This is an outline of the steps to do a self-propelled 6 DOF turning analysis, beginning with a straight ahead run to get to equilibrium and then deflecting the thrust direction. NOTE: This requires a Premium license. 


At the end of this article there are links to do a moving appendage (e.g., a rudder or turning outboard) which is a little more complex than deflecting the thrust. 

 

  1. Prepare the model in Orca3D for a self-propelled analysis, selecting the RPM that will produce the desired speed. Be sure to check the “Full Asymmetric Run” box. Note that inertias will be important to the analysis, so you should give your best estimates of the roll, pitch, and heave inertias (or gyradii).
  2. Load the .spro model in Simerics.
  3. Run the analysis straight ahead until the model has reached equilibrium (speed, pitch, and heave). During this phase, the other degrees of freedom will be heavily damped, in order to ensure that the vessel stays on course.
    1. Change to a 6DOF analysis
      1. In the Model tab, select the Marine module.
      2. In the Properties pane, change the Setup Options to Extended mode. 
      3. Change the Analysis Type to User Analysis
      4. Change the Dynamic Option to 6DOFs
    2. Set the damping
      1. In the Model tab, select Dynamics (6 DOFs)
      2. In the Properties tab, change Setup Options to Advanced Mode
      4. Under Frame options:
        1.  select the Y translation (sway) and enter a damping coefficient of approximately 1000 * the displacement of the vessel
        2. Select the X (roll) and Z (yaw) rotation coefficients and enter a value approximately 1000 * the roll inertia and yaw inertia, respectively, of the vessel (estimates for the inertias are shown in the Orca3D Marine CFD dialog, using the estimates for gyradius as function of vessel length) 
    3. Start the simulation, and stop it once the time histories for speed, pitch, and heave have converged to a steady value
  4. Save the simulation under a different name, and close and re-start Simerics-MP
  5. Load the project file (.spro) and the latest results file (.sres)
  6. Remove the damping, and use the Expression Editor to deflect the thrust
    1. In the Model tab, select Dynamics (6 DOFs) marine6DOF
    2. In the Properties tab, under Frame options:
      1. Be sure the X, Y, and Z translations have a damping coefficient of 0
      2. Be sure the X, Y, and Z rotations have a damping coefficient of 0
    3. Open the Expression Editor, and add the lines shown in the figure below. In this example, the thrust is being turned at 2 deg/second for 15 seconds; enter your own values as appropriate.
    4. In the Model tab, select the Marine module
    5. In the Properties tab, under Propulsion option, change the X and Y direction of the propulsion to -xDir and yDir as shown in the figure below (xDir and yDir are the variables that were defined in the Expression editor)
  7. Change the Numerical Option from Medium (Steady) to Medium (Transient)
    1. Select the Marine module in the Model tab
    2. Under Analysis Type, change the Numerical Option to Medium (Transient)

  8. Change to “Start from Solution” (which will reset the Time to 0) and click the Start button to re-start the simulation. 

 

 If you wish to initiate the turn by turning rudders or outboards, please see these videos on how to set up moving appendages:

https://download.orca3d.com/Orca3D Marine CFD Premium Training Exercise Maneuvering Analysis - Part 1.mp4

https://download.orca3d.com/Orca3D Marine CFD Premium Training Exercise Maneuvering Analysis - Part 2.mp4