Development of a Coupled 3-D DEM-LBM Model for Simulation of Dynamic Rock-Fluid Interaction

Scour of rock is a challenging and interesting problem that combines rock mechanics/nand hydraulics of turbulent flow. On a practical level, rock erosion is a critical issue facing/nmany of the world’s dams at which excessive scour of the dam foundation or spillway can/ncompromise the stability of the dam resulting in significant remediation costs, if not direct/npersonal property damage or even loss of life. The most current example of this problem is/nOroville Dam in Northern California where massive scour damage to both the service and/nemergency spillways during the flood events of February 2017 led to the evacuation of more/nthan 188,000 people living downstream of the dam./nThis research is specifically aimed at developing the ability to numerically evaluate rock-/nwater interaction, building upon the experimental and analytical work by George and Sitar/n. The focus is on producing simulation techniques capable of consid-/nering the interaction between three-dimensional polyhedral rock blocks interacting with fluid/nsuch that the complex shape of the blocks is captured in both the fluid and solid numerical/nmodels. Accounting for the rock block geometry and orientations is essential in capturing/nthe correct kinematic response./nTo this end, a three-dimensional, open-source program to generate the fractured rock/nmass was developed based on a linear programming approach. The application runs on/nApache Spark which enables it to run locally, on a computer cluster or on the Cloud. The/nprogram automatically maintains load balance among parallel processes and can be scaled/nup to meet computational demands without having to make any changes to the underlying/nsource code. This enables the program to generate real-world scale block systems containing/nmillions of blocks in minutes./nThe second stage of this research effort focused on developing a new open-source Discrete/nElement Method (DEM) program capable of analyzing the kinematic response of fractured/nrock. The contact detection computations for DEM are also based on a linear programming/napproach such that similar logic and data structures can be used in both the block generation/nand DEM code, though the DEM code is written in C++. The program was validated against2/nanalytical solutions as well as other numerical solutions and has been shown to accurately/ncapture the kinematic response of three-dimensional polyhedral rock blocks./nThe DEM formulation was then extended to perform coupled fluid-solid interaction anal-/nyses by coupling it with the weakly compressible Lattice Boltzmann Method (LBM). A/nnew algorithm, which extends the partially saturated approach, was developed to consider/nthree-dimensional convex polyhedra moving through the fluid domain. The algorithm uses/nboth linear programming and simplex integration for the coupling process. The LBM code/nand the new fluid-solid coupling algorithm were validated against experimental data and/nthe capabilities of the new coupled DEM-LBM implementation were explored by evaluating/nthe performance of the program in simulating several different problems involving fluid-solid/ninteraction. The results show that the program is able to accurately capture the interaction/nbetween polyhedral rock blocks and fluid; however, further performance improvements are/nnecessary to simulate realistic, field scale problems. Particularly, adaptive mesh refinement/nand multigrid methods implemented in a parallel computing environment will be essential/nfor capturing the highly computationally intensive and multiscale nature of rock-fluid inter-/naction.

Advisor: Sitar, Nicholas