This special issue of the International Journal for Multiscale Computational Engineering is dedicated to the field of computational poromechanics. We refer to the term poromechanics as a discipline that studies the coupled responses of multiphase materials that contain voids filled with one or multiple types of fluids. Materials fitting this description include many geological materials (e.g., sand, clay, and rock), live matters (e.g., bones, skins, periodontal ligament), and manufactured materials (e.g., concrete, diaper cores, and polymeric gels), among others. Inside a porous medium, the fluids in the voids may either be trapped inside the isolated pores or they may diffuse in the connected pore space. The multiple fluid constituents may also trigger chemical reactions among themselves or with the solid constituents. As a result, the deformation of the solid skeleton and the diffusion of the pore fluid are processes that strongly influence each other. This coupling effect is important for many engineering applications central to our daily lives. For instance, the buildup of the pore fluid pressure may lead to the fracture of the solid constituent, which in return allows hydro-carbon to be extracted, as in the case of hydraulic fracture. If an enormous amount of fluid is injected underground, the resultant pore pressure buildup may also reactivate previously stable faults due to the reduction of effective mean pressure. Meanwhile, the hydro-mechanical coupling effect has also been used to characterize hydraulic properties that are difficult to obtain otherwise. For instance, one may indirectly estimate the effective permeability of the porous medium by examining the stress history of a given load, such as bending load applied on a beam or indentation applied on a poro-elastic half-space. The aforementioned engineering applications are just a few examples in which the knowledge of poromechanics is crucial. In recent years, the advancement of computational resource and the availability of more accurate and detailed experimental data and in situ data has made it possible to develop models with a new level of sophistication and a justifiable complexity. Meanwhile, new engineering challenges, such as geological disposal of captured carbon dioxide, nuclear waste, and the development of horizontal wellbores for hydraulic fractures, and forensic geotechnical engineering have motivated a growing interest to incorporate numerical modeling as an integral part of engineering design and analysis. This special issue provides a forum for presenting the state-of-the-art computational modeling for porous media. In the paper “Poromechanical cohesive surface element with elastoplasticity for modeling cracks and interfaces in fluid-saturated geomaterials,” written by Regueiro, Wang, Sweetser, and Jensen, a multiphysical cohesive element is introduced to capture the multiphysical responses of fluid-saturated geomaterials. While the solid constitutive response of the cohesive surface element is governed by a traction-separation law, the effective hydraulic conductivity of the embedded strong discontinuity depends on the mechanical aperture, the distance between the upper and lower surfaces of the fracture. The numerical examples have shown that such a numerical treatment is useful for capturing the hydro-mechanical responses of existing cracks as well as interface between soil and foundation. In the cases where cracks or shear slip may propagate and the evolving crack geometry is not known a priori, a proper algorithm to predict the onset, propagation direction, and branching of the cracks without injecting mesh bias is essential. In the paper “Simulating fragmentation and fluid-induced fracture in disordered media using random finite-element meshes,” by Bishop, Martinez, and Newell, a computational approach based on random close-packed Voronoi tessellations is introduced to simulate fracture initiation, propagation and coalescence. By using meshes discretized by polygon finite elements to minimize mesh bias, the authors have demonstrated that the proposed algorithm is able to replicate complex fluid patterns. Their results indicate that the simulations based on this new approach may achieve mesh convergence in a weak or distributed sense. At the reservoir or field scale, explicitly modeling each individual crack over a large volume becomes unfeasible due to high computational cost. The authors of the paper “Multiscale model for damage-fluid flow in fractured porous media,” Wan and Eghbalian, attempt to provide closed-form solutions to predict the homogenized responses of fractured porous media distributed with strong discontinuities. By incorporating shape and orientation of the distributed cracks into the up-scaling process, macroscopic mechanical and hydraulic properties of the effective medium are obtained solely from those of the micro-constituents.

中文翻译：

---

前言：计算多孔力学

国际多尺度计算工程杂志的这一特刊致力于计算多孔力学领域。我们将术语多孔力学称为一门研究多相材料的耦合响应的学科，这些材料包含填充有一种或多种类型的流体的空隙。符合此描述的材料包括许多地质材料（例如沙子、粘土和岩石）、活物质（例如骨骼、皮肤、牙周韧带）和人造材料（例如混凝土、尿布芯和聚合物凝胶）等. 在多孔介质中，空隙中的流体可能被困在孤立的孔隙内，也可能扩散到连通的孔隙空间中。多种流体成分也可引发它们之间的化学反应或与固体成分的化学反应。因此，固体骨架的变形和孔隙流体的扩散是相互强烈影响的过程。这种耦合效应对于我们日常生活中的许多工程应用来说都很重要。例如，孔隙流体压力的增加可能导致固体成分的破裂，这反过来又允许提取碳氢化合物，如在水力压裂的情况下。如果将大量流体注入地下，由于有效平均压力的降低，由此产生的孔隙压力增加也可能重新激活先前稳定的断层。同时，水力-机械耦合效应也被用于表征难以通过其他方式获得的水力特性。例如，人们可以通过检查给定载荷的应力历史来间接估计多孔介质的有效渗透率，例如施加在梁上的弯曲载荷或施加在多孔弹性半空间上的压痕。上述工程应用只是其中几个例子，其中多孔力学知识至关重要。近年来，计算资源的进步以及更准确和详细的实验数据和原位数据的可用性使得开发具有新水平的复杂性和合理复杂性的模型成为可能。同时，新的工程挑战，例如捕获的二氧化碳的地质处置、核废料以及用于水力压裂的水平井筒的开发，和法医岩土工程已经激发了越来越多的兴趣，将数值建模作为工程设计和分析的一个组成部分。本期特刊为介绍多孔介质的最新计算建模提供了一个论坛。在 Regueiro、Wang、Sweetser 和 Jensen 撰写的论文“具有弹塑性的具有弹塑性的多孔机械粘性表面元素用于模拟流体饱和地质材料中的裂缝和界面”中，引入了一种多物理粘性元素来捕获流体饱和地质材料的多物理响应。虽然粘性表面单元的固体本构响应受牵引-分离定律控制，但嵌入的强不连续性的有效水力传导率取决于机械孔径，裂缝上下表面之间的距离。数值例子表明，这种数值处理对于捕捉现有裂缝以及土壤和地基之间的界面的流体力学响应很有用。在裂纹或剪切滑移可能传播且演化的裂纹几何形状未知的情况下，一种适当的算法来预测裂纹的开始、传播方向和分支而不注入网格偏差是必不可少的。在 Bishop、Martinez 和 Newell 的论文“使用随机有限元网格模拟无序介质中的破碎和流体诱导裂缝”中，介绍了一种基于随机密堆积 Voronoi 细分的计算方法来模拟裂缝的起裂、扩展和聚结。通过使用由多边形有限元离散化的网格来最小化网格偏差，作者证明了所提出的算法能够复制复杂的流体模式。他们的结果表明，基于这种新方法的模拟可以在弱或分布式意义上实现网格收敛。在油藏或油田规模上，由于计算成本高，在大体积上对每个单独的裂缝进行显式建模变得不可行。“断裂多孔介质中损伤流体流动的多尺度模型”一文的作者 Wan 和 Eghbalian 试图提供封闭形式的解决方案，以预测具有强不连续性分布的断裂多孔介质的均匀响应。通过将分布裂纹的形状和方向纳入放大过程，