Proceedings of COBEM 2005 18th International Congress of Mechanical Engineering Copyright © 2005 by ABCM November 6-11, 2005, Ouro Preto, MG UNDERWATER VEHICLE DYNAMIC MODELING Sebastião Cícero Pinheiro Gomes Carlos Eduardo Motta Moraes Paulo Lilis Drews Jr. Tomás Garcia Moreira Fundação Univesidade Federal do Rio Grande Núcleo de Matemática Aplicada e Controle e-mail: dmtscpg@furg.br hp: www.numa.furg.br Adilson Melcheque Tavares CEFET-RS e-mail: Abstract. This paper presents an approach to develop dynamic models of underwater vehicles which have open frame architecture and symmetrical planes. A ROV (Remotely Operated Vehicle) was especially constructed to perform experimental results to validate the used dynamic model approach. This dynamic model validation was performed through confrontation between open loop experiments and simulation results. One of the motivations to develop this research is that the underwater robotics in Brazil is a recent scientific domain, mainly in experimental aspects. It was verified that it is very difficult to obtain two identical open loop responses in two experiments made under the same conditions. This happens because it is difficult to reproduce the initial state of the ROV and the water conditions. Comparisons between experimental and simulation results in open loop showed that the dynamic model reproduce relatively well the experiments, indicating that the model approach can be used to ROVs or AUVs(Autonomous Underwater Vehicles) avec symmetrical planes and open frame architecture. Keywords: Underwater vehicles, kinematics, dynamics, robotics, ROV. 1. Introduction The main objective of the present work is to validate a dynamic model of an underwater vehicle, actively controlled in four degrees of freedom and having an open frame architecture and well approximately three symmetrical planes. The vehicle used to obtain the experimental results is a ROV (Remotely Operated Vehicle), constructed specially to validate experimentally the dynamic modeling theory (Moraes et al., 2005). Most of the bibliography divides the underwater robotic vehicles in two groups (Yuh, 2000): Remotely Operated Vehicles (ROV) and Autonomous Underwater Vehicles (AUV). A ROV receives energy and changes information with the panel of control placed at the surface through an umbilical cable. From the control panel the operator can plan tasks or use one joystick to maneuver the vehicle directly. An AUV does not suffer the intervention from the human operator during the mission and also it does not possess umbilical cable. The power plant is onboard in the vehicle, as well as the central processing unit. Due to the inexistence of handle the vehicles, they are independents and have greater freedom of movement and its use grows up because of the advances in the processors and in the ways of energy storage, that guarantee a bigger autonomy of them. The domain of underwater robotics is not yet very developed in Brazil, compared with international recent works. One of the first works was the master dissertation of Dominguez (1989), in which it was developed a ROV dynamic model software simulation. After this work, Cunha (1992) proposed an adaptive control to track the position of a ROV. In a more recent work, Hsu et al.(2000) proposed a procedure to dynamic model identification of actuators used in ROVs and AUVs (motor with helices). Barros and Soares (2002) showed a proposition of a low cost vehicle which may be in ROV or AUV format. Souza e Maruyama (2002) investigated the performance of some position control laws applied to underwater vehicles. Tavares (2003) presented a very complete work in the dynamic modeling and control of underwater vehicles, restricted to simulation results. In the world-wide level there are a great number of published works in the area of underwater vehicles. An important work was developed by Fossen (1994), in which there are concepts of kinematics, dynamics and control. Fossen and Fjellstad (1995) and Ridao et al. (2001) worked with modeling of the interaction between fluid and structure. There are many vehicles developed mainly by universities or research centers of the USA and Europe (Aoki et al., 1999, Chardard and Copros, 2002, Koh et al., 2002, Liddle, 1986, Newman e Stakes, 1994). Observing the international references on underwater robotics, it can be seen that, even out of Brazil, the experimental research grows up intensively in the Nineties. 2. Experimental setup A ROV was constructed at the Applied Mathematics and Control Laboratory of the Federal University of Rio Grande (FURG, RS, Brasil), actively controlled in four degrees of freedom and having two degrees of freedom with passive control. A photograph of this vehicle can be seen if Fig. 1. A few project specifications were established, and