Submarine Movement in Water: 1-DOF, Dynamic Mesh

Submarine Movement in Water by Dynamic Mesh (1-DOF), ANSYS Fluent

Description

This simulation models the motion of a submarine in water using the Dynamic Mesh method in ANSYS Fluent, with a computational domain containing both air and water phases at a defined water level, with the submarine positioned within this domain.

The submarine geometry was designed first, followed by a computational domain incorporating two-phase (air-water) flow around it. Both were modeled in 3D using Design Modeler. The domain includes distinct inlet and outlet sections, with symmetry conditions applied to the four surrounding faces.

Meshing was carried out in ANSYS Meshing using an unstructured mesh totaling 316,846 elements.

Methodology

Since the submarine moves within the computational domain, affecting the surrounding grid elements, the mesh requires continuous, time-dependent updates based on the displacement occurring at adjacent mesh boundaries. This is achieved through the dynamic mesh model, applying smoothing and remeshing methods, with the submarine's wall defined as a Rigid Body.

The submarine is constrained to a single degree of freedom (1-DOF), permitted to rotate only about its central axis (x-axis), with no translational or additional rotational motion. This rotational behavior is defined through a UDF, with rotational velocity varying between +1.5 rad/s and -1.5 rad/s over the 0–3 second simulation window.

The rigid body settings also require specifying the spatial coordinates of the submarine's center of gravity and its axis of rotation.

Since the domain contains two phases, the VOF multiphase model is applied, with air occupying the upper region and water the lower region. To represent the submarine operating in open sea conditions, wave behavior is introduced via the open channel wave boundary condition — incoming water enters at an average velocity of 10 m/s along the horizontal (x-axis), with the wave trough set at -10.16 m and its crest at 0 m. Inlet airflow enters at atmospheric pressure (zero relative pressure), with air discharged at atmospheric pressure as well.

Given the dynamic mesh foundation of this model, the simulation is run as a transient (time-dependent) case, spanning 3 seconds with a time step of 0.01 seconds — necessarily unsteady due to the dynamic mesh method employed.

Conclusion

The results include 2D contours of velocity and volume fraction for both water and air phases, along with 2D pathlines around the submarine — captured on a plane perpendicular to the submarine's horizontal axis (parallel to the Y-Z plane) at multiple points throughout the simulation.

Consistent with the defined UDF, the submarine exhibits reciprocating rotational motion about its central axis, alternating between clockwise and counterclockwise rotation over the course of the simulation.