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1.
Quasisteady extinction of diffusion flames with nonunity Lewis numbers is analyzed for counterflow diffusion flames in the diffusion-flame regime of activation-energy asymptotics. Particular attention is placed on an excess or deficiency of the total energy in the reaction region, associated with leakage of the reactants. If the Lewis number is less than unity, there is diminished diffusive loss of thermal energy that leads to an increase of the total energy in the reaction zone as reactants penetrate. The resulting excess total energy strengthens the chemical reaction, so that the flame becomes more robust and resistant to extinction. On the other hand, flames with Lewis numbers greater than unity are found to extinguish more easily. An extinction criterion is provided that is valid for nonunity Lewis numbers.  相似文献   

2.
The general framework of large-eddy simulations (LES) is presented first, with Smagorinsky's model. Afterwards, Kraichnan's spectral eddy-viscosity is introduced and it is shown how it can be handled for LES purposes in isotropic turbulence. The spectral eddy viscosity is generalized to a spectral eddy diffusivity. The nonlocal interaction theory is used to discuss the backscatter issue, and a generalization of spectral eddy coefficients is presented. This so-called spectral-dynamic model allows the representation of non-developed turbulence in the subgrid scales. Utilization of these spectral models in physical space is envisaged in terms of, respectively, the structure function and hyperviscosity models. Two applications of these models to shear flows are considered, namely the plane mixing layer and channel flow, with statistical results and information on the topology of coherent vortices and structures presented.  相似文献   

3.
刘伟 《工程数学学报》2006,23(1):139-146
给出了多孔介质中一维混溶驱动问题在时间和空间上进行局部网格加密的有限差分格式,压力方程采用中心差分格式近似,饱和度方程采用修正迎风格式,且在交界面上采用线性插值,并利用极大值原理给出了误差估计。最后给出了数值算例。  相似文献   

4.
ECAP细化晶粒法的仿真与分析   总被引:7,自引:0,他引:7  
ECAP(Equal Channel Angular Extrusion)方法,是实现材料纯剪切变形的有效方法。本文采用有限元(FEA)分析软件ANSYS对Al的挤压过程进行仿真与分析。分析结果表明:外切角Φ、圆角半径、试样与凹模之间的摩擦系数、凹模本身的特性(如弹性模量、泊松比等)等等,对材料的变形量都有不同程度的影响。  相似文献   

5.
赵国英  牛建平 《材料导报》2007,21(F11):259-262
论述了高强度低合金(HSLA)钢晶粒细化理论及强度提高途径,综述了高强度低合金(HSLA)钢晶粒细化技术及近年来的研究成果,探讨了超细晶技术的理论依据及存在问题。为高强度低合金钢组织超细化技术的理论研究和实际工程应用提供参考。  相似文献   

6.
针对复杂曲面环形刀五轴数控加工中的局部干涉问题,提出了一种基于曲率匹配及网格点的干涉处理技术。首先,利用曲率匹配原则选出合理的刀具半径,以保证在切触点处沿任何方向上刀具与被加工曲面之间不会发生干涉,然后在各个切触点处通过比较刀具曲面最小主曲率与加工曲面最大主曲率确定出刀具的初始倾角。为了判断切触点邻近区域是否存在干涉问题,采用了网格点来快速自动生成检测区域及初始检测点。文中对有效检测点的筛选以及干涉的判断和处理技术分别进行了详细论述。最后,以非均匀有理B样条曲面为加工实例,对上述算法进行了测试和验证。  相似文献   

7.
深过冷Ni-Si共晶合金晶粒细化机制   总被引:1,自引:0,他引:1  
采用熔融玻璃净化和循环过热相结合的方法,在Ni-Si共晶合金中取得了最大330K的大过冷度.研究了大块过冷Ni-Si共晶合金晶粒细化,发现在某一关键过冷度(△T*=184K)以上,合金晶粒尺寸明显细化.实验证实在过冷Ni-Si共晶合金中枝晶重熔和碎断是晶粒细化的主要原因.为了更好地分析其晶粒细化机制,基于枝晶生长LKT-BCT模型完成了相关的计算.  相似文献   

8.
高含水期油藏多轮次调剖数值模拟研究   总被引:1,自引:0,他引:1  
刘伟 《工程数学学报》2005,22(4):579-584
在水驱油田开发中后期,多轮次调剖足一项重要的稳油控水措施。本文提出了高含水期油藏三维三相多轮次调剖数学模型,研制出多轮次调剖模拟器。模拟器中给定考虑了堵剂驱油过程中的物理特性,并使用了局部网络加密技术,为高含水期油藏进行多轮次调剖油藏工程方案研究提供了有力的工具。并结合实际生产情况,对一试验区块进行了多轮次调剖油藏工程方案研究,研究了调剖时机,堵剂用量对调剂效果的影响。  相似文献   

9.
A nanostructured surface layer with a mean ferrite grain size of ~8 nm was produced on a Fe-9Cr steel by means of surface mechanical attrition treatment. Upon annealing, ferrite grains coarsen with increasing temperature and their sizes increase to ~40 nm at 973 K. Further increasing annealing temperature leads to an obvious reduction of ferrite grain sizes, to ~14 nm at 1173 K. The annealing-induced grain refinement is analyzed in terms of phase transformations in the nanostructured steel.  相似文献   

10.
高能球磨中促进粉体细化的主要因素研究   总被引:1,自引:1,他引:1  
高能球磨技术作为一种制备包括纳米粉体在内的多种亚稳相材料的有效方法,已获得广泛应用.通常可以添加过程处理剂或在低温下球磨来抑制球磨过程中的冷焊,促使粉末细化.利用外加物理能场辅助高能球磨,使物理能与机械能协同作用到粉末,也是提高高能球磨效率的一种有效途径.根据不同条件下Fe粉的球磨细化结果,分析了高能球磨中过程处理剂、低温和外加能场辅助等主要促进粉体细化的因素及其作用.研究表明,采用等离子体辅助球磨仅仅10h,铁粉颗粒就被细化到了100nm.这种高的细化效率是因为等离子体辅助球磨中,等离子体对粉体产生的热爆效应和热应力的协同作用使粉体更易细化.  相似文献   

11.
直接热处理方法具有工艺简单、成本低廉、显微组织易于控制和适用性广等优点,是细化TiAl基合金铸件组织的重要方法之一,概括和总结了直接热处理方法在工艺和机理方面的研究进展,提出了直接热处理工艺存在的问题及解决的途径。  相似文献   

12.
一种细化金属凝固组织的新方法   总被引:1,自引:0,他引:1  
提出了用强脉冲磁场改善金属凝固组织的新技术。实验结果表明,强脉冲磁场能把铝合金的凝固组织从粗大的树枝晶细化为等轴晶,而且磁场愈强,细化效果愈显著。强脉冲磁场细金属凝固组织的新技术可应用于各金属材料,并可在工业上推广应用。  相似文献   

13.
讲课在课堂教学质量环节中起到重要的作用,而备好课是讲好课的必要条件,文章通过讨论如何做好课后备课及教案、讲稿的提炼这一重要的环节来达到更好地完成传授知识,培养高素质人才的任务.  相似文献   

14.
本文研究了16Mn 钢奥氏体动态再结晶、晶粒大小、晶粒细化率及γ→α相变后铁素体晶粒大小与工艺参数:变形量ε,变形温度之间的关系。通过大量数据的回归处理,得到奥氏体晶粒细化率在一定温度条件下,与变形量ε之间满足指数函数关系:动态再结晶完成后,奥氏体晶粒平均直径与形变速率温度修正系数 z 之间符合线性关系:γ→α相变后铁素体晶粒大小在一定温度条件下与变形量之间也存在指数函数关系:  相似文献   

15.
    
A local grid refinement scheme for the material point method with B-spline basis functions (BSMPM) is developed based on the concept of bridging domain approach. The fine grid is defined in the local large-deformation regions to accurately capture the complex material responses, whereas other spatial domains are discritized by coarse grids. In the overlapping domain between the fine and coarse grids, the constraint of particle displacements obtained with different grids is enforced using the Lagrange multiplier method to eliminate the spurious stress reflection at the fine/coarse grid interface. Representative numerical examples have shown that the BSMPM simulations with the proposed local grid refinement scheme could provide the solutions in good agreement with those obtained with the uniformly fine grid, and that no significant spurious stress reflection is induced at the fine/coarse grid interface, even for the bridging domain size as small as the cell size of the fine grid. It is also found that the proposed local grid refinement method can significantly reduce the BSMPM computational time compared with the cases for uniformly fine grids. A multitime-step algorithm is presented and shown to considerably enhance the efficiency of the present local grid refinement scheme with no compromise in accuracy.  相似文献   

16.
基于Bevington方法对自由衰减曲线进行全谱拟合,并应用于多功能内耗仪自由衰减模式下的高精度内耗测量中。内耗稳定性研究表明:采用该方法测量精度可达±7×10^-6,比振幅法提高近一个量级。特别是在高阻尼情况下,全谱拟合方法得到的内耗测量值精确度相对较高。  相似文献   

17.
Three Optical Procedures for Local Large-Strain Measurement   总被引:3,自引:0,他引:3  
R. Rotinat  R. Tié bi    V. Valle  J.-C. Dupré 《Strain》2001,37(3):89-98
Abstract: Optical methods have been developed to measure large strains. Two alternatives are presented: the first one uses a cross grating, obtained by an innovative manufacturing process and the second one uses a mark-tracking technique. The production of the grating is based on the deposit of a thin film through a master grid under vacuum. This creates small studs independent of each other, on the specimen surface. For the grid interrogation two techniques are discussed, one using the analysis of the optical diffraction figure and the other one the Fast Fourier Transform algorithm. Markers are simply deposited on the studied surface with a pen and strain determination is then obtained by mark-tracking. The experimental validation consists of several simple tensile tests. Experimental results for polymers and latex materials confirm the quality of measurement. Strains are measured for values up to 1,200% without loss of information, with a strain accuracy close to 5times10-4 at minimum gauge lengths of 0.125 mm.  相似文献   

18.
采用熔融玻璃与循环过热相结合的方法使Fe85 B15 合金熔体获得了320K的大过冷度,并在共晶组织中获得了晶粒尺寸为100~200nm的共晶相.理论分析和实验结果表明,合金熔体的大过冷为晶粒细化提供了驱动力,而形核率和晶粒生长速度随过冷度的变化决定了晶粒的细化.实验结果为通过深过冷快速凝固技术制备块体纳米晶材料提供了新的思路和重要的实验依据.  相似文献   

19.
等径通道挤压中晶粒细化影响因素的研究进展   总被引:17,自引:1,他引:17  
本文总结了近些年等径通道挤压(equal-channel angular pressing,简称ECAP)技术晶粒细化的机理、影响晶粒细化的因素及挤压后材料宏观力学性能的改善等方面的研究进展,并结合金属塑性变形理论进行了解释.最后提出了几项需要进一步深入研究的工作.  相似文献   

20.
空调房间内气流组织的数值模拟   总被引:1,自引:0,他引:1  
本文叙述空调房间内气流组织的紊流模型的种类,讨论了应用最为广泛的高雷诺数k-ε模型和低雷诺数模型的模拟性能,及其数值计算方法,并提出了针对室内气流组织模拟的研究方向.  相似文献   

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