The "ship-in-transit-simulator" is a set of python classes that can be used to build and run s imulations a ship in transit.

Simulation model

Ship

The ship model describes the motion of a ship in three degrees of freedom (surge, sway and yaw), and contains the 6 states:

• North position [meters]
• East position [meters]
• Yaw angle [radians]
• Surge speed [meters per second]
• Sway speed [meters per second]
• Turn rate [radians per second]

Additionally, models including machinery system dynamics will have in addition on of the following states

• Propeller shaft angular velocity [radians per second] (advanced machinery model)
• Thrust forces [Newton] (simplified machinery system)

The equations of motion includes inertial forces, forces induced by the added mass effect, Coriolis forces, linear and non-linear friction forces, environmental forces (described later) and control forces for the main propeller and rudder if a machinery system is included.

Machinery system

The ship model has a single propeller shaft and a single rudder. The propeller shaft can be powered either by the main power source (typically a diesel engine) or by a hybrid shaft generator. The hybrid shaft generator is powered (when running as a motor) by an electrical distribution. The electrical distribution is typically powered by a set of diesel generators.

The simulator offers two models for this propulsion system. One with propeller shaft dynamics included and one simplified model where the thrust force is modelled as a second order transfer function.

The machinery system can be operated in three operating modes:

• PTO (Power Take Out): The main power source is responsible for both the propulsion load and the hotel loads. Hotel loads are served via the hybrid shaft generator acting as a generator.
• MEC (Mechanical): The main power source is only responsible for the propulsion load while the electrical distribution serves the hotel loads.
• PTI (Power Take In): The main power source is offline and both propulsion and hotel loads are served by the electrical distribution. Propulsion power is provided via the hybrid shaft generator acting as a motor.

The model can be run as a "single engine"-ship by selecting to use only the main engine. Using PTO-mode, the hotel loads and propulsion loads will be served by the main power source.

Navigation

The model offers a heading-by-heading-reference controller and a controller that can follow a list of waypoints (see provided examples)

Environmental forces

The ship is subject to wind forces (constant wind speed), and current forces (constant current speed).

Speed control

Speed control can be achieved by:

• The simulator takes a "engine trottle"-signal which represents the load percentage on the available power for propulsion to be used for generating thrust
• A speed controller that can controls propeller shaft speed according to ship speed setpoint is provided.

Equations

Details regarding the equations of motion can be found in the file ship_dynamics.pdf

Usage

See examples

Installation

Import models.py into your code.

Using the simulator

Examples on how to setup and use to simulator can be seen in the files under the "examples" folder.

Contributors

Børge Rokseth (borge.rokseth@gmail.com)

Licence

This project is published under the MIT license.