Modification of the Ship Coarse Alignment Algorithm on a Wavy Pier in the Case Where Sensors Are Not Located in the Center
Seyed Ali Zahiripour · Journal of Aerospace Mechanics · 2025
In this paper, assuming that the inertial measurement unit is not located in the center of the ship, the initial alignment accuracy of the inertial navigation system on the oscillating base is investigated using one of the common methods, and then a solution is presented to modify this algorithm and increase the alignment accuracy using the output of gyroscopes. First, using the Poisson equation in a secondary inertial frame and the decomposition of the transformation matrix between body and geographic frames, the alignment algorithm for the inertial navigation system located on an oscillating base is presented. For this purpose, a short-term navigation algorithm is proposed and the initial conditions of its equations will be known by defining a secondary inertial frame, which is the same as the initial body frame. In order to ensure the observability of the level and heading angles, the theorem of independence of an orthogonal set is used. Next, to increase the accuracy of the algorithm, acceleration terms resulting from the distance of the inertial measurement unit from the center of the object are calculated and used to modify the conventional algorithm. Finally, the ability of the modified method to increase accuracy compared to the conventional method is evaluated through simulation.