A feature extracting and meshing approach for sheet-like structures in rocks

Abstract

Meshing rock samples with sheet-like structures based their CT scanned volumetric images, is a crucial component for both visualization and numerical simulation. In rocks, fractures and veins commonly exist in the form of sheet-like objects (e.g. thin layers and distinct flat shapes), which are much smaller than the rock mass dimensions. The representations of such objects require high-resolution 3D images with a huge dataset, which are difficult and even impossible to visualize or analyse by numerical methods. Therefore, we develop a microscopic image based meshing approach to extract major sheet-like structures and then preserve their major geometric features at the macroscale. This is achieved by the following four major steps: (1) extracting major objects through extending, separation and recovering operations based on the CT scanned data/microscopic images; (2) simplifying and constructing a simplified centroidal Voronoi diagram on the extracted structures; (3) generating triangular meshes to represent the structure; (4) generating volume tetrahedron meshes constrained with the above surface mesh as the internal surfaces. Moreover, a shape similarity approach is proposed to measure and evaluate how similar the generated mesh models to the original rock samples. It is applied as criteria for further mesh generation to better describe the rock features with fewer elements. Finally, a practical CT scanned rock is taken as an application example to demonstrate the usefulness and capability of the proposed approach.

An effective 3D meshing approach for fractured rocks

“…The process includes three steps: (1) initial mesh generation; (2) mesh repairing; and (3) mesh optimization. Firstly, the JW together with the simplified centroidal Voronoi diagram (SCVD) is utilized to generate an initial mesh for fractures. Then, we propose an innovative algorithm to repair the initial mesh.…”

“…Simplified centroidal Voronoi diagram used in is based on the pseudo‐surface assumption. Directly involving SCVD to construct a triangular mesh for fractures may lead to a number of topology defects and geometric errors at fracture junctions.…”

“…We generate a mesh model to represent the fractures and discuss issues such as the choice of JW threshold, the effectiveness of the umbrella operation as well as the element quality of the mesh representation. According to our previous research , Voronoi cell radius r = 7 is utilized to generate SCVDs for the corresponding volumetric fracture images.…”

“…Although the element quantity is smaller compared with the directly converting methods, the generated meshes are still far from models suitable for analysis. The most adequate approaches for generating fracture meshes are directly representing fractures through lines/surfaces in 2D/3D. Such approaches could naturally describe the geometry properties of fracture and significantly reduce the number of elements.…”

Automatic mesh generation and adaptive remeshing for geological modelling

“…Alternatively, approaches [138][139][140] utilize a small number of elements to directly represent fractures through lines/surfaces in 2D/3D. Such approaches could naturally describe the geometry properties of fracture and significantly reduce the element quantity.…”