基于"块-单元"数据结构的分子动力学并行计算

开发了一种基于"块-单元"数据结构的可扩展并行算法,以实现大规模、非均匀分子动力学模拟.它采用空间填充曲线将三维区域分解转换为-维负载平衡问题,然后用基于实测的多层均权法求解,以保持处理机间负载均衡.在一个MPP并行机的500个CPU上,模拟包含2.1×108个粒子的三维金属微喷射模型,该算法获得了420倍的加速比.     

浅谈科学计算

科学计算是指利用计算机再现、预测和发现客观世界运动规律和演化特性的全过程.在实际应用牵引下,依托高性能计算机的发展,近年来科学计算得到了快速的发展.与传统的理论研究和实验研究一起,科学计算已经成为推动科技创新的重要研究手段.文章首先介绍丫作者对科学计算的认识:科学计算的本质是求真,置信度是科学计算的核心;做好科学计算,需要以应用为牵引,需要物理、数学与计算机等方面人才的合作,需要多学科交叉融合.文章还讨论了影响科学计算置信度的几个环节.最后就如何做好科学计算发表了看法.     

浅谈科学计算

科学计算是指利用计算机再现、预测和发现客观世界运动规律和演化特性的全过程.在实际应用牵引下,依托高性能计算机的发展,近年来科学计算得到了快速的发展.与传统的理论研究和实验研究一起,科学计算已经成为推动科技创新的重要研究手段.文章首先介绍了作者对科学计算的认识：科学计算的本质是求真,置信度是科学计算的核心;做好科学计算,需要以应用为牵引,需要物理、数学与计算机等方面人才的合作,需要多学科交叉融合.文章还讨论了影响科学计算置信度的几个环节.最后就如何做好科学计算发表了看法.     

在大学物理教学中培养学生的科学计算能力

计算机技术以及计算能力的迅猛发展使我们逐渐认识到在课堂教学中培养学生科学计算能力的重要性。本文在分析国内高校在科学计算能力培养方面的现状的同时,介绍了自己在大学物理教学中培养学生科学计算能力方面的实践探索。     

改进的3维粒子模拟并行算法

 提出了两种改进的3维粒子模拟并行算法,改进的并行算法能在每个时间步减少一次进程同步。算法分析和数值模拟表明,由于粒子运动路径和发射的初始位置与随机函数有关,只有一种改进的并行算法能保证并行计算正确。在3维粒子模拟软件CHIPIC3D上实现了改进的并行算法,应用CHIPIC3D对一种相对论返波管进行了并行模拟,模拟结果表明改进的并行算法能取得更高的加速比和效率。     

改进的3维粒子模拟并行算法

提出了两种改进的3维粒子模拟并行算法,改进的并行算法能在每个时间步减少一次进程同步。算法分析和数值模拟表明,由于粒子运动路径和发射的初始位置与随机函数有关,只有一种改进的并行算法能保证并行计算正确。在3维粒子模拟软件CHIPIC3D上实现了改进的并行算法,应用CHIPIC3D对一种相对论返波管进行了并行模拟,模拟结果表明改进的并行算法能取得更高的加速比和效率。     

加工误差对马氏理论关于超微孔微穿孔板吸声结构适用性的影响

从理论和实验上探讨了加工误差对马氏理论关于超微孔微穿孔板(micro-perforated panel,MPP)吸声结构适用性的影响。建立了计及加工误差的MPP理论分析模型,并应用MEMS工艺制作了超微孔MPP,由于工艺本身存在一定的加工误差,造成实际孔径与设计孔径10%-20%的偏差,在阻抗管中测量得到其垂直入射吸声系数。将实验结果和计及加工误差的理论预测值与马氏理论预测值进行对比发现,差别均较小,最大误差仍在6%以内,说明马氏理论在计及加工误差的情况下仍然适用。此外,对马氏理论关于加工误差的适用极限进行了仿真计算,结果表明,适用极限的大小具体依赖于超微孔MPP的孔径大小。     

科学计算的历史与展望

近期,中国科学院院士、欧洲科学院院士汤涛教授的线上报告《科学计算的历史与展望》受到了来自科研院所和高校师生的广泛好评,并广为传播。应《计算物理》主编江松院士的邀请,汤涛院士为《计算物理》的读者倾心打造了专版——科学计算的历史与展望,和读者们分享他40年潜心研究计算数学的心得体会。除了引言之外,这个专版有4个主要部分:计算机与计算数学、数学与科学计算、什么是科学计算,以及人工智能时代的科学计算。汤院士非常高兴能够有机会与《计算物理》的读者们和广大科学爱好者们分享科学计算的历史与展望。     

基于Python的网页版物理实验快速建设技术

如何使用科学计算软件自动与数据库进行交互,实现网页版实验结果的快速输出,共享实验结果并应用于教学工作是大学物理实验领域核心和热点的关注问题。一直探索使用Matlab解决上述问题,但是其Complier二十几万的商业使用费用,使得科学计算函数与数据库通讯和基于Java的网页开发方案有始无终。然而,Python多领域大规模的函数包、基于网页开发的免费、公开、快捷的框架设计快速、有效并轻量级地解决了上述问题。本文在介绍Python科学计算语言,比较Matlab、Python进行网页版实验的技术框架的基础上,完成实验数据的数据读取、科学计算函数库的使用、网页版实验结果的生成,并以光学物理实验劈尖的等厚干涉条纹实验为例完成网页版物理实验的建设。通过本文可以帮助具备Matlab基础的科学实验者,快速实现物理实验的网页版输出。     

民族地方高校普通物理数字化教学探索与实践

本文以西藏大学为例,探索在民族地方高校新设"计算物理基础"课程的目的、做法及实施情况.以Matlab为平台,将计算机数值计算与模拟实验引入普通物理教学中,促进Matlab的数值计算及模拟功能与普通物理课程教学的整合,对学生进行科学计算教育,培养学生的科学计算能力,推进民族地区普通物理数字化教学改革.     

JEMS- FDTD超大规模并行计算测试

介绍了JEMS- FDTD在大规模并行计算机上进行的并行性能测试,包括网格片大小对性能的影响、单节点MPI/OPENMP混合并行性能、多节点MPI/OPENMP混合并行性能、大规模并行性能等。同时,也给出了一个包含电大尺寸复杂、真实结构模型的算例,并对其进行了计算、分析。测试表明,JEMS- FDTD可高效使用数万个处理器核进行并行计算。大型算例测试表明：JEMS- FDTD可针对电大尺寸复杂、真实结构模型进行有效的计算、分析。     

Improvement of sound absorption characteristics under low frequency for micro-perforated panel absorbers using super-aligned carbon nanotube arrays

Super-aligned carbon nanotube (SACNT) arrays are grown on the surface of micro perforated panel (MPP) in the hope of improving the acoustic performance of MPP absorbers by virtue of their unique properties. Scanning electron microscopy reveals that SACNT arrays did not block the perforations of MPPs or changed the perforation diameter due to their “super-aligned” nature, although MPPs are thickened. The absorption effect of SACNT arrays which are of the same and different lengths with different incident side on MPP absorbers are investigated, and standing wave tube method is used to determine the normal sound absorption coefficient. Results show that both of the lengths of SACNT arrays and the incident side have effects on the sound absorption performance of MPP absorbers. And generally SACNT arrays help to improve the sound absorption capacity of MPP absorbers in low-frequency regions only when the SACNT arrays surface is the incident side. SACNT arrays decrease absorption performance of MPP absorbers when the MPP surface is used as the incident side. Moreover, SACNT arrays are found to increase the acoustic ability of MPP absorbers with the same structure parameters monotonically at lengths up to 600 μm in the condition that the SACNT arrays surface is used as the incident side.     

A pilot study on improving the absorptivity of a thick microperforated panel absorber

Microperforated panel (MPP) absorbers are promising as a basis for the next-generation of sound absorbing materials. MPPs are typically made of a thin metal or plastic panel. However, thin limp panels are generally not suitable as an interior finish of room walls because they do not have sufficient strength, which prevents practical application of MPPs as an interior finish of room walls. In order to overcome the lack of appropriate strength required for room walls, it is possible to make an MPP out of a thick panel. However, thick MPPs are usually not efficient because the resistance and/or reactance become too high. In this study, trial production of thick MPPs and measurement of their normal absorption coefficients were carried out. Results show that efficient absorption can be given with a thick MPP by using a tapered perforation.     

Fluorescence investigations of pure and mixed evaporated dye layers

Fluorescence spectroscopy is used to investigate energy transfer processes in evaporated layers consisting of several different dyes. In this study films ofN,N-dimethylperylene-3,49,10-bis-dicarboximide (methylperylene pigment, MPP), coevaporated with copper phthalocyanine (CuPc) at varying ratios, and double layers of MPP and CuPc with different thicknesses are investigated. It is shown that energy transfer from MPP to CuPc occurs in both mixed and double layers. The energy transfer leads to a strong quenching of the MPP fluorescence and sensitized CuPc emission in the NIR region. The concentration dependence of the fluorescence quenching in mixed layers can be described by a Stern-Volmer plot. A simple model based on exciton diffusion between MPP molecules toward active quenching centers is used to determine the diffusion length.     

一种基于时空变换和压缩感知的磁共振螺旋采样的图像重建算法

螺旋采样磁共振快速成像在功能性成像、并行成像和动态成像等领域发挥着越来越重要的作用.螺旋采样图像重建的传统算法是用核函数将螺旋状分布的k空间数据插值到均匀网格中,再利用傅里叶变换和最小二乘法进行重建.但是基于网格化的算法对核函数过于依赖,在网格化过程中产生难以避免的误差.该文提出了基于时空变换和压缩感知的l1范数的最优化模型和重建算法.时空变换矩阵描述了空间上的磁共振图像与采集到的时域信号间的关系,使得算法直接使用采集到的数据作为保真约束项,避免了网格化过程产生的误差.此外,基于图像处理单元的并行计算被用来提高时空变换矩阵的运算速度,使得算法具有较强的应用价值.     

Sound absorption of a double-leaf micro-perforated panel with an air-back cavity and a rigid-back wall: Detailed analysis with a Helmholtz-Kirchhoff integral formulation

So far the electro-acoustical equivalent circuit analysis has been widely used to analyse micro-perforated panel (MPP) absorbers, however, as for the double-leaf MPP the equivalent circuit analysis inevitably includes an approximation. In this paper, the sound absorption characteristics of a double-leaf MPP absorber backed by a rigid wall are analysed by wave theory using Helmholtz-Kirchhoff integral formulation to obtain a strict solution. The present wave theory is experimentally validated with existing measured results. The theory is also compared with the equivalent circuit solutions so that the differences between the two theories appear and the effect of the approximation is clarified. The comparison shows that the difference mainly appears in the vicinity of the resonance peaks: the differences occur in the resonance frequencies and the absorption coefficient at frequencies between the two resonance peaks.     

煤油超燃冲压发动机三维大规模并行数值模拟

在我国巨型计算机上,采用1024个CPU对煤油燃料超燃冲压发动机燃烧流场进行三维大规模并行数值模拟.计算软件采用自主研发的并行软件AHL3D,控制方程采用雷诺平均的N-S方程,无粘项计算采用Steger-Warning矢通量分裂格式,湍流模型采用k-ω双方程模型,煤油分子式采用正癸烷代替.计算给出的发动机壁面压强分布与试验测量结果有较好的一致性.结果表明,凹槽是发动机主要的着火区和火焰稳定区,同时,由于燃料的喷注形成的回流区也起到一定的稳焰作用.计算结果验证了AHL3D程序和采用的理论模型可以用于模拟煤油燃料超燃冲压发动机内部的复杂流动.     

并行代数多重网格算法可扩展性能分析

对当今求解大型稀疏线性代数方程组最有效的迭代方法之--代数多重网格(AMG)算法的并行计算进行可扩展性能分析.给出一套并行计算可扩展性能分析方法,用于分析和指导并行迭代算法及实现技术的设计与优化并应用于并行AMG算法.分析表明,网格算子的平均模式大小和迭代过程的算法效率分别制约了AMG算法启动阶段和迭代求解阶段并行性能的发挥,成为该类算法急需解决的两个关键问题.     

并联谐振电路在调制器充电电源中的应用

文章探讨了一种新颖的并联谐振高压开关电路, 该电路无需使用外加谐振元件, 只利用变压器的漏感和分布电容作为谐振参数, 既减小了变压器寄生参数的影响, 也简化电路. 设计采用调频器件CD4046对MOS管进行开关频率控制, 且令变换器工作于过谐振模式时, 该电路能够体现出对电容恒流充电的特性. 文中对电路的工作过程进行了简要分析, 并给出了功率计算和实验波形.     

Sound absorption of microperforated panel mounted with helmholtz resonators

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, MPP mounted with Helmholtz resonators (MPPHR) is introduced. Based on the MPP, Helmholtz resonators theory and electro-acoustical equivalent circuit principle, sound absorption properties of MPPHR are studied. Simulation and experimental results show that MPPHR have two peak frequencies and one anti-resonant frequency. The low-frequency peak is dependent on the Helmholtz resonators, while the high frequency peak is close to the peak of the single-layer MPP. The low-frequency sound absorption peaks move to low frequency with the neck length and the volume of Helmholtz resonators increasing. The high-frequency sound absorption peaks move to high frequency with the volume of Helmholtz resonators cavity increasing. Multiple Helmholtz resonator parallel MPP structure can provide more sound absorption than single MPPHR at low frequency range due to the introduction of more additional sound absorption peaks.