Dynamic modeling and optimal control of a positive buoyancy diving autonomous vehicle

The positive buoyancy diving autonomous vehicle combines the features of an Unmanned Surface Vessel (USV) and an Autonomous Underwater Vehicle (AUV) for marine measurement and monitoring. It can also be used to study reasonable and efficient positive buoyancy diving techniques for underwater robots. In order to study the optimization of low power consumption and high efficiency cruise motion of the positive buoyancy diving vehicle, its dynamic modeling has been established. The optimal cruising speed for low energy consumption of the positive buoyancy diving vehicle is determined by numerical simulation. The Linear Quadratic Regulator (LQR) controller is designed to optimize the dynamic error and the actuator energy consumption of the vehicle in order to achieve the optimal fixed depth tracking control of the positive buoyancy diving vehicle. The results demonstrate that the LQR controller has better performance than PID, and the system adjustment time of the LQR controller is reduced by approximately 56% relative to PID. The motion optimization control method proposed can improve the endurance of the positive buoyancy diving vehicle, and has a certain application value

Lumped hydrodynamics identification-based cascade control for vertical-plane tracking of a fin-driven autonomous underwater vehicle

This paper aims to achieve a simplified and effective vertical-plane trackingcontrol for a kind of fin-driven under-actuated autonomous underwater vehicles(AUVs). To this end, a two-layer framework of offline identification and online control is constructed and implemented for depth-pitch coupled trackingcontrol of an under-actuated AUV at a constant forward speed. A simplifiedthree-order identification model for pitch dynamics is derived and then a dedicated recursive weighted least squares algorithm is used to complete the offline estimation of lumped hydrodynamics. Subsequently, relying on identification results, an online cascade controller with just two gains and without any adaptive estimation is proposed to track the pitch guidance angle and it is proven to be input-to-state stable. Finally, comparative simulation results illustrate the effectiveness and out performance of this two-layer framework for vertical-plane tracking control of fin-driven under-actuated AUVs.<br/

Vertical Motion Control of an Underwater Glider with a Command Filtered Adaptive Algorithm

Underwater gliders are widely used in oceanic observation, which are driven by a hydraulic buoyancy regulating system and a movable mass. Better motion performance can help us to accomplish observation tasks better. Therefore, a command filtered adaptive algorithm with a detailed system dynamic model is proposed for underwater gliders in this paper. The dynamic model considers seawater density variation, temperature variation and hull deformation according to dive depth. The hydraulic pump model and the movable mass dynamic are also taken into account. An adaptive nonlinear control strategy based on backstepping technique is developed to compensate the uncertainties and disturbances in the control system. To deal with the command saturation and calculation of derivatives in the backstepping process, command filtered method is employed. The stability of the whole system is proved through the Lyapunov theory. Comparative simulations are conducted to verify the effectiveness of the proposed controller. The results demonstrate that the proposed algorithm can improve the motion control performance for underwater gliders under uncertainties and disturbances

Robust variable-depth path following of an under-actuated autonomous underwater vehicle with uncertainties

2543-2551This paper treats the subject of variable-depth path following control of an under-actuated autonomous underwater vehicle (AUV) with multiple uncertainties. The modeling uncertainties of the investigated AUV are composed of inaccurate hydrodynamic coefficients and unknown environmental disturbances. For this uncertain system,  a  nonlinear control law integrating line-of-sight (LOS) guidance with fuzzy sliding mode control (FSMC) algorithm is designed to guarantee global κ-exponentially convergence of path following errors. The LOS guidance in the Serret-Frenet frame is adopted to guide the under-actuated AUV to move towards the curved variable-depth path. The sliding mode control algorithm ensures the stability and the robustness of the designed control law in the presence of multiple uncertainties. The fuzzy logic algorithm is integrated to adjust sliding mode gain in order to weaken chattering. In addition, the angle of attack is considered in the design of dynamics control law to ensure that the under-actuated AUV follows the predefined path with a given resultant speed. Finally, a comparative simulation study illustrates the effectiveness of the designed FSMC algorithm for variable-depth path following of an under-actuated AUV with multiple uncertainties

Subsea Cable Tracking by Autonomous Underwater Vehicle with Magnetic Sensing Guidance

The changes of the seabed environment caused by a natural disaster or human activities dramatically affect the life span of the subsea buried cable. It is essential to track the cable route in order to inspect the condition of the buried cable and protect its surviving seabed environment. The magnetic sensor is instrumental in guiding the remotely-operated vehicle (ROV) to track and inspect the buried cable underseas. In this paper, a novel framework integrating the underwater cable localization method with the magnetic guidance and control algorithm is proposed, in order to enable the automatic cable tracking by a three-degrees-of-freedom (3-DOF) under-actuated autonomous underwater vehicle (AUV) without human beings in the loop. The work relies on the passive magnetic sensing method to localize the subsea cable by using two tri-axial magnetometers, and a new analytic formulation is presented to compute the heading deviation, horizontal offset and buried depth of the cable. With the magnetic localization, the cable tracking and inspection mission is elaborately constructed as a straight-line path following control problem in the horizontal plane. A dedicated magnetic line-of-sight (LOS) guidance is built based on the relative geometric relationship between the vehicle and the cable, and the feedback linearizing technique is adopted to design a simplified cable tracking controller considering the side-slip effects, such that the under-actuated vehicle is able to move towards the subsea cable and then inspect its buried environment, which further guides the environmental protection of the cable by setting prohibited fishing/anchoring zones and increasing the buried depth. Finally, numerical simulation results show the effectiveness of the proposed magnetic guidance and control algorithm on the envisioned subsea cable tracking and the potential protection of the seabed environment along the cable route

Guidance-error-based robust fuzzy adaptive control for bottom following of a flight-style AUV with delayed and saturated control surfaces

This paper addresses the problem of robust bottom following control for a flight-style autonomous underwater vehicle (AUV) with both delayed and saturated control surfaces by using a pair of rudders. First, the time-delayed dynamics of rudders is considered, which renders a high-order nonlinear dynamics analysis and design in the model-based backstepping controller by utilizing guidance errors; Second, to overcome the shaking control behaviour resulted by the model-based high order derivative calculation, a fuzzy approximator-based modelfree controller is proposed, in order to online approximate the unknown part of the ideal backstepping architecture. In addition, the adaptive error estimation technology is resorted to compensate the system approximation error, ensuring that all the position and orientation errors of robust bottom following control tend to zero; Third, to further tackle the potential unstable control behaviour from inherent saturation of control surfaces driven by rudders, an additional adaptive fuzzy compensator is introduced, in order to compensate control truncation between the unsaturated and saturation inputs. Subsequently, Lyapunov theory and Barbalat lemma are adopted to synthesize asymptotic stability of the entire bottom following control system; Finally, comparative numerical simulations among the model-based benchmark controller, the unsaturated and saturated model-free controllers are provided to illustrate adaptability and robustness of the proposed bottom following controller for a flight-style AUV with delayed and saturated control surfaces

Motion forecast of intelligent underwater sampling apparatus —— Part II: CFD simulation and experimental results

1971-1979The part II of the paper adopts the steady-state superposition algorithm proposed in Part I to simulate the vertical surfacing motion and the horizontal drift of the intelligent underwater sampling apparatus (IUSA) under sea current, in order to figure out the surfacing time and horizontal recovery range on the surface of the sea. Through dividing the surfacing process into a number of infinitesimal segments, the velocity, fluid force and displacement of the IUSA are obtained by resorting to Computational Fluid Dynamics (CFD) software, and the procedure of pre-treatment, solver and post-treatment of Fluent is presented in detail. Simulation results based on SolidWorks and FLUENT are compared which also show the proposed algorithm can meet the requirements of the motion forecast of the IUSA. Preliminary experimental results in East Lake validate that the theoretical algorithm and the computational method are effective within the allowable error range, which can guide the mission operator to recover the IUSA on the broad sea area

Motion forecast of intelligent underwater sampling apparatus —— Part I: Design and algorithm

1962-1970This paper introduces a novel intelligent underwater sampling apparatus (IUSA) mounted on autonomous underwater vehicle (AUV) with an essential practical sense, as the IUSA can be conveniently released from AUV to accomplish the underwater sampling task and then surface up by releasing the ballast itself. Mechanical design of the IUSA is briefly introduced, which has the feature of simple structure to carry the sampling sensor, low power consumption, high reliability of release and recycling utilization. It easily achieves the ability to dive in and surface up only by adjusting its buoyancy. However, it is rather difficult to confirm the surfacing time of the IUSA in order to timely recover it, since the underwater motion forecast of the IUSA is largely disturbed by complex fluid hydrodynamics. This paper presents a steady-state superposition algorithm to address the problem of motion forecast of the sampling apparatus, with the assistant of computational fluid dynamics software to take into account the dynamics of the IUSA in sea water, which is instrumental in helping the mission operators recover the apparatus for recycling utilization

Optimization of Heterogeneous Container Loading Problem with Adaptive Genetic Algorithm

This paper studies an optimized container loading problem with the goal of maximizing the 3D space utilization. Based on the characteristics of the mathematical loading model, we develop a dedicated placement heuristic integrated with a novel dynamic space division method, which enables the design of the adaptive genetic algorithm in order to maximize the loading space utilization. We use both weakly and strongly heterogeneous loading data to test the proposed algorithm. By choosing 15 classic sets of test data given by Loh and Nee as weakly heterogeneous data, the average space utilization of our algorithm reaching 70.62% outperforms those of 13 algorithms from the related literature. Taking a set of test data given by George and Robinson as strongly heterogeneous data, the space utilization in this paper can be improved by 4.42% in comparison with their heuristic algorithm

Manoeuvring-based actuation evaluation of an AUV with control surfaces and through-body thrusters

For an autonomous underwater vehicle (AUV), control surfaces are usually used for high-speed manoeuvres, while at low speed the AUV relies upon through-body thrusters for manoeuvring. In this paper, the speed interval-s of high-speed and low-speed manoeuvres are quantitatively analyzed. To this end, the AUV’s dynamics equations composed of body hydrodynamics and actuator models are first established with specific regard to operation at different speeds. Resorting to the above complete dynamics model, turning manoeuvring tests are carried out to forecast the AUV’s advance and turning time at different speeds. Initial turning ability criterion approved by International Maritime Organization is then used to calculate thresholds for low-speed and high-speed manoeuvres. Due to non-overlap, the entire speed profile is divided into low-speed, medium-speed and high-speed inter-vals, where different actuator combinations and characteristics are analyzed. Finally, a smooth switching law is designed to manage the contribution of two types of actuators through the entire AUV’s speed profile