Disc-type Underwater Glider Modeling and Analysis for Omnidirectional and Steering Motion Characteristics

A disc-type underwater glider (DTUG) has a highly symmetrical full-wing shape that allows it to move omnidirectionally and have the same hydrodynamic characteristics in all directions in the horizontal plane. These characteristics make the viscous hydrodynamic coefficients measured by conventional methods unsuitable for simulating the omnidirectional and steering motions of the DTUG. To further reveal the omnidirectional and steering motion characteristics of the DTUG, this paper proposes a new theoretical method for calculating the DTUG motion control equations in the velocity frame rather than the body frame. Based on the structural characteristics of the DTUG, the motion control equations are derived and then solved using the fourth-order Runge-Kutta method. The omnidirectional and steering motions of the DTUG are simulated in the velocity frame and compared with the results calculated in the body frame. The results show that the viscous hydrodynamic coefficients obtained by conventional methods are not suitable for analyzing the omnidirectional motion of the DTUG, and the method of calculating the motion control equations in the body frame has limitations in studying the steering motion. The new method proposed in this paper solves these limitations well and can more accurately reveal the motion characteristics of the DTUG without recalculating the hydrodynamic coefficients. The results also show that the DTUG can change the heading angle more easily than a torpedo-type underwater glider (TTUG), and the steering radius is much smaller, which means that the DTUG has greater flexibility in a small body of water. The DTUG can remain stable when the control variables are within the control range and the new method is adopted.