Statistical Scatter Research Articles

Using probabilistic fuzzy models for the prediction of functional failures of microwave LSI with radiation exposure

The article presents an analysis of microwave LSI behavior under radiation exposure at the functional-logical level of description. The analysis is based on fuzzy digital automaton and topological probabilistic models of workability assessment. It is shown that in certain cases both deterministic and non-deterministic failures are typical. Each operation threshold in logic elements under radiation influence has a zone of uncertainty and can be expressed quantitatively by a fuzzy number. This case, the real nature of microwave LSI radiation behavior is determined by the specific ratio of radiation-sensitive parameters of its elements and by taking into account the influence of their statistical scatter. Methods are proposed for simulating failures of microwave LSI under radiation exposure that are based on the model of a fuzzy digital Brauer automaton and a probabilistic reliability automaton.

A Lagrangian dispersion model with a stochastic equation for the temperature fluctuations

A new plume rise scheme for the Lagrangian stochastic model SPRAYWEB is developed and tested. The plume rise scheme is based on a stochastic differential equation for the potential temperature fluctuations coupled with the equations for the wind velocity fluctuation components. The new approach is tested against measured data from a water tank experiment (Weil et al., 2002). The results are discussed in terms of statistical indices and scatter plots. For the sake of comparison, the new scheme's performance is compared with the algorithm used in SPRAYWEB formerly proposed by Anfossi et al. (1993) which doesn't account for the temperature fluctuations. The results obtained with the novel plume rise scheme are generally satisfactory. A better agreement is found for the vertical standard deviation with respect to the results given by the Anfossi et al. (1993) scheme.

Application of Support Vector Regression for Modeling Low Flow Time Series

Hydrologic time series modeling using historical records plays a crucial role in forecasting different hydrological processes. The objective of this study is to analyze the suitability of Support Vector Regression (SVR) for modeling monthly low flows time series for three stations in Mahanadi river basin, India. The ‘low flow’ threshold was taken as the Q75 discharge, i.e., the flow is equal to or surpassed for the duration of 75% of the observation period which was obtained from the daily discharge data. The potential applicability of SVR model is assessed with two different framework models (ANN-ELM, GPR) based on various statistical measures (r2, RMSE, MAE, Nash-Sutcliffe coefficient, objective function (OBJ), Scatter Index (SI) and BIAS). The model selection was based on lowest OBJ value for each station amongst three models (SVR, ANN-ELM, GPR). The SVR model was trained using the Radial Basis Function (RBF). Using the same inputs, the other two models (ANN-ELM and GPR) was also tested. From results, among all the stations, the SVR outperformed GPR and ANN-ELM with lowest OBJ value for the three stations a (1.378, 1.202, 1.570). In addition, the accuracy of the three models were checked using mean forecasting error which were (0.474, 0.421, 0.509) for SVR, (0.507, 0.489 0.500) for GPR and (0.564, 0.603, 0.772) ANN-ELM for the three stations. The results confirm that SVR can be used satisfactorily for modeling monthly low flows in the Mahanadi river basin, India. Hence, the SVR model could be employed as a new reliable and accurate data intelligent approach for predicting the ‘low flow’ (Q75 discharge) based on precedent data in water resources and its allied field.

Applying linear and nonlinear models for the estimation of particulate matter variability

In this study, data collected from an urban air quality monitoring network are being used for the purpose of evaluating various methodologies used for spatial interpolation in the context of proposing an effective yet simple to apply scheme for PM spatial point estimations. The examined methods are the Inverse Distance Weighting, two linear regression models, the Multiple Linear Regression and the Linear Mixed Model, along with a Feed Forward Neural Network (FFNN) model. These schemes utilize daily PM10 and PM2.5 concentrations collected from five and three air quality monitoring sites respectively. In order to obtain the resulted estimations, the leave-one-out cross-validation methodology is used for all methods. The evaluation of their predictive ability is performed by using a combination of difference and correlation statistical measures, scatter plots and statistical tests. The results indicate the usefulness of FFNNs as they are found to be statistically significantly superior for modelling the particulate matter spatial variability. The model performance statistics show that in most cases the error values are considerably lower for the FFNN model. Additionally, the rank and Wilcoxon rank tests reveal that the null hypothesis for equal predictive accuracy is rejected for the majority of monitoring sites and schemes (values lower than the critical t-value). According to the comparison results, the FFNN model is selected for forecasting air quality limit exceedances set by the European Union and World Health Organization air quality standards. For two monitoring sites in which the largest number of exceedances occurred, the probability of detection is high while the probability of false detection is very low, further establishing the neural networks’ predictive ability.

Coupling of state-resolved rovibrational coarse-grain model for nitrogen to stochastic particle method for simulating internal energy excitation and dissociation.

We propose to couple a state-resolved rovibrational coarse-grain model to a stochastic particle method for simulating internal energy excitation and dissociation of a molecular gas. A coarse-grained model for a rovibrational reaction mechanism of an ab initio database developed at the NASA Ames Research Center for the N2-N system is modified based on variably spaced energy bins. The thermodynamic properties of the modified coarse-grained model allow us to closely match those obtained with the full set of rovibrational levels over a wide temperature range, while using a number of bins significantly smaller than the complete mechanism. The chemical-kinetic behavior of equally and variably spaced bin formulations is compared by simulating internal energy excitation and dissociation of nitrogen in an adiabatic, isochoric reactor. We find that the variably spaced formulation is better suited for reproducing the dynamics of the full database at conditions of interest in the Earth atmospheric entry. Also in this paper, we discuss the details of our particle method implementation for the uniform rovibrational collisional bin model and describe changes to the Direct Simulation Monte Carlo (DSMC) collision algorithm, which become necessary to accommodate our state-resolved reaction mechanism for excitation and dissociation reactions. The DSMC code is then verified against equivalent master equation calculations. In these simulations, state-resolved cross sections are used in analytical form. These cross sections verify micro-reversibility relations for the rovibrational bins and allow for fast execution of the DSMC code. In our verification calculations, we obtain very close agreement for the concentrations profiles of N and N2, as well as the translational and rovibrational mode temperatures obtained independently through both methods. In addition to macroscopic moments, we compare discrete internal energy populations predicted at selected time steps via DSMC and the master equations. We observe good agreement between the two sets of results within the limits imposed by statistical scatter, which is inherent to particle-based DSMC solutions. As future work, the rovibrational coarse-grain model coupled to the particle method will allow us to study 3D reentry flow configurations.

Adhesive contact of rough brushes.

The adhesive contact between a rough brush-like structure and an elastic half-space is numerically simulated using the fast Fourier transform (FFT)-based boundary element method and the mesh-dependent detachment criterion of Pohrt and Popov. The problem is of interest in light of the discussion of the role of contact splitting in the adhesion strength of gecko feet and structured biomimetic materials. For rigid brushes, the contact splitting does not enhance adhesion even if all pillars of the brush are positioned at the same height. Introducing statistical scatter of height leads to a further decrease of the maximum adhesive strength. At the same time, the pull-off force becomes dependent on the previously applied compression force and disappears completely at some critical roughness. For roughness with a subcritical value, the pressure dependence of the pull-off force qualitatively follows the known theory of Fuller and Tabor with moderate modification due to finite size effect of the brush.

A method for the empirical formulation of current profile

ABSTRACTIn this study, an advanced method was proposed for the empirical formation of current profiles. A probabilistic approach was adopted to generate a reliable empirical model which can be expressed as a function of current velocity and water depth from the obtained best-fit probability density function (PDF) with sub-parameters. It is recognised that the statistical scatter of current velocity at each normalised water depth is wide and requires a reliable method (or technique) with a refined manner to generate a simplified current profile model. From the probabilistic approach, the best-fit PDF of the current velocity distribution, including all ranges of normalised water depth is decided. In addition, sub-parameters of PDF (i.e. shape, scale, location parameters) can also be formulated as a function of normalised water depth through curve-fitting. For better understanding, three main steps which are (1) individual, (2) overall, and (3) optimised outcomes have been highlighted in order to propose the empirical formulation of current profiles. Applicability of the proposed method was verified by collecting 54 current profiles obtained from existing offshore fields, thus making it possible to generate a more accurate current profile model.

Prediction of welding residual stresses using machine learning: Comparison between neural networks and neuro-fuzzy systems

Safe and reliable operation of power plants invariably relies on the structural integrity assessments of pressure vessels and piping systems. Welded joints are a potential source of failure, because of the combination of the variation in mechanical properties and the residual stresses associated with the thermomechanical cycles experienced by the material during welding. This paper presents comparative studies between methods based on artificial neural networks (ANN) and fuzzy neural networks (FNN) for predicting residual stresses induced by welding. The performance of neural network and neuro-fuzzy systems are compared based on statistical indicators, scatter plots and several case studies. Results show that the neuro-fuzzy systems optimised using a hybrid technique can perform slightly better than a neural network trained using Levenberg-Marquardt algorithm, primarily because of the inability of the ANN approach to provide conservative estimates of residual stress profiles. Specifically, the prediction accuracy of the neuro-fuzzy systems trained using the hybrid technique is better for the axial residual stress component, with root mean square error (RMSE), absolute fraction of variance (R2) and mean absolute percentage error (MAPE) error of 0.1264, 0.9102 and 22.9442 respectively using the test data. Furthermore, this study demonstrates the potential benefits of implementing neuro-fuzzy systems in predicting residual stresses for use in structural integrity assessment of power plant components.

Effects of hydrogen on fatigue behavior of near-alpha titanium alloys

The influence of hydrogen content on fatigue response was examined for a near-α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, in bimodal microstructural condition with ~70 vol% primary α. The hydrogen content was varied in the range 7–127 ppm (by weight). The fracture mechanism at crack-initiation sites changed from ductile tearing with localized plasticity in low (<50 ppm) hydrogen alloys to a more brittle fracture with facets in high (≥100 ppm) hydrogen alloys. The variation in fatigue life (by a factor of ≤1.8) was partially associated with the differences in hydrogen level and partially with the statistical scatter in life.

Properties and performance of spin-on-glass coatings for the corrosion protection of stainless steels in chloride media

Spin-on-glass deposition was investigated as viable alternative to increase the durability and performance of 316L steel in chloride environment. The buildup of a detrimental interface oxide was prevented by non-oxidative thermal curing of the coatings, which leads to a transformation to an inorganic, SiO2-like material. The degree of polymerization was found dependent on the curing temperature; however, even curing at the maximum investigated curing temperature of 800 °C led to still incomplete transformation, showing less SiO2-like character with respect to thermally grown oxide or fused silica. Electrochemical analysis by cyclic polarization indicated that the coatings behave as imperfect barrier coatings, which may enhance the passive properties of the substrates; however, there is still some statistical scatter in the quality of the coatings. While there is a tendency for an increase of the upper limit of the breakdown potential, there is also a decrease of the lower limit. It was found that such lower quality coatings showed, in association with substrate defects, unevenly distributed coating flaws, which may act as initiation points of pitting corrosion and decrease the corrosion resistance of coated substrates. Further, the films showed instability in aqueous environment due to imperfect polymerization.

Shell buckling, without ‘imperfections’

The buckling behaviour of thin shell structures under load has been a persistent challenge to engineering designers and researchers over many decades. In this article I consider two unusual experimental studies on the buckling of thin-walled elastic cylindrical shells, each of which sheds intriguing light on the buckling phenomena. The classical theory of buckling of thin cylindrical shells under axial compression predicts that the buckling stress will be proportional to t/ R– the ratio of thickness to radius – other things being equal. But collected results of experimental studies from many laboratories, when plotted on log–log scales, show clearly that the buckling stress is actually proportional to ( t/ R)1.5, with the measured buckling stresses being scattered through a factor of about 4 for shells with R/ t &gt; 200. Such scatter is commonly judged to be in accord with Koiter’s theory of ‘imperfection sensitivity’. But that theory lays no claim to an understanding of the empirical 1.5-power law. I claim that a key to this situation is the experimental performance of some small-scale open-topped silicone rubber shells, buckling under their own weight, which clearly demonstrates a 1.5-power law, but with very little scatter. The buckling mode of these shells involves almost entirely inextensional deformation, with a single small dimple growing near the base, separated from the rest of the shell by a narrow boundary layer that accounts for almost all of the dimple’s elastic strain energy. A straightforward, simple analysis of the mechanics of the dimple is consistent with the experimental 1.5-power law. As noted above, experimental buckling loads of shells that are closed at both ends also show the empirical 1.5-power law, but now with significant statistical scatter. A second aim of the paper is to throw light on that phenomenon. I venture to attribute it to the effect of the boundary conditions of the shell. I adduce support for this view from experimental observations on the buckling of a shell with special, frictional end-fittings. That feature produces significantly higher collapse loads, and with much smaller scatter, than for corresponding shells with fixed boundaries; and it permits striking pre-buckled deformations to occur, of a kind not previously noted. It will be appreciated that neither of the two parts of this article depends on the widely accepted theory of imperfection-sensitivity; hence my choice of title. It is a pleasure for me to submit this article to a special publication in honour of Michael Rotter, with whom I have discussed matters of this sort through three decades.

The actual operation assessment of the railway bridge superstructure using a mobile monitoring system

Deviations in the operation of the operated bridge structures on the railway are detected when damage occurs. At the same time, early detection and prognosis of damage progress can be obtained using monitoring systems. The article presents the methods and technologies for the use of mobile monitoring systems for assessing the actual operation of the metal superstructure of the railway bridge with the main driving trusses. The hardware of the measuring complex is considered, the main measuring instrument is the glued electrical strain gauges. The monitoring system kept a continuous record of sensor readings for 28 days. To process the data received by the monitoring system, specialized software has been developed that systematizes the incoming information. Analysis of the actual supertructure operation is carried out by finding the relationship of stresses in the various elements of the superstructure, arising under the same load. This approach allowed us to exclude the factor of unknown intensity of the temporary load. The results of monitoring the work of the superstructure are given. In total, over 680 train passage records were analyzed, which allowed for a statistical description of the data. The theoretical values of the relationship of stresses in the elements of the superstructure are determined using the apparatus of the influence lines obtained by a numerical method. The conclusions are made about the distribution of deformations of the superstructure under temporary load and about the degree of compliance with theoretical calculations. The construction factors and the values of their statistical scatter are determined, the actual dynamic factors are statistically calculated. The construction factors calculated from the stress ratios lie in the range of 0.8-1.116. Dynamic factors are within 1.13 and do not exceed the rated values.

Crystallographic orientation-dependent growth mode of microstructurally fatigue small crack in a laminated Ti–6Al–4V alloy

The fatigue life of Ti–6Al–4V alloy exhibits significant scatter, which is derived from the statistical scatter of uncontrollable material factors. In particular, crack propagation behaviors in microstructurally small cracks strongly depend on material factors. It is necessary to understand the mechanisms underlying the scatter of fatigue properties. In this study, the dominant material/mechanical factors of microstructurally small fatigue crack growth behaviors are extracted, and the mechanisms of fatigue crack propagation life scatter derived from them are clarified. A Ti–6Al–4V billet was studied in which the microstructure was fully laminated with α and β phases. The major constituent phase was α. Microstructurally small artificial defects were introduced at a center of prior β grains by a focused ion beam (FIB). A fatigue test was carried out at a stress ratio R = 0, stress amplitude σa = 400 MPa, and frequency 1.3 × 10-2 Hz in a vacuum using scanning electron microscopy (SEM). In situ SEM observation was carried out around each FIB notch. After the fatigue test, the dependence of the crack growth path on crystallographic orientation was investigated by using electron backscattered diffraction. It was found that microstructurally small crack growth behaviors depended on crystallographic orientation. The dominant crack growth mechanism was the mode II crack growth mechanism by shear stress along the basal plane as a driving force. The dominant factor that causes large scatter of fatigue life in a α- Ti–6Al–4V alloy is the difference in resolved shear stress along the basal plane. Specifically, the difference in the angle between the basal plane and loading direction, the low reproducibility of the mode II crack growth mechanism, and the random position of pre-existing damage cause the scatter of fatigue crack growth rate.

DSMC 및 IP 방법을 이용한 2차원 아음속 희박기체 유동 해석

In the present study, to investigate the characteristics of subsonic rarefied gas flows efficiently, the information preservation(IP) method was applied to the direct simulation Monte-Carlo(DSMC) method to reduce statistical scatters from the DSMC method for low speed rarefied gas flows. To find the effects of the IP method, the results of the IP method were compared to the results of the DSMC method for the same numbers of sampling. Before the comparison, it was necessary to verify the DSMC solver. The verification of the solver was conducted by simulations of the micro-channel flows by comparing to the other researchers’ DSMC results. The velocity profiles at the 2/3 section of the channel agreed well with the other researchers’ results. In addition, the normalized slip velocity distributions on the wall and the pressure distributions along the centerline also agreed well with the other researchers’ results. After the DSMC solvers were verified, two types of Couette flows were considered. One is the flows that have temperature differences between two plates, and the other is the flows that have moving plates. For the first Couette flows, the temperature of 373K was used for the upper plate, and of 173K for lower plate. For the second Couette flows, the upper plate is moving at 300m/s, and the temperature of 273K was used for both two plates. All simulations of Couette flows were conducted from near-continuum to free-molecular regimes. From both Couette flow simulations, it was found that the temperature jump and the velocity slip occurred on the plate surface. In addition, it was also shown that the temperature and the velocity differences between the plate and the gas became larger as the flow fields became more rarefied. Lastly, flow simulations around a NACA0012 airfoil were conducted to identify the effects of the IP method. The freestream Mach number of 0.8 was used, and the Knudsen number of 0.014 was considered. It was observed that more clear contours were obtained from the IP method than the DSMC method, since the statistical scatter error was reduced by the IP method. In addition, it was found that the velocity slip on the airfoil surface occurred due to the effects of the rarefied atmospheric environment.

Characterization and photometric performance of the Hyper Suprime-Cam Software Pipeline

Abstract The Subaru Strategic Program (SSP) is an ambitious multi-band survey using the Hyper Suprime-Cam (HSC) on the Subaru telescope. The Wide layer of the SSP is both wide and deep, reaching a detection limit of i ∼ 26.0 mag. At these depths, it is challenging to achieve accurate, unbiased, and consistent photometry across all five bands. The HSC data are reduced using a pipeline that builds on the prototype pipeline for the Large Synoptic Survey Telescope. We have developed a Python-based, flexible framework to inject synthetic galaxies into real HSC images, called SynPipe. Here we explain the design and implementation of SynPipe and generate a sample of synthetic galaxies to examine the photometric performance of the HSC pipeline. For stars, we achieve 1% photometric precision at i ∼ 19.0 mag and 6% precision at i ∼ 25.0 in the i band (corresponding to statistical scatters of ∼0.01 and ∼0.06 mag respectively). For synthetic galaxies with single-Sérsic profiles, forced CModel photometry achieves 13% photometric precision at i ∼ 20.0 mag and 18% precision at i ∼ 25.0 in the i band (corresponding to statistical scatters of ∼0.15 and ∼0.22 mag respectively). We show that both forced point spread function and CModel photometry yield unbiased color estimates that are robust to seeing conditions. We identify several caveats that apply to the version of HSC pipeline used for the first public HSC data release (DR1) that need to be taking into consideration. First, the degree to which an object is blended with other objects impacts the overall photometric performance. This is especially true for point sources. Highly blended objects tend to have larger photometric uncertainties, systematically underestimated fluxes, and slightly biased colors. Secondly, &amp;gt;20% of stars at 22.5 &amp;lt; i &amp;lt; 25.0 mag can be misclassified as extended objects. Thirdly, the current CModel algorithm tends to strongly underestimate the half-light radius and ellipticity of galaxy with i &amp;gt; 21.5 mag.

On the definition of design values for loads on silos and tanks

Silos and tanks are both industrial storage containers, so it may be imagined that they can be treated in a common manner for structural design. However, the statistical base of reliability theory shows that tanks are exceptionally invariant in their loading, while loads in silos are possibly the most unpredictable of all structural engineering loads. This article sets out the arguments why the statistical scatter of loads on tanks should be seen as very small indeed. It then treats the problems of loads on silos at length, showing that a wide range of different factors dramatically influence the safety of the structure, leading to a situation in which the use of a single value for the partial factor on stored solid loads could be either very uneconomic or else unsafe. It shows that the known key parameters that define the form of the structure, the aspect ratio, the properties of the stored solids, the manner of filling and discharge, and the frequency of usage of the silo should all play a strong role in determining appropriate values of design partial factors. The recommended values for the partial factors should therefore be evaluated using rules placed in EN 1991-4.

Fatigue and fracture life-cycle cost assessment of a Miter gate with multiple cracks

Abstract Fatigue cracks in Miter gates are considered a nuisance as they require periodic inspection and repair. If left unattended, the cracks could grow to reach a critical length and threaten the integrity of the structure. Although the cracks are typically characterized by a stable propagation rate, the scatter in fatigue performance is difficult to quantify and could be on the order of thousands or even millions of cycles. The development of maintenance and management programs for Steel Hydraulic Structures (SHSs) should therefore account for the inherent scatter in performance through probabilistic fatigue assessment. The assessment can be performed through conducting large number of numerical (e.g. finite element analysis) or analytical (e.g. mathematical formulation) simulations that account for the inherent statistical scatter in both load and resistance. In this study, a framework for probabilistic assessment of the propagation rate of cracks in Miter gates using finite element Monte Carlo simulations was developed. The parameters influencing the propagation rate were treated as random variables with predefined statistical distributions. In addition, a life-cycle cost optimization framework was devised using the results of the probabilistic assessment to derive optimal inspection/repair schedule patterns such that the service life of the Miter gate could be extended as required. The framework was tested on nine different cases and an optimal schedule is obtained for each case successfully.

Probabilistic Analysis of Prestress Loss due to Creep in Concrete Box Girders

The cross-section warping effect and warping-induced long-term prestress loss due to creep are investigated in this paper. Both phenomena were analyzed deterministically and stochastically. The random character of concrete creep and environmental factors have substantial effects on the statistical scatter of the total prestress loss. To obtain the real development of concrete long-term performance, sophisticated models for concrete creep and shrinkage prediction were used. The Monte Carlo–Latin hypercube sampling method was applied to capture the statistical variability of boundary and environmental conditions. It is shown that the severity of cross-section warping can be important, particularly in the case of short spans and unevenly distributed and isolated tendons in a cross section. The three-dimensional effects and the statistical variability of creep are considered to enable reliable design of box girder bridges.

Dynamics of Elongation and Breaking of Complex Yarns and Its Dependence on Filament Properties in Modeling Semicyclic Deformations

The results of a study of dependence of elongation resistance of complex yarns on the same characteristics of filaments with reference to Orlon fibre are presented. The computer model developed for these purposes takes account of nonlinear type of elastic deformation of filaments, dynamics of deformation and breaking, and statistical scatter of breaking characteristics.

Backcalculation of pavements incorporating Grouted Macadam technology

Applying cement grout with a high compressive strength to a porous layer made of asphalt concrete results in a pavement with the properties of an intermediate type that combines the characteristics of both flexible and rigid pavements. This solution is known as Grouted Macadam (GM). Despite a wide range of test results on the GM pavements presented in the literature, there are very few advanced modelling solutions formulated in the scope of bearing capacity measured in situ be means of a Falling Weight Deflectometer. This paper turns out that the seemingly small frequency of loading (≈20 Hz) generated during pavement deflection measurements using a Falling Weight Deflectometer-like device, has a significant impact on the backcalculation results of GM pavements. The study shows that, introducing frequency normalisation of both the pavement loading and vertical displacements to the backcalculation, can limit the statistical scatter of backcalculation results by close to a half in comparison with the classical backcalculation procedure.