激光熔凝加工中瞬时温度场及残余应力数值模拟

以激光熔凝表面强韧化处理为背景，应用空间弹塑性有限单元和高精度数值算法同时考虑材料组织性能的变潜模拟工件的温度场及残余应力，研究激光熔凝加工中瞬时温度场及残余应力数值模拟，同时考虑相变潜热及相变塑性的影响，用算例验证了模型的正确性，给出了不同时刻温度场分布及残余应力分布。

应力波在多层介质中传播特性数值分析

通过与相关文献结果的对比,在验证了数值模拟应力波传播可行性的基础上,比较了应力波通过3层花岗岩和夹层为泡沫铝的3层介质后,发现后者应力波幅值的衰减远大于前者,应变能增加为前者的1.6倍,证明了软夹层在研究的速度量级上对能量耗散具有显著作用;在入射波波长为3层介质总厚度1/2的条件下,当泡沫铝的厚度占总厚度约0.2时,得出了3层介质的应变能约为系统总能量的60%,此时入射波波长为泡沫铝厚度的2.5倍,组合介质获得较佳的衰减性能.

低渗透油藏渗吸法采油的数值模拟

针对渗吸法采油中的毛管力驱动项和流动系数的取值问题，根据地下流体渗流特征，建立了低渗透油藏渗吸法采油数学模型，给出了数值解法．定量分析了渗吸法采油的主要影响因素，通过实例验证，用该方法计算的各项动态指标与矿场实际值符合程度较高．结果表明：基质与裂缝渗透率之比小于O．Ol，油水黏度比小于15，毛管力较大的水湿油层比较适合于渗吸法采油，能够提高水驱采收率2％左右．

断续节理岩体随机模型三维离散元数值模拟

针对断续节理岩体提出了一种随机计算模型.在该模型中,假设结构面的形状为正方形,通过岩体结构面的统计分布函数模拟结构面的空间随机分布.给出了随机节理模型的实现方法,对该随机模型的算法可靠性进行了验证.通过单向加载模拟试验研究了节理岩体破坏强度与节理倾角及节理连通率等因素的关系,并与极限平衡条件推导的理论结果进行了比较,分析了数值模拟结果与极限平衡理论结果的异同性,进而验证了节理随机计算模型的可靠性.同时,研究了节理连通率与岩体等效弹性模量之间的影响关系,给出了二者的影响关系式.

氢氧爆轰波在变截面扩张管道中传播的数值模拟

采用二阶精度频散控制耗散格式(DCD)和8组分20个方程的基元反应模型,对轴对称变截面管道中氢氧爆轰波传播进行数值模拟.结果表明,爆轰波传播至突变截面扩张管道时,由于稀疏波的作用可能会使爆轰波局部熄爆甚至完全熄爆,对于某些敏感度高的反应气体爆轰波可以二次起爆.而在渐变截面扩张管道爆轰波相对不易熄爆.

甲烷超声速燃烧过程的数值模拟

提出了一种CH_4/O_2在超声速气流中燃烧的6方程化学反应模型，并且用在超声速高温空气中横向喷射的二维流场进行了数值模拟验证。特别模拟了不同来流条件和壁面条件对燃烧效率的影响及CH_4和空气中的氧气混合燃烧的过程。数值方法采用二阶精度的Harten-Yee隐式TVD格式，计算结果表明6方程反应模型能较好地反映CH_4/O_2的燃烧过程。

含节理岩块单轴受压试验三维离散元数值模拟

采用三维离散元方法，模拟含节理岩块的单轴受压试验。并针对节理空间分布，给出了解析解与数值计算比较的结果，验证了数值模拟的正确性。当节理正交时，离散元与有限元的计算结果一致。计算结果定量地说明了岩体的各向异性和尺寸效应。

超音速流动中侧向喷流干扰特性的数值模拟

通过与实验结果的比较验证Fluent软件可以用于超音速流动中侧向喷流干扰特性数值研究．使用Fluent软件对超音速流动中不同喷流压力和攻角下侧向喷流干扰特性进行的数值研究表明，超音速流动中，随喷流压力和负攻角增大，喷流前的高压区明显增大，喷流的控制效果更好．喷流包裹作用的影响范围在90°弹面内．喷流压力增大，喷流包裹作用加强，影响范围增大．

激光熔凝加工中瞬时温度场数值模拟

以激光熔凝表面强韧化处理为背景,应用空间弹塑性有限单元和高精度数值算法同时考虑材料组织性能的变化模拟工件的温度场,主要研究激光熔凝加工中瞬时温度场数值模拟,同时考虑相变潜热的影响,为第二步热应力场及残余应力的数值模拟做准备.用算例验证了模型的正确性,最后给出了激光熔凝加工不同时刻温度场分布.

气-液两相流界面迁移现象的数值模拟研究

借助于Level Set函数,建立了气-液两相的统一控制方程组,并在交错网格中进行离散.用两种格式,即Superbee-TVD格式和5阶WENO格式求解Level Set函数的输运方程,用SIMPLER算法的思想对主流场控制方程的求解方法进行改进.数值实验结果表明,在求解Level Set的控制方程时,5阶WENO方法比Superbee-TVD格式的结果更准确;用改进的数值算法可成功实现对密度比大于1 000/1的气-液两相流界面迁移问题的数值模拟.对几种典型大密度比气-液两相流问题的计算结果与实际问题的物理规律完全一致,验证了该方法的有效性和可靠性.

Oscillatory Instability of Rayleigh-Marangoni-Benard Convection in Two-Layer System

The convective instabilities in two or more superposed layers heated from below were studied extensively by many scientists due to several interfacial phenomena in nature and crystal growth application. Most works of them were performed mainly on the instability behaviors induced only by buoyancy force, especially on the oscillatory behavior at onset of convection (see Gershuni et. Al.(1982), Renardy et. Al. (1985,2000), Rasenat et. Al. (1989), and Colinet et. Al.(1994)) . But the unstable situations of multi-layer liquid convection will become more complicated and interesting while considering at the same time the buoyancy effect combined with thermocapillary effect. This is the case in the gravity reduced field or thin liquid layer where the thermocapillary effect is as important as buoyancy effect. The objective of this study was to investigate theoretically the interaction between Rayleigh-Bénard instability and pure Marangoni instability in a two-layer system, and more attention focus on the oscillatory instability both at the onset of convection and with increasing supercriticality. Oscillatory behavious of Rayleigh-Marangoni-Bénard convective instability (R-M-B instability) and flow patterns are presented in the two-layer system of Silicon Oil (10cSt) over Fluorinert (FC70) for a larger various range of two-layer depth ratios (Hr=Hupper/Hdown) from 0.2 to 5.0. Both linear instability analysis and 2D numerical simulation (A=L/H=10) show that the instability of the system depends strongly on the depth ratio of two-layer liquids. The oscillatory instability regime at the onset of R-M-B convection are found theoretically in different regions of layer thickness ratio for different two-layer depth H=12,6,4,3mm. The neutral stability curve of the system displaces to right while we consider the Marangoni effect at the interface in comparison with the Rayleigh-Bénard instability of the system without the Marangoni effect (Ma=0). The numerical results show different regimes of the developing of convection in the two-layer system for different thickness ratios and some differences at the onset of pure Marangoni convection and the onset of Rayleigh-Bénard convections in two-layer liquids. Both traveling wave and standing wave were detected in the oscillatory instability regime due to the competition between Rayleigh-Bénard instability and Marangoni effect. The mechanism of the standing wave formation in the system is presented numerically in this paper. The oscillating standing wave results in the competition of the intermediate Marangoni cell and the Rayleigh convective rolls. In the two-layer system of 47v2 silicone oil over water, a transition form the steady instability to the oscillatory instability of the Rayleigh-Marangoni-Bénard Convection was found numerically above the onset of convection for ε=0.9 and Hr=0.5. We propose that this oscillatory mechanism is possible to explain the experimental observation of Degen et. Al.(1998). Experimental work in comparison with our theoretical findings on the two-layer Rayleigh-Marangoni-Bénard convection with thinner depth for H<6mm will be carried out in the near future, and more attention will be paid to new oscillatory instability regimes possible in the influence of thermocapillary effects on the competition of two-layer liquids

Rayleigh-Marangoni-Bénard Convective Instability

The Rayleigh-Marangoni-Benard convective instability (R-M-B instability) and flow patterns in the two-layer system of silicon oil 10cSt and Fluorinert FC70 liquids are studied theoretically and experimentally. Both linear instability analysis and 2D numerical simulation (A=L/H=10) were performed to study the influence of thermocapillary force on the convective instability of the two-layer system. Time-dependent oscillations arising at the onset of convection were investigated in a larger various range of two-layer depth ratios (Hr=H1/H2) from 0.2 to 5.0 for different total depth less than 12mm. Our results are different from the previous study on the Rayleig-B閚ard instability and show the strong effects of thermocapillary force at the interface on the time-dependent oscillations at the onset of instability convection. Primary experimental results of the critical instability parameters and the convective structure in the R-M-B convection have been obtained by using the digital particle image velocimetry (DPIV) system, and a good agreement in comparison with the results of numerical simulation was obtained.

Transient Temperature Distribution in a Sheet Metal by Low-Energy Laser Scanning

Low-energy laser-heating techniques are widely used in engineering applications such as, thinfilm deposition, surface treatment, metal forming and micro-structural pattern formation. In this paper,under the conditions of ignoring the thermo-mechanical coupling, a numerical simulation on the spatialand temporal temperature distribution in a sheet metal produced by the laser beam scanning in virtue of thefinite element method is presented. Both the three-dimensional transient temperature field and thetemperature evolution as a function of heat penetrating depth in the metal sheet are calculated. Thetemperature dependence of material properties was taken into account. It was shown that, after taking thetemperature dependence of the material absorbance effect into consideration, the temperature change ratealong the scanning direction and the temperature maximum were both increased.

Optimization of Off-Null Ellipsometry for Optical Biosensor Applications

The optimization of off-null ellipsometry is described with emphasis on the improvement of resolution for visualizing biomolecule layers. For optical biosensor with layer thickness below 6.5 nm, a numerical simulation for the dependence of resolution on the azimuth settings of polarizer and analyzer is presented first. For comparison, three different resolutions are given at three azimuth settings which are near null and far away from null condition, respectively. Furthermore, the square or linear approximation relationship between the intensity and the layer thickness are also given at these settings. The difference among their accuracy is up to 100 times or so. Experimental results of the biosensor sample verify the optimization.