Submarine Movement in Water by Dynamic Mesh

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

Description

The present problem simulates the motion of a submarine in water using the Dynamic Mesh method in ANSYS Fluent software. In this simulation, a computational domain including air and water with a certain level of water is designed; So that a submarine is located in this area.

Initially, a submarine was designed for this simulation, and then a computational domain consisting of two phases of air and water around the submarine was designed. We model the present model in three dimensions using Design Modeler software. The model includes a computational domain with air and water flow and a submarine within this area.

This computational area has a section called an input and an output section, and the four faces around this area have a symmetry condition.

We carry out the meshing using ANSYS Meshing software, and the mesh type is unstructured. The element number is 316,846.

Submarine Movement in Water Methodology

Since this submarine is moving within the computational domain and thus affects the surrounding grid elements, there is a need for momentary and time-dependent changes in meshing based on the type of displacement at the adjacent boundaries of the mesh.

Therefore, the dynamic mesh model defines the instantaneous change of meshing. In determining dynamic mesh methods, smoothing and remeshing methods have been used. In defining areas under the dynamic mesh, the wall part of the submarine is defined as the Rigid Body.

Since the submarine has only one degree of freedom (1-DOF) and can only rotate around its central axis (x-axis), and in other degrees, it is constrained and has no transitional or rotational motion, we use a UDF for defining this type of movement, considering one degree of freedom.

The UDF of submarine rotational motion is defined so that at 0 s to 3 s of this modeling, the rotational velocity value changes between +1.5 rad/s and -1.5 rad/s.

It should be noted that in the section’s settings related to the rigid body, the spatial coordinates of the center of gravity of the submarine as well as the axis of its rotation should be defined.

Since the submarine is moving within a computational domain with two phases of water and air, the VOF multiphase flow model must be used; So that air is defined in the upper part of the computational area and water in the lower part.

Since we assume that the submarine is moving in seawater, the wave behavior is defined as the flow of water entering the computational domain. To do this, the open channel wave BC option must be activated.

Therefore, the incoming water flow enters with an average flow rate equal to 10 m.s-1 in the direction of the horizon (x-axis); So, the bottom of the wave is defined at the height of -10.16 m, and its peak at the height of 0 m.

Inlet airflow also enters the area with the condition of inlet pressure equal to atmospheric pressure (relative pressure zero). Finally, the airflow is discharged at a pressure equal to atmospheric pressure.

Due to the main nature of the model based on the use of dynamic mesh, the simulation process should be defined in terms of time (Transient Solver). The simulation process is performed in 3 seconds with a time step of 0.01 seconds. The simulation is unsteady since we are applying the dynamic mesh method.

Submarine Conclusion

At the end of the solution process, we obtain two-dimensional contours related to the velocity and volume fraction of each of the water and air phases and two-dimensional path lines in the areas around the submarine.

We obtain these contours locally on a plane perpendicular to the horizontal axis of the submarine (parallel to the Y-Z plane).

We present these contours at different times of the simulation process. According to the defined UDF, the submarine rotates around its central axis (x-axis), and this rotational motion has clockwise and counterclockwise reciprocating motions over time.