Self-Propelled Submarine Motion: Dynamic Mesh, 6-DOF

Self-Propelled Submarine Motion, Dynamic Mesh (6-DOF)

Description

This project simulates the motion of a self-propelled submarine floating on the water surface using the dynamic mesh method in ANSYS Fluent.

This product is the fourth chapter of the Dynamic Mesh Training Course.

The computational domain includes both air and water at a defined level, with the self-propelled submarine floating at the water's surface. The 3D geometry was designed using AutoCAD, CATIA, and ICEM CFD, with the submarine measuring 16.25 m in horizontal length and featuring several impellers with a diameter of 0.825 m at its rear.

A cylindrical computational region was defined around the submarine within a larger cubic domain representing the full computational space. Meshing was carried out in ICEM CFD using a hybrid mesh — unstructured near the submarine hull, transitioning to a generally structured mesh across the remainder of the domain — totaling 2,802,219 elements.

Methodology

Since the grid cells shift position over time due to displacement at adjacent boundaries, the dynamic mesh model was used to capture this instantaneous grid movement. Three computational zones were established around the submarine, with smoothing and remeshing methods applied to handle the dynamic mesh behavior.

Six degrees of freedom (6-DOF) were used to define the submarine's motion, allowing translational and rotational movement across all six directions. Mass and moment-of-inertia properties for the 6-DOF behavior were defined via a UDF.

The submarine's hull was defined as a Rigid Body, along with a small surrounding cylindrical region also treated as rigid — together forming an integrated body capable of moving and rotating without internal mesh deformation. A larger cubic region surrounding this rigid zone was defined as a Deforming region to accommodate the motion. The rigid body definition also required specifying the submarine's center of gravity and its position within the model, with the submarine positioned floating at the water's surface.

The VOF multiphase model was used to represent air in the upper portion of the domain and water in the lower portion, with both phases flowing horizontally (X-axis) at 1.62 m/s and exiting at atmospheric pressure. The open channel condition was applied at the outlet to define the water level, with the free surface set at 1.084824 m and the domain floor positioned at -100 m.

Given the dynamic mesh foundation of this model, the simulation was run as transient, spanning 10 seconds with a time step of 0.001 seconds.

Conclusion

Results include 2D contours of velocity and volume fraction for both air and water phases across the floating submarine's surrounding regions, presented on the X-Y and Y-Z planes at the final second of the simulation. Additionally, diagrams tracking the submarine's translational and rotational displacement along all three axes (X, Y, Z) are provided, capturing the full 6-DOF motion behavior induced by the self-propulsion and surrounding flow conditions.