并行多步法及其在两铰圆拱动力响应中的应用

本文在基于个人计算机ｔｒａｎｓｐｕｔｅｒ并处理子母板系统上提供了一种结构动力分析中适合于并行处理的对时间域积分的多步法－并行多步法。并用此方法对两铰弹性圆２拱在矩形荷载作用下的动力响应进行分析，算例表明，对于四处理器系统算法加速比可达３．０５，效率为７６．２５％，对圆拱的分析表明，当中心角之半θ０较小时，矩形荷载作用完后圆拱在偏离原静止状态的位置附近自由振动，这主要是由于几何非线性所致。     

弹性圆拱在考虑几何非线性和初始缺陷情况下的动力稳定性分析

本文由虚功原理建立弹性圆拱的平衡方程,用有限差分法对非线性偏微分方程组进行求解(Park法对时间进行差分)。在考虑几何非线性和初始几何缺陷情况下对铰支、固支圆拱在均布突加阶跃荷载作用下的动力稳定性进行分析。结果表明:圆拱中心角的大小、边界条件及初始缺陷幅值都对圆拱失稳模态有影响。文中分析了直接、间接两种失稳形式。并给出了不同初始缺陷及边界条件下圆拱中心角对比值Pd/Pa(Pd为动力稳定临界值,Ps为静力稳定临界值)的影响。     

几何缺陷浅拱的动力稳定性分析

研究了几何缺陷对粘弹性铰支浅拱动力稳定性能的影响。从达朗贝尔原理和欧拉-贝努利假定出发推导了粘弹性铰支浅拱在正弦分布突加荷载作用下的动力学控制方程,并采用Galerkin截断法得到了可用龙格-库塔法求解的无量纲化非线性微分方程组。同时引入能有效追踪结构动力后屈曲路径的广义位移控制法,对含几何缺陷浅拱的响应曲线进行几何、材料双重非线性有限元分析。用这两种方法分析了前三阶谐波缺陷对浅拱动力稳定性能的影响,其中动力临界荷载由B-R准则判定。主要结论有:材料粘弹性使浅拱动力临界荷载增大且结构响应曲线与弹性情况差别很大;二阶谐波缺陷影响显著,它使动力临界荷载明显下降且使得浅拱粘弹性动力临界荷载可能低于弹性动力临界荷载。     

两铰弹性圆拱的动力屈曲

1 引言稳定性准则在系统稳定分析中占有极其重要的地位.对于保守系统而言,Budiansky-Roth 准则,或称运动方程法,是目前动力稳定数值分析中普遍采用的方法.对于弹性结构,若荷载参数的微小变化,引起响应幅值的巨大变化,则称结构丧失动力稳定性,即结构在Liapunov 意义上丧失稳定性.本文采用此准则判别弹性圆拱在均布突加阶跃荷载作用下的动力稳定性.     

拉索预应力巨型网格结构参激振动及动力稳定性研究

针对拉索预应力巨型网格结构的参激振动及动力稳定性问题进行了研究。首先建立索-拱简化模型，分析了桁架拱拉索参激振动的诱发机制与特征，并利用ANSYS软件进一步探究了参激振动的影响因素，然后对简谐荷载作用下拉索预应力桁架拱及整体结构的动力稳定性进行了分析。研究表明：当结构振动频率为索基频的2倍左右时，拉索会发生参激振动，振动响应特征与激励幅值、阻尼、拉索初张力、支承方式等相关；拉索预应力桁架拱在水平简谐荷载作用下一般会发生动力失稳破坏，在竖向简谐荷载作用下发生动力强度破坏，拉索预应力巨型网格整体结构在简谐荷载作用下通常发生动力失稳破坏。     

动支座对拱结构抗爆承载力的影响

建立了具有动支座拱的计算模型,该模型考虑了竖向的弹性支承和阻尼支承、水平向弹性支承和扭转约束等柔性支承形式。基于大变形动力微分方程并利用有限差分方法,研究了动支座拱在爆炸荷载作用下的动力响应,并分析动支座对结构承载力的影响。研究表明:动支座对拱的抗爆承载能力有较大影响,不同形式的柔性支承对拱承载力的影响截然不同,竖向弹性支承能够使爆炸荷载作用下拱的弯矩峰值减小,并且使到达峰值的时间增加,提高了拱的抗爆或承受瞬态荷载的能力。而水平弹性支承使拱的内力值和相对位移值增大,对结构的承载力不利。     

钢筋混凝土拱的水下抗爆性能

为探究水下爆炸荷载作用下钢筋混凝土拱的动力响应特性和破坏特征,制作了两个钢筋混凝土拱试件,并开展了水下爆炸试验。试验分为拱外爆炸和拱内爆炸两组,采用10 g乳化炸药,试验时爆源距结构面最小距离为10 cm（起爆点位于拱结构正上方和正下方）,通过传感器记录爆炸试验中钢筋混凝土拱典型断面处的水压力及加速度时程曲线。基于Arbitrary Lagrange-Euler (ALE)算法,建立了空气-水-炸药-钢筋混凝土拱等多介质动态耦合作用模型,将数值模拟结果与试验结果对比,验证了数值方法的可靠性。采用验证后的数值模型进一步研究了拱外及拱内爆炸荷载作用下钢筋混凝土拱的动力响应差异。结果表明：相同炸药当量下,内部爆炸有更多的能量作用于混凝土拱,使结构的动力响应更强烈;外部爆炸下,拱顶、拱腰处产生较大裂缝;内部爆炸时,迎爆面裂缝数量明显增多,拱肩位置出现裂缝。钢筋混凝土拱形结构抵抗外部爆炸荷载的能力明显强于内部爆炸荷载。     

子弹撞击作用下固支浅圆拱的弹塑性动力响应

基于大变形动力学微分方程并利用有限差分离散分析,研究了子弹撞击作用下固支浅圆拱的弹塑性动力响应。通过对响应不同时刻内力分布特征的分析,阐明了圆拱的响应模式和变形机制。研究表明,弹塑性响应过程可分为六个阶段。在响应早期,拱的变形以塑性弯曲挠动由撞击点向拱根部传播为主;在响应后期,则主要以轴力主导下的轴向拉伸变形为主。在高速撞击下,塑性弯曲挠动的不均匀性可以引起浅拱的反向弯曲变形。固支浅圆拱的动力响应对撞击速度的某个变化范围非常敏感,在此范围内,撞击速度的较小增加可以导致响应的很快增长,但动力响应随撞击速度连续变化,未发生突然的跳跃失稳。本文中计算结果同实验数据吻合较好。     

拱暨索拱面内稳定性研究的传递矩阵法

为探究拱桥面内稳定问题求解的新途径,应用传递矩阵法对径向均布荷载作用下的圆拱面内屈曲微分方程进行解答,利用边界条件导出其特征方程,从而求得其屈曲荷载。同时,结合力法以及拱上荷载集度与轴力的关系,将该理论方法推广到承受集中荷载的变截面拱以及索拱组合结构的稳定分析中,并和有限元ANSYS计算结果进行对比,验证了本文理论和方法的正确性。最后,研究了不同荷载工况下的边界条件、圆心角和截面惯性矩对拱结构面内稳定性的影响。结果表明,索拱结构的面内稳定性优于纯拱结构。     

跨中集中荷载作用下弹性约束圆弧拱的稳定性分析

研究了跨中集中荷载作用下两端由不同转动刚度弹性约束的铰支圆弧拱的面内稳定性。由变形几何关系、变分原理得到了拱的非线性平衡方程,建立了外荷载、结构内力、径向位移的对应关系,通过定义拱的深浅参数和约束刚度参数进行分析,并得到了跳跃屈曲和分岔屈曲的发生条件及存在区间。通过数值分析可知本文方法所得屈曲路径和屈曲荷载与有限元法所得结论吻合良好,极值点、临界荷载相对差值在1%左右。对不同结构参数区间圆弧拱在集中荷载作用下的屈曲路径和临界荷载进行了分析,结果表明约束刚度对屈曲路径和临界荷载起决定性的作用,深浅参数决定屈曲发生条件、屈曲形式、极值点对数。     

Nonlinear dynamic buckling of pinned–fixed shallow arches under a sudden central concentrated load

The structural behavior of a shallow arch is highly nonlinear, and so when the amplitude of the oscillation of the arch produced by a suddenly-applied load is sufficiently large, the oscillation of the arch may reach a position on its unstable equilibrium paths that leads the arch to buckle dynamically. This paper uses an energy method to investigate the nonlinear elastic dynamic in-plane buckling of a pinned–fixed shallow circular arch under a central concentrated load that is applied suddenly and with an infinite duration. The principle of conservation of energy is used to establish the criterion for dynamic buckling of the arch, and the analytical solution for the dynamic buckling load is derived. Two methods are proposed to determine the dynamic buckling load. It is shown that under a suddenly-applied central load, a shallow pinned–fixed arch with a high modified slenderness (which is defined in the paper) has a lower dynamic buckling load and an upper dynamic buckling load, while an arch with a low modified slenderness has a unique dynamic buckling load.     

Numerical modeling of elastic waves in micropolar plates and shells taking into account inertial characteristics

Mathematical models of micropolar plates and shells are considered within the framework of the approximation approach. The governing equations of the theories are written in a thermodynamically consistent form of the conservation laws. This ensures hyperbolicity and correctness of the initial boundary value problems. For numerical solution, we propose parallel algorithms for supercomputers with graphics processing units. The algorithms are based on the splitting method with respect to spatial variables. We present the results of numerical computations of wave propagation in micropolar rectangular plates and cylindrical panels for media with different types of microstructure particles.     

Improved frequency modeling and solution for parallel liquid-filled pipes considering both fluid-structure interaction and structural coupling

The dynamic characteristics of a single liquid-filled pipe have been broadly studied in the previous literature. The parallel liquid-filled pipe (PLFP) system is also widely used in engineering, and its structure is more complex than that of a single pipe. However, there are few reports about the dynamic characteristics of the PLFPs. Therefore, this paper proposes improved frequency modeling and solution for the PLFPs, involving the logical alignment principle and coupled matrix processing. The established model incorporates both the fluid-structure interaction (FSI) and the structural coupling of the PLFPs. The validity of the established model is verified by modal experiments. The effects of some unique parameters on the dynamic characteristics of the PLFPs are discussed. This work provides a feasible method for solving the FSI of multiple pipes in parallel and potential theoretical guidance for the dynamic analysis of the PLFPs in engineering.     

Parallel CFD fire modelling on office PCs with dynamic load balancing

Parallel processing techniques have been used in the past to provide high performance computing resources for activities such as Computational Fluid Dynamics. This is normally achieved using specialized hardware and software, the expense of which would be difficult to justify for many fire engineering practices. In this paper, we demonstrate how typical office‐based PCs attached to a local area network have the potential to offer the benefits of parallel processing with minimal costs associated with the purchase of additional hardware or software. A dynamic load balancing scheme was devised to allow the effective use of the software on heterogeneous PC networks. This scheme ensured that the impact between the parallel processing task and other computer users on the network was minimized thus allowing practical parallel processing within a conventional office environment. Copyright © 2006 John Wiley & Sons, Ltd.     

基于统一强度理论抗滑桩桩间距的计算

在已有抗滑桩桩间距研究的基础上,对桩间土拱进行受力分析。从侧阻力条件和土拱强度条件两个方面对抗滑桩桩间距进行了计算,将统一强度理论引入土拱强度的分析,藉此分别判断拱顶前缘、后缘及拱脚处土体是否处于临界状态,可得3个桩间距值,取相应的最小桩间距作为设计桩间距。此方法对于滑坡推力的矩形、三角形和梯形分布形式均适用,并可考虑土体自重应力的影响,同时可推及锚索抗滑桩桩间距的计算。对两个计算实例进行了分析,本方法的计算值与已有计算值或设计值的比较表明本方法效果良好。具体计算中统一强度参数b取0.2~0.7较为合适,滑坡推力为矩形分布时b值约为0.3,滑坡推力为三角形分布时b值约为0.6,滑坡推力为梯形分布时b值介于两者之间。     

The method of fundamental solutions for Stokes flow in a rectangular cavity with cylinders

Numerical solutions based on the method of fundamental solutions are discussed for Stokes flow inside a rectangular cavity in the presence of circular cylinders. The Stokeslets are used as the fundamental solutions to obtain the solution for the flow field by a linear combination of fundamental solutions. Flow results on the cellular structure of flow field resulting from the dynamics of cylinders and the horizontal walls of the cavity are reported for (i) one rotating cylinder in a rectangular cavity with two parallel horizontal sides moving in the same directions as well as in the opposite directions, (ii) two rotating cylinders kept apart in a rectangular cavity with two parallel horizontal sides moving in the same directions as well as in the opposite directions. The effect of aspect ratio of the rectangular cavity, direction of movement of the two parallel horizontal sides of the cavity and the diameter of the rotating cylinder on the flow structure are studied. The flow results obtained for the single cylinder case are in accordance with the results available in the literature. From the computational point of view, the present numerical procedure based on the method of fundamental solutions is efficient and simple to implement as compared to the mesh-dependent schemes, which needs complex mesh generation procedure for the multiply connected geometrical domains considered in this article.     

The dynamic behavior of MEMS arch resonators actuated electrically

In this paper, we investigate the dynamic behavior of clamped-clamped micromachined arches when actuated by a small DC electrostatic load superimposed to an AC harmonic load. A Galerkin-based reduced-order model is derived and utilized to simulate the static behavior and the eigenvalue problem under the DC load actuation. The natural frequencies and mode shapes of the arch are calculated for various values of DC voltages and initial rises. In addition, the dynamic behavior of the arch under the actuation of a DC load superimposed to an AC harmonic load is investigated. A perturbation method, the method of multiple scales, is used to obtain analytically the forced vibration response of the arch due to DC and small AC loads. Results of the perturbation method are compared with those obtained by numerically integrating the reduced-order model equations. The non-linear resonance frequency and the effective non-linearity of the arch are calculated as a function of the initial rise and the DC and AC loads. The results show locally softening-type behavior for the resonance frequency for all DC and AC loads as well as the initial rise of the arch.     

Dynamic Characteristics of a Prototype Arch Dam

This study determines the dynamic characteristics of a prototype arch dam-reservoir-foundation system using Operational Modal Analysis method. Achievement of this purpose involved construction of a prototype arch dam-reservoir-foundation system under laboratory conditions. Ambient vibration tests on the arch dam model identified its natural frequencies, mode shapes, and damping ratios. Natural excitations such as small impact loads vibrated to arch dam. Sensitivity accelerometers which were placed on the dam’s crest collected signals in measurements. Measurements were recorded for empty and full reservoirs. Operational Modal Analysis software processed signals which were collected from the ambient vibration tests. Enhanced Frequency Domain Decomposition technique estimated dynamic characteristics of the dam. Results showed that there was an approximate 20–25% difference between natural frequencies related to empty and full reservoirs.     

Dynamic, multimode buckling of thin-walled columns subjected to in-plane pulse loading

The present paper deals with dynamic, coupled buckling of long, prismatic columns simply supported at the ends. This investigation concerns thin-walled structures of a square cross-section with or without intermediate stiffeners under in-plane pulse loading. The dynamic load of a rectangular shape has been assumed in the analysis. The structures are composed of rectangular plates interconnected along longitudinal edges. A plate model is adopted in the analysis. The material of the structure is isotropic. The problem has been investigated on the basis of the disturbance theory. The dynamic critical load factor DLF has been determined using the Budiansky and Hutchinson criterion. The results obtained with the analytical-numerical method (ANM), which employs the asymptotic perturbation theory, have been compared with the finite element method (FEM).