Session: 12-02-01 Wave-Structure Interactions I
Paper Number: 121513
121513 - Impact Force of Roll Waves Against Hydraulic Structures With Various Shapes and Orientations
Terrestrial landslides represent a constant and ubiquitous threat to the population in mountainous areas. Thousands of landslides occur annually across Canada and the United States. The landslide destructions are estimated to be billion dollars annually (Canada.ca, 2003; Jonathan et al., 2022). The destructive events of the landslides are often associated with the spontaneous development of roll waves in the mudflow. The slumping of unconsolidated materials can lead to mudslides of clay, silt and sand particles and the transport of rocks and even boulders on steep channels (Iverson et al., 1997; Jacob et al., 2005). In Jiang-Jia Ravine, boulders have been moved downhill by the enormous force of the mudflow (Li et al., 1997; Cui et al., 2005). As reported by Li et al. (1983), Engelund & Wan (1984) and Scott & Wang (2004), the roll waves in Jiang-Jia Ravine can reach a height of several meters transporting boulders as much as 2 m in dimensions.
With the presence of clay minerals, mudflow is highly viscous and non-Newtonian. Roll waves in mud often are laminar, occurring at relatively small Froude numbers. Re-analyzing mudflow rheology from various landslide materials has led to supporting data for a power-law model for calculating the force of roll waves against obstacles. We conduct two-dimensional shallow-mud simulations to determine the impact force on structures in numerical simulations using the Gerris Flow Solver by Popinet (2003) on an adaptive quadtree mesh that dynamically refines and coarsens depending on the flow feature. Simulations were conducted for obstacles of various shapes and orientations. Grid adaptation criteria are based on the gradient and discretization error of the depth to faithfully capture steep wave fronts of roll waves and bow shock waves around obstacles. The computational efficiency of the quadtree adaptive mesh for 2D shallow-water flow simulation has been reported in several publications. Liang et al. (2007) and An & Yu (2012) simulated shock reflection by a circular cylinder. They found approximately 80% saving of the CPU time compared with using uniform mesh. Popinet (2015) simulated the Tohoku tsunami, and he found a 97% saving of CPU time.
We focus on the front runner of a wave packet developed from the spatial instability of the mudflow. Simulations were conducted for various power-law indexes relevant to terrestrial landslides and sub-critical and super-critical mudflow Froude numbers. The numerical results include the standoff distance of the bow shock wave, the front face's run-up height, and the wave force on the obstacle. The strength of the impact depends on the power-law index, the non-Newtonian viscosity and the Froude number of the undisturbed flow. It depends on the obstacle's distance from the local disturbance but not much on the form of the perturbation that initiates the instability. We found that the wave impact force raised sharply to a peak on the arrival of the front runner of the wave packet. The wave force could reach a peak of more than an order of magnitude greater than the force on the structure without the roll waves. However, an obstacle with a sharp and pointy front can deflect the incident waves, significantly reducing the impact force. We propose a heuristic interpretation for impact reduction following the method described in a previous paper by Yu & Chu (2023) for turbulent roll waves. In a departure from the turbulent flow, the impact-force reduction of the laminar mudflow is perfectly proportional to the direction-cosine square despite the significantly large amplitude of the roll waves in mud.
Presenting Author: Vincent H. Chu McGill University
Presenting Author Biography: Professor of Civil Engineering
McGill University
Authors:
Boyuan Yu McGill UniversityVincent H. Chu McGill University
Impact Force of Roll Waves Against Hydraulic Structures With Various Shapes and Orientations
Submission Type
Technical Paper Publication