Implementation and verification of a user‐defined element (UEL) for coupled thermal‐hydraulic‐mechanical‐chemical (THMC) processes in saturated geological media
Implementation and verification of a user‐defined element (UEL) for coupled thermal‐hydraulic‐mechanical‐chemical (THMC) processes in saturated geological media
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DOI：
10.1002/nag.3556
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发表时间：
2023
影响因子：
4
通讯作者：
Xiang Zhou;Yida Zhang
中科院分区：
文献类型：
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作者：
Xiang Zhou;Yida Zhang
高效、准确地模拟各种岩层中的热-水-力-化学耦合（THMC）过程对于设计能源地质结构（如高放核废料地下储存库）是必不可少的。这项工作的重点是开发和验证一个隐式有限元求解器的通用耦合THMC问题的地质设置。从质量、动量和能量平衡定律出发，导出了一套专门的控制方程和热多孔弹性本构模型。该系统，然后解决了隐式有限元（FE）计划。具体而言，残差和雅可比矩阵在用户定义单元（UEL）子程序中编写脚本，然后与通用有限元软件Abaqus Standard结合使用，以求解初边值问题。考虑到系统的复杂性，UEL的开发遵循逐步的方式，首先求解耦合的水力-机械（HM）和热力-水力-机械（THM）方程，然后再转向完整的THMC问题。每个实施步骤包括至少一个验证测试，通过将计算结果与封闭形式的解析解进行比较，以确保正确实现各种耦合效应。为了证明算法的鲁棒性和验证UEL，参考20世纪80年代在比利时的ATLAS现场加热试验进行了三维案例研究。然后通过激活化学浓度自由度并在加热器表面规定恒定的高浓度来模拟假设的放射性核素泄漏事件。该模型预测了一个有限的污染政权后，六年考虑扩散和平流对物种运输的影响。
Efficient and accurate modeling of the coupled thermal‐hydraulic‐mechanical‐chemical (THMC) processes in various rock formations is indispensable for designing energy geo‐structures such as underground repositories for high‐level nuclear wastes. This work focuses on developing and verifying an implicit finite element solver for generic coupled THMC problems in geological settings. Starting from the mass, momentum, and energy balance laws, a specialized set of governing equations and a thermoporoelastic constitutive model is derived. This system is then solved by an implicit finite element (FE) scheme. Specifically, the residuals and the Jacobians are scripted in a user‐defined element (UEL) subroutine which is then combined with the general‐purpose FE software Abaqus Standard to solve initial‐boundary value problems. Considering the complexity of the system, the UEL development follows a stepwise manner by first solving the coupled hydraulic‐mechanical (HM) and thermal‐hydraulic‐mechanical (THM) equations before moving on to the full THMC problem. Each implementation step consists of at least one verification test by comparing computed results with closed‐form analytical solutions to ensure that the various coupling effects are correctly realized. To demonstrate the robustness of the algorithm and to validate the UEL, a three‐dimensional case study is performed with reference to the in‐situ heating test of ATLAS at Belgium in 1980s. A hypothetical radionuclide leakage event is then simulated by activating the chemical‐concentration degree of freedom and prescribing a constant high concentration at the heater's surface. The model predicts a limited contaminated regime after six years considering both diffusion and advection effects on species transport.