Prediction of Course-Keeping Control Coefficients of DARPA Suboff

This chapter aims to determine PID parameters for course control in submerged bodies using computational fluid dynamics (CFD), with a focus on the DARPA Suboff submarine (AFF-8). Propulsion characteristics were evaluated under straight-ahead conditions at V=2.75m/s and validated with experimental and computational data. Subsequently, 10/10 zig-zag maneuvers were performed, allowing the submarine to surge, sway, and yaw motions, thereby providing insights into its course-keeping performance. The flow around the AFF-8 was modeled as single-phase, incompressible, three-dimensional, and fully turbulent using the SST k−ω model. Transient maneuvering computations employed segregated flow and implicit unsteady models, supported by adaptive mesh and all y⁺ wall treatment models. In order to facilitate and accelerate the solution of the maneuvering problem without compromising accuracy, the dynamic fluid body interaction (DFBI) method was preferred for determining the hull motions, the moving reference frame (MRF) method for the propeller rotation, and the rigid body motion (RBM) method for the rudder rotation. Additionally, a proportional-integral (PI) controller was implemented to determine the self-propulsion point using the proportional gain K_P and integral gain K_I. The self-propulsion point of the DARPA form was estimated to be 9.4025 rps using a PI controller. Additionally, the dimensionless thrust K_T and torque K_Q coefficients were consistent with values reported in the literature. During the zig-zag test, data including yaw angle (ψ), rudder angle (δ), hydrodynamic forces (F_x,F_y), moment (M_z), velocity (U,V), and acceleration (dudt,dvdt) were simultaneously collected. The 10-10 zig-zag test revealed that the DARPA form exhibited significant overshoot angles. This behavior is primarily attributed to its geometric characteristics and relatively small rudder surface area. These findings indicate that the DARPA Suboff form requires a dedicated control system to maintain course stability effectively. This approach is expected to enhance the course-keeping capabilities of the DARPA Suboff, addressing its inherently low maneuverability.