大型锅炉支架结构承载性能的有限元分析

为准确快速地求解重型锅炉支架承载能力、变形和应力分布等,根据某重型锅炉支架结构的特点,利用ANSYS建立有限元模型.为真实反映整个支架的结构,减小因大量简化和近似带来的求解误差,所有梁柱的截面尺寸均与实际结构相符;在支架刚度和强度校核中考虑支架自重、锅炉重量和风载荷对支架的共同作用;对外围立柱进行变截面分析.计算结果表明当前设计的结构承载体是可靠的,支架变截面分析可以为进一步优化支架截面尺寸提供参考.     

Optimization of retaining wall design using evolutionary algorithms

This paper explores the performance of three evolutionary optimization methods, differential evolution (DE), evolutionary strategy (ES) and biogeography based optimization algorithm (BBO), for nonlinear constrained optimum design of a cantilever retaining wall. These algorithms are based on biological contests for survival and reproduction. The retaining wall optimization problem consists of two criteria, geotechnical stability and structural strength, while the final design minimizes an objective function. The objective function is defined in terms of both cost and weight. Constraints are applied using the penalty function method. The efficiency of the proposed method is examined by means of two numerical retaining wall design examples, one with a base shear key and one without a base shear key. The final designs are compared to the ones determined by genetic algorithms as classical metaheuristic optimization methods. The design results and convergence rate of the BBO algorithm show a significantly better performance than the other algorithms in both design cases.     

空间钢框架全焊接节点抗火设计的有限元分析

为考察钢框架梁-柱连接的抗火性能,建立平面钢框架全焊接节点有限元模型,用ANSYS分析其在火载荷作用下的行为,得到的温度-转角曲线与试验数据基本吻合;通过数值模拟得到不同载荷比值下的4种空间钢框架全焊接节点的温度-转角曲线.结果表明:载荷比值不同,空间钢框架全焊接节点在火灾作用下的临界温度不同;在相同的载荷比值下,不同空间钢框架全焊接节点的临界温度也不相同.在空间钢框架全焊接节点的抗火设计中,应加强对H型柱翼缘与梁连接方向的边节点和角节点的防火保护.     

Buckling analysis of imperfect frames using a stochastic finite element method

A stochastic finite element method is developed for the buckling analysis of frames with random initial imperfections, uncertain sectional and material properties. The random geometrical imperfections of the frames are described by member initial crookednesses which are modeled as given initial displacement functions with amplitudes treated as random variables. The effects of the random initial geometric imperfections are formulated as a set of equivalent random nodal coordinates in the finite element discretization of the members. The mean-centered second-order perturbation technique is used to formulate the stochastic finite element method for the buckling analysis of the imperfect frames. Use of the present method is illustrated by several examples of buckling analysis of random frames. Results derived from the Monte Carlo method are also obtained for comparison.     

Finite element response sensitivity analysis: a comparison between force-based and displacement-based frame element models

This paper focuses on a comparison between displacement-based and force-based elements for static and dynamic response sensitivity analysis of frame type structures. Previous research has shown that force-based frame elements are superior to classical displacement-based elements enabling, at no significant additional computational costs, a drastic reduction in the number of elements required for a given level of accuracy in the simulated response. The present work shows that this advantage of force-based over displacement-based elements is even more conspicuous in the context of gradient-based optimization methods, which are used in several structural engineering sub-fields (e.g., structural optimization, structural reliability analysis, finite element model updating) and which require accurate and efficient computation of structural response and response sensitivities to material and loading parameters. The two methodologies for displacement-based and force-based element sensitivity computations are compared. Three application examples are presented to illustrate the conclusions. Material-only non-linearity is considered. Significant benefits are found in using force-based frame element models for both response and response sensitivity analysis in terms of trade-off between accuracy and computational cost.     

Static stress analysis of a composite bevel gear using a three-dimensional finite element method

The possibility of using composite materials for power transmission spur gear, from a static strength point of view, have been proved by the authors in their previous study. In this present work an attempt has been made to study the behaviour of composite bevel gear from a static load point of view using a three-dimensional finite element method. The performance of two composite material bevel gears are presented and compared with a carbon steel gear. From a static strength point of view a glass epoxy bevel gear is slightly closer to a carbon steel bevel gear than a boron/epoxy bevel gear; but from a displacement point of view glass/epoxy deviates from that of carbon steel much more than boron/epoxy, unlike the case of a composite spur gear, where boron/epoxy was better both from strength and displacement points of view. Hence from the results it is concluded that composite materials such as boron/epoxy can be very much thought of as a material for power transmission bevel gears.     

Shape sensitivity analysis using the indirect boundary element method

The paper describes a novel formulation for the computation of the design sensitivities required for shape optimization problems using the indirect boundary element method. As a first stage, the system of equations that evaluate the fictitious traction sensitivities is differentiated with respect to shape design variables. The stress or displacement sensitivities are then evaluated by direct substitution of the fictitious traction sensitivities into the differentiated stress or displacement kernels. Two other finite difference-based techniques for the evaluation of the stress sensitivities, using the indirect boundary element method are also presented. The advantages and the drawbacks of each approach are discussed. These methods have been shown to be effective, accurate and can be incorporated in an existing BE code with much less programming effort than other BE-based techniques. The efficiency of the three methods is illustrated by optimizing the shape of a 90° V-notch. In all cases, convergence is achieved within three to four iterations.Various approximate techniques are suggested to minimize the computation cost of the optimization problem. These techniques are based on the fundamental features of the stress field, the differentiated kernels and the system of matrices of the optimization problem. Investigations have shown that employing these techniques yields more than a 50% reduction in computer time with insignificant loss of accuracy.     

A robust predictive model for base shear of steel frame structures using a hybrid genetic programming and simulated annealing method

This study presents a new empirical model to estimate the base shear of plane steel structures subjected to earthquake load using a hybrid method integrating genetic programming (GP) and simulated annealing (SA), called GP/SA. The base shear of steel frames was formulated in terms of the number of bays, number of storey, soil type, and situation of braced or unbraced. A classical GP model was developed to benchmark the GP/SA model. The comprehensive database used for the development of the correlations was obtained from finite element analysis. A parametric analysis was carried out to evaluate the sensitivity of the base shear to the variation of the influencing parameters. The GP/SA and classical GP correlations provide a better prediction performance than the widely used UBC code and a neural network-based model found in the literature. The developed correlations may be used as quick checks on solutions developed by deterministic analyses.     

Nonlinear analysis of skew plates using the finite element method

In this paper finite element analysis of the large deflection behaviour of skew plates has been done. A high precision conforming triangular plate bending element has been used. The central deflection, bending and membrane stresses have been reported for simply supported and clamped rhombic plates. The variations of these quantities have been studied for different skew angles.     

Finite element analysis of triangular fins attached to a thick wall

Heat conduction in an array of triangular fins with an attached wall is modeled using the finite element method. An adaptive mesh refinement technique is developed giving accuracy comparable to uniform mesh refinement and much increased computational efficiency. The effects of wall thickness and fin spacing are examined for various Biot numbers. It is shown that for low Biot numbers (Bi < 0.1), the one-dimensional assumption is valid but for higher Biot numbers (Bi 0.1), two-dimensional heat conduction must be considered, temperature distributions at the fin root are always non-uniform and the fin is found not to be effective.     

Stability analysis for plates using the multivariable spline element method

The multivariable spline element method is used in this paper to solve the stability problems of plates and beams. The bicubic spline functions are employed to construct the bending moments, twisting moments and transverse displacements field. The spine eigenvalue equations with multiple variables are derived based on the Hellinger-Reissner mixed variational principle. Some numerical examples are given, the results are good agreement with other methods.     

Inverse analysis FOR two-dimensional structures using the boundary element method

Inverse analysis is currently an important subject of study in several fields of science and engineering. The identification of physical and geometric parameters using experimental measurements is required in many applications. In this work a boundary element formulation to identify boundary and interface values as well as material properties is proposed. In particular the proposed formulation is dedicated to identifying material parameters when a cohesive crack model is assumed for 2D problems. A computer code is developed and implemented using the BEM multi-region technique and regularisation methods to perform the inverse analysis. Several examples are shown to demonstrate the efficiency of the proposed model.     

输电角钢铁塔试验与有限元分析对比方法研究

目前,国内设计研究人员进行了大量的真型铁塔试验,但这些试验大多侧重于对铁塔整体进行承载能力的验证,而对主要受力构件在试验加载情况下的实测内力与理论计算内力进行对比分析的不多,并且在已有的对比分析文献中,构件的试验结果与有限元分析计算结果出入较大的情况比较多。有鉴于此,本文对铁塔主要受力构件进行了理论计算与试验结果的对比方法研究,分析了不同类型构件应力、应变的分布特点,提出了换算内力对比法,将试验应变实测值换算成试验内力值,与有限元分析的理论计算内力值进行对比,得出了较为满意的结果。这一方法对于提升试验成果应用价值,帮助设计人员深刻认识结构传力途径,进一步优化结构设计具有重要意义。     

Finite element analysis of steel rolling processes

The numerical simulation of rolling processes requires the coupling of several models that describe different physical phenomena such as the deformation of the work-piece together with its thermo-metallurgical evolution and the thermal evolution of the rolls together with its mechanical deformation. In this paper we develop the coupling between the purely mechanical model of the work-piece and the thermo-mechanical model of the rolls. We test the numerical formulation in the analysis of the hot rolling of steel coils and in the analysis of the hot mandrel rolling of seamless steel tubes.     

Shape and topology optimization for closed liquid cell materials using extended multiscale finite element method

A new multiscale shape and topology optimization method is presented to design closed liquid cell materials based on the extended multiscale finite element method, which directly captures the small scale features to the large scale computation. The multiscale optimization method firstly focuses on seeking the optimum geometrical parameters and volume expansion of the fluid in the closed liquid cells in the microscale level in terms of maximizing the macroscale mechanical response of the structure. Furthermore, a new hierarchical multiscale optimization method is developed to optimize the macroscale distributions of closed liquid cells and the microscale shape of the fluid inclusion in the cells. In the macroscale level of the multiscale optimization method, the macroscale design domain is discretized by the multiscale coarse elements, while the shape of the fluid inclusions is set to be the design parameters in the microscale level. This method is firstly utilized to minimize the system compliance of the closed liquid cell structure. Moreover, due to the fact that non-uniform volume expansions of the fluid in cells can induce the elastic action, the multiscale optimization method is further extended to design biomimetic compliant actuators of the closed liquid cell materials. The multiscale optimization methods developed are implemented in the FE-package SiPESC, and the numerical examples are carried out to validate the accuracy of the methods proposed.     

Elasto-plastic analysis of single-angle bolted-welded connections using the finite element method

The results of an extensive numerical elaslo-plastic study of single-angle connections subjected to cyclic loading consisting of end shear and bolt-moment are discussed. The thrust of the study is directed towards an improved understanding of the stress variations and the propagation of plastic zones in the vicinity of the weld.     

A Large scale finite element analysis using domain decomposition method on a parallel computer

A parallel finite element analysis based on a domain decomposition technique (DDT) is considered. In the present DDT, an analysis domain is divided into a number of smaller subdomains without overlap. Finite element analyses of the subdomains are performed under the constraint of both displacement continuity and force equivalence among them. The constraint is satisfied through iterative calculations based on either the Uzawa algorithm or the Conjugate Gradient (CG) method. Owing to the iterative algorithm, a large scale finite element analysis can be divided into a number of smaller ones which can be carried out in parallel.

The DDT is implemented on a parallel computer network composed of a number of 32-bit microprocessors, transputers. The developed parallel calculation system named the ‘FEM server type system’ involves peculiar features such as network independence and dynamic workload balance.

The characteristics of the domain decomposition method such as computational speed and memory requirement are first examined in detail through the finite element calculations of homogeneous or inhomogeneous cracked plate subjected to a tensile load on a single CPU computer.

The ‘speedup’ and ‘performance’ features of the FEM server type system are discussed on a parallel computer system composed of up to 16 transputers, with changing network types and domain decompositions. It is clearly demonstrated that the present parallel computing system requires a much smaller amount of computational memory than the conventional finite element method and also that, due to the feature of dynamic workload balancing, high performance (over 90%) is achieved even in a large scale finite element calculation with irregular domain decomposition.     

Error analysis of a Galerkin method to solve the forward problem in MEG using the boundary element method

Sources of brain activity, e.g. epileptic foci, can be localized with Magnetoencephalography (MEG) measurements by recording the magnetic field outside the head. For a successful surgery a very high localization accuracy is needed. The most often used conductor model in the source localization is an analytic sphere, which is not always adequate, and thus a realistically shaped conductor model is needed. In this paper we examine a Galerkin method with linear basis functions to solve the forward problem in MEG using the boundary element method. Its accuracy is compared to the collocation method with constant and linear basis functions. The accuracies are determined for a unit sphere for which analytic solutions are available. The Galerkin method gives a clear improvement in the accuracy of the forward problem especially for the tangential component of the magnetic field. At realistic MEG measurement distances from the brain the Galerkin method reaches a given accuracy with lower computational costs than the collocation methods starting from a few hundreds of unknowns. With larger meshes the difference for the Galerkin method increases significantly.     

A new strategy for stress analysis using the finite element method

In this paper the authors examine the effectiveness of the Powell-Toint strategy for evaluating the Hessian of the potential energy surface of a finite element model that can be used for linear stress analysis and transient response predictions of structures. Cases for which the Powell-Toint strategy may be cost-effective with the conventional method of stress analysis are identified.