Study on sub‐cycling for flexible multi‐body dynamics based on Newmark method

A sub‐cycling algorithm presented by Belytschko and Mullen (Int. J. Numer. Meth. Engng 1978; 12 (10):1575–1586) has been successfully applied in the finite element method. However, the problem of how to apply the sub‐cycling to flexible multi‐body dynamics (FMD) still lacks investigation. This paper presents a Newmark‐based sub‐cycling, which is suitable for solving condensed FMD models. Common‐step update formulae and sub‐step update formula for the sub‐cycling are established based on the original Newmark integration algorithm. Stability of the procedure is validated by means of energy balance checking during the integral process. Numerical examples indicate that the sub‐cycling is able to enhance the computational efficiency without dropping accuracy greatly. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulation of Rayleigh waves in cracked plates

The aim of this paper is to develop new numerical procedures to detect micro cracks, or superficial imperfections, in thin plates using excitation by Rayleigh waves. We shall consider a unilateral contact problem between the two sides of the crack in an elastic plate subjected to suitable boundary conditions in order to reproduce a single Rayleigh wave cycle. An approximate solution of this problem will be calculated by using one of the Newmark methods for time discretization and a finite element method for space discretization. To deal with the nonlinearity due to the contact condition, an iterative algorithm involving one multiplier will be used; this multiplier will be approximated by using Newton's techniques. Finally, we will show numerical simulations for both cracked and non‐cracked plates. Copyright © 2006 John Wiley & Sons, Ltd.     

论隐喻的翻译--兼评刘重德、Newmark的相关见解

隐喻的首创和使用反映出作家的创作个性和想象力,它以新颖、奇妙、鲜明的形象感染读者,具有不同寻常的认知、审美能力.在分析隐喻的本质的基础上,评估了刘重德和Newmark关于翻译中隐喻移植问题的观点,将他们倡导的隐喻翻译方法,加以比较,提出建构在"归化"基础上的五种译法.     

Pseudo-dynamic analysis of a cemented hip arthroplasty using a force method based on the Newmark algorithm

The main goal of this work was to develop an approached model to study dynamic behavior and prediction of the stress distribution in an in vitro Charnley cemented hip arthroplasty. An alternative version of the described pseudo-dynamic procedure is proposed by using the time integration Newmark algorithm. An internal restoring force vector is numerically calculated from the displacement, velocity, and acceleration vectors. A numerical model of hip replacement was developed to analyze the deformation of a dynamically stressed structure for all time steps. The experimental measurement of resulting internal forces generated in the structure (internal restoring force vector) is the second fundamental step of the pseudo-dynamic procedure. These data (as a feedback) are used by the time integration algorithm, which allows updating of the structure's shape for the next displacement, velocity, and acceleration vectors. In the field of Biomechanics, the potentialities of this method contribute to the determination of a dynamically equivalent in vitro stress field of a cemented hip prosthesis; implant fitted in patients with a normal mobility or practice sports. Consequences of the stress distribution in the implant zone that underwent cyclic fatigue loads were also discussed by using a finite element model. Application of this method in Biomechanics appears as a useful tool in the approximate stress field characterization of the peak stress state. Results show a peak value around two times the static situation, more for making possible the prediction of future damage and a programed clinical examination in patients using hip prosthesis.     

主动液压激波作用下管道振动控制的运动分析与试验研究

为研究在主动液压激波作用下管道振动的动力学特性,建立流体的数学模型,设计出变频液压管网激振测试系统,用特征线法编程对激波作用下的有压脉动内流进行数值模拟。采用有限元法把管道简化为梁模型,建立考虑流固耦合的充液管道在激波作用下的振动方程,在保证特征线各断面与有限元节点重合的前提下,采用Newmark法编程将特征线法求得的流体各断面横向压力载荷施加到管道有限元的单元节点上,求得各断面处的动力响应。仿真结果表明,管道在轴向弹性支撑条件下,在激波作用下管道各断面压力和流速为简谐波,但两者呈反相关系。其横向各断面运动为简谐振动,振幅随系统压力的升高而升高,发现管道横向各断面振动波明显滞后于各断面对应的压力波,而轴向振动则由于弹簧与液体轴向力的耦合作用而出现较高的振动频率。数值模拟结果与试验结果基本比较吻合,揭示出流体动力学参数与管道振动之间的耦合关系,为激波作用下管道的二维振动特性及可控性研究提供了一些理论依据。     

An ALE finite element method for baffled fuel container in Yawing motion

A computational analysis of engineering problems with moving domain or/and boundary according to either Lagrangian or Eulerian approach may encounter inherent numerical difficulties, the extreme mesh distortion in the former and the material boundary indistinctness in the latter. In order to overcome such defects in classical numerical approaches, the ALE (arbitrary Lagrangian Eulerian) method is widely being adopted in which the finite element mesh moves with arbitrary velocity. This paper is concerned with the ALE finite element formulation, aiming at the dynamic response analysis of baffled fuel-storage container in yawing motion, for which the coupled time integration scheme, the remeshing and smoothing algorithm and the mesh velocity determination are addressed. Numerical simulation illustrating theoretical works is also presented.     

求解弹塑性结构动力响应的变步距直接积分法

本文提出了一种适用于直接积分法的单步误差估计、步距自适应控制算法,并用于求解弹塑性结构的动力响应。本算法可以明显地提高直接积分法的计算精度和计算的过程收敛速度。     

Time probabilistic evaluation of seismically induced landslide hazard in Irpinia (Southern Italy)

A recently proposed method, which incorporates the Newmark model to evaluate the earthquake-induced landslide hazard at regional scale, was applied to Irpinia, one of the most seismically active regions of Italy. The method adopts a probabilistic approach to calculate values of critical acceleration a_c representing the minimum strength required for a slope not to fail at a fixed probability level in a given time interval. Regional probabilistic hazard maps were generated for the two failure types most common in Irpinia (slump–earthflows and rock falls). The results suggest that quite moderate critical acceleration (0.05–0.08 g) could suffice to keep the slope failure probability low. However, the available data indicate that potential slide surfaces with a_c below these values could be common in Irpinia, where, perhaps in relation to particular geo-environmental conditions, a relative large number of marginally stable slopes might survive other destabilising actions and fail even on occasion of not particularly strong earthquake shaking.     

蒙特卡罗模拟在区域地震滑坡灾害评价中应用

2004年10月23日,日本新泻中越地区发生史上最强地震之一,震级达到Mw6.6。这次地震诱发上千个规模大小不一、形式各样的滑坡,造成一定的灾害损失和人员伤亡。因此,为了有效地避免和减轻这方面的灾害,有必要有效地、科学地预测和评价地震诱发滑坡的空间发生规律。为此以一定的地区作为研究对象,提出了蒙特卡罗随机模拟和Newmark滑动体位移分析法在区域地震斜坡失稳概率分析中的应用。该法充分考虑到岩土参数和相关地震参数空间变异性,结合地理信息系统空间分析的优势,以网格模型为基础,分析该区斜坡滑动体位移分布规律,并以2cm为失稳临界值探讨网格斜坡破坏的概率。实例证明,所提出的模型有效地预测了滑坡发生的空间分布规律。     

汽车碰撞波形梁半刚性护栏的简化计算

应用Newmark β法,对汽车碰撞半刚性护栏进行简化计算,解决碰撞过程中的非线性问题.分别对不考虑汽车转动和考虑汽车转动建立了简化模型,对汽车碰撞护栏进行时程分析.通过与LS-DYNA有限元模拟结果对比表明,考虑汽车转动的简化计算方法能较准确地对碰撞过程进行时程分析,帮助护栏设计人员更清楚了解碰撞过程和碰撞作用机理,有利于护栏的优化设计.