Solid object water entry is a common problem in various natural, industrial and military applications, which involves large deformation of free surfaces and violent fluid–structure interactions. In computational fluid dynamics (CFD), this is a type of problem that tests the robustness and capacity of any CFD numerical algorithm. In this work, the newly-developed updated Lagrangian particle hydrodynamics (ULPH) method, which is a fluid version of peridynamics, is enhanced and applied to simulate solid object water entry problems. ULPH method is Lagrangian meshfree particle method that can ensure the specific free surface conditions automatically satisfied. The density filter and artificial viscosity diffusion are adopted in the ULPH scheme to stabilize and smooth the pressure field. In the process of a rigid body entering water, it may induce negative pressure in some areas of impact region, which can cause spurious tensile instability in some meshfree particle simulations, such as SPH and ULPH. A tensile instability control technique based on the ULPH framework has been developed to overcome the numerical instability. To validate the stability and accuracy of the ULPH approach in simulating water entry problems, several 2D and 3D examples of water entry have been carried out in this work. The necking and cavity pinch-off phenomena are visible in the numerical results. The simulation results of the ULPH method are well compared with experimental data and other numerical solutions. The water crown, cavity shapes and stream pattern formed around the rigid body entering the water can be well captured. The computation results show that the ULPH method has the ability to simulate the complex solid object water entry precess accurately.

固体物体的入水是各种自然，工业和军事应用中的常见问题，涉及自由表面的大变形和剧烈的流体-结构相互作用。在计算流体动力学（CFD）中，这是一类问题，可测试任何CFD数值算法的鲁棒性和容量。在这项工作中，新开发的更新的拉格朗日粒子流体动力学（ULPH）方法（一种流体动力学的近场动力学）得到了增强，并被用于模拟固体物体入水问题。ULPH方法是拉格朗日无网格粒子方法，可以确保自动满足特定的自由表面条件。ULPH方案中采用了密度过滤器和人工粘度扩散来稳定和平滑压力场。在刚体进入水中的过程中，它可能会在撞击区域的某些区域产生负压，这可能会在某些无网格的粒子模拟（例如SPH和ULPH）中引起虚假的拉伸不稳定性。为了克服数值不稳定性，已经开发了基于ULPH框架的拉伸不稳定性控制技术。为了验证ULPH方法在模拟进水问题中的稳定性和准确性，已在这项工作中进行了一些2D和3D进水示例。缩颈和型腔夹断现象在数值结果中可见。ULPH方法的仿真结果与实验数据和其他数值解决方案进行了很好的比较。可以很好地捕获进入水的刚体周围形成的水冠，空腔形状和流型。