Floating Vessel Motion in Water: Dynamic Mesh

Description

This project simulates a floating vessel's motion on water using the dynamic mesh method in ANSYS Fluent. The vessel is positioned at the center of a three-part computational domain, designed so its center of gravity sits along the vertical axis for simulation convenience. The geometry is built in 3D in Design Modeler, and meshed in ANSYS Meshing with an unstructured grid near the vessel and a structured grid elsewhere, totaling 902,808 elements.

Methodology

Because the vessel's motion requires the mesh to deform continuously around it, the Dynamic Mesh model is used, combining smoothing, which adjusts mesh boundaries without changing node count or connectivity, with remeshing, which reconstructs cells that become too distorted when boundary displacement is large relative to local cell size. The domain is divided into a small moving zone around the vessel, a surrounding deforming zone, and a larger stationary outer zone, with the vessel and its moving zone treated as a rigid body via the Six Degrees of Freedom (6-DOF) model. Since the vessel is physically constrained to only vertical translation and rotation about its central axis, a UDF restricts the 6-DOF motion down to these two degrees of freedom, with the vessel's center of gravity and rotation axis specified explicitly in the rigid body setup. The water and air phases are captured with the VOF multiphase model, air above and water below, both entering horizontally at 1.44 m/s and exiting at atmospheric pressure, with an Open Channel boundary condition at the outlet defining the water level. Given the fundamentally time-dependent nature of dynamic mesh motion, the simulation runs transient, covering 7 seconds at a 0.01 second time step.

Analysis

The results include 2D pressure contours on the vessel and 2D velocity and volume fraction contours in the surrounding air-water region, taken at the final second of the simulation, along with time-history plots of the vessel's vertical displacement and rotation angle over the full 7 seconds. These plots show the oscillation amplitude in both displacement and rotation decreasing over time, with the vessel's motion becoming effectively damped by the seventh second. At that point, the vessel settles near a vertical position of z = 0.021 and a rotation angle of Y_theta = -1.338, indicating it reaches a stable floating equilibrium consistent with the physical damping expected in this kind of fluid-structure interaction.