Edgar An

VHF radar detects oceanic submesoscale vortex along Florida Coast

Escalating national interest in the coastal ocean underscores the need for high-quality surface current data that can improve our understanding of surface circulation and its impact on societal and environmental issues related to coastal pollution, beach restoration, oil spill mitigation, and coastal air-sea interaction. Coastal regimes exposed to strong ocean currents,surface waves, and winds during storm conditions may frequently require beach renourishment to restore valuable beaches that are key to local economies. Maintaining water quality is a problem, too, particularly where shipping dominates the traffic in and out of harbors. These environmental issues are increasingly difficult to manage due to evolving oceanic and atmospheric conditions. Inferring evolving spatial patterns of the coastal ocean current fields from single-point measurements such as moorings or drifters that propagate away from divergent flow regimes is difficult at best. The Doppler radar technique is one approach that effectively measures the evolution of surface current fields in near-real time.

Design Robust Nonlinear Controllers for Autonomous Underwater Vehicles with Comparison of Simulated and At-sea Test Data

Successful controller development involves three distinct stages, namely, control law design, code debugging and field test. For Autonomous Underwater Vehicle (AUV) applications, the first two stages require special strategies. Since the dynamics of an AUV is highly nonlinear, and the environment that an AUV operates in is noisy with external disturbance that cannot be neglected, a robust control law must be considered in the first stage. The control law design is even more difficult when optimal criteria are also involved. In the second stage, since the software architecture on an AUV is very complicated, debugging the controllers alone without all the software routines running together often can not reveal subtle faults in the controller code. Thorough debugging needs at-sea test, which is costly. Therefore, a platform that can help designers debug and evaluate controller performance before any at-sea experiment is highly desirable. Recently, a 6 Degree of Freedom (DOF) AUV simulation toolbox was developed for the Ocean Explorer (OEX) series AUVs developed at Florida Atlantic University. The simulation toolbox is an ideal platform for controller in-lab debugging and evaluation. This paper first presents a novel robust controller design methodology, named the Sliding Mode Fuzzy Controller (SMFC). It combines sliding mode control and fuzzy logic control to create a robust, easy on-line tunable controller structure. A formal proof of the robustness of the proposed nonlinear sliding mode control is also given. A pitch and a heading controller have been designed with the presented structure and the controller code was tested on the simulation software package as well as at sea. The simulated and at-sea test data are compared. The whole controller design procedure described in this paper clearly demonstrates the advantage of using the simulation toolbox to debug and test the controller in-lab. Moreover, the pitch and heading controller have been used in the real system for more than 2 years, and have also been successfully ported to other types of vehicles without any major modification on the controller parameters. The similarity of the controller performances on different vehicles further demonstrates the robustness of the proposed Sliding Mode Fuzzy Controller. The main contribution of this paper is to provide useful insights into the design and implementation of the proposed control architecture, and its application in AUV control.

6 DOF nonlinear AUV simulation toolbox

This paper describes the organization of 6 DOF nonlinear autonomous underwater vehicle (AUV) simulation toolbox, which is currently under development for the Ocean Explorer (OEX) series AWs developed at Florida Atlantic University. This software development is part of 5-year OM MURI effort of which its goal is to develop innovative tools and methodologies for the control of complex nonlinear dynamic systems. The purpose of this software simulation is to supply a flexible 3D-simulation platform for motion visualization, in-lab debugging and testing of mission-specific strategies as well as those related to C3 purposes. This software is currently jointly developed by the Ocean Engineering Department at Florida Atlantic University and Naval Postgraduate School for the FAU OEX and NPS Phoenix AUVs.

Using small AUV for oceanographic measurements

The use of Florida Atlantic Universitys the Ocean Explorer, a small autonomous underwater vehicle, as a mobile platform for oceanographic measurements is described. The OEX is a 2.4 m long versatile, Gertler body which can perform pre-programmed underwater missions to a depth of 300 m. At a speed of 1-2 m/s, it can perform missions over a period of several hours, collecting in-situ oceanographic data and storing it on an on-board data-logger. Three missions are described, two in shallow waters off the coast of South Florida during December, 1997, and one in the Gulf Stream during July 1997 at depths of up to 130 m. During the missions, the AUV was equipped with a 1200 kHz broad band ADCP, a CTD package and, on the Gulf Stream mission, a small-scale turbulence measurement package. The vehicle may also carry a side-scan sonar or other instruments for subsidiary measurements. The versatility of the AUV allows measurement of oceanographic data over a substantial region, the motion of the platform being largely decoupled from that of the sea surface. In the missions of Dec. 5 and 11, 1997, lawn-mower pattern AUV surveys were conducted over 1 km2 regions on the east coast of Florida, north of Fort Lauderdale, at a depths of 7 m and 3 m respectively in a water column where depth ranged from 10-32 m. During Dec. 5, the region was subjected to a cold front from the northwest. Local wind measurements show presence of up to 10 m/s winds at temperatures of up to 10-150 C below normal for the, time of the year. Measurements are compared with those of a fixed ADCP. In the Gulf Stream missions, significant shear layers were encountered. Bathymetry, current, CTD and small-scale turbulence measurements obtained during the missions are presented and the problems associated with making such measurements and choosing sampling strategies is discussed.

Modeling and simulation for the FAU AUVs: Ocean Explorer

This paper describes the research progress made on modeling and simulation development for the Florida Atlantic University autonomous underwater vehicles (AUV). Recent addition of simulation components include kinematic effect of longitudinal waves, inertial and position sensor dynamics so that realistic scenarios can be better accommodated. In addition, the existing FAU communication protocol used for the onboard acoustic modem has been ported to the simulation platform, thereby enabling multiple vehicle operations and communication to be simulated. At this stage acoustic propagation for the model is assumed to be ideal although a more realistic model for shallow water propagation will be developed in the near future. This research endeavor is supported by a 5-year ONR MURI project and is jointly carried out by FAU and Naval Postgraduate School.