Robust optimal control of a nonlinear surface vessel model with parametric uncertainties

This paper presents a fast alternative optimization method for developing a reliable optimal controller that can handle system model parameter uncertainties. The source of uncertainty in this study is identified as hydrodynamic coefficients, which are prone to errors due to the challenges involved in obtaining accurate values. The proposed optimization method utilizes a complex nonlinear ship model provided by Maneuver Modelling Group (MMG) as the reference for the ship motion model. The optimization process is divided into two stages: a blind search followed by bisection optimization, to obtain a robust optimal controller. To demonstrate the effectiveness of the proposed approach, system response analysis and practical tests were performed on Step, M-Turn, and Doublet maneuvers. The results show that the controller parameters obtained from the proposed optimization method are capable of achieving high success rates in controlling a system with uncertain parameters

Practical Coordination of Multi-Vehicle Systems in Formation

This thesis considers the cooperation and coordination of multi vehicle systems cohesively in order to keep the formation geometry and provide the string stability. We first present the modeling of aerial and road vehicles representing different motion characteristics suitable for cooperative operations. Then, a set of three dimensional cohesive motion coordination and formation control schemes for teams of autonomous vehicles is proposed. The two main components of these schemes are i) platform free high level online trajectory generation algorithms and ii) individual trajectory tracking controllers. High level algorithms generate the desired trajectories for three dimensional leader-follower structured tight formations, and then distributed controllers provide the individual control of each agent for tracking the desired trajectories. The generic goal of the control scheme is to move the agents while maintaining the formation geometry. We propose a distributed control scheme to solve this problem utilizing the notions of graph rigidity and persistence as well as techniques of virtual target tracking and smooth switching. The distributed control scheme is developed by modeling the agent kinematics as a single-velocity integrator; nevertheless, extension to the cases with simplified kinematic and dynamic models of fixed-wing autonomous aerial vehicles and quadrotors is discussed. The cohesive cooperation in three dimensions is so beneficial for surveillance and reconnaissance activities with optimal geometries, operation security in military activities, more viable with autonomous flying, and future aeronautics aspects, such as fractionated spacecraft and tethered formation flying. We then focus on motion control task modeling for three dimensional agent kinematics and considering parametric uncertainties originated from inertial measurement noise. We design an adaptive controller to perform the three dimensional motion control task, paying attention to the parametric uncertainties, and employing a recently developed immersion and invariance based scheme. Next, the cooperative driving of road vehicles in a platoon and string stability concepts in one-dimensional traffic are discussed. Collaborative driving of commercial vehicles has significant advantages while platooning on highways, including increased road-capacity and reduced traffic congestion in daily traffic. Several companies in the automotive sector have started implementing driver assistance systems and adaptive cruise control (ACC) support, which enables implementation of high level cooperative algorithms with additional softwares and simple electronic modifications. In this context, the cooperative adaptive cruise control approach are discussed for specific urban and highway platooning missions. In addition, we provide details of vehicle parameters, mathematical models of control structures, and experimental tests for the validation of our models. Moreover, the impact of vehicle to vehicle communication in the existence of static road-side units are given. Finally, we propose a set of stability guaranteed controllers for highway platooning missions. Formal problem definition of highway platooning considering constant and velocity dependent spacing strategies, and formal string stability analysis are included. Additionally, we provide the design of novel intervehicle distance based priority coefficient of feed-forward filter for robust platooning. In conclusion, the importance of increasing level of autonomy of single agents and platoon topology is discussed in performing cohesive coordination and collaborative driving missions and in mitigating sensory errors. Simulation and experimental results demonstrate the performance of our cohesive motion and string stable controllers, in addition we discuss application in formation control of autonomous multi-agent systems

Attitude Control and Parameter Optimization: A Study on Hubble Space Telescope

In this work, we build a satellite attitude Proportional-Integral-Derivative (PID) controlled system by using the Hubble Space Telescope (HST) parameters as a reference and tune its controller parameters using various tuning methods. First, we give the equations for the motion of a satellite. We elaborate the control structure as controller, actuator, dynamics, and kinematics subsystems and construct an external disturbance model. We use a reaction wheel assembly used in the HST with the same configuration as the actuator. We evaluate the performance of the linearization by comparing it with the nonlinear model output. By working on the linearized model, we tune the PID controller parameters using two different methods: “Model-Based Root Locus Tuning” and “Genetic Algorithm Based Tuning”. First, we obtain the controller parameters by manipulating the poles on the root locus plot of the linearized system. In addition, we use genetic algorithms to find the optimized controller values of the system. Finally, we compare the performances of the two methods based on their cost function values and find that the Genetic Algorithm-based tuned parameters are more fruitful in terms of the cost function value than the parameters obtained by the Root Locus-based tuning. However, it is found that the Root Locus-based tuning performs better in disturbance rejection

A practical feedforward speed control system for autonomous underwater vehicles

© 2020 Elsevier Ltd The autonomy of any airborne, land borne or waterborne vehicle starts with controlling its speed. To achieve cruise speed control, the conventional approach is to use closed-loop feedback control systems that require high precision sensors. Underwater sensors are expensive due to harsh environment and corrosive properties of seawater. In this study, we propose a speed control system for autonomous underwater vehicles (AUVs) that closes the control loop via a feedforward mechanism, eliminating the need for these expensive sensors. The feedforward control is based on the recently developed self-propulsion estimation model which can accurately predict propeller rotation rate for conventional AUV forms. The model is first validated by comparing the predicted resistance and propeller rotation rate of DARPA Suboff with the experimental and numerical results published in the literature. After observing a good match, the feedforward control system is used to ensure that the AUV reaches a predetermined surge speed. Two different underwater vehicles are considered in presenting the results of this study: the DARPA Suboff and the Gavia AUV, which has real time measurements available in the literature. The feedforward control system developed in this study achieves the desired speed with negligible errors. Transient response analysis shows that the computer simulation results are in good agreement with experimental results for the Gavia AUV

Effects of Photodynamic Therapy With Verteporfin for the Treatment of Chronic Central Serous Chorioretinopathy: An Uncontrolled, Open-Label, Observational Study

KARA, ISMAIL HAMDI/0000-0003-2022-1882; KARA, ISMAIL HAMDI/0000-0003-2022-1882WOS: 000280083100004PubMed: 24683263BACKGROUND: Central serous chorioretinopathy is an idiopathic disorder that leads to serous neurosensory retinal detachment. The disorder is usually self-limited and resolves spontaneously; however, sometimes neurosensory retinal detachment persists. This form of the disorder is called chronic central serous chorioretinopathy (CCSC). OBJECTIVE: The aim of this study was to assess the effects of photodynamic therapy (PDT) on visual acuity with full-dose verteporfin for CCSC. METHODS: The eyes of patients with CCSC were included in the study. Ophthalmic examination including best-corrected visual acuity (BCVA), fundus examination, fluorescein angiography, and optical coherence tomography was performed before treatment and at 1, 3, 6, 9, and 12 months. PDT with full-dose verteporfin (6 mg/m(2) of body surface area) was applied only to areas of active leakage. BCVA was converted to a log of the minimum angle of resolution (logMAR) equivalent for statistical analysis. Central foveal thickness and BCVA between baseline and follow-up were compared. RESULTS: Seventeen eyes of 16 patients (13 males, 3 females; mean [SD] age, 39.75 [7.51] years; mean duration of follow-up, 13.06 [1.82] months) were used in the study. The mean (SEM) logMAR BCVA was 0.26 (0.07) at baseline and 0.04 (0.02) at 12 months. Mean logMAR BCVA values at baseline (0.259) and after treatment (0.112, 0.053, 0.047, 0.041, and 0.041 at 1, 3, 6, 9, and 12 months, respectively) differed significantly (P = 0.006, P = 0.005, P = 0.005, P = 0.005, and P = 0.005). There was a significant difference in the mean central foveal thickness at the final visit (169 pm) compared with the baseline value (383 pm; P < 0.001). BCVA decreased in one eye (20/20 vs 20/25) and persisted during follow-up; in the other 16 eyes, BCVA either increased (n = 10) or remained stable (n = 6). CONCLUSIONS: In this small, open-label study, patients with CCSC treated with a single course of PDT with full-dose verteporfin had significant improvement from baseline in BCVA and resolution of subretinal fluid accumulation and active leakage. Treatment was generally well tolerated, but one patient had worsening in BCVA. (Curr Thor Res Clin Exp. 2010;71:173-185) (C) 2010 Excerpta Medica Inc