Brad Buckham

Integrated Path Planning and Tracking Control of an AUV: A Unified Receding Horizon Optimization Approach

This paper attempts to develop a unified receding horizon optimization (RHO) scheme for the integrated path planning and tracking control of an autonomous underwater vehicle (AUV). Considering that the effective sensing range of onboard sensors is practically short, we formulate the path planning into RHO problems with the spline path template. The planned path is subsequently viewed as the state trajectory of a virtual reference system having the same kinematic and dynamic properties as the AUVs. Appropriately constructed error dynamics makes the AUV tracking control equivalent to the regulation problem of the error dynamic system, which facilitates the derivation of theoretical results via nonlinear MPC techniques. The model predictive control (MPC) tracking controller is designed so that closed-loop stability can be ensured. Due to the inherent RHO nature, both the path planning and tracking control are incorporated into an unified scheme. Simulation studies are conducted using a realistic dynamic model of the Falcon AUV, which was created in our previous experimental work. The simulation results demonstrate the effectiveness of the proposed control algorithm.

Modified C/GMRES Algorithm for Fast Nonlinear Model Predictive Tracking Control of AUVs

This brief presents a nonlinear model predictive control (NMPC) method for the trajectory tracking problem of an autonomous underwater vehicle (AUV). By augmenting the desired output trajectory to a reference dynamical system, the tracking task can fit into the standard NMPC framework, which effectively avoids possible numerical difficulties in the following fast NMPC implementation. To relieve the conflict between short sampling period and high demand of online calculation, Ohtsuka’s continuation/generalized minimal residual (C/GMRES) algorithm is investigated. In order to handle the realistic constraints on the AUV thrusters, we incorporate the log barrier functions into the cost function and modify the C/GMRES algorithm. Several different reference trajectories are tested using the identified dynamic model of the Saab SeaEye Falcon open-frame ROV/AUV, which demonstrate the effectiveness and efficiency of the proposed fast algorithm for the AUV tracking control.

The importance of mooring line model fidelity in floating wind turbine simulations

Accurate computer modelling is critical in achieving cost effective floating offshore wind turbine designs. In floating wind turbine simulation codes, mooring line models often employ a quasi-static approximation that neglects mooring line inertia and hydrodynamics. The loss of accuracy from using this approach has not been thoroughly quantified. To test whether this widely-used simplified mooring line modelling approach is adequate, the open-source floating wind turbine simulator FAST was modified to allow the use of an alternative, fully dynamic, mooring model based on the hydrodynamics simulator ProteusDS. The OC3-Hywind floating wind turbine design was implemented in this newly-coupled simulator arrangement and tested using a variety of regular wave conditions. The static equivalence between the built-in quasi-static mooring model and the newly-coupled dynamic mooring model is very good. Tests using both models were performed looking at scenarios of the response of the system in still water and the response to regular waves and steady winds. The dynamic mooring model significantly increased the overall platform damping in translational DOFs during motion decay tests in still water. There was very little difference between the models in coupled tests where regular wave excitation was the primary driver of platform motions, except for the addition of small levels of power in the higher frequencies of the platform motion spectrum. The nature of the different tests suggests that it is only in situations where the platform motions and wave velocities are not synchronized that the damping from the dynamic mooring model makes a large difference. This points to irregular wave conditions as providing a better test of the differences between mooring models.

Nonlinear model predictive control for trajectory tracking of an AUV: A distributed implementation

This paper investigates the nonlinear model predictive control (NMPC) method for the trajectory tracking application of an autonomous underwater vehicle (AUV). To formulate the tracking control problem into the standard MPC scheme, the desired spatial reference trajectory is augmented according to the kinematic property of the AUV motion, which facilitates the following distributed model predictive control (DMPC) implementation. Considering that the computational complexity of the nonlinear programming (NLP) problem associated to the NMPC tracking control could be prohibitively high, the DMPC implementation is proposed attempting to alleviate the computational burden. The six degree of freedom (DOF) AUV model is then decomposed into three slightly coupled subsystems, and the DMPC subproblems are well defined with the original cost function broken down appropriately. Warm start strategy is adopted to enhance the control performance. Simulation studies are carried out, which verifies the effectiveness of the proposed method.

Path-following control of an AUV using multi-objective model predictive control

The path-following (PF) problem of an autonomous underwater vehicle (AUV) is studied, in which the speed profile of the vehicle is taken into consideration as a secondary task. A multi-objective model predictive control (MO-MPC) framework is developed attempting to accommodate the prioritized tasks in PF. To solve the MO-MPC problem, we adopt the weighted sum method with the introduction of a logistic function that automatically selects the appropriate weights for each objective function. Pontryagin minimum principle (PMP) is subsequently applied for the implementation. Simulations using identified hydrodynamic coefficients of the Saab SeaEye Falcon open-frame ROV/AUV are carried out, which validates the effectiveness of the proposed MO-MPC path-following control.

A new Kriging–Bat Algorithm for solving computationally expensive black-box global optimization problems

ABSTRACT Many global optimization (GO) algorithms have been introduced in recent decades to deal with the Computationally Expensive Black-Box (CEBB) optimization problems. The high number of objective function evaluations, required by conventional GO methods, is prohibitive or at least inconvenient for practical design applications. In this work, a new Kriging–Bat algorithm (K–BA) is introduced for solving CEBB problems with further improved search efficiency and robustness. A Kriging surrogate model (SM) is integrated with the Bat Algorithm (BA) to find the global optimum using substantially reduced number of evaluations of the computationally expensive objective function. The new K–BA algorithm is tested and compared with other well-known GO algorithms, using a set of standard benchmark problems with 2 to 16 design variables, as well as a real-life engineering optimization application, to determine its search capability, efficiency and robustness. Results of the comprehensive tests demonstrated the suitability and superior capability of the new K–BA.

Effect of Chordwise Flexibility and Depth of Submergence on an Oscillating Plate Underwater Propulsion System

The first part of this work was dedicated to the experimental study of basic principles of oscillating plate propulsors undergoing a combination of heave translation and pitch rotation. The oscillation kinematics are inspired by swimming mechanisms employed by fish and some other marine animals. The primary attention was the propulsive characteristics of such oscillating plates, which was studied by means of direct force measurements in the thrust-producing regime. Experiments were performed at constant Reynolds number and heave amplitude. By varying the Strouhal number, experimental depth and chordwise flexibility of the plate it was possible to investigate corresponding changes in thrust and hydromechanical efficiency. After numerous measurements it was possible to establish an optimal set of parameters, including the system’s driving frequency, the ratio of rigid to flexible segment length of the plate and the range of Strouhal number, that led to a peak efficiency near 80%. The experiments for different values of chordwise flexibility showed that greater flexibility increases the propulsive efficiency and thrust compared with similar motion of the purely rigid foil. By submerging the plate at different depths, it was observed that the proximity of the propulsor to the channel floor led to overall increase in the thrust coefficient. However the increase in thrust coefficient was pronounced in