Application of a Bayesian model for the quantification of the European methodology for qualification of non-destructive testing

The European methodology for qualification of non-destructive testing is a well-established approach adopted by nuclear utilities in many European countries. According to this methodology, qualification is based on a combination of technical justification and practical trials. The methodology is qualitative in nature, and it does not give explicit guidance on how the evidence from the technical justification and results from trials should be weighted. A Bayesian model for the quantification process was presented in a previous paper, proposing a way to combine the “soft” evidence contained in a technical justification with the “hard” evidence obtained from practical trials.This paper describes the results of a pilot study in which such a Bayesian model was applied to two realistic Qualification Dossiers by experienced NDT qualification specialists. At the end of the study, recommendations were made and a set of guidelines was developed for the application of the Bayesian model.     

A contribution for thermoeconomic modelling: A methodology proposal

This work presents a thermoeconomic optimization methodology for the analysis and design of energy systems. This methodology involves economic aspects related to the exergy conception, in order to develop a tool to assist the equipment selection, operation mode choice as well as to optimize the thermal plants design. It also presents the concepts related to exergy in a general scope and in thermoeconomics which combines the thermal sciences principles (thermodynamics, heat transfer, and fluid mechanics) and the economic engineering in order to rationalize energy systems investment decisions, development and operation. Even in this paper, it develops a thermoeconomic methodology through the use of a simple mathematical model, involving thermodynamics parameters and costs evaluation, also defining the objective function as the exergetic production cost. The optimization problem evaluation is developed for two energy systems. First is applied to a steam compression refrigeration system and then to a cogeneration system using backpressure steam turbine.     

European developments in theoretical modelling of NDE for pipework

Ultrasonic, non-destructive examinations are used to detect and size crack-like defects in a variety of structures such as railway rails, bridges, pressure vessels and pipework. Such inspections are carefully designed to detect cracks which, if not repaired, could lead to loss of the component. If the response from a defect can be calculated then it is possible to examine the inspection strategies and procedures and to demonstrate that they are adequate for the purpose for which they are intended. A survey is given of various problems tackled by European modellers of NDT, concentrating on areas which have not been recently reviewed elsewhere. Emphasis is placed on physical features of defects, such as defect roughness, material ingress, the effects of compressive stress, the effects of crack size, and the implications of variation in the reliability of ultrasonic testing due to these effects for structural integrity.     

Calculation of the velocity of creeping waves and their application to non-destructive testing

A method of ultrasonic inspection called ‘time-of-flight’ is intended to provide accurate sizing of crack-like defects in structures such as pressure vessels and piping and the principles can also be applied to the sizing of volumetric defects. Accurate measurement can only be made if the velocity of the ultrasonic wave is known along the entire path. For structures that have curved surfaces (as do pressure vessels and piping) and for the sizing of volumetric defects, this aspect is important for the so-called creeping waves that propagate around the curved surfaces, comparable to the ‘lateral’ or ‘near-surface’ waves on a flat plate. It is shown that the velocity of creeping waves is a sensitive function of the curvature of the surface. The velocity can be predicted accurately from the bulk wave velocity and the radius of curvature of the defect. Detailed calculations are made for steel and are discussed in terms of 4 MHz ultrasonic waves. The results have consequences relating to the accurate sizing by time-of-flight methods of volumetric defects or for accurate depth determination of crack-like defects in pressure vessels and piping.     

Validation of a methodology for determining the PEM fuel cell complex impedance modelling parameters

In this paper, we present a new methodology for determining the complex impedance parameters for a Proton Exchange Membrane (PEM) Fuel Cell in order to have a general model for embedded diagnosis. The modelling of Fuel Cells is a very important phase because it contributes to a better understanding and representation of the internal phenomena in this type of generator. After obtaining the experimental results of the complex impedance using a realized test bench for Proton Exchange Membrane (PEM) Fuel Cell using an electrochemical method which is the electrochemical impedance spectroscopy (EIS), we treat these results with an identification algorithm based on least squares method in the objective to determine the variations laws of the complex impedance parameters then implement in a PEM Fuel Cell model with Matlab/Simulink software. The established model of the complex impedance is based on electrical components and takes into account the mathematical equations of the different elements. The simulation results of this implemented model inform us about the state of the PEM Fuel Cell and validate the choice of the parameters. The validation of this choice is done by a comparative study using residual analysis method between the experimental and the simulation results. The general model is obtained from the superposition of the measured and theoretical results.     

Statistical methodology for predicting the life of lithium-ion cells via accelerated degradation testing

Statistical models based on data from accelerated aging experiments are used to predict cell life. In this article, we discuss a methodology for estimating the mean cell life with uncertainty bounds that uses both a degradation model (reflecting average cell performance) and an error model (reflecting the measured cell-to-cell variability in performance). Specific forms for the degradation and error models are presented and illustrated with experimental data that were acquired from calendar-life testing of high-power lithium-ion cells as part of the U.S. Department of Energy's (DOEs) Advanced Technology Development program. Monte Carlo simulations, based on the developed models, are used to assess lack-of-fit and develop uncertainty limits for the average cell life. In addition, we discuss the issue of assessing the applicability of degradation models (based on data acquired from cells aged under static conditions) to the degradation of cells aged under more realistic dynamic conditions (e.g., varying temperature).     

World energy modelling: the development of Western European oil prices

In the belief that the world's energy problems cannot be lastingly solved in a piecemeal manner, one nation or one industry at a time, a computer model is being constructed to cover the whole international energy industry. This paper presents some of the concepts upon which the model is based, some of the evidence behind these concepts and some preliminary results from the model in the field of product prices.     

A new multibody modelling methodology for wind turbine structures using a cardanic joint beam element

This paper presents a new multibody modelling methodology for wind turbine structures. The methodology is based on the hybrid multibody system being composed of rigid, flexible bodies, force elements and joints. With a cardanic joint beam element based on the Timoshenko beam theory, the flexible bodies, e.g. rotor blades and tower, shafts, are modelled by a set of rigid bodies connected by cardanic joints geometrically and constrained by spring forces elastically, thus a whole wind turbine structure can be represented by a discrete system of rigid bodies, springs, and dampers. Using some concepts of the differential geometry, the Lagrange's motion equations of the multibody system are represented in explicit form. With this model, the global natural vibrations of a wind turbine structure of 600 kW are analysed.     

Cyclic thermo-mechanical material modelling and testing of 316 stainless steel

A programme of cyclic mechanical testing of a 316 stainless steel, at temperatures of up to 600 °C under isothermal conditions, for the identification of material constitutive constants, has been carried out using a thermo-mechanical fatigue test machine (with induction coil heating). The constitutive model adopted is a modified Chaboche unified viscoplasticity model, which can deal with both cyclic effects, such as combined isotropic and kinematic hardening, and rate-dependent effects, associated with viscoplasticity. The characterisation of 316 stainless steel is presented and compared with results from tests consisting of cyclic isothermal, as well as in-phase and out-of-phase thermo-mechanical fatigue conditions, using interpolation between the isothermal material constants to predict the material behaviour under anisothermal conditions.     

The future of the European natural gas market: A quantitative assessment

The debate over the availability of conventional natural gas has been nearly as strong as that for conventional oil. In Europe, the debate is strengthened due to the region’s dependence on natural gas from outside countries. In addition, concern has been expressed by some energy experts in recent years about an imminent shortage of natural gas from Europe, caused supposedly by dwindling natural gas resources. Thus, the purpose of this analysis is to address the concern by assessing the availability of natural gas in the region. This is done by estimating a cumulative availability curve showing natural gas endowment versus production costs. The findings indicate that natural gas in Europe is more available and economic than often assumed. Increased research and development of this potential could help increase energy security in the region.     

Effects of boundary conditions on testing of pipes and finite element modelling

The design of many submarine pipelines, especially for operating in deep water, relies on accurate test results for the local buckling collapse of pipes subjected to bending loading. Recent test results have shown apparently anomalous values of axial tensile and compressive strains in comparison to the values that would be expected on the basis of simple bending theory. This could have important consequences for the efficacy of the design factors derived using these anomalous results. Examples of anomalous test results are given in the paper and the cause of the differences between the strain values obtained in the tests and those expected on the basis of simple bending theory are explained using finite element modelling.The major point is that the general application of the simplified engineering theory of bending can be erroneous when ovalisation is imposed or, on the contrary, the boundary conditions of the section are restrained from ovalising deformations.This is a crucial limit state for the design of onshore and offshore pipelines.     

欧盟钢焊工资质考试标准ISO9606-1与EN287-1对比分析

从2015年10月开始,欧盟钢类别的焊工考试标准EN287-1已经被ISO9606-1替代,两标准在内容上有所不同。本文结合两个标准的内容,从填充材料、熔敷金属厚度及母材厚度的认可范围、试件类型、焊接位置等方面着重分析了两者主要异同点,有利于更深入理解钢类焊工资质考试标准内容。     

A methodology for modelling synthetic daily sequences of hourly power demand for villages and small towns, based on stochastic processes

A model to generate daily sequences of hourly power demand values is described. Inputs are the daily values of energy consumption and load-factors (the ratio between mean and peak load). The whole model covers three independent first-order autoregressive models to generate data sequences of, respectively, daily energy consumption, daily load-factor and hourly power demand. The analysis of a power demand data set reveals that energy consumption and load-factor are independent variables; two independent time series of daily values of energy consumption and load-factor are built; their statistical and sequential properties can be described with first-order autoregressive models. Assuming a villlage’s consumption-structure as characterized by load curves with a peak load at night, the load-factor is taken as a shape-factor for these curves. A frequency distribution is built on daily load factors. The data sequence is, then, sorted into groups of daily curves, each one characterized by a load-factor-class. A daily average load curve is estimated for each class, along with its daily standard deviation curve. An analysis of each group of daily curves shows that the statistical and sequential properties of each one can be also described with first-order autoregressive models. For modelling purposes, the autocorrelation coefficient is determined for each load-factor class. Thus, energy and power relate to each other under different load-factors. Application examples are offered, for design purposes.     

Equipment qualification in the United Kingdom for the Sizewell 'B' pressurized water reactor

Information is presented regarding the equipment qualification program for Sizewell B, a pressurized water reactor presently being built by the Central Electricity Generating Board in Suffolk, England with commercial operation scheduled for 1994. The program is being established in accordance with IEEE Standards 627-1980, 323-1983 and 344-1975. Specific differences between testing performed in the US and those intended for Sizewell B are highlighted, with the reasons behind such differences explained.<>     

Quantifiable destructive and non-destructive methods for lifetime assessments of Eskom''s high temperature plant

Over long exposure periods high temperature and high pressure components suffer degradation of their properties and this accumulated damage subsequently leads to cracking and failure. State-of-the-art quantifiable destructive and non-destructive methods for lifetime assessment of reliability and maintainability of Eskom's plant are used. Geometry, strain rate, mode of load, materials, fabrication technique and history are all important factors affecting the component life and material microstructure. Novel cost-effective techniques have been developed by Eskom for the assessment of the effective temperature of components operating in the creep regime. Accumulated creep strain is measured directly on the component during a certain service interval. This information is then used to calculate the remanent life of a component. A library of more than 30 000 metallographic replicas representative of approximately 6000 components exists and these ‘fingerprints’ are of great value in the overall life predictions.     

Preparation, testing and modelling of a hydrogen selective Pd/YSZ/SS composite membrane

A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10⁻⁸ mol/(s m Pa^0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.     

Solar radiation modelling for the simulation of photovoltaic systems

The effect of 12 different combinations of diffuse–global correlations and tilted surface radiation models on the accuracy of PV output simulation of a grid-connected photovoltaic (PV) system was studied using statistical methods. A site specific diffuse–global correlation was developed using local insolation data and the performance of this model was compared with those of two other diffuse–global correlations. The impact of diffuse–global correlations on the calculated inclined insolation for four different tilted surface radiation models was investigated on annual, seasonal and monthly basis. The accuracies of predicted 45° inclined plane insolation and PV output were improved when the site specific diffuse–global correlation was used in the main simulation model. The error between measured and predicted inclined insolation was higher in winter than summer. The prediction of PV output was improved by using an isotropic sky tilted surface radiation model instead of the anisotropic models. The accuracy of PV output was also improved when the proposed diffuse–global correlation was used.     

A general procedure for the small-scale modelling of buildings

A procedure for the development of physically similar small-scale model buildings, based on dimensional analysis, is outlined. Theoretical considerations are discussed, and the example of a scale of model, based on an existing prototype test building in Nigeria, is presented. The model will be built and tested at the University of Trieste in Italy. Test results should assist in verifying and improving the modelling technique.