Finite element of slender beams in finite transformations: a geometrically exact approach

This article is devoted to the modelling of thin beams undergoing finite deformations essentially due to bending and torsion and to their numerical resolution by the finite element method. The solution proposed here differs from the approaches usually implemented to treat thin beams, as it can be qualified as ‘geometrically exact’. Two numerical models are proposed. The first one is a non‐linear Euler–Bernoulli model while the second one is a non‐linear Rayleigh model. The finite element method is tested on several numerical examples in statics and dynamics, and validated through comparison with analytical solutions, experimental observations and the geometrically exact approach of the Reissner beam theory initiated by Simo. The numerical result shows that this approach is a good alternative to the modelling of non‐linear beams, especially in statics. Copyright © 2003 John Wiley & Sons, Ltd.     

A coupling of multi‐zone curved Galerkin BEM with finite elements for independently modelled sub‐domains with non‐matching nodes in elasticity

When the different parts of a structure are modelled independently by BEM or FEM methods, it is sometimes necessary to put the parts together without remeshing of the nodes along the part interfaces. Frequently the nodes do not match along the interface. In this work, the symmetric Galerkin multi‐zone curved boundary element is a fully symmetric formulation and is the method used for the boundary element part. For BEM–FEM coupling it is then necessary to interpolate the tractions in‐between the non‐matching nodes for the FEM part. Finally, the coupling is achieved by transforming the finite element domains to equivalent boundary element domains in a block symmetric formulation. This system is then coupled with a boundary element domain with non‐matching nodes in‐between. Copyright © 2004 John Wiley & Sons, Ltd.     

Three‐dimensional finite element computations for frictional contact problems with non‐associated sliding rule

This paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non‐associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non‐associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi‐axes ratio. The frictional contact law and its inverse are derived from a single non‐differentiable scalar‐valued function, called a bi‐potential. The convexity properties of the bi‐potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time‐integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no‐contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour. Copyright 2004 John Wiley & Sons, Ltd.     

A spectral‐element method for modelling cavitation in transient fluid–structure interaction

In an underwater‐shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite‐element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high‐order Legendre‐polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non‐conformal coupling method for the structure and fluid finite‐element models, and (iv) introducing structure–fluid time‐step subcycling. Field separation provides flexibility, as it admits non‐acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non‐conformal coupling affords order‐of‐magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd.     

A changing range genetic algorithm

During the last decade various methods have been proposed to handle linear and non‐linear constraints by using genetic algorithms to solve problems of numerical optimization. The key to success lies in focusing the search space towards a feasible region where a global optimum is located. This study investigates an approach that adaptively shifts and shrinks the size of the search space to the feasible region; it uses two strategies for estimating a point of attraction. Several test cases demonstrate the ability of this approach to reach effectively and accurately the global optimum with a low resolution of the binary representation scheme and without additional computational efforts. Copyright © 2004 John Wiley & Sons, Ltd.     

Assessment of oxygen levels in convenience‐style muscle‐based sous vide products through optical means and impact on shelf‐life stability

An optical oxygen analyser was used in two small‐scale industrial trials to non‐destructively assess the quality of packaged convenience foods and packaging process. Beef lasagne packed under 70% vacuum and cooked under standard sous vide conditions was monitored for residual oxygen, using disposable sensors incorporated in each pack and a benchtop optical oxygen analyser. High levels of residual oxygen close to ambient were determined in the majority of packs after packaging, as opposed to anticipated levels of 4–5%. Residual oxygen was monitored over product shelf‐life (4 weeks at +4–10°C) along with measurement of microbial growth and lipid oxidation in food by conventional destructive methods. Oxygen levels in packs went down to almost zero between weeks 2 and 3 indicating deterioration of packaged product. Correlation between oxygen profiles and the rate of microbial growth and lipid oxidation was established. The optical oxygen sensor system was shown to provide valuable information about performance of the packaging process, product storage conditions and food quality in a convenient and cost‐efficient fashion and non‐destructively. Copyright © 2004 John Wiley & Sons, Ltd.     

限幅型非光滑吸振器模型的稳定性与周期运动研究

本文研究具有分段光滑特性的限幅型吸振器模型的稳定性与周期运动. 建立一类限幅型非光滑吸振器的动力学模型,探讨模型容许平衡点的存在性,通过Liénard-Chipart稳定性准则,分析容许平衡点的稳定性. 通过参数变换,将限幅型吸振器模型转化为具有两个切换流形的四维分段光滑系统. 通过计算系统首次积分,获得四维含参分段光滑动力系统在其未扰系统存在一族周期轨条件下的Melnikov函数. 探讨不同参数条件下系统周期轨的存在性及个数,并利用数值模拟方法给出其相图构型,验证理论结果的正确性. 研究结果表明不同的间隙参数影响系统周期轨个数及相对位置.     

消应力退火对无取向硅钢组织和磁性能的影响

采用连续退火和井式退火两种消应力退火工艺生产35SW440牌号的爱泼斯坦方圈样,并对不同消应力退火工艺与组织、析出及磁性能之间的关系进行了比较研究。结果表明：一次退火板经消应力退火后铁损明显降低,磁感增加。与井式退火工艺相比,连续退火工艺生产的铁心在高磁密条件下磁性能较差,主要原因是带钢表面出现了明显的表面渗氮现象。表面渗氮源于其保护气氛、退火工艺设计不合理,形成大量细小弥散的AlN析出物。AlN析出物通过影响磁畴壁和磁矩运动,恶化磁性能。井式退火工艺由于有效控制了带钢表面渗氮,显著降低了电工钢片高磁密下铁损值,使成品铁心性能指标得到改善。     

低强度锚固体养护时间和频率对导波速度的影响

组装了一套超声导波无损检测系统.制作了两个长度为1 m,28 d锚固体单轴抗压强度分别为4.36 MPa和4.69 MPa的全锚锚杆.利用该系统对这两个锚杆在各个养护期,从40～100 kHz的超声导波速度进行了测试,以研究水泥砂浆的养护期和导波频率对波速的影响.研究结果表明,在测试频率范围内,低强度锚固锚杆中导波速度随频率的增加而增加,在试件1和试件2中分别增加了10.1%和8.2%;水泥砂浆的养护期对导波速度影响也很大,尤其在养护初期速度随时间的增加而明显下降,最大降幅达29.4%(养护第7天),但在中后期波速变化不太明显,只有略微上升.试验结果与理论分析相吻合.     

1 000 MW超超临界锅炉分离器制造难点解析

介绍了超超临界锅炉中分离器的主要特点及制造难点,对非向心孔的加工,非向心管接头坡口的加及其装焊等问题,分别进行了论述。