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A true 3D frictional hardening elastoplastic constitutive model of concrete based on a unified hardening/softening function

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2018年 119卷 250-273页

作者： Wang, Guosheng Lu, Dechun Du, Xiuli Zhou, Xin Cao, Shengtao Beijing Univ Technol Inst Geotech & Underground Engn Beijing 100124 Peoples R China China Acad Bldg Res Beijing 100013 Peoples R China

This paper discusses three hardening modes of a shear-type yield surface and proposes a true three-dimensional (3D) frictional hardening method using the transformed stress. The proposed method reasonably reflects the stress-induced anisotropy of concrete for a wide range of hydrostatic pressures. A unified hardening/softening function is proposed based on the uniaxial compressive stress-strain relationship. The plastic potential function is obtained by studying the influence of linear and nonlinear plastic potential function on the dilatancy, and the relationship between the yield surface and plastic potential surface is analyzed. The loading-unloading criterion suitable for the softening behavior is obtained by transforming the yield function expressed by stress into the one expressed by strain. Furthermore, a true 3D frictional hardening elastoplastic constitutive model is established. The explicit stress integral algorithm and semi-implicit stress integral algorithm are used to implement the numerical computation. Finally, five sets of biaxial and triaxial test results of high-strength and normal-strength concrete are used to verify the established constitutive model. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Concrete True 3D frictional hardening Unified hardening/softening function Stress-induced anisotropy numerical algorithm

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Hybrid Bernstein Block-Pulse functions for solving system of fractional integro-differential equations

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INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS 2018年第11期95卷 2287-2307页

作者： Hesameddini, E. Shahbazi, M. Shiraz Univ Technol Dept Math Sci POB 71555-313 Shiraz Iran

This paper deals with the numerical solution of system of fractional integro-differential equations. In this work, we approximate the unknown functions based on the hybrid Bernstein Block-Pulse functions, in conjunction with the collocation method. We introduce the Riemann-Liouville fractional integral operator for the hybrid Bernstein Block-Pulse functions. This operator will be approximated by the Gauss quadrature formula with respect to the Legendre weight function and then it is utilized to reduce the solution of the fractional integro-differential equations to a system of algebraic equations. This system can be easily solved by any usual numerical methods. The existence and uniqueness of the solution have been discussed. Moreover, the convergence analysis of this algorithm will be shown by preparing some theorems. numerical experiments are presented to show the superiority and efficiency of proposed method in comparison with some other well-known methods.

关键词： Hybrid Bernstein Block-Pulse functions system of fractional integro-differential equations convergence analysis numerical algorithm Gaussian quadrature

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ast forward kinematics algorithm for real-time and ligh-precision control of the 3-RPS parallel mechanism

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Frontiers of Mechanical Engineering 2018年第3期13卷 368-375页

作者： Yue WANG Jingjun YU Xu PEI Robotics Institute Beihang University Beijing 100191 China Department of Mechanical Design Beihang University Beijing 100191 China

A new forward kinematics algorithm for the mechanism of 3-RPS （R： Revolute; P： Prismatic; S： Spherical） parallel manipulators is proposed in this study. This algorithm is primarily based on the special geometric conditions of the 3-RPS parallel mechanism, and it eliminates the errors produced by parasitic motions to improve and ensure accuracy. Specifically, the errors can be less than 10 6. In this method, only the group of solutions that is consistent with the actual situation of the platform is obtained rapidly. This algorithm substantially improves calculation efficiency because the selected initial values are reasonable, and all the formulas in the calculation are analytical. This novel forward kinematics algorithm is well suited for real-time and high-precision control of the 3-RPS parallel mechanism.

关键词： 3-RPS parallel mechanism forward kinematics numerical algorithm parasitic motion

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A three-dimensional plasticity-damage constitutive model for timber under cyclic loads

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COMPUTERS & STRUCTURES 2018年 195卷 47-63页

作者： Sirumbal-Zapata, Luis F. Malaga-Chuquitaype, Christian Elghazouli, Ahmed Y. Imperial Coll London Dept Civil & Environm Engn London England

The performance of timber structures is governed by the nonlinear response at their connections, where high deformation levels and stress concentrations are developed, particularly when subjected to load reversals. To date, no constitutive model for wood under cyclic load exists which is able to incorporate its most important failure modes while considering plastic deformations and cyclic stiffness and strength degradation simultaneously. This paper presents the formulation and implementation of a plasticity damage model with these characteristics within a continuum mechanics approach. The theoretical framework of both plasticity and damage models is described, and a detailed derivation of the constitutive equations required for their computational implementation and coupling as well as the return mapping and iterative algorithms for their integration are presented. The damage evolution process is handled by two independent scalar variables for tension and compression. A general orthotropic plasticity yield surface with isotropic hardening is employed to incorporate timber plastic flow in compression. A closed-form expression for the plasticity-damage consistent tangent operator is derived. It is demonstrated that the proposed constitutive model captures all the key characteristics required for an accurate modelling of timber under large deformation levels until failure. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Timber Plasticity Continuum damage mechanics Orthotropy Cyclic loading numerical algorithm

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On the plastic flow rule formulation in anisotropic yielding aluminium alloys

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INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY 2018年第1-4期99卷 255-274页

作者： Mendiguren, Joseba Galdos, Lander Saenz de Argandona, Eneko Mondragon Unibertsitatea Dept Mech & Ind Prod Loramendi 4 Arrasate Mondragon 20500 Gipuzkoa Spain

In the last decade, an increasing trend has been observed in the use of advanced anisotropic material models to improve the numerical predictions about sheet metal-forming processes. Among the actions following this trend, the use of non-associated flow rule (NAFR) models has been presented as an alternative to the classic associated flow rule (AFR) models. In this work, the influence of the flow rule in advanced anisotropic models has been analysed, following a systematic methodology. To evaluate both advantages and disadvantages of the flow rule, models with similar flexibility (i.e. with 8 and 16 parameters) have been compared by performing a finite element (FE) simulation of a cup-drawing process to study earing phenomena regarding accuracy, computational time and complexity. From the present study, it has been concluded that the main drivers on the final cup-drawing profile prediction are the model flexibility and the coefficient selection rather than the flow rule. Even though the NAFR formulation is complex when compared to the AFR regarding numerical implementation, this study shows that the total simulation time in a cup-drawing process while using explicit FE solvers is reduced in some cases, this one being strongly dependent on the material parameter definition.

关键词： Yield condition Anisotropic material Constitutive behaviour Metallic material numerical algorithm Non-associated flow rule

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Sparse representation via optimal matching convolution framelets

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IET SIGNAL PROCESSING 2018年第9期12卷 1082-1090页

作者： Wang, Zelong Zhu, Jubo Natl Univ Def Technol Coll Liberal Arts & Sci Changsha 410073 Hunan Peoples R China

Recently, a tight frame, called convolution framelets (CFs) and constructed by convolving local and non-local bases, is proposed to provide valuable insights in understanding the patch-based processing approaches in the viewpoint of sparse representation (SR). However, it is still unclear how to represent signals with energy concentration guarantee in its lifted space and how to optimise the local base for a given non-local base. To address these issues, the equivalence between the signal space and its lifted space is established by the Hankel operator. In the lifted space, the energy concentration property of signals is measured by the sparsity instead of the Euclidean norm and the rank. With the new objective function, an optimisation model is built to train the optimal local base for a given nonlocal base from the training samples, motivating us to propose the optimal matching convolution framelets (OMCFs). In addition, a numerical algorithm is also designed to solve the proposed model using alternating optimisation strategy. The OMCF for SR is tested on the speech signals, and the comparisons with traditional popular SR tools, such as discrete cosine transform (DCT) and Haar wavelets, demonstrate its better performance.

关键词： speech processing signal representation convolution optimisation Hankel matrices sparse representation optimal matching convolution framelets local basis nonlocal basis patch-based processing approaches signal representation energy concentration Hankel operator signal space energy concentration property objective function optimisation model OMCF numerical algorithm alternating optimisation strategy speech signals

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Geometrical shape optimization in fluid mechanics using FreeFem plus

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STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION 2018年第6期58卷 2761-2788页

作者： Dapogny, Charles Frey, Pascal Omnes, Florian Privat, Yannick Univ Grenoble Alpes CNRS Grenoble INP LJK F-38000 Grenoble France UPMC Univ Paris 06 Sorbonne Univ CNRS Lab Jacques Louis LionsUMR 7598 F-75005 Paris France UPMC Univ Paris 06 Sorbonne Univ ISCD F-75005 Paris France

In this article, we present simple and robust numerical methods for two-dimensional geometrical shape optimization problems, in the context of viscous flows driven by the stationary Navier-Stokes equations at low Reynolds number. The salient features of our algorithm are exposed with an educational purpose;in particular, the numerical resolution of the nonlinear stationary Navier-Stokes system, the Hadamard boundary variation method for calculating the sensitivity of the minimized function of the domain, and the mesh update strategy are carefully described. Several pedagogical examples are discussed. The corresponding program is written in the FreeFem++ environment, and it is freely available. Its chief features-and notably the implementation details of the main steps of our algorithm-are carefully presented, so that it can easily be handled and elaborated upon to deal with different, or more complex physical situations.

关键词： Shape optimization Shape sensitivity Fluid mechanics Educational article numerical algorithm

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A limited-feedback approximation scheme for optimal switching problems with execution delays

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MATHEMATICAL METHODS OF OPERATIONS RESEARCH 2018年第3期87卷 347-382页

作者： Perninge, Magnus Linnaeus Univ Dept Phys & Elect Engn PG Vejdes Plats S-35252 Vaxjo Sweden

We consider a type of optimal switching problems with non-uniform execution delays and ramping. Such problems frequently occur in the operation of economical and engineering systems. We first provide a solution to the problem by applying a probabilistic method. The main contribution is, however, a scheme for approximating the optimal control by limiting the information in the state-feedback. In a numerical example the approximation routine gives a considerable computational performance enhancement when compared to a conventional algorithm.

关键词： Optimal switching Impulse control Real options Delivery lag Execution delay Stopping time Snell envelope numerical algorithm

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Variational assimilation with covariance matrices of observation data errors for the model of the Baltic Sea dynamics

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RUSSIAN JOURNAL OF numerical ANALYSIS AND MATHEMATICAL MODELLING 2018年第3期33卷 149-160页

作者： Agoshkov, Valery I. Parmuzin, Eugene I. Zakharova, Natalia B. Shutyaev, Victor P. RAS Inst Numer Math Moscow 119333 Russia Moscow Inst Phys & Technol Dolgoprudnyi 141701 Moscow Region Russia

The mathematical model of the Baltic Sea dynamics developed at the Institute of numerical Mathematics of RAS is considered. The problem of variational assimilation of average daily data for the sea surface temperature (SST) is formulated and studied with the use of covariance matrices of observation data errors. Based on variational assimilation of satellite observation data, we propose an algorithm for solving the inverse problem of the heat flux reconstruction on the sea surface. The results of numerical experiments on reconstruction of the heat flux function are presented for the problem of variational assimilation of observation SST data.

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

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Novel algorithms to estimate nonlinear FDEs: Applied to fractional order nutrient-phytoplankton-zooplankton system

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JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS 2018年 339卷 193-207页

作者： Asl, Mohammad Shahbazi Javidi, Mohammad Univ Tabriz Fac Math Sci Tabriz Iran

In this paper, dynamical behavior of a mathematical model for the interaction of nutrient phytoplankton and its predator zooplankton is investigated numerically. Stability analysis of the phytoplankton-zooplankton model is studied by using the fractional Routh-Hurwitz stability conditions. We have studied the local stability of the equilibrium points. Then a new numerical algorithm, as well as its modification for solving fractional differential equations (FDEs) based on the polynomial interpolation, is proposed. The algorithms are designed to estimate linear and nonlinear FDEs and they have the capability to apply for solving fractional order systems. The convergence order and stability of the fractional higher order algorithms are proved and stability regions of the algorithms are achieved. Extensive numerical simulation results are provided and compared with the literature for illustrating the effectiveness and applicability of the presented algorithms to solve fractional differential equations. The obtained analytical results are validated by numerical simulations and the global dynamics of the model system is studied. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Nutrient Plankton numerical algorithm Fractional order system Stability

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