Defining the 6-DOF Motion

In this simulation, you model the overall system (the boat and its components) as a 6-DOF rigid body. Simcenter STAR-CCM+ calculates the motion of the center of mass of the system based on the properties of the body (mass and moment of inertia) and the forces and moments exerted by the surrounding fluid.

To define a 6-DOF body, you first activate a DFBI motion model. The DFBI motion model determines how the calculated 6-DOF motion is applied to the surrounding fluid region:
  1. Right-click the Tools > Motions node and select New > DFBI Rotation and Translation.
    With this motion, the whole fluid region is rigidly rotated and translated (rather than morphed at the boundaries) based on the calculated 6-DOF motion.
  2. Select the Regions > Fluid (Boat) > Physics Values > Motion Specification node and set Motion to DFBI Rotation and Translation.
    Simcenter STAR-CCM+ adds the DFBI node to the simulation tree. This node allows you to define the properties of the 6-DOF body and its motion.
To create a 6-DOF body:
  1. Right-click the DFBI > 6-DOF Bodies node and select New Body > 3D > Continuum Body.
    A continuum body is a rigid body that is coupled with a fluid boundary—in this case, the fluid wall boundaries that mark the surfaces of the boat and its components.
  2. Rename the 6-DOF Bodies > Body 1 node to BoatWithPropeller.


For the 6-DOF body, you define its properties and type of motion. For convenience, the starting simulation contains predefined parameters and coordinate systems that you can use for the definition of the 6-DOF motion.
  1. Select the DFBI > 6-DOF Bodies > BoatWithPropeller node and set the properties of the 6-DOF body. Specifically, you specify the fluid boundaries that define the body surfaces, the mass of the body, the time at which Simcenter STAR-CCM+ starts calculating the motion, and the type of motion. When selecting the fluid boundaries, include the fluid-structure interface.
    Property Setting
    Body Surface
    • Fluid (Boat) > Boundaries > BoatAndEngine
    • Fluid (Boat) > Boundaries > PropellerHub
    • Fluid (Propeller) > Boundaries > Blades
    • Fluid (Propeller) > Boundaries > Fluid (Propeller)/Propeller [0]
    • Fluid (Propeller) > Boundaries > Hub
    Body Mass ${Mass}

    Mass is a parameter that is provided in the starting simulation, under Automation > Parameters.

    Release Time 0.1 s
    Ramp Time 0.1 s
To simulate the motion of the boat due to the waves at the air-water surface, allow the boat to translate along the Z axis and to rotate around the Y axis:
  1. Select the BoatWithPropeller > Free Motion node and activate Z Motion and Y Rotation.
As initial values, you define the position of the center of mass of the body and the moment of inertia of the body:
  1. Expand the BoatWithPropeller > Initial Values node and set the following properties:
    Node Property Setting
    Center of Mass Coordinate System Laboratory > Cartesian_BoatInitial
    Moment of Inertia Diagonal Components $${MomentOfInertia}
    Coordinate System Laboratory > Cartesian_BoatInitial
  2. Save the simulation.