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Axisymmetric flow simulations of fiber suspensions as described by 3D probability distribution function

JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 2020年 284卷 104367-104367页

作者： Ferec, Julien Mezi, Dihya Advani, Suresh G. Ausias, Gilles Univ Bretagne Sud IRDL UMR CNRS 6027 F-56100 Lorient France Univ Delaware Ctr Composite Mat Dept Mech Engn 101 Acad St Newark DE 19716 USA

Numerical models are developed to examine fiber suspension flows through axisymmetric geometries, such as a circular pipe, a center-gated disk and a die exit. The fiber orientation micro-structure is fully described by using the entire probability distribution function (PDF) in 3D instead of the second and fourth moments of the PDF, which introduce errors due to the closure approximation when using orientation tensor descriptions. A Newtonian suspending fluid is considered for the constitutive relationship and simulations are performed with and without coupling the flow and fiber orientation. Results are compared with numerical simulations obtained by using the standard evolution equation for the second-order orientation tensor and the IBOF closure approximation. It is found that the IBOF closure approximation does a relatively good job of matching the exact orientation results given by the probability distribution function. For the three explored flows, the difference between the predicted orientation results using the coupled and decoupled approaches is not significant. There is a noticeable difference in the velocity field solutions, specifically at the die exit where the coupled approach increases the die swell ratio when the fibers enter the inlet with random orientation state.

关键词： Fiber suspension Polymer composite Fiber orientation Numerical modeling probability distribution function Axisymmetric flow

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Study of convective air turbulence based on the probability distribution function of angle of arrival fluctuations

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OPTICS AND LASER TECHNOLOGY 2024年 171卷

作者： Razi, Ebrahim Mohammadi Rasouli, Saifollah Niemela, J. J. Univ Bojnord Fac Basic Sci Dept Phys POB 1339 Bojnord Iran Inst Adv Studies Basic Sci Dept Phys POB *** Zanjan Iran Inst Adv Studies Basic Sci Opt Res Ctr POB 451951159 Zanjan Iran Abdus Salam Int Ctr Theoret Phys Str Costiera 11 I-34151 Trieste Italy

This study investigates the probability density function (PDF) of angle of arrival (AoA) fluctuations of a laser beam propagating through convective air turbulence in two settings: indoor turbulence and atmospheric surface layer. The indoor turbulence is generated by an electric heater with a 50 cm x 100 cm surface area placed horizontally on the bottom. The atmospheric turbulence experiments are conducted over a level at 60 cm height from an asphalted area using a slightly divergent laser beam that propagates along 350 m. Image motion monitoring of four sub-apertures installed in front of the receiving telescope aperture is used to record the AoA fluctuations and their PDFs over the entrance pupil at the sub-aperture locations for both types of turbulence. The observations are made in two perpendicular directions to the propagation of the laser beam. The experimental PDFs of the AoA fluctuations are fitted with Gaussian, Lognormal, Weibull, and Gamma distribution functions. The results show that the Weibull and Gamma models are more consistent with the experimental data for the indoor convective air and atmospheric turbulence respectively. For the indoor convective turbulence, the full width at half maximum and the peak location of the measured PDFs increase with the heater temperature, as well as the goodness of fit, which saturates at high temperatures.

关键词： Atmospheric turbulence Angle of arrival Convective turbulence Image motion monitoring probability distribution function

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probability distribution function of crossover frequency of operational amplifiers

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MEASUREMENT 2021年 179卷 109509-109509页

作者： Mishonov, Todor M. Petkov, Emil G. Dimitrova, Iglika M. Serafimov, Nikola S. Varonov, Albert M. Bulgarian Acad Sci Georgi Nadjakov Inst Solid State Phys 72 Tzarigradsko Chaussee Blvd BG-1784 Sofia Bulgaria Univ Chem Technol & Met Fac Chem Technol 8 Kliment Ohridski Blvd BG-1756 Sofia Bulgaria

For the first time the cumulative distribution function and histogram of the crossover frequency of a contemporary operational amplifier ADA4898-2 is experimentally studied. Using a USB lock-in amplifier, which allows automatic frequency sweep of the current response of a non-inverting amplifier with significant static amplification, we measure the crossover frequency of 200 samples of ADA4898-2 operational amplifiers. This new method gives a significant advantage in accuracy and speed of study of every operational amplifier. The theory we use is based on the universal relation between time dependent output and input voltages. This common relation for all operational amplifiers is applicable for frequencies much smaller than the crossover frequency and the frequencies of non-dominant poles. In other words, this approximation is adequate, when an operational amplifier is included in a circuit with significant amplification.

关键词： Operational amplifier Crossover frequency measurement probability distribution function Cumulative distribution function Histogram

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A new approximation algorithm for obtaining the probability distribution function for project completion time

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COMPUTERS & MATHEMATICS WITH APPLICATIONS 2007年第2期54卷 282-295页

作者： Yao, Ming-Jong Chu, Weng-Ming Tunghai Univ Dept Ind Engn & Enterprise Informat Taichung 407 Taiwan

This paper focuses on the application of the techniques of discretization to obtain an approximated probability density function (pdf) for the completion time of large-size projects, in which we allow any type of pdf for the duration of activities. In this study, we improve the techniques of discretization in the following two ways: first, we propose to replace the max operation with an approximation procedure to save significant computational loading;and second, to reduce the error from assuming independence between paths using a simple heuristic rule. To evaluate the performance of our proposed algorithm, we randomly generated 20 sets of 100-node instances in our numerical experiments. Taking the results from a Monte Carlo simulation using 20,000 samples as a benchmark, we demonstrate that the proposed algorithm significantly outperforms the PERT model and Dodin's [B.M. Dodin, Approximating the distribution function in stochastic networks, Comput. Oper. Res. 12 (3) (1985) 251-264] algorithm in both the running time and the precision aspects. (c) 2007 Elsevier Ltd. All rights reserved.

关键词： stochastic activity networks completion time probability distribution function approximation discretization

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A LABEL-CORRECTING TRACING ALGORITHM FOR THE APPROXIMATION OF THE probability distribution function OF THE PROJECT COMPLETION TIME

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JOURNAL OF INDUSTRIAL AND PRODUCTION ENGINEERING 2007年第2期24卷 153-165页

作者： Yao, Ming-Jong Chu, Weng-Ming Tseng, Tsueng-Yao Tunghai Univ Dept Ind Engn & Enterprise Informat POB 985 Taichung 407 Taiwan

When facing projects with uncertain factors, most of the project managers are interested to secure the pdf of the completion time of the project so as to have full insights into its randomness. For large-size SAN with general types of pdf for the duration of activities, the project managers must turn to the techniques of discretization since the other approaches in the literature become too demanding in computational loading. In this study, we find that there are two problems when applying the techniques of discretization to obtain an approximated probability density function (pdf) of the project completion time in stochastic activity networks. Namely, first, there exists neither exact data structure nor systematic scheme for the computer programming when applying the techniques of discretization;and second, error may arise from assuming independency between sub-paths in the activity network. Therefore, we are motivated to propose a Label-Correcting Tracing Algorithm (LCTA) to improve the techniques of discretization. To evaluate the performance of the proposed LCTA, we randomly generate 20 sets of 100-node instances in our numerical experiments. Using the pdf's resultant from Monte Carlo simulation using 20,000 samples as the benchmark, we compared the pdf's obtained from the PERT model, Dodin's [ 10] algorithm and the proposed LCTA. Based on our experimental results, we conclude that the proposed LCTA significantly outperforms the others in both the run time and the precision aspects.

关键词： stochastic activity networks project completion time probability distribution function approximation

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Predictions of the solar wind speed by the probability distribution function model

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SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 2014年第6期12卷 337-353页

作者： Bussy-Virat, C. D. Ridley, A. J. Univ Michigan Dept Atmospher Ocean & Space Sci Ann Arbor MI 48109 USA

The near-Earth space environment is strongly driven by the solar wind and interplanetary magnetic field. This study presents a model for predicting the solar wind speed up to 5 days in advance. probability distribution functions (PDFs) were created that relate the current solar wind speed and slope to the future solar wind speed, as well as the solar wind speed to the solar wind speed one solar rotation in the future. It was found that a major limitation of this type of technique is that the solar wind periodicity is close to 27 days but can be from about 22 to 32 days. Further, the optimum lag between two solar rotations can change from day to day, making a prediction of the future solar wind speed based solely on the solar wind speed approximately 27 days ago quite difficult. It was found that using a linear combination of the solar wind speed one solar rotation ago and a prediction of the solar wind speed based on the current speed and slope is optimal. The linear weights change as a function of the prediction horizon, with shorter prediction times putting more weight on the prediction based on the current solar wind speed and the longer prediction times based on an even spread between the two. For all prediction horizons from 8 h up to 120 h, the PDF Model is shown to be better than using the current solar wind speed (i.e., persistence), and better than the Wang-Sheeley-Arge Model for prediction horizons of 24 h.

关键词： probability distribution function

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Interval Estimation of the probability distribution function

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OPTOELECTRONICS INSTRUMENTATION AND DATA PROCESSING 2015年第2期51卷 120-123页

作者： Kuleshov, E. L. Far Eastern Fed Univ Ul Sukhanova 8 Vladivostok 690950 Russia

The Moivre - Laplace asymptotics is used to construct an interval estimate of the probability distribution function that is an interval with random boundaries, which covers the true value of the distribution function with a given confidence factor. It is shown that the use of the asymptotic instead of a binomial probability distribution results in an error whose value is tolerable for small sampling sizes and monotonically reduces with decreases sampling size.

关键词： interval estimate probability distribution function confidence factor goodness-of-fit test statistical hypothesis

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Numerical simulation of the probability distribution function of precipitation over Morocco

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CLIMATE DYNAMICS 2009年第7-8期32卷 1055-1063页

作者： Driouech, Fatima Deque, Michel Mokssit, Abdalah Direct Meteorol Natl CNRM Casablanca Morocco CNRS GAME Meteo France CNRM Toulouse France

A variable resolution version of the global GCM ARPEGE is constructed, so that Morocco has maximum resolution. A 30-year simulation, driven by observed sea surface temperature 1971-2000, is carried out. This paper examines the precipitation over northern Morocco during the extended winter season (from October to March), comparing model simulations with daily values at 14 stations. An approach utilising weather regimes has been adopted. The model is successful in representing the frequency and the interannual variability of the regimes. The precipitation over Morocco differs from one regime to another, but the model is not enough rainy along the Atlantic coast in general. The model is too persistent with too long dry spells, but is able to produce heavy rainfall as well as long dry periods in the centre of the area.

关键词： Precipitation Morocco probability distribution function Regional climate modeling Variable resolution model

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A note on the probability distribution function of the surface electromyogram signal

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BRAIN RESEARCH BULLETIN 2013年第1期90卷 88-91页

作者： Nazarpour, Kianoush Al-Timemy, Ali H. Bugmann, Guido Jackson, Andrew Newcastle Univ Inst Neurosci Newcastle Upon Tyne NE1 7RU Tyne & Wear England Univ Plymouth CRNS Plymouth PL4 8AA Devon England

The probability density function (PDF) of the surface electromyogram (EMG) signals has been modelled with Gaussian and Laplacian distribution functions. However, a general consensus upon the PDF of the EMG signals is yet to be reached, because not only are there several biological factors that can influence this distribution function, but also different analysis techniques can lead to contradicting results. Here, we recorded the EMG signal at different isometric muscle contraction levels and characterised the probability distribution of the surface EMG signal with two statistical measures: bicoherence and kurtosis. Bicoherence analysis did not help to infer the PDF of measured EMG signals. In contrast, with kurtosis analysis we demonstrated that the EMG PDF at isometric, non-fatiguing, low contraction levels is super-Gaussian. Moreover, kurtosis analysis showed that as the contraction force increases the surface EMG PDF tends to a Gaussian distribution. (C) 2012 Elsevier Inc. All rights reserved.

关键词： Electromyogram signal Higher order statistics probability distribution function

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Comparative Study of Cepstral Editing and Unitary Sample Shifted probability distribution function Method for Bearing Fault Diagnosis 1st

Comparative Study of Cepstral Editing and Unitary Sample Shi...

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1st International and 4th National Conference on Reliability and Safety Engineering, INCRS 2018

作者： Jahagirdar, Ankush C. Gupta, Karunesh Kumar Birla Institute of Technology and Science PilaniRajasthan India

ISBN: (纸本)9789811537455

This paper presents a comparative study of cepstral editing and unitary sample shifted probability distribution function method used for bearing fault diagnosis. Traditionally, different signal processing techniques are employed for this application. This study compares recent methods including cepstral editing and unitary sample shifted Laplacian window method. The superiority of these methods under different conditions and fault types is discussed based on the squared envelope spectrum (SES) feature and kurtosis. It is concluded from this study that use of cepstral pre-whitening (CPW) before the unitary sample shifted Laplacian window method significantly improves the performance for the diagnosis of ball faults. © Springer Nature Singapore Pte Ltd. 2020.

关键词： Cepstral editing Hilbert transform probability distribution function Rolling element bearing

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