Incorporation of linear multipoint constraints in domain-decomposition-based iterative solvers - Part II: Blending FETI-DP and mortar methods and assembling floating substructures

Two approaches are presented for extending the FETI-DP domain-decomposition-based iterative method to the solution of problems with Linear Multipoint Constraints (LMPCs). Both cases of arbitrary LMPCs and LMPCs generated by the mortar method for enforcing a weak continuity of the solution across non-matching finite element interfaces are considered. In the first approach, the LMPCs are addressed during the preconditioning step but enforced only at convergence. In the second approach, the LMPCs are enforced at each iteration through the solution of an auxiliary coarse problem. Both extended FETI-DP solvers are benchmarked on a parallel processor for a wide range of constrained structural mechanics problems. The obtained results reveal that both solvers are numerically scalable and complement each other from the memory and CPU performance viewpoints.     

Instrument-Independent MS/MS Database for XQQ Instruments: A Kinetics-Based Measurement Protocol

A detailed kinetics-based measurement protocol is proposed for the development of a standardized MS/MS database for XQQ tandem mass spectrometers. The technical basis for the protocol is summarized. A CAD database format is proposed.     

钢筋混凝土梁-板子结构抗连续性倒塌性能研究

该文通过试验与有限元模拟研究边柱失效工况下钢筋混凝土（RC）梁-板子结构抗连续倒塌性能。在实验室通过对RC梁-板子结构缩尺模型开展pushdown试验研究梁-板子结构的破坏模态,并进一步讨论了梁-板子结构在倒塌过程中的荷载传递机理和抗力机制。试验结果表明:RC梁-板子结构在倒数第二个边柱失效下可以形成有效的梁机制、压拱机制、悬链线机制以及拉膜机制抵抗倒塌。在小变形阶段,楼板在负弯矩区作为梁翼缘可以显著提升RC梁抗弯承载力（T型梁作用）;在大变形阶段,楼板发展拉膜作用早于梁发展悬链线机制。此外,根据有限元软件LSDYNA开展的数值分析结果表明:楼板提升RC框架屈服承载力与极限承载力分别高达65%和61%。     

基于经验模态分解和模型缩聚的动力响应重构方法研究

大型工程结构自由度数量巨大,采用现有基于全局有限元模型的时域方法重构此类结构动力响应效率低、计算难度大,因此,提出一种结合经验模态分解和模型缩聚的动力响应重构方法.基于模态综合法,将有限元全模型适当划分为多个子结构,通过坐标转换,得到自由度数目更少的超单元模型,结合带有间歇准则的经验模态分解法进行重构.由于该方法无需考...     

New decentralized control technique based on substructure and LQG approaches

Decentralized control is more suitable for structural control of large-scale structures. In this paper, a new decentralized control technique is proposed based on the linear quadratic Gaussian (LQG) and substructure approaches. A large-scale structure is divided into a set of smaller substructures. Each substructure is controlled by its own local controller with interaction forces at substructural interfaces, which are considered as “unknown external inputs” to the substructure concerned. An algorithm of recursive least squares estimation for the unknown excitation is proposed. A numerical example of the decentralized control of a tall building is studied to illustrate the new proposed algorithm. Simulation results show that the proposed decentralized control provides satisfactory control performance when comparing with the conventional centralized LQG control algorithm and is viable for the future structural control of large-scale structures.     

Multibody Dynamics of Very Flexible Damped Systems

An efficient multibody dynamics formulation is presented for simulating the forward dynamics of open and closed loop mechanical systems comprised of rigid and flexible bodies interconnected by revolute, prismatic, free, and fixed joints. Geometrically nonlinear deformation of flexible bodies is included and the formulation does not impose restrictions on the representation of material damping within flexible bodies.The approach is based on Kane's equation without multipliers and the resulting formulation generates 2ndof+m first order ordinary differential equations directly where ndof is the smallest number of system degrees of freedom that can completely describe the system configuration and m is the number of loop closure velocity constraint equations. The equations are integrated numerically in the time domain to propagate the solution.Flexible bodies are discretized using a finite element approach. The mass and stiffness matrices for a six-degree-of-freedom planar beam element are developed including mass coupling terms, rotary inertia, centripetal and Coriolis forces, and geometric stiffening terms.The formulation is implemented in the general purpose multibody dynamics computer program flxdyn. Extensive validation of the formulation and corresponding computer program is accomplished by comparing results with analytically derived equations, alternative approximate solutions, and benchmark problems selected from the literature. The formulation is found to perform well in terms of accuracy and solution efficiency.This article develops the formulation and presents a set of validation problems including a sliding pendulum, seven link mechanism, flexible beam spin-up problem, and flexible slider crank mechanism.     

内燃机复杂轴系扭振计算的动态子结构法

本文给出了一种改进的动态子结构法,并用该方法分析内燃机复杂轴系扭转振动问题.实例计算表明,该方法能有效地压缩分析规模,节约运算时间,是分析复杂轴系扭转振动问题的有效方法.     

用部件模态综合法计算冷却塔整体结构的动力响应

冷却塔整体结构由旋转壳塔简和循环对称的支柱梁系组成。本文将它们作为两个子结构,用双协调模态综合法计算塔整体的固有振动、动力响应,并着重进行了地震应力分析,既相当精确地反应了壳体底局部应力和支柱梁系中的应力,又保持了单独分析两个子结构时精度高、计算量小的特点。理论分析和计算程序已被应用于冷却塔的设计。     

Large strains associated with sliding contact of metals

 Dislocation studies, especially at large strains, are important for understanding materials aspects of tribological processes. Metallographic evidence shows that sliding causes very large plastic strains and strain gradients adjacent to the interface between the interacting materials. Dislocation densities increase, perhaps achieving saturation values. The resulting microstructures, including LEDS, are typical of those produced by other ways of producing large strains. Friction can be related to the dissipative processes associated with plastic deformation. Also, the material near the surface becomes unstable to local shear, allowing transfer of pieces of deformed material to the counterface. The transfer material is further deformed and mixed with the counterface material and/or environmental components to produce very fine grained structures, often in the nanocrystal range. Loose wear debris particles are commonly derived from this mixed material, not directly from the base material. Received: 22 September 1997 / Accepted: 16 December 1997