核反应堆蒸汽发生器二次侧的流动不稳定现象不仅会影响控制系统,而且会使设备结构的压力边界疲劳损坏。两相流不稳定性的表现形式多样、影响因素众多、机理复杂、研究方法种类多,一直是蒸汽发生器和两相流领域的经典问题之一。首先,该...核反应堆蒸汽发生器二次侧的流动不稳定现象不仅会影响控制系统,而且会使设备结构的压力边界疲劳损坏。两相流不稳定性的表现形式多样、影响因素众多、机理复杂、研究方法种类多,一直是蒸汽发生器和两相流领域的经典问题之一。首先,该文介绍了两相流不稳定性的常见分类和3种典型不稳定性的机理,包括流量漂移、密度波型脉动和压力降型脉动。其次,从守恒方程出发,总结了各种研究方法。再次,系统性总结了3种典型不稳定性的研究现状,并重点介绍了清华大学核能与新能源技术研究院堆工团队的工作。然后,该文提出了使用新无量纲数描述复杂过热系统,包括两相数、过热数、无量纲泵数和无量纲旁通数,明确和统一了Froude数、摩擦数、管长和管径等对密度波型脉动的影响规律,并解释了此前研究中矛盾的结论。同时,该文给出了有关模型简化和边界条件对稳定边界影响的理论推导和证明,并明确了实验室小规模单管或简化并联管试验段及工程验证试验回路与实际核电厂蒸汽发生器及二回路系统之间的替代条件。最后,该文介绍了高温气冷堆示范工程(high temperature gas-cooled reactor-pebble bed module, HTR-PM)蒸汽发生器如何通过设计来避免不稳定性问题。展开更多
The airborne electromagnetic （AEM） method has a high sampling rate and survey flexibility. However, traditional numerical modeling approaches must use high-resolution physical grids to guarantee modeling accuracy, e...The airborne electromagnetic （AEM） method has a high sampling rate and survey flexibility. However, traditional numerical modeling approaches must use high-resolution physical grids to guarantee modeling accuracy, especially for complex geological structures such as anisotropic earth. This can lead to huge computational costs. To solve this problem, we propose a spectral-element （SE） method for 3D AEM anisotropic modeling, which combines the advantages of spectral and finite-element methods. Thus, the SE method has accuracy as high as that of the spectral method and the ability to model complex geology inherited from the finite-element method. The SE method can improve the modeling accuracy within discrete grids and reduce the dependence of modeling results on the grids. This helps achieve high-accuracy anisotropic AEM modeling. We first introduced a rotating tensor of anisotropic conductivity to Maxwell＇s equations and described the electrical field via SE basis functions based on GLL interpolation polynomials. We used the Galerkin weighted residual method to establish the linear equation system for the SE method, and we took a vertical magnetic dipole as the transmission source for our AEM modeling. We then applied fourth-order SE calculations with coarse physical grids to check the accuracy of our modeling results against a 1D semi-analytical solution for an anisotropic half-space model and verified the high accuracy of the SE. Moreover, we conducted AEM modeling for different anisotropic 3D abnormal bodies using two physical grid scales and three orders of SE to obtain the convergence conditions for different anisotropic abnormal bodies. Finally, we studied the identification of anisotropy for single anisotropic abnormal bodies, anisotropic surrounding rock, and single anisotropic abnormal body embedded in an anisotropic surrounding rock. This approach will play a key role in the inversion and interpretation of AEM data collected in regions with anisotropic geology.展开更多
文摘核反应堆蒸汽发生器二次侧的流动不稳定现象不仅会影响控制系统,而且会使设备结构的压力边界疲劳损坏。两相流不稳定性的表现形式多样、影响因素众多、机理复杂、研究方法种类多,一直是蒸汽发生器和两相流领域的经典问题之一。首先,该文介绍了两相流不稳定性的常见分类和3种典型不稳定性的机理,包括流量漂移、密度波型脉动和压力降型脉动。其次,从守恒方程出发,总结了各种研究方法。再次,系统性总结了3种典型不稳定性的研究现状,并重点介绍了清华大学核能与新能源技术研究院堆工团队的工作。然后,该文提出了使用新无量纲数描述复杂过热系统,包括两相数、过热数、无量纲泵数和无量纲旁通数,明确和统一了Froude数、摩擦数、管长和管径等对密度波型脉动的影响规律,并解释了此前研究中矛盾的结论。同时,该文给出了有关模型简化和边界条件对稳定边界影响的理论推导和证明,并明确了实验室小规模单管或简化并联管试验段及工程验证试验回路与实际核电厂蒸汽发生器及二回路系统之间的替代条件。最后,该文介绍了高温气冷堆示范工程(high temperature gas-cooled reactor-pebble bed module, HTR-PM)蒸汽发生器如何通过设计来避免不稳定性问题。
基金financially supported by the Key Program of National Natural Science Foundation of China(No.41530320)China Natural Science Foundation for Young Scientists(No.41404093)+1 种基金Key National Research Project of China(Nos2016YFC0303100 and 2017YFC0601900)China Natural Science Foundation(No.41774125)
文摘The airborne electromagnetic （AEM） method has a high sampling rate and survey flexibility. However, traditional numerical modeling approaches must use high-resolution physical grids to guarantee modeling accuracy, especially for complex geological structures such as anisotropic earth. This can lead to huge computational costs. To solve this problem, we propose a spectral-element （SE） method for 3D AEM anisotropic modeling, which combines the advantages of spectral and finite-element methods. Thus, the SE method has accuracy as high as that of the spectral method and the ability to model complex geology inherited from the finite-element method. The SE method can improve the modeling accuracy within discrete grids and reduce the dependence of modeling results on the grids. This helps achieve high-accuracy anisotropic AEM modeling. We first introduced a rotating tensor of anisotropic conductivity to Maxwell＇s equations and described the electrical field via SE basis functions based on GLL interpolation polynomials. We used the Galerkin weighted residual method to establish the linear equation system for the SE method, and we took a vertical magnetic dipole as the transmission source for our AEM modeling. We then applied fourth-order SE calculations with coarse physical grids to check the accuracy of our modeling results against a 1D semi-analytical solution for an anisotropic half-space model and verified the high accuracy of the SE. Moreover, we conducted AEM modeling for different anisotropic 3D abnormal bodies using two physical grid scales and three orders of SE to obtain the convergence conditions for different anisotropic abnormal bodies. Finally, we studied the identification of anisotropy for single anisotropic abnormal bodies, anisotropic surrounding rock, and single anisotropic abnormal body embedded in an anisotropic surrounding rock. This approach will play a key role in the inversion and interpretation of AEM data collected in regions with anisotropic geology.
