Modeling & Simulation > SHIP and Wave 6DOF Trajectory Generator

SHIP 6DOF - An Easy to Use WGS84 Ship with Wave Model Trajectory Generator

The SHIP.EXE Ship & Wave Waypoint based trajectory generator, developed by Network Sensing Technologies (NST), uses a 6DOF simulation to create ship trajectories and the required states (angular rates, accelerations etc.) for trajectory file use. The Ship 6DOF creates a trajectory that passes through a sequence of user defined waypoints. The ship altitude is constrained to the surface of the WGS84 ellipsoid. After the ideal trajectory is generated, random heave (vertical motion), pitch, and roll are added to the ideal trajectory to simulate the ship response to random ocean waves. Random waves of various lengths and periods are generated using the Joint North Sea Wave Project (JONSWAP) wave spectrum model. SHIP.exe is a generic point mass 6-Degee-of-Freedom path trajectory generator. It generates a trajectory that passes through a sequence of user defined waypoints referenced to the World Geodetic System 1984 (WGS-84) ellipsoid

E6DOF is a 32/64-bit C#/C++ software application that executes on Windows 10 platforms. SHIP GUI creates scenarios which are saved in XML format. E6DOF parses the XML input file that contains airframe maneuverability parameters, initial conditions, and a sequence of waypoints. output is a time history ASCII output file containing the trajectory data. It can be invoked via command line with corresponding .XML input file.

Defining SHIP Trajectories

Methodology for waypoint based 6DOF trajectory generation is rather simple; specify the maneuverability parameters, initial conditions, waypoint laydown via mouse map entry or manual inputs, a pre-validation phase, modification if necessary and finally trajectory generation. The default step size interval is 5 msec.

The Maneuverability Parameters section defines several fields that allow you to constrain the motion of the platform. The parameters are:

  • Maximum Lateral Acceleration:
  • Maximum Thrust Acceleration:
  • Wind Speed:The wind speed 19.5 meters above mean sea level
  • FetchThe distance that the wind has been blowing across an unobstructed sea.
  • Tunning Parameters A tuning parameter that can be used to adjust the peak wave height.
  • Wave Heading: Direction of the Waves
  • Random Motion: Heave, Pitch, RollThe random motion dynamic model describes the ship response to wave height. The Steady State Gain, Damping Coefficient, Natural Frequency, and Time Constant define a second-order transfer function that models the heave, pitch, and roll response to wave height. The heave, pitch, and roll response models can be independently enabled/disabled by checking/clearing the Enabled box in the Random Motion Dynamic Models view.
  • Autopilot Type: Select autopilot type: Bank-to-Turn or Skid-to-Turn

    • The Parameter Type allows guidance law selection for platform velocity control Two options are:

  • Velocity – The platform will command a thrust that generates the specified velocity before reaching a waypoint.
  • Time – The platform will use an optimal control law (Zero-effort miss) that generates the thrust needed to arrive at the waypoint at a user defined time.
  • Waypoints & Velocity:>Waypoints may be entered either as Latitude, Longitude, Altitude or by clicking on the World Map

    • Exported Trajectory Files -

    Pilot allows exporting of trajectory data to four ASCII files, each a bit different and intended for unique purposes:

    Trajectory File – Space Delimited:

    Column Parameter Units
    1 Time Seconds
    2 Longitude Degrees
    3 Latitude Degrees
    4 Altitude Meters Relative to WGS84
    5..7 ECEF Vel X,Y,Z Meters/Seconds
    8..10 ECEF Accel X,Y,Z Meters/Second2
    11.13 Roll, Pitch, Yaw (hdg) Degrees
    14..16 Body Rate X,Y,Z Radians/Second
    17..18 Angular Accel X,Y,Z Radians/Second2

    Trajectory File – CSV Formatted:

    Column Parameter Units
    1 Time Seconds
    2 Longitude Degrees
    3 Latitude Degrees
    4 Altitude Meters Relative to WGS84
    5..7 NEU Velocities Meters/Seconds
    8 Total Velocity Meters/Seconds
    9..11 NEU Acclerations Meters/Second2
    12 Dive Angle Degrees
    13 Bearing Degrees
    14 Roll Degrees
    15..17 Body Rate X,Y,Z Radians/Second
    18..20 Angular Accel X,Y,Z Radians/Second2

    Trajectory Full State File – ASCII Space Delimited:

    Column Parameter Units
    1 Time Seconds
    2..4 ECEF Position X,Y,Z Meters
    5..7 ECEF Velocity X,Y,Z Meters/Seconds - Relative to Earth
    8..10 ECEF Acceleration X,Y,ZMeters Relative to Earth
    11..13 ECEF Jerk X,Y,Z Meters/Second3
    14..16 Roll, Pitch, Yaw (hdg) Degrees
    17..19 Body Rate X,Y,Z Radians/Second Relative to an Inertial Frame In Body Cords
    20..21 Angular Accel X,Y,Z Radians/Second2 Relative to an Inertial Frame In Body Cords

    Note: Things Change Rapidly! Specifications, Capabilities, Features and Availability Subject to Change Without Notice and May Be Restricted to Certain Users.