Numerical Simulation On The Penetration Process Of The Free-fall Penetrometers And Gravity Installed Anchors

Free-fall penetrometers/anchors penetrate into the seabed by their kinetic energy gained from the free fall in water column and their self-weight,without additional loading equipment.But the soil-structure interaction is complex during the dynamic penetration procedure,where the soil shear strain rate effect and drag force should be considered.Thus it's important to analyze the forces acting on the penetrometers to improve the precision of the measurement.The first part of this article simulated the penetration of the free-fall cone penetrometer and free-fall ball penetrometer into uniform clay using the commercial software ANSYS CFX17.0,which is based on the CFD?computational fluid dynamics?approach.The large deformation problem was simulated using the moving mesh method in CFX.The thin layer element method was proposed to simulate the soil-structure interaction.In the CFX simulation,the soil was modeled as non-Newtonian fluid and the shear strain rate effect was considered.Varied penetrometer velocities,soil strengths and densities,interface frictional coefficients and shear strain rate parameters were considered to investigate their effects on the resistances of the penetrometers.The fitted formulas of the bearing capacity factor,the strain rate coefficients and drag force coefficients were established based on the present numerical results.In addition,the process to back-analyses the undrained shear strength,rate parameter and interface friction coefficient of clayey soils was put forward,which may be beneficial for analyzing the recorded data from free-fall penetrometers.The second part of this article studied the effect of booster on the penetration depth of OMNI-Max^TM anchor.Owing to the complex geometric configuration of OMNI-Max^TM anchor,its drag force coefficient is quite large.Thus the anchor penetration depth is limited,especially in regions with high soil shear strength.Simulation of the hybrid anchor?assembly of the anchor and booster?penetration in strong soil was conducted using the CFX software to study the improvement of the boosters.The shear strain rate effect and frictional force were considered in the simulation.The results show that the hybrid anchor penetration depths were improved by 26.5%⁷8.7%compared with the OMNI-Max^TM anchor.