Laboratory Study of Lagoonal Environments Evolution: Setup and Control of the Tidal Wave Generation System

Tidal environments are complex landform located along coasts, characterized by a dominance of tidal currents over riverine flows. Lagoon and salt marshes buffer the coastline against storm surges and marine flooding and filter nutrients and pollutants providing rare and unique habitats. Therefore, studying the processes that underlie the formation and development of tidal environments is a critical step to understand their evolution and to address issues of management and protection of these peculiar systems exposed to climate change and human disturbances. Due to the time scale of these phenomena, physical modelling with laboratory experiment represents a particularly useful tool to understand the dynamics of the complex interplay between tidal forcing and sediment transport. To reproduce a typical lagoonal environment we designed a large indoor experimental set-up, in which the tide is generated by a variation of the water level through a vertical oscillating sharp-edged weir. A suitable LabVIEW interface allows users to set the parameters of the tide (i.e. amplitude, period and mean sea level of propagation) and to control the weir and different sensors through NI CompactRIO 9066. Because of the scale effect and conditions required by the hydrodynamic similitude, the problem of the tide generation in the experimental apparatus has to be carefully addressed. To this aim, we developed a suitable control system, which allow to generate tidal waves of any prescribed form and mean sea level of propagation. The control algorithm has to be as simple as possible but able to ensure suitable performance, even when the system operating conditions change or if certain system parameters vary over time. Thanks to the National Instruments hardware and software tools, we have developed and tested different control algorithms. In particular, we have compared the performance of the so-call "intelligent" PID (Proportional Integral Derivative) controller with that of a standard regulator. In general, the integral error is accepted as a good measure for the system performance. In our tests, given the error between the water level and its reference, the integral of time squared error (ITSE) is lower for the "intelligent" PID. The good performance of the control systems gives the chance to conduct meaningful in-scale experiments.