effects, external force fields, fluid flow and fluid-dynamic interactions. The generalized conformation-space diffusion equations are rigorously derived from kinetic theory. The equivalent stochastic differential equations are used as our basis for development of the associated Brownian dynamics algorithms. These algorithms may be employed to carry out equilibrium as well as non-equilibrium simulations of the conformational dynamics and transport properties for a wide class of nanoparticle systems embedded in viscous fluids. To test the validity of the theory and the numerical algorithms, we present the results from a simulation example.     

A theoretical and experimental investigation of a small-scale solar-powered barometric desalination system

This paper describes and evaluates a theoretical and experimental study of a solar-powered barometric desalination system in which drinking water can be distilled from seawater. The paper describes the system and the experimental apparatus used to test a simple design theory. Experimental results are provided and compared with the given theory. A good correlation between theory and experiment indicates that the distillate production rate depends on the heat exchanger effectiveness of the condenser, solar insolation and evaporator pressure. Results are used to provide an outline specification for a device able to provide fresh water to a small family group.     

不同配筋率对钢筋混凝土三点弯曲梁断裂韧度的影响

为深入了解配筋率对钢筋混凝土断裂韧度的影响,制作了3组12根带预制裂缝的钢筋混凝土三点弯曲梁并做了断裂试验,根据试验导出了钢筋混凝土三点弯曲梁试件断裂参数解析计算公式,分析了不同配筋率对钢筋混凝土三点弯曲梁断裂韧度的影响程度。结果表明,钢筋混凝土三点弯曲梁试件的开裂荷载主要由混凝土主体结构所决定,最大荷载主要由混凝土内部配置的钢筋情况所决定;裂缝亚临界扩展相对值随着配筋率的增加呈线性增加;配筋率的变化对失稳断裂韧度有一定影响,但对起裂断裂韧度影响不大;配筋率的增加,可有效提高试件的韧性和抵抗失稳破坏的能力。     

A comparison of approximate methods for estimation of the creep relaxation of a curved pipe

The relaxation of stress in a linear, thin shell model of a curved pipe constrained to have a fixed rotation and expanding inelastically due to creep is represented by an equation of evolution in time. Using finite differences this continuous system is reduced to a finite set of initial value problems which are numerically integrated using a second order Runge-Kutta method. Thus the relaxation of the resultant in-plane bending moment can be deduced. Results are compared with two simple approximate methods with important repercussions on high temperature pipework design.     

A theory on cracked pipe

Based on the conservation law and bending theory, a very simple method is proposed to estimate intensity factors for circumferential cracked pipe. The examples show that the present method can produce the results obtained from complete shell analysis. This method can also be used to analyze the periodic cracked pipe under tension.     

Theory of heat transfer during condensation in microchannels

A theoretical model for condensation in microchannels takes account of the effects of gravity and streamwise shear stress on the condensate surface as well as the transverse pressure gradient due to surface tension in the presence of change in condensate surface curvature. Numerical solutions of the relevant conservation equations have been obtained for various channel shapes, dimensions, vapor-to-surface temperature differences and vapor mass fluxes. The theory is reviewed and updated. The effect of channel inclination is included and new results are presented. When using boundary conditions of uniform vapor and surface temperature it is found that, over a certain length of channel, the local mean (around the channel perimeter) heat-transfer coefficient is essentially independent of gravity and vapor shear stress. For the surface tension dominated regime, an equation for the Nusselt number as a function of a single dimensionless group, analogous to that occurring in the simple Nusselt theory except that the gravity term is replaced by a surface tension term, has been derived both on the basis of dimensional analysis and by approximate theory. The equation represents all of the data satisfactorily. This is a step towards the goal of representing the solutions, including those conditions where shear stress and gravity play important roles, by relatively simple dimensionless algebraic equations, valid for any fluid and channel geometry, for convenient use in design and optimization.     

The synergistic effects of hydrogen embrittlement and transient gas flow conditions on integrity assessment of a precracked steel pipeline

We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation.     

应用信息谱系图法检测火电厂的异常数据

从数据自身的性质出发,提出了一种应用谱系图进行异常数据检测的方法。针对某电厂生产过程中采集到的数据,利用数据间的关联特性,应用系统聚类构造传感器信息谱系图,从中寻找到一种稳定模式———强相关测点集合,通过分析研究实际运行过程中这种模式的变化,来达到异常数据检测的效果。理论和实验分析证明,该方法具有简便、直观的异常数据检测特点,较适合工程实际应用。图7表4参3