No abstract

Ao meu orientador, Prof. Dr. Julio Cezar Adamowski, por todo o apoio, encorajamento e orientação durante o mestrado. Ao Prof. Dr. Kazuo Nishimoto, pela idealização do presente projeto. Ao Prof. Dr. Flávio Buiochi, pelas sugestões durante o desenvolvimento do sensor de altura de ondas por ultra-som. A Patricia, por todo o incentivo e carinho. Ao Heitor pela ajuda com o Linux e o L A T E X. Ao Pedro pela ajuda na montagem do protótipo, no algorítmo de reflexão de ondas e na realização dos ensaios. Aos amigos do laboratório do Departamento de Engenharia Naval e Oceânica, Carlos, João e Marlei, pelas sugestões para a melhoria do protótipo e pela ajuda durante os ensaios. Ao Nilson, pelas sugestões no desenvolvimento da eletrônica do sensor de altura de ondas por ultra-som. Aos técnicos da usinagem Gilberto e Adilson, que fabricaram algumas das peças do protótipo e outros dispositivos para ensaios.

This paper presents the new active absorption wave basin constructed at the University of Sa˜o Paulo (USP), in the Numerical Offshore Tank (TPN) Laboratory. The square (14m × 14m) tank is able to generate and absorb waves from 0.5Hz to 2.0Hz, by means of 148 active flap-type wavemakers. An independent mechanical system drives each flap by means of a 1HP servo-motor and a ball-screw based transmission system. A customized ultrasonic wave probe is installed in each flap, and is responsible for the measurement of wave elevation in the flap. These sensors do not require constant calibration, differently from the capacitive or resistive sensors normally used in similar tanks. A complex automation architecture was implemented, with 3 Programmable Logic Computers (PLC), and a low-level software is responsible for all the interlocks and maintenance functions of the tank. Furthermore, all the control algorithms for the generation and absorption are implemented using higher level software (MATLAB®/Simulink block diagrams). These algorithms calculate the motions of the wavemakers both to generate and absorb the required wave field by taking into account the layout of the flaps and the limits of wave generation. The experimental transfer function that relates the flap motion to the generated wave is used for the calculation of the motion of each flap. Absorption tests were conducted with a prototype wave generator in a 2D wave flume with regular waves. Two different algorithms were tested. The first one is the frequency domain method based on Maeda et al. (2004), in which the commanded variable is the motor velocity. Furthermore, the time domain algorithm proposed by Schaffer (1996) was also tested. It is based on a digital filter and uses the position of the motor as the commanded variable. Both algorithms have hydrodynamic feedback based on the measurement of surface elevation at each flap. The first algorithm needs an extensive test procedure to calibrate its control parameters while the second one, after optimizing the digital filter, is ready to use. Both algorithms presented similar results with reflection coefficient smaller than 10.7% for regular waves in the frequency range of 0.5 to 2.0 Hz. The paper also presents the first results obtained in the tank.

No abstract

A new Active Absorption Basin (AAB) is under development, and will be used for the calibration of simulation models developed in the Numerical Offshore Tank of University of Sa˜o Paulo (TPN-USP). The AAB will be equipped with 148 independent flap-type wave makers arranged around its 14×14m rectangular section. Due to the small dimensions of the tank, it is necessary to use active absorption, in order to avoid the contamination of the wave field by the reflected waves, allowing the emulation of the infinite multi-directional ocean behavior. The wave maker actuation feedback control is based on the measurement of surface elevation at each flap, as proposed by [1]. The generation-absorption algorithm disregards the evanescent wave modes that are present in the sensor measurements. In the present paper, the absorption algorithm was tested in a 2D wave flume. A wave probe array installed in the middle of the flume was used to check the quality of the absorption algorithm. With this experiment, several implementation problems could then be identified and solved. High-frequency oscillations and drift of the flaps were observed using the original algorithm. Novel terms were then introduced, in order to reduce the overall gain of the controller, include the effect of the evanescent wave and eliminate the drift of position. The modified version of the algorithm was then used in an extensive calibration procedure for regular waves, in order to improve the absorption efficiency. Reflection coefficients smaller than 11% were obtained for waves up to 1,5Hz, proving the efficiency of the method.