09:45 〜 10:00
[HCG21-03] Modeling sand-rich submarine debris flow: Sand deposition, turbidity current generation and separation
キーワード：堆積物重力流、海底土石流、混濁流、数値計算モデル
The flow characteristics of submarine debris flows differs by their sediment composition, i.e., clay to sand ratio. Clay-rich debris flows exhibit matrix-supported, coherent flow structure, generally described by viscoplastic rheology. In contrast, sand-rich debris flows with moderate clay content have been reported to show complex flow dynamics in both longitudinal and vertical directions. In the previous experimental works of sand-rich debris flows, sand particles gradually deposited from dense sand-rich flow body with partial fluidization during its flow path. At the same time, the pore fluid with clay migrated upward, generating dilute turbidity cloud over the sand-rich flow. A turbidity current developed from this cloud may be separated from a dense sand-rich flow after its deposition. Modeling of these complicated behaviors of high-concentration flows still remains a challenge.
In this work, a numerical model of sand-rich debris flows incorporating sand deposition, turbidity current generation and separation is proposed based on two-layer shallow water equations: the lower layer represents fluidized sand-rich flow and the upper one corresponds to turbidity cloud. In this model, the simulation initialized with a fluidized sand-rich flow, and a turbidity cloud is generated depending on the upward flux of the pore fluid with clay from the sand-rich flow. To close the model, the upward flux of the pore fluid is coupled with the sand deposition rate, assumed that the sand deposition induces contractive motion of sand particles and this squeezes the pore fluid to the upper layer.
We conducted preliminary simulations of the model over a uniform slope with a given rate of sand deposition. The results reproduced important qualitative features of sand-rich debris flows reported in the literature, though further comparison with the experiment is needed in the future study to constrain the relationship between sand deposition and pore fluid migration assumed in this model.
In this work, a numerical model of sand-rich debris flows incorporating sand deposition, turbidity current generation and separation is proposed based on two-layer shallow water equations: the lower layer represents fluidized sand-rich flow and the upper one corresponds to turbidity cloud. In this model, the simulation initialized with a fluidized sand-rich flow, and a turbidity cloud is generated depending on the upward flux of the pore fluid with clay from the sand-rich flow. To close the model, the upward flux of the pore fluid is coupled with the sand deposition rate, assumed that the sand deposition induces contractive motion of sand particles and this squeezes the pore fluid to the upper layer.
We conducted preliminary simulations of the model over a uniform slope with a given rate of sand deposition. The results reproduced important qualitative features of sand-rich debris flows reported in the literature, though further comparison with the experiment is needed in the future study to constrain the relationship between sand deposition and pore fluid migration assumed in this model.