Integrity assessment of a 3D tubeplate using the linear matching method. Part 1. Shakedown,reverse plasticity and ratchetting

The Linear Matching Method (LMM) has been developed recently for the integrity assessment for the high temperature response of structures. In this article, a complex 3D tubeplate in a typical AGR superheater header is analysed for the shakedown limit, reverse plasticity and ratchet limit based upon the LMM. At this stage, both the perfectly plastic model and the cyclic hardening model are adopted for the evaluation of the plastic strain range. Comparisons of LMM results with other results by ABAQUS step-by-step inelastic analyses for several material models are given. Further cyclic creep-reverse plasticity analyses are presented in an accompanying paper [Int. J. Pressure Vessels Piping (2004)].     

Integrity assessment for a tubeplate using the linear matching method

A series of numerical procedures have been presented recently for the integrity assessment of structures based upon the Linear Matching Method. A typical example of a holed plate has been used to verify these procedures for the evaluation of plastic and creep behaviours of components. In this paper, a more complex 2D tubeplate at the outlet from a typical AGR heat exchanger is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on the application of the Linear Matching Method for a thorough case study. Both a constant material yield stress and a temperature-dependent yield stress are adopted for the evaluation of the ratchet limit. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a monotonic creep computation is performed, where the start-of-dwell stress is the rapid cycle creep solution at the beginning of the dwell period. An estimation of the tubeplate lifetime is then obtained by the evaluation of fatigue and creep endurances.     

Shakedown and limit analyses for 3-D structures using the linear matching method

A recently developed method for 3-D shakedown and limit analyses is evaluated in the present paper. The shakedown and limit loads of a holed plate subjected to biaxial loading are calculated by implementing the upper bound linear matching method into the commercial FE code ABAQUS. A defective pipeline under the combined action of internal pressure and axial tension is also analysed for both shakedown and limit capacities and the results compared with a standard programming method. All the numerical examples confirm the applicability of this procedure to complex 3-D structures.     

Studies on the Fe2+/Fe3+ redox system using D.C. linear polarisation and impedance techniques

This paper reports experimental data for the solution and polarisation resistances, exchange-current density, and rate constant of the Fe²⁺/Fe³⁺ redox couple. To use this couple in redox batteries, it is concluded that the concentrations of Fe²⁺ must be greater than 0.4 M and that of the supporting HCl must be below 2 M.     

The linear matching method applied to the high temperature life integrity of structures. Part 1. Assessments involving constant residual stress fields

Design and life assessment procedures for high temperatures are based on ‘expert knowledge’ in structural mechanics and materials science, combined with simplified methods of structural analysis. Of these, R5 is one of the most widely used life assessment methods internationally with procedures based on reference stress techniques and shakedown calculations using linear elastic solutions. These have been augmented by full finite element analysis and, recently, the development of a new programming method, the linear matching method (LMM), that allows a range of direct solutions that include shakedown methods and simplified analysis in excess of shakedown. In this paper, LMM procedures are compared with calculations typical of those employed in R5 for cyclic loading problems when the assumption of a constant residual stress field is appropriate including shakedown and limit analyses, creep rupture analysis and the evaluation of accumulated creep deformation. A typical example of a 3D holed plate subjected to a cyclic thermal load and a constant mechanical load is assessed in detail. These comparisons demonstrate the significant advantages of linear matching methods for a typical case. For a range of cyclic problems when the residual stress field varies during the cycle, which include the evaluation of plastic strain amplitude, ratchet limit and accumulated creep strains during a high temperature dwell periods, the corresponding LMM and R5 procedures are discussed in an accompanying paper.     

High Reynolds number unsteadiness assessment using 3D and 2D computational fluid dynamics simulations of a thick aerofoil equipped with a spoiler

An operating 2-MW wind turbine has been scanned and analysed using 2D computational fluid dynamics (CFD) and blade element momentum (BEM) analysis. The current work illustrates using full-scale 3D CFD simulations the differences between 2D and 3D simulations and its impact on the local aerofoil vortex shedding frequency. The outcome shows that despite a pressure redistribution and lift change introduced by the blade span and rotation, the vortex shedding frequency remains similar between 2D and 3D thereby validating the novel fatigue calculation method previously proposed.     

Uncertainty in wave energy resource assessment. Part 2: Variability and predictability

The uncertainty in estimates of the energy yield from a wave energy converter (WEC) is considered. The study is presented in two articles. The first article considered the accuracy of the historic data and the second article, presented here, considers the uncertainty which arises from variability in the wave climate. Mean wave conditions exhibit high levels of interannual variability. Moreover, many previous studies have demonstrated longer-term decadal changes in wave climate. The effect of interannual and climatic changes in wave climate on the predictability of long-term mean WEC power is examined for an area off the north coast of Scotland. In this location anomalies in mean WEC power are strongly correlated with the North Atlantic Oscillation (NAO) index. This link enables the results of many previous studies on the variability of the NAO and its sensitivity to climate change to be applied to WEC power levels. It is shown that the variability in 5, 10 and 20 year mean power levels is greater than if annual power anomalies were uncorrelated noise. It is also shown that the change in wave climate from anthropogenic climate change over the life time of a wave farm is likely to be small in comparison to the natural level of variability. Finally, it is shown that despite the uncertainty related to variability in the wave climate, improvements in the accuracy of historic data will improve the accuracy of predictions of future WEC yield.     

Development of a H2-permeable Pd60Cu40-based composite membrane using a reverse build-up method

A new reverse build-up method is developed to fabricate an economical H₂-permeable composite membrane. Sputtering and electroplating are used for the formation of a membrane comprised of a 3.7-μm-thick Pd₆₀Cu₄₀ (wt.%) alloy layer and a 13-μm-thick porous Ni support layer, respectively. The H₂-permeation measurements are performed under the flow of a gaseous mixture of H₂ and He at 300–320 °C and 50–100 kPa of H₂ partial pressure. The H₂/He selectivity values exceed 300. The activation energy at 300–320 °C is 10.9 kJ mol⁻¹. The H₂ permeability of the membrane is 1.25 × 10⁻⁸ mol m⁻¹ s⁻¹ Pa^−0.5 at 320 °C after 448 h. The estimated Pd cost of the proposed membrane is approximately 1/8 of the cost for a pure Pd₆₀Cu₄₀ membrane. This study demonstrates that the proposed method allows the facile production of low-cost, Pd-based membranes for H₂ separation.     

Indirectly heated biomass gasification using a latent heat ballast. Part 2: modeling

Experiments carried out in an indirectly heated biomass gasifier successfully demonstrated that throughput and gas heating value could be increased by using a latent heat ballast. A mathematical model describing heat transfer and chemical reaction in the system was developed. The heat transfer submodel is accurate to within 13 K for both ballasted and unballasted scenarios. However, the chemical submodel, based on thermodynamic equilibrium calculations, proved inadequate and underpredicted cooling times during the pyrolysis phase of the process by about 50%. Improvement was made by substituting the measured product gas composition for the calculated gas composition.     

On the thermoeconomic approach to the diagnosis of energy system malfunctions: Part 2. Malfunction definitions and assessment

This paper goes further with the aim at demonstrating the capabilities of the thermoeconomic approach to the diagnosis of energy utility systems. This paper deals with a common vocabulary, definitions of concepts and mathematical principles, and above all, focuses on the concept of malfunction, starting from an engineering point of view and then shifting to a pure formalization as thermoeconomic parameters. Possible malfunctions of components of a combined cycle power plant are described in this part in terms of causes and effects. In addition, the main theoretical aspects of the thermoeconomic approach are shown. In particular the fuel impact formula, which constitutes the main thermoeconomic tool for quantifying the effects of degradation, is discussed.     

Investigation of 2D drop evaporation on a smooth and homogeneous surface using Lattice Boltzmann method

In this study, we present a numerical simulation on behavior of a liquid droplet on a heated horizontal substrate to investigate the contact line motion using multiphase Lattice Boltzmann method. For this purpose, the model of Lee is used which is applicable to a wide range of density ratios. A proper source term is incorporated at the liquid-gas interface to account for the phase change process and the passive scalar method is employed to simulate the temperature field. The cubic boundary condition is adopted to model the effects associated with the wall boundary. Effects of Stefan number and density ratio on the dynamic of the evaporation are illustrated. The adopted method allows us to carry out the simulations with density ratios up to 1000 which previous LB models were unable to analyse. Finally the contact line motion of an evaporating droplet on a smooth substrate is investigated. The results show that the properties of the surface play an important role on the dynamic of the evaporation which was observed in other researches.     

View factor calculation using the Monte Carlo method for a 3D strip element to circular cylinder

The discussion includes the application of the Monte Carlo method to determine view factor for the plate including strip elements to circular cylinder as a case in heating and cooling processes in material processing. The results involving the relationships between different discretization schemes, number of rays used for the view factor calculation, CPU time and accuracy are presented. The analysis also displays the differences between the numerical results obtained and analytical solutions for the 20, 30 and 45 element discretized figures and for (30⁴), (50⁴) and (70⁴) rays per element. The results obtained from the Monte Carlo solution indicate that smaller elements require more effort to obtain an accurate view factor.     

Fouling in a Steam Cracker Convection Section Part 2: Coupled Tube Bank Simulation using an Improved Hybrid CFD-1D Model

Abstract

Performing an adequate fouling study for the heat exchangers in the convection section of a steam cracker requires reliable data on circumferential tube wall temperature profiles. A hybrid Computational Fluid Dynamics (CFD)-1D convection section model, developed to perform coupled flue gas/process gas side simulations of convection sections, is improved by the implementation of flue gas radiation modeling and extended to include typical tube banks. A complete naphtha cracker convection section is simulated with the improved hybrid CFD-1D model. All tubes show distinct maximum heat fluxes on the tube walls due to the high flue gas velocity. Based on the calculated circumferential heat flux profiles, the maximum heat flux value is calculated to be 1.8 times the average tube heat flux value. As computational costs associated with a hybrid CFD-1D simulation are high, a convective heat flux profile reconstruction scheme is developed. Using the scheme, circumferential heat flux profiles are reconstructed, based on the heat fluxes calculated when performing a fully 1D coupled convection section simulation. The heat flux reconstruction profile scheme enables fast retrieval of circumferential heat flux profiles and, thus, tube wall temperature profiles. Optimization and/or design of a steam cracker convection section becomes less computationally demanding.     

Assessing the sustainability of the UK society using thermodynamic concepts: Part 2

By building on the first part of our analysis, this second part attempts to provide a further understanding of the UK society's metabolism, its impact and offer policy suggestions that could promote a shift towards sustainability. The methodologies employed in this second part include Exergy Analysis (EA) and Extended Exergy Analysis (EEA). Exergy inputs and outputs amounted to 17423.9 and 11888.7 PJ, respectively, with energy carries, mainly fossil fuels, being both the predominant inputs (15597.1 PJ) and outputs (5147.1 PJ). Exergy consumption and efficiency for various economic sectors and subsectors have been calculated with the residential and service sector showing the lowest exergy conversion efficiencies (11.2% and 12.3%, respectively) while certain industrial subsectors, such as the aluminium and iron/steel industries showed the highest exergy conversion factors (67.0 and 62.1%). Extended exergy efficiencies were somewhat different owing to the different calculation procedure. Extended exergy efficiencies were 91.4% for the extraction sector, 38.9% for the conversion sector, 49.1% for the agriculture sector, 31.5% for the transportation sector, 38.6% for the industrial sector and 80.0% for the tertiary sector.     

3D creep cavitation characteristics and residual life assessment in high temperature steels: a critical review

Abstract

The need for a new paradigm to estimate remaining creep life of service exposed steels is critically assessed. New approaches to residual life assessment are proposed, in the light of a decade’s experience of the use of micro-tomography to characterise the three-dimensional (3D) nature of cavitation damage in structural materials. Imaging of conventional structural materials such as steels with high absorption to X-rays has been realised by synchrotron micro-tomography (SR-μCT), providing new insights into phenomena such as creep failure. The unique feature of SR-μCT studies is the direct imaging in 3D of cavities (hundreds of micrometres in size) present in the bulk, revealing the spatial characteristics and morphology of the creep voids. Quantitative analyses of the cavitation characteristics revealed by 3D datasets, when scaled with respect to time, stress and temperature, provide functional information suitable for developing constitutive equations for creep. The application of SR-μCT, a non-destructive technique providing high fidelity data, significantly reduces the ambiguity in developing functional relationships to predict creep failure. The explicit use of such constitutive equations to estimate the residual life of components in creep, and the consequent assessment of structural integrity, would prove invaluable. Micro-tomography studies related to creep in materials are reviewed, with special emphasis on a 10·86%Cr heat resistant steel, to demonstrate the type of data available for life assessment and design against creep failure. A brief discussion of current methods to estimate residual life in the light of recent 3D micro-tomography data follows. Finally, the possibility of new approaches, using micro-tomography data in conjunction with destructive 3D approaches such as serial sectioning, to formulate advanced residual life estimates, is briefly considered.     

Simulations of coupled radiative and convective heat transfer in 2D and 3D semitransparent medium by the moving least square method

The aim of the paper is to use the moving least square meshless method to study the coupled problem between radiation and natural convection in semitransparent medium of 2D and 3D geometries. The flow is incompressible, laminar, and governed in the vorticity-stream function formulation (2D) and vorticity-vector potential formulation (3D) of Navier–Stokes equations. We use the discrete ordinate method to solve the radiative transfer equation. We study the influence of optical thickness, albedo, heat source, and geometry shape to the flow patterns and temperature distributions. The examples (square, cylindrical ring, and cubic) are taken to compare to the references to check the performance of the proposed method. The results show that the moving least square meshless method is capable to deal with the coupled radiation and natural convection with stability and accuracy.     

Solidification of a 2-D semitransparent medium using the lattice Boltzmann method and the finite volume method

This article deals with the analysis of solidification of a 2-D semitransparent absorbing, emitting and scattering medium. An enthalpy based formulation was employed to simulate the phase-change process. Solidification was assumed to occur over a range of temperatures, and accordingly distinct liquid-, mushy- and solid-zones were considered. The problem was solved using the lattice Boltzmann method. The finite volume method was used to compute the radiative information required in the LBM formulation. Effects of various parameters such as the extinction coefficient, the scattering albedo, the conduction–radiation parameter and the latent heat were studied on temperature and liquid fraction distributions in the medium. These parameters were found to have significant effect on results.     

Rapid optimization of stall‐regulated wind turbine blades using a frequency‐domain method: Part 2, cost function selection and results

A fast and effective frequency‐domain optimization method was developed for stall‐regulated blades. It was found that when using linearized dynamics, typical cost functions employing damage‐equivalent root bending moments are not suitable for stall‐regulated wind turbines: when the cost function is minimized, the edgewise damping can be low, and the flapwise damping can approach zero during an extreme operating gust. A new cost function is proposed that leads to nicely balanced stall behavior and damping over the entire operating windspeed range. The method was used to design the blades of two multi‐MW, stall‐regulated, offshore wind turbines, comparable with the NREL 5 MW and NTNU 10 MW pitch‐regulated turbines. It is shown that the optimal stall‐regulated blade has a unique aerodynamic profile that gives high flapwise and edgewise damping and a uniform mean power output above the rated windspeed. The blades are described in sufficient detail that they can be used in further aeroelastic analyses, to compare large stall‐regulated and pitch‐regulated turbines. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimization of multistage vapour compression systems using genetic algorithms. Part 2: Application of genetic algorithm and results

Genetic algorithms involve the coding of a solution into a binary string in the same manner that DNA is a biological coding. A population of binary strings are randomly created, evaluated, allowed to mate and are mutated to form a new generation of strings. There is a mating preference given to those strings which rate the highest to simulate the survival‐of‐the‐fittest theory that exists in nature. This process of evaluation, mating and mutation is repeated until some termination criteria are met. A computer code was written in Visual C++ to simulate the vapour compression systems and perpetuate the genetic algorithm. The genetic algorithm functioned adequately enough to provide general trends but it did not find a universal optimum. After numerous runs, the code produced data that suggest that systems which employ intercooler/flash tanks and operate at lower evaporating temperatures have a higher multistage effectiveness. Copyright © 2001 John Wiley & Sons, Ltd.