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Multiaxial ratcheting assessment of Z2CND18.12N steel using modified A-V hardening rule

STEEL AND COMPOSITE STRUCTURES 2023年第1期49卷 1-17页

作者： Chen, Xiaohui Zhou, Yang Liu, Wenwu Zhao, Xu Northeastern Univ Qinhuangdao Sch Control Engn Qinhuangdao 066004 Peoples R China

Based on Ahmadzadeh-Varvani hardening rule (A-V model), multiaxial ratcheting effect of Z2CND18.12N austenitic stainless steel is simulated by ABAQUS with user subroutine UMAT. The results show that the predicted results of the origin multiaxial A-V model are lower than the experimental data, and it is difficult to control ratcheting strain rate. In order to improve the predicted capability of A-V model, the A-V model is modified. In this study. Moreover, under the assumption of the von Mises yield criterion and normal plasticity flow rule, we develop a numerical algorithm of plastic strain with the improved model to implement the finite element calculation of the model. Internal iteration in the numerical algorithm was implemented with the Euler backward method, which calculated the trial strain for each equilibrium iteration using the consistent tangent matrix. With a user subroutine, the proposed model is programmed into ABAQUS for a user -executable version. By simulating the uniaxial ratcheting of a round bar made of Z2CND18.12N austenitic stainless steel, we observe that the predicted results simulated by ABAQUS with UMAT are compared with the experimental data. The predicted results of the improved multiaxial A-V model are consistent well with the experimental data.

关键词： austenitic stainless steel constitutive model euler backward method multiaixal ratcheting numerical algorithm

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Spacecraft Magnetic Control Using Dichotomous Coordinate Descent algorithm with Box Constraints

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MODELING IDENTIFICATION AND CONTROL 2010年第4期31卷 123-131页

作者： Schlanbusch, Rune Kristiansen, Raymond Nicklasson, Per Johan Narvik Univ Coll Dept Technol N-8505 Narvik Norway

In this paper we present magnetic control of a spacecraft using the Dichotomous Coordinate Descent (DCD) algorithm with box constraints. What is common for most work on magnetic spacecraft control is the technique for solving for the control variables of the magnetic torquers where a cross product is included which is well known to be singular. The DCD algorithm provides a new scheme which makes it possible to use a general control law and then adapt it to work for magnetic torquers including restrictions in available magnetic moment, instead of designing a specialized controller for the magnetic control problem. A non-linear passivity-based sliding surface controller is derived for a fully actuated spacecraft and is then implemented for magnetic control by utilizing the previous mentioned algorithm. Results from two simulations are provided, the first comparing the results from the DCD algorithm with older results, and the second showing how easily the derived sliding surface controller may be implemented, improving our results.

关键词： Magnetic attitude control numerical algorithm sliding surface control space vehicle control

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A continuous fracture front tracking algorithm with multi layer tip elements (MuLTipEl) for a plane strain hydraulic fracture

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JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING 2022年 217卷

作者： Dontsov, E. V. ResFrac Corp 555 Bryant St 185 Palo Alto CA 94301 USA

The problem of a plane strain hydraulic fracture propagating in a layered formation is considered. Fracture toughness, in-situ stress, and leak-off coefficient are assumed to vary by layer, while the elastic properties are kept constant throughout the domain for simplicity. The purpose of this study is to develop a numerical algorithm based on a fixed mesh approach, which is able to solve the above problem accurately using elements which can even be larger than the layer size. In order to do this, the concept of fictitious tip stress is first introduced for determining the fracture front location. In this technique, an additional stress is applied to the tip element to suppress the opening and to mimic the width corresponding to the actual fracture front location. A theoretical basis for this concept has been established and it is further calibrated for piece-wise constant elements. Once the ability to track the crack front location is developed, the effect of layers is included by varying properties as a function of front location. Several numerical examples benchmarking the numerical solution, as well as highlighting capabilities of the algorithm to tackle multiple thin layers accurately are presented.

关键词： Hydraulic fracturing numerical algorithm Thin layers Plane strain

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Variational assimilation of mean daily observation data for the problem of sea hydrothermodynamics

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RUSSIAN JOURNAL OF numerical ANALYSIS AND MATHEMATICAL MODELLING 2017年第3期32卷 187-195页

作者： Parmuzin, Eugene I. Agoshkov, Valery I. Zakharova, Natalia B. Shutyaev, Victor P. RAS Inst Numer Math Moscow 119333 Russia Moscow Inst Phys & Technol Dolgoprudnyi 141700 Moscow Region Russia

The mathematical model of hydrothermodynamics of the Baltic Sea is considered with the pole moved to a neighbourhood of St. Petersburg in order to improve the horizontal resolution in the Gulf of Finland. The problem of variational assimilation of mean daily data for sea surface temperature (SST) is formulated and studied for the given type of calculation grid of this model. A new algorithm of solution of the inverse problem for reconstruction of the heat flux on the interface of two media is proposed on the base of variational assimilation of satellite observation data. Results of numerical experiments are presented for reconstruction of heat fluxes in the problem of variational assimilation of mean daily observations of SST data.

关键词： Variational assimilation numerical algorithm determination of heat fluxes sea surface temperature

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On implementing the implicit discrete-time super-twisting observer on mechanical systems

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INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL 2023年第13期33卷 7532-7562页

作者： Winkler, Alexander Grabmair, Gernot Reger, Johann Univ Appl Sci Upper Austria Control Engn Grp Wels Austria Tech Univ Ilmenau Control Engn Grp Ilmenau Germany Univ Appl Sci Upper Austria Control Engn Grp Stelzhamerstr 23 A-4600 Wels Austria

In this paper, an extension of an algorithm for the implicit discretization of a super-twisting sliding mode observer is presented. Implicit and explicit discretization algorithms for homogeneous differentiators, where no physical model information is considered, are investigated in literature. This article studies the behavior when considering models of a rather general class of nonlinear systems. The discrete equations of the super-twisting observer are reformulated as generalized equation and an algorithm for the step-by-step solution is given. The uniqueness of the derived algorithm is investigated with an equivalent variational inequality formulation which is derived for a class of nonlinear systems. Furthermore, a semi-implicit predictor-corrector discretization is presented which is an approximation method for the presented algorithms and allows an explicit implementation in practical applications. Accuracy properties under noise and sampling are given. The algorithm is applied on two mechanical example systems taken from practice.

关键词： implicit discrete-time implementation mechanical system numerical algorithm robust state estimation super-twisting algorithm

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Application of genetic algorithms to texture analysis

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CRYSTAL RESEARCH AND TECHNOLOGY 1999年第8期34卷 1073-1079页

作者： Salek, P Tarasiuk, J Wierzbanowski, K Akad Gorniczo Hutnicza Wydzial Fiz & Tech Jadrowej PL-30059 Krakow Poland

Application of genetic algorithms to texture analysis is presented in this paper. The genetic algorithm technique was applied to the calculation of the orientation distribution function from a set of pole figures. The results are very satisfying. The same algorithm may be also applied to other problems of texture analysis, e.g., to find an optimal texture for a given application.

关键词： genetic algorithm crystallographic texture orientation distribution function pole figure texture analysis numerical algorithm

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Composite material design of two-dimensional structures using the homogenization design method

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INTERNATIONAL JOURNAL FOR numerical METHODS IN ENGINEERING 2001年第9期50卷 2031-2051页

作者： Fujii, D Chen, BC Kikuchi, N Univ Michigan Dept Mech Engn & Appl Mech Ann Arbor MI 48109 USA

Composite materials of two-dimensional structures are designed using the homogenization design method. The composite material is made of two or three different material phases. Designing the composite material consists of finding a distribution of material phases that minimizes the mean compliance of the macrostructure subject to volume fraction constraints of the constituent phases, within a unit cell of periodic microstructures. At the start of the computational solution, the material distribution of the microstructure is represented as a pure mixture of the constituent phases. As the iteration procedure unfolds, the component phases separate themselves out to form distinctive interfaces. The effective material properties of the artificially mixed materials are defined by the interpolation of the constituents. The optimization problem is solved using the sequential linear programming method. Both the macrostructure and the microstructures are analysed using the finite element method in each iteration step. Several examples of optimal topology design of composite material are presented to demonstrate the validity of the present numerical algorithm. Copyright (C) 2001 John Wiley & Sons, Ltd.

关键词： composite material homogenization method topology optimization microstructures numerical algorithm

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Efficient Collision Detection in a Simulated Hydrocyclone

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JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY 2015年第10期36卷 1483-1492页

作者： van Eijkeren, D. F. Krebs, T. Hoeijmakers, H. W. M. Univ Twente Fac Engn Engn Fluid Dynam NL-7500 AE Enschede Netherlands VORtech BV NL-2624 ES Delft Netherlands FMC Technol Separat Syst Arnhem Netherlands

Hydrocyclones enhance oil-water separation efficiency compared to conventional separation methods. An efficient collision detection scheme with N-p In N-p dependency on the number of particles is proposed. The scheme is developed to investigate the importance of particle-particle interaction for flow and particle behavior in dilute oil-water separators. However, the proposed scheme can also be used for efficient multigrid soft collision calculation with long-range particle-particle interaction models. The collision detection scheme is first validated using a case of settling spheres. Subsequently, the scheme is applied to a simplified flow field, similar to the flow fields observed in hydrocyclones.

关键词： Collision detection hydrocyclone Lagrangian particle tracking numerical algorithm oil-water separation

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An algorithm for accurate modeling and simulating reactor cores with involute-shaped fuel plates by Monte Carlo

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INTERNATIONAL JOURNAL OF ENERGY RESEARCH 2021年第8期45卷 12449-12463页

作者： Zhang, Shen Gui, Nan Kai, Tan Yang, Xingtuan Tu, Jiyuan Jiang, Shengyao Tsinghua Univ Inst Nucl & New Energy Technol Collaborat Innovat Ctr Adv Nucl Energy Technol Key Lab Adv Reactor Engn & SafetyMinist Educ Beijing 100084 Peoples R China RMIT Univ Sch Engn Melbourne Vic Australia

A real three-dimensional representation of reactor core with involute fuel plates via Monte Carlo method is still lacking at the present, and usually equivalent homogeneous models of water coolants and simplified fuel plate shapes have been used. This work proposed an algorithm to simulate the reactor core composed of involute fuel plates with an explicit accurate description of its involute surfaces. The description of involute surfaces is through its governing equations. The mathematical function methods to depict the involute curves and the schemes to compute the distance between any neutron particle and an involute surface along a ray are presented and demonstrated step-by-step. The algorithm is realized in the Monte Carlo code and validated by the published data of a high flux isotope reactor. This study definitively provides a method to model the involute fuel plates in the Monte Carlo simulation.

关键词： fuel plate involute shape Monte Carlo method numerical algorithm reactor core

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An iterative aggregation/disaggregation procedure for modelling the long-term behaviour of continuous-time evanescent random processes

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JOURNAL OF STATISTICAL COMPUTATION AND SIMULATION 1996年第1期56卷 77-95页

作者： Stewart, DE Bebbington, MS MASSEY UNIV DEPT STATPALMERSTON NORTHNEW ZEALAND

We describe a multilevel aggregation/disaggregation method for finding the quasistationary distribution and decay parameters for continuous-time Markov chains. This complements existing techniques dealing with the discrete-time case, or for finding the stationary distribution. Finding the quasistationary distribution is equivalent to calculating the eigenvector corresponding to the smallest eigenvalue of the q-matrix restricted to the non-absorbing class. The method presented here is similar to an algebraic multigrid, with restriction operators that depend on the current approximation to the solution. The smoothers are short Arnoldi iterations or Gauss-Seidel iterations. numerical results are presented for a variety of models of differing character, including simple epidemic, bivariate SIS, predator-prey, and the cubic auto-catalator. These indicate that the number of cycles required grows only very slowly with the size of the problem.

关键词： quasistationary distribution numerical algorithm V-cycle

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