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本文讨论了k个独立正态总体的均值和方差同时在简单半序约束下的极大似然估计的求解问题,给出了计算极大估计的迭代算法,且证明该算法收敛。 相似文献
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Fluid-solid coupling model for studying wellbore instability in drilling of gas hydrate bearing sediments 总被引:1,自引:0,他引:1
As the oil or gas exploration and development activities in deep and ultra- deep waters become more and more, encountering gas hydrate bearing sediments (HBS) is almost inevitable. The variation in temperature and pressure can destabilize gas hydrate in nearby formation around the borehole, which may reduce the strength of the formation and result in wellbore instability. A non-isothermal, transient, two-phase, and fluid-solid coupling mathematical model is proposed to simulate the complex stability performance of a wellbore drilled in HBS. In the model, the phase transition of hydrate dissociation, the heat exchange between drilling fluid and formation, the change of mechanical and petrophysical properties, the gas-water two-phase seepage, and its interaction with rock deformation are considered. A finite element simulator is developed, and the impact of drilling mud on wellbore instability in HBS is simulated. Results indicate that the re- duction in pressure and the increase in temperature of the drilling fluid can accelerate hydrate decomposition and lead to mechanical properties getting worse tremendously. The cohesion decreases by 25% when the hydrate totally dissociates in HBS. This easily causes the wellbore instability accordingly. In the first two hours after the formation is drilled, the regions of hydrate dissociation and wellbore instability extend quickly. Then, with the soaking time of drilling fluid increasing, the regions enlarge little. Choosing the low temperature drilling fluid and increasing the drilling mud pressure appropriately can benefit the wellbore stability of HBS. The established model turns out to be an efficient tool in numerical studies of the hydrate dissociation behavior and wellbore stability of HBS. 相似文献
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针对光散射细胞微粒测量中真实形体细胞的取向对测量结果的影响问题,基于Rayleigh-Debye-Gans理论和双椭球核式(CEM)模型在应用中的差异,建立了CEM的修正模型(MCEM),根据此模型系统讨论了细胞在不同入射角变化情况下其光散射强度分布所产生的变化,得到了不同入射角下有核细胞光散射强度分布与有核细胞相关物理特征量的动态响应关系;此外,对有核细胞光散射强度分布进行拟合,得到了有核细胞光散射强度分布函数。误差分析表明:拟合结果可有效地应用于真实细胞光散射测量中的数值反演计算。 相似文献
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