Fast Time Simulator
Lanterna Fast Time simulator has been implemented because of the need to statistically manage the results of port and offshore installation entering and exiting maneuvers, in order to assess the risk and define the operative constraints. In order to make a statistical analysis, a large amount of data is needed, the collection of which would be very expensive and time consuming using a real time simulator. These considerations gave the impetus to search for new solutions that can be satisfied with Fast Time Simulation.
In the designed solution, still under development, the Fuzzy Logic approach has
been found as the most suitable tool to reach the goal, as per the following items:
IIt is the set of chosen maneuvers as a function of the port or offshore installation layout, the type of maneuver and of the local environmental conditions. These maneuvers will be executed by one or more captains and/or port pilots with a real time simulator, and they will be the base for the development of the new methodology.
During the execution of the maneuvers with the real time simulator, at each integration interval of the mathematical model differential equations, all force contributions from the ship control devices and from the environment will be recorded, Also recorded together with the devices status and the six degrees of ship motions.
Determination of areas with variation
of weather and sea conditions.
Area with variation of weather and sea conditions is defined as the interval of direction and intensity where the same manoeuvre strategy is adopted.
Based on studies on weather and sea states in the operation site, and with respect to the manoeuvre tipology for each of the environment states (sea waves, wind and current), the ranges of directions (sectors) and intensities will be defined where, as for the captain experience, the same strategy will be used.
The validity of the areas choice will be verified by the results of the FAST-TIME simulations. In cases where the area results are too wide, an increase in the number of manoeuvring strategies would be necessary and as a consequence also an increase of the population of the manoeuvre layers.
Identification of control devices critical areas
Control devices within a critical area is defined as the time and intensity window around the instant where an important variation of one of the ship control devices occurred.
In the time data stream recorded during the real time simulation, for each control device: steering (rudder, transversal thrusters), propulsion (propellers), mooring (anchors and lines), auxiliary aids (tugs), the time instant is identified where its state has been significantly modified such to have an effect on the ship dynamics. Around all of these instants a time interval and a variation intensity are defined, which gives the uncertainty of each action taken during the simulation. This uncertainty is human factor dependent.
Fast-Time Simulation with Fuzzy regulator
The execution is performed by the Fast-Time simulation described above, which is interfaced with the fuzzy regulator at each integration interval. The process receives as input the control devices status (4) and has the scope to reproduce one of the simulations defined at (1), inside a tolerance interval. By changing one of the control inputs (device A) at a certain time, with respect to the reference simulation, the procedure is to try to obtain the same output by correcting, during the run, the other control device inputs included the same device A in the time following.
At each integration step the fuzzy regulator, via an interactive process, defines the best combination of weights to be assigned to each control device, among all possible combinations. It is evident that the more is the number of iterations, the more the control device variation was critical in the maneuver economy.
Fuzzy logic determination of the control
devices state and sea and weather conditions
On the base of the critical areas as defined above (3) the status of all control devices will be generated and given as input to the fuzzy logic FAST TIME simulations. The number of simulations will be a function of the number of critical areas and their dimensions.
As for the above point (3) the generation of the control devices status (rudder, transversal thrusters, engine telegraph, anchors, lines, tugs) will take into account not only the critical area dimension, but also the probability density distribution considered around the area centre.
With the same procedure new weather and sea state conditions will be set, and further fuzzy logic FAST-TIME simulations will be executed. As already highlighted in the above point, they not only increase the data population, but they give also the tool to verify the validity of the variation of area and environmental condition dimensions.