Influence Of Non-stationarity Research Articles

Rock Joint Roughness Measurement and Quantification—A Review of the Current Status

This paper provides a review of the present status of the topic dealt with. The contact and non-contact methods used for rock joint roughness measurement are summarized including their salient features, advantages, and disadvantages. A critical review is given of the empirical, statistical, and fractal-based methods used for rock joint roughness quantification identifying their salient features, shortcomings, and strong attributes. The surface topography of rough rock joints is highly erratic. Fractional geometry is better suited than Euclidean geometry in representing highly erratic rock joint surfaces. The influence of non-stationarity on accurate quantification of roughness is discussed. The existence of heterogeneity of natural rock joint roughness and its effect on computed roughness parameters are well illustrated. The controversial findings that have been appearing in the literature on roughness scale effects during the last 40 years have resulted from neglecting the effect of roughness heterogeneity on scale effects. The roughness heterogeneity controls the rock joint roughness scale effect, and it can be either negative, positive, or no scale effect depending on the type and level of the roughness heterogeneity of the rock joint surface. The importance of consideration of the existence of possible anisotropy in the quantification of roughness is well illustrated. The indices available to quantify the level of anisotropy are given. Effects of sampling interval and measurement resolution on the accurate quantification of roughness are discussed. A comparison of results obtained by using different quantification methods is discussed. A few recommendations are given for future research to address the shortcomings that exist on the topic dealt with in the paper.

Influence of nonstationarity and dependence of extreme wave parameters on the reliability assessment of coastal structures - A case study

The current general consensus is that because of global climate change, coastal infrastructures may be subject to more extreme loads in the future than in the past. There has been an increased recognition that more attention should be paid to incorporating nonstationarity within the design process of coastal structures. In this regard, the present study examines the reliability of a conventional rubble mound breakwater using a variety of probabilistic techniques, incorporating ten nonstationary models to study the impacts of nonstationarity, as well as six copula functions to explore the dependence effects of wave extremes. The Gumbel copula most accurately represents the dependence structure of wave heights and periods in the study area. When the dependence of wave parameters is not correctly modeled, the failure probability of the studied structure is significantly underestimated. Assuming the Gumbel copula for modeling dependence of wave parameters, the results indicate that the maximum failure probability of the structure is underestimated by about 33% when a stationary extreme value distribution is fitted to wave height extremes, compared to a nonstationary Generalized Pareto Distribution (GPD). The insights gained from this study suggest that considering nonstationarity in extreme coastal events has more significant impacts on the reliability of coastal structures when the dependence structure of the marine variables is accurately modeled.

The influence of non-stationarity and interphase curvature on the growth dynamics of spherical crystals in a metastable liquid

This manuscript is concerned with the theory of nucleation and evolution of a polydisperse ensemble of crystals in metastable liquids during the intermediate stage of a phase transformation process. A generalized growth rate of individual crystals is obtained with allowance for the effects of their non-stationary evolution in unsteady temperature (solute concentration) field and the phase transition temperature shift appearing due to the particle curvature (the Gibbs-Thomson effect) and atomic kinetics. A complete system of balance and kinetic equations determining the transient behaviour of the metastability degree and the particle-radius distribution function is analytically solved in a parametric form. The coefficient of mutual Brownian diffusion in the Fokker-Planck equation is considered in a generalized form defined by an Einstein relation. It is shown that the effects under consideration substantially change the desupercooling/desupersaturation dynamics and the transient behaviour of the particle-size distribution function. The asymptotic state of the distribution function (its 'tail'), which determines the relaxation dynamics of the concluding (Ostwald ripening) stage of a phase transformation process, is derived. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

The influence of climate model uncertainty on fluvial flood hazard estimation

Floods are the most common and widely distributed natural hazard, threatening life and property worldwide. Governments worldwide are facing significant challenges associated with flood hazard, specifically: increasing urbanization; against the background of uncertainty associated with increasing climate variability under climate change. Thus, flood hazard assessments need to consider climate change uncertainties explicitly. This paper explores the role of climate change uncertainty through uncertainty analysis in flood modelling through a probabilistic framework using a Monte Carlo approach and is demonstrated for case study catchment. Different input, structure and parameter uncertainties were investigated to understand how important the role of a non-stationary climate may be on future extreme flood events. Results suggest that inflow uncertainties are the most influential in order to capture the range of uncertainty in inundation extent, more important than hydraulic model parameter uncertainty, and thus, the influence of non-stationarity of climate on inundation extent is critical to capture. Topographic controls are shown to create tipping points in the inundation–flow relationship, and these may be useful and important to quantify for future planning and policy. Full Monte Carlo analysis within the probabilistic framework is computationally expensive, and there is a need to explore more time-efficient strategies which may result in a similar estimate of the full uncertainty. Simple uncertainty quantification techniques such as Latin hypercube sampling approaches were tested to reduce computational burden.

Effect of gripping conditions and strip oscillations on vibrations originating at cold rolling

The process of continuous rolling is subjected to non-stationarity, accompanied by oscillations of not only basic technological and power parameters, but also parameters in the hearth of deformation. Non-stationarity at the rolling accounting high dynamic of the process results in origination of negative vibration effects. To prevent the vibrations originations the rolling speed is decreased, which prevents the reaching of the designing parameters of rolling mills operation. The study of influence of non-stationarity of the rolling technological process on gripping conditions and origination of dangerous oscillations was carried out. Characteristics of rolling mode of strip of 2.0–0.45 × 970 mm dimension, accompanied by vibration was presented, as well as graphs of the strip oscillations in the process of stationary rolling and under conditions of vibrations origination presented. An assumption made, that during vibrations origination the gripping conditions of the strip by rollers are disturbed. It means that provision of the grip stationarity will decrease the risk of the vibrations originating at the rolling. The assumption was confirmed by the studies of the cold rolling at five-stand mill 1700 of Cherepovets steel-works. The calculations of the hearth of deformation parameters were made by application of an elaborated dynamic model of the rolling process. The higher probability of vibrations originating at the rolling of strips of smaller thickness explained. It was shown, that due to the strip length, the rolling of the thinner metal is accomplished at higher speeds, comparing with the rolling of thicker metal. In addition, it was shown that the friction coefficient value at that would promote increase of risk of non-stationary rolling mode originating. The support of stable friction conditions in the hearth of deformation is promoted by usage of chrome-plated working rollers and asymmetrical rolling.

Deviation of Wind Stress From Wind Direction Under Low Wind Conditions

AbstractThe deviation of the wind stress vector from the wind direction at the air‐sea interface under low wind conditions was investigated based on direct eddy covariance flux measurements taken at a coastal tower in the northern South China Sea. The wind stress deviates significantly from the mean wind direction under low wind conditions, with the deviation angle sometimes exceeding 90°, indicating upward momentum transfer from the ocean to the atmosphere. Negative downwind drag coefficient values begin to occur at a wind speed of approximately 4 m/s. Our results show that ocean swells and nonstationary airflow play critical roles in wind stress. Prominent peaks at the dominant swell frequency in the vertical velocity spectra are observed at a height of 17 m over the mean sea surface, implying that swell‐induced perturbations can reach a height of at least 17 m, and the wave boundary layer can extend more than 10 m above the sea surface. The results of our analysis indicate that at the observation height, the influence of nonstationarity in the wind field is more significant than that of swell‐induced motions on the deviation of wind stress. After the removal of nonstationary motions, the deviation angles of the wind stress from the wind direction are generally reduced and vary substantially at low wind speeds.

The influence of non-stationarity in extreme hydrological events on flood frequency estimation

AbstractSubstantial evidence shows that the frequency of hydrological extremes has been changing and is likely to continue to change in the near future. Non-stationary models for flood frequency analyses are one method of accounting for these changes in estimating design values. The objective of the present study is to compare four models in terms of goodness of fit, their uncertainties, the parameter estimation methods and the implications for estimating flood quantiles. Stationary and non-stationary models using the GEV distribution were considered, with parameters dependent on time and on annual precipitation. Furthermore, in order to study the influence of the parameter estimation approach on the results, the maximum likelihood (MLE) and Bayesian Monte Carlo Markov chain (MCMC) methods were compared. The methods were tested for two gauging stations in Slovenia that exhibit significantly increasing trends in annual maximum (AM) discharge series. The comparison of the models suggests that the stationary model tends to underestimate flood quantiles relative to the non-stationary models in recent years. The model with annual precipitation as a covariate exhibits the best goodness-of-fit performance. For a 10% increase in annual precipitation, the 10-year flood increases by 8%. Use of the model for design purposes requires scenarios of future annual precipitation. It is argued that these may be obtained more reliably than scenarios of extreme event precipitation which makes the proposed model more practically useful than alternative models.

Statistical criteria for estimation of the cerebral autoregulation index (ARI) at rest

The autoregulation index (ARI) can reflect the effectiveness of cerebral blood flow (CBF) control in response to dynamic changes in arterial blood pressure (BP), but objective criteria for its validation have not been proposed. Monte Carlo simulations were performed by generating 5 min long random input/output signals that mimic the properties of mean beat-to-beat BP and CBF velocity (CBFV) as usually obtained by non-invasive measurements in the finger (Finometer) and middle cerebral artery (transcranial Doppler ultrasound), respectively. Transfer function analysis (TFA) was used to estimate values of ARI by optimal fitting of template curves to the output (or CBFV) response to a step change in input (or BP). Two-step criteria were adopted to accept estimates of ARI as valid. The 95% confidence limit of the mean coherence function (0.15–0.25 Hz) () was estimated from 15 000 runs, resulting in = 0.190 when using five segments of data, each with 102.4 s (512 samples) duration (Welch’s method). This threshold for acceptance was dependent on the TFA settings and increased when using segments with shorter duration (51.2 s). For signals with mean coherence above the critical value, the 5% confidence limit of the normalised mean square error (NMSEcrit) for fitting the step response to Tieck’s model, was found to be approximately 0.30 and independent of the TFA settings. Application of these criteria to physiological and clinical sets of data showed their ability to identify conditions where ARI estimates should be rejected, for example due to CBFV step responses lacking physiological plausibility. A larger number of recordings were rejected from acute ischaemic stroke patients than for healthy volunteers. More work is needed to validate this procedure with different physiological conditions and/or patient groups. The influence of non-stationarity in BP and CBFV signals should also be investigated.

Method of Sliding Bearings Static Characteristics Calculation

The direct problem of researching the load capacity of segment gas-static bearing is being discussed. In calculation the movement of the shaft in the bearing is considered slow comparing than the rotational velocity. Vibrations and the influence of non-stationarity are neglected. The given geometry of the bearing and the pressure of lubrication supply in the gap between the bearing and the shaft are considered initial data. The result of the calculation is the value of the resultant pressure force, applied to the bearing segments. Summing the forces the value of the static load capacity can be found. For segments that may spontaneously rotate about the joint axis, described a method of calculating the rotation angle, at which the main moment of pressure forces applied to the segment is equal to zero and the segment's position is stable.

About properties of estimations of correlation characteristics of non-stationery modulated signals

The influence of non-stationarity on estimation properties of correlation function stationary approximation of periodically correlated random processes is analyzed. It is shown that non-stationarity considerably changes variance value and its behavior as time shift increases.

Mode Superposition Method of Non Stationary Seismic Responses for Non Classically Damped Linear Systems

The real earthquake ground accelerations are usually non stationary vibration process. In order to estimate the influence of the non stationarity of ground motion on the accuracy of modal superposition rule of complex complete quadratic combination (CCQC), a new time-dependent CCQC(t) algorithm is derived by using a determinate envelope function to modulate a stationary random white noise process and remaining other assumptions same as normal CQC method. The proposed time-dependent CCQC(t) method needs to calculate the variances, covariance, and cross variances for different modes as time functions. For CCQC(t) method, the cross variances between a pair of two different modes are usually named cross correlation coefficients and play very important role in estimation of maximum responses just as for CQC method, but in this case the cross correlation coefficients are time dependent. Moreover, CCQC(t) and CQC(t) methods need to define envelop function and to calculate the corresponding non stationary seismic response rather than CCQC and CQC methods where only stationary steady-state responses are concerned. Hence, the analyses and computations related to envelop function in CCQC(t) and CQC(t) methods also play very a important role in this article. Several closed form formulas of time-dependent variances and cross variances are derived by using integration technique developed in time domain for four popularly used envelope functions. In order to verify these closed form formulas deduced in this article, we use four different envelope functions to fit identical envelope curve of real acceleration time history and then to carry out numerical analyses for certain examples. The numerical analysis based on proposed CCQC(t) algorithm shows that all the seismic responses of the examples computed from the adopted four different envelope functions which are used to depict same envelop curve of input acceleration are almost the same. The example analyses also show that for normal structure and ground motion input the discrepancy of the maximum seismic responses calculated from CCQC(t) and CCQC methods for non classically damped linear system and that from CQC(t) and CQC methods for classically damped linear system is of insignificance because the occurrence times of the variance responses and cross covariance responses usually concentrate within very narrowed time interval and close to the peak value location of the input motion at time axis. Further analyses show that the significance of the non stationarity mainly depends on how far the peak value arrival times of the modal responses shift each other and how sharper the shape of the envelop of input motion. Generally speaking, the larger the peak values arrival time shift and the sharper the shapes of the different modal response envelops, the greater the influence of non stationarity of ground motion on the results of mode superposition based on response spectra. These results are obtained on the basis of white noise input assumption. In addition, it is also shown that if using colorful spectrum such as Kanai power spectrum density function to replace white noise to simulate the power spectrum of the input acceleration records, the results coming from both CCQC(t) and CCQC methods may be improved to certain degree.

Atmospheric Boundary Layers: Nature, Theory and Applications to Environmental Modelling and Security

Atmospheric boundary layers: nature, theory and applications to environmental modelling and security.- Some modern features of boundary-layer meteorology: a birthday tribute for Sergej Zilitinkevich.- Energy- and flux-budget (EFB) turbulence closure model for stably stratified flows. Part I: steady-state, homogeneous regimes.- Similarity theory and calculation of turbulent fluxes at the for the stably stratified atmospheric boundary layer.- Application of a large-eddy simulation database to optimisation of first-order closures for neutral and stably stratified boundary layers.- The effect of mountainous topography on moisture exchange between the surface and the free atmosphere.- The influence of nonstationarity on the turbulent flux-gradient relationship for stable stratification.- Chemical perturbations in the planetary boundary layer and their relevance for chemistry transport modelling.- Theoretical considerations of meandering winds in simplified conditions.- Aerodynamic roughness of the sea at high winds.- Modelling dust distributions in the atmospheric boundary layer on Mars.- On the turbulent Prandtl number in the stable atmospheric boundary layer.- Micrometeorological observations of a microburst in southern Finland.- Role of land-surface temperature feedback on model performance for the stable boundary layer.- Katabatic flow with Coriolis effect and gradually varying eddy diffusivity.- Parameterisation of the planetary boundary layer for diagnostic wind models.

Nonstationarity and duration of the cardiac interval time series in assessing the functional state of operator personnel

The influence of nonstationarity in the time series of cardiac intervals on the assessment of the functional state (FS) of operator personnel was analyzed with a three-factor model of heart rhythm variability (HRV). ECG recordings were made in supine position at rest and in the sedentary position before and after important operator testing. In all three cases, the FS assessments were not influenced by nonstationarity of the input data. The effect of nonstationarity was also negligible for some particular HRV indices. Reliable assessments could be obtained from relatively short samples (256 down to 32 RR intervals) with prior norming of the factor indices for the corresponding segment length. The influence of the time series duration on the HRV indices was examined in various FSs; stable indices and proper recording conditions were determined.

正方形平面建物の風応答・風圧特性に対する風向の非定常性の影響 : 実測と風洞実験結果との比較に基づく一考察

正方形平面建物の風応答・風圧特性に対する風向の非定常性の影響 : 実測と風洞実験結果との比較に基づく一考察

Stochastic prediction of maximum seismic response of light secondary systems

A stochastic model is presented for predicting the elastic response of light multi-degree-of-freedom secondary systems to strong motion earthquakes. Secondary systems may include light mechanical or electrical equipment, piping, or other light systems attached at one or several points to walls or floors of the supporting or primary structures. The critical functions of these secondary systems in nuclear power plants make the accurate prediction of their maximum responses important. The response of such secondary structures may be obtained by a direct time-history analysis, or more approximately, by the response spectrum method. The time-history solution is, of course, expensive; moreover, there is no single representative earthquake and thus a number of possible earthquake ground motions have to be considered. On the other hand, the response spectrum method applied to secondary systems can lead to unreliable results. Within the framework of the normal mode method, a decoupled stationary random vibration model is developed based on the assumption of Gaussian response process and Poisson barrier crossings. The accuracy of the proposed model is verified by comparing the calculated responses, at the 10 and 50% probability of exceedance level, with the second highest and average of the time-history responses from eight normalized accelerograms. The influence of decoupling, i.e. ignoring the dynamic interaction between the primary and the secondary systems, on the response is examined. The influence of nonstationarity is also evaluated. It is observed that nonstationarity is unimportant for earthquakes of relatively long duration, and that for a given damping most of the error can be accounted for by a simple scaling. It is also shown that one aspect of the proposed method constitutes the basis for some of the approximations in the response spectrum method; however, the proposed method yields results that are consistently more reliable than the response spectrum method. Moreover, results obtained with the proposed method represent maximum response statistics from an ensemble of earthquakes rather than a single earthquake.

Influence of nonstationarity of the free-stream temperature on the heat exchange in the neighborhood of the forward stagnation point

Influence of nonstationarity of the free-stream temperature on the heat exchange in the neighborhood of the forward stagnation point