Study on a novel two-part underwater towed system for near-surface towed vehicle test

A new underwater two-part towed system is proposed and studied for the test of near-surface towed vehicles. The near-surface towed vehicle is towed by submarines or the large displacement unmanned undersea vehicle, and plays the role of the communication relay with the onshore station. To deal with the influence of the harsh wave environment and create a stable test platform, a fuzzy-PID control method and an active heave compensation device are applied in the towed system. The mathematical model of the two-part towed system is built. In the model, the nonlinear aspects are considered, such as the interaction of the multi-body, the flexibility of the cable, the wave force, the heave compensation. Based on the model, the simulation results indicate that the Fuzzy-PID control method can significantly reduce the depth fluctuation of the towed vehicle under different sea state. Besides, it is also demonstrated that the active heave compensation device can obviously improve the stability performance of the two-part towed system by greatly reducing the depth fluctuation of the ballast, and create a very stable test environment similar to the submarine or large underwater vehicle.