You can use a rigid body section to perform a fluid structure interaction simulation (FSI) of a rigid body moving in a coupled manner with the fluid flow. The forces that the fluid exerts on the body are incorporated to the 6 degrees of freedom equations of motion, which are resolved to obtain the new location of the structure. The app can perform a multi-body simulation by creating a new section for each body. The rigid body section defines the main properties required to predict the linear and angular motion of a rigid body: its mass, center of gravity, and rotational inertia. Given that the relative position of the particles of a rigid body is constant, the kinematics of a rigid body can be represented by the motion of a reference node. The app formulates the equations of motion with respect to the center of gravity; all quantities (such as rotational inertia, translations, rotations, external forces, and external moments) are expressed with respect to that location. When the equations of motion are expressed with respect to the center of mass (which is equivalent to the center of gravity for constant gravitational fields), the linear degrees of freedom are decoupled from the rotational degrees of freedom. The translational displacements and velocities of the body are provided in global coordinates. The app expresses the rotation angles and angular velocities in intrinsic angles using the Tait-Bryan convention, also known as Cardan angles or nautical angles. These angles express rotation and angular velocity in terms of yaw, pitch, and roll. | |||||||||