Research On Estimation Methods Of Optimal Headings For Dynamic Positioning Ships

This paper discusses methods for finding optimal headings when a dynamic positioning ship maintains its position at hover point. Finding optimal headings is one of the key technologies of dynamic positioning. Guiding a ship at an optimal heading, the energy consumption of the ship will fall greatly.When a dynamic positioning ship is working in a long period task, the energy consumption depends much on whether guiding the ship at an optimal heading. Aiming at reducing the energy consumption of dynamic positioning ships, this paper gives two different methods for finding optimal headings.The first method is basing on the judgment of lateral load of thrusters, to find the optimal headings by means of changing the heading continuously. The advantages of this method are that it is independent of any environment models, and it is effectively for any other dynamic positioning ships; the disadvantage is that dynamic positioning ships may consume excess energy, during the time they were finding optimal headings. However, it is sufficiently valuable for dynamic positioning ships to find optimal headings in a short period of time, and thereby to reduce the energy consumption in a long period of time.The second one is firstly to estimate the speed and direction of sea current depending on the models of environment and thrusters, thereby to estimate the optimal headings according to the speed and direction of sea current. It separately gives four different ways to estimate optimal headings, according to the speed, direction of sea current. The advantage of this method is that it doesn't need excess energy consumption, which means that if we can guide the ship at an optimal heading, the energy consumption will fall greatly during the long period task; the disadvantage is that the model of environment is not precise yet, which leads to the speed, direction of sea current and the optimal heading are not precise. However, a dynamic positioning ship finally can reduce its energy consumption by guiding the ship at an optimal heading the method works out, only the decrease of energy consumption is fewer than the first method does.The result of digital simulation shows that the power of thrusters falls obviously by means of guiding the ship at the optimal headings got from the two methods separately after the ship maintains its position at hover point. It indicates that the two methods mentioned can help the ship reduce the energy consumption.