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Gunnerus Path-following

This document describes the Functional Mock-up Units (FMUs) necessary to run the simulation case of a vessel following waypoints (WPs) using line-of-sight (LOS) guidance principle.

System Description

Each component/FMU of the simulation case will be described in the following sections. Only relevant variables will be described for each FMU. The names of the simulation objects are given in the table below. For additional information about the individual FMUs and their variables, unpack the FMU and open the modelDescription.xml file

Table 1: List of FMUs in the Gunnerus Path-following system.

FMU name Description
TrajectoryController Controls the speed and heading angle to make vessel follow path..
WaypointProvider2DOF Issues waypoints (target and previous) to controller.
Converter A simple unit conversion
ThrusterDrive  
PMAzimuth  
PowerPlant  
VesselFmu  

Trajectory Controller

This FMU holds the controller functionality required in order to converge to a certain desired vessel speed and heading angle. The latter is calculated by the LOS guidance scheme and the aggressiveness may be altered by changing the input variable “lookaheadDistance” > 0. Otherwise, the convergence properties of the speed and heading angle to desired values are controlled by the ProportionalIntegral-Derivative (PID) regulator parameters.

Table 2: Trajectory Controller inputs and outputs (I/O).

Name I/O Description
enable I Boolean variable. Outputs updated rudder/force commands only if true.
autopilot.heading.kp I Proportional gain for heading regulator
autopilot.heading.ki I Integral gain for heading regulator
autopilot.heading.kd I Derivative gain for heading regulator
autopilot.speed.kp I Proportional gain for speed regulator
autopilot.speed.ki I Integral gain for speed regulator
autopilot.speed.kd I Derivative gain for speed regulator
northPosition I North position of vessel [m]
eastPosition I East position of vessel [m]
surgeVelocity I Velocity of vessel in surge direction [m/s]
swayVelocity I Velocity of vessel in sway direction [m/s]
headingAngle I Heading angle of vessel [deg]
targetWP.north I North position of the target WP
targetWP.east I East position of the target WP
prevWP.north I North position of the previous WP
prevWP.east I East position of the previous WP
forceCommand O The force command requested from each of the two main thrusters [N]
rudderCommand O The azimuth angle of the two main thrusters [deg]

Waypoint Provider

This FMU holds the positions (North/East) of the WPs. The TrajectoryController.fmu receives a target WP and a previous WP and tries to converge to the straight line between the two WP in the direction of the target WP. When the horizontal plane distance between the vessel and the target WP is less than the numerical value of the variable “wpSwitchDistance”, the next WP in the list is assigned to the target WP and the previous target WP is assigned to the previous WP.

Table 3: Waypoint Provider inputs and outputs (I/O).

Name I/O Description
northPosition I North position of vessel [m]
eastPosition I East position of vessel [m]
headingAngle I Heading angle of vessel [deg
mode I If mode = 1, the fmu accepts additional wps input at runtime to a list. If mode != 1, the fmu uses a list specified at initialization. Either a hardcoded list (packman shape) or a user-specified list will be used based on the numerical value of wp1. If wp1 is initialized to a value not equal to 0.0, the user-specified list is used.
wpSwitchDistance I The horizontal plane distance, between the target WP and the vessel, at which the WP list is incremented. Threshold for accepting a target WP as “reached”.

Converter

This is a simple unit converter created to convert between radians per second, issued by ThrusterDrive.fmu -> Shaft.f, and Revolutions Per Minute (RPM), received by PMAzimuth.fmu -> input_act_revs.

Table 4: Converter inputs and outputs (I/O).

Name I/O Description
input.radPerSec I Input frequency in radians per second
output.rpm O Output frequency in revolutions per minute

Thruster Drive

Table 5: Thruster Drive inputs and outputs (I/O).

Name I/O Description
d_in.e I  
q_in.e I  
ThrustCom I  
Shaft.e I  
d_in.f O  
q_in.f O  
Shaft.f O  

PM Azimuth

Table 5: PM Azimuth inputs and outputs (I/O).

Name I/O Description
input_enabled I  
input_is_main_propulsion I  
input_x_rel_ap I  
input_y_rel_cl I  
input_z_rel_bl I  
input_prop_diam I  
input_t I  
input_distancetohull I  
input_bilgeradius I  
input_rho I  
input_act_revs I  
input_act_angle I  
input_cg_x_rel_ap I  
input_cg_y_rel_cl I  
input_cg_z_rel_bl I  
input_cg_surge_vel I  
input_cg_sway_vel I  
input_yaw_vel I  
input_lpp I  
output_force_heave O  
output_force_surg O  
output_force_sway O  
output_x_rel_ap O  
output_y_rel_cl O  
output_z_rel_bl O  

VesselFMU

Holds the vessel model and models applying environmental forces onto the vessel.

Table 6: VesselFMU and outputs (I/O).

Name I/O Description
vesselZipFile I Absolute path of vessel model zip archive
global_cur_dir I The direction of ocean current (0 is towards North) [deg]
global_cur_vel I The ocean current velocity [m/s]
input_global_wind_dir I The wind direction (0 is from North) [deg]
input_global_wind_vel I The wind velocity [m/s]
additionalBodyForce[0] I Magnitude (Newtons) of surge/sway/heave force produced by the port azimuth thruster and the point of attack of the force on the hull relative to AP/BL/CL.
additionalBodyForce[1] I Magnitude (Newtons) of surge/sway/heave force produced by the port azimuth thruster and the point of attack of the force on the hull relative to AP/BL/CL.
cgShipMotion.ned.north O North position of vessel (1st element of the “NED positions” vector in below figure)
cgShipMotion.ned.east O East position of vessel (2nd element of the “NED positions” vector in below figure)
cgShipMotion.angularDisplacement.yaw O Yaw angle of the vessel relative to north direction given in the below figure as the “heading” variable
cgShipMotion.angularVelocity.yaw O The angular velocity of the vessel about the yaw axis (deg/s)
cgShipMotion.linearVelocity O Components of the vessel velocity along the surge, sway and heave axes (m/s)
cg_x_rel_ap, cg_y_rel_cl, cg_z_rel_bl O Location of the center of gravity (CG) of the vessel relative to AP/BL/CL
Figure 1: Connections for Gunnerus Waypoints