USP Active Absorption Wave Basin: From Conception to Commissioning

Abstract

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.

A new time domain Rankine panel method for simulations involving multiple bodies with large relative displacements

“…Thus, small interferences from reflected waves coming from the tank walls may disturb the results, demanding a good performance of the CH-TPN's active control system that should absorb these waves. As reported by Mello et al [24], the system has a better performance when absorbing waves in the range of frequencies between 3.14 rad/s and 7.5 rad/s and, therefore, the wave frequencies were all selected within this range. In addition, since this experimental campaign was conducted focusing on the verification of the linear numerical method, the tests considered only regular waves of small amplitude and steepness (H/ ≤ 2%), which were previously calibrated in the absence of the models.…”

“…The algorithm calculates the motions of the wave makers to generate and absorb the required wave field by taking into account the layout of the flaps, the limits of wave generation and also the experimental transfer function that relates the flap amplitude to the wave elevation amplitude. The details of CH-TPN-USP as well as the control system implemented can be observed in Mello et al [24,25]. A perspective view of the wave basin is illustrated in Fig.…”

Um método de elementos de contorno do domínio do tempo para análise de comportamento no mar de sistemas oceânicos.

“…The results are compared to experimental data previously obtained in wave tests carried out at the CH-TPN-USP, in Sao Paulo, Brazil, which is a wave basin with dimensions of 14 m×14 m and water depth of 4 m (MELLO et al, 2010). This tank is equipped with a set of 148 independent flaps for the generation and active absorption of waves, which provides good precision and stability for the wave field during the tests.…”

“…Thus, small interferences from reflected waves coming from the tank walls may disturb the results, demanding a good performance of the flaps active control system on absorbing the waves. As presented in Mello et al (2010), the CH-TPN-USP has a better performance when absorbing waves in the range of frequencies between 3.14 rad/s and 7.5 rad/s and, therefore, the wave frequencies were selected within this range. In addition, since this experimental campaign was conducted focusing on the verification of the present linear numerical method, the tests considered only regular waves of small amplitude and steepness (H/λ ≤ 2%), which were previously calibrated without the models.…”

Desenvolvimento de um simulador simplificado para estudo de geração de ondas em tanques dotados de geradores segmentados.

“…Por fim, Carneiro et al (2009) e de Mello et al [5] apresentam as características do desenvolvidas, aquela apresentada por Maeda [10] foi a primeira teoria testada para utilização no Calibrador Hidrodinâmico. A onda plana pode ser caracterizada pelos seguintes parâmetros: Ondas, uma simplificação do problema é proposta mediante a hipótese de pequenas amplitudes de onda e conseqüente linearização desta condição de contorno.…”