Formation and estimation of peak impact force on suspended pipelines due to submarine debris flow

In recent years, submarine debris-flow impact on suspended pipeline has been extensively investigated. Typical modes of impact force are identified: At low Reynolds number, it increases till reaches a stable plateau; otherwise, it sharply rises to a peak before decreasing to a stable value. However, the formation mechanism of peak impact force remains an open question. To address this issue, a two-dimensional (2D) biphasic (slurry and water) numerical model is developed using ANSYS Fluent 18.0. This model is used to simulate the constant-speed submarine debris-flow impact on a suspended pipeline. Herein, similar modes of peak and stable impact coefficients, which are nondimensionalized impact forces, on a suspended pipeline are observed. The formation mechanism of peak impact force is revealed. It is found that, the stable impact force relies on the constant speed of a submarine debris flow, while peak impact force depends on its velocity and local acceleration at initial impact. Moreover, the relationships between Reynolds number and coefficients of inertia and drag are proposed to estimate the peak and stable impact forces. The relations are compared to experimental and numerical datasets available in literatures, and laboratory experiments are recommended in future to obtain more measured datasets for further verification.