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121.
P. Gmez J. Hernndez J. Lpez 《International journal for numerical methods in engineering》2005,63(10):1478-1512
A local level set algorithm for simulating interfacial flows described by the two‐dimensional incompressible Navier–Stokes equations is presented. The governing equations are solved using a finite‐difference discretization on a Cartesian grid and a second‐order approximate projection method. The level set transport and reinitialization equations are solved in a narrow band around the interface using an adaptive refined grid, which is reconstructed every time step and refined using a simple uniform cell‐splitting operation within the band. Instabilities at the border of the narrow band are avoided by smoothing the level set function in the outer part of the band. The influence of different PDE‐based reinitialization strategies on the accuracy of the results is investigated. The ability of the proposed method to accurately compute interfacial flows is discussed using different tests, namely the advection of a circle of fluid in two different time‐reversed vortex flows, the advection of Zalesak's rotating disk, the propagation of small‐amplitude gravity and capillary waves at the interface between two superposed viscous fluids in deep water, and a classical test of Rayleigh–Taylor instability with and without surface tension effects. The interface location error and area loss for some of the results obtained are compared with those of a recent particle level set method. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
122.
The solidification structure, microstructure evolution during rolling and precipitates with nanometers in dimension of the low carbon steels produced by CSP process with thin slabs have been studied in recent years. Important differences in microstructure and mechanical properties between the CSP products and the conventional one were observed. These differences may arise from the much rapider solidification rate and cooling rate after casting of the thin slabs. Some aspects of the microstructure for the low carbon steels of the CSP thin slabs are summarized and compared with the conventional one. 相似文献
123.
The paper pursues two main goals. First, an attempt is made to specify and verify protocols in a completely rigorous manner using the formalisms of temporal logic and algebraic specification. Second––and even more important––the protocol specifications are not presented as monolithic pieces of text, but rather are developed in a stepwise process, evolving from simple genotypes into the final complex products. This is illustrated with selected fragments of the TCP/IP protocol. 相似文献
124.
并行程序设计是并行计算的难点之一。提出了一种将设计模式用于程序精化演算的并行程序设计方法。它通过在Z语言的Schema演算体系中扩充并行的概念和表示,使用设计模式,将问题求解和并行开发的知识进行形式化的定义与描述,通过扩充的Schema演算将其与模型规范进行复合,逐步精化得到抽象并行程序。通过实例对这一方法进行了详细的描述。 相似文献
125.
稀土对锌铝合金晶粒的细化作用 总被引:5,自引:0,他引:5
田卫平 《昆明理工大学学报(自然科学版)》2003,28(1):28-30,38
锌铝合金由于加入了较多的铝,明显提高了其强度和冲击韧性,其中的镁可阻滞合金体积改变、减轻合金的晶间腐蚀。锌铝合金因以上优良的综合性能而被广泛应用,可用做铸件或加工产品。在锌铝合金中加入适量稀土可以明显细化晶粒,根据hall-petch关系式,合金性能也将得到提高,从而扩大合金的应用范围,成为黄铜、锡青铜、铝青铜和铅基巴氏合金的良好替代材料。 相似文献
126.
在大豆叶子中大豆皂甙总配糖体提取工艺的基础上,进一步对总配糖体进行了分离纯化研究,主要研究了大豆皂甙总配糖体的脱色澄清、萃取以及萃取后得到大豆皂甙总配糖体的柱分离精制,从而得到了大豆皂甙分离纯化最佳的工艺条件. 相似文献
127.
The action system formalism has been succesfully used when constructing parallel and distributed systems in a stepwise manner within the refinement calculus. Usually the derivation is carried out manually. In order to be able to produce more trustworthy software, some mechanical tool is needed. In this paper we show how action systems can be derived and refined within the B-Toolkit, which is a mechanical tool supporting a software development method, the B-Method. We describe how action systems are embedded in the B-Method. Furthermore, we show how a typical and nontrivial refinement rule, the superposition refinement rule, is formalized and applied on action systems within the B-Method. In addition to providing tool support for action system refinement we also extend the application area of the B-Method to cover parallel and distributed systems. A derivation towards a distributed load balancing algorithm is given as a case study. 相似文献
128.
This paper presents the design and preliminary evaluation of hierarchical partitioning and load-balancing techniques for distributed structured adaptive mesh refinement (SAMR) applications. The overall goal of these techniques is to enable the load distribution to reflect the state of the adaptive grid hierarchy and exploit it to reduce synchronization requirements, improve load-balance, and enable concurrent communications and incremental redistribution. The hierarchical partitioning algorithm (HPA) partitions the computational domain into subdomains and assigns them to hierarchical processor groups. Two variants of HPA are presented in this paper. The static hierarchical partitioning algorithm (SHPA) assigns portions of overall load to processor groups. In SHPA, the group size and the number of processors in each group is setup during initialization and remains unchanged during application execution. It is experimentally shown that SHPA reduces communication costs as compared to the Non-HPA scheme, and reduces overall application execution time by up to 59%. The adaptive hierarchical partitioning algorithm (AHPA) dynamically partitions the processor pool into hierarchical groups that match the structure of the adaptive grid hierarchy. Initial evaluations of AHPA show that it can reduce communication costs by up to 70%. 相似文献
129.
Xigui Song Xiufang BIAN Xiaogang Qi Xiangfa Liu Junyan Zhang Baopei Wang Limin Zhu 《北京科技大学学报(英文版)》2004,11(1)
To obtain the finer primary silicon crystals, the proprietary Al-P master alloy was adopted to modify the eutectic Al-Si alloys and the most suitable modification process was made in the experiments. The SEM (Scanning Electron Microscope) and DSC (Differential Scanning Calorimeter) analysis indicate that the Al-P modifier has more advantages over Cu-P and Fe-P modifier in easily addition, no elemental alteration and less undercooling of primary silicon′s solidification, which suggests the Al-P master alloy is an effective modifier of eutectic Al-Si alloys. 相似文献
130.
J. Paul Attfield 《Journal of research of the National Institute of Standards and Technology》2004,109(1):99-106
The scope of Rietveld and other powder diffraction refinements continues to expand, driven by improvements in instrumentation, methodology and software. This will be illustrated by examples from our research in recent years. Multidataset refinement is now commonplace; the datasets may be from different detectors, e.g., in a time-of-flight experiment, or from separate experiments, such as at several x-ray energies giving resonant information. The complementary use of x rays and neutrons is exemplified by a recent combined refinement of the monoclinic superstructure of magnetite, Fe3O4, below the 122 K Verwey transition, which reveals evidence for Fe2+/Fe3+ charge ordering. Powder neutron diffraction data continue to be used for the solution and Rietveld refinement of magnetic structures. Time-of-flight instruments on cold neutron sources can produce data that have a high intensity and good resolution at high d-spacings. Such profiles have been used to study incommensurate magnetic structures such as FeAsO4 and β–CrPO4. A multiphase, multidataset refinement of the phase-separated perovskite (Pr0.35Y0.07Th0.04Ca0.04Sr0.5)MnO3 has been used to fit three components with different crystal and magnetic structures at low temperatures. 相似文献