Active Control of A Piston-Type Absorbing Wavemaker with Fully Reflective Structure
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rol of A Piston-Type Absorbing Wavemaker with Fully Reflective Structure Saeed MAHJOURIa, Rasoul SHABANIa, *, Ghader REZAZADEHa, b, Peyman BADIEIc a Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran b South Ural state University, Chelyabinsk, Russian Federation c Department of Civil Engineering, Tehran University, Tehran, Iran
Received February 19, 2020; revised May 23, 2020; accepted June 30, 2020 ©2020 Chinese Ocean Engineering Society and Springer-Verlag GmbH Germany, part of Springer Nature Abstract Multiple reflections of the waves between structure and wavemaker in hydraulic flumes could change the frequency content of the desired incident wave or result in resonance. A prominent approach to avoid multiple reflections is active control of the wavemaker. This paper proposes a simple and practical active control algorithm for piston-type wavemaker. The block diagram of the control system is presented in real time domain. It is shown that there is no need to use any transfer function or filter in the feedback and feed forward loops and the use of constant gains can yield acceptable results. In the operating frequency range (0.25−2 Hz), it is revealed that the proposed system is very effective at suppressing the excitation of resonant sloshing for regular wave. In the case of irregular waves, it is depicted that the experimental waves agree quite well with the desired wave elevation in frequency domain. In addition, comparison of the results obtained both with and without absorption discloses the good characteristics in time domain. Key words: wave flume, piston-type wavemaker, active absorption, mathematical modeling, reflective waves Citation: Mahjouri, S., Shabani, R., Rezazadeh, G., Badiei, P., 2020. Active control of a piston-type absorbing wavemaker with fully reflective structure. China Ocean Eng., 34(5): 730–737, doi: https://doi.org/10.1007/s13344-020-0066-9
1 Introduction To investigate the wave-structure interactions, researchers have developed numerical and experimental wave flumes. In a numerical wave flume, a semi-infinitely or bounded, constant depth, long channel has been considered as a domain. Assumed waves are generated by an oscillating boundary and an artificial beach or porous region has been considered at the other end to restrict reflection (Clément, 1996). For small wave amplitudes the linear velocity potential theory has been used to simulate the wave propagation (Yueh and Chuang, 2013). However, in the case of finite or large wave amplitudes the second order Stokes equations (Senturk, 2011, Khait and Shemer, 2019) and/or nonlinear Navier−Stocks equations have been used (Anbarsooz et al., 2013; Lin and Liu, 1999). However, it was shown that the different theories did not exhibit the same level of accuracy, especially for steep and deep water waves (Saincher and Banerjee, 2015). An experimental wave flu
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