# Degrees of Freedom

Before beginning the analysis, it is important to understand the coordinate system used in this project. The movement techniques are pitch, sway, yaw, heave, surge, and roll. Here is a diagram of the following conditions.

There are six main forces acting on the UUV: hydrostatic pressure, gravitational, buoyant, hydrodynamic drag & lift, and thrust forces. Each of these forces must be calculated to obtain the expected net force on the UUV under the different conditions specified in the design requirements.

Hydrostatic pressure acts on the outside of an object submerged in water, in a direction perpendicular to the interface between the object and the fluid (Navy, 2006).

Gravitational force is proportional to the mass of the vessel, and the acceleration due to gravity at the vessel’s current position (Zee).

The buoyant force is proportional to the mass of fluid displaced by the vessel and acts opposite to the direction of gravity (Pickover).

Hydrodynamic drag and lift forces are components of the resultant pressure and shear forces exerted on the vessel by the fluid as it moves around the exterior. Drag force acts in the direction of fluid flow; lift force acts perpendicular to the direction of fluid flow (Drayton & Martyn, 2009).

Thrust force is the force generated by the powered propellers or thrusters used to move the vessel through the water (Newton, 1999).