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Development of a Coupled 3-D DEM-LBM Model for Simulation of Dynamic Rock-Fluid Interaction
- Gardner, Michael Henry
- Advisor(s): Sitar, Nicholas
Abstract
Scour of rock is a challenging and interesting problem that combines rock mechanics
and hydraulics of turbulent flow. On a practical level, rock erosion is a critical issue facing
many of the world’s dams at which excessive scour of the dam foundation or spillway can
compromise the stability of the dam resulting in significant remediation costs, if not direct
personal property damage or even loss of life. The most current example of this problem is
Oroville Dam in Northern California where massive scour damage to both the service and
emergency spillways during the flood events of February 2017 led to the evacuation of more
than 188,000 people living downstream of the dam.
This research is specifically aimed at developing the ability to numerically evaluate rock-
water interaction, building upon the experimental and analytical work by George and Sitar
. The focus is on producing simulation techniques capable of consid-
ering the interaction between three-dimensional polyhedral rock blocks interacting with fluid
such that the complex shape of the blocks is captured in both the fluid and solid numerical
models. Accounting for the rock block geometry and orientations is essential in capturing
the correct kinematic response.
To this end, a three-dimensional, open-source program to generate the fractured rock
mass was developed based on a linear programming approach. The application runs on
Apache Spark which enables it to run locally, on a computer cluster or on the Cloud. The
program automatically maintains load balance among parallel processes and can be scaled
up to meet computational demands without having to make any changes to the underlying
source code. This enables the program to generate real-world scale block systems containing
millions of blocks in minutes.
The second stage of this research effort focused on developing a new open-source Discrete
Element Method (DEM) program capable of analyzing the kinematic response of fractured
rock. The contact detection computations for DEM are also based on a linear programming
approach such that similar logic and data structures can be used in both the block generation
and DEM code, though the DEM code is written in C++. The program was validated against2
analytical solutions as well as other numerical solutions and has been shown to accurately
capture the kinematic response of three-dimensional polyhedral rock blocks.
The DEM formulation was then extended to perform coupled fluid-solid interaction anal-
yses by coupling it with the weakly compressible Lattice Boltzmann Method (LBM). A
new algorithm, which extends the partially saturated approach, was developed to consider
three-dimensional convex polyhedra moving through the fluid domain. The algorithm uses
both linear programming and simplex integration for the coupling process. The LBM code
and the new fluid-solid coupling algorithm were validated against experimental data and
the capabilities of the new coupled DEM-LBM implementation were explored by evaluating
the performance of the program in simulating several different problems involving fluid-solid
interaction. The results show that the program is able to accurately capture the interaction
between polyhedral rock blocks and fluid; however, further performance improvements are
necessary to simulate realistic, field scale problems. Particularly, adaptive mesh refinement
and multigrid methods implemented in a parallel computing environment will be essential
for capturing the highly computationally intensive and multiscale nature of rock-fluid inter-
action.
Main Content
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