围绕变壁温水平圆柱热源接触熔化的理论分析

研究围绕变壁温热源的接触熔化,建立表面温度随角度变化的水平圆柱热源接触熔化模型.对紧密接触熔化区的液体传热与运动状态进行分析,运用Nusselt液膜理论建立熔化控制方程,并采用理论求解,得到稳定熔化时的熔化速度解析解,所得结果包含了文献关于定壁温热源熔化的分析结果.通过分析不同温度分布下发生接触熔化的熔化速度、液膜厚度和压力分布情况,得到温度分布对熔化影响的规律.     

几何位置对封闭方腔内水平孤立平板自然对流换热的影响

本文以冰箱蒸发器等实际问题为背景，以空气为介质用数值模拟方法研究了封闭方腔内水平孤立平板层流自然对流时Ｒａ数及平板位置变化对Ｎｕｍ的影响，得出了可供工程应用参考的结论。同时用烟可视化的实验验证了计算结果的正确性。     

基于周向SH0导波的管道轴向缺陷定量表征

随着管道服役时间的增加,其损伤逐渐累积,最终导致泄漏或爆炸事故。引入导波在线监测管道损伤是确保其安全运行的重要保障。周向零阶水平剪切(CSH0)波具有不易频散、对管道轴向缺陷敏感等优秀特性,非常适用于管道轴向缺陷的定量表征。该文基于周向SH0导波在管道的传播特性,通过有限元模拟和试验对管道周向SH0模态导波与轴向缺陷的定量关系展开研究。结果表明:管道曲率半径越大,周向SH0模态的传播特性越接近板中SH0模态的传播特性;导波信号的反射系数和透射系数对轴向缺陷的长度和深度均呈现单调变化。依此建立了缺陷定量表征的关系云图,可用于评估缺陷尺寸。     

超临界R134a水平圆管内冷却换热模拟研究

采用增强壁面函数的标准k-ε模型对超临界R134a水平圆管内冷却换热进行了模拟研究.分析了管内不同截面上流体温度、速度和湍动能的分布情况及对应关系。研究了质量流量和浮升力对换热系数的影响。结果表明,流体速度随着温度的降低而减小,并且最大速度处对应着最高温度和最小湍动能.换热系数随着质量流量的增加而增大,其峰值出现在准临界温度附近。浮升力在似液体区的影响较大,对流体换热起到增强的效果。     

激振面积对低应变动测法影响的数值研究

利用ABAQUS有限元软件建模, 分析了基桩横向尺寸对低应变检测的影响. 结果表明: (1)在建模过程中, 当桩端土厚度及桩周土半径达到桩长的1/2以上时, 计算所得数值解可以收敛稳定; (2)基桩横向尺寸对低应变法检测有显著影响, 具体与施加激振面积相关, 当激振面积较大时, 横向尺寸影响能有效弱化; (3)通过实测曲线与数值解比较, 二者较为吻合, 本文所述规律和方法对工程实践具有一定指导意义.     

THE OPTIMAL CONTROL SYSTEM OF 3D HORIZONTAL WELL AND ITS APPLICATION

A multi-objective optimal control model for nonlinear multilevel dynamicalsystem is built in this paper. The existence of the solutions to this systemand the controllability and the polykeys of the control are discussed. In orderto obtain the global optimal solution, Uniform Design method is introducedto select initial1 feasible points, then an improved Hooke-jeeves algorithm isproposed. The new algorithm and its corresponding software we developed hasvalidated in more than 12 horizontal wells, which show their advantages suchas less length of trajectory designed, more accuracy of target hitting and lesstime-consuming comparison with present conventional method.     

Maximum survival capability of an aircraft in a severe windshear

This paper is concerned with guidance strategies and piloting techniques which ensure near-optimum performance and maximum survival capability in a severe windshear. The take-off problem is considered with reference to flight in a vertical plane. In addition to the horizontal shear, the presence of a downdraft is assumed.First, six particular guidance schemes are considered, namely: constant alpha guidance; maximum alpha guidance; constant velocity guidance; constant absolute path inclination guidance; constant rate of climb guidance; and constant pitch guidance. Among these, it is concluded that the best one is the constant pitch guidance.Next, in an effort to improve over the constant pitch guidance, three additional trajectories are considered: the optimal trajectory, which minimizes the maximum deviation of the absolute path inclination from a reference value, while employing global information on the wind flow field; the gamma guidance trajectory, which is based on the absolute path inclination and which approximates the behavior of the optimal trajectory, while employing local information on the windshear and the downdraft; and the simplified gamma guidance trajectory, which is the limiting case of the gamma guidance trajectory in a severe windshear and which does not require precise information on the windshear and the downdraft.The essence of the simplified gamma guidance trajectory is that it yields a quick transition to horizontal flight. Comparative numerical experiments show that the survival capability of the simplified gamma guidance trajectory is superior to that of the constant pitch trajectory and is close to that of the optimal trajectory.Next, with reference to the simplified gamma guidance trajectory, the effect of the feedback gain coefficient is studied. It is shown that larger values of the gain coefficient improve the survival capability in a severe windshear; however, excessive values of the gain coefficient are undesirable, because they result in larger altitude oscillations and lower average altitude.Finally, with reference to the simplified gamma guidance trajectory, the effect of time delays is studied, more specifically, the time delay ₁ in reacting to windshear onset and the time delay ₂ in reacting to windshear termination. While time delay ₂ has little effect on survival capability, time delay ₁ appears to be critical in the following sense: smaller values of ₁ correspond to better survival capability in a severe windshear, while larger values of ₁ are associated with a worsening of the survival capability in a severe windshear.This research was supported by NASA-Langley Research Center, Grant No. NAG-1-516, and by Boeing Commercial Airplane Company.     

饱和含混多孔介质中环绕水平圆柱的自然对流

本文运用达西流模型，对饱和含湿多孔介质中环绕水平等温圆柱发生的自然对流进行了数值模拟和分析。流函数和温度分布采用傅里叶级数的形式，以联立求解二维流动的控制方程组，傅里叶级数项的系数由一维常微分方程的解得到。文中同时给出局部和平均努谢尔数随修正瑞利数的变化关系以及修正瑞利数处在０．１～１０范围内时二维流场和温度场分布。     

Numerical Estimation of the Degree of Reservoir Permeability Heterogeneity Using Pressure Drawdown Tests

This study aims to correlate the response of pressure transient test to permeability distribution type. For this purpose, correlated permeability distributions in x–y direction are generated using fractional Brownian motion (fBm) as it has been shown in literature that permeability in carbonate reservoirs exhibits an fBm type distribution horizontally. 2-D fBm permeability distributions created using mid point displacement method are employed as data to a black oil simulator. The intermittence exponent, H or fractal dimension of the distribution, D, as defined by D=2 – H, characterizes the distribution type. All permeability distributions are normalized to represent the same arithmetic mean (20, 100, and 500 mD) and uniform variance so that only their fractal dimension that underlies the smoothness of the distribution distinguishes them. Many different realizations of permeability distributions are generated based on the random number seeds used and pressure transient (drawdown) tests are simulated using a black oil simulator package (ECLIPSE 100). Pressure transient analysis is performed using PanSystem package. As a base case and for the comparison purpose, the same procedure is repeated for the totally homogeneous case (the same permeability for all grids) and a random (normally distributed) permeability distribution with the same mean and uniform variance. The effects of permeability distribution type on the pressure response are clarified. A strong impact of heterogeneity is observed as an increase in skin effect with increasing fractal dimension of permeability distribution. This additional (or pseudo) skin effect due to heterogeneity is correlated to the fractal dimension of the permeability distribution. As a further step, the procedure is repeated for different flow rates applied during the drawdown test. The correlation between the fractal dimension of permeability distribution and additional skin is improved by incorporating the rate into it. The methodology followed can be used in the assessment of reservoir heterogeneity quantitatively using pressure transient response.     

水平摆振下环形巴西果分离效应模拟研究

为了研究水平摆振下混合颗粒体系的分离行为及其机理,利用离散单元法进行数值模拟,对二元混合颗粒振动下的运动行为进行了研究,观察到圆筒形容器内一种新的分离现象,即"环形巴西果"分离。通过对比不同振动参数、不同区域内混合颗粒体系的运动特性,分析了颗粒的整体流态、能量、离心力作用以及颗粒间的力链结构强度,对混合颗粒的中心偏析、边界堆积以及整体分离行为,揭示了"环形巴西果"分离构型的内在机理。结果表明:频率为1Hz、振幅为160°时,混合颗粒出现"环形巴西果"分离现象;频率为3Hz、振幅为40°时,混合颗粒出现"巴西果"分离现象,且通过调整振幅和频率可以控制中心区域大颗粒偏析程度,实现"环形巴西果"分离构型与"巴西果"分离构型之间的转换。