When using the SimericsMP expression editor, there are numerous pre-defined variables in the marine module as described in the Orca3D Help File topic, "Using the Expression Editor." As an example to get the vertical motion of the vessel at the towing point (which defaults to the CG), the variable is marine.heave and rotation about the transverse axis is marine.pitch. However, when using the coupled 6-DOF dynamics module, those variables are no longer defined. Instead, the body dynamics are defined using the variable names below. The reference location for all of these variables is the towing point (CG by default).
dynamics_6d.marine6DOF.displacement (the translation vector of the body in world coordinates)
dynamics_6d.marine6DOF.angle (the rotation vector, defined as Euler angles, of the body)
dynamics_6d.marine6DOF.bodyVelocity (the translational velocity vector of the body in body coordinates)
dynamics_6d.marine6DOF.bodyOmega (the rotational velocity vector of the body in body coordinates)
dynamics_6d.marine6DOF.absVelocity (the translational velocity vector of the body in world coordinates)
dynamics_6d.marine6DOF.absOmega (the rotational velocity vector of the body in world coordinates)
so to create a variable called heave, the expression would look like:
heave = dynamics_6d.marine6DOF.displacement.z