A general topology-based framework for adaptive insertion of cohesive elements in finite element meshes

Large-scale simulation of separation phenomena in solids such as fracture, branching, and fragmentation requires a scalable data structure representation of the evolving model. Modeling of such phenomena can be successfully accomplished by means of cohesive models of fracture, which are versatile and effective tools for computational analysis. A common approach to insert cohesive elements in finite element meshes consists of adding discrete special interfaces (cohesive elements) between bulk elements. The insertion of cohesive elements along bulk element interfaces for fragmentation simulation imposes changes in the topology of the mesh. This paper presents a unified topology-based framework for supporting adaptive fragmentation simulations, being able to handle two- and three-dimensional models, with finite elements of any order. We represent the finite element model using a compact and “complete” topological data structure, which is capable of retrieving all adjacency relationships needed for the simulation. Moreover, we introduce a new topology-based algorithm that systematically classifies fractured facets (i.e., facets along which fracture has occurred). The algorithm follows a set of procedures that consistently perform all the topological changes needed to update the model. The proposed topology-based framework is general and ensures that the model representation remains always valid during fragmentation, even when very complex crack patterns are involved. The framework correctness and efficiency are illustrated by arbitrary insertion of cohesive elements in various finite element meshes of self-similar geometries, including both two- and three-dimensional models. These computational tests clearly show linear scaling in time, which is a key feature of the present data-structure representation. The effectiveness of the proposed approach is also demonstrated by dynamic fracture analysis through finite element simulations of actual engineering problems.

An atomistic-continuum inhomogeneous material model for the elastic bending of metal nanocantilevers

The equivalent elastic modulus of nanocantilever can be obtained using atomistic simulation. However, the use of this modulus to predict the bending of nanocantilever results in significant error compared with direct atomistic simulation. The error originates from the surface effect. In our current work, the nanocantilever is considered as an inhomogeneous continuum material. The distributions of materials parameters at the cross-section, such as atomistic elastic constants, are calculated from atomistic simulations. These atomistic-information-based materials parameters are used as inputs to continuum model. A numerical example case validates the presented model and methodology. To correctly predict the structure-property relations of elemental nano-structures are very important for the design of nano-devices. Our continuum model includes nano-effects and provides another way to study nanomechanics.     

基于UML可适应的教学考评系统分析与设计

该文给出了UML的概念与要点,应用UML对教学考评系统进行了建模。给出了系统的用例模型、整体结构模型、静态模型、动态模型,并分析了模型对教学考评变化的可适应性。     

基于信任域的移动adhoc网络信任模型研究

详细阐述了基于信任域的信任模型策略分析、模型的基本设计思想、模型中的数据结构,探讨了保障簇代理安全性的措施,研究了计算机信任值及修正信任值的方法。     

人才信息系统数据库设计

在人才信息系统的功能需求基础上,设计了一个信息数据库,能够实现招聘信息发布与查找、应聘信息发布与查找以及人才信息统计等功能。整个设计过程从需求分析、概念设计、逻辑设计等方面进行探讨。     

时间序列季节调整方法在中国的发展:PBC版X-12-ARIMA

中国人民银行(PBc)版X-12-ARIMA软件是基于中国特点而定制的时间序列季节调整软件.通过总结时间序列季节调整方法的特点以及相应软件在国外的发展,针对我国应用的特点,尤其是春节因素的考虑,在解剖X-12-ARIMA方法原理的基础上,在春节因素计算方法、软件应用界面以及用户使用帮助等3个主要方面加以改进,具有数据导入、调整设置文件、运行方式以及结果输出4方面的特色.     

基于方案本体的决策模型组装

决策模型组装是智能决策系统中的重要功能。基于本体的决策模型组装在模型之间的匹配上提供了丰富的语义信息,但本体推理的效率造成的响应速度较慢依然是需要解决的问题。本文提出一种基于方案本体的决策模型组装方法,可有效地减少本体建模的复杂度,并设计了相应的算法实现这种方法。     

Modeling sediment resuspension and transport induced by storm wind in Apalachicola Bay, USA

Sediment is an important environmental factor for aquatic ecosystem and oyster productivities of Apalachicola Bay located in Florida, USA. Based on the data analysis in this study, surface wind speed is highly correlated to the turbidity of water column, which results from sediment resuspension and transport in the Apalachicola Bay. In this paper, an application of a 3D sediment transport model to predict the wind-induced sediment transport in Apalachicola Bay is described. The sediment model is coupled with a 3D hydrodynamic module in the Environmental Fluid Dynamics Code (EFDC) model that provides information on estuarine circulation and salinity transport under normal temperature conditions. The hydrodynamic model was calibrated with field observations of water levels and salinity. The sediment transport model solves the transport equation with sources and sinks terms to describe sediment deposition and resuspension. The coupled hydrodynamic and sediment transport models were used to investigate wind-induced total suspended sediments (TSS) resuspension and transport in the bay. For the period June 1–July 30, 2005 two storm events with strong winds gave model results of TSS concentrations that compared well with the field observations. Model simulations reasonably reproduce the sudden increase of sediment concentrations during the storm events. Maximum sediment concentrations in the bay during the two storm events were 10 times or more than those in the pre-storm conditions. Spatial sediment transport from model simulations indicate active sediment resuspension and transport near areas of highly productive oyster beds. The model predictions of TSS and salinity can be used as inputs to an oyster dynamic model (Wang, H., Huang, W., Harwell, M., Edmiston, L., Johnson, E., Hsieh, P., Milla, K., Christensen, J., Stewart, J., Liu, X., 2008. Modeling eastern oyster population dynamics in response to changing environment in Apalachicola Bay, Florida. Journal of Ecological Modeling 211, 77–89) to support the ecological study of oyster growth and mortality in the aquatic ecosystem of Apalachicola Bay.     

Computational simulation of Belousov–Zhabotinskii oscillating chemical reaction

The suitability of computational simulation of the Belousov–Zhabotinskii oscillating chemical reaction by differential kinetic methodology for resolving nonlinear multi-component system is demonstrated in this work. According to the Field–KÖrÖs–Noyes mechanism and the Oregonator model, the change of the concentrations of HBrO₂, bromide ion and cerium ion are simulated. The results of computational simulation are consistent with experimental results very well. At the same time, the effect of variables and parameters, especially the rate constant on the oscillation curve, are investigated deeply. A simple method of estimating rate constants is obtained through simulation the concentrations of key components of the system, and then comparison the simulation results with the experimental ones. The reasonable rate constant is also proposed.     

入侵容忍系统的安全性量化方法分析

入侵容忍系统的安全性量化评估技术目前已取得了初步研究成果。本文首先简要阐述该技术的进展情况,然后从构建安全模型和分析攻击行为两大方面,横向比较了目前国内外在该领域的研究成果,并进行总结和分析,提出了一些未来的研究设想。