Neural network approach to estimate 10-min solar global irradiation values on tilted planes

Calculation of solar global irradiation on tilted planes from only horizontal global one is particularly difficult when the time step is small. We used an Artificial Neural Network (ANN) to realize this conversion at a 10-min time step. The ANN is developed and optimized using five years of solar data and the accuracy of the optimal configuration is around 9% for the RMSE and around 5.5% for the RMAE i.e. similar or slightly lower than the errors obtained with empirical correlations available in the literature and used for the estimation of hourly data.     

A damage mechanics approach to the prediction of creep crack growth

Based upon the local damage hypothesis and utilizing similarity solutions, a theoretical equation for the calculation of creep crack growth rate has been derived in this paper. Creep crack growth tests under constant load and constant load-pin-displacement-rate have been carried out at 550°C and 565°C in a 2·25Cr-1Mo steel. It has been shown that the prediction of creep crack growth rate using the local damage model would be on the safe side, as the prediction line ties in with the upper limit of the experimental data. In this paper, the validity of the C* parameter in the case of a small damage zone has been examined and confirmed. An empirical formula for the evaluation of the ‘creep constraint factor’ has been established to meet the needs of calculation of creep crack growth using the local damage model.     

Creep crack growth in welds: a damage mechanics approach to predicting initiation and growth of circumferential cracks

The results of damage mechanics finite element analyses have been used to estimate the initiation and growth of type IV cracks in a series of internally pressurised circumferential pipe welds, in main steam pipelines made of 1/2CrMoV steel. The material properties used, for the various zones of new, service-aged and repaired welds, were produced from creep test data at 640°C. Damage distributions and accumulation with time within the HAZ are presented, from which the crack initiation times and positions for these welds, under a closed-end condition, and with additional axial (system) loading, were identified. By investigating the propagation of damage through the wall thickness, the remaining lives of the various weld types were estimated. The method provides a means for predicting the initiation and growth of type IV cracks in these CrMoV weldments, and for estimating the length of time a weld can safely be left in service, after damage, or type IV cracking, is identified during inspection.     

Simplified stable crack growth analyses of welded CT specimens—comparison study of GE/EPRI, reference stress and R6 methods

This paper describes some simplified stable crack growth analyses of two kinds of inhomogeneous CT specimens. The one is machined from a submerged are welded plate of a nuclear pressure vessel A533B Class 1 steel, while the other is machined from an electron-beam welded plate of the A533B Class 1 steel and a high strength HT80 steel. In both specimens, initial cracks are placed to be normal to the fusion line. The ratio of yield stresses of the weld metal and the base metal of the A533B Class 1 steel is about 1·15, while that of the HT80 and the A533B Class 1 steels is about 1·4.

The generation phase crack growth analyses using the GE/EPRI and the reference stress methods are performed, calculating an applied load (P) and the J-value, while the application phase analyses of analyses using the R6 method are performed to calculate the maximum value of the applied load (P_max). Finally, some modification procedures of the three simplified estimation schemes are discussed in order to apply them to inhomogeneous material regimes.     

A local approach to creep fracture by slow crack growth in an MDPE: Damage modelling

Slow crack growth (SCG) behaviour has been investigated under creep conditions in a medium density ethylene–butene copolymer (MDPE) on both axisymmetrical Full Notched Creep Tensile (FNCT) and Double Edge Notched Tensile (DENT) samples tested at 60 °C. An attempt is made to predict the long-term failure of a component under creep loading conditions, using an incremental damage law. The experimental creep damage observations were compared to the creep stress–strain distributions calculated by finite element method. Such comparison can provide a damage evolution law as a function of the maximum principal stress and the creep strain. The failure criterion is expressed in terms of a critical creep damage over a critical distance. This model is applied to creep crack growth on the FNCT and DENT samples.     

Neural network approach for food temperature prediction during solar drying

In the present study, the application of artificial neural network (ANN) for prediction of temperature variation of food product during solar drying is investigated. The important climatic variables namely, solar radiation intensity and ambient air temperature are considered as the input parameters for ANN modeling. Experimental data on potato cylinders and slices obtained with mixed mode solar dryer for 9 typical days of different months of the year were used for training and testing the neural network. A methodology is proposed for development of optimal neural network. Results of analysis reveal that the network with 4 neurons and logsig transfer function and trainrp back propagation algorithm is the most appropriate approach for both potato cylinders and slices based on minimum measures of error. In order to test the worthiness of ANN model for prediction of food temperature variation, the analytical heat diffusion model with appropriate boundary conditions and statistical model are also proposed. Based on error analysis results, the prediction capability of ANN model is found to be the best of all the prediction models investigated, irrespective of food sample geometry.     

An engineering approach for examining crack growth and stability in flawed structures

This paper summarises progress made in two research programmes, sponsored by the Electric Power Research Institute (EPRI), to identify viable parameters for characterising crack initiation and continued extension. An engineering/design methodology, based on these parameters, for the assessment of crack growth and instability in engineering structures which are stressed beyond the regime of applicability of linear elastic fracture mechanics is developed in this paper. The ultimate goal in the development of such a methodology is to establish an improved basis for analysing the effect of flaws (postulated or detected) on the safety margins of pressure boundary components of light water-cooled type nuclear steam supply systems. The methodology can also be employed for structural integrity analyses of other engineering components.Extensive experimental and analytical investigations undertaken to evaluate potential criteria for crack initiation and growth and the selection of the final criteria for analysing crack growth and stability in flawed structures are summarised. The experimental and analytical results obtained to date suggest that parameters based on the $\text{J-}\text{integral}$ and the crack tip opening displacement, δ, are the most promising. This is not surprising since, from a theoretical basis, the two approaches are similar if certain conditions are met.An engineering/design approach for the assessment of crack growth and instability in flawed structures is outlined. The approach exploits the consequences of $\text{J-}\text{controlled}$ crack growth—the $\text{J}$ resistance ($\text{J}{}_{\mathrm{<mtext>R</mtext>}}$) curve is a material property and crack driving forces can be determined from deformation plasticity analyses. Crack driving forces for the complete range of elastic-plastic deformation are obtained from a simple estimation scheme. The basic elements of the estimation scheme are the linear elastic solutions and the fully plastic solutions for the relevant crack configuration; the latter solutions are catalogued in a plastic fracture handbook. Crack-driving force diagrams, together with the $\text{J}{}_{\mathrm{<mtext>R</mtext>}}$ curve, are employed to construct stability diagrams and predict the load deformation and crack growth behaviour of several crack geometries. The predictions are in good agreement with experimental data and full-blown numerical crack growth calculations.Using the driving force computed from the estimation scheme failure assessment diagrams can also be constructed from $\text{J-}\text{controlled}$ growth. The shape and position of the failure line depend on the crack configuration and material properties.Relative merits and difficulties associated with the $\text{J}$ or δ resistance curve approach for treating stable crack growth and fracture instability in structural components are also discussed. In applications involving relatively small amounts of crack extension, the $\text{J}$ resistance approach assuming $\text{J-}\text{controlled}$ growth has significant advantages, and the fracture predictions are in good agreement with actual test data. For larger amounts of crack extension, the situation is less certain. The limited studies carried out under $\text{non}\text{-J-}\text{controlled}$ conditions suggest that the predictions from the engineering/design methodology will be conservative.     

Application of a modified damage potential to predict ductile crack initiation in welded pipes

The mesh dependency of the cavity growth model due to Rice and Tracey has been overcome by integrating it over a process zone surrounding the crack tip. This integral represents a modified damage potential. The critical value of the integral for crack initiation in weld material has been determined from a welded CT specimen by comparing the computed J with the experimentally measured J-initiation value. This critical value is then employed in 8 and 12 in. welded pipes having different through-wall cracks at the centre to predict the crack initiation loads under four-point bending. Close agreement between the computed crack initiation loads and the experimentally measured values justifies the usefulness of the present modified damage potential.     

Genetic algorithm approach to estimate transport energy demand in Turkey

Transport energy modeling is a subject of current interest among transport engineers and scientists concerned with problems of sustainable transport. Transport energy planning is not possible without a reasonable knowledge of past and present energy consumption and likely future demands. In this study, three forms of the energy demand equations are developed in order to improve transport energy demand estimation efficiency for future projections based on genetic algorithm (GA) notion. The Genetic Algorithm Transport Energy Demand Estimation (GATEDE) model is developed using population, gross domestic product and vehicle-km. All equations proposed here are linear and non-linear, of which one is linear, second is exponential and third is quadratic. The quadratic form of the GATEDE model provided better-fit solution to the observed data and can be used with a high correlation coefficient for Turkey's future transport energy projections. It is expected that this study will be helpful in developing highly applicable and productive planning for transport energy policies. The GATEDE gives transport energy demand in comparison with the other transport energy demand projections. The GATEDE model plans the sectoral energy demand of Turkey until 2020.     

Creep crack growth in welded components — a numerical study and comparison with the R5 procedures

In the present study, creep crack growth (CCG) in a circumferentially welded low alloyed pipe is numerically investigated for a number of different combinations of weldment constituent material properties. A creep ductility based damage model describes the accumulation of creep damage ahead of the crack tip where a constraint parameter and the creep strain rate perpendicular to the crack plane are used as characterising parameters. It is assumed that a fully circumferential creep crack, located in the heat affected zone with a depth of one quarter of the pipe thickness, is growing at a constant rate from the outer surface towards the inside. The numerical results reveal that not only the properties of the zone containing the crack, but also the deformation properties of the surrounding material influence the CCG behaviour. This influence can be noted on the characterising parameters used for the CCG rate predictions as well as on the CCG rate itself. The mismatch influence on corresponding C^* values is, however, marginal. This indicates that determination of the CCG rate in weldments, based on the C^* value only, may result in uncertain estimates.The numerically investigated cases are also assessed by use of the R5 procedures for the sake of comparison. Considering the stress re-distribution, due to the mismatch effect, the CCG rate is determined for the different weldment configurations. The comparison shows that the assumption of plane strain or plane stress conditions in the R5 analysis is essential for the agreement of the results between R5 and the two-parameter approach. Assuming plane stress conditions at the crack tip results in a relatively good agreement for the axial stress dominated cases investigated. However, for the hoop stress dominated cases, the R5 procedures predict higher CCG rates by an order of magnitude.     

Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

A strong geometry dependence of ductile crack growth resistance emerges under large scale yielding. The geometry dependence is associated with different levels of crack tip constraint conditions. However, in a recent attempt to identify appropriate fracture mechanics specimens for pipeline steels, an “independent” relationship between the crack growth resistance curves and crack depths for SENT specimens has been observed experimentally. In this paper, we use the complete Gurson model to study the effects of crack depth and specimen size on ductile crack growth behavior. Crack growth resistance curves for plane strain, mode I crack growth under large scale yielding conditions have been computed. SENB and SENT specimens with three different specimen sizes, each specimen size with three different crack depths, have been selected. It has been found that crack tip constraint (Q-parameter) has a weak dependence on the crack depth for specimens in the low constraint regime.     

A novel approach to estimate the clear day global radiation

A model based on the modified version of Gaussian distribution function has been proposed to estimate the clear day global radiation. The model fits very well on the recorded data which is further exploited to develop a relationship between the ratio of hourly to daily global radiation and day length (time between sunrise to sunset). This has helped us to calculate the distribution of the broad-band global radiation on any clear day of the year.     

Ant colony optimization approach to estimate energy demand of Turkey

This paper attempts to shed light on the determinants of energy demand in Turkey. Energy demand model is first proposed using the ant colony optimization (ACO) approach. It is multi-agent systems in which the behavior of each ant is inspired by the foraging behavior of real ants to solve optimization problem. ACO energy demand estimation (ACOEDE) model is developed using population, gross domestic product (GDP), import and export. All equations proposed here are linear and quadratic. Quadratic_ACOEDE provided better-fit solution due to fluctuations of the economic indicators. The ACOEDE model plans the energy demand of Turkey until 2025 according to three scenarios. The relative estimation errors of the ACOEDE model are the lowest when they are compared with the Ministry of Energy and Natural Resources (MENR) projection.     

A multivariate approach to estimate design loads for offshore wind turbines

The design of offshore wind farms is a complex process that requires a detailed study of the oceanographic, meteorological and geotechnical conditions at the site. The structure and all structural members shall be designed in a way that they can be resistant against different kinks of loads: permanent, variable, environmental, accidental and deformations. This paper is focused on those called environmental loads. The main environmental conditions that may contribute to structural damage, operational disturbances or other failures are wind, waves, currents and sea ice. Thus, the combination of the different parameters may produce many different critical situations for the integrity of the structure, requiring the calculation of long time series corresponding to long‐term historical data situations. The most accurate techniques available at the moment to estimate loads acting upon a structure are numerical and physical models; however, they are very time consuming, and the calculation of long time series of data is unfeasible. Therefore, a new hybrid methodology to select waves–wind–current representative conditions that allow the interpolation of long time series of forces on a wind turbine is proposed. The methodology consists of a selection of a subset of representative cases of wave–wind–current climate at the structure's location by using a maximum dissimilarity algorithm, then estimating loads acting upon the structure for the sea–wind states selected and the reconstruction of loads corresponding to historical data using an interpolation technique based on radial basis function. To validate the proposed methodology and because of there is no availability of long time records of loads on wind turbines, the well‐known IEC 61400–3 has been applied to estimate the loads for the complete reanalysis time series of waves, winds and currents. The validation of the results confirms the ability of the methodology developed to reconstruct time series of forces on the structure on the basis of the previously selected cases. This methodology permits application of numerical and physical models to offshore wind farm design, considerably reducing the number of tests or simulations. Copyright © 2012 John Wiley & Sons, Ltd.     

A new approach to estimate irradiation embrittlement of pressure vessel steels

The idea of an engineering version of the local approach to brittle fracture as well as the possibility for it to be employmed to estimate irradiation embrittlement of pressure vessel (PV) steels is considered. Unlike the conventional temperature-shift-based methodology, the approach presented utilises the concept of stability of the ductile state of the metal. A new characteristic “parameter of mechanical stability” P_ms is proposed. This characteristic enables quantification of the level of stability of the ductile state of an irradiated PV steel in a specimen or in a reactor vessel with a crack at the specified level of loading. Within the framework of the proposed concept, a value for end-of-life fluence for a reactor PV is predicted by the condition of exhaustion of stability of a ductile state of a steel ahead of the crack (P_ms=1).     

Fracture mechanics analysis of stable crack growth under sustained load and instability of circumferential cracks in straight water-steam pipes

In order to determine the component behaviour of pipes made from X 20 CrMoV 121 steel for the water-steam circulation system of a helium-cooled high-temperature reactor component, tests were carried out under load conditions similar to the case of emergency cooling. The aim of the tests was to determine the stable and unstable crack growth in the less tough weld filler metal of girt-welded pipes of 18·5 mm wall thickness and 400 mm inside diameter. The tests were carried out with weld filler metals of two different toughnessesSuch stable crack growth could be of particular importance in the case of residual heat removal. For this reason two tests were carried out on pipes with a circumferential crack under sustained load.In the second part of the test programme pipes with defects were loaded under sustained internal pressure, and additionally an increasing bending moment was applied. The aim of this investigation was to determine the boundary conditions for failure occurring by leak or by fracture with regard to the different toughness of the weld filler metal.The fracture mechanics analysis was carried out using a modified version of the flow-stress criterion for circumferential cracks (Batelle approach) and using also the so-called ‘effective fracture toughness’ $\text{K}{}_{\mathrm{<mtext>eff</mtext>}}$.The investigation has revealed that the component toughness is adequately high and component failure by fracture is not expected. The experimental results can be described theoretically using either the Battelle approach or the formulae of linear-elastic fracture mechanics if the data obtained in the test characterising component behaviour (flow stress or effective toughness) are used as a basis. The results show that an evaluation of component behaviour using $\text{K}{}_{\mathrm{<mtext>Jo</mtext>}}$ values determined by CT specimens according to the $\text{J}$ integral procedure is too conservative.     

The stability of crack growth in pipes subject to tensile loads

This paper presents a simple analysis for the stability of crack growth in 304 stainless steel pipes subject to tensile loads. The model of two identical part-through and part-circumference cracks, symmetrically situated with regard to the pipe cross-section, is examined for crack stability under displacement control tensile loading. Irrespective of the crack depth, the instability condition for a wide range of crack lengths, i.e. except for very short cracks and long cracks, is: $\text{2σ}{}_0\text{L}\text{πER}{}_{\mathrm{\chi }}\text{≡}\text{2L}\text{πR}\text{·}\text{1}\text{T}{}_{\mathrm{MAT}}\text{> 1}$ where σ₀ is the flow stress, E is Young's modulus, L is the pipe length, R is the pipe radius, χ is the crack tip opening angle, CTOA, associated with the crack growth and T_MAT is the material's tearing modulus. With a CTOA of 20° (i.e. T_MAT ～ 200), $\text{L}\text{R}$ must exceed 300 for instability. Since this number is far in excess of the $\text{L}\text{R}$ values for typical piping systems, the stability of cracks in pipes subject to tensile loads is essentially demonstrated.