Jiaming Wu

A hydrodynamic model of a two-part underwater towed system

A three-dimensional model of a two-part underwater towed system is studied. In the model, the governing equations of cables are established based on the Ablow and Schechter method. The boundary conditions for the two-part underwater towed system are derived. The six-degrees-of-freedom equations of motion for submarine simulations are adopted to predict the hydrodynamic performance of a towed vehicle. The established governing equations for the system are then solved using a central finite difference method. In this paper several algorithms are used to solve this special form of finite difference equations. The results in this paper indicate that the two-part underwater towed system improves the dynamic behavior of the towed vehicle and is an easy way to decouple the towing ship motion from the towed vehicle. Because the model uses an implicit time integration, it is stable for large time steps and is an effective algorithm for simulation of a large-scale underwater towed system.

Investigation on a two-part underwater manoeuvrable towed system

A hydrodynamic model of a two-part underwater manoeuvrable towed system is proposed in which a depressor is equipped with active horizontal and vertical control surfaces, and a towed vehicle is attached to the lower end of a primary cable. In such a system the towed vehicle can be manoeuvred in both vertical and horizontal planes when it is towed at a certain velocity and the coupling effect of excitations at the upper end of the primary cable and disturbances of control manipulations to the towed vehicle can be reduced. In the model the hydrodynamic behavior of an underwater vehicle is described by the six-degrees-of-freedom equations of motion for submarine simulations. The added masses of an underwater vehicle are obtained from the three-dimensional potential theory. The control surface forces of the vehicle are determined by the wing theory. The results indicate that with relative simple control measures a two-part underwater manoeuvrable towed system enables the towed vehicle to travel in a wide range with a stable attitude. The method in this model gives an effective numerical approach for determining hydrodynamic characteristics of an underwater vehicle especially when little or no experimental data are available or when costs prohibit doing experiments for determining these data.

Experimental investigation on a two-part underwater towed system

Abstract An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472].

Numerical Simulation on Hydrodynamic Behaviors of Ducted Propeller in Yawing Motion of an Underwater Vehicle

A practical approach to simulate hydrodynamic performance of ducted propellers attached in an underwater vehicle under the influence of flow field of the vehicle is proposed, hydrodynamic characteristics of the propeller when the vehicle in a dynamic yawing motion is studied numerically. In the research, 3D geometric models of the duct, propeller and underwater vehicle are first constructed according to their geometrical features. Computational fluid dynamics (CFD) technique based on the finite volume method and multi-sliding mesh technique are applied to solve the Navier-Stokes equations which govern the fluid motions around the duct, propeller and underwater vehicle when the vehicle are in a yawing motion. These equations are solved numerically with the CFD code FLUENT. With the proposed numerical simulation approaches, the hydrodynamic phenomenon of thrusts generated from the ducted propellers in the vehicle system under the flow field influence of the vehicle’s yawing motion are analyzed. Results of our numerical simulation indicate that the influence of flow field caused by the underwater vehicle on the thrusts of the ducted propellers is not negligible; when studying the thrust characteristics of a ducted propeller in an underwater vehicle system, the thrust nature of the propeller can only be evaluated objectively on the condition that the vehicle and the ducted propeller are combined together into an integrated system, and the numerical simulation are conducted in such an integrated system.Copyright

Hydrodynamic and Control Analysis of a Self-Controllable Underwater Towed Vehicle

The hydrodynamic and control performances of a self-stable controllable underwater towed vehicle developed by South China University of Technology under different depth trajectory control operations are analyzed by means of a proposed hydrodynamic numerical model. The model is established based on LMBP algorithm of neural network theory. Training samples for the neural network model are provided from the experimental data of the vehicle prototype towing experiments conducted in a large-scale ship model towing tank under the manipulation of a depressing wing installed in the vehicle. After the LMBP model is established, a depth trajectory control system for the towed vehicle is designed in order to accomplish vehicle trajectory control. This system is mainly composed of tow parts: a neural network identifier based on genetic algorithm and a fuzzy neural network controller based on genetic algorithm simulated annealing. Hydrodynamic performances of the vehicle under various control operations can then be numerically simulated with the proposed LMBP model and the depth trajectory control system of the towed vehicle. In numerical simulation of trajectory control to the towed vehicle, deflection of the vehicle’s depressing wing is adjusted at every time step by the proposed control system to match the trajectory of the vehicle with a pre-designated one. The value of the deflection is taken as input parameter for the LMBP neural network model, trajectory and attitude behavior of the towed vehicle under the control manipulations can then be predicted by the LMBP model.Copyright

Trajectory and Attitude Control of an Underwater Towed Vehicle

A new concept of control technique to perform operation of trajectory maneuvering to a controllable underwater towed vehicle moving in a designated path with a required attitude is presented. A trajectory and attitude control technique for the towed vehicle is proposed in order to accomplish the vehicle’s trajectory and attitude manipulations. This technique is based on a fuzzy algorithm. The towed vehicle in the research consists of a cylindrical main body equipped with several active horizontal and vertical control surfaces. Numerical simulation on the hydrodynamic and control behavior of the towed vehicle under this control manipulation is conducted based on a fully 3-D hydrodynamic model of an underwater towed vehicle. In the model the governing equation of the towed cable is based on the Ablow and Schechter method. The six-degrees-of-freedom equations of motion for an underwater vehicle simulation proposed by Gertler and Hagen are adopted to estimate the hydrodynamic performance of the towed vehicle. In numerical simulation the deflections of vehicle’s control surfaces are governed by the proposed fuzzy controller to manipulate the vehicle traveling along a 3-D stipulated trajectory configuration and required attitude. The values of the deflections are taken as input parameters for the hydrodynamic model at every time step. The performance of the towed vehicle under different designated trajectory and attitude control manipulations can then be investigated with the hydrodynamic model.Copyright