In this paper, we propose a three-dimensional diffuse-interface immersed-boundary (3D DIIB) method for the simulations of fluid-structure interaction (FSI) with dynamic wetting, complex geometry and contact angle hysteresis. In particular, the movement of rigid solid objects is allowed to have six degrees of freedom. In the method, the complex solid boundaries are represented by a set of Lagrangian patches that cover the whole surface of the solid objects, while the flows are solved on a staggered Cartesian grid. The couplings between the object movement and surrounding fluid flows are performed using an immersed boundary method. A simple model of contact angle hysteresis is used to ensure pinned contact lines if local contact angle is within the window of contact angle hysteresis. To relieve the stress singularity at moving contact lines, a characteristic moving contact line model [1] is adopted at 3D curved solid surfaces, after the geometrical information of interface is constructed in the vicinity of the contact line. For 3D simulations of FSI with dynamic wetting, it is crucial but difficult to estimate capillary force, of which the process consists of locating the moving contact line on complex solid surfaces, discretizing it into line segment, and determining the local tangent to the interface at the contact lines. Special consideration is given to the modeling of the capillary force and associated torque, in order to have accurate approximations. The performance of the 3D DIIB method is systematically examined through a series of numerical experiments, of which the results are either verified against theoretical predictions or compared with experimental data. Finally, we simulate the collision process of raindrops with 3D mosquito body, to show the potential of the 3D DIIB method in practical applications.

在本文中，我们提出了一种三维扩散界面浸入边界（3D DIIB）方法，用于模拟具有动态润湿，复杂几何形状和接触角滞后的流体-结构相互作用（FSI）。特别地，刚性固体物体的运动被允许具有六个自由度。在该方法中，复杂的固体边界由一组覆盖固体对象整个表面的拉格朗日斑块表示，而流在交错的笛卡尔网格上求解。使用浸入边界方法执行对象运动与周围流体流之间的耦合。如果局部接触角在接触角磁滞的窗口内，则使用接触角磁滞的简单模型来确保固定接触线。为了减轻移动接触线上的应力奇异性，在接触线附近构造了界面的几何信息后，在3D曲面曲面上采用了特征性的移动接触线模型[1]。对于具有动态润湿的FSI的3D模拟，至关重要但很难估计毛细作用力，其过程包括将移动接触线定位在复杂的固体表面上，将其离散化为线段，并确定与界面的局部切线接触线。为了获得精确的近似值，需要特别考虑毛细作用力和相关转矩的建模。通过一系列数值实验系统地检查了3D DIIB方法的性能，其中的结果要么根据理论预测进行验证，要么与实验数据进行比较。最后，