• Title/Summary/Keyword: exponential power-law

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Dynamic analysis of a functionally graded tapered rotating shaft under thermal load via differential quadrature finite elements method

  • Fethi, Hadjoui;Ahmed, Saimi;Ismail, Bensaid;Abdelhamid, Hadjoui
    • Advances in aircraft and spacecraft science
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    • v.10 no.1
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    • pp.19-49
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    • 2023
  • The present study proposes a theoretical and numerical investigation on the dynamic response behaviour of a functional graded (FG) ceramic-metal tapered rotor shaft system, by the differential quadrature finite elements method (DQFEM) to identify the natural frequencies for modelling and analysis of the structure with suitable validations. The purpose of this paper is to explore the influence of heat gradients on the natural frequency of rotation of FG shafts via three-dimensional solid elements, as well as a theoretical examination using the Timoshenko beam mode, which took into account the gyroscopic effect and rotational inertia. The functionally graded material's distribution is described by two distribution laws: the power law and the exponential law. To simulate varied thermal conditions, radial temperature distributions are obtained using the nonlinear temperature distribution (NLTD) and exponential temperature distribution (ETD) approaches. This work deals with the results of the effect on the fundamental frequencies of different material's laws gradation and temperature gradients distributions. Attempts are conducted to identify adequate explanations for the behaviours based on material characteristics. The effect of taper angle and material distribution on the dynamic behaviour of the FG conical rotor system is discussed.

Bayesian Value of Information Analysis with Linear, Exponential, Power Law Failure Models for Aging Chronic Diseases

  • Chang, Chi-Chang
    • Journal of Computing Science and Engineering
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    • v.2 no.2
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    • pp.200-219
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    • 2008
  • The effective management of uncertainty is one of the most fundamental problems in medical decision making. According to the literatures review, most medical decision models rely on point estimates for input parameters. However, it is natural that they should be interested in the relationship between changes in those values and subsequent changes in model output. Therefore, the purpose of this study is to identify the ranges of numerical values for which each option will be most efficient with respect to the input parameters. The Nonhomogeneous Poisson Process(NHPP) was used for describing the behavior of aging chronic diseases. Three kind of failure models (linear, exponential, and power law) were considered, and each of these failure models was studied under the assumptions of unknown scale factor and known aging rate, known scale factor and unknown aging rate, and unknown scale factor and unknown aging rate, respectively. In addition, this study illustrated developed method with an analysis of data from a trial of immunotherapy in the treatment of chronic Granulomatous disease. Finally, the proposed design of Bayesian value of information analysis facilitates the effective use of the computing capability of computers and provides a systematic way to integrate the expert's opinions and the sampling information which will furnish decision makers with valuable support for quality medical decision making.

Empirical Correlations for Penetration Height of Liquid Jet in Uniform Cross Flow - A Review

  • No, Soo-Young
    • Journal of ILASS-Korea
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    • v.16 no.4
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    • pp.176-185
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    • 2011
  • The empirical correlations for the prediction of penetration height of liquid jet in crossflow are reviewed and classified in this study. Around thirty different correlations had been proposed by many investigators. It has generally known that the penetration height of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized downstream distance from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. The existing correlations can be grouped as correlations in a power-law, logarithmic, and exponential forms, respectively. Correlations in a power-law form can be further classified as three groups such as basic form, Weber number form and other parameters form. It should be pointed out that correlations in a logarithmic form in terms of Weber number or any other parameters could not be found. Universal correlation has still not been established due to the significant discrepancies between various correlations suggested to date. Several of the studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, and nozzle/injector geometry. Evaluation of validity for the correlations proposed recently by several investigators is essentially required. Those include eight power-law forms, two logarithmic forms, and one exponential form.

Bending analysis of power-law sandwich FGM beams under thermal conditions

  • Garg, Aman;Belarbi, Mohamed-Ouejdi;Li, Li;Tounsi, Abdelouahed
    • Advances in aircraft and spacecraft science
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    • v.9 no.3
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    • pp.243-261
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    • 2022
  • Broad writing on the examination of sandwich structures mirrors the significance of incorporating thermal loadings during their investigation stage. In the current work, an endeavor has been made to concentrate on sandwich FGM beams' bending behaving under thermal loadings utilizing shear deformation theory. Temperature-dependent material properties are used during the analysis. The formulation includes the transverse displacement field, which helps better predict the behavior of thick FGM beams. Three-different thermal profiles across the thickness of the beam are assumed during the analysis. The study has been carried out on both symmetric and unsymmetric sandwich FGM beams. It has been observed that the bending behavior of sandwich FGM beams is impacted by the temperature profile to which it is subjected. Power-law exponent and thickness of core also affect the behavior of the beam.

Tsunami Hazard Evaluation for the East Coast of Korea by using Empirical Tsunami Data (경험자료에 의한 동해안의 지진해일 재해도 평가)

  • Kim, Min-Kyu;Choi, In-Kil;Kang, Keum-Seok
    • Journal of the Earthquake Engineering Society of Korea
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    • v.14 no.4
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    • pp.17-22
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    • 2010
  • In this study, a tsunami hazard curve was determined for a probabilistic safety assessment (PSA) of a tsunami event at a Nuclear Power Plant site. A Tsunami catalogue was developed by using the historical tsunami record prior to 1900 and the instrumental tsunami record after 1900. For the evaluation of the return period of the tsunami run-up height, power-law, upper-truncated power law and exponential function were considered for the assessment of regression curves and each result was compared. Although there were in total only 9 tsunami records on the east coast of Korea during the time period of the tsunami catalogue, there is no research like this about tsunami hazard curve evaluation, so this research lays a foundation for probabilistic tsunami hazard assessment (PTHA)

Accelerated Life Tests under Uniform Stress Distribution (스트레스함수가 균등분포인 가속수명시험)

  • 원영철
    • Journal of the Korea Safety Management & Science
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    • v.2 no.2
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    • pp.71-83
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    • 2000
  • This paper presents accelerated life tests for Type I censoring data under probabilistic stresses. Probabilistic stress, $S_j$, is the random variable for stress influenced by test environments, test equipments, sampling devices and use conditions. The hazard rate, ,$theta_j$, is the random variable of environments and the function of probabilistic stress. Also it is assumed that the general stress distribution is uniform, the life distribution for the given hazard rate, $\theta$, is exponential and inverse power law model holds. In this paper, we obtained maximum likelihood estimators of model parameters and the mean life in use stress condition.

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3-D Vibration analysis of FG-MWCNTs/Phenolic sandwich sectorial plates

  • Tahouneh, Vahid
    • Steel and Composite Structures
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    • v.26 no.5
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    • pp.649-662
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    • 2018
  • In this study, based on the three-dimensional theory of elasticity, free vibration characteristics of sandwich sectorial plates with multiwalled carbon nanotube-(MWCNT)-reinforced composite core are considered. Modified Halpin-Tsai equation is used to evaluate the Young's modulus of the MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. In this paper, free vibration of thick functionally graded sandwich annular sectorial plates with simply supported radial edges and different circular edge conditions including simply supported-clamped, clamped-clamped, and free-clamped is investigated. A semi-analytical approach composed of two-dimensional differential quadrature method and series solution are adopted to solve the equations of motion. The material properties change continuously through the core thickness of the plate, which can vary according to a power-law, exponentially, or any other formulations in this direction. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated sectorial plates.

Static bending and free vibration of FGM beam using an exponential shear deformation theory

  • Hadji, L.;Khelifa, Z.;Daouadji, T.H.;Bedia, E.A.
    • Coupled systems mechanics
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    • v.4 no.1
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    • pp.99-114
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    • 2015
  • In this paper, a refined exponential shear deformation beam theory is developed for bending analysis of functionally graded beams. The theory account for parabolic variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Contrary to the others refined theories elaborated, where the stretching effect is neglected, in the current investigation this so-called "stretching effect" is taken into consideration. The material properties of the functionally graded beam are assumed to vary according to power law distribution of the volume fraction of the constituents. Based on the present shear deformation beam theory, the equations of motion are derived from Hamilton's principle. Analytical solutions for static are obtained. Numerical examples are presented to verify the accuracy of the present theory.

Time-Censored Ramp Tests with Stress Bound for Exponential (스트레스 한계가 있는 램프시험의 최적설계: 지수수명분포의 경우)

  • Bai, Do-Sun;Chun, Young-Rok;Cha, Myung-Su
    • Journal of Korean Institute of Industrial Engineers
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    • v.22 no.3
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    • pp.459-471
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    • 1996
  • This paper considers ramp tests for exponential lifetime distribution when there are limitations on test stress and test time. The inverse power law and a cumulative exposure model are assumed. Maximum likelihood (ML) estimators of model parameters and their asymptotic covariance matrix are obtained. The optimum ramp test plans are also found which minimize the asymptotic variance of the ML estimator of the log mean life at design constant stress. For selected values of the design parameters, tables useful for finding optimal test plans are given. The effect of the pre-estimates of design parameters is studied.

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Performance of water-jet pump under acceleration

  • Wu, Xian-Fang;Li, Ming-Hui;Liu, Hou-Lin;Tan, Ming-Gao;Lu, You-Dong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.13 no.1
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    • pp.794-803
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    • 2021
  • The instantaneous acceleration affects the performance of the water-jet pump obviously. Here, based on the user-defined function, the method to simulate the inner flow in water-jet pumps under acceleration conditions was established. The effects of two different acceleration modes (linear acceleration and exponential acceleration) and three kinds of different acceleration time (0.5s, 1s and 2s) on the performance of the water-jet pump were analyzed. The results show that the thrust and the pressure pulsation under exponential acceleration are lower than that under linear acceleration at the same time; the vapor volume fraction in the impeller under linear acceleration is 27.3% higher than that under exponential acceleration. As the acceleration time increases, the thrust gradually increases and the pressure pulsation amplitude at the impeller inlet and outlet gradually decreases, while the law of pressure pulsation is the opposite at the diffuser outlet. The main frequency of pressure pulsation at the impeller outlet is different under different acceleration time. The research results can provide some reference for the optimal design of water-jet pumps.