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A robust method for quantifying surface grain size

SURFACE SCIENCE 2008年第2期602卷 L11-L14页

作者： Rideout, J. L. Beaulieu, L. Y. Mem Univ Newfoundland Dept Phys & Phys Oceanog St John NF A1B 3X7 Canada

A robust quantitative method has been developed for measuring the size of hemispherical surface grains as observed in SPM topographs. This method uses a modified form of a Savitzky-Golay filter, by fitting successive overlapping search areas within an image to a two-dimensional and using the second derivative test to find the crest of the grains. Methods for characterizing surface grains vary from analyzing X-ray diffraction patterns by using the Scherrer equation to performing random cross-sectional analyzes of SPM images. Multiple maxima are often often found for one grain during the first iteration because of the overlap between search areas. The results showed that it is important to choose the proper search area size and polynomial order.

关键词： surface grain size scanning probe microscopy numerical algorithm surface characterization

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A new approach to thermal segregation in petroleum reservoirs: algorithm and case studies

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JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING 2021年 201卷 108367-108367页

作者： Baghooee, Hadise Montel, Francois Galliero, Guillaume Yan, Wei Shapiro, Alexander Tech Univ Denmark DTU Danish Hydrocarbon Res & Technol Ctr Lyngby Denmark Tech Univ Denmark DTU CERE Ctr Energy Resources Engn Dept Chem & Biochem Engn Lyngby Denmark Univ Pau & Pays Adour LFCR Lab Fluides Complexes & Leurs Reservoirs UMR 5150 CNRS Total UPPAE2S UPPA Pau France Tech Univ Denmark DTU CERE Ctr Energy Resources Engn Dept Chem Lyngby Denmark

In many petroleum reservoirs, the fluid properties vary through the reservoir thickness. Variation of the composition, i.e. compositional grading, can affect reserve estimation, production and enhanced oil recovery strategies. Apart from gravity, the geothermal gradient may also contribute to the fluid distribution. Thermodiffusion is the governing phenomenon determining the contribution of the geothermal gradient. The non-equilibrium thermodynamics models are applied for the calculation of the compositional gradients under the varying temperature. In order to determine the variations in pressure and composition with depth and to be able to indicate if/where a gas-oil contact exists, we have developed a model based on the principles of irreversible thermodynamics, within the approach to thermodiffusion in porous media proposed by Montel et al. (2019). Based on the relationships where pressure, chemical potentials, and thermal gradient are linked, the distribution of hydrocarbons in a petroleum reservoir is described. A computational algorithm accounting for non-ideality of the mixture, characterization, and phase transitions has been developed. The model and the computational procedure have been validated by comparison with the case studies reported in the literature for a North Sea reservoir, and with sample component distributions produced by application of molecular dynamics simulations. It has been shown that the model is capable of predicting the fluid distributions with depth with no or a minimum of adjustable parameters. The thermal gradient modifies the predicted fluid distributions making them closer to the observed data points. Depending on the mixture composition, the thermal diffusion may either enforce the effect of gravity or counteract it.

关键词： Gravity segregation Thermal gradient Thermodiffusion numerical algorithm Reservoir cases

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Double Scalar Variables Plastic-Damage Model for Concrete

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JOURNAL OF ENGINEERING MECHANICS 2022年第2期148卷 04021143-04021143页

作者： Lu, Dechun Meng, Fanping Zhou, Xin Wang, Guosheng Du, Xiuli Beijing Univ Technol Key Lab Urban Secur & Disaster Engn Minist Educ Beijing 100124 Peoples R China

A framework of the plastic-damage model with double scalar variables is established in nominal stress space under the small deformation assumption. In the damaged part, a damage tensor composed of double scalar variables is presented to comprehensively characterize the isotropic damage behavior in three-dimensional (3D) conditions. The damage laws of Young's modulus and shear modulus are proposed to capture their different damage characteristic observed in the test. For one-dimensional (1D) and 3D conditions, the applicability of single scalar and double scalar damage variables is discussed. The macroscopic damage difference between these two damage variables when describing damage under 3D conditions is analyzed. In the plastic part, the plastic strain increment is determined by two parts of magnitude and direction. The magnitude is obtained by the consistency condition, and the flow direction is defined by the nonorthogonal flow rule that can satisfactorily reproduce the dilatancy behavior of concrete. The proposed model is implemented by the explicit Runge-Kutta (RK) method with the fifth-order accuracy and the Pegasus method. The performance of the model is assessed by the comparison results between the model and the cyclic loading and unloading test data under different stress paths.

关键词： Concrete Plastic-damage model Damage variables Flow rule numerical algorithm

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Mechanism of Solute and Thermal Characteristics in a Casson Hybrid Nanofluid Based with Ethylene Glycol Influenced by Soret and Dufour Effects

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ENERGIES 2021年第20期14卷 6818页

作者： Hafeez, Muhammad Bilal Sumelka, Wojciech Nazir, Umar Ahmad, Hijaz Askar, Sameh Gdansk Univ Technol Fac Mech Engn & Ship Technol Narutowicza 11-12 PL-80233 Gdansk Poland Poznan Univ Tech Inst Struct Anal Piotrowo 5 St PL-60965 Poznan Poland Inst Space Technol Dept Appl Math & Stat POB 2750 Islamabad 44000 Pakistan Int Telemat Univ Uninettuno Sect Math Corso Vittorio Emanuele II 39 I-00186 Rome Italy King Saud Univ Coll Sci Dept Stat & Operat Res POB 2455 Riyadh 11451 Saudi Arabia

This article models a system of partial differential equations (PDEs) for the thermal and solute characteristics under gradients (concentration and temperature) in the magnetohydrodynamic flow of Casson liquid in a Darcy porous medium. The modelled problems are highly non-linear with convective boundary conditions. These problems are solved numerically with a finite element approach under a tolerance of 10-8. A numerical algorithm (finite element approach) is provided and a numerical procedure is discussed. Convergence is also observed via 300 elements. Simulations are run to explore the dynamics of flow and the transport of heat and mass under parametric variation. To examine the impact of a temperature gradient on the transport of mass and the role of a concentration gradient on the transport of heat energy, simulations are recorded. Remarkable changes in temperature and concentration are noted when Dufour and Soret numbers are varied.

关键词： numerical algorithm heat energy mass transfer convergence finite element method

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Optimization of a Simulated Well Cluster using Surrogate Models

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IFAC Proceedings Volumes 2012年第8期45卷 275-280页

作者： Bjarne Grimstad Håvard Ausen Victoria Lervik Vidar Gunnerud Dag Ljungquist Department for Engineering Cybernetics NTNU Department of Industrial Economics and Technology Management NTNU FMC Technologies Asker Norway

In this paper we present an implementation of a partly Derivative-Free Optimization (DFO) algorithm for production optimization of a simulated multi-phase flow network. The network consists of well and pipeline simulators, considered to be black-box models without available gradients. The algorithm utilizes local approximations as surrogate models for the complex simulators. A Mixed Integer Nonlinear Programming (MINLP) problem is built from the surrogate models and the known structure of the flow network. The core of the algorithm is IBM's MINLP solver Bonmin, which is run iteratively to solve optimization problems cast in terms of surrogate models. At each iteration the surrogate models are updated to fit local data points from the simulators. The algorithm is tested on an artificial subsea network modeled in FlowManager ™ , a multi-phase flow simulator from FMC Technologies. The results for this special case show that the algorithm converges to a point where the surrogate models fit the simulator, and they both share the optimum.

关键词： Derivative-Free Optimization Non-linear Optimization Non-convex Optimization Mixed Integer Programming Process Simulators Interpolation algorithm numerical algorithm

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An algorithm to Calculate Numerators of Higher Kinds

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IFAC Proceedings Volumes 1984年第2期17卷 525-530页

作者： H.A. Spang Corporate Research and Development. General Electric Company. NY 12345 USA

Numerators of higher kinds are defined as determinants obtained by expanding the characteristic polynomial of a multi-input multi-output system in terms of its feedback coefficients. They are generalizations of the usual numerator polynomial and have been shown to be the characteristic polynomial for the system under infinite feedback gain. As such, they can be used to examine individual loop behavior when other loops have high gain. Previously, they have been calculated in terms of determinants using Cramer's rule which generally can be poorly behaved numerically. In tnis paper, an algorithm is developed based on Van Dooren's recent numerically stable generalized eigenstructure algorithms. This approach clearly illustrates the connection between these numerators of higher kinds and transmission zeros.

关键词： Numerators of higher kind numerical algorithm computer-aided design multivariable control systems transmission zeroes

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Modelling crowd pressure and turbulence through a mixed-type continuum approach

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TRANSPORTMETRICA B-TRANSPORT DYNAMICS 2024年第1期12卷

作者： Liang, Haoyang Yang, Liangze Du, Jie Shu, Chi-Wang Wong, S. C. Tongji Univ Key Lab Rd & Traff Engn Minist Educ Shanghai Peoples R China Anhui Univ Sch Math Sci Hefei Anhui Peoples R China East China Normal Univ Sch Math Sci Shanghai Peoples R China East China Normal Univ Shanghai Key Lab PMMP Shanghai Peoples R China Minist Educ Key Lab MEA Shanghai Peoples R China Brown Univ Div Appl Math Providence RI USA Univ Hong Kong Dept Civil Engn Hong Kong Peoples R China

Empirical studies of large gatherings and natural disasters have revealed two important features of dense crowds: extremely high crowd pressure and crowd turbulence. In this study, a mixed-type continuum model for multidirectional pedestrian flow was developed that explicitly considered the phase transition of different anticipation characteristics under different densities. Non-hyperbolicity was used to model the strong instabilities during crowd turbulence. In addition, by estimating the aggregated crowd pressure, the proposed model could clarify the effects of both force chains and panic sentiment, phenomena commonly observed during crowd disasters. The non-hyperbolic partial differential equations were solved using the mixed-type finite difference method, and Eikonal equations were solved using the fast sweeping method. Subsequently, the continuum model was applied to simulations of two real-world scenarios - the 2015 Hajj crowd disaster and the 2010 Love Parade crowd disaster - and validated through comparison with empirical observations. Overall, the proposed model is an efficient tool for evaluating crowd management strategies to predict and assess the crowd state.

关键词： Crowd dynamics phase-transition continuum modelling numerical algorithm crowd turbulence

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Calibration of a multi-mobile coil magnetic manipulation system utilizing a control-oriented magnetic model

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MECHATRONICS 2022年 84卷 102774-102774页

作者： Osinde, Nahashon O. Etievant, Maxime Byiringiro, Jean Bosco Andreff, Nicolas Univ Bourgogne Franche Comte FEMTO ST Inst 15B Ave Montboucons F-25000 Besancon France Dedan Kimathi Univ Technol Mechatron Engn Nyeri Kenya Dedan Kimathi Univ Technol Siemens Mechatron Certificat Ctr Nyeri Kenya

In this paper, we address the calibration of a family of magnetic manipulation systems composed of several coils that are moved around by serial robot manipulators. We show in this paper that the calibration of the whole system ultimately results in calibrating the manipulator and coil separately up to an unknown rigid transformation. For calibration of the coil, we propose to use a model that has not been used so far in the literature;a control-oriented model which is sufficiently accurate and computes the magnetic field in real time. A protocol for calibrating the magnetic manipulation system using the Nelder-Mead algorithm to estimate the model parameters is presented. Calibration was performed through simulations and validated experimentally on a physical system. It was observed that the root mean square error was reduced by 37% after calibration of the physical system, indicating an improvement in accurately estimating the magnetic model.

关键词： Calibration Multi-mobile coil Magnetic manipulation Microrobotics numerical algorithm

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Regularization of localization due to material softening using a nonlocal hardening variable in an Eulerian formulation of inelasticity

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INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE 2022年 176卷 1页

作者： Kroon, Martin Rubin, M. B. Linnaeus Univ Dept Mech Engn Vaxjo Sweden Technion Israel Inst Technol Fac Mech Engn IL-32000 Haifa Israel

It is known that damage or inelastic softening can cause an ill-posed problem leading to localization and mesh-dependence in finite element simulations. In this paper, a nonlocal hardening variable, (k) over bar, is introduced in a finite deformation Eulerian formulation of inelasticity with a rate-independent smooth elastic-inelastic transition. This nonlocal variable is defined over an Eulerian region of nonlocality, which is a sphere with radius equal to the characteristic length, L-c, defined in the current deformed geometry of the material. Two models of this nonlocal hardening variable are explored. One model where kappa is the minimum value of the local hardening kappa within the region of nonlocality, and another model where kappa is the average of kappa in the same region. The influence of the nonlocal hardening variable is studied using an example of a plate that is loaded by a prescribed boundary displacement causing formation of a shear band. Predictions of the applied load vs. displacement curves and contour plots of the total distortional deformation of the plate and the hardening variable kappa are studied. The model based on the minimum value of kappa in the nonlocal region predicts mesh-independent post-peak response of the load vs. displacement curve. Also, it is shown that the characteristic material length, L-c, controls the structure of the shear band developed in the plate.

关键词： Localization Finite deformation Elastic-plastic Mesh-sensitivity numerical algorithm

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algorithm for density of angle distribution in random sections of polyhedron

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EXPERT SYSTEMS WITH APPLICATIONS 2024年 235卷

作者： Konstantinova, Elizaveta P. Shchur, Lev N. HSE Univ Moscow 101000 Russia Landau Inst Theoret Phys Pl Ak Semenova 1A Chernogolovka 142432 Russia

Scanning electron micrographs of solid materials are a source of analysis for hardness, defects, etc. A micrograph is a two-dimensional image of a material being cut. Typical photomicrographs contain about a hundred thousand structural elements, such as grain boundaries, boundary junctions, etc., which are not easy to analyze with the naked eye. Currently, computer vision can be used to analyze the geometric properties of structural elements. One of the important properties is the cross section of the grain, which is the result of cutting the material. In the article we turn to one of the geometric properties of random grain cuttings. The statistical properties of the cross sections of grains in an alloy are equivalent to the statistical properties of the cross sections of individual grains by random planes if the grains do not touch each other. We present two stages of mathematical analysis of the grain cross-sections. First, using the algorithm for generating random planes with a uniform distribution, a method is proposed for generating random sections of polyhedra. The method can be useful in stochastic geometry and computational geometry, as well as in materials science. Second, sections of polyhedra with random planes are considered, and a numerical algorithm for estimating the distribution density of angles of convex polyhedra is also implemented. Examples of distribution densities in random sections for a cube, a regular triangular prism, and a truncated prism are given. The developed algorithm and the obtained distribution densities are of practical use in the analysis of micrographs of thin sections of crystalline alloys.

关键词： Random plane Polyhedra random section numerical algorithm Angle distribution Crystalline alloys

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