考虑颗粒间碰撞的气固两相流拉格朗日模拟

在均匀,稳定的各向同性气固两相紊流场颗粒弥散的拉格朗日模拟计算方法基础上,进一步考虑了流场中颗粒之间的碰撞对于模拟计算结果的影响。与Lavieville用大涡模拟所做的计算结果进行了对比,以对本方法进行验证,并考察了颗粒间的碰撞分别对流体相和颗粒相的影响。     

轧制过程的显式动力学有限元模拟

采用显式动力学弹塑性有限元方法对平板轧制问题进行了模拟计算,得出咬入,稳定轧制和抛钢阶段整个轧制过程的应力应变场。通过将板宽对称中心线轧制压力分布的计算结果与实验值进行对比,表明计算结果准确。     

SPH 方法在聚能装药射流三维数值模拟中的应用

采用有限元软件LS-DYNA中的SPH 算法实现聚能装药射流形成过程的三维数值模拟。将SPH方法和FEM 方法与理论计算结果相比较。研究结果表明:SPH 数值模拟计算过程十分稳定,避免了有限元数值模拟过程中的网格扭曲、缠绕和物质穿透等问题,而且计算精度比有限元方法更高;采用SPH 方法计算的射流速度、射流长度与有限元计算结果和理论计算结果的误差均小于5%,因此该方法对于模拟诸如聚能装药等多介质、大变形问题十分有效;初始相邻粒子数N 的最佳取值范围为600~1800,在该范围内计算结果的误差小于3%,且计算效率高。     

混凝土受拉性能多尺度均匀化数值模拟研究

为研究混凝土的细观结构对其受拉性能的影响,本文首先采用蒙特卡罗方法生成了多组混凝土随机骨料模型;然后划分有限元网格并映射到所建立的混凝土随机骨料数值模型上,采用复合材料均匀化方法建立了混凝土多尺度均匀化数值模型。考虑骨料随机分布和骨料形状,通过数值分析得到了在单轴拉伸情况下混凝土损伤分布特性及宏观应力-应变关系,在考虑随机性与非均质性的同时得到了较为理想的结果。运用多尺度均匀化的建模方法不仅能反应混凝土细观结构的影响,而且等效化模型的模拟计算时间大大减少,节约计算资源,提高了计算效率,具有优越性。     

低速冲击下复合材料合板的响应过程模拟

运用一种精度较高的高阶位移模型分析了复合材料层合板在低速击下的响应过程,该位移模型能够同时考虑层间正应力和横向剪应力,另外,采用修正的Hertz接触定律与Newmark积分方法相结合,建立了冲击接触的有限元模型,本文的数值模拟计算结果与解析结果相比较证明了该方法的有效和精确性。     

内压载荷作用下薄膜椭球的稳定性分析

超弹性橄榄状和南瓜状薄膜椭球在内压载荷作用下存在不同的分岔形式.对橄榄状薄膜椭球来说,细长比大于某一临界值时,在一定内压作用下会发生梨形分岔;小于该临界值时,薄膜椭球的分岔行为与圆管的局部起鼓现象相类似.对南瓜状薄膜椭球,无论圆扁,当内压达到某载荷值时都会发生梨形分岔.本文采用能量判据,分析了在压强控制和质量控制两种加载方式作用下,不同形状的薄膜椭球的均匀解及分岔解的稳定性.通过计算要考察的平衡状态及施加小扰动之后状态的能量差来判断当前状态是否稳定,结果表明,在压强控制下,P-V曲线下降段的均匀解和分岔解均为不稳定解.但在质量控制下,在P-V曲线下降段中只有均匀解出现时,均匀解为稳定解;而在均匀解和分岔解共存的区间内,均匀解为不稳定解,分岔解为稳定解.另外,P-V曲线两个上升段的均匀解则均为稳定解.     

用均匀化理论分析蜂窝结构的等效弹性参数

在线弹性范围内,根据均匀化理论,并结合有限元方法推导出适用于二维周期性结构的均匀化的有限元格式（Homo FEM）,计算出不同相对密度下的规则蜂窝结构的等效弹性模量Ee和泊松比νe.同时,利用蜂窝结构的代表胞元模型,用常规的有限元方法（FEM）模拟计算出相应的等效弹性参数.最后将两种数值计算结果与己有的理论公式进行了比较和分析讨论.结果表明:在考察的相对密度全场范围内（0～0.4）,HOmO FEM得到的蜂窝结构的 Ee和νe 与 FEM使用平面实体单元模拟计算得到的结果一致吻合,反映出 Homo FEM数值方法的客观准确性和可行性.而 Gibson公式和 W-K得到的等效弹性模量值 Ee只是在较小相对密度的情况下（小于0.15）与数值计算结果吻合.当结构的相对密度较大时,必须考虑胞棱附近区域由应力集中导致的复杂的应力和应变分布的影响.     

卵形杆弹对铝靶的斜侵彻

在Lagrange有限元基础上,扼要介绍了一种适用于三维斜侵彻数值模拟计算的滑移面处理技术。该方法放弃了传统滑移计算中从单元的设置,而代之以预设从节点,从而避免三维斜侵彻数值计算中主从单元的相交、滑移面的识别、修正与再定义的困难。在确保计算精度的同时,有效地提高了计算效率。卵形杆弹对铝靶侵彻的系列数值模拟计算表明,无论对于正撞击或斜撞击,本文中所获结果与实验结果都有良好的一致性,这说明本文中所述方法和所建程序的合理性和有效性,为侵彻贯穿过程的数值分析提供了一种实用和有效的手段。     

分离涡方法对梢涡中脉动量的数值模拟

分别用RANS-SA方法和DES方法对NACA0012翼端梢涡进行模拟计算,分析了梢涡区域网格局部加密对梢涡计算结果的影响,并与实验结果进行了对比.相比于RANS-SA方法,DES方法在梢涡流场计算中具有更好的适用性,能够得到更准确的流动信息和更精细的涡结构;另外,网格局部加密对脉动量的计算影响很大.通过对脉动量的分析发现,在近尾缘处,几股涡的融合产生了比较强烈的脉动,随着梢涡的逐渐稳定,脉动量也逐渐减小;现有的实验结果显示在偏下游处会产生梢涡的振荡现象,使统计脉动量增大,而本文计算中未发现该现象.     

含有随机夹杂非均匀体的有效弹性模量

在对含有随机夹杂的非均匀体求有效弹性模量时,一般多根据Eshelby的等效夹杂法,但由于该方法没有充分考虑非均匀体内部的微结构,所以其理论具有一定的局限性。本文认为Kunin的微结构理论与Eshelby的等效夹杂法相比更具一般性,因而本文采用了文[9]中一些合理的思想,摒弃了其中不合理的假设,并且建立了一种新的理论模型.最后,本文针对球夹杂的情况给出了非均匀体有效弹性模量依赖于夹杂体积份数的关系,并将该结果与文[10]中的结果进行了比较.     

湍流横掠固定颗粒的全尺度直接数值模拟

气固两相流模拟中,当固相尺度接近或大于Kolmogorov尺度时,普通的点源模型将不再适用,固体相的体积效应和表面效应将对流体相产生显著的影响。通过采用直接数值模拟方法,结合内嵌边界方法对湍流中不同湍流强度流体横掠大于Kolmogorov尺度的固相颗粒进行了全尺度模拟,讨论分析了在两种湍流度下方形颗粒对湍流的调制影响以及颗粒的受力情况。     

On basic equations of turbulent swirling gas-solid flows and their application in cyclones

The basic equations of turbulent gas-solid flows are derived by using the pseudo-fluid model of particle phase with a refined two-phase turbulence model. These equations are then applied to swirling gas-particle flows for analyzing the collection efficiency in cyclone separators.     

Direct Numerical Simulation of Statistically Stationary One- and Two-Phase Turbulent Combustion: A Turbulent Injection Procedure

A new turbulent injection procedure dedicated to fully compressible direct numerical simulation (DNS) or large eddy simulation (LES) solvers is proposed. To avoid the appearance of spurious acoustic waves, this method is based on an accurate tracking of the turbulent structures crossing the boundary at the inlet of the domain. A finite difference DNS solver has been coupled with a spectral simulation in which a statistically stationary homogeneous turbulence evolves to provide fluctuating boundary conditions.A new turbulence forcing method, dedicated to spectral solvers, has been developed as well to control the major properties of the injected flow (turbulent kinetic energy, dissipation rate and integral length scale). One-dimensional Navier–Stokes characteristic boundary conditions extended to non-stationary flows are coupled with the injection procedure to evaluate is potential in four various configurations: spatially decaying turbulence, dispersion of vaporizing sprays, propagation of one- and two-phase V-shape turbulent flames.     

Turbulent cascade modeling of single and bubbly two-phase turbulent flows

The analysis of turbulent two-phase flows requires closure models in order to perform reliable computational multiphase fluid dynamics (CMFD) analyses. A spectral turbulence cascade-transport model, which tracks the evolution of the turbulent kinetic energy from large to small liquid eddies, has been developed for the analysis of the homogeneous decay of isotropic single and bubbly two-phase turbulence. This model has been validated for the decay of homogeneous, isotropic single and two-phase bubbly flow turbulence for data having a 5 mm mean bubble diameter. The Reynolds number of the data based on bubble diameter and relative velocity is approximately 1400.     

Transport, Mixing and Agglomeration of Particles in Turbulent Flows

This paper describes methods and approaches that have been used to simulate and model the transport, mixing and agglomeration of small particles in a flowing turbulent gas. The transported particles because of their inertia are assumed not to follow the motion of the large scales of the turbulence and or the motion of the small dissipating scales of the turbulence. We show how both these behaviours can be represented by a PDF approach analogous to that used in classical kinetic theory. For large scale dispersion the focus is on transport in simple generic flows like statistically stationary homogeneous and isotropic turbulence and simple shear flows. Special consideration is given to the transport and deposition of particles in turbulent boundary layers. For small scale transport the focus is on how the small scales of turbulence together with the particle inertial response enhance collision processes like particle agglomeration. In this case the importance of segregation and the formation of caustics, singularities and random uncorrelated motion is highlighted and discussed.     

FLOW DYNAMICS OF GAS-SOLID FLUIDIZED BEDS WITH EVAPORATIVE LIQUID INJECTION

1. Introduction Injections of evaporative liquids into fluidized solid parti- cles are routinely practiced in industrial processes involv- ing gas-solid fluidization systems such as fluid catalytic cracking, polymerization, and plastic coating (Fan et al., 2001). In the FCC riser system, heavy oil is injected into the system to evaporate rapidly by contact with the hot catalyst particles. Simultaneously, thermal and catalytic cracking reactions take place. During a polymerization process, a …     

A model for the flow of solid particles in gases

The flow of solid particles in air streams involves a great deal of variables and complex phenomena, difficult to analyse. In practice the flow quantities in gas-solid flows are predicted by the use of empirical correlations of data or semi-empirical methods. The predictive power of these methods varies substantially between different systems. This paper presents an analytical approach to the subject of gas-solid flows, based on a turbulent model. The mixture is modeled as a variable density fluid flowing in a duct; the equations for the Reynolds stress incorporate the variation of velocity and density together, and yield the velocity profile of the flow and average quantities of interest such as the mass flux, the friction factor, the average density and average areas occupied by each phase. The predicted values for the friction factor are compared with known correlations emanating from experimental data. It is found that there is a very good agreement between the predicted values and the experimental correlations.     

Energy-balance equation for turbulent pulsations in the theory of the free turbulent boundary layer

Semiempirical expressions are proposed for the coefficient of turbulent viscosity and for the scale of turbulence in the equations for the free turbulent boundary layer in an incompressible fluid, these equations consisting of the equation of continuity, the equations of motion, and the equation for the average energy balance in the turbulent pulsations. The advantage of the expressions over the existing ones is that the two empirical constants in the equations have nearly the same values for circular and plane turbulent streams and also for a turbulent boundary layer at the edge of a semiinfinite homogeneous flow with a stationary fluid. The mean-energy distribution and the mean energy of the turbulent pulsations computed in this paper agree well with the experimental values.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 75–79, November–December, 1970.