A granular energy-controlled boundary condition for discrete element simulations of granular flows on erodible surfaces

Entrainment of the substrate, which can cause the volume of geophysical flows to increase by many times and greatly affects its mobility, occurs frequently. Even though many large-scale studies have been conducted to investigate entrainment during flows, particle-scale studies are urgently needed to understand this complex process. We propose a novel configuration with an energy-controlled boundary to model inclined granular flows on erodible surfaces with the aim of investigating the rheological features of granular flows with entrainment. The erosion degree is controlled by adjusting the energy of the bottom granular bed. The bulk velocity, stress, microstructure, and constitutive behavior are systematically analyzed. Our simulations capture the exponentially decaying velocity in the creeping region, confirming that this configuration can be applied to study geophysical flows with entrainment. The velocity at the free surface increases with erosion depth, which means entrainment can greatly enhance the mobility of granular flow. However, the flow in the shear band still belongs to the inertial regime. The novel energy-controlled configuration provides effective and efficient way to investigate granular flows on erodible surfaces, serving as an initial step to understand geophysical flows involving entrainment, which is essential to develop new geo-disaster mitigation strategy.

Automated summary

Entrainment of the substrate in geophysical flows is a common phenomenon that significantly affects their volume and mobility. In this study, we propose a novel energy-controlled boundary model to simulate inclined granular flows on erodible surfaces and investigate their rheological behavior with entrainment. By adjusting the energy of the bottom granular bed, we systematically analyze the bulk velocity, stress, microstructure, and constitutive behavior. Our simulations confirm that this configuration can be used to study geophysical flows with entrainment. The results show that entrainment greatly enhances the mobility of granular flow, but the flow in the shear band remains in the inertial regime. This energy-controlled model provides an effective approach to investigate granular flows on erodible surfaces and is crucial for developing strategies to mitigate geo-disasters.