基于主动学习Kriging模型的地下管线抗震可靠度分析

为提升地下承插式接口铸铁管线抗震可靠度的计算效率,提出基于主动学习Kriging代理模型的Monte Carlo模拟方法(AK-MCS)进行地下管线抗震可靠度计算。采用梁单元模拟管线结构,均布弹簧反映管土相互作用,接口弹簧模拟邻接管道约束作用,建立了地下管线地震响应分析模型;考虑管线接口允许位移、管线埋深、土体容重和内摩擦角等模型参数随机性的影响,以管线接口位移量为安全准则,采用主动学习Kriging模型方法建立管线接口位移响应与随机变量参数关系的代理模型,从而获得管线接口安全状态。算例结果表明,AK-MCS法计算得到的管线失效概率与传统Monte Carlo模拟计算的结果相对误差在5%以内,且AK-MCS法计算时间约为传统Monte Carlo模拟计算时间的2%。因此在进行管线可靠度计算时,主动学习Kriging代理模型方法具有准确性与高效性。     

焊接热影响区微观结构演化的蒙特卡罗计算机模拟方法

焊接热影响区是影响焊接性能的主要区域。焊接热影响区的晶粒长大常常导致焊接热影响区成为性能薄弱的环节，对焊接热影响区晶粒长大的研究一直是焊接接头的重要研究课题。焊接热影响区微观结构演化与诸多因素密切相关，是一个复杂的过程。运用适当的计算机方法进行模拟，完成对晶粒生长的完全预测，具有重要的意义，可以为优化焊接工艺参数，提高焊接质量提供依据。在此对在模拟焊接热影响区微观结构的演化时采用的基本方法进行综述。     

热成形过程微观组织模拟研究进展

金属在热成形过程中微观组织发生诸如晶粒长大、再结晶等一系列的复杂变化,会直接影响加工过程与产品的力学性能。对近年计算机技术在热成形微观组织演变模拟方面的研究进展做了比较全面的评述,比较了相关的微观组织模拟方法,分析了利用各种模拟技术所取得的研究成果。     

The Effects of Random Porosities in Resonant Frequencies of Graphene Based on the Monte Carlo Stochastic Finite Element Model

With the distinguished properties in electronics, thermal conductivity, optical transparence and mechanics, graphene has a powerful potential in nanosensors, nano-resonators, supercapacitors, batteries, etc. The resonant frequency of graphene is an important factor in its application and working environment. However, the random dispersed porosities in graphene evidently change the lattice structure and destroy the integrity and geometrical periodicity. This paper focuses on the effects of random porosities in resonant frequencies of graphene. Monte Carlo simulation is applied to propagate the porosities in the finite element model of pristine graphene. The statistical results and probability density distribution of porous graphene with atomic vacancy defects are computed based on the Monte Carlo finite element model. The results of porous graphene with atomic vacancy defects are compared and discussed with the results of graphene with bond vacancy defects. The enhancement effects of atomic vacancy defects are confirmed in porous graphene. The influences of atomic vacancy defects on displacement and rotation vector sums of porous graphene are more concentrated in local places.     

纯铜动态再结晶的Monte Carlo法模拟

本文建立了一种基于能量判据的确定动态再结晶各个阶段临界应变的方法，并基于此种方法Monte Carlo(MC)法进行了纯铜动态再结晶的二维模拟，定量计算了变形引起的存储能与变形之间的关系，计算出了发生动态再结晶的临界应变。模拟结果表明，采用MC法可以揭示动态再结晶的形核生长过程与应变历史之间的关系。结合本文所建立的基于能量判据的确定动态再结晶各个阶段临界应变的方法，可以预测开始发生动态再结晶的临界变形条件。     

小样本条件下某机载设备挂架结构的可靠性研究

某机载设备挂架结构的工作应力属于小样本事件，本文针对该结构利用有限元进行应力分析，以分析结果为样本，分别建立了结构工作应力与外载荷及结构尺寸的非线性映射关系。在此基础上形成了应力-强度干涉模型，并对结构进行了可靠性分析，得出了载荷波动对可靠性的影响大于尺寸波动的影响，为挂架结构的可靠性优化设计奠定了基础。     

Development of the semi-empirical equation of state for square-well chain fluid based on the Statistical Associating Fluid Theory (SAFT)

A semi-empirical equation of state for the freely jointed square-well chain fluid is developed. This equation of state is based on Wertheim’s thermodynamic perturbation theory (TPT) and the statistical associating fluid theory (SAFT). The compressibility factor and radial distribution function of square-well monomer are obtained from Monte Carlo simulations. These results are correlated using density expansion. In developing the equation of state the exact analytical expressions are adopted for the second and third virial coefficients for the compressibility factor and the first two terms of the radial distribution function, while the higher order coefficients are determined from regression using the simulation data. In the limit of infinite temperature, the present equation of state and the expression for the radial distribution function are represented by the Carnahan-Starling equation of state. This semi-empirical equation of state gives at least comparable accuracy with other empirical equation of state for the square-well monomer fluid. With the new SAFT equation of state from the accurate expressions for the monomer reference and covalent terms, we compare the prediction of the equation of state to the simulation results for the compressibility factor and radial distribution function of the square-well monomer and chain fluids. The predicted compressibility factors for square well chains are found to be in a good agreement with simulation data. The high accuracy of the present equation of state is ascribed to the fact that rigorous simulation results for the reference fluid are used, especially at low temperatures and low densities. This paper was presented at the 8th APCChE (Asia Pacific Confederation of Chemical Engineering) Congress held at Seoul between August 16 and 19, 1999.     

Janus II: A new generation application-driven computer for spin-system simulations

This paper describes the architecture, the development and the implementation of Janus II, a new generation application-driven number cruncher optimized for Monte Carlo simulations of spin systems (mainly spin glasses). This domain of computational physics is a recognized grand challenge of high-performance computing: the resources necessary to study in detail theoretical models that can make contact with experimental data are by far beyond those available using commodity computer systems. On the other hand, several specific features of the associated algorithms suggest that unconventional computer architectures–that can be implemented with available electronics technologies–may lead to order of magnitude increases in performance, reducing to acceptable values on human scales the time needed to carry out simulation campaigns that would take centuries on commercially available machines. Janus II is one such machine, recently developed and commissioned, that builds upon and improves on the successful JANUS machine, which has been used for physics since 2008 and is still in operation today. This paper describes in detail the motivations behind the project, the computational requirements, the architecture and the implementation of this new machine and compares its expected performances with those of currently available commercial systems.     

CUDA programs for the GPU computing of the Swendsen–Wang multi-cluster spin flip algorithm: 2D and 3D Ising,Potts, and XY models

We present sample CUDA programs for the GPU computing of the Swendsen–Wang multi-cluster spin flip algorithm. We deal with the classical spin models; the Ising model, the q$q$-state Potts model, and the classical XY model. As for the lattice, both the 2D (square) lattice and the 3D (simple cubic) lattice are treated. We already reported the idea of the GPU implementation for 2D models (Komura and Okabe, 2012). We here explain the details of sample programs, and discuss the performance of the present GPU implementation for the 3D Ising and XY models. We also show the calculated results of the moment ratio for these models, and discuss phase transitions.