A simple approach to solve boundary-value problems in gradient elasticity

Summary We outline a procedure for obtaining solutions of certain boundary value problems of a recently proposed theory of gradient elasticity in terms of solutions of classical elasticity. The method is applied to illustrate, among other things, how the gradient theory can remove the strain singularity from some typical examples of the classical theory.     

Hybrid TSSA algorithm-based approach to solve warehouse-scheduling problems

Managing a supply chain efficiently is one of the most promising tasks for enterprises these days. Therefore, all the major factors that contribute to the success of the supply chain have to be handled carefully. Warehousing being the vital component of the supply chain contributes towards the storage and timely and efficient delivery of products. The role of warehouses in the overall success of the supply chain has shifted the inclination of researchers towards finding ways that can ease the complexities prevailing under such a scenario. Motivated by these facts, the present paper deals with the issues pertaining to the modelling of the warehouse management system. The paper emphasizes various matters related to warehouse scheduling and aims for an overall minimization of tardiness. It also proposes a Tabu sample-sort simulated annealing (TSSA) algorithm to solve the complex warehouse-scheduling problems. The comparative result with simulated annealing (SA), Tabu search (TS), and hybrid Tabu-SA algorithms at the end of the proposed work reveals the efficacy and robustness of the TSSA algorithm.     

A genetic approach to solve numerical problems in the Preisach model identification

This paper introduces an identification procedure of the classical and modified scalar Preisach models based on genetic algorithms. It can be used when a reduced set of experimental data is known. The main advantage of this approach is the numerical stability of the solution. The results show that the coupling between our genetic identification procedure and the modified scalar Preisach model is able to reproduce the experimental behavior of different magnetic soft steels.     

Multiagent approach to solve project team work allocation problems

In today's fiercely competitive market, embedded software development teams are driven to do more with less: reduce time to market, costs and risk, while improving quality and predictability. There is also an increasing need to deliberately organise the teams that initially involves the division of the project into tasks; the selection of the right people; and the correct allocation of those tasks for the selected people. Team configuration process is typically performed by a project manager based on his/her past experience and the available (though frequently scarce, uncertain and dynamic) information about the cognitive, emotion and social characteristics of the potential team members. To support this decision-making process we propose the Fuzzy Belief-Desire-Intention architecture, a multiagent approach that given an initial team configuration and a set of tasks, simulates the most possible team performance. Its architecture bases are fuzzy set theory and fuzzy logic and it is implemented using Multiagent Systems technology in Java and Jadex. Tests have been carried out in which the architecture has been applied to a set of tasks involving the embedded software development. The result predicted by our architecture with the performance of an engineering team in a real industrial project is made.     

Applied column generation-based approach to solve supply chain scheduling problems

More and more enterprises have chosen to adopt a made-to-order business model in order to satisfy diverse and rapidly changing customer demand. In such a business model, enterprises are devoted to reducing inventory levels in order to upgrade the competitiveness of the products. However, reductions in inventory levels and short lead times force the operation between production and distribution to cooperate closely, thus increasing the practicability of integrating the production and distribution stages. The complexity of supply chain scheduling problems (integrated production and distribution scheduling) is known to be NP-hard. To address the issues above, an efficient algorithm to solve the supply chain scheduling problem is needed. This paper studies a supply chain scheduling problem in which the production stage is modelled by an identical parallel machine scheduling problem and the distribution stage is modelled by a capacitated vehicle routing problem. Given a set of customer orders (jobs), the problem is to find a supply chain schedule such that the weighted summation of total job weighted completion time and total job delivering cost are minimised. The studied problem was first formulated as an integer programme and then solved by using column generation techniques in conjunction with a branch-and-bound approach to optimality. The results of the computational experiments indicate that the proposed approach can solve the test problems to optimality. Moreover, the average gap between the optimal solutions and the lower bounds is no more than 1.32% for these test problems.     

Efficient numerical approach to unbounded systems subjected to a moving load

The present paper solves numerically the problem of vibrations of infinite structures under a moving load. A velocity formulation of the space–time finite element method was applied. In the case of simplex shaped space–time finite elements, the ‘steady state’ dynamic behaviour of the system was obtained. A properly performed discretization allowed of propagating information in a given direction at a limited velocity. The solutions were obtained under the assumption that the deformation is quasi-stationary, i.e., stationary in the coordinate system that moves with the load. The unbounded Timoshenko beam subjected to a distributed moving load was used as a test example. The dynamical system is placed on an elastic foundation. The matrices describing an infinite dynamical system subjected to a moving load are derived and the stability of the numerical scheme is analysed. The numerical results are compared with the analytical solutions in the literature and the classical numerical method.     

Perturbation technique and method of fundamental solution to solve nonlinear Poisson problems

We show in this work that the Asymptotic Numerical Method (ANM) combined with the Method of Fundamental Solution (MFS) can be a robust algorithm to solve the nonlinear Poisson problem. The ANM transforms the nonlinear problem into a sequence of linear ones which can be solved by MFS. This last method consists of approximating the solution of the linear Poisson problem by a linear combination of fundamental solutions. Some examples are presented to show the efficiency of the proposed method.     

Finite element solution to an elastica problem of beams

In this study, finite element solution procedures are developed for an elastica problem of inextensible beams. The element stiffness matrices are obtained by using Galerkin's method. Results of a numerical example compare reasonably well with those obtained by using the elliptical integral. Extensions of this research are currently being made to include membrane effects of beams and to develop plate element stiffness matrices for elastica problems of plate structures.     

高速滚动球轴承动态载荷计算改进方法的研究

在离心力和陀螺力矩的作用下,滚动球轴承高速旋转时的内部载荷分布与轴承静止情况下的载荷分布具有显著差异,其主要影响因素包括,滚动轴承的接触角、轴承预紧位移以及旋转速度等。基于JonesHarris(简称JH)力学模型的轴承载荷分布的分析方法已经得到了广泛的应用。然而其计算公式多、迭代繁琐、收敛速度慢。针对此现象,研究了轴承动态载荷分布规律及其算法,提出了改进的JH轴承数值计算模型,给出相应的简化计算步骤。计算与对比结果表明,改进的JH计算模型在其应用范围内,可以大幅减少计算时间。     

Approximate approach to solution of three-dimensional heat conduction problems

An approximate approach is presented for the solution of a three-dimensional heat conduction problem for one type of heat-protective coating frequently encountered in practice. The method proposed, based on the reduction of the initial three-dimensional problem to a set of two problems of less dimensionality, makes it possible, with satisfactory precision, to shorten substantially the computer time spent in determining thermal conditions of elements of a given design.Translated from Inzherneno-fizicheskii Zhurnal, Vol. 61, No. 2, pp. 319–322, August, 1991.     

An algebraic multigrid approach to solve extended finite element method based fracture problems

This article proposes an algebraic multigrid (AMG) approach to solve linear systems arising from applications where strong discontinuities are modeled by the extended finite element method. The application of AMG methods promises optimal scalability for solving large linear systems. However, the straightforward (or ‘black‐box’) use of existing AMG techniques for extended finite element method problems is often problematic. In this paper, we highlight the reasons for this behavior and propose a relatively simple adaptation that allows one to leverage existing AMG software mostly unchanged. Numerical tests demonstrate that optimal iterative convergence rates can be attained that are comparable with AMG convergence rates associated with linear systems for standard finite element approximations without discontinuities. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Multivariable approach to the finite difference solution of elasto-plastic problems

The solutions of plane elasto-plastic problems usually use one or two field variables—namely a stress functions or the displacements. The use of three, four or five field variables is investigated and it is concluded that the three stresses from the best basis for a multivariable approach. Attempts to solve the governing equations with an initial value technique were exhaustively tried and discarded in preference to a boundary value or elliptical technique. The problem solved to check the method is that of a hole in plane strain uniaxial tension. Effective plastic strain distributions are plotted, along with stress and strain concentration data and distributions of the mean to effective stress ratio. Comparison is made between solutions produced using incremental and deformation theories.     

3D-image restoration technique using Genetic Algorithm to solve blurring problems of images

Most images may not be sharp and clear due to various reasons like noise interference and is said to be in a blurred condition. Image de-blurring is fundamental in making pictures sharp and useful. Normally, along with the input blurred image, Point Spread Function (PSF) of the original image is required for the process of restoration and de-blurring. In this paper, we introduce a technique for image restoration by Richardson–Lucy algorithm where the optimised PSF is generated by the use of Genetic Algorithm (GA). Use of optimised PSF ensures that our proposed technique does not need the original image for the de-blurring purpose and can be greatly beneficial in the real time scenario cases. The dataset used for the evaluation of the proposed technique are real 3D images and the evaluation metrics used are peak signal-to-noise ratio (PSNR), Second-Derivative like Measure of Enhancement (SDME) and mean squared error (MSE). The technique is compared with existing techniques such as de-convolution method, regularisation filter, Wiener filter and Richardson–Lucy algorithm. From the results, we can observe that our proposed technique has achieved higher PSNR and SDME values and lower MSE values when compared with other techniques. We have achieved average PSNR of 70·94, SDME of 71·46 and MSE of 0·0063. The values obtained show the superior performance of the proposed technique.     

An accurate solution for the responses of circular curved beams subjected to a moving load

In this paper, an accurate and effective solution for a circular curved beam subjected to a moving load is proposed, which incorporates the dynamic stiffness matrix into the Laplace transform technique. In the Laplace domain, the dynamic stiffness matrix and equivalent nodal force vector for a moving load are explicitly formulated based on the general closed‐form solution of the differential equations for a circular curved beam subjected to a moving load. A comparison with the modal superposition solution for the case of a simply supported curved beam confirms the high accuracy and applicability of the proposed solution. The internal reactions at any desired location can easily be obtained with high accuracy using the proposed solution, while a large number of elements are usually required for using the finite element method. Furthermore, the jump behaviour of the shear force due to passage of the load is clearly described by the present solution without the Gibb's phenomenon, which cannot be achieved by the modal superposition solution. Finally, the present solution is employed to study the dynamic behaviour of circular curved beams subjected to a moving load considering the effects of the loading characteristics, including the moving speed and excitation frequency, and the effects of the characteristics of curved beams such as the radius of curvature, number of spans, opening angles and damping. The impact factors for displacement and internal reactions are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Boundary integral equation solution of moving boundary phase change problems

Boundary integral equation methods are presented for the solution of some two-dimensional phase change problems. Convection may enter through boundary conditions, but cannot be considered within phase boundaries. A general formulation based on space-time Green's functions is developed using the complete heat equation, followed by a simpler formulation using the Laplace equation. The latter is pursued and applied in detail. An elementary, noniterative system is constructed, featuring linear interpolation over elements on a polygonal boundary. Nodal values of the temperature gradient normal to a phase change boundary are produced directly in the numerical solution. The system performs well against basic analytical solutions, using these values in the interphase jump condition, with the simplest formulation of the surface normal at boundary vertices. Because the discretized surface changes automatically to fit the scale of the problem, the method appears to offer many of the advantages of moving mesh finite element methods. However, it only requires the manipulation of a surface mesh and solution for surface variables. In some applications, coarse meshes and very large time steps may be used, relative to those which would be required by fixed grid domain methods. Computations are also compared to original lab data, describing two-dimensional soil freezing with a time-dependent boundary condition. Agreement between simulated and measured histories is good.     

A general boundary element method approach to the solution of three-dimensional frictionless contact problems

A direct boundary element method is presented for three-dimensional stress analysis of frictionless contact problems. The isoparametric formulation of the boundary element method is implemented for the general case of contact in the absence of friction, which is limited to linear elastic homogeneous and isotropic materials. An iterative procedure is employed to determine the correct size of the contact zone by finding a boundary solution compatible with the contact condition. The applicability of the procedure is tested by application to three problems of advancing and conforming contact. The computed results are compared with numerical and analytical solutions where possible.     

用于多目标优化的蚁群算法的构建及其应用

从蚁群的生物学行为出发,将成群募集和海量募集两种机制融入蚁群算法,并针对多目标优化的特性,综合考虑解的被支配度和分散度,抽提出一种启发式规则,用以评价食物源的优劣,进而构建多目标连续蚁群优化算法(MO-CACO).通过两个多目标典型函数的优化测试,验证了MO-CACO具有较强的多目标全局寻优能力,且稳健性良好,所求得的最优解集的多目标值能均匀地逼近Pareto最优前沿的各部分.将MO-CACO用于二甲苯异构化装置的操作优化,取得了满意的结果,MO-CACO可为化工过程多目标决策提供支持.