Maritime Tutorial 5 : Adding Heave Compensation

In this training pack, we will go over key concepts and guidelines to get you started with nautical simulations in Vortex® Studio.

This module focuses on using Vortex Studio a Python script coupled with the GSPID Controller object to implement a heave compensation system.

Prerequisites

You need to have Vortex® Studio and the Vortex Studio Demo Scenes installed to be able to follow all steps in this tutorial. Working knowledge of Python or coding languages in general will facilitate the understanding of this module as well.

Adding a GSPID Controller

1. Start the Vortex Studio Editor. Open OffshoreCrane.vxmechanism. This is the mechanism you created in Marine Module 3: Building an Offshore Crane

2. Double-click on GSPID Controller from the Dynamics section of the Toolbox to add it to the scene.

3. Rename the GSPID to "Heave Compensation Controller".

Modifying the Control Script

1. Right-click on the ControlScript script and click on Edit.

2. Add the following inputs:

   Name	Type	Physical Dimension
   >PID Value	>Double	>None
   >Activate Heave Comp	>Boolean	>None
   >Hook Position	>Vector 3	>Length (m)

3. Add the following outputs:

   Name	Type	Physical Dimension
   Hook Desired Position	Double	None
   Hook Current Position	Double	None

   Data types being used in this script: Boolean: Data type which may only have one or two values (ie. True or False, 1 or 0). Double: A double-precision floating point data type. Mathematical operations can be used on this data type. (ex. 1227.39, 5.19e^-10). Vector: Data which is a fixed-length collection of values of a certain type (ex. [0,5,3.25]).

4. In the Code section of the script, replace the code with the following:

   from VxSim import *
    
    
   def on_add_to_universe(self, universe):
       self.heaveCompToggle = False
       self.activateHeaveComp = False
    
    
   def pre_step(self):
       # Toggle Heave Compensation
       if self.inputs.Activate_Heave_Comp.value and not self.heaveCompToggle:
           self.heaveCompToggle = True
           self.activateHeaveComp = not self.activateHeaveComp
       elif not self.inputs.Activate_Heave_Comp.value:
           self.heaveCompToggle = False
    
       self.outputs.Arm_Actuator_Velocity.value = self.inputs.Arm_Actuator.value * 0.2
       self.outputs.Elbow_Actuator_Velocity.value = self.inputs.Elbow_Actuator.value * 0.2
    
       if (self.inputs.Hoist_Up.value):
           drumVelocity = -0.2
       elif (self.inputs.Hoist_Down.value):
           drumVelocity = 0.2
       else:
           drumVelocity = 0.0
    
       self.outputs.Hook_Current_Position.value = self.inputs.Hook_Position.value.z
    
       if not self.activateHeaveComp:
    
           self.outputs.Drum_Velocity.value = drumVelocity
           self.outputs.Hook_Desired_Position.value = self.outputs.Hook_Current_Position.value
    
       elif self.activateHeaveComp:
            
           self.outputs.Hook_Desired_Position.value += 0.1*drumVelocity
           self.outputs.Drum_Velocity.value = self.inputs.PID_Value.value
            
       self.outputs.Turret_Slew_Velocity.value = self.inputs.Turret_Slew.value * 0.2
   

5. Click on Apply.
6. Save the mechanism.

Connecting the PID's Inputs and Outputs

1. Access the Connection Container by double-clicking on it.
2. From the ControlScript script, drag-and-drop the recently added Inputs and Outputs.
3. From the Heave Compensation Controller, drag-and-drop Setpoint, Process Variable and Control Output.
4. From the Joystick, drag-and-drop the Y button (Button4) to the Connection Container.
5. Drag-and-drop the World Transform of the Platform_KnuckleBoom_Hook part of the Hook assembly into the Connection Container.
6. Make the connections as shown:
   

Testing and Adjusting the PID's Parameters

1. Access the Properties of the Heave Compensation Controller PID.
2. From the Gain Range section, set the gain ranges of the PID to these values :
   
3. Save the mechanism.
4. Open MarineScene.vxscene
5. Open a Plotter Window by clicking on the Plotter button.
6. Drag-and-drop Current Value and Desired Value inputs from the Heave Compensation Controller script into the plotter window.
7. Start the simulation and activate the heave compensation by clicking on the Y button on the gamepad.
8. Modify the PID parameters in order to fine tune the response of the module's depth.

Up Next: Maritime Tutorial 6 : Adding an Animated Buoy