三维FDTD众核算法的设计与实现

在电磁学中,时域有限差分算法(FDTD)能够精确地模拟空间中电磁场的变化,在电介质器件设计领域得到了广泛的应用。众核(many-core)处理器片上计算资源丰富,对于计算密集型课题有较好的适应性。通过对麦克斯韦方程FDTD仿真算法的分析,并根据众核处理器的特性,实现了FDTD算法的众核并行。实验结果表明,FDTD算法在众核处理器平台上具有较好的计算效率,能够很好地发挥众核结构的优势。     

基于MPI的FDTD并行算法及其优化策略

由高性能PC机通过网络互联构成的集群(COW)并行计算系统上应用基于消息传递(Message Passing)的方式实现FDTD的并行算法,获得了足够的加速比,有效地解决了传统的FDTD方法计算电大尺寸目标电磁散射问题时的不足.通过区域分割,各个子区域在边界处与其相邻的子区域进行场值的数据传递,从而实现了FDTD算法的并行化.利用并行FDTD方法研究了电磁波的介质层的散射,结果表明并行算法和串行计算结果的一致性,并有效提高计算效率.最后还给出了对算法进行通信隐藏的优化方法,进一步提高了并行计算的效率.     

基于国产十亿亿次超算系统的近连续过渡流区N-S/DSMC耦合算法并行优化研究

过渡流区气动问题的数值模拟一直是空气动力学领域的难点。首先介绍了在已有 N-S解算器和 DSMC方法研究基础上,采用 MPC耦合技术建立N-S/DSMC 耦合算法,把 DSMC 方法和 N-S 方法的应用范围拓展到近连续过渡流区。然后详述了基于国家超级计算无锡中心的国产十亿亿次超级计算机开展的耦合算法多级并行优化技术,并首次实现了耦合算法的众核并行。测试表明,本文的进程级优化技术取得了超线性加速比;众核级优化受制于原算法特点和系统特点没有取得预期效果,但进行了探讨和分析,为 N-S/DSMC 耦合算法的众核并行提供了研究和分析依据,为过渡流区高超声速气动特性数值模拟研究提供了有效的途径。     

基于CUDA架构的三维CPML-FDTD并行方法

为解决时域有限差分（FDTD）算法应用于电大尺寸目标仿真的巨大耗时问题,应用FDTD算法的并行特性和通用图形处理器（GPGPU）技术,实现了一种基于计算统一设备架构（CUDA）的三维FDTD并行计算方法,采用了时域卷积完全匹配层（CPML）吸收边界条件模拟开域空间,对不同网格数目标仿真计算。进一步结合FDTD算法和CUDA的特点进行了优化,当计算空间元胞数在十万数量级及以上时,优化前后GPU运算相对于同时期的CPU分别可获得10和25倍以上的加速,结果表明该方法较适合用于实际电磁问题的仿真。     

多物理数值模拟中一种有效的并行耦合方法

在实现多物理并行数值耦合模拟中,需要处理多个物理过程之间网格、并行区域分解的差异.针对该同题,该文基于三维流体力学与激光传播耦合的并行数值模拟,提出了一种实用的并行耦合方法:引入辅助状态将本地插值与通信相分离;构建并行耦合图并定义主导属性,以确定过程间传输的最小数据集合;提供并行数据重分配算法来完成通信.并行数值结果表明:该方法是有效的,在64台处理机上使整体程序获得50.07的加速比.     

三维粒子模拟并行化技术研究

自行研制的三维并行全电磁PIC模拟软件UNIPIC-3D具有模拟高功率微波器件的能力。软件实现了并行的三维FDTD、粒子推进算法以及边界条件处理。软件通过读入输入文件进行规则与不规则两种区域划分方式,电磁场和粒子的并行化采用MPI机制,让粒子和电磁场的计算与通信同步,在高性能并行计算机上对软件的并行效率进行了测试。通过与2.5维UNIPIC软件的结果比较,验证了UNIPIC-3D软件并行模块的正确性。     

基于FDTD二维光子晶体器件设计软件的开发

介绍了一个基于时域有限差分法（FDTD）的二维光子晶体器件设计软件PCCAD,所用的核心算法是时域有限差分法。与同类FDTD商业软件相比,特点在于其具有多种光子晶体结构编辑模板,多种点源、线源,先进的边界吸收技术及多种参数优化扫描等功能。快速傅里叶变换及Pade算法在软件设计中的应用使模拟更加精确、快速。软件适用于各种平面光子晶体的仿真设计,探索新的器件结构。最后,利用此软件设计了直波导、T型波导等二维平面光子晶体器件。     

柔性-微环光波导耦合结构的集成光学加速度传感器

给出了一种利用柔性-微环光波导耦合结构的集成光学加速度传感器.通过聚合物材料设计的柔性光波导,在外力作用下产生形变.该形变改变了柔性光波导与微环光波导的层间距,从而改变波导耦合器的耦合比,使得微环光波导谐振腔输出谱特性发生相应改变.继而有效地实现了加速度的传感.本文给出了这种新型的设计,推导了其检测原理并同时分析了其灵敏度的影响因素.     

并行子空间优化在无人机总体设计中的应用

飞机设计是一个多学科的复杂的系统工程,各个学科通常相互影响、相互耦合.这使得飞机设计过程日趋复杂,设计周期越来越长,开发成本越来越高,而并行子空间优化(CSSO)是解决这些问题的一种有效方法.文中对基于神经网络响应面的并行子空间优化算法及其在无人机总体方案设计优化中的应用进行了研究.并行子空间优化算法将多学科耦合的无人机设计优化问题分解为不同的子空间问题,在不同的子空间中建立各自的神经网络响应面,通过响应面完成各子空间之间的数据交换与协调,以此来逼近设计空间最优解.应用结果表明,CSSO算法能有效地应用于无人机总体方案优化设计.     

SMB协议在异构网络并行FDTD计算中的应用研究

在多系统异构局域网中,由于不同操作环境的消息传递接口（MPI）程序缺乏互操作性,使得并行时域有限差分运算(FDTD)难以充分利用局域网内的计算资源。对此,提出利用应用层服务消息块（SMB）协议实现异构FDTD计算,并通过内存文件存取、内存映射数组以及引入冗余计算等方法来缓解与克服SMB通信延迟对并行性能的影响。数值模拟实例验证了新方法的可行性与正确性,所得加速比、并行效率等性能指标参数与常规同构MPI消息传递方法基本相当。     

A new parallel meshing technique integrated into the conformal FDTD method for solving complex electromagnetic problems

A new efficient parallel finite-difference time-domain （FDTD） meshing algorithm, based on the ray tracing technique, is proposed in this paper. This algorithm can be applied to construct various FDTD meshes, such as regular and conformal ones. The Microsoft F# language is used for the algorithm coding, where all variables are unchangeable with its parallelization advantage being fully exploited. An improved conformal FDTD algorithm, also integrated with an improved surface current algorithm, is presented to simulate some complex 3D models, such as a sphere ball made of eight different materials, a tank, a J-10 aircraft, and an aircraft carrier with 20 aircrafts. Both efficiency and capability of the developed parallel FDTD algorithm are validated. The algorithm is applied to characterize the induced surface current distribution on an aircraft or a warship.     

大规模并行时域有限差分法电磁计算研究

基于我国超级计算机平台,开展了大规模并行时域有限差分法(Finite-Difference Time-DomainFDTD)的性能和应用研究。在我国首台百万亿次"魔方"超级计算机、具有国产CPU的"神威蓝光"超级计算机和当前排名世界第一的"天河二号"超级计算机上就并行FDTD方法的并行性能进行了测试,并分别突破了10000 CPU核,100000 CPU核和300000 CPU核的并行规模。在不同测试规模下,该算法的并行效率均达到了50%以上,表明了本文并行算法具有良好的可扩展性。通过仿真分析多个微带天线阵的辐射特性和某大型飞机的散射特性,表明本文方法可以在不同架构的超级计算机上对复杂电磁问题进行精确高效电磁仿真。     

Study on the propagation properties of TM electromagnetic wave in Lossy left‐handed material based on CUDA‐implemented parallel

By using the method of Finite Difference Time Domain (FDTD) and the technology of Compute Unified Device Architecture (CUDA), the propagation characteristics of electromagnetic waves in Left‐Handed Materials (LHM) have been studied in this paper. The LHM slab was matched with the free space and the secondary focusing phenomenon of LHM was simulated. Compared with the serial FDTD program, our work showed that this method had a high accuracy. The phase compensation effect and the inverse Snell effect of LHM were also discussed by using the parallel FDTD method based on CUDA, which further proved that our results were consistent with the theoretical study. By comparing the calculation time of traditional FDTD program with that of the CUDA based parallel FDTD program, we conclude that the latter is more efficient than the former. This parallel method can be used as a more efficient way to study LHM.     

A novel hybrid algorithm based on FDTD and WCS‐FDTD methods

In this article, a hybrid algorithm based on traditional finite‐difference time‐domain (FDTD) and weakly conditionally stable finite‐difference time‐domain (WCS‐FDTD) algorithm is proposed. In this algorithm, the calculation domain is divided into fine‐grid region and coarse‐grid region. The traditional FDTD method is used to calculate the field value in the coarse‐grid region, while the WCS‐FDTD method is used in the fine‐grid region. The spatial interpolation scheme is applied to the interface of the coarse grid region and fine grid region to insure the stability and precision of the presented hybrid algorithm. As a result, a relatively large time step size, which is only determined by the spatial cell sizes in the coarse grid region, is applied to the entire calculation domain. This scheme yields a significant reduction both of computation time and memory requirement in comparison with the conventional FDTD method and WCS‐FDTD method, which are validated by using numerical results.     

MPICH在Windows操作系统中的实现与应用

该文给出了对应于MPI标准的MPICH软件包在Windows操作系统中的配置和在MSVC＋＋中的实现方法，并对MPI与C／C＋＋绑定的基本编程进行了简要介绍。然后将其与一种电磁场数值算法——时域有限差分法相结合，以一维情况为例，讨论了网络并行时域有限差分法的实现方法。通过在由两台PC机构成的最简单的PC机群上的编程实现，验证了这种方法的可行性和高效性，实验结果表明通过MPICH软件包实现时域有限差分法的网络并行运算，可以使这种算法的加速比达到1．8。     

Microwave tomography for breast cancer detection on Cell broadband engine processors

Microwave tomography (MT) is a safe screening modality that can be used for breast cancer detection. The technique uses the dielectric property contrasts between different breast tissues at microwave frequencies to determine the existence of abnormalities. Our proposed MT approach is an iterative process that involves two algorithms: Finite-Difference Time-Domain (FDTD) and Genetic Algorithm (GA). It is a compute intensive problem: (i) the number of iterations can be quite large to detect small tumors; (ii) many fine-grained computations and discretizations of the object under screening are required for accuracy. In our earlier work, we developed a parallel algorithm for microwave tomography on CPU-based homogeneous, multi-core, distributed memory machines. The performance improvement was limited due to communication and synchronization latencies inherent in the algorithm. In this paper, we exploit the parallelism of microwave tomography on the Cell BE processor. Since FDTD is a numerical technique with regular memory accesses, intensive floating point operations and SIMD type operations, the algorithm can be efficiently mapped on the Cell processor achieving significant performance. The initial implementation of FDTD on Cell BE with 8 SPEs is 2.9 times faster than an eight node shared memory machine and 1.45 times faster than an eight node distributed memory machine. In this work, we modify the FDTD algorithm by overlapping computations with communications during asynchronous DMA transfers. The modified algorithm also orchestrates the computations to fully use data between DMA transfers to increase the computation-to-communication ratio. We see 54% improvement on 8 SPEs (27.9% on 1 SPE) for the modified FDTD in comparison to our original FDTD algorithm on Cell BE. We further reduce the synchronization latency between GA and FDTD by using mechanisms such as double buffering. We also propose a performance prediction model based on DMA transfers, number of instructions and operations, the processor frequency and DMA bandwidth. We show that the execution time from our prediction model is comparable (within 0.5 s difference) with the execution time of the experimental results on one SPE.     

Implementation and optimization of GPU‐based parallel one‐step leapfrog ADI‐FDTD for far‐field scattering problems

The one‐step leapfrog alternative‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD), free from the Courant‐Friedrichs‐Lewy (CFL) stability condition and sub‐step computations, is efficient when dealing with fine grid problems. However, solution of the numerous tridiagonal systems still imposes a great computational burden and makes the method hard to execute in parallel. In this paper, we proposed an efficient graphic processing unit (GPU)‐based parallel implementation of the one‐step leapfrog ADI‐FDTD for the far‐field EM scattering simulation of objects, in which we present and analyze the manners of calculation area division and thread allocation and a data layout transformation of z components is proposed to achieve better memory access mode, which is a key factor affecting GPU execution efficiency. The simulation experiment is carried out to verify the accuracy and efficiency of the GPU‐based implementation. The simulation results show that there is a good agreement between the proposed one‐step leapfrog ADI‐FDTD method and Yee's FDTD in solving the far‐field scattering problem and huge benefits in performance were encountered when the method was accelerated using GPU technology.