A new fully nonisothermal coupled model for the simulation of ice sheet flow

A shallow ice thermocoupled model for the complex nonlinear polythermal ice sheet dynamics is proposed and solved by means of efficient numerical methods. A novelty is the obstacle problem formulation associated to a nonlinear integro-differential equation (with nonlocal temperature dependent coefficients) for the ice sheet profile. This formulation is motivated by the free boundary feature and the influence of the temperature on the profile (fully nonisothermal model). Concerning the temperature equation, a dynamically prescribed surface temperature, obtained from an Energy Balance model corrected by the altitude effect, is posed. As the profile and temperature equations are fully coupled, a nonlinear PDE system governing the upper ice sheet profile, the velocity field, the temperature and the basal stress is stated. In addition to the numerical difficulties associated to the new profile equation, several techniques have been considered for the numerical solution of the temperature, velocity and basal magnitudes. Discussions concerning the nonlinear dynamics of the different involved magnitudes and the improvement in their computed values with respect to previous works are also presented.     

液态金属自由表面膜流MHD效应的数值模拟

对液态金属自由表面膜流在强磁场下的磁流体力学效应进行了数值模拟研究,获得了液态金属自由表面的形状、截面流速分布及截面上的电动势分布,从而能对膜流的一些磁流体动力学行为作出解释。数值计算结果与理论分析和实验结果符合较好。由实验和数值模拟结果可以得出,液态金属膜流通过强磁场时,磁场会阻碍膜流的运动。     

Numerical simulation of bubble dynamics in a Phan-Thien–Tanner liquid: Non-linear shape and size oscillatory response under periodic pressure

We study non-linear bubble oscillations driven by an acoustic pressure with the bubble being immersed in a viscoelastic, Phan-Thien–Tanner liquid. Solution is provided numerically through a method which is based on a finite element discretization of the Navier–Stokes flow equations. The proposed computational approach does not rely on the solution of the simplified Rayleigh–Plesset equation, is not limited in studying only spherically symmetric bubbles and provides coupled solutions for the velocity, stress fields and bubble interface. We present solutions for non-spherical bubbles, with asphericity being addressed by means of Legendre polynomials or associated Legendre functions. A parametric investigation of the bubble dynamical oscillatory response as a function of the fluid rheological properties shows that the amplitude of bubble oscillations drastically increases as liquid elasticity (quantified by the Deborah number) increases or as liquid viscosity decreases (quantified by the Reynolds number). Extensive numerical calculations demonstrate that increasing elasticity and/or viscosity of the surrounding liquid tend to stabilize the shape anisotropy of an initially non-spherical bubble. Results are shown for pressure amplitudes 0.2–2 MPa and Deborah, Reynolds numbers in the intervals of 1–8 and 0.094–1.256, respectively.     

A volume of fluid approach for crystal growth simulation

A new approach to simulating the dendritic growth of pure metals, based on a recent volume of fluid (VOF) method with PLIC (piecewise linear interface calculation) reconstruction of the interface, is presented. The energy equation is solved using a diffuse-interface method, which avoids the need to apply the thermal boundary conditions directly at the solid front. The thermal gradients at both sides of the interface, which are needed to obtain the front velocity, are calculated with the aid of a distance function to the reconstructed interface. The advection equation of a discretized solid fraction function is solved using the unsplit VOF advection method proposed by López et al. [J. Comput. Phys. 195 (2004) 718–742] (extended to three dimensions by Hernández et al. [Int. J. Numer. Methods Fluids 58 (2008) 897–921]), and the interface curvature is computed using an improved height function technique, which provides second-order accuracy. The proposed methodology is assessed by comparing the numerical results with analytical solutions and with results obtained by different authors for the formation of complex dendritic structures in two and three dimensions.     

CICC导体轧制过程有限元模拟

利用显式动力学有限元分析软件ANSYS/LS-DYNA对CICC导体的轧制过程进行了模拟,得到了导体在不同轧制道次中所需的轧制力以及轧制道次对导体形状和残余应力的影响。轧制力的计算结果与参考的实验数据吻合,能为导体轧制成型设备的研制提供依据。     

低温气液两相流数值计算

低温工质两相流动在很多场合都存在,研究深冷剂在两相流动时参数的分布有着很重要的作用.文中采用一维均相流模型对液氮循环流动过程进行稳态数值模拟,得到了循环流动过程中液氮含汽率、压力和温度沿管程方向的分布情况,并对由于不同回路条件引起的不同结果进行了分析.     

大气压射频氧气放电特性的数值模拟研究

基于漂移扩散近似,对大气压下氧气射频放电产生的等离子体建立了一维流体模型,包括了电子、正离子和负离子的连续性方程、电子能量方程及泊松方程。采用有限差分法对所建立的模型进行了自洽的数值模拟,得到了相应的数值结果。通过对所得数值结果的分析,研究了大气压下氧气放电的基本特性。研究表明,大气压氧气放电中等离子体密度可达到10¹²cm^-3 ,电子温度约在1.23eV,放电中主要的负离子是O^-离子;随着电压峰值的增加,电子密度、电子温度都增加,但n_O-/n_e 的比率先增加到7.5%又后减小到5%,在电压峰值为700V 时达到最大。     

近海平面大气湍流对光波传输影响的数值模拟

针对近海平面大气湍流的特点,采用多相位屏法,对平面波在不同湍流强度下的近海平面的传播进行了数值模拟。对最终的能量分布与在真空中传播相同距离的传播结果进行了比较。结果表明,湍流对光波强度的影响显著,且湍流强度越大,光波强度起伏越大。     

Numerical simulation of Bessel beams by FDTD employing the superposition principle

Finite difference time domain (FDTD) method is adopted to build a Bessel beams simulation model according to homogeneousness and linearity of the Maxwell equations in source-free region. Validation for this model is confirmed by comparing the simulation results with the theoretical results solved with a vector Helmholtz equation in free space and good agreement with maximum error 2% has been demonstrated. It is indicated that FDTD could be an effective approach to analyze other complicated models of Bessel beams in source-free region by means of superposition principle.     

表面垂直裂痕诱发瑞利波散射的数值分析

激光激发的声表面波为材料表面缺陷的检测提供了有力的工具.针对含缺陷材料在模型边界上的复杂性,建立了基于平面应变的有限元模型并选取了相同厚度但含有不同深度的表面裂痕的单层铝板进行了对比计算,得到了声表面波经过不同深度的表面裂痕时产生的反射及透射信号波形的时域特征.进而引入了基于Wigner-Ville分布理论的时-频分析方法计算裂痕前、后散射的瞬态表面波的能量在时间-频率平面内分布的情形.结果显示：声表面波接近中心频率的某一频率成分在经过深度小于其中心波长的表面缺陷时,随着裂痕深度的增加,对应于该频率的反射系数呈现单调递增的趋势;而透射系数呈现递减的特征,这一结果可以为激光超声检测表面缺陷提供一种定量的表征手段.     

Numerical simulation of the ultrasonic waves generated by ring-shaped laser illumination patterns

The generation of ultrasound in aluminum plate subjected to ring-shaped laser beam illumination has been studied quantitatively by using the finite element method. The superposition effects of surface acoustic waves on the top surface and the bulk ultrasonic waves on the rear surface of specimen have been obtained in a single simulation. The typical displacement profiles of the bulk ultrasonic wave at various depths along the central axis of the ring are obtained for three different radii, and the effect of the ring radius on the focal depths of the compression and shear mode are determined. The numerical results confirm that the focal depth of a bulk acoustic mode is determined by the directivity patterns of the acoustic mode generated by point-like laser sources via a thermoelastic mechanism, which depends on the physical constants of elastic medium.     

Numerical simulation of laser-generated ultrasound in non-metallic material by the finite element method

The use of a pulsed laser for the generation of the elastic waves in non-metallic materials in the thermoelastic regime is investigated by using finite element method (FEM), taking into account not only thermal diffusion and the finite spatial and temporal shape of the laser pulse, but also optical penetration and the temperature dependence of material properties. The optimum finite element model is established based on analysis of two important parameters, meshing size and time step, and the stability of solution. Temperature distributions and temperature gradient fields in non-metallic material for different time steps are obtained, this temperature field is equivalent to a bulk force source to generate ultrasonic wave. The laser-generated ultrasound waveforms at the epicenter and surface acoustic waveforms (SAWs) are obtained and the influence of optical penetration into the material on the temperature field and the ultrasound waveforms are analyzed. The numerical results indicate that the heat penetration into non-metallic material is caused mainly by the optical penetration, and the ultrasound waveforms, especially the shape of the precursor, are strongly dependent on the optical penetration depth into non-metallic material.     

固体热容激光器冷却方式的数值模拟

 固体热容激光器连续运转一段时间后，需要进行冷却，以进行下一次运转，因此冷却速度直接影响着热容激光器运转的效率和实用性。从热传导方程出发，以沉积热为内热源模型，利用有限元分析方法对激光二极管阵列从4个方向对称泵浦的板条Nd:GGG激光介质的温度场和和热应力场进行了数值模拟。并对冷却阶段分别采用过冷气体、水循环、喷雾、相变冷却方式时的介质温度和应力随时间变化过程进行了模拟。结果表明在相同条件下采用相变冷却方式能在较短时间内将介质冷却到初始温度。     

微喷颗粒与气体混合过程的数值模拟研究

冲击波作用下金属与气体界面将发生微喷混合现象,即金属表面产生的微喷射物质在气体中的输运过程.提出采用散体颗粒分布代替微喷初始状态,基于气体-颗粒两相流模型对微喷混合现象进行了模拟研究.数值模拟给出了微喷混合的动力学演化过程,分析了初始气体压力和颗粒尺寸因素对混合层的影响规律;在数值模拟中发现了微喷颗粒的气动破碎现象,这可导致颗粒尺度明显减小,成为影响微喷混合演化性质的重要物理因素.本文模拟结果与相关实验结果取得一致,初步表明,气粒两相流模型是模拟微喷混合过程的一种有效方法.     

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以磁流体理论为基础,采用基于有限体积法的通量差分分裂格式数值求解具有双曲保守律形式的电阻磁流体方程组.编写C++程序对平板几何位形下的等离子体双撕裂模进行了长时间数值模拟,得到双撕裂模不稳定性的演化图景,捕捉到了双撕裂模非线性发展过程中磁场重联的几个典型阶段,讨论了等离子体电阻和两个有理面之间的距离对双撕裂模不稳定性非线性发展的影响.为研究磁流体动力学提供了一种可行的高精度数值算法.     

刮膜蒸发器内非牛顿流体流场特性数值模拟

刮膜蒸发器是通过旋转刮板强制成膜,可实现高黏度非牛顿流体类物料平稳蒸发的新型高效蒸发器.蒸发器内流体的流动、分布与传输机制直接决定了蒸发器的蒸发效率与功耗.不同于现有研究主要基于牛顿流体开展,本文针对不同黏度的非牛顿流体,建立蒸发器三维计算流体动力学模型,系统研究了蒸发器内的流场分布特性和成膜机理.结果表明:低黏非牛顿流体的流场分布特性和牛顿流体类似,物料可在壁面形成均匀且连续的液膜;随着黏度的增加,液膜的均匀性和连续性逐渐变差.通过对流场分布与传输形式的研究,结合液膜分布、速度分布、剪应变率分布,以及黏度分布进行对比分析发现,蒸发器内部结构与运行状态形成的剪切场与黏度分布是蒸发器良好成膜的关键.此外,提出对刮板前缘进行弯折可辅助高黏流体液膜铺展,并对最佳弯折角度进行探索.本研究为刮膜蒸发器的设计和应用提供了理论指导与依据.     

刮膜蒸发器内非牛顿流体流场特性数值模拟

刮膜蒸发器是通过旋转刮板强制成膜,可实现高黏度非牛顿流体类物料平稳蒸发的新型高效蒸发器.蒸发器内流体的流动、分布与传输机制直接决定了蒸发器的蒸发效率与功耗.不同于现有研究主要基于牛顿流体开展,本文针对不同黏度的非牛顿流体,建立蒸发器三维计算流体动力学模型,系统研究了蒸发器内的流场分布特性和成膜机理.结果表明:低黏非牛顿流体的流场分布特性和牛顿流体类似,物料可在壁面形成均匀且连续的液膜;随着黏度的增加,液膜的均匀性和连续性逐渐变差.通过对流场分布与传输形式的研究,结合液膜分布、速度分布、剪应变率分布,以及黏度分布进行对比分析发现,蒸发器内部结构与运行状态形成的剪切场与黏度分布是蒸发器良好成膜的关键.此外,提出对刮板前缘进行弯折可辅助高黏流体液膜铺展,并对最佳弯折角度进行探索.本研究为刮膜蒸发器的设计和应用提供了理论指导与依据.     

基于有限体积法数值模拟双撕裂模非线性演化

以磁流体理论为基础,采用基于有限体积法的通量差分分裂格式数值求解具有双曲保守律形式的电阻磁流体方程组。编写C++程序对平板几何位形下的等离子体双撕裂模进行了长时间数值模拟,得到双撕裂模不稳定性的演化图景,捕捉到了双撕裂模非线性发展过程中磁场重联的几个典型阶段,讨论了等离子体电阻和两个有理面之间的距离对双撕裂模不稳定性非线性发展的影响。为研究磁流体动力学提供了一种可行的高精度数值算法。     

Self-consistent three-dimensional modeling and simulation of large-scale rectangular surface-wave plasma source

A self-consistent and three-dimensional (3D) model of argon discharge in a large-scale rectangular surface-wave plasma (SWP) source is presented in this paper, which is based on the finite-difference time-domain (FDTD) approximation to Maxwell's equations self-consistently coupled with a fluid model for plasma evolution. The discharge characteristics at an input microwave power of 1200~W and a filling gas pressure of 50~Pa in the SWP source are analyzed. The simulation shows the time evolution of deposited power density at different stages, and the 3D distributions of electron density and temperature in the chamber at steady state. In addition, the results show that there is a peak of plasma density approximately at a vertical distance of 3~cm from the quartz window.     

A New Numerical Solution of Fluid Flow in Stratigraphic Porous Media

A new numerical technique based on a lattice-Boltzmann method ispresented for analyzing the fluid flow in stratigraphic porousmedia near the earth's surface. The results obtained for therelations between porosity, pressure, and velocity satisfy wellthe requirements of stratigraphic statistics and hence are helpfulfor a further study of the evolution of fluid flow instratigraphic media.