Abstract Free Fall Penetrometer (FFP) testing consist of a torpedo-shaped body freefalling into a soil target. The use of this type of device is becoming popular for the characterization of shallow sediments in near-shore and off-shore environments because it is a fast, versatile, and non-expensive test capable of recording acceleration and pore pressures. In recent years, the data analysis advanced considerably, but the soil behavior during fast penetration is still uncertain. Hence, there is a need to develop numerical models capable of simulating this process to improve its understanding. This paper proposes a numerical framework to simulate the deployment of an FFP device in dry sands using the Material Point Method (MPM). A moving mesh technique is used to ensure the accurate geometry of the FFP device throughout the calculation, and the soil-FFP interaction is modelled with a frictional contact algorithm. Moreover, a rigid body algorithm is proposed to model the FFP device, which enhances the performance of the computation and reduces its computational cost. The sand is simulated by using two constitutive models, a non-associate Mohr-Coulomb (MC) and a Strain-Softening Mohr-Coulomb (SSMC) that reduces, exponentially, the strength parameters with the accumulated plastic deviatoric deformation ( Yerro et al., 2016 ). Variable dilatancy, which reduces as a function of the plastic strain, is also taken into account, and the strain-rate effects have been evaluated in terms of peak friction angle. In general, the behavior predicted by the MPM simulations is consistent with the experimental test. The results indicate that the soil stiffness has a big impact on the deceleration time-history and the development of a failure mechanism, but less influence on the magnitude of the peak deceleration and the penetration depth; the soil dilatancy reduces the FFP rebound, and the FFP-soil contact friction angle and the peak friction angle are highly linked to the peak deceleration.

中文翻译：

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使用物质点法对自由落体式贯入仪部署进行数值模拟

摘要 自由落体式贯入仪 (FFP) 测试包括一个鱼雷形物体自由落体进入土壤目标。使用这种类型的设备来表征近岸和离岸环境中的浅层沉积物越来越受欢迎，因为它是一种快速、通用且不昂贵的测试，能够记录加速度和孔隙压力。近年来，数据分析取得了长足的进步，但快速渗透过程中的土壤行为仍不确定。因此，需要开发能够模拟该过程的数值模型以提高其理解。本文提出了一个数值框架，用于使用材料点法 (MPM) 模拟干砂中 FFP 设备的部署。移动网格技术用于确保整个计算过程中 FFP 设备的准确几何形状，土壤-FFP 相互作用采用摩擦接触算法建模。此外，提出了一种刚体算法来对 FFP 设备进行建模，从而提高了计算性能并降低了计算成本。沙子通过使用两个本构模型进行模拟，一个非关联莫尔库仑 (MC) 和一个应变软化莫尔库仑 (SSMC)，它以指数方式降低强度参数与累积塑性偏变形 (Yerro 等人 2017)。 ，2016 年）。还考虑了随塑性应变而减小的可变剪胀性，并根据峰值摩擦角评估了应变率效应。一般而言，MPM 模拟预测的行为与实验测试一致。结果表明，土体刚度对减速时程和破坏机制的发展影响较大，对峰值减速大小和穿透深度影响较小；土壤剪胀降低了 FFP 回弹，FFP-土壤接触摩擦角和峰值摩擦角与峰值减速度高度相关。